KR910000560B1 - Method of manufacturing a cylinder liner - Google Patents

Abstract

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Description

Manufacturing method of cylinder liner

The present invention relates to a method for producing a cylinder liner for an internal combustion engine, which comprises processing an inner piston engagement surface of a cylinder liner made of mild steel to have abrasion resistance to an associated piston and piston ring.

Pistons in many internal combustion engines reciprocate in a cylinder formed of a cylindrical dry liner that is typically pressurized, retracted or inserted into the engine block. The inner surface (or " inner diameter ") of the cylinder liner is in contact with the associated piston and therefore prone to wear and scuffing. In addition, dry liners can be freted relative to the associated engine block, so that a satisfactory dry cylinder liner is abrasion resistant to such wear and at the same time can be easily pushed in or slipped into the associated engine block and in the associated engine block. It must be able to be disassembled.

One material commonly used in such liners is low carbon mild steel, but this material does not have satisfactory wear resistance. For this reason, various techniques have been used to improve wear resistance. One such technique is to use materials that are harder than mild steel and more wear resistant. Cast iron or steel, for example high in nickel, chromium and molybdenum content, can be used especially when hardening or tampering. However, although they have great abrasion resistance, their ductility is much lower than that of mild steel, and they have a disadvantage in that it is difficult to machine the required finished shape. In addition, cylinder liners completed using such materials may be brittle and may break when the liner is pressed into the cylinder block.

A second technique is to provide a hard surface layer on a cylinder liner formed of mild steel or cast iron. One such layer is a hard chrome plated layer at the inner diameter of the liner. However, since chromium plating is an uneconomical method, the cost of the liner is high, and such plating does not easily hold oil, so it is susceptible to scuffing during operation. In addition, since chromium plating can be softened at a temperature above 300 ° C., the wear resistance of chromium plating is reduced, which requires an additional finishing process. Therefore, separate hard surface treatments are additionally costly corresponding to the application.

According to the present invention, there is provided a method for producing a mild steel cylinder liner for an internal combustion engine, comprising processing the inner piston engagement surface of a cylinder liner made of at least mild steel to have wear resistance with respect to the associated piston and piston ring, the method comprising: a cylinder The liner is molded from mild steel to the final shape, and then the molded cylinder liner is placed in an air free chamber and 25:75 to 75:25 (volume%) at a temperature of 500 to 650 ° C. to carburize the cylinder liner. It is characterized by supplying a gas mixture of carburized gas and nitrogen-containing gas in the ratio.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

Example 1

Dry cylinder liners are made of low carbon steel. For example, the material may have the following composition.

Nickel, chromium, molybdenum: May exist as trace elements (difficult to express quantitatively) or as fairly low alloying element additives.

Rest: iron

A billet of this material is first punched, drawn or extruded through a suitably shaped die to produce a cylindrical blank. This blank is then machined into the final shape by machining the end flanges as necessary and forming the cylindrical inner and outer surfaces with the required dimensions.

The molded cylinder liner is then placed in an air free chamber. Then, at a temperature of 500 to 650 ° C, a noble gas such as ammonia is fed to the chamber. The ratio of these two gases, that is, the ratio of nitrogen-containing gas to carburizing gas, shows that the ratio of 50:50 (% by volume) or 60:40 (% by volume) is improved even when tested with ammonia and pyrogenic hydrocarbon gas Although given, it can be 25:75 (% by volume) -75: 25 (% by volume). These gases come into contact with the inner and outer surfaces of the cylinder liner, from which carbon and nitrogen diffuse from these surfaces into the mild steel of the liner, which forms a thin layer (so-called "epsilon") of 25-20 μm thickness, the diffusion being From the layer to the fuselage of the liner. For a particular material, the total depth of penetration depends on the time the gas is supplied, which may be adjusted to provide, for example, a 10 μm thick “epsilon” layer and a total penetration length of 0.1-0.3 mm. For example, the time may be 2-4 hours. Surface hardness above 800 HV can be achieved by gradual and non-uniform reduction in the hardness of the base material. This hardness is maintained as the liner is continuously exposed to operating temperatures up to 550 ° C.

The cylinder liner is then removed from the chamber and ready for immediate use without any further processing steps. The cylinder liner has a hard wear resistant outer surface and a flexible core. In addition, this treatment significantly increases the fatigue strength of the liner.

This can be particularly important if the flange is provided on the liner and protrudes significantly out of the liner, because the large fatigue strength increases the fatigue strength of the flange, thereby reducing the risk of the flange breaking and cracking in the flange zone. Because.

Example 2

Dry cylinder liners were prepared in extensions having a carbon content of 0.18% by any of the methods described in connection with Example 1. The molded liner was then carburized and placed in an air free chamber as described in connection with Example 1. The temperature was 57 ° C. and the treatment time was 3 hours.

After treatment, the liner was rapidly gas cooled and then moved out of the chamber and examined and the inner and outer surfaces of the liner had the same carburizing layer. A 0.04 mm thick white surface of the "ipsilon" layer overlaps the composite structure of iron nitride, which is a needle-like structure in ferrite crystals, up to 0.2 mm in depth of 0.3 mm in total measurement depth. In the volume structure, the hardness decreased from 540 HV just below the surface layer to 380 HV at a depth of 0.15 mm. The core hardness of the material was 160/178 HV at 0.35 mm below the surface.

The cylinder liner treated as above was then used in a turbo-charged diesel engine. After 300 hours of operation, wear on the liner surface was negligible. Oil consumption could be satisfied as 0.5% of fuel consumption and power was about 1% greater than the untreated cylinder liner due to the low friction liner surface with a glassy appearance after operation. After 550 hours, the oil consumption slowly increased to 0.7% of fuel consumption due to the piston ring installation, but still satisfactory. Power increased by 1.3% without increasing fuel supply.

The above-described manufacturing method and the cylinder liner manufactured as described above have many important advantages. Since the liner is made of soft mild steel and all the machining is carried out before carburizing, nitriding of the cylinder liner can be achieved easily and quickly. Since moderate mild steel and cast iron are inexpensive, the cost of the cylinder liner is reduced. The carburizing step gives the cylinder liner a high wear resistant surface, which is still effective at elevated temperatures (up to 550 ° C.) and penetrates the surface to significant depths (00.1 to 0.3 mm).

The liner can be pressed into the engine block without the risk of brittle fracture because the liner is held in a soft core. The outer surface is wear resistant against fretting with the engine block. The inner piston insertion surface is abrasion resistant against wear and scuffing of the associated piston and piston ring since this insertion surface is adequately wetted by the oil film. It is also particularly advantageous if the piston ring is carburized, for example as described in British Patent Publication No. 2112025. The hard surface of the piston ring tended to wear the cylinder liner in the absence of the corresponding hard surface of the liner. It has been found that when the liner is a wet liner, the outer surface has good wear resistance against cavitation erosion.

In addition, the cylinder liner prepared as described above has increased oxidation resistance to oxidation of the atmosphere, thus reducing packaging and transportation costs.

Claims (8)

A method of manufacturing a mild steel cylinder liner for an internal combustion engine, comprising: processing an inner piston engagement surface of a cylinder liner made of at least mild steel to have abrasion resistance to an associated piston and piston ring, wherein the cylinder liner is molded from mild steel into a final shape, The molded cylinder liner is placed in an air-free chamber and a gas mixture of carburized gas and nitrogen gas at a ratio of 25:75 to 75:25 (volume%) at a temperature of 500-600 ° C. to carburize the cylinder liner. Method for producing a cylinder liner, characterized in that the supply to the chamber. The method of claim 1, wherein the nitrogen-containing gas is ammonia and the carburized gas is a pyrogenic hydrocarbon gas. The method of claim 1, wherein the ratio of gas is 50: 50-60: 40 (volume%). The method of manufacturing a cylinder liner according to claim 1, wherein the temperature is 550 ° C. 2. The cylinder according to claim 1, wherein the cylinder liner is treated for a period of time during which the total penetration depth of the carburizing layer is 0.1-0.3 mm and the thickness of the epsilon surface layer is 0.005-0.020 mm into the surface of the cylinder liner. Method for producing liner. The method of claim 5 wherein the treatment time is 2-4 hours. The method according to any one of claims 1 to 6, characterized in that a cylindrical cylindrical blank of mild steel is formed before carburizing, and machined into a final cylinder liner, followed by a carbonization of the final cylinder liner. Method for producing a cylinder liner. 8. The method of claim 7, wherein the cylindrical cylinder blank is molded by extrusion, press or dip drawing.