JPH051083B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reducing mill that reduces and rolls a blank pipe using a group of rolling rolls consisting of a plurality of stands.
Generally, a rolling mill is comprised of a plurality of stands, each of which is installed at a constant interval, by applying tension to the raw pipe to reduce its wall thickness and reduce its diameter to a predetermined diameter.

Conventionally, nothing is disposed between these stands, or as shown in FIG.
Claw-shaped covers 6, 6, . . . were attached to the cases of the stands 4, 4, . . . to close the gaps between the stands.

The claw-like covers 6, 6, . . . were installed for the purpose of preventing the tip of the raw tube 3 from getting caught in the abutting portion of the roll flange and damaging the roll edge. When the raw pipe 3 is reduced and rolled using these conventional devices, the tip of the raw pipe 3 that has passed through each stand 4, 4... may have a maximum thickness of 10 mm at the tip due to uneven wall thickness or uneven cooling conditions. When the tip of the raw tube 3 is bitten in the next stand, it once collides with a part of the rolls 4A, 4A, etc., and is bitten and subjected to reduction rolling.
Therefore, at the time of this collision, seizure occurs at the tip of the raw tube, and collision flaws occur on the surface of the roll 4A. Furthermore, there was a drawback that these collision flaws were transferred to the surface of the raw pipe and became external flaws. FIG. 7A shows the occurrence of external defects in the conventional example, and it can be seen that they are concentrated on the surface of the raw tube in the vicinity of positions that are integral multiples of the circumference l of the rolls from the top of the raw tube.

The present invention was proposed in order to eliminate the above-mentioned drawbacks, and provides a reducing rolling mill equipped with a pipe guide that controls the conveyance path of the raw tube between each stand so as not to cause external flaws and seizures on the raw tube. The purpose is to

The gist of the present invention is that by arranging a cone-shaped ring that can cover almost the entire roll caliber immediately in front of the rolls constituting each stand, even a raw pipe with a curved tip can be prevented from colliding with the rolls. This guides the tube to the center of the roll caliber, thereby preventing the tip of the tube from burning and causing scratches on the outside surface.

As a result of detailed investigation by the present inventors into the location where external surface flaws occur, the shape and size of the flaws, and the correlation with product components or size, it was found that many external surface flaws that occur during reduction rolling occur at the tip of the blank tube 3. I realized what I was doing. Furthermore, as shown in Fig. 2, if the trajectory of any point on the roll caliber is represented by center O, radius R, and circumferential speed V ₁ , the raw pipe 3 enters at a speed V ₂ and collides with the above trajectory at point A. _When doing so, it has _a velocity component as follows: Also, the raw pipe 3 is the roll 4
After being bitten by A, 4A..., the radial velocity of the raw tube 3 becomes zero.

Therefore, the impact force (change in impulse) in the radial direction is expressed as Y=V ₂ ·sinθ, and the speed difference in the circumferential direction between the blank tube 3 and the roll 4A is expressed as V ₁ -V ₂ ·cosθ.

As a result, if the collision position between the raw pipe 3 and the roll 4A is separated from the pass line due to the bending of the tip of the raw pipe 3, the angle θ becomes large, and both the above-mentioned collision force and speed difference become large. It has been found that burn-in is more likely to occur between surfaces, and these burn-in marks cause defects on the surface of the product.
The present invention is based on this knowledge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments with reference to the drawings.

3 and 4, a pipe guide 5 constituting an embodiment of the present invention is shown, and the inner diameter of the inlet hole of the base pipe 3 disposed in the center is large, and the inner diameter of the outlet hole is small. It consists of a cone-shaped ring 1, and support fittings 2, 2 for attaching to each stand 4, 4, etc. arranged around the ring.

The cone-shaped ring 1 is formed to open toward the inlet hole of the raw pipe 3, and the inner diameter D of the outlet hole is slightly larger than the outer diameter of the raw pipe 3 passing through it. As a result, even if the raw pipe 3 with a curved tip is transported, it is guided to the center of the roll caliber without difficulty. In this embodiment, the inner diameter D of the outlet hole of the ring 1 is set to be 2 to 6 mm larger than the maximum diameter of the blank tube 3. In order to prevent scratches according to this embodiment, a gap is provided.

As shown in FIGS. 5 and 6, the tube 3 whose outer diameter has been sequentially reduced by each stand 4, 4, etc. is controlled in its conveyance path by installing a pipe guide 5, and the product size is reduced without causing any external surface flaws. Finished in.

The raw pipe 3, which has been uniformly heated at a high temperature, is conveyed to the mill center line of a reducing mill consisting of a plurality of stands 4, 4, .

After this, the raw tube 3 is moved at a speed almost equal to the circumferential speed of the roll 4A placed on the No. 1 stand of the reducing rolling mill.
The tube is conveyed in the axial direction by _V2 , and the outer diameter is gradually reduced from the first stand to the last stand, and finished to the product size.

Bolt holes 2A, 2A... are drilled in the support fittings 2, 2... of the pipe guide 5 constituting this embodiment, and by attaching it to the case of the stands 4, 4..., the distance between the pipe guide 5 and the roll 4A can be increased. can be made extremely small. This is important in order to reliably guide the raw pipe 3 after passing through the pipe guide 5 to the center of the roll caliber.

Note that the pipe guide 5 is used in pair with the rolls 4A, 4A, etc. determined by the size of the raw pipe 3, so when changing the size, it is replaced at the same time as the rolls 4A, 4A, etc.

FIG. 7A shows the state of occurrence of external defects in the conventional reducing rolling mill before the installation of the pipe guide 5.
Figure B shows the appearance of external flaws in this example after the pipe guide 5 was attached, and the external flaws were significantly reduced.

As explained above, the present invention places a pipe guide in front of each stand to control the transport direction of the raw pipe, and in order to properly guide the raw pipe to the roll caliber, the bending of the tip of the raw pipe reduces contact with the rolls. This has the effect of reducing the occurrence of external flaws and seizures on the raw tube and improving product quality.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a stand to which a claw-like cover is attached in a conventional reducing rolling mill, Fig. 2 is an explanatory diagram of the relationship between the raw pipe and the rolls, and Fig. 3 is a pipe guide constituting an embodiment of the present invention. , FIG. 4 is a side view, FIG. 5 is a schematic diagram of the assembly of the embodiment shown in FIG. FIG. 7B is an explanatory diagram of the occurrence of external flaws according to the embodiment of FIG. 3. 1...Ring, 2...Supporting metal fittings, 3...Main pipe,
4...Stand, 4A...Roll, 5...Pipe guide.

Claims (1)

[Claims] 1. In a reducing mill that reduces and rolls a raw pipe by a group of rolling rolls consisting of a plurality of stands, a pipe guide equipped with a tapered hole that decreases in the traveling direction of the raw pipe is arranged so that its outlet hole is concentric with the roll caliber and A reduction rolling mill characterized by being installed directly in front of each stand.