RU2535932C2 - Manufacturing method of brushes of electrical machines - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrical brush production, namely to production of brushes for starters, generators and automobile motors with supply voltage of 12 and 24 V. A manufacturing method of brushes of electrical machines involves mixing of filler with a binding agent, crushing, pressing and sintering. Combined grinding of graphite filler with a polymer biding agent is performed in a vibratory mill. A polymer is dissolved in a granulator with ethyl alcohol for preparation of resin-graphite granules. Then, the solvent is dried in a vibrofluidised bed of an infrared drier. After pressing with simultaneous wire pressing, brushes are heated up to 200°C for polymerisation of the binding agent and sintered in a nitrogen medium with addition of hydrogen at 680-950°C.

EFFECT: obtaining homogeneous bulk moulding powder with good compactability, stable particle size composition for manufacture of a strong body of an electrical brush.

2 cl, 1 tbl

Description

The invention relates to brush production, in particular to the manufacture of brushes for starters, generators and automotive electric motors with a supply voltage of 12 and 24 V.

Brush materials of various grades differ from each other by the raw materials used in their manufacture, the ratio of the individual types of this raw material and the schemes of the technological process of its processing.

The decisive element in electric coal production are binding materials, methods for their preparation and introduction into brush products.

A known method of manufacturing metallographic graphite brushes (Livshchits P.S. Handbook for brushes of electric machines. M., Energoatomizdat, 1983, p.13). Powders of graphite, copper (> 75%) and other metals are mixed without binders, pressed and sintered at a temperature of about 1000 ° C.

The disadvantage of this method is the need for a high content of metal (usually copper) component, to provide a hard sintered metal frame of the brush, due to the absence of another binder. The increased copper content in the brush increases wear and reduces the service life of the assembly: brush - collector. Batch segregation occurs during interoperational storage.

A known method of manufacturing electric brushes with coal (pitch) binder (Temkin T.V. Production of electric carbon products. M., High School, 1975, p.184-189). The semifinished product is pre-mixed with heated, then milled chilled, averaged, pressed and fired. The process can take place in one or two stages.

The disadvantage of this method is that the process is time consuming. There is no guarantee of uniform mixing of the mixture. The sealing of the wire into the brush can only be done with caulking, which is less reliable compared to the press fitting.

A known method of manufacturing brushes of electric machines, in which a thermosetting oligomer is used as a binder (RF Patent 2097886, CL H01R 43/12, 1997). The components, graphite and thermosetting oligomer, are mixed with heated 100-140 ° C, sintered 190-270 ° C, mixed 95-100 ° C (rolled), crushed, heat pressed 100-120 ° C and subjected to stabilization at 200 ° C.

The disadvantage of this method is the presence of difficultly controlled thermal operations (mixing, rolling), in which the resin is partially polymerized, which leads to a deterioration of the compressibility of the powder during the pressing process. In the Z-shaped mixer there is no guarantee of homogeneous mixing of the mixture, organic components can remain in the finished electric brushes, which can lead to overheating of the assembly: brush - collector. These shortcomings affect the stability of the properties of the brush and reduce its resource.

The aim of the invention is to obtain a non-segregated, homogeneous, free-flowing press powder with good compressibility, stable grain composition, for the manufacture of a durable electric brush body, with a reduced content of the metal component, and an increase in the resource of its operation.

This goal is achieved by the fact that in the known method of manufacturing brushes of electric machines, including mixing the filler with a binder, grinding, pressing, sintering, the graphite filler is mixed together with a solid polymer binder in a vibratory mill, the polymer is dissolved in ethylene granulator to prepare resinous granules, then the solvent is dried in a vibratory boiling layer of an infrared dryer. After pressing the brushes with the wire, the brushes are heated to 200 ° C to polymerize the binder and sintered in a nitrogen medium with the addition of hydrogen at 870 ° C, to protect the copper wire from oxidation and to form a strong coke frame and metal bonds in the brush body (if used in the filler metal).

The method is as follows. Graphite powder and grains of a thermosetting polymer (phenol-formaldehyde resin) 9-20% by weight of graphite are loaded into a vibrating mill for 15-45 minutes. There is a grinding and mutual penetration of the components. Then the mixture is treated in a turbopaste granulator, adding ethyl alcohol 5-15% of the weight of the powders for 1-3 minutes, at maximum rotor speeds, the components are moistened and mixed. The resin is soluble in alcohol and due to the liquid phase bonds are formed at the molecular level of graphite with a binder. The number of revolutions is reduced to 30% of the maximum and during the next 2-5 minutes the granulation process takes place. Alcohol evaporates in a vibro-boiling layer of an infrared dryer. The temperature is controlled by an optical pyrometer, it should not be higher than 100-120 ° C so that the resin does not polymerize. The mixture is screened from impurities through a mesh of +1 mm. The mixture obtained in this way is homogeneous, stable grain composition, free-flowing, with good compressibility, does not segregate during storage. Ready-made electric brushes are pressed from it with the simultaneous crimping of the wire. Then the brushes are subjected to a two-stage heat treatment in a bed of activated carbon: stage 1 - 200 ° C in an air atmosphere for 2-4 hours, the thermosetting resin is polymerized; Stage 2 - 680-950 ° C in a nitrogen-hydrogen (10%) atmosphere for 5-20 hours. The nitrogen-hydrogen sintering atmosphere protects the copper wire from oxidation, and coal filling contributes to the formation of a strong coke frame in the brush body. High firing temperature promotes the formation of reliable metal bonds (if metal is used in the filler). After heat treatment, the backfill is screened out.

Depending on the purpose of the brush, additional fillers, for example copper and other components, are introduced into its composition for the operation of turbopaste granulation or an additional operation.

Comparative tests of electric brushes obtained in different ways are carried out. The results are tabulated. The first row of the table shows the results of the analysis of the MGS-20 brand brush obtained without the use of an organic binder. In the second line, the results of the MGS-5 brand obtained with the use of a pitch binder. In the third row, the results of the MGS-23 brand obtained with a thermoset polymer binder. The fourth row shows the results of the analysis of the brush obtained by the proposed method.

The table shows that the low coefficient of friction of the sample obtained by the proposed method (column 5) provides minimal wear (column 6) and, therefore, increases the service life. The wear of the brush obtained by the proposed method is 5 times lower than that of the prototype (table to patent 2097886). The voltage drop across two brushes sliding across the collector characterizes the commutation index (column 7). Its high value indicates the formation of a reliable layer of varnish on the copper surface of the collector, which improves sliding, reduces sparking and wear. Pressing the wire (column 8) is performed in combination with the pressing operation, its reliability is characterized by a low transition resistance. The options in columns 3 and 4 depend on the purpose of the brush. The proposed method allows to obtain these parameters of the required size, depending on the purpose and brand of the brush, and also allows you to use a lower content of an expensive metal component, while maintaining the operational characteristics of the electric brush.

Thus, the proposed method allows to obtain durable electric brushes with increased service life, the required operational characteristics, with a reduced content of metal filler.

Table Test results of electric brushes obtained in different ways No. Mark The content of metal powder,% Specific email resistance, μOhm · m Coef. friction Wear over 50 h, mm Voltage drop per pair of brushes 2ΔU, in Wire fastening, transitional el. resistance, mOhm one 2 3 four 5 6 7 8 one MGS-20 80 0.5 0.19 0.6 0.7 Calibration 0.5 2 MGS-5 fifty 7 0.17 0.15 0.9 Caulking 1.25 3.75 in a year 3 MGS-23 80 1,5 0.25 2.0 0.6 Pressing 0.8 four MGB-5 * fifty 5 0.14 0.1 1,2 Pressing in 0.5 * The authors suggest introducing the letter “B” in the marking of electric brushes as a hallmark of their receipt by the proposed method.

Claims (2)

1. A method of manufacturing brushes of electric machines, including mixing a filler with a binder, grinding, pressing, sintering, characterized in that the joint grinding of the graphite filler with a polymer binder is carried out in a vibrating mill, in the granulator the polymer is dissolved with ethanol to prepare resinous granules, then the solvent is dried in vibro-boiling layer of an infrared dryer. 2. The method according to claim 1, characterized in that after pressing the wires in, the brushes are heat treated at temperatures up to 200 ° C and sintered in a nitrogen medium with the addition of hydrogen at a temperature of 680-950 ° C.