Effect of repressing on the mechanical properties of the valve guides manufactured by powder metallurgy

Characterization of hardness, mass loss, and friction coefficient, was carried out on valve guides for internal combustion engines, manufactured by powder metallurgy, with the aim of finding out if they fulfill the requirements of an internal combustion engine and to be mass produced. Currently available brass casting valve guides were used as comparative parameter. It was analyzed whether properties were present in a homogeneous way in the piece lengthwise; the additional repressing process carried out in the production line with respect to the sintered guides was evaluated. Therefore, Brinell, Vickers and dry slip pin-on-disk tests were done in order to determine the friction coefficient and the wear rate. Scanning electron microscopy SEM and the metallographic analysis were used to study the wear mechanism, chemical composition of the guides, and the effect of repressing -quantifying the porosity. It was clear that these pieces manufactured by powder metallurgy process showed lower values in their mechanical-tribological properties compared to commercially available valve guides taken as reference. With these results, the company which manufactures the guides by powder metallurgy will make some adjustments suggested for the parameters at the guide’s production line