hardness of rubber under higher temp

[TeckBeng]

Hi

Is there a standardized method to measure the hardness of rubber (say in Shore A) at higher temperature?

If not, anyone try doing this before? Can share your experiences?

Cheers

 

[GrahamBennett]

When I worked for a Japanese tyre company's technical centre (based in Rome), we would test hardness at about 70°C as well as at room temperature. I think the hardness button was heated to about 70 - 75°C before being quickly transferred to a bench-mounted hardness machine and tested. Obviously the temperature would have fallen somewhat but would still be over 60°C.

 

[TeckBeng]

Thanks Graham,

I have a bench top type machine also...the Bareiss Digi Test II Digital Automated Duro-meter...

But i am worried it may damage the electronics inside.

From your experience, the hardness will drop somewhat right?

cheers

 

[GrahamBennett]

The hardness will drop 5 or 6 points if memory serves me correctly. The machine won't get so hot it will damage the electronics I wouldn't have thought.

 

[tom1953]

I think the hardness change at elevated temperatures will be at least somewhat dependent on the polymer and the formulation. If the room temperature hardness is influenced by polymer crystallinity (for high ethylene EPDMs, for example) or crystalline resins (e.g., high styrene resins), the reduction in hardness at elevated temperatures will be more than if the hardness at RT was obtained by filler or crosslinking.

I haven't done elevated temp hardness testing in a while, but we just used to put a (gloved) hand with a hand-held durometer in the oven for the quick hardness tests.

 

[Compositepro]

The probe of a shore hardness tester is pretty small so I don't think that the probe temperature would have a large effect on the measurement. I think tom1953's method is quite reasonable.

 

[Compositepro]

The probe of a shore hardness tester is pretty small so I don't think that the probe temperature would have a large effect on the measurement. I think tom1953's method is quite reasonable.

 

[GrahamBennett]

In my opinion a hand-held hardness tester can give very unreliable values because of the force you can apply. Bench-mounted equipment is far more accurate as the dead-load is a fixed mass.

 

[stancom]

The answer to the 1st query is that standard hard tests such as ISO 48 for dead load IRHD and ISO 7619 for pocket meters do allow for elevated temperature tests. However, standards bodies have been reluctant to promote the practice for specification purposes because of questionable reproducibility, unavailability of suitable equipment and, it must be said, lack of sustained demand. Users are encouraged to measure stiffness in terms of properties such as shear and compression moduli. Naturally there are exceptions and rubber covered rollers come to mind. With the 2nd query in mind note that Katsura Roller Mfg has published a table of hardness vs temperature for a range of rubber (visit katsura-r.com)

 

[TeckBeng]

@tom1953 thanks for the info on the formulation part, i never thought about it this way

@stancom, yes, i found the table at katsure-r.com site. Thanks for the pointer. It's good reference.

I think i will try use my bench top unit to test.