Sometimes the answers to long-standing questions are right under our noses, even if they are not recognized as such. And some solutions to problems come from unexpected sources. Who would have expected that experts at Oregon State University's College of Forestry would propose a solution to the problem of noxious fumes emitted by binder chemicals used by sand casting foundries to form molds and cores? Or, that their recommendation would be such a simple one?
Sand binders currently available are generally effective, but containing or eliminating the fumes they emit is an ongoing problem, and a cost factor. In the U.S., phenol-formaldehyde resins are widely used, and can emit toxic air pollutants. In China and elsewhere, the emissions may be even worse because the binder chemicals in use are often furan resins and combinations of furan resins and urea-formaldehyde resins.
Kaichang Li, a professor of wood science and engineering at OSU, and other researchers there, have applied for a patent on a new use for an "environmentally benign" compound that works well to bond sand. It also would be much less expensive than the range of commercially available formulations. It's sugar.
"We were surprised that simple sugar could bind sand together so strongly," said Li, who noted that sugar and other carbohydrates are "abundant, inexpensive, food-grade materials. The binder systems we've developed should be much less expensive than existing sand binders, and not have toxicity concerns," he said.
Sugar is highly water-soluble, of course, and the OSU team discovered a novel way to use it to make strong and moisture-resistant sand molds. An inaccurate reading of temperature in a baking oven helped lead to their discovery, they said.
Li and OSU faculty research assistant Jian Huang identified combinations of sugar, soy flour, and hydrolyzed starch, or even sugar alone, bind sand very effectively for molds used to solidify molten metal. The molds set up rapidly and retain their bonded strength in high humidity, which is critical to their effectiveness.
Sugar or the other agricultural products used for this purpose should have no environmental drawbacks, because all or most of the residuals will decompose into carbon dioxide and water.
Li told FM&T that his team has tested its binders in U.S. metalcasting plants, and though no data was available on the results of those tests he indicated that the operators in those locations found the products were "satisfactory to the overall performance of our binders."
Asked if there may be any restrictions to the types of sands that would be used with the sugar binder, Li said the formulation has worked well with silica and olivine grades of sand – the two most commonly used by domestic metalcasters.
The OSU project has not researched the results for recycling and reusing bonded sand, but Li offered that it is "highly likely" that such material can be reused without significant effect on performance or quality.
No commercial-scale research has been conducted, but Li said the binder technology is ready for more applied research and testing. OSU is seeking investors and industrial partners to commercialize it. Private sector financing of OSU research has increased 42% to $35 million since 2012, as the university increases its emphasis on academic/industrial partnerships.
Li's laboratory at OSU has developed and commercialized other products in recent years, too, including a resin made from soy flour that is being used to replace formaldehyde-based adhesives in the manufacture of some wood products. For that achievement, in 2007, he was awarded the U.S. Environmental Protection Agency's Presidential Green Chemistry Challenge Award, which recognizes innovators who have helped to reduce manufacturing process waste or toxins.
Sand castings are estimated at 70% of all cast metal products, in all types of ferrous, nonferrous, and specialty metals, and for products used in automaking, mining, transport, industrial processes, domestic products, and numerous other markets. The impact of a low-cost, low-environmental impact binder could be vast.