A ratchet-activated height-adjustment device raises and lowers the cooling and polishing rolls relative to the sheet die. Developed and patented by Processing Technologies International (PTi), Aurora, Ill., the new mechanism is said to be simpler, less time-consuming, and more cost-effective than competitive manual and motorized methods.
Typical sheet lines are set up with the die exit directly in-line with the primary roll-nipping point. While this works for many materials, it is less effective on low-viscosity polymers such as PET, where the sheet tends to droop on the lower roll before nipping. This creates a skinning effect, which results in undesirable stresses in the extruded sheet. Repositioning the roll nip so it is lower than the die exit effectively minimizes the droop and significantly improves sheet quality. This repositioning is accomplished through adjusting the roll height.
The mechanism is standard on PTi’s G-Series roll stand. PTi incorporated a jack-screw arrangement with ratchet operating mechanism for uniformly raising or lowering the stand on both sides with ±1 in. range of adjustability. It allows adjustments while in full operation. An indicator shows the exact positioning of the rolls.