Upgrading an old hardness tester: digital controller, load-cell and camera retrofits

Definition: A hardness tester retrofit replaces the measuring, loading and control parts of a mechanically sound Rockwell or Brinell machine — dial gauge, hand lever, dead-weights or hand microscope — with a digital depth transducer, motorised or load-cell loading, a touch-screen controller and, for Brinell, a measuring camera, after which the machine is verified as new under IS 1586 (Part 2) / ISO 6508-2 or IS 1500 (Part 2) / ISO 6506-2.

1. Retrofit or replace: a checklist

Two lists decide it: what must still be sound, because a retrofit cannot fix it, and what may be obsolete, because a retrofit replaces it.

If the left column passes and two or more items on the right apply, a retrofit is the economical route, at a fraction of a new machine. If anything on the left fails, read section 6 first.

2. What can be retrofitted on a Rockwell tester

• Digital depth measurement. An LVDT or linear encoder replaces the dial gauge. One Rockwell unit is 0.002 mm of depth, so a transducer resolving 0.0002 mm gives 0.1 HR. Zeroing at the preliminary force is automatic; parallax and interpolation errors disappear.
• Scale and conversion tables. Every regular scale (A to K) and, where the frame carries 15/30/45 kgf, the superficial N and T scales, with conversion to HB, HV and tensile strength per ASTM E140 / ISO 18265.
• Motorised load and dwell. A motor drive replaces the hand lever: force applied at a controlled rate, held for the prescribed dwell (10–15 s for Brinell under IS 1500 Part 1 / ISO 6506-1), removed automatically, identically for every operator.
• Load-cell closed-loop force. In a deeper conversion the dead-weights and lever are removed and an actuator applies force through a load cell, so any force in range — Rockwell, superficial and light Brinell — is available on one frame. The trade-off is verification: a dead-weight cannot drift, a load cell can, so force must be directly verified at each test force at the intervals the standard sets.
• Touch-screen HMI. Scale selection, tolerance limits with pass/fail, statistics, operator and batch identification.
• Data output. Printer, USB, RS-232/Ethernet to a PC; every reading stored with date, time, scale, operator and batch.
• Auto-start on contact. The transducer senses the preliminary force as the anvil is raised and starts the cycle without a button press.

3. What can be retrofitted on a Brinell tester

On a Brinell machine the loading train is usually still adequate; the dominant error is the hand-microscope reading. HBW is very sensitive to the measured diameter d:

HBW = 0.102 × 2F / (πD (D − √(D² − d²)))   →   for D = 10 mm, d = 3.5 mm, a 0.05 mm error in d changes HBW by about 3 %

IS 1500 (Part 2) / ISO 6506-2 asks for the measuring system to be verified to within 0.5 % of the diameter — about 0.018 mm on a 3.5 mm indent. A 0.01 mm graticule read by eye against a ragged edge rarely achieves this, which is why two operators report 190 and 196 HBW on the same indent.

• Camera-based indent measurement. A portable camera head is placed over the indent; the software finds the edge, measures two diameters at right angles and calculates HBW. The ETS-BIMS kit covers 1–7 mm indents (10, 5 and 2.5 mm balls) on any Brinell tester of any make.
• Any F/D² combination. Every ratio the standard lists — 30, 10, 5, 2.5, 1.25 and 1 — with the correct designation, e.g. HBW 10/3000 or HBW 2.5/187.5.
• Image storage. Each indent image is stored with diameters, force, ball and batch, so a disputed result can be re-measured later.
• Conversion display. HBW to HRC, HV and approximate tensile strength per ASTM E140 / ISO 18265.

4. The retrofit process step by step

1. Site survey. Measure dial-gauge mounting, plunger diameter and travel, lever geometry, weight stack, throat and daylight; check indenter squareness.
2. Mechanical adaptor design. Brackets for transducer, drive and load cell designed for that frame — old machines rarely share dimensions.
3. Controller and HMI. Configured for the scales and forces the frame can deliver, with the report format and tolerances the laboratory needs.
4. Installation. Old readout and lever removed, adaptors fitted, transducer aligned to the plunger axis, machine levelled.
5. Direct verification. Force at each test force with a force-proving instrument; depth system against a displacement calibrator; indenter inspected or replaced.
6. Indirect verification. Five indentations on certified reference blocks at each level and scale in use, checked against the repeatability and error tables of the standard.
7. Operator training. Normal cycle, block check at shift start, error messages, data export and backup.
8. Documentation. Verification report, certificate, parts list, manual and a record of what changed, filed with the machine history.

5. Verification the standards require after modification

Both standards require direct verification when a machine is new and after any repair or adjustment affecting the force, the measuring system or the test cycle. A retrofit changes all three, so the machine is treated as new and must pass direct and indirect verification before returning to service.

• Rockwell (IS 1586 Part 2 / ISO 6508-2): each preliminary test force within ±2.0 % and each total test force within ±1.0 %; depth-measuring device verified by known incremental displacements; indenter and cycle timing checked. Then reference blocks at a minimum of two hardness levels per scale in use, five indentations each.
• Brinell (IS 1500 Part 2 / ISO 6506-2): each test force within ±1.0 %; the camera verified against a certified stage micrometer or reference indents to within 0.5 % of diameter; ball certified; dwell checked. Then reference blocks for each ball and force combination in use.
• Afterwards: indirect verification at least annually and after any move, plus a daily check on a reference block.

Identify the machine on the certificate by the original frame serial number and the retrofit controller serial number, so the direct-verification record shows the force and depth chain was re-established after modification.

6. Typical gains, and when not to retrofit

A retrofit is not the right answer when:

• the frame is bent or cracked, or the indenter is not square to the anvil — the transducer will faithfully report a wrong depth;
• dead-weights are missing or have been ground or drilled, and a load-cell conversion is not intended;
• the elevating screw or lead-screw is worn so the anvil sinks under load — drift during dwell that no controller can remove;
• the throat or daylight is too small for the parts you now test;
• you need a different load range altogether, for example a 150 kgf Rockwell frame wanted for 3000 kgf Brinell.

7. Software, data and service after the upgrade

For most laboratories the data side is the real reason for the upgrade. The software should give you:

• Batch reports — part number, heat or lot, operator, scale, readings, mean, range and pass/fail, printed or saved as PDF;
• Statistics — mean, standard deviation, minimum and maximum per batch, and trend across batches;
• Export to Excel or CSV, with the indent image alongside Brinell results;
• Integration with QMS or ERP where required — a shared folder, database table or text stream, so results are not re-typed.

After the upgrade the machine needs the same care as any hardness tester: annual indirect verification on certified test blocks and direct verification after any repair or move. An annual maintenance contract covering verification, transducer and load-cell checks and breakdown response keeps the certificate current; the block calibration chain is described in our test block guide.

Frequently asked questions

Which ETS machine

• ETS-BIMS portable camera measurement kitFits any Brinell tester of any make; measures 1–7 mm indents automatically with image storage and ASTM E140 conversion.
• Retrofit and upgrade serviceDigital depth readout, motorised loading, load-cell conversion and touch-screen controllers for older Rockwell and Brinell frames, designed and built in-house.
• Calibration and verification supportDirect and indirect verification after the upgrade, reference blocks and an annual maintenance contract to keep the certificate current.
• RSNE-T and RASN-TSFAReplacement options when the old Rockwell frame fails the checklist: touch-screen and fully automatic Rockwell testers.
• ETS-LB3000Load-cell Brinell tester with industrial PC and camera measurement, for laboratories that need a new 3000 kgf machine rather than a retrofit.