Abstract
Airborne wear particle emission has been investigated in a pin-on-disc tribometer equipped with particle analysis equipment. The pins are cut out from commercial powder metallurgy automotive brake pads as with and without copper content. The discs are cut out from a commercial grey cast iron automotive brake disc as cut out and as in addition to a laser cladded with a powder mix of Ni-self fluxing alloy + 60% spheroidized fused tungsten carbide and then fine-ground. Dry sliding wear testing runs under a contact pressure of 0.6 MPa, sliding velocity of 2 m/s and a total sliding distance of 14,400 m. The test results show both wear and particle emission improvement by using laser cladded discs. The laser cladded discs in comparison to the reference grey cast iron discs do not alter pin wear substantially but achieves halved mass loss and quartered specific wear. Comparing in the same way, the friction coefficient increases from 0.5 to 0.6, and the particle number concentration decreases from over 100 to some 70 (1/cm3) and the partition of particles below 7 µm is approximately halved.
Highlights
For many years grey cast iron (GCI) brake discs have been a state of art in the automotive industry offering a good braking performance for an affordable cost [1]
The hard metal alloys are not specified in detail but according to cross sectional views of the overlays, it is likely to be deposited by laser cladding and using a powder mix of Ni-self fluxing base powder (Ni-SF) and over 50% spherical fused tungsten carbides (SFTC)
The cell consisted of a commercial pin-on-disc tribometer (VTT) in a sealed polycarbonate enclosure with an air handling system and particle emission analyzers, see Figure 2
Summary
For many years grey cast iron (GCI) brake discs have been a state of art in the automotive industry offering a good braking performance for an affordable cost [1]. A way to reduce airborne wear particle emission appears to be coating and overlay welding of GCI brake discs. In combination with stainless steel powder alloys as welding consumables [22], it opens for wear and corrosion resistant hard faces for GCI brake discs. Gramstat et al [20] reported about brake dynamometer testing of GCI brake discs overlay welded with hard metal- and metal-alloys including a stainless steel buffer overlay. Investigation [18] appears to need a completion to clarify friction, wear and airborne wear particle emission of Ni-SF/SFTC weld overlays. The aim of this investigation is to generate reference data on friction, wear and wear particle emission for laser cladded Ni-base/SFTC overlays of GCI brake discs by using pin-on-disc testing and compare the results with previous reports
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