Question about test block for ASTM E18

[unp1]

Recently I got my Rockwell hardness testing machine calibrated. The guy from the calibration service told me that ASTM E18 is a new standard for this test and I will have to buy new B-scale tungsten balls and appropriate test block for the future use. Could anyone please tell me what exactly do I need to buy? My current B-scale test block has a Mean Hardness Value of 96.69 and I am wondering if I can still use it for the new E18 standard! Thanks.

 

[kenvlach]

See ASTM E18-05e1 Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials.
from Notes 2 & 3 (available in the on-line, free abstract!).
"The National Institute of Standards and Technology (NIST) maintains the national Rockwell hardness standards for the United States. In June 1998, NIST released new Rockwell C scale (HRC) test blocks as Standard Reference Materials (SRMs). The blocks were calibrated using NIST's primary reference standardizing machine...
...The revision of E 18 requires that all performance verifications of Rockwell hardness indenters and hardness machines must be made using test blocks calibrated traceable to the Rockwell standards maintained by NIST...
...steel and tungsten carbide balls have been shown to give different results. For example, depending on the material tested and its hardness level, Rockwell B scale tests using a tungsten carbide ball indenter have given results up to one Rockwell point lower than when a steel ball indenter is used."

http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/E18.htm?L+mystore+vwrl9304

See also NIST Special Publication 960-5 Rockwell Hardness Measurement of Metallic Materials.

http://www.msel.nist.gov/practiceguides/SP960_5.pdf

(from CoryPad in thread330-141635)

 

[EdStainless]

RB 96, I sure would be using W balls for that. Actually I would be using a superficial scale. We use steel balls, when they take a reading that is over 92 they replace the ball.

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[redpicker]

I hate to hijack a thread, but I, too, wonder about the NIST traceable test blocks. We upgraded to the WC balls years ago, when the standard changed, but we are still using the standard test blocks that we get from our vendor. I have heard of the NIST blocks and know our calibration service uses them for our annual calibration, but for routine calibration checks, we do not use the NIST blocks.

My question is, if NIST blocks are used for the annual calibration are the cheaper non-NIST reference blocks suitable for routine verification? The last time I read E-18 it gave me the impression that the NIST blocks were available, but not required to be used. I'll admit, this was a few years ago and we do not "ceritfy" our test results, but I'd like to know if ASTM requires NIST test blocks be used.

rp

 

[CoryPad]

You don't have to use NIST blocks for routine verification.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dbooker630]

I upgraded to the carbide balls for HRB testing but I still use the same blocks. For calibration our service engineer uses NIST blocks but for routine verification the blocks are not necessarily NIST.

 

[unp1]

Thanks for all the responses that I received. From all these responses, I understood that it is not required to use NIST blocks for routine verifications; I will keep using my old block. unp1

 

[kenvlach]

Give ASTM E18 a close reading. If certifying hardness measurements, you basically need to calibrate the instrument & routine test blocks using the NIST calibration blocks and keep a chain of calibration paperwork ('traceability').

 

[unclesyd]

All the test blocks I've purchased have been certified/traceable to NIST standards by the suppier.

One of the biggest problems I've seen with hardness testing is the sample preperation, things like using the first reading taken on the sample, and not accounting for round stock.

 

[swall]

Are these test blocks from NIST the ones that are accurate to +/- 0.1 Rc point? If so, I was under the impression that these were only valid using Rockwell testers with the new indentor configuration and loading mechanism.

 

[unclesyd]

swall,
Sorry it took so long to get back to you, broken computer.

The majority of our blocks are either the Wilson or Yamamoto supplied by Wilson Instruments. The ranges are much larger than the 0.1 point you mention.

I can see a lot of problems if someone without the knowledge of the inhomogeneity of metals calling a specification of 58 Rc +/- 0.2.