The present invention is related to a deep-drawing apparatus for the fabrication of polymer products, said apparatus comprising a framework, heater elements mounted to said framework in a polymer sheet infeed/heating arrangement, clamping elements for fixing said polymer sheet in place and a mould, on which the heated polymer sheet is arranged placeable for the purpose of moulding said sheet into a desired shape.

In deep-drawing moulding of polymer products, the polymer blanks are heated by means of heater elements to a moulding temperature suitable for each process and the polymer blank used. Subsequently, the heated polymer sheet is placed above the mould surface in the mould, and the mould surface is moved relative to the polymer sheet and the sheet is processed by deep-drawing moulding into a product having the shape of the mould surface.

Concurrently, the heating of the polymer sheets is conven¬ tionally accomplished by means of infra-red radiators aligned to heat, the surface of the polymer blank. When using infra-red radiators, the heating of the sheet blank takes a relatively long time and is secondarily hampered by the need of heating the body, and thereby, the thermal mass of the infra-red heater itself before the heating of the sheet can be commenced, thus lengthening the heating-up time. A further disadvantage is that the impinging infra-red radiation may cause damage to the sheet surface.

In conventional apparatuses, the polymer sheet blanks are mechanically fixed by clamp means to the framework of the apparatus for the duration of the heating cycle. Such a fixing method provides clamping at discrete points and slow in use.

It is an object of the present invention to provide a deep- drawing apparatus capable of overcoming the drawbacks of conventional equipment. It is a particular object of the present invention to provide a deep-drawing apparatus featuring a rapid heating cycle combined with low cost and simple construction. It is a still further object of the invention to provide a deep-drawing apparatus offering fast and uniform clamping of the polymer sheet blank.

The goal of the invention is achieved by virtue of a deep- drawing apparatus characterized in the annexed claims.

According to the invention, the heater elements comprise tubular incandescent halogen lamps emitting light at wave¬ lengths less than 1 micrometer. The warm-up time of halogen lamps is approx. 0.15 - 0.2 seconds, and their use overcomes the need to heat a substantial thermal mass in the radiant source. Hence, the blank heating time with the use of halogen lamps is reduced to a fraction of that required when heating with an infra-red radiator. Furthermore, the manufacturing costs of the apparatus remain much lower than those of an apparatus equipped with infra-red radiators. In fact, halogen lamps can be used on demand which permits switching on/off as required. An additional benefit is therein that the radiant heat applied from the lamps is transmitted to the inside of the polymer sheet blank without causing damage to the sheet surface. A further advantage of the apparatus is that the radiant power per square meter can be elevated up to as much as six-fold in regard to that possible with an apparatus using infra-red radiators.

In a preferred embodiment of the invention, the light emit¬ ted by the tubular halogen lamps has a spectral wavelength range of 0.5-0.9 micrometers, advantageously 0.5-0.8 micro¬ meters. In this type of radiant source, the useful wave¬ length range is peaked in the output curve and the specific

input energy consumption with respect to the absorbed heating power is extremely low.

In the preferred embodiment of the invention, the tubular halogen lamps are placed on the interior concave surface of segmental curved reflectors. Thus, the emitted radiation can be effectively directed onto the polymer sheet blank intro¬ duced in front of the reflectors, whereby a sufficient heating energy can readily be applied. The reflector surfaces are advantageously shaped to have a semicircular cross section giving a uniform and sufficiently high radiant output.

In another preferred embodiment of the invention, the clamp¬ ing means incorporates a frame on which one side of the sheet blank edge is arranged to rest, while against the other side of the sheet edge is adapted to press a compressive clamping element made from a hollow, resilient material that is finable with a pressurized medium. Into such a expanding clamping element can be released compressed air or other pressurized medium, whereby the clamping ele¬ ment makes an intimate contact with the sheet blank. The sheet is thus clamped evenly and rapidly between the frame and the clamping element. According to the invention, the clamping element is a tubular member, advantageously made from silicon rubber. Such an expanding tubular clamp is resilient and provides cost-effective and fast clamping of the sheet blank.

In a third preferred embodiment of the invention, the deep- drawing apparatus incorporates connected to the mould an ejector for applying a vacuum onto the mould surface. This application of an ejector for generating a vacuum in unknown in prior-art equipment. In the apparatus according to the invention, the vacuum is generated by the ejector and the compressed air of the ejector circuit can also be used for lifting the sheet, preblowing and cooling. Herein, the most

economical choice is an ejector featuring more advantageous operating costs and pricing than a vacuum pump of equivalent capacity. A further benefit of an ejector is that it contains no moving parts.

In the following, the invention will be examined in more detail with reference to the attached drawing illustrating schematically in a side view an embodiment of the deep- drawing moulding apparatus according to the invention.

Referring to the Figure, the deep-drawing moulding apparatus shown therein comprises a framework 1 with heater elements 2 , clamping elements 4 and a mould 5 mounted thereon. The heater elements 2 are tubular halogen lamps mounted on support structures 9. On the support structures are further located reflectors 6 with a semicircular cross section, including the halogen lamp heater elements 2 placed to the center of the inner surface of said reflectors. The appara¬ tus incorporates two opposed support structures having the tubular halogen lamps 2 of the structures facing each other. The polymer sheet blank 3 to be heated is introduced between these support structures, and thus, between the opposed arrays of tubular halogen lamps.

The clamping elements 4 of the polymer sheet blank are placed outside the support structures, and the clamping elements of the illustrated embodiment further comprise a frame 7 and an expanding silicon rubber tube 8 opposed to the frame. The frame and the silicon rubber tube encircle the support structure, thus facilitating uniform clamping of the sheet blank at its edges in the apparatus. These clamping elements are complemented with conventional quick- clamping means 10 for additional securing of sheet clamping.

The mould 5, which is placed below the support structures, comprises the shaped moulding surface facing the polymer sheet 3 and transfer means 11 for shifting the mould surface

vertically relative to the framework. The mould is connected by a hose or equivalent duct 12 to an ejector (not shown). The mould transfer means and mould platform is advantageous¬ ly a conventional scissor lift platform, which is a low- cost, durable and low-maintenance standard component. Moreover, such a lift platform offers a sufficiently high lift capacity permitting the use of, e.g., wood, aluminium or concrete as the mould material.

During the use of the apparatus, the polymer sheet blank is transferred into the interior of the apparatus and fixed in place by means of the clamping elements. Subsequently, power is switched on to the tubular halogen lamps for heating the sheet. Next, the mould is elevated supported by the transfer means 11 until the mould meets the surface of the polymer sheet blank, after which the blank is deep-drawn to the desired shape. The deep-drawing moulding step is augmented by a vacuum generated with help of the ejector. Finally, the moulded product is removed from the apparatus and a new blank can be introduced into the apparatus.

In the apparatus according to the invention, all steps of the moulding cycle are performed in the same position of the blank, which permits a smaller size of the apparatus. An additional benefit is that the polymer material need not be moved during moulding.

Not limited by the exemplifying embodiment described above, the invention may be varied within the scope and spirit of the annexed claims.