Dimensional tolerance allowance for tread rubber-(HOT PROCESS/DIE SIZE)

DIMENSIONAL TOLERANCE ALLOWANCE ON TREAD RUBBER Another area where the tread manufacture has to concentrate is the dimensions [width and thickness] of rubber. Here also Rubber Manufacturer’s Association based at New York has spelled out tolerance limits in dimensions for Tread Rubber.

STANDARD DIMENSIONAL TOLERANCES FOR TREAD RUBBER – Specified by The Retread and Repair Materials Committee of the Rubber Manufacturer’s Association, INC, New York.

For the purpose of measuring the width and thickness of tread rubber, a cut should be made straight across the full width of the tread rubber with a sharp knife. The cut should be made not less than three feet or more than six feet from the outside end of the roll and also it must be away from the point where the weight of the roll or other pressure may have distorted the dimensions.

Dimensions should be measured with an accurate scale which is marked to read directly in thirty-seconds fractions of an inch.

Dimension tolerances

1. Thickness includes cushion if used, but does not include backing:For nominal gauge of 13/32nds inch and less, a tolerance of minus zero and plus 3/64ths inch is established [This excludes tread rubbers containing traction producing additives]For nominal gauges of 14/32nds inch up to and including 18/32nds inch, a tolerance of minus 1/64th inch and plus 2/64th inch is established.For nominal gauges of 20/32nds inch and up to and including 24/32nds inch, a tolerance of minus 1/64th inch and plus 3/64th inch is established.For nominal gauges of 26/32nds inch and up to and including 32/32nds inch, a tolerance of minus 2/64th inch and plus 4/64th inch is established.For nominal gauges over 1″, tolerance to be established by tread rubber manufacturer.2. WidthFor tread rubber sizes with a base width of 6 inches and less, a tolerance of plus 1/16th inch and minus 1/8th inch established.For Tread Rubber sizes with a base width of more than 6 inches but not more than 12 inches, a tolerance of plus 1/8th inch and minus 1/8th inch is established.For Tread Rubber with a base width of over 12 inches a tolerance of plus 1/4th inch and minus 1/4th inch is established.3. Bevel or wing width [Wings should be straight neither concave nor convex]
Wing width Control
For ‘Wing size’ tread rubber with a base width of 6 inches or less, the centre-line of the crown should coincide with the centre-line of the base within 1/16th inch. For ‘wing size’ tread rubber with a base width of 6 inches but not over 12 inches , the center line of the crown should coincide with the centre-line of the base within 1/8th inch. For ‘wing size’ tread rubber with a base width of over 12 inches, the center line of the crown should coincide with the center line of the base within 1/4th inch.
Bevel width
For all ‘Bevel’ tread rubber the center-line of the crown should coincide with the center-line of the base within 1/16th inch.4. Wing edge thickness
A maximum edge thickness of 7/64th inch is established [This excludes tread rubbers containing traction producing additives]The thickness should be measured by using a calipers with graduations in 64ths of an inch.The cal lipers should have the jaws opened at 7/64th inch and the wing edge inserted. If the edge is admissible, it meets the required dimension.5. Center line marking
The center of the center line marking should be located within 1/16th inch of the exact center-line of tread rubber having a crown width of 10 inches or less. If the crown width exceeds 10 inches a tolerance should be within 1/8th inch.

Strict adherence to the correctness of size or tolerance limits as specified above can obviate a number of retreading failures arising out of insufficient thickness and width of tread rubber supplied.