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16 MECHANICAL TRANSMISSIONS

Roller Chain

Roller chain is by far the most popular means of power
transmission used on a drilling rig. Two typical applications of
roller chain are a double strand of 2-in. pitch chain is used as a cat
shaft drive within a selective transmission and a single strand of
motorcycle-size chain is used to drive a lubrication pump. Some
advantages of roller chain drives are:
1. Efficient operation — 98%
2. Positive drive, without slip.
3. Compact drive, requires relatively little space.
4. Requires no initial tension.
5. Can provide great speed reduction (10-1).
6. Needs slightly less perfect shaft alignment than gears.
7. Is easy to maintain and replace.
8. Is not affected by reasonable changes in climate or
surroundings.
9. Is durable.
10. Can be run in either direction.
As the speed of chain drive has been continually raised
during recent years the majority of chain drives on most modern
internal combustion powered rigs now use chains of 2,5-in. pitch
or less rather than the long pitch API chain.
The roller chain used in drilling rig main power transmission
drives is usually manufactured in accord with the requirements of
the American Standards Association. Normally used sizes are 2 in.
and 1-in. pitch. With some exceptions, chain nomenclature when
divided by 80 results in the chain pitch. For example, chain
number 140H is (140/80) 1,75-in. pitch_chain with heavy (H)
strength side bars.

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