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Can someone help me understand durometer and shore hardness testing with relation to rubber hardness?

My understanding is durometer measures hardness, shore is a different type of scale. The image below was captured from Rubber Hardness Chart

enter image description here

Is it safe say that Shore 60A is same as Shore 20D. A and D represents the scale. Why not use one scale Shore 00 ranging from 0-200.

Reference:

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  • $\begingroup$ The differing scales allow for finer measurements and comparison between similar materials. $\endgroup$
    – jko
    Sep 9 '20 at 14:45
  • $\begingroup$ To lazy to type an answer but the forces and testing bodies are different between OO and D (table on wp), presumably the 'softer' tests don't yield real results on harder materiels, the 'harder' teste would damage some materials too much. $\endgroup$
    – mart
    Sep 9 '20 at 15:12
  • $\begingroup$ @mart, thank you for the hints. Looks like their is a pin in the instrument. Does the pin change with Shore A, and Shore D or are they different instruments altogether. $\endgroup$ Sep 9 '20 at 15:25
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The basic method for hardness measurement is using an indender and a standard force on a material surface and then measuring either the depth or the area of the imprint.

However, is happening with almost all hardness scales is that you cannot obtain meaningful results for all types of materials, for a given force and a specific indender. Therefore what you are doing is you change either the force level or the indender.

In the case of Shore A, and D you can see in the following image, enter image description here

the indender for D, is more sharper compared to A, and as a result it can more easily leave an imprint on harder materials. On the other hand A, will leave a moderate imprint.

The overlap region is basically a good way to validate to make sure that the interpretation of the results from both methods is properly normalized.

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Different strokes (tests) for different folks. Metal hardness test methods include Rockwell ( A B C D E,etc), Rockwell superficial, brinell 3000 & 500, vickers, knoop, diamond pyramid, Shore ; and the portable variations of most of these methods. I don't know about rubber but there are books written to describe the nuances of difference of the metal hardness test methods.

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  • $\begingroup$ Rockwell superficial, Brinell, Vicker, shore, are test standards or test instrument vendors or both. $\endgroup$ Sep 9 '20 at 15:22

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