Method and apparatus for restraining glass during tempering

In tempering glass sheets vertically hung from tongs, the uniformity with which tempering medium is applied onto the glass sheets during quenching is improved by providing the quenching apparatus with a plurality of discs carried on wires on one side of the path taken by glass sheets through the quenching apparatus. The flow of tempering medium is controlled so as to force the glass sheets against the discs, thereby avoiding uncontrolled buffeting of the glass sheets during quenching. The discs are designed to minimize interference with the flow of tempering medium and preferably include openings through which the tempering medium may flow, such as serrations along the edges.

BACKGROUND OF THE INVENTION 
A technique commonly employed for tempering glass sheets, especially when a 
series of glass sheets are to be sequentially bend and then tempered, is 
to vertically hand each glass sheet from tongs which grip the upper 
marginal edge portion of each glass sheet and to thus convey each glass 
sheet through heating, bending, and tempering steps. The heating step 
entails suspending the glass sheets within a heating chamber until the 
temperature of the glass approaches its softening point, and then each 
sheet in series is conveyed out of the heating chamber and into a bending 
station. A typical vertical bending operation is disclosed in U.S. Pat. 
No. 3,367,764 to S. L. Seymour, wherein a heat-softened glass sheet is 
bent between a pair of complementary, horizontally reciprocated bending 
molds. After bending, with the glass sheet still at an elevated 
temperature sufficient for tempering, the glass sheet is conveyed into a 
quenching station where it is rapidly cooled by blasts of tempering medium 
so as to establish compressive stresses in the surface portions of the 
sheet, thereby strengthening the sheet. The tempering medium is usually 
air, but as used herein, the term may encompass any fluid capable of 
cooling a hot glass sheet. Such a process has proved to be an economical, 
high-speed method for mass producing bent and tempered glass sheets, such 
as those used for automobile glazing and the like. 
One difficulty encountered with tempering glass sheets that are freely hung 
from tongs is that, when directing the blasts of tempering medium onto the 
glass sheets, it is usually found to be virtually impossible to precisely 
duplicate flow conditions on both sides of a curved glass sheet. As a 
result, sharp side-to-side buffeting of the glass sheet is often induced 
during quenching. This problem is made more difficult by the fact that it 
is usually necessary to provide relative motion between the glass sheets 
and the nozzles applying the tempering medium in order to avoid creating 
iridescent patterns in the glass due to uneven cooling. Buffeting of the 
glass sheets impedes uniform application of the tempering medium onto the 
glass sheets, which in turn leads to imbalanced stresses in the tempered 
product. Such uneven stresses can result in the tempered glass sheet 
failing to meet strength specifications and may even cause glass breakage 
during processng. The problem of buffeting is especially troublesome with 
thin glass (i.e., glass about 4.5 millimeters or less in thickness), the 
demand for which has been increasing for use in automobiles. Not only is 
thin glass lighter in weight and thus more susceptible to buffeting, but 
also the faster rates of cooling required to temper thin glass entail the 
use of higher pressure blasts of tempering medium, which in turn increases 
the amount of buffeting. 
Efforts to reduce buffeting in the prior art have included the use of guide 
wires extending through a quenching apparatus, an example of which may be 
seen in U.S. Pat. No. 4,006,002 to Hetman. However, such an approach has 
not been found adequate to stabilize glass sheets in the quench to the 
extent desired. Moreover, prolonged contact between such guide wires and 
glass sheets may mar the glass surface in cases where the glass is still 
sufficiently softened, or may cause lines of distortion in the glass by 
absorbing heat at a rate different from the rate at which the remainder of 
the sheet is cooled. 
Another prior art approach to limiting the degree of buffeting is disclosed 
in U.S. Pat. No. 3,824,090 to S. L. Seymour et al. In that arrangement a 
number of solid rollers are rigidly mounted on brackets attached to the 
quenching nozzles. However, the relatively large mass of the rollers and 
brackets serves as a heat sink, which can lead to undesirable non-uniform 
cooling of the glass. Also, the location of the rollers and brackets 
within the quenching zone renders adjustments to them very difficult when 
the apparatus is in use. Furthermore, in the arrangement in the patent, 
every mode of operation requires the rollers to roll continuously over 
extended areas of the glass surface. 
SUMMARY OF THE INVENTION 
In the present invention, buffeting of glass sheets hung vertically from 
tongs in the quenching section of a glass tempering operation is minimized 
by providing the quenching zone with a plurality of lightweight discs 
spaced apart on wires extending along one side of the position taken by a 
glass sheet in the quench. The pressure with which tempering medium is 
applied to the opposite sides of the glass sheets is controlled so as to 
force each glass sheet to one side into contact with the discs. Each disc 
provides minimal interference with the flow of the tempering medium and 
minimal heat absorption, and thus a large number of the discs may be used, 
thereby distributing the restraining force over a wide area. 
Because the discs of the present invention are carried on wires which have 
resiliency in the transverse direction, the initial impact between the 
glass and the discs may be cushioned, and the wires tend to be forced to 
follow the curvature of the bent glass, thereby bringing more discs into 
contact with the glass surface and dividing the load among a greater 
number of contact points. Another advantage attained by the wire support 
arrangement of the present invention is that the ends of the wires can be 
supported outside the quench area itself, where they are readily 
accessible for making adjustments without the necessity of halting 
production. Additionally, this arrangement permits the support for the 
wires to be independent from the support means for the tempering nozzles. 
This permits a preferred, advantageously stable method of operation 
whereby the discs and the glass remain stationary with respect to one 
another while the nozzles are oscillated or reciprocated in any direction 
or mode.

DETAILED DESCRIPTION 
In FIG. 1, a bent sheet of glass 10 is shown in an edgewise view being 
supported by tongs 11 within a quenching station. The glass sheet may be 
bent immediately prior to entering the quenching station by any of the 
well-known means for press bending vertically disposed glass sheets, for 
example, that shown in U.S. Pat. No. 3,367,764 to S. L. Seymour. Although 
only a single set of tongs can be seen in the drawing, the most common 
practice is to employ two or more sets of tongs to grip each glass sheet. 
The particular design of glass gripping tongs used is not essential to the 
present invention, but additional details of a preferred design may be 
found in U.S. Pat. No. 3,089,727 to W. J. Hay. 
The present invention is not limited to any particular quench design, and 
thus the quench arrangement shown in the drawings is merely for the 
purpose of illustration. Any known quench design may be used which is 
capable of applying blasts of tempering medium (preferably air) onto 
opposite sides of a glass sheet. A specific embodiment which may be used 
to particular advantage with the present invention is disclosed in U.S. 
Patent Application Ser. No. 871,873, filed on Jan. 24, 1978, by V. R. 
Imler, the disclosure of which is hereby incorporated by reference. Other 
applications which may be referred to for improvements in the operation of 
that particular quench design are U.S. Patent Application Ser. Nos. 
871,876 and 871,888, both filed on Jan. 24, 1978, by V. R. Imler, the 
disclosures of which are also incorporated by reference. 
Immediately after being heated and bent, the still hot sheet of glass 10 is 
conveyed into a quenching station as shown in FIG. 1. There it is stopped 
between opposed blast heads 12 and 13 which direct tempering medium onto 
the opposite surfaces of the glass and quickly cool surface portions of 
the glass below the strain point of the glass so as to temper the glass. 
It is usually expedient to move the blast heads 12 and 13 to more widely 
spaced positions as the glass sheet is being conveyed into position in the 
quenching station and then, when the glass has stopped, to move the blast 
heads toward one another into close proximity to the glass as shown in 
FIG. 1. While the glass sheet is being conveyed into and out of the 
quenching station, it is usually desirable to cut off the flow of 
tempering medium. 
As depicted in FIGS. 1 and 2, each blast head may consist of a number of 
modules 13, each of which is supplied with pressurized tempering medium by 
way of a conduit 14. The glass-facing side of each module 13 includes an 
array of nozzles 15 which direct air or other tempering medium toward the 
adjacent portion of the glass sheet. In order to avoid creating patterns 
of iridescence caused by unequal impingement of the tempering medium onto 
the glass surface, it is necessary to impart relative motion between the 
nozzles 15 and the glass. Such relative motion is usually achieved by 
reciprocating or rotating the blast heads in directions substantially 
parallel to the major glass surfaces. However, an alternate, preferred 
method of achieving relative motion with the present invention is to 
oscillate each quench module separately about a horizontal axis as 
disclosed in the aforesaid copending applications of Vaughn R. Imler. 
In order to stabilize the glass sheet against the buffeting normally 
associated with the type of tempering operation which has been described, 
the present invention provides a pair of spaced-apart restraining wires 21 
extending between the blasts heads and which carry a plurality of discs 
20. The opposite ends of each wire 21 are fastened to mounting brackets 22 
between which the wire is maintained taut. As shown in FIG. 2, the 
mounting brackets 22 may be located outside the area between the blast 
heads and may be adjustably fastened to a frame member 23. Frame member 23 
may be either stationary and independent from the blast heads, or it may 
be part of the framework supporting the blast heads and thus travel in 
unison with the blast heads as they reciprocate. 
The term "wire" as used herein is intended to include any thin, flexible, 
elongated thread, cord, filament, or the like. The wire should be capable 
of maintaining strength while being exposed periodically to elevated 
temperatures, and should be able to withstand some abrasion. Thus, the 
wire is preferably made of metal such as steel (e.g., piano wire). 
The discs 20 carried on each wire serve to space the surface of the glass 
sheet from the wires, thereby preventing contact between the wires and the 
hot glass and reducing undesirable thermal effects. In the preferred 
embodiment, the discs 20 take the form of thin, circular pieces of 
heat-resistant material 24, each having a plurality of serrations 25 for 
improving circulation of tempering medium in the vicinity of each disc. A 
material found to be particularly suitable for this purpose is "Synthane" 
grade G-7, an electrical insulator material sold by the Synthane Taylor 
Company of Valley Forge, Pennsylvania, and which is believed to be a fiber 
glass reinforced epoxy resin. A thickness of about 3 millimeters and a 
diameter of about 2 to about 4 centimeters have been found to be 
satisfactory. Other materials which may be used for the circular portions 
of the discs include boron nitride, Teflon (polytetrafluoride plastics 
sold by DuPont Co.) or the like, and wood (particularly maple). In order 
to maintain the flat, circular portion of each disc perpendicular to the 
wire, a short piece of a small diameter metal tube 26 may be inserted 
through the center of the thin, circular portion and adhered in place by a 
temperature resistant adhesive, such as an epoxy type adhesive. The tube 
26 is selected to have an inner bore 27 of a diameter slightly greater 
than the diameter of the wires 21 so that a wire may be inserted through 
each bore 27 with sufficient clearance for each disc to rotate. The 
spacing between discs will be determined largely by the curvature of the 
bent glass sheets. A typical spacing between discs is about 30 
centimeters. 
The ability of the discs to rotate on the wires is an advantage when the 
blast leads and the wires reciprocate vertically as a unit, whereby the 
discs roll over the surface of the glass and avoid abrasive contact 
between the wires and the glass surface. In other modes of operation, 
however, the rotational feature may not be essential, in which case the 
discs may be rigidly affixed to the wire such as by gluing, welding, or 
crimping the tube 26. If the discs are rigidly affixed to the wire, the 
wires may extend through the quenching station in directions other than 
the horizontal direction shown in the drawings. Another variation, which 
would permit rotation of the discs while preventing their displacement 
along the wire, would be to affix small retainer clips on either or both 
sides of each disc, thereby preventing the discs from sliding along the 
wires. 
While some of the advantages of the present invention may be attained when 
using discs having solid circular portions, it is preferred that the discs 
have serrations or other type of perforations in order to avoid dead spots 
in the flow of tempering medium adjacent to the glass surface. The 
preferred embodiment is to provide perforations in the form of radially 
extending serrations 25 as shwon in FIG. 3, since such an arrangement 
permits flow through a large area of each disc including both the outer 
edge portions and central portions. Examples of alternate arrangements for 
providing flow through the discs are shown in FIGS. 5 and 6. In FIG. 5, 
disc 20' has a flat circular portion 24' and a central hub 26', as in the 
preferred embodiment, but is provided with a pluraity of drilled holes 30 
through the flat, circular portion. It should be apparent that openings of 
any shape could be cut instead of the circular openings shown. In FIG. 6, 
disc 20" is likewise provided with a flat circular portion 24" and a 
central hub 26". The air flow openings in this case take the form of 
indentations 32 around the perimeter of the flat, circular portion in a 
pattern resembling gear teeth. 
In operation, a vertically hanging glass sheet 10 is conveyed into the 
quenching area along either a horizontal or vertical path while the blast 
heads 12 and 13 are in their open, horizontally separated positions, at 
which time the wires 20 are also laterally retracted from the path of 
glass travel. The glass is oriented so as to place its convex side toward 
the wires 21 and discs 20. When the glass has stopped in the quench, the 
blast heads are moved closer together to bring the nozzles 15 and the 
wires 21 into closer proximity to the glass, whereby some of the discs 20 
closely approach or contact the convex side of the glass sheet. The flow 
of pressurized tempering medium is then initiated and the relative 
pressures on opposite sides of the glass sheet are maintained so as to 
force the convex side of the glass sheet into contact with several of the 
discs along each wire. At a given applied pressure, the generated lateral 
force on the concave side of the glass sheet will be greater than that on 
the convex side. Thus, urging the glass sheet against the discs does not 
necessarily require higher pressure to be supplied to the blast head on 
the concave side. 
While blasts of tempering medium are being applied onto the glass sheet, 
relative motion between the nozzles and the glass may be provided in any 
of a number of ways, the choice of which will depend upon a number of 
factors such as the shape of the glass sheet being tempered and the design 
of the particular blast heads being employed. In some cases, individually 
oscillating quench modules 13 have been found to be preferred, as 
disclosed in the aforementioned copending patent applications of V. R. 
Imler. When such a quench module arrangement is employed in connection 
with the present invention, the glass and the wires advantageously may 
both remain stationary while the quench modules oscillate. In other cases, 
when each blast head moves as a whole, it is preferred that relative 
motion be provided by reciprocating each blast head vertically while the 
glass remains stationary. In the latter case, the wires may move in unison 
with the blast head on the convex side, whereby the discs roll over the 
convex surface of the glass sheet. Other modes which may be utilized 
advantageously with the present invention include reciprocating the blast 
heads horizontally in the longitudinal direction while the glass and the 
wires remain stationary, or rotating the blast heads about a horizontal 
transverse axis while the glass and the wires remain stationary. Also, if 
the wires run vertically through the quench, the blast heads and the wires 
may be reciprocated together in the horizontal, longitudinal direction so 
as to roll the discs over the surface of the glass. 
When tempering is completed, the flow of tempering medium is stopped, the 
blast heads separate, the wires are retracted from the path of glass 
travel, and the glass sheet is conveyed out of the quench station to an 
unloading station. 
Other variations and modifications as are known to those of skill in the 
art may be resorted to within the spirit and scope of the present 
invention as defined by the appended claims.