Calibration of Hardness Tester

[Wesley Richardson]

There are several considerations for calibration of Rockwell Hardness testers. Start with ASTM E18-08b Standard Test Methods for Rockwell Hardness of Metallic Materials. ASTM E18 - 19 Standard Test Methods for Rockwell Hardness of Metallic Materials

When the indentor is changed, there is a requirement to "seat" the indentor. More than one reading is taken, often 3 readings, and the values averaged. Each indentation must be at least 2-1/2 indentation diameters from any other indentation, and at least 3 indentation diameters from an edge of the block. Indentations may only be made on one side of the block. The blocks cannot be resurfaced or ground to reveal a new surface. The indentor must be checked to assure that it is not cracked or chipped. The readings taken with a steel ball are now replaced with tungsten carbide balls and the HBS designation changed to HBW. Diamond indentors each give slightly different readings, depending upon the actual diamond.

The uncertainty of the results depend upon the type of indentor and the range being reported.

At a lab where I worked previously, we kept a log and each day that a different indentor was used, we reported the three readings, after seating the indentor. This was a validation and not a calibration. We used an Accredited calibration supplier that also did cleaning, oiling, adjusting of the indentation rate.

NIST has only within the past 10 to 15 years become involved with providing Standard Reference Materials (SRM) for Rockwell hardness testing, and then only for a limited number or hardness ranges, with HRC being the primary one. http :// www. nist.gov/msel/metallurgy/materials_performance/hardness-standardization.cfm - OBSOLETE BROKEN 404 LINK(s) UNLINKED - PLEASE HELP - REPORT POSTS WITH BROKEN LINKS

My recommendation is to select an ISO/IEC 17025 Accredited calibration laboratory, with a Scope of Accreditation which includes you tester, to perform the calibration. Then do the daily, or interval you select, verifications using traceable blocks.

Wes R.

 

[JaxQC]

Sorin,
# 1 Daily Calibration – Yes, but let’s call it a verification (confirming) rather than calibration (making adjustment) at this point instead, explain in minute. The standard below walks you through each level of verification.
# 2 Yes, outside source (
# 3 Refer to standard ASTM E 18 2007 Test Methods for Rockwell Hardness & ASTM E 140 Rev 2007 Standard Hardness Conversion Tables for Metals as a good starting point. . There are different layers of verification laid out in the standard.

There are (3) levels. Direct, Indirect, Daily.
Direct – When a machine fails an indirect check, looks at the indenter depth & the whole thing in detail etc..
Indirect – What you’d call calibration by an outside, certified company @ 12 month interval.
Daily – monitor performance, use standard blocks

 

[Sorin]

Sorin,
# 1 Daily Calibration – Yes, but let’s call it a verification (confirming) rather than calibration (making adjustment) at this point instead, explain in minute. The standard below walks you through each level of verification.
# 2 Yes, outside source (
#3 Refer to standard ASTM E 18 2007 Test Methods for Rockwell Hardness & ASTM E 140 Rev 2007 Standard Hardness Conversion Tables for Metals as a good starting point. . There are different layers of verification laid out in the standard.

There are (3) levels. Direct, Indirect, Daily.
Direct – When a machine fails an indirect check, looks at the indenter depth & the whole thing in detail etc..
Indirect – What you’d call calibration by an outside, certified company @ 12 month interval.
Daily – monitor performance, use standard blocks

Heh...I know all that...was just asking becasue it was not clear from your original post.

Anyway, this is the form that I am using...see if it's any help.