Abstract:
A magnetic clamping device which uses rollers or wheels to create an air-gap between the clamping edges and a ferromagnetic work-piece, thereby reducing friction so that the clamp is able to be rolled or easily moved upon the surface or surfaces to which it is clamped.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present Utility Patent Application claims priority benefit of the U.S. Provisional Application for patent No. 60/706,726 filed on Aug. 10, 2005 under 35 U.S.C 119(e) 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention pertains to permanent magnetic clamping devices and specifically to permanent magnetic clamping devices used to clamp ferromagnetic workpieces together during fusion of said workpieces such as by welding or other joining processes.  
       BACKGROUND OF THE INVENTION  
       [0003]     The clamping together of ferromagnetic workpieces with magnetic clamping devices during welding or similar processes is made awkward by the limited manoueverability of such clamping devices once they are magnetically clamped to such workpieces.  
         [0004]     This limitation in manoueverability makes it difficult to adjust a workpiece to a pre-determined position or mark once the magnetic clamping device has gripped the surface of either of the ferromagnetic workpieces. It is common to use hammers or other implements to effect such adjustment, with the consequent risk of damage to either the workpieces or the magnetic clamping device.  
         [0005]     Furthermore, such clamping devices often require relatively excessive force to remove from the workpieces after use.  
         [0006]     In view of the foregoing, there is a need for a magnetic clamping device that can more easily be manouevered once in position on a workpiece or workpieces.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0007]     The present invention is illustrated by way of example, and not by way of limitation in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:  
         [0008]      FIG. 1  illustrates but by no means limits with respect to shape or type a common type and shape of magnetic clamping device employing a magnetizing element, Item A of ferrite, rare earth or other magnetized material with its direction of magnetization through its thickness and with said magnetizing element sandwiched between two ferromagnetic pole plates, Item B. The assembly is usually held together with a combination of adhesive bonding and typically a rivet or rivets, Item C, preferably of non-magnetic material. Such clamping devices may be triangular, square, arrowhead shape, rectangular or any other shape suitable for the purpose of clamping ferromagnetic workpieces together at a right angle, 45 degrees or other angles.  
         [0009]      FIG. 2  illustrates another typical shape of magnetic clamping device, with Item D being the magnetizing element, Item E the pole plates and Item F a rivet. In some embodiments a number of rivets are used, disposed about the area of the pole plates.  FIG. 3  shows a preferred embodiment of a magnetic clamping device having rollers or wheels, Item G, each having an axle or a reduced diameter portion bearing within a hole, Item H in the pole plates B. In this preferred embodiment the width of the rollers or wheels is something less than the inside distance between the clamping device&#39;s pole plates so as to allow the wheel to rotate unhindered whilst they are retained between the pole plates. The said rollers are disposed upon the clamping device in such a position and are of such outer diameter that they provide an air-gap, Item I between the device&#39;s pole plate edges and any ferromagnetic surface upon which the clamp is placed, such as ferromagnetic work-pieces Items J and K. The said rollers or wheels in the preferred embodiment will be of non-magnetic material so as not to shunt the magnetic field between the pole plates and impair the available clamping force.  
         [0010]      FIG. 4  illustrates an alternative embodiment wherein the rollers, Item L, are positioned outside the pole plates of the clamp rather than between them. In this embodiment the rollers or wheels may be of either magnetic or non-magnetic material. In a preferred embodiment the wheels are secured by means of a non-magnetic axle, Item M, through their centre and bearing in the holes, Item N in the pole plates, Item B. The said axle preferably has threaded ends for a locking nut, Item O. However, other means such as a central rivet, rivet forming part of the wheel, or screw into a threaded centre hole in each wheel may be deemed appropriate.  
       SUMMARY OF THE INVENTION  
       [0011]     To achieve the foregoing and other objectives of the purpose of the invention a typical embodiment is described. In one embodiment rotatable rollers or wheels of preferably non-magnetic material which could be plastic or non-magnetic metal such as brass or aluminum are of such diameter and so disposed on the magnetic clamping device as to provide a small air-gap between the clamping edges of the pole plates and the surface on which the clamping device is placed, such that there is no frictional contact between the edges of the pole plates and the clamped surface. This small air-gap, provided by the rollers or wheels ensures that magnetic clamping is still effected but also that the clamping device may be manually propelled along the ferromagnetic surface to which it is magnetically clamped. In a typical embodiment these rollers or wheels have their axle through the pole plates of the clamping device. The rollers or wheels may be near the corners or disposed at any points around the perimeter of the clamping device. In an alternative embodiment the rollers or wheels may be disposed on the outside of the pole plates. In a further alternative embodiment the rollers or wheels may be of ferromagnetic material and disposed within or outside the pole plates in such a manner that they do or do not not provide a shunt to the magnetic field between the pole plates. Further alternative embodiments may include rollers or wheels that are not rotatable or a combination of rotatable and non-rotatable elements to provide the necessary air-gap.  
         [0012]     The embodiments disclosed are not intended to limit the invention to those forms. The invention is thus to cover all modifications, equivalents and alternatives falling within the spirit and scope of the following claims.