GB2070484A - Rolling mill for bars or wire rods - Google Patents

Abstract

A rolling mill for bars or wire rod, has two driven work rolls which are supported by the mill housing in cantilever fashion, and, for each roll, two back-up rolls. The two back-up rolls each contact the associated work roll and are carried in a support 2a or 2b which is adjustable by a screw assembly. <IMAGE>

Description

SPECIFICATION Rolling mill for bars or wire rods This invention relates to a rolling mill for bars, rods, or wire rods.

For convenience' sake, the description hereinafter is directed to a mill for steel wire rods. However, this invention is not limited to a rod mill and can be also adapted to a bar mill.

A rod mill is also called an elongation mill because it can provide a large amount of elongation. In a conventionally known typical steel rod mill, a 100 - 120 mm square (100 ~ 120 mmo) billet is rolled or reduced into a 5-5 mm diameter (5.5 mme) wire rod with the total elongation above 500 by diamond, square, oval or round pass systems with 20 ~ 30 passes in a hot continuous rolling process. In this hot continuous rolling process, the rolling speed of the mill at the final pass is 50 ~ 70 m/sec at the highest.

The pass system and arrangement of the mill have been modified and improved to increase the productivity, thus resulting in saving energy. For example, there has been proposed a finishing block mill arrangement for rolling a 1 6 mm gage into a 5.5 mm. The block mill arrangement has about ten stands arranged on a base. Furthermore, in such finishing block mills, the diameters of the rolls are decreased by modifying and improving the materials of which the rolls are made, in order to provide a compact or small rolling mill block.

It has been found that the decrease of the roll diameter in a block mill increased the efficiency of deformation so that the mean elongation for ten passes was 1.25/pass, which has been 1.20/pass in a mill prior to the improved block mill.

However, in a conventional rod mill as mentioned above, the reduction of the roll diameter is limited, and, accordingly, a remarkable increase in the elongation for pass cannot be expected.

The object of the present invention is to provide an easily operable and high productive bar or rod mill which is composed of work rolls each having a shaft which at one end is connected to a drive, the work rolls being supported by a mill frame only at their one side adjacent to the end connected to the drive, the work rolls having on their cylinder portions a plurality of passes, and back-up rolls which are brought into contact with the corresponding work rolls to radially force the latter and to support the roll force.

In order to make a rolling line more compact, it is necessary to considerably increase the amount of elongation for pass, in comparison with that in a prior art. According to the present invention, in order to remarkably increase the amount of elongation for each pass and to increase the efficiency of deformation the diameter of the work rolls is minimized within a capable limit so that the diameter is smaller than an actual rolling diameter.

It is also possible to make the work rolls smaller by modifying the material thereof, for example to cungsten carbide. However, the approach to improvement from the point of view of the material is not advantageous, because as long as the work roll bearings support the roll force, the bearings have to be strong and sufficient to support the roll force, which results in an increase of the diameter of the work rolls. That is, the diameter of the work rolls depends on the size of the bearings and, accordingly, cannot be largely decreased.

in order to solve this problem, the roll force can be supported by back-up rolls which come in contact with the cylinder portions of the work rolls and which are rotated by the latter, rather than the bearings of the work rolls. By this solution, the dimensional limitation of the work rolls resulting from the bearing construction can be removed and, accordingly, the diameter of the work rolls can be remarkably decreased within a certain limit.

Furthermore, according to the present invention, the work rolls are supported by open-side type or cantilever support means, to easily exchange the work rolls and to make the construction of the mill simpler. That is, the work rolls have bearing portions only on their one side adjacent to the ends which are connected to a drive.

In the present invention, it is not necessary for the bearing portions of the work rolls provided on their one side to have a strength enough to support the roll force, and, accordingly, the bearing portions do not become obstacles for minimizing the work rolls.

The invention wiil be discussed below in detail with reference to the drawings showing preferred embodiments of the present invention, in which: Fig. 1 is a partially sectioned side elevational view of a rolling mill according to the present invention; Fig. 2 is a front elevational view of Fig. 1; Fig. 3 is a side elevational view of a screw down device of work rolls in a rolling mill according to the present invention; Fig. 4 is a side elevational view of a single back-up roll arrangement, according to a variant of Fig. 3;; Fig. 5A is a diagram showing elongation in the present invention, in comparison with a prior art, Fig. 5B is a diagram showing a roll load in the present invention, in comparison with a prior art, and, Fig. 5C is a diagram showing a rolling torque in the present invention, in comparison with a prior art.

Fig. 1 shows a rolling mill of this invention, viewed from a work side, in which two upper back-up rolls 21 and two lower back-up rolls 22 support a pair of work rolls 11 and 12 located between the back-up rolls. Fig. 2 shows a rolling mill viewed from the rolling direction, in which the work rolls are supported by an open side type supporting device. Fig. 3 shows a screw-down device of the work rolls, viewed from the work side.

With reference to Figs. 1-3, the discussion is first below directed to the construction of the rolling mill of the invention.

A mill housing 3 has a pair of openings 1 A and 1 B through which a blank (not shown) to be rolled passes. Guides (not shown) may be mounted on to the housing 3 to guide the blank passing through the openings 1 A and 1 B. The housing 3 is provided, on its top and bottom, with screw rods 4a and 4b which form top and bottom screw-down devices 5A and 5b and fixed nuts 6a (6b is not shown) in which the screw rods 4a and 4b are screwed.In each screw down device, there is arranged a worm wheel 1 8a (or 1 8b not shown) which is connected to a drive (not shown) such as a motor (not shown), by means of a worm 33a (or 33b) and which has a threaded center opening 18art (or 1 8b' not shown) in which the screw rod 4a (or 4b) is engaged so that when the worm wheel 1 8a (or 18b) rotates, the screw rod 4a (or 4b) moves in its axial directions. The worms 33a and 33b can be driven by a common drive or separate drives. To enlarged ends 7a (7b is not shown) of the screw rods 4a and 4b are mounted back-up frames 2a and 2b by means of bearing plates 8a and 8b secured to the back-up frames, respectively. The enlarged end 7a (or 7b) is rotatably held in and by the bearing plate 8a (or 8b).

Thus, the bearing plate 8a (or 8b) and the back-up frames 2a (or 2b) move in the axial directions of the screw rod 4a (or 4b) together with the latter, without rotating.

The top back-up rolls 21 are rotatably supported by means of bearings 20a on their respective shafts 15a which are in turn supported by the top back-up frame 2a. The top back-up rolls 21 come in contact with the top work roll 11 which are removably supported on its drive shaft 9a and are secured to the latter by clamp 1 Oa so as to rotate with the shaft 9a. The drive shaft 9a is rotatably held by a bearing box 1 3a which is mounted on to the housing 3. One end 9a' (9b') of the shaft 9a (9b) is connected, by means of a coupling 62a (62b), to a spindle 61 a (61 b) of the mill, which is in turn connected to a gear 64a (64b) by means of a coupling 63a (63b). The gear 64a is engaged by the gear 64b which is connected to a drive 66, such as a motor, so that the spindles 61 a and 61 b can be synchronously rotated.The work rolls 11 and 12 have one or more peripheral grooves which define a predetermined shape passes 60.

Alternatively, it is also possible to provide work rolls having flat cylindrical portion with no peripheral groove. In this cas,e for example, a square billet is first twice or more rolled into an oval shape by the flat work rolls and is finally rolled into a round shape by a final pass defined by work rolls with peripheral grooves.

The bottom back-up rolls 22 and the bottom work roll 12 are constructed in the same fashion as those of the top back-up rolls 21 and the top work roll 11, as mentioned above. The affixes "a" and "b" after the reference numerals of components illustrated in the drawings represent a top half unit and a bottom half unit of the mill, respectively.

The top and bottom work roll units which are composed of the work rolls 11 and 12, the back-up rolls 21 and 22, the bearing boxes 1 3a and 13b, the drive shafts 9a and 9b, etc, respectively, have yokes 27a and 27b, respectively, which are secured to the respective bearing boxes 1 3 and 14. The top and bottom yokes 27a and 27b have threaded holes 36a and 36b in which screw shafts 30 are screwed. One of the threaded holes 36a and 36b is left-handed and the other is right-handed and each screw shaft has left and right hand threaded portions corresponding to the threaded holes, so that when the screw shafts 30 rotate, the yokes 27a and 27b, and, accordingly, the bearing boxes 1 3a and 1 3b come close to and away from each other.Thus, the roll gap between the work rolls 11 and 1 2 can be adjusted by rotating the screw shafts 30. Preferably, two screw shafts 30 are provided on the opposed sides of the work rolls, i.e., on the entry side and on the exit side of the mill, respectively. The screw shafts 30 are connected to screw down reduction gears 1 9 which have worms 38 and worm wheels 37, respectively. That is, the screw shafts 30 are rigidly connected to the worm wheels 37. The worms 38 are interconnected by means of a coupling 1 7 so as to synchronously drive the two reduction gears 19. A worm shaft 28 of one of the worms 38 is connected to a drive (not shown) such as a motor.

As can be understood from the above discussion, the back-up rolls are displaced up and down by means of screw down devices as shown in the illustrated embodiment. However, instead thereof, hydraulic cylinder devices or a combination of screw down devices and hydraulic cylinder devices can be used.

Furthermore, it is also possible to provide an arrangement of a rolling mill according to the present invention, in which, on one hand, the work rolls and the corresponding back-up rolls can be moved up and down together during rolling while keeping their operational position in which the work rolls are in contact with the corresponding back-up rolls and, on the other hand, the work rolls and the corresponding back-up rolls can be independently moved up and down, for example when the work rolls are exchanged.

The rolling mill of this invention operates as follows.

When the roll gap between the work rolls is reduced after the work rolls have been set, the worm shaft 28 of the worm reduction gears 1 9 is rotated in a predetermined direction by the drive, so that the screw shafts 30 are rotated in a predetermined direction. As a result of this rotation of the screw shafts 30, the bearing boxes 1 3a and 1 3b come close to each other and, thus, the work rolls 11 and 12 come close to each other, resulting in the reduction of the roll gap.

When the work rolls 11 and 12 move to decrease the roll gap therebetween, gaps between the work rolls 11, 12 and the back-up rolls 21 and 22 increase. That is, the work rolls are separated from the respective back-up rolls. In order to adjust this separation, the worm wheels 1 8a (1 8b is not shown) is driven by the drive (not shown), to rotate the screw rods 4a, 4b. The rotation of the screw rods 4a and 4b causes the back-up frames 2a and 2b to move close to each other, and, thus, bringing the back-up rolls 21 and 22 into contact with the work rolls 11 and 12, respectively.

When the roll gap between the work rolls is increased, the back-up rolls are first retracted from the respective work rolls. After that, operations opposite to the above mentioned operations can be effected.

After the adjustment of the roll gap is completed, the work rolls 11 and 12 are driven to roll a rolling blank. According to the present invention, since the work rolls are supported by the respective back-up rolls, the work rolls are subject to both the reaction force from the blank and the reaction force from the back-up rolls. Since these reaction forces have an identical magnitude and different directions of action, they are cancelled. That is, no bending moment is applied to the work rolls. This enables the diameter of the work rolls to be decreased.

When the work rolls 11 and 12 are exchanged by other ones, the work rolls can be easily removed from their shafts 9a and 9b by releasing and removing the clamps 1 0a and 1 Ob after the back-up rolls 21 and 22 have been retracted from the work rolls, respectively.

During continuous rolling of the blank, the work rolls may be subjected to an external force in the lengthwise direction of the blank, due to a tension or compression force acting on the blank. However, since the work rolls 11 and 12 are held by and between the back-up rolls 21 and 22, neither distortion nor displacement of the work rolls occurs, so that the work rolls ensure a reliable and stable rolling.

Furthermore, since each work roll is held by two back-up rolls, that is, since each work roll is supported in a two-point support fashion, the contact pressure between each work roll and the corresponding back-up rolls becomes half when it is compared with a one-point support fashion.

This increases the service life of the work rolls.

In the present invention, a back-up roll system is adopted instead of a conventional double roll system which requires the provision of large sized bearings enough to bear against a high roll force which is produced by a large amount of elongation for pass, resulting in the necessity of large sized work rolls, which is contradictory to the object of this invention. According to the back-up roll system in this invention, the roll force applied to the work rolls in the course of rolling can be all supported by the back-up rolls. Therefore, the diameter of the work rolls can be designed and determined, only taking factors relating to the rolling operation, such as necking of the work rolls, slip of the rolls during rolling or the like, into consideration. This makes the diameter of the work rolls smaller.

It is of course necessary that the work rolls have a diameter large enough to bear against the rolling torque. However, since the reduction of the diameter of the work rolls decreases the rolling torque, the above mentioned factors such as necking are more important, in designing the diameter of the work rolls.

It goes without saying that the roll gap between the top and bottom work rolls can be maintained not only at no load position in which rolling is not effected, but also at a working position in which the blank is rolled.

Figs. SA-SC show experimental results tried by the use of a bar mill as constructed above, according to the present invention. In the experiments, a round steel blank having a diameter of 45.6 mmç is rolled into a round bar having a diameter of 1 5.2 mmç by the use of oval passes, under the following conditions.

TABLE

number of mean amount Diameter of passes- of elongation work rolls Remarks prior art 10 passes 1.24 450-300 finishing speed -11.5 m/s rolling temperature = 900N1000'C present invention 6 passes 1.44 200 As can be seen from Figs. SA-SC, according to the present invention, the mean elongation for each pass was 1.44/pass which was considerably higher than that of prior art, and the roll force and the torque were both rather decreased in comparison with prior art.

In order to roll the blank from 45.6 mmf to 1 5.2 mm, the prior art required ten passes, whereas the present invention required only six passes, because the rod mill of the present invention presents a higher elongation per pass.

It has been also found that the present invention presented an elongation rate considerably higher than that of a prior art, as can be seen from Fig. 5A.

The discussion mentioned above is directed to a double back-up roll type of rolling mill. However, the present invention can be also applied to a single back-up roll type of rolling mill. Fig. 4 shows such a single back-up roll system, in which a top work roll 50 is supported by a top back-up roll 51 which is in turn rotatably held by a back-up frame 52. The back-up frame 52 can be displaced up and down by means of a screw rod 56 and a screw down reduction gear 55. The other part of the construction and the operation are substantially the same as those of a double back-up roll system illustrated in Figs.

1-3. Furthermore, the bottom half of the single back-up roll mechanism shown in Fig. 4 is same as the top half thereof.

It is also possible to provide block mills which are arranged on a base and which comprise a plurality of rolling mills as shown in Figs. 1-3 or Fig. 4 which are commonly driven or which are independently driven or which are driven independently in part and commonly in part. In such a multi mill system, various sorts of arrangement, such as HV type in which horizontal rolls and vertical rolls are alternately arranged, or X type in which roll axes are alternately inclined at +450 with respect to the horizontal axis can be provided.

Furthermore, the present invention can be also applied to different types of mill, such as a mill in which one of a pair of work rolls cannot move up and down and the rolling torque can be given only by the other work roll, or a mill in which only one of a pair of work rolls can be driven by a drive, or a mill in which pairs of work rolls have different peripheral speeds.

As can be understood from the above discussion, according to the present invention, the elongation for one pass can be highly increased; the efficiency of deformation can be improved; the work rolls can be easily and simply exchanged by ones since the work rolls are held by cantilever or open side type support means: and, accordingly, the pass numbers can be largely decreased; space necessary for locating the mill can be decreased; the total weight of the mill can be considerably decreased; a compact mill arrangement can be provided; and, an easy operable rolling mill can be provided.

A bar or rod mill of the present invention can be adapted to cold-roll steel wire rods, in place of wire drawing dies.

Claims (6)

1. A rolling mill for a blank such as a rod, a bar or a wire rod, comprising a mill housing, at least one pair of work rolls on their respective rotatable shafts which are connected at one end to a drive and which are movably supported by the mill housing in a cantilever fashion, and at least one pair of back-up rolls corresponding to each work roll, said back-up rolls being brought into contact with the corrresponding work rolls so as to radial force the latter and to support the roll force of the blank.

2. A rolling mill according to Claim 1, wherein the work rolls have cylindrical portions provided with predetermined shapes of peripheral grooves which define at least one pass therebetween.

3. A rolling mill according to Claim 1, wherein the work rolls have flat cylindrical portions.

4. A rolling mill according to Claim 1, 2 or 3, having means for moving the rotatable shafts of the work rolls, and accordingly, the work rolls, towards and away from one another to adjust a roll gap between the work rolls.

5. A rolling mill according to any one of Claims 1 to 4 having bearing means on one side of each work roll, when viewed in the axial directions of the rotating shafts of the work rolls, for rotatably supporting the rotatable shafts in a cantilever fashion.

6. A rolling mill according to any one of Claims 1 to 5, having means for moving the pairs of backup rolls towards and away from one another.

-7. A rolling mill according to any one of Claims 1 to 6, having screw down devices for pressing the back-up rolls against the corresponding work rolls.