Optimization of an Oil Film Journal Bearing for Temperature Reduction

Rotating machines are generally equipped with tilting-pad journal bearings. In general, during the design phase, the aspects that are most taken into account are the dynamic performances in terms of stiffness and damping and the minimum thickness of the oil film to avoid mixed lubrication conditions that can lead to white metal wear phenomena. The thermal aspect, on the other hand, is often underestimated and can be critical for machines operating at high speed and high load. Thermal heating is caused by shear stresses in the lubricating film. In general, an increase in lubricant temperature corresponds to a reduction in oil viscosity followed by a reduction in lubricant film thickness. This has a beneficial effect on bearing stiffness. On the contrary, a high temperature in the oil film is detrimental to the mechanical characteristics of the white metal which is characterized by a low melting temperature and subject to thermal creep phenomena. The article analyzes, by means of numerical simulations, the influence of the bearing geometry on the thermal behavior of the bearing. The bearing geometry will then be optimized to reduce the maximum temperature in the bearing.

Mechanical Properties of White Metal on SCM440 Alloy Steel by Laser Cladding Treatment

The bearing is a machine element that plays an important role in rotating the shaft of a machine while supporting its weight and load. Numerous bearings have been developed to improve durability and life, depending on the functions and operating conditions in which they are desired. White metal is one of method to improve durability that is soft and bonded to the inner surface of the bearing to protect the bearing shaft. Currently, the centrifugal casting process is used as a white metal lamination method, but it involves problems such as long processing times, high defect rates and harmful health effects. In this paper, a laser cladding treatment is applied to bond powdered white metal to SCM440 alloy steel, which is used as bearing material in terms of replacing the risks of a centrifugal process. In order to understand whether laser cladding is a suitable process, this paper compares the mechanical properties of white metal produced on SCM440 alloy steel by centrifugal casting and the laser cladding process. The laser power, powder feed rate and laser head speed factors are varied to understand the mechanical properties and measure the hardness using micro Vickers and conduct field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and friction testing to understand the mechanical properties and surface characteristics. Based on the results, the hardness values of the cladding (white metal) layer ranged between 24 and 26 HV in both the centrifugal casting and laser cladding methods. However, the hardness of the white metal produced by laser cladding at about a depth of 0.1 mm rose rapidly in the cladding process, forming a heat-affected zone (HAZ) with an average hardness value of 200 HV at a laser power of 1.1 kW, 325 HV at 1.3 kW and 430 HV at 1.5 kW. The surface friction testing results revealed no significant differences in the friction coefficient between the centrifugal casting and laser cladding methods, which allows the assumption that the processing method does not significantly influence the friction coefficient.

SILVER OR “THE WHITE METAL”? REVISITING THE QUESTION OF THE MATERIAL USED IN ETHNIC JEWELRY OF THE MIDDLE EAST AND NORTH AFRICA

This article discusses the problem of identifying metals and alloys as a material for the manufacture of folk jewelry in the Middle East and North Africa in the 19th-20th centuries. Changes in the composition of metal in traditional jewelry in this period are analyzed. General recommendations are given for determining the material of jewelry and approximate dating of items.

Copper Extraction from Black Copper Ores through Modification of the Solution Potential in the Irrigation Solution

This article presented the behavior of ores containing black copper under acid leaching. The solution potential was modified by adding agents, and five leaching conditions were evaluated, one as a control based on sulfuric acid leaching (conventional), and the others by changing the solution potential with: ferrous sulfate (FeSO4), white metal (Cu2S), sulfur dioxide (SO2), and ozone (O3). Leaching behavior was evaluated with laboratory bottle (ISO-pH) and column leaching tests. Two ores samples from the Lomas Bayas mine were used. The samples, identified as low (LG) and high grade (HG), were characterized as 0.13–0.25% Cu and 0.15–0.38% Mn, respectively. The mineralogical analysis indicated that black copper represented around 20% of total Cu (0.05% Cu). The results of the bottle tests indicated that the solution potential decreased with the addition of reducing agents, while the copper extraction rate with the HG sample increased to 83.7%, which exceeded the extraction rate obtained by conventional acid leaching by 25%. Ozone did not favor the extraction of Mn and Cu extraction when the solution potential increased. Cu and Mn extraction were directly related. The results of the column leaching tests showed that it was possible to maintain the solution potential at values below 600 mV (SHE) with the addition of white metal and sulfur dioxide while obtaining the highest copper extraction rate of approximately 60%, which was 18% higher than the rate obtained with conventional leaching. Sulfuric acid consumption was 11 kg/t over 45 days of leaching.