A graphite commutator is one of the most important parts of an oil pump motor. The quality of a graphite commutator is important to the performance of a motor.
An existing graphite commutator is mainly composed of graphite (charcoal) sheets and copper sheets. The graphite sheets are used to conduct electricity and as wear parts. The copper sheets are used for electric conduction and are connected with motor windings. The connection and assembly of the graphite sheets and the copper sheets is one of key points of the graphite commutator manufacturing process. One of the existing manufacturing processes is to firstly metallize the surface of the graphite sheet by an electroplating method and then welding the copper sheet together by means of a solder-fill process. The manufacturing processes has the disadvantages of high cost of electroplating process, environmentally-unfriendly and easiness to fall off the graphite sheet. A second existing manufacturing process is to press the graphite powder and pure metal powder (mainly copper powder) through direct powder pressing process and then forming the surface metallized graphite sheet through low temperature curing thermal treatment process. The copper sheets are also connected by welding. The design has the disadvantages that the resistance of the product is high and the efficiency of the motor is low as the high temperature thermal treatment (such as sintering temperature above 500 degrees) cannot be used. If the product is subject to high temperature thermal treatment, due to the difference in the thermal expansion coefficient of the graphite material and the metal material, the junction of the graphite layer and the metal layer is very easy to crack. A third existing manufacturing process is to direct weld the graphite sheet and the copper sheet by a high-temperature soldering method. This process has the disadvantage of high cost, and causing the softening of the copper sheet which increases the difficulty to the motor assembly.
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