Measuring flexible materials like sponge, epdm, and felt

[qualityengineer]

Hi,
My company produces flexible products for autmotive industry like sponge, epdm, felt with severel thicknesses varying between 1mm to 30mm. We are using caliper and thickness measuring device (we call it comparator but i'm not sure it's true). I need some comments on the usefullness of caliper and comparator because sometimes we are suspecting that the original thickness has changed while contacting the meausring device. Is micrometer is a better device to measure flexible products or do you know any other methods or devices? Any contribution is welcomed.

 

[Jim Wynne]

Hi,
My company produces flexible products for autmotive industry like sponge, epdm, felt with severel thicknesses varying between 1mm to 30mm. We are using caliper and thickness measuring device (we call it comparator but i'm not sure it's true). I need some comments on the usefullness of caliper and comparator because sometimes we are suspecting that the original thickness has changed while contacting the meausring device. Is micrometer is a better device to measure flexible products or do you know any other methods or devices? Any contribution is welcomed.

Not sure what you're referring to as a "comparator," but in general some form of non-contact measurement (such as an optical comparator, or an electronic "vision" system is desireable, although not without issues.

 

[ScottK]

In vinyl extrusion we used a Romidot (that's the brand name) - it's similar to a flatbed scanner with software that measures the profile against a CAD drawing.

 

[SteelMaiden]

What tolerances are required? How "squishy" is the product? For a product that is very firm, a caliper may be good enough if the tolerance is not exceptionally tight? Do you periodically evaluate the measurements between operators? (gage r&r?) You can find measurement devices ranging from cheap home made go/no-go jigs, right on up through lasers, optical comparators. You need to pick the one that measures what you need, not too precise, not too inaccurate. What is the standard in your industry?

OK, so now that I have only clouded the issue.....

 

[Govind]

Low pressure series

Not sure what you're referring to as a "comparator," but in general some form of non-contact measurement (such as an optical comparator, or an electronic "vision" system is desireable, although not without issues.

Good point, where contact measurement is inevitable, you may consider “low pressure” series from measurement equipment manufacturers (if the measuring pressure is acceptable)
Example:
Mitutoyo Series 573, 536contact pressure is (0.49 to 0.98 N) or 50 to 100 gf
http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1399
Low Pressure Micrometers - Series 227
http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1101

There may be similar low-pressure series from other manufacturers as well.

Regards,
Govind.

 

[andygr]

For rubber products the standard is to use a flat anvel of a set size with a standard pressure. Think that this practice was defined in a Fed Standard some where. Set up of flat anvels of .25 dia and a load of 10 (?) grams.
You can probaly set up something on these lines and determin what reduces your variability to something you can live with. The other non mechanical measurement item to look at would be something based on eddycurrent or magnetic field lift off such as used in coating measurements.
Hope this give you some ideas to follow

 

[True Position]

Someone before me mentioned optical methods, the best method I've seen for optical parts is a vision system, if you're looking for something accurate and relatively easy to use.

http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1020

Other less expensive options are the optical comparator mentioned before, but the issue oh how do you hold the part perpendicular to the light source is there. A measuring microscope is probably better, but can cause eye strain issues for someone using it all day.

A GR&R would be a good starting place for you, just to see how bad your problems are and how much is reasonable to spend to fix them.

To everyone else in the thread, by comparator my guess is he meens something like a dial thickness gage.

 

[apestate]

If something is that flexible, is it possible for it to grow or shrink significantly with changes in temperature or humidity? Sponge might be better measured with displacement or weight.

Weight is a great way to measure mass produced items. I always wanted to set this up in a screw machine shop, and it would have made a world of difference to our customer at the time. I guess not.

 

[harry]

One of my client use a profile projector. Not only can you measure the thickness, you can also see how uneven the surface is as the image is blowned up many times. As someone pointed out, care must be exercised when preparing the sample.

Another instrument used is a modified vernier caliper with anvil as mentioned by another fellow 'Cover'. You just gently lower down the anvil to get the required reading.