GB2128119A - Method and apparatus for the recirculation of mandrels in a restrained mandrel rolling mill for manufacturing seamless tubes - Google Patents

Abstract

A method of recirculating mandrels in a restrained mandrel rolling mill is described in which a new mandrel 2, or at least a mandrel reconditioned for rolling, is pre-engaged in a pierced blank 35 in a position to one side of the rolling axis and is subsequently transferred to a position on the rolling axis upstream of the rolling mill, simultaneously with the removal from this position of a used mandrel recovered from the rolling mill itself at the end of a previous rolling cycle. <IMAGE>

Description

SPECIFICATION Method and apparatus for the recirculation of mandrels in a restrained mandrel rolling mill for manufacturing seamless tubes The invention relates to a method of recirculating mandrels in a restrained mandrel rolling mill particularly for the manufacture of seamless tubes.

The invention also relates to apparatus for carrying out the said method.

In a rolling mill operating in accordance with the so-called restrained mandrel method, an axiallypierced blank engaged on a corresponding mandrel is rolled by passage through a plurality of successive rolling stands and during this passage the mandrel is "restrained" by a suitable motor-driven restraining device. At the end of the rolling operation, the mandrel, after being removed from the corresponding tube, is returned by the same restraining device to its initial position upstream of the first rolling stand, passing back through the said plurality of stands.

It is known that in the production of seamless tubes by means of a rolling mill of the said type, great importance is given to the surface conditions, the lubrication and the temperature of the mandrel used, all of which must clearly be the optimum. It is also known that once rolling has been finished, a mandrel is returned to the initial position and a whole series of operations is carried out on it to recondition it for a new rolling cycle.

The time required for completing these operations is not excessively long but is, however, much greater than the time needed for rolling a tube. Consequently in order to maximisethe potential of the rolling mill and to have available optimally-conditioned mandrels (surface, lubrication and temperature optimal) upstream ofthe rolling mill, there is provided a mandrel recycling system including successively all the stations necessary for completing the said operations, four to five mandrels being kept in circulation in this recycling system. In this manner, it is possible to ensure that there will always be a mandrel in the optimum condition at the entry to the rolling mill, ready to be used in the rolling cycle and, hence, the potential of the rolling mill can be more fully utilised.

In accordance with the known art, when a mandrel is returned to its initial position after the rolling, it is immediately removed since a new mandrel may be brought into this position equally rapidly, the end of this mandrel furthest from the rolling mill being locked in the restraining device.

Between the free end of the mandrel and the entry to the rolling mill there mut be left a space for receiving the blank to be rolled. Consequently there is a dead period between two successive rolling cycles to allow the restraining device to reach a position spaced from the entry to the rolling mill by distance greater than the length of the mandrel and the blank (about 30-35 m), the removal of the used mandrel, the positioning of a new mandrel, the positioning of the blankto be rolled and the engagement of the mandrel in the blank.

The main object of the present invention is to provide a. method and apparatus for recirculating mandrels in a rolling mill of the type under consideration, which permits a further substantial shortening of the dead periods that at present exist between two successive rolling cycles.

This object and others which will become more apparent from the description which follows, are achieved by a method of recirculating mandrels which, in the present invention is characterised in that it comprises the step of pre-engaging a new mandrel, or a mandrel reconditioned for rolling, in a corresponding axially-pierced blank to be rolled, this step being carried out to one side of the rolling axis, and the further step of transferring the mandrel and its blank into a predetermined position on the rolling axis upstream of the rolling mill simultaneously with the removal from this position of a used mandrel brought there at the end of the preceding rolling cycle.

Further characteristics and advantages of the invention will become clearer from the description given below of a method of recirculating mandrels according to the invention, reference being made to the appended drawings in which apparatus for carrying out the method is shown by way of non-limiting example.

In the drawings: Figure 1 is a schematic view of apparatus for carrying out the mandrel-recirculating method of the invention; Figure 2 is a view, again schematic but to an enlarged scale, of a detail of the apparatus of Figure 1; Figures 3 and 4 are a view from above and a front view respectively, to a further enlarged scale, of a transfer device used in the apparatus of the preceding Figures.

With reference to the said Figures, reference 1 generally indicates a plurality of rolling stands of a rolling mill operating in accordance with the socalled restrained mandrel method, for manufacturing seaimess tubes, the stands being aligned along a horizontal rolling axis A. A mandrel 2 is shown in an operative position extending between the plurality of stands 1 in exact alignment with the axis A. A blank is engaged on the mandrel 2 and is undergoing rolling but is not shown for clarity of the drawings.

The spigot 3 of the mandrel 2 is engaged in a mandrel carrier block 4 of known type fixed to the end of a rack rod 5 which extends along the rolling axis A and is driven by a plurality of motorised pinions 6. The pinions, the rack rod 5 and the mandrel carrier block 4 constitute a mandrel restraining device by means of which the feeding of a blank to the rolling mill, the restraining of the mandrel during rolling and the recovery of the mandrel from the rolling mill once rolling is finished are carried out, as will be better understood from the following description.

Clearly the restraining device described schematically above is merely preferred, any other type of restraining device of the known art being usable instead, according to the technical requirements and availability.

Once rolling has been finished, the tube 8 (as soon as it has been formed) is freed from the mandrel 2 by means of a plurality of removal stands (three or four) schematically indicated 7 and the mandrel thus released from the tube is returned to an initial position (Figure 2) by the restraining device 4, 5 and 6 described above. In this initial position, the mandrel 2 is supported by a plurality of rollers 9 aligned with the rolling axis A upstream of the rolling mill.

More particularly and in accordance with the known art, the rollers 9 are of the so-called disappearing type to allow the rectilinear displacements of the rack rod 5 and the mandrel carrier block 4 along the rolling axis A.

A roller track 10 extends laterally of the plurality of rollers 9 parallel to the axis A and a plurality of transfer arms 11 operate between the track 10 and the rollers 9.

Figures 3 and 4 show a preferred but non-limiting example of one of the transfer arms.

A lever 13 is keyed onto a driven shaft 12 extending parallel to the rolling axis A, the lever 13 comprising two arms 14, 15 the free ends of which support a freely rotatable pin 18 with the interposition of respective bearings 16,17. On this pin 18, between the arms 14 and 15 is keyed a rod-shaped vertical support 19 the upper end 20 of which is cradle shaped and has such a size as to receive a mandrel. Also keyed onto the pin 18 is a gear wheel 21 which is in engagement with a gear wheel 22 rotatable on a pin 23 carried by the arm 14 of the lever 13. This wheel 22 is in its turn engaged with an annular rack 24 which is fixed to a support 25 and coaxially surrounds the driven shaft 12.From what has been described and illustrated it is clear that if the shaft 12 is rotated the rod shaped support 19, although maintaining its vertical position, will rotate about the axis of the shaft 12 at a distance therefrom determined by the length of the lever 13. More particularly, the rod-shaped support is counterweighted by a mass 26 formed with or otherwise fixed to the lever 13 in an eccentric position relative to the axis of the driven shaft 12.

The roller track 10 extends as far as a mandrelcooling station 27 to which mandrels can be transferred by devices, not shown since they are entirely conventional, for example transfer devices constituted by lever systems. Similar devices then transfer cooled mandrels from the station 27 to a roller track 28 extending parallel to the axis A on that side thereof opposite that occupied by the roller track 10 mentioned above.

This roller track 28 is extended by a chain conveyor 29 which may, but need not, pass through an induction oven 30 and then subsequently through a lubricating station 31 preferably constituted by a suitably dimensioned chamber provided for the spraying of predetermined lacquers onto the mandrels passing therethrough.

At the exit from the lubricating station there is a chain conveyor 32 also extending parallel to the rolling axis A essentially as an extension of the chain conveyor 29 mentioned above. The chain conveyor 32 is then extended by a roller conveyor 33 which terminates close to the arrival zone 34 of pierced blanks 35 to be rolled.

Between the conveyor 33 and the plurality of rollers 9 is a line 36 for the pre-engagement of a mandrel in a blank 35. This line basically comprises an initial, chain section generally indicated 37 followed by a roller section 38. The chain section 37 has means of known type, not shown, for grasping and pushing forward a mandrel loaded thereon.

Between the roller conveyor 33 and the line 36 is a "reservoir" 39 which can receive various mandrels in case of any interruptions in the working cycle of the rolling mill or of the various stations constituting the mandrel recycling system upstream of the rolling mill itself. Obviously it is possible to by-pass this reservoir in order to effect rapid transfer of the mandrels.

Between the roller track 33, the reservoir 39 and the pre-engagement line 36 are transfer members operable to allow either the accumulation of the mandrels or their rapid transfer. Similar transfer devices to those described with reference to Figures 3 and 4 are operatively disposed between the pre-engagement line 36 and the plurality of disappearing rollers 9.

The method of the invention is effected by means of the apparatus described above and is described below.

During rolling, a mandrel 2 is "restrained" by the restraining device comprising the driven rack 5 and the mandrel carrying block 4. A second mandrel 2A is on the roller track 10 while a further pair of mandrels 2B,2C is in the cooling station 27. Another mandrel 2D is undergoing the lubricating treatment and a still further mandrel 2E is being pushed by the chain 37 into a pierced blank 35 located on the end rollers 38 close to the entrance to the rolling mill.

After a rolling operation, the used mandrel 2 is recovered and returned to its initial postion by the same restraining device (4, 5, 6) where it is supported by the plurality of rollers 9. From this position the mandrel 2 is immediately transferred onto the roller track 10. Simultaneously, the mandrel 2E with its blank 35 engaged thereon is located on the vacated plurality of rollers 9. The spigot of this mandrel 2E is automatically engaged by the mandrel carrier block 4 and after this engagement the rack rod 5 is driven by the plurality of motorised pinions 6. In this manner, a new rolling cycle is started.

During rolling, the mandrel 2D which has been lubricated, is transferred to the pre-engagement line 36 while the mandrel 2C cooled to a suitable temperature of about 110 -120 may be transferred to the induction oven 30 and the to the lubricating station 31. In the meantime, the used mandrel 2 as it travels along the roller track 10 undergoes cooling in air and, occasionally, its surface conditions and the straightness of its axis is checked. When, as a result of these checks, it is found that the mandrel 2 is not re-usable for a new rolling cycle, it will be discharged, for example at an intermediate station 40 and a new mandrel will be fed into the mandrel cycle from store 41 of new mandrels.

At the end of the roller track 10, the mandrel 2 having completed its first cooling phase in air, is transferred into the water cooling station 27.

The pre-engagement of the mandrel in a blank 35 while rolling is being carried out gives rise to the indisputable advantage of a substantial reduction in the dead time between one rolling cycle and the next.

Indeed, the time required for the transfer of a used mandrel from its initial position to the roller line 10 and simultaneously for the positioning of a preengaged mandrel on the rolling line is considerably less than the time required according to the known art for the transfer of a used mandrel away from the rolling line, the positioning on the rolling line of a new mandrel in and a blank, and then the engagement of the mandrel in the blank and the feeding of the mandrel-blank unit into the rolling mill. The dead time is also reduced as a result of the fact that the "return" path of the mandrel carrier block according to the invention is shorter than that which is necessary according to the known art, if account is taken of the length of a mandrel together with a pierced blank.

Claims (3)

1. A method of recirculating mandrels in a restrained mandrel rolling mill for manufacturing seamless tubes, characterised in that it comprises the step of pre-engaging a new mandrel, or a mandrel reconditioned for rolling, in a corresponding axiallypierced blankto be rolled, this step being carried out to one side of the rolling axis, and the step of transferring the mandrel and its blank into a predetermined position on the rolling axis upstream of the rolling mill simultaneously with the removal from this position of a used mandrel brought there at the end of the preceding rolling cycle.

2. A method as claimed in claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

3. Apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.