JPH1163223A - Piston rod for cylinder device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resistance-weld a bracket to the tip of a piston rod without causing any spark mark in the oxidized sliding surface of the rod. SOLUTION: A jig 10 is formed in its body 13 with a concave 12 of a radius of curvature larger than that of a convex 11a on the tip of a rod base material 11. The rod base material 11 is then uprighted on the jig 10 with the convexed tip in the concave 12. The jig 10 in this state is put in a gas soft-nitriding furnace, oil tank, washing machine and oxidizing furnace in this order for gas soft nitriding, oil cooling, washing and oxidizing processes. During the last two processes, the jig 10 and rod base material. 11 keep oil 16 used for oil cooling in the clearance gap δ held therebetween to suppress oxidation of the tip of the rod base material 11 or to thin the oxide film made on the tip, to which a bracket is resistance-welded with lower current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a gas spring,
The present invention relates to a piston rod used for a cylinder device such as a hydraulic shock absorber and a method of manufacturing the same.

[0002]

2. Description of the Related Art As shown in FIG. 4, a cylinder device of this type is usually mounted on a tip of a piston rod 2 extending from a piston (not shown) in a cylinder 1 to the outside of the cylinder 1 and a bottom of the cylinder 1. The bracket 3 (cylinder bottom side is omitted) as an application member is joined and used. Conventionally, the joining of the bracket 3 to the piston rod 2 involves the lower electrode 4 as shown in FIG.
After the piston rod 2 is clamped to fix the position thereof, the lower end bent portion 3a of the bracket 3 is pressed against the end surface of the piston rod 2 by the upper electrode 5 to apply a current, so-called resistance welding.

Conventionally, the piston rod 2 is generally made of hard chromium plating. However, recently, in order to further improve wear resistance and corrosion resistance, gas nitrocarburizing treatment and oxidation treatment have been carried out. In this case, a structure in which a nitride layer and an oxide layer are laminated on the surface by successively performing treatments has been used. However, when the bracket 3 is to be joined to the piston rod 2 having the nitrided layer and the oxide layer formed in this manner by the above-described resistance welding method, the electric current of the outermost oxide layer (Fe ₃ O ₄ layer) is increased. Since the resistance is large, a high current is required for the welding, and as a result, spark marks are often generated on the peripheral surface (sliding surface) of the piston rod 2 which comes into contact with the lower electrode 4, which has been a problem. If the piston rod with the spark trace is incorporated into the cylinder device as it is, the spark trace will damage the seal member in the cylinder 1 during use, causing gas leakage and oil leakage.

[0004]

SUMMARY OF THE INVENTION Therefore, Japanese Patent Laid-Open No.
In Japanese Patent No. 3834, as shown in FIG. 6, a flat flat plate portion 7 is integrally provided at the tip of a piston rod (rod base material) 6 in advance, and the entire rod base material 6 is subjected to a gas soft nitriding treatment. After the oxidizing process, the bracket 8 is superimposed on the flat plate portion 7 and the two are joined to the upper electrode 9a and the lower electrode 9b.
It has been proposed to sandwich between the two and perform resistance welding. According to this proposal, a spark mark caused by the oxide layer is generated in the flat plate portion 7, and the above-described damage to the seal member is prevented beforehand.

However, according to the proposal described in the above-mentioned publication, the flat plate portion 7 must be provided integrally with the tip portion of the rod base material 6 by forging or welding. However, there is a problem that the number increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to suppress the generation of spark marks by improving the weldability with a mounting member.
Accordingly, it is an object of the present invention to provide a piston rod for a cylinder device and a method for manufacturing the same, which does not require a special shape change and improves the manufacturability.

[0007]

In order to achieve the above object, a piston rod for a cylinder device according to the present invention has a nitride layer and an oxide layer laminated on the surface thereof, and the outermost oxide layer has a sliding surface. It is characterized by having a thickness exceeding 1.0 μm on the peripheral surface serving as the moving surface, and having a thickness of 0.2 to 1.0 μm on the tip end surface serving as the resistance welding surface of the mounting member. .

[0008] In the piston rod for a cylinder device configured as described above, the thickness of the oxide layer on the tip end surface, which is the resistance welding surface of the mounting member, is as thin as 1.0 µm or less. It is as small as possible and can be welded with a relatively low current, preventing the occurrence of spark marks. Further, since the thickness of the oxide layer is at least 0.2 μm on the front end surface, the corrosion resistance of the front end surface is not significantly reduced, and further, 1.0 μm on the peripheral surface serving as the sliding surface. Because of the thickness, the sliding surface maintains the desired corrosion resistance.

In the method of manufacturing a piston rod according to the present invention, a jig on which a plurality of rod base materials are erected is sequentially sent to a gas nitrocarburizing furnace, an oil bath, a washing machine, and an oxidation furnace to perform gas nitrocarburizing, oil cooling, and cleaning. And a method of manufacturing a piston rod for sequentially performing each process of oxidation and oxidation, wherein a concave surface is formed in the jig, and the rod base material is erected on the jig in a state where the rod tip is in contact with the concave surface. It is characterized by.

In the above manufacturing method, the rod base is placed on the jig in a state where the rod tip is in contact with the concave surface of the jig. Oil liquid penetrates into the gap with the tip, and a small amount of the penetrated oil liquid remains even after the subsequent cleaning treatment. As a result, oxidation of the rod tip is suppressed during the subsequent oxidation treatment, and oxidation formed at the rod tip is prevented. The thickness of the layer is smaller than the sliding surface.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

When manufacturing a piston rod, a jig 10 as shown in FIG. 2 is prepared in advance, and a plurality of rod base materials 11 which have been cut and ground as shown in FIG. Is set in an upright state, and is sequentially sent to a gas nitrocarburizing furnace, an oil bath, a washing machine, and an oxidation furnace to sequentially perform each process of gas nitrocarburizing, oil cooling, washing, and oxidation.

The jig 10 has a plurality of concave surfaces 1 on its upper surface.
2, a jig main body 13 in the form of a rectangular plate, a column 14 standing upright at four corners of the jig main body 13, and a small-diameter portion 14a at the upper end of the column 14 are inserted through the jig main portion 13 to form a jig. And a support plate 15 seated on the step 14b. The concave surface 12 on the upper surface of the jig body 13 has a slightly larger radius of curvature than the convex surface 11a at the tip of the rod base 11, as shown in FIG. When the rod base material 11 is set up in a state where the rod base material 11 is in contact with the concave surface 12 of the jig body 13, a minute gap δ gradually expanding toward the periphery of the convex surface 11 a or the concave surface 12 is formed between the two. become. Jig body 13
The concave surface 12 of the rod base 11 also has a convex surface 11a
The rod base 11 is formed in the minimum necessary depth enough to substantially accommodate the portion, and thus the rod base 11 is set on the jig main body 13 as described above.
Is completely released from the jig body 13.

At the base end of the rod base 11, a thread 11b for attaching a piston is provided.
The threaded portion 11b of the rod base 11 is fitted into a through hole 15a provided in the support plate 15 so that its position is fixed. Each support 14 has a screw portion 14 c provided at the lower end thereof and a screw hole 1 of the jig body 13.
The jig body 3 is fixed to the jig body 13 by screwing the jig body 3a.

In this embodiment, after a plurality of rod bases 11 are set on the jig 10 as described above, first, the jig 10 is charged into a gas nitrocarburizing furnace, and a gas nitrocarburizing process is performed. Do. As an example, the gas nitrocarburizing treatment is performed under the condition that a mixed gas (nitriding gas) of ammonia, nitrogen and carbon dioxide gas is sealed in a gas nitrocarburizing furnace and kept at 580 ° C. for about 2 hours. Thereby, on the surface of the rod base material 11,
A nitride layer having a thickness of about 18 to 20 μm (ε layer: Fe _2-3 N)
Is formed.

When the gas nitrocarburizing is completed, the jig 10 is immediately immersed in an oil tank provided in the gas nitrocarburizing furnace, and the rod base 11 on the jig 10 is subjected to oil cooling (rapid cooling). Thereafter, the jig 10 is taken out of the gas nitrocarburizing furnace, and the jig 10 is loaded into a cleaning machine (for example, a vacuum cleaning machine) to remove the cooling oil adhering to the surface of the rod substrate 11. Thus, during the oil cooling process, the oil liquid enters the gap δ between the concave surface 12 of the jig 10 and the convex surface 11a of the rod base material 11,
This penetrated oil liquid remains in a small amount even after the subsequent washing treatment. Reference numeral 16 in FIG. 1 represents the remaining oil liquid.

After the above cleaning process, the jig 10 is placed in an oxidation furnace, and the rod substrate 11 on the jig 10 is oxidized. The method of oxidation treatment is arbitrary, for example,
When performing steam oxidation, first, the inside of the oxidation furnace is heated to 470 to 480 ° C. in a nitrogen gas atmosphere, and then steam is blown into the oxidation furnace for a predetermined time (for example, 1.5 hours).
After that, the inside of the oxidation furnace is replaced with nitrogen gas, and the rod substrate 11 is replaced.
Is cooled in the furnace to about 300 ° C., and thereafter taken out of the oxidation furnace and cooled in the atmosphere. By this oxidation treatment, the surface of the rod substrate 11 is laminated on the nitrided layer,
An oxide layer (Fe ₃ O ₄ layer) of ₃ μm is formed.
0 between the concave surface 12 and the convex surface 11a of the rod substrate 11.
Is small, and the oil liquid 1
6 remains, the tip of the rod substrate 11 (the convex surface 1
The oxidation of 1a) is suppressed, and the thickness of the oxide layer formed on the convex surface 11a at the tip of the rod description 11 is smaller than the peripheral surface (sliding surface) of the rod base material 11. Here, the gap δ
It is desirable that the diameter of the end of the concave surface 12 is 0.5 mm or less and that the oil liquid 16 can penetrate (depending on the shape of the rod end).

After the steam oxidation treatment, the rod base material 11 is removed from the jig 10 and buffed one by one to finish it to a desired surface accuracy (for example, about Rmax 0.6 μm). (FIG. 3) is completed. As shown in FIG. 3, the thickness of the oxide layer 21a on the peripheral surface (sliding surface) of the piston rod 20 completed in this way exceeds 1 μm, while the thickness of the oxide layer 21b on the distal end surface is increased. The thickness is as thin as 0.2 to 1.0 μm, and particularly, the thickness of the oxide layer at the center of the tip surface is the thinnest. As a result, as shown in FIG.
After the piston rod 20 is clamped by the lower electrode 22 to fix its position, the lower end bent portion 23a of the bracket 23 is pressed against the distal end surface of the piston rod 20 by the upper electrode 24 to perform resistance welding. Since the electric resistance of the front end face of the metal is small, welding can be performed with a relatively low current. As a result, no spark is generated between the piston rod 20 and the lower electrode 22, and the occurrence of spark marks on the sliding surface of the piston rod 20 is prevented.

In the above embodiment, by forming the concave surface 12 of the jig 10 into a spherical shape, even when processing rod substrates having different diameters, the convex surfaces 11a of the rod substrates have substantially the same radius of curvature. If so, the same jig can be used.

The shape of the concave surface 12 of the jig 10 is not limited to a spherical shape, and the oil liquid remains on the concave surface, and
The opening of the narrow gap where the residual oil liquid is unlikely to evaporate during the subsequent processing, that is, the gap formed between the concave surface and the tip of the rod (the section indicated by δ in FIG. 1) is 0.5 mm or less. Any shape may be used as long as a gap is formed such that an oil liquid can enter.

The entire structure of the jig 10 is arbitrary. For example, instead of the support plate 15,
A wire mesh having an eye through which the wire 1 can be inserted is stretched by using the support 14 so that the rod base 11 can be erected through the mesh of the wire mesh. In this case, the setting of the rod base material 11 becomes easy, and for example, it becomes possible to process the rod base material 11 in large quantities in units of several hundreds. In addition, the present invention does not limit the type of the mounting member to be resistance-welded to the distal end surface of the piston rod 20.
Instead of 3, for example, a bolt can be selected.

[0022]

As described above in detail, according to the piston rod for a cylinder device according to the present invention, the thickness of the oxide layer on the rod tip surface, which is the resistance welding surface of the mounting member, is reduced to enable welding. Since the resistance is improved, no spark marks are generated on the sliding surface even if the mounting member is resistance-welded, and troublesome measures such as changing the shape are not required, and the manufacturing cost is reduced. . Further, according to the method for manufacturing a piston rod according to the present invention, the thickness of the oxide layer on the rod end surface can be reduced by a simple method in which the rod end is brought into contact with the concave surface of the jig, and the efficiency is improved. And a piston rod can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view showing a portion where a jig used in a method of manufacturing a piston rod according to the present invention and a rod base material are joined.

FIG. 2 is a cross-sectional view showing an overall structure of a jig used in a method of manufacturing a piston rod according to the present invention and a setting state of a rod base material with respect to the jig.

FIG. 3 is a sectional view showing a state of an oxidized layer of a piston rod obtained by the present method and an embodiment of welding a bracket to the oxidized layer.

FIG. 4 is a front view showing the appearance of a cylinder device incorporating a piston rod.

FIG. 5 shows the welding of the bracket to the piston rod;
It is a front view which shows the conventional embodiment.

FIG. 6 is a front view showing an embodiment of a conventional deformed piston rod and welding of a bracket to the piston rod.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Jig 11 Rod base material 11a Convex surface of the tip of rod base material 12 Concave surface of jig 13 Jig body 14 Post 15 Support plate 20 Piston rod 21a, 21b Oxide layer 23 Bracket

Claims (2)

[Claims] 1. A piston rod for a cylinder device in which a nitrided layer and an oxide layer are laminated on a surface, wherein the outermost oxide layer has a thickness exceeding 1.0 μm on a peripheral surface serving as a sliding surface. On the other hand, the piston rod for a cylinder device has a thickness of 0.2 to 1.0 [mu] m on a tip end surface serving as a resistance welding surface of the mounting member. 2. A piston which sequentially sends a jig on which a plurality of rod base materials are erected to a gas nitrocarburizing furnace, an oil bath, a washing machine, and an oxidation furnace to sequentially perform each process of gas nitrocarburizing, oil cooling, cleaning and oxidation. A method for manufacturing a piston rod, wherein a concave surface is formed on the jig, and the rod base material is erected on the jig in a state where the rod tip is in contact with the concave surface. .