JP2000009107A - Method of reinforcing cylinder tube of hydraulic cylinder and hydraulic cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of reinforcing the cylinder tube of a hydraulic cylinder and also the hydraulic cylinder, capable of making lightweight without increasing production costs and of preventing a decrease in fatigue strength at a welding part. SOLUTION: A hydraulic cylinder 1 is formed by integrating a cylinder tube 2 with a bottom member 3 by welding. Where, belt-like overlay welding 5 is applied to the outer boundary part of the cylinder tube 2 at a required zone b at a partial tube side adjacent the welding part 4. Contracting force caused at coagulation is applied to the adjacent part from the welding part 4. The resulting hydraulic cylinder is provided with a surface part from the connected boundary of the cylinder tube 2 and the bottom member 3 toward the cylinder tube 2 side and a melted, coagulated part with width, 0.07-0.25 time the outside diameter of the cylinder tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic cylinder, and more particularly, to a method for strengthening a cylinder tube of a hydraulic cylinder in which the strength of a weld at a joint between a cylinder tube and a bottom is increased to improve durability. It relates to a hydraulic cylinder.

[0002]

2. Description of the Related Art Generally, when a hydraulic cylinder is manufactured with a light weight, a bottom member 102 is welded to an end of a cylinder tube 101 as shown in FIG. In order to weld the bottom member 102 to the end of the cylinder tube 101 in this manner, the bottom member 102 whose end is stepped 103 is fitted to the end of the cylinder tube 101 whose inner surface has been finished in advance. The end of the cylinder tube 101 and the joint 104 of the bottom member 102 are welded 105 to be integrated.

[0003] Japanese Utility Model Publication No. 4-9095 discloses an improvement in fitting a bottom member 102 having a step 103 formed on an end portion of a cylinder tube 101 with the above-described in-row fitting structure. In order to improve the fatigue strength at the welded portion at the joint end, the end of the cylinder tube 101 is expanded within the allowable range of the elastic deformation to press-fit the step 103 of the bottom member 102 or to bake it. Means for insertion by means of a fit or a cold fit are taken.

According to Japanese Utility Model Publication No. 4-17851, as shown in FIG. 6, an annular wall of a bottom member 106 having the same inner diameter with substantially the same thickness as one end of a cylinder tube 101 is provided. 107, and a buckling 108 is fitted inside the joint between the two, and the welded portion 10
9 is welded at a distance of 0.08 to 0.20 times the inner diameter of the cylinder tube 101 from the inner bottom of the bottom.

[0005]

However, in the case of welding by the former means (in-row fitting structure), the stress concentration at the welding residual root portion is large, and it is necessary to ensure a sufficient welding throat thickness. Is difficult. Although the former disclosed in Japanese Utility Model Publication No. 4-9095 attempts to improve the former, equipment is required to perform press-fitting, shrink-fitting, cold-fitting, etc. is there.

[0006] In Japanese Utility Model Publication No. 4-17851, the welding strength is improved because there is no residual route in the welded portion, but high precision machining is required to perform butt welding. However, since buckling is also required, there is a problem that the cost is also significantly increased.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is an object of the present invention to provide a hydraulic cylinder capable of reducing the thickness of a cylinder tube without increasing the production cost and preventing a decrease in fatigue strength of a welded portion. It is an object of the present invention to provide a method for reinforcing a cylinder tube and a hydraulic cylinder.

[0008]

In order to achieve the above-mentioned object, a method for reinforcing a cylinder tube of a hydraulic cylinder according to a first aspect of the present invention provides a hydraulic cylinder comprising a cylinder tube and a bottom member integrated by welding. In the cylinder, the surface layer is melted in a band shape from the joint boundary between the cylinder tube and the bottom member to the cylinder tube side,
It is characterized in that a squeezing force generated when solidified is applied.

With this arrangement, the hydraulic cylinder acts in the direction in which the hydraulic cylinder expands at the time of operation due to the contraction force applied to the surface layer in a portion adjacent to the cylinder tube side from the joint boundary between the cylinder tube and the bottom member. In response to the stress, work to reduce the expansion stress,
This has the effect of eliminating stress that has conventionally been concentrated at the welding residual route portion in the fitting welded portion, improving durability, and making it possible to reduce the thickness and weight of the cylinder.

Further, in the present invention, the band-shaped melt-solidification processing portion is provided with a cylinder tube outer diameter of 0.07 to 0.25.
The width should be doubled. In this way, reasonably,
It is possible to maintain the strength corresponding to the portion where the stress load during operation of the hydraulic cylinder is the strictest, and it becomes difficult to deform under the load during operation as described above. This has the effect of reducing the stress at the residual route in the welded portion.

The melting and solidifying treatment on the outer peripheral portion of the cylinder tube is preferably performed by consumable electrode welding. By doing so, the outer peripheral portion on the cylinder tube side from the joining boundary portion of the cylinder tube integrated by welding with the bottom member is welded by overlaying, and in addition to the above effect, the end of the cylinder tube is increased by welding overlaying. Therefore, the rigidity of the part is increased, it is more difficult to be deformed by the load during operation as described above, causing a function of contracting the tube from the outer circumference toward the axis by the so-called welding stress, The effect of reducing the stress acting in the direction in which the tube expands during operation of the hydraulic cylinder to extend the life can be achieved with a very inexpensive method.

Further, in the present invention, the melt-solidification treatment on the outer peripheral portion of the cylinder tube is preferably performed by non-consumable electrode type welding. According to a welding method using such a non-consumable electrode (as one specific example, Tig welding),
The surface layer of the cylinder tube is melted and then solidified to generate a crimping force on the outer periphery of the cylinder tube in the same manner as the above-mentioned welding overlaying, so that it is economically advantageous without requiring special equipment This has the effect that the durability of the cylinder can be increased by such means.

A hydraulic cylinder according to a second aspect of the present invention is a hydraulic cylinder in which a cylinder tube and a bottom member are integrated by welding, wherein a surface layer portion is formed from a joint boundary between the cylinder tube and the bottom member to the cylinder tube side. It is characterized in that it is a melt-solidified portion having a width of 0.07 to 0.25 times the outer diameter.

With this configuration, it is possible to provide a hydraulic cylinder having the above-described effects of the first invention.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a specific embodiment of a method for reinforcing a cylinder tube of a hydraulic cylinder according to the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a main part of a hydraulic cylinder as one embodiment according to the present invention.

The hydraulic cylinder 1 shown in this figure has a thin cylinder tube 2 at one end thereof.
The bottom member 3 having a connecting pin hole for attachment to a device or the like is integrated by welding. The other end of the cylinder tube 2 is removably mounted with a cylinder head having a bearing for projecting and supporting a piston rod (not shown) to the outside, and a piston is provided inside the cylinder head. The description of the parts other than the main parts in FIG.

At the joint between the end portion 2a of the cylinder tube 2 and the bottom member 3, the cylinder tube 2 has an inner peripheral portion finished to required dimensions,
At the end 3a of the bottom member 3 to be joined, a step having a diameter corresponding to the inner diameter of the end 2a of the cylinder tube 2 is formed. The joint is welded and joined by a method such as arc welding.

Following the work of welding and joining the end 2a of the cylinder tube 2 and the end 3a of the bottom member 3 in this manner, the welded portion 4 is applied to the outer peripheral surface of the cylinder tube 2 in the axial direction. In the required section b, welding is performed. For the weld overlay 5, the bottom member 3
Is welded to the end 2a of the cylinder tube 2 and then the cylinder tube 2 is clad using a normal welding rod while rotating the cylinder tube 2 on the axis in the circumferential direction. In this case, welding can be efficiently performed without impairing workability. The build-up height h forming the weld build-up portion 5 may be about 3 mm (however, it is not limited to this value).

The welded portion 4 thus joined to the bottom member 3
Then, when welding welding is performed on the outer peripheral portion of the cylinder tube 2, an acting force for contracting the cylinder tube 2 from the surroundings acts by welding stress accompanying the welding, and the welding overlay 5 is formed. As a result, the rigidity of the weld overlay 5 is increased, and as a result, the weld overlay 5 is hardly deformed by the load during operation as a hydraulic cylinder, and the stress at the residual route portion of the weld is reduced. The effect is obtained.

When performing the above-mentioned welding overlay, the width b of the weld overlay 5 is set such that the longer the width is, the greater the stress relaxing effect of the residual root portion in the weld 4 is. In addition, distortion due to welding generated in the inner diameter of the cylinder tube also increases, and the required roundness of the cylinder tube cannot be secured.

Then, when the impulse fatigue test and the measurement of the inner diameter distortion of the tube were performed using several types of cylinders having different weld overlay widths as test samples, the weld overlay width b was 0.07 times the outer diameter of the cylinder tube. In the following, it was found that there was no effect of improving the life due to stress relaxation, and that when the diameter exceeded 0.25 times the outer diameter of the cylinder tube, the strain became larger than the standard. From this result, regarding the weld overlay width b,
It is preferable to carry out within a range of 0.07 to 0.25 times the outer diameter of the cylinder tube. The specimen used for the impulse fatigue test was prepared under the following conditions. Welding method: arc welding Tube outer diameter: φ132 mm Welding wire diameter: φ1.2 mm Current: 300 A Voltage: 32 V Tube rotation speed: 1.0 rpm Weaving frequency: 1.5 Hz

The results of the impulse fatigue test and the measurement of the strain on the inner diameter of the tube are shown in Table 1 and the graph of FIG. The life of the impulse fatigue test in the graph is represented assuming that the value of the conventional one is 1. Also, regarding the weld overlay width b and the tube inner diameter measurement position,
Represented by FIG.

[0024]

[Table 1]

Next, in the second embodiment, as illustrated in FIG. 2, the cylinder tube 2 and the bottom member 3 as described above are used.
Instead of welding overlay as a means of strengthening the cylinder at the joint with the end portion, the end 2a of the cylinder tube 2 and the end 3a of the bottom member 3 are fitted and welded, and then the required welding from the welded portion 4 is performed. In section b, the outer surface layer of the cylinder tube 2 is melted by Tig welding and cooled to form a hardened layer 6.

By doing so, the cylinder tube 2
By the hardened layer 6 formed on the outer peripheral surface portion from the welded portion 4 to the tube side with the bottom member 3, the acting force for contracting the cylinder tube 2 as in the case of the weld overlay portion 5 in the above embodiment is increased. Given. Therefore, the contraction force makes it difficult to be deformed by the load during operation as the hydraulic cylinder, and the effect of reducing the stress at the residual route portion of the welded portion 4 can be obtained.

As described above, according to the welding method using the non-consumable electrode, the stress load during operation as a hydraulic cylinder in the vicinity of the joint with the bottom member 3 is reduced without adding a separate member or the like to the cylinder tube 2. The most severe part,
The reinforcement can be easily performed, and the intended purpose can be easily achieved by switching to Tig welding (in some cases, plasma welding) while continuing the joining operation by arc welding. Moreover, according to this method, since nothing is added to the cylinder tube 2, there is an advantage that the weight can be further reduced and strengthened.

The strengthening process of the second embodiment was performed under the following conditions, and a value close to the test result by the strengthening method of the first embodiment could be obtained. Welding method: Tig welding Tube outer diameter: φ132 mm Current: 250 A Voltage: 30 V Tube rotation speed: 1.0 rpm Weaving frequency: 1.5 Hz The best hardened layer formation width in this test is 15 m
m.

[Brief description of the drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of a hydraulic cylinder according to a strengthening method of the present invention.

FIG. 2 is a sectional view of a main part of another embodiment of a hydraulic cylinder according to the strengthening method of the present invention.

FIG. 3 is a diagram illustrating a relational dimension of a cylinder in which a test was performed on a strengthened state of the cylinder in the first embodiment.

FIG. 4 is a graph showing an impulse fatigue test life and a strain rate of a tube inner diameter.

FIG. 5 is a sectional view of a main part showing a welding structure of a bottom portion in a conventional hydraulic cylinder.

FIG. 6 is a cross-sectional view of a main part showing another welding structure of a bottom portion in a conventional hydraulic cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic cylinder 2 Cylinder tube 2a End of cylinder tube 3 Bottom member 3a End of bottom member 4 Weld part 5 Weld build-up part 6 Hardened layer

Claims (5)

[Claims] 1. A hydraulic cylinder in which a cylinder tube and a bottom member are integrated by welding, wherein the surface layer is melted into a band shape from the joint boundary between the cylinder tube and the bottom member to the cylinder tube side and solidified when solidified. A method for strengthening a cylinder tube of a hydraulic cylinder, wherein a compressive force is applied. 2. The method according to claim 1, wherein the band-shaped melt-solidified portion has a width of 0.07 to 0.25 times the outer diameter of the cylinder tube. 3. The method according to claim 1, wherein the melting and solidifying process on the outer periphery of the cylinder tube is performed by consumable electrode welding. 4. The process of melting and solidifying the outer peripheral portion of the cylinder tube by non-consumable electrode welding.
3. The method for reinforcing a cylinder tube of a hydraulic cylinder according to item 1. 5. A hydraulic cylinder in which a cylinder tube and a bottom member are integrated by welding, wherein a surface layer extends from a joint boundary between the cylinder tube and the bottom member to the cylinder tube side to have a cylinder tube outer diameter of 0.07 to 0.00. A hydraulic cylinder having a melt-solidified portion having a width of 25 times.