RU2035278C1 - Electrical contact application of coatings - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: powder metal welding material is preliminarily sintered into a ribbon, which is welded to the workpiece surface in overlapping spots by regulated current pulses. Ribbon porosity is 8 to 37%. Use can be made of several layers of ribbon with a different porosity, of different composition. Welding zone may be cooled by liquid or gas. EFFECT: facilitated procedure. 5 cl

Description

 The invention relates to technological processes for hardening and restoration of machine parts and can be used in mechanical engineering and machine repair, as well as in other industries where an increase in the service life of parts is required.

 A number of methods are known for electrical contact coating of powder materials in order to restore or harden parts. Closest to the claimed are a method of applying metal coatings of powder materials according to ed. USSR N 1526940 1989, and the method of electrical contact powder deposition according to ed. USSR N 1310147, 1987.

 These methods have the following disadvantages. Autoswap method N 1526940, the closest one, allows coating only on local areas of a flat surface with a single current pulse using an electrode having a groove for accommodating the filler material. Autoswap method N 1310147 does not provide a coating of a given thickness and properties (when using a mixture of powders, they will be separated by density, magnetic properties, particle size, etc.). The use of a coolant is also excluded, which will wash off the powder, the retention of which on a cylindrical part in itself is very problematic.

 The aim of this invention is to improve the manufacturability and productivity of the process, as well as the quality of the coating.

This goal is achieved by the fact that a porous, sintered from metal powder tape with a porosity in the range of 8-37% is used as an expandable layer
In addition, porous sintered tape from a mixture of metal and 9-42% current-conducting powders can be used.

 Using several tapes (tape package) for welding, it is possible to control the layer-by-layer composition of the coating and, accordingly, the heat dissipation mainly in one of the layers, in a layer located at the fusion boundary of the package with the body of the part, using a package tape with a higher porosity for this.

 When surfacing, the main goal is to obtain the coating of the desired composition and with the necessary properties. However, a change in composition changes the resistance of the tape. The necessary adjustment of resistance can be realized due to porosity. This technology allows you to get the desired coating composition.

 The porosity of the tape does not affect the porosity of the coating in the tape, heat is predominantly generated and sintering-fusion under pressure occurs, leading to the formation of a monolithic practically non-porous layer.

 The method is as follows. A porous sintered tape or several tapes of the required thickness and composition are applied to the hardened (restored) surface of the appropriate size and welded along the entire surface of the layer to be built up with overlapping points using adjustable current pulses while supplying coolant or gas to the welding zone.

 This invention is based on the following patterns.

 In contact welding (surfacing) by current pulses, the decisive role in the formation of the welded joint is played by contact and internal resistance (Kochergin K. A. Contact welding. L. Mashinostroyenie, 1987, p. 45.58). In addition, when connecting different thickness parts, the core is mixed into a thick part, that is, welding does not occur, and the strength and duration of the current pulses have to be increased many times (ibid. P. 161).

 This process can be controlled by changing the internal resistance of the welded thin material. An increase in the porosity of the tape sintered from metal powders increases its resistance and, accordingly, the amount of heat released in it. A similar role is played by the introduction of current-conducting powders (aluminum oxide, silicon carbide) with a particle size of 12-140 μm into the sintered strip). Given the composition of the tape, taking into account the requirements for coating, the porosity of the tape can be easily adjusted during the rolling of powders into the tape and its subsequent sintering. Rational values of resistances are known (Shavyrin V.N. Ryazantsev V.I. Glue-welded structures. M. Mechanical Engineering, 1981, pp. 64-74).

 The limits of the suitable porosity of the tape were determined experimentally: from 8 to 37% depending on its chemical composition and the limits of the content of current-conducting particles: from 9 to 42 vol.

 The lower limit of the porosity of the sintered tape (the content of non-conductive particles in it) is determined by the effect of a significant increase in the concealment of a given thickness at the minimum values of the welding current and the duration of the welding pulse.

 The upper limit of porosity was determined by the explosive effect during the passage of a current pulse, the fragility and fragility of the tape, which breaks when a load is applied to the electrodes, and the inability to use sintered tape for coating parts with a diameter of 20-40 mm, as well as large shrinkage of the tape, i.e. decrease in effective coating thickness.

 PRI me R. Creation of a bimetallic (hardening, restoration) cylindrical part with a diameter of 50 mm made of low-carbon steel St20. The required hardness of the coating is 60 НРС, and the layer thickness is 0.1 mm. The composition of the sintered tape, providing such a hardness, carbon 0.05; chrome 3.0; nickel 4,5; copper 1.5; silicon and manganese 0.7% of the rest of the iron. These components are rolled into a strip and sintered. Desired porosity of 16%. Porosity is achieved by rolling pressure, temperature and sintering time. To ensure a given layer thickness, a tape with a thickness of 1.7 mm is required (taking into account shrinkage and machining allowance).

 The mode of welding the tape to the surface of the part: current pulse duration 0.1 s current strength per pulse 6 kA, pause duration between pulses 0.12 s, the amount of coolant supplied to the welding zone, 1.8-2.0 l / min, pressure 2.5 at electrodes, part speed 4 rpm, feed rollers along the part 4 mm / rev.

 The porosity and volumetric content of conductive particles in the sintered tape has a close in magnitude effect on the specific resistance of the tape. When materials with high electrical conductivity (copper, aluminum, silver, etc.) are introduced into the tape, the porosity should be increased.

 The proposed method allowed: to reduce the cost of electricity by 35-25% to increase the productivity of the process by 15-25% with the same energy consumption; reduce splashes on the surface of the coating and reduce processing allowances; 4-6 times increase the resistance of the electrodes; increase the thickness of the layer welded in 1 pass up to 2 times.

Claims (4)

1. METHOD OF ELECTRIC CONTACT COATING of conductive materials on the surface of products, in which a material sintered from metal powders is placed on the part, it is welded with adjustable current pulses, characterized in that welding is made to the surface of the part with overlapping dots, while using as a weldable material tape with porosity of 8-37%
2. The method according to p. 1, characterized in that they use a tape containing 9-42% of conductive powders.  3. The method according to claim 1, characterized in that several layers of tapes of the same composition with different porosity are used.  4. The method according to claim 1, characterized in that several layers of tapes of various compositions with different porosity are used.  5. The method according to PP. 1-4, characterized in that the welding zone is cooled by a liquid or gas.