RU2427444C1 - Method of producing piston rings and cylinder sleeve billets - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention relates to spun casting. Proposed method comprises feeding portion of liquid cast iron into revolving steel mould and crystallising it at centrifugal forces. Prior to filling liquid cast iron, steel mould inner surface is coated with heat insulating 5.0-6.5 mm-thick layer of the following compositions, in wt %: silver graphite - 5-5, pulver bakelite - 2.5-4, quartz sand making the rest. Produced layer is hot cured at 260-320C. ^ EFFECT: ruling out chill spot in casting microstructure and higher antifriction properties. ^ 4 cl, 1 dwg, 1 ex

Description

The invention relates to the field of metallurgy, namely to foundry, in particular to the technology for the manufacture of oils, that is, cast cylindrical billets for the production of piston rings and cylinder liners of internal combustion engines, mainly diesel engines, by centrifugal casting.

The invention is aimed at improving the quality of cast billets by ensuring a high level of operational properties by obtaining a given macro-and microstructure of the metal.

A known method of centrifugal casting of billets of cylinder liners of internal combustion engines (ICE), described in patent RU 2062680 (published on June 27, 1996). The method includes pouring a cast alloy into a rotating mold, solidifying the metal, and removing the casting. The mold from the side of the inner surface is pre-painted with heat-insulating paint and heated to 100-150 ° C. Silumin is used as a cast alloy.

This technical solution cannot provide castings with a high level of performance when using gray cast iron as a casting alloy, which is the preferred material for the manufacture of cylinder liners of massive diesel engines.

The temperature of molten iron during pouring it into the mold is not less than 1380 ° C, which is significantly higher than the pouring temperature of silumin. Therefore, the lining of the mold in the form of a layer of heat-insulating paint is clearly insufficient.

There is a known method of lining a centrifugal mold according to USSR author's certificate SU 476076 (published on 10.29.1975), according to which successive application of bulk materials and a liquid-moving facing refractory mass containing refractory powder, graphite, electrode fight and a binder is carried out in a rotating form. Liquid lining does not ensure the stability of the dimensional parameters of the casting and the surface quality of the resulting workpiece.

The closest analogue of the invention is the method of centrifugal casting of cylinder liners of internal combustion engines, known from the USSR author's certificate: SU 1328064, published on 08/07/1987. This method of manufacturing centrifugally cast cylinder liners of internal combustion engines differs in that in a rotating mold with a heat-insulating coating cast iron is poured with a carbon content of 3.5-3.7% and silicon 2.4-2.7%. Starting from a temperature of 1200-1250 ° C, the inner surface is forcedly cooled until it hardens with the introduction of a water-air mixture at a flow rate of 20-30 ml / kg of cast iron. The method provides improved machinability of the outer surface and increased wear resistance of the surface of the finished sleeves. The molds have a heat-insulating coating on the working surface with a thickness of 1.5 mm, consisting (in wt.%) Of 95% hot-clad sand and 5% dust-like ferrosilicon. The specified composition and thickness of the heat-insulating layer create conditions for obtaining an increased crystallization rate of the casting, which leads to the priority formation of carbide phases on the surface of the crystallizing metal in the form of a bleached layer, the increased hardness of which leads to rapid wear of the mating surfaces in friction pairs.

The invention is aimed at eliminating the disadvantages of technical solutions known from the prior art.

The technical result of the invention is to ensure the crystallization rate of castings, eliminating the bleaching of cast billets from the microstructure, which guarantees a given level of antifriction properties of the finished product.

An additional technical result of the proposed method, in addition to a given crystallization rate, is the creation of conditions for directional crystallization of the casting, which allows to obtain a microstructure in the finished product, providing an increase in its wear resistance.

The essence of the claimed method for producing blanks of piston rings and cylinder liners of internal combustion engines is that to obtain castings (oils), the centrifugal casting method is used, which involves pouring a portion of molten iron into a rotating mold and its crystallization under the action of centrifugal forces. In this case, before pouring, a layer of heat-insulating mixture with a thickness of 5.0-6.5 mm is preliminarily applied to the internal surface of the mold receiving the liquid metal, with the following ratio of components of the specified layer, wt.%:

Silver graphite 5-7 Pulverbakelite 2.5-4 Quartz sand rest,

then conduct hot curing of the obtained layer at a temperature of 260-320 ° C.

Metal filling and crystallization of the workpiece is carried out at a mold rotation speed of 600-800 rpm and while maintaining the workpiece crystallization rate of not more than 1 mm / s.

As metal for the preparation of blanks, gray cast iron alloyed with nickel and chromium is used. The use of gray cast iron of various grades makes it possible to provide the required antifriction surface properties of the obtained parts, which work mainly on wear in friction pairs, which requires the presence of a microstructure in the casting containing inclusions of finely evenly distributed graphite.

To create conditions for directed crystallization on the inner surface of molten iron after pouring it, an additional heat-insulating layer is introduced into the mold in the form of a thermosetting mixture or a mixture of quartz sand and silver graphite. In this case, the outer surface of the rotating mold is intensively cooled by water or a sprayed water-air mixture.

The invention is illustrated in the drawing and example.

The drawing shows a casting 1 in the form of a blank for producing a cylinder liner of a diesel engine, placed in the case of the mold 2 of the centrifugal casting installation. At the same time, a layer 3 of a heat-insulating mixture is applied to the inner surface of the mold. At one end of the mold placed rod 4, made in the form of a ring. At the opposite end of the mold there is a cover 5 provided with thermal insulation.

Compared with traditional methods of casting billets into the ground, such as “maslot”, that is, casting in sand and clay molds, the claimed method allows to achieve high productivity of 6-8 castings per hour by using a centrifugal casting unit, with a minimum consumption of molding materials. In addition, the claimed method in the manufacture of piston rings can significantly reduce labor costs, loss from marriage, save the consumption of molding materials (30 times compared with traditional methods of casting in sand and clay molds), reduce energy costs, improve sanitary and hygienic working conditions.

Example.

According to the proposed technology, blanks were obtained for the manufacture of cylinder liners and piston rings for diesel engines D50, D100, D67, 5D49.

A portion of molten cast iron was poured into a rotating mold 2 at a speed of 600 ~ 800 rpm (depending on the diameter of the cast billet). As the casting metal, various grades of gray cast iron alloyed with nickel and chromium were used. The crystallization of cast iron 1 was carried out under the influence of centrifugal forces, providing a decrease in porosity, that is, increased density of the metal in the product compared to the gravitational conditions for producing castings.

The proposed technology has successfully solved the problem of obtaining a crystallization rate within the limits completely eliminating the appearance of “bleached” (structurally free cementite) in the microstructure of cast iron, and obtaining a structure of graphite inclusions that is close to the structure obtained by the traditional method of casting in sand-clay molds - graphite fine plate, uniform distribution. This microstructure of gray cast iron is optimal to guarantee the wear resistance and functional antifriction properties of the finished rings and bushings.

The proposed technology allows to obtain a sufficient thickness of the healthy part of the casting 1 to obtain a piston ring blank, using additional machining, devoid of shrinkage defects (porosity).

The first part of the problem is solved by preliminarily applying a layer of heat-insulating mixture 3 (containing ceramic particles) to the inner surface of the mold taking liquid cast iron in the form of a mixture based on quartz sand with the addition of pulverbakelite 3% and silver graphite 6%, which is subjected to further hot curing at a temperature 260-320 ° C.

The layer of heat-insulating mixture 3 with a thickness of 5.0-6.5 mm provides a predetermined crystallization rate of gray cast iron, not higher than 1 mm per second, which allows to obtain the structure of piston rings without any signs of bleaching and the prerequisites for "growing" the necessary thickness of a healthy metal without casting defects . The thickness of the heat-insulating layer 3 less than 5 mm leads to the appearance of “bleached” the metal base of the casting, and exceeding the upper limit value above 6.5 mm leads to a decrease in the rate of crystallization and the formation of defects of shrinkage origin (shells, pores, friability, etc.).

The second task, which allowed us to solve the proposed method, in addition to a given crystallization rate, is the creation of directed crystallization conditions. To solve this problem, after pouring it into the cast iron mold, a heat-insulating layer 6 was introduced into the mold 2 in the form of a thermoset mixture or a mixture of quartz sand and silver graphite. In this case, the outer surface of the rotating mold was intensively cooled with water or a sprayed water-air mixture.

The allowance set on the inside of the casting (oil), equal to 6-8 mm, served to “nourish” the healthy part of the casting (as a profit).

As a result of the implementation of the actions according to this example, a blank (oil) of the cylinder liner was obtained.

In the manufacture of the piston ring, the resulting oil is divided into cuts by a predetermined number of piston rings.

Claims (4)

1. A method of producing blanks of piston rings and cylinder liners of diesel engines by centrifugal casting, comprising pouring a portion of molten iron into a rotating mold and its crystallization under the action of centrifugal forces, characterized in that prior to casting, a layer is preliminarily applied to the mold inner surface receiving molten iron heat insulating mixture with a thickness of 5.0-6.5 mm and having the following composition, wt.%:
Silver graphite 5-7 Pulverbakelite 2.5-4 Quartz sand rest,
then conduct hot curing of the obtained layer at a temperature of 260-320 ° C. 2. The method according to claim 1, characterized in that the casting of cast iron and crystallization of the preform is carried out at a mold rotation speed of 600-800 rpm while maintaining the preform crystallization rate of not more than 1 mm / sec. 3. The method according to claim 1, characterized in that cast iron is used to produce billets using gray cast iron alloyed with nickel and chromium to obtain a microstructure in the casting containing finely distributed uniformly distributed graphite. 4. The method according to claim 1, characterized in that to create conditions of directional crystallization on the inner surface of the molten iron after pouring it into the mold, a heat-insulating layer is applied in the form of a thermosetting mixture or a mixture of quartz sand and silver graphite, while the outer surface of the rotating mold is intensively cooled water or sprayed water-air mixture.

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