The birth of the fully automatic Brinell tester

One of the traditional challenges of the Brinell test is operator influence on the measurement of the indentation (the possibility of inaccurately measuring the indentation diameter across one, or both, axes).  Part of this is due to lighting effects, as I discussed a week or two ago.

We overcome this in the 1980s by pairing a purpose-built optical microscope with a dedicated computer (4K memory!) that could measure hundreds of axes in a split second then instantly calculate the hardness value at an accuracy that was then unheard of in Brinell testing.

The logical next step was to physically incorporate this optical-digital system into a Brinell tester, because until this was done there would still be unnecessary delay at the test station as technicians would still be required to remove test pieces from the machine, place them on a workbench and carefully position the microscope over the indentation.  Building a tester with an integral microscope would also dispense with the external microscope, cable and other associated hardware.

In our view, both then and now, a critical requirement was that the microscope be fixed in direct (linear) alignment with the path of the indenter to ensure complete stability in the system throughout the test cycle, rather than moving the microscope in and out of position at the end of every test, or even having a rotating measurement turret as you might find on a laboratory-based machine because, given the harsh working environment on the shop floor, the fewer moving parts, the better. So, it was obviously far better to have the indenter swing into position directly below the microscope, do its stuff and then immediately swing out of the way, allowing the microscope sight of the indentation.

At this time, of course, nobody had made so complex an indenter head. And this planned indenter head had to meet the ever-present Foundrax requirement that it be as ‘steelworks proof’ as practicable.  Accuracy, reliability and durability were non-negotiable. Foundrax emerged from a background in the foundry industry; from ‘Foundry Suppliers’, which had an industrial pedigree going back 200 years. We’d always prided ourselves on understanding, and building machines for, the toughest of steelworks conditions.

The design process took several years to get right (far longer than anyone expected) and we needed cutting-edge image analysis software to go alongside the force control system.  After extensive testing both at Foundrax and at customer sites, we had a working – revolutionary – indenter head that could complete a full test cycle and provide the Brinell hardness value in about 12 seconds (in line with the minimum time allowed by the standards).  It’s no coincidence that it looks like it could be hit by a truck and go through a wall but stay in calibration – this actually happened once, many years ago..