GB2046240A

GB2046240A - Bending flat glass sheets

Info

Publication number: GB2046240A
Application number: GB8005803A
Authority: GB
Original assignee: BFG Glassgroup GIE
Current assignee: BFG Glassgroup GIE
Priority date: 1979-03-08
Filing date: 1980-02-20
Publication date: 1980-11-12
Also published as: BE882023A; FR2450787A1; IT1130308B; DE2908998B1; FR2450787B1; GB2046240B; IT8020381A0; DE2908998C2

Abstract

Dies (6, 7) are kept closed together between bending operations performed on a time-spaced succession of glass sheets, and are preferably opened to the minimum extent necessary to permit entry and removal of the sheets, detected by sensors 13, 14. The thus-conserved heat permits the bent sheets to be subsequently pre-stressed without re-heating the glass. <IMAGE>

Description

SPECIFICATION A process and equipment for bending flat glass sheets This invention refers to a process and equipment for bending flat glass sheets to form sheet glass blanks (with single or double curvature) which are subsequently transferred to a pre-stressing installation, in which the glass sheets, heated to bending temperature, are individually fed at time-intervals dt, into an opened bending press with a lower and an upper die, are pressed for the duration of a press-time dt2 which is short in relation to the time-interval dt1, and the sheet glass blanks are subsequently removed from the re-opened bending press and immediately afterwards are transferred to the pre-stressing installation.

The time-interval dt, results from the preceding preparation of the glass sheet and determines the interval which the glass sheets to be bent follow one another. The invention also relates to a bending press to carry out such a process.

Press bending of sheets of glass that are lying down, suspended, or standing up, are within the scope of the invention. Usually the lower and the upper dies of the press are unheated, and it is within the scope of the invention to work with a heated lower die and/or a heated upper die. It suffices that one of these tools should be a so-called "complete tool". A "complete lower die" or "complete upper die" signifies that these are not merely outer frame devices or roll devices but on the contrary have complete tool surfaces facing the glass sheet. "Unheated" means that heating equipments are not made part of the lower or the upper die. Both heated and unheated tools experience heating-up during bending in the press. The expression "time interval" specifies, as already mentioned, the differences in time at which the glass sheets that are to be bent follow one another.To avoid misunderstandings it should be mentioned that in the press-bending and prestressing of sheets of glass reference is made to a "working cycle time" or a "cycle time".

This in fact corresponds to the time which elapses from the sheet of glass leaving the pre-heating furnace until it leaves the prestressing installation. This time comprises transport from the door of the furnace to the empty bending press, the closing, dwell and opening of the bending press, transport to the air-blast installation, blasting, and the commencement of removal. The latter begins at exactly the same moment as the transport of the next heated glass sheet from the preheating furnace. In principle the sheet of glass could be removed earlier from the air-blast installation without any gear of affecting the degree of pre-stressing.

In processes known in practice, the bending press in respect of its opening and closing operates with a press-time dt2 and thereby with a press-cycle time which is short in relation to the time-interval dt,. When, after a bending process, a sheet glass blank has left the bending press, the latter remains open until a further sheet of glass is introduced for bending. Consequently when time is averaged statistically, the bending press is found to be open for most of the time and this is detrimental. According to the known manner of working, the sheet glass to be bent, which has been heated to bending temperature, imparts heat to the lower die and/or the upper die, and accordingly are already known to be cosntructed to be heat-insulating.If the known process is carried out over a lengthy period, then after an initial warming-up time a temperature balance is established in the lower and upper die. However when the temperature balance has been attained the temperature of the lower die and/or the upper die is, as a rule, considerably lower than the bending temperature at which the glass sheets are introduced into the bending press. This particularly applies if the tools in question are unheated. In fact the lower and/or upper die radiates a considerable amount of heat to the surroundings on account of the long opening periods which are determined by the timeinterval dt,.As a result, the temperature, at least that of the surface layers, at which the sheet glass blanks leave the press in accordance with the known process is below the bending temperature at which the glass sheets have been fed in, and is normally below the temperature required at the pre-stressing installation. If the sheet glass blanks are relatively thick this effect is not troublesome, as it is only the surface layers that are cooled, and the sheet glass blanks themselves form a reservoir of heat that restores the sheet glass blank as a whole to the temperature that the prestressing installation requires.If however the glass sheets and sheet glass blanks are relatively thin, e.g., only 3mm thick, then when treated according to the known process the sheet glass blank cools in the bending press throughout its body to such an extent that the temperature in the pre-stressing installation is no longer adequate for the quality improvement process. The result of this is that before introducing the sheet glass blanks into the pre-stressing installation a further heating has to be carried out. Of course if working with heated tools one could also consider heating the lower die and upper die to a higher temperature and more intensively, but this is not feasible as the bending temperature is determined by the properties of the materials.

The primary object of the present invention is to provide a bending process in which sheet glass blanks that are introduced into the bending press at bending temperatures still pos sess an adequate temperature when they enter the pre-stressing installation, even when dealing with press-bending of thin glass sheets and consequently with thin sheet glass blanks According to the present invention, a process for bending flat glass sheets in a press to form sheet glass blanks with single or double curvature, which are subsequently transferred to a pre-stressing installation comprises heating the glass sheets to bending temperature, the sheets being fed individually at timeintervals dt, into an opened bending press with a lower and an upper die, and pressed for the duration of a press-time dt2 which is short in relation to the time-interval dt1, removing the sheet glass blanks from the reopened bending press and subsequently transferring them to the pre-stressing installation, the press, immediately after the removal of each sheet glass blank being re-closed and only re-opened immediately before the introduction of a further glass sheet for bending Preferably the bending press is opened for the introduction of a glass sheet to be bent, and for the removal of a sheet glass blank, only to the extent of the contour of the sheet glass blank, so that the opening gap is as small as possible.

In comparison with the known method, the number of opening and closing movements of the bending press is doubled according to the process of the invention, such that when carrying out the process the bending press is no longer normally open, and closed during the pressing period, but instead it is normally closed, and only opened to introduce a glass sheet and to remove a sheet glass blank. This allows a temperature equalization of the dies with a tool temperature that is considerably higher than that which develops according to the known method, and which is sufficiently high for the sheet glass blanks to beidirectly introduceable into the pre-stressing installation for quality improvement. The reduction of the extent of the opening movement of the press to that of the contour of the sheet glass blank further reduces the heat loss.It is also a basic problem of the invention to provide a bending press which is particularly suitable for carrying out the above defined process according to the invention According to a further aspect of the invent tion, a bending press comprises a press frame, pressure plates, lower die and upper die attached to the pressure plates, of which at least one is constructed as a complete tool, and driving and control equipment for the pressure plates, which control equipment for the pressure plates, which control equipment operates the closing and opening of the pressure plates in accordance with the press-time dt2, the driving and control equipment being constructed as short press-cycle equipment whose closing time dts and opening time dto is short in comparison with the time-interval dt1, and the control equipment having an additional control impulse transmitter which produces a closing movement of the bending press whenever a sheet glass blank is removed, and produces an opening movement whenever a further glass sheet arrives to be introduced.

Thus, the simple bending press becomes, according to the invention, a double-cycle press with a closed, unloaded, period dt, for the purpose of temperature stabilization. dts represents the time for the closing movement and dto represents that for the opening movement. It is obvious that within the scope of the invention the lower die and the upper die can with advantage be made heat-insulating, or if required can be made heat-insulating with the exception of the bending surfaces, whilst in addition heating means can be arranged surrounding the lower and/or the upper die. Preferably the additional control impulse transmitter is equipped with sensors located behind or in front of the bending press, which respond to the motion of a sheet glass blank being removed, or to the motion of a glass sheet being introduced.These can be contact sensors or contact-less sensors. In large installations with very precisely-controlled time-intervals dt1, the bending press can be controlled according to a fixed programme. The motions of the bending press described can be very easily performed by the resources of modern driving and control technique for bending presses and hence do not need to be dealt with in detail. It is obvious that to obtain as high a temperature as possible in the sheet glass blanks entering the prestressing installation, further means which in themselves are known can be additionally applied, namely shielding of the intermediate path between the furnace for heating the glass sheets to be bent and the press, or between the press and the quality-improvement installation, for which reflective surfaces and/or heated surfaces can be used. It is also possible to insulate the backs of the pressure surfaces of the lower and the upper die and to increase the resistance to heat flow of all connections leading away from the pressure surfaces. As energy losses are avoided according to the invention and steps are taken to prevent an opened bending press from radiat ins heat to the surroundings in detrimental manner, the process described is also advantageous if the lower and upper dies are equipped with heating devices.

One embodiment of the invention will now be described with reference to the accompanying schematic drawings, in which: Figure 1 is a bending press for carrying out the process according to the invention in plan view and in the opened position; and Figure 2 is a time-diagram of the operation of the bending press of Fig. 1 in accordance with the process of the invention.

A bending press 1 represented in Fig. 1 consists of a press frame 2 with a front pressure plate 3 and a rear pressure plate 4.

Normal driving piston-cylinder devices 5 are associated with the movable pressure plates 3, 4. The tools are attached to the pressure plates 3, 4, the lower die 6 being attached to the rear pressure plate 4 and the upper die 7 to the front pressure plate 3. Control equipment 8, part of the driving device already described for pressure plates 3 and 4, controls the opening and closing of pressure plates 3 and 4 in accordance with the presstime dt2. The glass sheets that are to be bent are transported to the bending press 1 by a conveyor 9 (not shown in detail).

The time-diagram of Fig. 2 clearly shows that the driving and control equipment 8 is constructed as a short press-cycle equipment.

By this it will be understood that its closing time dts and opening time dto is short in comparison with the time-interval dt,. Closing time means the time for the closing movement, and opening time the time for the opening movement. The ordinates indicate the distance sthat the tools or pressure plates 3 and 4 traverse during opening and closing. In position I the bending press is open, in position lit is closed. The control equipment 8 has an additional control impulse transmitter 11. This brings about an additional closing movement whenever a sheet glass blank 1 2 is removed. The control impulse transmitter 11 also brings about an additional opening movement whenever a glass sheet 10 arrives to be introduced into bending press 1 for bending.

The additional control impulse transmitter 11 works with sensors 13, 14 located behind or in front of bending press 1, which respond to the approach of a glass sheet 10 or to the removal of a sheet glass blank 1 2 in such a way that the process described is brought about.

Fig. 2 will be understood from the above statements and from its captions. It shows that the bending press 1 is re-closed immediately after the removal of each sheet glass blank 1 2 and is only re-opened immediately before' the introduction of a further glass sheet 10 to be bent. It is thus closed in the empty condition for a relatively long interval dtL. The bending press 1 has been further developed into a double-cycle press with a closed but unloaded cycle for the purpose of increasing and stabilizing the temperatures of the lower die 6 and the upper die 7.

Claims

1. A process for bending flat glass sheets in a press to form sheet glass blanks with a single or double curvature, which are subsequently transferred to a pre-stressing installation comprising heating the glass sheets to bending temperature, the sheets being fed individually at time-intervals dt, into an opened bending press with a lower and an upper die, and pressed for the duration of a press-time dt2 which is short in relation to the time-interval dt1, removing the sheet glass blanks from the re-opened bending press and subsequently transferring them to the prestressing installation, the press, immediately after the removal of each sheet glass blank being re-closed and only re-opened immediately before the introduction of a further glass sheet for bending.

2. A process as in Claim 1, wherein the bending press is opened for the introduction of a glass sheet to be bent, and for the removal of a sheet glass blank, only to the extent of the contour of the sheet glass blank.

3. A bending press to carry out the process according to Claim 1 or Claim 2, comprising a press frame, pressure plates, lower die and upper die attached to the pressure plates, of which at least one is constructed as a complete tool, and driving and control equipment for the pressure plates, which control equipment operates the closing and opening of the pressure plates in accordance with the press-time dt2, the driving and control equipment being constructed as short press-cycle equipment whose closing time dts and opening time dto is short in comparison with the time-interval dt,, and the control equipment having an additional control impulse transmitter which produces a closing movement of the bending press whenever a sheet glass blank is removed, and produces an opening movement whenever a further glass sheet arrives to be introduced.

4. A bending press as in Claim 3, wherein the lower die and the upper die are made heat-insulating, or if required are made heatinsulating with the exception of the bending surfaces.

5. A bending press as in Claim 3, or Claim 4, wherein the upper and/or lower die is provided with heating means.

6. A bending press as in any of Claims 3 to 5, wherein the additional control impulse transmitter is equipped with sensors located behind or in front of the bending press, which respond to the motion of a sheet glass blank being removed, or to the motion of a glass sheet being introduced.

7. A process of bending flat glass sheets in a press substantially as hereinbefore described with reference to the accompanying drawing.

8. A bending press for carrying out the process of Claim 1, substantially as hereinbefore described with reference to the accompanying drawing.