The sharpness testing of plain edges such as kitchen knives, professional knives, folding and sporting knives, razors, scalpel blades, utility blades, machine knives, industrial blades and even hand tools such as chisels can now be achieved with a small bench top instrument that uses a simpler system than that specified in ISO 8442.5. CATRA has developed this special machine which uses cutting force measurement as a determination of edge sharpness. The test media is a specially calibrated silicon rubber produced exclusively for CATRA.
CATRA has a 53 year history of sharpness measurement in all fields of sharp edge cutting technology and has been designing, building and using sharpness testing machines coupled with a very detailed working knowledge of sharpening techniques. The developments over recent years in technological improvements to blades and their coatings has created a demand for ever more accurate, realistic and precise methods of sharpness measurement. The ISO 8442.5 system developed by CATRA in the form of the AUTOMATIC EDGE TESTER however is often not ideal for certain blades particularly if a shear cut is required. The size of equipment and complexity of the ISO system makes simple sharpness only measurements time consuming and destructive. As result CATRA's latest development follows on from the RAZOR EDGE DURABILITY and SHARPNESS (REDS) tester but without the blade wear system but with the ability to test larger blades.
The test utilises the constant cut depth method in which the blade is pushed normally without longitudinal travel into the test media The cutting force is recorded as a measure of the sharpness, which means the lower the force the sharper the blade. The test media is either 8 mm square or with a 3 mm wide side bead silicon rubber which is bent around a 20 mm former and the cut is made into the outer periphery of this bend. This causes the rubber to open up the cut as the blade penetrates, thereby reducing the point of contact of rubber and blade to the tip of the edge only.
As the blade contacts the rubber the force increases to a maximum at which cutting starts to take place after which this cutting force falls to lower level. It is this maximum force that is used as the sharpness related figure. Although the above curve is not visually produced by the standard instrument the maximum cutting force is numerically recorded, however it is visible with the computer interface option.
For needles and other sharp pointed blades an optional alternative feed unit can be fitted using a polyurethane membrane as the test media, which is pulled taught, the point of the needle then penetrating through it. A similar force curve is generated and the instrument again displays this peak force as a measurement of sharpness. This test system has been proved by extensive trials to be able to accurately evaluate blade sharpening techniques and edge coatings, providing an essential tool for blade quality control and research and development such as heat treatments, sharpening and coating technology.
Note this equipment is only partly suitable for scalpel blades which are better suited to the more accurate Razor Edge Durability and Sharpness tester
Note As this system is different to the ISO 8442.5 testing technique for sharpness measurement the results from this system are not directly comparable as the cutting performance of any specific blade or knife varies dependant on the material being cut. For example a razor blade is great for shaving , but is useless at cutting down trees!
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