The present invention relates to a shaping apparatus, according to the preamble of Claim 1, for a membrane in curved glass and a method in shaping a membrane.

Polyvinyl butyral membranes, which are used particularly in the manufacture of windscreens, are shaped in a continuous process, from membranes on rollers, with the aid of heat treatment. The heat treatment is implemented as radiation heat in a multi- lamp infrared-radiation unit, in such a way as to form a temperature difference between the different edges of the strip, in the transverse direction across the strip. Typically, the hot edge is heated to a temperature of about 90°C, whereas the cold edge is typically at a temperature of 40°C. By creating direct stretching in such a heat-treated material strip, the desired curvatures are created in the windscreen. The curvature is adjusted with the aid of both the temperature and the stretching. When the tensile stress prevailing during the heat treatment and the cooling stage is removed, the desired curvature forms during the cooling stage. This technique is disclosed in, among others, US patent 6 031 971.

A drawback of the prior art is that the desired temperature profile is only reached at the end of the heating stage, and thus the treatment remains insufficient. Insufficient treatment is compensated by a long relaxation time, which in turn demands additional storage for the processed membrane blanks. The storage stage required by relaxation naturally increases the space demanded by the apparatus and increases the transit time in the process.

The present invention is intended to eliminate the defects of the prior art disclosed above and for this purpose create an entirely new type of shaping apparatus for a membrane in curved glass and a method in the shaping of a membrane in glass.

The invention is based on dividing the heating unit into at least two consecutive, separate, and independently adjustable heating units, in which case the transverse temperature profile, which runs at right angles across the direction of travel of the strip,

profile can also be adjusted. Temperature sensors, directly measuring the temperature of the strip and located after each radiation unit, further improve adjustment. Typically, it is desired to keep the same the temperature profile in the direction of travel of the strip for as long as possible, preferably so that the first heating unit raises the temperature to conform to the desired transverse temperature profile, the second unit then maintaining the profile as desired.

More specifically, the apparatus according to the invention is characterized by what is stated in the characterizing portion of Claim 1.

The method according to the invention is, in turn, characterized by what is stated in Claim 3.

Considerable advantages are gained with the aid of the invention.

Thanks to the invention, the membrane can be further processed immediately after the cooling stage, nor is there any need for additional storage. With the aid of the invention, less space is needed for the entire apparatus, thus reducing the costs of factory buildings.

The invention also permits a faster process time, as the storage stage can be bypassed.

In the following, the invention is examined with the aid of examples of embodiments according to the accompanying drawings.

Figure 1 shows a side view of a shaping apparatus according to the prior art.

Figure 2 shows a side view of a shaping apparatus according to the invention.

According to Figure 1, the membrane-shaping apparatus according to the prior art includes a pair of feed rollers 1 and 2, between which the strip 8 travels to the heating zone 9. The heating zone 9 is formed between the pair of feed rollers 1 and 2, and a support roller 3. In the solution according to the figure, the strip thus travels from left to right. The heating equipment 6 is located above the strip 8. The heating equipment 6 consists of several lamps, positioned more or less in the direction of travel of the strip.

These lamps of the heating equipment can be used to adjust the temperature profile of the strip across the strip (at right angles to the direction of travel). After the support roller 3, the strip leaves the heating zone 9 and enters the cooling zone 10, which is, in turn, formed between the support roller 3 and the drive rollers 4 and 5. The feed rollers 1 and 2 and the drive rollers 4 and 5 are typically parallel to each other. Between the feed rollers 1 and 2 and the drive rollers 4 and 5, stretching is created in the strip 8, which is then released to create curvature in the strip 8, due to the strip's transverse temperature profile. Temperature sensor (IR sensor) 7, which is located beneath the strip 8, is used as aid to adjust the temperature profile. The sensor then measures the real temperature of the strip 8. The sensor 7 extends across the strip and consists of several individual sensors, which allows it to determine the transverse temperature distribution of the strip 8.

The heating unit 6 of the heating zone 9 thus includes several radiation sources, of which there can be, for example, eighteen. The radiation sources are located more or less in the direction of travel of the strip 8, the angle between the direction of travel and the radiation sources being about 5°-10°. In addition, the radiation sources are positioned at equal intervals transversely and are typically infrared radiators. Other alternatives include halogen lamps or IR-gas radiators. Typically, one radiation element has a maximum output of about 1-2 kW. Each element's radiation output can be adjusted individually. A typical target for the temperature distribution of a polyvinyl butyral strip 8 is 90°C-40°C, from the hot edge to the cold edge. The distance of the radiation sources from the strip 8 is typically 10-15 cm. A radiation unit is typically 125-cm wide and 100-cm long. The total radiation output is typically about 30 kW. There is a ventilated space above the radiation sources, from which enough air, typically at least 1000-1500 m3/min, is arranged to circulate to improve the control of the temperature.

According to Figure 2, the heating apparatus according to the invention mainly includes all the elements of Figure 1. In it, however, the heating unit is divided into two independently adjustable units, a first heating unit 11 and a second heating unit 12, each with its own infrared sensor 13 and 14 according to Figure 1, set beneath the strip 8.

Typically, there is a clear gap of, for example, 10-20 cm, between the units 11 and 12, in the direction of travel of the strip 8. The heating unit 11 is intended to raise the

temperature of the strip 8 to the desired level, the heating unit 12 having the task of maintaining the target temperature. The use of the arrangement according to the invention achieves a longer residence time for the strip 8 at the target temperature in the heating zone 9, which avoids excess post-relaxation. Shaping apparatus according to the invention has a radiation output that is roughly equal to, or slightly greater than that of a similarly dimensioned solution according to the prior art (Figure 1), the solution according to the invention, however, achieving a clearly higher production capacity with the same dimensions.

In connection with the invention, it is naturally possible to use radiation limit plates according to the prior art, which are located essentially at right angles to the plane of the strip and essentially parallel to the direction of travel of the strip. These radiation limit plates can be used to limit the IR radiation to desired parts of the strip, for example, to the darkened parts of membranes intended for the upper parts of windscreens. This technique is disclosed in greater detail in the aforementioned US patent 6 031 971.

In addition to the membranes of windscreens, the invention is naturally also applicable to the manufacture of membranes in all laminated, curved glass structures. Besides windscreens, the end products can also be other curved windows in means of transport and buildings.

In addition to the two heating units 11 and 12, there can also be several independent heating units in the heating zone.