GB2202484A

GB2202484A - Extruding sheaths around intumescent cores

Info

Publication number: GB2202484A
Application number: GB08706733A
Authority: GB
Inventors: Keith Richard Patterson
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-03-20
Filing date: 1987-03-20
Publication date: 1988-09-28
Anticipated expiration: 2007-03-20
Also published as: GB8706733D0; GB2202484B

Abstract

A process for sheathing elongate intumescent fire-sealing core materials (40) with a thermoplastics material e.g. PVC, or nylon, comprises extruding the plastics material through an annular orifice (32) in a cross-die head (10), feeding the core material (40) having a cross-sectional area less than that enclosed by the annular orifice (32) through the die head (10), such that the extrusion (42) converges thereon at a position remote from the die head (10) to encase the core intumescent material (40) in a thermoplastics sheath. The process avoids deterioration of the intumescent material, that would otherwise occur by contact of the materials within the extrusion die. <IMAGE>

Description

IMPROVEMENTS RELATING TO TUBULAR EXTRUSIONS This invention relates to a process and apparatus for extruding a tubular sheath of plastics material around a core, particularly a core of heat-sensitive material, such as, for example, intumescent fire-sealing material.

Fire seals for sealing on the outbreak of fire a gap in a structure, such as the gap between a fireresistant door and the surrounding frame, commonly comprise a strip of intumescent material such as hydrated sodium silicate encased in a PVC sleeve which protects the intumescent material against mechanical damage and chemical degradation caused by the action of atmospheric moisture and carbon dioxide.Currently, such intumescent fire seals are produced by cutting strips from a sheet of intumescent material; stacking an array of cut strips on edge in a tray with the interposition of separators; sealing the exposed cut faces with a coating of epoxy resin; drying the resin; reversing the separated strips and repeating the sealing and drying steps; curing the resin; inserting the end strip into a PVC sleeve after coating one major face of each strip with PVA adhesive; and then allowing the adhesive to set with the strips lying with said major face downwards. The conventional process is thus extremely labour intensive and leaves great scope for improvement.

There have been many proposals for extruding a sheath over a core material, which may be a pre-formed strip or rod, or a simultaneously-formed extrusion.

By its very nature intumescent material suffers irrever sible physical and chemical change if exposed to heat, for example material of the hydrated sodium silicate type will undergo this change if its temperature exceeds 1000C, and softens at 40-60 C, becoming very soft above 600C. Such heat-sensitivity renders intumescent material difficult to sheath by extruding thereon a coating of PVC which is extruded at a temperature of about 175 to 1800C. Nonetheless the Specification of British Patent No. 2 079 669 B describes and claims a process for producing an intumescent fire seal which comprises the steps of extruding a core of intumescent material and extruding a cover which encapsulates the extruded core of intumescent material.The extrusion of the core may be performed in a first die head, the thusformed core being coated and then fed through a second die head for production of the covering. Alternatively the core of intumescent material and the cover are produced within a single die head having a first die for extruding the intumescent material and a second die for extruding the covering and provided with a heatinsulating layer. The Specification stresses that the distance between the first and second die is chosen to be a minimum bearing in mind that the distance should be sufficient to enable the polyvinylchloride to adhere to the core material without the creation of air gaps.

Despite ostensibly providing a solution to the economical production of intumescent fire seals the invention of British Patent 2 079 669 B has apparently not yet been commercially exploited.

According to a first aspect of the present invention there is provided a process for sheathing elongate core material with a plastics material, comprising extruding a plastics material through an annular orifice in a cross-die head, feeding core material having a cross sectional area less than that of said orifice through the die head such that the extrusion converges thereon at a position remote from the die head to encase the core material in a sheath of plastics material.

It will be noted that, in contrast to the prior art as constituted by the above British Patent and the Search Report thereon, the core material is not contacted by the plastics material until both have passed through the die head. This feature is particularly significant where the core material is heat-sensitive (e.g. is an intumescent material), as the extruded plastics material is cooled by ambient air as it converges in a generally frusto-conical path between issuing from the die and contacting the core material. However the plastics material should not be allowed to cool to such an extent that is insufficiently plastic to come into intimate contact with the core.The intimate contact which is partly a shrink-wrapping effect not only secures the core within the sheath but also, where the core is constituted by strips cut from hydrated sodium silicate intumescent sheet material effectively seals the cut faces from contaminating exposure to the atmosphere, thus replacing the numerous sealing steps of the prior art process.

Preferably the sheathed core material is hauled off to create a tension in the plastics material while it is following the frusto-conical path, and the thickness of material can be controlled at this stage by adjusting the rate of extrusion in relation to the draw-off speed.

Particularly if the plastics material is high melting and is for - example nylon rather than PVC, it is important that the coated core material should pass immediately into a cooling bath in which it is preferably calibrated and sized.

According to a second aspect of the present invention there is provided apparatus for encasing an elongate core material in a sheath of plastics material, the apparatus comprising a cross-head die arranged to be fed by an extruder for the plastics material, the die having an annular orifice defined by the body of the die and an insert having an aperture for the passage of core material, and feeding means for feeding core material through the aperture such that it is contacted by a convergent extrusion of said plastics material after both the plastics material and the core material have left the die.

Although the invention may obviously be put into effect in a variety of different ways and using many different combinations of materials, one particular embodiment thereof will now be described, by way of example, with reference to the single figure of the accompanying drawings which is a diagrammatic vertical section through an extrusion apparatus for carrying out the process of the present invention.

In the figure 10 represents a cross-head die comprising an annular body 12 having a radially disposed inlet 14 fed from a conventional extruder (not shown); inset into the front of the body 12 and retained by a ring 16 is a die 18 having an internally-coned surface 20 terminating in a land 22. Located within the die 18 by means of an axially-apertured rear plug 24 having an inclined front face 26 is a generally frusto-conical and annular insert 28 having an outwardly cylindrical tip 30 which defines with the land 22 an annular orifice 32; a reducing axial duct 34 of oblongate section; and a rear face mating with the face 26 of the rear plug 24.

Spaced from the die 18 is a water bath 36 having an end wafl 38 including a gasket, through which the extrusion passes in water tight manner, and containing a conventional calibrator (not shown) which ensures thedesired external dimensions of the extrusion, and which may optionally be transversely slotted to allow the application of sub-atmospheric pressure, again in known manner.

In operation, molten PVC is fed into the inlet 14 and passes through the convergent frusto-conical annular channel between the die 18 and insert 28, smooth flow being assisted by the inclination of the front face 26 of the rear plug 24, and through the annular orifice 32.

Feeding means (not shown) are located at the back of the die 10 and arranged to feed in abutting succession strips 40 cut from intumescent sheet material (for example the hydrated sodium silicate material manufactured by BASF AG and sold under the Registered Trade Mark PALUSOL or the vermicular graphite material manufactured by Chemie Linz AG and sold under the Registered Trade Mark INTUMEX L). As a strip 40 emerges from the apertured tip 30 it is initially surrounded by, but spaced from, a gaiter-like web 42 of PVC which converges on the strip 40 at a point just before it passes into the waterbath 36, there to be cooled and vacuum-calibrated.

There thus issues from the bath 36 intumescent strips 40 tightly encased in a PVC of constant external crosssection and good external finish, which may be cut to a desired length in conventional manner.

It has been found that the intumescent strip 40 is not harmed by contact with the still warm PVC, and that the insert 28 and plug 24 need not be insulated from the die head body 12 providing that the internal contact area of the tip 30 with the strips 40 is maintained small enough and the speed of the strips 40 fast enough.

The invention thus provides a simple and effective way of encasing intumescent strip in a mechanically protective and aesthetically pleasing sheath which also, where necessary, affords protection against atmospheric contamination.

Claims

Claims:

1. A process for sheathing elongate core material with a plastics material, comprising extruding a plastics material through an annular orifice in a cross-die head, feeding core material having a cross-sectional area less than that of said orifice through the die head such that the extrusion converges thereon at a position remote from the die head to encase the core material in a sheath of plastics material.

2. A process as claimed in claim 1, wherein the core material is an intumescent fire-sealing material.

3. A process as claimed in claim 1 or 2, wherein the plastics material is PVC or nylon.

4. A process as claimed in any preceding claim, wherein the sheathed core material is hauled off.

5. A process as claimed in any preceding claim, wherein the plastics material is cooled after it has been contacted by the core material.

6. A process as claimed in claim 5, wherein the plastics material is water cooled.

7. A process as claimed in any preceding claim, wherein the sheathed core material is calibrated.

8. A process as claimed in claim 7, wherein the calibration is vacuum-assisted.

9. A process as claimed in claim 1 and substantially as herein described.

10. A process for sheathing an elongate core material substantially as herein described with reference to the accompanying drawings.

11. Elongate core material when sheathed by a process as claimed in any preceding claim.

12. Apparatus for encasing an elongate core material in a sheath of plastics material, the apparatus comprising a cross-head die arranged to be fed by an extruder for the plastics material, the die having an annular orifice defined by the body of the die and an insert having an aperture for the passage of core material, and feeding means for feeding core material through the aperture such that it is contacted by a convergent extrusion of said plastics material after both the plastics material and the core material have left the die.

13. Apparatus as claimed in claim 12 and additionally comprising haul-off means for applying tension to the sheathed core material.

14. Apparatus as claimed in claim 12 or 13 and additionally comprising cooling means arranged downstream of the point of contact of the plastics material with the core material.

15. Apparatus as claimed in claim 14, in which the cooling means are water-cooling means.

16 Apparatus as claimed in any one of claims 12 to 15# and additionally comprising calibration means for ensuring that the sheath has the desired crosssection.

17. Apparatus for encasing elongate core material in a sheath of plastics material substantially as herein described with reference to the accompanying drawings.

17. Apparatus as claimed in claim 16, in which the calibration means are vacuum-assisted.

18. Apparatus as claimed in claim 12 and substantially as herein described.

19. Apparatus for encasing elongate core material in a sheath of plastics material substantially as herein described with reference to the accompanying drawings.

20. The features as herein disclosed, or their equivalents, in any novel patentable selection.

Amendments to the claims have been filed as follows Claims: 1. A process for sheathing elongate core material with a plastics material, comprising extruding a plastics material through an annular orifice in a cross-die head, feeding core material having a cross-sectional area less than that encompassed by said orifice through the die head, such that the extrusion converges thereon at a position remote from the die head to encase the core material in a sheath of plastics material, and hauling off the sheathed core material.

4. A process as claimed in any preceding claim, wherein the plastics material is cooled after it has been contacted by the core material.

5. A process as claimed in claim 4, wherein the plastics material is water cooled.

6. A process as claimed in any preceding claim, wherein the sheathed core material is calibrated.

7. A process as claimed in claim 6, wherein the calibration is vacuum-assisted.

8. A process as claimed in claim 1 and-substantially as herein described.

9. A process for sheathing an elongate core material substantially as herein described with reference to the accompanying drawings.

10. Elongate core material when sheathed by a process as claimed in any preceding claim.

11. Apparatus for encasing an elongate core material in a sheath of plastics material, the apparatus comprising a cross-head die arranged to be fed- by an extruder for the plastics material, the die having an annular orifice defined by the body of the die and an insert having an aperture for the passage of core material, feeding means for feeding core material through the aperture such that it is contacted by a convergent extrusion of said plastics material after both the plastics material and the core material have left the die, and haul-off means for applying tension to the sheathed core material.

12. Apparatus as claimed in claim 11 and additionally comprising cooling means arranged downstream of the point of contact of the plastics material with the core material.

13. Apparatus as claimed in claim 12, in which the cooling means are water-cooling means.

14. Apparatus as claimed in any one of claims 11 to 13 and additionally comprising calibration means for ensuring that the sheath has the desired crosssection.

15. Apparatus as claimed in claim 14, in which the calibration means are vacuum-assisted.

16. Apparatus as claimed in claim 11 and substantially as herein described.