The results from two case studies involving the application of a durable, two-part castable refractory system to aluminum melting furnaces are discussed in this article.
Reducing furnace downtime is a key element in maintaining adequate productivity in foundry operations. One of the most common maintenance problems encountered in any given foundry is the repair and replacement of the refractory materials used to line the melting furnaces. The linings of aluminum melting furnaces are constantly exposed not only to high temperatures, but also other adverse conditions that may include impact and gouging when aluminum ingots are charged into the furnace.
Another main contributor to the deterioration of aluminum melting furnace linings is the formation of alumina or dross on the surface of the melt which can penetrate a refractory brick lining, thus requiring constant maintenance and repair. In many instances, a furnace may have to be repaired monthly and/or completely relined every one to three years in order to keep it operational.
A two-part refractory system (ThermbondR) has been developed by Stellar Materials, Inc., Delray Beach, FL, within the last several years and is showing promise as a durable, alumina-resistant furnace lining material. Below are two case studies that describe the application of this stable, abrasion-resistant refractory material and the benefits realized by two aluminum melting operations.
Magnode's casting operations include a 95,000 pound gas-fired reverberatory melting furnace, a 65,000 pound gas-fired reverberatory holding furnace and a degassing well furnace (Schaefer) arranged in an in-line configuration. The company places a premium on continuous operation because if any one of the firm's furnaces is out of the service, the entire casting operation is down. Magnode uses primary aluminum feedstock, as well as its own high-quality scrap, to produce the billets used for the extrusion operations.
Prior to the installation of the alumina-resistance refractory (Thermbond), Magnode's foundry experienced frequent downtime. One major factor contributing to this downtime was the damage incurred by the conventional ceramic brick refractories while charging the furnace. Aluminum ingots and scrap pigs are often so large that they can gouge and tear the walls of the furnace as they are inserted. The charging hearth of Magnode's melting furnace is eight feet wide, yet much of the scrap generated by the firm is three to four feet long.
Other problems occurred when the furnace was cooled. Hot metal and oxides stuck to the refractory brick so tightly that the refractory itself frequently broke off during the cleaning process. It was necessary to shut down the furnace and perform emergency repairs on the refractory insulation before continuing safe operation.
The ceramic brick refractories also required extensive preventative maintenance. Approximately once per quarter, the furnaces were shut down for three or four days to perform necessary repair work. The cost of materials ranged from $5,000 to $10,000 dollars and labor costs were also high since the job required a crew of four or five persons. In addition, the furnaces had to be completely relined every three years. This required a two-week shut down at a cost of about $25,000 for materials and occupied a crew of five people.