RU2274537C1 - Method for restoration of worn resting planes of aluminum alloy heads of block of internal combustion engines - Google Patents

Abstract

FIELD: restoration of worn parts of aluminum alloys, possibly restoration and corrosion protection of resting surfaces of heads of block of internal combustion engines.

SUBSTANCE: method comprises steps of preliminarily preparing surface; electric arc metal plating of it at using additive wire of given kind; mechanically working worn surface and forming protective coating on it by micro-arc oxidizing in aqueous electrolyte containing 2.8 - 3.2 g/l of potassium oxide and 10 - 12 g/l of liquid glass at electric current density 20 A/dm² for 1.5 h; subjecting surface to heat treatment at temperature 200 - 250° C and impregnating it with suspension of fluoroplast of given mark for further dying at temperature 90 - 95°C.

EFFECT: improved corrosion resistance of part.

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Description

The invention relates to the field of recovery of worn parts from aluminum alloys, for example, to restore and protect against corrosion the mating plane of the heads of a block of internal combustion engines from aluminum alloys.

In the repair industry, there is a known method for the restoration of worn parts from aluminum alloys, including the increment (surfacing in a protective gas environment) of the surface to be restored, machining and hardening of this surface by microarc oxidation [1].

The disadvantage of this method is the overheating of the metal of the deposited part, low productivity when restoring the mating planes of the heads of the block of internal combustion engines, as well as the low corrosion resistance of these planes.

A known method of obtaining heat-resistant insulating coatings on products from aluminum alloys, including processing parts by microarc oxidation and subsequent filling of the pores of the coating with fluoroplastic [2].

The disadvantage of this method is the production of thin coatings (up to 0.2 mm), which do not provide compensation for wear of the mating planes of the heads of the block of internal combustion engines (according to statistical analysis, the maximum wear is 3.5 mm).

Closest to the proposed method in terms of technical nature and the achieved result is a method of restoring the mating planes of the cylinder heads of automotive engines made of aluminum alloys, including preliminary surface preparation, increment by electric arc metallization, machining and hardening of this surface by microarc oxidation [3].

The disadvantage of this method is the increased through porosity and, as a result, low corrosion resistance.

The problem to which the invention is directed, is to increase corrosion resistance by reducing the through porosity of the coating.

The problem is achieved in that in the known method, including preliminary surface preparation, increment by electric arc metallization, machining and obtaining a protective coating on the surface by microarc oxidation, according to the invention, surface increment by electric arc metallization is carried out using filler wire Sv-AMg6, the formation of a protective coating by microarc oxidation in an aqueous electrolyte containing 2.8 ... 3.2 g / l of potassium hydroxide and 10 ... 12 g / l of liquid glass, etc. and a current density of 20 A / dm ² for 1.5 hours, an additional heat treatment is carried out at a temperature of 200 ... 250 ° C and impregnation with a suspension of fluoroplastic F-4D, followed by drying at a temperature of 90 ... 95 ° C.

The method is as follows.

To restore the worn-out mating planes of the heads of the block of internal combustion engines from aluminum alloys, preliminary preparation of the part for metallization is carried out. It includes machining on a 6M12P vertically milling machine until traces of wear are removed, notches are obtained at the outer edges of the abutment plane, combustion chambers and all recesses (except through stud holes) using a special percussion device or hydraulic press, processing in a closed chamber with an air stream containing corundum and chipped steel. The air pressure during processing in a closed chamber is 0.6 ... 0.9 MPa, the material consumption is on average 1.7 m ³ / min, the processing distance is 140 ... 160 mm, the angle of inclination of the air stream with the material to be processed the mounting plane of the cylinder head is 80 °, the speed of movement of the cylinder head relative to the spray gun is 0.6 m / min. Preliminary preparation is necessary to create a certain roughness on the attachment plane in order to improve the adhesion of the metal layer applied by electric arc metallization during increment.

Before electric arc metallization, the openings of the combustion chambers and the water jacket for cooling the head of the block are closed with asbestos-laminate plugs. Electric arc metallization is carried out on a mechanized installation, which contains an upgraded EM-14M electrometallizer, a control unit, filler wire cassettes, a metallization chamber and a VDU-504 power source. The process is carried out in a metallization chamber. Metallization modes: arc current - 310 A, voltage - 30 ... 35 V, filler wire supply of Sv-AMg6 grades with a diameter of 2 mm - 8.5 m / min, compressed air flow rate - 2.8 m ³ / min, compressed pressure air - 0.5 ... 0.7 MPa, the distance from the metallizer nozzle to the mounting plane of the cylinder head is 100 ... 120 mm, the metallization time is 9 ... 10 min, the thickness of the deposited metal layer is up to 3.5 mm . As filler material, you can use wire Sv-AD1 or rods made of AK9ch alloy.

After applying the metal layer, the abutment plane of the head of the block is subjected to mechanical processing — milling on a model 6M12P vertically milling machine to certain sizes, taking into account their increase during microarc oxidation. Milling is performed at a rotational speed of the mill 2000 min ^-1 , a cutting depth of 0.5 ... 0.8 mm and a table feed speed of 200 m / min. Then they perform the necessary drilling work: they countersink the chamfers of the mounting holes to a depth of 2 ... 3 mm and the chamfers for the studs.

Before microarc oxidation, the plane is degreased in an aqueous solution containing 5 ... 10 g / l NaOH, 40 ... 50 g / l Na ₃ PO ₄ and 3 ... 5 g / l Na ₂ SiO ₃ , after which the surfaces non-hardening, insulate with alkali-resistant silicone sealant. Next, a protective coating is formed on the abutment plane of the head of the block by microarc oxidation in an aqueous electrolyte containing potassium hydroxide KOH - 2.8 ... 3.2 g / l, liquid glass Na ₂ SiO ₃ - 10 ... 12 g / l. Processing modes: current density D _t - 20 A / dm ² , electrolyte temperature T - 18 ... 23 ° C, oxidation time t - 1.5 hours. The increase in the size of the part after MAO is 90 ... 100 microns.

After microarc oxidation, the block head is subjected to heat treatment, placed in a furnace and heated to a temperature of 200 ... 250 ° C, which allows you to free the pores of the coating from moisture. Then, the pores of the coating are filled by immersing the mating plane of the block head in a container filled with a F-4D fluoroplastic suspension. The processing temperature is 30-50 ° C, the exposure time 15 ... 30 minutes Dry the coating at a temperature of 90 ... 95 ° C. The result of the last operation is the elimination of through porosity of the coating, which significantly increases the corrosion resistance of the coating (see table).

The through porosity of the hardened mating planes of the heads of the block of internal combustion engines from aluminum alloys was determined in accordance with the method described in GOST 9.302-88 “Metallic and non-metallic inorganic coatings. Control methods".

Corrosion and corrosion resistance of the mating planes of the heads of the block of internal combustion engines made of aluminum alloys were evaluated in accordance with GOST 9.308-85 “Metallic and non-metallic inorganic coatings. Accelerated Corrosion Test Methods ”for mass loss per unit surface area.

The results of comparative tests of the proposed method and prototype are presented in the table.

Indicators Prototype The proposed method without impregnation with impregnation 1. Through porosity, pore / cm ² 48 39 - 2. Weight loss, g / m ² 7.1 6.3 2.1

As can be seen from the table, the proposed method for restoring worn-in mating planes of the heads of the block of internal combustion engines from aluminum alloys allows, as a result of impregnation, to remove the through porosity of the coating and increase corrosion resistance by 2.5 ... 3 times.

Information sources

1. RF patent 2119420, В 23 Р 6/00.

2. RF patent 2237758, C 25 D 11/06, 11/18.

3. RF patent 2228246, В 23 Р 6/00 - prototype.

Claims (1)

A method for restoring worn-in mating planes of heads of a block of internal combustion engines from aluminum alloys, including preliminary surface preparation, surface increment by electric arc metallization, machining and obtaining a protective coating on the surface by microarc oxidation, characterized in that surface increment by electric arc metallization is carried out using filler wire Sv- AMGB, the formation of a protective coating by microarc oxidation in water ohm electrolyte containing 2.8 ... 3.2 g / l of potassium hydroxide and 10 ... 12 g / l water glass at a current density of 20 A / dm ² for 1.5 h, further conduct the heat treatment at a temperature 200 ... 250 ° C and impregnation with a suspension of fluoroplastic F-4D, followed by drying at a temperature of 90 ... 95 ° C.