GB2481030A

GB2481030A - Method and apparatus for extruding a pipe, gutter or the like with a textured outer surface

Info

Publication number: GB2481030A
Application number: GB1009602.2A
Authority: GB
Inventors: Gary Stenson; Anthony Patrick Walden
Original assignee: Polypipe Ltd
Current assignee: Polypipe Ltd
Priority date: 2010-06-08
Filing date: 2010-06-08
Publication date: 2011-12-14
Anticipated expiration: 2030-06-08
Also published as: GB2481030B; GB201009602D0

Abstract

An apparatus 10 for extruding a pipe, gutter, or the like 20, is provided. An extruding die 12 is provided for extruding a heated mixture of a first material and particles of a second material, a calibrating and/or sizing die 14 is also provided for receiving the extrudate and for sizing and cooling the extrudate from the extruding die, for outputting extrudate with a textured external surface formed by the particles of the second material. Further, cooling means 16 is provided for cooling at least an external surface of the extrudate before it enters the calibrating and/or sizing die. A method of forming an extrudate and such an extrudate are also provided. The apparatus and method are particularly suitable for manufacturing a pipe, gutter or the like with a textured outer surface.

Description

Method and apparatus for extruding a pipe, gutter or the like, and a pipe, gutter or the like There is a growing requirement to make plastic gutter and down-pipe systems which have the appearance of traditional cast iron rainwater products whilst retaining the benefits of modern plastics manufacture. Such products are typically used in the renovation of old buildings. The external appearance of the old cast iron products is maintained, usually by painting the plastic extrusions and mouldings with special paint systems which give textured outer surfaces, which look very similar to the finish of old cast iron products with a series of irregular indentations and projections in the surfaces.

The plastic versions retain the usual advantages of plastic products, such as light weight, corrosion resistance and relatively low cost manufacture.

As shown in Figure 1, conventional PVC extrusions 1 are given a good finish and an accurate external shape and size by pulling an extrudate 2 through a water cooled sizing die or calibrator 3 to which vacuum is applied to pull the outer surfaces of the extrudate to contact a metal surface of the sizing die to hold the shape whilst the extrudate cools below its deformation temperature and to give a good surface finish.

As an example, a calibrator for a pipe would be a metal tube 4 with water cooling built in and a series of circumferential slots 5 milled through the section along the length of the calibrator. The sizing die is fitted inside a bath and can either be immersed under water or sprayed with water. Vacuum is applied to the inside of the bath which causes the outer diameter of the pipe to contact the inner diameter of the calibrator sleeve forcing it into contact with the sleeve as described above. The extrusions are then painted to create the cast iron effect.

The cost of painting the products is a significant proportion of the total cost, particularly in the case of the extruded down-pipes and gutter sections which constitute the largest proportion of an external rainwater system. The present invention has been developed to seek to overcome these constraints.

Aspects of the invention provide continuously extruded sections, the outer surfaces of which are provided with a cast iron-effect texture as part of the extrusion process. The cost of painting is removed, issues of paint adhesion therefore do not have to be considered and the corrosion and external weathering performance are the same as conventional PVCu rainwater systems which have a long history of good performance in the UK.

In an embodiment, a mixture of particles of cured rubber or particles of a thermoplastic material which has a higher melting point than a first material are mixed into the first material, which may be PVCu. The particles have a typical particle size (e.g. average maximum or minimum diameter, average, maximum or minimum opposing side to opposing side distance) of around 0.1 to 1mm, typically 0.25mm. The particles may be irregularly shaped or may be spherical or generally spherical. In an aspect, a co-extrusion die is used to produce a profile with a thin outer skin (around 0.1 to 1mm, typically 0.5mm). The modified PVCu compound is extruded into the thin outer layer and in the present embodiment, the bulk inner layer may be extruded from a different material, or a similar or the same conventional PVCu material (around 0.5 to 5mm, typically 1.5mm). The "filIer' particles are able to deform when extruded through the narrow annular gap of the outer channel of the die, but they can at least partly recover their original shape when they exit the narrow confines of the die so that they protrude through the outer surface of the PVCu profile. The effect of the protrusions, when the extruded profile finally cools, is a textured surface, very similar to the painted cast-iron effect referred to above.

In the case of rubber particles, their particle size is partly recovered when the extrudate exits the extrusion die because of the elastomeric properties of the material. In the case of the thermoplastic particles, as the melting point of the particles is higher than the PVCu base material, the particles do not melt but are able to be deformed because they are softened by the relatively high extrusion temperature but are not permanently deformed so that the shape of the particle is partly recovered when the extrudate exits the extrusion die.

The cured rubber particles can be obtained by grinding up scrap rubber mouldings or runners as once rubber is cured, it cannot be reprocessed through conventional rubber moulding or extrusion machines and is often simply thrown away. Scrap tyres could also be used as a source of this material. Similarly, in the case of thermoplastic materials, scrap or recycled products could be ground up rather than using prime materials.

One of the issues in producing extrusions with a textured outer surface is that the protrusions in the outer surface occur as soon as the extrudate leaves the extrusion die and the melt pressure is equalized.

In the case of the textured extrusions it has been found that for preferred results the extruded profile should be partly cooled after it leaves the extrusion die but before it enters the calibrator as otherwise the protrusions would be forced back within the wall thickness of the profile when the profile is pulled into contact with the inner surface of the calibrator under vacuum. As the profile is being intensively cooled in this part of the process, the protrusions would be contained within the profile and no cast-iron effect finish would be produced. An intensive water spray between the extrusion die and the calibrator has been found to chill off the outer surface so that the protrusions are still above the outer surface even after the profile has passed through the calibrator. This can be done by applying spray cooling from water jets positioned in-between the extrusion die and the calibrator sleeve so that the jets of water contact the outside of the pipe, and possibly increasing the distance between the two.

The process described above can be used with solid wall extrusions instead of the preferred co-extrusion method. The principle is exactly the same as described above but the size of the particles may have to be adjusted to give the required visual Cl-effect.

The process can be used with thermoplastic extrusions other than PVCu.

An aspect of the invention provides a method according to claim 1. Another aspect of the invention provides an apparatus according to claim 9. Another aspect of the invention provides a pipe, gutter or the like, as claimed in claim 14.

At least some of the particles may be raised and others recessed from a notional surface profile of the extrudate, pipe, gutter or the like, to produce the textured surface, An external surface layer may be provided which is formed from the mixture of the first and second materials. The external surface layer may be between 0.1mm and 1mm thick. It may be around 0.5mm thick.

An inner layer (which may be of the first material) without any of the second material mixed therein may be provided inside the external surface layer and is adjacent thereto. The inner layer may be 0.5 -5 mm thick, in particular around 1.5mm thick.

The particles may be deformable at a melting temperature of the first material. The particles may be of thermoplastic material and at least partially return to their undeformed shape on cooling. The particles may be resiliently deformable. The particles may be comprised of cured rubber.

The particles may have a typical size of between 0.1 and 1mm. The particles may have a typical size of 0.25mm.

The first material may be an extrudable thermoplastic material, and possibly may be chosen from PVCu, PVCC, MUPVC, PP, PE, ABS. The particles of second material may have a higher melting point than that of the first material.

The invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows an extrusion process according to the prior art: Figure 2 shows a co-extrusion die and apparatus according to a first embodiment of the invention: Figure 3 shows an extrusion process apparatus according to a second embodiment of the invention: and Figures 4 to 6 show a pipe according to an embodiment of the present invention.

As shown in Figure 2, an apparatus 10 for extruding a pipe, gutter, or the like 20, is provided. An extruding die 12 is provided for extruding a heated mixture of a first material and particles of a second material, a calibrating and/or sizing die 14 is also provided for receiving the extrudate and for sizing and cooling the extrudate from the extruding die, for outputting extrudate with a textured external surface formed by the particles of the second material. Further, cooling means 16 is provided for cooling at least an external surface of the extrudate before it enters the calibrating andlor sizing die. In the present embodiment, the cooling means is a water spray, but this may be exchanged for, or augmented by, other means, such as air cooling etc. A cooling bath 18 is provided to fully cool the extrudate 20 as it is pulled through the calibrating die to fix its shape and size.

The extruding die 12 is a co-extruding die, which in the present embodiment heats, or at least maintains the temperature of the extrusion materials passing through it. The temperature of the extrudate may be around 200°C as it leaves the die. An inner layer 22 of the extruded pipe 20 is formed from a first extrusion material 26 and an outer or external layer 24 is formed from a second extrusion material 28 which in an embodiment is a mixture of the first material and particles of a second material. In another embodiment the second extrusion material is not the same as the first extrusion material but still includes particles of the second material. In the present embodiment, the particles are of cured rubber, but a thermoplastic with a melting temperature higher than that of the extrusion process but a softening temperature below that of the extrusion process could also be used. In that case, the thermoplastic is softened during the extrusion process so that it is deformable, but it at least partially returns to its previous shape when the deforming force is removed. Also, in alternative embodiments the inner layer material may not be the same material used in the outer layer, together with the particles.

An alternative method of pre-cooling is shown in Figure 3 in which an extension mandrel 30 is fixed to the mandrel within the extrusion die. The outside of this mandrel 30 contacts the inside of the profile of the pipe before it enters the cooling die 14 and supports the profile to prevent it from collapsing if a water spray is applied. This additional support mandrel is, in the present embodiment, insulated from the heated extrusion die with insulation 32, to further aid cooling. However, this is not essential.

Similarly, in this embodiment, water spray 16 is provided but may be omitted, or substituted for different cooling means, for example as discussed above. Figure 3 does not show the co-extrusion feature of the die for simplicity but the extension mandrel could be applied to a co-extrusion die in the same way.

Figure 4 shows a part cross-sectional view of a pipe according to an embodiment of the invention. In this embodiment, the pipe is an extrusion, in particular a co-extrusion. A pipe, gutter or the like 20 according to an embodiment of the invention comprises a first material 26 having particles of a second material 24A provided therein. At least some of the particles 24A give a textured outer surface to the pipe, gutter or the like 20. An inner layer 22 is also provided, which in the present embodiment is also formed of the first material, which does not have particles of the second material 24A added thereto.

Again, it may instead be formed from a different material. As explained above, the inner and outer layers are co-extruded. However, it would be possible to have a solid wall extrusion instead of the shown co-extrusion. In the present embodiment, the particles 24A have a size of around 0.25 mm and the thickness of the outer layer 24 is 0.5 mm. the inner layer 22 is around 1.5 mm thick. As shown in Figures 4, 5 and 6, the presence of the particles 24A in the second material 26 of the outer layer 24 provides a textured surface as the radial position of the particles 24A from the centre of the pipe varies. As the particles 24A are thoroughly mixed with the first material 26, a textured surface is provided over all of the outer surface of the extrudate, pipe, gutter or the like 20. Further, as the distribution of the particles 24A is random through the mixing, a textured surface, which closely resembles that of a cast iron finish, can be provided. The first material 26 follows the contour of the outermost particles, so providing the textured surface. By providing such a textured surface through the extrusion process, a separate painting step can be avoided, so significantly reducing the cost involved in producing the extrusion.

The present invention has been described purely by way of example and various modifications, additions and omissions will be apparent to a person skilled in the art, those modifications, additions and omissions falling within the spirit and scope of the invention. Unless the context of this application clearly requires otherwise, the terms "comprises", "comprising" and the like are intended to be used in an inclusive sense, i.e. including, but not limited to".

Claims

CLAIMS: 1. A method for extruding a pipe, gutter or the like, comprising: mixing at least one first material with particles of a second material; heating the mixed materials, passing the mixed materials through an extruding die to produce an extrudate, particles of the second material within the first material providing a textured outer surface of the extrudate passing out of the extrusion die; initially cooling at least the external surface of the extrudate; passing the cooled extrudate through a calibrating andlor sizing die, and further cooling the extrudate to form a cooled extrudate with a textured surface.
2. A method according to claim 1, wherein the second material has a melting point higher than the extrusion temperature.
3. A method according to claim 1, wherein the second material is cured rubber.
4. A method according to any preceding claim, wherein the external surface of the extrudate is cooled with one or more water jets in the initial cooling step before it is passed through the calibrating and/or sizing die.
5. A method according to any preceding claim, wherein the initial cooling is sufficient to harden an outer surface of the extrudate, the extrudate being passed over a mandrel while being cooled to maintain the shape of the extrudate as the external surface is cooled.
6. A method according to any preceding claim, wherein the extrudate is extruded as a coextruded extrudate with an outer layer formed from the mixture of first and second materials, and an inner layer comprising material without any particles of second material added thereto.
7. A method according to any preceding claim, wherein the extrudate is extruded as a solid wall extrusion.
8. An extrusion formed by the method of any of claims 1 to 7.
9. An apparatus for extruding a pipe, gutter, or the like, comprising: an extruding die for extruding a heated mixture of a first material and particles of a second material; a calibrating and/or sizing die for receiving the extrudate arid for sizing and cooling the extrudate from the extruding die, for outputting extrudate with a textured external surface formed by the particles of the second material; and cooling means for cooling at least an external surface of the extrudate before it enters the calibrating and/or sizing die.
10. An apparatus according to claim 9, wherein the extruding die is annular.
11. An apparatus according to claim 9 or 10, wherein the cooling means comprises at least one cooling jet of water for reducing the outer surface temperature of the extrudate.
12. An apparatus according to any of claims 9 to 11, wherein the cooling means comprises a mandrel for maintaining the shape of the extrudate as it is cooled.
13. An apparatus according to any of claims 9 to 12, wherein the extrudate is formed as a co-extrusion, said heated mixture being extruded as an outer, annular layer.
14. A pipe, gutter or the like, comprising a first material having particles of a second material provided therein, at least some of the particles giving a textured outer surface to the pipe, gutter or the like.
15. A pipe, gutter or the like according to claim 14, wherein the particles are cured rubber.
16. A pipe, gutter or the like according to claim 14 or 15, wherein the pipe, gutter or the like is an extrusion.
17. A pipe, gutter or the like according to any of claims 14 to 16, wherein at least some of the particles are raised and others recessed from a notional planar surface profile of the pipe, gutter or the like, to produce the textured surface.
18. A pipe, gutter or the like according to any of claims 14 to 17, wherein an external surface layer is provided which is formed from the mixture of the first and second materials.
19. A pipe, gutter or the like according to claim 18, wherein the external surface layer is between 0.1mm and 1mm thick.
20. A pipe, gutter or the like according to claim 19, wherein the external surface layer is around 0.5mm thick.
21. A pipe, gutter or the like according to any of claims 18 to 20, wherein an inner layer of the first material without any of the second material mixed therein is provided inside the external surface layer and is adjacent thereto.
22. A pipe, gutter or the like according to claim 21, wherein the inner layer is around 1.5mm thick.
23. A pipe, gutter or the like according to any of claims 14 to 22, wherein the particles are deformable at a melting temperature of the first material.
24. A pipe, gutter or the like according to any of claims 14 to 23, wherein the particles are of thermoplastic material and at least partially return to their undeformed shape on cooling.
25. A pipe, gutter or the like according to any of claims 14 to 24, wherein the particles are resiliently deformable.
26. An A pipe, gutter or the like according to any of claims 14 to 25, wherein the particles have a typical size of between 0.1 and 1mm.
27. A pipe, gutter or the like according to any of claims 14 to 26, wherein the particles have a typical size of 025mm.
28. A pipe, gutter or the like according to any of claims 14 to 27, wherein the first material is chosen from PVCu, PVCC, MUPVC, PP, PE, ABS.
29. A pipe, gutter or the like according to any of claims 14 to 28, wherein the particles of second material have a higher melting point than that of the first material.
30. A pipe, gutter or the like, substantially as hereinbefore described with reference to any of Figures 2 to 6 of the accompanying drawings.
31. A method of extruding a pipe, gutter or the like, substantially as hereinbefore described with reference to any of Figures 2 to 6 of the accompanying drawings.
32. An apparatus for extruding a pipe, gutter or the like, substantially as hereinbefore described with reference to any of Figures 2 to 6 of the accompanying drawings.