WO2007132225A2

WO2007132225A2 - A method and an apparatus for the extrusion of a plastic profile

Info

Publication number: WO2007132225A2
Application number: PCT/GB2007/001768
Authority: WO
Inventors: Chesney Orme
Original assignee: Chesney Orme
Priority date: 2006-05-13
Filing date: 2007-05-14
Publication date: 2007-11-22
Also published as: WO2007132225A3; GB2437938B; GB2437938A; GB0609552D0

Abstract

The present invention relates to the moulding of plastics and composite plastics profiles for use in the building and construction industry comprising a moulding device (2) into which is fed a plasticized plastics or plastics composite material the device (2), having a least one oscillating moulding surface (8) which acts to shape a profile from extruded plastics and walk said forming profile through the moulding device (2) in a continuous manner. The moulding device (2) may have integral cooling means (14), which extracts heat from the forming profile in order to set the profile.

Description

Moulding of Plastics to Form Continuous Extruded Profiles The present invention relates to the moulding of plastics and/or plastic composite profiles for use in the building and construction industry.

Plastic composites are often used as wood substitutes and are made of plastics and cellulose-based fibers such as wood fibers (e.g. sawdust, pulp, waste wood etc), cotton husks, peanut hulls, nut shells, bamboo, straw, rice hulls etc, and mixtures thereof. The advantage of this composite material is that it can be made to look like wood and has many of the qualities of wood including the ability to be shaped using wood workings tools, whilst being more moisture, rot and termite resistant than a pure wood product. It has the further advantage that it can be made from waste and/or recycled materials.

There are various known methods for forming plastic profiles. In one known method the plastic profile is manufactured using a carousel machine in which the plastics raw material is plasticized in an extruder and the hot mix then forced into a closed mould. The carousel has a plurality of such moulds and once filled rotates the respective mould submerged through a cooling bath to solidify the plastic. Once solidified an air jet is used to blow the plastic profile from the mould. This method has the disadvantage that it will only work for plastics containing a high proportion of polyethylene (PE). This is because polyethylene shrinks slightly once solidified, enabling its release from the mould; it being necessary for the profile to shrink by approximately 1% in order to facilitate its release. This method is therefore not suitable for use with plastics which do not shrink upon cooling. Furthermore, it is not

suitable for the manufacture of profiles which are more than 3m in length, this is because the plastic solidifies before a larger mould can be completely filed. Also in order to further facilitate the release of the profile from the mould, the mould has to be slightly tapered and this method is therefore unable to produce a profile having a symmetrical shape. Furthermore, the presence of the cellulose fibres in a plastic composite at high percentage does effect the shrinkage of a profile making this method not particular suitable for the mass production of many plastics composite profiles, furthermore the presence of filler material creates the tendency for the profile to become jammed in the mould.

In both plastic and plastic composite profiles it is known to add a foaming agent to the molten mix to lighten the final composition and to reduce overall material costs. The above described method is not particular suitable for the production of such profiles because the pressure of the mould acts to compress and destroy the bubbles formed by the foaming agent in the mixture.

Profile extrusion of plastics is used to make continuous lengths of plastics. In this method plastics raw material is plasticized in an extruder and forced through a die, with the die containing the cross-section of the profile of the extrusion required. Take-off rollers are used to draw the still molten plastic from the die and to pull it through a cooling bath in order to solidify the plastic.

This method has the advantage of being able to produce long lengths of plastics relatively quickly. However, this method is not suitable for the production of a foamed plastics or plastics composite because if the haul off by the take off rollers is not running precisely in tandom with the speed of the extruded mix the bubbles become oval and the profiles can easily break and pull apart. This is because of the weakness of the foamed material until it is set on the surface enough to be pulled

through the water in the cooling bath. This drawback also leads to a reduction in speed at which this method can be run. Furthermore, with foamed profiles the molten mixture quickly expands upon release from the mould and makes it difficult for the profile to retain the shape formed by the die. In this instance it is necessary to reduce the speed at which the molten plastics is released from the die in order to better control the shape of the profile, with a resultant lower speed of production.

In a further method a vacuum calibration device may be present in the said cooling bath and the soft plastic extrusion is passed through the centre thereof, whilst a vacuum is drawn on the outside to provide a continuous vacuum forming process. This adaption to the above described method is also not suitable for the formation of a foamed product, because the introduction of the foaming agent causes a rapid expansion and the calibration device is not suitable for enabling the profile to keep its desired shaped at high speed, it is also limited to plastics which shrink slightly upon cooling thus enabling their release from the calibration device.

It is an object of the present invention to provide an apparatus and method for moulding a plastics profile which overcomes or alleviates the above described

disadvantages.

In accordance with a first aspect of the present invention there is provided a method for the continuous manufacture of a plastics profile comprising the steps of plasticizing a plastics material, feeding said plasticized plastics material into an inlet of a moulding device said moulding device having at least one moulding surface, oscillating at least one of said moulding surfaces, extracting heat from the plasticized material in order to set the plastics, and removing said set plastics profile from the moulding device.

This has the advantage that the shaping of the profile can be conducted in a continuous manner without the need for an expensive die on the outlet of an extruder/rnelt pump, in that the shaping of the profile takes places inside the mould with the oscillating surface allowing the pressure exerted by the mould to be adjusted thereby caressing the profile as it forms, rather than destroying the necessary formation of bubbles in for example a foamed composite. Typically a foamed composite has about a 2:1 expansion. Furthermore, a conventional haul-off device is not required because the oscillation of the moulding surface(s) effectively walks the forming profile through the mould thereby preventing damage to the profile by use of such haul-off devices as per the previously known methods. It is also possible to run this process at a much higher speed than previously known methods because the shaping of the profile takes place in the mould rather than by a die. Conventional throughput is in the order of 300kg per hour whilst the present invention enables a throughput in excess of 3 tonnes per hour depending on the size of the extruder. This method is also suitable for use with plastics which do not shrink when they set and plastic composites because the oscillation of the mould enables release of the profile.

The moulding device may comprise at least two moulding surfaces, the method comprising the step of operating the oscillation of each moulding surface in at least one of the following manners: to operate at the same speed, to operate at different speeds, to operate in a synchronous manner, and to operate in a sequential manner.

The method may comprise the step of extracting less heat from the plasticized material in the region of the inlet to the moulding device. This enables the molten plastics to fill all the die, before it starts to set.

The method may comprise the step of guiding at least one reinforcing material into the plastics material.

The method may comprise the step of adding at least one foaming agent into the plasticized plastics material.

The method may comprise adding cellulosic fibers into the plasticized material.

The method further comprises the step of controlling the volume and/or speed that the plasticized material is fed into and/or through the moulding device. This enables the expanding material to expand to fill the mould.

In accordance with a second aspect of the present invention there is provided an apparatus for the continuous moulding of a plastics profile comprising a mould having an inlet and an outlet, the mould having at least one oscillating moulding surface.

The apparatus may comprise a control means to adjust the rate of oscillation of the or each oscillating moulding surface. The oscillation of each moulding surface may be by way of a respective cam.

The mould may have at least two oscillating moulding surfaces and in a preferred embodiment four oscillating moulding surfaces.

The control means may operate the oscillating moulding surfaces in a sequential manner. This has the advantage that the speed and/or sequence at which each surface operates can be adjusted to best caress and hold the shape of the profile without distorting any bubble formation if a foaming agent is used, enabling transportation through the mould at the ideal speed for profile formation, and enabling

a clean release of the set profile. The control means may operate at least one cam which acts to oscillate a respective moulding surface. The mould may have integral cooling means. The cooling means may have means to control the extraction of heat from the profile during moulding. The cooling means may comprise means to graduate the degree of cooling throughout the mould, and the least amount of heat may be extracted in the region of the inlet to the mould. A heater may be provided at the inlet to the mould. The cooling means may comprise at least one cooling liquid, the mould having at least one internal cavity through which the liquid is passed.

By providing the cooling means integrally this eliminates the need for a cooling bath and thereby reduces industrial accidents because the liquid does not directly contact the molten material, it also reduces the amount of space required, since a more rapid cooling can be achieved because it is possible to use lower temperatures then present in a bath, this is because the cooling agent is confined within the mould and therefore the temperature may be taken below zero degrees.

The mould may comprise at least one adjustable moulding surface. The adjustable moulding surface may comprise at least one removable insert forming a moulding surface. The or a moulding surface may be textured. The apparatus may have means to reposition the adjustable moulding surface. The at least one adjustable moulding surface may be said oscillating moulding surface.

The apparatus may have means to tilt the mould. In one embodiment the apparatus comprises means to feed reinforcing means into the mould.

In accordance with a third aspect of the present invention there is provided a

plastics profile constructed by the method disclosed herein. The plastics profile may comprise at least one of cellulose fibers, inorganic fibers, foaming agents, stabilizers and additives. The fibers may form between 50% to 60% of the profile. The fibers may have a plurality of different sizes. The profile may comprise at least one of recycled plastics, regranulated plastics, or virgin plastics. The plastics profile may comprises strengthening materials which may comprise filaments and/or fibers and/or webbing material in a continuous form.

The advantage of using recycled plastics is that it can reuse household and industrial waste thereby reducing it disposal in landfill. The use of a foaming agent enables upto 50% density reduction, with corresponding reduction in material costs and weight. The presence of a strengthener enables the profile to be more rigid and increases its load bearing.

By way of example only specific embodiments of the invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a schematic view of a mould for forming a plastics and/or plastics composite profile which is constructed in accordance with one embodiment of the present invention;

Figure 2 is a schematic view of the mould of Figure 1 mounted in a supporting frame;

Figure 3 is schematic sectional view of the mould of Figure 1 illustrating its use in conjunction with a tool head for incorporating a webbing into the profile; and

Figure 4 is a view similar to that of Figure 1 illustrating the positioning of an insert in the mould.

As best illustrated in Figures 1 and 2 a moulding device constructed in accordance with one embodiment of the invention comprises a substantially rectangular moulding tube 2 having an inlet 4 at one end and an outlet 6 at its opposite end. The tube 2 is held in a supporting frame 7. The tube comprises four side walls 8, each in the form of a hollow rectangular plate. Each plate 8 has an inlet 10 at said inlet 4 end of the tube 2 and an outlet 12 at said opposite outlet 6 end of the tube 2. The plate inlet 10 and outlets 12 are connected into a liquid cooling system 14.

Each plate 8 is suspended on a respective linear bearings 16 and has a respective electric motor 18 which operates a cam 20 which contacts the outer surface of its respective plate 8. Each electric motor 18 is connected to a control system (not illustrated). The supporting frame 7 is mounted on runners which enables the inlet 4 of the tube 2 to be offered up to an extruder.

In use a plastics material or plastics composite material is plasticized in an extruder and the hot melted material is fed into the inlet 4 to the tube 2. A cooling liquid is pumped through the hollow plates 8 and the electric motors 18 are operated whereby the cams 20 act on the outer surface of the hollow plates 8 causing them to oscillate. The motion of the plates 8 act to caress the molten material and to move it along the tube 2. The cooling system 14 extracts the heat from the material enabling it to cool and set during its transportation through the tube 2. The set material exits the tube 2 via its outlet 6. The control system enables the speed of each motor 18 to be individually adjusted whereby each plate 8 can be oscillated in a specific sequence and/or speed to enable the creation of the profile within the moulding tube 2 best adapted to the particular materials used for its creation. For example if a foaming agent is

introduced into the plastics material the oscillation of each plate 8 is adjusted to enable the forming profile to hold its shape without distorting the formation of the necessary bubbles.

In a second embodiment of the invention as illustrated in Figure 3, the moulding device is modified to enable the incorporation of webbing straps 22a, 22b within the profile formed. To this end a tool head 24 is provided at the outlet of the extruder 26. The tool head 24 provides a first ramped surface 28a into the inlet 4 to the moulding tube 2 and a second ramped surface 28b, opposite said first ramped surface 28a. The ramped surfaces 28a, 28b reduce the overall height of the inlet 4 and provide a guide surface for the placement of the webbing straps 22a, 22b. A roll of webbing 30a, 30b is provided adjacent each ramped surface 28a, 28b. In use as molten material 32 is fed into the moulding tube 2 it is squeezed through the reduced inlet created by the ramped surfaces 28a, 28b of the tool head 24 and pulls the webbing 22a, 22b into the moulding device from their rolls 30a, 30b. Once the molten material 32 passes through the reduced inlet it expands to fill the moulding tube 2, whilst the webbing straps 22a, 22b remain within the body thereof having been located by the respective ramped surfaces 28a, 28b and kept apart by the plastics material 32. The webbing straps 22a, 22b are fixed within the body of the profile as it sets.

The above described profile formed by the moulding device is solid, however it is to be understood, that a hollow profile could be formed for example by placing a mandrel at the entrance to the moulding device and placing the molten material into the mould about the mandrel. Alternatively further oscillating surfaces could be

provided internally to the moulding device which form the required shaped hollow within the profile. Although the side walls of the moulding device have been described as being rectangular plates, the plates could have other shapes for example more rounded, or have a textured surface. Alternatively, or in addition to, the moulding device may comprise an insert 34, as best illustrated in Figure 4. The insert 34 forming a removable textured surface 36 which can be fastened to at least one of the plates 8 to provide a template which enables a textured surface to be formed in the profile.

Although four side walls have been described, any number of side walls could be provided at least one of which can be moved to enable the forming profile to be transported along the mould. Also the side plates could be adjustable in that they can be moved closer together, or further apart, or tilted to enable different sizes and shapes of profile to be made with the same mould.

Although a fixed cooling system has been described, the system could be modified to provide different degrees of cooling along the length of the moulding tube. To this end the plates could comprise a plurality of internal chambers, whereby the chamber nearest the tube inlet can be kept warmer than subsequent chambers downstream thereof. This enables the molten material to remain molten at its entry into the tube and to enter into all corners and shapes of the interior of the moulding tube before cooling fully commences. The increased temperature at the entrance could be controlled using heating means, or the chambers could each have a separate supply with the temperature of each supply individually controlled, or cooled liquid could enter the system from the outlet end and work its way upstream, the cooling

liquid becoming warmer as it approaches the inlet to the tube as it absorbs heat from

the molten material. While the invention has been described in detail in terms of specific embodiments thereof, it will be apparent that various changes and modifications can be made therein by one skilled in the art without departing from the scope thereof.

Claims

1. A method for the continuous manufacture of a plastics profile comprising the steps of plasticizing a plastics material, feeding said plasticized plastics material into an inlet of a moulding device said moulding device having at least one moulding surface, oscillating at least one of said moulding surfaces, extracting heat from the plasticized material in order to set the plastics, and removing said set plastics profile from the moulding device, wherein at least one of said moulding surfaces is adjustable and the method includes the additional step of adjusting said adjustable moulding surface to enable a different size and/or shape of profile to be made by the mould.

2. A method according to claim 1, wherein said adjustable moulding surface is also a said oscillating moulding surface.

3. A method according to claim 1 or 2, wherein the moulding device comprises at least two moulding surfaces, the method comprising the step of operating the oscillation of each moulding surface in at least one of the following manners: to operate at the same speed, to operate at different speeds, to operate in a synchronous manner, and to operate in a sequential manner.

4. A method according to claim 1, 2 or 3, comprising the step of extracting less heat from the plasticized material in the region of the inlet to the moulding device.

5. A method according to any one of claims 1 to 4, comprising the step of guiding at least one reinforcing material into the plastics material.

6. A plastics profile according to claim 5, wherein the at least one reinforcing material comprises at least one of filaments and/or fibers and/or webbing material in a continuous form.

7. A method according to any one of the preceding claims, comprising the step of adding at least one foaming agent into the plasticized plastics material.

8. A method according to any one of the preceding claims, comprising the step of adding at least one of cellulosic fibers and inorganic fibres into the plasticized material.

9. A method according to claim 8, wherein the fibers form between 50% to 60% of the profile.

10. A method according to claim 8 or 9, wherein the fibers have a plurality of different sizes.

11. A method according any one of the preceding claims, wherein said plastics comprises at least one of recycled plastics, regranulated plastics, or virgin plastics.

12. A method according to any one of the preceding claims comprising the step of controlling the volume and/or speed that the plasticized material is fed into and/or through the moulding device. .

13. An apparatus for the continuous moulding of a plastics profile comprising a mould having an inlet and an outlet, the mould having at least one oscillating moulding surface, and at least one adjustable moulding surface adapted to be adjusted to enable different sizes and/or shapes of profiles to be made by the mould.

14. An apparatus according to claim 13, comprising a control means to adjust the rate of oscillation of the or each oscillating moulding surface.

15. An apparatus according to claim 13 or 14, wherein the mould has, at least two oscillating moulding surfaces.

16. An apparatus according to claim 13 or 14, wherein the mould has four oscillating moulding surfaces.

17. An apparatus according to claim 14, 15 or 16, wherein the control means operates the oscillating moulding surfaces in a sequential manner.

18. An apparatus according to any one of claims 13 to 17, wherein the mould has integral cooling means.

19. An apparatus according to any one of claims 13 to 18, comprising means to control the extraction of heat from the profile during moulding.

20. An apparatus according to any one of claims 13 to 19 comprising means to graduate the degree of cooling throughout the mould.

21. An apparatus according to claim 20, wherein the means to graduate is adapted to extract the least amount of heat in the region of the inlet to the mould.

22. An apparatus according to any one of claims 17 to 21, wherein the cooling means comprises at least one cooling liquid, the mould having at least one internal cavity through which the liquid is passed.

23. An apparatus according to any one of claims 13 to 22, comprising a heater at the inlet to the mould.

24. An apparatus according to any one of claims 13 to 23, wherein the adjustable moulding surface comprises at least one removable insert forming a moulding surface.

25. An apparatus according to any one of claims 13 to 24, comprising means to reposition the adjustable moulding surface.

26. An apparatus according to any one of claims 13 to 25, wherein the at least one adjustable moulding surface is said oscillating moulding surface.

27. An apparatus according to any one of claims 13 to 26, wherein the or a moulding surface may be textured.

28. An apparatus according to any one of claims 13 to 27, wherein the apparatus has means to tilt the mould.

29. An apparatus according to any one of claims 13 to 28, comprising at least one cam which operates a respective moulding surface.

30. An apparatus according to any one of claims 13 to 29, comprising means to feed reinforcing means into the mould.

31. A method for the continuous manufacture of a plastics profile substantially as described herein with reference to the accompanying drawings.

32. An apparatus for the continuous manufacture of a plastics profile constructed and adapted to operate substantially as described herein with reference to and as illustrated in the accompanying drawings.