JPH074637B2 - Hollow screw manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a hollow material having a spiral protrusion on its outer surface, that is, a hollow screw.

[Conventional technology]

For the purpose of increasing the bond strength of concrete and easily and mechanically connecting steel bars, a deformed steel bar having spiral knots formed on the surface of the steel bars is used. Such a deformed steel bar is a 2-roll type HV (horizontal-vertical) with several dozen stages.
It is manufactured by forming an uneven groove on the final pass in a continuous rolling mill for steel bars in an array and forming a spiral knot in the steel bar. That is, as shown in FIG. 10, two rolling rolls 21 and 2 each having an uneven groove having a predetermined lead surface at a predetermined pitch are engraved on the outer peripheral surface of the finishing round roll hole die.
According to 1, the spiral path is formed on the circumferential surface of the steel bar while finishing the oval shape (Fig. 10a) from the leader path on the upstream side of the finishing pass to the circular shape (Fig. 10b). .

By the way, a hollow screw formed by forming a spiral knot on the outer surface of the hollow bar material is known, and this hollow screw can flow a fluid such as air, water or oil. Moreover, since it has a spiral ridge (so-called screw shape) on the outer surface, it can be used as a screw member, and can also be used as a member for increasing the adhesion strength of concrete similarly to the above-mentioned deformed steel bar.

When manufacturing such a hollow screw by the above-mentioned method, unlike the steel bar, there is a hole in the center, so as shown in Fig. 11, when rolling with two rolling rolls, a leader pass is used. The pipe is crushed at and it cannot be molded in the finishing pass. Further, the protrusion formed on the outer surface by this method has a drawback that a sufficient height cannot be obtained.

In addition, as a second method, a method of inserting a core metal into a hollow material having a circular cross section and manufacturing the hollow material can be considered. The method that is the basis of this method is a hollow bar material with holes used for the purpose of flowing a fluid such as air, water, oil, that is, a hollow bar used as a drill rod for various structural members or oil well drill collars. This is a method for manufacturing a material, and a general method for manufacturing this hollow rod is as follows. That is, as shown in FIG. 12, the central portion of the billet 31 is perforated using a drill 32, and after inserting a manganese steel cored bar 33, the billet 31 is heated to a required temperature in a heating furnace 34 to form a hole-shaped roll. The hollow material is passed through a continuous steel bar rolling machine 35 consisting of several dozen stand rows having 35a, the hollow material is finished so that its outer circumference and wall thickness match the target values, and then the cored bar 33 is removed. Straightening is performed by a straightening machine 36 having two rolls on the top and bottom. Therefore, in the method as described above, a spiral roll is formed by using a rolling roll that has been subjected to groove-grooving of irregularities as shown in FIG. 10 in the finishing pass, and then the core metal is extracted to form a hollow screw. The method to be manufactured is the second manufacturing method.

Next, one of the inventors of the present application proposed in Japanese Patent Publication No. 61-11122 as an attempt to solve the drawbacks of the method for manufacturing a hollow rod which is the basis of the second manufacturing method. This method is shown in Fig. 13 (Fig. 12 (a) is a front view and Fig. 13 (b) is
As shown in FIG. 13 (a), a cross-sectional view taken along the line bb, and FIG. 13 (c) is a cross-sectional view taken along the line cc in FIG. 13 (b)). A hollow material 42 is rolled without using an inner surface regulating tool by using an inclined rolling machine having three (or four) cone type rolls 41 whose crossing angle and inclination angle can be adjusted according to the thickness. The outer diameter is reduced and the wall thickness is reduced to finish the target dimension (Fig. 13 (d)). This method is generally applied to hot working.
The third manufacturing method is a method of manufacturing a hollow screw by forming a spiral ridge on the outer circumference of a hollow material using a roll having a grooved outer peripheral surface in this method.

[Problems to be Solved by the Invention]

In the case of the second manufacturing method described above, rolling is performed with the core metal that is the inner surface regulation tool inserted, so the core metal itself also plastically deforms, the roundness of the product is poor, and uneven thickness is avoided. No, the core metal is disposable, so the tool cost is high, and the core metal extraction process is required. In addition, when a hollow screw having a thread processed is straightened by a straightening machine, there is a problem that the thread is crushed by the rolling of the roll.

Further, in the third manufacturing method, since the surface of the hollow material is hot formed by screw forming, it is necessary to remove the bend by straightening after forming to straighten it, and this straightening causes a problem that the screw thread is crushed. .

The present invention has been made in view of such circumstances, and by manufacturing a screw thread by cold rolling using a hollow metal tube as a material, a hollow screw with high dimensional accuracy can be manufactured by a simple manufacturing process. It is an object of the present invention to provide a method for manufacturing a hollow screw that can be manufactured.

[Means for solving problems]

In the method for manufacturing a hollow screw according to the first aspect of the invention, a plurality of annular grooves for shaping the spiral protrusion are formed in the circumferential direction of the outer peripheral surface so that the pitch thereof gradually becomes wider from the inlet side to the outlet side. Form rolls 3 at equal intervals around the pass line
A method for producing a hollow screw by cold-rolling a hollow metal tube by means of an intersecting type inclined rolling machine having four to four pieces, the wall thickness (t) of the metal tube, the metal tube (D), the maximum outer diameter of the hollow screw to be manufactured (thread diameter; D ₁ ) and the minimum outer diameter of the hollow screw to be manufactured (thread root diameter; D ₂ ) are set as shown below. It is characterized by

t / D ≧ 0.15 D ₂ / D ₁ ≧ 0.8 D ₂ <D <D ₁ 0.23 (t / D) +0.94 <D ₁ /D<0.23 (t / D) +0.99 The second invention, hollow The screw manufacturing method is such that a pair of rolling rolls are equally arranged with a pass line interposed therebetween, and a pair of guide shoes are equally arranged with a pass line interposed between the rolling rolls. A plurality of annular grooves are formed in the circumferential direction so that the pitch of the spiral ridge is gradually widened from the entrance side to the exit side, and the spiral ridge to be shaped is formed on the surface of the guide shoe. A method for producing a hollow screw by cold-rolling a hollow metal with an intersecting type inclined rolling mill in which a plurality of aligned grooves are formed, comprising: a wall thickness (t) of the metal pipe; minimum hollow screw being and manufacturing; outer diameter of the metal tube (D), the maximum outer diameter (D ₁ crest diameter) of the hollow screw to be manufactured And sets the relationship shown below; diameter (D ₂ screw core diameter).

t / D ≧ 0.15 D ₂ / D ₁ ≧ 0.8 D ₂ <D <D ₁ 0.23 (t / D) +0.94 <D ₁ /D<0.23 (t / D) +0.99 [Action] 1st, 1st In the second aspect of the invention, a plurality of annular grooves are used so that the pitch of the annular grooves is gradually widened from the inlet side to the outlet side in the circumferential direction of the outer peripheral surface. Wall thickness t, its outer diameter D, maximum outer diameter (thread diameter) D _{1 of the} hollow screw to be manufactured, and its minimum outer diameter (thread root diameter) D ₂
T / D ≧ 0.15, D ₂ / D ₁ ≧ 0.8, D ₂ <D <D ₁ and 0.23 (t / D) +
The relationship of 0.94 <D ₁ / D <0.23 (t / D) + 0.99 is set, and cold rolling is performed, so no core metal is used, and the life of the cold tool life can be extended. It becomes possible to efficiently manufacture a hollow screw having no structure.

〔Example〕

The present invention will be specifically described below with reference to the drawings. FIG. 1 is a front view (showing a groove omitted) showing a first embodiment of the present invention, that is, an embodiment in which three rolling rolls are used, and FIG. 2 is a line II-II in FIG. It is a partial enlarged side view by
In the figure, 4 indicates a metal tube having a circular cross section, and 5 indicates a hollow screw to be manufactured. The metal tube 4 is transferred in the axial direction and cold-rolled by the rolling rolls 1, 2, and 3 which constitute a set of three rolling mills provided at the rolling position of the pass line.

The rolling rolls 1, 2 and 3 have the same cone half angles α ₁ and α ₂ , respectively,
It is provided on the exit side (however, α ₂ is not shown), and its axis is inclined so that the shaft ends on the same side face the same side in the circumferential direction (the angle β of this axis with respect to the pass line is called the inclination angle). ) Inclination so that the shaft end on the same side approaches or separates toward the pass line side (The angle γ of this axis with respect to the pass line is called the crossing angle. Is defined as γ; the direction of separation on the outgoing side is defined as positive).

And, a portion where the distance between the outer peripheral surface of the rolling rolls 1, 2, 3 and the pass line is smaller than the radius of the outer periphery of the metal pipe 4 passing therethrough, that is, the outer periphery of the rolling portion has a plurality of annular grooves 10.
For example, 5 to 7 strips are cut in the circumferential direction at appropriate intervals in the axial direction. The positions, intervals, widths, and depths of the grooves 10 are different among the rolls, as partially shown in FIG. 2, and the intervals of the respective rolling rolls are also different in the axial direction.

The positions and intervals of the grooves are determined according to the heights and intervals of the threads to be formed, and the α, β, γ, etc. of the inclined rolling rolls related thereto are determined. The positions of the grooves are different between the rolling rolls.For each rolling roll, the interval (pitch) is gradually widened from the metal pipe inlet side to the metal pipe outlet side according to the stretching amount, as described later. The screw thread from one roll is guided to the groove of the next roll and sequentially formed. The width and depth of the groove are substantially the same between the rolling rolls. The groove depth of each roll is
It is appropriately changed from the inlet side to the outlet side so that a desired thread height can be obtained at the outlet side end.

The manufacturing process of the hollow screw by the rolling mill thus configured will be described with reference to FIG. 3 showing the process step by step.

First, the metal tube 4 as a material is selected. Metal tube (outer diameter
It is desirable that D, wall thickness t) satisfy the conditions of the following formulas (1) to (3), and that the screw shape of the hollow screw 5 to be manufactured satisfies the following formula (4). However, D ₁ is the thread diameter (maximum outer diameter) of the hollow screw 5 to be manufactured, and D ₂ is the thread root diameter (minimum outer diameter) of the hollow screw 5 to be manufactured.

t / D ≧ 0.15… (1) D ₂ <D <D ₁ … (2) 0.23 (t / D) ＋0.94 <D ₁ /D<0.23(t/D)＋0.99…(3) 0.8 ≦ D ₂ / D ₁ <1.0 (4) Such a metal tube 4 is transferred to an inclined rolling mill having a rolling roll as described above. In FIG. 3, the arrow indicates a metal tube 4.
Indicates the direction of load applied to. When the metal tube 4 {see Fig. 3 ◎} is started to be rolled by the inclined rolling mill, the metal tube 4 is sequentially bitten into the rolling rolls 1, 2, and 3 and thereafter, the metal tube 4 is circumferentially moved by 3
It is rolled at a point {see Fig. 3} and rotates while rotating around its axis. For this reason, the subsequent rolling is performed in a spiral manner, and the rolled metal tube 4 advances to the roll exit side.

And sequential rolling with three rolls {Fig. 3,
The ridge between the valleys pressed by the reference} gradually rises. During this period, the meat of the valley changes into swelling to the crest and extension in the axial direction, and the spacing between the threads slightly widens. In this embodiment, the roll is designed so that the valleys and crests of the tool that contribute to the next rolling come to the threads and troughs with wide intervals, so the threads are not crushed during rolling, Moreover, the threads can be formed at a predetermined pitch.

Next, numerical limitation in the present invention, that is, (1) to
The contents of equation (4) will be described.

In the third hollow screw manufacturing method according to the present invention, the t / D of the metal tube is set to 0.15 or more. When a thin-walled pipe with a t / D of less than 0.15 is used as the metal pipe, the pipe will be squared as shown in Fig. 4, and the groove processing on the surface will extend to the inner surface. As shown in FIG. 5, the corrugated tube shape is formed, and the thread portion is less likely to be lifted up, which makes it difficult to form the thread portion. On the other hand, when t / D is 0.15 or more,
When a portion that should be a valley on the rolling-in side is rolled, the portion between the depressed valleys is likely to bulge in the radial direction of the metal pipe, and in the latter half of rolling, this bulged portion gradually increases. The shape of the protrusion may be finished while molding. Since the metal pipe is also stretched in the axial direction during this processing, the pitch of the annular grooves formed on the outer peripheral surface of the rolling roll is gradually widened from the metal pipe inlet side to the metal outlet side as described above. is there. It is desirable that the pitch of the exit finish be substantially constant and the dimensional accuracy be high.

It is not necessary to specify the upper limit of t / D. For example, t / D = 0.5
In the case of, the material is a solid metal rod, but at this time, a screw (however, a solid screw) can be manufactured.
Of course, in this case as well, it is desirable to process the outer diameter bulge based on the equation (3).

Further, in the present invention, it is desirable that the thick-walled pipe is rolled so that the thread portion is expanded more than the raw metal pipe. The working method of the present invention is not a hot working in which the outer diameter and the wall thickness can be reduced and finished to a required dimension as in the third manufacturing method described in the prior art, but cold rolling can be used. Therefore, it is necessary to complete the molding within the range of the processing rate (reduction rate) in the state where the thread ridges are raised by the amount corresponding to the pressing of the thread roots. If rolling down beyond this range, for example, make the thread diameter much smaller than the outer diameter of the metal pipe (D ₁ <
D) In the case of processing, in addition to cracking of the material, the surface pressure may be increased to deteriorate the surface texture and further shorten the tool life.

By the way, the amount of protrusion of the crest portion, that is, the relationship between the outer diameter of the metal tube before rolling and the thread diameter after rolling changes according to t / D of the metal tube. That is, as the thickness of t / D becomes thicker, the thickness of the material near the axial center is constrained, so the material does not stretch in the axial direction, and the processing strain in the thread trough does not become elongation strain in the axial direction, but rather peaks. The bulging in the radial direction of the part is apt to occur. Therefore t /
The larger D is, the easier the mountain portion is to swell and the smaller the axial extension is. As a result of examining the relationship between t / D and the swelling ratio D ₁ / D, the relationship between the two was set as in the above equation (3). By the way, the smaller the t / D is, the smaller the swelling is. As can be understood from the above formula (3), when t / D is small, there is a range in which thread forming is possible even if D ₁ is slightly smaller than D. .

Further, the height of the thread to be molded is 0.1 times or less (D ₂ / D ₁ ≧ 0.8) the outer diameter of the manufactured hollow screw. This value is due to the fact that when a thread with a higher height is formed by cold working, cracking occurs even when the material is ordinary steel or low alloy steel due to work hardening.

In this way, by predicting the bulge of the outer diameter, the wall thickness and outer diameter of the metal tube are set, and the thread height of the hollow screw to be manufactured is set, thereby preventing the adverse effects caused by cold rolling. be able to.

The formula (3) is a formula obtained by many experiments, and D ₁ <D shown in the formula defines the amount by which the formed thread diameter D ₁ expands with respect to the outer diameter D of the raw pipe.

The lower limit condition of the equation (3) is set to 0.23 (t / D) + 0.94 because the reduction is applied to the metal pipe 4 of this t / D so that the thread diameter D ₁ is further reduced. , The metal pushed into the disc flows to the peaks and rises, not only staying in the metal flow of the surface layer but also deforming to the inner surface side of the metal tube 4, the roll load suddenly increases, and the surface pressure applied to the roll disc increases. Is increased, the roll life is shortened, and the surface texture of the material is deteriorated.

When the deformation extends to the inner surface, there also arises a problem that the cornering as shown in FIG. 4 easily occurs.

On the other hand, the upper limit condition is set to 0.23 (t / D) + 0.99. How to select the shape of the roll disk when rib processing is performed on such a t / D metal tube without an inner surface control tool Even so, he found that it was difficult to inflate the threads any further, and decided. FIG. 9 shows the above relationship for a tube having an outer diameter of 30 mm.

In Fig. 9, the horizontal axis is D ₁ /D-0.23 (t / D), and the vertical axis is roll reaction force (TON).
It is a graph which shows the relationship when t / D is set to 15%, 25%, and 35%, respectively. As is apparent from this graph, the 0.94 as the lower limit of D ₁ /D-0.23, also without the roll reaction force becomes excessive by taking 0.985 as an upper limit value, moreover can be rolled in lean range and Become.

The method of cold rolling a metal tube to manufacture a hollow screw using an inclined rolling mill composed of four rolling rolls is substantially the same as that of the above-mentioned three, so here The description is omitted.

Next, a second embodiment of the present invention, that is, an example of manufacturing a hollow screw by using two rolling rolls will be described. FIG. 6 is a schematic front view showing the implementation state of the second embodiment (grooves are omitted), FIG. 7 is an enlarged side view taken along line VII-VII of FIG. 6, and FIG. It is a perspective view of two guide shoes 6 and 7 used in an example.

The inclined rolling mill in the second embodiment has two rolling rolls 1, 2 arranged at two equally spaced positions around the pass line, as in the case of a normal Mannesmann type seamless pipe facility (piercer).
And the guide shoes 6 and 7 arranged between them, different from the first embodiment, a set of two guide shoes is required. However, since a cored bar is not required, there is no plug or mandrel. An annular groove 10 is cut on the outer circumference of the rolling rolls 1 and 2 in accordance with the height and spacing of the formed threads. Further, on the surfaces of the guide bushes 6, 7, there are formed grooves 11 aligned with the spiral traveling direction of the screw threads that are gradually formed in the process of rolling the metal tube 4,
The thread from the previous rolling roll does not get crushed when it enters the groove of the adjacent guide shoe, but enters the groove of the next rolling roll.

In the second embodiment as well, as in the first embodiment described above, since the above formulas (1) to (4) are adopted as the setting conditions, a hollow screw having high dimensional accuracy is cold rolled. It can be manufactured.

By the way, when an inclined rolling mill is composed of five or more rolling rolls, not only is the equipment complicated and expensive, but also
The ratio of the roll diameter to the material set diameter cannot be increased due to the condition that adjacent rolls contact each other. Therefore, since the roll shaft diameter becomes smaller than the material diameter, the shaft strength becomes small and sufficient rigidity cannot be obtained, and the roll peripheral speed becomes small and sufficient production efficiency cannot be obtained. Therefore, in practice, the number of rolling rolls is set to 2 to 4.

Here, a comparison between the first and second embodiments will be described. When the number of rolls increases, the roll diameter cannot be increased relative to the material diameter, so the roll diameter can be increased in the second embodiment, and a higher production rate can be obtained. However, in the second embodiment, since two guide shoes are required, frictional resistance is generated between the guide shoes and the metal pipe, so that the surface is covered with an eaves or a sharp ridge, When forming a ridge having a short pitch, there is a drawback that the ridge is likely to be crushed. Since each method has advantages and disadvantages as described above, a manufacturing method according to the shape and pitch of the hollow screw to be manufactured may be selected and used.

As described above, since the present invention is finished by cold working, it has various advantages. First, as in hot working, there is no deterioration in outer diameter accuracy and pitch accuracy due to uneven material temperature, etc., and extremely high dimensional accuracy can be obtained. Further, since it is cold working, bending hardly occurs during rolling, and a product with high straightness can be manufactured.

Further, in the method of the present invention, by the work hardening, for example, S45C
In the case of using the medium carbon steel as described above, it is possible to achieve the same strength level as when the temper treatment is applied. When tempering is performed after hot working, the steps of hot working, quenching, tempering, and straightening are performed. Of these steps, the steps of quenching, tempering, and straightening are performed in the present invention. It can be omitted. Thus, in the present invention, even if medium carbon steel such as S45C is used without using low alloy steel, for example, a shaft member having axial strength having a tensile strength of about 70 kgf / mm ² can be easily manufactured. be able to.

Next, an example in which a hollow screw is manufactured using the manufacturing method of the present invention will be described with specific numerical values.

[Numerical Example 1] Outer diameter: 31.8 mmφ, wall thickness: 8 mm, and metal pipe of S45C material is cold-rolled by 3 rolls (first example), so that the screw thread interval: 12.7 mm, screw thread diameter: 32.4 mmφ , We manufactured a hollow screw with a screw root diameter of 28.4 mm and an inner diameter of 15 mm. The manufacturing conditions are: rolling roll inclination angle β: 7.5 °, rolling roll crossing angle γ: 3 °,
Rolling roll diameter: 160 mmφ, Rolling roll material: SKD11, Rolling roll speed: 80 rpm, Rolling entrance cone half angle α ₁ : 5.5 °, Rolling exit cone half angle α ₂ : 3 °, Groove spacing on inlet side: 11.4 mm, Exit Groove spacing on the side: 12.7 mm. As a result, outer diameter accuracy: ± 0.0
Hollow screw with 3mm, pitch accuracy: ± 0.2%, straightness: 0.5mm / m is manufactured, and dimensional accuracy and straightness are good. The results of investigation of the mechanical properties of the hollow screw manufactured in [Numerical Example 1] are shown in Table 1 below.

[Numerical Example 2] A hollow screw similar to that of [Numerical Example 1] was manufactured by cold rolling (second embodiment) using an inclined rolling mill composed of two rolling rolls and a guide shoe. The manufacturing conditions were the same as in [Numerical Example 1] except that the rolling roll diameter was 400 mmφ. As a result, a hollow screw could be manufactured with good dimensional accuracy and straightness. Note that the rolling speed in [Numerical example 1] is
In contrast to 0.08 m / sec, in [Numerical example 2], the rolling speed was 0.22 m / sec, which was a great improvement.

[Numerical Example 3] Using the same metal tube as that used in [Numerical Example 1] as a material, a thread rolling diameter of 31.5 was obtained by using an inclined rolling mill composed of three rolling rolls.
A hollow screw was manufactured by setting it to be mmφ. As a result, a hollow screw having a rough surface was produced. In addition, the material temperature increased due to the generation of processing heat, and the rolling power was double that of [Numerical example 1].

[Numerical Example 4] Using the same metal tube as that used in [Numerical Example 1] as a material, an inclined rolling mill composed of three rolling rolls was used, and the screw root diameter was 29.5.
A hollow screw was manufactured by setting it to be mmφ. As a result, the work hardening was remarkable, and the elongation of the material in the axial direction was large, and the material cracked.

[Numerical Example 5] Outer diameter: 31.8 mmφ, wall thickness: 12 mm, and a metal tube of S45C material is cold-rolled by 3 rolls (first example), so that the thread pitch is 12.7 mm, the thread diameter is 33.4 mmφ , Hollow screw with screw root diameter: 29.4mmφ and inner diameter 7.5mmφ was manufactured. The manufacturing conditions are: rolling roll inclination angle β: 7.3 °, rolling roll crossing angle γ: 3
°, Rolling roll diameter: 160mmφ, Rolling roll material: SKD11, Rolling roll speed: 80rpm, Rolling entrance cone half angle α ₁ : 5.5 °, Rolling exit cone half angle α ₂ : 3 °, Groove spacing on inlet side: 11.8mm The groove spacing on the outlet side is 12.7 mm. As a result, dimensional accuracy,
A hollow screw was produced which had good straightness.

〔The invention's effect〕

As described above in detail, in the case of the present invention, an inclined rolling mill provided with two to four rolling rolls having an annular groove formed on the outer peripheral surface thereof is used, and the wall thickness t of the metal pipe and the outside of the metal pipe are Since the diameter D, the maximum outer diameter (thread diameter) D ₁ and the minimum outer diameter (thread root diameter) D ₂ of the hollow screw to be manufactured are maintained in a predetermined relationship and cold rolling is performed, dimensional accuracy and straightness are improved. It is possible to manufacture a hollow screw having an excellent degree.

At this time, by using a metal tube with an appropriate thickness as the material and setting the height of the thread to be formed to an appropriate value, cracks on the inner surface and swelling due to cold rolling can be completely eliminated. Therefore, there is no problem even if cold rolling is used.

Further, in the present invention, since the core metal is not required and the process is not complicated, the present invention has excellent effects such that a hollow screw can be easily manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a front view showing an implementation state of a first embodiment of the present invention, FIG. 2 is a side view showing a partially enlarged cross section taken along line II-II of FIG. 1, and FIG. Illustration of rolling content of the invention,
4 and 5 are explanatory views of the contents of numerical limitation of the present invention, FIG.
FIG. 7 is a front view showing an implementation state of the second embodiment of the present invention, FIG. 7 is a side view showing a partially enlarged cross section taken along line VII-VII of FIG. 6, and FIG. Fig. 9 is a perspective view, Fig. 9 is a graph showing the lower limit condition and the upper limit condition for a pipe having an outer diameter of 30 mm, and Fig. 10 to Fig. 13 are the execution state of the conventional manufacturing method or the conventional manufacturing method. It is a schematic diagram which shows an apparatus. 1,2,3 ... rolling rolls, 4 ... metal tubes, 5 ... hollow screws,
6, 7 ... Guide shoe, 10 ... Annular groove, 11 ... Groove

Claims (2)

[Claims] 1. A pass line comprising a conical rolling roll having a plurality of annular grooves formed in the circumferential direction of the outer peripheral surface, the pitch of which gradually increases from the entrance side to the exit side. A method for producing a hollow screw by cold rolling a hollow metal tube by means of a cross-type inclined rolling mill having 3 to 4 pieces arranged at equal intervals around the wall thickness of the metal tube ( t), the outer diameter (D) of the metal pipe, the maximum outer diameter (thread diameter; D ₁ ) of the hollow screw to be manufactured, and the minimum outer diameter (thread root diameter; D ₂ ) of the hollow screw to be manufactured are as follows. A method for manufacturing a hollow screw, characterized in that the relationship shown in (4) is set. t / D ≧ 0.15 D ₂ / D ₁ ≧ 0.8 D ₂ <D <D ₁ 0.23 (t / D) ＋0.94 <D ₁ /D<0.23 (t / D) +0.99 2. A structure in which a pair of rolling rolls are equally arranged with a pass line interposed therebetween, and a pair of guide shoes are equally arranged with a pass line interposed between the rolling rolls. A plurality of annular grooves are formed in the circumferential direction so that the pitch of the spiral ridge is gradually widened from the entrance side to the exit side, and the spiral ridge to be shaped is formed on the surface of the guide shoe. A method for producing a hollow screw by cold-rolling a hollow metal tube with an intersecting type inclined rolling machine having a plurality of aligned grooves, comprising: a wall thickness (t) of the metal tube; The following shows the relationship between the outer diameter (D) of the metal pipe, the maximum outer diameter of the hollow screw to be manufactured (thread diameter; D ₁ ) and the minimum outer diameter of the hollow screw to be manufactured (thread root diameter; D ₂ ). A method for manufacturing a hollow screw, characterized in that t / D ≧ 0.15 D ₂ / D ₁ ≧ 0.8 D ₂ <D <D ₁ 0.23 (t / D) ＋0.94 <D ₁ /D<0.23 (t / D) +0.99