JPH04312207A - Manufacture of drill screw - Google Patents

Abstract

PURPOSE:To improve dimensional accuracy by forming a drill part on a shank tip by forging or the like, forming twisting of the shank, realizing quenching and tempering by cementing or the like, immersing the shank in a melting bath of zinc-tin alloy or the like, and shaking off and removing the remainder of the melted alloy affixed on the immersed drill screw after lifting it out of the melting bath. CONSTITUTION:A steel drill screw 10 is formed by a threaded shank part 11 extending continuously from a head part and a drill part 14 in an integrated manner through cold forging by means of a pair of dies. And a pair of longitudinal grooves 15 (right and left), a pair of inclined advancing end surfaces 16, a chizel edge 18 and a tip blade 20 are formed. The drill screw 10 is heated and cemented(?) by means of a cementation furnace, then put into the oil to realize quenching. After tempering, alkali washing, pickling and water rinsing are realized, and flux coating of ammonium chloride or the like is applied, then the drill screw is immersed in a melting bath of zinc-tin alloy. The drill screw is lifted out of the melting bath, then, excessive melting alloy affixed on the immersed drill screw is shaken off and removed by means of a centrifugal device.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method of manufacturing a drill screw in which a drill portion for drilling a pilot hole in a fastened object is integrally formed at the tip of the screw. be.

0002

[Prior Art] The present applicant has discovered that in order to improve the drilling performance and screwing performance of this type of drill screw, it is possible to form a zinc-iron alloy layer on the surface of the drill part and thread. Focusing on the fact that it is extremely effective, the earlier patent applications (Japanese Patent Application No. 63-233328, Japanese Patent Application Laid-open No. 2-8
No. 0805), a drill part is formed at the tip of the shank by forging or cutting, a thread is formed on the shank, and then a hardening process such as carburizing or carbonitriding is performed, followed by a tempering process, and then , a zinc film is formed on at least the surfaces of the threads and the drilled part by zinc electroplating or immersion in a molten zinc bath, and then heated to coat the surfaces of the threads and the drilled part with zinc-
We proposed a method for manufacturing drill screws that forms a layer of iron-based alloy.

[0003]The drill screw manufactured by this manufacturing method can form a zinc-iron alloy layer on the thread and the surface of the drill part, so that the time required for the drill part to penetrate the plate to be fastened is shortened. (Drilling time) can be significantly shortened, and the screwing torque to the fastened plate can also be significantly reduced.

0004

[Problems to be Solved by the Invention] However, in the method for manufacturing a drill screw according to this prior application, at least the threads and the surface of the drill part of the drill screw are coated with zinc by electroplating with zinc or by immersing it in a molten zinc bath. A zinc-iron alloy layer is formed on the surface of the screw thread and the drill part by heating after forming the film, and the process includes the step of forming the zinc film on the surface of the thread and the drill part, and the subsequent steps. This requires a heating process.

In addition, since the zinc coating is oxidized by the heating, a step is required to remove the zinc oxide, which significantly increases manufacturing costs. In addition, in order to prevent the generation of oxides during the heating, it is recommended to perform the heating in an inert gas atmosphere, which will significantly reduce productivity and further increase manufacturing costs. Become.

[0006] In particular, on the surface of the thread and the drill part,
After quenching and tempering, when forming a zinc film by zinc electroplating, during the zinc electroplating, the threads and drilled portions are coated with:
So-called hydrogen embrittlement occurs, in which hydrogen penetrates and becomes brittle. Although this hydrogen embrittlement can be eliminated to some extent by the subsequent heating process, it cannot be completely eliminated, and therefore, the quenching process Also, during the tempering process, there was a problem in that the hardness of the drill part could not be made sufficiently high.

[0007] Furthermore, on the surface of the thread and the drill part,
After quenching and tempering, when forming a zinc film by immersing in a molten zinc bath, the temperature of the molten zinc bath is approximately 500°C. Since the temperature (tempering temperature) is considerably higher than about 360°C, immersion in the molten zinc bath not only causes the hardness of the drill part to be lower than a predetermined value, but also causes damage to the threads and the surface of the drill part. Since the thickness of the zinc coating that is formed becomes thicker overall and also thicker in some areas, there is a problem in that the dimensional accuracy of each part of the drill screw is significantly reduced.

The technical object of the present invention is to provide a method for manufacturing a drill screw that solves all of these problems at once.

[0009]

[Means for Solving the Problems] In order to achieve this technical object, the present invention forms a drill part at the tip of the shank by forging or cutting, forms a thread on the shank, and then carburizes or carburizes the shank. In a method for manufacturing a drill screw in which a hardening treatment such as nitriding is performed, and then a tempering treatment is performed, the screw is immersed in a molten bath of zinc-tin alloy or zinc-aluminum alloy, and then pulled out. , it was decided to perform centrifugal shaking off of the molten alloy.

0010

[Operation] By immersing the drill screw that has been hardened and tempered in a molten bath of zinc-tin alloy or zinc-aluminum alloy, the entire surface of the drill screw is coated with zinc-tin alloy. It is possible to form an alloy film or an alloy film of zinc-aluminum alloy, and
Between this alloy film and the surface of the thread and drill part,
A zinc/tin-iron alloy layer or a zinc/aluminum-iron alloy layer can be formed.

In this case, the melting temperature of the zinc-tin alloy or zinc-aluminum alloy is much lower than the temperature of the zinc molten bath and lower than the heating temperature (tempering temperature) during the tempering treatment. Therefore, the hardness of the drill part does not decrease by immersion in the molten bath of zinc and tin alloy or zinc and aluminum alloy. Because it is only necessary to do this, hydrogen embrittlement will not occur in drill screws that have been quenched and tempered.

[0012] After the zinc/tin alloy or zinc/aluminum alloy is withdrawn from the molten bath, the molten alloy is shaken off to remove excess of the zinc/tin alloy or zinc/aluminum alloy on the surface of the drill screw. This allows the thickness of the alloy film formed on the surface of the drill screw to be uniformly thin over the entire surface.

[0013]

Therefore, according to the present invention, when manufacturing a drill screw that has high drilling performance due to the presence of a zinc-iron alloy layer, it is possible to remove the zinc coating after quenching and tempering as in the prior invention. Since there is no need for the steps of heat treatment after formation and further removal of oxides, the manufacturing method is simple and a drill screw with high drilling performance can be provided at a low cost.

Moreover, according to the present invention, hydrogen embrittlement does not occur during the manufacturing process, and the quenching hardness of the drill part can be increased, so the drill performance can be further improved. Since the thickness of the alloy film on the surface of the drill screw can be uniformly thinned over the entire surface, the dimensional accuracy of each part of the drill screw does not deteriorate, and the appearance becomes beautiful, increasing the product value. It has the effect of improving

[0015]

Embodiments Hereinafter, a case will be described in which an embodiment of the present invention is applied to a steel drill screw of the form shown in FIGS. 1 to 4. Steel drill screw 10 shown in FIGS. 1 to 4
For example, a drill part 14 integrated with a shank part 11 with a thread 13 extending integrally from a head part 12 is manufactured by Japanese Patent Publication No. 48
As disclosed in No. 13139, it is formed by cold forging by sandwiching a pair of left and right dies.

However, in this figure, reference numeral 15 indicates a pair of left and right vertical grooves provided in the drill portion 14, and reference numeral 16 indicates a pair of vertical grooves provided on the drill portion 14.
A pair of inclined entry end faces 18 are formed in the two land parts 17 between the longitudinal grooves 15 so as to extend obliquely outward from the free end of the drill part 14 toward the shank 11. A chisel edge 20 is formed by intersecting the end surfaces 16 at the free end of the drill part 14 at the intersection of one groove surface 19 constituting both the vertical grooves 15 and the both entry end surfaces 16. It is a cutting edge at the tip.

The diameter D of the cold-forged screw is 4 m.
m size drill screw 10, ■. After heating and carburizing in a carburizing furnace, quenching is performed by rapidly cooling by pouring into oil, followed by tempering by heating to a temperature of about 360° C. for about 60 minutes and cooling in air. ■． Next, the drill screw 10 is subjected to alkali degreasing treatment, pickling treatment, and water washing treatment. ■． Next, after applying flux such as ammonium chloride to the surface of the drill screw 10, 40% zinc
・Approximately 1
Soak for just a minute. ■． Next, after the drill screw 10 is pulled out of the molten bath of the zinc-tin alloy, it is immediately placed in a bucket in a centrifuge (before the molten alloy has solidified), and centrifugal force caused by rotation is applied to the drill screw 10.
The excess molten alloy on the surface of the drill screw 10 is shaken off.

A drill screw "A" according to the present invention having a screw thread diameter D of 4 mm manufactured by the method described above and a drill of the same size and shape that have just been subjected to the quenching and tempering treatments described above. Screw "B" and a drill screw "C" of the same size and shape, which had been subjected to the above-mentioned quenching and tempering treatment and then electroplated with zinc, were rotated at 2000 revolutions per minute. When screwing into a 3.2 mm thick iron plate with a pressing force of 18.1 kg at a rotating speed of ) was measured, and the average value for each 10 pieces was determined, and the results were as shown in FIG.

That is, according to the method of the present invention, a zinc-tin-iron alloy layer can be formed on the surface of the drill part 14 by immersing it in the molten bath of the zinc-tin alloy. The time required to drill through the hole (drill time) can be significantly reduced. Note that the above example shows the case of immersion in a molten bath of zinc-tin alloy, but when zinc is alloyed with aluminum,
Since its melting point is lower than the tempering temperature, the present invention is not limited to using a zinc-tin alloy, but can also use a zinc-aluminum alloy.

[Brief explanation of drawings]

FIG. 1 is a front view of a drill screw.

FIG. 2 is a bottom view of FIG. 1;

FIG. 3 is a side view taken along line III-III in FIG. 2;

FIG. 4 is a side view taken along line IV-IV in FIG. 3;

FIG. 5 is a diagram showing measured values of drilling time for a drill screw.

[Explanation of symbols]

10 Drill screw 11 Shank 12 Head 13　　　　　　　　　　　Screw thread 14 Drill part

Claims (1)

[Claims] Claim 1: A drill portion is formed at the tip of the shank by forging or cutting, a thread is formed on the shank, and then,
In a method for manufacturing a drill screw in which a tempering treatment is performed after a quenching treatment such as carburizing or carbonitriding,
After the above tempering treatment, zinc/tin alloy or zinc/tin alloy
After being immersed in a molten aluminum alloy bath, it is pulled out and
A method for manufacturing a drill screw, characterized in that the molten alloy is shaken off.