ASTM specs and what they mean for rubber.



There are many standards used to qualify rubber. ASTM, NACE as well as others which attempt to define and standardize the industry.

I will attempt to simplify and clarify some of the standards and usefulness.

Some specifications are valid as a key performance indicators for wear, while others are simply elemental, the physical characteristics.

ASTM D297 or Specific gravity is a good example of an elemental specification. The fact that rubber has a specific gravity less than one is a good indicator that it will float. Floating does not necessarily indicate that the rubber will perform better or worse in a slurry application.

In the old days this was used to determine the actual content of natural rubber. Adders and filler like clay and carbon’s can affect the buoyancy of rubber they can also affect it’s wear characteristics most times in a positive way. Material science has gone a long way since the floating test.

Cut and Chip The best indicator for how rubber sheet will perform in a real world application is the  “Cut and Chip” resistance. This test is used to measure the performance of a rubber in a wear application. This test was originally devised by the tire companies to evaluate service life of tires in various conditions. This is a much better indicator of how a compound will perform in a wear application and much less an elemental test, describing the physical properties.

ASTM D2240 or Hardness Shore A although this is a very popular way of describing rubber. Effectively this is another elemental specification. People will argue that the durometer of rubber aid in different wear characteristics and they would be right. But it is still not a final indicator of how it will wear. It simply defines it’s hardness.

ASTM  D412 This one covers Tensile and Elongation this is an interesting specification because elongation and tensile are very good when describing rubber for track. Let’s take a snowmobile track for example. The moment you spin a track, you want the rubber to have enough elongation to absorb some of the initial  inertia. In a rubber lining application it is somewhat irrelevant. When bonding a rubber sheet to steel sub-straight the elongation will never really come into play for wear.

ASTM D624 Tear Die C another elemental indicator. In rubber lining, the force at which the rubber sheet will tear is not good wear resistance indicator. When building a tire, snowmobile or tank track this is a great indicator. Adhered to steel tearing it is the least of your concerns. Ultimately all these factors only help to describe how this material could perform. The forces required for an adhesive pull test is 25lbs to pass ASTM and Nace pull tests are very low compared to most sheet listed tear specifications.

ASTM D7121 Rebound and Resilience Although rarely listed in a rubber sheet or specification, the ability of a rubber to return to it;s original  shape is important especially when defending against rocks, slurry and wear.

ASTM D5963 Wet and Dry Abrasion loss This is a good indicator of if your rubber will last in a wear application. This test directly measures wear. The best wear resistant rubbers will have good wet and dry abrasion properties mixed with excellent cut and chip resistance.

ASTM D573 Heat Aging Depending on the application this is a good test to evaluate rubber longevity. As rubber is generally a cocktail of materials how they perform over time and temperature will vary. This test monitors the physical changes of rubber with aging. This elemental test will give indication of  how the rubber will perform over time.

Rubber wear characteristics are complex and understanding what the specification mean will help you in the long term choice for the various applications.