Pull roll apparatus and method for controlling glass sheet tension
A pull roll apparatus and method are described herein that can control a cross-draw tension and a down-draw tension of a glass sheet while manufacturing the glass sheet. In one embodiment, the pull roll apparatus includes a first driven stub roll pair, a second driven stub roll pair and a control device (e.g., PLC) that controls the first and second driven stub roll pairs while a first edge portion of the glass sheet is drawn between two vertically downtilted rolls associated with the first driven stub roll pair and while an opposing second edge portion of the glass sheet is drawn between two vertically downtilted rolls associated with the second driven stub roll pair. If desired, the pull roll apparatus may include a pulling roll assembly (located below the first and second driven stub rolls) or another set of driven stub roll pairs (located below the first and second driven stub roll pairs).
1. A method for manufacturing a glass sheet, said method comprising the steps of:
a) melting batch materials and forming the glass sheet;
b) delivering the glass sheet to a pull roll apparatus;
c) drawing the glass sheet and creating a cross-tension in the glass sheet using the pull roll apparatus which comprises:
(i) a cantilevered vertically downtilted first stub roll pair for drawing a first edge portion of the glass sheet out away from a center of the glass sheet;
(ii) a cantilevered vertically downtilted second stub roll pair for, at a location transversely opposite the first stub roll pair, drawing a second edge portion of the glass sheet out away from the center of the glass sheet, thereby creating a cross-tension in the glass sheet between the first stub roll pair and the second stub roll pair;
(iii) a pull roll pair disposed below the first and second stub roll pairs for drawing the first edge portion and the opposing second edge portion of the glass sheet and creating a vertical draw tension on the glass sheet between the pull roll pair and the first and second stub roll pairs;
d) monitoring the torque of at least one of the pull rolls in the pull roll pair;
e) monitoring the torque of at least one of the stub rolls in the first stub roll pair and at least one of the stub rolls in the second stub roll pair;
f) controlling the torque of at least one of the pull rolls in the pull roll pair; and
g) controlling the torque of at least one of the stub rolls in the first stub roll pair and the torque of at least one of the stub rolls in the second stub roll pair to be a predetermined percentage of the torque of the at least one pull roll.
2. The method of claim 1 , further comprising the step of controlling and adjusting a downtilt position of said first stub roll pair and said second stub roll pair.
3. The method of claim 1 , wherein said drawing step further comprising a step of positioning each of the stub rolls to have a desired splay angle which is a horizontal angle that a corresponding roll face is positioned relative to a major surface of the glass sheet.
4. The method of claim 1 , wherein said controlling the torque of at least one of the stub rolls in the first stub roll pair and in at least one of the stub rolls in the second stub roll pair step further comprising controlling and adjusting angular velocities of at least one of the stub rolls in each of the first and second stub roll pairs while idling the other one of the stub rolls in each of the first and second stub roll pairs.
5. The method of claim 1 , wherein said controlling the torque of at least one of the pull rolls step further comprising controlling and adjusting an angular velocity of motors operatively connected to the stub rolls of said first and second stub roll pairs.
6. The method of claim 1 , wherein the step of controlling the torque of the stub rolls comprises controlling the torque of the at least one of the stub rolls in the first stub roll pair and the torque of the at least one of the stub rolls in the second stub roll pair to be 50% to 100% of the torque of the at least one pull roll.
7. A method for manufacturing a glass sheet, said method comprising the steps of:
a) melting batch materials and forming the glass sheet;
b) delivering the glass sheet to a pull roll apparatus;
c) drawing the glass sheet and creating a cross-tension in the glass sheet using the pull roll apparatus which comprises:
(i) a cantilevered vertically downtilted first stub roll pair for drawing a first edge portion of the glass sheet out away from a center of the glass sheet;
(ii) a cantilevered vertically downtilted second stub roll pair for, at a location transversely opposite the first stub roll pair, drawing a second edge portion of the glass sheet out away from the center of the glass sheet, thereby creating a cross-tension in the glass sheet between the first stub roll pair and the second stub roll pair;
(iii) a cantilevered vertically downtilted third stub roll pair disposed below said first stub roll pair, for drawing the first edge portion of the glass sheet out away from the center of the glass sheet;
(iv) a cantilevered vertically downtilted fourth stub roll pair, disposed below said second stub roll pair at a location transversely opposite the third stub roll pair, for drawing the second edge portion of the glass sheet out away from the center of the glass sheet, thereby creating a cross-tension in the glass sheet between the third stub roll pair and the fourth stub roll pair;
d) monitoring the torque of at least one of the stub rolls in the first stub roll pair and at least one of the stub rolls in the second stub roll pair;
e) monitoring the torque at least one of the stub rolls in the third stub roll pair and at least one of the stub rolls in the fourth stub roll pair;
f) controlling the torque of at least one of the stub rolls in the third stub roll pair and at least one of the stub rolls in the fourth stub roll pair; and
g) controlling the torque of the at least one of the stub rolls in the first stub roll pair and at least one in the stub rolls of second stub roll pair to be a predetermined percentage of the torque of at least one of the stub rolls in the third stub roll pair and at least one of the stub rolls in the fourth stub roll pair.
8. The method of claim 7 , wherein the step of controlling step the torques of the stub rolls further comprising the steps of controlling and adjusting angular velocities of master motors operatively connected to at least one of the stub rolls in the third stub roll pair and at least one of the stub rolls in the fourth stub roll and also controlling and adjusting torques of slave motors operatively connected to at least one of the stub rolls in the first stub roll pair and at least one in the stub rolls of second stub roll pair.
9. The method of claim 7 , wherein the step of controlling the torque the at least one of the stub rolls in the first stub roll pair and at least one of the stub rolls in the second stub roll pair comprises controlling the torque of at least one of the stub rolls in the first stub roll pair and the torque of at least one in the stub rolls to be 0% to 10% of the torque of the at least one of the stub rolls of third stub roll pair and at least one of the stub rolls of fourth stub roll.
10. The method of claim 7 , further comprising the step of controlling and adjusting a downtilt position of said first stub roll pair and said second stub roll pair.
11. The method of claim 10 , further comprising the step of controlling and adjusting a downtilt position of said third stub roll pair and said fourth stub roll pair.
12. The method of claim 7 , wherein said drawing step further comprising positioning each of the stub rolls to have a desired splay angle which is a horizontal angle that a corresponding roll face is positioned relative to a major surface of the glass sheet.
13. The method of claim 7 , wherein the controlling the torque of the at least one of the stub rolls in the first stub roll pair and in the second stub roll pair step further comprising controlling and adjusting angular velocities of the at least one of the stub rolls in each of said first and second stub roll pairs while idling the other one of the stub rolls in each of said first and second stub roll pairs.
14. The method of claim 7 , wherein the controlling the torque of the at least one of the stub rolls in the third stub roll pair and at least one of the stub rolls in the fourth stub roll pair step further comprising controlling and adjusting an angular velocity of motors operatively connected to the at least one of the stub rolls in the third stub roll pair and at least one of the stub rolls in the fourth stub roll pair.