GrafTech (United States)

Carbonaceous refractory materials are widely accepted in many reducing smelting processes such as iron and ferroalloys. Oxidizing processes such as copper concentrate smelting traditionally use magnesia and/or alumina/silica refractory materials. The main objection to the use of carbon-based refractories as the exposed working lining in oxidizing applications is the potential for free oxygen to react with the carbon at high temperature, which could rapidly degrade the refractory lining.

Large LED (light emitting diode) array lights are currently being designed and sold as replacements for lights on roadways, tunnels, parking lots and other large areas. These lights are typically 75 W to 200 W in thermal dissipation, and the lighting structure is designed to handle a predominately conductive heat path until contact with the outer air is made. At this point convection to the ambient air removes the heat from the system. To handle this internal conduction path to a suitable area for convection, most LED array lights have been developed using an aluminum heat sink, which causes a weight problem and additional costs over conventional light systems which are manufactured with sheet metal. Conventional sheet metal designs are deficient in providing an adequate thermal path for the LED thermal dissipation. A proposed solution is given in this paper with a sheet metal design enhanced for thermal conduction with flexible graphite. Eliminating the typical LED heat sink, it is shown that a sheet metal and graphite system can effectively cool the same thermal load. To prove this, an off-the-shelf LED street light was purchased, tested as a baseline, and then modified with the sheet metal and graphite design. Initial design work was performed with an analytical model, and then a prototype created from this design and shown to be of similar performance to the baseline - a system thermal resistance of 3°C/W from the PCB to the ambient, and a savings of 0.9 kg. A detailed CFD was also performed to evaluate the performance of the system and suggest possible improvements in air flow paths. Comparisons of the experimental and numerical results are given showing agreement in most areas.

The unique combination of physical properties inherent to graphite makes it an attractive material for use as a moderator in high-temperature nuclear reactors. High-temperature physical properties of three nuclear-grade graphites manufactured by GrafTech International Holdings Inc. (GrafTech, Parma, OH), PCEA™, PCIB-SFG™, and PPEA™, have been determined experimentally and are presented here. Tensile strength, Young’s modulus, thermal conductivity, specific resistance, and coefficient of thermal expansion (CTE) data are collected at temperatures from 25°C to as high as 2000°C, and are found to be consistent with classical graphite behavior.

Hydronic radiant floor heating systems are recognized as an efficient means of heating residential and commercial buildings. These systems utilize water flowing in tubes to move thermal energy from a heat source to a radiant panel located beneath the floor of the room being heated. The efficiency of such systems depends on many factors but a major concern is the ability of the radiant panel to remove heat from the water tubes and spread it effectively across the floor. Conventional radiant panels use aluminum heat spreaders to do this. Much work has been done to determine the overall performance of rooms heated by radiant panels, but little work has been done to measure the thermal performance of heat spreaders in these panels. This paper describes the development of a test method, using thermal imaging of test panels, to measure the performance of these heat spreaders. This method is used to determine the thermal performance of commercially available aluminum heat spreaders and of advanced heat spreaders made from flexible graphite. Graphite heat spreaders have found wide acceptance in a variety of electronic applications including plasma and LED displays, laptop computers and cell phones. This paper also examines the thermal properties of graphite that make it attractive as a radiant panel heat spreader. The development of high thermal conductivity, flexible graphite spreaders for various radiant panel applications is described. These graphite heat spreaders improve the performance of radiant panel systems and allow the use of high efficiency, low temperature heat sources.

Abstract Plasma display panel (PDP) manufacturers are motivated to reduce costs to broaden consumer acceptance and to fend off competition from other flat panel and projection display technologies. This paper introduces a novel approach to designing the plasma display panel chassis that represents the lowest cost and lightest weight chassis system in the industry while significantly reducing the average screen temperature compared to conventional chassis designs. The new chassis design is enabled by the use of a natural graphite based thermal spreader sheet that renders redundant the thermal spreading function of the solid aluminum chassis.

Heat sinks constructed from natural graphite/epoxy composites are a high performance, lightweight alternative to traditional copper and aluminum designs. For applications where the heat source is the same size as the heat sink, laminated graphite/epoxy heat sinks have been shown to perform equivalently to copper heat sinks at a 75% lower weight. However, when the heat source is smaller than the heat sink, laminated graphite/epoxy heat sinks perform poorly. For this situation, a hybrid graphite epoxy heat sink has been developed. This hybrid construction incorporates graphite/epoxy fins bonded to a copper base. This paper examines the thermal performance of this heat sink and includes both computer models and experimental results. The effects of fin material and bonding techniques on thermal performance were examined. An optimized hybrid heatsink was found to have a thermal performance nearly equivalent to that of a copper heat sink combined with a 40% reduction in weight.