Bearing Industry

Designing Hydrodynamic Bearing

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Important Factors for Designing Hydrodynamic Bearing:

Most Babbitt bearings are operated as hydrodynamically lubricated bearings and the design considerations for hydrodynamic bearings are significant as well. To ensure minimized friction and bearing wear, the bearing material for hydrodynamic bearings should have moderate shaft deflection and adequate strength at operating temperature conditions. At the hydrodynamic bearing inlet, there must be continuous and adequate supply of clean and cool oil.

Additional grooves can be machined into the bearing for easy distribution of oil that covers the whole journal. The appropriate combination's of clearance and oil viscosity for any hydrodynamic operation condition should be chosen correctly by taking into consideration the load and time elapsed during start-up and shutdown process. Two other important considerations for designing hydrodynamic bearings include the heat dissipation and friction. The lubrication systems should be set up such that lowest temperatures for the bearings are achieved with minimum oil film thickness. Similarly, friction should be kept as low as possible to refrain from power loss.

Principles of Journal Bearing Design

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The role of a bearing is to provide relative positioning and rotational freedom while transmitting the load of the shaft to the bearing housing. The factor, which controls the length of the bearing to journal diameter, is known as the L/D ratio. When this ratio is greater than unity, it results in a long bearing, while a ratio less than unity would result in short bearings.

The deflection produced by the journal within the bearing can adversely affect its load carrying ability. This deflection can be greatly reduced by increasing the diameter and decreasing the length of the journal.

The resultant short bearing has a greater flow of oil at the ends, which helps in transferring the heat from the bearing and consequentially reducing the bearing's temperature.

The load carrying ability of the bearing can be increased by reducing the roughness of the sliding surface. A good quality finish and minimum clearance can ensure that the load carrying capability of the bearing is maximized. However, the clearance should not be too small, as it would result in higher bearing temperatures and reduced film thicknesses. Surface treatment also improves the bearing design.

Composition of Babbitt Materials

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Babbitt alloys possess excellent conformability and embeddability. These materials are not used in applications where operating temperatures exceed 300°F, but have relatively low compressive and fatigue strength. The commonly used compositions of bearing materials are:

Tin-base babbitts with 89% Sn, 8% Pb and 3% Cu
Lead-base babbitts with 75% Pb, 15% Sb and 10% Sn
Copper alloys such as Cu- 10% to 15% Pb

Babbitts can also be made of other materials, such as tin or leaded bronze, copper lead alloy, aluminum bronze or alloys, and cast iron, which are widely used in many applications.

Bearing Materials

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An integral part of designing a bearing is selecting the material, since the bearing materials constitute an important part in the journal bearing. This maxim is particularly important for Babbitt bearings. The materials that are chosen are especially significant when considering the beginning of the hydrodynamic lubrication process, when contact occurs between the rotating shaft and the bearing. The bearing materials must be soft enough to resist the wear and endure load under gas pressure. In addition, they must also possess good compressive and fatigue strength.

While the compressive strength is to withstand the temperature variations, the fatigue strength is to resist cyclic loading of the journal when it is revolving. Finally, the material should also have a low shear strength aimed at easy smoothing of surface asperities.

Some other important considerations of the bearing materials include a low coefficient of friction, reliability, and resistance to corrosion. In addition, they must also have good thermal conductivity to dissipate the frictional heat. Considering all these requirements, Babbitt alloys are one of the most commonly used bearing materials.

Characteristics of Bearing

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As one of eight special industries in Linqing city, the bearing industry started early and had rapid development. It has a history of more than 50 years. The Yandian bearing market has developed into a specialized market which has the largest scale and the most complete variety. Besides, it has the most professional personnel listed on the market. Currently, the market covers an area of 1200 acres, with the building area of 320,000 square meters. There are about ten thousand business models of bearings in this market.

With the quick development of this market, Linqing bearing industry has also gone through an evolution which was from family workshops to large-scale and specialized production. The Linqing city was named "Bearing City of China." It has the following characteristics:

Firstly, the scale of industrial clusters expands gradually. The bearing processing enterprises in the city have reached 2064, 118 of which having a large scale. There are about twelve thousand of distributors and more than sixty thousand people involved in the bearing industry. In 2008, the bearing industry had a total business income of 14.16 billion Yuan. At the same time, some backbone bearing companies such as Halu bearing, Camry bearing, Yujie bearings, Hengtong steel pipe grow rapidly and become the main force of the bearing industry.

Secondly, the industrial chain continues to improve. At present, Linqing bearing industry has formed a production and processing marketing system which is from the steel production to forging, lathing, grinding, installation and sale. Additionally, it has developed an industry chain that can produce eleven categories of bearing products with more than 5000 models. The daily consumption of steel is more than 800 tons, and the consumption of rolling element is more than 150 tons. It can produce 358 million sets of bearing products, 171 million sets of bearing rings, 19 million units of bearing retainers, twenty-four hundred tons of bearing forging, and 1.1 million tons of steel pumps. Meanwhile, Linqing has a huge sales force. There are about 8,000 dealers who stayed in foreign countries for a long time. And the Linqing bearing distribution departments are scattered over many cities in the country.

Thirdly, the vitality of the bearing industry is growing. Currently, the city has about 42 registered trademarks. And more than forty enterprises have passed the ISO9000 quality system certification.

Fourthly, the level of opening up is constantly improved. At present, bearing manufacturers throughout the country set branch offices in the Yandian bearing market. And their bearing products are sold throughout the country as well as other 40 regions.The national market share is over 10%. A lot of good products are exported to many developed countries such as Japan, the United States, and Germany, etc.

Bearing Manufacturing Process

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At present, parameters of the internal structure of China's sealed deep groove ball bearings are almost the same as that of foreign products. However, the level of vibration and noise of such products is very different from that of foreign products. It is mainly resulted from the manufacturing factors and working conditions. From the point of view of the bearing industry, the working condition factors can be considered through making reasonable demands on the main engine. However, how to reduce vibration and noise that are caused by the manufacturing is become an urgent problem for the bearing industry.

Many tests from home and abroad show that: the processing quality of the cage, bearing ring, and steel balls has different effect on the bearing vibration. Among all of them, the processing quality of steel balls has the most significant effect on the bearing vibration. The main factors that have influences are roundness of bearing rings, the waviness, surface roughness and surface bump and hurt.

The most prominent problem of China's steel ball products is that vibration value is large. The surface has serious defects (such as single point, cluster points and pits). Even though the surface roughness, size, shape and errors are not lower than the level of outside rings, the bearing vibration value is very high after the combination. The main problem is that the ripple is not controlled.

As to the rings, most serious impacts on the bearing vibration are the channel waviness and surface roughness. For example, if the circularity of inside and outside channel of small and medium sized deep groove ball bearings is larger than 2μm, it will have distinctive effect on the bearing vibration.

The waviness is resulted from grinding as to the steel balls and rings. Although superfinishing can improve the waviness and decrease roughness, the most fundamental measure is to reduce the grinding process of waviness and avoid random bump and hurt.

How to reduce noise of ball bearings? There are two points which should be taken into consideration. One is the manufacturing process. The refinement of the manufacturing process mainly refers to the shortness of the process and the combination of the process and manufacturing. The process of the manufacturing should be clean. Besides, bearings should be produced in a large scale for this can improve the competitiveness in the world market. The other is the equipment. High-speed grinding, spindle accuracy, stiffness and many other detection performances have much impact on the grinding accuracy and efficiency.

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