KR20090126391A - Manufacturing method of cam for low-speed marine engines - Google Patents

Abstract

PURPOSE: A method for manufacturing a cam for a low speed engine of a large vessel is provided to reduce manufacturing time and to improve mechanical property of the cam by processing a heat-treatment using heavy carbon alloy steel. CONSTITUTION: An inducing coil(30) is installed near a profile contact surface of a cam(10). The base / medium frequency alternating current of 3~10 kHz is applied for the inducing coil and for the coil to heat to 900~1100°C. The heat-treated cam is cooled with a water or oil cooling mode to 230~250°C and is tempered. The cam has the predetermined and irregular profile contact surface. The cam is made of Cr-Mo alloy steel, Ni-Cr-Mo alloy steel and alloy steel.

Description

Manufacturing Method of Cam for Low-speed Marine Engines

BACKGROUND OF THE INVENTION Field of the Invention The present invention generally relates to a method of manufacturing a heat treatment of a cam such as a fuel cam and an exhaust cam for a large vessel low speed engine, and more particularly, a medium carbon alloy steel for surface hardening to increase the base material strength of the cam and to increase wear resistance. By performing the heat treatment process by low / medium frequency induction heating on the surface of the cam machined by using and performing the rapid cooling process, the space requirements of the manufacturing equipment are reduced and the manufacturing time is greatly shortened, and at the same time the mechanical properties of the cam base material It relates to a new cam manufacturing method that can improve the productivity and improved productivity.

Currently, the surface heat treatment of fuel cams and exhaust cams for large ships and low speed engines is made of low carbon alloy steel (less than 0.2% carbon) having low carbon content as carburizing process is applied.

In general, large ship low speed engine cams should have excellent durability such as mechanical properties, abrasion resistance and fatigue resistance as a main driving part of the engine along with the crankshaft. In addition, the low-speed engine cam has a relatively large shape, so when the carburizing process is applied, the productivity of the low speed engine is accompanied by a decrease in productivity, such as spatial constraints and long carburizing time, which leads to an increase in manufacturing cost. .

Carburization is one of the surface hardening methods used to harden only the surface of a material to improve the wear resistance and fatigue resistance of parts. The low carbon steel or low carbon alloy steel containing less than 0.2% carbon is charged into the carburizing furnace and heated to the austenite range. Then, it is a surface hardening method that invades and diffuses carbon on the surface. The formed carburized layer has a residual compressive stress to improve the fatigue resistance of the material, and the wear resistance property according to the high surface hardness is improved, thereby increasing the durability of the material even under a high load environment.

As shown in FIG. 2, the low / medium frequency heat treatment is performed by passing a current of 3 to 10 kHz frequency band through the surface of a heated object (heater) by using the principle of induction heating (generally about It is a surface hardening method that forms a martensite structure on the surface layer by rapid heating and rapid cooling to about 900 ~ 1100 ℃). The use of a low / medium frequency band has the advantage of being able to sufficiently obtain the desired depth of the cured layer and suppressing the formation of superheated structure due to the increase of the curing time. In addition, the induction hardened layer part exhibits equivalent characteristics in application of a product having a simple shape even under fatigue resistance and high load environment compared to the carburized layer.

In general, the high frequency heat treatment method may not form a sufficient depth of the hardened layer and may cause a defect of components due to the formation of a superheated structure when it is heated for a long time with an excessive heat source.

In the case of European auto parts makers, the production system is changing from the conventional heat treatment method to high frequency heat treatment in order to solve the two goals of high quality mass production and cost reduction.

The conventional heat treatment method for a fuel cam and an exhaust cam for a large ship low speed engine is a general carburizing method (surface hardening by infiltrating and diffusing carbon), as shown in FIG. 1 attached to the present specification, carburizing → diffusion → water cooling. Or oil cooling → low temperature tempering. Existing cams are made of low carbon alloy steel (Cr-Ni alloy steel, Ni-Cr alloy steel, Ni-Cr-Mo alloy steel) and are composed of the chemical composition shown in Table 1. The conventional cam manufacturing method of heat-treating the cam of the low carbon alloy steel material as a carburizing process has the following problems.

1) Large ship low speed engine cam is large and needs carburizing equipment of large scale by heat treatment.

2) It takes a long heat treatment time, for example 4 hours or more is required to obtain a carburized layer of about 1mm.

3) The carburizing process must remove the oxide on the surface before heat treatment, masking the parts that are not carburized with copper for the purpose of bulletproofing, and unmasking the carburizing part.

4) Even if the ballistic treatment is performed, the surface hardness of the front part is accompanied by the carburization, which is accompanied by a problem that the production time is increased in the machining process, which is a treatment process after the carburization process.

5) Loss of raw materials occurs as the inner diameter of the cam is cut and manufactured before the carburizing process.

6) As a result, productivity declines and manufacturing costs are inevitable.

7) Furthermore, as the carbon potential increases, reticulated cementite may form at the grain boundaries.

As described above, the conventional cam manufacturing method is cumbersome, resulting in a decrease in productivity due to the space constraint of the carburizing heat treatment equipment and the long heat treatment time.

Table 1 below shows the chemical composition of the conventional low carbon alloy steel.

Referring to Table 1, the conventional low carbon alloy steel has a low carbon content, so that the mechanical properties of the base metal are relatively low, and in order to improve abrasion resistance, an increase in heat treatment time due to carbon intrusion and diffusion is inevitable. Equipment and space were also needed.

Therefore, in the manufacturing method using induction heating to increase the wear resistance and fatigue resistance of the cam surface for a large ship low speed engine, the carburizing process is also performed for problems such as improvement of mechanical properties of the material, wear on the cam, torsional moment, damage by fatigue, etc. There is still a need for new cam fabrication techniques that not only have comparable properties, but are not space constrained and can improve productivity by reducing heat treatment time.

The present invention has been invented to improve the problems present in the manufacturing method of the cam, such as the fuel cam or exhaust cam for the conventional large vessel low speed engine described above, and to provide a variety of additional advantages, to increase the base material strength of the cam and increase the wear resistance By performing the heat treatment process by low / medium frequency induction heating on the surface of the cam machined using medium carbon alloy steel for the surface hardening and performing the rapid cooling process, the space requirement of the manufacturing equipment is reduced and the manufacturing time is greatly shortened. It is an object of the present invention to provide a new cam manufacturing method which can improve the mechanical properties of the cam and improve productivity.

This object is achieved by a cam manufacturing method provided according to the present invention.

Cam manufacturing method according to an aspect of the present invention, a method of manufacturing a cam cam processed in the form having a predetermined irregular profile contact surface as a fuel cam or exhaust cam of a low speed engine for large ships, the cam has a carbon content of 0.4 It is made of medium-carbon Cr-Mo alloy steel and Ni-Cr-Mo alloy steel with% ~ 0.6%, and low / medium frequency band of 3 ~ 10 kHz in induction coil installed adjacent to the profile contact surface of the cam without additional carburizing process. A heat treatment step of applying a current and heating to 900 to 1100 ° C .; After the heat treatment and cooled in a water or oil-cooled manner comprises a post-treatment step of finishing by low temperature tampering at a temperature of 230 ~ 250 ℃.

In the preferred embodiment, the induction coil is a coolant flow portion consisting of an empty space inside, a coolant injection portion for injecting a coolant for water cooling or oil cooling from the outside of the coolant flow portion, and the induction from the coolant flow portion And a cooling liquid discharge part for discharging the cooling liquid between the coil and the side of the cam, wherein the cooling of the cooling liquid by the water cooling or the oil cooling method after the heat treatment in the post-processing step comprises: a cooling liquid injection part and a cooling liquid flow part formed in the induction coil; It is made by supplying the said coolant through a coolant discharge part.

In another preferred embodiment, the induction coil used in the heat treatment step is formed as a single winding coil formed to be integrally or separately coupled in a form corresponding to a predetermined irregular profile contact surface of the cam or the single winding coil shape is It consists of several adjacent multi-coil coils along the cam's profile contact surface.

In another preferred embodiment, the induction coil used in the heat treatment step is arranged in the form of a ring adjacent to the predetermined irregular profile contact surface of the cam, and a cooling ring is disposed in parallel with the induction coil, and the heat treatment is performed by the induction coil. The cam moves or the induction coil and the cooling ring move so that the cooling ring is close to the side position of the cam.

Cam manufacturing method according to the present invention, in the production of cams such as fuel cams or exhaust cams for large marine low-speed engines, to improve the base material strength of the cam and to increase the wear resistance and fatigue resistance for hardening the carbon alloy steel By performing a heat treatment process by low / medium frequency induction heating on the surface of the processed cam and performing a rapid cooling process, the manufacturing time can be greatly reduced and the mechanical properties of the cam can be improved to improve productivity. Provide effect.

Hereinafter, with reference to the accompanying drawings illustrating the present invention with a specific example as follows.

1 is a schematic process chart comparing a cam manufacturing method according to the prior art and a cam manufacturing method according to an embodiment of the present invention, and FIG. 2 is a low / medium frequency heat treatment method of a cam manufacturing method according to embodiments of the present invention. A schematic diagram illustrating the principle. 3 is a view showing an example of the shape of the fuel cam and the exhaust cam for a large ship low speed engine that can be heat-treated by a cam manufacturing method according to another embodiment of the present invention, Figure 4 is according to an embodiment of the present invention It is a schematic diagram for demonstrating the low / medium frequency heat treatment method of the cam manufacturing method. 5 is an exemplary view for explaining the shape of the induction coil that can be used in the cam manufacturing method according to various embodiments of the present invention. 6 is an exemplary diagram of an induction coil and a cooling ring that can be used in a cam manufacturing method according to another embodiment of the present invention.

The present invention is a new cam manufacturing method for changing the material and heat treatment by the low / medium frequency heat treatment of the low carbon alloy steel in the method of carburizing heat treatment of low carbon alloy steel in order to solve the problem of the heat treatment method of the conventional large vessel low speed engine cam To provide.

The cam manufacturing method according to an aspect of the present invention is a method for manufacturing a cam (10, 20) by processing the cam (10, 20) processed in the form having a predetermined irregular profile contact surface as a fuel cam or exhaust cam of a large speed low-speed engine for ships. In general, the cam of the low speed engine of a large ship can be divided into a fuel cam 10 and an exhaust cam 20, as shown in FIG. As shown in the drawing, the fuel cam 10 and the exhaust cam 20 have a hollow in which a shaft is penetrated and fixed by hot shrinkage in the center thereof, and has a shape of a concave and convex, unique and irregular profile contact surface around the core.

In the present invention, the cams 10 and 20 use those manufactured using medium carbon alloy steel. The medium-carbon alloy steel is specifically processed into a medium-carbon Cr-Mo alloy steel and a Ni-Cr-Mo alloy steel having a carbon content of 0.4% to 0.6%. Examples of component configurations of preferred medium carbon alloy steels that can be used in the present invention are illustrated in Table 2 below.

According to the present invention, there is provided a cam manufacturing method for curing the surface using induction heating in the low / medium frequency range without a separate carburizing process.

In the low / medium frequency induction heating, induction coils 30, 40, and 50 are provided adjacent to profile contact surfaces of the cams 10 and 20, and low / medium frequencies of 3 to 10 kHz are provided in the installed induction coils 30, 40 and 50. It is composed of a heat treatment step of heating to 900 ~ 1100 ℃ by applying a medium frequency alternating current. At this time, the induction coils 30, 40, 50 are adjusted to be positioned at a distance at which sufficient hardened layer 12 can be formed in the cam 10, as shown in FIG. 4. In the present invention, such heat treatment is characterized in that it is rapidly performed within a few minutes.

After the heat treatment, cooling is also rapidly performed. The water is cooled by water cooling with oil as a coolant or oil cooling with oil as a coolant. This is followed by a low temperature tampering in a conventional manner, for example for the purpose of improving toughness, at a temperature of about 200 to 260 ° C., preferably at a temperature of about 230 to 250 ° C. Can proceed. In the method for manufacturing a large vessel low speed engine cam according to the present invention, the heat treatment and cooling process may be performed within about 5 minutes as illustrated in FIG. 1.

In a preferred embodiment, as shown in Figure 4, the induction coils 30, 40 is a coolant flow section 34, the interior of the empty space, the cooling liquid for cooling or oil cooling to the coolant flow section 34 Coolant injecting part 32 for injecting water from the outside, and a coolant ejecting part for ejecting the coolant from the coolant flow part 34 between the induction coils 30 and 40 and the sides of the cams 10 and 20. 36 is provided. The structure of the induction coil is induction after heat treatment without having to move the induction coil 30 for heat treatment, as can be seen in FIG. 4 (b) which is a cross section taken along the line aa of FIG. This enables a rapid cooling process through the coil 30 itself. That is, the process of cooling by water or oil cooling after heat treatment is performed by supplying the coolant through the coolant injection unit 32, the coolant flow unit 34, and the coolant discharge unit 36 formed in the induction coils 30 and 40. Can be done.

In the present invention, the induction coil 30 used in the heat treatment step corresponds to a predetermined irregular profile contact surface of the cams 10 and 20 to be processed, as shown in FIGS. 4 and 5 (b). It can be made as a single winding coil formed to be integrally or separately coupled to the furnace. In the case of the separate type, for example, a configuration capable of being separated by a-a line of FIG. 4 is possible. In some cases, an induction coil 40 may be used to form a plurality of adjacent multi-coil coils along the profile contact surfaces of the cams 10 and 20. In general, in the case of a cam for a low speed engine of a large ship, as the size of the engine increases, the shape and dimensions of the cam also increase. In this case, as shown in (a) of FIG. 5, both of the induction coil 30 and the induction coil 40 having the form of a single winding having a larger dimension than the cam can be used within the range in which the manufacturing is possible.

In another preferred embodiment, the induction coil 50 used in the heat treatment step is arranged in the form of a ring adjacent the predetermined irregular profile contact surfaces of the cams 10, 20 and parallel to the cooling ring 60. It may be in the form of being disposed. In this case, the cams 10 and 20 move or the induction coil 50 so that the cooling ring 60 approaches the side positions of the cams 10 and 20 heat-treated by the induction coil 50. And the cooling ring 60 may move.

As described above, the present invention can have the following effects by using a low / medium frequency heat treatment operation and a medium carbon alloy steel on a cam for a large vessel low speed engine, thereby satisfying the required characteristics of a fuel vessel and an exhaust cam for a large vessel low speed engine. You can.

1) Sufficient hardened layer can be obtained according to the frequency band. The lower the frequency, the higher the hardened layer depth. As a result, the product can be heat-treated at high speed in low / medium frequency heat treatment, and it can be quenched by controlling only the surface profile contact portion and rapidly controlling the depth of hardening. The low / medium frequency heat treatment can obtain a deeper hardened layer than the high frequency heat treatment.

Note that if the curing depth is too deep, high tensile stress is formed in the surface layer, which may cause cracks. This is due to the formation of tensile residual stress due to shrinkage and expansion of the material if quenching proceeds too rapidly during the transformation of austenite to martensite. As such, in order to suppress the occurrence of the defect, related work variables such as frequency, time, output, power density, and coil pattern should be selected accurately.

2) Good thermal efficiency by direct heating, extremely low oxidation by short time heating, local heat treatment is possible and less defects when quenched than other methods.

3) In addition, the heating element can be completely separated and cut off from the heating source, so non-contact heating is possible, and only the profile part where contact with the roller is generated can be selectively hardened.

4) Low / medium frequency heat treatment has the characteristics of rapid heating and surface heating by induction heating, so that micro grain size and high compressive residual stress are formed near the surface, which can cause damage and abrasion resistance due to the toughness, fatigue resistance, and torsional moment of various mechanical parts. It plays a significant role in the improvement of the mechanical properties better than any heat treatment.

5) Using the medium-carbon alloy steel with important properties as shown in Table 3 below as raw materials reduces the incidence of raw material defects, under-surface and surface defects that may occur in the low / medium frequency heat treatment process, which is a post process. The failure rate according to the medium frequency heat treatment can be minimized.

6) By applying the piercing process of the forging process to the inner diameter that is not applied in the existing carburizing process, it prevents material loss, shortens the processing time by not applying bulletproof and carburizing heat treatment, improves productivity by simplifying the process, and thus reduces manufacturing costs. It is possible.

7) Compared to general heat treatment, the equipment is relatively expensive and consumes a lot of power. However, the rapid heating, short time heating, and rapid cooling by the hole of the coil are possible, so that the rising temperature time and the total heating time are very short. Compared with carburizing heat treatment, the overall process is simpler and more efficient, so the total production cost can be lowered by less than half compared with carburizing process.

8) In addition, the low / medium frequency heat treatment process is easier to automate than the carburizing heat treatment.

As described above, the cam manufacturing method according to the present invention relates to a low / medium frequency heat treatment method of a cam made of a medium carbon alloy steel, which is capable of improving the mechanical properties of a fuel cam and an exhaust cam for a large vessel low speed engine. .

Table 4 below is a table comparing hardness change, heat treatment time, and cost of medium-carbon alloy steel in case of carburizing heat treatment and low / medium frequency heat treatment. Referring to Table 4, the mechanical properties and hardness of the base metal are shown to be superior to the carburizing process, and it can be seen that the initial cost is an economical method due to the significant reduction effect in terms of high cost and heat treatment time.

Although the present invention has been described through specific embodiments, various modifications are possible to those skilled in the art by referring to and combining various features described herein. Therefore, it should be pointed out that the scope of the present invention should not be limited to the described embodiments, but should be interpreted by the appended claims.

As described above, the present invention can be widely used in the field of cam manufacturing that performs heat treatment to improve mechanical properties, wear resistance and fatigue resistance of a cam base material which can be used as a fuel cam or exhaust cam for a low speed engine of a large ship. .

1 is a schematic process diagram comparing a cam manufacturing method according to the prior art and a cam manufacturing method according to an embodiment of the present invention.

Figure 2 is a schematic diagram for explaining the principle of low / medium frequency heat treatment of the cam manufacturing method according to embodiments of the present invention.

3 is a view showing an example of the shape of the fuel cam and the exhaust cam for a large ship low speed engine that can be heat-treated by a cam manufacturing method according to an embodiment of the present invention.

Figure 4 is a schematic diagram for explaining a low / medium frequency heat treatment method of the cam manufacturing method according to an embodiment of the present invention.

5 is an exemplary view for explaining the shape of the induction coil that can be used in the cam manufacturing method according to various embodiments of the present invention.

Figure 6 is an illustration of the induction coil and cooling ring that can be used in the cam manufacturing method according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10, 20: cam 30, 40, 50: induction coil

32: coolant injection part 34: coolant flow part

36: coolant discharge part 60: cooling ring

Claims (4)

As a fuel cam or exhaust cam of a large vessel low speed engine, a method is manufactured by heat treating cams 10 and 20 processed to have a predetermined irregular profile contact surface. The cams 10 and 20 are machined from a medium carbon Cr-Mo alloy steel and a Ni-Cr-Mo alloy steel having a carbon content of 0.4% to 0.6%. Heat treatment step of applying a low / medium frequency alternating current of 3 to 10 kHz to the induction coils 30, 40, and 50 installed adjacent to the profile contact surfaces of the cams 10 and 20 without a separate carburizing process, and heating them to 900 to 1100 ° C. Wow; After the heat treatment is cooled by water or oil cooling method after finishing step of low-temperature tampering to a temperature of 230 ~ 250 ℃ A cam manufacturing method for a large ship low speed engine, characterized by including. The method according to claim 1, The induction coils 30 and 40 may include a coolant flow part 34 having an empty space therein, a coolant injection part 32 for injecting a coolant for water cooling or oil cooling to the coolant flow part 34 from the outside, And a coolant discharge part 36 for discharging the coolant between the induction coils 30 and 40 and the sides of the cams 10 and 20 from the coolant flow part 34. In the post-treatment step, the process of cooling by the water-cooling or oil-cooling method is performed by the coolant injection unit 32, the coolant flow unit 34, and the coolant discharge unit 36 formed in the induction coils 30, 40, and 50. Method for producing a large ship, low speed engine cam, characterized in that made by supplying the coolant through. The induction coil (30, 40) used in the heat treatment step is made of a single winding coil formed to be integrally or separately coupled in a form corresponding to a predetermined irregular profile contact surface of the cam (10, 20). A method for manufacturing a large-sized low speed engine cam, characterized in that the single winding coil form is made of multiple coils adjacent to each other along the profile contact surfaces of the cams (10, 20). The method according to claim 1, wherein the induction coil 50 used in the heat treatment step is arranged in the form of a ring adjacent to the predetermined irregular profile contact surface of the cam (10, 20) and the cooling ring 60 is disposed in parallel therewith The cams 10 and 20 are moved or the induction coils 30, such that the cooling ring 60 approaches the side positions of the cams 10 and 20 heat-treated by the induction coil 50. 40, 50) and the cooling ring (60) is characterized in that, large vessel low speed engine cam manufacturing method.

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