Patent Publication Number: US-2005115295-A1

Title: Method and installation for the production of an aluminum sheet with a textured surface

Description:
BACKGROUND OF THE INVENTION  
      The invention relates to a process and unit for producing a cold rolled strip of aluminium or an aluminium alloy with a textured surface comprising passing a cold rolled strip immediately after cold rolling through a roll gap of two textured rolls bearing a roughness pattern, wherein the roughness pattern is transferred to the surface of the strip as a result of the force of the textured rolls acting on the strip, and, thereafter, coiling the textured strip.  
      In the automotive industry strips and sheets of aluminium alloys are employed for the manufacture of bodywork parts, whereby the sheets are shape-formed by deep drawing or stretch drawing. Lubricants have to be employed to carry out this deep drawing and other shape-forming steps. By pre-coating the strips or sheets in the rolling mill not only is the forming procedure simplified, but also optimal protection during transportation achieved.  
      In a procedure commonly used today the strip manufacturer coats the cold rolled strip with an oil or a water-soluble dry lubricant and the prepared strip supplied to the sheet-forming company for the purposes of deep drawing.  
      In the case of an aluminium strip that has been produced in the normal manner using work rolls with a roll finish corresponding to a mill-finish surface texture, the lubricants exhibit relatively poor adhesion and distribution.  
      The adhesion and distribution properties of dry lubricants on the strip surface can be markedly improved by providing the surface of the strip with a roughness pattern. To that end the roughening of the strip surface is effected by transferring the roughness pattern on the work rolls to the surface of the strip during cold rolling of the strip.  
      Today, the roughness patterns provided on the surface of the aluminium strip to improve the adhesion and distribution of a dry lubricant there are produced by work rolls which are roughened e.g. by electrical discharge texturing (EDT), by electron beam texturing (EBT) or by the PRETEX method. All of these methods of roughen-ing result in a surface texture with irregularly distributed, closed “lubricant pockets”.  
      The above mentioned roughness patterns are produced on the surface of the strip in an additional cold rolling pass using a roll pass involving a small thickness reduction approx. 0.05 to 15%. In practice this additional cold rolling pass incurs correspondingly greater production costs. In addition, in order to produce the roughness pattern, it is necessary to change the work rolls that have a conven-tional roll-grind pattern for textured rolls.  
      A process and unit of the above mentioned kind is known from EP-A-O 945 198.  
      The object of the present invention is to provide a process and a unit of the kind described at the start, by means of which the production costs for manufacturing textured strips can be reduced. A further objective is to avoid the loss of capacity on a production unit caused by an additional texturing roll pass.  
     SUMMARY OF THE INVENTION  
      The object of the invention is achieved by providing a process comprising passing a cold rolled strip immediately after cold rolling through a roll gap of two textured rolls bearing a roughness pattern, wherein the roughness pattern is transferred to the surface of the strip as a result of the force of the textured rolls acting on the strip, and, thereafter, coiling the textured strip.  
      With this process it is possible to dispense with a separate texturing roll pass and consequently save one roll pass compared with the state of the art method.  
      On performing the process according to the invention the cold rolled strip is drawn through the roll gap and the texturing rolls turned by the tension on the strip.  
      In order to adjust the thickness as uniformly as possible over the whole breadth of the strip, the texturing rolls are preferably set at a constant roll force.  
      To endow the strip surface with the above mentioned property whereby it acts as substrate for a dry lubricant, the texturing rolls are—to advantage—roughened using electrical discharge texturing (EDT).  
      It has been found that the process according to the invention is also suitable for smoothing cold rolled strips. To that end it can also be proved advantageous to provide the texturing rolls with the conventional, simple roll grind that results in the so called “mill finish” surface quality. The rolls are only ground over their outer surface direction, i.e. the roll grind comprises a plurality of parallel grooves distrib-uted over the outer surface of the rolls.  
      Preferred is an arrangement in which the texturing rolls in the texturing roll stand are supported by intermediate rolls, which are in turn supported by backing rolls. The backing rolls may be arranged in several sets of rolls across the width of the intermediate rolls.  
      The backing rolls are preferably joined up in co-action to hydraulic pistons set at a constant force.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Further advantages, features and details of the invention are revealed in the following description of preferred exemplified embodiments and with the aid of the drawing; this shows schematically in  
       FIG. 1 : the end view of a unit for producing a strip with a textured surface;  
       FIG. 2 : the front elevation of a texturing roll stand;  
       FIG. 3 : the cross-section through the roll arrangement of a roll stand shown in  FIG. 2 . 
    
    
     DETAILED DESCRIPTION  
      A unit for producing an aluminium strip with a textured surface according to  FIG. 1  comprises a cold rolling mill  17  with two work rolls  18 ,  20  forming a roll gap  19  and two backing rolls  22 ,  24  supporting the work rolls. The work rolls  18 ,  20  and the backing rolls  22 ,  24  are mounted in a mill stand  26  in a known manner.  
      Likewise installed in the stand  26  is a texturing roll stand  28  which is smaller than the cold rolling mill  17 .  
      As shown in  FIGS. 2 and 3 , the texturing roll stand  28  exhibits two texturing rolls  38 , 40  which delimit a roll gap  39  and are supported by a pair of intermediate rolls  42 ,  44 . Each pair of intermediate rolls  42 ,  44  is supported by five sets of three backing rolls  46 ,  48 . The backing rolls  46 ,  48  are mounted in beams  50 ,  52  which extend over the width of the rolls. The upper beam  50  is supported by an upper part  54  of the roll stand frame via hydraulic pressure type pistons  58 , the lower beam  52  lies directly on a lower part  56  of the roll stand frame. Both parts  54 ,  56  of the roll stand frame may be moved towards and away from each other by means of hydraulic raising or lowering pistons  60 ,  62  i.e. the roll gap  39  can be opened as desired viz., when no texturing pass is required, or when the necessary dimension for a texturing pass is being adjusted. The roll force is adjusted via the hydraulic pistons  58  and thus the reduction in strip thickness during the texturing roll pass. The roll force is set by via the hydraulic compressive piston  58  and with that the reduction in thickness of the strip during the texturing pass.  
      In order to produce the surface texture pattern, a cold rolled strip coiled onto a reserve roll  14  is passed over a deflection roll  16  then fed in the rolling direction x to the roll gap  19  of the cold rolling mill  17 . After it emerges from the roll gap  19 , the strip  12  enters the roll gap  39  of the texturing mill stand  28 . On leaving the texturing mill stand  28  the strip  12  is deflected around two further deflection rolls  30 ,  32  and coiled onto a spool  34 . The thickness of the strip is checked by a thick-ness measuring device  36  situated between the texturing mill stand  28  and the second deflection roll  30 . At the same time, the second deflection roll  30  serves to check the flatness of the textured strip  12 .  
      The work rolls  18 ,  20  of the cold rolling mill  17  are driven and the strip  12  is drawn into the roll gap  19  by the rolls themselves. The texturing rolls  38 ,  40  are not driven, the strip  12  must be drawn through the texturing roll stand. This is done by the driven spool  34 . The braking action of the texturing rolls  38 ,  40  results in a stress- regulating effect, which leads to better flatness in the textured strip  12 .  
      The diameter of the texturing rolls  38 ,  40  is of course smaller than the diameter of the driven work rolls  18 ,  20  of the cold rolling mill  17 . This produces a better texture in the strip surface with the result that a smaller reduction in thickness is necessary. The diameter of a texturing roll is e.g. around 350 mm.