The present invention relates to a moulding method and a moulding machine. In particular, although not exclusively, the present invention relates to a moulding method and a moulding machine for fabricating large flat panels having an outer skin and an inner core material.
Environmental Recycling Technologies Plc (ERT) have developed a moulding process for producing extremely rigid plastic structures such as panels, from recycled plastic material. This moulding process is known as the PIM process to those skilled in the art. The PIM process is an open mould technique, where a two part mould is machined so that when combined they form a cavity having the shape of the desired moulding. The two parts of the mould are mounted within a large oven on buttresses that support each mould part. Because the mould parts can be quite large, the buttresses have to be equally substantial in order to cope with the weight.
The two mould parts are arranged upwardly open and pre-heated. When up to the correct temperature of around 220° C., a first powdered plastic material is sprayed onto the mould in a methodical manner to layer the powdered plastic material to a desired thickness on the internal surfaces of each mould part. The residual heat in each mould part starts to melt the powdered plastic material causing it to adhere to the mould.
After being layered with the first powdered plastic material that will form an outer shell, one mould part is layered with a second layer of powdered plastic material including a blowing agent. This second layer will form a core.
Once one of the mould parts has been layered with the second powdered plastic material including the blowing agent, the other mould part is rotated and lifted on top. The lifting and rotating is affected by the buttress supporting the respective mould part. Again, the buttress has to be sufficiently large to copy with the bending forces generated during rotation. The two mould parts are held together by clamps or a compressive force applied by the buttresses. The buttresses and mould are placed within a curing oven and the mould heated to around 300° C. During the curing process the blowing agent within the second core layer expands causing a foam structure to rise upwardly from the lower mould until it meets the outer skin layer of the upper mould.
Once the curing process is complete, the mould is cooled. When sufficiently cool, the mould is opened and the moulding removed. The finished moulding has a hard outer skin and a rigid inner core having a foam type structure.
Since the PIM process is an open mould method, the buttresses are heated within a large oven in order to avoid loosing heat. Accordingly, a large proportion of the energy put into the oven, goes towards heating the buttresses. Furthermore, large ovens are often inefficient and have hot spots and cold spots within them caused by shielding (such as from the buttresses). The hot and cold spots cause the second, core material to reach the activating temperature of the blowing agent at different speeds. Consequently, some areas of the core can form before others. If this happens such that an area of core material becomes encased, as that area forms, an air bubble can be created. In order to conserve energy, the mouldings are often removed from the mould whilst the outer skin is still relatively pliable. This allows the moulds and buttresses to start the cycle over without having cooled too far. However, if a bubble has formed towards the surface of the outer skin, the pressure can cause the surface to also bubble and cause the surface to become distorted and weak.
It is an aim of the present invention to provide a moulding method and moulding machine capable of producing structures having an outer skin and inner core having improved energy efficiency.
It is a further aim of the present invention to provide a moulding method and machine for producing mouldings having an outer skin and inner core with improved dimensional accuracy.
According to a first aspect of the present invention there is provided a moulding method for moulding structures having an outer skin that at least partially encases an expanded inner core, the moulding method comprising: using a mould having an internal cavity; forming a first layer of particulate on inside surfaces of the mould to form an outer skin on at least two opposed sides of the internal cavity leaving the centre between the opposed sides free to accept a second material; forming a second layer of particulate on inside surfaces of the first layer to form an inner skin wherein the step of forming the second layer comprises opening the mould; and heating the mould to cause the inner skin to form an expanded core between the outer skin.
Advantageously, forming a second skin on the inside of the outer skin enables the wall thickness and core thickness of the resultant moulding to be tightly controlled. Each of the inner and outer skins is continuous.
In the exemplary embodiments, the method comprises heating the mould to form the outer and inner skins. Here, the method comprises heating the mould to form the first layer. As the mould heats, a hollow outer skin is formed on inside surfaces of the mould. The mould is then opened so that a second material can be placed inside the hollow outer skin and the mould heated to form a hollow inner skin. Thus the inner and outer skins form a hollow, continuous structure.
Preferably the method comprises forming the first layer by filling the mould with particulate material. Subsequently to filling the mould with particulate material, the method may comprise heating the mould to melt the particulate material via conduction with the mould. The method may comprise removing any unmelted particulate material from the mould once a desired thickness of inner skin has been formed.
Preferably, the method comprises forming the second layer by filling the formed outer skin with a particulate material. The particulate material of the second layer may include a blowing agent. Subsequent to filling the mould with particulate material to form the second layer, the method may comprise heating the mould to melt the second plastic material from the outside in. The method may comprise removing the un-melted particulate material from the outer skin once a desired thickness of the inner skin has been formed.
Preferably the method steps of heating the mould may comprise selectively heating sectors of the mould. The steps of heating the mould may comprise monitoring the temperature of each sector of the mould. The steps of heating the mould may comprise controlling the heating of each sector dependent on the monitored temperature.
Preferably the step of heating the mould to form an expanded core may comprise selectively heating the mould from one area towards another. Advantageously, this causes the blowing agent in the inner skin to activate in a controlled manner forcing excess gas towards a specified area where it may be released.
In the exemplary embodiments, the method uses a moulding machine. The moulding machine comprises an insulated enclosure. The insulated enclosure has an openable aperture for receiving the mould. The insulated box is moveable between a filling position and an emptying position. In the filling position the openable aperture is upwardly facing. In the emptying position the openable aperture is downwardly facing. Here the method step of filling the mould comprises moving the insulated enclosure to the filling position and pouring material in. The step of removing the material comprises moving the insulated enclosure to the emptying position and pouring the material out.
In one exemplary embodiment the method comprises arranging a filling station under the insulated enclosure. The method may comprise locking the filling station to the insulated enclosure after moving the insulated enclosure to the emptying position. Thus moving the insulated enclosure to the filling position automatically fills the mould. The method may comprise moving the insulated enclosure to aid material distribution through the mould.
Preferably the insulated enclosure includes a heater. The heater may comprise heating blankets. The method may comprise clamping the mould between two heating blankets. The method may comprise holding the mould between the blankets under pressure. Advantageously, because the mould is held by the heater, only the mould needs to be heated thus energy is conserved. The blankets may comprise a plurality of areas. Each area may be separately controlled. The method may comprise selectively heating the mould.
In the exemplary embodiments the method comprises forming an enclosed mould at least partially with an insulating member during the steps of forming the outer and inner skins. The method may comprise removing the insulating member during the start of causing the inner skin to form a core. During this step the enclosed mould may therefore be formed completely by heat conducting material.
In one exemplary embodiment, the first and second particulate materials are filled and removed from the mould via an end of the mould. Hence the end of the mould is removable. The end may be fabricated from a heat insulating material such that the outer skin and inner skin are not formed across said end. The method may comprise filling and removing the first and second particulate material from the end. The method may comprise removing an end of the insulated enclosure box after pre-heating the mould removing the end of the insulated enclosure may remove an end of the mould. The first and second particulate materials may be filled by rotating the insulated enclosure so that the open end is upwardly facing and subsequently pouring the particulate material in through the opened end. The particulate material may be removed by rotating the insulated enclosure to be downwardly facing and pouring the material out. The method may comprise arranging a hopper about the opened end of the enclosure. The method may comprise attaching the hopper to the enclosure and rotating the enclosure to up turn the hopper to fill material from the hopper into the mould and conversely rotating the enclosure to fill the hopper with material from the mould.
In an alternative exemplary embodiment the mould comprises a split mould formed from at least two mould pieces. The mould pieces are assembled with an insulating member between abutting faces of each mould piece. Here the method comprises filling the mould with a first particulate material and subsequently forming an outer skin. The method then comprises splitting the mould and removing any un-melted material. The method subsequently comprises filling the outer skin with particulate material and closing the mould still separated by the insulating member. The method comprising splitting the mould after forming the inner skin and removing any excess material and subsequently, removing the insulating member and closing the mould.
According to a second aspect of the present invention there is provided a moulding machine for moulding particulate structures having an outer skin that is at least partially encased by an expanded inner core using a method according to the first aspect, the moulding machine comprising: a moulding station having an insulated enclosure, the insulated enclosure being adapted to receive a mould through an openable aperture; wherein the insulated enclosure is moveable between a filling position wherein the openable aperture is upwardly open and an emptying position wherein an openable aperture is downwardly open.
The insulated enclosure may be pivotable between the filling and emptying positions.
Preferably the moulding machine includes a filling station. The filling station may be arrangeable to fill the mould. The filling station may be arrangeable to empty the mould. The filling station may be lockable relative to the insulated enclosure.
Preferably the mould comprises an encased cavity. The encased cavity may be formed at least partially from a non-conducting member. The non-conducting member may be a continuous member.
Preferably the insulated enclosure includes a heater. The heater may hold the mould under pressure. The heater may directly heat the outside surface of the mould. The heater may be controllable to heat different areas of the mould differently. The heater may be heat the different areas at different rates and/or at different times. The heater may comprise a heating blanket. The heater may comprise a plurality of heating blankets.
Preferably the moulding machine comprises a support. The support may move the insulated enclosure about a first axis. The support may move the insulated enclosure about a second axis. Suitably the support may comprise an inner gimball and an outer gimball.
The filling station may comprise a hopper. The filling station may comprise a lift. The lift may be arranged to lift the hopper into engagement with the insulated enclosure. The filling station may include a track. The hopper may be moveable along the track. The hopper may be automated.
Further optional or preferable features are described in the description that follows and the claims appended hereto.
Various embodiments of the invention will now be described in more detail with reference to the following drawings in which:
Referring to
Referring to
In use, the mould 50 is placed inside the insulated enclosure 30. For convenience, the insulated enclosure 30 can be rotated to a loading position wherein the openable aperture 40 is open to the side aspect in order to load the mould 50 (see
The insulated enclosure 30 can then be rotated back to the filling position and the mould filled with a second particulate, such as a powdered material including a blowing agent for forming the core of the moulding. It will be appreciated that suitably the powdered material includes a plastic material such as a thermoplastic material. As previously described, the second material is poured in until the centre between the hollow outer skin is filled and the mould heated until a desired inner skin thickness is reached. Once reached, the insulated enclosure is rotated to the emptying position and the un-melted material poured out of the mould. Consequently, the internal surfaces of the mould are coated with a first skin and a second hollow skin both of desired thicknesses.
The openable aperture 40 and entrance can then be closed and the heat source 80 used to complete the curing process (as shown in
Referring to
Rotating the insulated enclosure 30 therefore inverts the hopper 62 such that the material fills the mould via gravity (
Referring back to
Referring back to
In order to prevent the mould 50 from being deformed by the pressure and heat applied, it is advantageous to provide the mould with reinforcing ribs. Such ribs may be formed on the outside surfaces of the mould. Here the heating blankets would fit inbetween the reinforcing ribs. This is also advantageous as it allows the pressure plate that applies the pressure to act on the reinforcing ribs. Consequently, it will be appreciated that the reinforcing ribs protrude above the heating blanket for instance in the region of 1 mm. The reinforcing ribs are substantial enough to withstand the pressure and heat. For instance, ribs of around 5 mm width and 20 mm height have been found particularly useful. The reinforcing ribs cannot be too wide so as to avoid heat shadows in the mould.
The support 70 of the moulding station 20 suitably comprises an inner gimball 71. The cage 32 is fixed to the inner gimball 71 by a plurality of ribs 72. The inner gimball 71 includes pivot arms 73 that extend outwardly from the inner gimball on either side and coincident along the A-A axis. As will be appreciated, the inner gimball enables the rotation of the insulated enclosure between the filling position and the emptying position. The support 70 further comprises an outer gimball 74. The outer gimball 74 includes bearings 75 that engage the pivot arms 73. The bearings 73 include a control that can be operated to rotate the inner gimball 71 relative to the outer gimball 74. The support 70 further comprises stands 76 that are arranged to rotatably support the outer gimball 74 on a support surface. The outer gimball 74 is rotatably connected to the stands 76 at bearings 77. Consequently, the outer gimball can be rotated about axis B-B relative to the stands 76. Axis B-B is perpendicular to Axis A-A.
In use the moulding station 20 can therefore be used to rock the insulated enclosure 30 about axis B-B and roll the insulated enclosure 30 about axis A-A. A combination of rock and roll motion can be used to distribute the plastic material within the mould 80 in order to help the flow of the plastic around material the mould. Additionally, the mould 50 can be tipped or tilted to aid the plastic material in reaching particular portions of the mould.
As shown in
Referring to
A plurality of alignment pins 69 are arranged on the outside of the hopper. The alignment pins 69, co-operate with alignment holes 47 in the insulated enclosure.
In use, the moulding station 20 is controlled to rotate the insulate enclosure 30 to the loading position. The mould 50 is loaded on top of electrical heating blanket 82 and the heating blanket 82 raised to sandwich the mould between the two heating blankets 81, 82 under pressure. The door 42 is closed and the heating blankets 81, 82 activated to pre-heat the mould. Once a desired temperature is reached, the moulding station is controlled to rotate the insulated enclosure to the pre-filling/emptying position and the hopper filled with the first plastic material and moved to position under the moulding station. The door 42 is opened, which also opens the openable entrance of the mould. The hopper 62 is raised by the lift 64 so that the alignment pins 69 and holes 47 co-operate thereby locking the hopper 62 to the insulated enclosure. The aperture 66 enters the openable entrance and the plate 61 seals the entrance. The lift 64 is lowered and the moulding station controlled to rotate the insulated enclosure 30 to the filling position. The mould is heated to form an outer skin as herein described. The insulated enclosure is then rotated back to the emptying position, and the un-melted material automatically empties into the hopper. The hopper is then released and lowered which thereby opens the mould. The hopper can then be returned to an end of the rail, for re-filing. Preferably a second hopper can then be moved to beneath the moulding station from the other end and the process repeated to form the second, inner skin. The door can then be closed and the curing process complete.
During the curing process, the heating blankets may be controlled to bring the mould up to an actuating temperature of the blowing agent in a controlled manner. For instance the part of the mould furthest from the openable entrance may be cured first and then the heat brought on gradually towards the openable entrance. In this way the core forms methodically and forces any excess gas towards the entrance thereby minimising the risk of bubbling.
Any of the methods described above may create a mould having an outer shell on at least two opposed sides or on five sides of the moulding. The sixth side does not include an outer shell layer because this is the end forming the openable entrance. Whilst the core does seal over slightly when the openable entrance is closed by the mould part during the curing process. It may be desirable to provide a completely encased product. In this case, after filling the mould with the first powdered material, the hopper 62 can be removed and the openable entrance to the mould sealed by the mould part. However, an insulating member such as a seal is first arranged about the boundary of the openable entrance such that part of the seal is exposed to the inside of the mould forming a continuous face. When the mould is heated, the plastic melts and wets to all the internal mould faces. However, because the seal is non-conducting and remains cool, the plastic does not wet to this part. As such the openable entrance may still be opened to allow the un-melted material to be emptied. When an inner and outer skin has been formed on all the inner surfaces of the mould, the seal is removed before re-closing the mould and curing the moulding. The end of the mould may include air escape apertures so that when curing the inner core, excess gas is forced to one area and allowed to escape. Once the mould is closed without the seal, the outer skin on the two parts of the mould fuse and a completely encased product is achieved.
It will be appreciated that the moulding machine shown in
To improve the efficiency of the moulding machine, the mould can be removed from the moulding station to cool. Hence, the moulds are kept under pressure during cooling to reduce the risk of surface blowing. The mouldings may be removed before completely cool and the mould reused in order to retain residual heat in the mould. Furthermore, each moulding station may have two associated moulds whereby as one mould is filled, the other is being cooled.
Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including the claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
Number | Date | Country | Kind |
---|---|---|---|
0822899.1 | Dec 2008 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/GB09/51585 | 11/20/2009 | WO | 00 | 6/16/2011 |