CASTING INNOVATIONS
Microwave Energy May Improve Sand Reclamation President of St. Paul, Minn.-
based M-Wave Consulting Milt Mathis hopes to show the met- alcasting industry microwave energy is a viable method for processing and reclaiming sand, both green and chemically bonded. Like with most new technologies, though, the bur- den of proof lies on the inventor. “Te problems is, until that first
system is out there and doing what the industry wants it to do, it’s a tough sell,” he said. Mathis has developed a system that features a microwave-assisted rotary sand reclamation kiln. Te prototype processor measures 12 ft. long and 2 ft. in diameter, with an insulated processing section that is 6 ft. long and 8 in. in diameter. Materials that do not contain
water, such as silica and alumina components of clay and various sands, stay relatively cool within such a processor because they are functionally transparent to micro- wave energy. Clay in green sand and resins, urethanes and other materi- als in chemically bonded sand begin to absorb microwaves at relatively low temperatures. Te M-Wave prototype features
a hybrid approach that uses both thermal and microwave energy. First, the sand is heated in the rotary kiln until it reaches a point where the clay or resin will absorb microwaves. Te microwave energy then separates the clay or binding materials from the sand. Ideally, the hybrid thermal-
microwave system can reduce energy consumption, heating times and spatial requirements. Green sand can be processed at 1,022F (550C), while chemically bonded sand can be processed around 617F (325C). Mathis only began using the
M-Wave prototype with met- alcasting industry sands in No- vember 2013. Originally intended for processing precious metal ore, the unit has not been optimized for chemically bonded and green sands. Mathis hopes this will lead
to improved results, but it is still early in the process. “We’ve done a lot of lab tests and
have had good results with green sand and resin-bonded sand,” he said. “Te next step is going to be outfitting our process tube for more thermal character to help sand get to a little higher temperature and keep it there.” A major challenge facing the
development of technology is monitoring and maintaining the temperature within the kiln. “Temperature distribution is
hugely important,” he said. “If there are significant thermal gradients within the sand bed, the sand could be processed very differently, leading to non-uniform and inconsistent results. Tat’s been a crippling issue for typical microwave processes. However, using our concepts, we are capable of mitigating and overcom- ing those uniformity issues.” Te M-Wave prototype has only been tested in a laboratory setting, but Mathis recently reached an agreement to run tests in a met- alcasting facility, Midwest Metal Products in Winona, Minn. He
expects the prototype to be installed and functioning in the early summer. Using microwaves to reclaim sand in a metalcasting facility has been tried before without much success. But Mathis believes a commercially viable technology is within reach, provided those involved overcomg the biggest hurdle toward innovation. “It’s about understanding con- cepts and energy interactions,” he said. “Microwave as an industrial technique really hasn’t taken hold outside of drying and food process- ing. People have been trying starting from the late ’80s. Te problem is, you have chemists, ceramists and materials scientists, who all under- stand the material and what they’re trying to process very well, but they don’t understand how microwaves interact with materials. And then you have electrical engineers and physicists, who obviously understand microwaves and electromagnetics, but don’t know much about the ma- terials being processed within their units. Our concepts are a bridge between the microwave world and the materials world.”
The prototype began processing sands common in the metalcasting industry in November 2013. May 2014 MODERN CASTING | 61
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