Heavy Equipment

Turbocharger and SuperCharger

2011-11-20T09:40:00.000-08:00

Turbocharger
A turbocharger, or turbo (colloquialism), from the Greek "τύρβη" (mixing/spinning) is a centrifugal compressor powered by a turbinethat is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine (forced induction), thereby resulting in greater performance (for either, or both, power and efficiency). They are popularly used with internal combustion engines (e.g., four-stroke engines like Otto cycles and Diesel cycles). Turbochargers have also been found useful compounding external combustion engines such as automotive fuel cells.^[1]
The term turbocharger is a modern one, derived by shortening the turbosupercharger, which was widely used during the World War IIera and earlier. This term refers to the fact that turbochargers are a specific type of supercharger, one that is driven by a turbine. The most common form of supercharger at the time, which was often referred to as a "geared supercharger", was mechanically driven by the engine, whereas turbochargers are always driven by a turbine that gets its power from the engine's exhaust stream.^[2] Twinchargerscombine a supercharger and turbocharger.
Turbochargers are also employed in certain two-stroke cycle diesel engines, which would normally require a Roots blower for aspiration. In this specific application, mainly Electro-Motive Diesel (EMD) 567, 645, and 710 Series engines, the turbocharger is initially driven by the engine's crankshaft through a gear train and an overriding clutch, thereby providing aspiration for combustion. After the engine achieves combustion, and after the exhaust gases reach sufficient temperature, the overriding clutch disengages the turbo-compressor from the gear train and the turbo-compressor is thereafter driven exclusively by the turbine, which, in turn, is driven by the exhaust gases. In the EMD application, the turbocharger is utilized for normal aspiration during starting and low power output settings and is utilized for true turbocharging during medium and high power output settings. This is particularly beneficial at high altitudes, as are often encountered on western U.S. railroads. One EMD engine model was fitted with a "locked" turbocharger; it was utilized in normal aspiration mode during starting and all power output settings.

Contents
[hide]
1 History

2 Turbocharging versus supercharging

3 Operating principle
3.1 Pressure increase / boost

3.2 Turbo lag

3.3 Boost threshold

4 Key components and installation
4.1 Center housing and rotating assembly

4.2 Compressor

4.3 Turbine

4.4 Wastegate

4.5 Anti-surge/dump/blow off valves

4.6 Reliability

5 Applications
5.1 Automotive turbochargers, diesel and gasoline

5.2 Multiple turbochargers

5.3 Aircraft turbochargers

5.4 Marine and land-based diesel turbochargers

5.5 Motorsport and performance turbochargers

5.6 Motorcycle turbochargers

6 Manufacturers of turbochargers

7 See also

8 References

9 External links

[edit]History
Forced induction dates from the late 19th century, when Gottlieb Daimler patented the technique of using a gear-driven pump to force air into an internal combustion engine in 1885.^[3] The turbocharger was invented by Swiss engineer Alfred Büchi, who received a patent in 1905 for using a compressor driven by exhaust gasses to force air into a piston engine.^[4] During the First World War French engineer Auguste Rateau fitted turbochargers to Renault engines powering various French fighters with some success.^[5] In 1918, General Electric engineer Sanford Alexander Moss attached a turbo to a V12 Liberty aircraft engine. The engine was tested at Pikes Peak in Colorado at 14,000 feet (4,300 m) to demonstrate that it could eliminate the power loss usually experienced in internal combustion engines as a result of reduced air pressure and density at high altitude.^[5] General Electric called the system turbosupercharging.^[6]
Turbochargers were first used in production aircraft engines such as the Napier Lioness^[7] in the 1920s, although they were less common than engine-driven centrifugal superchargers. Ships and locomotives equipped with turbocharged Diesel engines began appearing in the 1920s. In the aviation world, turbochargers were most widely used by the United States, who led the world in the technology due to General Electric's early start. During World War II, notable examples of US aircraft with turbochargers include the B-17 Flying Fortress, B-24 Liberator, P-38 Lightning and P-47 Thunderbolt. The technology was also used in experimental fittings by a number of other manufacturers, notably a variety of Focke-Wulf Fw 190 models, but the need for advanced high-temperature metals in the turbine kept them out of widespread use.

Turbocharging versus supercharging

A supercharger uses mechanical energy from the engine to drive the supercharger. For example, on the single-stage single-speed supercharged Rolls Royce Merlin engine, the supercharger uses up about 150 horsepower (110 kW). Yet the benefits outweigh the costs: For that 150 hp (110 kW), the engine generates an additional 400 horsepower and delivers 1,000 hp (750 kW) when it would otherwise deliver 750 hp (560 kW), a net gain of 250 hp (190 kW). This is where the principal disadvantage of a supercharger becomes apparent: The internal hardware of the engine must withstand generating 1150 horsepower.In contrast to turbochargers, superchargers are not powered by exhaust gases but are connected directly or indirectly to an engine. Belts, chains, shafts, and gears are only a few of the ways this is performed. Most automotive superchargers are positive-displacement pumps, such as the Roots supercharger. Some superchargers are compressors such as World War II piston aircraft engines, to be specific the Rolls-Royce Merlin and the Daimler-Benz DB 601, which utilized single-speed or multi-speed centrifugal superchargers.

In comparison, a turbocharger does not place a direct mechanical load on the engine. It is more efficient because it converts the waste heat of the exhaust gas into horsepower used to drive the compressor. In contrast to supercharging, the principal disadvantages of turbocharging are the back-pressuring (exhaust throttling) of the engine and the inefficiencies of the turbine versus direct-drive.

A combination of an exhaust-driven turbocharger and an engine-driven supercharger can mitigate the weaknesses of the other. This technique is called twincharging. Some Crossley two-stroke diesel engines even used a triple system. As the exhaust was through ports, not valves, it was necessary to use exhaust pulse pressure charging. A Roots blower supplied air for scavenging and a turbocharger provided increased boost pressure when a high enough speed was reached.

Operating principle

This loss of potential power is often compounded by the loss of density seen with elevated altitudes. Thus, a natural use of the turbocharger is with aircraft engines. As an aircraft climbs to higher altitudes, the pressure of the surrounding air quickly falls off. At 5,486 m (18,000 ft), the air is at half the pressure of sea level, which means that the engine will produce less than half-power at this altitude.All naturally aspirated Otto and diesel cycle engines rely on the downward stroke of a piston to create a low-pressure area (less than atmospheric pressure) above the piston in order to draw air through the intake system. With the rare exception of tuned-induction systems, most engines cannot inhale their full displacement of atmospheric-density air. The measure of this loss or inefficiency in four-stroke engines is called volumetric efficiency. If the density of the intake air above the piston is equal to atmospheric, then the engine would have 100% volumetric efficiency. However, most engines fail to achieve this level of performance.

The objective of a turbocharger, just as that of a supercharger, is to improve an engine's volumetric efficiency by increasing the intake density. The compressor draws in ambient air and compresses it before it enters into the intake manifold at increased pressure. This results in a greater mass of air entering the cylinders on each intake stroke. The power needed to spin the centrifugal compressor is derived from the high pressure and temperature of the engine's exhaust gases. The turbine converts the engine exhaust's potential pressure energy and kinetic velocity energy into rotational power, which is in turn used to drive the compressor.

A turbocharger may also be used to increase fuel efficiency without any attempt to increase power. It does this by recovering waste energy in the exhaust and feeding it back into the engine intake. By using this otherwise wasted energy to increase the mass of air, it becomes easier to ensure that all fuel is burned before being vented at the start of the exhaust stage. The increased temperature from the higher pressure gives a higher Carnot efficiency.

The control of turbochargers is very complex and has changed dramatically over the 100-plus years of its use. A great deal of this complexity stems directly from the control and performance requirements of various engines with which it is used. In general, the turbocharger will accelerate in speed when the turbine generates excess power and decelerate when the turbine generates deficient power. Aircraft, industrial diesels, fuel cells, and motor-sports are examples of the wide range of performance requirements.

Pressure increase / boost

For example, to avoid engine knocking (aka pre-ignition or detonation) and the related physical damage to the host engine, the intake manifold pressure must not get too high, thus the pressure at the intake manifold of the engine must be controlled by some means. Opening the waste-gate allows the energy for the turbine to bypass it and pass directly to the exhaust pipe. The turbocharger is forced to slow as the turbine is starved of its source of power, the exhaust gas. Slowing the turbine/compressor rotor begets less compressor pressure.In all turbocharger applications, boost pressure is limited to keep the entire engine system, including the turbo, inside its thermal and mechanical design operating range. Over-boosting an engine frequently causes damage to the engine in a variety of ways including pre-ignition, overheating, and over-stressing the engine's internal hardware.

In modern installations, an actuator controlled manually (frequently seen in aircraft) or an actuator controlled by the car's Engine Control Unit, forces the wastegate to open or close as necessary. Again, the reduction in turbine speed results in the slowing of the compressor, and in less air pressure at the intake manifold.

In the automotive engines, boost refers to the intake manifold pressure that exceeds normal atmospheric pressure. This is representative of the extra air pressure that is achieved over what would be achieved without the forced induction. The level of boost may be shown on a pressure gauge, usually in bar, psi or possibly kPa. Anything above normal atmospheric level is considered to be boost. The table below is used to demonstrate the wide range of conditions experienced by automobiles in the western hemisphere. In the simple case, the pressure measurement "atm" is approximately equivalent to the effective volumetric efficiency (decimal fraction) as a result of driving at a different altitude. Clearly, turbocharging can be of practical value.

	Daytona Beach	Denver	Death Valley	Colorado State Highway 5	La Rinconada, Peru,
altitude	0m / 0 ft	1,609m 5,280 ft	-86m / -282 ft	4,347m / 14,264 ft	5,100m / 16,732 ft
atm	1.000	0.823	1.010	0.581	0.526
bar	1.013	0.834	1.024	0.589	0.533
psia	14.696	12.100	14.846	8.543	7.731
kPa	101.3	83.40	102.4	58.90	53.30

In most aircraft engines the main benefit of turbochargers is to maintain manifold pressure as altitude increases. Since atmospheric pressure reduces as the aircraft climbs, power drops as a function of altitude in normally aspirated engines. Aircraft manifold pressure in western-built aircraft is expressed in inches of mercury (Hg), where 29.92 inches is the standard sea-level pressure. In high-performance aircraft, turbochargers will provide takeoff manifold pressures in the 30- to 42-inch Hg (1- to 1.4-bar) range. This varies according to aircraft and engine types. In contrast, the takeoff manifold pressure of a normally aspirated engine is about 27 in. Hg, even at sea level, due to losses in the induction system (air filter, ducting, throttle body, etc.). As the turbocharged aircraft climbs, however, the pilot (or automated system) can close the wastegate, forcing more exhaust gas through the turbocharger turbine, thereby maintaining manifold pressure during the climb, at least until the critical pressure altitude is reached (when the wastegate is fully closed), after which manifold pressure will fall. With such systems, modern high-performance piston engine aircraft can cruise at altitudes above 20,000 feet, where low air density results in lower drag and higher true airspeeds. This allows flying "above the weather". In manually controlled wastegate systems, the pilot must take care not to overboost the engine, which will cause pre-ignition, leading to engine damage. Further, since most aircraft turbocharger systems do not include an intercooler, the engine is typically operated on the rich side of peak exhaust temperature in order to avoid overheating the turbocharger. In non-high-performance turbocharged aircraft, the turbocharger is solely used to maintain sea-level manifold pressure during the climb (this is called turbo-normalizing).

Turbo lag

All turbocharger applications can be roughly divided into 2 categories, those requiring rapid throttle response and those that do not. This is the rough division between automotive applications and all others (marine, aircraft, commercial automotive, industrial, locomotives). While important to varying degrees, turbo lag is most problematic when rapid changes in engine performance are required.

Turbo lag is the time required to change speed and function effectively in response to a throttle change. For example, this is noticed as a hesitation in throttle response when accelerating from idle as compared to a naturally aspirated engine. Throttle lag may be noticeable under any driving condition, yet becomes a significant issue under acceleration. This is symptomatic of the time needed for the exhaust system working in concert with the turbine to generate enough extra power to accelerate rapidly. A combination of inertia, friction, and compressor load are the primary contributors to turbo lag. By eliminating the turbine, the directly driven compressor in a supercharger does not suffer from this problem.

Lag can be reduced in a number of ways:

by lowering the rotational inertia of the turbocharger; for example by using lighter, lower radius parts to allow the spool-up to happen more quickly. Ceramic turbines are of benefit in this regard and or billet compressor wheel.
by changing the aspect ratio of the turbine.
by increasing the upper-deck air pressure (compressor discharge) and improving the wastegate response; this helps but there are cost increases and reliability disadvantages.
by reducing bearing frictional losses; by using a foil bearing rather than a conventional oil bearing. This reduces friction and contributes to faster acceleration of the turbo's rotating assembly.
Variable-nozzle turbochargers (discussed below) greatly reduce lag.
by decreasing the volume of the upper-deck piping.
by using multiple turbos sequentially or in parallel.

Boost threshold

Lag is not to be confused with the boost threshold. The boost threshold of a turbo system describes the lower bound of the region within which the compressor will operate. Below a certain rate of flow at any given pressure multiplier, a given compressor will not produce significant boost. This has the effect of limiting boost at particular rpm regardless of exhaust gas pressure. Newer turbocharger and engine developments have caused boost thresholds to steadily decline.

Electrical boosting ("E-boosting") is a new technology under development; it uses a high-speed electrical motor to drive the turbocharger to speed before exhaust gases are available, e.g., from a stop-light.^[8] An alternative to e-boosting is to completely separate the turbine and compressor into a turbine-generator and electric-compressor as in the hybrid turbocharger. This allows the compressor speed to become independent to that of the turbine. A similar system utilising a hydraulic drive system and overspeed clutch arrangement was fitted in 1981 to accelerate the turbocharger of the MVCanadian Pioneer (Doxford 76J4CR engine).

Turbochargers start producing boost only above a certain exhaust mass flow rate. The boost threshold is determined by the engine displacement, engine rpm, throttle opening, and the size of the turbo. Without adequate exhaust gas flow to spin the turbine blades, the turbo cannot produce the necessary force needed to compress the air going into the engine. The point at full throttle in which the mass flow in the exhaust is strong enough to force air into the engine is known as the boost threshold rpm. Engineers have, in some cases, been able to reduce the boost threshold rpm to idle speed to allow for instant response. Both Lag and Threshold characteristics can be acquired through the use of a compressor map and a mathematical equation.^{[citation needed]}

Key components and installation

On the left, the brass oil drain connection. On the right are the braided oil supply line and water coolant line connections.

Compressor impeller side with the cover removed.

Turbine side housing removed.

A wastegate installed next to the turbocharger.

The turbocharger has three main components:

A turbine, which is almost always a radial inflow turbine
A compressor, which is almost always a centrifugal compressor
The center housing/hub rotating assembly (CHRA).

The first two components are the primary flow path components. Depending upon the exact installation and application, numerous other parts, features and controls may be required.

Center housing and rotating assembly

Compressor

Impeller/diffuser/volute housing

Main article: Centrifugal compressor

Ported shroud/map width enhancement

Main article: Compressor map

The flow range of a turbocharger compressor can also be increased by allowing air to bleed from a ring of holes or a circular groove around the compressor at a point slightly downstream of the compressor inlet (but far nearer to the inlet than to the outlet).

The ported shroud is a performance enhancement that allows the compressor to operate at significantly lower flows. It achieves this by forcing a simulation of impeller stall to occur continuously. Allowing some air to escape at this location inhibits the onset of surge and widens the compressor map. While peak efficiencies decrease, areas of high efficiency may notably increase in size. Increases in compressor efficiency result in slightly cooler (more dense) intake air, which improves power. In contrast to compressor exhaust blow off valves, which are electronically controlled, this is a passive structure that is constantly open.

The ability of the compressor to accommodate high mass flows (high boost at low rpm) may also be increased marginally (because near choke conditions the compressor draws air inward through the bleed path). This technology is widely used by turbocharger manufacturers such as Honeywell Turbo Technologies, Cummins Turbo Technologies, and GReddy. When implemented appropriately, it has a reasonable impact on compressor map width while having little effect on the maximum efficiency island.

Charge air cooler/Intercooler

Illustration of inter-cooler location.

For all practical situations, the act of compressing air increases the air's temperature along with pressure. This temperature increase can cause a number of problems when not expected or when installing a turbocharger on an engine not designed for forced induction. Excessive charge air temperature can lead to detonation, which is extremely destructive to engines.

When a turbocharger is installed on an engine, it is common practice to fit the engine with an intercooler (also known as a charge air cooler, or CAC), a type of heat exchanger that gives up heat energy in the charge to the ambient air. To assure the intercooler's performance, it is common practice to leak test the intercooler during routine service, particularly in trucks where a leaking intercooler can result in a 20% reduction in fuel economy.

Fuel-air mixture ratio

Main article: Air-fuel ratio

In addition to the use of intercoolers, it is common practice to introduce extra fuel into the charge for the sole purpose of cooling. The amount of extra fuel varies, but typically reduces the air-fuel ratio to between 11 and 13, instead of the stoichiometric 14.7 (in gasoline engines). The extra fuel is not burned, as there is insufficient oxygen to complete the chemical reaction, and instead undergoes a phase change from vapor (liquid) to gas. This reaction absorbs heat (the latent heat of vaporization), and the added mass of the extra fuel reduces the average kinetic energy of the charge and exhaust gas. The gaseous hydrocarbons generated are oxidized to carbon dioxide, carbon monoxide, and water in the catalytic converter.

A method of coping with this problem is in one of several ways. The most common one is to add an intercooler or aftercooler somewhere in the air stream between the compressor outlet of the turbocharger and the engine intake manifold. Intercoolers and aftercoolers are types of heat exchangersthat allow the compressed air to give up some of its heat energy to the ambient air. In the past, some aircraft featured anti-detonant injection for takeoff and climb phases of flight, which performs the function of cooling the fuel/air charge before it reaches the cylinders.

In contrast, modern turbocharged aircraft usually forgo any kind of temperature compensation, because the turbochargers are in general small and the manifold pressures created by the turbocharger are not very high. Thus, the added weight, cost, and complexity of a charge cooling system are considered to be unnecessary penalties. In those cases, the turbocharger is limited by the temperature at the compressor outlet, and the turbocharger and its controls are designed to prevent a large enough temperature rise to cause detonation. Even so, in many cases the engines are designed to run rich in order to use the evaporating fuel for charge cooling.

Turbine

The housings fitted around the compressor impeller and turbine collect and direct the gas flow through the wheels as they spin. The size and shape can dictate some performance characteristics of the overall turbocharger. Often the same basic turbocharger assembly will be available from the manufacturer with multiple housing choices for the turbine and sometimes the compressor cover as well. This allows the designer of the engine system to tailor the compromises between performance, response, and efficiency to application or preference. Twin-scroll designs have two valve-operated exhaust gas inlets, a smaller sharper angled one for quick response and a larger less angled one for peak performance.

The turbine and impeller wheel sizes also dictate the amount of air or exhaust that can be flowed through the system, and the relative efficiency at which they operate. In general, the larger the turbine wheel and compressor wheel the larger the flow capacity. Measurements and shapes can vary, as well as curvature and number of blades on the wheels. Variable geometry turbochargers are further developments of these ideas.

The center hub rotating assembly (CHRA) houses the shaft that connects the compressor impeller and turbine. It also must contain a bearing system to suspend the shaft, allowing it to rotate at very high speed with minimal friction. For instance, in automotive applications the CHRA typically uses a thrust bearing or ball bearing lubricated by a constant supply of pressurized engine oil. The CHRA may also be considered "water-cooled" by having an entry and exit point for engine coolant to be cycled. Water-cooled models allow engine coolant to be used to keep the lubricating oil cooler, avoiding possible oil coking (the destructive distillation of the engine oil) from the extreme heat found in the turbine. The development of air-foil bearings has removed this risk. Adaptation of turbochargers on naturally aspirated internal combustion engines, on either petrol or diesel, can yield power increases of 30% to 40%.

Variable geometry

Garrett variable-geometry turbocharger on DV6TED4 engine

Instead of using two turbochargers in different sizes, some engines use a single turbocharger, called variable-geometry or variable-nozzle turbos; these turbos use a set of vanes in the exhaust housing to maintain a constant gas velocity across the turbine, the same kind of control as used on power plant turbines. Such turbochargers have minimal lag like a small conventional turbocharger and can achieve full boost as low as 1,500 engine rpm, yet remain efficient as a large conventional turbocharger at higher engine speeds. In many setups, these turbos do not use a wastegate. The vanes are controlled by a membrane identical to the one on a wastegate, but the mechanism operates the variable vane system instead. These variable turbochargers are commonly used in diesel engines.^[8]

Wastegate

Main article: Wastegate

View of a turbocharger from the turbine exhaust side, showing the integral wastegate to the right

To manage the pressure of the air coming from the compressor (known as the "upper-deck air pressure"), the engine's exhaust gas flow is regulated before it enters the turbine with a wastegate that bypasses excess exhaust gas entering the turbocharger's turbine.^[9] A wastegate is the most common mechanical speed control system, and is often further augmented by an electronic or manual boost controller. The main function of a wastegate is to allow some of the exhaust to bypass the turbine when the set intake pressure is achieved. This regulates the rotational speed of the turbine and thus the output of the compressor. The wastegate is opened and closed by the compressed air from the turbo and can be raised by using a solenoid to regulate the pressure fed to the wastegate membrane.^[10] This solenoid can be controlled by Automatic Performance Control, the engine's electronic control unitor a boost control computer.

Most modern automotive engines have wastegates that are internal to the turbocharger, although some earlier engines (such as the Audi Inline-5 in the UrS4 and S6) have external wastegates. External wastegates are more accurate and efficient than internal wastegates, but are far more expensive, and thus are in general found only in racing cars (where precise control of turbo boost is a necessity and any efficiency increase is welcomed).

Aircraft waste-gates and their operation are similar to automotive installations, however there are notable differences as well. Even within aircraft applications there are 2 distinctions, military/performance and non-performance.

Anti-surge/dump/blow off valves

A recirculating type anti-surge valve

Turbocharged engines operating at wide open throttle and high rpm require a large volume of air to flow between the turbo and the inlet of the engine. When the throttle is closed compressed air will flow to the throttle valve without an exit (i.e., the air has nowhere to go).

This causes a surge that can raise the pressure of the air to a level that can damage the turbo. If the pressure rises high enough, a compressor stall will occur, where the stored pressurized air decompresses backward across the impeller and out the inlet. The reverse flow back across the turbocharger causes the turbine shaft to reduce in speed more quickly than it would naturally, possibly damaging the turbocharger. In order to prevent this from happening, a valve is fitted between the turbo and inlet, which vents off the excess air pressure. These are known as an anti-surge, diverter, bypass, blow-off valve (BOV), or dump valve. It is a pressure relief valve, and is normally operated by the vacuum in the intake manifold.

The primary use of this valve is to maintain the spinning of the turbocharger at a high speed. The air is usually recycled back into the turbo inlet (diverter or bypass valves) but can also be vented to the atmosphere (blow off valve). Recycling back into the turbocharger inlet is required on an engine that uses a mass-airflow fuel injection system, because dumping the excessive air overboard downstream of the mass airflow sensor will cause an excessively rich fuel mixture (this is because the mass-airflow sensor has already accounted for the extra air that is no longer being used). Valves that recycle the air will also shorten the time needed to re-spool the turbo after sudden engine deceleration, since the load on the turbo when the valve is active is much lower than it is if the air charge is vented to atmosphere.

Reliability

A turbo timer can keep an engine running for a pre-specified period of time, to automatically provide this cool-down period. Oil coking is also eliminated by foil bearings. A more complex and problematic protective barrier against oil coking is the use of water-cooled bearing cartridges. The water boils in the cartridge when the engine is shut off and forms a natural recirculation to drain away the heat. Nevertheless, it is bad practice to shut the engine off while the turbo and manifold are still glowing with heat.Turbochargers can be damaged by dirty or ineffective oiling systems, and most manufacturers recommend more frequent oil changes for turbocharged engines. Many owners and some companies recommend using synthetic oils, which tend to flow more readily when cold and do not break down as quickly as conventional oils. Because the turbocharger will heat when running, many recommend letting the engine idle for up to three minutes before shutting off the engine if the turbocharger was used shortly before stopping. This gives the oil and the lower exhaust temperatures time to cool the turbo rotating assembly, and ensures that oil is supplied to the turbocharger while the turbine housing and exhaust manifold are still very hot; otherwise coking of the lubricating oil trapped in the unit may occur when the heat soaks into the bearings, causing rapid bearing wear and failure when the car is restarted. Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure. This problem is less pronounced in diesel engines, due to specifications of higher-quality oil.

In custom applications utilizing tubular headers rather than cast iron manifolds, the need for a cooldown period is reduced because the lighter headers store much less heat than heavy cast iron manifolds.

Race cars often utilize an Anti-Lag System to completely eliminate lag at the cost of reduced turbocharger life.

Applications

Automotive turbochargers, diesel and gasoline

The turbocharger's small size and low weight have production and marketing advantage to vehicle manufacturers. By providing naturally aspirated and turbocharged versions of one engine, the manufacturer can offer two different power outputs with only a fraction of the development and production costs of designing and installing a different engine. Improvements to robustness, reliability and cooling may be required to cope with the extra power. These can include sodium-cooled exhaust valves, better metallurgy for pistons or connecting rods, and increased piston cooling by spraying engine oil underneath the piston. The compact nature of a turbocharger means that bodywork and engine compartment layout changes to accommodate the more powerful engine are not needed. The use of parts common to the two versions of the same engine reduces production and servicing costs.

Today, turbochargers are most commonly used on gasoline engines in high-performance automobiles and diesel engines in transportation and other industrial equipment. Small cars in particular benefit from this technology, as there is often little room to fit a large engine. Volvo, Saab, Audi, Volkswagen, and Subaru have produced turbocharged cars for many years; the turbo Porsche 944's acceleration performance was very similar to that of the larger-engine non-turbo Porsche 928; and Chrysler Corporation built numerous turbocharged cars in the 1980s and 1990s. Buick also developed a turbocharged V-6 during the energy crisis in the late 1970s as a fuel-efficient alternative to the enormous eight-cylinder engines that powered the famously large cars and produced them through most of the next decade as a performance option. Recently, several manufacturers have returned to the turbocharger in an attempt to improve the tradeoff between performance and fuel economy by using a smaller turbocharged engine in place of a larger normally aspirated engine. The Ford EcoBoost engine is one such design, along with Volkswagen Group's TSI/TFSI engines, such as the Twincharger1.4 engine.

The Chevrolet Corvair's turbocharged engine. The turbo, located at top right, feeds pressurized air into the engine through the chrome T-pipe spanning the engine.

The first production turbocharged automobile engines came from General Motors in 1962. The Y-body Oldsmobile Cutlass Jetfire was fitted with a Garrett AiResearch turbocharger and the Chevrolet Corvair Monza Spyder with a TRW turbocharger.^[11]^[12]^[13] At the Paris auto show in 1974, during the height of the oil crisis, Porsche introduced the 911 Turbo – the world’s first production sports car with an exhaust turbocharger and pressure regulator. This was made possible by the introduction of a wastegate to direct excess exhaust gases away from the exhaust turbine.^[14]

The first turbocharged diesel truck was produced by Schweizer Maschinenfabrik Saurer (Swiss Machine Works Saurer) in 1938.^[15]

The world's first production turbo diesel automobiles were the Garrett-turbocharged Mercedes 300SD and the Peugeot 604, both introduced in 1978. Today, most automotive diesels are turbocharged.

1962 Oldsmobile Cutlass Jetfire
1962 Chevrolet Corvair Monza Spyder
1973 BMW 2002 Turbo
1974 Porsche 911 Turbo
1978 Buick Regal
1978 Saab 99
1978 Peugeot 604 turbodiesel
1978 Mercedes-Benz 300SD turbodiesel (United States/Canada)
1979 Alfa Romeo Alfetta GTV 2000 Turbodelta
1980 Mitsubishi Lancer GT Turbo
1980 Pontiac Firebird
1980 Renault 5 Turbo
1981 Volvo 240-series Turbo

Multiple turbochargers

A pair of turbochargers mounted to an Inline 6engine (2JZ-GTE from a MkIV Toyota Supra) in adragster.

Parallel

Some engines, such as V-type engines, utilize two identically sized but smaller turbos, each fed by a separate set of exhaust streams from the engine. The two smaller turbos produce the same (or more) aggregate amount of boost as a larger single turbo, but since they are smaller they reach their optimal RPM, and thus optimal boost delivery, more quickly. Such an arrangement of turbos is typically referred to as a parallel twin-turbo system. The first production automobile with parallel twin turbochargers was the Maserati Biturbo of the early 1980s. Later such installations include Porsche 911 TT,Nissan GT-R, Mitsubishi 3000GT VR-4, Nissan 300ZXTT, Audi RS6, and BMW E90.

Sequential

Some car makers combat lag by using two small turbos. A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher RPM. Below this RPM, both exhaust and air inlet of the secondary turbo are closed. Being individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher RPM range allows it to get to full rotational speed before it is required. Such combinations are referred to as a sequential twin-turbo. Porsche first used this technology in 1985 in the Porsche 959. Sequential twin-turbos are usually much more complicated than a single or parallel twin-turbo systems because they require what amounts to three sets of intake and waste gate pipes for the two turbochargers as well as valves to control the direction of the exhaust gases. Many new diesel engines use this technology not only to eliminate lag but also to reduce fuel consumption and reduce emissions.

Aircraft turbochargers

A natural use of the turbocharger is with aircraft engines. As an aircraft climbs to higher altitudes the pressure of the surrounding air quickly falls off. At 5,486 m (18,000 ft), the air is at half the pressure of sea level, and the airframe experiences only half the aerodynamic drag. However, since the charge in the cylinders is being pushed in by this air pressure, it means that the engine will normally produce only half-power at full throttle at this altitude. Pilots would like to take advantage of the low drag at high altitudes in order to go faster, but a naturally aspirated engine will not produce enough power at the same altitude to do so.

A turbocharger remedies this problem by compressing the air back to sea-level pressures, or even much higher, in order to produce rated power at high altitude. Since the size of the turbocharger is chosen to produce a given amount of pressure at high altitude, the turbocharger is over-sized for low altitude. The speed of the turbocharger is controlled by a wastegate. Early systems used a fixed wastegate, resulting in a turbocharger that functioned much like a supercharger. Later systems utilized an adjustable wastegate, controlled either manually by the pilot or by an automatic hydraulic or electric system. When the aircraft is at low altitude the wastegate is usually fully open, venting all the exhaust gases overboard. As the aircraft climbs and the air density drops, the wastegate must continuously close in small increments to maintain full power. The altitude at which the wastegate is fully closed and the engine is still producing full rated power is known as the critical altitude. When the aircraft climbs above the critical altitude, engine power output will decrease as altitude increases just as it would in a naturally aspirated engine.

With older supercharged aircraft, the pilot must continually adjust the throttle to maintain the required manifold pressure during ascent or descent. The pilot must also take great care to avoid overboosting the engine and causing damage, especially during emergencies such as go-arounds. In contrast, modern turbocharger systems use an automatic wastegate, which controls the manifold pressure within parameters preset by the manufacturer. For these systems, as long as the control system is working properly and the pilot's control commands are smooth and deliberate, a turbocharger will not overboost the engine and damage it.

Yet the majority of World War II engines used superchargers, because they maintained three significant manufacturing advantages over turbochargers, which were larger, involved extra piping, and required exotic high-temperature materials in the turbine and pre-turbine section of the exhaust system. The size of the piping alone is a serious issue; American fighters Vought F4U and Republic P-47used the same engine but the huge barrel-like fuselage of the latter was, in part, needed to hold the piping to and from the turbocharger in the rear of the plane. Turbocharged piston engines are also subject to many of the same operating restrictions as gas turbine engines. Pilots must make smooth, slow throttle adjustments to avoid overshooting their target manifold pressure. The fuel mixture must often be adjusted far on the rich side of stoichiometric combustion needs to avoid pre-detonation in the engine when running at high power settings. In systems using a manually operated wastegate, the pilot must be careful not to exceed the turbocharger's maximum RPM. Turbocharged engines require a cooldown period after landing to prevent cracking of the turbo or exhaust system from thermal shock. Turbocharged engines require frequent inspections of the turbocharger and exhaust systems for damage due to the increased heat, increasing maintenance costs.

Today, most general aviation aircraft are naturally aspirated.^{[citation needed]} The small number of modern aviation piston engines designed to run at high altitudes in general use a turbocharger or turbo-normalizer system rather than a supercharger.^{[citation needed]} The change in thinking is largely due to economics. Aviation gasoline was once plentiful and cheap, favoring the simple but fuel-hungry supercharger. As the cost of fuel has increased, the supercharger has fallen out of favor.

Turbocharged aircraft often occupy a performance range between that of normally aspirated piston-powered aircraft and turbine-powered aircraft. The increased maintenance costs of a turbocharged engine are considered worthwhile for this purpose, as a turbocharged piston engine is still far cheaper than any turbine engine.

Marine and land-based diesel turbochargers

A medium-sized six-cylinder marine Diesel-engine, with turbocharger and exhaust in the foreground

Turbocharging while common on diesel engines in automobiles, trucks, tractors, and boats is also common in heavy machinery such as locomotives,ships, and auxiliary power generation.

Turbocharging can dramatically improve an engine's specific power and power-to-weight ratio, performance characteristics, which are normally poor in non-turbocharged diesel engines.
Diesel engines have no detonation because diesel fuel is injected at the end of the compression stroke, ignited by compression heat. Because of this, diesel engines can use much higher boost pressures than spark ignition engines, limited only by the engine's ability to withstand the additional heat and pressure.

Motorsport and performance turbochargers

It is also important to understand that a gasoline engine's design and compression ratio effect the maximum possible boost. To obtain more power from higher boost levels and maintain reliability, many engine components have to be replaced or upgraded such as the fuel pump, fuel injectors, pistons, connecting rods, crankshafts, valves, head-gasket, and head bolts. The maximum possible boost depends on the fuel's octane rating and the inherent tendency of any particular engine toward detonation. Premium gasoline or racing gasoline can be used to prevent detonation within reasonable limits. Ethanol, methanol, liquefied petroleum gas (LPG) and compressed natural gas (CNG) allow higher boost than gasoline, because of their higher resistance to autoignition (lower tendency to knock). Diesel engines can also tolerate much higher levels of boost pressure than Otto cycle engines, because only air is being compressed during the compression phase, and fuel is injected later, removing the knocking issue entirely.

1970 Toyota 7, twin turbocharged racing car

Aircraft engineer Frank Halford experimented with turbocharging in his modified Aston Martin racing car the Halford Special, but it is unclear whether or not his efforts were successful. The first successful application of turbocharging in automotive racing appears to have been in 1952 when Fred Agabashian in the diesel-powered Cummins Special qualified for pole position at the Indianapolis 500 and led for 175 miles (282 km) before ingested tire shards disabled the compressor section of the Elliott turbocharger. Offenhauser's turbocharged engines returned to Indianapolis in 1966, with victories coming in 1968 using a Garrett AiResearch turbocharger. The Offenhauser turbo peaked at over 1,000 hp (750 kW) in 1973, which led USAC to limit boost pressure. In their turn, Porsche dominated theCan-Am series with a 1,100 hp (820 kW) 917/30. Turbocharged cars dominated the 24 Hours of Le Mans between 1976 and 1988, and then from 2000-2007.

In land speed racing, an 1,800 hp (1,340 kW) twin-turbocharged Pontiac GTA developed by Gale Banks of Southern California, set a land speed record for the "World's Fastest Passenger Car" of 277 mph (446 km/h). This event was chronicled at the time in a 1987 cover story published byAutoweek magazine.^{[citation needed]} Gale Banks Engineering also built and raced several diesel-powered machines, including what Banks erroneously^{[citation needed]} calls the "World's Fastest Diesel Truck," a street-legal 735 hp (548 kW) Dodge Dakota pick-up that towed its own trailer to the Bonneville Salt Flats and then set an official FIA record of 217 mph (349 km/h) with a one-way top speed of 222 mph (357 km/h). The truck also showed the fuel economy of a turbocharged diesel engine by averaging 21.2-mpg^{[clarification needed]} on the Hot Rod Power Tour. If it ran 50 mph (80 km/h) faster, it would almost match the actual fastest diesel truck, the "Phoenix" of R. B. Slagle and Carl Heap.^{[citation needed]}In Formula One, in the so called "Turbo Era" of 1977 until 1988, Renault, Honda, BMW, and Ferrari produced engines with a capacity of 1,500 cc (92 cu in) able to generate 1,000 to 1,500 horsepower (750 to 1,100 kW). Renault was the first manufacturer to apply turbo technology in F1.^{[citation needed]} The project's high cost was compensated for by its performance, and led other engine manufacturers to follow suit. Turbocharged engines dominated and ended the Cosworth DFV era in the mid-1980s. However, the FIA decided turbochargers were making the sport too dangerous and expensive. In 1987, FIA decided to limit the maximum boost before the technology was banned for 1989.

Modern Group N Rally cars are forced by the rules to use a 33 mm (1.3 in) restrictor at the compressor inlet, which effectively limits the maximum boost (pressure above atmospheric) that the cars can achieve at high rpm. Of note is that, at low rpm, they can reach boost pressures of above 22 psi (1.5 bar).

A Subaru Impreza WRX STI engine bay, showing the top mounted intercooler to the back of the engine. Cold fresh air enters through a bonnet/hood scoop

In rallying, turbocharged engines of up to 2,000 cc (120 cu in) have long been the preferred motive power for the Group A/N World Rally Car competitors, due to the exceptional power-to-weight ratios attainable. This combines with the use of vehicles with relatively small bodyshells for maneuverability and handling. As turbo outputs rose to levels similar to F1's category, rather than banning the technology, FIA restricted turbo inlet diameter (currently 34 mm).

Motorcycle turbochargers

Using turbochargers to gain performance without a large gain in weight was very appealing to the Japanese factories in the 1980s. The first example of a turbocharged bike is the 1978 Kawasaki Z1R TC. It used a Rayjay ATP turbo kit to build 0.35 bar (5 lb) of boost, bringing power up from c. 90 hp (67 kW) to c. 105 hp (78 kW). However, it was only marginally faster than the standard model.

The 1982 Honda CX500 Turbo, the world's first turbocharged production bike

In 1982, Honda released the CX500T featuring a carefully developed turbo (as opposed to the Z1-R's bolt-on approach). It has a rotation speed of 200,000 rpm. The development of the CX500T was riddled with problems; due to its being a V-twin engine, the intake periods in the engine rotation are staggered, leading to periods of high intake and long periods of no intake at all. Designing around these problems increased the price of the bike, and the performance still was not as good as the cheaper CB900 (a 16 valve in-line four). During these years, Kawasaki produced the GPz750 Turbo, Suzuki produced the XN85, and Yamaha produced the Seca Turbo. The GPz750 Turbo and XN85 were fuel-injected, whereas the Yamaha Seca Turbo relied on pressurized carburetors.

Since the mid-1980s, no manufactures have produced turbocharged motorcycles making these bikes a bit of an educational experience; as of 2007, no factories offer turbocharged motorcycles (although the Suzuki B-King prototype featured a supercharged Hayabusa engine). The Dutch manufacturer EVA motorcycles builds a small series of turbocharged diesel motorcycle with an 800cc smart cdi engine.

Underwater-welding for saving while rescuing

2010-11-02T16:18:00.000-07:00

SOLUTIONS with Effective, Powerful Advice

Underwater-welding
Should I take the plunge?

Underwater-welding , enclosure welding, hyperbaric enclosure welding, wet Underwater-welding, high pressure water jet welding, other welding processes: friction welding,resistance welding, arc welding, tig welding, mig welding, oxyacetylene welding, electron beam welding, laser beam welding, welding techniques, welding information, welding links, welding tips, welding instructions, improving welding results, welding safety issues, joining questions needing answers: these are some of the items developed in this Site for the benefit of interested readers.

What is in here for me?

Underwater-welding, one of the best examples of adapting a well known process to the harsh and dangerous environment of the sea, demonstrates what necessity, ingenuity and continuing efforts could accomplish, mostly to save huge investments in offshore structures that were damaged and needed repair.

What is there, deep in the water? Does it pay?

The advantages are of economical nature, because Underwater-welding for marine maintenance and repair jobs bypasses the need to pull the structure out of the sea and saves much valuable time. If one thinks of Underwater-welding the hull of a ship or of a partially submerged oil drilling tower, one understands that the alternative may be extremely expensive, if at all possible.

The limitations of Underwater-welding concern the inevitable bulky and expensive setup to provide the welder with all the support needed, for respiration, for protection from cold, for special welding equipment, for remote surveillance camera, for special non destructive testing.

Is it risky?

The main risks for the welder performing Underwater-welding are the potential for electricshock, the possibility of producing in the arc mixtures of hydrogen and oxygen in pockets, which might set up an explosion, and the common danger sustained by divers, of having nitrogen diffuse in the blood in dangerous proportions. Curiously the risk of drowning is not listed with the hazards of Underwater-welding.

First there were no demands for quality. Underwater-welding was just applied to weld apatch until a more thorough repair could be performed. But as soon as more experience was gained, ambitious individuals and companies joined forces to improve results and to establish achievable specifications.

Let us continue...

... with some more details on Underwater-welding. There are three main ways to perform Underwater-welding. One is to build an enclosure, a pit, around the place of repair and to pump away all the water: that amounts to prepare the conditions for normal welding in air, although the place may be deep under sea level.

Another method of Underwater-welding consists in preparing an enclosure to be filled with gas (helium) under high pressure (hyperbaric) to push water back, and have the welder, fitted with breathing mask and other protective equipment, weld quite normally out of water but under pressure.

The third is the wet Underwater-welding method, where no attempts are made to dry up the location of welding. Instead the power of the arc generates a bubble of a mixture of gases which lets metal melting and joining occur more or less normally, using specially covered electrodes to avoid that too much hydrogen be absorbed in the weld. The skilled welder must also be a diver, equipped for Underwater-welding, with all the extra equipment and protection a welder must use.

There is also a less used method of Underwater-welding which features a special torch which sprays a cone of high pressure water, within which protective gas under pressure insulates the weld location from the water during welding.

Frequently Asked Information

Basic informations and suggestions on this subject can be found by clicking on Taking the Plunge.

A short list of educational facilities is available by clicking on
Underwater-welding.

An informative article describing developments and achievements of this demanding specialty can be read by clicking here.

Another recommended article explaining the essential subjects of such a schooling and training program can be seen here.

Note: Let us make it clear at once that Underwater-welding has nothing to do and should not be confused with Submerged Arc Welding wich is a specialized process described in a page on Arc Welding, and which is performed outside water.

Other Welding Processes.

Even if you are not familiar with Underwater-welding, you certainly know your processes. But how could a different one be selected?

By first knowing what other processes look like. One can certainly learn the most by enrolling in training courses, if it makes sense.

You know that there is no universal welding process perfectly adapted and convenient to whatever form and material joining. However in most cases one or more processes may be selected which permit acceptable welds to be performed.

How would you select your process? Is the process you use the best one? How would you improve on it? What is the best process?

Tip! : The "best" process is the the least expensive and available one that can be used to produce acceptable welds performing the functions of strength and stability required for the joint.

If you are looking...

... for information on other welding PROCESSES, chances are you will be able to find what interests you just by browsing here. However, if you do not find what you look for, write us by e-mail. Click here.

The following descriptive information of only the most important processes is provided for general orientation leaving more specific details to be found in the underlined referenced pages hereafter.

For practical purposes of designation, processes are usually divided between PRESSURE and FUSION WELDING. In the first type, pressure is always applied, with or without external means to provide heat, while melting temperature may or may not be reached. In the second type melting temperature is usually reached locally without the use of pressure.

Did you know that...

Welding history recognizes FORGE WELDING, which belongs to the pressure category, as one of the oldest processes performed in the blacksmith's shop well before the twentieth century. Do you agree that it could be a very interesting experience for school-children to watch, if somebody wanted to revive the practice for a show? Would you organize that for your community?

This joining is achieved when two elements, usually steel bar ends, heated to white temperature in a coal burning forced air furnace, are brought rapidly together andhammered thoroughly on the anvil to expel any oxide layer which might be present and to work them intimately to complete union.

Similar but different...

A modern sophisticated version, called FRICTION WELDING was developed, which has some important applications, especially for mass production or for specialized repairs. In general it is not for job-shops, but small shops dedicated only to this specialty may thrive, given the right conditions. A description of the process follows in the dedicated page: click on Friction Welding Process.

Most important in the pressure category are RESISTANCE WELDING processes, further divided into spot, seam and projection welding, frequently highly automated. Many of our everyday household items and car bodies are held together by resistance welds. How would you decide if it is the right solution for your welding problems and how could you improve on it?

These processes share the fact that heating is produced by the resistance to the flow of a concentrated high electric current which is made to pass locally between special copper electrodes holding the elements to be welded together under applied pressure. For more details click on Resistance Welding.

On the other hand...

Of the fusion welding processes developed in the twentieth century, and acclaimed as a real and important breakthrough, GAS WELDING, using an open FLAME, is probably one of the earliest of modern welding history. In this manual process the heat required for local progressive melting is provided by the flame of combustion of acetylene gas (other gases were tried and abandoned) with oxygen. A filler metal rod of appropriate composition may or may not be used as required.

In preparation for Underwater-welding there may be a need to perform flame cutting using hydrogen gas. (Flame welding is not used). See details in Cutting.

ARC WELDING represents a family of quite different processes, each one best adapted to its particular application niche. In these processes the energy required for melting the metals is provided by an electric arc, struck between the electrode, held by the torch, and the workpiece, usually clamped on a welding table.

Underwater-welding is mostly performed by variations on this process, taking into account the particular environmental and operator's requirements.

In the general case, the electrode is either consumable, melting to provide filler material, or non consumable, being made from a refractory tungsten alloy. In this case, when needed, filler metal is provided separately either from a manually held filler rod or from a reel fed continuously in automatic or semi-automatic equipment.

The needed protective atmosphere is provided by gases from decomposition processes of suitable materials, enrobing the electrodes (sticks) or included in the core of specially prepared (flux cored) filler wires. Otherwise a stream of inert gas like Argon or carbon dioxide (CO 2) or mixtures thereof is continuously supplied to the molten pool through the torch.

Last but most important...

High Energy Welding processes are more specialized, in that they require sophisticated equipment, mostly precisely computer controlled, and are used for specific and important applications like aerospace, submarine (but not Underwater-welding!) and nuclear, or for mass production of delicate small implements.

SOURCE: Elia E. Levi and welding-advisers.com

Aluminum: Experience in Application

2010-11-02T16:16:00.000-07:00

What you should know about welding aluminum.

In recent years, the use of aluminum in manufacturing has become more prevalent because of its light weight and other attributes that make it an attractive alternative to steel. In fact, the aluminum welding market is expected to grow at a rate of 5.5 percent annually based primarily on the assumption that the automotive industry will continue to increase its use of aluminum.

But, those experienced in the welding of steel will find aluminum to be a different breed – the normal welding characteristics of steel don’t always apply to aluminum. For example, aluminum’s high thermal conductivity and low melting point can easily lead to burnthrough and warpage problems if proper procedures are not followed.

In this article, we will first take a look at various alloying elements and how they affect aluminum; then we will turn our attention to welding procedures and the parameters that will create the best quality weld. Lastly, we will examine some new technology breakthroughs that make welding aluminum a little easier.

Alloying Elements
To understand aluminum, you must first understand some basics about aluminum metallurgy. Aluminum can be alloyed with a number of different elements, both primary and secondary, to provide improved strength, corrosion resistance and/or general weldability.

The primary elements that alloy with aluminum are copper, silicon, manganese, magnesium and zinc. But, before we examine them in detail and what they bring to aluminum, it is important to note that these alloys fall into two classes: heat-treatable or nonheat-treatable.

Heat-Treatable vs. Nonheat-Treatable Alloys
Heat-treatable alloys are those that can be heated after welding to regain strength lost during the welding process. To heat-treat an alloy means heating it at a high temperature, putting the alloying elements into solid solution and then cooling it at a rate which will produce a supersaturated solution. The next step in the process is to maintain it at a lower temperature long enough to allow a controlled amount of precipitation of the alloying elements.

With the nonheat-treatable alloys it is possible to increase strength through cold working or strain hardening. To do this, a mechanical deformation must occur in the metal structure, resulting in increased resistance to strain, producing higher strength and lower ductility.

Further Distinctions
To further designate aluminum alloys, they can also be classified by a temper designation which are as follows: F = As fabricated, O = Annealed, H = Strain hardened; W = Solution heat-treated and T = Thermally treated, which can designated heat treatment, or cold working aging. For example an alloy may carry the designation of 2014 T6. This means that it is alloyed with copper (2XXX series) and the T6 refers to the fact that it is solution heat-treated and artificially aged.

For purposes of this article, we will discuss wrought alloys, which are those aluminum alloys that are rolled from ingot or extruded with customer specified shapes. But please note that alloys can also be divided into cast alloys. Cast alloys are those used to manufacture parts from molten alloys of aluminum poured into molds. Cast alloys are precipitation hardenable but never strain hardenable. The weldability of these alloys is affected by casting type – permanent mold, die cast, and sand – since the casting surface is critical to welding success. A three-digit number, plus one decimal i.e. 2xx.x designates the cast alloys. Weldable grades of aluminum castings are 319.0, 355.0, 356.0, 443.0, 444.0, 520.0, 535.0, 710.0 and 712.0.

Alloying Elements
Now, that you understand some of the terminology, let’s take a look at the different alloying elements:

Copper (which carries a wrought alloy designation of 2XXX series) provides high strength to aluminum. This series is heat-treatable and mainly used in aircraft engine parts, rivets and screw products. Most 2XXX series alloys are considered poor for arc welding because of their sensitivity to hot cracking. These alloys are generally welded with 4043 or 4145 series filler electrodes, which have low melting points to reduce the probability of hot cracking. Exceptions to this are alloys 2014, 2219 and 2519, which are easily welded with a 2319 filler wire.

Manganese (3XXX series) added to aluminum yields a nonheat-treatable series used for general-purpose fabrication and build-up. Moderate in strength, the 3XXX series is used for forming applications including utility and van trailer sheet. It is improved through strain hardening to provide good ductility and improved corrosion properties. Typically welded with 4043 or 5356 electrode, the 3XXX series is excellent for welding and not prone to hot cracking. Its moderate strengths do prevent this series from being used in structural applications.

Silicon (4XXX series) reduces the melting point of aluminum and improves fluidity. Its principle use is as filler metal. The 4XXX series has good weldability and is considered a nonheat-treatable alloy. Alloy 4047 is becoming the alloy of choice in the automotive industry, as it is very fluid and good for brazing and welding.

Magnesium (5XXX series), when added to aluminum, has excellent weldability with a minimal loss of strength and is basically not prone to hot cracking. In fact, the 5XXX series has the highest strength of the nonheat-treatable aluminum alloys. It is used for chemical storage tanks and pressure vessels at elevated temperatures as well as structural applications, railway cars, dump trucks and bridges because of its corrosion resistance. It looses ductility when welded with 4XXX series fillers due to formation of Mg2Si.

Silicon and Magnesium (6XXX series) combine to serve as alloying elements for this medium-strength, heat-treatable series. It is principally used in automotive, pipe, railings, structural and extruding applications. The 6XXX series is somewhat prone to hot cracking, but this problem can be overcome by the correct choice of joint and filler metal. This series can be welded with either 5XXX or 4XXX series without cracking – adequate dilution of the base alloys with selected filler alloy is essential. A 4043 electrode is the most common for use with this series.

Zinc (7XXX series) added to aluminum with magnesium and copper produces the highest strength heat-treatable aluminum alloy. It is primarily used in the aircraft industry. The weldability of the 7XXX series is compromised in higher copper grades, as many of these grades are crack sensitive (due to wide melting ranges and low solidus melting temperatures.) Grades 7005 and 7039 are weldable with 5XXX fillers.

Other elements (8XXX series) that are alloyed with aluminum (i.e. lithium) all fall under this series. Most of these alloys are not commonly welded, though they offer very good rigidity and are principally used in the aerospace industry. Filler metal selection for these heat-treatable alloys include the 4XXX series.

Pure Aluminum (1XXX series), though not an alloying element, is considered nonheat-treatable and is used primarily in chemical tanks and piping because of its superior corrosion resistance. This series is also used in electrical bus conductors because of its excellent electrical conductivity. 1XXX series are easily welded with 1100 and 4043 alloys.

In addition to the primary aluminum alloying elements, there is a number of secondary elements, which include chromium, iron, zirconium, vanadium, bismuth, nickel and titanium. These elements combine with aluminum to provide improved corrosion resistance, increased strength and better heat treatability.

Physical Properties
Now that you have a basic background on aluminum metallurgy, we will move into the physical properties of base metal aluminum and how it compares to other metals, primarily steel.

The reason why aluminum is becoming specified for so many jobs is its physical properties. For instance, aluminum is three times lighter than steel and yet offers higher strength when alloyed with the right elements. It can conduct electricity six times better than steel and nearly 30 times better than stainless steel. This high electrical conductivity makes the effect of electrical stick-out in GMAW (Gas Metal Arc Welding) less significant when compared to steel (we will cover this concept in more detail later in this article.)

In addition, aluminum provides excellent corrosion resistance, is easy to shape and join, and also is non-toxic for food applications. Since it is non-magnetic, arc blow is not a problem during welding. With a thermal conductivity rate that is five times higher than steel and being less viscous, aluminum can easily be welded out-of-position. Aluminum does have its drawbacks, though, since its high thermal conductivity tends to act as a heat sink making fusion and penetration more difficult.

Since aluminum has a low melting point 1,200 degrees F (half that of steel) for the same wire size, the transition current for aluminum is much lower than it is for steel. Also, for the same welding current, the burn-off rate is about twice that of steel.

Chemical Properties
In terms of chemical composition, aluminum has a high maximum solubility for hydrogen atoms in the liquid form and a low solubility at the solidification point. This means that even a small amount of hydrogen dissolved in the liquid weld metal will tend to escape as the aluminum solidifies and porosity is likely to occur – a great cause of concern during the welding process.

Also, aluminum combines with oxygen to form an aluminum oxide layer instantaneously as it is machined. This layer is very porous and can easily trap moisture, oil, grease and other materials. The oxide provides excellent corrosion resistance, but must be taken off before welding as it prevents fusion due to its high melting point (3700 degrees F). Mechanical cleaning, solvents, chemical etching and purging are used to take off the oxide layer.

Mechanical Properties
Mechanical properties such as tensile strength, yield and elongation are affected by the choice of aluminum base and filler alloys. For groove welds, the Heat Affected Zone (HAZ) dictates the strength of the joint. In nonheat-treatable aluminum alloys, the HAZ will be completely annealed and the HAZ will be the weakest point. Heat-treatable alloys require much longer periods at annealing temperatures combined with slow cooling to completely anneal them so that weld strength is less affected. Such items as preheating, lack of interpass cooling, and excessive heat input from slow, weaving weld passes all increase peak temperature and time at temperature, which means minimum strength levels might not be met.

For fillet welds, strength is dependent on the composition of the filler alloy used to weld the joint. In structural applications, the selection of 5XXX instead of 4XXX series filler can provide twice the strength

The nonheat-treatable alloys offer excellent ductility when using matching fillers, though lower ductility results from welds made with 4XXX series. Heat-treatable alloys do not exhibit high ductility, and post-weld heat treatments generally reduce ductility.

Taking Metallurgy to the Next Level
Now that we have some background on aluminum metallurgy, we now want to apply that knowledge to the actual welding of the alloy. To do this, we will first take a look at technology that produces outstanding welding characteristics on aluminum, combating common problems such as poor penetration, high spatter levels, burnthrough and porosity.

Today’s quick response inverters using Lincoln’s patented Waveform Control Technology™ precisely control welding waveforms for more efficient control of droplet transfer. This reduces the amount of spatter caused by the low density of aluminum while a high-energy pulse peak insures proper penetration.

In addition, since variations in chemistry dramatically change an alloy’s physical properties, these custom waveforms can be designed for specific alloys to best suit the physical properties of what is being welded.

Because aluminum has a high maximum solubility for hydrogen in its liquid state and a low solubility at its solidification point, pulsing output waveforms are further designed to minimize arc length by trimming the output as low as possible and reduce the likelihood of porosity.

Lincoln has recently taken custom waveforms to the next level with Wave Designer Software®. The software allows welding engineers and operators to manipulate and modify welding waveforms on their PCs as communicated from welding equipment in real time. This creates high quality, tailored performance, when used in conjunction with inverters.

New Welding Methods
The use of Constant Current power sources for the gas metal arc welding of aluminum has a long and very successful history. The use of “drooper” output has assisted in the delivery of a high energy axial spray transfer mode for aluminum that responds evenly and consistently with the proper welding current despite changes in arc length. The result of constant current is consistent penetration throughout the length of a given weld.

The evolution of the control of the arc has lead recently to the development of software controlled inverter power sources. The use of software to “optimize” arc characteristics for aluminum GMAW has been taken to a new level at Lincoln Electric and it is known as Waveform Control Technology. A modified constant current output is employed in a very high speed synergic pulsed output that incorporates many of the benefits of Constant Current GMAW for Aluminum. These benefits include the high energy input that occurs during the pulse peak. The pulse peak helps to provide a consistent penetration profile throughout the length of a given weld and the advantages of pulsing also includes reduced spatter levels, improved puddle fluidity with an increase in effective travel speeds, and reduced heat input and lower distortion levels.

Lincoln Electric’s Waveform Control Technology™ takes pulsing to the next level. This technology allows welding waveforms to be manipulated to form the “perfect”, user defined, waveform for a particular application. This Waveform Control Technology and the tailoring it provides, can be found in highly developed software such as that found in Lincoln’s Power Wave inverter power sources. The Power Wave can be utilized in either one of two ways. Operators can select pre-programmed waveforms for welding aluminum or, engineers can create their own tailored, waveforms using Lincoln’s Wave Designer Software. These waveforms, which are created on a PC, can be programmed into the Power Wave.

Anatomy of a Waveform

But what exactly is the waveform control technology provided by Wave Designer Pro? With this technology, the power source responds to changes demanded by the software instantaneously. Keep in mind that the “waveform” is the means for determining the performance characteristics of a single molten droplet of electrode. The area under the waveform determines the amount of energy applied to that single droplet. Current is raised to a level higher than the transition current for spray transfer for a few milliseconds. During this time the molten droplet is formed, detached, and it begins its excursion across the arc. Additional energy can now be applied to the molten droplet during its descent that allows it to maintain its fluidity or increase its fluidity. The pulse is now moving to a low background current that sustains the arc which cools the cycle but prepares for the advancement to the next pulse peak.

Lets look at the waveform in detail. The front flank (A) is the rise to peak, measured in amps per millisecond, where the molten droplet is formed at the end of the electrode. As the molten droplet reaches peak it detaches. A percent of current “Overshoot”, (B), provides arc stiffness and it assists with the detachment of the molten droplet from the end of the electrode. The time spent at peak, (C) determines the droplet size; less time results in larger droplets and more time results in smaller droplets. From here the detached molten droplet is affected by energy supplied by the rear flank. The rear flank is comprised of tailout, (D), and stepoff, (E). Tailout can add energy to the molten droplet if it is increased. It can assist with puddle fluidity especially when the tailout speed is decreased. Stepoff is the place where tailout ends but it has impact on the stability of the anode and manipulation of stepoff can result in the elimination of fine droplet overspray. From this point the waveform moves to the background current, (F), where the arc is sustained. The time at the background current as it decreases has the effect of increasing the pulse frequency. The higher the pulse frequency, the higher the average current will become. Increasing frequency will result in a more focused arc.

Superimposed, in a selective fashion, over the waveform is the “Adaptive” characteristic of synergic pulsed GMAW. Adaptive, or, adaptivity refers to the ability of the arc to maintain a specific length despite changes in electrical stickout. This is an important enhancement for weld bead consistency and sound weld metal.

Process Optimization via Manipulating Waveforms
Manipulating the waveform can have a predictable effect on travel speeds, final weld bead appearance, post weld cleanup and welding fume levels. The real beauty in the manipulation of the waveform in Wave Designer Pro is how easy it is to create a visual appearance for the waveform. The user can then make real-time “drag and drop” changes in a PC Windows™ environment while the arc is running. Real time changes, or the arc can be viewed on a five channel ArcScope where Current peaks, Voltage Peaks, Power, and heat input calculations can be instantaneously viewed. The ArcScope samples data at a rate of 10KHz and is a valuable, optional-addition to the Wave Designer Software. The ArcScope gives the engineer a visual compilation of the created waveform. Critiques can be made and adjustments can then be made to further optimize the Waveform.

On thin, .035”, aluminum base materials, we can reduce heat input, reduce distortion, eliminate spatter, eliminate cold lap, and eliminate burn-throughs with the use of Waveform technology. This has been done repeatedly in applications that can benefit from pulsed GMAW. Welding programs can be created that will apply to a very specific range of wire feed speeds and/or currents or they can be created to follow a very wide range of material thicknesses with a broad range of wire feed speed.

Conclusion
Aluminum has many attractive attributes that make it the material of choice for a host of applications, although it can be different to weld. But, with a good understanding of metallurgy and the latest tools and technology on the market, aluminum can be dealt with successfully.

Guidelines for Welding Cast Iron

2010-11-02T16:11:00.000-07:00

Background

Cast iron is difficult, but not impossible, to weld. In most cases, welding on cast iron involves repairs to castings, not joining casting to other members. The repairs may be made in the foundry where the castings are produced, or may be made to repair casting defects that are discovered after the part is machined. Mis-machined cast iron parts may require repair welding, such as when holes are drilled in the wrong location. Frequently, broken cast iron parts are repaired by welding. Broken cast iron parts are not unusual, given the brittle nature of most cast iron.

While there are a variety of types of cast iron, the most common is gray cast iron, and these guidelines are directed toward this type of material.

A few facts about cast iron help in understanding the welding challenges. Cast iron typically has a carbon content of 2% - 4%, roughly 10 times as much as most steels. The high carbon content causes the carbon to form flakes of graphite. This graphite gives gray cast iron its characteristic appearance when fractured.

When castings are made, molten iron is poured into a mold and allowed to slowly cool. When this high carbon material is allowed to cool slowly, crack free castings can be made.Remembering this is helpful when welding cast iron: during and after welding, the casting must either be allowed to cool slowly, or should be kept cool enough that the rate of cooling is not important.

A critical temperature in most cast iron is about 1450 degrees F. When at this temperature, conditions that can lead to cracking occur. While the arc will heat the casting to temperatures above this level, it is important that the casting not be held at this temperature for long periods of time.

Electrode selection

If the part is to be machined after welding, a nickel-type electrode will be required. Use Lincoln Softweld® 99Ni stick electrode for single pass, high dilution welds. Softweld 55 Ni is preferred for multiple pass welds. Sometimes, root passes are put in with Softweld 99 Ni, followed by fill passes with Softweld 55 Ni. For welds where machining is not required, and where the weld is expected to rust like the cast iron, Lincoln Ferroweld® stick electrode can be used.

To Heat, or not to Heat

In general, it is preferred to weld cast iron with preheat--and lots of it. But, another way to successfully weld cast iron is to keep it cool--not cold, but cool. Below, both methods will be described. However, once you select a method, stick with it. Keep it hot, or keep it cool, but don't change horses in the middle of the stream!

Welding Techniques with Preheat

Preheating the cast iron part before welding will slow the cooling rate of the weld, and the region surround the weld. It is always preferred to heat the entire casting, if possible. Typical preheat temperatures are 500-1200 degrees F. Don’t heat over 1400 degrees F since that will put the material into the critical temperature range. Preheat the part slowly and uniformly.

Weld using a low current, to minimize admixture, and residual stresses. In some cases, it may be necessary to restrict the welds to small, approximately 1-inch long segments to prevent the build up of residual stresses that can lead to cracking. Peening of weld beads can be helpful in this regard as well.

After welding, allow the part to slowly cool. Wrapping the casting in an insulating blanket, or burying it in dry sand, will help slow cooling rates, and reduce cracking tendencies.

Welding Techniques without Preheat

The size of the casting, or other circumstances, may require that the repair be made without preheat. When this is the case, the part needs to be kept cool, but not cold.

Raising the casting temperature to 100 degrees F is helpful. If the part is on an engine, it may be possible to run it for a few minutes to obtain this temperature. Never heat the casting so hot that you cannot place your bare hand on it.

Make short, approximately 1” long welds. Peening after welding is important with this technique. Allow the weld and the casting to cool. Do not accelerate the rate of cooling with water or compressed air. It may be possible to weld in another area of the casting while the previous weld cools. All craters should be filled. Whenever possible, the beads should be deposited in the same direction, and it is preferred that the ends of parallel beads not line up with each other.

Sealing Cracks

Because of the nature of cast iron, tiny cracks tend to appear next to the weld even when good procedures are followed. If the casting must be water tight, this can be a problem. However, leaking can usually be eliminated with some sort of sealing compound or they may rust shut very soon after being returned to service.

The Studding Method

One method used to repair major breaks in large castings is to drill and tap holes over the surfaces that have been beveled to receive the repair weld metal. Screw steel studs into the threaded holes, leaving 3/16” (5 mm) to ¼” (6 mm)of the stud above the surface. Using the methods discussed above, weld the studs in place and cover the entire surface of the break with weld deposit. Once a good weld deposit is made, the two sides of the crack can be welded together.

SOURCE: Lincoln Electric

http://www.weldinginfocenter.org/links/welding_advisers.html

Electrical Submersible Pump

2010-11-02T15:14:00.000-07:00

Electrical submersible pumps (ESPs), much like vertical turbine pumps in design, are typically used to pump liquid. Essentially, an electric motor drives the pump, and the fluid’s kinetic energy is increased. This energy is then partly converted into pressure, which lifts the fluid through the pump. ESPs are centrifugal pumps with vertical shafts, and as a result depend on basic rotating impellers to pressurize fluid.

Centrifugal Pump Basics

Centrifugal pumps feature rotating impellers, typically made from metal, which contain rotating vanes. These vanes transfer energy from the motor to the fluid they propel. As fluid enters the impeller, it accelerates as the impeller rotates. Eventually, the fluid exits the impeller’s vanes at an increased speed, and the kinetic energy is typically converted into pressure.

In an ESP, mechanical seals are used to prevent fluid from flowing into the motor—the motor is coupled to the pump itself, and the entire unit is submerged in the fluid it pumps. Without mechanical seals protecting the enclosed unit, the motor could short circuit and fail.

In cases where more than one impeller is used, the pump is said to be multistage. Multistage centrifugal pumps may feature multiple impellers located on one shaft, or impellers on separate shafts. The result of connecting impellers in a series is higher pressure; connecting impellers parallel to one another results in increased output. Regardless, the fluid will still garner itsenergy from the electric motor that drives the impellers.

ESP Applications

ESPs are used in many different applications. Single-stage pumps can be used for basic drainage and pumping, as in many industrial applications, and can also handle slurry pumping. Multistage pumps are more often found in water removal applications, and can be used in water and oil wells. Regardless of the application, double checking manufacturing specifications for a given ESP will help ensure its proper use.

ESPs and Oil Wells

Because ESPs can work with a variety of flow rates and depths, they are well-suited to work inside oil wells. When used accurately, an ESP pump can decrease well pressure at the bottom, enabling the withdrawal of a higher amount of oil than otherwise could be extracted under normal pressure conditions. Pump diameter size ranges from 90 millimeters (mm) to 254 mm, and pumps can be one to 8.7 meters long.

ESPs and Dewatering Gas Wells

Some gas reservoirs can produce a high amount of liquid, but because gas can damage ESPs, care must be taken when using an ESP to remove liquid from a gas well. However, ESP systems can be designed that enable the gas to flow freely up the pump’s casing, while the pump efficiently removes fluid. The gas flow depends largely on casing head pressure—there are typically four methods with which ESPs can be used to dewater gas wells, but depending on the exact well situation all ESP set-ups should be sufficiently researched before a method is employed.

turbins

2010-01-01T01:03:00.000-08:00