Resistors are electronic components used in various applications. Three prevalent types of resistors are: wire wound, film, and bulk. A wire wound resistor comprises a spiral of conductive material (normally metal wire or metal strip) wrapped around a ceramic rod or tube. A film resistor comprises a film of resistive material (normally carbon based or metallic oxide film) formed around a ceramic rod or tube. A bulk resistive resistor comprises a mixture of non-conductive ceramic material and conductive material.
Bulk resistive resistors are used in various high performance applications. Bulk resistive resistors may take the form of tubular, axial leaded, slab, and disc and washer resistors. With regard to tubular resistors, these typically include a bulk resistive material such as ceramic, having metal terminals or sleeves disposed at its end. Ceramic resistors are able to withstand short-time overloads and high peak power. They are chemically inert and thermally stable.
Difficulties arise when attempting to join the resistor to a coupling, which is typically metal. To solve this problem, metal ends are attached to the tube by etching off a portion of the tube, and attaching a metal sleeve. The coupling and tube are then soldered together. However, soldering is time-consuming and expensive. In addition, if the coefficient of thermal expansion differs between the tube and coupling, the joint will not be reliable and may result in cracking.
Another method includes attaching the coupling to an end of a tube with bonding material, such as epoxy or adhesives. A bonding material is interposed between the coupling and the tube. Like soldering, this method is time-consuming and expensive. In addition, the epoxy may deteriorate over time, possibly compromising the joint.
Additional problems are present with the use of resistors that are liquid-cooled. Liquid-cooled resistors are capable of dissipating more power in a smaller package. For example, air-cooled resistors dissipate approximately 370 watts of power whereas liquid-cooled resistors dissipate approximately between 3,000-4,000 watts of power. However, other problems may arise when joining the resistor in the liquid containing network. In particular, manufacture and use of a liquid-cooled resistor is difficult, particularly when making a joint. Because of the liquid factor, the coupling must be adequately sealed or leakage will occur.
To solve the problems of leakage, complicated mechanical couplings are used as an alternative to the soldering and bonding processes. For example, plastic ends of a liquid connection are held in compression with tie rods and an O-ring. An O-ring creates a liquid tight seal while the tie rods hold the plastic ends in compression. However, this type of mechanical connection is rather complicated and expensive.
Therefore, there is a need in the art for a connection between a coupling and a resistor that is simple, inexpensive, reliable and easy to assemble.