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  Dielectric welding methodsRelated Patent Categories: Electric Heating, Capacitive Dielectric Heating, Specific Heating ApplicationThe Patent Description & Claims data below is from USPTO Patent Application 20070164018. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This application is a divisional of U.S. patent application Ser. No. 11/128,277 filed on 13 May 2005 and entitled DIELECTRIC WELDING METHODS AND APPARATUS which claims the benefit under 35 U.S.C. .sctn.119 of U.S. provisional patent application No. 60/570,817 filed on 14 May 2004 and entitled DIELECTRIC WELDING METHODS AND APPARATUS which is hereby incorporated by reference herein. TECHNICAL FIELD [0002] The invention relates to methods and apparatus for welding dielectric materials such as plastics. Some embodiments of the invention relate to welding using electromagnetic signals (e.g. radiofrequency signals). The invention may be applied to welding plastic membranes together in the presence of metals or other exposed electrically conductive materials (hereinafter referred to as ECM). The invention has broad application for manufacturing products which include welded plastic membranes that have ECM near to the weld locations. BACKGROUND [0003] Dielectric welding, also known as capacitance, radio-frequency, or high frequency welding, provides a way to fuse materials together. The resulting weld can be as strong as the original workpiece materials. Dielectric welding is commonly used for joining various plastic materials together. [0004] In dielectric welding, an alternating electrical field (typically alternating at a high frequency) is applied across an area to be welded. This is typically done by applying a signal between electrodes. The signal creates a varying, high-frequency electromagnetic field. When a material which is a poor electrical conductor is exposed to such a field, heat is generated in the material. The heat results from electrical losses that occur in the material. The heat deposited in the material causes the temperature of the material to rise. The heated materials become fused together. [0005] Dielectric welding relies on certain properties of the material in the parts being welded, for example, the geometry and dipole moments of molecules of the material, to cause the generation of heat in a rapidly alternating electromagnetic field. Not all materials can be dielectric welded. Polyvinyl chloride (PVC) is commonly welded by dielectric welding. Other thermoplastics that can be dielectric welded are EVA and polyurethanes. [0006] A typical dielectric welding apparatus places materials to be joined between two electrodes, which are typically metal plates or bars. The electrodes are connected to an oscillator. The oscillator is turned on to heat the materials, which fuse together when they have been heated sufficiently. The electrodes may hold the materials together during heating and cooling. [0007] There are situations where it is desirable to make products which have ECM, e.g. metal components, embedded in or attached to one or more membranes or other parts of a dielectric material which are to be welded together. A problem is that ECM in the vicinity of the electrodes of a dielectric welder can cause electrical discharges in the form of arcs or sparks. Such electrical discharges can damage the product being made, the welding apparatus and/or the dielectric welder itself. Electrical arcing can be dangerous to machines and humans. [0008] It is not always possible or convenient to add ECM after welding has been completed. There is a need for methods and apparatus which may be used to perform dielectric welding in the vicinity of ECM. SUMMARY OF THE INVENTION [0009] The invention relates to methods and apparatus for welding plastic materials membranes together in the vicinity of electrically conductive materials. [0010] Various aspects of the invention and features of specific embodiments of the invention are described below. BRIEF DESCRIPTION OF THE DRAWINGS [0011] In drawings which illustrate non-limiting embodiments of the invention, [0012] FIG. 1 is a schematic view of a dielectric welding apparatus; [0013] FIG. 2 is an isometric view showing first and second electrode assemblies; [0014] FIG. 3 is a perspective view of one of the electrode assemblies of FIG. 2; [0015] FIG. 4 is a plan view of one of the electrode assemblies of FIG. 2; [0016] FIG. 4A is a cross sectional view (in the plane A-A of FIG. 4) of the electrode assembly of FIG. 4; [0017] FIG. 4B is an exploded view of the electrode assembly of FIG. 4; [0018] FIG. 5 is a plan view of the other one of the electrode assemblies of FIG. 2; [0019] FIG. 6 is an isometric view of a buffer member; FIG. 6A is a top plan view thereof; FIG. 6B is a section in the plane A-A thereof; and FIG. 6C is a section in the plane B-B thereof; Continue reading... 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