Small diameter evacuation head for VIG unit manufacture Field

This disclosure relates to a vacuum insulating glazing (VIG) unit. In particular, it relates to the vacuum evacuation head (also known as all metal cup) . And sealing of the evacuation tube with a heater inside the evacuation head .

BACKGROUND Vacuum insulating glazing (VIG) units typically comprise two glass panes spaced by pillars, sealed at the periphery and having an evacuated interior void. The void is evacuated with an evacuation head through a hole in the pane to a pressure such as 1E-6 bar.

US2006175767 discloses a VIG unit and an evacuation head being 70mm. The disclosure deals with a gasket to ensure a good seal. Paragraph [0061] does mention an evacuation head diameter of 50 mm to 100 mm.

US20120148795 deals with the sealing of the evacuation hole. It discloses a prior art evacuation tube and evacuation head with a coil heater (fig 2a) which is used to melt the tube tip (also known as the tip off) .

DISCLOSURE OF THE INVENTION

For decades there has been ongoing work with VIG gazing due to the promising insulation value which enables great energy savings to buildings. Production of VIG units however still has several drawbacks and lifetime challenges. It would be desirable to provide a better contact seal between the evacuation head and the glass pane. Further it would be desirable to provide an enhanced evacuation tube seal by better temperature application and better tube tip off. Further it would be desirable to provide a tempered glass VIG.

The invention relates to method according to claim 1, a VIG manufacture facility according to claim 15 and a VIG unit according to claim 19. Favorable embodiments are defined in the dependent claims. Other objectives, features and advantages will appear from the following detailed disclosure. In particular, the invention relates to the below specific aspects and embodiments.

In a first aspect and embodiment there is disclosed a method of producing a vacuum insulated glazing (VIG) unit comprising: providing first and second substantially parallel panes 1,2, a plurality of pillars 4 and a peripheral seal 3 provided between the first and second panes 1,2, where in the first pane 1 there is provided an evacuation hole 5 for evacuating a void V through the evacuation hole 5 to a pressure less than atmospheric pressure; wherein the panes 1,2 are tempered glass; on a glass pane face la, covering the evacuation hole 5 with an evacuation head 8, the evacuation head 8 adapted to have a substantially hermetic contact to the glass pane face la; wherein the evacuation head 8 contact width D to the pane face la is less than 50mm, preferably less than 45mm; and evacuating the void V through the evacuation head 8.

In a second embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to the previous embodiment, wherein the evacuation head 8 is adapted to reduce the temperature difference in the VIG body beneath the evacuation head 8 from the temperature in the surrounding VIG body.

In a third embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the VIG unit is in an oven and the void V is evacuated in the oven.

In a fourth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the VIG body production in an oven includes heating the VIG unit in the oven and in all steps keeping the temperature below an annealing temperature, which detrimentally affects the tempered glass, such as keeping the temperature below 400°C.

In a fifth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the evacuating of the void V is done at 150°C or more, preferably at 300°C or more.

In a sixth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the temperature of the oven is between 150°C and 400°C, preferably between 300°C and 400°C.

In a seventh embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the evacuating of the void V is done in the heated oven after substantially soldering the peripheral seal 3.

In an eighth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the peripheral seal 3 is substantially soldered in the heated oven and subsequently the evacuating of the void V is initiated .

In a ninth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein an evacuation tube tip 6b is sealed off by heat provided by a heat element 9 in the evacuating head 8 chamber 10.

In a tenth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the evacuation head 8 is substantially circular and the contact width D is a diameter D.

In an eleventh embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the pillars 4 are spaced a distance S and wherein the evacuation head 8 contact width D is equal or less than pillar 4 distance S.

In a twelfth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the evacuation head 8 has a ceramic heating element 9, and the method comprises: heating the ceramic heating element 9 and sealing off the tip 6b of an evacuation tube 6.

In a thirteenth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, comprising: heating the ceramic heater 9 to a first temperature to provide a more uniform VIG body 1,2 temperature T2 beneath the evacuation head 8, and heating the ceramic heater to a second temperature to tip off the tube 6b.

In a fourteenth embodiment of the first embodiment of the first aspect there is disclosed a method of producing a VIG unit according to any previous embodiment, wherein the evacuation tube 6 is an evacuation cap 18 comprising an evacuation port 20 and a solder glass ring 19 arranged around the evacuation port 20.

In a first embodiment of a second aspect there is disclosed a vacuum insulated glazing (VIG) unit manufacture facility comprising an oven with a compartment adapted for heating a VIG unit 1,2, the oven comprising an evacuation head 8 in fluid communication with at least one vacuum pump, wherein the evacuation head 8 contact width D to the VIG is less than 50 mm, preferably less than 45 mm.

In a second embodiment of the second aspect there is disclosed a VIG unit manufacture facility according to the previous embodiment of the second aspect, the evacuation head 8 further comprising a ceramic heating element 9.

In a third embodiment of the second aspect there is disclosed a VIG unit manufacture facility according to any of the previous embodiments of the second aspect, wherein the ceramic heating element 9 is displaceable and configured to contact an evacuation tube tip 6b and preferably press the tube tip 6b to tip off the tube 6.

In a fourth embodiment of the second aspect there is disclosed a VIG unit manufacture facility according to any of the previous embodiments of the second aspect, configured to perform the method according to any of the first to fourteenth embodiments of the first aspect of the present invention.

In a first embodiment of a third aspect there is disclosed a vacuum insulated glazing (VIG) unit comprising tempered glass panes 1,2 comprising an evacuation cap 18 comprising an evacuation port 20 and a solder glass ring 19 arranged around the evacuation port 20, wherein the evacuation cap 18 is arranged on a face la of a first or second pane 1,2 and the evacuation cap 18 has a center distance substantially less than 25 mm from the pane 1,2 periphery, preferably less than 20 mm.

In a second embodiment of the third aspect there is disclosed a VIG unit according to the first embodiment of the third aspect, where the evacuation cap 18 is further situated at the corner of the pane face la, and the center distance hereby applies to both pane peripheries of said corner .

In a second embodiment of the third aspect there is disclosed a VIG unit according to either the first or second embodiment of the third aspect, comprising a peripheral seal 3 and evacuation cap 18 seal 7 wherein both seals 3,7 are adapted to be soldered at substantially the same temperature .

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a VIG unit.

Fig. 2 shows a VIG unit and an evacuation head.

Fig. 3 shows a close up example of the evacuation head. Fig. 4 shows another example of the evacuation head.

Fig. 5 shows temperature reading locations.

Fig. 6 shows chart of temperature differences and heating steps .

Fig. 7 shows a displaceable heater.

Fig. 8 illustrate the non-planar pane surface effects. Fig. 9 illustrate alternative closures.

Fig. 10 illustrate alternative closures.

Fig. 11 show the temperature difference between surrounding air Tl and evacuation head T2. DETAILED DESCRIPTION

Figure 1 shows a vacuum insulating glazing (VIG) unit with 2 glass panes 1,2. The VIG production method is done by providing a first and second substantially parallel panes 1,2, a plurality of pillars 4 and a peripheral seal 3. The periphery 3 is sealed for example by solder frit or solder glass or metal solder. The panes 1,2 are spaced by pillars 4 which withstand the pressure when the VIG is evacuated and the atmosphere acts on the VIG. The pane 1 has an evacuation hole 5 with an evacuation tube 6. The evacuation tube 6 has a seal 7 for example solder glass or frit paste or metal solder. A part 6a of the evacuation tube thereby remains enclosed in the evacuation hole 5 by the pane 1 and the seal 7, leaving an evacuation tube tip 6b exposed to the atmosphere.

Figure 2 shows a VIG now with an evacuation head 8 placed in contact with the exterior pane 1 face. In a manufacture facility there may be several VIG units and evacuation heads 8 in one oven. The VIG production method comprises heating the VIG in an oven to seal the periphery seal 3 and the tube seal 7. When the VIG cools in the oven the evacuating of the void V is started. Typically, at 150°C or more, preferably at 300°C or more. At 300°C or more the seals 3,7 are still deformable and can hereby better settle properly. The evacuating of the void V is performed in a heating oven after substantially soldering the seal 3. The evacuation head 8 covers the evacuation hole 5 and associated tube 6 and is adapted to evacuate the interior void V. After evacuation a heater 9 melts the evacuation tube tip 6b to seal the void V (known as the tip off step) . The method of producing a VIG unit may hereby be performed in an oven. The evacuation head 8 performs best with a substantially hermetic contact to the glass pane 1,2. This assumes the glass 1,2 panes are planar.

The evacuation head 8 has a contact to the pane 1,2 having a diameter D. In the state of the art the diameter D is 50-100 mm. In the state of the art a large contact area (between glass pane and the evacuation head) is desired so that the air molecules have difficulty passing i.e. longer travel to pass the hermetic contact area.

However, the evacuation of the VIG exposes the glass panes 1,2 to an atmospheric pressure pressing towards the void V (fig. 1, Pa) and this may warp the pane 1,2 surface as illustrated in figure 8a. Further tempered glass is less planar than float glass due to the manufacturing process. In particular, tempered glass may have a curved periphery as illustrated in figure 8b. These factors work against the prior art evacuation head 8 and the hermetic contact to the pane face la as illustrated in fig. 8a, 8b. And as explained later a large evacuation head 8 also has adverse temperature distribution effects.

Consequently, it is advantageous that the contact width D is less than 50 mm. Preferably the evacuation head 8 contact width D is below 45 mm. Most preferably the evacuation head 8 contact width D is between 24-40 mm. In one aspect the width D is substantially circular and a diameter D.

With the specified size there is provided better evacuation and an enhanced VIG is produced. The pane non- planar face la has better contact to a smaller evacuation head 8. This is advantageous with tempered glass and during evacuation inside a heated oven.

The evacuation head 8 with reduced width enables VIG units where the evacuation hole is located closer to the periphery. The evacuation hole 5 or tube 6 has a center substantially less than 25 mm from the pane 1,2 periphery, preferably less than 20 mm. In one example the evacuation hole 5 or tube 6 is further situated at the corner of the VIG and the center distance applies to both peripheries.

The pillars 4 are spaced by a distance S. Typically in the range of 20-50 mm. With thick or strong glass 1,2 such as tempered glass the distance S is about 40 mm. It is desired to increase the distance S due to appearance and better thermal insulation. In one aspect the evacuation head 8 contact width D is equal or smaller than the pillar 4 spacing distance S. Hereby an enhanced evacuation and VIG is provided.

Reducing the contact width D has challenges, because the evacuation head 8 needs to accommodate a heater 9 and it needs a chamber 10 to accommodate the evacuation tube 6. Further the evacuation head 8 may have at least one surrounding conduit 13 (for vacuum suction to fix the evacuation head 8 to the pane) which also requires room and connectors 11, 12 to different vacuum pumps. Optionally also a seal, O-ring or gasket towards the glass contact surface (not shown) . Optionally also (fig. 4), a shield plate 15 placed in the chamber 10 so that the tube tip 6b is exposed to the heat in the chamber 10 and the remaining VIG is not affected by the heat.

Manufacture of VIG units is quite temperature dependent. The periphery seal 3, the glass pane 1,2 structure and treatments, the evacuation hole seal 7 and the degassing of materials all depend on the temperature. Through the steps of producing a VIG the temperature is varied (fig 6. shows three different steps) to degas the void V and solder the seals 3. In case the evacuation head 8 is used to tip off (i.e. seal off) the evacuation tube tip 6b there is a heating element 9 in the evacuation head which shortly heats to for example 700-1200°C degrees to melt the tip of the evacuation tube 6.

In particular, when using tempered glass, it is particularly important to keep the temperature of the tempered glass below the annealing temperature of the tempered glass, which otherwise will lead to loss of temper and reduced glass strength. Accordingly, a method of producing a VIG unit according to the invention, and wherein the VIG body production in an oven includes heating the VIG unit in the oven, may comprise in all steps keeping the temperature below an annealing temperature, which detrimentally affects the tempered glass, such as keeping the temperature below 400°C, which is a common annealing temperature for many tempered glasses. As, in some embodiments of the present invention, the evacuating of the void V is done at 150°C or more, preferably at 300°C or more, it is preferable that the temperature of the oven is between 150°C and 400°C, preferably between 300°C and 400°C during evacuation.

In the state of the art the heater element is typically a fixed tungsten coil heater. The prior art tungsten coil has the drawback, that it can produce metal deposits on the glass and it is less durable and produces a varied seal of the tube tip 6b. Further, the prior art evacuation head comprising a tungsten coil has the drawback, that the tungsten coil can only be operated under sufficient vacuum, which prevents heating with a tungsten coil under atmospheric pressures.

The evacuation head 8 has a heater 9. The heater 9 may be a ceramic heater. The ceramic heater 9 may comprise a heat generating resistor component. The ceramic heater may comprise a piezoresistive component. The ceramic heater may comprise an electrically resistive ceramic component.

The ceramic heater 9 can be located within the evacuation head 8. The power cables can for example be provided inside the evacuation tubes 11,12 and/or by the evacuation tubes 11,12 if they have sufficient electric conductivity. Hereby the hermetic properties of the evacuation head 8 are not affected by the heater 9.

A ceramic heater 9 is more durable and provides reliable VIG production. A ceramic heater 9 has a more constant heat profile. The heater 9 in the prior art shortly raises the local temperature to melt the tip 6b of the evacuation tube 6. But, as explained below, a ceramic heater 9 also enables heating to multiple temperatures.

As the majority of the heat transfer under vacuum is by heat radiation, particularly suitable sources of ceramic heaters are such ceramic heaters that emit most strongly within the IR-absorptive region of glass, in particular silicon nitride and/or aluminum nitride ceramic heaters. Such ceramic heaters have particularly strong emission in the frequency band from 4 to 13 μπι, making them particularly suitable in the VIG manufacture.

In some embodiments, the ceramic heater 9 may be a cylinder as depicted in the figures of the present disclosure. Where homogenous surface radiation is preferred, the ceramic heater can be flat disc shaped, or where focused radiation is desired, e.g. for better tip off of the evacuation tube tip 6b, parabolic shapes would be preferred. A further advantage of the use of ceramic heaters is the possibility to combine two or more differently shaped heaters to obtain a variety of radiation profiles based on the combined shaped heater. E.g. a flat disc shaped heater can be combined with an elongated cylinder shaped heater to provide both focused and planer energy to the surface. Further, by having separate energy supplies, the two or further heaters can be operated separately, depending on the design needs of the VIG manufacture .

The VIG manufacture is enhanced when the temperature throughout the VIG body is continuous i.e. minimize the temperature differences across the body. When the evacuation head 8 is placed on the face la of the pane it affects the local temperature. Figure 5 shows different locations for established temperature T2 inside the evacuation head 8. Temperature Tl in the surrounding air. And temperature T3 in the junction between the panes 1,2. Figure 6 shows a chart of the difference or delay in temperature during the VIG manufacture heating steps. It shows that the pane 1 glass temperature gradient is different at the location of the evacuation head 8. The local temperature T2 at the evacuation head 8 is lower.

It is advantageous to ensure the temperature under the evacuation head 8 matches the surrounding VIG body temperature (i.e. close to T3), respectively surrounding air temperature Tl. Even a 10-30°C temperature difference can adversely affect the VIG manufacture. To this aim, the evacuation head 8 can be equipped with a temperature sensor (not shown) to continuously measure the temperature difference exterior and interior to the evacuation head. A closed loop current feedback to the heater 9 would then be advantageously employed.

In particular, where the solder glass is a low temperature solder glass, in particular a lead-free low temperature solder glass, such as a VBZ-solder glass, it is important to compensate for the temperature difference between VIG body temperature, respectively surrounding air temperature Tl, and the temperature T2 under the evacuation head 8, as the narrow windows of temperatures applied leave little room for deviations if a sufficient solder glass is to be created by the soldering process. E.g. tempered glass is negatively influenced by high temperatures and long heating times, hence incomplete matching of the temperature T2 under the evacuation head 8 to the solder temperature, will lead to longer soldering times and hence to increased loss of temper in the glass.

In one aspect, the evacuating head 8 has fins to enhance the thermal transfer between the surrounding air and the evacuation head 8. Hereby the temperature under the evacuation head 8 T2 has a better match to the surrounding temperature Tl.

A further advantage of matching the temperature T2 under the evacuation head 8 to the temperature of the surrounding air Tl lies in securing adequate parture of the solvents and binders comprised in the solder glasses used for manufacturing the VIG units of the invention. If the temperatures under the evacuation head 8 is too low, reduced parture of solvents and binders will be observed, resulting in incomplete soldering of the solder glasses at a later stage or increased loss of temper due to increased soldering times.

In one aspect the heater 9 has a first heating temperature and a second heating temperature. The second heating temperature is nearly twice as high as the first heating temperature. The first heating temperature is the periphery seal 3 solder temperature (for example 300- 450°C), and the second heating temperature is the sealing temperature of the tube tip 6b (for example in the interval of 700-1200°C) .

In one aspect, when the heater is a ceramic heater, the heater 9 is on at least for 15 minutes for the first temperature. The heater 9 substantially heats for the duration of at least one heat step, preferably the solder step. The state of the art, tungsten heaters are usually on for seconds only.

The first temperature provides a substantially uniform VIG body 1,2 temperature T2 beneath the evacuation head 8. Hereby the temperature under the evacuation head 8 has a better match to the surrounding temperature Tl. This provides a better tube seal 7 solder and the remaining VIG is not affected by heat gradients and stress.

In another aspect (fig. 4) the evacuation head 8 first and second temperature is provided by a first heater 9 and a second heater 14. The second heater may be outside the chamber 10. Hereby each heater is customized to heat to the specified first and second temperature.

Figure 7 shows an evacuation head 8 with the ceramic heater 9. Here the ceramic heater 9 is displaceable and configured to move towards the tube tip 6b and contact the tube tip 6b. The ceramic heater 9 is heated to the tip off temperature such as of 700-1200°C and brought into contact with the tube tip 6b. The tube tip 6b may be pressed by the ceramic heater 9 and deformed during the seal off. Hereby the sealing of the tube tip 6b is reliable and has little influence on the remaining VIG body. The displaceable heater 9 may be employed in an oven during the VIG sealing and evacuation and tip off.

The ceramic heater 9 displacement may for example be in the interval of 1-3 mm. An actuator 16 may displace the ceramic heater 9. The actuator 16 may be based on a material which expands when heated to the tip off temperature. The actuator may be an electric piezo actuator. The actuator 16 may operate by way of an electromagnet 17 such as an external electromagnet 17, which displaces the heater 9. These examples of actuators ensure the hermetic properties of the evacuation head 8 are intact while providing operation in the hot oven environment. Other actuators may be employed.

Above, the present invention has been exemplified using an evacuation tube 6 inserted into evacuation hole 5 and soldered 7 to the front side la of the first pane 1. The present invention, however, is not limited in the manner in which evacuation occurs, nor in the art or construction of the evacuation tube 6.

In the art (c.f. e.g. US 2009/0155500 Al, US 2012/0148795 Al , both herein incorporated by reference) many other evacuation solutions are known for use with an all-metal cup of the prior art. The advanced in technology as described herein regarding the construction and design of evacuation heads 8 allow for improved implementation of these further advantageous implementations of the evacuation tube 6.

One common method of closing an evacuation hole 5 is by allowing solder glass 7 (in the form of a solder glass or frit ring, cf. e.g. Fig 5 of US 2012/0148795 Al ) to melt down into the evacuation hole 5, thus dispensing with the evacuation tube 6. This prior art method is advantageous in that it requires lower melting temperatures than what is necessary for melting the glass of the evacuation tube. However, disadvantageously, it requires significantly longer melt times. With the tungsten heater, as employed in the prior art, and in particular with the large evacuation heads of the prior art, this has been observed to result in damage to the pane 1, e.g. by the aforementioned deposit from the heater to the surface. By reducing the evacuation head diameter D as detailed herein and/or by using a ceramic heater 9 for localized heating, improved melting with shorter on-times can be achieved and concomitantly reduced damage to the pane 1. In the same manner, bung-like closures or cap-like closures can improved be soldered to the pane face la with less damage using the evacuation heads 8 detailed herein.

Fig. 9 details elements of the further improvements, which will be described below. In Fig. 9a, a disc shaped evacuation cap 18 has been soldered to the front side la of the first pane 1. Preferably, the evacuation cap 18 is partly inserted into the evacuation hole 5. The cap 18 comprises an evacuation port 20 and a solder glass ring 19 arranged around the evacuation port 20 on the cap 18, the solder glass ring 19 facing away from the interior void V, when the cap 18 is inserted into the evacuation hole 5. Preferably, the cap 18 has a depression for comprising the solder glass ring 19 and the evacuation port 20. Fig. 9b shows the situation after evacuation of the void V and subsequent closure of the evacuation port 20 by melting the solder glass ring 19, which under the influence of gravity, will flow into the evacuation port 20 thereby forming a tight seal for the evacuated void. For improved heat transfer and protection of the evacuated void V as well as the glass pane 1, the evacuation cap 18 is manufactured from metal, although glasses are suitable as well.

Such evacuation caps 18 are particularly preferable in VIG manufacture as they do not, contrary to the evacuation tubes 6, require further capping to protect the sealed tube from external damage, hence saving manufacturing steps and cost without loss of VIG life time in use. However, their use has hitherto been limited by the fact that with the prior art evacuation heads, unwanted heating of either or both of pane 1 and cap 18 would lead to thermal expansion of these elements and crack formation where pane 1 and cap 18 interact. The present, localized heating obtainable by the evacuation heads of the present disclosure, overcome these problems. Also suitable for use with the evacuation head 8 of the invention is a disc shaped evacuation cap 21 as depicted in Fig. 10a and 10b, wherein the solder glass ring 19 and the evacuation port 20 are no longer located on the top of the evacuation cap 21, but rather at its periphery and in between evacuation cap 21 and glass pane 1. Here, the disc shaped evacuation cap 21 is prepositioned in the evacuation hole 5 and provided with a discontinuous and/or dented solder 22 between the evacuation cap 21 and the glass pane 1, wherein the spaces and/or dents 23 between the discontinuous or indented solder 22 serve the function of the evacuation port 20 of the previous embodiment. When the ceramic heater 9 subsequently heats the solder to form the solder glass, the spaces and/or dents 23 between the discontinuous and/or dented solder 22 coalesce into a continuous solder glass in response to the heating. This evacuation cap is particularly suitable for use with a flat, disc shaped ceramic heater 9, having the added benefit that the distance between heater and evacuation cap can be reduced to within 0.5 mm to 2 mm for improved heat transfer between heater and evacuation cap.

Now some effects are described in particular with reference to Fig. 11, wherein is shown the experimentally measured surrounding air temperature Tl and the temperature T2 under the evacuation head 8 over 45 minutes. The solder seal 7 for the evacuation tube 6 is temperature sensitive because the seal 7 requires enough heat to seal properly (for example 300-450°C) and the reduced temperature beneath the evacuation head 8 as explained in figs. 5 and 6 may prevent a proper seal 7. This is solved by the heaters 9,14 and/or evacuation head 8 as presented in this disclosure. The disclosed evacuation head 8 provides more uniform temperature because it covers less area. And the heater 9 and optionally heater 14 provide a temperature at the evacuation head 8 which matches the surrounding oven sealing temperature.

The ceramic heater enables a compact evacuation head 8 with enhanced hermetic contact and enhanced thermal distribution below the evacuation head.

Further, the solder seal 7 for the evacuation tube 6 is temperature sensitive because the tube tip off heat (700-1200°C) may deteriorate the seal 7 and may weaken a tempered glass pane or coated pane. This drawback may be solved by the shield 15 (fig. 4) or by a ceramic heater 9 as disclosed (which may also be displaceable as explained) .

Generally, the disclosed embodiment of the ceramic heating element 9 and the disclosed embodiment of the displaceable heater 9 and the disclosed embodiment of the evacuation head 8 with a defined size D are suitable for combination, but likewise the three embodiments may also be employed separately.

Generally, the present disclosure is suitable and advantageous for a tempered glass VIG.

Generally, the evacuation head 8 and/or ceramic heater 9 may be employed outside an oven.

Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations and combinations can be made therein by those skilled in the art without departing from the scope of the appended claims. The temperatures indicated are not limiting unless stated otherwise.