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# The Four Most common Misunderstandings When Reading Rubber Test Reports

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Everyone, at some point, has read through a rubber test report and come to an incorrect conclusion. The pass/fail limits and the results are right there on the results, but we just misinterpret them for some reason. There could be a pass, but we see it as a failure. It would be the same as a police officer writing a ticket for someone going just under the speed limit rather than just over.

There's no problem with the test itself, rather our interpretation of it. This problem crops up in the rubber seal industry at least once a month. A pass could be interpreted as a fail, and good numbers could be read as bad ones. Here are the four most common misunderstandings when reading rubber test reports.

## Low Temperature

A lot of low temperature testing deals with negative numbers, which can create confusion with greater than/less than test limits. If the limit was -30 max then you might feel that -32 was a failure because 32 is greater than 30. Because we're dealing with minus numbers though, -32 would be a pass. -28 would be a failure. It's simple maths, but sometimes we forget what we learn if we never apply it.

## Compression Set

The compression set will always be expressed through a maximum limit, such as 20% max. This means that every value up to - and including - 20% would be a pass. Some people feel that 20% would fail against a limit of 20% because it isn't lower than the maximum. Barely passing is hardly ideal, but it's still a pass. The compression set measures how much of the original squeeze has been lost. 100% means that the material is now completely flat, while 0% means it has returned to its original dimensions. Small numbers are good for compression set, while big numbers are bad.

## Compressive Stress Relaxation

Compressive Stress Relaxation is typically used in the car and truck industry as a measure of the spring force left in the rubber following exposure to fluids and aging. Any limits are expressed as "10% min retained load force" or something similar. CSR is the opposite of compression set, which is why some people mistakenly believe that results of 15% are thought of as failing a "10% min" limit. The more retained seal force there is the better when it comes to CSR.

## One-Sided Limits

Most of the limits set for elongation and tensile strength change after fluid immersion and heat aging are one-sided limits; which basically means they have just one limit rather than two. So it could have a limit of "-30% max" for example. So what happens if the result is a positive number like +2? This would be a pass. There are no other implied limits to a one-sided limit. Anything above a 0 or above the number on the opposite sign is not automatically a failure. Even a result of 100% would be a pass with a one-sided limit of -30%. If the specification doesn't explicitly specify a two-sided limit then there is just one limit.

In an ideal world there would be someone on hand to explain these things to you, but we don't live in a perfect world. For now, we'll just have to make do with reading through fluid seal resources and taking a better look at the results.