KR101071632B1 - Surface treating method of engine valve - Google Patents

Abstract

The present invention relates to a surface treatment method of an engine valve, to provide a surface treatment method of an engine valve to maintain the bending strength of the coater groove while applying a soft nitriding method when the surface treatment of the engine valve with the coater groove is formed.

The present invention provides a method for treating a surface of an engine valve having at least one coater groove, the method comprising: cutting an entire length of a shaft portion such that a molded engine valve has a predetermined length (S110); After the length-cutting, the axis of the process of grinding (roughing) the shaft outer diameter of the engine valve with a grinder (S120); After finishing the shaft, the shaft finishing process of finishing and positioning the shaft portion of the engine valve between a pair of grinding wheels rotating at high speed at 1500 ~ 1750rpm (S130); After the shaft finishing, the nitriding process of forming a nitride layer through a chemical reaction by immersing the engine valve in a soft nitriding solution in the range of 550 ~ 590 ℃ 30 ~ 45 minutes (S140); After the soft nitriding process, the shaft end portion formed with the cotter groove of the engine valve is subjected to a high frequency heat treatment for 1.5 to 3 seconds in the range of 950 ~ 1050 ℃ and the shaft end heat treatment process for air cooling at room temperature (S150); After the shaft end heat treatment process, the shaft end tempering process for performing a medium frequency heat treatment for 1.5 to 3 seconds in the shaft end portion formed with the coater groove 180 ~ 250 ℃ (S160); After the shaft end tempering process, the coater groove grinding process for removing foreign matter and protrusions formed in the coater groove by grinding by the grinding wheel (S170); After grinding the cotter groove, the process of removing the harmful layer generated from the nitriding through the shaft buffing is carried out from the shaft of the engine valve shaft (S180); After the shaft buffing, the valve surface polishing process for polishing the valve surface formed in the head portion of the engine valve with a grindstone (S190); After polishing the valve surface, washing the engine valve to remove foreign matters (S200); characterized in that it comprises a.

Engine valve, coater groove, surface treatment, soft nitriding method, high frequency heat treatment

Description

Surface Treatment Method of Engine Valve {SURFACE TREATING METHOD OF ENGINE VALVE}

The present invention relates to a method for surface treatment of an engine valve, and more particularly, for an engine valve having at least one coater groove, the shaft portion is surface-treated by Tufftride-Nitride, but the shaft end on which the coater groove is formed is It relates to a surface treatment method of the engine valve to improve the bending strength through a separate surface treatment method.

In general, the shaft portion of the engine valve is formed with a coater groove in the circumferential direction at one end thereof, and the retainer is coupled to the coater groove with a coater, and the head portion of the engine valve is in close contact with the intake and exhaust holes of the cylinder head. A spring is provided between the cylinder head of the engine valve and the coater and the retainer to return the engine valve, which is vertically moved by the rotation of the cam shaft, to its original position.

In addition, the coater is divided into a single coater (Multi Cotter) and a multi coater (Multi Cotter) according to the type of the engine valve.

The single coater is an integrally assembled engine valve and coater, and rotates in the winding direction when the spring is repeatedly moved up and down, and the multi-coater is separated from the engine valve and the coater so that it can rotate freely without being influenced by the retainer and the spring. It is composed.

In the assembly configuration of the engine valve as described above, the vertical movement occurs in the form of pressing or pulling the engine valve at an angle when the camshaft is driven, the stress in the vertical direction and the left and right directions to the cotter groove lowers the strength of the coater groove or If vulnerable, damage could occur. On the other hand, if the surface hardness of the coater groove side is too high, the elastic force is lowered, causing damage.

In other words, the surface treatment work to improve the strength is essential to the shaft portion of the engine valve, but the surface treatment work on the shaft portion and the cotter groove side had to be performed respectively.

In general, two methods of surface treatment for wear of the engine valve shaft are mainly applied by hard chromium (Cr) plating and surface nitriding (soft nitriding).

Although chromium plating has excellent wear resistance, lubricity, heat resistance, corrosion resistance, etc., chromium produced from natural minerals is depleted and has a high scarcity value, resulting in a high price, and various harmful components. There was a problem.

In other words, chromium plating is processed while heating an aqueous solution of hexavalent chromium to trivalent chromium, but there is a problem in that a small amount of hexavalent chromium is contained in the vapor in the process of heating and accumulates in the human body in the process of breathing, It also acted as a cause of osteoporosis and various diseases. In addition, chromium has also contributed to environmental problems that pollute the surrounding soil.

On the other hand, surface nitriding (soft nitriding method) is obtained by a chemical reaction with the main components of K ₂ CO ₃ and KCNO, has the advantage of easy price fluctuation, infinite production.

In addition, surface nitriding (soft nitriding) is accompanied by the generation of highly toxic KCN, but is not accumulated in the human body and is known to be harmful to the human body even after prolonged contact.

In the Tufftride-Nitride, the nitride layer is composed of martensite and austenite.

1 is an enlarged cross-sectional view of a martensitic and austenitic nitride layer formed through a soft nitriding method.

FIG. 1A is an enlarged photograph of a cross section of a nitride layer made of martensite, and the diffusion layer 21 is formed to a predetermined thickness on the surface of the base material 20, and the nitrogen compound layer 22 and the outside of the diffusion layer 21 are formed. The white layer 23 is formed.

1 (b) is an enlarged photograph of a cross section of an austenitic nitride layer, which is formed of a predetermined white layer 26, a compound layer 27, and a surface oxide layer 28 on the surface of the base material 25.

However, the martensitic and austenitic back layers 23 and 26 are very hard and fragile, and there is a problem that breakage is impossible in the heat treatment process.

As shown in FIG. 2, in the conventional method for treating an engine valve having a coater groove, as shown in FIG. 2, the hard hard chromium plating section L is hardly plated at the shaft portion of the engine valve and the coater groove section ( S) is a method of improving the wear of the coater groove section (S) by performing a high frequency heat treatment without plating.

However, as described above, chromium plating has various problems such as scarcity, high price, and harmful components.

On the other hand, the surface treatment by soft nitriding method has many advantages over chromium plating. However, if the stresses in the up, down, left and right directions are concentrated in the cotter groove during the engine driving process, the soft nitride layer is partially part of the brittleness of the nitride layer The hard part remaining at the tip provides a breakage of damage, which eventually leads to a breakdown of the engine valve and leads to an unusable state.

In addition, even if the high-frequency heat treatment method is applied to the cotter groove after the soft nitriding method is applied to the engine valve shaft portion, the martensitic and austenitic back layers 23 and 26 are not easily destroyed during the heat treatment process. Due to the constitutive characteristics of the coater groove, the reaction state is nonuniform, which makes it more difficult to destroy the nitride layer and leaves a hard (weak) brittle part.

Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art, and provides a method for treating the surface of the engine valve to maintain the bending strength of the coater groove while applying a soft nitriding method during the surface treatment of the engine valve. There is a purpose.

As a technical means for achieving the above object, the present invention provides a surface treatment method of an engine valve having at least one coater groove, the process comprising: cutting the entire length of the shaft portion so that the molded engine valve has a certain length; An axis rolling process of grinding (roughing) the shaft outer diameter of the engine valve with a grinder after the full length cutting; An axis finishing process of finishing and positioning the shaft portion of the engine valve between a pair of grinding wheels rotating at a high speed at 1500 to 1750 rpm after the shaft is rolled; After the shaft finishing, the nitriding process of immersing the engine valve in a soft nitriding solution in the range of 550 ~ 590 ℃ 30 to 45 minutes to form a nitride layer through a chemical reaction; After the soft nitriding process, the shaft end heat treatment process for the high frequency heat treatment for 1.5 ~ 3 seconds in the range of 950 ~ 1050 ℃ the shaft end formed with the coater groove of the engine valve and air cooled at room temperature; After the shaft end heat treatment process, the shaft end tempering process of the intermediate frequency heat treatment for 1.5 to 3 seconds in the range of 180 ~ 250 ℃ shaft end portion formed with the coater groove; A cotter groove grinding process of removing foreign substances and protrusions formed in the cotter groove by grinding by a grinding wheel after the shaft end tempering process; After the cotter groove grinding, removing the harmful layer generated from nitriding through the shaft buffing performed by the shaft of the engine valve from the grindstone; A valve surface polishing process of polishing the valve surface formed on the head of the engine valve with a grindstone after the shaft buffing; After polishing the valve surface, washing the engine valve to remove the foreign matter; characterized in that it comprises a.

The preferred component ratio of the soft nitriding solution is characterized by consisting of CN ^- 4% by weight, CNO ^- 32% by weight, [CO ₃ ] ^2-19 % by weight, K ⁺ 40% by weight, Na ⁺ 5% by weight.

At this time, the nitride layer thickness of the engine valve formed through the soft nitriding process is characterized in that formed in 20 ~ 50㎛.

According to the surface treatment method of the engine valve according to the present invention, by applying a soft nitriding method in the surface treatment of the engine valve, various problems of chromium plating are solved, and the shaft end formed with the coater groove has a separate heat treatment process and nitriding on the coater groove side. Removing the layer has an effect of improving the bending strength of the coater groove side.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Figure 3 is a front view showing the external appearance of the engine valve according to an embodiment of the present invention, the engine valve 30 is composed of a head portion 31 and the shaft portion 32 as described above, the head of the head 31 The outer circumference forms a valve face 34 which is inclinedly connected to the shaft portion 32. In addition, at one end portion of the shaft portion 32 corresponding to the head portion 31, a coater groove 33 having a predetermined depth is formed around the shaft portion 32.

Figure 4 is a flow chart for the surface treatment method of the engine valve according to an embodiment of the present invention, as described above, the surface treatment of the engine valve according to the present invention, the full length cutting (S110)-> shaft support (S120)-> shaft Finish (S130)-> Soft Nitriding (S140)-> Shaft End Heat Treatment (S150)-> Shaft End Tempering (S160)-> Cotter Groove Grinding (S170)-> Shaft Buffing (S180)-> Polishing Valve Surface (S190) -> It is made, including the washing (S200) process.

Referring to the surface treatment method of the engine valve according to an embodiment of the present invention in more detail.

(1) Battlefield Cutting (S110)

The entire length of the shaft portion 32 is cut so that the engine valve 30 formed using the material of either SUH11 or STR11 has a constant length.

(2) shaft support (S120)

After cutting the entire length, primary processing is performed to grind (rough) the outer diameter of the shaft portion 32 of the engine valve 30 with a grinder.

(3) shaft mapping (S130)

After the shaft is rolled, the outer diameter of the shaft 32 is processed secondly, and a pair of grindstones composed of the main shaft and the minor shaft are rotated at a high speed at 1500 to 1750 rpm, and the shaft 32 of the engine valve 30 is positioned between the grindstones. To clean after finishing.

(4) soft nitriding (S140)

After the shaft finishing, the nitriding process is performed by immersing the engine valve 30 in a soft nitriding solution to form a nitride layer through a chemical reaction.

Component ratio of the soft nitriding solution is CN ^- 4% by weight, CNO ^- 32% by weight, [CO ₃ ] ^2- 19% by weight, K ⁺ 40% by weight, Na ⁺ 5% by weight, the engine valve 30 is The temperature of the soft nitriding solution is immersed for 30 to 45 minutes in the range of 550 ~ 590 ℃ is a soft nitriding process through a chemical reaction. Preferably, the nitride layer thickness of the engine valve 30 through the soft nitriding process is characterized in that made of 20 ~ 50㎛.

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(5) Shaft end heat treatment (S150)

After the soft nitriding process, the engine valve 30 is subjected to a high frequency heat treatment for 1.5 to 3 seconds in the range of 950 to 1050 ° C. in which the cotter groove 33 is formed, followed by air cooling at room temperature.

(6) shaft end tempering (S160)

The shaft end formed with the cotter groove 33 subjected to the heat treatment (high frequency) process is a process of removing internal stress by softening the tissue through a tempering process, and performing a medium frequency heat treatment for 1.5 to 3 seconds in a range of 180 to 250 ° C. The procedure is to soften the surface hardened layer.

(7) Cotter Groove Grinding (S170)

At the shaft end where the shaft end tempering process is performed, the coater groove 33 is a separate grinding operation, and removes foreign substances and protrusions formed in the coater groove 33 from the fibrous grindstone by grinding the smooth surface. To form.

(8) Shaft Buffing (S180)

 After grinding the cotter groove, the shaft 32 of the engine valve 30 removes the harmful layer generated from nitriding through a shaft buffing process performed from a fibrous grinding wheel.

(9) Polishing the valve surface (S190)

After the end of the shaft buffing process by supplying and grinding the head 31 of the engine valve 30 to the grindstone, the valve face 34 formed on the head 31 is polished from the grindstone.

(10) cleaning (S200)

After the polishing of the valve surface is completed, the engine valve 30 is washed to remove foreign substances, thereby completing the manufacture of the engine valve 30.

As the present invention can be seen through the above embodiment, the soft nitriding process (S140) is made for the entire engine valve 30, the shaft end is a high-frequency heat treatment process (S150) and shaft end tempering (S160) process is made separately The cotter groove 33 is to remove the nitride layer through the grinding process (S170) to prevent damage to the cotter groove 33 generated during operation of the engine valve 30 after the assembly of the coater.

5 is an enlarged view of the cross section of the engine valve coater groove from which the nitriding layer is removed and the cross section of the engine valve coater groove subjected to the soft nitriding process according to the embodiment of the present invention.

5A is an enlarged cross-sectional view of the engine valve coater groove that has undergone soft nitriding, and it can be seen that the nitride layer 41 is formed in both the outer diameter of the shaft portion 32 and the coater groove 33.

5 (b) is an enlarged cross-sectional view of the engine valve coater groove in which the nitride layer is removed through the cotter groove grinding after the soft nitriding process, and the nitride layer remains in the outer diameter of the shaft part 32, but the nitride layer ( It can be seen that 41) has been removed.

6 is to test the strength of the shaft end of the engine valve formed with a cotter groove using a universal material tester, by installing a cylindrical bar 11 in the lower center of the jig 10 to the coater groove of the engine valve 30 ( 33) is installed, and both sides of the coater groove 33 is supported by the pedestal 13 from the lower side, and the pedestal 13 is installed so that the frame 14 supports the test.

7 is a graph showing the results of the test using the tester.

That is, although the breaking strength of the engine valve shaft end having the cotter groove 33 is formed in the past, 700kg or more, the surface of the engine valve shaft end formed with the coater groove 33 is subjected to the surface treatment of the engine valve according to the embodiment of the present invention. Since the breaking strength is formed at 1400kg or more, the strength of about 700kg is improved to secure a stable load.

As described above, although the technical idea of the present invention has been described with reference to the preferred embodiments, those skilled in the art will be able to vary the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. Can be modified and changed.

1 is an enlarged cross-sectional view of a martensitic and austenitic nitride layer formed by soft nitriding;

Figure 1 (a) is an enlarged photograph of the cross section of the nitride layer made of martensite system,

Figure 1 (b) is an enlarged photograph of the cross section of the nitride layer made of austenitic.

Figure 2 is an exemplary view showing a conventional engine valve surface treatment section incorporating chromium plating and high frequency heat treatment method.

Figure 3 is a front view showing the appearance of the engine valve according to an embodiment of the present invention.

Figure 4 is a flow chart for the surface treatment method of the engine valve according to an embodiment of the present invention.

FIG. 5 is an enlarged cross-sectional view of the engine valve coater groove from which the nitriding layer is removed and the cross section of the engine valve coater groove that has undergone soft nitriding in accordance with an embodiment of the present invention.

5 (a) is an enlarged cross-sectional view of the engine valve coater groove which has undergone soft nitriding.

5B is an enlarged cross-sectional view of the engine valve coater groove from which the nitride layer is removed through the cotter groove grinding after the soft nitriding process.

Figure 6 is an exemplary test of the strength of the shaft end of the engine valve formed with a coater groove using a universal testing machine.

7 is a graph showing the results of the test using the tester of FIG. 6.

<Description of Symbols for Main Parts of Drawings>

30: engine valve 31: head portion

32: shaft 33: cotter groove

34: valve surface 41: nitride layer

Claims (3)

In the surface treatment method of the engine valve formed with at least one coater groove, Cutting the entire length of the shaft portion 32 such that the molded engine valve 30 has a predetermined length (S110); After the full length cutting, the axis of the grinding step (S120) for grinding (roughing) the outer diameter of the shaft portion 32 of the engine valve 30 with a grinder; After finishing the shaft, the shaft finishing process of finishing finishing by positioning the shaft portion 32 of the engine valve 30 between a pair of grinding wheels rotating at a high speed of 1500 ~ 1750rpm (S130); After the shaft finishing, the nitriding process of immersing the engine valve 30 in a soft nitriding solution in the range of 550 ~ 590 ℃ 30 to 45 minutes to form a nitride layer through a chemical reaction (S140); After the soft nitriding process, the shaft end heat treatment process for high frequency heat treatment for 1.5 to 3 seconds in the range of 950 ~ 1050 ℃ axial end portion formed with the cotter groove 33 of the engine valve 30 and air cooled at room temperature (S150); After the shaft end heat treatment process, the shaft end tempering process for performing the medium frequency heat treatment for 1.5 to 3 seconds in the shaft end portion formed with the coater groove 33 180 ~ 250 ℃ (S160); A cotter groove grinding process of removing foreign substances and protrusions formed in the cotter groove 33 by grinding by the grinding wheel after the shaft end tempering process (S170); After the cotter groove grinding, the process of removing the harmful layer generated from the nitriding through the shaft buffing the shaft 32 of the engine valve 30 from the grindstone (S180); A valve surface polishing process of polishing the valve surface 34 formed on the head portion 31 of the engine valve 30 with a grindstone after axial buffing (S190); After polishing the valve surface, washing the engine valve 30 to remove the foreign matter (S200); Surface treatment method of the engine valve comprising a. The method of claim 1, The component ratio of the soft nitriding solution is CN ^- 4% by weight, CNO ^- 32% by weight, [CO ₃ ] ^2- 19% by weight, K ⁺ 40% by weight, Na ⁺ 5% by weight of the surface of the engine valve, characterized in that Treatment method. The method of claim 1, The nitriding layer thickness of the engine valve 30 formed through the soft nitriding process (S140) is formed of 20 ~ 50㎛ surface treatment method of the engine valve.

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