Film heater

Abstract

An apparatus for heating a thermoplastic film moving along a path has a radiant heater to one side and generally above the path directed at the film so that the heater heats the passing film, a reflector to an opposite side and generally below the path opposite the heater, and a coller connected to the reflector for cooling it to a temperature below a melting point of the film.

Description

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing whose sole FIGURE is a largely schematic illustration of the present invention.

SPECIFIC DESCRIPTION

As seen in the drawing a heater 1 for a continuously running thermoforming machine for processing films 2 comprises a plurality of radiators 3, designed as IR radiant heaters and provided in a row inside a housing 4 and parallel to the direction of travel of the film (arrow), which are used for the emission of thermal radiation, thereby heating the film 2 to the deformation temperature to prepare it for deformation in a subsequent forming station. The film 2 moves along a straight path forming an angle of about 15° to the vertical in a direction D.

It is particularly important that a reflector 5 be provided on the side of the film 2 opposite from the radiator 3, and that the web of film 2 run between the reflector 5 and the radiator 3 together with the housing 4 at an angle of inclination that is inclined with respect to the vertical. The angle of inclination has a value between +45° and −45°. The reflector 5 is positioned beneath the film 2. The reflector 5 also is connected to a cooling device 7 so that in the event of a malfunction which could damage or even-tear the film 2, the damaged film sections drop onto the cooled reflector 5 under the effect of gravity, and the reflector 5 provides an increased measure of safety. For normal operation the reflector 5 offers the advantage that reduced power is sufficient to heat the film 2 to the required deformation temperature. The multiple reflection of the thermal radiation emitted by the radiator 3 is facilitated in particular when an inner surface 4′ of the housing 4 is designed as a counter-reflector to the reflective surface 5′ of the reflector 5.

The reflector 5 and/or counter-reflector may be made of aluminum, in particular polished aluminum. A highly reflective layer may be applied as an alternative to enhancing the reflectivity by polishing.

A pyrometer 6 is provided downstream from the housing, relative to the direction of travel of the film. It is connected to a controller 8 that can shut down the emitter 3 if it detects a malfunction. The film 2 being too hot would indicate that it had slowed, and the film 2 being to cool would indicate that it had stopped altogether.

Claims

1. An apparatus for heating a thermoplastic film moving along a path, the apparatus comprising: a radiant heater to one side and generally above the path directed at the film, whereby the heater heats the passing film;a reflector to an opposite side and generally below the path opposite the heater; andmeans for cooling the reflector to a temperature below a melting point of the film.

2. The heating apparatus defined in claim 1 wherein the reflector and radiator are both oriented at a small acute angle to the vertical.

3. The heating apparatus defined in claim 1 wherein the heater includes a concave heater shell open toward the path and an emitter in the shell.

4. The heating apparatus defined in claim 3 wherein the emitter emits radiant heat.

5. The heating apparatus defined in claim 3 wherein an inner surface of the shell is reflective.

6. The heating apparatus defined in claim 1 wherein the reflector has a highly reflective face directed generally upward at the film and toward the heater.

7. The heating apparatus defined in claim 6 wherein the reflector face is plated with gold or silver.

8. The heating apparatus defined in claim 6 wherein the reflector face is plated with silver in turn covered by a transparent corrosion-inhibiting coating.

9. The heating apparatus defined in claim 6 wherein the reflector is glass.

10. The heating apparatus defined in claim 1 wherein the reflector has a generally planar face forming an angle of less than 45° to the vertical.

11. The heating apparatus defined in claim 10 wherein the angle is less than 15°.

12. The heating apparatus defined in claim 1 further comprising a pyrometer juxtaposed with the film downstream of the theater relative to a film-travel direction.

13. The heating apparatus defined in claim 12 wherein the pyrometer is shiftable transverse to the film-travel direction.

14. The heating apparatus defined in claim 1 wherein the emitter is an IR emitter.

15. The heating apparatus defined in claim 14 wherein the IR emitter emits radiation with a wave length between 0.5 μm and 10 μm.

16. The heating apparatus defined in claim 1 wherein the heater includes a plurality of emitters spaced apart in a travel direction of the film.