WO2002102567A1

WO2002102567A1 - Moulding method and apparatus

Info

Publication number: WO2002102567A1
Application number: PCT/AU2002/000809
Authority: WO
Inventors: Nicholas William John Cherry; Edward Ireneusz Kosior
Original assignee: P.B.T. (Nsw) Pty Ltd
Priority date: 2001-06-20
Filing date: 2002-06-20
Publication date: 2002-12-27
Also published as: HK1070859A1; CN1541156A; AUPR583701A0; CN1308129C

Abstract

A rotational mould and method of using the rotational mould is described for producing a pipe or similar product. The mould is provided with a distribution means in the form of a spiral or helical ridge, rim or raised section located spirally or helically on the inner surface of the mould to assist in directing the movement of material added to the mould, so as to provide a uniform distribution of the material in the mould in accordance with the desired end products required of the finished product. The distribution means can take a number of different forms as needed to transport or convey and distribute the material throughout the mould.

Description

Moulding Method and Apparatus

The present invention relates generally to methods and apparatus for forming articles and in particular to moulding articles using a mould. More particularly, the present invention relates to the use of a one piece mould to mould articles, particularly articles which are substantially symmetrical, especially about their central axes. Even more particularly, the present invention relates to apparatus and methods of rotational moulding of substantially cylindrical objects such as pipes, hoses, tubes, conduits, and the like. The present invention finds particular application in improvements to rotational moulding methods and apparatus by providing the mould with a distribution means for improving the distribution of material admitted to the mould so that the finished article has predetermined properties or characteristics. The distribution means may be moveable with respect to the mould or may be moveable in accordance with movement of the mould to distribute material within the mould in a predetermined manner. In one form the distribution means is a spiral or helix provided internally within the mould, such as for example, on the inner wall of the mould to more or less uniformly distribute incoming material around the mould.

Although the present invention will be described with particular reference to one form of the moulding apparatus and process of the present invention, it is to be noted that the scope of the present invention is not restricted to the described embodiment but rather the scope of the present invention is more extensive so as to include other methods and apparatus for forming objects and the use of the method and apparatus in other applications than specifically described.

Rotational moulding has been used in the past to produce a number of objects, particularly cylindrical objects or objects which are symmetrical about their central axes. In the past, material is introduced into the mould, the mould rotated and the material is solidified to form the object or article. However, in previously available methods and apparatus problems have arisen regarding the distribution of material within the mould. In many instances, the material is not uniformly distributed. In situations where the object or article is to be made from two or more different materials it has been difficult to distribute both or all of the materials uniformly in accordance with the final requirements of the object or article so that it has the desired properties or characteristics. Accordingly, there is a need to provide better distribution of material introduced into the mould so that the desired properties or characteristics of the end product are more uniform. Therefore, it is an aim of the present invention to provide a method and apparatus for rotational moulding of objects or articles having an improved way of distributing the material or materials introduced into the mould. Further, in the past, the manufacture of pipes, tubes, hoses and the like usually involved using continuous processing equipment such as extrusion equipment and extruders. Small bore or small diameter pipes and the like made from extrusion processes have the disadvantage that the processing is continuous so that the pipes were made in continuous length. The continuous length of extrusion then had to be cut to size which requires an extra processing step which is costly of time. effort and expense. Additionally, there was a wastage of material during the start up of the extrusion machinery until the correct operating parameters had been established, usually by trial and error, since the extrusions up until this stage had to be discarded.

Sometimes further treatment of the ends of the hoses or pipes was required where the continuous extrusions had been cut, such as for example, to trim or neaten the ends of the hoses or pipes or to add suitable fittings or couplings on the end of the hoses or pipes.

When making relatively larger diameter pipes, such as for example, pipes having a diameter in excess of 200 mm the use of extrusion equipment was expensive since the pipe could be made in continuous length only which added considerably to the cost of materials and inventory of pipes, particularly where only a small number of pipes of selected lengths were required. Thus, there is a need to avoid the expense of providing expensive tooling and extrusion machinery in the manufacture of both small diameter and large diameter pipes, and the need to avoid wastage of raw materials.

Therefore, it is an aim of the present invention to provide a method and apparatus for rotational moulding of objects or articles of varying diameters in discrete lengths using a minimum of material in a relatively inexpensive mould.

Another problem of extrusion moulding either relatively small diameter pipes or relatively large diameter pipes is the inability of being able to produce extrusions of continuous length with pipe fittings of different shapes, such as joining flanges and the like. Rotational moulding of pipes and the like allowed fittings such as flanges, bell mouthed ends and the like to be moulded simultaneously with forming the pipe thereby eliminating post processing of the continuous lengths that was necessary when the pipes were extruded in continuous length in order to facilitate joining and sealing of discrete lengths of pipes together, such as for example, by providing fittings specifically for joining the two ends of the cut extruded pipe. Thus, there is a need to be able to provide fittings and different shapes when forming the pipes using rotational moulding and the like. Therefore, it is an aim of the present invention to provide a method and apparatus for rotational moulding of objects or articles having specific fittings or features moulded into either the end or wall or both of the object or article when the article or object is being moulded.

According to a first aspect of the present invention, there is provided an apparatus for forming an article including a forming means for use in forming the general shape of the article, an introduction means for introducing into the forming means material to be formed into the article in the forming means, and a distribution means for distributing the material introduced into the forming means throughout the forming means to assist in forming the general shape of the article wherein movement of the forming means and/or the distribution means distributes the material within the forming means in a preselected manner so that the article can be formed with predetermined properties or characteristics.

According to another aspect of the present invention there is provided a method of forming an article including the steps of providing a material for forming the article, introducing the material into the forming means by the use of an introduction means, providing a distribution means, moving the forming means and/or the distribution means to distribute material introduced into the forming means in accordance with the predetermined properties or characteristics required of the article, and using the forming means to form the article.

Typically, the object, item, article or the like, is a symmetrical object or substantially symmetrical object. More typically, the article is symmetrical or substantially symmetrical about its central axis. Even more typically, the object is a hollow cylindrical object. Even more typically, the article is a pipe, hose, conduit, tube or other substantially cylindrical hollow object or item.

Typically, the material for forming the object is either recycled material or virgin material or a mixture of both. More typically, the material is a thermoplastic material, preferably a recycled thermoplastic material. Even more typically, the material includes one, two, three, four or more different materials which are introduced into the apparatus of the present invention at different times depending upon the final properties of the object which are required.

Typically, the material is polyethylene. More typically, the material is low density polyethylene (LDPE) , linear low density polyethylene (LLDPE) , high density polyethylene (HDPE) , ethylene-vinyl acetate (EVA), polypropylene, acrylonitrile butadiene styrene (ABS) or the like.

Typically, the material is high density polyethylene (HDPE) or medium density polyethylene (MDPE) .

Typically, the material has a density of from about 950 to 960 kg/m³ and a melt flow rate (2.16 kg at 190°C) of 0.1 to 4 g/10 minutes, preferably 0.5 to 1.0 g/10 minutes. Typically, the material can be in a variety of different forms including free-flowing forms, such as powder, pellet, flake, granules, particles, beads, buttons, needles, scrapings, swarf or the like.

Typically, the material being used to form the object is used in a free-flowing form. A preferred form of the material is in a flat flake form that is about 0.5 to 1.5 mm thick and from about 5 to about 20 mm in length and width. A particularly preferred material is obtained from shredded HDPE bottles, such as for example, used milk containers or the like.

Typically, the thermoplastic materials can be applied in a wide number of ways to make pipes, hoses, conduits, tubes or the like with a corresponding wide range of properties. The plastics can be used singly, such as for example, to give a monolithic layer, of more or less uniform properties throughout the wall thickness of the article, sequentially in order to provide a structured layer effect in which different layers of materials forming the pipe or hose wall have different properties, or as a combined mixture in order to provide controlled dispersions of the different component materials or layered structures in the event that the melting points and particle size of the components have been carefully selected.

Typically, the method and apparatus of the present invention are very tolerant of contaminants. More typically, if any contaminants are present the article can be formed in such a manner that the contaminants are located away from the critical outer surface section and closer to the less critical inner surface of the pipe or hose Even more typically, the contaminants include moisture, other resins or plastics material, dirt, oils, grease, dust, foreign particles or the like.

Typically, the forming means is a mould. More typically, the mould is a one piece mould, typically a cylindrical mould having a one piece wall structure. More typically, the cylindrical mould is provided with one or both ends open. Even more typically, any surface features of the pipe can be formed in the wall of the mould, such as for example, the presence of inspection ports, cover plates, junctions, take-offs, flanges, bell mouths, or other fittings or the like.

Additionally, the method includes the step of heating the mould, including heating the external surface of the mould or the internal surface of the mould or both surfaces either sequentially or simultaneously.

Typically, the method includes the additional step of cooling the mould and/or article. More typically, cooling is applied either externally, internally or both, and may be sequentially or simultaneously. Even more typically, cooling is by the use of air, water, air/water mixtures including sprays, mists or the like. Even more typically, the cooling is achieved by the use of coolants which can be applied internally, externally or both internally and externally. Typically, the apparatus of the present invention uses single or multiple barrels in arrangement that allows the barrels to be charged and rotated during a heating and cooling cycle. A particularly preferred embodiment uses one or two barrels per manufacturing unit . Typically, the distribution means is provided on the internal wall of the mould. More typically, the distribution means rotates in accordance with rotation of the mould. Even more typically, the distribution means is fixed to the inner wall of the mould. Even more typically, the distribution means extends helically or spirally along the inner wall of the mould. A particularly preferred form of the distribution means is a spiral welded steel rim, rib, wire, ribbon or the like welded to the inner wall of the mould.

Typically, the distribution means is the weld joining adjacent edges of a spirally or helically wound ribbon or strip of metal. More typically, the weld is located on the outside of the mould as well as on the inside. More typically, the weld is up to about 10 mm in width, preferably 1 to 5 mm, more preferably 2 to 3 mm in width. Even more typically, the helix angle can be any angle, preferably between about 20 to 90°, more preferably between 45 and 85°, most preferably between 60 to 80°. Typically, the weld is up to about 10 mm in thickness, preferably up to about 5 mm in thickness, more preferably from 1 to 2 mm thick.

Typically, the use of a barrel made from a spirally wound ribbon of steel welded together in edge to edge relationship is particularly advantageous since it allows the slightly raised inner spiral surface to be used to distribute the flake away from, or towards, the point of material introduction. The direction of movement of the material introduced into the mould is controlled by the direction of rotation of the barrel relative to the spiral direction of the distribution means.

Typically, the barrel design incorporates an aperture at one end that allows the barrel to be rotated and for the material to be introduced to the cavity at the same time. Typically, the introduction means is one or both open ends of the barrel or mould. Even more typically, the end or ends of the mould are provided with a delivery hopper or the like for admitting selected amounts of materials into the mould.

Typically, heat is applied to the barrel to convert the thermoplastic material to a fluid material such as a liquid state where it can flow and consolidate between flakes of plastic can occur. Heating can be accomplished by various techniques, such as for example, by the use of gas burners directed at the length of the barrel surface. Typically, the mould, preferably the barrels of the mould, may be internally coated with a mould release agent, such as for example, a hydrocarbon oil, a vegetable oil or silicone oil or the like.

Typically, the method of the present invention can control the uniform distribution and density of the wall section of the pipe or similar by controlling the amounts loaded into the moulds of the different materials, the sequence of speeds of rotation of the mould and the material (s) therein, the duration of heating, and the temperature achieved at each particular stage. More typically, the elimination of voids between the particles can be controlled by the precise rotational speed sequence and temperature of the wall material of the pipe. This is achieved by designing the equipment to allow the measurement of internal air temperature and adjust operating conditions accordingly.

Typically, the density of the wall section and the elimination of the voids in the walls associated with rotational moulding can be controlled by the design of the equipment to allow pressurisation of the wall section by the gases and vapour exerting pressure of the material against the internal wall of the mould while the material is molten and in a formable state so as to achieve a more compacted product with less risk of the presence of voids and the like.

Typically, the cooling of the pipe is accelerated over conventional cooling rates by the introduction of coolants that have a greater heat capacity than air alone, ie., air is mixed with water mist or other materials. This is done with precise control of the cooling on the outside and the inside of the mould to avoid the formation of internal voids created by contraction of the molten plastics as it solidifies. The introduction of cooling pulses to the inside of the mould can accelerate the cooling without the formation of voids.

Typically, the cycle rate of the process strongly depends on the careful estimation of the cooling time to allow the ejection of properly solidified thermoplastic material. The measurement of internal air temperature along with the audio-detection of shrinkage of the diameter of the pipe allow the minimum cooling time to be determined and allow the mould to be freed for the next cycle, thereby increasing the rate of production and reducing the cost.

Typically, the heat is applied in an insulated enclosure that minimises the heat losses involved during heating part of the cycle. The rotation of the pipe is controlled by a variable speed motor that allows the rotational speed to be varied during the manufacturing process. The speed is set to slow rates during charging of the mould with plastics material and is increased to achieve a state where the material is "raining" while the distribution of the plastic flake is being controlled. The "raining" stage describes the process where flakes of plastic rotate with the pipe to the apex of the pipe and fall under gravity away from the wall back onto the surface below. This allows the flakes to be uniformly applied as a coating over the metal surface. Once a uniform distribution is obtained, the speed is increased to stop the particles of plastic from "raining" and the higher centripetal forces hold the material in place. At this stage the heating of the barrel is commenced. This allows the plastic to soften and melt . The higher centripetal forces are used to consolidate the flakes and speed up the melting process by excluding air bubbles and potential defects.

Typically, the pipe is cooled internally and externally after all of the plastic has been melted while the barrel is being rotated. The internal cooling is with dry or moist air that is blown into a special aperture in one end of the barrel during rotation. The external cooling is with dry air or water sprays. The cooling is balanced to ensure that the external cooling has the greatest control in solidification of the molten plastic. Too fast internal cooling causes void defects (due to the contraction of the molten plastic) to occur in the middle of the cross-section of the pipe.

Typically, once the pipe is cooled, the pipe is ready to be demoulded. The design of an integral flange or bell section at one end of the pipe allows not only the post-moulding joining of the pipe, but also provides automatic demoulding of the pipe from the mould. This is caused by the volumetric contraction of the molten plastic causing a 0.1 to 9% shrinkage, preferably a 0.5 to 3.0% shrinkage, and more preferably a 0.5 to 1.0% shrinkage, in linear dimensions. The positioning of the flange at one end of the pipe causes the free end of the pipe to contract towards the flange. The contraction of the diameter causes the pipe to debond from the mould surface. These two actions during cooling cause the pipe to automatically debond and be ready for removal from the mould. Typically, the inner wall of the mould is tapered to assist in the demoulding of the pipe from the mould

Typically, the modification of the design of the barrel allows the in situ moulding of specific flanges and bell-mouthed end sections to the pipe eliminating post processing that is necessary on extruded pipe to facilitate joining and sealing of lengths of pipe. Typically, heat is applied to the barrel to convert the thermoplastic resin to a liquid state where it can flow and consolidation between flakes of plastic can occur. This heat can be applied by various techniques, e.g., by the use of gas burners directed at the length of the barrel surface. Heat is applied to the barrel after the material has been charged and the barrel is being rotated to give uniform surface heating as well as control of removal of voids and pipe thickness. The temperature is raised to above the melting point of the plastic resin. In the case of HDPE the temperature of the inside of the pipe could be raised above 140°C and could be as high as

250°C. The present invention will now be described by way of a non-limiting example with reference to a preferred embodiment of the invention. The description is with reference to the accompanying drawings in which:

Figure 1 is a side perspective view of one form of the mould for forming a pipe in accordance with the method and apparatus of the present invention in close proximity to an end disc for closing one end of the mould; Figure 2 is a cross-sectional view of Figure 1 showing the mould part filled with flake material;

Figure 3 is a cross-sectional view of the mould when being rotated showing the flake formed into the wall of a pipe against the inner wall of the mould; Figure 4 is a perspective view of the mould shown in Figure 1 showing the pipe in the process of being removed from the mould;

Figure 5 is a partial cross-sectional view of one type of pipe formed using the method and apparatus of the present invention;

Figure 6 is a cross-sectional view of the mould and pipe showing the use of a heating or cooling means internally and externally of the mould and pipe;

Figure 7 is a cross-sectional view of a laminated form of the pipe formed using the method and apparatus of the present invention;

Figure 8 is a closer view of one form of the mould for forming a flange at one end of the pipe.

Figure 9 is a perspective view of one form of the pipe having a flange; and

Figure 10 is a schematic cross-section view of one form of the distribution means in the form of a spiral or helical weld around the periphery of the mould.

In Figures 1 to 7 of the drawings there is shown one embodiment of the forming means of the present invention which is in the form of a generally cylindrical mould generally denoted as 2, having a first opening 4 located at or towards one end of mould 2 and a second opening 6 located at or towards the other end of mould 2, thus forming an open ended one piece cylindrical mould in which a pipe, generally denoted as 10, or similar object can be formed. Opening 6 can be optionally closed by a removable cover 8, disc and plate or similar in use. Mould 2 can be filled through opening 6. Opening 6 can form an introduction means for allowing material to be moulded in mould 2 to be introduced into mould 2. Other forms of the introduction are possible and can include automatic feeding of the moulds.

Mould 2 can be made of any good thermal conducting material, such as for example, metal, such as, iron, steel or metallic alloy, or other suitable synthetic material, including combinations of different materials. The mould is preferably made from a material that is heat resistant and a good conductor of heat and is preferably made from steel. The barrel can be made with positive taper or no taper at all. The removal of the pipe from the barrel is facilitated by the process that allows the plastics material to shrink by approximately 0.5 to 1% in linear dimensions.

With particular reference to Figure 10, there is shown one form of the distribution means . This form of the distribution means 16 in the form of a spiral 12 or helical ridge, rim or similar and is provided internally of mould 2. In one form mould 2 is made from a strip or ribbon of suitable metal 14 spirally wound so as to be spiral welded in edge to edge relationship or in edge to edge overlapping relationship to form mould 2. The weld line or similar 16 traces a spiral or helical pathway on the inside surface of mould 2. Optionally, or additionally, there is a weld line 18 on the outside surface of mould 2. The use of a mould made from spiral welded steel is particularly advantageous since it allows the slightly raised inner spiral surface along one spiral edge to be used to distribute the material away from, or towards, the point of introduction of the plastics material. The direction of movement of the plastics material is controlled by the direction of rotation of mould 2 relative to the spiral direction formed by the spiral on the inner wall of mould 2. In another embodiment, the inside surface, and optionally the outside surface, is formed by having a strip of metal ribbon welded in partially nested overlapping relationship so that each segment of the spirally wound inner surface is tapered or angled to assist in directing the movement of the plastics material throughout the mould. Figures 1 and 2 show mould 2 being filled to a desired level 14 with granulated plastics material 16. In one form the plastics material is generally shredded flakes of plastics formed by comminuting bottles, caps and other containers of recycled plastics or similar materials. The plastics material 16 need not be cleaned prior to being introduced to mould 2 to remove liquid residues or have glued paper labels removed or small amounts of other contaminants removed since reasonable amounts of contaminants can be tolerated in the material being moulded.

The material can be of the same type or a mixture of various types, grades or compositions of plastics or other materials. A particularly preferred material is a material in flake form which is about 0.5 to 1.5 mm in thickness and from about 5 to about 20 mm in length and width. It is to be noted that wide variations in these sizes are permissible.

Figure 2 shows mould 2 at the commencement of being rotated slowly in the direction as indicated by its arrow A along lengthwise extending central axis 18 in which a layer of the plastics material 16 is collected in the lower portion of mould 2 as shown in Figure 2. As mould 2 continues to rotate slowly the plastics material 16 is also rotated so as to be forced up one side of the internal wall of the mould to fall back again as "rain" inside the mould against the inner wall of the mould to cover the entire wall of the mould The "raining" of the material will continue for as long as the mould is rotated at a relatively slow speed in order to uniformly distribute the material more or less uniformly or evenly around the internal wall of the mould The "raining" process can be maintained for as long as required. As the speed of rotation of mould 2 is increased the centripetal force on the flakes of material will increase to cause the material to accumulate in an even thickness against the inner wall of the mould. The speed of rotation of mould 2 will hold the material in place against the inner wall of the mould.

Typically, the rotation of the pipe is controlled by a variable speed motor that allows the rotational speed to be varied during the manufacturing process. The speed is set to slow rates during charging of the material into the mould and is then increased to achieve a state where the material is "raining" while the distribution of the plastic flake is being controlled. The "raining" stage describes the process where flakes of plastic rotate with the pipe to the apex of the pipe and fall under gravity away from the wall back onto the surface below. This allows the flakes to be uniformly applied as a coating over the metal surface. Once a uniform distribution is obtained, the speed is increased to stop the particles of plastic from "raining" and the higher centrifugal forces hold the material in place. At this stage the heating of the barrel is commenced. This allows the plastic to soften and melt. The higher centrifugal forces are used to consolidate the flakes and speed up the melting process by excluding air bubbles and potential defects.

In some embodiments of the apparatus of the present invention a burner or similar is provided externally of outer wall of mould 2 to apply heat to the wall of mould 2 to heat the material therein to soften and melt the material . One form of the burner is shown in Figure 6. The source of heat is not limited to having externally arranged burner but rather other arrangements for applying heat to mould 2 can be used, such as for example, by including heating within mould 2. Another form of heating is to provide electrical heating within the walls of mould 2.

In the embodiment shown in Figure 6 a gas manifold 20 is arranged to extend the length of mould 2. Burners 22 are located at spaced apart intervals over the length of manifold 20. Burners 22 allow combustible gases to be ignited to heat mould 2. Optionally, a further manifold 24 having spaced apart burners 26 can be provided inside mould 2 to provide additional heat to mould 2 and/or to allow a smoother final internal finish of the pipe being formed in the mould.

Operation of the apparatus of the present invention will now be described.

Suitable shredded recycled plastics material 16 is added to the inside of mould 2 through open end 6. In one embodiment a sufficient amount of plastic material 16 may be added to the inside of mould 2 before rotation commences whereas in another embodiment mould 2 commences rotation before any material is added. With mould 2 rotating material is added through the open end 6 of mould 2 and distributed along the length of mould 2 by the distribution means in the form of the internal spiral 12 or helix provided on the inner wall of mould 2. When sufficient material is added to the inside of mould 2 optionally cover 8 is located in place so that the mould 2 can continue to rotate at a relatively slow speed so as to "rain" material onto the inner wall to build up a substantially uniform layer of plastics material.

When there is a substantially uniform layer or covering of plastics material 16 on the inside wall of the mould the mould is rotated relatively more quickly so as to further distribute the material using the effect of centripetal motion or force. Heat is then applied to the mould either externally, internally or a combination of both.

Under the effect of increased speed of rotation and heat the plastics material melts and flows so as to form a uniform mixture of uniform thickness which is substantially homogenous. After the pipe has been formed heating is stopped and mould 2 is allowed to cool whilst rotating to ensure the shape of the pipe is retained. The plastics material will harden and shrink slightly during cooling. Typically, the amount of shrinkage is about 0.5 to 3% in linear dimensions, typically, 0.5 to 1% shrinkage in linear dimensions.

If necessary or desirable, cooling can be applied to the mould. Such cooling can be applied either externally, internally or both externally and internally. The cooling can be by air or fan assisted air or by air mixed with water such as in the form of a mist, spray or similar, or cooling can be accomplished by using a coolant. In one form the outside surface of mould 2 is located in a water bath or coolant bath whilst rotating so as to cool the pipe from the outside through the wall of mould 2 as the mould rotates . It is preferred that cooling be applied evenly or from both sides so as to have even cooling throughout the thickness of the pipe to prevent the pipe from delaminating or separating or forming voids during the cooling step.

If fitted, the cover at the end of the mould can be removed and the formed pipe can be readily removed from mould 2 owing to the shrinkage factor of the pipe. No separation of mould parts or other removal techniques are required which simplifies the overall production method as well as contributing substantially to reducing labour costs .

The separate loading of different plastics materials will allow concentric layers to be centrifugally formed. Thus a recycled material could be loaded first, followed by virgin material. A twin layer, pipe or similar will form as shown in Figure 7 with the recyc.7?="^:', layer 26 located on the outside of the pipe and the layer of virgin material 28 located on the inside. Such a construction will allow the formed pipe to be used for human grade purposes rather than being restricted for irrigation purposes, since the flow through the pipe will be in control with the virgin material only. If there was no inner layer of fresh or virgin material, the pipe could only be used for non human purposes such as irrigation.

The method and apparatus of the present invention allows various layering techniques to be used to form pipes having different layers. One method of layering different material types is to shred the material to be formed on the outside of the pipe into smaller more granular type flakes than the material to be formed as the inner layer. The mould can then be loaded with both sizes of flakes and the rotation speed of the mould increased until the granular flakes make their way through the material to form into a cylindrical shape on the inner surface of the mould to form an outer layer of the pipe whilst the larger flakes continue to tumble to form an inner layer of the pipe. As the rotational speed is increased the larger flakes form a concentric layer inside the more granular flakes. This layering technique can be assisted by increasing the air turbulence inside the mould. Such turbulence can be created by stationary or counter rotating vehicles inside the mould or air blown into the mould. The turbulence tends to dislodge the flakes but not the granular material.

Another method of layering is to set the temperature to melt one particular type of lower melting point plastics material first. A molten layer will be formed on the inner surface of the mould. As the temperature is increased a second skin of high melting point plastic will form the inner surface of the pipe. Thus, two discrete layers of different material can form. A still further method of layering is to load the mould with the first charge of plastics material and start the process. A second charge of different material is then added whilst the mould is still spinning. Depending on the pipe structure required and the properties of the individual materials the second charge may be added before or after the first charge has melted. If required, more than one additional charge could be added. Additionally, it is possible to retain pipes with three, four or more layers of different materials or of combinations of materials.

In Figure 8 a variation of the mould 2 shown in Figures 1 to 3 is illustrated. In this invention, cylindrical mould 2 has a flange 32 extending radially outwardly at end 34. An end cap 36 has an annular flange 38 extending radially outwardly around the cirumference of the end cap of the same or similar diameter as flange 32. Flange 38 mates with flange 32 to form an extension to the end of mould 2. A circular recess 40 extends through flange 38 into a blind bore in end cap 36. The diameter of circular recess 40 is greater than the outer diameter of mould 42.

Pipe 42 is formed in the mould having the flanged end and end cap in the same manner described with reference to Figures 1 to 3. The increased diameter of the recess 40 will allow flange 44 of pipe 42 to be integrally formed on pipe 42 as shown in Figure 9 simultaneously with the remainder of pipe 42. Flange 44 will be formed of solid plastics material and will be very strong as it is formed integrally with pipe 42. Similar pipes 42, all having flanged ends, can be butted toge^b^r and clamped to provide a pipe string or attached to a flanged fitting of another piece of equipment, such as for example, the outlet of a pump in an irrigation system.

If flanges are required at both ends of pipe 42, mould 2 could be formed from two or more components joined during moulding. When moulding is complete the mould components can be separated to allow ready removal of the formed pipe 42. Flanges 32, 34 can be omitted if the inside of mould 2 is stepped at end 34. Alternatively, the end of pipe 42 can be formed with an enlarged circular section such as an enlarged bell mouth section.

The method and apparatus of the present invention allows a useful product to be manufactured at a relatively low price with very little pretreatment or preconditioning or preprocessing or preparation of the raw materials. The process is extremely tolerant of variations in the quality of the raw materials and low grade plastics material may be used.

If desired, virgin plastics material may be used or incorporated into the process either as part of the recycled plastics material or as separate layers.

Chemical additives may also be readily added to the charge of raw materials.

Advantages of the present invention include the following. The methods and processes of the present invention extend and improve the concept of rotational moulding which is typically used for the discontinuous moulding of discrete objects such as fully enclosed hollow objects such as tanks and the like to the manufacture of pipes and tubes that are usually made using continuous processing equipment such as extruders. This has the advantage of reducing the minimum run length and reducing the amount of start up scrap product avoiding expensive tooling and extrusion machinery and hence, dramatically reducing the cost of production of pipes, particularly pipes having large diameters of the order of greater than 200 mm. Exact numbers of lengths of pipes can be made by the process of the present invention allowing considerable savings in materials and inventory of pipes. Pipes can be made to selected lengths without further processing ready for transportation, such as for example, without the need to cut pipes to the required lengths.

A wide range of different materials can be used in the production of pipes and the like including low grade materials, contaminated materials and mixtures of different materials.

The process allows the in situ moulding of specific features in the pipes such as inspection ports, junctions, specific flanges and bell-mouthed end sections of the pipe which eliminates post processing which is necessary on extruded pipe to facilitate joining and sealing of length of pipe. As extrusion results in the production of continuous lengths of pipe there is no opportunity for forming the pipes with integral fittings .

The described arrangement has been advanced by explanation and many modifications may be made without departing from the spirit and scope of the invention which includes every novel feature and novel combination of features herein disclosed.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope .

Claims

CLAIMS :

1. An apparatus for forming an article, including: a forming means for use in forming the general shape of the article; an introduction means for introducing into the forming means material to be formed into the article in the forming means; and a distribution means for distributing the material introduced into the forming means throughout the forming means to assist in forming the general shape of the article, wherein movement of the forming means and/or the distribution means distributes the material within the forming means in a preselected manner so that the article can be formed with predetermined properties or characteristics .

2. A method of forming an article, including the steps of: providing a material for forming the article; introducing the material into a forming means using an introduction means; operating the forming means and providing a distribution means for distributing the material throughout the forming means; moving the forming means and/or the distribution means to distribute material introduced into the forming means in a preselected manner so that the article can be formed; and using the forming means to form the article.

3. A method or apparatus according to any preceding claim, characterised in that the article is a symmetrical article or is substantially symmetrical.

4. A method or apparatus according to any preceding claim, characterised in that the article is symmetrical or substantially symmetrical about its central axis.

5. A method or apparatus according to any preceding claim, characterised in that the object is a hollow cylindrical object.

6. A method or apparatus according to any preceding claim, characterised in that the article is a pipe, hose, conduit, tube or other substantially cylindrical hollow object.

7. A method or apparatus according to any preceding claim, characterised in that the material for forming the object is recycled material, virgin material, fresh material or mixtures thereof.

8. A method or apparatus according to any preceding claim, characterised in that the material is a thermoplastic material, preferably a recycled thermoplastic material.

9. A method or apparatus according to any preceding claim, characterised in that the material includes one, two, three, four or more different materials, which are introduced into the apparatus at the same or at different times, depending upon the final properties and/or structure of the article.

10. A method or apparatus according to any preceding claim, characterised in that the material is polyethylene, including low density polyethylene (LDPE) , linear low density polyethylene (LLDPE) , medium density polyethylene (MDPE) , high density polyethylene (HDPE), ethylene-vinyl acetate (EVA), polypropylene (PP) , acrylonitrile butadiene styrene (ABS) including combinations thereof or the like.

11. A method or apparatus according to any preceding claim, characterised in that the material is a mixture of high density polyethylene and medium density polyethylene.

12. A method or apparatus according to any preceding claim, characterised in that the density of the material is from about 950 to 960 kg/m³, and has a melt flow rate (2.16 kg at 190°C) of 0.1 to 4g per 10 minutes, preferably 0.5 to l.Og per 10 minutes.

13. A method or apparatus according to any preceding claim, characterised in that the material is in a free flowing form, including powder, pellets, flakes, granules, particles, beads, buttons, needles, scrapings, swarf or the like.

14. A method or apparatus according to any preceding claim, characterised in that the material is in the form of a flat flake that is about 0.5 to 1.5 mm thick and from about 5 to about 20 mm in length and width.

15. A method or apparatus according to any preceding claim, characterised in that the material is obtained from shredded HDPE bottles, including used milk bottles.

16. A method or apparatus according to any preceding claim, characterised in that the material is a plastics material that can be used singly to provide a monolithic layer of more or less uniform properties throughout the wall thickness of the article, or the plastics material can be used sequentially in order to provide a structured layer effect in which different layers of materials forming the article have different properties, or the plastics material may be a combined mixture of one or more different plastics material in order to provide controlled dispersions of the different plastics materials or layered structures in the event that the melting points and particle size of the components have been carefully selected.

17. A method or apparatus according to any preceding claim, characterised in that the wall of the article is layered, having two or more layers of different materials superimposed on each other.

18. A method or apparatus according to any preceding claim, characterised in that the forming means is a mould, preferably a one piece mould, more preferably, a metal mould.

19. A method or apparatus according to any preceding claim, characterised in that the materials used to make the article are tolerant of contaminants.

20. A method or apparatus according to any preceding claim, characterised in that the cylindrical mould is provided with one or both ends open.

21. A method or apparatus according to any preceding claim, characterised in that the mould for forming the article is provided with a surface or wall feature, such as for example, the presence of inspection ports, cover plates, junctions, take offs, flanges, bell mouths or other fittings, couplings or the like.

22. A method or apparatus according to any preceding claim, characterised in that it further includes the step of heating the mould, including heating the external surface of the mould or the internal surface of the mould, or both surfaces of the mould, either sequentially or simultaneously.

23. A method or apparatus according to any preceding claim, further including the step of cooling the mould and/or article, either externally, internally or both, said cooling being either sequentially or simultaneously applied to the mould to cool the article.

24. A method or apparatus according to any preceding claim, characterised in that the cooling is achieved by the use of air, water, air/water mixtures, including sprays, mists or the like.

25. A method or apparatus according to any preceding claim, characterised in that the cooling step involves the use of coolants which can be applied internally, externally or both internally and externally, and wherein the coolant may be applied sequentially or simultaneously.

26. A method or apparatus according to any preceding claim, characterised in that the forming means is a barrel and in which the barrel is a single or multiple barrel in arrangement that allows the barrels to be charged and rotated during a heating and/or cooling cycle.

27. A method or apparatus according to any preceding claim, characterised in that the distribution means is provided on the internal wall of the mould or forms the internal wall of the mould.

28. A method or apparatus according to any preceding claim, characterised in that the distribution means rotates in accordance with rotation of the mould or ic capable of independent rotation.

29. A method or apparatus according to any preceding claim, characterised in that the distribution means is fixed to the inner wall of the mould or forms part of the inner wall of the mould.

30. A method or apparatus according to any preceding claim, characterised in that the distribution means extends helically or spirally along the inner wall of the mould.

31. A method or apparatus according to any preceding claim, characterised in that the distribution means is a spirally or helically welded steel rim, rib, wire, ribbon or the like, welded to the inner wall of the mould.

32. A method or apparatus according to any preceding claim, characterised in that the distribution means is a weld joining adjacent edges of a spirally or helically wound ribbon or strip of metal formed into a hollow cylindrical arrangement for forming the mould.

33. A method or apparatus according to any preceding claim, characterised in that the weld is located on the outside of the mould, as well as on the inside of the mould.

34. A method or apparatus according to any preceding claim, characterised in that the weld is up to about 10 mm in width, preferably 1 to 5 mm, more preferably 2 to 3 mm in width.

35. A method or apparatus according to any preceding claim, characterised in that the helical angle of the weld can be at any angle, preferably between about 20 to 90°, more preferably between 45 and 85°, most preferably between 60 and 80°.

36. A method or apparatus according to any preceding claim, characterised in that the barrel is made from a spirally wound ribbon of steel welded together in edge to edge relationship so that, on rotation of the barrel, the material is contacted by the slightly raised inner spiral surface of the barrel to distribute the flake away from, towards, or at the point of material introduction, in accordance with the direction of rotation of the barrel.

37. A method or apparatus according to any preceding claim, characterised in that the barrel is provided with an aperture at one end, allowing the barrel to be rotated and for material to be introduced internally within the barrel through the aperture .

38. A method or apparatus according to any preceding claim, characterised in that the introduction means is one or both open ends of the barrel or mould.

39. A method or apparatus according to any preceding claim, characterised in that the end or ends of the mould are provided with a delivery hopper or the like for admitting selected amounts of material into the mould, including an automated delivery means for delivering material from the hopper to the entrance of the mould.

40. A method or apparatus according to any preceding claim, characterised in that heat is applied to the barrel to convert the thermoplastic material to a fluid material, preferably in a liquid state, so that the fluid material can flow and consolidate between the flakes of plastic, thereby forming a layer of material .

41. A method or apparatus according to any preceding claim, characterised in that the barrels of the mould may be internally coated with a mould release agent, including a hydrocarbon oil, a vegetable oil, a silicon oil or the like.

42. A method or apparatus according to any preceding claim, characterised in that the method can control the uniform distribution and density of the wall sections or layers of the pipe by controlling the amounts loaded into the moulds of the different materials, the sequence of speeds of rotation of the mould, and the material therein, the duration of heating, and the temperature achieved at each particular stage.

43. A method or apparatus according to any preceding claim, involving the elimination of voids between the particles which can be controlled by the precise rotational speed sequence and temperature of the wall material of the pipe.

44. A method or apparatus according to any preceding claim, characterised in that the elimination of voids in the walls associated with rotational moulding can be controlled by allowing pressurisation of the wall section by gases or vapor exerting pressure on the material against the internal wall of the mould while the material is molten and in a formable state, so as to achieve a more compacted product with less risk of the presence of voids or the like.

45. A method or apparatus according to any preceding claim, characterised in that the rotation of the pipes is controlled by a variable speed motor allowing the rotational speed to be varied during the manufacturing process.

46. A method or apparatus according to any preceding claim, characterised in that the speed of rotation of the mould is relatively slow so as to achieve the effect of the plastic flakes raining down upon the material in the barrel followed by increasing the speed of rotation so that the particles no longer rain, but rather, are held in position by centripetal forces where the particles are heated, allowing the plastic material to soften and melt, and the flakes are consolidated.

47. A method or apparatus according to any preceding claim, characterised in that the article is formed with an integral fitting at or towards one end, or along the body of the article, preferably an integral flange or bell- mouth section at one end of the pipe, allowing two or more pipes to be joined together.

48. A method or apparatus according to any preceding claim, characterised in that the presence of the fitting at or towards one end assists in the moulding of the pipe from the mould.

49. A method or apparatus according to any preceding claim, characterised in that the inner wall of the mould is tapered to assist in the moulding of the pipe from the mould.

50. A method or apparatus according to any preceding claim, characterised in that the forming means is an open ended one piece cylindrical mould.

51. A method or apparatus according to any preceding claim, characterised in that the mould is provided with a removable cover, disc, end plate or the like.

52. A method or apparatus according to any preceding claim, characterised in that the introduction means is formed from a strip or ribbon of metal welded in edge to edge overlapping relationship.

53. A method or apparatus according to any preceding claim, characterised in that the mould is formed by having a strip or ribbon of metal welded in partially nested overlapping relationship, so that each turn of the spirally or helically wound inner surface is tapered, inclined or angled with respect to adjacent segments to assist in directing movement of the plastics material throughout the mould.

54. A method or apparatus according to any preceding claim, characterised in that the material introduced to the mould is selected from different types, grades or sizes of material so that a pipe having one, two, three, four or more layers of different material or of the same material with different characteristics can be formed.

55. A method or apparatus according to any preceding claim, characterised in that it further includes heating means for heating the mould, preferably the heating means is a burner provided externally of the mould.

56. A method or apparatus according to any preceding claim, characterised in that hot air is directed internally within the mould, preferably axially directed down the hollow centre of the mould.

57. A method or apparatus according to any preceding claim, characterised in that the mould is provided with cooling means, preferably a bath of coolant, in which the mould rotates so as to provide cooling for all of the mould.

58. A method or apparatus according to any preceding claim, characterised in that

59. A method or apparatus according to any preceding claim, in which the product is formed with a flanged end.

60. A product made using the apparatus of any preceding claim.

61. A product made using the method of any preceding claim.

62. An apparatus for forming an article substantially as herein described with reference to the accompanying drawings.

63. A method of forming an article substantially as herein described with reference to the accompanying drawings .

64. A product substantially as herein described with reference to the accompanying drawings.