1. Steel: Rockwell (HRC/HRA) or Brinell (HB)
Steel varies widely in hardness—from soft low-carbon steel to hard hardened alloy steel—but two methods stand out:
Rockwell C (HRC) or A (HRA): The go-to for most steels. Use HRC (diamond indentor, 150 kgf load) for medium-to-hard steels (e.g., tool steel, hardened alloy steel with 20–70 HRC). HRA (diamond indentor, 60 kgf) works for extra-hard steels (e.g., high-speed steel over 70 HRC) or thin steel parts (e.g., steel sheets). It’s fast (5–10 seconds per test) and ideal for production lines.
Brinell (HB): Best for soft-to-medium steels (e.g., low-carbon steel, annealed steel) or rough-surfaced steel parts (e.g., steel castings). Its large 10mm steel ball indentor averages out surface irregularities, avoiding false high readings. Use a 3000 kgf load for thick steel; reduce to 1500 kgf for thinner pieces.
2. Aluminum: Brinell (HB) or Vickers (HV)
Aluminum is soft (typically 20–100 HB), ductile, and often used in thin or machined parts—so gentle, precise methods are key:
Brinell (HB): Perfect for thick aluminum parts (e.g., aluminum castings, extrusions). Use a 500–1000 kgf load and 5mm steel ball (smaller than steel’s 10mm ball) to avoid over-indentation. It’s great for measuring large batches quickly, as it handles slight surface roughness from casting.
Vickers (HV): Ideal for thin aluminum (e.g., aluminum foils, aircraft-grade aluminum sheets) or precision components. Its small diamond pyramid indentor and low load (100–500 gf) prevent deformation. Vickers also works for heat-treated aluminum alloys, where detecting small hardness changes (e.g., after annealing) matters.
3. Copper: Brinell (HB) or Rockwell B (HRB)
Copper is softer than steel (30–150 HB) and highly ductile—methods must balance accuracy and sample protection:
Brinell (HB): The top choice for pure copper or thick copper parts (e.g., copper pipes, busbars). Use a 500 kgf load and 5mm steel ball to create a clear indentation without squashing the material. Brinell’s large indentor also works for copper alloys like brass or bronze (adjust load to 1000 kgf for harder alloys).
Rockwell B (HRB): Good for thin copper sheets or machined copper parts. It uses a 1/16” steel ball and 100 kgf load—faster than Brinell and better for high-volume testing (e.g., electronic copper components). Avoid Rockwell C (too hard) or Vickers (overly precise for basic copper QC).
4. Plastic: Shore (A/D) or Vickers (HV)
Plastics range from soft rubbers to hard thermoplastics—methods focus on non-destructive, low-force testing:
Shore A: For soft plastics and elastomers (e.g., rubber gaskets, silicone, soft PVC). Its spring-loaded blunt indentor measures indentation depth with minimal force, avoiding tearing. Shore A readings (0–100) correlate directly to flexibility—higher numbers mean harder material.
Shore D: For hard plastics (e.g., ABS, nylon, polycarbonate). It uses a sharper indentor and higher spring force than Shore A, perfect for measuring rigid plastic parts like automotive components or plastic gears.
Vickers (HV): For precision plastic testing (e.g., medical-grade plastics, thin plastic films). Low loads (10–100 gf) and small indentors prevent cracking, making it ideal for research or quality control of high-performance plastics.
Key Rule: Match Method to Material Traits
Always prioritize three things:
- Avoid over-hard methods (e.g., Rockwell C on aluminum) that damage samples.
- Use larger indentors (Brinell) for rough surfaces, smaller ones (Vickers) for smooth/thin parts.
3) Choose fast methods (Rockwell, Shore) for production, precise ones (Vickers) for research. By following this, you’ll get accurate, repeatable hardness data every time.