JPH0142763B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to an improvement in a method for manufacturing a deformed steel bar having a spiral knot pattern on the surface of the steel bar, that is, a threaded reinforcing bar, using a finishing rolling mill during hot rolling of the steel bar. The purpose is to prevent the steel bar from twisting.

This type of threaded reinforcing bar was developed for the purpose of increasing concrete adhesion strength and mechanically connecting reinforcing bars, and as mentioned above, its structure consists of spiral nodes formed on the surface of a steel bar. It has the excellent characteristics of having a higher concrete adhesion strength than ordinary deformed steel bars, which simply have ribs or knots on the surface of the steel bars, and can be easily joined by using threaded joints.

The threaded portion of such threaded reinforcing bars is formed in the final finishing rolling mill, just like ordinary deformed steel bars, and is generally produced in a two-roll rolling mill as shown in Figure 1. . That is, conventionally, the roll is formed by an upper roll 1' and a lower roll 2', each having calibers 3' and 4' having a predetermined pitch and a predetermined lead angle carved on the outer circumferential surface of a round-hole roll hole. As shown in FIG. 2, the resulting product has a groove 7' extending in the longitudinal direction of the steel bar between each end face of the threaded joint 6'.

However, in the conventional rolling method, the roll hole is provided perpendicular to the roll axis, so the steel bar is twisted due to the inclination of the caliber during rolling, resulting in distortion between the end faces of the threaded ribs. There was a drawback that the groove 7' was twisted in the longitudinal direction as shown in FIG. Moreover, as shown in FIG. 3, the torsion angle almost matches the screw lead angle of the product, and the larger the screw lead angle of the product, the greater the torsion phenomenon.

In the case of threaded reinforcing bars with such twisting, although there are no problems with adhesion strength and bonding of concrete, the product value is low. Furthermore, a particular problem is that when bending a threaded reinforcing bar into a circular shape, due to the difference in section modulus, both ends shift and do not match, causing trouble in the work.

This invention was made to eliminate the above-mentioned drawbacks of the conventional method, and proposes a method for manufacturing a deformed steel bar with spiral ribs that does not twist during rolling.

The gist of this invention is to provide a method for forming spiral knots on the surface of a steel bar by carving calibers having a predetermined lead angle at a predetermined pitch on the outer peripheral surface of a roll hole of a hot finishing mill. , the upper and lower roll grooves are aligned with the radial centerline of the roll so that a torsional force in the opposite direction to the torsional force caused by the inclination of the caliber acts on the steel bar due to the moment of circumferential speed difference generated between the upper roll groove and the lower roll groove. It is characterized by rolling at an angle substantially the same as the lead angle on the side opposite to the thread direction.

That is, when manufacturing a threaded reinforcing bar with a right-handed thread, since the steel bar is twisted to the right, the method of rolling is to tilt the hole shapes of the upper and lower rolls to the left.

FIG. 4 shows one embodiment of this invention.
1 is an upper roll, 2 is a lower roll, 1-1 is an upper roll hole type, and 2-1 is a lower roll hole type, each of which has calibers 3 and 4 having a predetermined pitch and a predetermined lead angle. is engraved. When producing a right-handed threaded reinforcing bar using the upper and lower rolls, the upper and lower roll holes 1-1 and 2-1 are rolled at an angle of θ in the thread direction with respect to the radial center line 0 of the rolls, as shown in the figure. That is, as shown in FIGS. 4A and 4B, when the upper and lower roll holes 1-1 and 2-1 are tilted by θ, considering the same cross section in the holes, the left half of the upper roll 1, The right half of the lower roll 2 has a faster circumferential speed than the right half of the upper roll 1 and the left half of the lower roll 2, respectively, and therefore receives a moment as a whole in the counter-hour direction in the figure. For this reason,
Twisting occurs in the steel bar in the opposite direction to the torsional force caused by the tilt of the caliber.

By balancing this peripheral speed difference moment with the twisting force caused by the inclination of the caliber, rolling can be performed without twisting.

In this invention, the inclination angle θ of the upper and lower roll holes is not particularly limited, but since the torsion angle is almost the same as the screw lead angle (Fig. 3), it is approximately the same angle as the screw lead angle. good.
The lead angle is the angle defined by tan β = L (πd), where d is the diameter of the screw, and L is the lead (the distance traveled in the axial direction when going around the axis along the thread). (angle of inclination).

Now, when a steel bar is rolled by finishing rolls 1 and 2 shown in FIG. The nodes are formed, but
At this time, a torsional force in the direction of arrow a acts on the steel bar, and at the same time, a torsional force in the opposite direction (in the direction of arrow b 5) is generated due to the circumferential speed difference moment generated between the upper and lower roll holes 1-1 and 2-1, which cancels each other out. By this, the steel bar is rolled without twisting.Therefore, the rolled product has no twisting at all.

Next, embodiments of the invention will be described.

〔Example〕

C: 0.23%, Si: 0.35%, Mn: 1.50%, P:
Mn steel containing 0.03%, S: 0.03% is melted and made into a billet of 180φ by ordinary blooming rolling. After heating in a rolling mill, it is rolled into a billet with a nominal diameter of 50.8φ using the pass schedule shown in Fig. 5. manufactured threaded reinforcing bars. The above pass schedule is a normal two-roll type rolling mill with stands No. 1 to No. 11 arranged vertically and horizontally alternately. was applied. In this example, after finishing the 180 square billet to 56.7φ in stand No. 10, a threaded reinforcing bar with a nominal diameter of 50.8φ was manufactured using a two-roll rolling mill in stand No. 12. The threaded portion of this threaded reinforcing bar is made by carving a caliber with a pitch of 20 mm and a lead angle of 7° on the round hole-shaped outer surface of the No. 12 stand, and aligning the upper and lower roll holes with respect to the radial center line of the roll. It was rolled and formed by tilting it at the same angle as the lead angle on the side opposite to the thread direction. As a result, as shown in FIG. 6, a threaded reinforcing steel bar without twisting was obtained.

In addition, as a result of rolling with the same pass schedule as above using a conventional two-roll rolling mill in which the upper and lower roll holes of the No. 12 stand are set perpendicular to the roll axis, the grooves formed between the respective end faces of the threaded ribs. A threaded reinforcing bar twisted by approximately 7° in the longitudinal direction was obtained, confirming the effectiveness of this invented method.

Furthermore, as a result of bending each of the threaded reinforcing bars obtained by the above-mentioned method of the present invention and the conventional method into a circular shape with a diameter of 8000 mm, in the case of the threaded reinforcing bars obtained by the conventional method, the two ends of the reinforcing bars were shifted by 170 mm, whereas the inventive method The threaded reinforcing bars manufactured by the method had good matching properties with almost no deviation at both ends.

As explained above, according to the method of this invention, it is possible to prevent the steel bar from twisting during rolling, so it has a high commercial value, and moreover, the threaded reinforcing bar has both ends that meet well even when bent into a circular shape. The characteristics of threaded reinforcing bars are further enhanced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of a conventional two-roll rolling mill, Fig. 2 is a front view showing an example of a conventional threaded reinforcing bar, and Fig. 3 is a diagram showing the relationship between the helix angle and lead angle of threaded reinforcing bars. , FIG. 4 is a diagram showing an embodiment of the present invention, in which A is a longitudinal sectional front view showing an enlarged view of the upper and lower roll holes, B is a front view showing the external appearance of the upper and lower roll shapes, and FIG. A drawing showing a rolling pass schedule in the example, and FIG. 6 is a front view showing a threaded reinforcing bar in the same example. In the figure, 1...upper roll, 2...lower roll, 1-1,
2-1... Roll hole type, 3, 4... uneven groove, θ... inclination angle of roll hole type.

Claims (1)

[Claims] 1. In a method of forming spiral knots on the surface of a steel bar by carving calibers with a predetermined lead angle at a predetermined pitch on the outer peripheral surface of the roll groove of a hot finishing mill, the upper roll groove and The upper and lower roll grooves are moved in the opposite direction to the screw direction with respect to the radial center line of the rolls so that a torsional force in the opposite direction to the torsional force caused by the inclination of the caliber acts on the steel bar due to the moment of circumferential speed difference generated between the lower roll grooves. A method for manufacturing a deformed steel bar with spiral ribs, which is characterized by rolling at an angle substantially the same as the lead angle.