I have just been notified that one of our engineers is implementing a durometer test on the material for one of our products. We have never tested for hardness before and I am an extreme novice in this area of measurement. Are there any experts on hardness out there? Does anyone have any good resources I could use to get up to speed in this measurement discipline? What can I expect to have to keep on hand to keep durometer measurements accurate and traceable? Any help with this subject will be greatly appreciated.:confused:

It's been awhile. I have used two types. The tips are different for different duro readings. A wider tip for lower Duro readings, like rubber/neoprene. Narrow tip for harder materials like teflon/epoxy. Everything you need to know about Shore Durometers is on their Website. I do know that each durometer comes with its own calibration device. It a spring that deflects to a reading. You just make sure that your dial reads within +/- 5 Duro of the device, each time you use it. It's an easy thing to use. If it's an o'ring, you have to be dead on center and the surface below the ring has to be hard and level. We used a surface block. Gaskets and sheets are easier. I'm guessing here, but you order by the durometer range you want. Like a "D" tip. One may go up to 70 Duro and the other goes above 70. I tried .
:ko: :smokin:

Testing is described in a few places including ASTM test methods.

You'll need a set of calibration blocks (varying hardness rubber/sponge/plastic). The type of material the engineer is using determines the dype of durometer and therefore the appropriate type of calibration blocks. Cal frequency is dependant upon specified requirement and environment. The reading calibration piece that comes with the durometers isn't worth much other than to tell you if someone really screwed the thing up.

The other advantage of the cal blocks is that it gets you used to depressing and holding the durometer, and getting the right readings. Frequently the hardness figure is quoted as initial and after 10 or 15 seconds, so you need to be proficient.

Test material thickness is also specified in the test methods to ensure you're not pushing the probe in with your finger or the flat surface under your test piece.

As E suggested, check their website.

Don't hear from you for ages, but your always there to put the barb up energy's posterior.:vfunny: I do not know of any other way to calibrate the device, do you? Other than that springy thingy mentioned? And, I used to count to five while balancing the tip on the center of the o'ring. But if you were only sorting Buna-N Butyl Duro 55-60 to E-515 Ethylene Propylene Duro 70+, who gave a rat's arse. You are so smart. I'm embarassed to have posted. Only kidding (about you being smart)! :bonk: Don't wig on me!:rolleyes: Nice to hear from you, even if it is just to do swings and roundabouts!:ko: :smokin:

Now if you want to talk about tensometers, wyzenbeek abrasion resistance, weatherometers, modulus of elasticity, tear resistance, load deflections and other distructive testing ... I'll see if I can remember any of that.

E - I have in my kit-bag of qualifications a certificate in rubber technology from the University of Akron (via correspondence). I think the year was 1985.:evidence: :biglaugh:

Bubba,

What material are you testing?

Shore "A"???

Or?????

Originally posted by David Mullins

E - I have in my kit-bag of qualifications a certificate in rubber technology from the University of Akron (via correspondence). I think the year was 1985.:evidence: :biglaugh:

That does it for me!:vfunny: I bet you're a blast at the neighborhood pharmacy!:p :ko: :smokin:

Bubba, can you give us an idea as to what kind of material your testing? Would make a reply much simpler.


Now if you want to talk about tensometers, wyzenbeek abrasion resistance, weatherometers, modulus of elasticity, tear resistance, load deflections and other distructive testing ... I'll see if I can remember any of that.

I remember it well...do it every day. If you ever have a brain fart and can't remember...give me a call. Fee's are small. :D :thedeal:

Thanks everyone for your replies thus far.

Al and Ken, the material we will be testing is a silicone rubber that, from what I have been told, will be in the Shore A category.

Energy and David, you mention visiting somebody's website. What website would that be?

Just punch Shore Durometer into whatever search engine you use. I went there after posting yesterday and it's all there. Materials, ranges and types of Testors. See all the rubber experts we have here? I use rubber worms!:biglaugh: :ko: :smokin:

You could start with:

http://www.durometer.com

Energy, I did a search on "shore durometer" and "shore durometer calibration," and found a lot about how to measure durometer, but I haven't been able to locate much information on how to properly maintain calibration and traceability on the durometer instrument.

David, I checked out the link that you provided and it said that the test blocks were not to be used for calibration purposes. For a calibration check they suggest using smooth glass or steel and making sure that the measuremet is within 1/2 pt. of 100. My question is how would that maintain traceability. Is smooth glass or steel considered an intrinsic standard for shore A durometer?:confused:

Bubba, get yourself a copy of ASTM D2240-02. Calibration is listed along with precision and bias. There is also a listing of other applicable ASTM standards.

Hope this helps. If not, let us know.

Originally posted by Bubba
Energy, I did a search on "shore durometer" and "shore durometer calibration," and found a lot about how to measure durometer, but I haven't been able to locate much information on how to properly maintain calibration and traceability on the durometer instrument.

David, I checked out the link that you provided and it said that the test blocks were not to be used for calibration purposes. For a calibration check they suggest using smooth glass or steel and making sure that the measuremet is within 1/2 pt. of 100. My question is how would that maintain traceability. Is smooth glass or steel considered an intrinsic standard for shore A durometer?:confused:

Bubba,

We used a precision ground 4" x 6" steel block as back up for the material we were checking. You could use a granite or steel surface plate if you so choose. They want you to be as level as you can be when taking measurements. As for maintaining calibration, the device comes with a standard for you to check the instrument with. You simply place this little spring type block on the flat surface described above and set the tip in the space provided and check that you are within 1/2 point of the device. I think it was set for 50 or 60 Duro. That's it. Take care of the instrument like any other measurement device. As for calibrating the standard, I guess you can always send it to Shore for calibration every two years, if you want. I never did. When you measure most of these rubber compounds, manufacturer's tolerance is usually +/- 5 Duro. I don't want to play down the importance of taking any measurements, but the readings may vary depending on the position of the tip, pressure, how long you keep it on the material. Rubber relaxes and they want you wait until the pointer stops moving. At best it's just a check of the material for type of material and possibly old dried out product. We only used it to verify that our o'ring compostion matched the color code on them. You will not, in my opinion, be working to +/- 1 Duro. It will be more like 5. Depends on how anal your engineer is. I have never used a digital Shore Testor. Ours was the dial type. Watch out for overkill! If you purchase one that reads 4/5 places after the decimal, good luck. :bonk: Check the material supplier's specifications and purchase accordingly. Hang in there. it's a piece of cake.


:ko: :smokin:

Originally posted by Ken K
Bubba, get yourself a copy of ASTM D2240-02.

Exactly!

Alternatively, if this testing is a one-off or very infrequent, and you can't be stuffed buying a duromenter, calibrating it, and performing the test, send the job to a testing lab that has this facility.

Don't know if this will help or hurt, but if you are trying to qualify rubbers using duro it is an exercise in futility. Too much variation in repeatability to give an accurate reading. Of course based on the specification.

If the spec calls for a 40 duro rubber you can have variation between 30 to 50 duro within a 5 foot roll sample. This has to do with the usable surface area and edge lines that tend to be a higher duro.

Not putting down duro totally, but there is so much between operator variation that the numbers scare me. The gages themselves are fine for their intended purpose, but the lower the duro on the material the more variation will be present. Ever try to get a duro on a piece of 4 or 6 pound open celled foam????????

If you are going to be doing a fair amount of testing, may I suggest you get a operating stand to hold your gage. This will eliminate a whole bunch of variables and make your life much easier.

The "spring device" that comes with the gage (IMHO) is for verification and not much else. The shore durometer should be sent out for calibration at a reasonable interval depending on the amount of use, etc.

As Al stated, depending on the material, variation can be encountered. Our materials have a spec limit of 83 +/- 6 and
90 +/- 5 when plied to 12mm's and a 15 second hold time. I can't ever recall a failure for hardness though.