GB2046163A

GB2046163A - Pre-heating Apparatus

Info

Publication number: GB2046163A
Application number: GB7910763A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-03-28
Filing date: 1979-03-28
Publication date: 1980-11-12
Also published as: GB2046163B

Abstract

A pre-heating apparatus for a thermoforming machine for uniformly heating a thermoplastics sheet or plate throughout comprises a first heating section (A), a cooling section (B) and a further heating section (C). Such arrangement ensures that both the outer and inner layers of the thermoplastics sheet or plate (1) are all at the same temperature when the sheet or plate is subjected to a thermoforming process in a mould (4). <IMAGE>

Description

SPECIFICATION A Pre-heating Apparatus for a Thermoforming Machine The present invention relates to improvements in thermoforming machines, particularly in such machines which work with thermosplastics sheet material, such as polypropylene. It is an object of the invention to increase the capacity of such machines by producing a uniform temperature throughout the thermoplastics sheet.

Known thermoforming machines are characterized by a final product in which, after a number of operations, the thermoplastics sheet attains a high temperature and is ready for the thermoforming process. It is, however, very common that the heated sheets do not receive a uniform temperature throughout, due to the fact that only the outer layers of the sheet reach an adequate temperature, the inner layers not reaching a sufficient temperature.

Generally, it is desired that the thermoplastics sheet has a uniform temperature throughout both for a better sheet utilization as well as for an improved final product.

It is an object of the present invention to provide a sheet pre-heating apparatus for a thermoforming machine which at least minimizes the above-mentioned disadvantage regarding attaining a uniform temperature throughout the thermoplastics sheet.

According to the present invention, there is provided a pre-heating apparatus for a thermoforming machine for uniformly heating a thermoplastics sheet or plate throughout, such apparatus comprising a heating section, followed by a cooling section and then a further heating section.

Preferably, the pre-heating apparatus of the invention comprises a vertical heating section, followed by a vertical cooling section and then a further horizontal heating section.

Also in accordance with the present invention there is provided a process for pre-heating a thermoplastics sheet or plate prior to subjecting such sheet or plate to a thermoforming process, comprising firstly passing the sheet or plate through a heating section, thereafter passing the sheet or plate through a cooling section and finally passing the sheet or plate through a further heating section.

Preferabiy, such process comprises firstly passing the sheet or plate vertically upwards through a heating section, thereafter passing the sheet or plate vertically downwardly through a cooling section and finally passing the sheet or plate horizontally through a further heating section.

The invention will be further illustrated, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of passage of a thermoplastics sheet through the pre-heating arrangement of the invention, prior to thermoforming; and Fig. 2 is a section through a thermoplastics sheet indicating the changes which take place as the sheet passes through the various heating and cooling sections.

As illustrated in Fig. 1, a thermoplastics sheet or plate 1, is initially passed vertically upwards through section (A) and between heaters 2, the said sheet or plate thereafter descending vertically through a cooling section (B) and then travelling horizontally through section (C) and between heaters 3. Only after such heat treatment is the sheet passed into the countermould 4.

As can be seen in Fig. 2, in the section (A) the outer layers 1' of the sheet are heated to a temperature of, for example, approximately 1 200C, while the inner layer 1" only reaches a temperature of, for example, approximately 1 000C. In the section (B), with a normal or forced cooling, the temperature of the outer layers 1' falls to approximately 700C, whilst the inner layer 1", on cooling more slowly, falls to approximately 900 C. As the sheet passes between the heaters of section (C), and as the outer layers 1' are subjected to a more rapid heating than the inner layer, the temperature of all layers reaches approximately 1400C, thereby creating ideal thermoforming conditions, when the sheet is passed into countermould 4.

Claims

1. A pre-heating apparatus for a thermoforming machine for uniformly heating a thermoplastics sheet or plate throughout, such apparatus comprising a heating section, followed by a cooling section and then a further heating section.

2. A pre-heating apparatus as claimed in claim 1, comprising a vertical heating section, followed by a vertical cooling section and then a further horizontal heating section.

3. A process for pre-heating a thermoplastics sheet or plate prior to subjecting such sheet or plate to a thermoforming process, comprising firstly passing the sheet or plate through a heating section, thereafter passing the sheet or plate through a cooling section and finally passing the sheet or plate through a further heating section.

4. A process for pre-heating a thermoplastics sheet or plate as claimed in claim 3, comprising firstly passing the sheet or plate vertically upwards through a heating section, thereafter passing the sheet or plate vertically downwardly through a cooling section, and finally passing the sheet or plate horizontally through a further heating section.

5. A process for pre-heating a thermoplastics sheet or plate prior to subjecting such sheet or plate to a thermoforming process, as claimed in claim 3 or 4, substantially as hereinbefore described and illustrated.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A Pre-heating Apparatus for a Thermoforming Machine The present invention relates to improvements in thermoforming machines, particularly in such machines which work with thermosplastics sheet material, such as polypropylene. It is an object of the invention to increase the capacity of such machines by producing a uniform temperature throughout the thermoplastics sheet. Known thermoforming machines are characterized by a final product in which, after a number of operations, the thermoplastics sheet attains a high temperature and is ready for the thermoforming process. It is, however, very common that the heated sheets do not receive a uniform temperature throughout, due to the fact that only the outer layers of the sheet reach an adequate temperature, the inner layers not reaching a sufficient temperature. Generally, it is desired that the thermoplastics sheet has a uniform temperature throughout both for a better sheet utilization as well as for an improved final product. It is an object of the present invention to provide a sheet pre-heating apparatus for a thermoforming machine which at least minimizes the above-mentioned disadvantage regarding attaining a uniform temperature throughout the thermoplastics sheet. According to the present invention, there is provided a pre-heating apparatus for a thermoforming machine for uniformly heating a thermoplastics sheet or plate throughout, such apparatus comprising a heating section, followed by a cooling section and then a further heating section. Preferably, the pre-heating apparatus of the invention comprises a vertical heating section, followed by a vertical cooling section and then a further horizontal heating section. Also in accordance with the present invention there is provided a process for pre-heating a thermoplastics sheet or plate prior to subjecting such sheet or plate to a thermoforming process, comprising firstly passing the sheet or plate through a heating section, thereafter passing the sheet or plate through a cooling section and finally passing the sheet or plate through a further heating section. Preferabiy, such process comprises firstly passing the sheet or plate vertically upwards through a heating section, thereafter passing the sheet or plate vertically downwardly through a cooling section and finally passing the sheet or plate horizontally through a further heating section. The invention will be further illustrated, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of passage of a thermoplastics sheet through the pre-heating arrangement of the invention, prior to thermoforming; and Fig. 2 is a section through a thermoplastics sheet indicating the changes which take place as the sheet passes through the various heating and cooling sections. As illustrated in Fig. 1, a thermoplastics sheet or plate 1, is initially passed vertically upwards through section (A) and between heaters 2, the said sheet or plate thereafter descending vertically through a cooling section (B) and then travelling horizontally through section (C) and between heaters 3. Only after such heat treatment is the sheet passed into the countermould 4. As can be seen in Fig. 2, in the section (A) the outer layers 1' of the sheet are heated to a temperature of, for example, approximately 1 200C, while the inner layer 1" only reaches a temperature of, for example, approximately 1 000C. In the section (B), with a normal or forced cooling, the temperature of the outer layers 1' falls to approximately 700C, whilst the inner layer 1", on cooling more slowly, falls to approximately 900 C. As the sheet passes between the heaters of section (C), and as the outer layers 1' are subjected to a more rapid heating than the inner layer, the temperature of all layers reaches approximately 1400C, thereby creating ideal thermoforming conditions, when the sheet is passed into countermould 4. Claims

6. A pre-heating apparatus for a thermoforming machine for uniformly heating a thermoplastics sheet or plate throughout, substantially as hereinbefore described with reference to and as illustrated in Fig. 1 of the accompanying drawings.