Abstract:
The invention relates to a method and apparatus for supporting the middle section of a glass panel to be bent in a mold. During a preheating process of a glass panel, its middle section is supported by middle support elements carried along with a mold carriage. At the start of a bending process, the middle support is released by pushing bearing rods through the bottom of the mold carriage. The middle support for the glass panel is lowered upon the bearing rods gradually under the control of glass panel thermometry. A controlled hoisting and lowering of the bearing rods is performed by a hoisting and lowering mechanism present in a carriage elevator. The invention makes it possible to implement a middle support also in an automatically operating serial furnace.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for supporting the middle section of a glass panel to be bent in a mould, in which method the middle section of a glass panel placed on a mould is supported during loading and a preheating process and the support is released at the start of a bending process for allowing the glass panel to deflect so as to be supported by the mould over its middle section as well. 
     The invention relates also to an apparatus for supporting the middle section of a glass panel to be bent in a mould, said apparatus comprising support elements for the middle section of a glass panel, which are secured to a mould or a mould carriage, as well as elements for releasing the middle support at the start of a bending process. 
     BACKGROUND OF THE INVENTION 
     A problem encountered in the process of bending large glasses, such as windshields for buses or trucks, is that the unsupported span or bearing distance for the middle section of a glass placed on a mould becomes excessively long, whereby the glass may break up upon bending under its own weight during a loading process in a cold condition or in a preheating process prior to reaching a bending temperature. It is prior known to provide a mould with various middle support systems for avoiding the break-up of a glass. However, the prior known middle support systems are such that the implementation thereof is impossible in an automated serial furnace. 
     It is an object of the invention to provide a method and apparatus for supporting the middle section of a glass panel to be bent in a mould in such a way that the middle support can be implemented also in an automated serial furnace. 
     A second object of the invention is to provide a method and apparatus, whereby the middle support can be controllably lowered during a bending process. 
     A third object of the invention is to provide a method and apparatus, whereby the two foregoing objects can be accomplished without having to construct the carriages and moulds with complicated actuators, which are replaced with an actuator common to all moulds and set up in a bending station. 
     These objects are achieved by means of a method of the invention. 
     These objects are also achieved by means of an apparatus of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The invention will now be described in more detail by way of an exemplary embodiment with reference to the accompanying drawings, in which 
     FIG. 1 shows an apparatus of the invention in a section taken along a line I—I in FIG. 2, i.e. with the apparatus in a standby condition at the start of a bending process; 
     FIG. 2 shows in a schematic side view an automated serial furnace for use in a bending process for glass panels and for applying a method and apparatus of the invention; 
     FIG. 3 shows a middle support apparatus of the invention in a more detailed design consistent with a section taken along a line III—III in FIG. 4; and 
     FIG. 4 shows the apparatus of FIG. 3 as seen from a direction IV (consistent with the viewing direction of FIG.  1 ). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The serial furnace shown in FIG. 2 comprises a number of sequential preheating stations  1   a  and therebelow a number of sequential cooling stations  2 . Moulds, along with glass panels to be bent, are placed in mould carriages  5 , which are closed e.g. in the bottom and sides but open in the top, such that the glass panels can be heated by means of heating resistances (not shown) mounted on the ceiling of the preheating stations  1   a  and an actual bending station  1   h.  The mould carriage  5  may vary in many ways regarding its design. The carriage may be e.g. one with an open bottom, whereby the heat possessed by glass panels presently cooling on the lower track of a serial furnace can be exploited for heating glass panels present on the upper track. The mould carriage  5  is only depicted in the bending station  1   h  but, as the furnace is in operation, the successive mould carriages  5  are advanced intermittently in the circulation direction indicated by arrows both on an upper track  3  and a lower track  4 . 
     As shown in more detail in FIG. 1, alongside the mould carriage  5  are carriage rails  5   r,  upon which the carriages travel on top of rollers present in the tracks  3  and  4 . The bending station  1   h  is provided with a carriage elevator  7 , having its wheel system  7   r  constitute extensions for the tracks  3  and  4  as the elevator  7  is in its top or bottom position, respectively. The elevator  7  is hoisted and lowered e.g. by means of upright helical shafts  8  rotatable by a motor  10  through the intermediary of herringbone gears  9 . The structural design and maneuvering mechanism of the elevator  7  are of secondary significance as far as the invention is concerned and can be implemented in a variety of ways. 
     FIG. 1 illustrates a mould  6  present in the mould carriage  5 , comprising a circular mould ring  6   m,  which constitutes an actual form face and includes end sections pivotable by means of hinges  6   a.  Through the action of weights  6   w  the end sections are pivotable to the position shown by dash-and-dot lines as soon as the glass panel becomes sufficiently heated and softened to enable its gravitational bending to a contour determined by the mould ring. There is such a long distance between the articulations  6   a  that a glass panel G could break up at its middle section without a middle support. 
     Middle support elements  11 - 19 , movable along with the mould carriage and in this case secured to the mould  6 , are depicted more closely in FIGS. 3 and 4. These support elements include horizontal bearing pads  11 , located adjacent to the long edges of a glass panel G and mounted on the ends of vertical rods  12 . The vertical rods  12  are connected to the ends of horizontal frame tubes  13 . The frame tubes  13  are telescopically insertable within an intermediate frame tube  14 , whereby the distance between the bearing pads  11  is adjustable to match various widths of the glass panel G. The frame tube  14  is provided on its bottom side with lugs  15 , which have downward open slots for taking up axles  17  present at the top ends of braces  16 . The braces  16  are provided at the bottom ends thereof with axles  19 , which are taken up in lugs  18  secured to a bottom mould framework  5   b.  The braces  16  retain the supporting position thereof as a result of the weight of the frame element  13 ,  14 , but are released from the supporting position thereof upon slightly raising the frame element  13 ,  14 , whereby the braces  16  swivel by themselves gravitationally to a substantially horizontal position. 
     In order to release the braces  16  and take up a middle support, there are bearing rods  21  adapted to be driven through apertures present in the mould carriage bottom  5   b.  In view of driving the bearing rods  21 , the carriage elevator  7  shown in FIG. 1 is accompanied by a hoisting and lowering mechanism  27 , from which rise lifting bars  23  which coincide with the axial line of the bearing rods  21  as the mould carriage  5  is parked in the carriage elevator  7 . The frame tube  14  is fitted with crosswise response elements  22 , which are contacted by the top ends of the bearing rods  21  as said bearing rods  21  are pushed to the top position thereof by means of the lifting bars  23 . The glass panel G can be bent slightly upwards in order to allow the braces  16  to fall and the middle support to be released upon the bearing rods  21  and the lifting bars  23 . If the invention is applied in a single furnace or a tunnel furnace, there is no need for the carriage elevator  7 . In this case, the hoisting and lowering mechanism  27  is set on the floor of a bending station in such a way that it remains underneath the bottom of a carriage arriving in the bending station. 
     When a given type of glass panel is bent for the first time, the controlled lowering of a middle support is carried out with manual control, such that a bending station window is used for monitoring the glass bending (e.g. swiveling of the end sections of mould  6 ), and a motor  25  for the hoisting and lowering mechanism  27  is controlled with manual input data M for a control unit  26 . During the bending process, the control unit  26  stores in its memory the glass temperature readings, which match various degrees of bending and are obtained from a pyrometer  28 . 
     Hereinafter, the controlled lowering of a middle support can be performed under the control of glass panel thermometry. Therefor, the pyrometer  28  (or some other measuring sensor, such as a thermoelement) keeps measuring the temperature of a glass panel, on the basis of which the control unit  26  drives the motor  25  for the hoisting and lowering mechanism  27 , which uses a transmission device  24  for bringing downward the middle support carried by the bars  23 . The engagement between transmission device  24  and bar  23  may be based on a screw spindle or a gear rack. 
     The invention does not necessarily require thermometrically controlled lowering of a middle support, as the invention is also capable of achieving its objectives by performing the controlled lowering of a middle support merely under manual control M. However, the thermometry-based control offers the benefit of relieving the operator of this control duty after teaching the apparatus how to perform the temperature dependent lowering. 
     The lifting bars has a diameter which is smaller than that of the bearing rods  21 , the lifting bars  23  being able to fit within bushings guiding the bearing rods  21  without exact tolerances. The bearing rods  21  are preferably heavy-duty solid metal shafts, hence descending under their own weight to a bottom position with a plate cap  21   a  resting against the mould carriage bottom  5   b  and plugging the bottom hole at the same time. In the illustrated case, the number of bearing rods  21  and, respectively, lifting bars  23  is four each, but the apparatus functions faultlessly also with two rods and bars (thus, the pair of rods  21  and bars  23  shown in FIG. 4 is replaced with just a single rod  21  and a single bar  23 ). 
     After the cooled glass is demoulded, the middle support can be reset in a working position by lifting the frame  13 ,  14  manually up to being supported by the braces  16 . Adjustable brackets  20  take up the braces  16  in a correct angular position for readily guiding the same into the slots of the lugs  15 . In addition, the brackets  20  support the braces  16  and hence the entire bearing mechanism in a lateral direction. 
     A particular advantage offered by the middle support of the invention is that those components carried along with the moulds  6  and the mould carriages  5 , a plurality of which are needed for each furnace, are simple, lightweight, and attractive in price, while the hoisting and lowering mechanism  27  serving the automated operation of the apparatus is arranged in a bending station, in the case of a serial furnace in conjunction with the carriage elevator  7 , whereby just a single hoisting and lowering mechanism  27  per furnace is required. In the case of a single or tunnel furnace, when there is no carriage elevator, the floor of a bending station can be provided with a suitable recess or well for receiving the hoisting and lowering mechanism  27 . The mechanism  27  has its hoisting action limited to lifting only the bearing rods  21  and to releasing the middle support from its clamping. Other than that, its function is a controlled lowering of the middle support.