Mandrel exchange in piercing mills
BACKGROUND OF THE INVENTION 
     The present invention relates to hot-rolling (piercing) of a heated metal billet under utilization of obliquely disposed, driven rolls. The billet is rolled onto and over a mandrel on a mandrel rod, the mandrel piercing the billet for obtaining the tubular configuration. 
     Processes of the type above employ mandrel and mandrel rods which are to be reused. The pierced tube is stripped off the mandrel and the latter is inspected and, possibly, replaced. It is also known to introduce the rolled tube as soon as possible into a water tank for cooling. This is particularly necessary as the metal tube, as made, is usually red hot following rolling. Moreover, insertion of water is necessary to prevent oxidation of the inner and outer surfaces, for example, of copper tubing. 
     DESCRIPTION OF THE INVENTION 
     It is an object of the present invention to combine cooling and mandrel replacement functions in rolling mills for seamless tubes. 
     It is another object of the present invention to provide a new and improved method of exchanging mandrels in such a mill. 
     It is a specific object of the present invention to improve rolling mills for rolling of seamless tubes under utilization of obliquely disposed rolls which roll a round billet onto a mandrel held by a mandrel rod in the range of the rolling gap. The improvement being related in particular to madrel exchange and tube-cooling functions. 
     In accordance with the preferred embodiment of the present invention, the mill, as per the specific object, is improved by providing two water tanks adjacent to the rolling gap, one behind the other, and being passed through by the tube as rolled and by the mandrel rod. The tank closest to the rolling gap contains the mandrel exchange device, and that tank can and will be emptied for the exchange of mandrels; the other tank remains filled. As the tank to be emptied must have openings for passage of the tube and the rod, these openings are provided with means for preventing the discharge of water. Also, the opening in the partition between the two tanks must be blocked when the one tank is emptied for the requisite mandrel exchange. 
     The invention, thus, permits the exchange of the mandrels under conditions which do not necessitate an underwater exchange. The water is usually quite dirty and turbid because of scale being washed off the tube. Thus, exchanging the mandrel inside the filled cooling tank is undesirable and unreliable since fastening of the new mandrel to the rod cannot be adequately observed. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     While the specification concludes with claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention, and further objects, features, and advantages thereof, will be better understood from the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematic cross-section view through a mill for rolling round billets into seamless tubing, showing also tube cooling and mandrel exchange facilities; the mill is shown in particular during a rolling operation; and 
     FIG. 2 shows the same mill and facilities, but during an exchange of mandrels. 
    
    
     Proceeding now to the detailed description of the drawings, FIG. 1 illustrates a round billet 1&#39;, being rolled into a seamless tube 1 by means of obliquely positioned rolls 7. A mandrel 4 on a mandrel rod 6 pierces the billet. The tube so made passes immediately through an opening 8 into a first water-filled tank 19a, and from there through a partition with an opening 9 into a second water-filled tank 19. Nozzles 23 are provided at opening 8 to blow any water, tending to escape, back into the tank. 
     As schematically indicated, tube 1 passes through and clears a mandrel holder 3 which holds one or more spare mandrels 5. Holder 3 is partially submerged in the water in tank 19a; but a spare madrel 5, possibly having been used in a prior pass, is available for inspection and can, if necessary, be replaced by another one during the particular rolling pass illustrated in FIG. 1. 
     Following the completion of rolling, the tube is withdrawn and gripped by a suitable rolling device, to be stripped off the current mandrel 4. This mandrel 4 will be captured by holder 3, and the rod is disconnected from the mandrel. 
     In order to effect the desired mandrel exchange, nozzles 23 at opening 8 are turned on full force as the tube is being taken out of the tank 19a. This tank is now emptied through a discharge valve 20. A pump (not shown) may be connected for otaining speedy discharge. As can be seen from FIG. 2, a pair of nozzles 21 in opening 9 is now turned on to prevent the water in tank 19 from flowing into the other tank, 19a. 
     After tank 19a has been emptied, the mandrels are exchanged. The capture of mandrel 4 and its disconnection from rod 6, the turning of turret-like holder 3 to place the other mandrel, 5, into the range of rod 6, the advance of rod 6 and its connection to the new mandrel 5, are operations, all of which are carried out while tank 19a is empty. Mandrel 4 can now be inspected; it remains outside tank 19a, even after tank 19a has been refilled. 
     Following the completion of the mandrel exchange, the water is returned into the tank 19a via inlet valve or tap 22. Nozzle pair 21 can be turned off as soon as the water level in tank 19a has sufficiently risen. The next pass, i.e., rolling and piercing of the next billet to obtain another seamless tube, can now proceed. 
     The invention is not limited to the embodiments described above; but all changes and modifications thereof, not constituting departures from the spirit and scope of the invention, are intended to be included.