CA1102067A - Method and apparatus for molding expandable polystyrene - Google Patents
Method and apparatus for molding expandable polystyreneInfo
- Publication number
- CA1102067A CA1102067A CA293,522A CA293522A CA1102067A CA 1102067 A CA1102067 A CA 1102067A CA 293522 A CA293522 A CA 293522A CA 1102067 A CA1102067 A CA 1102067A
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- mold
- expandable polystyrene
- chamber
- jacket
- steam
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- Moulds For Moulding Plastics Or The Like (AREA)
Abstract
METHOD AND APPARATUS FOR
MOLDING EXPANDABLE POLYSTYRENE
Abstract of the Disclosure This invention relates to improvements in molding expandable polystyrene, particularly for molding high density tubular parts, in which the molding tool is made with a sintercore metal on each side of the mold cavity, and which has an internal vacuum chamber, external steam jackets, and compressed air means capable of communicating with both the interior vacuum chamber and the exterior steam jacket. The process sequence comprise the steps of (l) applying a vacuum to the inner chamber of the mold, (2) filling the mold with expandable polystyrene beads, (3) charging the jacket with steam, said vacuum being maintained in the inner chamber during steps 2 and 3 to improve mold filling and steaming through the sintercore, (4) cooling the jacket with compressed air, or a water mist and (5) removing the jacket and then the molded article, with the article removal being assisted by application of compressed air to the inner chamber of the mold.
MOLDING EXPANDABLE POLYSTYRENE
Abstract of the Disclosure This invention relates to improvements in molding expandable polystyrene, particularly for molding high density tubular parts, in which the molding tool is made with a sintercore metal on each side of the mold cavity, and which has an internal vacuum chamber, external steam jackets, and compressed air means capable of communicating with both the interior vacuum chamber and the exterior steam jacket. The process sequence comprise the steps of (l) applying a vacuum to the inner chamber of the mold, (2) filling the mold with expandable polystyrene beads, (3) charging the jacket with steam, said vacuum being maintained in the inner chamber during steps 2 and 3 to improve mold filling and steaming through the sintercore, (4) cooling the jacket with compressed air, or a water mist and (5) removing the jacket and then the molded article, with the article removal being assisted by application of compressed air to the inner chamber of the mold.
Description
BACKGROUND OF T~IE INVENTION
1. Field of the Invention The present invention relates to a method and apparatus for molding expandable polystyrene and, more particularly, to such a method and apparatus in which shaped articles are molded in a fixed mold cavity from expandable polystyrene beads.
The invention is especially adapted for molding high density expanded polystyrene into shapes such as tubes, cones, cups and the like. Such articles are generally molded in a production type process, and it is the purpose of the invention to provide both qualitative and quantitative improvements in such production.
1. Field of the Invention The present invention relates to a method and apparatus for molding expandable polystyrene and, more particularly, to such a method and apparatus in which shaped articles are molded in a fixed mold cavity from expandable polystyrene beads.
The invention is especially adapted for molding high density expanded polystyrene into shapes such as tubes, cones, cups and the like. Such articles are generally molded in a production type process, and it is the purpose of the invention to provide both qualitative and quantitative improvements in such production.
2. Description of the Prior Art It is well known to mold expandable polystyrene beads into article configurations such as tubes and cups.
In general, the mold is charged with the requisite - amounts of pre-expanded but further expandable polystyrenebeads, and heated at a time sufficient to soften the polystyrene whereupon the beads expand a second time and fuse together. The mold is then generally cooled with cooling water, and the article or articles removed therefrom. These processes are generally satisfactory, but efforts have been made to effect improvements in such molding processes in order to increase the speed of production from a given unit, and to improve the properties of the molded composition.
The filling of cavities in molds is normally accomplished by transporting the pre-expanded beads into ~o these cavities with the help of an air stream. Venting '~.7' ' slots at different locations within these cavities are designed to permit the escape of the air and produce uniform filling. Such vents consist either of holes drilled into the walls of said cavities or inserts containing numerous slots. These surface interruptions are then found on the molded parts again since the expanding polystyrene during the molding step produces an exact replica of the surface it comes in contact.
In addition, efforts have been made to increase the application of steam by providing perforated walls, and U. S. Patent 3,081,488 shows the use of such perforated walls. This patentee also utilizes a vacuum interior to hold the beads on perforated walls to improve filling prior to molding. However, the perforated walls do not provide the desired smoothness for certain appli-cations such as high density tubular parts. In U. S.
Patent 3,259,677, there is a teaching of the use of porous permeable walls in a mold form, however, the patentee states that the mold is not suitable for molding expandable materials, because the material itself forms a closed barrier. Instead, the patentee limits his application to the formation of regular heat-softenable, non-expandable plastic material.
In addition, certain problems have been encountered with respect to obtaining a uniformly expanded article, because both a uniform distribution and an even softening of the bead particles is required to prevent certain areas from being heavy and other areas from being comparatively light.
Thus, it is a primary object of the invention to provide a method and apparatus for molding expandable polystyrene in which the molding operation is carried out in a minimum of time with a minimal amount of equip-ment.
Another object of the invention is to provide a method and apparatus for molding expandable polystyrene in which tubular parts and the like may be formed which are substantially uniform in density throughout.
It has now been found that these and other objects are achieved by providing a mold cavity having smooth, permeable walls together with means for providing a vacuum, steam and compressed air in order to operate the mold under improved process conditions. The smooth, permeable walls are preferably made with sintercore metal, which has the advantages of allowing passage of air or steam through the walls, which provides a smooth molding surface, and which provides good heat transfer character-istics.
Thus, the invention provides a mold assembly for forming a high density expandable polystyrene article of an open-ended, closed-curved, sheet-like configuration having an interior surface and an exterior surface. The assembly comprises an interior mold section formed with smooth permeable wall means having an interior surface defining an interior chamber and an exterior surface shaped to match the interior surface of the article to be molded and provide a part of a mold cavity, an outer mold section formed with smooth permeable wall means having an inner sur-face shaped to define the exterlor-s~rface o~ the article to be molded and formed for fitting against said inner section to form said mold cavity, a jacket means disposed to provide an exterior chamber adjacent to the outer surface of the outer section of the mold, said jacket means and outer mold sections being removable to expose the mold cavity, means for evacuating the interior or exterior chamber to provide a vacuum within the mold, means for supplying steam to the jacket or inner chamber, and means for cooling the mold.
Preferably, the mold cavity is tubular in configuration, and the assembly is adapted to form tubular parts, spools or cups. The permeable wall means are preferably made of sintercore metal, and the cooling means comprises means for supplying compressed air or vacuum or water to the steam jacket. In the preferred form, compressed air can also be supplied to the interior - chamber. In its process form, the invention provides a method of molding expandable polystyrene comprising the steps of providing a mold assembly having a mold cavity substantially enclosed by a permeable sintercore material, a first chamber in the center of the mold cavity and a second chamber on the other side of the mold cavity;
evacuating said first chamber to provide a vacuum therein;
placing a measured amount of pre-expanded but further expandable polystyrene beads in said mold cavity; charging said second chamber with steam whereby steam will move through the permeable mold walls and mold cavity into the first chamber; said steam being charged for a time sufficient to expand and fuse the expandable polystyrene within the entire mold cavity, shutting off said steam, ~ Q ~7 cooling the molded polystyrene, and removing the molded polystyrene article from the mold.
It is preferred to use metallic materials in the mold assembly to provide good heat transfer character-istics. The vacuum should best be used when loading the mold to retain the beads in an even distribution and when charging with steam so that steam is initially directed through the entire mold. Compressed air, water or a water mist are used for cooling assist in forming a cool outer surface on the outer surface of the poly-styrene article. Similarly, compressed air is directed to the inner chamber to assist interior cooling and help release the article from the inner mold walls.
The invention described in this patent appli-cation uses sintermetal to produce maximum venting by utilizing the entire surface of the mold.
The steaming process is normally carried out by injecting steam through the aforementioned vent holes which then penetrates into the beads and causes their expansion and subsequent fusion. The even distribution of the steam over the entire surface is particularly critical for high density applications. It was also found that the steaming rate is a decisive factor for uniform results. If the steam is applied too fast, then the expandable polystyrene tends to seal off at the surface and prevent the further penetration of the steam into the core of the part to be molded. It may also cause local melting of the expandable polystyrene, an effect known as "burning".
_ 6 --~ 6'7 The use of sintermetal permits the application of steam in two ways:
First, by applying low pressure the expanded beads in the cavity are preheated and start to expand from the heat conducted from the surface. The appli-cation of a vacuum through the sintercore permits then the even distribution of the steam over the entire outer surface of the part and penetration through to the core which permits even fusion throughout the cross section of the part.
If desired, the vacuum in the core can be substituted with steam and a vacuum applied to the outer shell so that the direction of steaming is reversed.
Cooling the molded article is normally required to form a sufficiently hard layer on the surface which is able to withstand the residual inner pressure from the expanded beads in the article. This is accomplished by the application of air, water or vacuum or combinations thereof to the walls of the mold for a certain period of time. It is generally advantageous to keep the quantity of water to a minimum and thus the application of a fog or water mist is all that is required to lower the wall temperature of a mold sufficiently.
The molded article is then removed from the mold. This removal presents usual difficulties with cylindrical cores, but is helped greatly in this invention by providing air pressure to the core and thus loosen up that article.
Thus, it is seen that the invention is best adapted to form tube-like configurations such as tubes, spools, or cups. The invention is also particularly 1 1~ 2~ ~ 7 valuable in forming the so-called high density foam articles.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing, in which like numerals are used to designate like parts throughout:
Figure 1 is a cross-sectional view of a mold constructed according to the invention together with a diagrammatic view of the associated parts;
Figure 2 is a cross-sectional view of the mold of Figure 1 taken in the plane of line 2-2 thereof; and Figure 3 is a cross-sectional, elevational view of a means for charging the mold with feed material.
While only the preferred embodiment is shown in the drawings, it should be understood that the invention is to be limited only by the spirit and scope of the appended claims.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now more particularly to the drawings, there is shown a mold assembly 11, comprising a mold 12 composed of a sintercore metal and formed with an inner mold section 1~ and an outer mold section 14. Between the inner and outer mold section, a mold cavity 16 is provided, in which the molded article 17 is formed. The inner mold section 13 is carried on a frame plate 18, which is mounted in conventional fashion on suitable supports (not shown).
In the embodiment of the drawing, the inner mold section 13 is generally cylindrical, and is permanently secured to frame plate 18, with the plate ~0 closing one end of the inner part of the cylindrical section. The other end is closed by a plate 19, which . ' . ' is permanently secured thereto. In this way, a central chamber 21 is formed within the sintercore inner mold section 13. The outer mold section 14 is also generally cylindrical, and forms the inner part of jacket assembly 22. The jacket assembly 22 also comprises an outer shell 23, which is cylindrical and concentrically disposed to the outer mold section 14 to form a jacket chamber 24 therebetween. The ends of the jacket chamber 24 are closed with end plate 26, and spacer plate 27. As here shown, a circular closure plate 28 is provided to close an end of the mold cavity 16, but it will be appreciated that plates 26 and 28 may be combined into a single plate unit, if desired.
In order to remove the molded article 17 from the mold, the jacket assembly 22 is removably attached to frame plate 18 through a circular flange 29 formed on outer shell 23. If desired, the flange 29 can be removably attached to frame plate 18 by suitable bolts or the like; however, it is preferred to use suitable, fast acting, removable clamping means (not shown) to speed up the production of the mold assembly.
As here shown, the jacket assembly 22 is constructed in two sections, with each section having a pair of longitudinal flanges 31. These flanges are also removably attached by suitable means (not shown), and removal of the jacket is facilitated by use of the two sections. However, it will be appreciated that the jacket assembly could be made in one piece, and removed axially, if desired.
_ g _ ~ 6 7 The mold assembly 11 also comprises feeding means 30 for supplying expandable beads to the mold at point F, means 32 for supplying steam to jacket 24, means 33 for supplying compressed air to the jacket 24 and central chamber 21, and means 34 for providing a vacuum in central chamber 21.
Feeding means 30 comprises a venturi tube 35 having a feed inlet 40 for receiving pre-expanded polystyrene beads from a suitable source such as a hopper (not shown), means 30 also comprises a movable compressed air supply tube 45 for directing a stream of alr and polystyrene beads into the mold.
Steam supply means 32 comprises a source of steam 36, line 37, which is controlled by multiposition valve 38, entry port 39 to jacket 24, and exhaust port 41 which can be closed by valve 44. As here shown, a branch line 42 is shown communicating with a second entry port 43.
However, it will be appreciated that more or even less entries and/or exhausts than those shown may be utilized, if desired. It will also be appreciated that the vacuum chamber and steam chamber could be reversed, along with their associated parts.
The vacuum means 34 comprises a source of vacuum such as vacuum pump 46, operative through line 47, valve 48 and line 49 to evacuate the central chamber 21.
Valve 48 is a multiposition valve capable of connecting line 47 to line 49 for connecting the vacuum pump 46 to the central chamber 21, and capable of connecting line 49 with a line 51. Valve 48 may also have a shut-off position, if desired.
~ 7 The compressed air means 33 comprises a compressed air supply 52, a line 53 connecting supply 52 to a multiposition valve 54, and lines 51 and 56. Line 56 is in communication with the jacket 24, and line 51 is attached to valve 48 for communicating with central chamber 21 when valve 48 is positioned to connect lines 49 and 51. Water or water mist can be used for cooling.
For example, water may be aspirated into the compressed air line 53 by means of a venturi 57 in water line 58 connected to water supply 59 through valve 61.
Thus, it is seen that with the sources of vacuum, compressed air and steam available, the central chamber 21 can be subjected to vacuum or compressed air and the jacket 24 can be charged with steam or compressed air or a reverse operation achieved simply by appropriate operation of valves 38, 48, 54 and 61. These valves are preferably operated automatically by appropriate control and timing devices (not shown).
In operation, the processlform of the invention is carried out by performance of the steps hereinafter given. First of all, the jacket and any article that may be in the mold are removed, the mold closed, and the valve 48 operated to evacuate chamber 21. Feeding means 30 is then positioned at F and air is charged to air supply tube 45 to supply expanded polystyrene beads evenly along the exterior surface of the outer surface of mold section 13. As herein used, the term "beads" is intended to cover any particulate form of expandable polystyrene regardless of shape, and preferably pre-expanded beads are used to minimize the amount of final expansion. These llUA~?6~' particles or beads will be distributed evenly on the inner mold wall by virtue of the vacuum within providing a suction through the pores of the permeable sintercore material, permitting an efficient means of venting.
With the beads in place, the jacket is charged with steam of suitable pressure by operation of valve 38.
Steam will pass through the porous wall 14, mold cavity 16, and through the porous wall 13 into the vacuum chamber 21, assisted by the suction maintained therein. Exhaust port 41 is provided to assure steam flow to the entire jacket and preheat the expandable beads in cavity 17 indirectly. This port is equipped with a suitable control valve 44 to provide a desired positive steam pressure in the jacket.
After a time sufficient to expand and fuse the polystyrene beads has elapsed (which time can be minimized by experimentation), finally the steam is shut off and the mold is cooled. The cooling is achieved by charging the jacket 24 with compressed air which draws in water through the venturi 57 and forms a mist. This purges the steam and rapidly cools the mold. In addition, the compressed air may be the sole cooling agent after a certain period of time and it also maintains a positive pressure on the exterior surface of the molded article to assist in the separation of the article from the mold wall as the valve 57 and exhaust 44 are shut.
The vacuum is shut off in the interior chamber and the jacket is removed. Compressed air alone or a water mist is then directed into the interior chamber to provide final interior cooling and to separate the molded 11~2~67 article from the interior wall. The article is then removed, and the compressed air is shut off leaving the apparatus in position to start another molding cycle.
It will be appreciatecl that mold release compounds and other uses of the usual applicable technique will be employed as is usual in the art. In addition, a preferred process utilizes the step of applying a fine spray of mineral oil to the beads prior to the expansion thereof. This step may be conveniently carried out when the beads are in position on the mold wall prior to the assembly of the jacket. It has been found that such spray assists in the formation of a good unitary article of uniform strength.
In accordance with the invention, improved articles are made by assuring an excellent uniformity of density. Surface characteristics of the article are also maintained as well as those made with solid mold walls.
In other words, the process advantages of perforated mold walls are obtained without the usual disadvantage of surface imperfection, and the invention provides excellent results with the so-called high density foam articles, i.e., articles having a density greater than 2 pounds per cubic foot.
In its broad aspect, the invention may be utilized for articles of any sheet-like configuration.
However, the invention is particularly advantageous when used to mold an article having a cylindric body, slightly conical body or conical body having at least one open end.
Thus, tubes, spools and cups may be made with particular advantage when fabricated according to the invention.
ll~Z~6~,~
From the foregoing description, it is seen that the present invention provicles an improved method and apparatus for molding expandable polystyrene.
In general, the mold is charged with the requisite - amounts of pre-expanded but further expandable polystyrenebeads, and heated at a time sufficient to soften the polystyrene whereupon the beads expand a second time and fuse together. The mold is then generally cooled with cooling water, and the article or articles removed therefrom. These processes are generally satisfactory, but efforts have been made to effect improvements in such molding processes in order to increase the speed of production from a given unit, and to improve the properties of the molded composition.
The filling of cavities in molds is normally accomplished by transporting the pre-expanded beads into ~o these cavities with the help of an air stream. Venting '~.7' ' slots at different locations within these cavities are designed to permit the escape of the air and produce uniform filling. Such vents consist either of holes drilled into the walls of said cavities or inserts containing numerous slots. These surface interruptions are then found on the molded parts again since the expanding polystyrene during the molding step produces an exact replica of the surface it comes in contact.
In addition, efforts have been made to increase the application of steam by providing perforated walls, and U. S. Patent 3,081,488 shows the use of such perforated walls. This patentee also utilizes a vacuum interior to hold the beads on perforated walls to improve filling prior to molding. However, the perforated walls do not provide the desired smoothness for certain appli-cations such as high density tubular parts. In U. S.
Patent 3,259,677, there is a teaching of the use of porous permeable walls in a mold form, however, the patentee states that the mold is not suitable for molding expandable materials, because the material itself forms a closed barrier. Instead, the patentee limits his application to the formation of regular heat-softenable, non-expandable plastic material.
In addition, certain problems have been encountered with respect to obtaining a uniformly expanded article, because both a uniform distribution and an even softening of the bead particles is required to prevent certain areas from being heavy and other areas from being comparatively light.
Thus, it is a primary object of the invention to provide a method and apparatus for molding expandable polystyrene in which the molding operation is carried out in a minimum of time with a minimal amount of equip-ment.
Another object of the invention is to provide a method and apparatus for molding expandable polystyrene in which tubular parts and the like may be formed which are substantially uniform in density throughout.
It has now been found that these and other objects are achieved by providing a mold cavity having smooth, permeable walls together with means for providing a vacuum, steam and compressed air in order to operate the mold under improved process conditions. The smooth, permeable walls are preferably made with sintercore metal, which has the advantages of allowing passage of air or steam through the walls, which provides a smooth molding surface, and which provides good heat transfer character-istics.
Thus, the invention provides a mold assembly for forming a high density expandable polystyrene article of an open-ended, closed-curved, sheet-like configuration having an interior surface and an exterior surface. The assembly comprises an interior mold section formed with smooth permeable wall means having an interior surface defining an interior chamber and an exterior surface shaped to match the interior surface of the article to be molded and provide a part of a mold cavity, an outer mold section formed with smooth permeable wall means having an inner sur-face shaped to define the exterlor-s~rface o~ the article to be molded and formed for fitting against said inner section to form said mold cavity, a jacket means disposed to provide an exterior chamber adjacent to the outer surface of the outer section of the mold, said jacket means and outer mold sections being removable to expose the mold cavity, means for evacuating the interior or exterior chamber to provide a vacuum within the mold, means for supplying steam to the jacket or inner chamber, and means for cooling the mold.
Preferably, the mold cavity is tubular in configuration, and the assembly is adapted to form tubular parts, spools or cups. The permeable wall means are preferably made of sintercore metal, and the cooling means comprises means for supplying compressed air or vacuum or water to the steam jacket. In the preferred form, compressed air can also be supplied to the interior - chamber. In its process form, the invention provides a method of molding expandable polystyrene comprising the steps of providing a mold assembly having a mold cavity substantially enclosed by a permeable sintercore material, a first chamber in the center of the mold cavity and a second chamber on the other side of the mold cavity;
evacuating said first chamber to provide a vacuum therein;
placing a measured amount of pre-expanded but further expandable polystyrene beads in said mold cavity; charging said second chamber with steam whereby steam will move through the permeable mold walls and mold cavity into the first chamber; said steam being charged for a time sufficient to expand and fuse the expandable polystyrene within the entire mold cavity, shutting off said steam, ~ Q ~7 cooling the molded polystyrene, and removing the molded polystyrene article from the mold.
It is preferred to use metallic materials in the mold assembly to provide good heat transfer character-istics. The vacuum should best be used when loading the mold to retain the beads in an even distribution and when charging with steam so that steam is initially directed through the entire mold. Compressed air, water or a water mist are used for cooling assist in forming a cool outer surface on the outer surface of the poly-styrene article. Similarly, compressed air is directed to the inner chamber to assist interior cooling and help release the article from the inner mold walls.
The invention described in this patent appli-cation uses sintermetal to produce maximum venting by utilizing the entire surface of the mold.
The steaming process is normally carried out by injecting steam through the aforementioned vent holes which then penetrates into the beads and causes their expansion and subsequent fusion. The even distribution of the steam over the entire surface is particularly critical for high density applications. It was also found that the steaming rate is a decisive factor for uniform results. If the steam is applied too fast, then the expandable polystyrene tends to seal off at the surface and prevent the further penetration of the steam into the core of the part to be molded. It may also cause local melting of the expandable polystyrene, an effect known as "burning".
_ 6 --~ 6'7 The use of sintermetal permits the application of steam in two ways:
First, by applying low pressure the expanded beads in the cavity are preheated and start to expand from the heat conducted from the surface. The appli-cation of a vacuum through the sintercore permits then the even distribution of the steam over the entire outer surface of the part and penetration through to the core which permits even fusion throughout the cross section of the part.
If desired, the vacuum in the core can be substituted with steam and a vacuum applied to the outer shell so that the direction of steaming is reversed.
Cooling the molded article is normally required to form a sufficiently hard layer on the surface which is able to withstand the residual inner pressure from the expanded beads in the article. This is accomplished by the application of air, water or vacuum or combinations thereof to the walls of the mold for a certain period of time. It is generally advantageous to keep the quantity of water to a minimum and thus the application of a fog or water mist is all that is required to lower the wall temperature of a mold sufficiently.
The molded article is then removed from the mold. This removal presents usual difficulties with cylindrical cores, but is helped greatly in this invention by providing air pressure to the core and thus loosen up that article.
Thus, it is seen that the invention is best adapted to form tube-like configurations such as tubes, spools, or cups. The invention is also particularly 1 1~ 2~ ~ 7 valuable in forming the so-called high density foam articles.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing, in which like numerals are used to designate like parts throughout:
Figure 1 is a cross-sectional view of a mold constructed according to the invention together with a diagrammatic view of the associated parts;
Figure 2 is a cross-sectional view of the mold of Figure 1 taken in the plane of line 2-2 thereof; and Figure 3 is a cross-sectional, elevational view of a means for charging the mold with feed material.
While only the preferred embodiment is shown in the drawings, it should be understood that the invention is to be limited only by the spirit and scope of the appended claims.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now more particularly to the drawings, there is shown a mold assembly 11, comprising a mold 12 composed of a sintercore metal and formed with an inner mold section 1~ and an outer mold section 14. Between the inner and outer mold section, a mold cavity 16 is provided, in which the molded article 17 is formed. The inner mold section 13 is carried on a frame plate 18, which is mounted in conventional fashion on suitable supports (not shown).
In the embodiment of the drawing, the inner mold section 13 is generally cylindrical, and is permanently secured to frame plate 18, with the plate ~0 closing one end of the inner part of the cylindrical section. The other end is closed by a plate 19, which . ' . ' is permanently secured thereto. In this way, a central chamber 21 is formed within the sintercore inner mold section 13. The outer mold section 14 is also generally cylindrical, and forms the inner part of jacket assembly 22. The jacket assembly 22 also comprises an outer shell 23, which is cylindrical and concentrically disposed to the outer mold section 14 to form a jacket chamber 24 therebetween. The ends of the jacket chamber 24 are closed with end plate 26, and spacer plate 27. As here shown, a circular closure plate 28 is provided to close an end of the mold cavity 16, but it will be appreciated that plates 26 and 28 may be combined into a single plate unit, if desired.
In order to remove the molded article 17 from the mold, the jacket assembly 22 is removably attached to frame plate 18 through a circular flange 29 formed on outer shell 23. If desired, the flange 29 can be removably attached to frame plate 18 by suitable bolts or the like; however, it is preferred to use suitable, fast acting, removable clamping means (not shown) to speed up the production of the mold assembly.
As here shown, the jacket assembly 22 is constructed in two sections, with each section having a pair of longitudinal flanges 31. These flanges are also removably attached by suitable means (not shown), and removal of the jacket is facilitated by use of the two sections. However, it will be appreciated that the jacket assembly could be made in one piece, and removed axially, if desired.
_ g _ ~ 6 7 The mold assembly 11 also comprises feeding means 30 for supplying expandable beads to the mold at point F, means 32 for supplying steam to jacket 24, means 33 for supplying compressed air to the jacket 24 and central chamber 21, and means 34 for providing a vacuum in central chamber 21.
Feeding means 30 comprises a venturi tube 35 having a feed inlet 40 for receiving pre-expanded polystyrene beads from a suitable source such as a hopper (not shown), means 30 also comprises a movable compressed air supply tube 45 for directing a stream of alr and polystyrene beads into the mold.
Steam supply means 32 comprises a source of steam 36, line 37, which is controlled by multiposition valve 38, entry port 39 to jacket 24, and exhaust port 41 which can be closed by valve 44. As here shown, a branch line 42 is shown communicating with a second entry port 43.
However, it will be appreciated that more or even less entries and/or exhausts than those shown may be utilized, if desired. It will also be appreciated that the vacuum chamber and steam chamber could be reversed, along with their associated parts.
The vacuum means 34 comprises a source of vacuum such as vacuum pump 46, operative through line 47, valve 48 and line 49 to evacuate the central chamber 21.
Valve 48 is a multiposition valve capable of connecting line 47 to line 49 for connecting the vacuum pump 46 to the central chamber 21, and capable of connecting line 49 with a line 51. Valve 48 may also have a shut-off position, if desired.
~ 7 The compressed air means 33 comprises a compressed air supply 52, a line 53 connecting supply 52 to a multiposition valve 54, and lines 51 and 56. Line 56 is in communication with the jacket 24, and line 51 is attached to valve 48 for communicating with central chamber 21 when valve 48 is positioned to connect lines 49 and 51. Water or water mist can be used for cooling.
For example, water may be aspirated into the compressed air line 53 by means of a venturi 57 in water line 58 connected to water supply 59 through valve 61.
Thus, it is seen that with the sources of vacuum, compressed air and steam available, the central chamber 21 can be subjected to vacuum or compressed air and the jacket 24 can be charged with steam or compressed air or a reverse operation achieved simply by appropriate operation of valves 38, 48, 54 and 61. These valves are preferably operated automatically by appropriate control and timing devices (not shown).
In operation, the processlform of the invention is carried out by performance of the steps hereinafter given. First of all, the jacket and any article that may be in the mold are removed, the mold closed, and the valve 48 operated to evacuate chamber 21. Feeding means 30 is then positioned at F and air is charged to air supply tube 45 to supply expanded polystyrene beads evenly along the exterior surface of the outer surface of mold section 13. As herein used, the term "beads" is intended to cover any particulate form of expandable polystyrene regardless of shape, and preferably pre-expanded beads are used to minimize the amount of final expansion. These llUA~?6~' particles or beads will be distributed evenly on the inner mold wall by virtue of the vacuum within providing a suction through the pores of the permeable sintercore material, permitting an efficient means of venting.
With the beads in place, the jacket is charged with steam of suitable pressure by operation of valve 38.
Steam will pass through the porous wall 14, mold cavity 16, and through the porous wall 13 into the vacuum chamber 21, assisted by the suction maintained therein. Exhaust port 41 is provided to assure steam flow to the entire jacket and preheat the expandable beads in cavity 17 indirectly. This port is equipped with a suitable control valve 44 to provide a desired positive steam pressure in the jacket.
After a time sufficient to expand and fuse the polystyrene beads has elapsed (which time can be minimized by experimentation), finally the steam is shut off and the mold is cooled. The cooling is achieved by charging the jacket 24 with compressed air which draws in water through the venturi 57 and forms a mist. This purges the steam and rapidly cools the mold. In addition, the compressed air may be the sole cooling agent after a certain period of time and it also maintains a positive pressure on the exterior surface of the molded article to assist in the separation of the article from the mold wall as the valve 57 and exhaust 44 are shut.
The vacuum is shut off in the interior chamber and the jacket is removed. Compressed air alone or a water mist is then directed into the interior chamber to provide final interior cooling and to separate the molded 11~2~67 article from the interior wall. The article is then removed, and the compressed air is shut off leaving the apparatus in position to start another molding cycle.
It will be appreciatecl that mold release compounds and other uses of the usual applicable technique will be employed as is usual in the art. In addition, a preferred process utilizes the step of applying a fine spray of mineral oil to the beads prior to the expansion thereof. This step may be conveniently carried out when the beads are in position on the mold wall prior to the assembly of the jacket. It has been found that such spray assists in the formation of a good unitary article of uniform strength.
In accordance with the invention, improved articles are made by assuring an excellent uniformity of density. Surface characteristics of the article are also maintained as well as those made with solid mold walls.
In other words, the process advantages of perforated mold walls are obtained without the usual disadvantage of surface imperfection, and the invention provides excellent results with the so-called high density foam articles, i.e., articles having a density greater than 2 pounds per cubic foot.
In its broad aspect, the invention may be utilized for articles of any sheet-like configuration.
However, the invention is particularly advantageous when used to mold an article having a cylindric body, slightly conical body or conical body having at least one open end.
Thus, tubes, spools and cups may be made with particular advantage when fabricated according to the invention.
ll~Z~6~,~
From the foregoing description, it is seen that the present invention provicles an improved method and apparatus for molding expandable polystyrene.
Claims (19)
1. A method of molding expandable polystyrene comprising the steps of providing a mold assembly comprising a mold having a cavity substantially enclosed by a smooth permeable material, a first chamber on one side of the mold cavity, and a second chamber on the other side of the mold cavity, evacuating said first chamber to provide a vacuum therein, placing an amount of expandable polystyrene beads in said mold cavity, charging said second chamber with steam while the first cavity is under vacuum, whereby steam will move through the permeable mold walls and mold cavity into the first chamber, said steam being charged for a time sufficient to expand and fuse the expandable poly-styrene within the entire mold cavity, shutting off said steam, cooling the molded article, and removing the molded article from the mold.
2. A method of molding expandable polystyrene, as defined in claim 1, in which compressed air is provided in said first chamber during the step of removing the expanded polystyrene from the mold.
3. A method of molding expandable polystyrene, as defined in claim 1, in which the cooling step is effected by blowing compressed air or a water mist through the second chamber.
4, A method of molding expandable polystyrene, as defined in claim 1, in which the mold is constructed of a metallic material.
5. A method of molding expandable polystyrene, as defined in claim 1, which also comprises the step of contacting the expandable polystyrene with a fine mist of mineral oil.
6. A method of molding expandable polystyrene into an open-ended, closed, sheet-like configuration, com-prising the steps of providing a mold assembly, comprising an inner mold section formed with smooth permeable wall means having an interior surface defining an interior chamber and an exterior surface shaped to define the interior surface of the open-ended, closed, sheet-like configuration to be molded, and an outer mold section formed with smooth per-meable wall means having an inner surface shaped to define the exterior surface of the configuration to be molded, said inner and outer section fittable to provide a mold cavity therebetween, and a jacket formed to provide an exterior chamber adjacent to the outer surface of the outer section of the mold, evacuating said interior chamber to provide a vacuum therein, placing expandable polystyrene in said mold cavity, charging said exterior chamber with steam for a time sufficient to expand the expandable polystyrene and fill the mold cavity therewith while maintaining the inner chamber under vacuum, cooling the expanded polystyrene, removing the jacket and the outer section of the mold, and removing the molded polystyrene from the mold.
7. A method of molding expandable polystyrene, as defined in claim 6, in which the mold cavity is shaped to form a substantially tubular article.
8. A method of molding expandable polystyrene, as defined in claim 6, in which the mold sections are composed of a sintercore metallic material.
9. A method of molding expandable polystyrene, as defined in claim 6, in which compressed air is charged into the interior chamber to assist in rapid removal of the molded article from the mold.
10. A method of molding expandable polystyrene, as defined in claim 6, in which the operations to the interior chamber and exterior chamber are reversed.
11. A method of molding expandable polystyrene, as defined in claim 6, in which the expanded product is of densities above 2 pounds per cubic foot.
12. A method of molding expandable polystyrene, as defined in claim 11, in which the expanded product is tubular in configuration.
13. A method of molding expandable polystyrene, as defined in claim 6, in which the cooling step is effected by blowing compressed air or a water mist through the chambers.
14. A mold assembly for forming a high density expandable polystyrene article of an open-ended, closed-curved, sheet-like configuration having an interior surface and an exterior surface, comprising an inner mold section formed with smooth permeable wall means having an interior surface defining an interior chamber and an exterior surface shaped to match the interior surface of the article to be molded and provide a part of a mold cavity, an outer mold section formed with smooth permeable wall means having an inner surface shaped to define the exterior surface of the article to be molded and formed for fitting against said inner section to form said mold cavity, a jacket means disposed to provide an ex-terior chamber adjacent to the outer surface of the outer section of the mold, said jacket means and outer mold sections being removable to expose the mold cavity, means for evacuating the interior chamber to provide a vacuum within the mold, means for supplying steam to the jacket, and means for cooling the mold.
15. A mold assembly, as defined in claim 14, in which the permeable wall means of the inner and outer mold sections are each composed of sintered metal.
16. A mold assembly, as defined in claim 14, in which the mold cavity is substantially tubular.
17. A mold assembly, as defined in claim 14, in which the means for cooling the mold comprises a means for supplying compressed air or a water mist to the jacket.
18. A mold assembly, as defined in claim 14, which also comprises means for supplying compressed air or a water mist to the interior chamber.
19. A mold assembly as defined in claim 14 where the application of steam, vacuum and cooling can be re-versed from the inner to the outer jacket.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US75274176A | 1976-12-21 | 1976-12-21 | |
| US752,741 | 1976-12-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1102067A true CA1102067A (en) | 1981-06-02 |
Family
ID=25027621
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA293,522A Expired CA1102067A (en) | 1976-12-21 | 1977-12-20 | Method and apparatus for molding expandable polystyrene |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1102067A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4627946A (en) * | 1983-11-07 | 1986-12-09 | Morval-Durofoam Ltd. | Method and molding apparatus for molding expanded polystyrene articles having smooth surfaces |
| US4781555A (en) * | 1987-01-07 | 1988-11-01 | Efp Corp. | Apparatus for forming molded patterns |
-
1977
- 1977-12-20 CA CA293,522A patent/CA1102067A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4627946A (en) * | 1983-11-07 | 1986-12-09 | Morval-Durofoam Ltd. | Method and molding apparatus for molding expanded polystyrene articles having smooth surfaces |
| US4781555A (en) * | 1987-01-07 | 1988-11-01 | Efp Corp. | Apparatus for forming molded patterns |
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