Case Study, Minnesota Technical Assistance Program, University of Minnesota
Viking Drill and Tool Company, located in St. Paul, Minnesota, employs over 100 people and specializes in manufacturing twist drills. Approximately 720,000 pounds of drills are manufactured annually, which range in diameter from 1/16 to 1½ inches with overall lengths of up to 6 inches.
Manufacturing Process
Viking manufactures drills using a variety of metal removal (milling) and heat-treatmenprocess steps. The production of large and small drills differs only in the sequence of these steps. For example, large drills (those with diameters greater than ¾ inches) are first milled to the required dimensions and then heat-treated to strengthen the drill. Millings or turnings resulting from this process are easily collected and sold to a scrap-metal broker. Conversely, smaller bits are first heat-treated and then machined with grinding wheels to produce the finished drill. The metal wastes from this process contain more contaminants (cutting oils, stone), which results in a lower demand and lower market value for the waste material.
During the grinding process of smaller drills, oil flows over the drill and cutting stone to help remove or carry away metal and stone contaminants. The resulting contaminated oil is filtered through a diatomaceous earth filter cake and reused. After filtration, compressed air is applied to the filter cake to remove any residual oil. The resulting solid waste is slightly oily, finely divided powder comprised of approximately 89 percent tool-grade steel, 6 percent oil, 4 percent diatomaceous earth and 1 percent grinding stone.
In 1992, Viking produced over 420,000 pounds of metal waste, which was landfilled as nonhazardous solid waste at a cost of $21,000. Because of the high cost of landfilling, Viking evaluated the potential for recycling the metal waste.
Barriers to Recycling
Viking worked with three local scrap-metal brokers to determine if the metal waste was marketable. Each broker was given a sample of the waste for visual and physical analysis. Thebrokers identified three potential barriers to recycling the metal wastes.
Handling and transporting problems. Most scrap metal in the U.S. is handled with magnets and shipped using railcars. However, since Viking's metal wastes were in a powder form (referred to by Viking as "sludge"), the brokers were concerned that the magnets might not work. Other concerns were: a) on windy days, some of the waste could blow into the air during loading and cause potential air quality issues; and b) the powdered material could "cake" inside the railcars making it difficult to unload.
Contamination. Approximately 11 percent of the metal waste consisted of nonmetal contaminants. This could decrease the magnetic properties of the waste, making it difficult to use magnets to transfer wastes into railcars for shipping.
Variable market value. Turnings, borings and metal dusts are classified as low-grade scrap that yield a low market value. To make it economically feasible, the brokers need to receive a market price that exceeds the cost of purchasing, handling and shipping the metal waste.
After Viking determined that the metal waste had sufficient magnetic properties, they evaluated two options for improving the handling:
Process the waste into small bricks, which could then be loaded into gaylord boxes. This process was found to be unfeasible.
Blend the metal waste with metal turnings and borings from other manufacturing processes to improve bulk handling and increase the total quantity of metal available for recycling.
After determining that the second option could eliminate the handling and transportation problems, one of the scrap brokers agreed to take Viking's metal waste. The broker graded Viking's waste as "turnings and borings" and mixed the metal wastes with turnings received from other sources. Viking is paid $20 per ton by the broker for its metal wastes.
To date, over 140,000 pounds of Viking's metal wastes have been successfully transferred to a foundry for recycling.
For more information about recycling or reducing metal wastes, call MnTAP at 612/627-4644 or 800/247-0015. In addition, MnTAP has a wide selection of publications that provide information on how to recycle, reduce and prevent industrial wastes. Call MnTAP and ask for a copy of the "Checklist of Printed Resources."
(6/94-94)