Selection of electric spark processing modes for electrodes from sintered bronze

The method of electrospark machining has proven itself well in the technology of repair and restoration of parts. The operational properties of coatings obtained by this method depend on the microstructure, chemical and phase composition of the electrode materials. A significant improvement in operational properties, for example, wear resistance, is achieved by the formation of nanostructured coatings using electrodes with a certain content of alloying nanomaterials. It is possible to obtain such materials at the lowest cost by electro-erosion dispersion of machine-building waste. This article discusses the electrodes obtained by sintering bronze powder obtained by the method of electroerosive dispersion. Such materials are new for the process of electrospark machining; therefore, it is important to study and select the optimal application modes, since a qualitative characteristic of the process is the indicator of the transfer of the electrode material to the part, which depends on the processing modes and installation parameters. The aim of the study is to select the modes of the installation for electrospark treatment for optimal deposition of the material, as well as to study the degree of coating increment during electrospark treatment. Coating was carried out using an installation for electrospark treatment mod. «Westron» type AI-007, electrode material was obtained by the technology of spark plasma sintering of bronze powder, surfacing was carried out on steel samples 14 × 14 × 40 mm in size, the work also used an Acculab ALC-210d4 analytical balance and an MG micrometer Н25 GOST 6507-90. All coatings were applied to samples with an equal area in three layers under different processing conditions. After that, the increment in the thickness and mass of the electrode material on the sample surface was measured. Based on the results of the work, formulas were obtained and graphs were built. The most optimal mode of coating with an electrode made of sintered bronze obtained from machine-building waste by the method of electroerosive dispersion was determined, which proves the consistency of this method of obtaining electrode materials.

Characterization of Sintered Bronze–MoS2 Composite With Solid Lubrication Effect

The most efficient method to reduce material loss and frictional energy losses is by using lubrication. An alternative is the use of solid lubrication, specifically by using solid lubricants evenly distributed in a metallic matrix, thus forming self-lubricating composites, which are capable to induce low coefficients of friction in mechanical systems. Molybdenum disulfide (MoS2) is a very versatile solid lubricant, suitable for lubrication in critical circumstances such as vacuum, high temperatures, and pressures. Therefore, the aim of this study is to produce samples of sintered composites consisting of homogeneously distributed MoS2 in a bronze matrix obtained by cold uniaxial pressing and to compare the wear-rates and friction coefficient between the MoS2-free bronze and the self-lubricating composites. Different MoS2 percentages were used to characterize the tribological properties of the composites as a function of the MoS2 content. At the end of the experiments, it was found that samples with 20% MoS2 did not sinter properly due to the large amount of lubricant between the bronze particles. It was also found that the mixture with 5.0 vol% MoS2 had proper sintering, satisfactory hardness, achieved lower friction coefficient, and better material wear performance due to the optimal amount and good distribution of MoS2 when compared with the rest of conditions studied.

Experimental Researches and Finite Element Analysis of Stress Distributions and Deformations of Al Based Powders during Compaction

In this paper, obtaining by PM of aluminum based materials, characterization of them and Finite Element Analysis (FEA) of compaction were investigated. Sintered aluminum alloys (Al-Cu and Al-Mg-Si) were tested from physical and mechanical point of view and the obtained experimental results were compared with those of sintered bronze powder materials. We studied the compressibility and densification mechanism of Al-Cu mixed powders and for prediction of compaction behavior we used FEA. The data was obtained on the stress distribution in the compacted material and on the deformations occurring throughout the mixed metal powder of the compacted samples. The results of FEA were compared with those obtained experimentally

Properties of Sintered Bronze-Graphite Containing Natural Anhydrite

This study examined the effect of natural anhydrite (CaSO4) powder additions on the microstructure and frictional properties of a 95 Bronze - 5 Graphite composite prepared by a powder metallurgy process. Natural anhydrite powder, ranging in content from 2 to 8 weight percent, was added to a premixed bronze powder composed of copper and tin and mixed, before the graphite was added. The powder mixture was compacted into disc shaped samples under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minute in a reducing atmosphere. The green and sintered densities of the samples were measured. A microstructural analysis of the sintered samples was also performed. It was found that the green density of the samples decreased with increased anhydrite content. The sintered densities were lower than the green densities due to sample expansion. A finer microstructure was observed in the samples containing anhydrite. The anhydrite additions resulted in the reduction of both the friction coefficient and wear of the bronze-graphite samples. The amount of anhydrite from 2 to 8 weight percent clearly altered the microstructure of the bronze-graphite samples, however, the level of reduction of the friction coefficient and wear were quite similar among the anhydrite containing samples.

Properties of Sintered Bronze-Graphite Containing Calcium Sulfate Derived from Waste Plaster Molds

This study examined the effect of calcium sulfate additions on the microstructure and frictional properties of a 95bronze-5graphite material, commonly used for frictional applications. The samples were prepared using a powder metallurgy process. The calcium sulfate powder was obtained from recycled plaster molds previously used for ceramic slip casting. The plaster molds were cleaned, crushed and ball milled to obtain powder, which was calcined at 400 °C for 4 hours and screened. 2 to 8 weight percent calcium sulfate powder was added to a premixed powder composed of copper and tin and mixed before the graphite was added. The powder mixture was compacted into a disc shape under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minutes in a reducing atmosphere. It was found that the green density of the samples decreased with increased amounts of calcium sulfate. After sintering, the densities were found to have decreased due to sample expansion. A finer microstructure was observed in the samples containing calcium sulfate powder, possibly due to a grain boundary pinning effect. The addition of calcium sulfate resulted in the reduction of both the measured friction coefficient and wear of the bronze-graphite samples. However, the addition of calcium sulfate powder above 6 weight percent appeared to show decreasing effects.

The Effect of Bottom Ash Additions on the Properties of Sintered Bronze-Graphite Composites

The aim of this research was to study the effect of bottom ash additions to a bronze-graphite composite on the sintering behavior, as well as on the resultant physical, mechanical and tribological properties. The composites were produced by a powder metallurgy technique from prealloyed Cu-10Sn bronze powder, graphite powder and milled bottom ash powder. The compositions studied were Cu-10Sn bronze with constant 5 wt.% graphite, and 0-20 wt.% bottom ash. Samples were die compacted under 795 MPa and sintered at 850 oC for 30 minutes in an open atmosphere furnace. It was found that the sintered density of the composites decreased with increasing amounts of bottom ash. The hardness of the samples increased with bottom ash additions and reached a maximum at 5 wt.% and decreased with further additions. The frictional properties were studied using a ball-on-disc test at ambient temperature. It was found that both the friction coefficient and the wear rate were increased with increasing amounts of bottom ash.

On Some Mechanical Properties and Wear Behavior of Sintered Bronze Based Composites Reinforced with Some Aluminides Microadditives

In the paper, the changes in some mechanical properties and wear behavior of CuSn10 sintered bronze and MMCs based on this bronze reinforced with composite ultrafine aluminide powders FeAl/15 % Al2O3, NiAl/15 % Al2O3and Ti-46Al-8Cr are described. It was observed that the presence of aluminides in the MMCs leads to an increase in the hardness, but the flexural strength may increase or decrease depending on the type of aluminide. The presence of aluminides in the MMC reduces the wear rate considerably. It is decreased in the direction of FeAl/15 % Al2O3→ NiAl/15 % Al2O3→ Ti-46Al-8Cr aluminides and for the best MMC composition the advantage is about 20 times. In the MMCs wear process, micro-craters are formed on the contact surface and it is the principal reason of a decrease in the wear rate.