1. Field
The present specification generally relates to pulling rolls for use in the manufacture of glass sheets and, more specifically, to pulling rolls comprising spring elements for applying a drawing force to glass sheets.
2. Technical Background
Pulling rolls are used in the manufacture of sheet glass to apply tension to a ribbon or web of glass from which individual sheets of glass are formed. The amount of tension applied by the pulling rolls to the glass is utilized to control the nominal thickness of the glass as the glass is drawn from molten glass, such as in an overflow down-draw fusion process, as described in U.S. Pat. Nos. 3,338,696 and 3,682,609, or in similar glass manufacturing processes.
Pulling rolls are generally designed to contact the glass web at its outer edges, usually in an area just inboard of the thickened beads that form at the very edges of the glass web. Because the pulling rolls are in direct contact with the surface of the glass web, damage to the surface of the glass can occur due to the wear characteristics of the pulling roll material. For example, glass particles can become embedded in the surface of the pulling roll resulting in damage to the glass as the pulling rolls contact the glass.
Similarly, the pulling roll may shed particulate matter if the material of the pulling roll degrades with use at the elevated temperatures of the glass drawing process. This particulate matter may become embedded in the soft glass thereby forming defects in the glass. In addition, particulate matter generated from the glass drawing process (e.g., debris, dust, glass shards and the like) may become embedded in the surface of the pulling roll thereby creating repetitive defects in the glass web. Damage to the glass web caused by any of these mechanisms may result in uncontrolled and/or premature breakage of the glass sheet during the drawing process thereby decreasing manufacturing efficiencies and increasing costs.
In addition, particulate matter generated from the glass drawing process may cause the pulling roll to lift off the glass sheet, resulting in a concentrated normal force to bear on not only the sheet but also the pulling roll, which could cause permanent deformations in the pulling roll material.
Accordingly, alternative designs for pulling rolls for use in glass manufacturing processes are needed.