FR2497477A1 - HEATING ELECTRIC INJECTION NOZZLE FOR SYNTHETIC MATERIAL - Google Patents

Abstract

In the case of electrical heating elements which are produced using highly compressed tubular heating elements, especially for plastic injection nozzles, it is highly important that the temperature drop between the actual heating element and the nozzle body or the like which is to be heated is as low as possible and that the heating element is absolutely sealed against moisture and components of the plastic to be processed. These objects are achieved in that a tubular heating element, which is wound around the nozzle body, is embedded in a metal powder under high compression, using an enveloping tube which sheaths this helix, and is compressed with the nozzle body.

Description

The present invention relates to an electric heating injection nozzle for synthetic material comprising a tubular heating element with high compression arranged helically in a socket.

By German patent NO 2 240 382, a tubular heating body in the form of a helicofd winding is already known; incorporated between two sockets and highly compressed, the assembly can be slid over an object to be heated.

In German patent NO 2 222 558, heating bodies for nozzles are described in which the helical heating conductor is arranged directly in a double socket and is incorporated therein by means of a metal oxide. This double socket can be slid over the object to be heated.

In this last known device, the heat transfer between the heating element and the object to be heated is better than in the first city; however, there are difficulties with regard to sealing against the introduction of particles of synthetic material and therefore a certain possibility of deterioration.

The object of the present invention is to eliminate the previous drawbacks and to create an electric heating body which has good heat transmission between the heating element proper and the object to be heated, which is absolutely moisture and against synthetic materials and which is insensitive to mechanical stresses during operation.

To this end, according to the invention, the electric heating injection nozzle for synthetic material is characterized in that the winding of the tubular heating element rests directly against the nozzle body to be heated, is incorporated under strong compression in a metallic powder thanks to the use of a sleeve closed at its two ends and is compressed with said nozzle body.

In the injection nozzle according to the invention, an optimal heat transfer is obtained between the heating element and the nozzle body to be heated, and moreover, the assembly obtained is particularly sealed and can operate at very high temperatures. .

According to another feature of the invention, between the turns of the tubular heating element, is interposed a profiled metal strip adapted to the space determined between the turns. Such a strip may be made of copper or a similar material. The metal powder then occupies the space remaining between the turns of the heating element and the metal profile.

The outer surface of the nozzle body may have a helical groove into which is screwed a preformed helical heating element.

The figures of the appended drawing will make it clear how the invention can be implemented.

Figure l is a longitudinal sectional view of an electric heating injection nozzle according to the invention.

Figure 2 is a cross section along line II-II of Figure l.

Figure 3 is a longitudinal section of the tubular heating element.

Figures 4 and 5 show alternative embodiments of the nozzle according to the invention with partial cutaway.

The heating nozzle shown in FIGS. 1 and 2 comprises a tubular heating element 1 in the form of a helix, an external sleeve 2, as well as metallic powder 3, for example copper powder, which fills the intermediate spaces between the heating element turns 1.

The heating element 1 for its part comprises a metal tube 4, heating conductors 6 incorporated in the latter by virtue of an insulating mass 5 and is strongly compressed in a known manner. The connections 7 of the heating conductors exit at one end, the other end of the tube 4 being sealed off by a welded disc 13.

The heating element 1 is applied by sliding directly against the nozzle body to be heated 8 and is covered externally by the sleeve 7. One end of the sleeve 2 is closed by a convex disc 9, after which the metal powder 3 is introduced from the other side and compacted, then the other end is closed by a disc 10 and the assembly is finally compacted by hammering or isostatic until the diameter of the sleeve 2 is reduced by about 20%.

One end of the heating element 1 passes through the sleeve 2 and serves as connection il for said heating element.

The metal powder 3 strongly compressed in this way surrounds on all sides the tubular heating element and ensures good heat conduction in the direction of the nozzle body 8.

As shown in Figure 4, the spaces between the turns of the tubular heating element l can be largely filled by a profiled metal strip 12, for example copper, put in place before compaction. The remaining spaces can be filled with copper powder and the assembly is then compacted as described. In the embodiment shown in Figure 5, the nozzle body 8 is provided in its outer surface with a helical groove 14, in which is screwed the prefabricated helical heating element.

The remaining spaces are filled with a metallic powder 3 and the assembly is compacted and compressed. This helical groove arrangement has the additional advantage that the contact area available for heat transfer to the nozzle body is further increased.

The heat transfer with the device according to the invention is practically the same as that which can be obtained with molded heating bodies. The structure of the device according to the invention is moreover resistant to vibrations and completely impermeable against humidity and the penetration of particles of synthetic material. Another very important advantage of the present invention consists in that the structure described has an additional reinforcement of the nozzle body itself, which is particularly important for high injection pressures of the order of 1000 bars at temperatures of 3000C. and even more.

 For the adjustment of the operating temperature, a thermoelectric element can be incorporated into the metal powder lining and its connections can be accessed laterally through the wall of the sleeve 2.

It will be noted that the present invention is not limited to the exemplary embodiments described, but can be used advantageously whenever hot-melt materials have to be heated to high temperatures under high pressure.

Claims (4)

1.- Electric heating injection nozzle for synthetic material comprising a highly compacted tubular heating element, arranged in a helix in a socket placed on the body of said nozzle, characterized in that the winding of the tubular heating element ( l) rests directly against the nozzle body (8) to be heated, is coated in a metal powder (3) strongly compacted by the use of a sleeve (2) closed at its two ends and surrounding said winding and is compressed with said nozzle body (8).  2.- injection nozzle according to claim 1, characterized in that, between the turns of the tubular heating element (1), is interposed a profiled metal strip (12) adapted to the space determined between said turns. 3.- injection nozzle according to claim 1, characterized in that the outer surface of the nozzle body (8) to be heated has a helical groove (14), in which is screwed a preformed heating element (1). 4.- injection nozzle according to any one of claims 1 to 3, characterized in that a thermoelectric element is incorporated in the metal powder (3) strongly compressed and in that its connection end passes through said sleeve (2).