To: Antonio Mazzaroppi

Inventor: Antonio Mazzaroppi

The present invention relates to an improved glass laminating furnace.

Namely, the present invention relates to a laminating furnace in which the heating of the sandwich (es) of sheets of glass enclosed in the laminating bag is improved due to an improved convection of the air outside the bag.

Background art

In reference to figures 1 (Patent Application EP 09425277 of the Applicant) and 2 (Patent GB317,476), compact glass lamination systems exist which use glass containers 210 that are closed by movable top panels 211 for the lamination.

A bag of the type numbered 25 in figure 2 is arranged inside the glass container 210. Sometimes, the bag consists of two sheets of silicone conveniently joined together. When the sheets are closed, a vacuum is created and heated to 135-140°C by means of resistors outside the bag. Certain apparatuses apply an air convection to move the air around the bag to make the heating more uniform and quicker.

To this end, in the prior art fans are applied to the ends of the glass container and therefore air movement is obtained in a generalized and non-optimal manner .

Once the cooking is complete, the movable top panel 211 is raised and bag 25 is removed and left to cool before removing the laminated glass. This excessive delay in removing the glass inside the bag may generate excessive cooking and generate defects in the laminated glass .

Moreover, apparatuses of the prior art are not suitable for performing a night production cycle (i.e. in the absence of an operator) because the panel is to be immediately removed as soon as the cooking is performed due to the above.

Document US2013/0075034 describes a furnace and a method for producing stratified sheets from prefabricated sheets. Prefabricated sheets comprise at least two sheets and at least one sheet of polymeric material. The furnace comprises a hot chamber which in turn comprises heating means and an inlet opening provided with first closing means. The furnace further comprises a cold chamber communicating with the hot chamber and capable of being separated from the hot chamber. The cold chamber comprises cooling means and an outlet opening provided with second closing means. The hot chamber comprises three compartments: a first heating compartment where a laminating bag is arranged, a second air emission compartment and an air recirculation compartment. It is worth noting that these compartments are separated by walls, even if the communication of fluid is not prevented because the walls do not completely close the spaces. However, the two partition walls are perpendicular to each other and prevent the direct flow of air into the compartments. Even more so, the air follows an indirect path between the generation of hot air and the laminating bag because in addition to the presence of the walls, the fan is directed parallel to the laminating bag. Also in this case, the heating is not optimized and among other things leads to the above problems.

It is the object of the present invention to provide a furnace which solves the problems and overcomes the drawbacks of the prior art.

The subject of the present invention is a furnace and a laminating method according to the appended claims, which are an integral part of the present description.

The invention will now be described by way of non- limiting example, with particular reference to the drawings in the accompanying drawings, in which:

- figure 1 shows a lamination apparatus according to the prior art;

- figure 2 shows a laminating bag according to the prior art;

- figure 3 shows an example of structure of the apparatus of the present invention; and

- figure 4 shows a top view of an example of arrangement of certain elements of the invention;

- figure 5 shows a perspective view of an air feed tube with internal resistors, according to one aspect of the invention;

- figure 6 shows a perspective view of a variant of the air feed tube in figure 5, in which the internal resistors are linear elements; and

- figure 7 shows a graph of the temperature trend and of the blowing times in the heating step, according to one aspect of the method according to the invention .

Detailed description of example embodiments of the invention

Throughout this description and in the appended claims, the word "comprises" can be replaced by the expression "consists of". Moreover, elements of the embodiments may be extracted therefrom and used also independently of the other elements and details.

In reference to figure 3, an example of a laminating furnace according to the invention is shown.

A glass container 300 of the type of the prior art (preferably rigid and consisting of a single compartment, without partition walls) has a glass bag 310 of the type of the prior art, in which at least one sandwich 320 of sheets of glass is arranged.

Glass sandwich means the classical sandwich comprising layers of glass and plastic material such as thermoplastic polyurethane, TPU, PC, polyethylene vinyl acetate EVA, PTE, such as glues or substantial layers. A series of resistors 330 for heating the container, and therefore the sandwich, are arranged above and/or below bag 310. Such resistors (or in general, heat radiation elements) are arranged on a plane facing the laminating bag and preferably substantially parallel thereto so that all the resistors substantially are at the same distance from the bag (measured in the perpendicular direction, i.e. the axis of the air cones emitted - see below) in order to provide a uniform heating to the bag and therefore laminated glass of increased quality. There may or may not be elements interposed between the resistors and the laminating bag, preferably there will be free space.

A perforated tube 340 (or other equivalent means equipped for example with nozzles with controllable opening valves) for blowing air 360, preferably compressed air, through the holes 350 in the direction of bag 310 is arranged above the resistors. Obviously, air cones will come out of such holes (or nozzles with valve or the like) . Such air cones are parallel to one another, in that the axes of the cones are parallel or any one direction within the cones is parallel to the corresponding direction of another cones.

In reality, the resistors may also or only be below the bag, and therefore also the tube will be lower than the resistors. In general, the tube will always be arranged so as to send air onto the resistors in the direction of the laminating bag.

The resistors (in general (active) heating elements) are distributed uniformly along the two directions of extension of the sandwich and preferably are at the same distance from the sandwich or from the laminating bag. They substantially are also at the same distance from the blowing elements 350 so that the heating of the bag is uniform. Also, if the drawing shows a tube in one direction, there will be several tubes in the actual device covering the whole heating surface and they preferably will be crossed with respect to the series of resistors, as shown in figure 4. Moreover, the tubes may instead be other diffusors. Moreover, the tubes or diffusors may blow over certain resistors, for example from one side alone of the laminating bag or from both sides (here, there will be a first group of resistors and diffusors on a first side, and a second group of resistors and diffusors on the opposite side of the laminating bag) .

In reference to figure 5, in a different embodiment of the invention, tube 340 (having square section this time, but it may have any section) contains therein the resistors 330, so that the air is both heated in the tube and blown outwards through the openings or nozzles 350, again in the direction of the laminating bag.

In reference to figure 6, a variant of the diffusor in figure 5 provides one or more linear resistors 330 inside tube 340' . The zig-zag shape inside the tube is only a symbol to indicate the resistor. Tube 340' provides a series of holes or valves 350.

There are also provided means (not shown) for pumping compressed air into the tube and electronic control means (not shown) for such pumping.

Such electronic means are configured to emit compressed air into the tube for short intervals of time according to a predefined sequence, typically at regular intervals . Preferably, there are provided means (not shown) for adjusting the temperature of the plurality of heat radiation elements 330, the temperature adjustment means being configured so as to perform blowing cycles at the same temperature alternated by blowing cycles at an increasing monotonic temperature, up to a predefined maximum temperature. Then the sandwich is cooled substantially by turning off the resistors.

According to the invention, blowing cycles are determined which last a time T, in which the blowing of compressed air occurs during the portion of time TON.

For example, T = 10 seconds, and TON = 0.5 sec and TOFF = 9.5 sec in the heating step, or TON = 1 sec with TOFF = 9 sec in the cooling step.

This is because bag 310 is to be heated due to an external convection which is improved but not cooled with continuous (and/or excessive) blowing.

Referring to figure 7, in one embodiment, the ratio varies between TON and TOFF by alternating constant ratio zones and increasing ratio zones.

In particular, in the heating step and/or in the cooling step, TON is a percentage of TOFF between 5 and 45%. Specifically, TON = 0.5-4.5 s and TOFF = 5.5-9.5 s,

A recirculation of the air blown over the laminating bag may also be provided. The air is taken at the ends of container 300, pressurized and put back into circulation, with means outside the container. This contrivance allows the consumption of energy to be lowered and the ratio between TON and TOFF to be modified. Indeed, in the case of recirculation, TON > TOFF, in particular TON is a percentage of TOFF between 55 and 100%. This is because now the air is already hot enough and the blowing does not risk lowering the temperature of the resistors and compromising the rising monotonic increase of the temperature.

Once bag 310 has reached temperature, there is the problem of cooling the bag.

According to the invention, there is no need to pull out the bag for cooling. Indeed, the above electronic means are configured to continuously blow air according to the invention or for a period of the type of the heating period but with longer blowing, e.g. T = 10 seconds, and TON = 9 sec and TOFF = 1 sec.

Instead, according to the invention, more air is provided at the end of the cycle (after turning off the resistors by means of electronic control means) . This way, there is no need for immediate manual intervention, with the risk of defects due to overcooking. So once the bag is empty, it may be moved immediately without having to wait for the slow cooling thereof.

According to the invention, the compressed air is at a pressure between 0.1 and 3 bar or between 0.1 and 4 bar .

Although air has been indicated, such a term means any gas adapted to create a gas convection inside the glass container, in particular a gas that may speed up the cooling (e.g. liquid nitrogen) .

The method of the invention is such that the lamination of the glass is quicker and more uniform, thus making the laminated glass of improved quality with respect to the one that may be obtained with traditional furnaces. Moreover, there are significant energy savings for the production of laminated glass.

Moreover, lengthy wait times are not required to remove the laminating bag after the cooling.

Night production is allowed because the sandwich is not removed immediately after the heating step.

The preferred embodiments were described above, and variants of the present invention were suggested, but persons skilled in the art may make modifications and changes without departing from the related scope of protection, as defined by the appended claims.