RU2476856C1 - Determination of hardness of galvanic coatings on machine-building parts - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: quality of galvanic coatings on parts is controlled using hardness reference minerals. When determining hardness of galvanic coatings on parts, hardness references with hardness value that is lower than on tested galvanic coatings of parts are taken. If hardness reference leaves no scratch on the surface of galvanic coatings of parts, surfaces of parts are harder than hardness reference, and it means that galvanic coatings of parts are acceptable. If hardness reference has left a scratch on galvanic coating of the part, coating is accepted as a rejected one and does not comply with hardness of galvanic coating.

EFFECT: possibility of determining the type of coating, controlling the quality of galvanic operations and checking hardness without damage to working surface of the part.

2 tbl, 2 dwg

Description

The invention relates to mechanical engineering and can be used in all sectors of the economy where galvanic coatings of parts are used. Electroplating parts used in mechanical engineering: nickel plating, chromium plating, etc., are used as protective-decorative, protective and corrosion-resistant, and as hard wear-resistant. Depending on the electrolysis conditions, three types of chrome coating are formed on the parts (see figure 1):

- gray, with low physico-chemical properties and not finding practical application;

- shiny, characterized by high values of hardness (HV-1100) (HRC-70) and wear resistance;

- dairy, least porous and most plastic.

Currently, the type of coating is checked only by electrolysis conditions (current density and electrolyte temperature), the color of the chrome coating. This is a subjective assessment of coverage. The obtained type of chrome coating after electrolysis on the part is very difficult to determine only during testing and operation of the product.

Therefore, when plating parts hard, checking the hardness of chrome coatings is a prerequisite, since violation of this parameter leads to seizure of parts.

At present, there are no hardness tests without disturbing the plating layer on engineering parts.

Instruments used in mechanical engineering to determine the hardness of parts are based on the resistance of a metal to the indentation of a solid metal or diamond tip.

Brinell instruments determine the hardness of parts by indenting a steel ball.

The Rockwell device determines the hardness of parts by the penetration depth of a diamond or steel tip into the metal.

The Vickers instrument determines hardness by pushing a tetrahedral diamond pyramid into the test metal.

According to Shore, the hardness of the parts is determined by the method of elastic recoil and measuring the height of the bounce from the test metal of the standard hammer, freely falling from a constant height.

Determination of the hardness of parts is carried out by calibrated files.

All of the above hardness testing methods lead to damage to the test surface of the part.

For a specific determination of what plating is obtained on the part, it is proposed to apply the method of determining the Mohs hardness.

A method for determining the hardness of minerals in the jewelry industry was proposed in 1822 by the Austrian mineralologist F. Moos, who used ten minerals with a known and constant hardness. This table consists of ten minerals-standards of hardness, which are gradually increasing: talc - 1, gypsum - 2, calcite - 3, fluorite - 4, apatite - 5, orthoclase - 6, quartz - 7, topaz - 8, corundum - 9, diamond - 10 (see table 1). The method is based on the ability of solid minerals to leave a scratch on the surface of less solid formations. Mineral standards (see figure 2) are specially made pencils of hardness - metal rods in which fragments of the above mineral standards are fixed with sharp edges. When determining the hardness of a galvanic coating on a part, a standard of hardness of lower hardness is taken than the permissible hardness on the coating of parts. Having determined the value of hardness of the galvanic coating on the part, the type of coating is determined, which allows you to control the quality of galvanic operations.

Example.

The gate detail (gate gate detail) coated with Khtv21, GOST 9306-85 chrome. Electroplated coating on the part with hard chromium, coating thickness min 21 microns, coating hardness according to the Vickers table HV - 1000 ... 1100, the same hardness according to the Mohs table 6.5 ... 7 (see table 2).

When checking the gate parts for hardness of the coating with chromium, we take a mineral with a lower hardness than is required by the technical specifications of the detail drawing, i.e. according to table 1, Mohs 6 - the mineral orthoclase (one of the most common varieties of feldspar).

Carefully, without much pressure, we scratch the surface of the part (gate) coated with chrome (Xtv), a hardness pencil 6 (mineral - orthoclase). If the standard of hardness 6 does not leave scratches on the surface of the chrome coating, then the test piece is harder than the standard of hardness 6. The part corresponds to the hardness according to the Mohs table 6.5 ... 7 and according to the Vickers table HV 1000 ... 1100.

If the standard leaves a scratch, a defective part on the surface of the gate part coated with chrome and does not correspond to hardness according to the technical specifications of the drawing of the part HV 1000 ... 1100 according to Vickers and 6.5 ... 7 according to Mohs, and does not correspond to the type of chrome coating due to violation electrolysis mode (current density and electrolyte temperature).

In mechanical engineering, not only the gate, but also the internal openings of the sleeves, the outer surfaces of the pistons and rods of hydraulic, pneumatic cylinders, etc. are coated with a hard wear-resistant galvanic coating.

Using the determination of the hardness of galvanic coatings on machine parts by the Mohs method, it is possible to determine the type of coating, control the quality of galvanic operations and check the hardness without disturbing the working surface of the part.

Table 1. Reference minerals of the Mohs scale. Reference Hardness Machinability Talc one Scratched with a fingernail Gypsum 2 Calcite 3 Scratched with a knife Fluorite four Apatite 5 Orthoclase 6 Scratched by a file Quartz 7 Amenable to processing Topaz 8 Scratches glass Corundum 9 Diamond 10 Cuts glass

Table 2. Hardness of basic abrasive materials Natural abrasives Hardness Mohs scale Vickers scale Talc one - Pumice 5-6 - Quartz 7 1100 Flint 7 900-1100 Garnet 7-8 1100-1300 Emery 7-9 1600 Corundum 9 2200 Technical diamond 10 10,000

Claims (1)

A method for determining the hardness of galvanic coatings on parts of mechanical engineering, which allows to control the quality of galvanic coatings on parts by using minerals-standards of hardness, based on the ability of solid minerals to leave scratches on the surfaces of less solid formations, characterized in that when determining the hardness of galvanic coatings on parts, standards are taken hardness of lower hardness than on tested galvanic coatings of parts, and if the hardness standard is not left a scratch on the surface of the electroplated coatings of the parts, then the surfaces of the part are harder than the hardness standard, which means that the galvanic coatings of the parts are considered suitable, and if the hardness standard left a scratch on the galvanic coating of the part, the coating is recognized as defective and does not correspond to the hardness of the galvanic coating, which allows controlling the quality of galvanic operations on engineering parts without disturbing the working surfaces of the fit parts.

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