WO1991012211A1

WO1991012211A1 - Variable pressure gas jet system for lifting and forming glass sheets

Info

Publication number: WO1991012211A1
Application number: PCT/US1991/000622
Authority: WO
Inventors: Ben M. Balestra; Gregory A. Ritz
Original assignee: Glasstech, Inc.
Priority date: 1990-02-06
Filing date: 1991-01-29
Publication date: 1991-08-22
Also published as: AU7320891A; CN1057445A

Abstract

A variable pressure gas jet system for lifting and forming glass including a controller (32) for providing an electrical signal corresponding to a preselected pressure to an electrical-to-pressure converter (34) which converts the received signal to a corresponding pressure. A remotely operated gas flow regulator (36) receives a small volume of the pressurized gas from the converter and transmits a large volume of gas at a corresponding pressure through the system to a series of gas jets (42) including an array of pumps or frustoconically shaped nozzles (24) which direct the pressurized gas onto the lower surface of the heated glass sheet to lift the glass sheet from the conveyor (16) to the downwardly facing surface of an upper mold (22). As the pressurized gas is communicated through the nozzles (24) and outwardly from the distal end of the nozzle (24) a primary gas flow is established.

Description

VARIABLE PRESSURE GAS JET SYSTEM FOR LIFTING AND FORMING GLASS SHEETS

TECHNICAL FIELD

This invention relates to furnaces for heatin and press bending glass sheets.

BACKGROUND ART

Bent glass sheets are used extensively fo vehicle windshields, side windows, and rear windows, a well as in various architectural applications. The ben sheets are also frequently tempered to improve th mechanical strength of the glass. In the United States, tempered bent glass sheets are used on vehicle side an rear windows while annealed bent glass sheets laminate to each other by polyvinyl butyryl are used for vehicl windshields. In other countries, tempered bent glas sheets are used for vehicle windshields as well as fo side and rear windows.

Glass sheet press bending is typically per formed by pressing a heated glass sheet on a mold, o between complementary curved molds so that the heate glass sheet is bent to conform to the curved shape o the mold or molds. One type of press bending system i disclosed in U.S. Patent No. 4,661,141, which disclose a glass sheet press bending system including a horizon tal conveyor on which glass sheets are conveyed in generally horizontally extending orientation for heat ing, and also includes an upper mold having a downwardl facing curved shape located above the conveyor at bending station. When a glass sheet is conveyed int the bending station, a vacuum drawn at the upper mol and/or upward gas flow from below the conveyor provide a preferred means for supplying a differential gas pressure to the heated glass sheet so as to lift the glass sheet upwardly off the conveyor against the downwardly facing surface of the mold and, preferably, to provide some or all of the bending required to conform the glass sheet to the shape of the mold sur¬ face. A lower mold having an upwardly facing, comple¬ mentary curved shape is typically mounted for movement into position directly below the upper mold, and for subsequent movement upwardly to press bend the heated glass sheet between the upper and lower mold. A trans¬ fer mold is thereafter moved horizontally under the upper mold and receives the press bent glass for subse- quent transfer therefrom. Normally, the transfer mold is formed as an open-center ring and transfers the press bent glass to a quench station where tempering is performed. This type of press bending system can be utilized with either a gas hearth or a roller-type conveyor.

These systems typically employed a gas jet system generally of the type illustrated in Figure 8 for providing positive gas pressure on the underside of the glass sheet for lifting the glass from the conveyor and blowing it to the upper forming mold. A control signal opened a "cold valve" solenoid which supplied pressur¬ ized air to a heat exchanger (not shown) in the furnace. The pressure level for the pressurized air was set on a pressure regulator. The heated high pressure air was then released to the lift jets by opening a "hot valve" solenoid, thereby lifting the glass from the rolls and blowing it to the forming mold. This system provided adequate though minimal control of the lift jet forces by providing one or more pre-set forced levels of pressurized air to the system. However, since the action of the lift jets could be controlled only by turning on and off the hot valve or cold valve, the system operated at a single, pre-set pressure. To change the lifting force for bending a different shape, the regulator required adjustment during initial set-up of the system for that shape.

Another problem with the previous system was that upon opening the cold valve, and prior to opening the hot valve, significant excess pressure often built- up in the pressurized gas in the heat exchanger so that, upon opening the hot valve to lift up the glass sheet, the initial surge of pressurized gas was greater than the desired force, causing damage to the protective covering on the mold or breakage of the glass sheet.

Also, if a different lifting force was needed during a different stage in a glass sheet press bending cycle, a second bypass regulator and bypass cold valve would need to be installed. Likewise, additional bypass regulators and bypass cold valves (shown as phantom lines in Figure 8) would need to be installed for each different lifting force required during the process.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a variable pressure gas jet system that receives a heated glass sheet from a horizontal conveyor and quickly provides accurate and quickly varying gas pressure on the underside of the heated glass sheet to quickly but gently blow the glass sheet from the convey¬ or to the upper forming mold.

Another object of the present invention is to provide a variable pressure gas jet system capable of providing variable controlled gas at relatively higher pressures than the gas pressure used to lift the glass sheet to the mold to assist in forming the heated glass sheet on selected areas of the mold.

Another object of the present invention is to provide a variable pressure gas jet system capable of delivering a preselected pressure, relatively lower than the lifting pressure, to the glass sheet as it is dropped onto, and transported on, the open center transfer ring to reduce the effect of gravity which tends to cause the formed glass to sag from its desired shape.

A further object of the invention is to provide a simplified nozzle design that requires virtu¬ ally no maintenance.

In carrying out the above objects, the vari¬ able pressure gas jet system of the present invention includes a controller for providing an electrical signal corresponding to a preselected pressure to an electri- cal-to-pressure converter which converts the received signal to a corresponding pressure. A remotely operated gas flow regulator receives a small volume of the pressurized gas from the converter and transmits a large volume of gas at a corresponding pressure through the system to a series of gas jets comprising an array of nozzles which direct the pressurized gas onto the lower surface of a heated glass sheet to lift the glass shee from a conveyor to the downwardly facing surface of a upper mold.

The control preferably comprises a compute including a microprocessor and adequate memory fo retaining a series of preselected pressures and prese lected process intervals which together, define profile of varying pressures suitable to softly lift th heated glass sheet from the conveyor into contact wit the upper mold, form the glass sheet on the mold, an subsequently provide support for the formed glass shee on an open-center transfer ring to abate the effects o gravity which cause the formed glass sheet to sag fro its desired shape during transport from the bendin station.

The preferred embodiment of the presen invention includes a heat exchanger and a "hot valve", each respectively located downstream of the regulato and upstream of the gas jets to provide preheating o the pressurized gas. The hot valve is automaticall opened or closed at preselected times by the controlle to quickly provide an infinitely varying preselected ga jet force throughout the glass sheet bending cycle.

The most preferred construction of the presen invention includes a plurality of independent arrays o gas jet nozzles configured to provide pressure on particular portion of the surface of the glass sheet, wherein the computer provides independent control o each array of gas jet nozzles according to a specifi pressure-time profile during the glass sheet bendin process. Each nozzle is of a frustoconical shap tapering inwardly toward a distal end and it has a circular bore extending through the nozzle for flow of the pressurized gas from the source toward the distal end. The source of pressurized gas is communicated through the circular bore and outwardly from the distal end to supply a primary gas flow. The primary gas flow also entrains heated air adjacent the frustoconical surface of the nozzle to induce a secondary gas flow. The gas jet pump is oriented such that the combined flow of heated gas therefrom is directed toward the conveyor to provide forced convection heating of conveyed glass sheets.

A hot glass sheet processing apparatus of the invention utilizes a source of pressurized gas that is located externally of the heating chamber. This pres¬ surized gas is supplied in the range of between 5 and 35 psi.

In a preferred embodiment of the invention, the hot glass sheet processing apparatus includes a shaping station including a forming mold mounted above the roller conveyor onto which the heated glass sheet is lifted, by the application of the primary gas flow from below the glass sheet. This action imparts a shape in the glass sheet as the glass sheet takes the shape of the forming mold. During the lifting, the secondary gas flow induced by the frustoconical shape of the nozzle reduces the isotropic effect of the primary gas flow.

In the preferred embodiment of the gas jet pump, the circular bore has a diameter generally in the range of between 1/8" to 1/4". Also, the nozzle has a length of at least as long as ten diameters of the bore. A chamfered recess at an inlet end of the gas jet pump and generally in the range of between 20 to 35 degrees with respect to the circular bore effects a non-tur¬ bulent flow transition from the source into the bore.

Best results are achieved with an array of the gas jet pumps spaced from each other transversely to the direction of conveyance so as to uniformly heat each conveyed glass sheet over its entire width. Both upper and lower arrays of the gas jet pumps are provided in the furnace embodiments disclosed. The upper array of gas jet pumps is located above the roller conveyor to provide forced convection heating of top surfaces of conveyed glass sheets by downward gas flow.

The lower array of nozzles is located below the conveyor to provide lifting of conveyed glass sheets by upward gas flow. Each array is disclosed as includ¬ ing a conduit support that mounts the gas jet pumps thereof above or below the conveyor within the heating chamber and also supplies the compressed gas to the jet pumps from the external source located outside of the heating chamber. An adjuster of each conduit support is provided to permit vertical adjustment thereof and appropriate positioning of the array of gas jet pumps mounted thereby with respect to the conveyor.

Preferably, the furnace includes a plurality of the gas jet pumps spaced transversely and longitudi¬ nally to the direction of conveyance within the heating chamber. This array of the gas jet pumps is provided below the conveyor to provide lifting of the conveyed glass sheets upwardly off the conveyor and onto a forming mold mounted above the roller conveyor to impart a shape in the glass sheet. Herein, as the primary gas flow lifts the glass sheet upwardly, the bottom surface of the glass sheet is being heated by forced convection and the radiant heating of the conveyor rolls. The gas jet pumps facilitate stretching of the bottom surface of the glass sheet during bending on a shaping surface having a convex shape. The secondary gas flow, induced by the combination of primary gas flow and frustoconical shape of the nozzle, reduces the isotropic effect of the primary gas flow.

The objects, features and advantages of the present invention are readily apparent from the follow¬ ing detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a schematic side elevational view of a glass sheet processing system including a horizon¬ tal roller conveyor furnace and bending station incorpo- rating the variable pressure gas jet system for lifting and forming glass sheets in accordance with the present invention;

FIGURE 2 is a schematic view of the variable pressure gas jet system;

FIGURE 3 is a schematic side elevational view of the bending section of the glass sheet processing system of Figure 1; FIGURE 4 is a perspective view of the array of gas jet nozzles utilized with the lifting arrangement of Figure 1;

FIGURES 5 and 6 illustrate the gas jet nozzles utilized in the preferred embodiment of the present invention;

FIGURE 7 is a chart illustrating typical time- pressure profiles utilized in forming a glass sheet in accordance with the present invention; and

FIGURE 8 is a schematic view of a prior gas jet system.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to Figure 1 of the drawings, the variable pressure gas jet system of the present inven- tion is preferably incorporated in a glass sheet bending furnace generally indicated by 10. Apparatus 10 in¬ cludes a heating chamber 12 for providing a heated ambient for heating glass sheets. A conveyor 16 in¬ cludes horizontally extending rolls 18 for conveying glass sheets G through the heating chamber 12 for heating to a desired temperature for processing at a press bending station 14. The conveyor 16 is preferably of the type including rolls 18 that are frictionally driven.

The press bending station 14 includes an upper mold 20 located above the conveyor 16 and having a downwardly facing curved shape that is defined by a curved surface 22 as illustrated in Figure 4. The -10-

furnace 10 also preferably includes a lower mold (not shown) that has an upwardly facing curved shape, which lower mold is mounted for horizontal movement by an actuator into position below the upper mold 20 for bending the glass sheet G between the upper mold 20 and the lower mold. The furnace 10 also preferably includes a transfer mold (not shown) having a curved shape corresponding to the curved shape of the bent glass sheet, positionable between the raised upper mold 20 and the conveyor 16 for receiving the bent glass sheet and transporting it to a subsequent processing station, such as a quench.

Referring to Figure 2, the variable pressure gas jet system of the present invention, generally referred to as 30, includes a control 32 for providing electrical signals corresponding to preselected desired gas pressures to the system, an electrical-to-pressure converter 34 connected to the output of the control for receiving the electrical signal from the control and generating a gas pressure corresponding to that electri¬ cal signal, a remotely controlled gas pressure regulator 36 including an input for receiving the pressurized gas transmitted from the converter 34 and an output for transmitting pressurized gas which varies as a function of the gas pressure sensed from the converter 34 through the conduits 38 of the system to a plurality of gas jets or nozzles 42, best seen in Figure 5, in the bending station 14 of the furnace 10.

The system 30 of the present invention also preferably includes a heat exchanger 46 typically in the form of a length of pipe located in the furnace 12 of a sufficient length to allow for heating of the pressur- ized gas to a desired temperature prior to impingeme by the gas on the^* glass sheet at the bending station 14 The system 30 of the present invention also preferabl includes a hot valve 40 positioned downstream from t heat exchanger 46 and relatively closer to the gas jet 42 in the bending station 14, which hot valve 40 i controlled via an on/off signal from the control 32 t quickly release the pressurized gas to the gas jets 4 during the glass sheet bending process. A source 44 o pressurized gas is located externally of the heatin chamber 12 and communicates with the converter 34 an the remotely operated regulator 36.

In the preferred embodiment, the control for the system 30 is a computer including a microproces sor and memory sufficient to store a series of variable corresponding to preselected pressures, process times and events germane to the glass bending process. Th microprocessor is preferably Motorola Model No. 6809. The microprocessor and remaining hardware required fo the computer control of the preferred embodiment i preferably a suitably programed MIKUL 6809-4 monocar microcomputer, manufactured by TL Industries, Inc. Norwood, Ohio. The MIKUL 6809-4 has a Motorola 680 microprocessor, serial RS-232-C port, four parallel I/ ports, a real time clock, up to 4K bytes of static RAM up to 32K bytes of EPROM as well as the digital-to analog (D/A) convertor.

The microprocessor is preferably suitabl programmed to monitor various selected conditions in th glass bending process, and generates signals in respons to monitored conditions which vary the gas pressur transmitted to the gas jets 42 according to preselecte pressure- values at preselected times during glass sheet bending and transport from the bending station 14.

The electrical-to-pressure converter 34 is preferably capable of generating a low flow pneumatic pressure varying from 0 to 100 psi in response to a 0- 10 volt signal received by the converter at its first input 45. One type of electrical-to-pressure converter which may be used is manufactured by the Norgren Company of Littleton, Colorado. The remotely controlled regula- tor 36 is preferably manufactured by Norgren. The regulator 36 is connected at its inlet port to receive the gas pressure output from the converter 34. Upon sensing the 0-100 psi pressure at its inlet port, the regulator 36 generates a corresponding pressure at greatly amplified flow rate through its output to supply the gas jets 42.

In the preferred embodiment, for example, the electrical-to-pressure converter 34 may transmit gas at 50 psi at a mass flow rate of .1 standard cubic feet per minute (SCFM) , while the remotely operated regulator 36 will, as a result, generate gas at a pressure of 50 psi and flow rate of over 100 SCFM. For greater accuracy, it is preferable that the regulator 36 be of the type having a feedback line, also available from Norgren.

In the preferred embodiment, the pressurized gas is transported through one and one-half inch diame¬ ter furnace.conduit 38.

Referring to Figures 3 and 4, the gas jets 42 preferably include an array of gas jet nozzles 24. The nozzles 24 are arranged to define a shape corresponding to a portion of the shape of the heated glass sheet. I this arrangement, one array 104 is mounted so that th distal end of the nozzles 24 are mounted generally i the range of 3-5 inches below the plane of conveyance of glass sheets G on horizontally extending rolls 18. Preferably, the nozzles 24 are horizontally spaced on a radius generally in the range of between 1 and 3 inches from each other. Most preferably, the nozzles 24 ar spaced on a radius of generally 2 inches.

Referring to Figures 5 and 6, each nozzle 24 is of a generally frustoconical shape tapering inwardly toward a distal end and having a circular bore extending through the nozzle for flow of the pressurized gas from the source toward the distal end and outwardly from the distal end to supply a primary gas flow. The primar gas flow entrains heated air adjacent the frustoconical surface of the nozzle 24 to induce a secondary gas flow. Preferably, the nozzle 24 has a length at least as long as 10 diameters of its circular bore. Preferably, circular bore 26 has a diameter generally in the range of between 1/8 inch to 1/4 inch. Most preferably, bore 26 has a diameter of 3/16 of an inch. A chamfere recess 28 at an inlet end 29 of each nozzle 24 is generally in the range of between 20-35 degrees wit respect to the circular bore 26 to affect a non-turbu lent flow transition of the pressurized gas from th source 27 into the bore. This chamfered recess 28 is most preferably 27 degrees.

Depending on the particular shape desired, plurality of arrays are employed to provide lifting an forming gas pressure upon the lower surface of the glass sheet G during the bending process. Referring again t Figure 4, arrays 104 and 106 are designed to supply lifting and forming pressure to the upstream and down¬ stream wing portions of the glass, respectively. Array 108 is designed to provide gas pressure generally in the center of the glass sheet, and array 110 has been configured to provide additional nozzles for pressure needed during the pick-up of the glass sheet from the conveyor. Additional arrays (not shown) may be provided at critical locations for particular surfaces, such as where inverse contours must be formed in a complex shaped part such as, for example, at the location designated at dashed lines 112.

Referring to Figure 7, the computer control 32 is preferably programmed to provide a unique profile of varying gas pressure to each array of gas jet nozzles 104-110. A set of variables corresponding to process time intervals and pressure levels may be preset by the system operator for each array of gas jet nozzles 104- 110 at the initial set-up of the furnace 10. Forming mold 102 mounted above roller conveyor 20 receives the heated glass sheet that is lifted by the application of the primary gas flow of the array 104 of gas jet pumps 42 located beneath the roller conveyor. Herein, the secondary gas flow induced by the frustoconical shape of the nozzle 24 reduces the isotropic effect of the primary gas flow on the glass sheet.

In Figure 7, glass sheet has been lifted up onto forming mold 102 by the application of the primary gas flow. The secondary gas flow induced by the frusto- conical shape of nozzles 24 reduces the isotropic effect of the primary gas flow. Thus, when this type of nozzle 24 is used within a furnace wherein the secondary gas flow is gas heated by radiant electric heating o another type of -heater within the furnace, no preheatin of the compressed gas that supplies the primary gas i necessary other than that which takes place during flo through the conduits that feed the nozzles.

In the preferred embodiment, each of th preselected time intervals is calculated from an even in the glass sheet bending process that is also sense by the computer. For example. El corresponds to th time at which the remotely controlled pressure regulato 36 is open to induce pressure in the supply lines 38. This event is controlled by the computer 32 through it signal to the electrical-to-pressure converter 34, an may be initiated upon receipt by the computer of posi tion information indicating that the heated glass shee has reached a preselected position in advance of th bending station 14. Similarly, E2 represents the star of the vacuum on the upper mold 22, E3 represents th opening of the hot valve 40, E4 corresponds to when th lower mold (not shown) starts moving into positio underneath the upper mold 22, and E5 represents when th lower mold and upper mold are vertically actuated t press the glass sheet G therebetween. E6 is the time a which the hot valve 40 is turned off, again by a signa from the computer 32, and E7 represents when the mold 2 begins to drop the glass sheet to the transport rin upon completion of the press bending of the glass sheet.

The preprogrammed time-pressure sequence i preferably initiated for each of the gas jet nozzl arrays 104-110 when a position sensor (not shown) signals to the computer that a glass sheet has move into position in the bending station 14 on the conveyo 20, represented by event E2 in Figure 7. It should be noted that prior to the time when the glass sheet has reached the position on the conveyor 20 at which the bending process is to commence, the computer 32 has signalled the system to charge the lines in the heat exchanger with a nominal (5 psi) pressure, noted by the positive pressure levels indicated on each of the time- pressure lines between events El and E2.

Referring first to the time-pressure line for the pick-up jet array 110, a Pick-up Jets Soft Lift Pressure (LPS) of 40 psi is generated for a Soft Lift Time (SLT) of one second. The Pick-up Jet Full Up Pressure (LPF) of 40 psi is then generated until the lapse of Pick-up Jet On Time (PJT) which is set for an interval of eight seconds from the point in time when the lower mold starts to press (E5) . The hot valve 40 is then shut-off upon the lapse of a Hot Jet Turn Off Delay (HJD) time of 1.5 seconds.

Referring to the time-pressure line for the center jets 108, Center Jets Soft Lift Pressure (LCS) of

34 psi is generated for a Soft Lift Time for Pick-up

(SLT) interval of one second. The Center Jets Full Up

Pressure (LCF) of 49 psi is then generated until lapse of the Center Jet Reduction Time (CJRT) interval of two seconds, which is measured from the time at which the lower mold begins moving into position under the upper mold, at E4. After lapse of a Cross Bend Reduction Jet

Delay (CBD) of .1 second, a Center Jet's Cross Bend

Abatement Pressure (LCC) of 17 psi is generated for a Cross Bend Reduction Jet On Time (CBT) of four seconds. This pressure abates any sagging of the bent glass sheet as it is deposited on the transport ring for transport to the next station.

Referring to the time-pressure line for the upstream wing jet nozzle array 106, an Upstream Jets Soft Lift Pressure (LUS) of 28 psi is generated for an Upstream Soft Lift Time (USLT) of six seconds. The Upstream Jets Full Up Pressure (LUF) of 38 psi is then generated until lapse of the Upstream Wing Jet On Time (UJT) , which is six seconds from the time at which the lower mold begins to press, E5.

Referring now to the time-pressure line for the downstream wing jet nozzle array 104, a Downstream

Jet's Soft Lift Pressure (IDS) of 23 psi is generated during the Downstream Soft Lift Time (DSLT) of six seconds. A Downstream Jet's Full Up Pressure (LDF) of

36 psi is then generated until lapse of the Downstream Wing Jet On Time (DJT) which is six seconds from the time at which the lower mold starts to press, E5.

Referring now to the time-pressure line for a set of inverse bend ,^e_s, which are not shown, but which may, for example, be located below the site of an inverse bend in the glass sheet's surface, such as the area generally indicated by the dashed lines 112 in Figure 4. An Inverse Jet Soft Lift Pressure (LIS) of

37 psi is generated for a Soft Lift Time For Pick-up (SLT) of one second, after which an Inverse Jet Full Up Pressure (LIF) of 37 psi is generated. It should be noted that while the particular example illustrates identical Inverse Jets Soft Lift Pressure (LIS) and Inverse Jet Full Up Pressure (LIF) , one or both of these pressure variables may be programmed to different values depending upon the shape of the part. The Inverse Jet Full Up Pressure continues until lapse of the Center Jet Reduction Time (CJRT) , set at two seconds from the point in time when the lower mold begins to move into position underneath the upper mold, E4. After a Cross Bend Reduction Jet Delay (CBD) of .1 second (beginning from the time at which the upper mold 22 starts to drop the bent glass sheet, E7) , an Inverse Jet's Cross Bend Abatement Pressure (LIC) may be generated for a Cross Bend Reduction Jet On Time (CBT) of a preset duration.

It will be appreciated by those skilled in the art that various different preselected pressure values may be desirable for corresponding preselected time intervals depending on the particular part configura¬ tion and the bending process.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for carrying out the invention as described by the following claims.

Claims

WHAT IS CLAIMED IS;

1. In a glass sheet press bending syste including a furnace having a heating chamber for heatin glass sheets, a conveyor for conveying the glass sheet in generally horizontally extending orientation, and a upper forming mold located above the conveyor and havin a downwardly facing curved surface, a variable pressur gas jet system for lifting the glass sheet upwardly b the impingement of gas flow from the conveyor to th forming mold, the system comprising: control means including a first output fo providing an electrical signal corresponding to preselected pressure; a converter including a first input connecte to the first output of the control means for receivin the electrical signal from the control means, a secon input connected to a source of pressurized gas and second output for providing pressurized gas at a pres sure which varies as a function of the value of th electrical signal received in the first input; a gas flow regulator including a first inpu connected to the converter for receiving the pressur ized gas transmitted from the second output, a secon input connected to a source of pressurized gas, and first output for providing pressurized gas at a pres sure which varies as a function of the value of th pressurized gas received at the first input; and gas jet means connected to the gas flo regulator for directing the pressurized gas from th output of the gas flow regulator to the lower surface o the glass sheet. -20-

2. The variable pressure gas jet system of claim 1 wherein the control means includes a computer having memory for storing data corresponding to a preselected profile of varying pressures; and logic means for monitoring selected operating conditions in the glass sheet press bending system, and upon the occurrence of such selected conditions, calcu¬ lating the desired pressure according to the preselected profile, generating a control signal corresponding to that pressure, and transmitting the control signal to the first output of the control means.

3. The variable pressure gas jet system of claim 2 wherein the data corresponding to the prese¬ lected profile of varying pressures includes a plurality of pressure variables and a plurality of time variables, each time variable corresponding to one of the pressure variables, and wherein each time variable defining an interval of time during which the corresponding pressure is desired.

4. The variable pressure gas jet system of claim 2 wherein the glass sheet bending system includes an open center ring for conveying the glass sheet from the upper mold and wherein the preselected profile includes a profile of varying pressures suitable for supporting the formed glass sheet on an open center transfer ring to abate the effects of gravity which otherwise cause the formed glass sheet to sag from its desired shape during transport on the open center ring.

5. The variable pressure gas jet system of claim 1 further including a heat exchanger located in the furnace downstream of the gas flow regulator.

6. The variable pressure gas jet system of claim 7 wherein the control means further includes a second output for providing an electrical signal and further includes a hot valve positioned downstream from the heat exchanger and upstream from the gas jets, which hot valve includes a first input connected to the second output of the control means for receiving the electrical signal from the control means to activate the valve to quickly release the pressurized gas to the gas jets during the glass sheet bending process.

7. The variable pressure gas jet system of claim 1 wherein the gas jet means include an array of gas jet nozzles.

8. The variable pressure gas jet system of claim 1 or claim 7 wherein said gas jet means is defined by a gas jet pump for impinging the heated glass sheet on said conveyor with a gas flow; a source of pressur¬ ized gas communicated with the gas jet pump; and said gas jet pump being a nozzle of a frustoconical shape tapering inwardly toward a distal end and having a circular bore extending through the nozzle for flow of the pressurized gas from the source toward the distal end and outwardly from the distal end to supply a primary gas flow; the primary gas flow also entraining heated air adjacent the frustoconical surface of the nozzle to induce a secondary gas flow.

9. The variable pressure gas jet system of claim 8 including an array of the gas jet pumps spaced from each other transversely and longitudinally to the direction of conveyance.

10. The variable pressure gas jet system of claim 9 wherein the array of gas jet pumps is located below said conveyor to lift the heated glass sheet onto a forming mold by the application of the primary gas flow, the secondary gas flow reducing the isotropic effect of the primary gas flow.