The cooling belts are typically made of low carbon steel and are held under tension within the casting machine to ensure flatness and accuracy. As a "cold" belt enters the mold region, it is heated in the cast zone and is subject to powerful forces caused by thermal expansion. When casting wide strip, these forces must be controlled to eliminate buckling and reduce thermal distortion of the belt at the mold entrance. These forces can be controlled by preheating the belts before mold entry, or by magnetically stabilizing them once they have entered the mold.