Patent Description:
A crawler drill has a guide shell mounted to the tip of a boom disposed to a traveling carriage, a carriage, which advances and retracts by drive force of a feed mechanism, is disposed on the guide shell, and a rock drill is mounted on the upper surface of the carriage.

As an example is illustrated in <FIG>, a shank rod <NUM> is mounted to a rock drill <NUM> of this type, a rod <NUM> is screwed to the tip of the shank rod <NUM> via a sleeve <NUM>, and a not-illustrated bit is screwed to the tip of the rod <NUM>. Hereinafter, the shank rod, the sleeve, and the rod are also collectively referred to as "drill tools" DTp.

The rock drill <NUM> includes a known hammering mechanism and rotation mechanism. The rotation mechanism includes the shank rod <NUM>, a chuck <NUM>, a chuck driver <NUM>, a driving gear <NUM>, and a motor <NUM>, as illustrated in <FIG>. The rotation mechanism transmits rotational driving force of the motor <NUM> to the driving gear <NUM>, the chuck driver <NUM>, the chuck <NUM>, and the shank rod <NUM> and thereby makes the shank rod <NUM> rotate.

The hammering mechanism includes a hammering piston <NUM>, which is disposed in a cylinder <NUM> in an advanceable and retractable manner, and a not-illustrated switching valve, and the hammering piston <NUM> strikes a rear end surface <NUM> of the shank rod <NUM>. The shank rod <NUM>, by being struck by the hammering piston <NUM>, transmits hammering energy to the rod <NUM> and the bit via the sleeve <NUM> and, in conjunction therewith, transmits rotational driving force of the rotation mechanism to the rod <NUM> and the bit as described afore and thereby crushes bedrock.

Among the members constituting the rock drill <NUM>, for example, the hammering piston <NUM> and the shank rod <NUM> are required to have high surface hardness because the hammering piston <NUM> and the shank rod <NUM> collide with each other. The hammering piston <NUM> is in sliding contact with the inner diameter surface of the cylinder <NUM>, and the shank rod <NUM> is in sliding contact with the inner diameter surface of a front bush <NUM> and the inner diameter surfaces of seals <NUM> of a swivel <NUM>.

As such, the hammering piston <NUM> and the shank rod <NUM> are respectively required to also have high wear resistance in conjunction with the high surface hardness. Therefore, as a material of the hammering piston <NUM> and the shank rod <NUM>, alloy steel, known as nickel-chromium-molybdenum steel, is employed, and heat treatment by carburizing-quenching is performed on the nickel-chromium-molybdenum steel. Further, rotational torque also acts on the shank rod <NUM>, as described above. As such, the hammering piston <NUM> and the shank rod <NUM> are required to have high toughness in addition to surface hardness and wear resistance.

Thus, a technology in which, in the conventional rock drill <NUM>, alloy steel composed of the following chemical components: <NUM> to <NUM> wt% of Ni, <NUM> to <NUM> wt% of Cr, <NUM> to <NUM> wt% of Mo, <NUM> to <NUM> wt% of Mn, <NUM> to <NUM> wt% of C, and Fe and inevitable impurities as the balance is used for the drill tools DTp, such as the shank rod <NUM>, the sleeve <NUM>, and the rod <NUM>, and a surface-hardened layer in which hardness decreases from a surface layer portion toward a central portion is formed by performing surface treatment on the alloy steel under a condition illustrated in <FIG> has been proposed (PTL <NUM>).

Furthermore, PTL <NUM> discloses a carburizing carbon potential distribution control technology of a material for a 23CrNi3MoA rock drilling tool.

PTL <NUM> describes a cored steel for the rod of a rock drill fit for use under the generation of heat to a high temperature by subjecting a steel containing proper amounts of C, Si, Mn, Ni, Cr and Mo to induction hardening or carburizationhardening and tempering.

PTL <NUM> relates to a drill rod comprising the following components in percentage by mass of: <NUM>-<NUM>% of C, <NUM>-<NUM>% of Si, <NUM>-<NUM>% of Mn,<NUM>-<NUM>% of Cr, <NUM>-<NUM>% of Ni, <NUM>-<NUM>% of Mo, <NUM>-<NUM>% of V, P being lower than or equal to <NUM>%, and S being lower than or equal to <NUM>%, and a balance of Fe, wherein the ratio of Mn/Mo in the drill rod is controlled to be <NUM>-<NUM>, and the ratio of Cr/Ni is controlled to be <NUM>-<NUM>.

Recent years, rock drills have been provided with high output power, and there have occurred cases where drill tools DTp as described above are insufficient in strength.

In other words, while the front bush <NUM> and a centralizer (not illustrated) as bearing members are disposed to the drill tools DTp of the above-described rock drill <NUM> as a rotational deflection preventing mechanism, wear of the bearing members also tends to progress rapidly due to influence of the rock drill <NUM> having been provided with high output power.

When wear of the bearing members has progressed, there is a possibility that bending stress acts on the drill tools DTp due to thrust force of the feed mechanism and stress concentrates on threaded portions <NUM> of the drill tools DTp and the drill tools DTp are broken.

Accordingly, the present invention has been made in view of the problem as described above, a problem to be solved by the present invention is to provide a production method for a drill tool and a drill tool that are capable of coping with a rock drill provided with high output power.

The solution is defined in the independent claims.

Since this configuration causes the internal structure to be troostite with respect to only the threaded portions at both ends, bending rigidity is improved. Therefore, when the drill tool using the rod (drill tube) is used for a rock drill provided with high output power, damage to the drill tool is prevented or suppressed even when wear of a bearing member has progressed and bending stress acts on the drill tool.

The present invention enables a drill tool capable of coping with a rock drill provided with high output power and a method for producing the drill tool to be provided.

A drill tool of a rock drill that is one embodiment of the present invention will be described below with reference to the drawings as appropriate. Note that the drawings are schematic. Therefore, it should be noted that relations between thicknesses and planar dimensions, ratios, and the like are different from actual ones and portions having different dimensional relationships and ratios from one another among the drawings are included.

In addition, the following embodiment indicates devices and methods to embody the technical idea of the present invention by way of example, and the technical idea of the present invention does not limit the materials, shapes, structures, arrangements, and the like of the constituent components to those described below. Note that, in the following embodiment and examples, description will be made with the same signs assigned to similar or corresponding constituent components to those of the above-described conventional rock drill.

As illustrated in <FIG>, a crawler drill <NUM> of the present embodiment has a guide shell <NUM> mounted at the tip of a boom <NUM> disposed to a traveling carriage <NUM>, a carriage <NUM>, which advances and retracts by drive force of a feed mechanism <NUM>, disposed to the guide shell <NUM>, and a rock drill <NUM> mounted on the upper surface of the carriage <NUM>.

A shank rod <NUM> is mounted to the rock drill <NUM>, a rod <NUM> is screwed to the tip of the shank rod <NUM> via a sleeve <NUM>, and a bit <NUM> is screwed to the tip of the rod <NUM>. In the present embodiment, the shank rod <NUM>, the sleeve <NUM>, and the rod <NUM> correspond to a drill tool described in Solution to Problem. Hereinafter, in the description of the present application, the shank rod <NUM>, the sleeve <NUM>, and the rod <NUM> are also collectively referred to as drill tools DT.

The rock drill <NUM> includes a known hammering mechanism and rotation mechanism. As illustrated in <FIG>, the hammering mechanism includes a hammering piston <NUM>, which is disposed in a cylinder <NUM> in an advanceable and retractable manner, and a not-illustrated switching valve and is configured such that the hammering piston <NUM> strikes a rear end surface <NUM> of the shank rod <NUM>, which will be described later. The cylinder <NUM> includes a known damper mechanism <NUM> configured to press the drill tools DT against an object to be crushed while buffering repulsion that the drill tools DT receive from the object to be crushed.

The rotation mechanism includes a housing that has a front head <NUM> and a front cover <NUM> disposed in front of the front head <NUM>. A front cap <NUM> is mounted ahead of the front cover <NUM>, and a motor <NUM> is mounted in the rear of the front head <NUM>. Inside the front head <NUM>, a driving gear <NUM>, which is connected to the output shaft of the motor <NUM>, is supported in a freely rotatable manner.

In the housing of the rotation mechanism, the shank rod <NUM> is disposed coaxially with the hammering piston <NUM> and a chuck <NUM> and a chuck driver <NUM> are disposed coaxially with the shank rod <NUM>. The shank rod <NUM> is a rod-shaped member that has a sliding portion <NUM> formed at a middle portion, an outer-diameter square spline <NUM> formed at the rear end, and a threaded portion <NUM> formed at the front end, and a water hole <NUM> through which flushing fluid flows is disposed at the central axis.

Between the rear end surface <NUM> of the shank rod <NUM> and the damper mechanism <NUM>, a chuck driver bush <NUM> is disposed. The chuck driver <NUM> has an inner-diameter square spline 34a formed on the inner diameter surface thereof and a gear portion formed on the outer diameter surface thereof. The chuck <NUM> has an inner-diameter square spline 35a formed on the inner diameter surface thereof and an outer-diameter square spline 35b formed on the outer diameter surface thereof.

The outer-diameter square spline <NUM> of the shank rod <NUM> is fitted with the inner-diameter square spline 35a of the chuck <NUM>, and the outer-diameter square spline 35b of the chuck <NUM> is fitted with the inner-diameter square spline 34a of the chuck driver <NUM>, and rotational driving force of the motor <NUM> is transmitted to the shank rod <NUM> via the driving gear <NUM>, the chuck driver <NUM>, and the chuck <NUM>.

In the front cap <NUM>, a swivel <NUM> is disposed in a rotatable manner, and, on the inner diameter surface of the swivel <NUM>, seals <NUM> are mounted. In addition, on the tip side of the front cap <NUM>, a front bush <NUM>, which is a bearing member, is fitted. The sliding portion <NUM> of the shank rod <NUM> is in sliding contact with the inner diameter surfaces of the seals <NUM> and is supported by the inner diameter surface of the front bush <NUM> in a rotatable and slidable manner.

On the front end of the shank rod <NUM>, the sleeve <NUM> is mounted with a threaded portion <NUM> of the shank rod <NUM> and a threaded portion <NUM> of the sleeve <NUM> screwed to each other. The sleeve <NUM> also has a threaded portion formed on the not-illustrated front side, and the rod <NUM> is screwed to the threaded portion.

The shank rod <NUM>, by being struck by the hammering piston <NUM>, transmits hammering energy to the rod <NUM> and the bit <NUM> via the sleeve <NUM> and, in conjunction therewith, transmits rotational driving force of the rotation mechanism to the rod <NUM> and the bit <NUM> as described afore and thereby crushes bedrock, which is an object to be crushed.

The material of principal members constituting the rock drill <NUM> is alloy steel except that the material of the chuck <NUM> and the front bush <NUM> is copper alloy and the material of the swivel <NUM> is stainless steel. Since, among the members made of alloy steel, the hammering piston <NUM> and the shank rod <NUM>, in particular, repeatedly collide with each other, nickel-chromium-molybdenum steel, which excels in high hardness and high wear resistance, is employed for the hammering piston <NUM> and the shank rod <NUM> and carburizing heat treatment is performed on the nickel-chromium-molybdenum steel.

While, among the drill tools DT, the shank rod <NUM> and the rod <NUM> are bearing-supported by the front bush <NUM> and a centralizer <NUM>, respectively, progression of wear of the bearing members tends to be accelerated in association with the rock drill <NUM> having been provided with high output power.

When wear of the bearing members has progressed and backlash thereof has become large, bending stress acts on the drill tools DT due to thrust force of the feed mechanism <NUM> and there is a possibility that breakage may occur at stress concentration sites, such as a threaded portion. As such, the drill tools DT are required to have bending rigidity in addition to hardness and wear resistance.

Accordingly, for the shank rod <NUM> of the present embodiment, alloy steel the constituent materials of which are composed of the following chemical components: <NUM> to <NUM> wt% of C, <NUM> to <NUM> wt% of Si, <NUM> to <NUM> wt% of Mn, <NUM> to <NUM> wt% of Ni, <NUM> to <NUM> wt% of Cr, <NUM> to <NUM> wt% of Mo, and Fe and inevitable impurities as the balance is used.

In addition, the shank rod <NUM> is produced by, performing carburizing-quenching and tempering on the material as heat treatment, including the heat treatment with the quenching after carburizing performed by means of oil cooling with cold oil temperature <NUM> to <NUM>° C and tempering temperature set at <NUM> to <NUM>.

Because of this method, the shank rod <NUM> of the present embodiment has a carburized layer on the shank rod surface causing not only surface hardness (<NUM> to <NUM> HRC, see <FIG>) and wear resistance to be secured but also the internal structure to be troostite and is thereby substantially improved in bending strength. As such, the shank rod <NUM> of the present embodiment is capable of coping with the rock drill <NUM> provided with high output power.

However, in the shank rod <NUM> of the present embodiment, while bending strength is substantially improved, hardness is slightly reduced instead. The inventors have found that sub-zero treatment and electroless nickel plating treatment are effective as a means for compensating for the reduction in hardness.

In particular, increasing heating temperature to a tempering temperature of <NUM> to <NUM> after performing electroless nickel plating treatment enables the surface hardness to be raised higher than a surface hardness achievable by regular carburizing-quenching.

Note that the electroless nickel plating treatment enables corrosion resistance of not only the outer surface of the shank rod <NUM>, such as the sliding portion <NUM>, the outer-diameter square spline <NUM>, and the threaded portion <NUM>, but also the inside of the water hole <NUM> to be improved. As such, the shank rod <NUM> of the present embodiment is suitable for the rock drill <NUM> that uses water as flushing fluid.

Hereinafter, description will be made based on examples and comparative examples.

In a first example, using alloy steel (hereinafter, also referred to as "alloy steel for the present invention") the constituent materials of which are composed of the following chemical components: <NUM> to <NUM> wt% of C, <NUM> to <NUM> wt% of Si, <NUM> to <NUM> wt% of Mn, <NUM> to <NUM> wt% of Ni, <NUM> to <NUM> wt% of Cr, <NUM> to <NUM> wt% of Mo, and Fe and inevitable impurities as the balance, a ϕ40 mm×<NUM> test piece, the size of which is close to the actual size of the shank rod, was prepared.

In the first example, heat treatment that is, as illustrated in <FIG>, composed of a carburizing-quenching process including: temperature raising; carburizing at <NUM> for <NUM>; diffusion at <NUM> for <NUM>; heating at <NUM> for <NUM>; and oil cooling with <NUM> cold oil in this order and a tempering process at <NUM> for <NUM> was performed on the test piece.

The structural state of the test piece in the first example was troostite, as illustrated in <FIG>. The surface hardness and the core hardness of the test piece were <NUM> HRC and <NUM> HRC, respectively. The result of the bending test performed in accordance with JIS Z2248 (hereinafter, the same applies) was that the test piece, although bent <NUM> under a load of <NUM> KN, was not broken.

The test device used in the bending test uses, as bushes B supporting both ends of a test piece P, bushes that are set to rotate following a bend of the test piece P when the middle of of the test piece P is pressed, as illustrated in a schematic diagram in <FIG>. Note that an arrow indicated by a sign F in <FIG> illustrates an image in which the middle of the test piece P is pressed, and arrows indicated by signs R in <FIG> illustrate an image in which the bushes B at both ends rotate following a bend.

In a second example, a test piece made of the alloy steel for the present invention, which is similar to that in the first example, was prepared. In the second example, the carburizing-quenching process and the tempering process were performed on the test piece under the same conditions as those in the first example, and, in conjunction therewith, sub-zero treatment (at -<NUM> for <NUM>) was performed between the carburizing-quenching process and the tempering process, as illustrated in <FIG>.

The structural state of the test piece in the second example was troostite and was densified more than that in the first example. The surface hardness and the core hardness of the test piece were <NUM> HRC and <NUM> HRC, respectively. The result of the bending test was that the test piece, although bent <NUM> under a load of <NUM> KN, was not broken.

In a third example, a shank rod <NUM> was produced using the alloy steel for the present invention as a material, and, after heat treatment similar to that in the first example was performed on the shank rod <NUM>, electroless nickel plating treatment was performed and a process of heating to <NUM> was further performed.

The structural state of the shank rod <NUM> in the third example was troostite. The surface hardness and the core hardness of the test piece were <NUM> HRC and <NUM> HRC, respectively. The bending test was not performed.

The shank rod <NUM> of the third example was incorporated into the above-described rock drill <NUM>, and a durability test in which the rock drill <NUM> is operated with a pressure of <NUM> MPa for <NUM> (regular working pressure is <NUM> MPa) was performed. As a result of the durability test, regarding the shank rod <NUM> of the third example, although a change in color was observed on the sliding portion, no damage was found. <FIG> are appearance photographs of the shank rod <NUM> of the third example before the durability test (<FIG>) and after the durability test (<FIG>).

In a first comparative example, a test piece made of the alloy steel for the present invention, which is similar to that in the first example, was prepared. On the test piece, heat treatment that is, as illustrated in <FIG>, composed of a carburizing-quenching process including: temperature raising; carburizing at <NUM> for <NUM>; diffusion at <NUM> for <NUM>; heating at <NUM> for <NUM>; and air cooling in this order and a tempering process at <NUM> for <NUM> was performed.

The structural state of the test piece in the first comparative example was martensite, as illustrated in <FIG>. The surface hardness and the core hardness of the test piece were <NUM> HRC and <NUM> HRC, respectively. The result of the bending test was that the test piece was bent <NUM> under a load of <NUM> KN and broken.

In a second comparative example, a test piece made of the alloy steel for the present invention, which is similar to that in the first example, was prepared. On the test piece, heat treatment that is composed of a carburizing-quenching process including: temperature raising; carburizing at <NUM> for <NUM>; diffusion at <NUM> for <NUM>; heating at <NUM> for <NUM>; and air cooling in this order and a tempering process at <NUM> for <NUM> was performed.

The structural state of the test piece in the second comparative example was martensite. The surface hardness and the core hardness of the test piece were <NUM> HRC and <NUM> HRC, respectively. The result of the bending test was that the test piece was bent <NUM> under a load of <NUM> KN and broken.

In a third comparative example, a test piece made of the alloy steel for the present invention, which is similar to that in the first example, was prepared. On the test piece, heat treatment that is composed of a carburizing-quenching process including: temperature raising; carburizing at <NUM> for <NUM>; diffusion at <NUM> for <NUM>; heating at <NUM> for <NUM>; and oil cooling with <NUM> cold oil in this order and a tempering process at <NUM> for <NUM> was performed.

The structural state of the test piece in the third comparative example was martensite. The surface hardness and the core hardness of the test piece were <NUM> HRC and <NUM> HRC, respectively. The result of the bending test was that the test piece was bent <NUM> under a load of <NUM> KN and broken.

In a fourth comparative example, a test piece made of the alloy steel for the present invention, which is similar to that in the first example, was prepared. On the test piece, heat treatment that is composed of a carburizing-quenching process including: temperature raising; carburizing at <NUM> for <NUM>; diffusion at <NUM> for <NUM>; heating at <NUM> for <NUM>; and oil cooling with <NUM> cold oil in this order and a tempering process at <NUM> for <NUM> was performed.

The structural state of the test piece in the fourth comparative example was martensite. The surface hardness and the core hardness of the test piece were <NUM> HRC and <NUM> HRC, respectively. The result of the bending test was that the test piece was bent <NUM> under a load of <NUM> KN and broken.

Heat treatment conditions and evaluation results of the first to third examples and the first to fourth comparative examples described above are collectively shown in Tables <NUM> and <NUM>, respectively.

Next, a variation of the drill tools DT will be described.

<FIG> is a longitudinal cross-sectional view of a drill tube <NUM>, which is employed in place of the above-described rod <NUM>, taken along the axis thereof, illustrated as a configuration of a drill tool DT' that is a variation of the drill tools DT.

As illustrated in <FIG>, the drill tube <NUM> has a tube <NUM> that has a hollow cylindrical shape and is disposed at the middle and a male threaded portion <NUM> and a female threaded portion <NUM> that are joined to both ends of the tube <NUM>.

The drill tube <NUM> is a drill tube that is produced by, with respect to only the male threaded portion <NUM> and the female threaded portion <NUM>, employing the alloy steel for the present invention, which was described in the above-described first example, as a material and, in conjunction therewith, performing the heat treatment described in the first example. Note that the tube <NUM>, the male threaded portion <NUM>, and the female threaded portion <NUM> are integrated with one another by performing the heat treatment on the male threaded portion <NUM> and the female threaded portion <NUM> and, subsequently, friction welding the tube <NUM> with the male threaded portion <NUM> and the female threaded portion <NUM>.

Since this production method causes the internal structure of the drill tube <NUM> to be troostite with respect to only the threaded portions at both ends, on which stress is likely to concentrate, the bending rigidity of the drill tube <NUM> is improved. As such, when the drill tools DT' including the drill tube <NUM> are used for the rock drill <NUM> provided with high output power, damage to the drill tools DT' is prevented or suppressed even when wear of bearing members has progressed and bending stress acts on the drill tools DT'.

As the embodiment and the examples and comparative examples of the present invention have been described above with reference to the drawings and the tables as appropriate, the present invention enables a drill tool capable of coping with a rock drill provided with high output power and a method for producing the drill tool to be provided.

For example, regarding the rod <NUM>, as with the drill tube, after, instead of applying the present invention to all regions, employing the alloy steel for the present invention as a material of and also performing the heat treatment according to the present invention on only a threaded portion, on which stress is likely to concentrate, a straight body portion at the middle and the threaded portion may be joined and thereby integrated with each other.

Claim 1:
A production method for a drill tool, the production method being a method for producing a drill tool used for a rock drill, wherein
the drill tool is produced by employing, as a material of the drill tool, alloy steel composed of following chemical components: <NUM> to <NUM> wt% of C, <NUM> to <NUM> wt% of Si, <NUM> to <NUM> wt% of Mn, <NUM> to <NUM> wt% of Ni, <NUM> to <NUM> wt% of Cr, <NUM> to <NUM> wt% of Mo, and Fe and inevitable impurities as the balance and, performing carburizing-quenching and tempering on the material as heat treatment, including quenching after carburizing by means of oil cooling with cold oil, setting an oil cooling temperature at <NUM> to <NUM> and setting a tempering temperature at <NUM> to <NUM>.