Incendivity of aluminium bronze in mechanical friction contacts

The occurrence and incendivity of mechanically generated sparks and hot surfaces in friction contacts are presented when using aluminium bronze. These ignition sources must be taken into consideration when using mechanical equipment in explosive atmospheres. Frictional processes can be caused by malfunctions. In the field of explosion protection, bronze is commonly considered to be an alloy with a low tendency to form mechanically generated sparks. This mainly applies to tin bronze. In many industrial applications, bronze alloys are used today which are particularly hard and have a relatively low thermal conductivity. The question arises therefore as to whether the low tendency to form mechanically generated sparks also applies to aluminium bronze. A second question to clarify is how incentive - compared to contacts of stainless steel and mild steel - frictional contacts of aluminium bronze are. The experimental set-up consisted in a friction pin which was pressed onto a rotating friction disc. The temperature development and the spark formation were observed. Subsequently, it was checked whether the potential ignition source had become effective. Furthermore, it was examined as to how far the incendivity of aluminium bronze differs from the incendivity of stainless steel and mild steel. The experiments showed that friction velocities between 1 m/s and 20 m/s and surface pressures between 1 N/mm2 and 40 N/mm2 did not cause any mechanically generated friction sparks. The temperature of the friction pin develops as a function of the mechanical power density applied. In the case of larger power densities, higher maximum temperatures were reached. Furthermore, the time until maximum temperature was reached was significantly longer at lower power densities. For power densities of 2 W/mm2 and 140 W/mm2, maximum temperatures of 165 °C and 872 °C were measured. The ignition tests proved that with friction partners made of aluminium bronze, hydrogen/air mixtures can be ignited. In all experiments, the effective ignition source originated from the hot surface. A power density of at least 10.5 W/mm2 is required for ignition. The ignition threshold of aluminium bronze is about two times higher than the value of homogeneous mild steel (5.5 W/mm2) and four times the value of homogeneous stainless steel (2.8 W/mm2). In ignition tests with ethene, no ignition was generated by friction of aluminium bronze.