Hardness testing explained
The term ‘hardness’ is used to describe a material’s ability to resist being deformed. Hardness testing gives definitive data on how hard a material is by giving tested material a number. Technicians use these numbers to decide if a particular material is suitable for a particular application and to make comparisons between materials, so the values generated from hardness testing are extremely useful in numerous industries.
Brinell hardness testing explained
The Brinell hardness test is employed to determine the hardness of metals and their suitability for particular applications. It tends to be used in harsh industrial shop-floor environments such as foundries, forges and steelworks. Brinell hardness testing is especially useful for materials that have coarse grain structure or rough, hand-prepared test surfaces.
In the Brinell test a tungsten carbide ball indenter is forced into the surface of the metal in a tightly controlled manner. The force is generated in a time period of between two and eight seconds, and is then maintained for a minimum of ten seconds (this may be increased when used with softer materials such as aluminium). This “dwell time” ensures that the indentation is what engineers call as ‘plastic’ (ie permanent) as possible, so that its dimensions do not change after the end of the indenting process. The diameter of the indentation is then measured in a minimum of two axes, normally with a purpose-built microscope. Foundrax’s automated machines measure the indentation across hundreds of diameters and then calculate the hardness for the operator. Without the benefit of automatic measurement, it is a question of doing a calculation with the hardness formula or, more commonly, reading the hardness off conversion tables.
Why hardness testing is important
Whether it be for aerospace, automotive, oil and gas or rail (among others), hardness testing machines are an essential investment for many companies because of the safety-critical nature of their products. The worst railway crash in Germany’s history was caused by a wheel being too brittle, and since that crash, in 1998, the manufacturer of the wheel has purchased several of our highest specification machines.
As an example, if you consider the pulleys that a lift cable goes around, overly hard ones would wear out the cable and excessively soft ones would be worn out by the cable. In either case, you’d prefer not to be in a lift at the point it became obvious that the materials were incorrect! Or consider a more ‘heavy duty’ example: every tank track link in use by the British Army since approximately 1982 has been tested by a Foundrax machine, testament to the accuracy, high quality and reliability of our products.
How to choose a hardness testing Machine
There are several factors to consider, including the rate of testing you wish to achieve, the burden on the operators, the degree of automation, and the size of the components being tested (for small industrial components the Rockwell test is preferred) – not to mention health and safety (it is not unknown for people to test longer items by holding one end in the testing machine and the other on a crane – without considering that not only may the results be incorrect as a result of movement under load, but if the machine should be pulled over by the component, the operator could easily be seriously injured).
Our hardness testing machines are suitable for every normal industrial application and are designed to give years of trouble-free service in
harsh industrial conditions. All are manufactured to meet the appropriate ISO and ASTM standards. Detailed information is here.
Special hardness testing machines
Certain circumstances require a unique solution. If you have a Brinell hardness testing requirement which is highly unusual we can design you a test machine ‘from the ground up’ – which is why we offer special-purpose hardness testing machines following detailed consultation with the customer. Every machine we supply is designed and manufactured in the UK.
If you need to know more about why hardness testing is so important, don’t hesitate to get in touch with the Foundrax experts on 01458274888 today.
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