Complex sentence: As a "cold" belt enters the mold region, it is subject to powerful "cold framing" forces that, when casting wide strip, must be controlled to eliminate buckling and reduce thermal distortion of the belt at the mold entrance.
Split into simpler sentences: As a "cold" belt enters the mold region, it heated in the cast zone and is subject to powerful "cold framing" forces. When casting wide strip, these cold framing forces must be controlled to eliminate buckling and reduce thermal distortion of the belt at the mold entrance.