Apparatus and method for measuring and of controlling the gap between polymer sheet cooling rolls
Heating and extruding a polymeric sheet having a predetermined thickness and introducing it into and through a gap between cooling rolls, measuring directly by laser beam and without reflection the gap between the cooling rolls, and controlling the gap to control minimal pressure on the softened and heat-plastified sheet.
1. A method of extruding a polymeric sheet, comprising the steps of:
heating and extruding a polymeric sheet having a predetermined thickness to provide a sheet of uniform thickness;
controllably introducing the polymeric sheet into a gap extending between a pair of adjacent cooling rolls;
measuring the thickness of the gap directly and without reflection between the adjacent cooling rolls, by aiming a laser beam into and through the gap to fall upon a corresponding laser detector;
comparing the measured gap thickness to a desired gap thickness;
adjusting the gap thickness by displacement of the cooling rolls, based on the measured gap thickness and the desired gap thickness.
2. The method of claim 1 wherein the cooling rolls are adjusted to exert minimal pressure on the polymeric sheet to cool the same.
3. The method of claim 1 , further comprising the step of maintaining the pressure of the rolls on the polymeric sheet between about 20 and 1000 pounds per linear inch of roll width throughout the sheet cooling period.
4. The method of claim 1 wherein a plurality of gaps are present, the method further comprising:
measuring the thickness of two or more of the plurality of gaps directly and without reflection between the adjacent cooling rolls, by aiming a separate laser beam through each of the gaps to fall upon a corresponding laser detector.
5. The method of claim 1 wherein there are more than two cooling rolls, the method further comprising:
arranging the cooling rolls in a stack and measuring and adjusting the gaps between adjacent cooling rolls as provided in claim 1 .
6. The method of claim 5 comprising arranging the rolls in a vertical stack.
7. The method of claim 5 comprising arranging the rolls in a horizontal stack.
8. The method of claim 5 comprising arranging the rolls in a stack between a vertical and horizontal position.
9. The method of claim 1 further comprising:
providing at least one of the cooling rolls with at least one end portion having a diameter less than the diameter of a roll portion having the extruded sheets thereon to provide space through which a laser beam can be sighted.
10. The method of claim 9 comprising providing the end portion as a separate component from the cooling roll.
11. The method of claim 9 comprising providing the end portion as an integral part of the cooling roll.
12. The method of claim 1 further comprising providing a positioning device connected to at least one of the rolls, the positioning device being mounted for selective positioning with respect to another of the cooling rolls;
adjusting the gap thickness using a controller wherein the controller is responsive to the measured thickness.
13. The method of claim 1 wherein the gap is adjusted using a pneumatic pressure system.
14. The method of claim 1 wherein the gap is adjusted using a hydraulic pressure system.
15. The method of claim 1 wherein the gap is adjusted using a screw device.