JP2001214683A - Drill rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drill rod capable of being used for a long time by preventing the abrasion in a screw section. SOLUTION: The surface of a joint screw is provided with a hardening layer prescribed as follows. 1) The hardening layer has 0.2 to 2.5 mm in thickness. 2) The hardening layer is formed by the surface quenching, and the hardness difference between a base metal and the hardening layer is HRC hardness 5 or more. 3) The hardening layer is provided within a range of a partial length from the front end of the screw to a work-length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drill rod, and more particularly, to a drill rod having a thread portion subjected to a wear prevention treatment.

[0002]

2. Description of the Related Art A drill rod has been treated as a product life when wear of a screw thread progresses due to repeated attachment and detachment of a screw, and when a wear limit is reached. However, at this point, in the tubular portion of the drill rod excluding the screw portion, the outer diameter portion is slightly worn, and the inner diameter portion is hardly worn. Nevertheless, drill rods which have reached the thread wear limit are actually scrapped, which is undesirable from the viewpoint of effective utilization of resources.

[0003] SCM or SNCM alloy steel specified by JIS may be used as the material of the drill rod. In particular, a drill rod for a rotary percussion drill has a tensile strength of 1000 to 1000 to prevent abrasion of a thread portion.
A high toughness and high tensile strength alloy steel whose strength is adjusted to 1200 N / mm ² (HRC hardness 30 to 41) is often used as a material. However, at this time, no countermeasures have been taken to prevent screw wear of the drill rod, and therefore, wear proceeds at a speed corresponding to the hardness of the material.

[0004] In order to prevent galling of the thread, a phosphate film or the like may be applied to the surface of the thread, but this has no effect of preventing abrasion. In addition, grease to which fine particles such as copper, zinc, and molybdenum are added may be applied at the time of screw connection, but this does not improve the performance of the drill rod and does not exceed the range of consideration for use.

[0005] A raw material of a drill rod for a rotary percussion drill is more expensive than a normal structural steel pipe, and the material cost accounts for 50 to 50% of the product cost depending on the size.
As high as 70%. In addition, if the time required to reach the wear limit of the screw is short, the material must be scrapped even when the material is almost new, and it cannot be said that consideration is given to environmental load.

[0006] On the other hand, the determination of the wear limit of the screw is based on the subjective opinion of the user. Even if the wear state exceeds the connection strength limit, if the consciousness of investment recovery is too strong, the screw is used beyond the limit. There is a tendency. For this reason, there is a high risk that an accident may occur due to loose or loose screws.

[0007]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above technical background, and has the following objects. An object of the present invention is to provide a drill rod that can be used for a long period of time by preventing abrasion of a screw portion.

[0008]

The present invention employs the following means to achieve the above object. That is, the present invention resides in a drill rod characterized in that a hardened layer defined as follows is provided on the surface of a connection screw. 1) The cured layer has a thickness of 0.2 to 2.5 mm. 2) The hardened layer is formed by surface quenching, and has a hardness difference of 5 or more from the base material. 3) The hardened layer is provided in a partial length range from the screw tip to the screw processing length.

The drill rod is for a percussion drill such as a rotary percussion drill.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an axial sectional view showing a drill rod for a rotary percussion drill. The drill rod 1 is tubular, and is made of SCM or SNCM alloy steel specified by JIS, or alloy steel whose strength has been adjusted to a tensile strength of 1000 to 1200 N / mm ² by increasing or decreasing the amount of alloying elements. It is made.

The drill rod 1 has a male thread 2 at the tip (pin) and a female thread 3 at the rear (box).
The male screw portion 2 of another drill rod is screwed into the female screw portion 3 to be sequentially added. At both sides in the axial direction of the male screw portion 2 and the female screw portion 3, stepped spigot (inro) portions 4, 5 are provided. When the spigot portions 4, 5 are fitted together at the time of screw connection, screw loosening occurs. When this occurs, the strength against bending force is ensured.

FIGS. 2 and 3 are enlarged sectional views showing the pin portion (a) and the box portion (b) of the drill rod 1. In the initial stage of use, as shown in FIG. Thread shape is maintained normally. By repeatedly attaching and detaching screws,
As shown in FIG. 3, the abrasion of the thread progresses from the mouth.
At this point, the back part indicated by the range N is almost in a normal state.

[0013] In order to prevent such screw wear,
As shown in FIG. 4, a hardened layer 6 is provided on the surfaces of the screw portions 2 and 3. In this figure, hatching is omitted for easy understanding of the hardened layer 6. The hardened layer 6 has a thickness of about 0.3 to 2.5 mm, and is induction hardened, flame hardened,
It is provided by performing surface quenching such as carburizing and quenching. As a result of this quenching, the hardness difference between the hardened layer 6 and the base material is set to an HRC hardness of 5 or more. Incidentally, the HRC hardness specified by JIS is 20-68, and therefore, for example, when the base material hardness is HRC35, the hardness of the hardened layer 6 is less than HRC40-68.

The hardened layer 6 is not provided over the entire processing length of the threaded portions 2 and 3, but is provided in a partial length range from the tip of the screw. That is, the quenching range Q is about 60% of the thread processing length. As described above, by performing the partial quenching process in accordance with the progress of screw wear (see FIG. 3), the non-quenched portion opposes the thermal stress caused by quenching, and the thermal distortion of the entire threaded portion 2, 3 is reduced. Occurrence can be suppressed.

[0015]

EXAMPLE A hardened layer was formed on a threaded portion of a drill rod made of an alloy steel having the components shown in Table 1 and the mechanical strength shown in Table 2 by flame quenching, and a wear test was conducted.

[0016]

[Table 1]

[0017]

[Table 2]

The drill rod used in the wear test was φ70
mm, the hardness of the hardened layer: HRC47, and the thickness of the hardened layer: 1 mm. The abrasion test was performed by a continuous pressing reverse test. The pressing load: 5625N, the rotating torque: 2850N · m, the number of rotations:
The conditions were 50 rpm. FIG. 5 is a graph showing the results of the wear test and showing the relationship between time and the amount of thread wear. As is clear from the graph, it can be seen that the life of the product of the present invention is about twice as long as that of the conventional product.

The present invention is not limited to the above-described embodiment, but includes an extension rod for connecting a cleaning swivel and an inner rod in a double-pipe rotary percussion drill or a master coupling screw for connecting a cleaning swivel and an outer rod. It can also be applied to parts.

That is, the drill rod according to the present invention is a concept including a general member for transmitting a feeding force and a rotational force (and a striking force) to a bit by screw connection. Therefore, the drill rod includes the extension rod. And master couplings are naturally included. These extension rods and master couplings are also provided with thread portions at both ends of the front and rear ends, but the hardened layer may be provided only in one of the thread portions as required.

[0021]

As described above, according to the present invention, since the hardened layer is provided on the connection screw portion, the life of the drill rod can be extended, and more specifically, the following effects can be obtained. . (1) The cost increase due to the provision of the hardened layer is about 5% of the manufacturing cost of the drill rod, but the life is extended about twice according to the experiment. Therefore, the total cost of the drill rod is reduced, and the site operation cost is reduced. (2) The time until the wear limit of the screw is reached is extended, and the material of the tube can be sufficiently consumed. That is, the environmental load of the drill rod material is reduced. (3) The user can be made aware of the wear of the pipe portion other than the threaded portion, and can be given the consciousness that "this is enough for use." That is, a sense of stopping the use within the connection strength limit of the screw occurs, and the occurrence rate of an accident due to the loose or looseness of the screw decreases.

[Brief description of the drawings]

FIG. 1 is an axial sectional view showing a drill rod to which the present invention is applied.

FIG. 2 is an enlarged sectional view showing a screw portion;

FIG. 3 is a cross-sectional view showing the progress of screw wear.

FIG. 4 is an enlarged cross-sectional view showing a thread portion of a drill rod provided with a hardened layer.

FIG. 5 is a graph showing the results of a wear test.

[Explanation of symbols]

 1: Drill rod 2: Male thread 3: Female thread 6: Hardened layer Q: Hardening range

Claims (2)

[Claims] 1. A drill rod, wherein a hardened layer defined as follows is provided on the surface of a connection screw. 1) The cured layer has a thickness of 0.2 to 2.5 mm. 2) The hardened layer is formed by surface quenching, and has a hardness difference of 5 or more from the base material. 3) The hardened layer is provided in a partial length range from the screw tip to the screw processing length. 2. The drill rod according to claim 1, wherein said drill rod is for a percussion drill.