Impact strength of guard materials for machine centres

Status:

completed 09/1997

Aims:

Machine tools are a source of multiple accidents: workers are hurt and injured because the guards do not stand the mechanical strain caused by tool or material fragments hurled out of the machine's work zone. Different metal sheets (steel or aluminium) as well as shields made from polycarbonate and polymethylmetacrylate were to be investigated in view of their impact strength. The final aim was to select suitable materials and safe designs for guards used in machine centres.

Activities/Methods:

Impact tests were conducted in accordance with the European draft standard prEN 12417 using a 100g-projectile. A special pneumatically-operated test device was used.

Results:

The results showed that for cuttings speeds up to 115 m/s three types of guards provide sufficient protection: 3-mm- steel sheets, 5-mm-aluminium sheets and 8-mm- polycarbonate shields. Polymethyl methacrylate, as it is not ductile enough, can only be used for cutting speeds up to approximately 25 m/s. Under the test conditions, the increase in impact strength was almost proportional to the square root of the fracture elongation, the ultimate tensile strength and the thickness of the tested materials. In addition, constructive measures can be taken to optimise the impact strength. If two shields of different thickness are used, the thicker one should always be mounted on the inside of the machine's work zone. The results can be used to select suitable guard materials and designs and evaluate the safety of splash guards used in machine centres.

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