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BEAD CHAIN DRIVE SYSTEMS

     
     
Design Considerations      
Choosing belt or chain: In deciding between bead belt and bead chain, the following factors should be considered:

Tensile load on the drive should be within the values given in table 1, "Maximum Static Loads" (listed below) if bead chain is to be used.  A safety factor of about 4 should be allowed.  Transient forces due to detents, stops, etc. must also be considered in calculating the maximum tension in the drive.

Pitch accuracy of bead chain is somewhat superior to that of bead belt.  Brass of better for point-to-point accuracy than stainless steel because the better cold working properties of brass result in more accurate geometry.

Bead chain loops can be joined in the field, whereas plastic bead belt must be factory assembled.

Plastic bead belt is a good electrical insulator and will not radiate electromagnetic energy when used in electronic instruments.  Metallic bead chain is an electrical conductor but can be insulated from other components by the use of plastic sprockets.

Stainless steel chain can be used for sanitary or corrosive applications.  This quality is important because the beads are hollow and can thus can carry contaminating liquids.  Generally. lubrication cannot be used in either sanitary or chemical applications.  Plastic belt cannot be used in the presence of many solvents.

Plastic bead belt can be used at temperatures up to 180 F.  Stainless steel should be used for high-temperature applications, although the oxides which form on the surface reduce flexibility.

While bead chain is more flexible than bead belt, its flexibility decreases when wrapped around small diameter sprockets with less than 16 bead sockets.

Choosing Sprockets

Drive ratio in a bead belt drive is the ratio of the number or bead-sockets rather than the pitch diameter of the sprockets.  The life expectancy of chain is determined by the total number of cycles through which it will operate and by the amount of bending that will take place during a cycle.  Small diameter sprockets therefore tend to shorten chain life.  Large diameter sprockets cause the chain to traverse at high linear speeds but provide better angular precision than small diameters.  In addition, the larger the sprockets, the smoother the drive.

Molded nylon sprockets are quieter than metal sprockets,and are less expensive.  However, their precision is somewhat less than for machined sprockets.

Joining Chain

If the chain or belt is to be an endless loop, provisions must be made for joining and installing.  Because joints for plastic bead belt are molded, they must be facrory made.  Bead chain can be joined in the field by means of special tools or by using double-bead connectors.  When endless chain is not required, a variety of other fittings are available for attaching the chain.

Length of Loop: If possible, loops should be ordered to size by specifying either the number of beads or the total length.  Belt length is rounded off to the nearest bead, so the design must allow for variations of +/- one pitch length.  Loops ordered by the number of beads will have the exact number specified, but the length may vary by the  amounts shown in table 2, "Dimensions and Materials for Metallic Bead Chain",  below.

Calculating the length of bead belt or chain generally requires a layout of the drive.  Because the pitch is a function of sprocket diameter, calculation can become difficult.  A scale drawing will generally give a good estimate of the number of beads in a loop.

Lubrication

Generally, lubrication between sprocket and chain is not practical.  In the case of metallic chain, internal lubrication can reduce wear and help maintain pitch accuracy.  Nondrip oils and liquid coating waxes are useful as lubricants.

Chain is impregnated by complete immersion in the lubricant, which is then heated to a maximum of 150F.  The chain is allowed to cool to room temperature before being removed from the lubricant.  A film of lubricant remains on the inside of the hollow balls.  Chains lubricated by oil should be drained. Those lubricated by wax should be drained and dried in air.  They will then feel dry to touch when ready for installation.  Lubrication for plastic bead belt is not recommended.

Table 1

Maximum Static Loads (MSL) for Metallic Bead Chain

Chain Size

Material

MSL(lbs.)

3

Brass

15

3

Stainless Steel

20

6

Brass

25

6

Stainless Steel

45

10

Brass

40

10

Stainless Steel

70

13

Brass

75

13

Stainless Steel

120

Table 2

Dimensions and Materials for Metallic Bead Chain

Chain Size

Bead Dia. (in Inches)

Nominal Pitch
(in Inches)

Cumulative Pitch Error (in./ft.)

3

.093 +/-.002

.117 +/-.001

+/- .050

6

.125 +/-.003

.166 +/-.003

+/- .085

10

.188 +/-.004

.240 +/-.005

+/- .125

13

.250 +/-.005

.324 +/-.009

+/- .165

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Last modified: 02/28/08