Polishing Rolls Have Adjustable Crowning

Chill-roll crowning allows cast PET film to run at higher speeds without danger of metal-to-metal damage between rollers.

Chill-roll crowning allows cast PET film to run at higher speeds without danger of metal-to-metal damage between rollers. An unusual technology for adjusting the crown uses a sealed cylinder filled with oil, which expands as roll temperature goes up, curving the roller. Within the 70 to 120 F processing window for PET, the change in curvature is linear with temperature and produces maximum crowning of 80 microns higher at the center of the roll than at the edges. This technology was developed years ago by Barmag in Germany, which was acquired by Bruckner Formtec in Germany (U.S. office in Greenville, S.C.). Bruckner has revived the technology and is adapting it to longer rolls—up to 2.7 meters.