Abstract:
A retainer is described for exerting a braking effect on wire provided as a spool in a container. The retainer has a plate-like elastic element with a contact surface adapted for resting on the wire, an outer circumference adapted for being guided in the container, and an inner circumference adapted for allowing the wire to pass through. The plate-like elastic element has an elasticity such that one of the inner and outer circumferences sags down, under the proper weight of the retainer, by a distance of at least 10 mm when the retainer is supported at the other of the inner and outer circumference.

Description:
[0001]    The invention relates to a retainer for a welding wire container and to a welding wire container. 
       BACKGROUND OF THE INVENTION 
       [0002]    The use of bulk polygonal packs or round drums containing large quantities of reverse wound aluminium welding wire (in some cases up to as much as 500 kgs) is becoming increasingly popular since it offers the advantage of great savings thanks to a reduced pack changeover downtime and a higher productivity. The ability to avoid unwanted weld interruptions in some applications like the production of vehicle components and automotive parts, is extremely important because stoppages in the middle of the automated weld process can cause cracks, weld defects, mechanical failures with consequent costly aftermarket product liability issues. A good weld with no defects or imperfections is absolutely necessary in order to prevent subsequent equipment failures. 
         [0003]    Unwanted production interruptions can offset the advantages of the so-called “lean manufacturing process” that relies on the optimization of the supply flow in sequential steps of production. 
         [0004]    The industry today, and in particular the automotive industry, is increasingly using aluminium welding wires for many applications, since aluminium has the advantage of being a resistant, fairly strong, corrosion-free metal but also much lighter (approximately three times lighter) than steel; vehicles with less weight bring relevant fuel savings. 
         [0005]    More and more manufacturers are choosing bulk containers with large quantities of twist-free reverse wound welding wire in combination with high performing low friction guiding liners with rolling elements inside. 
         [0006]    Aluminium wires are however very soft and can easily be deformed by friction or attrition in particular when the wire during payout is forced to scratch against the inner edge of the wire retainer. Deformed wires can cause serious weld defects that would either require repair where possible, or in the worst case scenario, the inevitable scrapping of valued parts because of their non conformance to the desired quality standards. 
         [0007]    This problem has been known for a while and several prior art attempts have been made to solve it. 
         [0008]    Barton and Carroscia in U.S. Pat. No. 7,398,881 propose a rigid retainer ring with embedded pockets of different shape and density in order to help reduce the overall retainer weight. The attempt to generate some weight relief is obvious but notwithstanding the pockets the retainer maintains its rigidity, and this could still deform soft aluminium wires (like, but not limited to, the grade AWS 4043) in the commonly used thin wire diameters like for example 1.20 mm. 
         [0009]    Again Carroscia in U.S. Pat. No. 7,410,111 describes, as a possible solution, the cut out of entire retainer sections in order to decrease the retainer plate weight by as much as 50% of its overall weight. This plate however is rigid and it can still deform the wire during payout; additionally this particular embodiment comes with the risk that the wire coil under the retainer can become excessively exposed to air contamination and oxydation. 
         [0010]    Edelmann and Zoller in EP 2 354 039 also try to address the problem of the possible impact of a heavy retainer on the wire coil and disclose a retainer exerting a contact pressure on the wire spool for maintaining the spirals of the spool which is between 10 and 25 N/m 2 . This retainer with a claimed thickness of up to 15 mm has a significant degree of rigidity. 
         [0011]    Gelmetti and Fagnani in EP 2 168 706 propose a flexible rubber retainer to smoothly control the wire payout but their retainer is quite expensive to build as it requires an outer periferical support frame and it is not designed to control aluminium welding wire since it features a plurality of flexible flaps which are freely hanging and pushed downwardly by the force of gravity into the middle of the pack. A soft aluminium wire would have to overcome the resistance of these flaps to be paid out, and that would also inevitably contribute to cause wire deformation. The flaps, in this invention, seem to be aimed at preventing possible tangles caused by the simultaneous feeding of multiple wire strands. 
         [0012]    While the first two prior art documents are expressly directed to resolve the problem of the wire deformation, the latter two attempt to rather address the issue of wire tangling during payout from the bulk container. 
         [0013]    Gelmetti in U.S. patent application Ser. No. 13/330,314 and International Patent Application PCT/EP2012/076081 teaches of a dynamic retainer to pay wires out of a bulk container such retainer being composed by the assembly of several individual “tiles” connected together but independently raising at the passage of wire. Notwithstanding the dynamic interaction of this retainer with the wire the tiles are rigid pieces and testing has demonstrated that deformation of softer aluminium wires can in fact still occur. 
         [0014]    There is a need for a retainer which allows a smooth pay-out of soft, deformable welding wire such as aluminum welding wire. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0015]    The invention provides a retainer for exerting a braking effect on wire provided as a spool in a container. The retainer has a plate-like elastic element with a contact surface adapted for resting on the wire, an outer circumference adapted for being guided in the container, and an inner circumference adapted for allowing the wire to pass through. The plate-like elastic element has an elasticity such that one of the inner and outer circumferences sags down, under the proper weight of the retainer, by a distance of at least 10 mm when the retainer is supported at the other of the inner and outer circumference. The invention is based on the recognition that a comparatively elastic retainer is particularly suitable for controlling pay-out of the welding wire as it on the one hand allows the wire to lift the retainer at the inner circumference, thereby locally adapting the shape and curvature of the retainer to the shape of the welding wire in the portion which is currently withdrawn from the upper surface of the welding wire coil, and on the other hand ensures that the remainder of the retainer remains flat on the upper surface of the wire coil, thereby exerting its braking effect on the upper windings of the welding wire coil. 
         [0016]    Preferably, the distance by which the inner or outer circumference sags down is at least 20 mm and not more than 50 mm. 
         [0017]    The invention also provides a retainer for exerting a braking effect on wire provided as a spool in a container, which has a plate-like elastic element with a contact surface adapted for resting on the wire, an outer circumference adapted for being guided in the container, and an inner circumference adapted for allowing the wire to pass through. The plate-like elastic element has an elasticity such that when the retainer is supported along a diameter, opposite sides of the retainer sag down, under the proper weight of the retainer, by a distance which is more than 5% of said diameter of the retainer. The elasticity which allows this deformation of the retainer also allows controlling pay-out of the welding wire in an advantageous manner as it on the one hand allows the wire to lift the retainer at the inner circumference, thereby locally adapting the shape and curvature of the retainer to the shape of the welding wire in the portion which is currently withdrawn from the upper surface of the welding wire coil, and on the other hand ensures that the remainder of the retainer remains flat on the upper surface of the wire coil, thereby exerting its braking effect on the upper windings of the welding wire coil. 
         [0018]    Preferably, the distance by which opposite sides of the retainer sag downwardly when the retainer is being supported centrally along a diameter is at least 10% of the diameter of the retainer and more preferably 15% of the diameter. 
         [0019]    In order to ensure that the retainer has a strength and rigidity which prevents the retainer from collapsing and falling into the interior of the welding wire coil, the distance by which opposite sides of the retainer sag downwardly when the retainer is being supported centrally along a diameter is not more than 40% of the diameter of the retainer. 
         [0020]    Preferably, the plate-like elastic element consists of plastic. This allows manufacturing the retainer at low costs with the desired elasticity. 
         [0021]    Polycarbonate is particularly advantageous as its properties, in particular the elasticity, can easily be controlled to be within desired values. 
         [0022]    According to a preferred embodiment of the invention, the retainer is transparent. This allows visually checking the welding wire coil which is being covered by the retainer. 
         [0023]    The plate-like elastic element of the retainer preferably has a thickness which is in a range of 0.3 mm to 12 mm. These values allow combining the desired elasticity with a low weight and a sufficient rigidity. 
         [0024]    According to an embodiment of the invention, the plate-like elastic element of the retainer is provided with a reinforcement ring which extends along said outer circumference. This allows using a very pliant and yielding plate-like elastic element, e.g. a rubber sheet, which is being conferred the necessary rigidity for staying on top of the welding wire coil by the frame-like reinforcement ring. 
         [0025]    Preferably, the retainer has a contact surface with a roughness which is different from a roughness of a surface which is opposite the contact surface. In other words, the two surfaces of the plate-like elastic element are manufactured with different surface roughnesses. If a higher braking effect of the retainer is desired, the retainer is employed such that the surface with the higher roughness acts as the contact surface. If a lower braking effect is desired, the retainer is reversed and the smoother surface is being used as contact surface. The different roughnesses can be achieved by molding the plate-like elastic element in a mould which has a polished and a non-polished or even roughened surface, or by a suitable surface treatment of the plate-like elastic element of the retainer. 
         [0026]    The invention also provides a welding wire container having a bottom, circumferential walls extending upwardly from the bottom, a welding wire coil formed from a plurality of windings of welding wire, and a retainer which rests on an upper surface of the coil. The retainer has a plate-like elastic element with a contact surface adapted for resting on the wire, an outer circumference adapted for being guided in the container, and an inner circumference adapted for allowing the wire to pass through. The plate-like elastic element has an elasticity E which is in a range of 0.05 to 0.4, with the elasticity E being determined by the following formula: 
         [0000]    
       
         
           
             E 
             = 
             
               
                 0.2 
                  
                 % 
                  
                 
                     
                 
                  
                 yieldlimit 
               
               
                 specificweight 
                 * 
                 B 
               
             
           
         
       
     
         [0000]    with:
       the 0.2% yield limit of the welding wire in N/mm 2 ;   the specific weight of the welding wire in g/cm 3 ;   B being the widths of the retainer from the inner to the outer circumference in mm;       
 
         [0030]    Preferably, the elasticity E as determined by the above formula is within a range of 0.08 to 0.14. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The invention will now be described with reference to the enclosed drawings. In the drawings, 
           [0032]      FIG. 1  shows a prior art container with retainer in a cross section; 
           [0033]      FIG. 2  shows the elastic behavior of the prior art retainer when tested in a first type of set-up; 
           [0034]      FIG. 3  shows a perspective view of a container according to the invention with a retainer according to a first embodiment of the invention; 
           [0035]      FIG. 4  shows a perspective view of a container according to the invention with a retainer according to a second embodiment of the invention; 
           [0036]      FIG. 5  shows the first type of set-up for determining the appropriate elasticity of a retainer according to the invention, and two embodiments of the retainer according to the invention; 
           [0037]      FIG. 6  shows a second type of set-up for determining the appropriate elasticity of a retainer according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    A welding wire container  10  with a welding wire retainer  12  as known from the prior art is shown in  FIGS. 1 to 3 . The container  10  has a rectangular inner cross section (e.g. octagonal), side walls  14  (two side walls are shown), a bottom  16  and a lid  18 . 
         [0039]    In the interior of the container  10 , a welding wire coil  20  is accommodated. The welding wire coil  20  consists of a certain amount of welding wire  22  which is coiled so as to form a hollow body with a ring-shaped cross section. The portion of the welding wire which is currently being withdrawn from the container is designated with reference numeral  24 . 
         [0040]    On the upper side of the welding wire coil  20 , the retainer  12  is provided. The retainer  12  has a plate-like body with a central opening  28  which is delimited by an inner circumference  30 . An outer circumference  32  of retainer  12  serves for guiding the retainer within the container, in particular between the side walls  14 . 
         [0041]    The retainer  12  lies on the upper side of the welding wire coil  20 , the retainer  12  being always generally parallel to lid  18 . 
         [0042]    Conventional prior art retainer are made from a thick plastic element which is generally rigid. This will be explained with reference to  FIG. 2 . If the retainer as used in the container of  FIG. 1  is supported along its outer circumference  32  by means of a support  40  which follows the outer contour of retainer  12  and has a small width x (e.g. not more than 10 mm), then the inner circumference  30  of the prior art retainer  12  sags downwardly by a distance s which is not more than 10 mm. This is due to the fact that the plate-like retainer is essentially rigid. 
         [0043]    The result of retainer  12  being rigid can be seen in  FIG. 1 . 
         [0044]    Retainer  12  exerts, owing to its weight and the friction between the retainer  12  and the welding wire  24 , a braking effect on the welding wire  24  when the welding wire is withdrawn from container  10 . This braking effect results in a certain traction force which is necessary for pulling the wire from the coil  20 . The traction force however results in the welding wire  24  being bent in a region B where it passes around the inner circumference  30  of retainer  12 . 
         [0045]    In order to avoid the welding wire  24  from being bent when passing around the inner circumference  30  of retainer  12 , the invention provides a retainer  12  which is elastic. A first embodiment of the retainer is shown in  FIG. 3 , where the same reference numerals are being used as in  FIG. 1 . 
         [0046]    Retainer  12  is as a plate-like elastic element  13  which can simply be cut out from a thin sheet made of elastic material. As elastic material, plastic with the necessary elasticity is preferred, in particular polycarbonate. The inherent elasticity of the plate-like elastic element allows deforming the plate-like element which however returns to its original position as soon as the pressure is released. 
         [0047]    The behavior of the retainer can be seen in  FIG. 3 . Retainer  12  bends and deforms only at the very point (and closely adjacent thereto) where it is engaged by the wire  24  being paid out while the remaining portion of retainer  12 , not engaged, remains still and undeformed to control the remaining strands and the rest of the wire coil  20 . 
         [0048]    As soon as the wire h 24  as passed the engaged point of plate-like elastic element  13 , the deformed portion returns to its original undeformed condition. This provides a dynamic controlling action that actively follows the movement of the wire strand being paid out, adapting itself to the wire  24  without deforming it. 
         [0049]    It can be seen that due to the particular elasticity of the plate-like elastic element which forms retainer  12 , the inner contour of the retainer adjacent inner circumference  30  is deformed by the wire such that the retainer is locally curved upwardly, thereby preventing any sharp bending of the welding wire. 
         [0050]    A second embodiment of the retainer is shown in  FIG. 4 . The difference between the first and second embodiment is that the second embodiment uses a reinforcement ring  50  which defines the outer contour of retainer  12 . The majority M of the width B of the annular retainer  12  is however not covered by reinforcement ring  50  so that the plate-like elastic element  13  is exposed. The advantage of the second embodiment over the first embodiment is that a very thin and thereby flexible plate-like elastic element  13  can be used with the second embodiment without there being any risk that the stability and rigidity of the entire retainer  13  is not sufficient for securely keeping it on top of the welding wire coil. The plate-like elastic element can here be formed of a very thin, flexible material like rubber or silicon, with the reinforcement ring  50  acting as a rigid, supportive frame. 
         [0051]    For both embodiments, the outer contour of retainer  12 , defined by outer circumference  32 , matches the contour of the inside of container  10 , with a slight play being provided between the inner contour of the container  10  and the outer contour of the retainer  12 . This play allows retainer  12  to freely descend in the interior of container  10  when the height of the welding wire coil  20  decreases. 
         [0052]    Further, the diameter of the opening  28  defined by the inner circumference  30  of the retainer  12  is slightly larger than the inner diameter of welding wire coil  20  so that no area of the top of the wire coil  20  is exposed to air contamination. In other words, the retainer plate completely covers the top side of the coil. 
         [0053]    The inner contour  30  of plate-like elastic element  12  has a uniform, uninterrupted edge, without there being any additional flaps, fingers or dents. 
         [0054]    The optimal thickness to obtain a sufficient level of elasticity of the retainer varies and is in relation with the dimensions of the retainer itself: the larger the plate, the thicker it must be, and vice versa. In general, the elasticity of the retainer must not be excessively high as this could result in a deformation of the entire retainer such that it drops into the interior of the welding wire coil, resulting in a jamming of the whole system. At the same time, the elasticity of the retainer must be sufficient for allowing the plate-like elastic element to yield under the traction forces acting on the welding wire such that the welding wire is not deformed. 
         [0055]    The suitable elasticity of the retainer can very easily be determined with the set-up as shown in  FIG. 5 . The set-up is the same as already shown in  FIG. 2 , namely a support  40  which is narrow (with a thickness x of no more than 10 mm) and which supports the outer circumference  32  of the retainer. 
         [0056]    The retainer  12  as shown in  FIG. 4  is shown in continuous lines in  FIG. 5 . It can be seen that the outer circumference  32  remains basically undeformed due to reinforcement ring  50 . The inner circumference  30  sags down by a distance s which is at least 10 mm and preferably at least 20 mm. 
         [0057]    The retainer of  FIG. 3  is shown in dashed lines. Here again, the inner circumference  30  sags down by a distance s which is at least 10 mm and preferably at least 20 mm. Owing to the desired stability of the retainer, the inner circumference  30  of retainer  12  will not sag down more than 50 mm. 
         [0058]    A retainer  12  according to the invention will exhibit the same behavior or the set-up is reversed such that it supports the retainer along the inner circumference  30  rather than along the outer circumference  32 . 
         [0059]    A different set up for choosing the correct elasticity of retainer  12  is shown in  FIG. 6 . Here, a narrow support (again having a width x of not more than 10 mm) is used which supports the retainer centrally along a diameter. A conventional, rigid retainer will, when supported by a narrow support  50  which extends along a diameter of the retainer, deform under its proper weight such that opposite sides sag down by a distance s which is not more than 5% of the diameter of the retainer. An inventive retainer  12  will show a larger deformation. Opposite ends of a retainer  12  according to the invention will sag down by a distance s which is more than 5% of the diameter of the retainer, in particular more than 15%. In order to guarantee a sufficient proper stability of the retainer, the elasticity is chosen such that opposite sides of the retainer do not sag down more than 40% of the diameter of the retainer. 
         [0060]    It has been determined that the 0.2% yield limit of the welding wire in the container and also the specific weight of the welding wire are decisive factors for determining a suitable elasticity of retainer  12 . Taking further into account the dimensions of the retainer, it has been found out that an elasticity factor E can be determined with the following formula: 
         [0000]    
       
         
           
             E 
             = 
             
               
                 0.2 
                  
                 % 
                  
                 
                     
                 
                  
                 yieldlimit 
               
               
                 specificweight 
                 * 
                 B 
               
             
           
         
       
     
         [0000]    with:
       the 0.2% yield limit of the welding wire in N/mm 2 ;   the specific weight of the welding wire in g/cm 3 ;   B being the widths of the retainer from said inner to said outer circumference in mm;       
 
         [0064]    The best results were achieved with an elasticity E in a range of 0.05 to 0.4, in particular well within the range of 0.08 to 0.14. 
         [0065]    If a transparent material like thin polycarbonate is used to produce the retainer, it is also possible to visually inspect the complete wire movements and layers behavior. 
         [0066]    It also possible to use, for cutting the retainer out, plastic sheets which have a polished and therefore more slippery surface on one side and a milled and therefore rougher surface on the opposite side, so that the retainer can conveniently be turned upside down as needed, in order to increase or decrease the retainer strands controlling action, for example depending on the wire diameter, the wire hardness or the wire surface finish.