RU2241783C1 - Method for applying antifriction coatings - Google Patents

Abstract

FIELD: metallurgy; internal-combustion engines.

SUBSTANCE: proposed method used for producing antifriction coatings on parts of piston-and-cylinder group, such as piston rings, to reinforce them includes anodic polarization of part in salt melt with current of 0.1 - 25.0 A/dm ³ for 1.5 - 2 at hardening temperature, water or oil hardening of part, boiling of the latter in water for 20 - 60 min to remove salt electrolyte film, and application of alignment layer using electrolytic method in ethylene-diamine electrolyte by cathodic polarization of part at current density of 0.95 - 1.1 A/dm ³ and temperature of 22 - 40 ^o C with metal-containing auxiliary electrode until metal layer of 30 - 60 μm in thickness is obtained.

EFFECT: reduced alignment time and coating wear under limited lubrication conditions.

1 cl, 1 tbl, 6 ex

Description

The invention relates to the field of metallurgy, in particular to methods for producing anti-friction coatings and hardening of parts of a cylinder-piston group of internal combustion engines, for example piston rings, and can also be used for coating products operating in friction conditions.

A known method of thermal spraying multilayer anti-friction coatings based on iron, which includes applying an adhesive layer with a thickness of 50-100 microns, applying a base layer with a thickness of 200-600 microns and spraying a running-in layer with a thickness of 150-250 microns with different porosity of the main and running-in layers [A.s . USSR No. 1696570, MKI ⁵ C 23 C 4/12, publ. 1991].

The specified method is characterized by complexity (including the complexity of preparatory operations before applying the layers) and the instability of the technology, the need to control the porosity of individual layers, which can only be done by the destructive method, as well as the need for final machining (grinding) after coating.

The closest in technical essence, selected as a prototype is a method of processing steel parts [RF Patent No. 2061089, MKI ⁶ C 23 C 8/42, publ. 1996], in which anodic polarization of the hardened parts is carried out in a salt melt with a current density of 0.1-25 A / dm ² at a temperature of 830-1190 K using a steel auxiliary electrode.

Known reasons that impede the achievement of the technical result that the invention provides are increased hardness and roughness of the known coating, which leads to an increase in the running-in period and increased wear during operation.

The problem to which the invention is directed is to increase the efficiency of parts, in particular piston rings.

In the implementation of the invention, the task is solved by achieving a technical result, which consists in reducing the running-in period and reducing the wear of the coating in conditions of limited lubrication.

The specified technical result is achieved by hardening the surface layer of the part and applying a running-in layer over it according to the following technology: 1) heating the part in a protective salt electrolyte, its anodic polarization with a current of 0.1-25.0 A / dm ² for 1.5- 2.0 hours at a quenching temperature selected in accordance with well-known heat treatment modes in the reference books; 2) quenching of the part in water or oil in accordance with accepted modes; 3) boiling the part in water for 20-60 minutes in order to remove the film of salt electrolyte; 4) applying the running-in layer by electrolysis in an ethylene diamine electrolyte by cathodic polarization of a component with a current density of 0.95-1.1 A / dm ² at a temperature of 22-40 ° C with a copper-containing auxiliary electrode to obtain a copper layer 30-60 microns thick.

There is the following causal relationship between the claimed technical result and the essential features of the invention: in the process of anodic polarization of the part in the salt melt at the quenching temperature, the alloying components and carbon that are part of the steel diffuse into the surface layer, which after quenching by known modes leads to microhardness of the surface of the part and increase its wear resistance; the part’s working life is improved by applying a servo-like copper film 30-60 μm thick on its surface, which has a thermodynamically unstable structure, prone to modification during the running-in period. Before the cathodic polarization of the hardened part, it is necessary to remove the remaining salt electrolyte by boiling in water for 20-60 minutes, depending on the shape and roughness of the part.

Residual salt electrolyte from smooth, simple-shaped parts like piston rings is removed by boiling for 20 minutes in water. At shorter durations, “softened” electrolyte residues may remain on the surface of the products. In the case of a more complex surface shape (for example, in the presence of grooves or stepped transitions from one diameter to another) and a greater roughness, the boiling time must be increased to 60 minutes to completely dissolve the remaining electrolyte.

The application of a running-in copper layer on the surface of a product operating under friction with lubrication is known. In the present invention, special conditions for the electrolysis of copper are selected, which make it possible to obtain a thermodynamically unstable structure during electrocrystallization that is prone to intensive modification during the running-in period. The protruding microroughnesses of the applied coating at the initial moments of operation are easily deformed, the area of the friction supporting surfaces increases and the force effect at the contact points decreases, and the quality of the worked-in surfaces improves. Under "severe" friction conditions, a copper film can serve as a solid lubricant due to its special structure formed during electrocrystallization with a current density of 0.95-1.1 A / dm ² and a temperature of 22-40 ° C in the known ethylene diamine electrolyte.

A temperature of 22-40 ° C is optimal for the electrolysis of copper in ethylene diamine electrolyte: lowering the temperature below 22 ° C requires additional costs and complicates the technology, increasing the temperature above 40 ° C affects the quality of the copper coating.

Electrocrystallization of coatings at current densities of less than 0.95 A / dm ² results in a copper layer with a columnar structure, which practically does not undergo the desired changes under “soft” friction conditions. On the other hand, the use of a cathode current density of greater than 1.1 A / dm ² leads to the production of powder coatings that are limitedly suitable for use as compact layers.

The running-in layer thickness of less than 30 microns does not provide correction of geometric errors in the inner surface of the cylinder liner, which leads to a loss of engine performance as a whole. An increase in the thickness of the copper layer above 60 μm causes unreasonable material and time costs that do not improve engine performance.

The possibility of implementing the proposed method for applying anti-friction coatings is confirmed by the following examples with samples of materials used for the manufacture of piston rings. Current leads made of steel 20 were attached to samples of size 40 × 10 × 10 mm. At anodic polarization, steel 20 rods were used as an auxiliary electrode, heating was carried out in a resistance furnace with a power of 10 kW and a working volume of 3 dm ³ .

Example 1. After heating a crucible with a borax melt containing 0.5 wt.% Iron (II) oxide to 880 ° C, a 20X steel sample and an auxiliary electrode were immersed in the melt. The sample was connected to the positive pole of the UIT-1 direct current source, and the auxiliary electrode to the negative. A current of 14.3 A / dm ^{2 was} passed for 2 hours, after which the sample was quenched in oil. Then, the sample was boiled in water for 20 min, transferred to an ethylene diamine electrolyte, and cathodically polarized with a current density of 1.1 A / dm ² at a temperature of 40 ° C, using pure copper as the anode. The electrolyte composition: СuSO ₄ · 5Н ₂ О - 110-125 g / l, ethylenediamine (70%) - 60-70 g / l, Na ₂ SO ₄ · 10H ₂ О - 50-60 g / l, (NH ₄ ) ₂ SO ₄ - 50-60 g / l, pH 6.8-8.4.

Example 2. The method was carried out analogously to example 1, however, a sample of steel 50KhFA was used, and the anodic polarization was carried out for 1.5 hours at 850 ° C with a current density of 25.0 A / dm ² . The hardened sample was boiled for 30 min. The cathodic polarization was performed with a current density of 0.95 A / dm ² at 22 ° C using a BrOF 6.5–0.4 bronze bar as the anode.

Example 3. The method was carried out analogously to example 1, however, a sample of cast iron VChKhNMD was used, anodic polarization was carried out for 1.9 hours at 870 ° C with a current density of 0.1 A / dm ² . The hardened sample was boiled for 60 min. Cathodic polarization was performed with a current density of 1.05 A / dm ² at 29 ° C.

Example 4. The method was carried out analogously to example 1, however, the anodic polarization was carried out 2.5 hours with a current density of 0.05 A / DM ² . The hardened sample was boiled for 70 min. Cathodic polarization was performed with a current density of 0.75 A / dm ² at 20 ° C.

Example 5. The method was carried out analogously to example 1, however, the anodic polarization was carried out for 1.0 h at 830 ° C with a current density of 27.2 A / dm ² . The hardened sample was boiled for 10 min. Cathodic polarization was performed with a current density of 1.25 A / dm ² at 52 ° C. Salt electrolyte residues were observed on the surface of the sample.

Example 6. For comparison, strengthened a sample of steel 20X in accordance with the prototype without applying a running-in layer. Anodic polarization and hardening was carried out analogously to example 1.

The wear of the coated samples was determined on an SMT-2 friction machine according to the “disk-plate” scheme without lubrication by weight loss. The running-in period was estimated by the stabilization time of the wear value. The results shown in the table show the advantages of the invention in comparison with the prototype: the running-in period is reduced by 33-42%, and the amount of wear during operation is 23-38%. At the same time, the implementation of the method of applying antifriction coatings with parameters beyond the scope of the claimed does not provide the required technical result: although the running-in period is reduced compared to the prototype, the wear rate increases markedly.

Claims (1)

A method of applying antifriction coatings, including heating, anodic polarization of a part in a salt melt with a current of 0.1-25.0 A / dm ^{2 for a} duration of 1.5-2.0 hours using an auxiliary electrode and hardening, characterized in that the polarization of the part is carried out at hardening temperature, after hardening, the component is boiled in water for 20-60 minutes and a running-in layer of 30-60 μm thickness is applied by cathodic polarization of the product in an electrolyte with a copper-containing auxiliary electrode with a current density of 0.95-1.1 A / dm ² at a temperature of 22 -40 ° C.