State of cure - quick test 1

[Elastomatt]

Is there a consistent/recognised method for quickly checking/verifying a good state of cure on EPDM or NBR extrusion?

I would like the operator to verify set-up and processing of material is OK before the lab perform the final product tests (lab testing occurs around 12-16hrs after curing and takes just over 24 hours to complete all tests).

Any ideas or suggestions welcome....

 

[GrahamBennett]

Are we talking about the extrudate after being cured in a tunnel?

 

[Elastomatt]

Yes, microwave and/or hot air cured extrudate.

The uncured rubber is tested on an MDR before release and a button is tested on a Shore A deadload.

Machine parameters are preset and the operators work within them. Parameters are established during the pre-production runs.

 

[GrahamBennett]

Thanks. I don't understand what you want the operators to do. They are already following established SoPs.

Regarding testing of cured product, I think BS, ISO and ASTM standards all require a minimum of 16hours conditioning before testing to ensure the rubber compound has fully matured.

 

[Elastomatt]

We have had some problems lately off one line with compression set, which I feel is down to mechanical problems (actual temps in oven v set-point) and possibly environmental issues (ambient temp).
My boss has asked if there is a quick test for verifying the state of cure that goes beyond a hardness check.
So I thought I would ask on here and see if anybody has any ideas.
This check wouldn't replace the test but would stop the operator running x metres of extrudate that then fails testing and subsequently needs post curing.

 

[btrueblood]

So, recalibrate the sensors to remove any error issues, and install some insulation or cooling fans as required to control ambient temp....

Or, you could do a little Taguchi type testing to find an optimal batch composition to make your end product insensitive to minor changes in controlled variables.

 

[GrahamBennett]

Good answer btrueblood

 

[tom1953]

Seems like a good spot for a calibrated fingernail test . . .

 

[GrahamBennett]

Yeah - it's been a few years since my thumbnails were calibrated (left = 60 Shore A, right = 70 Shore A) as well lol.

 

[edine]

If you think it is a problem with temperature fluctuations in the production equipment, you need to figure out how far out of operating parameters it was. If it isn't very far than you need to look for ways to make the process more robust (slow the line, bump up the temperature, get better controllers). If it was way out then maybe you need an alarm to alert the operator. There are few checks that can be done on the line to check state of cure besides hardness. DSC can do it for peroxide cure systems, but that is an off-line skilled test and an expensive piece of equipment.

Don't discount poor mix from the equation if the problem comes and goes batch to batch.

The fingernail test isn't so good for non-resilient materials.

 

[mhallin]

A quick test that I sometimes find useful, is to use a pair of scissors to cut a thin section of the profile in the direction of the extrusion. I then pull and hold for a little bit. If the section returns to its original length, that gives me an idea about the grade of vulcanization. I suppose it’s a kind of a quick field version of the tension set.

I admit that this test falls under the same category as the fingernail but like a chef tasting his sauce; it could give you a hunch...

/Mathias