A process of transferring heat energy electromagnetically, evenly and quickly throughout a part or coating, enabling better process temperature control, shorter cure cycles, and less energy use.
Microwave heating and curing techniques are continually being refined and applied to more products. Microwave systems have long been used for curing paints and coatings. Variable frequency microwave (VFM) technology was introduced in 1998 to the microelectronics packaging market. VFM technology has also been used for curing adhesives in the fiber optics and optoelectronics industries. VFM offers advantages of faster curing, selective heating, and elimination of the formation of hot and cold spots. Adhesive cure is usually 2 to 10 times faster with VFM than with conventional ovens. With support from the U.S. DOE, equipment for microwave sintering of metals, composites and ceramics has been developed.
Sintering and heat treating is conventionally performed by autoclaves. In autoclaves, a composite part heats from the outside in. Process duration is determined by the rate of heat flow into the structure. The flow rate depends on specific heat, thermal conductivity, density and viscosity. As a result, edges and corners achieve the setpoint temperature before the center. Temperature in an autoclave must be slowly ramped to minimize part stress. In contrast, microwave technology produces uniform volumetric heating. Heat is transferred electromagnetically and distributed evenly and quickly throughout a part, enabling better temperature control and resulting in shorter cure cycles.
Aerospace companies have began to experiment with microwaves as an alternative to autoclaves for curing composites for aerospace applications. Results show that microwave technology consumes about 80 percent less energy with a 40 percent cycle time reduction. Microwave ovens requires minimal ramp-up to setpoint temperature and the process has less thermal lag. Further, when cure is complete there is no heat loss due to cool-down when the oven shuts off.
Microwave curing occurs with an overall energy efficiency of about 50% relative to the 10% to 30% achieved with fuel-fired processes. Secondary benefits include better production speed, waste reduction, and improved product quality. Microwave heating has been applied in the food processing industry, in investment (lost wax) casting, wood drying, papermaking, polymer and epoxy drying, and textile drying.
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Baseline Description: Batch Ceramic Sintering Baseline Energy Use: 1172500 kWh per year per unit
Japan's National Institute of Fusion Technology reports reduction of ceramic sintering time from 8 hours to 2 hours with an energy consumption reduction from 335 kWh to only 63 kWh per batch. Assuming that 10 batches per day are processed with 350 working days per year, the baseline annual energy use would be 1,172,500 kWh/year. In another project, large-part alumina sintering time was reduced from 3 days to 8 hours with energy consumption being reduced from 12 MWh to 1.2 MWh. Asian industry has been leading the development of microwave sintering equipment and is replacing inefficient gas and electric furnaces with this new technology (Source: GreenProgress).
"Typical" Savings: 81% Energy Savings Reliability: 4 - Extensive Assessment
Energy Use of an Emerging Technology is based upon the following algorithm. Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
Susan Essien Etok, 12/01/2006. Microwave curing of composites Materials World Magazine
Composites World, 06/20/2011. Ceralink wins grant to develop microwave-cure composites Composites World
Mortez Oghbaei, 04/01/2010. Microwave versus conventional sintering: A review of fundamentals, advantages and applications Journal of Alloys and Compounds
Jeff Sloan, 05/02/2011. Microwave: An Alternative to the Autoclave? High Performance Composites
ECW, 01/01/2001. Microwave Heating Energy Center of Wisconsin Fact Sheet
GreenProgress, 01/01/2014. Hi-Temperature Microwave Furnace Reduces Energy Use Up to 80% GreenProgress.com
Keith Peltzman, 01/01/2004. Emerging Microwave Technology Heat Treating Progress , ASM International
Dinesh Agrawal, 11/01/1999. Microwave Sintering of Metals Materials World , 7