Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
  • B29C44/10—Applying counter-pressure during expanding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C33/00—Moulds or cores; Details thereof or accessories therefor
  • B29C33/30—Mounting, exchanging or centering
  • B29C33/308—Adjustable moulds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/34—Auxiliary operations
  • B29C44/3484—Stopping the foaming reaction until the material is heated or re-heated
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/34—Auxiliary operations
  • B29C44/58—Moulds
  • B29C44/586—Moulds with a cavity increasing in size during foaming
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/34—Auxiliary operations
  • B29C44/58—Moulds
  • B29C44/587—Moulds with a membrane, e.g. for pressure control

Definitions

• the present invention relates to a press system, more in detail the invention relates to a press system for production of partially expanded polymer bodies.
• PVC based rigid foam polymer materials are being widely used, mainly as core material in sandwich structures in the naval or aeronautic sector, or as thermal/acoustic insulators in the building sector.
• the core separates two structurally more rigid materials, such as fibre reinforced plastics (FRP), metal or the like.
• FRP fibre reinforced plastics
• sandwich structures have many advantages compared to more traditional single layer structures, such as lower weight, insulation properties etc.
• other rigid foam polymer materials such as foamed polyurethane etc. can be produced using streamlined continuous extrusion methods
• the production of PVC based rigid foam polymer materials involves moulding of discrete partially expanded bodies (hereafter referred to as embryo bodies) under high pressure in a press. The embryo bodies are subsequently subjected to a chemical-physical treatment to obtain the rigid foam polymer material.
• the production process of a PVC based rigid foam polymer material initially involves formation of a plastisol paste consisting of a mixture of powders (PVC and other compounds) and liquid substances (in particular isocyanates).
• the paste filled in a closed mould cavity and is subjected to a heating and subsequent cooling process under high pressure resulting in a partially expanded embryo body.
• the embryo body is then further expanded through an additional heat treatment in water and/or a steam oven.
• the formation of the final rigid foamed material is a result of a hydrolysis reaction of the isocyanate groups present in the material, with subsequent build up of a polymer which crosslink the chemical structure.
• the methods for the production of embryo bodies involves filling the each mould with an excess amount of paste with respect to the polymer content in the finished product.
• the excess amount is then allowed to leak out from the mould during the moulding process.
• the moulding process comprises heating the plastisol in a closed mould, whereby a high pressure is created by the thermal expansion of the plastisol and the activation of the blowing agent dissolved therein. During this expansion step, the excess amount is allowed to leak out.
• the plastisol is kept at elevated temperature a predetermined time to allow the plastisol to gelatinize, where after the mould cavity is cooled to a temperature that is low enough to remove the embryo body from the mould.
• the excess amount is approximately equal to about 8%, in terms of weight of the product leaving the mould.
• the object of the invention is to provide a new press system for production of rigid expanded polymer embryo bodies which overcomes the drawbacks of the prior art. This is achieved by the press system and the method as defined in the independent claims.
• Figs. Ia to Ie schematically show a cross sectional view of a press system for production of partially expanded polymer bodies, in different stages of moulding an embryo body.
• Fig. 2 is a schematic diagram of selected process parameters of a mould process in a press system according to the embodiment of figs. Ia to Id.
• Figs. 3a to 3d schematically show another embodiment of the press system.
• Fig. 4 is a schematic diagram of selected process parameters of a mould process in a press system according to the embodiment of figs. 3a to 3d.
• Figs. 5a to 5c schematically show another embodiment of the press system.
• Fig. 6 is a schematic diagram of selected process parameters of a mould process in a press system according to the embodiment of figs. 5a to 5c.
• Figs. 7a and 7b schematically show another embodiment of the press system.
• Fig. 8 schematically show another embodiment of the press system.
• Fig. 9 is a flow chart over a method according to the present invention.
• Figs. Ia to Id schematically show a cross sectional view of a press system 10 according to the present invention in different stages of moulding a partially expanded polymer body.
• the press system 10 comprises a mould cavity 20 of variable volume, temperature control means 30, counter pressure means 40 arranged to counteract expansion of the mould cavity 20 during moulding, wherein the pressure applied by the counter pressure means 40 is arranged to increase in response to expansion of the mould cavity 20.
• the press system 10 comprises a mould cavity 20 of variable volume, temperature control means 30, counter pressure means 40 arranged to counteract expansion of the mould cavity 20 during moulding, wherein the pressure applied by the counter pressure means 40 is arranged to increase in response to expansion of the mould cavity 20.
• the press system 10 further comprises a press arrangement comprising a press base 120 and a press top 50 with a moveable press member 130 urged in the downwards direction by the counter pressure means 40, and a replaceable mould tool 60 arranged between the press base 120 and the moveable press member 130.
• the press base 120 and the press top 50 are firmly interconnected by clamps 140 to avoid relative movement.
• the mould cavity 20 is provided as a replaceable mould tool 60 comprising a first mould member 70 and a second mould member 80.
• a recess in the first mould member 70 defines a portion of the mould cavity volume 20 and sealing means 90 is fitted in between the mating side flanges 100 and 110 respectively.
• the first mould member 70 and the second mould member 80 are moveable with respect to each other during moulding, and the sealing means 90 is arranged to provide an essentially hermetic seal between the first 70 and second 80 mould members during at least a portion of such a volume expansion of the mould cavity 20.
• the mould cavity 20 of variable volume may be formed as an integrated part of the press system 10, or in other suitable ways.
• the temperature control means 30 are provided to effectively control the temperature of the plastisol in the mould cavity 20 during the moulding process. Initially, the formation of the partially expanded polymer body requires heat to activate the blowing agent and to initiate the gelatinization of the plastisol, thereafter when the gelatinization has reached a certain point the heat created by the process exceeds the amount consumed and the plastisol has to be cooled in order to avoid overheating. This will be discussed more in detail below.
• the temperature control means 30 comprises conduits for a heating/cooling media, such as water or the like.
• the temperature control means may be provided as separate heating and cooling means, e.g. electrical heating means and cooling conduits for cooling media.
• the mould cavity 20 is formed to produce embryo bodies of flat rectangular panel shape that in later stages of the process are further expanded and cured to form panels of rigid polymer foam material with excellent mechanical properties.
• the mould cavity 20 may be of different shapes, such as spherical, tubular, cylindrical etc.
• each one of the first and second mould members 70 and 80 of the replaceable mould tool 60 comprises a major wall 140 and 150 respectively, parallel with and arranged to be adjacent the respective first and second press members 120 and 130 respectively.
• the first mould member 70 comprises an essentially perpendicular side flange 100 that circumscribes the major wall 140
• the second mould member 80 comprises a corresponding side flange 110 that mates with the side flange 100, defining a narrow gap there between, wherein the sealing means 90 is fitted.
• the replaceable mould tool 60 may be integrated with the press 10, by forming the first mould member 70 and the press base 120 as a press mould base and by forming the second mould member 80 and the moveable press member 130 as a moveable press mould member.
• the counter pressure means 40 are formed by an arrangement of spiral springs 45 that urge the moveable press member 130 in the direction opposite the expansion direction of the mould cavity 20.
• the expansion direction is upwards but the press system may also be designed so that the expansion direction is downwards sideways or anything there between.
• a counter pressure means 40 in the form of a spring arrangement will apply a counter pressure that increases as the expansion commences, but which cannot be actively controlled during a step of moulding.
• the counter pressure means 40 may be arranged so that the pressure applied increases essentially linearly or exponentially in response to expansion of the mould.
• the counter pressure means 40 may be arranged so that the pressure applied increases stepwise at one or more points of expansion. Further, the counter pressure means 40 may be arranged to provide any suitable combination of linear, exponential or stepwise increase of the applied pressure. Hence, the expansion of and the pressure in the mould cavity can be controlled accordingly.
• passive counter pressure means 40 include any types of arrangements that applies an increasing non controllable force on the moveable member 130.
• the counter pressure means 40 may be comprised of an arrangement that allow the force applied on the moveable press member 130 to be controlled according to a predetermined scheme during the expansion process.
• One example of such a counter pressure means 40 of controllable type is a hydraulic press system, wherein the applied pressure can be controlled by rising or lowering the hydraulic pressure in the system.
• a hydraulic press system may be controlled by a pressure controlled relief valve according to the description below.
• the mould cavity 20 is filled with plastisol in fig. Ia.
• the second mould member 110 (being the top one) in the disclosed embodiment is provided with a small evacuation opening 160.
• the evacuation opening 160 is formed to allow air to pass, but to prevent plastisol to escape from the mould cavity 20.
• the evacuation opening 160 is so small that the plastisol itself closes the opening due to the high viscosity, whereby only a small amount of plastisol is allowed to leak out of the mould cavity 20.
• other types of self closing evacuation openings may be used, such as valve type openings, wherein the plastisol act on a valve body to close the opening.
• the evacuation opening 160 is formed to avoid that the gelatinized embryo body get stuck therein.
• One way to avoid this is to make the evacuation opening 160 of conical shape with the broad end open to the mould cavity 20 and a small top opening open to the outside of the mould tool 60.
• the mould tool 60 is adapted to be used in a press system with parallel press planes, whereby the small top opening is covered by a press plane 130 and the open area is further reduced.
• Fig. 2 is a schematic diagram of some process parameters of a mould process in a press system 10 according to the embodiment of figs. Ia to Id.
• the mould process of fig. 2 comprises heating the plastisol, T control, in a closed mould cavity 20, whereby a high pressure P is created by the thermal expansion of the plastisol and the activation of the blowing agent dissolved therein.
• T control heating the plastisol
• the counter pressure means 40 By selecting suitable characteristics for the counter pressure means 40, the pressure P in the mould cavity 20 will, as a result of the heating T control, exceed the pressure applied by the counter pressure means 40, whereby the volume V of the mould cavity 20 will increase.
• the plastisol is kept at elevated temperature a predetermined time to allow the plastisol to gelatinize, where after the mould cavity 20 is cooled to a temperature that is low enough to allow removal of the embryo body 170 from the mould cavity 20.
• the gelatinization process produces heat, and must be cooled in order to avoid over heating.
• fig. 2 it is indicated that the pressure P continues to rise during a short period after the T control has been switched to cooling, which is a result of the heat produced by the gelatinization process.
• the point of maximum pressure is indicated by the dotted line in fig. 2. For the same reason the mould cavity 20 volumes will continue to increase until the pressure has reached its maximum.
• Fig. Ib shows the press system 10 when the volume of the mould cavity 20 has reached its maximum volume defined by the characteristics of the counter pressure means 40 the type of plastisol mix and the process parameters that are used. Typically, the volume expansion corresponds to 5 to 20 percent or more compared to the filling volume.
• Fig. Ic shows a step of unlocking the press system according to this embodiment, wherein the elastic properties of the partially expanded polymer body 170 is utilized to release the interconnection clamp members 140.
• a compression force exceeding the final pressure in the mould cavity 20 is applied on the press top 50, whereby the counter pressure means 40 and the embryo body 170 are compressed so that the clamps 140 can be withdrawn to unlock the press system 10.
• Fig. Id shows the press system 10 when the press top 50 and the second mould member 110 are lifted off the first mould member 100 and the press base 120, whereby the compressed embryo body 170 is starting to pop out from the mould 60 by the internal expansion forces
• fig. Ie shows the relaxed embryo body after it has popped out from the first mould member 100.
• the resulting relative movement of the first and second mould members, 100 and 110 respectively is exaggerated for illustrative purposes, whereby excess material 180 formed between the upper surface of the side wall 80 and the major wall 70 of the second mould member represent an significant volume of waste material that has to be removed. However, in production scale mould tools 60, the excess material 180 will be less than the previously accepted leakage volume of 8 %.
• the evacuation opening 160 produces a nipple 190 on the gelatinized embryo body, which is removed together with the excess material 180.
• the mould members 70, 80, the press base 120 and the moveable press member 130 may be comprised of any suitable rigid material with reasonable thermal conductivity. They may e.g be comprised of a metal such as aluminium, stainless steel or the like. Alternatively, or in combination they may be comprised of a composite material, such as fiber reinforced plastics. Due to the high pressure in the mould during the mould process; up to and exceeding 200 atm, all parts of the press system must be designed accordingly.
• the mould is designed so that the moveable mould member 110 provides an essentially hermetic sealing effect at an increase of mould cavity 20 volume of a predetermined value between 6 and 20% with respect to a filling volume, where after the sealing effect is arranged to be reduced to avoid overpressure in the mould cavity.
• the sealing effect is gradually reduced.
• one of the mould members may be designed to provide an adjustable expansion limit.
• Figs. 3a to 3d show an embodiment of a press system, wherein, the press base 121 and the press top 51 are attached by a hinge arrangement 200 along one side and by interlocking means 210 on the opposite side.
• the interlocking means 210 is shown as a rotary lock mechanism, but it may be any suitable interlock mechanism.
• the counter pressure means 40 is comprised of compression springs 220 and secondary compression members 230.
• the counter pressure means 40 according to this embodiment is arranged to allow an initial expansion of the mould cavity 20 under a counter pressure from the compression springs 220, followed by a secondary expansion under an elevated counter pressure in form of the combined force from the compression springs 220 and the compression members 230.
• Fig. 4 is a schematic diagram of some process parameters of a mould process in a press system 10 according to the embodiment of figs. 3a to 3d.
• the point when the expansion of the mould cavity 20 has reached the secondary expansion is indicated by the left dashed line.
• the increase in pressure P during the secondary expansion results in reduced expansion rate of the volume V.
• Fig. 3 c illustrates the step of unlocking the press system 11, wherein a force is applied on the left hand side of the press top 51 to compress the embryo body 170 to allow unlocking of the rotary locking mechanism 210 where after the press system can be flipped open as is shown in fig. 3d.
• Figs. 5a to 5c show an embodiment of a press system 12, wherein the mould cavity 20 is integrated with the press base 122 and the moveable press member 132.
• the press base 122 and the moveable press member 132 are illustrated as a plunger type arrangement wherein the mould cavity 20 is formed by a recess in the press base 122 and the press member 132 is formed as a mating plunger defining the upper wall of the mould cavity 20.
• the press member 132 is arranged to be moveable between a lower position set by a lower shoulder 260 and an upper position set by expansion termination means 250 hindering further movement of the press member 132 in the expansion direction.
• the final predetermined mould cavity volume is set by the position of the expansion termination means 250, and the resulting peak pressure depends on the volume of plastisol filled into the mould.
• the volume of the mould cavity 20 is defined by the expansion termination means 250, which corresponds to a volume expansion of 5 to 20 percent or more compared to the filling volume depending on the type of plastisol mix and the process parameters that are used.
• Fig. 6 is a schematic diagram of some process parameters of a mould process in a press system 12 according to the embodiment of figs. 5a to 5c.
• the counter pressure means 40 of the press system 12 are arranged to allow an initial expansion of the mould cavity 20 under a counter pressure from the compression springs 240, followed by a secondary expansion under an elevated counter pressure caused by the expansion termination means 250.
• the compression springs 240 are arranged to provide an essentially linear increasing counter pressure, followed by a counter pressure peak, caused by the terminated volume expansion.
• Partially expanded polymer bodies with different characteristics can thus be achieved by altering the volume of plastisol filled into the form and/or by altering the final mould cavity volume by changing the position of the expansion termination means 250.
• the expansion termination means 250, and thus also the final mould cavity volume are adjustable.
• Figs 7a and 7b show still another embodiment of a press system 13, wherein the mould cavity
• the press system 13 is comprised of a press top 53 and a press base 123 that are firmly interconnected by clamps 140.
• the press top 53 comprises, temperature control means 30, the flexible wall member 300 and hydraulic conduits 350 connecting the hydraulic fluid side of the flexible wall member 300 with a source of hydraulic pressure 330 illustrated by an arrow.
• the pressure applied by the hydraulic pressure fluid 310 is supplied and controlled by the source of hydraulic pressure 330.
• the press base comprises a lower section of the mould cavity 20 and control means 30.
• the counter pressure applied by the hydraulic pressure fluid 310 is controlled by a pressure controlled relief valve 340.
• the pressure controlled relief 340 valve is arranged to open when a predefined or controllable pressure threshold is reached, and the hydraulic fluid from the valve is fed to a reservoir 350.
• the pressure threshold may be a static pressure, or it may be controllable in order for the pressure in the mould cavity to be controlled according to a predetermined scheme.
• the above method may be performed with the press system according to the present invention, but it may also be performed in large facility press system, using mould tools of variable volume.
• the counter pressure may either be actively controlled by e.g. a hydraulic pressure system, or passively controlled by selection of counter pressure members with predetermined characteristics.
• the counter pressure may increase linearly or exponentially during the expansion, or it may be varied according to a predetermined scheme during the expansion. According to one embodiment, the counter pressure increases stepwise.
• the method comprises the step of:

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Citations (5)

• 2007
  • 2007-08-16 WO PCT/SE2007/050558 patent/WO2009022954A1/en active Application Filing
  • 2007-08-16 CA CA2696510A patent/CA2696510A1/en not_active Abandoned
  • 2007-08-16 BR BRPI0721934-2A patent/BRPI0721934A2/pt not_active IP Right Cessation
  • 2007-08-16 KR KR1020107005687A patent/KR20100071989A/ko not_active Application Discontinuation
  • 2007-08-16 EA EA201000336A patent/EA201000336A1/ru unknown
  • 2007-08-16 EP EP07794168A patent/EP2178686A1/en not_active Withdrawn
  • 2007-08-16 CN CN200780100821.0A patent/CN101827695A/zh active Pending
  • 2007-08-16 JP JP2010520961A patent/JP2010536603A/ja not_active Abandoned

Patent Citations (5)

Non-Patent Citations (1)

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