JP2006152981A - Spray piston ring and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems in a conventional spray piston ring wherein (1) the surface roughness of a spray film is worse though it can perform spraying without taking an inlaid spraying method (Figs. 4 to 6, not shown) and (2) since a chamfered part cannot be polished by a thermet spray film, it must rely on the inlaid spraying method. <P>SOLUTION: In this spray piston ring, the chamfered part 4 of 0.05 mm or longer in radial depth and 0.3 mm or shorter in axial width is formed at least at the axial one end of the outer peripheral surface of the piston ring 1. The thermet spray film formed on the outer peripheral surface is formed mainly of particles with grain sizes of 10 μm or smaller, and its thickness is 0.03 to 0.2 mm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a piston ring having a thermal spray coating on an outer peripheral sliding surface and a manufacturing method thereof in a piston ring for an internal combustion engine.

Piston rings used in diesel engines and leaded gasoline engines have a thermal spray coating with excellent wear resistance and seizure resistance. The thermal spray coating can be imparted with various properties by spraying a composite or mixture of metal such as Mo, Ni, Cr and hard ceramic particles such as Cr ₃ C ₂ and TiC. is there.

  The names of the piston ring parts used in the following description are shown in FIG. 1 (without chamfered parts) and FIG. 2 (with chamfered parts).

Today, a high-speed flame spraying method (hereinafter referred to as HVOF method or HVAF method) is often used to form a sprayed coating on a piston ring because of the adhesion of the sprayed coating.
The particle diameter of the thermal spraying powder used for the HVOF thermal spraying method is generally 15 to 45 μm, and the surface coating roughness of the thermal spraying coating formed using this thermal spraying material powder is about Rmax of about 50 μm. When the thermal spray coating composition is cermet or ceramics, the hard particles in the coating wear the liner which is the counterpart material. Therefore, the coating with such roughness cannot be used as it is. After finishing to a certain degree of roughness, lapping polishing with abrasive grains is performed to finish the surface roughness to at least 1 Rz.

In order to improve productivity in the outer peripheral surface treatment of the piston ring, the piston ring is usually stacked in a cylindrical shape as shown in FIG. 3, and then the outer peripheral surface is subjected to surface treatment.
However, in the process of forming the “film” on the outer peripheral surface of the piston ring by “plating”, “ion plating”, “thermal spraying”, etc. among the outer surface treatments, when the thickness of the film to be formed increases, so-called “crossover” Occurs and the rings cannot be individually disassembled. Naturally, the outer peripheral edge of the piston ring is chamfered to prevent “crossover”, but there is a limit to this, and “crossover” always occurs when the construction film thickness increases.

4-6 illustrate the inlaid spraying method commonly used in the manufacture of sprayed piston rings. That is, in the inlaid spraying method, a plurality of piston rings are stacked and fixed from both side surfaces in a cylindrical shape with the joint of the piston ring having a groove-like recess formed on the outer peripheral surface of the piston ring in a closed state. When a sprayed layer is formed on the outer peripheral surface of the piston ring that is stacked and cylindrical, the piston ring is in close contact with the side surface, so that a “crossover” occurs completely in the formation of the sprayed coating, resulting in an integral cylindrical body. When this cylindrical outer peripheral surface is polished with a grindstone until the base material of the piston ring outer peripheral edge comes out (peripheral cylindrical polishing), the sprayed film remains only in the groove portion of the piston ring outer peripheral surface, so that the piston rings can be individually disassembled. become.
The disassembled piston ring is then subjected to various processes such as BF polishing for processing the outer peripheral surface with a grindstone into a barrel face (BF) shape and outer peripheral BF lapping with abrasive grains. Many of the thermal spray piston rings are manufactured by a method called this inlaid thermal spraying method.

  In this inlaid spraying method, it is necessary to polish about 100 μm from the surface in order to eliminate the runout and the roughness of Rmax of about 50 μm when the outer peripheral cylinder of the piston ring stacked in a cylindrical shape is polished. Further, the outer peripheral BF polishing for processing the outer peripheral surface into a barrel face shape requires a machining allowance of about 50 μm, and the machining allowance for the outer peripheral lapping by the abrasive grains is also required to be about 20 μm. Therefore, the applied sprayed film thickness becomes “appropriate film thickness from coating performance” + about 170 μm. After spraying the spray coating thickly in this way, the outer periphery sprayed surface is polished and the piston ring is individually disassembled by exposing the base material of the outer peripheral edge in the axial direction of the piston ring outer periphery. It was expensive compared to other surface treatment rings such as “plating” because of the large amount of materials used and the great man-hours for polishing.

  As a means for forming a thermal spray coating on the entire outer peripheral sliding surface of the piston ring, an outer diameter larger than the outer diameter of the piston ring between the piston rings as in Patent Document 1, Japanese Patent Application Laid-Open No. 11-37292 (manufacturing method of the thermal spray piston ring). In order to stack the piston rings and thin metal plates alternately to form a cylindrical body, the joints of the individual piston rings must be connected to the nominal diameter of the piston ring in advance. There is a problem that it must be closed and fixed, resulting in a deterioration in productivity and high cost.

  In order to solve this problem, Patent Document 2, Japanese Patent Application Laid-Open No. 55-134166, “Method for Manufacturing Thermal Spray Piston Ring” is a piston in which a chamfering process of 0.1 to 0.3 C is performed on at least one edge of the outer peripheral surface of the piston ring. The rings are stacked in a cylindrical shape so that the chamfering directions are the same direction, and spraying is performed by inclining the spray gun at an angle so that the spray particles do not adhere to one of the chamfered portions. In this way, sprayed coating can be formed without causing thermal spraying between the piston ring and the piston ring that have been stacked, and it is possible to reduce the number of sprayed materials and polishing man-hours, etc. It can be lowered significantly.

The size of the chamfered portion of the piston ring, particularly the radial size (depth) of the piston ring, is related to the thermal sprayability, and a step greater than the sprayed coating is required between the ends of the outer peripheral surface of the piston ring facing each other. . Therefore, when the sprayed film thickness is thick, a step greater than the sprayed film thickness is required. On the other hand, if only the depth of the edge part of the piston ring is increased, the tapered surface of the chamfered part of the piston ring Thermal spray coating does not adhere. From the viewpoint of peeling of the thermal spray coating, it is preferable that the thermal spray coating partially covers the chamfered portion. Therefore, a chamfering angle θ (relative to the side surface of the piston ring) of 30 ° to 60 ° is appropriate. However, when the chamfering depth is 0.2 mm, the chamfering width in the piston ring axial direction is large and is about 0.35 mm. Therefore, the width of the outer peripheral sliding surface of the piston ring is reduced accordingly, and a piston ring with a thin axial width has a high possibility of causing problems such as the analysis loss of the piston ring.
JP-A-11-37292 JP 55-134166

However, it has been found that there are the following problems when manufacturing by the thermal spraying method of Patent Document 2.
The surface roughness of the piston ring chamfered portion is rough when the sprayed surface remains as it is. Therefore, when the outer peripheral sliding surface is subjected to grinding wheel lapping or lapping polishing, the unevenness of the ridgeline that becomes the boundary portion becomes severe. As a result, it has been found that when the piston ring is inserted into the cylinder or during use, the sprayed particles are likely to fall off or the sprayed film is broken, and the mating material is worn. In addition, when the chamfered portion is polished to solve the above problems, when a hard coating such as a cermet coating is used as the sprayed coating, chipping (coating chipping) occurs during polishing of the coating.

  As described above, since the surface roughness of the sprayed coating is poor in the conventional sprayed piston ring, it could not be used as a piston ring even if sprayed without using the inlaid spraying method. Further, polishing the chamfered portion cannot be performed with a cermet sprayed coating or the like, and eventually, an inlaid spraying method has to be relied upon.

  The present invention was made paying attention to such problems, and the first invention is that at least one outer peripheral edge in the axial direction of the outer peripheral surface of the piston ring main body is axially oriented at a radial depth of 0.05 mm or more. A chamfered portion having a width of 0.3 mm or less is formed, and a thermally sprayed piston ring having a cermet sprayed coating formed on the outer peripheral surface, the sprayed coating being mainly composed of a cermet powder having a powder particle diameter of approximately 10 μm or less. The piston ring is characterized in that the sprayed film thickness is 0.03 to 0.20 mm, and the second invention is that the angle (θ) between the chamfered portion and the piston ring side surface is 30 ° to 60 °. The third and fourth inventions are characterized in that the thermal spray coating is a cermet coating having a hard phase of a carbide such as tungsten carbide or chromium carbide, and the fifth invention. Is the Pis of claims 1-4 A chamfering with a radial depth of 0.05 mm or more and an axial width of 0.3 mm or less is formed on at least one end (3) in the axial direction of the outer peripheral surface of the piston ring body (1). A first step of forming a cermet sprayed coating whose main component is a particle having a particle diameter of 10 μm or less on the entire outer peripheral surface with a thickness not more than the radial depth of the chamfered portion, the thermal spraying 5. The method for manufacturing a piston ring according to claim 1, further comprising a third step of lapping polishing the outer peripheral surface of the coating.

Compared to the inlaid spraying method in which grooves are formed on the outer periphery of the piston ring and sprayed, the present invention eliminates the need for a step of polishing the cylindrical body outer diameter for separating the piston ring, and the grinding allowance after spraying is rough. It is only necessary to remove the thickness, and the number of grinding processes can be greatly reduced. In addition, since the coating thickness during spraying can be reduced and the amount of sprayed material used can be reduced, a low thermal spray coating with excellent wear resistance and seizure resistance is formed on the entire piston ring outer periphery sliding surface. It is possible to manufacture a thermal spray piston ring.

Effect in the present invention is about 10μm or less in the thermal spraying powder (for granulated powder secondary particle) is characterized by using a fine powder particles.
The surface roughness of the thermal spray coating greatly depends on the particle size of the thermal spray powder, and if the thermal spray coating is formed by using fine powder as the thermal spray raw material powder, the surface roughness of the thermal spray coating can be reduced. That is, the particle size of the thermal spray powder currently used in the HVOF method and the HVAF method is about 10 μm to 50 μm, and the thermal spray surface roughness is Rmax 50 μm or more. However, if a sprayed powder having a particle diameter of 10 μm or less is used as in the present invention, the sprayed surface roughness can be reduced to Rmax 10 μm or less. This means that the surface roughness of the thermal spray coating on the piston ring chamfered portion also becomes finer, and the unevenness of the ridgeline that becomes the boundary between the polished outer peripheral surface and the chamfered portion is reduced, and the coating is applied when the piston ring is inserted into the cylinder. It is possible to reduce the catch of the film and to eliminate the chip of the film. Further, chipping of the film during sliding can be prevented.

  Further, in the piston ring of the present invention, if the chamfering angle θ is small, a problem occurs that the sprayed film does not adhere to the chamfered portion, and if the chamfering angle θ is large, the axial width of the chamfering becomes large. There arises a problem that the width per sliding surface becomes small. Therefore, a chamfer angle of 30 ° to 60 ° with respect to the side surface of the piston ring is preferable.

  Within the above angle range, at least one end in the vertical direction of the outer peripheral surface of the piston ring body is chamfered at a radial depth of 0.05 mm or more and an axial width of 0.3 mm or less and 30 ° to 60 ° with respect to the piston ring side surface. 4 is formed (see FIG. 7). When the depth in the radial direction of the chamfered portion is less than this, thermal spraying occurs. Since the surface roughness of the finely sprayed coating of the present invention is about Rmax of about 10 μm, polishing of 10 μm or more is necessary to make this roughness 1 Rz or less. Further, in order for the sprayed film 3 (FIG. 8) to exhibit its sliding performance, a film thickness of at least 30 μm is necessary. Considering the variation in the sprayed film thickness and the variation in the polishing allowance due to the processing, the sprayed film thickness is as large as possible. 50 μm is required, and therefore the depth in the radial direction of the chamfered portion of the piston ring is required to be 0.05 mm or more in order to prevent spraying. Moreover, the depth in the radial direction of the chamfered portion is equal to or greater than the thickness of the construction sprayed film.

  The axial chamfer width is related to the sliding contact width of the piston ring. If the contact width is too small, the piston ring of the present invention is not preferable in terms of function since it is used as a pressure piston ring. Therefore, the present invention is limited to 0.3 mm or less.

  In the present invention, the spraying is performed by rotating the piston ring, reciprocating the spray gun 5 away from the outer peripheral surface of the piston ring at a predetermined speed in parallel with the piston ring axis, and spraying the outer peripheral surface of the piston ring with a predetermined film thickness. Repeat until a film is formed. The direction of thermal spraying may be a direction perpendicular to the piston ring axis or inclined as shown in FIG.

  The thermal spray coating of the cermet formed on the outer peripheral surface of the piston ring according to the present invention is preferably that according to claims 2 and 3. This thermal spray coating is a fine powder thermal spray coating mainly composed of powder having a powder particle diameter of 10 μm or less. When the surface roughness of the thermal spray coating is reduced, polishing with a grindstone can be omitted, and lapping using direct abrasive grains can be performed. The effect which can be prevented is also born and the productivity of the thermal spraying process can be greatly improved. Of course, the amount of sprayed material used can also be greatly reduced. Furthermore, the cermet coating with a hard phase such as WC or CrC as the hard phase is prone to chipping in the grinding stone polishing process, but the thermal spray coating of the present invention can eliminate the grinding with the grinding stone. Can be avoided. Hereinafter, it explains in full detail based on an Example.

Example 1
A martensitic stainless steel piston with a chamfered chamfer with a diameter of 0.15 mm, a width of 0.2 mm, and an angle (θ) of 53 ° on one axial side of a piston ring with an outer diameter of 122 mm and a height of 3 mm. 50 rings were overlapped and fixed from both sides using fastening plates having an outer diameter of 121.5 mm and a thickness of 10 mm to form a cylindrical body having a diameter of about 122 mm and a length of 170 mm. Next, in order to improve the adhesion between the base material and the sprayed layer, the usual grit blasting with alumina # 60 was performed to roughen the outer peripheral surface of the cylindrical body.

After that, HVOF thermal spraying was performed on finely granulated and sintered cermet powder of Cr-C / 25NiCr with a particle diameter of 10 μm or less, which is excellent in wear resistance and seizure resistance (FIG. 9). As the thermal spray gun 5, a θ gun (manufactured by Witco) was used, and a thermal spray layer was formed so as to be inclined by about 30 ° from the vertical direction of the outer peripheral surface of the piston ring and to be perpendicular to the chamfered surface. A sprayed film with a film thickness of 0.07 mm and a surface roughness of 11.2 Rmax was obtained.

After spraying, the piston rings could be disassembled individually by removing the clamp plates on both sides of the piston ring. Thereafter, lapping polishing using carborundum abrasive grains # 2000 was performed, and a piston ring having a product film thickness of about 0.05 mm and a surface sprayed film roughness of 0.35 Rz could be obtained. The surface roughness of the thermal spray coating on the chamfered part is about 12.0Rmax, and there are few irregularities on the outer peripheral sliding surface and ridge line, and processing is performed without causing coating flaking even when inserted into a lapping polishing cylinder. Was made.

Comparative Example 1
When the same thermal spraying and machining were performed on the same piston ring as in Example 1 except that the chamfering angle (θ) was changed to 8 °, the thermal spraying particles that did not adhere to the chamfered portion accumulated at the bottom of the groove, resulting in “crossover”.

Comparative Example 2
When the same thermal spraying and machining was performed on the same piston ring as in Example 1 except that the radial depth was changed to 0.03 mm, the axial width was 0.03 mm, and the chamfering angle was 45 °, the thermal spray particles that did not adhere to the chamfered portion were found to be the bottom of the groove. And “crossover” occurred.

    A chamfered portion with a radial depth of 0.05 mm or more and an axial width of 0.3 mm or less is formed on at least one axial end portion of the outer peripheral surface of the piston ring body so that the chamfered portions are in the same direction. By stacking cylindrically and spraying a coating with a particle diameter of 10 μm or less on the outer peripheral surface and having a thickness of 0.03 to 0.2 mm, the cylindrical body is not integrated into each piston ring. It becomes possible to separate. In addition, since the surface roughness of the thermal spray coating on the chamfered portion is fine, the piston ring has a thermal spray coating with excellent wear resistance and seizure resistance, which can prevent chipping during sliding when the piston ring is inserted into the cylinder. Can be manufactured.

It is a figure explaining the name of each part of a piston ring without a chamfer. It is a figure explaining the name of each part of a piston ring with a chamfer. It is an external view of the cylindrical body which piled up the some piston ring. FIG. 6 is a cross-sectional view of a piston ring in which a groove is formed on the outer peripheral surface of the piston ring by a conventional method as a cylindrical body. It is sectional drawing when a thermal spraying is applied to the cylindrical body of FIG. It is sectional drawing when the external shape of the cylindrical body of FIG. 6 is ground. It is sectional drawing when chamfering is given to the outer peripheral end of a piston ring by this invention, and it piles up to make a cylindrical body. It is sectional drawing when spraying is applied to the cylindrical body of FIG. It is a schematic diagram for demonstrating the condition of the thermal spraying in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piston ring 2 ... Cylindrical body 3 ... Thermal spray coating 4 ... Chamfering 5 ... Thermal spray gun

Claims (5)

A sprayed piston ring with a chamfered portion with a radial depth of 0.05 mm or more and an axial width of 0.3 mm or less formed on the outer peripheral surface of at least one axial end of the outer peripheral surface of the piston ring body. A piston ring, wherein the cermet sprayed coating is mainly composed of particles having a particle diameter of 10 μm or less and has a thickness of 0.03 to 0.2 mm. 2. The piston ring according to claim 1, wherein an angle (θ) of the chamfered portion with a side surface of the piston ring is 30 ° to 60 °. 3. The piston ring according to claim 1, wherein the cermet sprayed coating is mainly composed of tungsten carbide and cobalt or tungsten carbide and a cobalt-chromium alloy. 3. The piston ring according to claim 1, wherein the cermet sprayed coating is mainly composed of chromium carbide and a nickel-chromium alloy or chromium carbide and a cobalt-chromium alloy. The first step of forming a chamfered portion with a radial depth of 0.05 mm or more and an axial width of 0.3 mm or less at at least one end (3) in the axial direction of the piston ring body (1) outer peripheral surface, the entire outer peripheral surface A second step of forming a cermet sprayed coating mainly composed of particles having a particle diameter of 10 μm or less at a thickness not more than the depth in the chamfered portion radial direction, and lapping polishing the outer peripheral surface of the sprayed coating. The method for manufacturing a piston ring according to any one of claims 1 to 4, comprising three steps.

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