Ceramic welding offers Commercial Intertech longer-lasting furnace repairs.

Ceramic Welding Offers Commercial Intertech Longer-Lasting Furnace Repairs

Ceramic welding has been providing extended repair life and cost savings in channel furnace maintenance at Commercial Intertech Corp, Youngstown, OH. Although ceramic welding is a new concept in the foundry industry, Commercial Intertech was so satisfied with the results that it has contracted with Fosbel, Inc to continuously use this method to maintain its channel furnace lining.

"Many people in the foundry industry use gun refractory materials to repair the furnace," said William Dornan, foundry general foreman at Commercial Intertech. "However, those materials do not last very long. Some foundries have had to gun material every week. We chose to maintain our channel furnace with ceramic welding because the repaired section holds a lot longer than gunning the refractory materials."

Ceramic welding is a process used at operational temperatures for making durable repairs to refractories. It originally was developed for repairing coke oven refractories but is now being used in glass furnaces and metallurgical vessels.

The process consists of projecting a dry mixture of refractory powder and finely divided metals in a current of oxygen onto the hot face of the refractory to be restored. As a result of the exothermic reaction of the constituents, the refractory powder rapidly approaches its melting point and bonds to the repair zone substrate.

The success of the process is attributable to the development of a crystalline bond between the deposited weld mass and the refractory to be repaired. Exothermic oxidation of the metallic fuels in the ceramic welding powder raises the temperature of the refractory surface to be repaired to 4000-5500F. The base refractory and grog being applied are softened, or even partially melted together, and so develop a close bond.

Commercial Intertech became interested in ceramic welding in October 1986, after Dornan attended a presentation at AFS Headquarters by John Briggs, Fosbel general manager and now president of Foseco, Inc.

To keep its 80 ton channel induction furnace in operation, Commercial Intertech had Fosbel maintain its furnace's slag line and vertical wall near the tap hole beginning in November 1986 and until it was relined about a year later.

A pneumatic cleaning tool with a rotating head removed slag from the damaged area and a lance was used to install 150 lb of 60% alumina refractory. Needing repair were the tap hole, the surrounding refractory and an eroded area on the sidewall. Refractories to be repaired were high alumina, 95% alumina shapes and 90% alumina plastic ram, although the tap hole sleeve (which was welded in place) was a silicon carbide/alumina shape. A 60% alumina weld mass was developed using silicon and aluminum powder, together with alumina and silica as the refractory grog.

Overall, the major problem throughout the repair process was the continuing expansion of slag line erosion. This problem was solved after a larger capacity welding machine was used to apply 1050 lb of 72% alumina weld mass at a rate of 5 lb/min.

Extended repair life has meant significant savings in time and money at Commercial Intertech, which produces about 60 tons a day of gray and compacted graphite iron castings. A typical lining for the firm's type of channel furnace costs $60,000-$80,000 and lasts at least two years. Ceramic welding costs averaged $5500 a visit, with four being needed at Commercial Intertech to maintain the furnace lining from November 1986 until late 1987.

Refractory costs alone, in Commercial Intertech's view, help to justify use of the ceramic welding process. If the furnace had been shut down and relined, day melting would have been needed to maintain production, resulting in an incremental marginal cost of $15,000-$25,000.