Search Results

Applying hydrodynamic lubrication theory for porous bearings and boundary lubrication theory, this paper presents a method of analyzing the performance of a water-lubricated sleeve type porous bushing in an automotive water pump design. Relations of bearing load capacity versus shaft speed have been obtained and compared for sintered iron-graphite bushings (a cermet material developed by the Ford Motor Co.), sintered iron or sintered bronze bushings, and steel bushings. The load capacity was computed, based on a minimum allowable film thickness during hydrodynamic operation, and on a maximum allowable temperature during boundary lubrication operation. The results show that sintered iron-graphite bushings are superior to sintered iron or sintered bronze bushings, as well as steel bushings, in this application, due to the lower coefficient of friction.

The effect of carbon content and hardness on the rate of abrasive wear of plain carbon steels was determined using a wet-sand erosion test machine. The type of abrasion simulated in this device is commonly referred to as “low-stress scratching abrasion.” The machine employs a revolving rubber wheel which picks up the abrasive grit and rubs it against the steel specimen with a minimum breakdown of the abrasive grit particles. It has been found for normalized plain carbon steels that the abrasive wear rate decreases as the carbon content increases. The same steels heat-treated by quenching and tempering also show a decreasing wear rate as the carbon content increases. For a given heat-treated steel the wear rate decreases as the hardness increases. The combined data show that the abrasive wear rate of heat-treated steels depends both on their hardness and carbon content.

Increased use of powder-forged connecting rods in the automotive industry prompted an investigation into the suitability of powders from different suppliers for this application. Specifications developed by North American users call for ultra clean powders to enhance machinability and fatigue life. Powders from four manufacturers were each blended with graphite and lubricant, then pressed, sintered and forged to full density. Metallographic samples were prepared and evaluated for inclusion content. In addition, the powders were mixed to the composition of connecting rods, (C - 0.5%, Cu - 2% and MnS - 0.3%), and were similarly pressed, sintered and forged. Test bars were machined from the forged discs. Uniaxial fatigue tests were performed in the tension-compression mode and strain-life curves were developed. It was determined that all powders examined were very clean and were comparable in their inclusion content.

The constant challenge for automotive engineers to design vehicles with greater reliability at lower cost has brought powder metallurgy (P/M) to the foreground. This technology provides parts to or near net shape and results in savings of material, energy, capital equipment and floor space. This paper is an extension of SAE reports 850458 and 870133 and describes automotive powder metal components not previously identified. It should help engineers find cost effective applications early in the design stage so that P/M technology can be efficiently adopted. In addition, recent important technological developments in the P/M field applicable to automotive parts are highlighted. In particular, increased reliability achieved through SPC is stressed. A novel blending process is described whereby the alloying ingredients are “glued” to iron powder particles resulting in an increase in P/M quality through improved homogeneity.

The trend to production of near net shape components in the automotive industry and the constant crusade for cost reduction has brought powder metallurgy technology to the foreground. Savings of material, energy, manufacturing cost and the avoidance of capital expenditure are some of the principal benefits of this process. This paper is an extension of the previously published report. SAE 850458, which describes P/M components in the automobile. It also includes a new family of parts recently identified by the authors, i.e., sensors used in conjunction with electronics and microcomputers. In addition, progress made in recent years in P/M technology is summarized. This article is written for automotive design engineers to show various new applications of P/M and allow them to take advantage of the potential savings this technology offers.

In line with the present trend to make structural parts at or near net shape, the powder metallurgy process is being studied more and more by automotive design and materials engineers who are finding an increased application for this energy and cost saving process. Many new applications, besides some older ones, of P/M by domestic and overseas automotive manufacturers are presented outlining material specifications and service conditions for engine, transmission and chassis parts. In addition to conventional porous P/M parts, examples of high tensile fully dense precision hot formed P/M parts are presented which give superior service life and lighter weight than conventional wrought steel. Despite the decreased size and weight of future automobiles, an increased number of applications of powder metal is likely to result in a greater usage of P/M materials per vehicle.

Samples of commercial powders were sintered at the conventional sintering temperature of 1120°C (2050°F) and also at high temperatures of 1232°C and 1288°C (2250°F and 2350°F) using different time cycles in an industrial walking-beam furnace. Pore morphology is shown in a series of photomicrographs. The spheroidization of pores is rapid at high temperatures and the rate of spheroidization increases with the complexity of powder particles. Pore rounding is also associated with the elimination of prior particle identity as shown in a series of fractographs. High temperature sintered parts, due to improved impact strength and ductility, have potential for expanding the field of powder metallurgy, because parts so processed can be substituted for all but the most demanding forgings and also for nodular iron castings. A nitrogen-base atmosphere of 96:4 N2/H2 composition with a small addition of CO gas performed satisfactorily during high temperature sintering.