1. Field of the Invention
This invention relates to press bending, and in particular to a press face support and alignment system for press bending hot glass sheets.
2A. Technical Considerations
Press bending is a well known forming technique used to shape heat softened sheet materials, and in particular glass sheets. In general, flat sheet material is conveyed through a furnace and heated to its heat softening temperature. The sheet is then conveyed between a pair of vertically aligned upper and lower pressing molds and sandwiched between the molds to impart the final desired shape to the sheet. In a press bending arrangement as taught in U.S. Pat. No. 4,526,605 to Frank et al., the sheet is conveyed by conveyor rolls over a lower slotted pressing mold that lifts the sheet off the rolls and into contact with a full surface upper vacuum mold. The lower mold thereafter retracts while the upper mold holds the sheet thereagainst by vacuum. The sheet is thereafter deposited on a tempering ring positioned below the sheet after shaping and transported to a quench station where it is cooled to impart a temper in the shaped glass sheet. In a press bending arrangement as taught in U.S. Pat. No. 4,290,796 to Reese et al., overlaying glass sheets are preliminarily shaped by gravity on an outline mold by conveying them through a heating lehr. The outline mold is then positioned in a shaping station wherein a full surface lower mold passes through the outline mold to lift and press the glass sheets against a full surface upper mold. After shaping the lower mold deposits the shaped glass sheet back onto the outline mold for further processing.
As the bent shape of glass sheets becomes more complex due to the emphasis placed on increasingly aerodynamic automotive and aircraft designs, it is very important that the pressing faces of the shaping mold maintain proper alignment. Any small misalignment which may occur during the pressing operation may result in a defectively shaped glass sheet that will be rejected.
In addition, with the great variety of shapes and patterns required by users of shaped glass sheets, many different sets of molds must be utilized. Each time a different curved shape is required, the current set of molds must be removed and replaced with a new set that must be positioned and aligned prior to restart of the press bending operation.
It would be advantageous to have a press bending arrangement wherein the relative positions of the upper and lower mold may be easily and accurately checked to ensure that the molds are properly aligned, as well as provide an aligning arrangement to quickly realign the molds if required. In addition, it would be advantageous to have a mold mounting arrangement that allows for quick replacement and realignment of the mold in a press bending operation.
2B. Patents of Interest
U.S. Pat. No. 4,290,796 to Reese et al., teaches a mold alignment arrangement for a glass sheet shaping apparatus. Outline molds support glass sheets as the molds are conveyed through a heating lehr and bent by gravity sagging. The outline mold stops at a shaping station in approximate alignment between a pair of upper and lower vertically aligned pressing molds. As the outline mold enters the shaping station, pin members at the end of rods move inward from the side walls of the lehr to engage J-shaped members in the outline mold to align the outline mold relative to the pressing molds. In addition, the upper and lower pressing molds are each provided with two pairs of elongated slots; a first pair extending longitudinally along a longitudinal reference line and second pair extending along a transverse reference line. The slots are arranged so that the longitudinal reference line which connects the first pair of slots interconnects the transverse reference line connecting the second pair of slots at the geometric center of the mold. The pins within the slots maintain the geometric center at a fixed location at all times despite any change in temperature of the mold during operation.
U.S. Pat. No. 4,526,605 to Frank et al., discloses a press bending operation wherein an upper vacuum mold for shaping glass sheets includes vertical side walls with an inwardly extending circumferential ledge which supports a corresponding outwardly extending ledge of a vacuum mold press face. The press face is supported by the support structure without any metal attachments that may induce high local stresses. A vertical wall of the support structure can be removed to permit replacement of the vacuum press face.
The art discloses various press bending arrangements but does not teach or disclose techniques for adjusting, aligning and realigning pressing molds to ensure accurately bent glass sheets.