Tentang Mesin

Density of Metals *

2011-04-09T00:44:00.000-07:00

http://www.bibliobase.com/Chemistry/Brenstein/pdf_doc/05.pdf

You are certainly aware that different materials weigh differently, even if they have the same volume. In this experiment, you will determine the density of several unknown solid metal samples from their masses and volumes. You will then identify the unknown samples based on your calculated densities.

Densities of selected metals

Metal	Density (g/cm³)
Aluminum	2.699
Chromium	7.13
Copper	8.89
Gold	19.33
Iron	7.86
Lead	11.347
Magnesium	1.738
Mercury	13.596
Nickel	8.85
Osmium	22.5
Potassium	0.87
Silver	10.6
Tin	7.184
zinc	7.19

Note that the density of metals actually varies somewhat depending on how the metal is produced. Your measured value may thus be different from the value listed above, but it may still be correct.

Helical Gears

2011-04-01T21:16:00.000-07:00

Introduction

Helical gears are similar to spur gears except that the gears teeth are at an angle with the axis of the gears. A helical gear is termed right handed or left handed as determined by the direction the teeth slope away from the viewer looking at the top gear surface along the axis of the gear. ( Alternatively if a gear rests on its face the hand is in the direction of the slope of the teeth) . Meshing helical gears must be of opposite hand. Meshed helical gears can be at an angle to each other (up to 90^o ). The helical gear provides a smoother mesh and can be operated at greater speeds than a straight spur gear. In operatation helical gears generate axial shaft forces in addition to the radial shaft force generated by normal spur gears.

In operation the initial tooth contact of a helical gear is a point which develops into a full line contact as the gear rotates. This is a smoother cycle than a spur which has an initial line contact. Spur gears are generally not run at peripheral speed of more than 10m/s. Helical gears can be run at speed exceeding 50m/s when accurately machined and balanced.

Standards ... The same standards apply to helical gears as for spur gears

AGMA 2001-C95 or AGMA-2101-C95 Fundamental Rating factors and Calculation Methods for involute Spur Gear and Helical Gear Teeth
BS 436-4:1996, ISO 1328-1:1995..Spur and helical gears. Definitions and allowable values of deviations relevant to corresponding flanks of gear teeth
BS 436-5:1997, ISO 1328-2:1997..Spur and helical gears. Definitions and allowable values of deviations relevant to radial composite deviations and runout information
BS ISO 6336-1:1996 ..Calculation of load capacity of spur and helical gears. Basic principles, introduction and general influence factors
BS ISO 6336-2:1996..Calculation of load capacity of spur and helical gears. Calculation of surface durability (pitting)
BS ISO 6336-3:1996..Calculation of load capacity of spur and helical gears. Calculation of tooth bending strength
BS ISO 6336-5:2003..Calculation of load capacity of spur and helical gears. Strength and quality of materials

Helical gear parameters

A helical gear train with parallel axes is very similar to a spur gear with the same tooth profile and proportions. The primary difference is that the teeth are machined at an angle to the gear axis.

Helix Angle ..

The helix angle of helical gears β is generally selected from the range 6,8,10,12,15,20 degrees. The larger the angle the smoother the motion and the higher speed possible however the thrust loadings on the supporting bearings also increases. In case of a double or herringbone gear β values 25,30,35,40 degrees can also be used. These large angles can be used because the side thrusts on the two sets of teeth cancel each other allowing larger angles with no penalty

Pitch /module ..

For helical gears the circular pitch is measured in two ways
The traverse circular pitch (p) is the same as for spur gears and is measured along the pitch circle
The normal circular pitch p _n is measured normal to the helix of the gear.
The diametric pitch is the same as for spur gears ... P = z _g /d_g = z _p /d _p ....d= pitch circle dia (inches).
The module is the same as for spur gears ... m = d_g/z _g = d _p/z _p.... d = pitch circle dia (mm).

Helical Gear geometrical proportions

p = Circular pitch = d _g. p / z _g = d _p. p / z _p
p _n = Normal circular pitch = p .cosβ
P _n =Normal diametrical pitch = P /cosβ
p _x = Axial pitch = p _c /tanβ
m _n =Normal module = m / cosβ
α _n = Normal pressure angle = tan ^-1 ( tanα.cos β )
β =Helix angle
d _g = Pitch diameter gear = z _g. m
d _p = Pitch diameter pinion = z _p. m
a =Center distance = ( z _p + z _g )* m _n /2 cos β
a _a = Addendum = m
a _f =Dedendum = 1.25*m
b = Face width of narrowest gear

Herringbone / double crossed helical gears

Crossed Helical Gears

When two helical gears are used to transmit power between non parallel, non-intersecting shafts, they are generally called crossed helical gears. These are simply normal helical gears with non-parallel shafts. For crossed helical gears to operate successfully they must have the same pressure angle and the same normal pitch. They need not have the same helix angle and they do not need to be opposite hand. The contact is not a good line contact as for parallel helical gears and is often little more than a point contact. Running in crossed helical gears tend to marginally improve the area of contact.

The relationship between the shaft angles E and the helix angles β ₁ & β₂ is as follows

E = (Same Helix Angle) β ₁ + β ₂ ......(Opposite Helix Angle) β ₁ - β ₂

For gears with a 90^o crossed axis it is obvious that the gears must be the same hand.

The centres distance (a) between crossed helical gears is calculated as follows

a = m * [(z ₁ / cos β ₁) + ( z ₁ / cos β ₁ )] / 2

The sliding velocity V_sof crossed helical gears is given by

V_s = (V₁ / cos β ₁ ) = (V ₂ / cos β ₂ )

Strength and Durability calculations for Helical Gear Teeth

Designing helical gears is normally done in accordance with standards the two most popular series are listed under standards above: The notes below relate to approximate methods for estimating gear strengths. The methods are really only useful for first approximations and/or selection of stock gears (ref links below). � Detailed design of spur and helical gears should best be completed using :

a) Standards.
b) Books are available providing the necessary guidance.
c) Software is also available making the process very easy. A very reasonably priced and easy to use package is included in the links below (Mitcalc.com)

The determination of the capacity of gears to transfer the required torque for the desired operating life is completed by determining the strength of the gear teeth in bending and also the durability i.e of the teeth ( resistance to wearing/bearing/scuffing loads ) .. The equations below are based on methods used by Buckingham..

Bending

The Lewis formula for spur gears can be applied to helical gears with minor adjustments to provide an initial conservative estimate of gear strength in bending. This equation should only be used for first estimates.

σ = F_b / ( b_a. m. Y )

F_b = Normal force on tooth = Tangential Force F_t / cos β
σ = Tooth Bending stress (MPa)
b_a = Face width (mm)
Y = Lewis Form Factor
m = Module (mm)

When a gear wheel is rotating the gear teeth come into contact with some degree of impact. To allow for this a velocity factor is introduced into the equation. This is given by the Barth equation for milled profile gears.

K _v = (6,1 + V ) / 6,1

V = the pitch line velocity = PCD.w/2

The Lewis formula is thus modified as follows

σ = K _v.F_b / b_a. m. Y

The Lewis form factor Y must be determined for the virtual number of teeth z' = z /cos³β The bending stress resulting should be less than the allowable bending stress S_b for the gear material under consideration. Some sample values are provide on this page ef Gear Strength Values

Surface Strength

The allowable gear force from surface durability considerations is determined approximately using the simple equation as follows

F_w = K _v d _p b _a Q K / cos²β

Q = 2. d_g /( d_p + d_p ) = 2.z_g /( z_p +z_p )

F_w = The allowable gear load. (MPa)

K = Gear Wear Load Factor (MPa) obtained by look up ref Gear Strength Values

Lewis Form factor for Teeth profile α = 20^o, addendum = m, dedendum = 1.25m
Number of teeth	Y	Number of teeth	Y	Number of teeth	Y	Number of teeth	Y	Number of teeth	Y
12	0.245	17	0.303	22	0.331	34	0.371	75	0.435
13	0.261	18	0.309	24	0.337	38	0.384	100	0.447
14	0.277	19	0.314	26	0.346	45	0.401	150	0.460
15	0.290	20	0.322	28	0.353	50	0.409	300	0.472
16	0.296	21	0.328	30	0.359	60	0.422	Rack	0.485

http://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.html

Worm Gears

2011-04-01T21:12:00.000-07:00

Introduction

A worm gear is used when a large speed reduction ratio is required between crossed axis shafts which do not intersect. A basic helical gear can be used but the power which can be transmitted is low. A worm drive consists of a large diameter worm wheel with a worm screw meshing with teeth on the periphery of the worm wheel. The worm is similar to a screw and the worm wheel is similar to a section of a nut. As the worm is rotated the wormwheel is caused to rotate due to the screw like action of the worm. The size of the worm gearset is generally based on the centre distance between the worm and the wormwheel.

If the worm gears are machined basically as crossed helical gears the result is a highly stress point contact gear. However normally the wormwheel is cut with a concave as opposed to a straight width. This is called a single envelope worm gearset. If the worm is machined with a concave profile to effectively wrap around the wormwheel the gearset is called a double enveloping worm gearset and has the highest power capacity for the size. Single enveloping gearsets require accurate alignment of the worm-wheel to ensure full line tooth contact. Double enveloping gearsets require accurate alignment of both the worm and the wormwheel to obtain maximum face contact.

The worm is shown with the worm above the wormwheel. The gearset can also be arranged with the worm below the wormwheel. Other alignments are used less frequently.

Nomenclature

As can be seen in the above view a section through the axis of the worm and the centre of the gear shows that , at this plane, the meshing teeth and thread section is similar to a spur gear and has the same features

α_n = Normal pressure angle = 20^o as standard
γ = Worm lead angle = (180 /π ) tan^-1 (z ₁ / q)(deg)   ..Note: for α _n= 20^o  γ should be less than 25^o
b _a = Effective face width of worm wheel. About 2.m √ (q +1) (mm)
b _l = Length of worm wheel. About 14.m. (mm)
c = clearance   c _min = 0,2.m cos γ ,  c _max = 0,25.m cos γ (mm)
d ₁ = Ref dia of worm (Pitch dia of worm (m)) = q.m (mm)
d _a.1 = Tip diameter of worm = d ₁ + 2.h _a.1 (mm)
d ₂ = Ref dia of worm wheel (Pitch dia of wormwheel) =( p _x.z/π ) = 2.a - d ₁ (mm)
d _a.2 = Tip dia worm wheel (mm)
h _a.1 = Worm Thread addendum = m (mm)
h _f.1 = Worm Thread dedendum , min = m.(2,2 cos γ - 1 ) , max = m.(2,25 cos γ - 1 )(mm)
m = Axial module = p _x /π (mm)
m _n = Normal module = m cos γ(mm)
M ₁ = Worm torque (Nm)
M ₂ = Worm wheel torque (Nm)
n ₁ = Rotational speed of worm (revs /min)
n ₂ = Rotational speed of wormwheel (revs /min)
p _x = Axial pitch of of worm threads and circular pitch of wheel teeth ..the pitch between adjacent threads = π. m. (mm)
p _n = Normal pitch of of worm threads and gear teeth (m)
q = diameter factor selected from (6   6,5   7   7,5   8   8,5   9  10   11   12   13   14   17   20 )
p _z = Lead of worm = p _x. z ₁ (mm).. Distance the thread advances in one rev'n of the worm.   For a 2-start worm the lead = 2 . p _x
R _g = Reduction Ratio
q = Worm diameter factor = d ₁ / m - (Allows module to be applied to worm )
μ = coefficient of friction
η= Efficiency
V_s = Worm-gear sliding velocity ( m/s)
z ₁ = Number of threads (starts) on worm
z ₂ = Number of teeth on wormwheel

Worm gear design parameters

Worm gears provide a normal single reduction range of 5:1 to 75-1. The pitch line velocity is ideally up to 30 m/s. The efficiency of a worm gear ranges from 98% for the lowest ratios to 20% for the highest ratios. As the frictional heat generation is generally high the worm box is designed disperse heat to the surroundings and lubrication is and essential requirement. Worm gears are quiet in operation. Worm gears at the higher ratios are inherently self locking - the worm can drive the gear but the gear cannot drive the worm. A worm gear can provide a 50:1 speed reduction but not a 1:50 speed increase....(In practice a worm should not be used a braking device for safety linked systems e.g hoists. . Some material and operating conditions can result in a wormgear backsliding )

The worm gear action is a sliding action which results in significant frictional losses. The ideal combination of gear materials is for a case hardened alloy steel worm (ground finished) with a phosphor bronze gear. Other combinations are used for gears with comparatively light loads.

Specifications

BS721 Pt2 1983 Specification for worm gearing � Metric units.
This standard is current (2004) and provides information on tooth form, dimensions of gearing, tolerances for four classes of gears according to function and accuracy, calculation of load capacity and information to be given on drawings.

Worm Gear Designation

Very simply a pair of worm gears can be defined by designation of the number of threads in the worm ,the number of teeth on the wormwheel, the diameter factor and the axial module i.e z1,z2, q, m .

This information together with the centre distance ( a ) is enough to enable calculation of and any dimension of a worm gear using the formulea available.

Worm teeth Profile

The sketch below shows the normal (not axial) worm tooth profile as indicated in BS 721-2 for unit axial module (m = 1mm) other module teeth are in proportion e.g. 2mm module teeth are 2 times larger

Typical axial modules values (m) used for worm gears are

0,5 0,6 0,8 1,0 1,25 1,6 2,0 2,5 3,15 4,0 5,0 6,3 8,0 10,0 12,5 16,0 20,0 25,0 32,0 40,0 50,0

Materials used for gears


Material	Notes	applications
Worm
Acetal / Nylon	Low Cost, low duty	Toys, domestic appliances, instruments
Cast Iron	Excellent machinability, medium friction.	Used infrequently in modern machinery
Carbon Steel	Low cost, reasonable strength	Power gears with medium rating.
Hardened Steel	High strength, good durability	Power gears with high rating for extended life
Wormwheel
Acetal /Nylon	Low Cost, low duty	Toys, domestic appliances, instruments
Phos Bronze	Reasonable strength, low friction and good compatibility with steel	Normal material for worm gears with reasonable efficiency
Cast Iron	Excellent machinability, medium friction.	Used infrequently in modern machinery

Design of a Worm Gear

The following notes relate to the principles in BS 721-2
Method associated with AGMA are shown below..

Initial sizing of worm gear.. (Mechanical)

1) Initial information generally Torque required (Nm), Input speed(rpm), Output speed (rpm).
2) Select Materials for worm and wormwheel.
3) Calculate Ratio (R _g)
4) Estimate a = Center distance (mm)
5) Set z ₁ = Nearest number to (7 + 2,4 SQRT (a) ) /R _g
6) Set z ₂ = Next number < R _g . z ₁
7) Using the value of estimated centre distance (a) and No of gear teeth ( z ₂ )obtain a value for q from the table below
8) d ₁ = q.m (select) ..
9) d ₂ = 2.a - d ₁
10) Select a wormwheel face width b _a (minimum =2*m*SQRT(q+1))
11) Calculate the permissible output torques for strength (M _{b_1} and wear M _{c_1} )
12) Apply the relevent duty factors to the allowable torque and the actual torque
13) Compare the actual values to the permissible values and repeat process if necessary
14) Determine the friction coefficient and calculate the efficiency.
15) Calculate the Power out and the power in and the input torque

6) Complete design of gearbox including design of shafts, lubrication, and casing ensuring sufficient heat transfer area to remove waste heat.

Initial sizing of worm gear.. (Thermal)

Worm gears are often limited not by the strength of the teeth but by the heat generated by the low efficiency. It is necessary therefore to determine the heat generated by the gears = (Input power - Output power). The worm gearbox must have lubricant to remove the heat from the teeth in contact and sufficient area on the external surfaces to distibute the generated heat to the local environment. This requires completing an approximate heat transfer calculation. If the heat lost to the environment is insufficient then the gears should be adjusted (more starts, larger gears) or the box geometry should be adjusted, or the worm shaft could include a fan to induced forced air flow heat loss.

Formulae

The reduction ratio of a worm gear ( R _g )

R _g = z ₂ / z ₁

eg a 30 tooth wheel meshing with a 2 start worm has a reduction of 15

Tangential force on worm ( F _wt )= axial force on wormwheel

F _wt = F _ga = 2.M ₁ / d ₁

Axial force on worm ( F _wa ) = Tangential force on gear

F _wa = F _gt = F _wt.[ (cos α _n - μ tan γ ) / (cos α _n . tan γ + μ ) ]

Output torque ( M ₂ ) = Tangential force on wormwheel * Wormwheel reference diameter /2

M ₂ = F _gt* d ₂ / 2

Relationship between the Worm Tangential Force F _wt and the Gear Tangential force F _gt

F _wt = F _gt.[ (cos α _n . tan γ + μ ) / (cos α _n - μ tan γ ) ]

Relationship between the output torque M ₂and the input torque M ₁

M ₂ = ( M ₁. d ₂ / d ₁ ).[ (cos α _n - μ tan γ ) / (cos α _n . tan γ + μ ) ]

Separating Force on worm-gearwheel ( F _s )

F _s = F _wt.[ (sin α _n ) / (cos α _n . sin γ + μ .cos γ ) ]

Sliding velocity ( V _s )...(m/s)

V _s (m/s ) = 0,00005236. d ₁. n ₁ sec γ
= 0,00005235.m.n (z ₁² + q ² ) ^1/2

Peripheral velocity of wormwheel ( V _p) (m/s)

V _p = 0,00005236,d ₂. n ₂

Friction Coefficient

Cast Iron and Phosphor Bronze .. Table x 1,15
Cast Iron and Cast Iron.. Table x 1,33
Quenched Steel and Aluminum Alloy..Table x 1,33
Steel and Steel..Table x 2

Friction coefficients - For Case Hardened Steel Worm / Phos Bros Wheel

Sliding Speed	Friction Coefficient	Sliding Speed	Friction Coefficient
m/s	μ	m/s	μ

0	0,145	1,5	0,038
0,001	0,12	2	0,033
0,01	0,11	5	0,023
0,05	0,09	8	0,02
0,1	0,08	10	0,018
0,2	0,07	15	0,017
0,5	0,055	20	0,016
1	0,044	30	0,016

Efficiency of Worm Gear

The efficiency of the worm gear is determined by dividing the output Torque M2 with friction = μ by the output torque with zero losses i.e μ = 0

First cancelling [( M ₁. d ₂ / d ₁ ) / M ₁. d ₂ / d ₁ ) ] = 1
Denominator = [(cos α _n / (cos α _n . tan γ ] = cot γ

η = [(cos α _n - μ tan γ ) / (cos α _n . tan γ + μ ) ] / cot γ

= [(cos α _n - μ .tan γ ) / (cos α _n + μ .cot γ )]

Graph showing worm gear efficiency related to gear lead angle ( γ )

Worm Design /Gear Wear / Strength Equations to BS721

Note: For designing worm gears to AGMA codes AGMA method of Designing Worm Gears

The information below relates to BS721 Pt2 1983 Specification for worm gearing � Metric units. BS721 provides average design values reflecting the experience of specialist gear manufacturers. The methods have been refined by addition of various application and duty factors as used. Generally wear is the critical factor..

Permissible Load for Strength

The permissible torque (M in Nm) on the gear teeth is obtained by use of the equation

M _b = 0,0018 X _b.2σ _bm.2. m. l _f.2. d ₂.

( example 87,1 Nm = 0,0018 x 0,48 x 63 x 20 x 80 )

X _b.2 = speed factor for bending (Worm wheel ).. See Below
σ _bm.2 = Bending stress factor for Worm wheel.. See Table below
l _f.2 = length of root of Worm Wheel tooth
d ₂ = Reference diameter of worm wheel
m = axial module
γ = Lead angle

Permissible Torque for Wear

The permissible torque (M in Nm) on the gear teeth is obtained by use of the equation

M _c = 0,00191 X _c.2σ _cm.2.Z. d ₂^1,8. m

( example 33,42 Nm = 0,00191 x 0,3234 x 6,7 x 1,5157 x 80^1,8 x 2 )

X _c.2 = Speed factor for wear ( Worm wheel )
σ _cm.2 = Surface stress factor for Worm wheel
Z = Zone factor.

Length of root of worm wheel tooth

Radius of the root = R _r= d ₁ /2 + h _ha,1 (= m) + c(= 0,25.m.cos γ )
R _r= d ₁ /2 + m(1 +0,25 cosγ)

l _f.2 = 2.R _r.sin^-1 (2.R _r / b _a)
Note: angle from sin^-1(function) is in radians...

Speed Factor for Bending

This is a metric conversion from an imperial formula..
X _b.2 = speed factor for bending = 0,521(V) ^-0,2

V= Pitch circle velocity =0,00005236*d ₂.n ₂ (m/s)

The table below is derived from a graph in BS 721. I cannot see how this works as a small worm has a smaller diameter compared to a large worm and a lower speed which is not reflected in using the RPM.

Table of speed factors for bending

RPM (n₂₎	X _b.2	RPM (n₂₎	X _b.2
1	0,62	600	0,3
10	0,56	1000	0,27
20	0,52	2000	0,23
60	0,44	4000	0,18
100	0,42	6000	0,16
200	0,37	8000	0,14
400	0,33	10000	0,13

Additional factors

The formula for the acceptable torque for wear should be modified to allow additional factors which affect the Allowable torque M _c

M _c2 = M _c. Z _L. Z _M.Z _R / K _C

The torque on the wormwheel as calculated using the duty requirements (M _e) must be less than the acceptable torque M _c2 for a duty of 27000 hours with uniform loading. For loading other than this then M _e should be modified as follows

M _e2 = M _e. K _S* K _H

Thus
uniform load < 27000 hours (10 years) M _e ≤ M _c2
Other conditions M _e2 ≤ M _c2

Factors used in equations

Lubrication (Z _L)..
Z _L = 1 if correct oil with anti-scoring additive else a lower value should be selected

Lubricant (Z _M)..
Z _L = 1 for Oil bath lubrication at V _s < 10 m /s
Z _L = 0,815 Oil bath lubrication at 10 m/s < V _s < 14 m /s
Z _L = 1 Forced circulation lubrication

Surface roughness (Z _R ) ..
Z _R = 1 if Worm Surface Texture < 3μ m and Wormwheel < 12 μ m
else use less than 1

Tooth contact factor (K _C
This relates to the quality and rigidity of gears . Use 1 for first estimate
K _C = 1 For grade A gears with > 40% height and > 50% width contact
= 1,3 - 1,4 For grade A gears with > 30% height and > 35% width contact
= 1,5-1,7 For grade A gears with > 20% height and > 20% width contact

Starting factor (K _S) ..
K _S =1 for < 2 Starts per hour
=1,07 for 2- 5 Starts per hour
=1,13 for 5-10 Starts per hour
=1,18 more than 10 Starts per hour

Time / Duty factor (K _H) ..
K _H for 27000 hours life (10 years) with uniform driver and driven loads
For other conditions see table below

Tables for use with BS 721 equations

Speed Factors

X _c.2 = K _V .K _R
Note: This table is not based on the graph in BS 721-2 (figure 7) it is based on another more easy to follow graph. At low values of sliding velocity and RPM it agrees closely with BS 721. At higher speed velocities it gives a lower value (e.g at 20m/s -600 RPM the value from this table for X _c.2 is about 80% of the value in BS 721-2

Table of Worm Gear Speed Factors

Note -sliding speed = V_s and Rotating speed = n₂ (Wormwheel)

Sliding speed	K _V	Rotating Speed	K _R
m/s		rpm
0	1	0,5	0,98
0,1	0,75	1	0,96
0,2	0,68	2	0,92
0,5	0,6	10	0,8
1	0,55	20	0,73
2	0,5	50	0,63
5	0,42	100	0,55
10	0,34	200	0,46
20	0,24	500	0,35
30	0,16	600	0,33

Stress Factors

Table of Worm Gear Stress Factors

	Other metal (Worm)	P.B.	C.I.	0,4% C.Steel	0,55% C.Steel	C.Steel Case. H'd
Metal (Wormwheel)	Bending (σ_bm )	Wear ( σ _cm )
Metal (Wormwheel)	MPa	MPa
Phosphor Bronze Centrifugal cast	69		8,3	8,3	9,0	15,2
Phosphor Bronze Sand Cast Chilled	63		6,2	6,2	6,9	12,4
Phosphor Bronze Sand Cast	49		4,6	4,6	5,3	10,3
Grey Cast Iron	40	6,2	4,1	4,1	4,1	5,2
0,4% Carbon steel	138	10,7	6,9
0,55% Carbon steel	173	15,2	8,3
Carbon Steel (Case hardened)	276	48,3	30,3			15,2

Zone Factor (Z)

If b _a < 2,3 (q +1)^1/2 Then Z = (Basic Zone factor ) . b _a /2 (q +1)^1/2
If b _a > 2,3 (q +1)^1/2 Then Z = (Basic Zone factor ) .1,15

Table of Basic Zone Factors

	q
z1	6	6,5	7	7,5	8	8,5	9	9,5	10	11	12	13	14	17	20
1	1,045	1,048	1,052	1,065	1,084	1,107	1,128	1,137	1,143	1,16	1,202	1,26	1,318	1,402	1,508
2	0,991	1,028	1,055	1,099	1,144	1,183	1,214	1,223	1,231	1,25	1,28	1,32	1,36	1,447	1,575
3	0,822	0,89	0,989	1,109	1,209	1,26	1,305	1,333	1,35	1,365	1,393	1,422	1,442	1,532	1,674
4	0,826	0,83	0,981	1,098	1,204	1,701	1,38	1,428	1,46	1,49	1,515	1,545	1,57	1,666	1,798
5	0,947	0,991	1,05	1,122	1,216	1,315	1,417	1,49	1,55	1,61	1,632*	1,652	1,675	1,765	1,886
6	1,131	1,145	1,172	1,22	1,287	1,35	1,438	1,521	1,588	1,625	1,694	1,714	1,733	1,818	1,928
7			1,316	1,34	1,37	1,405	1,452	1,54	1,614	1,704	1,725	1,74	1,76	1,846	1,98
8					1,437	1,462	1,5	1,557	1,623	1,715	1,738	1,753	1,778	1,868	1,96
9							1573	1,604	1,648	1,72	1,743	1,767	1,79	1,88	1,97
10									1,68	1,728	1,748	1,773	1,798	1,888	1,98
11										1,732	1,753	1,777	1,802	1,892	1,987
12											1,76	1,78	1,806	1,895	1,992
13												1,784	1,806	1,898	1,998
14													1,811	1,9	2

Duty Factor

Duty - time Factor K _H

Impact from Prime mover	Expected life hours	K _H
		Impact From Load
		Uniform Load	Medium Impact	Strong impact
Uniform Load Motor Turbine Hydraulic motor	1500	0,8	0,9	1
	5000	0,9	1	1,25
	27000	1	1,25	1,5
	60000	1,25	1,5	1,75
Light impact multi-cylinder engine	1500	0,9	1	1,25
	5000	1	1,25	1,5
	27000	1,25	1,5	1,75
	60000	1,5	1,75	2
Medium Impact Single cylinder engine	1500	1	1,25	1,5
	5000	1,25	1,5	1,75
	27000	1,5	1,75	2
	60000	1,75	2	2,25

Worm q value selection

The table below allows selection of q value which provides a reasonably efficient worm design. The recommended centre distance value "a" (mm)is listed for each q value against a range of z ₂ (teeth number values). The table has been produced by reference to the relevant plot in BS 721
Example
If the number of teeth on the gear is selected as 45 and the centre distance is 300 mm then a q value for the worm would be about 7.5

Important note: This table provides reasonable values for all worm speeds. However at worm speeds below 300 rpm a separate plot is provided in BS721 which produces more accurate q values. At these lower speeds the resulting q values are approximately 1.5 higher than the values from this table. The above example at less than 300rpm should be increased to about 9

Table for optimum q value selection

Number of Teeth On Worm Gear (z ₂)
q	20	25	30	35	40	45	50	55	60	65	70	75	80
6	150	250	380	520	700
6.5	100	150	250	350	480	660
7	70	110	170	250	350	470	620	700
7.5	50	80	120	180	240	330	420	550	670
8	25	50	80	120	180	230	300	380	470	570	700
8.5		28	90	130	130	180	220	280	350	420	500	600	700
9			40	70	100	130	170	220	280	330	400	450	520
9.5			25	50	70	100	120	150	200	230	300	350	400
10				26	55	80	100	130	160	200	230	270	320
11				25	28	55	75	100	130	150	180	220	250
12						28	45	52	80	100	130	150	100
13								27	45	52	75	90	105

AGMA method of Designing Worm Gears

The AGMA method is provided here because it is relatively easy to use and convenient- AGMA is all imperial and so I have used conversion values so all calculations can be completed in metric units..

Good proportions indicate that for a centre to centre distance = C the mean worm dia d ₁ is within the range
Imperial (inches)

( C ^0,875 / 3 ) ≤ d ₁ ≤ ( C ^0,875 / 1,6 )

Metric ( mm)

( C ^0,875 / 2 ) ≤ d ₁ ≤ ( C ^0,875 / 1,07 )

The acceptable tangential load (W _t) _all

(W _t) _all = C _s. d ₂^0,8 .b _a .C _m .C _v . (0,0132) (N)

The formula will result in a life of over 25000 hours with a case hardened alloy steel worm and a phosphor bronze wheel

C _s = Materials factor
b _a = Effective face width of gearwheel = actual face width. but not to exceed 0,67 . d ₁
C _m = Ratio factor
C _v = Velocity factor

Modified Lewis equation for stress induced in worm gear teeth .

σ _a = W _t / ( p _n. b _a. y )(N)

W _t = Worm gear tangential Force (N)
y = 0,125 for a normal pressure angle α _n = 20^o

The friction force = W _f

W _f = f.W _t / (. cos φ _n ) (N)

γ = worm lead angle at mean diameter
α _n = normal pressure angle

The sliding velocity = V _s

V _s = π .n ₁. d ₁ / (60,000 )

d ₁= mean dia of worm (mm)
n ₁= rotational speed of worm (revs/min)

The torque generated γ at the worm gear = M _b (Nm)

T _G = W _t .d ₁ / 2000

The required friction heat loss from the worm gearbox

H _loss = P _in ( 1 - η )

η = gear efficiency as above.

C _s values

C _s = 270 + 0,0063(C )³... for C ≤ 76mm ....Else

C _s (Sand cast gears ) = 1000 for d ₁ ≤ 64 mm ...else... 1860 - 477 log (d ₁ )

C _s (Chilled cast gears ) = 1000 for d ₁ ≤ 200 mm ...else ... 2052 -456 log (d ₁ )

C _s (Centrifugally cast gears ) = 1000 for d ₁ ≤ 635 mm ...else ... 1503 - 180 log (d ₁ )

C _m values

N_G = Number of teeth on worm gear.
N_W = Number of stards on worm gear.
m_G = gear ration = N_G /N_W

C _v values

C _v (V _s > 3,56 m/s ) = 0,659 exp (-0,2167 V _s )

C _v (3,56 m/s ≤ V _s < 15,24 m/s ) = 0,652 (V _s) ^-0,571 )

C _v (V _s > 15,24 m/s ) = 1,098.( V _s ) ^-0,774 )

f values

f (V _s = 0) = 0,15

f (0 < V _s ≤ 0,06 m/s ) = 0,124 exp (-2,234 ( V _s ) ^0,645

f (V _s > 0,06 m/s ) = 0,103 exp (-1,1855 ( V _s ) ) ^0,450 ) +0,012

http://www.roymech.co.uk/Useful_Tables/Drive/Worm_Gears.html

Perhitungan Power Motor

2011-04-01T20:44:00.001-07:00

Perhitungan power pada umumnya,
P = W/t dalam watt (J/s).
Dengan,
P = Power, watt
W = Usaha, J

Perhitungan dari usaha, W

W= F x s, dalam Nm = J

Dengan,

W = Usaha, Nm

F = Gaya, N

s = Jarak, m

t = Waktu, s

karena W= F x s,

sehingga P = ( F x s)/ t , dalam watt (J/s)

Perhitungan kecepatan

v = s/t, dalam m/s,

Sehingga P = F x v , dalam watt.

   2. Perhitungan efficiency
    η = P_out/P_in, dalam %
       dengan,
    ŋ = Efficiency, %
      P_out = power keluar, kW
      P_in = power masuk, kW

Bagian – Bagian Utama Mesin Milling ( Frais )

2011-04-01T20:33:00.000-07:00

1. Spindle utama
Merupakan bagian yang terpenting dari mesin milling. Tempat untuk mencekam alat potong. Di bagi menjadi 3 jenis :

a. Vertical spindle

b. Horizontal spindle

c. Universal spindle

2. Meja / table
Merupakan bagian mesin milling, tempat untuk clamping device atau benda kerja. Di bagi menjadi 3 jenis :

a. Fixed table

b. Swivel table

c. Compound table

3. Motor drive
Merupakan bagian mesin yang berfungsi menggerakkan bagian – bagian mesin yang lain seperti spindle utama, meja ( feeding ) dan pendingin ( cooling ). Pada mesin milling sedikitnya terdapat 3 buah motor :

a. Motor spindle utama

b. Motor gerakan pemakanan ( feeding )

c. Motor pendingin ( cooling )

4. Tranmisi
Merupakan bagian mesin yang menghubungkan motor penggerak dengan yang digerakkan. Berdasarkan bagian yang digerakkan dibedakan menjadi 2 macam yaitu :

a. Transmisi spindle utama

b. Transmisi feeding

Berdasarkan sistem tranmisinya dibedakan menjadi 2 macam yaitu :

a. Transmisi gear box

b. Transmisi v – blet

5. Knee
Merupakan bagian mesin untuk menopang / menahan meja mesin. Pada bagian ini terdapat transmisi gerakan pemakanan ( feeding ).
6. Column / tiang
Merupakan badan dari mesin. Tempat menempelnya bagian – bagian mesin yang lain.
7. Base / dasar
Merupakan bagian bawah dari mesin milling. Bagian yang menopang badan / tiang. Tempat cairan pendingin.
8. Control
Merupakan pengatur dari bagian – bagian mesin yang bergerak. Ada 2 sistem kontrol yaitu :

a. Mekanik

b. Electric

Dibagi menjadi 2 bagian :

1. Sederhana

2. Komplek ( CNC )

Mixer Ribbon Jacket Tank

2010-12-16T01:57:00.000-08:00

hs.suanda@gmail.com

Chilli washer

2010-12-16T01:49:00.000-08:00

hs.suanda@gmail.com

Mesin cuci cabe. Untuk membersihkan cabe sebelum di proses ke tahap selanjutnya, biasa di gunakan di perusahaan-perusahaan produsen sambal.

Stainless Steel - Grade 316 – Properties, Fabrication and Applications

2010-12-16T00:45:00.000-08:00

Chemical Formula

Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S

Topics Covered

Background

Grade 316 is the standard molybdenum-bearing grade, second in importance to 304 amongst the austenitic stainless steels. The molybdenum gives 316 better overall corrosion resistant properties than Grade 304, particularly higher resistance to pitting and crevice corrosion in chloride environments. It has excellent forming and welding characteristics. It is readily brake or roll formed into a variety of parts for applications in the industrial, architectural, and transportation fields. Grade 316 also has outstanding welding characteristics. Post-weld annealing is not required when welding thin sections.

Grade 316L, the low carbon version of 316 and is immune from sensitisation (grain boundary carbide precipitation). Thus it is extensively used in heavy gauge welded components (over about 6mm). Grade 316H, with its higher carbon content has application at elevated temperatures, as does stabilised grade 316Ti.

The austenitic structure also gives these grades excellent toughness, even down to cryogenic temperatures.

Key Properties

These properties are specified for flat rolled product (plate, sheet and coil) in ASTM A240/A240M. Similar but not necessarily identical properties are specified for other products such as pipe and bar in their respective specifications.

Composition

Table 1. Composition ranges for 316 grade of stainless steels.

Grade		C	Mn	Si	P	S	Cr	Mo	Ni	N
316	Min	-	-	-	0	-	16.0	2.00	10.0	-
316	Max	0.08	2.0	0.75	0.045	0.03	18.0	3.00	14.0	0.10
316L	Min	-	-	-	-	-	16.0	2.00	10.0	-
316L	Max	0.03	2.0	0.75	0.045	0.03	18.0	3.00	14.0	0.10
316H	Min	0.04	0.04	0	-	-	16.0	2.00	10.0	-
316H	max	0.10	0.10	0.75	0.045	0.03	18.0	3.00	14.0	-

Mechanical Properties

Table 2. Mechanical properties of 316 grade stainless steels.

Grade	Tensile Str (MPa) min	Yield Str 0.2% Proof (MPa) min	Elong (% in 50mm) min	Hardness
Grade	Tensile Str (MPa) min	Yield Str 0.2% Proof (MPa) min	Elong (% in 50mm) min	Rockwell B (HR B) max	Brinell (HB) max
316	515	205	40	95	217
316L	485	170	40	95	217
316H	515	205	40	95	217

Note: 316H also has a requirement for a grain size of ASTM no. 7 or coarser.

Physical Properties

Table 3. Typical physical properties for 316 grade stainless steels.

Grade	Density (kg/m³)	Elastic Modulus (GPa)	Mean Co-eff of Thermal Expansion (µm/m/°C)			Thermal Conductivity (W/m.K)		Specific Heat 0-100°C (J/kg.K)	Elec Resistivity (nΩ.m)
			0-100°C	0-315°C	0-538°C	At 100°C	At 500°C
316/L/H	8000	193	15.9	16.2	17.5	16.3	21.5	500	740

Grade Specification Comparison

Table 4. Grade specifications for 316 grade stainless steels.

Grade	UNS No	Old British		Euronorm		Swedish SS	Japanese JIS
Grade	UNS No	BS	En	No	Name	Swedish SS	Japanese JIS
316	S31600	316S31	58H, 58J	1.4401	X5CrNiMo17-12-2	2347	SUS 316
316L	S31603	316S11	-	1.4404	X2CrNiMo17-12-2	2348	SUS 316L
316H	S31609	316S51	-	-	-	-	-

Note: These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.

Possible Alternative Grades

Table 5. Possible alternative grades to 316 stainless steel.

Grade	Why it might be chosen instead of 316?
316Ti	Better resistance to temperatures of around 600-900°C is needed.
316N	Higher strength than standard 316.
317L	Higher resistance to chlorides than 316L, but with similar resistance to stress corrosion cracking.
904L	Much higher resistance to chlorides at elevated temperatures, with good formability
2205	Much higher resistance to chlorides at elevated temperatures, and higher strength than 316

Corrosion Resistance

Excellent in a range of atmospheric environments and many corrosive media - generally more resistant than 304. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Considered resistant to potable water with up to about 1000mg/L chlorides at ambient temperatures, reducing to about 500mg/L at 60°C.

316 is usually regarded as the standard “marine grade stainless steel”, but it is not resistant to warm sea water. In many marine environments 316 does exhibit surface corrosion, usually visible as brown staining. This is particularly associated with crevices and rough surface finish.

Heat Resistance

Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 316 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 316L is more resistant to carbide precipitation and can be used in the above temperature range. Grade 316H has higher strength at elevated temperatures and is sometimes used for structural and pressure-containing applications at temperatures above about 500°C.

Heat Treatment

Solution Treatment (Annealing) - Heat to 1010-1120°C and cool rapidly. These grades cannot be hardened by thermal treatment.

Welding

Excellent weldability by all standard fusion methods, both with and without filler metals. AS 1554.6 pre-qualifies welding of 316 with Grade 316 and 316L with Grade 316L rods or electrodes (or their high silicon equivalents). Heavy welded sections in Grade 316 require post-weld annealing for maximum corrosion resistance. This is not required for 316L. Grade 316Ti may also be used as an alternative to 316 for heavy section welding.

Machining

A “Ugima” improved machinability version of grade 316 is available in round and hollow bar products. This machines significantly better than standard 316 or 316L, giving higher machining rates and lower tool wear in many operations.

Dual Certification

It is common for 316 and 316L to be stocked in "Dual Certified" form - mainly in plate and pipe. These items have chemical and mechanical properties complying with both 316 and 316L specifications. Such dual certified product does not meet 316H specification and may be unacceptable for high temperature applications.

Stainless Steel - Grade 304

2010-12-15T03:42:00.000-08:00

Chemical Formula

Fe, <0.08% C, 17.5-20% Cr, 8-11% Ni, <2% Mn, <1% Si, <0.045% P, <0.03% S

Background

Stainless steel types1.4301 and 1.4307 are also known as grades 304 and 304L respectively. Type 304 is the most versatile and widely used stainless steel. It is still sometimes referred to by its old name 18/8 which is derived from the nominal composition of type 304 being 18% chromium and 8% nickel.

304 Stainless Steel

Type 304 stainless steel is an austenitic grade that can be severely deep drawn. This property has resulted in 304 being the dominant grade used in applications like sinks and saucepans.

304L Stainless Steel

Type 304L is the low carbon version of 304. It is used in heavy gauge components for improved weldability. Some products such as plate and pipe may be available as “dual certified” material that meets the criteria for both 304 and 304L.

304H Stainless Steel

304H, a high carbon content variant, is also available for use at high temperatures.

Property data given in this document is typical for flat rolled products covered by ASTM A240/A240M. ASTM, EN or other standards may cover products sold by Aalco. It is reasonable to expect specifications in these standards to be similar but not necessarily identical to those given in this datasheet.

Chemical Composition

Table 1. Typical chemical composition for 304 stainless steel alloys

%	304	304L	304H
C	0.08 max	0.03 max	0.10 max
Mn	2.0	2.0	2.0
Si	0.75	0.75	0.75
P	0.045	0.045	0.045
S	0.03	0.03	0.03
Cr	18-20	18-20	18-20
Ni	10.5	12	10.5
N	0.1	0.1	-

Properties

Mechanical Properties

Table 2. Typical mechanical properties for 304 stainless steel alloys

Grade	304	304L	304H
Tensile Strength (MPa)	520	500	520
Compression Strength (MPa)	210	210	210
Proof Stress 0.2% (MPa)	210	200	210
Elongation A5 (%)	45	45	45
Hardness Rockwell B	92	92	92

Physical Properties

Table 3. Typical mechanical properties for 304 stainless steel alloys

Property	Value
Density	8.00 g/cm³
Melting Point	1400-1450°C
Modulus of Elasticity	193 GPa
Electrical Resistivity	0.072x10^-6 Ω.m
Thermal Conductivity	16.2 W/m.K at 100°C
Thermal Expansion	17.2x10^-6 /K at 100°C

Alloy Designations

Stainless steel 304 also corresponds to the following standard designations and specifications:

Euronorm	UNS	BS	En	Grade
1.4301	S30400	304S15 304S16 304S31	58E	304
1.4306	S30403	304S11	-	304L
1.4307	-	304S11	-	304L
1.4311	-	304S11	-	304L
1.4948	S30409	304S51	-	304H

Corrosion Resistance

304 has excellent corrosion resistance in a wide variety of environments and when in contact with different corrosive media. Pitting and crevice corrosion can occur in environments containing chlorides. Stress corrosion cracking can occur at temperatures over 60°C.

Heat Resistance

304 has good resistance to oxidation in intermittent service up to 870°C and in continuous service to 925°C. However, continuous use at 425-860°C is not recommended if corrosion resistance in water is required. In this instance 304L is recommended due to its resistance to carbide precipitation.

Where high strength is required at temperatures above 500°C and up to 800°C, grade 304H is recommended. This material will retain aqueous corrosion resistance.

Fabrication

Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Cold Working

304 stainless steel readily work hardens. Fabrication methods involving cold working may require an intermediate annealing stage to alleviate work hardening and avoid tearing or cracking. At the completion of fabrication a full annealing operation should be employed to reduce internal stresses and optimise corrosion resistance.

Hot Working

Fabrication methods, like forging, that involve hot working should occur after uniform heating to 1149-1260°C. The fabricated components should then be rapidly cooled to ensure maximum corrosion resistance.

Heat Treatment

304 stainless steel cannot be hardened by heat treatment.

Solution treatment or annealing can be done by rapid cooling after heating to 1010-1120°C.

Machinability

304 has good machinability. Machining can be enhanced by using the following rules:

 Cutting edges must be kept sharp. Dull edges cause excess work hardening.

 Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material.

 Chip breakers should be employed to assist in ensuring swarf remains clear of the work

 Low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities.

Welding

Fusion welding performance for type 304 stainless steel is excellent both with and without fillers. Recommended filler rods and electrodes for stainless steel 304 is grade 308 stainless steel. For 304L the recommended filler is 308L. Heavy welded sections may require post-weld annealing. This step is not required for 304L. Grade 321 may be used if post-weld heat treatment is not possible.

BRIX CONVERTION TO VISCOSITY

2010-12-15T03:25:00.000-08:00

X
%	10º	20º	30º	40º	50º	60º	70º
TS
60	77.6	40.9	23.6	14.7	9.8	6.7	4.8
61	93.6	48.4	27.5	16.8	11.0	7.6	5.4
62	114.1	57.7	32.2	19.4	12.5	8.5	6.0
63	140.2	69.3	37.9	22.5	14.3	9.6	6.7
64	174.3	84.0	45.1	26.3	16.0	11.0	7.6
65	219.1	103.0	54.1	31.1	19.2	12.5	8.6
66	276.9	127.4	65.4	36.8	22.4	14.4	9.6
67	359.5	159.4	79.8	44.1	26.4	16.7	11.2
68	470.4	201.9	96.5	53.1	31.3	19.5	12.8
69	624.7	259.1	122.9	64.8	37.3	23.0	14.9
70	844.2	337.1	155.1	79.8	45.1	27.3	17.5
71	1160.0	445.4	198.3	99.4	54.8	32.6	20.5
72	1630.0	596.4	257.3	125.2	67.5	39.2	24.4
73	2338.0	818.0	339.0	159.9	84.0	47.8	29.2
74	3434.0	1141.7	453.9	207.2	106.4	58.8	35.4
75	5181.0	1629.0	619.3	272.6	135.1	73.1	42.9
76	7980.0	2373.0	689.0	374.5	172.9	91.7	53.7
77	12740.0	3507.0	1,260.0	514.5	226.8	118.0	66.8
78	21490.0	5509.0	1,876.0	735.0	308.7	154.7	85.4
79	36750.0	8680.0	2,807.0	1,050.0	422.1	204.4	109.2
80	65310.0	14490.0	4,396.0	1,575.0	598.5	275.8	142.1
81	124600.0	24990.0	7,070.0	2,415.0	868.0	383.0	190.0
82	245700.0	45220.0	11,970.0	3,885.0	1,302.0	541.0	261.0
83	525000.0	86100.0	21,140.0	6,461.0	2,016.0	796.0	363.0
84	1,19x10⁴	175000.0	38,500.0	11,340.0	3,290.0	1,204.0	541.0
85	2,95x10⁴	378700.0	77,700.0	21,000	5,600.0	1,916.0	819.00

KONVERSI VESCOSITY

2010-12-15T03:19:00.000-08:00

pascal second [Pa*s] = 1

kilogram-force second/square meter = 0,102

newton second/square meter [N*s/m²] = 1

millinewton second/square meter = 1000

dyne second/square centimeter = 10

poise [P] = 10

centipoise [cP] = 1000

millipoise [mP] = 10000

micropoise [µP] = 1000000

pound-force second/square foot = 0,021

poundal second/square foot = 0,672

gram/centimeter/second [g/(cm*s)] = 10

slug/foot/second [slug/(ft*s)] = 0,021

pound/foot/second [lb/(ft*s)] = 0,672

pound/foot/hour [lb/(ft*h)] = 2419,088

Belt Length Changes

2010-12-15T02:15:00.001-08:00

By Norm Christopherson

In the process of making a motor pulley size change the old belt may no longer be the correct length. A new belt of the correct length will need to be obtained. But, how can the new belt length be determined without resorting to the trial and error method?

The belt length formula solves the problem. First of all, some basic measurements of the pulleys and shaft center-to-center distances must be made. See figure 13-3 for an illustration of the pulley sizes for this example.

Figure 13-3

The original 8" pulley, which was used with the old 3000 cfm, has been replaced with the new 10.7" motor pulley to give the corrected 4000 cfm, matching the 10-ton system. Now the belt length is different and needs to be calculated. The dimensions in the diagram above were taken and will be used to make the calculation.

When solving math problems, which contain brackets and parentheses, remember to work from the inside of the problem to the outside. That is, solve the parentheses first, then the brackets next and finally the remainder of the math as this example problem does. The capital letter D stands for the larger diameter pulley and the small letter d stands for the smaller pulley. The two shafts are measured center to center and are 20 inches apart in this example. The letter C stands for this center-to-center measurement. Prior to taking the center-to-center measurements, the motor hold down bolts should be loosened and the motor moved to asit in the center of the bolt adjustment slots. This ensures that after the new belt is installed, there is some adjustment available in both directions for belt tension.

Purchasing an 82-inch belt will fit the requirements for the new pulley and there will be sufficient space on the motor base to adjust the belt tension. Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications.