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August 12, 2015
Bimetallic parts manufacturing technology
In machine building, development of high-performance sliding bearings is of great importance, provided that their manufacturability is ensured and the materials used are not deficient. Bearing material shall have many properties: antifriction, durability, wettability, lubrication, absorption (ability to absorb contaminants from a lubricant), corrosion resistance, high thermal conductivity, etc. Required combination of properties can be more effectively achieved by using a bimetallic sliding bearing design consisting of a durable steel base and cladding layer of antifriction material.
Low-carbon steel having the required strength and sufficient ductility are usually used as the basis for the manufacture of bimetallic sliding bearings. Babbits, aluminum and copper alloys are mainly used as an anti-friction layer.
NTV Scientific & Technical Firm developed a technology for manufacturing bimetallic steel-and-bronze sliding bearings (cylindrical and tapered liners, ball sockets, thrust bearings, working cylinders, guides, etc.) instead of bronze casting.
The manufacturing technology of bimetallic parts consists in electric arc semi-automatic depositing of the BrOF 6.5-0.4 tin-phosphor bronze layer on a steel surface.
Low carbon or medium carbon steel St3, 20, 30, 35, 40, 45 is used for the manufacture of the workpiece.
Minimum thickness of the deposited bronze layer is 3 mm. The maximum thickness is not limited and is determined by the requirements of the Customer and economic feasibility.
Deposition can be performed on the surface of any configuration and size, with the exception of holes with a diameter of less than 100 mm.
Typical chemical composition of deposited bronze: Sn 6.90-6.95 %; Р 0.76-1.08 %; Cu – the rest.
The structure of the deposited layer is shown in the figure and is an α-solution (microhardness H=1500-1600 MPa), eutectoid Cu31Sn8 and phosphide Cu3Р (microhardness H=2600 MPa), formed when the phosphorus content is more than 0.3%. It improves casting properties, increases hardness, strength, elastic and anti-friction properties. The change in the chemical composition of the material in the deposition process leads to the fact that it is close in properties to the BrOF 10-1 bronze.
The use of these parts allows you to increase the life cycle at lower prices compared to casting from BrOTsS 5-5-5 bronze.
The results of comparative tests for wear resistance, carried out on a friction machine according to the "worn-out hole” method, are given in the figure. They showed that the deposited bronze under conditions of moderate loads is comparable in wear resistance to the BrOTsS 5-5-5 bronze, however, a further increase in load leads to a sharp increase in the wear of the BrOTsS 5-5-5 bronze up to seizure, while the wear of the deposited bronze only slightly changes. During the tests, a significantly smaller effect of the mating steel surface roughness on the wear of the deposited bronze was noted.
Collar of the shift sleeve
Liner of the rubber mixer bearing after machining
Microstructure of the deposited bronze layer (magnification x445)