Abstract:
In a method for adjusting a rolling curve of drive pinions of ring rollers to a neutral zone within a tapering portion of a roll pass of the ring rollers of a cold pilger rolling mill, circular pinions are arranged and secured eccentrically on a roller axis of the ring roller. The circular pinions are driven by sine-shaped tooth racks.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a method for adjusting the roll curve of the drive pinions of ring rollers to the neutral zone within the tapering roll pass of the ring rollers of a cold pilger rolling mill.  
           [0003]    2. Description of the Related Art  
           [0004]    Cold pilger rolling mills are suitable to reduce extruded hot-rolled or continuously cast thick-walled metal loops, in particular, copper loops, in a single working pass with comparatively great stretching to produce elongate, thin-walled as well as drawable pipes with minimal eccentricity.  
           [0005]    The cold pilger method used in this context is a forming rolling method for metal pipes in which with a larger number of forming steps the diameter and wall thickness are reduced.  
           [0006]    In this connection, a stationary rolling mandrel, tapering in the rolling direction, is positioned in the interior of the pipe during the rolling process. The rolling mandrel is fastened on a long mandrel rod which is clamped and secured in a mandrel thrust block.  
           [0007]    A roller pair rolls in a reciprocating fashion the tubular rolling stock positioned on the mandrel and stretches it, similar to a rolling pin used for rolling and stretching dough.  
           [0008]    The roller pair is supported in a roll stand, which can be reciprocated back and forth, and is driven, as the roll stand moves by pinions connected to the roller pair and meshing with two stationary tooth racks. In this connection, the roll passes roll in a reciprocating fashion synchronously with the oscillating rolling stand.  
           [0009]    The rolling stand itself is moved back and forth by a motor piston driven by a crank drive. In the conventional configurations according to the prior art, the roll passes are substantially circular and decrease along the roller circumference. The decreasing or tapering cross-section between rollers and the rolling mandrel reduces simultaneously the diameter and wall thickness of the rolling stock.  
           [0010]    In the area of at least one of the two dead centers the rollers release the loop briefly so that the loop is advanced and/or rotated at the same time, for example, by approximately 60°, respectively. In this method, the advancing stroke as well as the return stroke are used for forming. The advancing stroke and the rotational angle at both dead centers depend on the pipe material and the quality requirements. The yield strengths of rolled pipes covers a range from 400 N/mm 2  up to more than 1,500 N/mm 2  for special alloys.  
           [0011]    A purely schematic illustration of the afore described pipe rolling method is shown in FIGS. 2 a  to  2   d . FIG. 2 a  shows a reduction during an advancing stroke. FIG. 2 b  shows the exit cross-section along section line A-B. FIG. 2 c  shows a reduction during the return stroke, and FIG. 2 d  shows an exit cross-section along section line A-B.  
           [0012]    The combination of a cold pilger rolling mill with an inline coiler makes possible the manufacture of coiled pipes of, for example, 250 m length. In this connection, the pipe, exiting from the cold pilger rolling mill and rotating back and forth upon step-wise advancing during rolling, is bent to a coil by the rolling process and is placed directly into a basket which is required for the subsequent drawing process.  
           [0013]    The afore described forming process according to the cold pilger method, despite relatively minimal production speed, is of great advantage for several applications:  
           [0014]    it provides, in certain situations, relatively large cross-sectional reductions of the diameter and wall thickness, and  
           [0015]    a considerable reduction of the eccentricity as a result of compensating flow in the circumferential direction, as well as  
           [0016]    an optimization of the material microstructure as a result of mechanical hardening, in the case of  
           [0017]    production of great pipe lengths.  
           [0018]    The cold pilger method for producing pipes provides an improved roundness, more uniform stress homogenization and more uniform roughness of the surface, while  
           [0019]    narrower tolerances for diameter and wall thickness of the rolling stock can be obtained,  
           [0020]    there is no process-caused material loss,  
           [0021]    being suitable also for materials that are difficult to form, with  
           [0022]    high economic efficiency made possible by using large loop weights and loop lengths, as well as  
           [0023]    manufacture of different end product sizes from single loop size.  
           [0024]    Even so, in the prior art, as a result of the geometric conditions across the stroke length of a pilger step rolling mill, disadvantages result from the fact that, for an unchanged radius of the drive wheels, the rolling radius of the rolling passes changes in wide ranges during one rotation of the roller. In this connection, they necessarily slip on the pipe to be rolled so the pipe&#39;s product quality is decreased. The axial shearing force, which is disadvantageously generated by slipping and acts on the rolling stock, causes a series of problems. For example, it becomes more difficult or even impossible to roll thin-walled blanks with conventional advancing strokes because the end faces of the blanks during rolling will become wedged in one another so that the rolling mill output is correspondingly reduced. Moreover, the rolling mill with all its functional elements is loaded and stressed greatly as well as subjected to premature wear. In particular, roller failure and mandrel failure are observed as well as other expensive damages to the roll stand.  
           [0025]    A further disadvantage of the prior art resides in that the return stroke of the roll stand can be used only to a limited extent for the forming work. This is so because the highest reversing rolling forces occur usually during the return stroke. This has the result that the principally beneficial additional advance of the blanks at the exit dead center area cannot be fully employed and that the possible production output is accordingly reduced.  
           [0026]    Moreover, the prior art also limits the diameter reduction that is possible by the forming technology. It is obvious that with increasing diameter reduction the problem in regard to the reference circle of the pinion which is not locally adjusted increases. This also impedes the economic efficiency of the cold pilger method.  
           [0027]    In order to overcome this, the prior art suggests inter alia: a correlation of the reference circle of round, centrally arranged pinions and of the roller diameter to the actual rolling dimension or size. However, this allows only an unsatisfactory improvement of the rolling process.  
           [0028]    The patent document DE-OS 17 52 996 suggests, on the other hand, the use of spiral pinions which mesh with a suitable straight tooth rack. The known solution has the decisive disadvantage that useful roll pass length is lost and the rolling output is reduced. Moreover, this solution is limited to the straight shape of the tooth rack. However, since the roll pass developed view follows a parabola of higher degree, the approximation to the set-point curve is possible only to a limited extent.  
         SUMMARY OF THE INVENTION  
         [0029]    It is an object of the present invention to provide a method for driving the roller pair of a cold pilger rolling mill which realizes a substantially improved adjustment of the rolling curve of the pinion to the neutral zone within the tapering roll pass of the ring rollers.  
           [0030]    In accordance with the present invention, this is achieved in that for adjustment of the rolling curve of the drive pinions of ring rollers to the neutral zone within the tapering roll pass of the ring rollers circular pinions are used and these circular pinions are eccentrically arranged and secured on the roller axis. The invention achieves the following goals:  
           [0031]    reduction of the pressure load on the advancing slides,  
           [0032]    prevention of uncontrolled advancing by relative movements between roller profile and rolling stock,  
           [0033]    wear reduction at the roller profile,  
           [0034]    reduction of energy consumption by reduced frictional work,  
           [0035]    adjustment of the rolling curve of the pinion to the neutral zone within the tapering roll pass of the ring rollers,  
           [0036]    prevention of the still present disadvantages of known solutions.  
           [0037]    One embodiment of the invention resides in that for driving the pinions—and thus the ring rollers—corresponding sine-shaped tooth racks are used.  
           [0038]    This solution according to the invention reduces or prevents the disadvantages of the unsatisfactory methods and devices of the prior art, such as the slipping of the roller pair on the rolling stock with the afore described disadvantages for the rolled product and the rolling mill as well as the reduced production.  
           [0039]    A further embodiment of the method according to the invention provides that, when using circular eccentric pinions which mesh with corresponding sine-shaped tooth racks, the following four parameters can be adjusted to the current rolling size or dimension:  
           [0040]    roller diameter  
           [0041]    reference circle of pinion  
           [0042]    eccentricity  
           [0043]    angular position of eccentricity to the approach dead center of the roll stand.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0044]    In the drawing:  
         [0045]    [0045]FIG. 1 shows a diagram of the geometric conditions across the stroke length of a cold pilger rolling mill;  
         [0046]    [0046]FIGS. 2 a  to  2   d  illustrate a rolling method according to the invention with the following method steps:  
         [0047]    [0047]FIG. 2 a  a reduction during advancing stroke with eccentrically arranged pinions;  
         [0048]    [0048]FIG. 2 b  an exit cross-section along section line A-B;  
         [0049]    [0049]FIG. 2 c  a reduction obtained by the return stroke;  
         [0050]    [0050]FIG. 2 d  an exit cross-section along section line A-B.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0051]    A cold pilger rolling process, as it is well known in the prior art, is illustrated in FIGS. 2 a  to  2   d . It is used for producing or forming a pipe  12  by means of a cold pilger roller pair  10 ,  10 ′ which is supported in a roll stand, not illustrated. The pipe  12  to be processed is guided on a rolling mandrel  13 . The roll stand performs during the rolling process an oscillating movement wherein stroke frequencies up to 300 per minute and more are possible. The pipe  12  is reduced by the roll passes  11 ,  11 ′ to its finished shape or final contour. The rolling passes  11 ,  11 ′ are cut along the entire external circumference into the oppositely positioned rollers  10 ,  10 ′ and circumferentially fully enclose the pipe  12  within the rolling gap (compare FIGS. 2 b  and  2   d ). In this connection, the roll passes  11 ,  11 ′ have, according to their size, different widths and/or depths, when viewed in a developed view across the roller circumference, which is indicated by the hatched roll pass contours  11  and  11 ′ in FIGS. 2 a  and  2   c.    
         [0052]    The pipe  12  is moved during rolling in the advancing direction R. During the advancing stroke, which is indicated schematically in FIG. 2 a , the complementary cold pilger roll pair  10  and  10 ′ rolls in the conveying direction on the pipe  12  which is enclosed in the rolling gap by the roll passes  11  and  11 ′. During the return stroke, which is schematically illustrated in FIG. 2 c , the rolling of the roller pair  10  and  10 ′ on the pipe  12  is carried out counter to the conveying direction R (compare the arrows for the rotational direction  14  and the translatory direction  15  in the Figures).  
         [0053]    In FIG. 1 the geometric conditions across the stroke length of a cold pilger rolling mill are illustrated in the form of diagrams. The following data and parameters of one embodiment are used:  
                                                                         rolling of copper   87 × 11 to 40 × 2                roller diameter   375   mm           reference circle of pinion   336   mm           stroke of the stand   1,023   mm           reduction pass length   600   mm           smoothing pass length   140   mm           pinion eccentricity   13   mm           angular spacing   140   degrees                      
 
         [0054]    The roll pass developed view as a roll pass basic curve is comprised of  
         [0055]    the zone  1  in which the rollers release the rolling stock for advancing and rotation,  
         [0056]    reduction zone  2  which follows a parabola function  
         [0057]    cylindrical smoothing zone  3   
         [0058]    transition  4  in which the rolling stock can be additionally rotated and/or advanced.  
         [0059]    The curve  5  shows the neutral zone in which the longitudinal forces of the different rolling speeds are neutralized.  
         [0060]    The rolling stock proportion between the roll pass base and the neutral zone is rolled with a relatively reduced speed, the proportion between roll diameter  6  and neutral zone  5  at a higher speed.  
         [0061]    The reference circle of the pinion, which could follow the curve  5 , would also neutralize the longitudinal forces which result from the changing rolling conditions across the roll pass length. A round, centrally arranged pinion  7  can approximate these requirements only incompletely. This is so because in the leading roll pass area the proportion of the circumferential speed which is too large dominates while the circumferential speed is too small within the smoothing area of the smoothing zone  3 . Only at approximately 120° of the developed view of the roller the conditions are momentarily correct.  
         [0062]    However, when the pinion is eccentrically arranged ( 8 ) according to the present invention, an extremely far-reaching approximation of the desired curve  5  is obtained and the movement tendencies of the rolling stock are neutralized as much as possible. The roller circumference can be used to an unlimited extent and the rolling curve follows substantially the nominal curve in a much improved way in comparison to the prior art.  
         [0063]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.