Process and apparatus for applying a plastics enclosure to surfaces that are to be protected

The invention relates to a process and an apparatus for applying a plastics enclosure to surfaces of articles that are to be protected, especially for applying plastics enclosures to a metal housing.

For a long time, efforts have been made to protect against corrosion those surfaces of articles that are exposed to moisture, especially their outer surfaces. For example in the field of broad band communications cables metal housings are typically provided at junctions of such cables. It is known to protect these metal housings in shrinkable plastics enclosures, as described, for example, in DE-30 40 864 Al, DE-31 27 869-A1 and DE-31 24 374-A1. .

As an example, DE 3127869 describes a method of producing a connection and/or branch between coaxial cables using a kit comprising a metal housing containing an electronics plate, and a heat shrinkable polymeric sleeve enclosing the housing. The housing is provided with cable entries to receive the cables to be connected and/or branched, and these cable entries are connected to the electronics plate. The heat shrinkable sleeve is provided in two halves having corresponding cable entry pipes, the two halves are pre-shrunk over the housing at the factory, and the resulting branch set can then be delivered to the building site.

It is also known to spray a liquid plastics material onto the outer surface of the housings as a corrosion protection. The coating procedure may take place in several stages, for example a curable synthetic resin may be sprayed first, and then a filler sprayed on subsequently, as disclosed in DE-AS 21 09 393. Similarly, plastics tubes that are closed by spraying on polyethylene are disclosed in DE-AS 18 01 933, and application of

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Thus, a first aspect of the invention provides a process for applying a polymeric enclosure to surfaces of articles that are to be protected, comprising

(i) extruding a polymeric part in the form of a strip or tube, which is slit or split, or is in the form of two strips,

(ii) positioning the article to be enclosed in the extrusion path of the semi finished part, through the slit or split or between the two strips while the part is still in a deformable state, and

(iii) applying moulding presses against the semi finished part to urge it against the surfaces of the article to be enclosed.

A second aspect of the invention provides an apparatus suitable for carrying out the process according to the first aspect of the invention, comprising

(a) a semi finished polymeric part extruder, a holder for the article or articles to be enclosed and a tool holder containing moulding presses for pressing against the semi finished polymeric part which moulding presses can be moved from an opening state in which the semi finished polymeric part can be inserted around the article to be enclosed and within the moulding presses, to a closed state in which the moulding process urge the semi finished part against the article to be enclosed .

The invention has a number of advantages over known procedures. Since the semi- finished polymeric part that surrounds the article to be enclosed is still in a deformable state, it is possible to enclose and protect not only regularly shaped articles, but also articles having comparatively complicated outer contours in a simple manner. Also the

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process can be carried out virtually continuously, which means, in particular, that it can be carried out very economically.

A process for the manufacture of an insulated connection between electrical conductors with a thermoplastic plastics foil, in which inter alia a thermoplastic plastics tube is pushed over the connected conductors upstream of the connection, is known from DE-OS 16 46 408. The connection site is coated with a plastics paste and the plastics screw tube is pushed over the corresponding site including the plastics insulation and the entire assembly is then welded to form a homogeneous body with the aid of a kind of waffle iron. It will be appreciated that this procedure is very complicated. Also, it does not employ semi-finished parts in their deformable state, nor is it suitable for continuous operation.

Further embodiments of the process and apparatus according to the invention is apparent from the sub claims. In preferred embodiments the semi-finished polymeric part is in the form of a double strip of polymeric material or in the form of a slit polymeric tube. The wall thickness of the strip or tube may or may not vary in cross-section.

Especially by providing an extruded polymeric part that varies in wall thickness across its surface, it is possible to provide an accumulation of material in some regions should that be necessary, for example, for reasons of the use to which the finished article enclosed by the polymeric part is to be put. If the article to be enclosed is, for example, a cable entry pipe into a housing, eg for connection or branching of coaxial cable leads via an electronics plate or similar within the housing, the tips of the cable entries can be provided with an accumulation of material in order to render possible a higher tensile strength or the like when the cable leads or the like have been inserted.

A moulding process is used to urge the semi finished part against the article. Preferably the moulding involves the application of pressing tools against the semi finished polymeric part towards the article to be

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enclosed. The inner surface of the pressing tools may be arranged to correspond generally with that of the outer surface of the article to be enclosed.

In one embodiment, compressed air may be applied to the semi¬ finished polymeric part to apply, or to enhance application of the part around the article to be enclosed. The compressed air may be used in addition to cooling air applied to the semi-finished polymeric part. In another embodiment air may be withdrawn from within the article to be enclosed, thereby applying a drawing pressure on the polymeric part, to apply or to enhance application of the part. A combination of compressed air applied to the outer surface, and drawing pressure may also be used.

Blow moulding equipment may be used in the above embodiment of the present invention, which may be considered as an 'inside-out' blow moulding process.

The invention provides as well as a method, an apparatus as set out above in accordance with the second aspect of the invention.

Preferred constructions of the apparatus are apparent from the sub claims.

The tool holder is advantageously constructed to be displaceable together with the article holder so that the article can be brought into the extrusion path of the semi-finished polymeric part.

In a preferred embodiment of the apparatus, the holder for the article to be enclosed is equipped with a suction channel. This channel can be used for at least partially evacuating air from the region of the article to be enclosed. This apparatus makes it possible to produce, at least temporarily, a slight vacuum in the interior of the article to be enclosed, which assists the application of the outer plastics enclosure. Instead, or in addition, the pressing tools can be equipped at their surfaces, facing

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process can be carried out virtually continuously, which means, in particular, that it can be carried out very economically.

A process for the manufacture of an insulated connection between electrical conductors with a thermoplastic plastics foil, in which inter alia a thermoplastic plastics tube is pushed over the connected conductors upstream of the connection, is known from DE-OS 16 46 408. The connection site is coated with a plastics paste and the plastics screw tube is pushed over the corresponding site including the plastics insulation and the entire assembly is then welded to form a homogeneous body with the aid of a kind of waffle iron. It will be appreciated that this procedure is very complicated. Also, it does not employ semi-finished parts in their deformable state, nor is it suitable for continuous operation.

Further embodiments of the process and apparatus according to the invention is apparent from the sub claims. In preferred embodiments the semi-finished polymeric part is in the form of a double strip of polymeric material or in the form of a slit polymeric tube. The wall thickness of the strip or tube may or may not vary in cross-section.

Especially by providing an extruded polymeric part that varies in wall thickness across its surface, it is possible to provide an accumulation of material in some regions should that be necessary, for example, for reasons of the use to which the finished article enclosed by the polymeric part is to be put. If the article to be enclosed is, for example, a cable entry pipe into a housing, eg for connection or branching of coaxial cable leads via an electronics plate or similar within the housing, the tips of the cable entries can be provided with an accumulation of material in order to render possible a higher tensile strength or the like when the cable leads or the like have been inserted.

A moulding process is used to urge the semi finished part against the article. Preferably the moulding involves the application of pressing tools against the semi finished polymeric part towards the article to be

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tools 2a and 2b are then advanced towards each other according to the double arrow 9 in Figure IB, until the position shown in Figure 1C is reached, in which position shown in Figure 1C cutting operations or the like can be simultaneously performed.

The tool holder 1 is then moved back to the left in the direction of the arrow 10 (Figure 1C), the moulding tools 2a, 2b are subsequently opened according to the double arrow 11, and the holding rod 4 is withdrawn to the left according to arrow 12, so that the finished enclosed article 5, which is then designated 5' in Figure ID, can be removed or ejected. The sequence of steps according to Figures 1A to ID can then be repeated on other parts.

The article holder 3, may be constructed in a different manner. For example it may be designed as a revolving holder, i.e. by rotating, it can in one operating process remove one article already enclosed and introduce the next article 5 that is to be enclosed.

The described embodiment can, of course, be further modified in various respects. For example, the semi-finished polymeric part 7 may be in the form of a closed tube or a tube that is open at one side and so on. In order to assist moulding, the insides of the moulding tools 2 can be loaded with compressed air. As another option, or in addition air can be sucked out of the interior of the article being enclosed via he holder 4. Other methods of assisting moulding can also be used.