Guards must be so designed that tools, workpieces or parts of the latter cannot be flung out of the machine's working zone and injure persons. To achieve this protective aim guard materials have to make proof of a sufficient impact resistance.
Impact tests using blunt, cylindrical steel projectiles in accordance with prEN 12 415 "Machine tools - Safety - Small numerically controlled turning machines and turning centres" were conducted to determine the impact resistance of steel and aluminium sheets as well as of transparent screen materials.
The following conclusions in terms of guard design and dimensioning could be drawn from the investigations: · The impact resistance of a material increases together with its thickness, tensile strength and breaking elongation. · In the case of composite structures with thicker and thinner sheet metals, the thicker one should always face the working zone. · Energy-absorbing intermediate layers improve the impact resistance. · Polycarbonate is an especially suitable material for transparent guard screens, because it possesses a high energy absorption capacity. · Several thin polycarbonate panes achieve better impact resistance results than one thicker polycarbonate pane, even if the total thickness is the same. · Additional protective panes facing the working zone and the operator's side should be used together will polycarbonate screens, since the latter show little ageing stability when exposed to cooling lubricants.
mechanical engineeringType of hazard:
Maschinensicherheit, Mechanische GefährdungDescription, key words:
guards, turning machines, impact resistance, sheet steel, sheet aluminium, composite steel sheets, transparent screens