JP2006097875A - Treatment method of sliding surface of cylinder unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method of the sliding surface of a cylinder unit that can block up easily and certainly a channel crack on a plating layer without relying on buff polishing. <P>SOLUTION: A shot of a grain size of 40 to 200 μm is injected at an injection speed of 100 to 300 m/sec to the surface of a body 20 of a piston rod 4, which blocks up the channel crack by generating a big plastic flow to a plating layer. In this case, the shot of an upper limit size of 200 μm or nearly the same size to this is injected at a comparatively low speed (less than 200 m/sec) for improving strength mainly to a predetermined range B including an annular groove 11 for a rod stopper. It is desirable to inject the shot of a lower limit size of 40 μm or nearly the same size to it at a comparatively high speed (more than 200 m/sec) for forming a micro dimple having an oil membrane formation function to a sliding range A to a rod guide and an oil seal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for treating a sliding surface used in a cylinder device such as a hydraulic shock absorber or a hydraulic cylinder.

  For example, as shown in FIG. 6, a twin tube type shock absorber (cylinder device) includes an inner cylinder 2 in which a piston 1 is slidably housed in a bottomed outer cylinder 3, and one end connected to the piston 1. The other end of the piston rod 4 is slidably inserted through the rod guide 5 and the oil seal 6 that are fitted in the open ends of the inner cylinder 2 and the outer cylinder 3 and extended to the outside. The oil liquid sealed inside is caused to flow through a piston valve 7 provided on the piston 1 and a base valve 8 provided on the inner bottom portion of the outer cylinder 3 to generate a damping force for an extension stroke and a contraction stroke. The oil liquid entered and withdrawn is compensated by a reservoir 9 filled with gas and oil liquid between the inner cylinder 2 and the outer cylinder 3, and the extended end of the piston rod 4 is a rod fixed in the middle thereof. The stopper 10 is connected to the rod guide 5 It has a structure for restricting by abutment.

  The oil seal 6 has a structure in which a metal core 6b is integrally formed with a rubber seal 6a as shown in FIG. Further, recently, the rod stopper 10 is caulked and fixed to the annular groove 11 formed in the piston rod 4 by metal flow bonding (plastic flow bonding) as shown in FIG. The rebound rebound cushion 12 is joined. The bottom of the outer cylinder 3 has an eye 13 that serves as a mounting part on the axle side, the tip of the piston rod 4 has a bolt part 13 that serves as a mounting part on the vehicle body side, and an intermediate part of the outer cylinder 3. Spring receivers 14 are provided for receiving coil springs.

  By the way, the above-described piston rod 4 is usually subjected to hard chrome plating for the purpose of improving wear resistance, but the plating layer has many cracks reaching the metal base, so-called channel cracks, As it is, a decrease in corrosion resistance cannot be avoided. In general, therefore, a countermeasure has been taken in which buffing is performed after the hard chromium plating to cause plastic flow on the surface of the plating layer to block the channel cracks. However, according to the countermeasures for blocking channel cracks by buffing in this way, it is difficult to sufficiently cause plastic flow on the surface of the plating layer, so that channel cracks cannot be completely blocked. The time required for polishing is inevitably reduced in productivity.

Note that shot peening is well known as a surface treatment method for the purpose of improving wear resistance and fatigue resistance of mechanical parts. Particularly, fine shots having a particle diameter of 40 to 200 μm are performed at a high speed of 100 m / sec or more. It has been reported that the surface modification effect is large when spraying with a gas (see, for example, Patent Document 2).
JP 2004-3558 A JP 62-278224 A

  The inventor pays attention to the shot peening in which the above-mentioned fine shot is jetted at high speed, and applies this to the surface treatment of the piston rod of the cylinder device to which the hard chrome plating is applied, thereby removing the channel cracks existing in the plating layer. It was confirmed that it could be blocked.

  The present invention has been made based on the above-described knowledge, and the problem is that the sliding surface treatment of the cylinder device can easily and reliably close the channel cracks existing in the plating layer without relying on buffing. It is to provide a method.

  In order to solve the above-mentioned problem, the invention according to claim 1 injects shots having a particle diameter of 40 to 200 μm at an injection speed of 100 to 300 m / sec onto the surface of a piston rod of a cylinder device to which hard chrome plating is applied. It is characterized by that. In the sliding method of the sliding surface of the cylinder device performed in this way, a large plastic flow occurs on the surface of the plating layer by high-speed jetting of fine shots, and channel cracks are closed. In the present invention, the reason why the particle size of the shot is in the above range is that if it is too small, the energy causing the plastic flow is insufficient, and conversely if it is too large, the surface roughness is deteriorated. The reason why the injection speed is in the above range is that if it is too small, the energy causing the plastic flow is insufficient, and on the other hand, it is industrially difficult to obtain an injection speed exceeding 300 m / sec.

  As described above, according to the sliding surface treatment (shot peening) in which fine shots are jetted at high speed, the surface layer is reformed into a fine structure having high strength and high toughness, so that the strength is improved. On the other hand, as described above, piston rods for hydraulic shock absorbers are provided with an annular groove for a rod stopper that is caulked and fixed by metal flow bonding in the middle of the longitudinal direction as described above. Decreasing strength due to down. The invention according to claim 2 is intended for a piston rod for a cylinder device having such an annular groove. In this case, the surface layer inside the annular groove has a high strength by high-speed injection of fine shots. The microstructure is improved toughness, and the strength reduction due to the size reduction due to the formation of the annular groove is compensated. In addition, since compressive residual stress is generated in the surface layer portion, the fatigue strength of the annular groove portion is also improved.

  Also, for improving the strength including the fatigue strength described above, the larger the particle size is selected as a shot within the particle size range of the present invention, and the effect is greater as it is injected at a lower speed. . On the other hand, in shot peening in which fine shots are jetted at high speed, when a shot having a smaller particle diameter is selected and jetted at a higher speed, fine dimples (microdimples) are formed on the surface of the piston rod. . This micro dimple has an oil film holding function. Therefore, when this sliding surface treatment method is applied to the piston rod of the cylinder device, the piston rod slides smoothly with respect to the rod guide and the oil seal. Thus, the stick-slip phenomenon is eliminated, and as a result, the damping force characteristic is improved.

  The inventions according to claims 3 and 4 have been made in consideration of the above-described improvement in strength and elimination of the stick-slip phenomenon, and the invention according to claim 3 is the invention according to claim 2 in the rod stopper. For a predetermined range including an annular groove, a shot having an upper limit of the particle size range or a particle size close thereto is injected at an injection speed of less than 200 m / sec, and the sliding range with respect to the rod guide and the oil seal is A shot having a particle size lower limit or a particle size close to this is jetted at a jetting speed of 200 m / sec or more. According to a fourth aspect of the present invention, in the second aspect of the invention, after the lower limit of the particle size range or a shot having a particle size close thereto is injected at a low injection speed of 200 m / sec or more over the entire piston rod. A shot having a particle size close to or close to the upper limit of the particle size range is jetted at a jet velocity of less than 200 m / sec with respect to a predetermined range including an annular groove for a rod stopper.

  The invention according to claim 5 is characterized in that shot peening similar to that of claim 1 is applied to a mold for forming an oil seal constituting the cylinder device.

  According to the first aspect of the present invention, channel cracks are reliably closed by high-speed injection of fine shots, which greatly contributes to improvement of corrosion resistance.

  Further, according to the invention of claim 2, when the piston rod for a hydraulic shock absorber having an annular groove for a rod stopper that is caulked and fixed by metal flow bonding in the middle in the longitudinal direction, the annular groove is used. Strength reduction due to size reduction of the portion is compensated, and strength guarantee is sufficient.

  Furthermore, according to the invention according to claim 3 or claim 4, in addition to further improving the strength of the annular groove portion, the formation of micro dimples having an oil film holding function also eliminates the stick-slip phenomenon, and the cylinder device It will greatly contribute to performance improvement.

  Further, according to the invention of claim 5, fine dimples (micro dimples) can be formed on the sliding surface of the oil seal (sliding surface of the cylinder device). Further, the oil film is held, the piston rod slides more smoothly, the stick-slip phenomenon is eliminated, and as a result, more appropriate damping force characteristics can be obtained.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
The piston rod to be used in this embodiment is the piston rod 4 used in the shock absorber as the cylinder device shown in FIG. 6, and as shown in FIG. A small-diameter piston mounting portion 21 for mounting the piston 1 is provided continuously. An annular groove 11 (FIG. 8) for caulking and fixing the rod stopper 10 by metal flow bonding is provided in a portion of the main body 20 close to the piston mounting portion 21. The main body portion 20 of the piston rod 4 has a space between a portion P1 slightly spaced away from the piston mounting portion 21 rather than the annular groove 11 and a continuous portion P2 of the bolt portion 14 serving as a mounting portion to the vehicle body. A sliding range A with respect to the rod guide 5 and the oil seal 6 is provided. In the present embodiment, the main body portion 20 of the piston rod 4 is divided into the sliding range A and the range excluding the sliding range A (predetermined range including the annular groove 11) B. Thus, shot peening (sliding surface processing) is performed under different shot conditions described later.

  After machining, the piston rod 4 is subjected to surface hardening treatment (for example, induction hardening) on the main body 20, processing of the annular groove 11 (for example, rolling), hard chromium plating on the main body 20, and dimension adjustment. It is manufactured through each process of buffing, and finally the shot peening according to the present invention is applied to the main body 20 (sliding surface treatment).

  In this embodiment, the shot peening for the main body portion 20 of the piston rod 4 is performed in the predetermined range B including the annular groove 11 for the rod stopper 10 and the sliding range A for the rod guide 5 and the oil seal 6 as described above. Select different shot conditions. Specifically, for the predetermined range B including the annular groove 11, a shot having a particle size of 200 μm, which is the upper limit of the particle size range of the present invention, or a particle size close thereto, is made at a relatively low speed of 100 to 200 m / sec. On the other hand, for the sliding range A, a shot having a particle size of 40 μm, which is the lower limit of the particle size range, or a particle size close thereto is jetted at a relatively high speed of 200 to 300 m / sec. The material of the shot used here is arbitrary as long as it has a hardness equal to or harder than the quenching hardness of the surface portion of the piston rod 4, and is not only quenched steel but also alumina, silicon carbide, titanium nitride, etc. High hardness ceramic materials can be used.

  By performing shot peening on the main body portion 20 of the piston rod 4 as described above, a large plastic flow occurs on the surface of the plating layer formed on the main body portion 20, and channel cracks existing in the plating layer are reliably closed. FIG. 2 shows the surface state of the main body after shot peening, and a surface state without cracks is obtained. Therefore, the piston rod 4 subjected to the sliding surface treatment is remarkably excellent in corrosion resistance. Incidentally, as shown in Fig. 2, a large number of channel cracks (white parts) are seen in the plated layer after the hard chrome plating, and these channel cracks can be surely blocked only by buffing for dimensional adjustment. I can't let you.

  Further, by performing the shot peening described above, the surface layer portion inside the annular groove 11 has high strength in the predetermined range B in which a shot having a relatively large particle size (200 μm or a particle size close thereto) is injected at a relatively low speed. It is modified to a fine structure rich in toughness. As a result, the formation of the annular groove 11 compensates for the strength reduction due to the size reduction, and therefore the piston rod 4 has sufficient strength assurance. In addition, since this shot peening causes compressive residual stress in the surface layer portion inside the annular groove 11, the fatigue strength is improved and the durability of the piston rod 4 is sufficient.

  On the other hand, a large number of microdimples D are formed in the sliding range A in which a shot having a relatively small particle size (40 μm or a particle size close thereto) is jetted at a relatively high speed, as shown in FIG. Since the micro dimple D has an oil film holding function, when the piston rod 4 is incorporated in an actual hydraulic shock absorber (FIG. 6), unstable movement of the piston rod 4, that is, the so-called stick-slip phenomenon is eliminated. The That is, the piston rod 4 slides smoothly with respect to the rod guide 5 and the oil seal 6, and as a result, the damping force characteristic as a hydraulic shock absorber is improved. When the surface is finished only by buffing, a large number of fine grooves (streaks) E that are continuous to some extent are formed as shown in FIG. 5, and in this case, oil flows along the streaks E by capillary action. Therefore, the oil retention function cannot be expected so much.

  Here, in the above embodiment, the shot condition is changed between the sliding range A with respect to the rod guide 5 and the oil seal 6 and the predetermined range B including the annular groove 11. After a shot with a relatively small particle diameter is sprayed at a relatively high speed on the entire body 20, a shot with a relatively large particle diameter is relatively slow with respect to a predetermined range B including the annular groove 11 for the rod stopper 10. You may make it inject by. Even when shot peening is performed in this manner, channel cracks existing in the plating layer are surely closed, and the micro dimple D is formed in the sliding range A, while the annular groove 11 is included. The strength of the predetermined range B is increased, and the same effect as in the above embodiment can be obtained.

  Further, in the present invention, a shot having a particle diameter of 40 to 200 μm is applied to the entire surface of the main body 20 of the piston rod 4 without changing the shot condition between the sliding range A and the predetermined range B including the annular groove 11. In this case, the channel cracks present in the plating layer can be reliably blocked. Of course, even in this case, the strength of the entire body 20 including the annular groove 11 for the rod stopper 10 is increased, so that the strength guarantee is sufficient. Moreover, since micro dimples are formed depending on conditions, it is possible to take measures against stick slip.

  Further, the oil seal 6 is usually formed by a mold, but shot peening similar to that in the sliding range A is performed in advance on the inner side of the mold (side on which the oil seal is stored). In this case, since the micro dimple D shown in FIG. 4 is similarly formed on the sliding surface of the oil seal 6, the sliding range A of the piston rod 4 on which the micro dimple D is formed In addition, the stick-slip phenomenon is eliminated, and as a result, more appropriate damping force characteristics can be obtained.

  In the above embodiment, the piston rod for a twin tube type shock absorber is targeted. However, the present invention may be applied to a piston rod or an oil seal for a monotube type (absorbing type) shock absorber. Of course. Since the carbon pressure shock absorber has a high internal pressure, there is a problem that the oil seal is easily deformed and a stick-slip phenomenon is likely to occur, so this sliding surface treatment method is particularly useful. In addition to the shock absorber, the present invention may be directed to piston rods and oil seals for strut type hydraulic shock absorbers and piston rods and oil seals for hydraulic cylinders.

It is a front view which shows the shape of the piston rod for shock absorbers (cylinder apparatus) which is the object of the sliding surface processing method which concerns on this invention, and the implementation range of a sliding surface processing. It is a photograph which shows the structure | tissue state of the plating layer of the piston rod which implemented this sliding surface processing method. It is a photograph which shows the state of the channel crack which exists in the plating layer after hard chrome plating. It is a perspective view which shows typically the surface state of the piston rod which implemented this sliding surface processing method. It is a perspective view which shows typically the surface state of the piston rod which implemented the conventional buffing. It is sectional drawing which shows the whole structure of the shock absorber incorporating the piston rod in the cylinder apparatus which is the object of this invention. It is sectional drawing which shows the upper structure of the shock absorber shown in FIG. It is sectional drawing which shows the assembly structure of the piston and rod stopper of the shock absorber shown in FIG.

Explanation of symbols

1 Piston 4 Piston rod 5 Rod guide 6 Oil seal 10 Rod stopper 11 Annular groove 20 Piston rod body

Claims (5)

  A method for treating a sliding surface of a cylinder device, characterized in that a shot having a particle size of 40 to 200 μm is sprayed at a spray speed of 100 to 300 m / sec onto a surface of a piston rod to which hard chrome plating is applied.   2. The cylinder device slide according to claim 1, wherein the piston rod is used for a cylinder device, and has an annular groove for a rod stopper that is caulked and fixed by metal flow bonding in the middle of the longitudinal direction of the piston rod. Moving surface processing method.   For a predetermined range including an annular groove for a rod stopper, a shot having a particle size at or near the upper limit of the particle size range is injected at an injection speed of less than 200 m / sec. On the other hand, a method for treating a sliding surface of a cylinder device according to claim 2, wherein a shot having a particle diameter close to or lower than the particle diameter range is injected at an injection speed of 200 m / sec or more.   After injecting a shot having a particle size close to or close to the lower limit of the particle size range to the entire piston rod at an injection speed of 200 m / sec or more, the particle size is determined for a predetermined range including an annular groove for a rod stopper. 3. The method of treating a sliding surface of a cylinder device according to claim 2, wherein a shot having a particle diameter close to or at the upper limit of the range is injected at an injection speed of less than 200 m / sec. Cylinder device sliding, characterized in that an oil seal is formed by injecting a shot having a particle diameter of 40 to 200 μm onto a mold for forming an oil seal of the cylinder device at an injection speed of 100 to 300 m / sec. Surface treatment method.

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