Accurately measuring the diameter of a Brinell indentation is, of course, as important as making the indentation properly in the first place. But this is no straightforward task. The process of making an indentation does not simply ‘squash’ metal downwards, it also spreads it sideways and creates an edge ‘pile up’ that is higher than the undented surface of the block; something like the very rough sketch above. And this ‘pile-up profile’ varies depending upon both the metal under test, and the diameter of the indenter that was used. If you are attempting to make a diameter measurement using a microscope you have to estimate where the pile up ends and the true indentation begins. And, if you can see that on the hardest metals, it doesn’t necessarily mean you’ll be able to see it on soft ones. Sometimes you think you can see it but what you’re actually seeing isn’t the edge of the indentation at all. As anyone familiar with this subject knows, different metals behave differently, they look different and the apparent position of the indentation edge can change depending upon the type and angle of the illumination used. Consider the indentation in the photograph below – a challenging example. Finally, the indentation has to be measured twice – normally North-South and East-West, as it were, and the mean calculated.
It is these difficulties that impaired the Brinell test right up until 1982 when the first automatic indentation measurement microscope was launched (you can read more about that here). But not all companies want to make a major investment in an automatic microscope, so manual microscopes will remain in use in Brinell testing until an automatic system can be made so cheaply that every business buys one. For this reason Foundrax has long offered a manual microscope, with its own illumination, that is rugged enough for years of steel works use. In the image below is a vintage example from the mid-1970s – still working flawlessly.
In 2021, in an effort to improve the lives of manual microscope users and, more importantly, reduce the risk of reading errors, Foundrax introduced the BRINscope ‘Duo’. It retains the ruggedness that characterises all Foundrax products while offering an illuminated graticule to complement the LED array – see next photo. The black-graticule-against-grey-block problem has been completely eliminated but for those who like a challenge the option of the black graticule is still built into the unit! Unsurprisingly it has been very well received.