Chain Drive

The advantages of chain drive systems are as follows:

1. Shaft center distances are

relatively unrestricted. Whereas

gear drive center-to-center

distances are restricted to

specific dimensions for a given

set of gears, the center distances

between two chained sprockets

can vary anywhere from 50% to

300% or more of their pitch

diameters.

2. Chain Drive are relatively easy

to install. Assembly tolerances

are not as restrictive as those for

gear drives. Chain drives are a

better choice for less experienced builders working with a minimum of machine tools.

3. Chain drives can be readily redesigned and reconfigured in comparison to gear drive

systems.

4. Chains perform better than gears under shock loading conditions.

5. Chain drives spread operating loads over many teeth whereas the operating loads acting

on gear drives are concentrated on one or two teeth.

6. Chain drives do not require tension on the slack side (Belt drives do) thus bearing loading

is reduced.

7. Chain drives require less space for a given loading and speed condition than pulleys and

belts.

8. Chain drives systems are (usually) less costly to build and maintain than an equivalent

gear drive.

While chain drives offer many advantages, there are good reasons to choose a gear drive system,

particularly when:

1. Compact drive requirements

demand the shortest possible

distance between shaft

centers.

2. High speed ratios are

required.

3. High rotating speeds (RPM)

are required.

4. High horsepower AND high

speed loading is required.

Belt and pulley systems also offer design advantages with respect to either chain or gear drives.

These advantages include:

1. Belts slip, chain and gears drives do not. This is a useful advantage for drive systems that

do not require positive speed

ratios to be maintained.

Momentary overloading

loading conditions may cause

a belt to slip over the pulleys

whereas a chain may break or

a gear tooth may shear. Belts

offer built in “Clutching”. Of

course sustained overloading

will cause premature wear and

“Burned out” belts.

2. Belt drives are not as noisy as

chain or gear drive systems.

3. Belt drives can operate over

longer center distances than

chain drives.

Belts are better suited to extremely high-speed ratios.

Flat belt

Flat belts — Most of the general

principles of belt drive operation discussed

earlier apply to flat belt drives.

In calculating tension ratios for flat

belts, consult the manufacturer for

typical values of the friction coefficient,

f. For a flat belt drive, k = 1.

Several useful formulas for endless

belts follow (refer to Figure 4). For

belt length in an open belt drive:

L0=2C+1.57(d+D)+(D-d)square/4C

For Crossed belt Drive:

Lx=2C+1.57(d+D)+(D+d)sq/4C

Belt Creep/Slip

Belt creep and slip — All belts

(except synchronous) creep, but creep

must be differentiated from slip. For

example, a V-belt under proper tension

creeps about 0.5% because of its

elasticity and the changes in cross

section and length taking place as a

section of the belt moves from the

tight side to the slack side of the drive

and back. That cyclical stressing, plus

the bending action of the belt as it

travels around the sheaves, causes

only a slight increase in belt temperature.

Most of that heat will be dissipated

by the sheaves so that they will

be only slightly warm if touched. (Of

course, the belt drive must be at rest

before an operator would dare touch

the sheaves.)

Slip, which is a movement greater

than the 0.5% creep, can create

enough heat to be very uncomfortable

if the sheaves are touched (again,

when the drive is stopped). Anotherway to check for slip is to touch the

belt (when it is stopped). If the belt is

uncomfortable to the touch (over 140F), it probably needs to be tightened.

Advantages/Drawbacks of Flat belt Drives

Advantages of belt
drives include:
1. No lubrication isrequired,
or desired.
2. Maintenance is
minimal and infrequent.
3. Belts dampen
sudden shocks or
changes in loading.
4. Quiet, smooth operation.
5. Sheaves (pulleys)
are usually less expensive
than c h a i n
d r i v e s p r o c k e t s
and e x h i b i t l i t t l e
wear over long periods
of operation.

Disadvantages:

1. Endless belts usually

cannot be repaired when

they break. They must be

replaced.

2. Slippage can occur, particularly

if belt tension is not properly set

and checked frequently. Also, wear of

belts, sheaves, and bearings can reduce

tension, which makes retensioning

necessary.

3. Adverse service environments

(extreme temperature ranges, high

moisture, oily or chemically filled atmospheres,

etc.) can damage belts or

cause severe slipping.

4. Length of endless belts cannot be

adjusted.