Metal deforming – By deflecting successively-presented portions of work during... – By use of deflector arranged to bend work transversely of...
Patent
1989-06-14
1991-05-21
Combs, E. Michael
Metal deforming
By deflecting successively-presented portions of work during...
By use of deflector arranged to bend work transversely of...
72 52, 72182, B21D 514, B21D 512
Patent
active
050164597
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and roll stand for guiding strip material to a fin-pass rolls of a pipe mill for producing thin pipe, such as seam welded steel pipe.
In general, when producing pipe in a pipe mill, a strip of material is first formed into a semicircular shape with break down rolls, then its center portion is formed with cluster rolls and fed to squeeze rolls after adjusting the edge angle and finishing and centering with fin-pass rolls in preparation for welding.
The shaping by the fin-pass rolls is decisive to the quality of the final product, and consideration must be given to prevent such strains as edge stretch, edge buckling and roll marks, and various types of fin-pass rolls have been proposed.
On the other hand, the material which has been formed in the break down or cage rolls, proceeds in a state wider than at forming due to spring back, and since horizontal movement of the edges is larger than the rest of the material, guidance or threading to the fin-pass rolls may not conducted smoothly, requiring more time for the material to be gripped by the fin-pass rolls.
Also, when the material is fed into the fin-pass rolls, forming is effected by halved or quartered rolls, but since the sectional shape of the material before the fin-pass rolls is not the final shape, due to the insufficient forming, the material is susceptible to contact flaws caused by the difference in circumferential velocity arising from the difference between the center and end diameters of the roll.
In the past, in order to avoid such slip flaws, pipe mill provided with an edge guide roll stand, in which pairs of vertical rolls and edge guide rolls with a V-shaped section, disposed upstream of the fin-pass roll stand, has been proposed in Japanese patent No. 53447/81.
A method of producing seam welded steel pipe, wherein the edge portion is restrained for forming with the V roll at the front of the fin pass, thus improving the formability and reducing the gap between the cage rolls and fin pass rolls, has been proposed in Japanese published patent application No. 166321/84.
This aforementioned prior art are both efficacious for correcting insufficient forming of the sectional shape of the material before passing into the fin pass rolls. But, at threading of the material end, as shown in FIG. 6, since the horizontal V roll 30 rotates to restrain the material edge 21 and a large angle appears between the tangential direction F of the frictional force and the moving direction S of the material 20, a component D of the frictional force is produced and acts to depress the edge portion 21 and shift it horizontally. As a result, slipping takes place on the roll face, producing edge wave and stretch, particularly in the case of thin steel pipe.
Also, in order to facilitate the threading, the V of the roll must be deep. However, if the V roll is deep, the material is susceptible to roll marking so the roll diameter must be reduced or a plurality of V rolls must be used, resulting in difficulty of adjusting the roll position and eventually of avoiding the edge stretch and scratching.
Taking into account such a situation in a pipe mill, it is an object of the present invention to provide a method of guiding material to fin-pass rolls and a guide roll stand therefor, which largely facilitates gripping of the material at threading, preventing the edge stretch and scratch, having a high correcting effect to the desired circular shape and suitable for producing thin steel pipes.
According to the present invention, in a method of forming a pipe by bending a strip of material in a pipe mill, the step of guiding the material to fin-pass rolls comprises bending edge portions of the U-shaped material inwardly towards one another by a pair of coaxial, axially spaced, frusto conical horizontal rolls, which contact respective edge faces of the material, and by a pair of vertical rolls the axes of which are orthogonal to and intersect the axis of the horizontal rolls, and which contact the outwardly facing surfaces of the edge p
Brown Laurence R.
Combs E. Michael
Nakata Manufacture Company Limited
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