Pyrotek manufactures underheated holding furnaces for low-pressure (LP) casting to help aluminium foundries around the world meet the market and customer demands for higher quality metal.
“We understand the current state and the future of aluminium casting and the requirements for lighter and thinner castings, resulting in the need for high metal quality,” says Dusty Ousley, Pyrotek’s low-pressure/holding furnace business development manager. “We also know the demands to reduce operational costs.”
Pyrotek’s underheated LP furnaces position the heating elements close to the floor. This way the heating source is completely submerged in molten aluminium, allowing for both efficient conductive heat and the promotion of convection currents. This combination results in a more uniform temperature, varying no more than 5°C (41°F). In contrast, a top-heated furnace can have a thermal gradient as much as 22°C (72°F). The underheated technology has proven to be 25–30 percent more energy efficient than top-radiant furnaces.
Top-mounted heat elements create higher atmospheric temperatures in the holding chamber, resulting in oxide generation. A thick oxide layer insulates the top of the bath, not allowing the heat to transfer to the metal properly, thus increasing the temperature of the heating element and decreasing furnace energy efficiency. Additionally, the resulting oxide growth will damage the furnace body and heating elements.
“The underheated design offers greater metal cleanliness due to reduced oxide generation,” Ousley says.
With a heat source fully immersed oxide production is minimized in the holding chamber.
Another advantage of Pyrotek’s underheated holding furnace is it takes up less space, which leads to energy savings.
“When horizontal underheating is used, a smaller overall footprint can be used,” Ousley says. “This allows for reduced floor space and aluminium surface area, resulting in less exposure to open air and less oxidation of the surface.”
A small exposed surface area results in more homogenous metal temperature throughout the entire bath.
“Overall, this results in energy savings,” he says.
The underheated LP furnace utilizes a divider wall and stopper rod to isolate the holding chamber from the pressure chamber. This allows dross generation from charging to be isolated to the holding chamber.
The quiet metal transfer between chambers leaves very clean metal in the pressure chamber.
Molten aluminium can be delivered anytime during a casting cycle. Skimming and light cleaning of the holding chamber can also be done anytime, and there is no need to shut down the casting machine. This results in more casting machine uptime.
The stopper rod opens and closes after each cycle to replenish and maintain a consistent metal level in the pressure chamber. The consistent metal level creates a more uniform temperature and allows for the use of a shorter stalk/riser tube. This allows the metal to be drawn from cleaner metal in the upper to middle part of the bath. It also results in reduced consumable cost.