GB2121338A - Improvements in press piercing mills - Google Patents

Abstract

Apparatus is described for increasing the rigidity and providing centering support for a mandrel backup bar 2 on the rolling and piercing axis of a press-piercing rolling mill, the apparatus comprising a plurality of substantially cradle-like structures aligned along the piercing axis and each supporting a trio of rollers 18, 19, 25 which are angularly displaceable towards and away from the axis with substantially self- centering movements. Each trio of rollers forms a substantially rigid ring around the mandrel back-up bar but provides a basically bezel-type support for the pierced intermediate blank 2a as it is advanced along the bar. <IMAGE>

Description

SPECIFICATION Improvements in press-piercing mills The present invention relates to apparatus for supporting the mandrel back-up bar of an axial piercing machine for hot working billets, ingots and the like. More particularly the invention concerns apparatus for increasing the rigidity and providing centering support for the mandrel backup bar on the piercing axis of a press-piercing rolling mill.

A press-piercing mill is a machine which can convert a square billet into an axially pierced, round, intermediate blank. This machine comprises a rolling stand with two driven rolls defining a circular gorge, a piercing mandrel carried at one end of an associated bar extending along the rolling and piercing axis from the exit side of the stand, and a pusher for thrusting a square billet between the rolls and against the piercing mandrel.

In order to effect hot axial piercing of a billet or ingot, bar or the like, with as small a degree of eccentricity as possible, it is necessary for the mandrel back-up bar of a press-piercing mill to be firmly held on the piercing axis so as to give a considerable degree of rigidity. This requirement is particularly necessary at the beginning of the piercing operation and particularly when the ratio between the length and the diameter of the piercing to be made is of the order of 25 or more.

Up till now the mandrel back-up bar has been supported and retained on the piercing axis by a plurality of pairs of constraining elements supported by a suitable bed and located in two parallel lines which are symmetrical relative to the piercing axis. Each constraining element is basically constituted by a vertical-axis roller supported at one end of an arm the other end of which is rotatably mounted on a vertical pin carried by a slide. An hydraulic cylinder or similar actuator provides for the angular displacement of the arm about the corresponding vertical pin, to position the roller in contact with the mandrel back-up bar or to space it therefrom. The slide mentioned above is movable on horizontal guides perpendicular to the piercing axis and its position is adjustable on the guides.In this manner, the vertical rollers of each pair constraining elements may be located at different distances from the piercing axis to suit mandrel back-up bars of different transverse dimensions.

This method of supporting the mandrel back-up bar although widely used, has the disadvantage of not giving the bar itself sufficient rigidity to withstand all the considerable forces (mandrel loads) exerted thereon during operation of the press-piercing mill. Indeed, in accordance with the said method, the mandrel back-up bar is supported and retained in correspondence with two diametrically opposite generatrices by pairs of vertical rollers while it is completely free above and below. The known method thus achieves a substantially pincer-like grip on the mandrel backup bar.

Moreover as piercing proceeds, the load situation on the mandrel back-up bar gradually worsens. Indeed, while, on the one hand, the number of constraints which hold the mandrel back-up bar diminishes since successive pairs of constraining elements are opened to allow the passage of the pierced blank, on the other hand, a gradually increasing lateral load is added to the mandrel load due to the weight of the blank itself.

The forces on the mandrel back-up bar may thus make it bend, starting a stress-deformation situation which is highly undesirable since it may increase the degree of eccentricity of the piercing produced to unacceptable levels.

In addition, the inevitable existence in each constraining element of play in the couplings between the slide and the corresponding guide, in the pivot couplings of the roller-carrying arm to the corresponding slide and to the hydraulic actuator, results in inexact positioning of the constraining element itself relative to the piercing axis and hence, increases the eccentricity of the mandrel back-up bar relative to the axis to a greater or lesser extent.

The problem which underlies this invention is to provide apparatus for supporting the mandrel back-up bar in a central position on the rolling and piercing axis of a press piercing rolling mill, which has structural and functional characteristics such as to ensure correct and efficient rigidifying constraint of the bar itself as well as supporting it in exact alignment with the piercing axis even during the progressive advance of the pierced blank therealong.

This problem is resolved according to the invention by apparatus for increasing the rigidity and providing centering support for a mandrel back-up bar on the piercing axis of a presspiercing rolling mill, characterised in that it comprises a plurality of substantially cradle-like support structures aligned along a common horizontal axis (A) coincident with the piercing axis of the mill, each supporting structure comprising;; three levers pivoted on respective horizontal pins parallel to the said axis A, the axes of the pins, considered in a vertical plane perpendicular to said axis A, being disposed at the vertices of an equilateral triangle, the centroid of which is the intersection of the axis A with the said vertical plane, three identical rollers each mounted for free rotation at the ends of a respective lever and at the same distance from the corresponding pins, the axes of rotation of the rollers lying in a common vertical plane perpendicular to the axis A and each intersecting in the same plane the axis of the corresponding pin, drive members for angularly displacing the levers and their respective free-rotatable rollers about the said pins towards and away from the axis A.

Further characteristics and advantages of the invention will become clearer from the description given below of one embodiment of the apparatus according to the invention for supporting and increasing the rigidity of the mandrel back-up bar of a press-piercing mill, reference being made to the appended drawings, given purely by way of non-limiting example, in which: Figure 1 is a schematic side elevation view of apparatus according to the invention; Figure 2 is a schematic plan view of the apparatus of Figure 1; Figure 3 is a schematic sectional view on an enlarged scale taken on line Ill-Ill of Figure 2; Figures 4 to 6 show the detail of Figure 3, schematically and on an enlarged scale, in different conditions of operation.

With reference to Figure 1, reference numeral 1 generally indicates apparatus according to the invention for supporting and increasing the rigidity of a mandrel back-up bar 2 used in a presspiercing rolling mill 3, the rolling stand of the mill being schematically indicated as 4 and the rolls as 5, 6.

The apparatus includes a plurality of identical cradle-shaped supporting structures 7 aligned along a horizontal axis A coincident with the rolling and piercing axis of the mill 3.

In the embodiment illustrated the apparatus 1 includes seven cradle structures of the aforesaid form disposed in three successive groups mutually spaced apart by predetermined distances.

Since the cradle structures 7 are all identical both structurally and functionally only one of these is described below with reference to Figures 3 to 6.

Each of the cradle structures 7 supports three horizontal pins 8, 9, and 10 parallel to the axis A.

More particularly the spacial disposition of the pins 8, 9, and 10 is such that their axes lie in a vertical plane perpendicular to the axis A, for example the plane of Figure 3, and constitute the vertices of an equilateral triangle the centroid of which coincides with the axis A in the vertical plane considered. On each of the pins 8, 9, and 10 is pivoted a corresponding first-order lever 11, 12 and 13. The lever 11, which is basically in the form of a crank, has a forked end 11 a carrying a horizontal pin 14 which is parallel to the pin 8. On this pin 14 is pivoted the end 1 5 of the shaft 1 6 of a hydraulic cylinder 1 7 pivotally supported in a conventional manner by the support structure 7.

On the other end of the cranked lever 11 is mounted an idle roller 18. A second idle roller 19 is mounted by conventional means not shown on the end 1 2a of the lever 12. This lever is mechanically driven by the lever 11 through a rod 20 on the opposite ends 21, 22 of which are rotatably mounted on horizontal pins 23, 24 which are parallel to the pin 8 and are carried by the lever 11 and the lever 1 2 respectively.

The lever 13 also supports an idle roller 25 at its end facing inwardly of the cradle structure 7. It should be noted that the axes of rotation of the idle rollers 18, 19 and 25 lie in the same vertical plane perpendicular to the axis A and intersect the axes of the pins 8, 9, and 10 respectively in this plane. It should also be noted that the rollers 18, 1 9, 25 are identical and equally spaced from the axes of the pins 8, 9, and 10 about which they are angularly displaceable towards and away from the axis A with a self centering type movement as will be better understood from the description below.

A tie rod 26 has an end 27 rotatable mounted on a horizontal pin 28 which is parallel to the axis A and is supported in a conventional manner by the lever 12. At its other end 29, the tie rod 26 slidingly passes through a cylindrical body 30 rotatably mounted in a cylindrical seat 31 which has a horizontal axis parallel to the axis A. The seat 31 is formed close to the end of the lever 13, opposite the roller 25. A stop, for example a nut 32, which is adjustable in position is mounted on the end portion 29 of the tie rod 26 to prevent the tie rod from being withdrawn from the cylindrical body 30.

A hydraulic cylinder 33 is pivotably supported by the cradle structure 7 and its shaft 34 is rotatably mounted on a horizontal pin 36 which is parallel to the axis A and is carried by a pair of lugs 35,35 fixed to the lever 13.

The lever 13 and its roller 25 are angularly displaceable in an anti-clockwise sense (with reference to Figures 3-6) while the levers 11 and 12 remain fixed. Similarly, these levers 11 and 1 2 with their rollers 18, 19 can be angularly displaced in a clockwise sense while the lever 1 3 remains fixed or even displaced angularly in an anticlockwise sense.

The preferred disposition of the fixed pins 8, 9 and 10 and of the levers 11,12 and 13 relative to these pins is such that the idle rollers 1 8, 1 9 are moved towards the axis A along ascending paths while the roller 25 is moved towards the axis A along a descending path.

With reference to Figure 2 it should be noted again that the cradle supporting structures which constitute the second and third groups are mutually interconnected and rigidified in a direction parallel to the axis A by tie rods and spacers shown schematically by 37, 38 and 39, 40 respectively.

Respective arms 41,42 of known type operate in the spaces between the groups of cradle structures mentioned above, these arms being used in known manner to carry a mandrel back-up bar 2 into an operative position on the axis A and to move the mandrel back-up bar and a blank 2a engaged thereon away from this position. The arms 41,42 are mounted on horizontal shafts 43, 44 supported on both sides of the apparatus of the invention, preferably in positions which are symmetrical relative to the axis A. The shafts 43, 44 are driven by drive members, not shown since they are conventional, to effect angular displacement of the arms 41, 42.

At the free ends of the arms 41,42, are pivoted respective basically cradle-shaped heads 45 of known type while the other ends of the arms are suitably counterweighted by masses 46, 47.

The operation of the apparatus described above is as follows.

In an initial operative condition (Figure 3), the trios of rollers 1 8, 19, 25 of each of the cradle structures 7 are maintained in firm contact with the mandrel back-up bar 2 by means of the action of the respective hydraulic cylinders 1 7. In this condition the rollers 1 8, 19 and 25 hold the mandrel back-up bar 2 firmly centered on the piercing axis A and form a substantially rigid ring around the bar, that is, a constraint, which by effectively stiffening the bar improves its resistance to the loads experienced by the mandrel.

Not only does this result in a smaller degree of eccentricity of the axial piercing of the intermediate blank produced, but it also has the advantage of enabling the use of longer bars to produce axially pierced intermediate blanks of a greater length in accordance with current technical trends.

When the end of the intermediate blank 2a reaches a trio of rollers 18, 19, 25, for example those of the first cradle structure 7, detection devices (not shown since they are conventional) send a command to the hydraulic cylinder 17 of this structure. The operation of this cylinder 1 7 causes an angular displacement (in an anticlockwise sense with reference to Figure 3) of the lever 11 around the axis of the pin 8 resulting in the movement of the corresponding roller 1 8 away from the mandrel back-up bar 2.

Because of the connection of the lever 11 to the lever 12 by the tie rod 20 and the lever 12 to the lever 13 by means of the tie rod 26, the levers 12, 13 also undergo equal angular displacements in an anticlockwise sense about the axes of their corresponding pins 9, 1 0 simultaneously with the lever 11. At the end of these simultaneous equal angular displacements in the same sense, the rollers 18, 1 9, and 25 take up a position illustrated in Figure 4, a position which is calculated to allow not only the passage and the advance of the intermediate blank 2a on the bar but also and above all a centered support (a bezel type of support) on the axis A for the blank itself during its movement.

As a consequence, the gradually increasing weight of the blank is completely supported by the trio of rollers 1 8, 19 and 25, and during the entire rolling and piercing phase, the bar 2 is subject solely to the mandrel loading and not to a simultaeous lateral load as occurred in the known art. The bar is thus not subject to bending deformations, and this contributes substantially to maintaining it in aiignment with the piercing axis.

All the operations described above are then carried out for the roller trios subsequent to the first as they are reached by the blank being produced.

At the end of the piercing operation, the intermediate blank obtained and the bar inserted therein must be removed from the plurality of cradle structures 7 and a new mandrel back-up bar must be brought into the position thus vacated.

For this purpose the plurality of cylinders 33 are first actuated simultaneously (or otherwise) in the sense so as to displace their respective levers 1 3 further angularly in the anti-clockwise sense about the axes of the pins 10.

All the rollers 25 (the upper rollers) are thus brought into the non-operative position illustrated in Figure 5. As already described, during the angular displacement of the levers 13, the levers 11 and 12 and their rollers 18, 19 remain stationary. The tie rods 26 do not obstruct displacement of the levers 1 3 since they are freely slidable in the cylindrical bodies 30 and these latter may rotate freely in their respective seats 31 of the levers 13.

When all the rollers 25 are safely in a position remote from the axis A, the position shown in Figure 5, in which the intermediate blank and its mandrel back-up bar are supported by the rollers 18, 1 9 while they are upwardly free, the shaft 44 is operated which results in the angular displacement of the corresponding over-turning arms 42 and the removal of the intermediate blank 2a and the mandrel back-up bar 2 engaged therein (Figure 6).

Operation of the hydraulic cylinders 1 7 then brings the rollers 18 and 19 into the initial position illustrated in Figure 3 to form a support for a new mandrel back-up bar 2. This new bar is placed in position by the operation of the other shaft 43 and the corresponding over-turning arms 41. In this condition the mandrel back-up bar 2 is already exactly aligned on the piercing axis A.

Subsequently, operation of the cylinders 33 brings all rollers 25 down into contact probably with the new mandrel back-up bar 2, thus forming the desired plurality of rigid rings which lock the mandrel back-up bar in a centered position on the pieruing axis, giving it the desired rigidity.

Claims (4)

1. Apparatus for increasing the rigidity and providing centering support for a mandrel back-up bar on the piercing axis of a press-piercing rolling mill, characterised in that it comprises a plurality of substantially cradle-like support structures aligned along a common horizontal axis coincident with the piercing axis of the mill, each supporting structure comprising:: three levers pivoted on respective horizontal pins parallel to the said axis, the axes of the pins considered in vertical plane perpendicular to the said axis, being disposed at the vertices of an equilateral triangle, the centroid of which is the intersection of the said axis with the said vertical plane, three rollers each mounted for free rotation at the end of a respective lever and at the same distance from the corresponding pins, the axes of rotation of the rollers lying in a common vertical plane, perpendicular to the said axis and each intersecting in the same plane the axis of the corresponding pin, drive members for angularly displacing the levers and their respective rollers about the said pins towards and away from the said axis with substantially self-centering type movements.

2. Apparatus according to claim 1, characterised in that the levers are kinematically interconnected by means of respective tie rods one of the levers being operated by a drive member.

3. Apparatus according to claim 2, characterised in that one lever of the said levers is angularly displaceable about the corresponding pin by an associated drive member independently of the other two levers.

4. Apparatus for increasing the rigidity and providing centering support for a mandrel back-up bar on the piercing axis of a press-piercing rolling mill substantially as herein before described with reference to and as shown in the accompanying drawings.