JPS63268528A - Production of screw - Google Patents

Abstract

PURPOSE:To enlarge the dimensional range capable of production and to reduce a production cost by providing the conical roll having the annular groove whose interval is gradually widened by specified number on a cross-interaction slanted rolling mill and performing hot drawing rolling on a circular sectional metal stock. CONSTITUTION:Three-four pieces of conical rolling rolls 1-3 are formed as the same conical half angle alpha to compose a cross-interaction slanted rolling mill. The rolling rolls 1-3 from the same inclination and cross axes angle and are arranged at equal intervals for a pass line. Plural annular grooves with intervals gradually widened are formed on the rolling part in order to form a spiral projection bar toward the outlet side from the inlet side on each roll. When the circular sectional metal stock 4 having the outer diameter D1 larger than that DF of a product is subjected to warm rolling by this slanted rolling mill, the product dimensional shape can freely be set. Due to the mechanism being simple, the equipment cost can be reduced. And the dimensional range capable of production is enlarged and the production cost is reduced as well.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing screws using an inclined rolling mill, and specifically relates to a method for manufacturing screws using an inclined rolling mill, and specifically, a method for manufacturing screws using an inclined rolling mill. The present invention also relates to a method of manufacturing screws such as spiral finned rods.

[Prior art]

Screw feeders use spiral finned rods (hereinafter referred to as screw shafts) in which the fins and the fin bottom base material are integrated, and the method of manufacturing this screw shaft is mainly from solid round rods. A method of cutting out by machining is used. However, in this case, the material yield is k
Moreover, since it is difficult to increase the machining speed when machining the screw shape, there is a problem that the machining cost is extremely high.

As a method other than this, application of a thread rolling method can be considered. This thread rolling method is a method in which threads provided on the surface of a rolling die are transferred to the surface of a cylindrical body of a raw material.

However, with this method, it is only possible to process so-called thread-shaped fins with a short pitch and in which the peaks and valleys of the fins are arranged alternately.For example, a fin with a flat groove bottom between the fins It was impossible to apply this method to the production of screw feeders with long pitches and tall, thick fins.

Further, as a second method, there is a rolling method used for manufacturing heat exchanger tubes such as heat exchangers. In this rolling method, as shown in FIG. 9, the metal tube 34 is cold (or hot) rolled using three rolling rolls 31, 32, and 33 arranged around the pass line of the hollow metal tube 34. This is a method of rolling.

The shapes of the rolling rolls 31, 32, and 33 are all the same. For example, as shown in FIG. 10 (cross-sectional view taken along the line X-X in FIG. 9), a thin disc-shaped outer peripheral portion is attached to one shaft. Several dozen rolls with a pattern-like thin cross-sectional shape are mounted so that they are coaxial.

In the case of the above method using such rolling rolls 31, 32, 33, as shown in FIG.
. . . with a reduction blade in the wall thickness direction (see Fig. 11 ■), and then with a disk-shaped roll to form grooves 35a, 3.
5b... is rolled down, and the direction perpendicular to the groove surface at that time (
Processing is performed while increasing the depth by the force acting in the direction of the arrow (see Fig. 11), and the amount of metal displaced by this groove processing is transferred to the disk shape of the rolling roll. The fins 35 are formed by moving the rolls into the gaps between the rolls. During this time, there is almost no stretching in the longitudinal direction of the tube axis, and it is pushed away by the disk-shaped rolls, so the spiral fin tube has a wide fin spacing and has a surface parallel to the inner surface of the tube at the bottom of the fin between the fins. (hereinafter referred to as a finned tube), the finned tube that can be manufactured using this method is, for example, a fin groove bottom diameter of 28 mm.
11+1φ, fin height 8.5 fins, fin thickness 0.
It has 5 fins and the fin spacing is as short as 3.5 fins, and the fin height and thickness are 15 fl each only when the material is soft metal such as copper or aluminum.
, about 0.2 to 0.5 m, and as the fin height increases, the thickness decreases, and as in the case of thread rolling described above, there were many restrictions on product dimensions.

There is a third method proposed by the present inventors as a method that can solve the problems associated with these rolling methods and dramatically expand the range of dimensions that can be manufactured. 124
No. 203). In this third method, a plurality of annular grooves are cut on the outer circumferential surface of the rolling part of the inclined rolling roll so that the intervals gradually increase from the material input side to the material output side. This method produces a finned tube with high fins and long fin spacing by hot elongating a hollow metal tube with a regulating tool inserted inside. More specifically, Figs. 12 and 13 (x in Fig. 12)
As shown in the cross-sectional view taken along the line m-' Using a cross-type inclined rolling mill in which rolling rolls 41, 42, and 43 are arranged facing around the pass line (a model with four rolling rolls may be used), an inner surface regulating tool, in the illustrated example, a mandrel bar 46, is used. In this method, a hollow metal tube 44 inserted therein is hot stretched and rolled to produce a metal tube with spiral fins having a fin bottom parallel to the inner surface of the tube.

In this method, since the metal tube can be hot-rolled at a high reduction rate using a cross-type inclined rolling mill, elongation rolling is performed using this method, and each position of the rolling part of the rolling rolls is adjusted according to the elongation length. By cutting a groove in the area, this rolling roll can be used to form a shape shown in ■ in Fig. 14.

As shown in (1), (2), and (2), a pressure (represented by arrows) that increases sequentially is applied to the metal tube 44 to form a spiral fin having a desired fin height and thickness while increasing the fin spacing.

[Problem that the invention seeks to solve]

By the way, when attempting to manufacture a finned rod by processing a solid circular cross-section metal material using the second method, it is not possible to use an inner surface regulating tool, so that the axial center of the material is not aligned in the axial direction. This results in elongation, which tends to cause material whiskers in the radial direction, making it impossible to form high fins.

In addition, when applying the third method and trying to manufacture a finned rod using a solid material as a material without an inner surface regulating tool, the axial center of the material is stretched in the axial direction, so the metal material is The strain component in the radial direction toward the axis of the roll increases, and the outer diameter of the fins formed in the roll groove gradually decreases as the rolling progresses (■-■-■-■), as shown in Fig. 15. Moreover, the fins did not fill the roll grooves, and as a result, the fin portions of the manufactured finned rods were sometimes shorter in height and thickness than the target values.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a screw that allows the height and thickness of the fin portion to be manufactured to target values.

[Means to solve the problem]

The method for manufacturing a screw according to the first invention is a method for manufacturing a screw from a solid circular cross-section metal material by inclined rolling, in which an annular groove forming a helical protrusion gradually widens from the entry side to the exit side. The circular cross-section metal material is hot rolled using a cross-type inclined rolling mill in which a plurality of conical rolling rolls are formed at intervals in the circumferential direction of the outer peripheral surface and are arranged at equal intervals around the pass line. Stretch and roll.

A method for manufacturing a screw according to a second aspect of the present invention is a method for manufacturing a screw from a solid metal material with a circular cross section, in which an annular groove forming a helical protrusion is formed at intervals that gradually become wider from the input side to the output side. A plurality of rollers are formed in the circumferential direction of the outer peripheral surface of the rolling part,
The circular cross-section metal material is produced using a cross-type inclined rolling mill in which three or four rolling rolls, each of which has a groove width narrower from the entry side to the exit side, are arranged facing around the pass line. Hot elongation rolling.

A method for manufacturing a screw according to a third aspect of the present invention is a method for manufacturing a screw from a solid metal material with a circular cross section, in which an annular groove of the same width forming a spiral protrusion gradually becomes wider from an input side toward an output side. The circular cross-section metal material is hot rolled using a cross-type inclined rolling mill in which a plurality of rolls are formed in the circumferential direction of the outer peripheral surface of the rolling part at intervals of 3 or 4 facing around the pass line. Stretch and roll.

[Effect]

In the method of the present invention, it is possible to freely set the height, thickness, and pitch of the spiral expansion ridges.

[Example 1] The present invention will be specifically explained below based on the drawings.

Fig. 1 is a front view showing the implementation state of the present invention (grooves are omitted), Fig. 2 is a partially enlarged side view taken along the line ■-■ in Fig. 1, and 4 in the figure has a circular cross section. A certain solid metal material, 5
indicates the product, a spiral finned rod.

The metal material 4 is transferred in the axial direction and rolled by a set of three cone-shaped rolling rolls 1, 2.3 in a cross-shaped inclined rolling mill.

The rolling rolls 1, 2.3 each have the same conical half angle α (see Fig. 2), and their axes are inclined so that the shaft ends on the same side face in the same direction. The angle β with respect to the path line of ,
The direction in which the roll axis separates from the pass line on the exit side is γ (defined as positive).

Then, in the part where the distance between the outer peripheral surface of the rolling roll 1.2.3 and the pass line is smaller than the radius of the outer periphery of the metal material 4 passing therethrough, that is, in the outer periphery of the rolling part, the opening side is wider. A plurality of annular grooves, for example, 5 to 7 annular grooves each having a trapezoidal cross section, are cut in the circumferential direction at appropriate length intervals in the axial direction. The position of the groove is 9 intervals.

The width and depth are different among the rolls, as partially shown in FIG. 2, and the intervals between the rolls are also different in the axial direction.

In accordance with the height interval of the fins to be formed, the interval between the two groove positions is determined, and the cone half angle α, the inclination angle β, the crossing angle γ, etc. of the inclined rolling rolls related thereto are determined. The positions of the grooves are different for each rolling roll, and for each rolling roll, the interval (pitch) is gradually widened from the material input side to the material output side according to the amount of stretching, as will be explained later. The fins coming out of one roll are guided into the grooves of the next roll and are successively shaped. The groove width and groove depth are approximately the same between the rolling rolls. Note that the groove depth on each roll is changed as appropriate from the entry side to the exit side so that a desired fin height can be obtained at the exit end.

On the other hand, the groove width is made narrower from the inlet side to the outlet side, and the groove width at the outlet end is made to match the target fin thickness. However, as shown in FIG. 2, the groove width t1 at the entrance end is about 1.5 times the target fin thickness t to be manufactured, preferably 1.2t<
Let t be <2,5i.

In addition, here 1. ．． 1 means the average value of the groove width and the thickness of the fin portion coming out of the roll at the bottom and top, respectively.

In addition, in the case where the fins to be formed are perpendicular to the surface of the metal material, the inclination angle with respect to the roll axis in the depth direction of each groove is the same as the above-mentioned intersecting angle T in the direction of the material exit side of the groove bottom. Form a slope at an angle.

That is, when forming fins on the material surface so as to be inclined at a predetermined angle, the intersecting angle γ and the inclination angle of each groove with respect to the roll axis in the depth direction are made different. By the way, the above-mentioned groove width means the groove width seen in the material axis direction at each roll setting angle.

Manufacturing of screws using the rolling mill configured as described above is carried out as follows.

First, the outer diameter DF of the screw to be manufactured (see Figure 2)
A solid metal material 4 having a circular cross section with an outer diameter DI larger than DF is selected, and the size of D is 1.
1DF <D, <1.3 r), the degree is preferred. Next, the selected metal material 4 is heated in a heating furnace (not shown) to a predetermined temperature, for example, 1100° C. in the case of medium carbon steel, and then transferred to a cross-type inclined rolling mill having rolls as described above. As a result, the metal material 4 is rolled as shown in FIG.

FIG. 3 is a diagram showing the process step by step, and the arrow in the diagram indicates the direction of the load applied to the metal material 4.

When rolling of the metal material 4 (see Fig. 3 ■) is started in the inclined rolling mill, the metal material 4 is sequentially bitten by the rolling rolls 1°2.3 and then rolled by them at three locations in the circumferential direction. (see Fig. 3 ■), and moves forward while rotating around the axis. Therefore, subsequent rolling is performed in a spiral manner, and the rolled metal material 4 advances toward the roll exit side.

Then, sequential rolling with three rolls (Fig. 3 ■, ■
), the inside of the rolled portion is stretched in the axial direction, thereby widening the fin spacing. The roll is designed so that the grooves that contribute to the next rolling are located in the fin parts where the interval has widened, so the fins are not crushed during rolling, and the fins are tall and thick, and the fins are wide apart. can be formed.

Note that the setting range of the crossing angle γ and the inclination angle β is 0"
5 @ 3 @ × β < 20° 5" × γ + β <30", even if defects exist inside the metal material 4, it is possible to manufacture a screw in which the defects disappear by the stretch rolling method of the present invention. There is an advantage.

This is Japanese Patent Application Laid-Open No. 59-490, which the applicant has already filed.
It is based on No. 2, and if the present invention is applied to this,
Even if the metal material 4 has defects, it is possible to produce a high-quality spiral finned bar 5 as shown in FIG. 4 without causing Mannesmann fracture peculiar to inclined rolling.

The reason why a cross-type inclined rolling mill with three or four rolling rolls is used is that when the number of rolling rolls is reduced to two, a rotary forging effect (so-called Mannesmann effect) peculiar to inclined rolling acts, and for example, inclusions This is because cracks tend to occur in the center of the metal material, starting from porosity and porosity. Therefore, when a solid metal material is reduced by inclined rolling, the number of rolls is required to be three or more, and if the number of rolls is actually three or more, the above-mentioned rotary forging effect can be suppressed.

Conversely, as the number of rolls increases, the set gap cannot be made smaller because adjacent rolls come into contact with each other, and the number of rolls increases.
In addition to making the structure of the rolling mill complicated, if the roll diameter is larger than the material diameter, it becomes geometrically impossible to make the roll diameter and roll shaft diameter thicker than the material diameter, which reduces the mill rigidity and roll shaft strength. descend.

Therefore, in practice, it is appropriate to set the number of rolls to three to four.

[Numerical example]

A solid circular cross-section metal material of 5US304 with an outer diameter near 0fiφ is hot-rolled to have a spiral fin as shown in Fig. 4 with fin spacing: 20m, outer diameter: 60mφ, and fin bottom diameter: 30φ. Bar 5 was manufactured.

The manufacturing conditions are: rolling roll inclination angle β: 8 @, crossing angle γ: 2
@, Roll rotation speed: 1100 rp, Rolling temperature: 1100°C, Roll material: SCM440. Roll diameter: 180 mm φ, rolling roll inlet cone half angle α: 1
4.5 "Groove spacing on the inlet side: 11.□n, groove spacing on the outlet side = 20.0+n. In the middle, the spacing gradually changes from the inlet to the outlet according to the elongation and twist of the material. As a result, in the case of the present invention, it was possible to manufacture a high-fin screw shaft with a fin spacing of 20 mm and a fin height of 15 mm, which was previously impossible to manufacture by rolling.

[Example 2] This example is a method suitable for forming thick and low spiral protrusions, and the width of the annular groove formed on the roll from the input side to the output side is constant, The depth of the grooves and the pitch of the grooves are set so that the depth of the grooves becomes deeper from the entry side to the exit side, and the interval between the grooves, that is, the pitch, It is set to be wide.

The case where the number of rolling rolls is three will be specifically explained below.

5 is a front view seen from the V-V line direction in FIG. 6 (rolling roll grooves are omitted), and FIG.
FIG. 7 is a schematic side view (roll grooves are omitted) showing the inclination state of the roll with respect to the pass line X--X. Three cone-shaped rolling rolls 11, 12, and 13 constituting the inclined rolling mill are arranged at equal intervals around the bus line XX, and each rolling roll 11.
i2.13 has gorge parts 11a and 12a at the exit end.
, 13a, and a gorge portion 11a.

The diameter of the inlet side of the metal material 14 is gradually reduced toward the shaft end, and the diameter of the metal material 14 is gradually reduced from 12a and 13a, and the outlet side is enlarged to form an approximately truncated conical shape.
Equipped with 1C212c and 13c. Exit surface 11c+
12c and 13c are the distances from the pass line XX to the gorge parts 11a, 12a, 13a and the pass line XX
and the entrance surfaces 11b, 12b,
13b is positioned on the upstream side in the moving direction of the metal material 14, and the axis line Y- of the rolling rolls 11, 12.
The intersection point 0 (hereinafter referred to as the roll setting center) between Y and the plane including the gorge parts 11a, 12a, and 13a is the metal material 1
They are arranged at approximately equal intervals around the pass line XX on the same plane perpendicular to the pass line XX of No. 4. The axial center line Y-Y of each rolling roll 11, 12, 13 is about the roll setting center O in relation to the pass line X-X line of the metal material 14, as shown in FIG. Cross by the crossing angle γ so as to approach the line X-X1 (
As shown in FIGS. 6 and 7, the front shaft end is tilted toward the same side as the circumferential direction of the metal material 14 by an inclination angle β. Roll 11.12.13
are connected to a drive source (not shown), and are driven to rotate in the same direction as indicated by arrows in FIG.

Note that it is desirable that the roll shaft holding mechanism be of a dual support type. The reason why the roll shaft is of a double-sided type is that in the case of a double-sided type, the accuracy of the outer diameter of the screw is ±0.2%.
This is because in the case of the cantilever type, the mill rigidity is low, and the dimensional accuracy of the screw outside diameter deteriorates to ±0.7%.

The outer peripheral surface of the rolling roll 11.12.13 and the pass line X-
The portion where the distance between the They are formed with a phase shift of 173 rotations in each direction. The position of the groove is 9 intervals.

The width and depth are different for each rolling roll 11.12.13, and each rolling roll 11.12.13
The groove spacing is varied in the axial direction, and the groove width is approximately constant at the groove bottom.

The groove positions and 9 intervals are determined according to the height of the helical protrusions, which are the helical protrusions, and the number of 9 grooves, and the conical half angle α and inclination angle of the rolling rolls 11, 12, and 13 related to these. β
, intersection angle γ, etc. are determined. The position of the groove is the rolling roll 11
．． 12.13 are different from each other, and each rolling roll 11.
In 12.13, the interval is gradually widened from the inlet side to the outlet side of the metal material 14 according to the amount of stretching and the amount of twist of the metal material 14,
Moreover, the pitch of the grooves on the reeling surface on the exit side of the gorge portions 11a, 12a, and 13a is made constant.

The groove spacing (pitch) from the inlet side to the gorge parts 11a, 12a, and 13a is longer from the inlet side to the outlet side in consideration of elongation and twisting of the material during rolling, and this range is as follows: It is.

0.25 Pg <P+ <0.8S P! however,
P2: Outlet groove spacing P,: Inlet groove spacing Outside this range, the reduction may be too light and a sufficient thread height may not be obtained, and if the reduction is too strong, force fluctuations during rolling and shape defects may occur. be.

As a result, the threads coming out of the grooves of one rolling roll are guided to the grooves of the next rolling roll, and are shaped one after another to obtain a trapezoidal thread 15 as a screw.

FIG. 8 is a diagram showing the process, and the arrow in the diagram indicates the direction of the load applied to the metal material 14. When the metal material 14 (see Fig. 8 ■) starts rolling in the inclined rolling mill, the metal material 14 is sequentially bitten by the rolling rolls 11, 12, and 13, and then rolled by them at three locations in the circumferential direction ( (see FIG. 8 (2)), it advances toward the rolling roll exit side along the pass line XX in a so-called spiraling state in which it advances while rotating around the axis.

Then, sequential rolling with three rolls (Fig. 8 ■, ■
(see), the inside of the rolled part is stretched in the axial direction, which widens the thread spacing, and the roll is designed so that the grooves that contribute to the next rolling are placed in the thread threads where the spacing has widened. Of course, the threads are not crushed during rolling, and dimensional accuracy is improved by rolling down only the thread root portions one after another while keeping the width of the groove bottom equal to the width of the top of the threads to be formed. It is possible to form a threaded thread that does not cause curvature or flaws during rolling.This allows the trapezoidal screw 15, which has a relatively thick threaded thread and a long pitch, to be made with high accuracy and good surface quality. This makes it possible to manufacture

[Numerical Example 1] Outer diameter = 55flφ, material: 545C solid circular cross section metal material was hot rolled, thread spacing: 14m.

A trapezoidal screw with an outer diameter of 55 fiφ and a thread root diameter of 39 φ was manufactured. In addition, the manufacturing conditions are rolling roll inclination angle β: 5°
, rolling roll intersection angle γ: 1″, rolling roll rotation speed 10o
rpm, rolling temperature: 1000°C, rolling roll material:
SCM440, rolling roll diameter 7 180 flφ, rolling roll inlet cone half angle α: 12.5°.

Note that the groove spacing is P+ = 10.5n+ at the entrance and P at the exit.
2=14. Osn, and in the middle part, the interval was gradually widened in accordance with the elongation and twisting of the material 6 widths from the inlet to the outlet. In addition, the area from the gorge to the exit side was a finished part of the product shape, and the groove width was kept constant. The groove spacing was set to increase from the entrance to the gorge, increasing toward the gorge. The shape of the manufactured trapezoidal screw was good.

[Numerical Example 2] The metal material was manufactured under the same conditions as Numerical Example 1 above, with an outer diameter of 65 mm. In this case as well, the shape of the trapezoidal thread was good.

In both numerical examples 1 and 2, the groove bottom width is constant at 5.0 mm, and the angle of the groove side walls is 1 on the entry side with respect to the direction perpendicular to the roll axis.
6", closed at 14@ on the exit side. As a result, by adding a roll intersection angle of 1°, the angle on both sides becomes a trapezoid with an open angle of 15@. A trapezoid with a low thread and a large thread thickness. In the case of screws, even if the width of the rolling roll groove is constant from the entry side to the exit side, it is possible to sufficiently process the thread.
It was possible to suppress the curvature and rough skin caused by excessive reduction of the ridge side surface during rolling, and improve the texture and dimensional accuracy of the finished product.

Note that the above-mentioned 1. In the second embodiment, a configuration was explained in which a large-diameter metal material 4.14 was used as the material for the product screw barrel with spiral fins and trapezoidal screw. It is also possible.

〔effect〕

As detailed above, in the case of the present invention, a plurality of annular grooves for forming screws are provided in the circumferential direction of the outer peripheral surface of the rolling part at intervals that gradually become wider from the input side to the output side, and each groove width is constant or from the input side. Since circular cross-section metal materials are stretched and rolled using a cross-type inclined rolling mill with rolling rolls that are narrower on the exit side, the height, thickness, and pitch of the spiral protrusions can be freely set. The present invention has excellent effects such as being able to manufacture screws according to the intended use.

[Brief explanation of drawings]

FIG. 1 is a front view showing the implementation state of the first embodiment of the present invention;
Figure 2 is a partially enlarged side view taken along the line ■-■ in Figure 1;
The figure is a detailed explanatory diagram of the present invention, FIG. 4 is an external view of a screw manufactured by the method of the present invention, FIG. 5 is an implementation state of the second embodiment of the present invention, and the line V-V in FIG. FIG. 6 is a partially enlarged side view taken along the line Vl-Vl in FIG. 5, FIG. 7 is a side view showing how the rolling rolls are arranged with respect to the pass line, and FIG. Fig. 9.12 is a front view showing the implementation state of the conventional method, Fig. 10.13 is a partially enlarged side view, and Fig. 11.14 is an explanatory diagram of rolling contents.
The figure is an explanatory diagram of the details of rolling in the conventional method, and FIG. 15 is an explanatory diagram of the problems of the conventional technique. 1.2.3... Roll roll 4... Metal material 5...
Spiral finned rod 11.12.13 Roll roll 14 Metal material 15 Trapezoidal screw patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney
Noboru Kono Figure 1 % 2 Figure 6 Illustration 7 (!l Figure 8 vJ q Mouth 1. rr Figure i % +o Figure J, Gu procedure amendment (voluntary) February 19, 1988

Claims (1)

[Claims] 1. In a method for manufacturing a screw from a solid circular cross-section metal material by inclined rolling, an annular groove forming a spiral protrusion is formed on the outer periphery at intervals that gradually widen from the input side to the exit side. Hot elongation-rolling of the circular cross-section metal material is performed using a cross-type inclined rolling mill in which a plurality of conical rolling rolls are formed in the circumferential direction of the surface and three to four rolling rolls are arranged at equal intervals around the pass line. A method for manufacturing a screw, characterized by: 2. The method for manufacturing a screw according to claim 1, wherein the outer diameter of the solid circular cross-section metal material is the same as or larger than the outer diameter of the screw. 3. In a method of manufacturing a screw from a solid metal material with a circular cross section, a plurality of annular grooves forming a spiral protrusion are formed in the circumferential direction of the outer peripheral surface of the rolling part at intervals that gradually become wider from the input side to the output side. Using a cross-type inclined rolling mill in which three or four rolling rolls are arranged facing around the pass line and each groove width is narrower from the entry side to the exit side, the circular cross-section metal is rolled. A method for producing a screw, characterized by hot elongation rolling of a material. 4. The method of manufacturing a screw according to claim 3, wherein the outer diameter of the solid circular cross-section metal material is larger than the outer diameter of the screw. 5. In a method for manufacturing a screw from a solid circular cross-section metal material, annular grooves of the same width forming the helical protrusions are formed around the outer peripheral surface of the rolled part at intervals that gradually become wider from the input side to the exit side. The circular cross-section metal material is hot elongated using a cross-type inclined rolling mill in which three or four rolling rolls formed in a plurality of directions are arranged facing around the pass line. Method of manufacturing screws.