Hardness Testing FAQ: 10 Questions from Lab Managers and Quality Engineers
Hardness Testing FAQ: 10 Questions from Lab Managers and Quality Engineers
1. How often should a hardness tester be verified and calibrated?
Daily (or each shift) indirect verification with certified test blocks in the scale you use, plus periodic direct calibration per the governing standard (typically annual). Log the daily block readings — drift trends warn you before results go wrong.
2. Why do my Rockwell readings scatter on the same part?
Usual causes in order: dirty or damaged anvil/indenter, part not seated rigidly (curved or burred underside), testing too close to an edge or a previous indent (keep 3-4 indent diameters), too-thin specimen (need ~10× indent depth), or genuinely inhomogeneous material — where Brinell may be the better scale.
3. Can I convert between HRC, HB, HV and Leeb values?
Only through standardized conversion tables, and only within their stated material families. Conversions are empirical, not exact — for certification, test in the scale the specification names.
4. What is the minimum thickness for a hardness test?
Rule of thumb: at least 10× indentation depth (Rockwell/Vickers) or one ball diameter (Brinell). For thin sheet, coatings and case layers, use superficial Rockwell or micro-Vickers with reduced loads.
5. How do I measure case hardening depth (CHD)?
Micro-Vickers hardness traverse on a polished cross-section: a row of indents from surface inward, plotting hardness versus depth; CHD is the depth where hardness falls to the limit value (commonly 550 HV1). This requires proper metallographic prep — cutting cool and retaining the edge.
6. Which durometer scale for rubber and plastics?
Shore A for soft rubbers and elastomers, Shore D for hard rubbers and rigid plastics; readings taken after the standard dwell time on flat, sufficiently thick specimens. For GRP/composites and aluminum, Barcol is the common scale; for painted surfaces, pencil hardness per ISO 15184.
7. How accurate are portable Leeb testers?
Good to a few percent on heavy, rigid, well-prepared parts in the material groups the conversion supports. Light or thin parts need coupling to a massive support. Use Leeb for large-part verification and incoming checks; use bench methods for certificates.
8. What are hardness test bars for and how are they used?
Certified reference blocks verify your tester daily in each scale/range you use. Use the working surface only, distribute indents evenly, never re-test over old indents, and replace when the surface is consumed. Store dry — corrosion invalidates them.
9. Do I need an automatic turret or image analysis on a Vickers tester?
For occasional testing, manual reading suffices. For case-depth traverses and volume work, automatic turret + software reading removes operator subjectivity, speeds traverses 5-10×, and archives every indent image — worth it the first time an auditor asks for raw data.
10. How do I choose a supplier and get a quotation?
Match instruments to your parts and cited standards, insist on certified test blocks with each machine, and check calibration and after-sales support. Send Skyline your specimen types, hardness ranges and standards; the ValuePro range covers Rockwell, Brinell, Vickers, micro, portable and polymer scales, and we return a configuration proposal with pricing within one working day.