Laminated glass offers superior safety. Because it doesn't break into sharp fragments like ordinary glass, it is an ideal material for applications where safety is paramount - from windows that protect against break-ins to bulletproof screens. Laminated glass can be used in glass roofs and partition walls at shopping arcades, theatres, banks, halls and other public buildings. It's also used as screens for balconies and in railings and increasingly in various everyday facilities such as schools and kindergartens, as well as in private homes.

Introduction

Laminated glass is an excellent construction material, offering good sound insulation and shielding against harmful thermal and UV radiation. It also helps to save energy. Different colour combinations of PVB-film and glass can be used to produce an attractive match with other building materials.

More and more applications today use flat tempered glass, which is then laminated. This means that the laminates have to be cut to size. Lines that are designed for the production of stock size jumbo glasses only, will not usually have the flexibility required by this custom size production concept.

Traditionally associated with bent laminated glass for automotive and architectural applications, Glassrobots also offers complete lines for the production of flat laminated safety glass.

General

The basic concept in the production of laminated glass is to bond together two or more sheets of glass. This can be done by means of resin, PVB-film (polyvinyl butyral plastic) or EVA-film (ethylene vinyl acetate plastic).

In the resin process, resin is poured in between the sheets of glass and then cured with UV lamps. Air-cured resins are also available. These are comparatively slow processes which means that they cannot be used for high capacity output,, but on the other hand they offer the advantage of eliminating the need for an autoclave. There are also some restrictions with respect to where it can be used; one example is provided by overhead glazing.

In some cases resin laminated products offers superior sound insulation properties on account of the fact that the resin between the glasses is softer. Where polycarbonate is used for bulletproof glass, the resin can be used between the polycarbonate and the glass. When using PVB, a polyurethane film has to be used against the polycarbonate surface.

The laminate with EVA-film only goes through a de-airing process, not an autoclave process. The laminate with PVB-film is usually de-aired and autoclaved, but an autoclave-free PVB-film is also available on the market. However the processes are slow and have not yet made a very great impact.

When the laminate is de-aired in a vacuum chamber for bent or flat glass (this can also be done in an autoclave) or in a pre-pressing unit for flat glass, the air is sucked out with a vacuum pump or pressed out with nip-rolls.

The vacuum process consists of a cold vacuum and a hot vacuum cycle. Vacuum rings around the edges of the glass or vacuum bags or disposable PE plastic around the whole glass sheets are used to suck out the air between the glasses. Vacuum bags or polyethylene plastic (or similar) are usually preferred especially in glasses involving sharp corners, difficult shapes and many holes.

The difference between the vacuum processes with the two different types of PVB-film -- "normal" and autoclave free -- is that the autoclave free PVB (AF PVB) requires a higher temperature (135 º C instead of 80 º C) and a longer process time. The autoclave free PVBs available can only be processed in a vacuum chamber (or conveyor), not in a pre-pressing unit.

The most common process is thus the one which uses "normal" PVB, which goes through both the de-airing process and the autoclave.

Process

The flat laminating process involves a number of steps that can be implemented in slightly different ways. These are loading, washing, positioning, assembling, de-airing, unloading and autoclaving.

Loading

Loading can be done with a loading lifter, free falling table or a tilting table. The choice depends in part on the size primarily manufactured by the client. The loading table can feed directly into the washing machine, or an additional full-length in-feed conveyor may be installed in front of the washing machine.

Washing

Horizontal washing machines are mainly used on flat laminating lines. It is possible to have a vertical washing machine followed by a tilting conveyor, with the glass then proceeding to the laminating room.

The most critical factor in feeding a flat laminating line is that the glass is completely dry before the laminating process is started.
It is also important that soft water is used. If mains water is not soft enough, a softener should be added. Some prefer to use mineralised water, produced using a water demineralisation system, either by reverse osmosis or ion exchange.

Modern washing machines can always be used for soft-coated glass as well.

Positioning

Accurate lamination requires first of all that the sheets of glass are positioned on the positioning table. This is always done to the same position by slightly tilting the positioning table and then driving the glass towards a limit switch.

Lamirobot then picks up the glass and moves it to the assembly table, always to the same place on that table. Lamirobot's suction cups are usually manually operated, i.e. if a glass sheet is small, the vacuum valves have to be manually closed and opened. The automatic suction cups will automatically sense whether there is a glass sheet underneath them.

Assembly

At the assembly table the PVB-film is inserted between the glass sheets: placing and cutting usually takes place manually. The film is drawn from the PVB-film roll-holder and then cut. When interleaved PVB is used, this protective film is automatically winded onto the PVB roll-holder.

Where automatic PVB-film feeding and cutting is provided, the operator may choose the desired length of the film prior to automatic cutting. When the film is drawn it will stop at the given length, with the PVB-cutter then will cut it. Trimming will be done immediately after cutting. In a fully automatic version, the PVB-film will be placed on the glass surface automatically, i.e. without any need to pull it out.

The surplus PVB-film around the edges is usually trimmed manually: the human eye will provide a better end-result than automatic trimming. Especially in mixed production the automatic mode is not particularly handy, given the constant need to re-set measures.

The assembly table is divided into two halves, allowing glass pieces to be laminated on the latter half. In this situation the Lamirobot is not in use and the first half of the assembly table is in down position so that small glass sheets can be moved directly to the latter half for assembly.

It is also possible to send a large number of small glass sheets to the pre-pressing unit in one batch, providing increased capacity in the production of small laminates. At the same time the assembly table will move the whole length or half the length to the pre-pressing unit.

De-airing

The most typical set-up for de-airing is a pre-heating tunnel followed by a first nip-roll, a main heating tunnel and a second nip-roll. Either IR-radiation or convectional heating can be used. Where convectional heating is used the radiation from the heating elements will of course also contribute.

The purpose of the pre-heating tunnel is to soften the PVB-film before it goes through the first nip-roll, where most of the air is pressed out before the edges begin to seal in the main heating tunnel. The remainder of the air is pressed out in the second nip-roll.

Glassrobots uses a combination of convectional and radiation heating (heating elements and fans), which has proved to be a highly effective method in mixed production and especially with multi-layers, reflective glass, painted glass, screen printed glass, etc. It eliminates the need to play around with the wave lengths on the IR elements, and provides even heat all around.

The convectional heating tunnels are also available as high convection units, in which the air is even more efficiently circulated and the heating elements are inside canals. Their capacity can be up to twice that of normal convection. In the production of thick glasses it might not be necessary to oscillate the glasses in the main heating tunnel.

Unloading

Unloading after the pre-pressing unit can be done to a castor table, from which the laminate is unloaded either manually or with the help of an unloading lifter. A tilting table is also commonly used nowadays. From this the glass is lifted to the autoclave rack.

Autoclaving

After the laminating line the glass will still have to be autoclaved. This is done in an autoclave. Slightly different temperatures and pressures are required for different types of glasses during the autoclave cycle.

Process Control

Process control is normally via a small control display. At Glassrobots a PC is now being used for this purpose, providing the operator with a wide range of trends data such as temperatures, nip-roll position and conveyor speed. The trends can be saved once a day, for instance, for later retrieval.. It is also possible to take printouts, incorporate animations of the line function, and modify the alarms for greater diversity.

PC control also gives the option of remote control with the GlassButlerä. This allows Glassrobots technicians to keep in touch with the customers' line via a modem.

Data on temperature and humidity in the laminating and PVB storage rooms can also be incorporated in the PC system.

Summary

Glassrobots' flat laminating lines offer the following innovative features:

• Equally suited for the production of stock or custom sizes.
• Batch processing for small lites to optimize the line capacity.
• 2-stage heating and pressing for high quality and efficiency.
• High convection for effective heating - for clear, coloured or coated glass.
• Automatic measurement of laminate thickness, ensuring correct settings for press rollers and conveyor speed.
• Designed specifically for ease of operation and maintenance with user-friendly Windows-based graphic interface, showing all line functions and including the option of saving process parameters. Optional recording of humidity and temperature data in the clean room and storage room.
• Full technical support during installation and after start-up.
• Innovative solutions for laminating tempered glass and special glass in particular.

Maximum working widths 1600 mm, 2200 mm and 2500 mm.