Patent Publication Number: US-2013239636-A1

Title: Method and devices for connecting an aluminum strip to a copper strip under protective gas

Description:
The invention relates to a method for a metallurgically firm connection of an aluminum band with a copper band through which the two bands that are moved relative to one another in their longitudinal direction are continuously cleaned from oxides in a cleaning device under protective gas at their contact surfaces and are subsequently provided to a compression device in which the bands are pressed together with their clean surfaces and connected with another to form a one-piece band. The invention also relates to a device for performing the method (EP 1 469 486 B1). 
     A one-piece band made from two different metals produced through a method of this general type is used in particular for high frequency applications. Through the known effect of current displacement, only rather thin copper layers are required in conductors of high frequency cables. The aluminum band connected with the copper band through the described method is only used for stabilizing the copper band and as a carrier for the copper band. In order for the metallurgic connection to be maintained, the bands and in particular the easily and quickly oxidizing aluminum band have to be cleaned from oxides. 
     A method is known from U.S. Pat. No. 2,414,511 A through which two bands that are made from metal shall be connected with one another, One band is for example made from steel and the other band is for example made from copper. The two bands are fed to a large volume housing in which they are cleaned and heated through flames. The bands thus treated are pressed together through rollers inside the housing to form a one-piece band which subsequently exits the housing. In order for a band made from copper not to oxidize after cleaning and heating, a controlled atmosphere is maintained in the housing. 
     In the method according to EP 1 469 486 B1, recited supra, a copper band and an aluminum band are cleaned from oxide layers in a cleaning device using rotating brushes at flat sides for mutual contact using an protective gas, for example argon. 
     The protective gas prevents a reformation of oxides. The two bands are then run through a gap between two rollers of a roller arrangement and thus metallurgically connected. Simultaneously, the thickness of the one piece band is reduced. The two bands and thus also the one piece band are moved in their longitudinal direction by the driven rollers of the roller assembly. The protectiveial gas zone terminates at the outlet of the cleaning device used in this application. On a path of the two bands from the cleaning device to the rollers of the roller arrangement, in particular the aluminum band can oxidize quickly again so that a continuous metallurgic connection with the copper band cannot be guaranteed. 
     It is an object of the invention to improve the method recited supra so that a recurring oxide formation at both bands can be excluded before joining. The object is achieved according to the invention by performing the following steps:
         cleaning the two bands separately in separate housing compartments of a contingent housing under protective gas, in particular cleaning the two bands from oxide materials,   subsequently running the two bands to the compression device under continuous protective gas coverage through channels connected hermetically tight with the two housing compartments,   subsequently contacting the two bands under pressure in a compression device enveloped by a proper housing connected with the channels hermetically tight under continuous protective gas coverage, and   pulling the two bands or the one piece band through the cleaning device and the compression device through a pull off device arranged behind the compression device.       

     The protective gas used in this method is a special gas which prevents a formation of oxides. Respective gases are for example noble gases, inert gases and reducing gases. Through using this method, a formation of oxide layers on the two bands to be connected, in particular on the aluminum band, can be excluded, since the two clean bands are moved under the protective gas until they are firmly contacted in the compression device and pressed against one another. This is essentially facilitated in that the dimensions of the compression device can be kept small because the two bands or the produced one piece band are not moved through driven large volume rollers but are pulled by a separate pull off device. Accordingly, for example, two rotatably support rollers with relatively small dimensions can be used in the compression device, wherein the rollers are separated from one another through an adjustable gap through which the bands are being pulled. For example also a slot nozzle with adjustable slot can be used for the compression device. A housing enclosing a compression device of this type can have rather small dimensions and can be easily connected with a housing enclosing the cleaning device in order to form a one piece housing. The one piece housing is filled with protective gas while the method is performed. The coverage of the two bands with protective gas preventing a formation of oxide layers is only terminated according to this method when the one piece band which is formed by metallurgically connecting the two bands, leaves the compression device. 
    
    
     
       The method according to the invention is subsequently described based on an embodiment with reference to drawing figures, wherein: 
         FIG. 1  schematically illustrates an arrangement for performing the method according to the invention; and 
         FIG. 2  illustrates a detail of  FIG. 1  in a more defined configuration. 
     
    
    
     The arrangement for connecting an aluminum band with a copper band includes two rotatably supported coils  1  and  2 , a cleaning device  3 , a compression device  4 , a pull off device  5 , and a wind up coil  6 . The pull off device  5  is advantageously configured as a track pull off, the cleaning device  3  and the compression device  4  are arranged in a common housing  7 , which is filled with an inert gas when the method is performed, for example filled with argon. A copper band  8  is wound onto the bobbin  1 , whereas an aluminum band  9  is wound onto the bobbin  2 . Both bands  8  and  9  preferably have the same width. 
     The method according to the invention is performed for example as follows. 
     The two bands  8  and  9  are pulled from their bobbins  1  and  2  in a direction of the arrow  10  and pulled through the cleaning device  3  and the compression device  4 . In the cleaning device  3 , the mutual contact surfaces of the two bands  8  and  9  are cleaned from contaminations and in particular oxide materials in continuous operation. This is performed under protective gas, so that no oxide layers can form on the clean surfaces of the bands  8  and  9  after leaving the cleaning device  3 . In order to maintain the protective gas coverage in the housing  7 , it includes sealed inlets for passing the two bands  8  and  9  through. 
     The two cleaned bands  8  and  9  are joined within the housing  7  under continued protective gas coverage in the compression device  4  and pressed against each other so that they are metallurgically connected with one another to form a one piece band  11 , The one piece band  11  exits the housing  7  through a sealed outlet. It can be subsequently wound onto the bobbin  6 . 
     The unit including the housing  7 , the cleaning device  3  and the compression device  4  is configured according to FIG,  2 . The housing  7  illustrated in one piece in  FIG. 1  is divided into components connected with one another in the embodiment according to  FIG. 2 . The cleaning device  3  accordingly includes an upper housing component  12  and a lower housing component  13 . In both housing components  12  and  13 , a plurality of grinding discs or metal brushes  14  or  15  is arranged that is rotatable about an axis. The compression device  4  includes a proper housing  16 . The two housing elements  12  and  13  of the cleaning device  3  are connected hermetically tight through channels  17  and  18  with the housing  16  of the compression device  4  so that the integral contiguous space that is filled with protective gas is implemented which is designated in  FIG. 2  through a dash dotted line which corresponds to the housing  7  according to FIG,  1 . According to  FIG. 2 , the cleaning device  3  and the compression device  4  are passed through by the bands  8  and  9 , for example as follows. 
     The copper band  8  initially enters the housing element  12  of the cleaning device  3  while the aluminum band  9  is pulled through the lower housing element  13  of the cleaning device  3 . The copper band  8  is thus for example pulled along metal brushes  14 , while the aluminum band  9  is advantageously pulled along grinding discs  15 . Both bands  8  and  9  are thus in particular cleaned from oxides at the flat sides which shall be brought into mutual contact. Metal brushes or grinding discs can also be used for both bands  8  and  9  or also other components can be used through which the described cleaning can be performed. The metal brushes  14  or grinding discs  15  clean the surfaces of the two bands  8  and  9  in continuous pass through and thus remove in particular oxide materials. The two bands  8  and  9  are simultaneously heated through the cleaning process to an adjustable temperature. The cleaned bands  8  and  9  which are respectively metallically clean at their flat sides configured for mutual contact are run to the compression device  4  through the channels  17  and  18  which are connected with the cleaning device  3  and the compression device  4  seamlessly. The bands  8  and  9  heated up as recited supra are brought into contact under pressure. Aluminum dust generated through the cleaning process can be removed for safety reasons from the lower housing element  13  in particular time intervals. Two rollers  19  and  20  are rotatably supported in the housing  16  of the compression device  4  according to the illustrated embodiment. The two rollers  19  and  20  are arranged in parallel with one another and separated by an adjustable gap. The size of the gap is adjustable through adjusting a distance of the rollers  19  and  20  from one another. The two bands  8  and  9  are run in contact with one another through the gap between the two rollers  19  and  20  and thus compressed. Thus the two rollers  19  and  20  are loaded with pressure. Instead of the rollers  19  and  20 , the compression device  4  can also be configured with a slot nozzle with an adjustable slot. The bands  8  and  9  are then run through the slot of the slot nozzle with the described method and pressed together so that the one piece band is produced. 
     The pressure imparted by the two rollers  19  and  20  or the slot nozzle upon the bands  8  and  9  can be adjusted so that the one piece band  11  that is produced is simultaneously reduced in a thickness and thus with the advantage by an amount which is between 5% and 20%. This measure on the one hand side depends on the thickness of the bands  8  and  9  as base material and on the desired thickness of the one piece band as a finished, product.