JPH0631653A - Chisel for shock moving tool - Google Patents

Abstract

PURPOSE:To improve durability by quenching/annealing chisel main unit, slidably inserted into a chisel bush, to form a hard layer in the peripheal part, and thereafter annealing a contact part with the chisel bush to form a softened layer. CONSTITUTION:A chisel main unit 1 is formed of low alloy steel, and a total unit is quenched and annealed, to form a hard layer 3 of predetermined hardness distribution. Next, a contact part 2 with a chisel bush is annealed, to provide a soft layer 4. In this annealing, its depth is adjusted to about several mm by such as natural cooling after heating to about 650 deg.C and further repetition of heating/cooling divided into several times little by little to about 750 deg.C. Since this heating is in only the contact part 2, a high frequency induction heating method is preferable. Hardness of the soft layer 4 is preferable about HRC20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chisel for an impact power tool.

[0002]

2. Description of the Related Art As shown in FIG.
The piston 11 is slidably incorporated into the cylinder 10, and the chisel 13 is slidably inserted into the inside of a chisel bush 12 attached to the lower portion of the inner circumference of the cylinder 10. The chisel 1 is pressed against an object to be destroyed such as concrete.
3 is repeatedly hit by the vertical movement of the piston 11 to destroy the object to be destroyed.

Hardness is required because the chisel 13 of the impact power tool slides along the inner surface of the chisel bush 12 and impacts an object to be destroyed. Therefore, the chisel 13 is hardened and tempered to increase its hardness and durability.

FIG. 3 shows a hardness transition curve of a conventional general chisel 13 that has been quenched and tempered. The hardness of the outer peripheral portion is H _R C53, and the hardness of the central portion is about H _R C40. Many.

[0005]

By the way, the impact tool is often used in a state in which the chisel 13 pressed against the portion to be destroyed is inclined with respect to the vertical. In this case, the chisel 13 slides in a state of locally contacting the edge of the inner circumference of the chisel bush 12, and the contact portion rises above the quenching temperature by repeated sliding.

Since the temperature rising portion is a shallow and limited area of the surface layer of the chisel, it is rapidly cooled by the chisel 13 itself to form a hard and very brittle hard brittle layer in which cracks easily occur.

In the conventional chisel, as described above,
Since the outer peripheral portion is hard, when a crack is generated in the hardening brittle layer, the crack easily propagates to the hard portion on the outer periphery, and there is a problem that the chisel is easily broken due to the progress of the crack.

The present invention solves the above-mentioned conventional problems,
The technical challenge is to improve the durability of the chisel.

[0009]

In order to solve the above problems, in the present invention, a chisel body slidably inserted in a chisel bush is quenched and tempered to form a hard layer on the outer peripheral portion. After that, the contact portion contacting with the chisel bush was annealed to form a softened layer on the surface layer portion of the hard layer.

Here, the annealing depth is set to a range of several mm from the outer periphery of the chisel body so as not to affect the overall strength.

[0011]

As described above, since the softening layer is formed in the portion of the chisel body that comes into contact with the chisel bush by annealing, the surface of the softening layer is heated to the quenching temperature or higher due to the contact with the chisel bush, Even if a hard brittle hard brittle layer is formed by cooling, since a softening layer is present between the hard brittle layer and the hard layer formed by the initial hardening, cracks occur in the hard brittle layer. Also can prevent the propagation of cracks in the softened layer. Further, since the amount of carbon contained in the softened layer is reduced, it is possible to make it difficult to form the hardened layer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1A shows a chisel body 1, and 2 shows a contact portion which comes into contact with the chisel bush 12 shown in FIG.

The chisel body 1 is made of low alloy steel as in the conventional case, and is entirely quenched and tempered to obtain the hardness distribution shown by the hardness transition curve in FIG. Reference numeral 3 in FIG. 1B shows a hard layer formed by quenching and tempering.

The contact portion 2 of the chisel body 1 is annealed after quenching and tempering the chisel body 1.

When annealing, a method of adjusting the annealing depth by heating to about 650 ° C., naturally cooling, and then repeating heating and cooling in small increments up to about 750 ° C. There is a method in which the entire portion to be annealed is heated once and the annealing depth is adjusted by the heating time.

Since the above-mentioned annealing is a local annealing of only the surface layer of the contact portion 2, it is preferable to employ a high frequency induction heating method for heating by the annealing. By the annealing, the softened layer 4 is formed on the surface layer of the hard layer 3.

Here, if the annealing depth becomes too deep, the overall strength of the chisel body 1 decreases, so the depth is set to about several mm. The hardness of the softening layer 4 formed by annealing is preferably about H _R C20 in order to suppress initial wear due to contact with the chisel bush 12.

As described above, when the softening layer 4 of about several mm is formed on the contact portion 2 with the chisel bush 12, the contact portion 2 with the chisel bush 12 rises above the quenching temperature due to the inclined use of the chisel. Even if a hard brittle layer that is hard and brittle is formed by cooling and a crack is generated in the hard brittle layer, the softening layer 4 is interposed between the hard brittle layer and the hard layer 3 due to the initial quenching. Does not propagate.
Moreover, since the carbon content of the softened layer is reduced, the hardened brittle layer is less likely to be formed.

[0020]

As described above, in the chisel according to the present invention, since the softening layer is formed on the surface of the contact portion which comes into contact with the chisel bush, a hard and brittle hardening brittle layer is formed on the surface of the softening layer. Even if a crack is generated, the crack can be prevented from propagating to the inside, and a chisel having excellent durability can be obtained.

[Brief description of drawings]

FIG. 1A is a front view of a chisel according to the present invention,
(B) is a cross-sectional view of the contact part with the chisel bush

FIG. 2 is a schematic view of an impact tool.

FIG. 3 is a graph showing the hardness of a conventional chisel.

[Explanation of symbols]

 1 Chisel 2 Contact part 3 Hard layer 4 Softening layer

Claims (1)

[Claims] A chisel body slidably inserted into a chisel bush is quenched and tempered to form a hard layer on an outer peripheral portion, and then a contact portion that comes into contact with the chisel bush is annealed to obtain the hard layer. Chisel for impact tools with a softened layer formed on the surface layer of.