Luigi Alzati

Copper Substitution and Noise Reduction in Brake Pads: Graphite Type Selection

Graphite is commonly used in brake pads. The use of graphite powder has the main goal of solid state lubrication and friction coefficient stabilization. In this article results on resin bonded brake pads with focus on noise performance and heat dissipation are presented. Experimental tests are based on model friction materials with a known formulation and a reduced number of components for a better identification of the role of the graphite type. Results clearly indicate that both noise performance and thermal conductivity are strongly affected by the type of graphite. Guidelines for the selection of graphite types for optimized friction materials are given.

Dissolution of carbon in Cr-prealloyed PM steels: effect of carbon source

Abstract Modern water-atomised steel powder grades are characterised by the presence of two types of surface oxides: a thin iron oxide layer, covering more than 90% of the powder surface, and more thermodynamically stable particulate oxides. The development of inter-particle necks and carbon dissolution in the iron matrix both require efficient removal of the iron oxide layer. Hence, carbon reactivity strongly affects the surface oxide reduction that determines inter-particle neck development and carbon dissolution, and so microstructure development. An analysis is presented of the effect of three carbon sources – synthetic graphite, natural graphite and carbon black – on microstructure and inter-particle neck development in Cr-alloyed PM steels. Metallographic and fractographic studies indicate that the most significant property of the carbon sources affecting reactivity is the carbon powder size. Carbon black shows the highest reactivity at elevated temperatures but is fully inert at temperatures below 900°C.

Reduced Weight Scatter with Bonded Powder Mixes

Organically bonded P/M mixes have been developed to improve the stability of dimensional properties by reducing the segregation of the mix constituents and improving the filling characteristics. Robustness and reliability are key factors for the promotion of P/M as cost effective substitute of competing manufacturing technologies. Based on the production of four different belt pulleys, this paper presents the achievement of reduced weight scatter and close dimensional control realizable by using a StarmixTM that is organically bonded.

Bonded mix rises to the challenge of belt pulleys

The shape of the belt pulley can make production difficult, due to a teeth section where a narrow and deep cavity is to be filled when the parts are pressed. A high performance bonded mix may provide an answer…

How to pick a winner when choosing a PM graphite

In discussions of alloying additives for improving PM manufactured parts the role of carbon is often overlooked. However the role of carbon is crucial in two key respects. First, carbon assists steel matrix hardening by diffusion into iron particles. Second, it decreases the co-efficient of friction by solid state lubrication. Swiss/Italian research has looked at how graphite type and particle size distribution can affect flowability of the mix, dimensional change after sintering and mechanical properties of PM parts. So how do manufacturers select graphite powder when considering their process metallurgy?