Patent Publication Number: US-2010107713-A1

Title: Method and device for rolling a rolling stock in a rolling mill with a cross-rolling mill

Description:
The invention relates to a method and a device for rolling a rolling stock in a rolling mill with a cross-rolling mill and claims the priority of the German patent application 10 2007 014 079.9. 
     Rolling mills with cross-rolling mills are used for rolling, for example, seamless metal pipes or other rolling stock with a round cross-section, for example rods. 
     In a cross-rolling mill, several rollers are arranged at the periphery of rolling stock to be rolled. The rolling stock is rotated between the rollers which rotate with the same rotation direction and is thereby deformed. For moving the rolling stock in the longitudinal direction, the rollers are tilted at a certain angle with respect to the longitudinal axis of the rolling stock in the tangential plane. This arrangement then produces a helical movement of the rolling stock. 
     The aforementioned construction of a cross-rolling mill has a number of disadvantages which may result from the rotation of the rolling stock about its longitudinal axis. This relates, in particular, to a limit for the maximal length of the rolling stock, complex support and guiding devices and a low throughput speed. Variations in the rotation of the rolling stock are detrimental for the quality of the rolling stock. 
     These disadvantages have led to the development of planetary cross-rolling mills which superimpose the rotation motions of several components to thereby allow milling without rotating the rolling stock about its longitudinal axis. The German patent 195 10 715 C2 describes a planetary cross-rolling mill of this type. The structure of the device disclosed in DE 195 10 715 C2 has a rotor moved by way of a main drive, wherein four planetary rollers are rotatably supported in the rotor which surrounds the rolling stock. These planetary rollers rotate in unison with the rotor. In addition to rotation with the rotor, the planetary rollers are rotationally driven about their longitudinal axis by an additional drive. 
     An additional rolling mill is frequently provided downstream of a planetary cross-rolling mill in order to continue the deformation process started by the planetary cross-rolling mill. For example, a longitudinal rolling mill or an additional planetary cross-rolling mill can be arranged downstream. 
     It is an object of the invention to propose a method and a device which obviates the aforementioned disadvantages and enhances the efficiency of the rolling process. 
     The object is attained with the features of the independent claims. Advantageous embodiments are recited in the dependent claims. 
     The invention is a based on the concept to roll the rolling stock, at least during a certain time period, simultaneously on a mandrel rod both in the planetary cross-rolling mill and in the additional rolling mill arranged downstream. The invention includes a mandrel rod which has a length that is greater than the distance between the planetary cross-rolling mill and the additional rolling mill in the rolling direction and, in particular, is greater than the hollow block length. The intent is to make the mandrel rod so long that it engages with at least one roller set of the downstream rolling mill, when the pipe exiting the planetary cross-rolling mill reaches that roller set. The mandrel rod comes into engagement when the wall thickness of the pipe is reduced by the rollers of the respective rolling mill on the mandrel rod. 
     More particularly, the invention makes it possible to better distribute the deformation work over the two rolling mills. The planetary cross-rolling mill can now be used to roll a first product which may have relaxed requirements for precision. The precise finish rolling is then performed in a downstream rolling mill. With this approach, the rollers in the planetary cross-rolling mill need to be changed less frequently. The wall thickness can be calibrated with the downstream rolling mill to the desired dimension without requiring reconfiguration. Moreover, only a few mandrel rod with predetermined diameters need to be kept in inventory for the planetary cross-rolling mill, because the rolling stock can be deformed to any intermediate cross-section in the additional rolling mill. This reduces the number of mandrel rods that an operator must keep in inventory. In addition, the mandrel rod require less frequent changes which improves time utilization. Stretching of the milling stock can also be distributed to both stands which allows higher rolling speeds in the finish rolling mill. 
     According to the invention, a rolling mill for rolling a rolling stock with a planetary cross-rolling mill and an additional rolling mill arranged downstream in a rolling direction, has a mandrel rod of a length that is greater than the distance between the planetary cross-rolling mill and the additional rolling mill in the rolling direction, and that is, in particular, preferably longer than the hard block length. The distance between the planetary cross-rolling mill and the additional rolling mill in the rolling direction is defined as the distance between the point of the planetary cross-rolling mill where the rolling stock is for the last time in engagement with the rollers of the planetary cross-rolling mill, and the point where the rolling stock is for the first time in engagement with the first rollers of the additional rolling mill. 
     As intended with the invention, the mandrel rod is long enough to extend through the rolling stock while the rolling stock is both in the rolling gap of the planetary cross-rolling mill as well as in the rolling gap of the additional rolling mill. 
     In a preferred embodiment, a holder for the mandrel rod is provided which is able to hold the mandrel rod in a position where the mandrel rod extends through the rolling gap of the planetary cross-rolling mill and simultaneously protrudes at least partially into a rolling gap of the additional rolling mill. In a preferred embodiment, the holder is disposed on the side of the planetary cross-rolling mill that faces away from the additional rolling mill. In a preferred embodiment, a linear drive is provided for linearly moving the holder of the mandrel rod. In this way, the mandrel rod can be retracted for receiving the rolling stock, and the mandrel rod can then be brought into a position where the mandrel rod extends through the rolling gap of the planetary cross-rolling mill and simultaneously at least partially protrudes into a rolling gap of the additional rolling mill. 
     In a preferred embodiment, a longitudinal rolling mill is arranged downstream of the planetary cross-rolling mill in the rolling direction. A longitudinal rolling mill is defined here as a rolling mill with rollers having axles that are arranged parallel to one another and/or perpendicular to the rolling direction. 
     In a preferred embodiment, the mandrel rod is formed in several parts. The mandrel rod has in a preferred embodiment different diameters. If the mandrel rod is formed of several parts, then the change in diameter along the longitudinal axis of the mandrel rod can be easily adjusted, for example by removing a section with a smaller diameter and attaching on the remaining part of the mandrel rod a mandrel rod section with a somewhat larger diameter. 
     In a preferred embodiment, a measuring device for measuring the rotation of the rolling stock is arranged between the additional rolling mill and the planetary cross-rolling mill. In particular, when the additional rolling mail is a longitudinal rolling mill, where the rolling stock is to be rolled almost without rotation, it is advantageous to provide a controller for the planetary cross-rolling mill, which controls the operation of the planetary cross-rolling mill based on measurements from the measuring device such that the rolling stock does not rotate. For the actual structure of a device that performs such a control function and for an actual methods for such control, reference is made to DE 103 49 056 A1, the disclosure in these application documents is incorporated herein by reference. 
     In a preferred embodiment, the planetary cross-rolling mill includes a main drive for rotating a rotor surrounding the rolling stock and planetary rollers rotatably supported in the rotor. In a preferred embodiment, the planetary cross-rolling mill also includes an additional drive for rotating the planetary rollers about their longitudinal axis. For a preferred structure of a planetary cross-rolling mill, reference is also made to DE 195 10 715 C2 which describes as part of the written description a configuration for a planetary cross-rolling mill. The planetary cross-rolling mill preferably includes three or more planetary rollers, in particular four planetary rollers. 
     In the method of the invention for rolling a rolling stock in a rolling mill with a planetary cross-rolling mill and an additional rolling mill arranged downstream in a rolling direction, the rolling stock is located, during a time period when the rolling stock is rolled, both in a rolling gap of the planetary cross-rolling mill and also in a rolling gap of the additional rolling mill. Preferably, during the major portion of the rolling operation, the rolling stock is located both in the rolling gap of the planetary cross-rolling mill as well as in the rolling gap of the additional rolling mill. Preferably, the rolling stock is either only in the rolling gap of the planetary cross-rolling mill or in the rolling gap of the additional rolling mill only during the necessary startup and shutdown phase. 
     The mandrel rod extends through the rolling stock while the rolling stock is both in the rolling gap of the planetary cross-rolling mill and in the rolling gap of the additional rolling mill, wherein the mandrel rod has a length that is greater than the distance between the planetary cross-rolling mill and the additional rolling mill in the rolling direction. 
     The method of the invention is preferably used for rolling tubular rolling stock into so-called loops. The rolling stock is preferably metallic, but may also be made of a different material, for example plastic. 
     The method of the invention and the rolling mill of the invention are particularly suited for rolling predominantly thin-walled rolling stock. 
    
    
     
       The invention will now be described with reference to a drawing which shows an exemplary embodiment. 
         FIG. 1  shows in a schematic side view the rolling mill according to the invention with a planetary cross-rolling mill and a longitudinal rolling mill together with milling stock to be milled, and 
         FIG. 2  shows in a schematic side view the rolling mill of  FIG. 1  in a rolled-out state. 
     
    
    
       FIG. 1  is a rolling mill with a planetary cross-rolling mill  20 , a longitudinal rolling mill  25  and an interposed measuring device  8 . A mandrel rod  10  is held in a holder  11 . A linear drive  12  is configured to linearly move the holder  11 . As illustrated in  FIG. 1 , the mandrel rod  10  has a length which is greater than the distance between the planetary cross-rolling mill  20  and the longitudinal rolling mill  25 . The rolling stock  6  is rolled on a mandrel rod both in the planetary cross-rolling mill  20  as well as in the longitudinal rolling mill  25 . 
     The planetary cross-rolling mill  20  includes several planetary rollers  1  which roll with their lower sections on the rolling stock  6 . The planetary rollers  1  are inclined relative to the longitudinal axis of the rolling stock  6  both in the vertical and in the horizontal plane. 
     The rearward end of the planetary rollers  1  is rotatably supported in a rotor  2  having a rotation axis that is identical with the longitudinal axis of the rolling stock. The rotor  2  is driven from the driveshaft  3  of a main drive by way of a gear. The rotor  2  and the planetary rollers  1  supported in the rotor rotate about the rolling stock  6 . 
     In addition, gear wheels  4  which mesh with a planetary gear  5  are disposed on the planetary rollers  1 . Meshing with the planetary gear  5  causes the planetary rollers  1 , due to the rotation of the rotor  2 , to rotate about their own axis. 
     The planetary gear  5  is driven via a gear by the driveshaft  7  of an additional drive. This rotation of the planetary gear results in a superimposed rotation of the planetary rollers  1  which is the result of the sum of the two rotary motions. 
     The rolling stock  6  does not rotate due to the superimposed rotations of the planetary rollers  1  and the rotor  2 . While the rolling operation continues, the required ratio between the number of rotations of the rotor  2  and of the planetary rollers  1  changes due to changes in the parameters, for example changes of the material characteristic of the material of the rolling stock in certain areas, temperature variations, scale deposits or changes in the surface friction parameters. A measuring device  8  is arranged at the exit of the planetary cross-rolling mill, wherein the measuring device  8  measures the rotary motion n Pipe  of the rolling stock  6  that may be caused by changes in the parameters, and transmits the rotary motion to a computer which then controls the drives of the planetary cross-rolling mill  20  so as to prevent the pipe from rotating. 
       FIG. 2  shows the rolling mill in a so-called “rolled-off” state where the mandrel rod  10  protrudes from the end of the longitudinal rolling mill  25 .