IE47672B1 - Process and device for effecting a complex protective sheating - Google Patents

Abstract

1. A method for applying protective complex coating layers for hoses and channels, characterized by the extrusion from two or several extruding machines (1, 1') of bands of various natures (5, 6) passing thereafter into a single die (3) for forming a band having a single thickness and juxtaposed parallel longitudinal sections of various products used for the coating, said operation being followed by the helical winding of said band on the tubular element (8) to be coated, the helical winding being carried out such that a lower layer (10) of same nature, in one or several thicknesses, is formed on the tube as well as an outer layer (11) of a different nature.

Description

The invention relates to a device and method for forming a sheath which may be then used to sheath an article such as a pipe, conduit, or the like.

Known techniques for protecting pipes, conduits and other shaped articles have made use of an apparatus which when supplying the sheath mixes the various components of the sheath. Such admixture generally makes the agents which comprise the sheath lose a portion of their own qualities.

Thus, for example, polyethylene of low, medium or high 10 density has been used as a sheathing material because of its desirable properties. However, because of exposure to light rays, more particularly to ultra-violet rays, it has been necessary to protect the sheathing from ageing too quickly. The prior art has attempted to solve this problem by charging the polyethylene with a carbon black filler. However, such an admixture has resulted in the resin losing some of its own intrinsic qualities, particularly its adhesiveness and its resistance.

It is thus an object of the invention to provide a sheathing which while being protected from the natural elements, nevertheless does not degrade the sheathing components as a result of using a mixture of sheathing components.

It is a further object of the invention to provide a deyice for producing a complex sheathing, i.e., a sheathing comprising a plurality of components, without having to admix the components to a substantial extent so as to detract from each of their individual qualities.

These and other objects are fulfilled by means of the device of the invention for sheathing an article with a plurality of different sheathing materials which comprises at least two extruders and a die. The extruders are adapted to feed the die with separate streams of material to form the sheathing at the outlet of the die and are arranged adjacent to the die.

In a preferred embodiment of the invention the extruders are arranged in parallel so as to simultaneously feed the die with each of the streams'so as to'form the sheathing without affecting complete admixture of the streams.

In one preferred embodiment of the invention the die is adapted to extrude each of the streams concentrically so as to sheath the article. Alternatively, the die may be adapted to form the sheathing materials in the form of a tape which may then be wound around the pipe, conduit or other article being sheathed.

The objects of the invention are further fulfilled by means of a method for forming a sheathing for sheathing an article which comprises the steps of: forming two distinct streams of different sheathing material by extruding each of the streams out of two extruders arranged in parellel, and passing each of the streams in parallel through a die in a manner which prevents substantial admixture of each of the streams.

In one embodiment of the invention, the method may comprise passing each of the streams through the die concentrially. In an alternative embodiment of the invention the method comprises passing each of the streams through the die so as to form a tape or ribbon having substantially distinct layers.

In one embodiment of the invention one of the streams may comprise substantially pure or virgin polyethylene while the second stream comprises polyethylene having a carbon black filler.

As shown in the annexed drawings, by way of example: Figure 1 .illustrates the extruder assembly feeding a single die resulting in the output.of a complex or multjlayered tape; Figure 2 illustrates the tape as it is wound around a pipe in cross-section; / and Figure 3 shows an alternative embodiment of the invention for forming a tubular sheathing.

According to the invention a process and device are provided which make it possible to produce a complex protective sheathing which may be used to encase or sheath tubes, pipes or the like.

The invention is adapted to be used to protect pipes, conduits and other shaped articles which, for various reasons, * must be encased within a complex or multilayered protective sheath or casing which comprises a plurality of agents. The agents may be used to serve different functions. Thus, chemical additivies may be present in the sheath for serving various functions, e.g., screens or screening devices, dialectrics, and mechanical agents.

Whereas conventional techniques have relied upon incorporation of a plurality of different agents within a single layer 47673 of the sheath thus causing it to lose some of its desirable properties, the invention overcomes these disadvantages and conserves the adhesive and other qualities of the layers in their totality by means of a single operation which forms the sheath. The method and device of the invention likewise provide in a single operation, the protective covering or encasement of the element or body to be covered which while contacting the part to be covered with a pure or treated product, spreads a second layer which may be either pure or treated.

Although the invention ultimately relies upon a single die or extrusion head, the invention makes it possible to use a plurality of materials having different colours, and qualities without there being substantial admixture between them, thus conserving the qualities of each of the layers independently of the other layers.

The thickness of the sheath covering the pipe or other element may be controlled by adjusting the number of successive layers used to build up the sheath. Such a process is particularly applicable with respect to the sheathing of buried tubes or pipes. The material used to form the sheath may be either low, medium or high density polyethylene, although other materials may be clearly used.

The layers of material can be secured to the tubes by means of a primary coatinn or layer which is either extruded or electrostatically deposited onto the pipes although other techniques may clearly be used. 47073 As was noted above, the invention serves to protect the sheathing material against the acceleration of the ageing process due'to ultra-violet rays or to other agents or elements. This is particularly true when using polyethylene.

As was noted above, polyethylene is conventionally charged with carbon black in varying percentages. However, the incorporation of carbon black detracts from the qualites of the polyethylene, specifically its flexibility, and the ease with which it may be thermo-bonded to the other sheathing layers, particularly to the primary layer. Thus, although pure polyethylene is known to possess the most desirable qualities, the prior art 1 has found it necessary to incorporate carbon black which represents a costly operation whether it is done by means of a master batch, or colouration in the course of the extrusion process. This is true whatever charge is used.

With the process of the invention a tape, band or ribbon having a certain width and thickness may be extruded to form a helicoidal winding so as to provide along a portion of the width of the sheath, an extrusion layer of pure polyethylene which comes into direct contact with the primary layer.

The pure or virgin tape which has not been charged will be wound upon itself in a helicoidal spiral until the desired thickness has been obtained. The last layer of the spiral will be made of tape which has been charged with carbon black. The carbon black charged portion of the tape will, therefore, only be used where it is needed at the upper layer which is exposed to ultra-violet radiation. Thus, it is unnecessary to charge the tape with the carbon black until the proper thickness of the sheath has been achieved and the tape being extruded is to form the upper layer of the sheath.

The tape or ribbon material used to form the upper layer of the sheath may itself be charged with the carbon black or other material over only a portion of its thickness (+ or -).

The portion of the tape which is charged may either comprise a majority or minority of the overall thickness of the tape depending on the extent of protection desired.

Turning now to the drawings, Figure 1 illustrates the t use of at least two extruders, although more may be used, each one being fed with a different material. Either pure or coloured feedstocks may be used. The die is fed by a single conduit or feed and the mixture of the products can only occur over a very small zone which may be varied according to the extrusion conditions.

The lack of admixture between the feeds coming off of each of the extruders is the result of the close spacing between the extruders and the die or single extrusion head, This close spacing is chosen so as to minimize the relative admixture of the two feeds.

In the drawings the extruders 1 and 1' extrude material into the conduits 2 which then feed into a single conduit leading to the die or extrusion head 3 which forms the complex layer of tape comprising materials 5 and 6 which adhere to one another at 7. 4767½ As shown in Figure 2, the tube 11 covered with a primary or subjacent layer 10 is covered with the layers of different materials 5 and 6.

Figure 3 illustrates an alternative embodiment of the 5 invention in which extruders 1 and 1' once again feed into line 2, However, the die 4 is constructed such that it generates multiple concentric layers of material 8 and 9 on top of the subjacent or primary layer 10 covering the pipe 11.

The invention has been described with respect to various 10 specific materials and embodiments. It is to be noted, however, that the invention is in no way limited to these embodiments i and its scope is to be construed in light of the claims.

Claims (7)

1. A method of applying a complex protective sheathing on tubular elements such as pipes and conduits, which comprises the steps of : 5 a) extruding tapes of different sheathing materials from two or more extruders, b) passing the tapes into a single die to form a tape having a single thickness and juxtaposed parallel longitudinal sections of different materials used in the sheathing, 10 c) helically winding said tape on a tubular element, such that an inner layer of the same material in one or several thicknesses is formed whilst forming an outer layer of a different material.

2. A method as claimed in Claim 1 in which the sheathing material comprises substantially pure polyethylene. 15

3. A method as claimed in Claim 1 or Claim 2 in which the outer layer sheathing material includes an ultraviolet screening agent.

4. , A method of applying a complex protective sheathing on tubular elements such as pipes or conduits, substantially as des20 cribed herein with reference to the accompanying drawings.

5. Apparatus for use in a method as claimed in any one of the preceding claims including two or more extruders arranged in parallel, a die, and helicoidal winding means. - 9 47672

6. A complex protective sheathing for tubular elements such as pipes or conduits produced by a method as claimed in any one of Claims 1 to 4.

7. A pipe or conduit whenever covered in a complex protective 5 sheathing as claimed in Claim 6.