Device for heating preforms consisting of thermoplastic material

Abstract

A device for heating thermoplastic preforms, including a heating channel formed from a heating module and through which the regions of the preforms to be heated are guided by a conveyor device. Radiant heaters are arranged on a side wall of the heating channel. In the region of a side that lies opposite the radiant heaters and/or the base of the heating channel, reflector elements which act as counter or base reflectors are arranged. The reflector has a reflection layer and a carrier layer. The reflection layer includes a material with a silicon dioxide base and an IR reflection value greater than 90% in the range of 500 to 2500 nm. The carrier layer is a material with greater mechanical strength than the reflection layer and is used as a carrier for the reflection layer. Both layers have a similar coefficient of thermal expansion and are permanently interconnected.

Claims

1. A device for heating preforms of thermoplastic material, comprising: a heating module that forms a heating channel through which parts of the preforms to be heated are conducted in sequence by a conveying device, wherein heating devices that emit infrared radiation are arranged on a side wall of the heating channel, and reflector elements are arranged in an area of a side wall opposite the heating devices and/or in area of a base of the heating channel to serve as a counter-reflector and a base reflector, which reflector elements ensure a lowest possible heat loss in the heating channel, wherein the reflector element serving to form the counter-reflector and/or base reflector has two layers, comprising a reflective layer and a carrier layer, wherein the reflective layer comprises a material based on silicon dioxide with an IR reflection value of greater than 90% in a range of 500-2500 nm, wherein carrier layer consists of a material with a mechanical strength greater than the mechanical strength of the reflective layer and is a support for the reflective layer, and wherein the two layers have similar coefficients of thermal expansion and are bonded permanently to each other.

2. The device according to claim 1, wherein the reflective layer comprises a silicon dioxide content of more than 95%.

3. The device according to claim 2, wherein the reflective layer comprises a silicon dioxide content of more than 99%.

4. The device according to claim 2, wherein the reflective layer is a two-dimensional molded part produced from amorphous silicon dioxide fibers.

5. The device according to claim 1, wherein the carrier layer is a two-dimensional molded part containing quartz glass, aluminum silicate, or calcium silicate.

6. The device according to claim 1, wherein the reflective layer is applied to the carrier layer by a wet method.

7. The device according to claim 6, wherein the reflective layer is applied to the carrier layer by spraying or dipping.

8. The device according to claim 1, wherein the two layers are bonded to each other by an adhesive or by lamination.

9. The device according to claim 1, wherein the reflective layer has a thickness that is no more than 50% of a thickness of the carrier layer.

10. The device according to claim 1, wherein at least one of the reflector elements is arranged so that the carrier layer of the reflector element faces the heating channel.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a heating module according to a first embodiment of the invention; and

(2) FIG. 2 shows a heating module according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) FIG. 1 shows a cross section through a heating module 10, in which a heating channel 11 with a U-shaped profile defined by side walls 12, 13 and a base wall 14 is formed.

(4) A preform 16 is shown in the heating module 10; the preform is held in the area of its neck 17 on the top cover 18 of the heating module, and its lower part 19 to be molded projects into the heating channel 11.

(5) Heating elements 20 are provided in the area of the side wall 13. The heating elements 20 are horizontally oriented heating tubes, which emit radiation preferably in the near-infrared region. A reflector element 21, which can also be called the primary reflector and which can consist of aluminum dioxide, for example, is also arranged on the side wall 13.

(6) In the area of the base wall 14 and the side wall 12, reflector elements 21 and 22 are arranged, which serve as a counter-reflector and a base reflector, respectively.

(7) The reflector elements 21, 22 are built out of two layers 23, 24; 25, 26, consisting of different materials, which can be bonded to each by means of an adhesive or by lamination.

(8) One of the layers is an outer reflective layer 23, 24, facing the heating channel 11; this layer consists of a highly reflective material based on silicon dioxide, but it has relatively little mechanical strength.

(9) To increase its stability, the reflective layer is applied to a carrier layer 25, 26, which fulfills in particular a support function for the reflective layer 23, 24. The carrier layer is preferably quartz glass, but ceramic layers are also conceivable.

(10) The carrier layer is fastened in turn to the side wall 12 or the base wall 14 by means of clamps (not shown), for example, or by other types of retaining elements. There is therefore no direct contact between the reflective layers 23, 24 and the walls 12, 14 of the heating module, and the vibrations which occur during operation do not lead to any friction which could grind away the material.

(11) FIG. 2 shows another exemplary embodiment of the invention with a heating channel 11 corresponding to the schematic structure previously described. The difference versus the exemplary embodiment shown in FIG. 1 pertains essentially to the nature of the reflector elements 21 and 22 serving as counter-reflector and base reflector, respectively.

(12) Each of the reflector elements 21 and 22 comprises a quartz glass plate 25, 26, which serves as the carrier layer and which is coated with a silicon dioxide-containing reflective layer 23, 24. The reflective layers 23, 24 are applied to the quartz glass plates 25, 26 by a wet method, for example, and thus cannot be produced at all without a carrier layer. Of course, corresponding reflector elements consisting of coated carrier layers can also be realized with carrier layer materials other than quartz glass.

(13) The reflector elements 21, 22 are arranged in such a way, for example, that the reflective layers 23, 24 are facing the interior of the heating channel 11, that is, facing the preforms 19 to be heated. This arrangement is also adapted to carrier layer materials which are impermeable in the infrared region.

(14) The arrangement shown in FIG. 2, however, is especially advantageous; here the quartz glass plates 25, 26 of the reflector elements 21, 22 are facing the interior of the heating channel, which means that they are able to protect the reflective layers 23, 24 from dirt and damage. As a result, however, it is necessary to accept a slightly greater radiation loss through absorption in the material of the quartz glass plates; with respect to a viewpoint in the interior of the heating channel 11, this material is now in front of the reflective layer. This arrangement of the reflector elements 21, 22 is therefore appropriate only for carrier layer materials which have the lowest possible coefficient of absorption for infrared radiation.