Some 325,000 tons of steel parts are cast each year in Swedish foundries, with the automotive and machine tools industries as the largest markets. Engine blocks, brake drums, pump housings and countless thousands of other products are manufactured in one-use casting forms made from sand, bentonite clay binder and hard coal powder.
It’s been several decades since the discovery that adding coal powder to the form sand gives a fine finish to the forged product. At the same time, the coal makes it easier to separate cast parts from the sand, enabling efficient re-use of the form material. Every year, approximately 4 million tons of sand are recycled in Swedish foundries.
But there is a problem with adding coal to casting forms: Heat from the molten metal causes the coal powder to release volatile organic compounds (VOCs)—gases or vapours that may have adverse health effects. Also among the gases released from casting forms is methane, a greenhouse gas that is some 23 times more powerful than carbon dioxide at capturing the sun’s energy.
Peter Nayström, an environmental specialist with the Swedish Foundry Association, has patented a product called Nayvoc that performs as well as traditional coal powder but releases significantly less pollution. Nayvoc is manufactured through a proprietary process that removes most of the VOCs. Nayström says his alternative product could reduce greenhouse gas emissions by as much as 50,000 tons per year if it replaced the black coal powder used just in Swedish foundries.
Environmental advantages of processed coal
Peter Nayström spent several years in laboratory research before finding the right mixture of compounds that would provide equivalent technical performance while cutting production of VOCs during the casting process. In full-scale tests, Nayvoc has been used to replace half of the traditional coal powder, resulting in a corresponding reduction of about 50 percent in VOC emissions.
Since Nayvoc and traditional coal powder can be mixed, no new investment in equipment or process controls is required. Foundry operators can start on a small scale and test results on their specific applications. The more Nayvoc added to the mix, the less pollution is released. Nayström believes the potential greenhouse gas reduction could be well above the 50 percent achieved in tests so far.
Askania AB, a Swedish supplier of industrial sand, minerals and sodium silicate to the metals industry, has licensed Nayvoc for sales in Sweden and the rest of Europe. The product will initially be marketed in the Nordic region, but the long-term ambition is worldwide availability.
Article published in June 2009