Molds that have a melt conveying system that keeps the runner molten at all times in the mold. The method for doing this consists of a manifold (a larger piece of steel with holes that are in the center that allow the melt to be contained.) This large piece of steel referred to as a manifold is usually heated with cartridge heaters or cal rod heaters. You use the same rods in your oven at home. These heaters are controlled by the use of thermocouples hooked to controllers that turn the electricity to the heaters on or off depending on what the thermocouple signals the temperature of the block is.