Four Reasons Why Rubber Tolerance Ranges Are Wider

05-06-2016

A manufacturing tolerance can be defined as the difference between the upper and lower limit dimensions of a part. The manufacturing tolerance is usually expressed as a “plus” and/or “minus” which means the nominal dimension can vary within that “plus or minus” range and still be considered “in size.”

Here is an example:

The manufacturing tolerance of the inside diameter of a rubber tube was specified as: 0.250” +/- 0.010”

Based on that manufacturing tolerance specification, all three of these tubes would be considered ‘in size’ or ‘in spec’. Manufacturing tolerances will vary from industry to industry and from material to material. For instance, rubber tolerances tend to be wider than plastic or other rigid material tolerances.

Here are four reasons why:

1. Rubber is a soft material

It is difficult to hold tighter tolerances on soft materials because the measuring method often causes deformation, which can significantly alter the measured value.

2. Rubber is natural

Natural rubber is an organic material that comes from live trees; therefore, there can be material variances from lot to lot that will create relative tolerance variances.

3. Rubber is compounded

Other ingredients are added to the natural or synthetic rubber to help set off the cure, this mixture of added ingredients can affect the amount of swelling or shrinking.

4. The overall rubber manufacturing process

Variations, such as rubber shrinkage or swelling, can occur during manufacturing, sometimes affecting the tolerances because they cannot always be predicted.

These are the main reasons rubber has wider tolerance ranges than other materials, such as plastics. But for most applications it’s not a problem, which is why natural rubber is still used in many industries for many applications.

Even though rubber usually has a wider tolerance range, at The Hygenic Corporation we’ve learned to produce our natural and synthetic rubber products within very tight tolerance ranges due to many decades of experience.

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