RU2228972C1 - Method of application of multi-layer coats - Google Patents

Abstract

FIELD: mechanical engineering; application of quality multi-layer coats on surfaces of hydraulic cylinders, rods and other articles; restoration of worn parts. SUBSTANCE: proposed method includes electrolytic sedimentation and mechanical action performed by vibration rolling; first cycle of vibration rolling is performed before electrolytic sedimentation of coat and is repeated by cycles till obtaining required thickness; after application of each subsequent layer, vibration rolling is performed at time interval of t = δ/υ, where δ is total thickness of coat, mm; u is rate of sedimentation, mm/min. Proposed method is performed in the following mode: clearance between anode and surface being treated no more than 1.5 mm; cathode current density 6-9•10⁴ A/sq m; vibration rolling force, 250-300 N; rotational sped of blank, 10-30 m/min; indenter radius, 1.5-2.0 mm; indenter vibration amplitude, 1.0-1.5 mm; vibration frequency, 1400- 2800 min^-1; feed rate, 0.05-0.15 r/min. EFFECT: increased microhardness; enhanced resistance to wear; reduced roughness of surface. 2 cl, 2 dwg, 1 tbl, 1 ex

Description

The invention relates to the field of engineering technology, in particular to methods for applying multilayer coatings, and can be used to obtain high-quality multilayer coatings of large thickness on the surfaces of hydraulic cylinders, rods, etc., as well as when restoring worn parts.

There is a known method (magazine “Mashinostroitel” 1997, No. 10, pp. 23-24. VP Smolentsev, EV Smolentsev, S.Yu. coatings, which consists in periodic repeated electrolytic deposition of small (less than 1 μm) layers with subsequent plastic deformation of each layer.

However, the publication does not indicate the method of surface plastic deformation of the applied coating layers and the type of surface pretreatment before coating, which affects the adhesion quality of the base material with the coating.

As a prototype, a method of electrolytic chromium plating (RF patent No. 2175032, C 25 D 5/22 dated 10/20/2001) was adopted, including preliminary deposition of chromium and final chromium plating with mechanical action on the cathode film due to contact of the treated surface with honing bars making reciprocating movement during rotation of the workpiece with forced pumping of the electrolyte in the interelectrode gap, and before preliminary deposition, honing bars are installed with a guarantee gap, and in the process of honing, pause the supply of technological current with a subsequent increase in current density to the operating value.

The main parameters and modes of the electrolytic chromium plating method according to the prototype: the workpiece is a 9Kh2MF steel roller; preliminary guaranteed clearance between the bars and the treated surface of 0.3-0.5 mm (not more than 1.5 mm); the thickness of the preliminary layer of chromium is 55 microns; the speed of the reciprocating movement of the abrasive bars of 0.1 m / s with a clamping force of 2 MPa; processing time - 16 min; with a pause in the current supply of 11.7 minutes; with a final increase in current density to a working value.

The electrolytic chromium plating mode according to the prototype: the cathode current density varies from 0 A / m ² to 5 · 10 ⁴ A / m ² ; electrolyte temperature - 621 ° C; electrolyte flow velocity υ _e - 3.2 m / s; the electrolytic deposition rate of the coating υ _n - 3.2 mm / min The electrolyte is standard with the content of components: chromic anhydride - 250 g / l, sulfuric acid - 2.5 g / l.

As a result of comparative studies of coatings, it was found that electrolytic chromium plating is characterized by large grains (≈1.2 μm) with long microcracks through which pass through the entire coating. Moreover, large and small pores are formed at the interface between chromium and the base metal, which reduce the adhesion of the coating to the base metal.

However, this method does not sufficiently improve the quality of the bimetallic layer (steel-chromium) operating in difficult operating conditions.

This is due to the following circumstances: the combined processing method under consideration does not exclude the appearance of residual tensile stresses inherent in chromium plating, and honing, aimed at increasing the roughness by smoothing the surface, partially removes the applied chrome coating.

The task of developing the proposed method for applying multilayer coatings is to ensure high quality characteristics of the coatings.

The technical result is an increase in the microhardness of the coating and the base material, the formation of residual compressive stresses in the surface layer, an increase in wear resistance, and a decrease in surface roughness.

где δ - общая толщина покрытия, мм, υ - скорость хромирования, мм/мин. Причем способ осуществляют по следующему режиму: зазор между анодом и обрабатываемой поверхностью не более 1,5 мм, усилие вибронакатывания Р=250-300 Н, катодная плотность тока 6-9·10⁴ А/м², скорость вращения заготовки υ_з 10-30 м/мин, радиус индентора (шарика) R_инд=1,5-2,0 мм, амплитуда колебаний индентора А=1,0-1,5 мм, частота колебаний n=1400-2800 мин^-1, подача S=0,05-0,15 мм/об.This technical result is achieved by the fact that in the method of applying multilayer coatings, including electrolytic deposition and mechanical impact, mechanical action is carried out by vibro-rolling, the first vibro-rolling being carried out before electrolytic deposition of the coating and the process is repeated in cycles until the required thickness is obtained, after each subsequent layer is applied, vibro-rolling through time interval

where δ is the total coating thickness, mm, υ is the chromium plating rate, mm / min. Moreover, the method is carried out according to the following mode: the gap between the anode and the treated surface is not more than 1.5 mm, the vibration rolling force is P = 250-300 N, the cathodic current density is 6-9 · 10 ⁴ A / m ² , the workpiece rotation speed υ _з 10- 30 m / min, indenter (ball) radius R _ind = 1.5-2.0 mm, indenter oscillation amplitude A = 1.0-1.5 mm, oscillation frequency n = 1400-2800 min ^-1 , feed S = 0.05-0.15 mm / rev

In the structure of the surface layer obtained by the proposed method, tightly adjacent columns of small grains (≈ 0.2 μm) are formed with a shift and their orientation in the direction of the vibratory rolling force. Moreover, the proposed method is characterized by the absence of a pore base and other defects at the interface of chromium with the metal, as well as the presence of chromium, which is explained by the phenomenon of mass transfer that occurs during multilayer electroplating coating. With further layer-by-layer galvanic deformation coating (up to 1000 μm), further grinding and crushing of grains into fragments and blocks occurs (up to ≈ 0.01 μm).

When pre-treating the surface by vibro-rolling as compared with known processing methods, such as cutting, grinding, etc., characterized by a random arrangement of irregularities, a regular microrelief is formed, which increases the adhesion area of the base material and the coating. The quality of the coating improves. Along with this, a combination of galvanic deposition (for example, chromium plating, etc.), which is characterized by the appearance of residual tensile stresses with surface plastic deformation by vibro-rolling, allows the formation of residual compression stresses in the surface.

Figure 1, 2 shows a device for implementing the method.

The device includes a bath 1 for electrolytic coating and a device 2 for vibratory rolling. The bath 1 is equipped with an anode 3, a current source 4 and a device 5 for moving and rotating the workpiece 6, to which a gear 7 with a motor 8 is connected. The device 2 for vibro-rolling is equipped with a deforming element - indenter 9.

The method is as follows. The workpiece 6 to be processed is thoroughly washed and installed in the fixture 5. A deforming element, an indenter 9, is turned on and a process of surface plastic deformation by vibro-rolling takes place. Next, the workpiece in the device 5 is set so that the gap between the anode 3 and the workpiece surface 6 is small - not more than 1.5 mm. Then, at the same time, the electrolyte circulation system (bath filling 1) and the working movement (rotation) of the workpiece 6 are turned on, a direct current is turned on, and the process of electrodeposition begins. In this case, the current density should significantly (several times) exceed the value that is used in conventional electrodeposition. During the galvanic deposition of a coating layer with a thickness of (0.1-0.2) δ (where δ is the total coating thickness), a deforming tool is included in the work and a surface plastic deformation process occurs. Then the cycles are continuously repeated until the desired coating thickness is obtained.

As a result, a multilayer coating of large thickness (up to 1000 μm) is formed.

An example implementation of the method.

Comparative studies were carried out on samples with a hollow cylindrical inner diameter D _ext = 27-46,5 mm, an outer diameter D _n = 30-50 mm and a length L = 50 mm steel 9H2MF.

Preliminary operations: degreasing, washing in hot and cold water, installation in the device.

Standard electrolytic chromium plating mode: electrolyte temperature - 621 ° С; electrolyte flow velocity υ _e - 3-3.2 m / s; electrolytic deposition rate of the coating υ _n mm / min. The electrolyte is standard with the content of components: chromic anhydride - 250 g / l, sulfuric acid - 2.5 g / l.

The main parameters and modes of the proposed method of galvanic deformation deposition of multilayer coatings: the gap between the anode and the workpiece surface 1.5 mm; cathodic current density of 6-9 · 10 ⁴ A / m ² ; vibration rolling force P = 250-300 N, workpiece rotation speed υ _з = 10-30 m / min, indenter (ball) radius R _ind = 1.5-2.0 mm, indenter oscillation amplitude A = 1.0-1, 5 mm, the oscillation frequency n = 1400-2800 min ^-1 , the feed S = 0.05-0.15 mm / rev, the period of time through which vibro-rolling is carried out t = 3.5-4.0 min. The thickness of the resulting coating is 80 microns.

Reducing and increasing the gap between the anode and the workpiece surface under 1.5 mm reduces the performance of galvanic deposition.

A decrease in the cathodic current density of less than 6 · 10 ⁴ A / m ² does not provide a high adhesion strength between the coating layers.

The increase in cathodic current density of more than 9 · 10 ⁴ A / m ² does not provide the removal of intermediate recovery products from the interelectrode gap zone.

With a decrease in the vibration rolling force P of less than 250 N, the parameters: roughness R _a , residual stresses σ _ost , microhardness Нμ - are not optimal.

With an increase in the vibration rolling force P of more than 300 N, microcracks in the chrome coating are possible.

When reducing the speed of rotation of the workpiece υ _s less than 10 m / min, the processing productivity decreases, places ("islands") of under-riveting or not at all subject to vibration rolling are formed.

With an increase in the workpiece rotation speed υ _З more than 30 m / min, the indenter can pass through the same place, which causes re-riveting (microcracks, peeling).

With a decrease in the radius of the indenter R _ind less than 1.5 mm, the contact pressure increases, which causes perenaklep (microcracks, peeling).

With an increase in the radius of the indenter R _ind more than 2.0 mm, the contact pressure decreases, which negatively affects the formation of residual compressive stresses, reduces them.

A decrease of less than 1.0 mm and an increase of more than 1.5 mm in the amplitude of vibrations A, a decrease of less than 1400 min ^-1 and an increase of more than 2800 min- ^{1 of} the oscillation frequency n, a decrease of less than 0.05 mm / rev and an increase of more than 0.15 mm / about feed parameters: roughness R _a , residual stresses σ _ost , microhardness Hμ - not optimal.

Reducing and increasing the time interval t through which vibro-rolling is carried out does not provide the required size and quality of the coating.

The table shows the results of comparative studies of the surface layer obtained after processing by the technology of the prototype and the proposed method.

The results of comparative studies presented in the table showed that the proposed method of galvanic deformation deposition of multilayer coatings provides an increase in the microhardness of the coating and base material by an average of 10-20%, formation in the surface layer compared to the prototype (from minus 18 MPa to plus 21 MPa) residual compressive stresses ranging from minus 400 MPa to minus 800 MPa, an increase in wear resistance by 200-400% compared to the prototype 26%, a decrease in surface roughness from R _a = 1.25 μm to R _a = 0.32-0, 16 microns.

Claims (2)

1. The method of applying multilayer coatings, including electrolytic deposition and mechanical impact, characterized in that the mechanical impact is carried out by vibro-rolling, the first vibro-rolling being carried out before electro-deposition of the coating and repeating the process in cycles until the required thickness is obtained, after each subsequent layer is applied, vibro-rolling is carried out after a period of time

where δ is the total coating thickness, mm; υ is the electrolytic deposition rate of the coating in mm / min. 2. The method according to claim 1, characterized in that it is carried out according to the following mode: the gap between the anode and the treated surface is not more than 1.5 mm, the cathode current density is 6-9 · 10 ⁴ A / m ² , the vibration rolling force is P = 250 -300 N, workpiece rotation speed υ _з = 10-30 m / min, indenter (ball) radius R _ind = 1.5-2.0 mm, indenter vibration amplitude A = 1.0-1.5 mm, vibration frequency n = 1400-2800 min ^-1 , feed S = 0.05-0.15 mm / rev.

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