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METU ME 308 Machine Elements II Spring 2012

1Prepared by:Ferhat SalamRoom: C-210 Phone: 5267

E-mail:[email protected] SPRING 2012 Date: 24.05.2012

ME 308 MACHINE ELEMENTS II

TUTORIAL 9

Design of Chain Drives

Problem 1:A roller chain is to transmit 60 kW at a speed of 500 rpm. Reduction ratio is 3. Driven

machinery may cause heavy shock loads while the driving motor has normal torque

characteristics. Center distance should be within and chordal speed variationshould be 1.5%. Design the power transmission system.

Problem 2:In a roller chain drive, chordal speed variation should be less than 1.3 %.and the center

distance is to be adjusted within Reduction ratio of the chain system is 4.Determine:

a) pitch diameters of the sprocketsb)

the chain lengthc) exact center distance

Do not use offset link.
mailto:[email protected]:[email protected]:[email protected]:[email protected]

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2Problem 1 Solution:For smooth operation at moderate and high speeds it is considered good practice to use adriving sprocket with at least 17 teeth. Using 19 or 21 teeth will, of course, give a better life

expectancy with less noise.

From the chordal speed variation: [ ], or approximately:

For , Then, the teeth number of the driving sprocket can be selected as , and the teethnumber of the driven sprocket will be .Lets try to have a solution using a single strand first.

Allowable power can be written as: The factors in this equation can be obtained as follows:

Tooth correction factor, , for from Table 17-22.Multiple strand factor,

, for one strand from Table 17-23.

Load service factor, , for heavy shocks from Table 17-15.Minimum rated capacity for the stated power transmission: Referring to Table 17-20 with the sprocket speed 500 rpm, chain with ISO(ANSI) Type C#140 is appropriate where Htab=85.8 kW.

But when speed is 500 rpm, chain-140 is of lubrication type C which requires oil-stream

lubrication since it needs a sophisticated lubrication system. It would be better to use a

type-B chain for which bath lubrication is sufficient. This can be achieved by increasing thestrand number and therefore reducing the required rated power capacity of the chain.

Therefore use 2 strands chain drive.

, for two strands. Then ISO(ANSI) type-B 120 is appropriate for this case where Now we can proceed to determine dimensions of the components;

From Table 17-19 for chain #120

The pitch for the sprockets: Center distance range can be used to determine the length of the chain:

()

()

() Similarly,

()

The number of pitches can be 67, 68 or 69. In order to avoid a special link, it is advised to

have even number of pitches in the chain. So, , is selected. Center distance can be found by using the following equations:

and ( )

Pitch diameters of the sprockets:

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3Problem 2 Solution:

From the chordal speed variation: [ ], or approximately: For

, Then, the teeth number of the driving sprocket can be selected as

, and the teeth

number of the driven sprocket will be . Since center distance is given in a very tight range all available pitch diameters for a chain

drive should be tried and one that gives even integer ratio should be used.Then, by using the following formula and Table17-19, a table of and for each available pitch value, can be constructed.

Chain Number Pitch, p[mm] (L/p)min (L/p)max

25 6.35 340.08 340.71

35 9.52 244.01 244.43

40-41 12.70 195.96 196.30

50 15.88 167.32 167.57

60 19.05 148.37 148.60

80 25.40 124.88 125.04

100 31.75 111.04 111.16

120 38.10 102.02 102.12

As seen from the table only two possibilities, which give integer (L/p) ratio, are found.

Since it does not require using of an offset link one should take even integer (L/p) ratiogiven in the third and fourth columns.

Then, chain size 40-41 is chosen. Therefore, and a)

b) , as found before c)Exact center distance can be obtained by using the above information

and ( )

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