Papers by Keyword: Bronze

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: Bronze based alloys have come to be used as bearing materials, and require low frictional properties. The present study describes the effects of surface finish machining history on the on tribological properties of sulfide-containing bronze sintered onto a steel disc. The sulfide phase consisted of copper, iron and sulfur, and acted as a solid lubricant. The relative density of the specimen was 90 % and the microstructure showed that the micro-sized sulfide dispersed into the bronze matrix and was accompanied by pores. Various processes, including cutting, burnishing, polishing were, applied to finish the surface. It was found that the area fraction of the sulfide phase depended on the cutting conditions. A further increase in the area fraction was achieved using roller burnishing after the cutting. Tribological properties were evaluated using chromium alloy steel (SUJ2) as the mating surface under dry conditions. The results showed that the friction coefficient depended on the surface finishing process. Therefore, the machining history had an effect on the frictional properties of the sulfide-containing bronze. Optimal cutting conditions for the sulfide containing bronze are also discussed.

Abstract: The study deals with the material survey of a raw material, bronze axe and sickle from the Late Bronze Age. Artefacts were chosen from a set of about thirty objects, which were found in a ceramic pot near to Křenovice in the South Bohemia. The ancient technology of the axe and the sickle production was determined by the evaluating of structural properties using prepared metallographic sections. The chemical composition of a metal matrix and intermediate phases were determined using a scanning electron microscope with an EDS analyzer and X-ray fluorescence. The corrosion products of the artefacts were analyzed by X-ray diffraction. The results showed that the axe was made from partly wrought bronze (CuSn10) processed by subsequent recrystallization annealing. The bronze sickle (CuSn11) was a cast without any further mechanical processing or heat treatment. The material of the a raw material was found to be an arsenical copper alloy (CuAs1), which was probably used as a starting material for the bronze alloy production.

Abstract: The article represents the results of thermal hardening of the stannic bronze alloyed with nickel without quenching. The samples were obtained by molding into a metal form applying centrifugal way of molding. Metallographic and phase analyses were carried out to define the mechanism of thermal hardening. The aging mode was chosen to ensure the maximum hardness of stannic bronze with nickel additives of the chosen structure.

Abstract: The effect of tin and nickel on the structure and properties of the leaded bronze obtained by means of the centrifugal casting has been studied. Regularities of change of strength properties and ductility explain the features of the structure formation under the influence of nickel and tin. The paper demonstrates that introduction of nickel promotes a uniform distribution of the plate-shaped lead in the interdendritic space. Introduction of tin sufficient for the formation of eutectoid results in a uniform and compact arrangement of lead in the intergranular space. Complex alloying with nickel and tin contributes to strength characteristics increase.

Abstract: For the examination of noxious emissions, cladding tests were performed according to EN ISO 6847. The filler materials were 1.2 mm diameter wire-electrodes, made of tin bronze, aluminium bronze, austenitic stainless steel, duplex stainless steel and nickel alloy.The low-energy metal transfer welding process, named CMT (cold metal transfer) was examined, on the welding source type Trans Puls Synergic 2700 CMT, of 270 A, produced by the company Fronius, Austria. For sampling welding smoke particles, an Apex type pump was used. For measuring the concentration of gases emitted by welding, a Triple Plus type multi-gas detector was applied.The particulate emission rate is 0.500 mg / m3 in the breathing zone, according to ISO 10882-1. For comparison, the measured emission rate is from 0.877 to 2.513 mg / m3 in the welding zone, according to ISO 15011-1. The concentration of the emitted gases is in the ranges: 0.14 to 0.16% CO2; 0.1-0.2 ppm NO2; 0-15 ppm H2; 0-5 ppm CO. These concentration levels are below the exposure limits (8 hours per day, five days a week): 5% CO2; 1.0 ppm NO2; 30 ppm CO. In conclusion, the emissions from the CMT welding process are without health risk for the welder.

Abstract: Investigations of crystal structure, microstructure and composition of laser welded coatings of bronze, IN625, PGSR-4 and stainless steel alloys on non-magnetic substrates have shown that from the raw alloy powders (wire) the additional crystalline phases are extracted with new compositions and sizes of units of microns, which randomly distributed in the coating volume. Due to formation of additional phases with increased electron concentration magnetic hysteresis loops have appeared at 4 K and 300 K for all welded coatings. Bronze and stainless steel coatings have demonstrated soft ferromagnetic properties with two type of magnetic domains with small magnetization that resulted in small value of saturation magnetization (M_s = 60-146 emu/cm³ at 300 K and M_s = 107-241 emu/cm³ at 4 K) and low values of coercive force (40 – 90 Oe) at 300 K and (50-170 Oe) at 4 K. En existence of one type of ferromagnetic domains with middle Curie temperatures (230-270 K) in laser welded IN625 and PGSR-4 coatings has determined soft ferromagnetic nature of magnetism at low temperature (M_s =274 – 398 emu/cm³) and transition in paramagnetic conditions at 300 K due to main contribution only paramagnetic grains with different composition.

Abstract: Continuous casting is the most productive method of casting. Manufacturers often tend to increase casting velocity without taking into account the fact that it can cause latent defects within the casting and accordingly lead to a deterioration of the mechanical properties of product. The casting process of tin bronzes encumbers high shrinkage and high segregation in the cross section of the castings. The research was performed on three types of tin bronze alloys CuSn12-C, CuSn5Zn5Pb2-C, and CuSn7Zn3Pb7-C (EN 1982:2008). Influence of casting velocity on mechanical properties and macrostructure was studied and optimal velocity parameters were given. The following study revealed a significant effect of the velocity of continuous casting on the mechanical properties of tin bronze, which was also reflected in the macrostructure of the selected samples. Based on the results of the study the recommendations about the optimal casting parameters to increase a quality of end-product were given. The recommendations were later implemented in the manufacturing confirming the value of this study.