Madison-Kipp "molds" an innovative ceramic fiber solution.

Madison-Kipp "Molds" an Innovative Ceramic Fiber Solution

When casting machines have an appetite for more than 2 million pounds of molten aluminum and zinc a month, maintaining a continuous flow is the name of the game. And the molten aluminum/zinc transport system is a major player.

Madison-Kipp Corp/Kippcast Div. Madison, WI, has 24 conventional aluminum and 17 mini zinc casting machines to produce 1.2 million pounds of parts a month for automotive industrial applications--ranging from cruise control covers to brake system components. Customers include General Motors, Dana Corp, Bendix, TRW, John Deere, Allen-Bradley and MicroSwitch.

Supplying the automotive industry requires two essential ingredients: consistent high quality and on-time delivery. A ceramic fiber material plays a key role in helping Madison-Kipp achieve these goals.

The plant's operating conditions are rigorous: five days a week for three eight-hour turns, and on some lines, seven days a week for three eight-hour turns, consuming up to 35,000 pounds (13,055 kg) of aluminum and zinc each turn.

Maintaining this schedule requires an uninterrupted flow of molten metal from the central melting furnace to the casters' holding furnace, from the reheat furnace troughs to the bull (transfer) ladle lining. The ladle lining is critical to the operation's success because it comes into direct contact with the molten aluminum or zinc.

Molten metal is more harmful to refractories than molten zinc, according to Gary Sholl, manager of process engineering at Madison-Kipp. "Since aluminum is quite reactive [just below magnesium], it oxidizes very readily," he said. "Secondly, aluminum is an excellent solvent, dissolving every known metal. Furthermore, we pour aluminum at a temperature 400-500 [degrees] F (204-260 [degrees] C) higher than zinc."

Until two years ago, Kippcast's refractory linings were a weak link in the transport system. Before then, Madison-Kipp lined its 1700 lb (634 kg) capacity bull ladle with a castable refractory. The castable lining was resistant to mechanical abuse but had low thermal shock resistance. Repairs to the castable ladle lining required excessive downtime.

"With the castable lining, we couldn't hotpatch repairs," said Dan Keyes, Madison-Kipp's refractory specialist, who is responsible for all refractory maintenance. "Making repairs was a two-day process that included cool down, extensive cleaning of the repair area and placement of anchors and casting form, followed by the mixing and installation of the castable refractory.

"And, often, when you patch a castable refractory you do not get a good bond to the existing lining. This poor bond creates a shearplane, where you get a delamination of the new patch from the old material."

Each disadvantage was especially detrimental to Madison-Kipp's operation because the cyclical use of the ladle made the lining susceptible to thermal shock and the constant demand for molten aluminum greatly reduced the time in which to make repairs.

Finding a Solution

Keyes had the task of finding a cost-effective solution. "My goal was to improve the performance of our transport system by installing a refractory that would stand up to our operating environment, reducing downtime required for repairs," he said.

Through aluminum industry associates, Keyes heard about a moldable ceramic fiber refractory and decided to give it a try. In June 1987, he lined his primary bull ladle 36 x 56 in. (91 cm x 127 cm) with a four in. (10 cm) layer of Fiberfrax [R] LDS Moldable ceramic fiber manufactured by The Carborundum Co's Fiber Division.

LDS Moldable ceramic fiber is an air- or heat-setting material that has a putty-like consistency. It has a 2300F (1260C) continuous use limit and a 40 lb/[ft.sup.3] (641 kg/[m.sup.3]) dry density with almost zero drying shrinkage. The moldable material also provides excellent wet adhesion to steel, refractories or other ceramic fiber materials, yet is not readily wet by molten lead, zinc, copper or aluminum.

After nearly two years of operation, the ceramic fiber moldable lining has performed well, especially in installation flexibility, thermal shock resistance and high insulation properties. Based on the success of the moldable material for lining the ladle, Keyes had it installed in various applications, including troughs spouts, the caster-holding furnace lining and patches for the central heating furnace (operating at temperatures up to 1850F/1010C).

"We have rebuilt and increased the capacity of our backup bull ladle to 1900 lb (709 kg) and lined it with LDS Moldable," Sholl said.

The biggest advantage of the moldable refractory lining is its installation flexibility. Because it can be used for either hot- or cold-patch repairs, the moldable material has proved to be a critical element in reducing downtime.

"We don't have to go through an elaborate cool down or cure cycle with this material," Keyes said. "For example, we can hot-patch a trough between pours and use it again in under 30 minutes. In contrast to the castable refractory, the moldable material provides an excellent bond to the existing refractory lining."

Another advantage of Fiberfrax is its high insulation capability, also a critical factor in transporting molten aluminum. The quicker the heat loss, the less time there is to purify the molten aluminum. With the castable-lined ladle, Madison-Kipp experienced about a 125-150 [degrees] F (52-66 [degrees] C) heat loss, Keyes noted. "With the LDS moldable-lined ladle, we lose far less heat," Sholl added, "only 35-40 [degrees] F (2-5 [degrees] C) from the time we fill the ladle at the central melting furnace, degas the ladle (about 15 minutes) and pour into the casting machines."

PHOTO : A worker fills a ladle with molten aluminum at Madison-Kipps's Kippcast Div. The ladle is

PHOTO : lined with a four in. (10 cm) layer of Fiberfrax [R] LDS Moldable ceramic fiber

PHOTO : manufactured by The Carborundum Co's Fibers Div.

PHOTO : Both hot- and cold-patch repairs can be made to the bull ladle, which is lined with the

PHOTO : Fiberfrax LDS Moldable ceramic filter.