Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Patent
1998-08-28
2000-08-01
Walberg, Teresa
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
432 5, 126 21, A21B 2706, A21B 100, F27D 500
Patent
active
060970022
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device for heating plastics sections, in particular sections made of PVC, the device including a cabinet to accommodate a section, which cabinet has a supporting plate, side walls and a cover, as well as means for introducing hot air at one end of the section, so that it can flow past on the inside and outside of the section.
2. The Prior Art
Plastics sections are usually made by extrusion of PVC material. Certain applications require bending of the sections in order to obtain round forms, etc. Such processes are frequently employed in making doors and windows. The change in shape is achieved upon heating the section to a suitable temperature. For this purpose an oil bath may be applied, in which the section is heated to about 125.degree. C. Although the devices known in this context will permit rapid heating, considerable effort and expense is required for the subsequent cleaning work, when the oil has to be removed from the section. For this reason devices of this type are avoided if possible.
In DE-B 11 66 451 a device for heating plastics sections is described where hot air is blown into and passed along a section. Various air ducts and flow obstructions are utilized for preferred heating of special parts of the section. Such device is complex and demands a large input of energy.
U.S. Pat. No. 3,706,824 is concerned with a device for heating and bending lengths of pipe. In that case heating elements are introduced into the pipe in order to heat the pipe from inside. Such devices are not suitable for parts with more intricate cross-sections.
It is an object of this invention to overcome the above problems and to propose a device which will ensure rapid and efficient heating accompanied by simplicity of design and low cost.
SUMMARY OF THE INVENTION
According to the invention this is achieved by providing a return duct for recirculating and reheating the air after it has passed through the section, in order to form a closed air circuit. The configuration proposed by the invention will offer a compact design where heat losses are largely eliminated and very little energy is required.
It is provided in a preferred embodiment that the return duct, a heating element and preferably a fan be arranged in the cabinet, i.e., below the supporting plate. This will result in a particularly compact design of the device.
Operation of the device, i.e., especially insertion and removal of the sections to be heated, may be simplified by designing the supporting plate so as to be liftable.
In a preferred variant the cabinet is provided on its upper side with an upwardly opening cover and a working surface. In this way the bending operation may be performed on the device itself as soon as the section has been lifted.
The invention further relates to a process for heating plastics sections, preferably sections made of PVC, where hot air is passed in longitudinal direction along the inside and outside of a section. The principal feature of this process is that the air is conducted in a closed loop.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described further, with reference to the accompanying drawings illustrating embodiments thereof, in which
FIG. 1 is an axonometric general view of the device proposed by the invention,
FIG. 2 is a longitudinal section through the device,
FIG. 3 is a section along line 3--3 in FIG. 2,
FIG. 4 shows a detail of FIG. 3,
FIG. 5 is a section along line 5--5 in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The device includes an elongated cabinet 1 which is designed to accommodate a plastics section 35 ready for heating. To permit accommodation of the different lengths of the sections to be heated, the cabinet 1 may have a length of 4 m or more.
The cabinet 1 essentially is a parallelepiped and encloses a heating compartment 2 which is closed off at the bottom by a supporting plate 3 on which the sections 35 to be heated are placed. On the upper side the cabinet 1 is closed by a
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Patent Abstracts of Japan, vol. 013, No. 320 (M-853), Jul. 20, 1989 entitled, "Process of Bending of Synthetic Resin Tube" (JP 01 108020A, Apr. 25, 1989).
Robinson Daniel
Technoplast Kunststofftechnik GmbH
Walberg Teresa
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