RU2529605C1 - Production method of sliding contacts - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: powder mix is rolled in a gauge formed by four driven cogging rolls thus providing for a semi-finished product with the section close to that of a ready contact and the length equal to several sliding contacts. Rolling is carried out at the ratio of container cross section to the gauge cross section equal to 1.5-3.0. After leaving the gauge the semi-finished product is divided into separate blanks and they are heated up to the temperature of 110-140°C prior to pressing.

EFFECT: improved strength and electric conductivity.

2 dwg

Description

The invention relates to electrical engineering, and in particular to methods of manufacturing sliding contacts of current collector assemblies, in particular brushes of electric machines and contact inserts of railway and city electric vehicles from graphite-phenol-formaldehyde resin powder compositions.

A known method for the manufacture of contact inserts (RF Patent for the invention No. 2267411. A method of manufacturing contact inserts, IPC B60L 5/08, from 10.01.2006), comprising mixing a graphite powder with a binder powder, pressing the product from a mixture at a temperature of 150-170 ° C and specific pressure 30-40 MPa with holding under pressure for 3-5 minutes and its subsequent heat treatment according to a given mode.

A significant drawback of this method is the reduced density of the products obtained to 1.55-1.60 g / cm ³ (Samodurova M.N. et al. Static and high-energy molding of carbon powder compositions // Metallurg, 2011, No. 11, p. 87 -91). At such a density, up to 30-32% of the pores are contained in the product’s volume, which increase the electrical resistivity of the inserts and reduce their electrical conductivity and strength properties.

The main reason for such a high porosity of the inserts is the increased adsorption capacity of graphite to atmospheric gases, water vapor, and other liquids. The mixing operation enhances the adsorption of gases and vapors on graphite particles. The operation of pressing the mixture in a closed mold with a sufficiently high speed of the upper punch up to 35 mm / s and a very small gap (about 150 μm) between the punch and the die does not allow at least some of the gases and vapors to be removed from the product. The operation of holding the product under pressure, intended for the polymerization of the binder, practically does not allow the removal of gases and vapors, since they are mainly located in the closed pores of the compacts.

The closest in technical essence and the achieved effect to the proposed solution is the method (RF Patent for the invention No. 21096545. A method of manufacturing contact inserts of current collectors of electric vehicles. IPC B60L 5/08, from 04/27/1998), including hot rolling of the mixture, grinding the resulting semi-finished product, sieving and hot pressing in a closed mold. Hot rolling of the mixture at a temperature of 110-140 ° C will provide significant removal of gases and vapors from it in the open deformation zone, but subsequent grinding operations of the rolling product and sieving of the grinding product will again lead to the adsorption of gases and vapors on graphite particles.

Hence, the main disadvantage of this method is the high porosity of the inserts, leading to their reduced physical and mechanical properties, especially strength and electrical conductivity.

The objective of the proposed solution is to eliminate this drawback, namely increasing the strength and conductivity.

The problem is solved in that in a method for manufacturing sliding contacts, including rolling a carbon-based powder mixture and pressing, according to the claimed solution, the powder mixture is cold-rolled in a caliber formed by four drive rolls, with a container cross-section to caliber cross-sectional ratio 1.5 ÷ 3, giving the resulting semi-finished product a cross section close to the cross section of the finished contact, and a length equal to the total length of several contacts, and after leaving the semi-finished caliber is divided into separate preforms, and before pressing, they are heated to a temperature of 110 ÷ 140 ° C.

Cold rolling of the powder mixture in a caliber formed by four drive rolls of a lengthy semi-finished product consisting of several contact blanks will allow the bulk (up to 85-90%) of atmospheric gases and liquid vapors to be removed from the semi-finished product. Heating the workpieces to a temperature of 110 ÷ 140 ° C will provide additional removal of 3-5% of gases and vapors. Thus, before the start of the main pressing operation, 90-93% of gases and vapors will be removed from the workpiece.

Hot pressing of such blanks in a mold heated to 170-180 ° C will provide a further increase in the contact density to 1.65-1.70 g / cm ³ and, consequently, an increase in strength and electrical conductivity.

A decrease in the ratio of the container’s cross-section to the caliber’s cross-section during rolling less than 1.5 will not allow to remove most of the gases and vapors from the mixture and provide the desired shape of the semi-finished product, and increasing it more than 3 will lead to a slipping of the rolling process due to the lack of friction forces on the contact surfaces of the mixture with rolls.

Heating the workpieces to a temperature of less than 110 ° C will not provide additional removal of gases and vapors from the workpiece and the specified conditions of exposure under pressure during pressing. Heating over 140 ° C is dangerous, because even before the start of pressing, the polymerization of products may begin, which leads to the destruction of the workpiece.

The proposed method is illustrated in figure 1, 2, where figure 1 shows a diagram of the rolling of the powder mixture, figure 2 is the same (top view).

On these drawings are indicated: 1 - powder mixture; 2 - container for the mixture; 3 - caliber; 4 - compression rolls; 5 - semi-finished product.

The method is as follows.

Powder mixture 1 is supplied to the master container 2 closed on the sides, the motor (not shown) of the rollers is switched on, in which all four compression rolls 4 are driven. The ratio of the cross section S _{0 of the} container 2 to the cross section S _{1 of} caliber 3 is 1.5 ÷ 3. The rollers 4, rotating, squeeze the powder mixture 1, and it leaves the caliber 3 in the form of a semi-finished product 5. After exiting the rollers 4, the defective end of the semi-finished product 5 is cut off and the semi-finished product 5 is divided into separate contact blanks, for example, cutting abrasive wheels. Then, individual contact blanks are fed into the heating device and heated to a temperature of 110-140 ° C.

After heating, the preform is fed into a heated mold and crimped in the thickness of the future contact.

The proposed method was tested for the manufacture of a prototype — a sliding contact in the form of an electric brush measuring 20 × 30 × 50 mm from a material containing 86% electrographite according to TU 1916-109-71-2000 and 14% phenol-formaldehyde resin of the SFP-OPA brand. The indicated mixture, weighing 545 g, was fed into a roll (rolling stand) with four drive rolls (L. Barkov et al. Rolling of low-plastic materials with multilateral compression. - Chelyabinsk, Metallurgy, 1988, pp. 144-253, Fig. 119, 123 ), where it was rolled at a ratio of S ₀ to S ₁ equal to 2.3, and came out with a speed ν _p = 0.5 m / s in the form of a semi-finished product with a cross section of 30 × 40 mm. This semi-finished product was cut into 8 blanks with a length of 50 mm, which were set into a heating device and heated to 135 ° C. Heated blanks were pressed from a size of 40 mm to a size in height of 20 mm.

The density of the obtained brush blanks was 1.68 g / cm ³ , the average specific electrical resistance was 45 μOhm · m, and the average compressive strength was 55 MPa.

The proposed method will find application in the production of electric car brushes, as well as contact inserts for current collector devices of both urban and railway electric vehicles.

Claims (1)

A method of manufacturing sliding contacts, including rolling a carbon-based powder mixture and pressing, characterized in that the powder mixture is cold rolled in a caliber formed by four drive rolls, with a cross-sectional ratio of the powder mixture container to a cross-section of caliber equal to 1.5 -3, with the formation of a semi-finished product with a cross section close to that of the finished contact, and a length equal to the total length of several contacts, after exiting the caliber, the semi-finished product is divided t into separate blanks, and before pressing them heated to 110-140 ° C.

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