GB2114929A - Rolling stand with interchangeable operative units, particularly for a press-piercing mill - Google Patents

Abstract

A rolling stand for a piercing mill is described in which the pair of working rolls 31, 32 and their roll chocks 27, 29 an accessories are mounted on a self-supporting frame 16 which can be inserted in and removed from the said stand in wheels 33, 34. With such a stand it is possible to change over the rolls with considerably greater rapidity than in the prior art. <IMAGE>

Description

SPECIFICATION Rolling stand with interchangeable operative units, particularly for a press-piercing mill The present invention relates to a rolling stand particularly for a press-piercing mill.

A press-piercing mill, which will be referred to in the following description by the initials PPM (corresponding to the English definition "presspiercing mill") is a machine which can convert a square billet into an axially pierced, rounds, intermediate blank.

Such a machine generally includes a rolling stand with two driven working rolls defining a circular gorge, an entry guide and an exit guide, a piercing mandrel carried at the end of a mandrel backup bar, extending along the rolling axis from the exit side of the PPM, members (constraining elements) for holding the mandrel backup bar firmly on the rolling axis against the forces exerted thereon during the rolling and simultaneous axial piercing of a billet.

The rolling stand is generally constituted by a steel structure comprising a base frame and four pillars connected together rigidly at their upper ends by a suitably dimensioned head plate. In general the front pair of pillars is rigidly connected to a frame which supports the entry guides of the PPM, while the rear pair of pillars is rigidly connected to a support frame for the exit guides.

These connections between the stand and the entry and exit guides of the PPM, enable a closed system of forces to be set up in the horizontal plane of the machine thus preventing these forces from acting on the foundations.

The working rolls are supported in the stand by means of respective roll chocks between which are generally interposed packs of plate-iike spacers, load cells and other similar devices which can be identified more simply as accessories of the working rolls in the following description.

It is well known that with a PPM is it necessary to change the working rolls more or less periodically either because the wear limits of the respective working surfaces have been reached or more generally because it is required to change the calibre of the pierced, round intermediate blanks to be produced. It is also known that at each change of rolls, the positioning of the new working rolls and their accessories in the stand must be carried out particularly carefully in order to ensure the re-establishment of rolling axis of the PPM. This operation is generally called the aligning operation.

On account of the number of pieces to be handled during a change-over of the working rolls, the interdependence of their positioning in their stand, the bulk and weight thereof and, not least, the difficulty of handling them, the aligning operation needs a relative long period of time.

Since a PPM cannot be stopped for a period of time of the order of the total time required to effect a change-over of rolls, such a change-over has until now been achieved by replacing the entire rolling stand with another stand which has been prepared outside the line and in which the new working rolls (new working surfaces and/or new calibre) and their accessories have been set up in position (and aligned so as to pre-define a rolling axis).

Although on the one hand this has the advantage of a considerable saving in time relative to a roll change carried out in the line, on the other hand this method has the disadvantage of a substantial consumption of energy for operating lifting and transfer apparatus of considerable power, as is required for the size and weight of the rolling stand of a PPM machine. Furthermore, another known disadvantage is the production and maintenance costs and the times of use for which the said lifting and transfer apparatus must be available which, among other things are only utilised to a small part of their potential.

A further disadvantage is also constituted by the time required for the replacement of a rolling stand which, although less than that for a roll change carried out in line, is still considerable.

Indeed such a change-over involves a whole series of operations starting from the detachment of the rolling stand from the underlying support frame and of the entry guide and the exit guide of the PPM from the support frame, the raising and transfer of the stand away from the rolling line, and operations relating to the disconnection of all the hydraulic, pneumatic and electrical lines etc.

such as the disengagement of the working rolls from their respective drive shafts. All these operations must then be repeated upon insertion of a new stand and this stand must be exactly aligned with the rolling axis.

The problem which is at the basis of this invention is to provide a rolling stand for a PPM, having such structural characteristics that the change-over of rolls can be carried out in such a manner as to overcome the disadvantages mentioned above with reference to the known art.

This problem is solved according to the invention by a rolling stand comprising two working rolls with their roll chocks and accessories, an entry guide, and at least one pair of constraining elements on the exit side for supporting a mandrel backup bar aligned with the rolling axis A of the stand, characterised in that the working rolls and their roll chocks and accessories are mounted on a self-supporting frame which can be inserted in and removed from the stand, locking means being provided for releasably locking the frame when positioned in the stand.

In accordance with a secondary characteristic of this invention, the self-supporting frame comprises four pillars fixed at their lower ends to a base or bed and made rigid at their upper ends by a removable head plate, opposing pairs of the said pillars defining corresponding seats for receiving the roll chocks of the said rolls and their accessories, the said head plate being provided with apertures overlying the said seats.

In accordance with a further characteristic of this invention, the lower part of the self-supporting frame is provided with wheels for engaging corresponding rails supported by the base of the stand and extending perpendicular to the rolling axis, the rails to advantage being of a withdrawable type.

Further characteristics and advantages will become clearer from the following description, made with reference to the appended drawings, in which an embodiment of a rolling stand according to the invention is illustrated.

In the drawings: Figure 1 is a schematic perspective view of a press-piercing mill (PPM) including a rolling stand according to the invention, Figure 2 is a partially-sectioned side view of a rolling stand according to the invention; Figure 3 is a section taken on line Ill-Ill of Figure 2; Figure 4 is a section of the same rolling stand as the previous figures.

With reference to the said drawings, a press piercing mill (PPM) is generally and schematically indicated 1 and comprises a rolling stand 2, an entry guide 3, which may be of a linear or roller type, a piercing mandrel 4, fixed or otherwise mounted on the end of a mandrel backup bar 5, which extends along the rolling axis A on the exit side of the PPM.

The stand 2 in its turn comprises two front pillars 6, 7 and two rear pillars 8, 9 fixed to a base frame 10 and made rigid at their upper ends by a head plate 11 so as to constitute a monolithic structure able to withstand the considerable forces generated during the rolling and simultaneous piercing of a billet.

A pair of constraining elements 12, 13 and respective actuator members, for example hydraulic cylinders 14, 1 5 are carried by the rear pillars 8,9 for the purpose of holding the mandrel back up bar 5 exactly in alignment with the rolling axis A during operation of the PPM.

A self-supporting frame 1 6 is releasably engaged in the rolling stand 2 in a manner which will be described below and comprises four pillars 17, 18 and 19, 20 all fixed at their lower ends to a base 21 and releasably received at their upper ends in respective seats 22, 23 and 24, 25 formed in a head plate 26. The head plate 26 has such a structure and size as to make the pillars 1 7 to 20 rigid and form an essentially cage-like selfsupporting structure.

Between the pillars 17, 19 and 18, 20 of the frame 16, and in face contact therewith, are releasably inserted roll chocks 27, 28 and 29, 30 of respective ones of the working rolls, that is, the lower roll 31 and upper roll 32. The positioning of these rolls 31 and 32 to define a corresponding rolling axis, is effected outside the line, with the use of essentially the same technique and means conventionally used for making ready a conventional rolling stand.

A lower part of the frame 1 6 has pairs of wheels 33, 33, 34, 34 of such a size and shape as to engage rails 35, 36 supported by the rolling stand 2 on the base thereof in a position between the pillars 6, 8 and 7, 9. More particularly, the rails 35, 36 are perpendicular to the rolling axis of the stand 2 and extend out of the stand on the opposite side from that facing the drive extensions 37, 38 of the working rolls.

Two apertures,39,40 are formed in the head plate 26 of the frame 1 6 for the passage of actuators 41,42 supported by the head plate 11 of the rolling stand 2. In this manner these actuators 41, 42 can exert forces on the roll chocks 27,28 and 29, 30 of the working rolls when the frame 16 is inserted in the rolling stand 2.

It should also be noted that, in accordance with a further characteristic of this invention, the pillars, 19, 20 of the frame 1 6 support a pair of constraining elements 43, 44, and respective hydraulic operating cylinders 45, 46, for cooperating with the constraining elements 12, 13 of the stand 2 to correctly maintain the position of the mandrel backup bar 5 against forces exerted thereon during operation of the PPM.

By 47, 48 are schematically indicated members for releasably locking the frame 1 6 in the rolling stand 2, a locking which occurs when the rolling axis defined by the rolls positioned in the frame 1 6 coincides with the rolling axis defined by the stand 2 and by the entry guide 3 mentioned above. An actuator indicated 49, in particular a hydraulic cylinder, is used for moving the frame 1 6 on the rails 35, 36 during the insertion of the frame itself in the stand 2 or its removal therefrom.

The advantages achieved by the rolling stand of this invention are entirely clear from what has been described with.reference to the appended drawings and are basically constituted by the rapidity with which it is possible to change the working rolls and the greater security with which the mandrel back up bar 5 is supported during operation of the PPM.

Indeed, in order to change-over the rolls, either because the wear limits have been reached or particularly when it is required to change the calibre of the pierced round intermediate blanks to be produced, it suffices to disengage the actuators 41, 42 from the frame 16, and after unlocking the members 47, 48 to push the operative unit constituted by the frame 1 6, the working rolls and the accessories mounted in the said frame, out from the stand. Subsequently another frame 1 6 with new working rolls and respective roll chocks is inserted in the rolling stand 2 which has thus been left vacant, the frame having been prepared to the side of the PPM while the substituted frame 1 6 was operative therein.

It should be noted that when the frame 1 6 with the new rolls is positioned appropriately in the stand 12, the pairs of wheels of the frame itself are disengaged from the rails 35, 36 by, for example, withdrawing the rails from beneath the bottom of the rolling stand 2.

It has been found that the rolls of a stand having the structure in accordance with this invention can be exchanged in fifteen to sixteen minutes, resulting in a considerable and valuable improvement in the daily productivity of the PPM.

Claims (5)

1. Rolling stand for a press-piercing mill, comprising two working rolls with their roll chocks and accessories, an entry guide, and at least one pair of constraining elements on the exit side for supporting a mandrel back up bar aligned with the rolling axis A of the stand, characterised in that the working rolls (31,32) and their roll chocks and accessories (27, 28 and 29, 30) are mounted in a self-supporting frame (16) which can be inserted in and removed from the stand (2), means (47, 48) being provided for releasably locking the frame (16) when positioned in the stand (2).

2. Rolling stand according to Claim 1, characterised in that the frame (16) comprises four pillars (17, 18 and 19,20) fixed at their lower ends to a bed or base (21) and made rigid at their upper ends by a removable head plate (26), pairs of the pillars (17, 18 and 19, 20) being mutually spaced apart by a predetermined distance to receive the roll chocks (27, 28 and 29, 30) of the working rolls (31,32).

3. Rolling stand according to Claim 2, characterised in that a pair of pillars (1 9, 20) of the said frame supports a pair of constraining elements (43, 44) and their respective actuator members (45, 46) for cooperating with the constraining elements (12, 13) of the stand (2) in supporting the mandrel backup bar (5).

4. Rolling stand according to Claim 3, characterised in that the lower part of the frame (16) has wheels (33, 34) for engaging respective rails (35,36) supported in the base of the stand (2) and extending perpendicular to the rolling axis (A) outside and laterally of the stand (2).

5. Rolling stand substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.