CA1281875C - Vacuum forming process for deep drawn plastic articles - Google Patents
Vacuum forming process for deep drawn plastic articlesInfo
- Publication number
- CA1281875C CA1281875C CA000545574A CA545574A CA1281875C CA 1281875 C CA1281875 C CA 1281875C CA 000545574 A CA000545574 A CA 000545574A CA 545574 A CA545574 A CA 545574A CA 1281875 C CA1281875 C CA 1281875C
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- mold
- vacuum
- article
- passageways
- outer shell
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Abstract
VACUUM FORMING PROCESS FOR DEEP DRAWN PLASTIC ARTICLES
ABSTRACT OF THE INVENTION
An improved vacuum forming process for forming a deep drawn plastic article wherein a mold having a hollow cavity and a relatively thick outer shell mounted on a base forms the shape of the article.
The shell has a plurality of small passageways through the outer surface connected to relatively large passageways within the outer shell and the passageways are connected to a vacuum pump. A sheet of hot plastic material is placed over the mold and a vacuum is drawn to form the plastic sheet into the shape of the mold to form the article.
The improved process provides for a first large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a first area of the mold outer shell that forms the deep drawn portion of the article and connected in flow communication with a vacuum pump. A second large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a second area of the mold and connected in flow communication with a vacuum pump. A sheet of hot plastic material is placed over the mold and a vacuum is first drawn through the first large passageway to form the deep draw portion of the article and then a vacuum is drawn through the second large passageway. This improved vacuum forming process provides for thicker material in the deep draw portion of the article than the rest of the article.
ABSTRACT OF THE INVENTION
An improved vacuum forming process for forming a deep drawn plastic article wherein a mold having a hollow cavity and a relatively thick outer shell mounted on a base forms the shape of the article.
The shell has a plurality of small passageways through the outer surface connected to relatively large passageways within the outer shell and the passageways are connected to a vacuum pump. A sheet of hot plastic material is placed over the mold and a vacuum is drawn to form the plastic sheet into the shape of the mold to form the article.
The improved process provides for a first large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a first area of the mold outer shell that forms the deep drawn portion of the article and connected in flow communication with a vacuum pump. A second large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a second area of the mold and connected in flow communication with a vacuum pump. A sheet of hot plastic material is placed over the mold and a vacuum is first drawn through the first large passageway to form the deep draw portion of the article and then a vacuum is drawn through the second large passageway. This improved vacuum forming process provides for thicker material in the deep draw portion of the article than the rest of the article.
Description
8~5 PATENT - 9D-HR-16813-Taylor et al BACKGROUND OF THE INYENTION
Vacuum forming by removing the air from between th;n plastic sheet and a mold is well known. Such a process is utflized in forming household refrigerator liners which are relatively larye. In the usual vacuum form;ng process the mold ;s made of aluminum and the plastic sheet ;s heated and blown into a bubble. The mold is then placed inside the bubble and a vacuum fs drawn so that the bubble collapses to conform to the shape of the mold. Upon coolfng the plastfc material solfd;fies and permanently assumes the shape of the mold. The air is pulled or vacuumed through small holes over most of the surface of the mold and sucked fnto a large vacuum storage tank by a vacuum pump. In such a process the plastfc materfal formfng areas of the back of the liner contact the mold and solidify first. As the remaining air is removed from the areas forming the top, sides and bottom of the lfner, the plastic materfal is stretched and thinned and as the th;n plast;c material ;s drawn down against the mold the rema;n;ng plast;c material has to str~tch further. In the final stage of the vacuum forming process the front flanges of the liner are-formed from very thin mater;al wh;ch ;s undes;rable as that port;on of the deep drawn plast;c article or liner is subject to high forming stresses and subject to stress cracking subsequently. It is desirable to have the front flanges the th;ckest port;on so that ;t can w;thstand handling and securfng the lfner to the outer case of a refr;gerator and prevent stress cracking. It is therefore desfrable to be able to form those areas of the plastfc article that are deep drawn wfth thfcker plast;c mater;al than the other areas of the art;cle. Thfs fs partfcularly advantageous as ft is desfrable to make plast;c l~ners for refrfgerators as thfn as possfble yet retafnfng desired thfckness ;n the areas that are deep drawn, thus savfng substantfal amounts of PATEIIT - ~D-HR-16813-Taylor et al material which of course reduces the cost of manufacturing such article5. By this invention a process is prov~ded that allows Forming a deep drawn plastic article wherein the deep drawn areas may be thickened relative to the rest of the areas of the article.
_UMMARY OF THE lNVENTION
An ~mproved process in a vacuum forming process for forming a deep drawn plastic article wherein a mold having a hollow cavity and a relatively thick outer shell mounted on a base forms the shape of the article. The shell has a plurality of small passageways through the outer surface and connected to relatively large passageways within the outer shell, the passageways being connected to a vacuum pump. A sheet of hot plastic mater;al ;s placed over the mold and a vacuum ;s drawn to form the plastic sheet ;nto the shape of the mold to form the article. The ;mprovement process provides for a first large passageway lS interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a first area of the mold outer shell that forms the deep drawn portion of the article and is connected in flow communication with a vacuum pump. A second large passageway is provided that interconnects to a plurality of small passsageways through the outer surface of the mold outer shell in a second area of the mold, which second large passageway ;s connected in flow communication with a vacuum pump. The sheet of hot plast;c material is placed over the mold and a vacuum is first drawn through the First large passageway to form the deep drawn portion of the article and then a vacuum is drzwn through the second large passageway. Th;s improved vacuum forming process provides for thicker mater~al in the deep drawn portion of the article than the rest of the article.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a mold used in the vacuum forming process of the present invention.
~.281~
PATENT - 9D-HR-16813-Taylor et al FIG. 2 is a side elevational cross-sectional view of vacuum forming process equipment showfng a first stage of a vacuum forming process in which hot plastic sheet material is formed into a bubble.
FIG. 3 is a side elevational cross-sectional view of vacuum forming process equipment showing a second stage of a vacuum forming process utilizing the mold of Fig. 1.
FIG. 4 is a side elevatfonal view partially in sectfon show;ng the third stage of a vacuum forming process utilfzfng the mold shown in Fig. 1 incorporating the present invention.
FIG. 5 is a side elevational view partially fn section showing the completion of forming the article utflizing the mold of Fig. 1 incorporat;ng the present invention.
FIG. 6 is a fragmentary vfew partially in section of a portion of the mold shown fn F;g. 1 incorporating the present invention.
DESCRIPTION OF THE PP~EFERRED EMBODIMENT
With reference to the drawing, there is shown a mold 10 used in a vacuum forming process for forming a deep drawn plastic article 11 (Fig. 5) such as liners for household ~efrigerators. In one type of vacuum forming process the sheet of plastic material 15 to be formed into the article 11 is held by clamps 17 on a carrier 19 having an opening 21 under the sheet. The material is heated to soften it, then blown into a bubble as shown in Fig. 2. The plastic material is then collapsed against the mold to conform to the shape of the mold. The mold is usually made from aluminum and has a hollow cavfty 12 surrounded by an outer shell 14 usually havfng a thickness of 4-6 fnches which is mounted on a base 16. The mold has a plurality of small passageways 18 over most of the outer surface 20 whfch small passageways extend part-way through the outer shell 14. The small passageways have a diameter of .06 to .08 fnches and they are spaced at ~8~87~
- PATENT - 9D-HR-16813-Tayl or et al an average of 2-4 inches apart. The small passageways 18 in the mold are for removal of the air between the mold 10 and the plastic material 15 to be formed into the article. As best seen in Figs. 3-6, the small passageways 18 are connected inside the outer shell 14 to large passageways 22 that have been formed through the center of the outer shell perpend;c~lar to the small passageways 18 as shown particularly in Fig. 6. The large passageways 22 have a d;ameter of .75 to 1.0 inches. It will be noted that the large passageways 22 have plugs 24 at the outer surface 20 of the outer shell 14 so that air being drawn between the mold Duter surface 20 and the plastic sheet mater~al 15 will be drawn in through the small passageways 18 only.
As can be seen particularly in Figs. 1, 4 and 5, the mold 10 has at the bottom thereof a flange portion 28 on all four sides of the - mold. The base 16 has a recess 30 also on all four sides of the mold and spaced outwardly of the flange portion 28. Between the flange portion 28 and the recess 30 ;n the base is a raised base portion 32, The deep drawn portion of the article 11 or liner is formed over the flange portion 28 and it is desirable that this flange 34 and the portion of the liner adjacent the flange 34 designated generally as sect;on 36 be thicker than the rest of the liner to withstand forces that cause stress cracking. In vacuum forming processes heretofore the flange 34 and section 36 were molded from thinner material as it was the last area drawn into the mold and the material was stretched to a thinner thickness by that time. By this invention there is provided in the outer shell 14 of the mold 10 a first large passageway 38 interconnected to a plurality of small passageways 18 which pass through the outer surface 20 of the mold outer shell in a first area designated A around the periphery of the outer shell 14 that forms the deep draw portion of the article 11 or liner. In the case of a refrigerator liner this would be an area extending from the flange 28 ~L~8~75 PATENT - 9D-HR-16813-Taylor et al upwardly for about 6 inches and there a plug 42 separates the first large passageway interconnected to the small passageways fronl a second area designated B wh;ch ;n the case of the preferred embod;ment ;s the rest of the outer shell 14. The small passageways 18 in the second 5 area B of the outer shell are interconnected through the outer surface of the mold outer shell in a second area of the mold by a second large passageway 46. With this arrangement then the mold outer shell 14 is divided ;nto two areas A and B. The first being area A that should have the pldstic material in the deep draw area thicker than the second 10 area B. Both the fir5t large passageway 38 and second large passageway 46 are connected to a vacuum pump 48 usually by means of an air hose 51. In the preferred embodiment there ;s sw;tching means such as a sw;tching valve assembly 50 located between the large passageways in the outer shell 14 an~ the vacuum pump 43. The vacuum switching valve 15 is arranged to connect the first large passageway 38 to the vacuum pump 48 in air flow commun;cat;on and stop the a;r flow from the second large passageway 46 to the pump unt;l the deep drawn port;ons 34 and 36 are formed in the liner 11 and the~n the sw;tching valve assembly 50 operates to connect the first large passageway 38 and second large 20 passageway 46 to the vacuun pump 48 in air flow communicat;on. If desired, the sw;tch;ng means may be arranged to close the a;r flow from the f;rst large passageway 38 and open the second large passageway 46 after the deep drawn portions 34 and 36 are formed in the l;ner 11.
W;th reference to F;g. 3, the sw;tch;ng valve 50 ;s shown in its first Z5 pos;tion where;n the f;rst large passageway 38 ;s connected through the swltch;ng valve assembly 50 to the vacuum pump v;a ~;r hose 51 whereas the second large passageway 46 ;s blocked by a plunger 52 and prevents air from be;ng drawn through the second large passageway and the small passageways 18 in the second area B of the outer shell connected ~.281~7~
PATENT - 9D-HR-16813-Taylor et al thereto. ~fter the deep drawn portions 34 and 36 of the article 11 have been formed by the mold, the switch;ng valve assembly 50 is arranged to withdraw the plunger 52 from the second large passageway 46 and allow the pump to draw a vacuum through both the first large passageway 38 and second large passageway 46 and the small passageways 18 connected thereto. The switching valve assembly 50 also includes a biasing means such as a spr;ng 54 which upon release of the vacuum will , , , automatically reclose the plunger 52 sealing off the second large passageway ready for the next molding cycle.
In the vacuum forming process of the present invention there is provided a flat sheet of plastic material 15 which is attached to a carrier 19 as by clamps 17 around the periphery of the sheet of material and the carrier 19 has an interior opening 21 inwardly of the clamps 17. The sheet of plastic material 15 is heated to an elevated temperature to soften it and then air is blown through the opening 21 underneath the plastic material and forms the bubble shown in Fig. 2.
The molding apparatus then moves the mold 10 including the base 16 upwardly through the opening 21 in the carrier 19 to the position shown in Fig. 3. It will be noted that the upper portions of the mold have engaged the bubble of heated plastic material 15 and there is some sl;ght forming of the plastic material over the mold 10 at this point.
An upper vacuum chamber wall 64 is shown in Fig. 3 in a position spaced above the carrier 19 and then it is moved downwardly to engage the carrier 19 outboard of the clamps 17. At this point it is desirable to Z5 form the deep draw portion of the article 11 or liner and the vacuum ! pump evacuates the first large passageway and the plurality of small passageways interconnected to the first large passageway to draw the bubhle of plastic material 15 into the first area A of the mold as shown in Fig. 4. It will be noted that as shown in Fig. 4 the flange ~28~87~
PATENT - 9D-HR-16813-Taylor et al 34 and section 36 of the liner have been pulled in against the outer surface of the outer shell 14 in the first area of the mold designated A. Once that forming has taken place and the a;r has been w;thdrawn between the plastic material 15 and the mold ;n the f;rst area A, the vacuum is suff;c;ent to overcome the bias force of spring 54 ;n the switching valve assembly 50 and move the plunger 52 away from plugging the second large passageway 46, thus allowing air to be drawn by the vacuum pump from between the plastic mater~al 15 and thè second area B
of the outer shell 14 of the mold. After the vacuum form;ng has been complete the sheet of plastic material 15 has now taken the shape of the outer surface of the mold 10 as shown in Fig. 5. With all of the air removed the plastic material forming the liner sol;d;fies into the shape of the mold. The air flow is then reversed so that the liner can be blown away from the mold and the mold removed from the now formed liner. The liner may then be removed from the molding apparatus for further processing. Once the vacuum operation is complete the sw;tch;ng valve assembl~ ~0 ;s reset by spr;ng 54 clos;ng plunger 52 and sealing off air flow from the second large passageway 46 to the vacuum pump 48 and is ready for another vacuum forming cycle.
While, in accordance with the Patent Statute, there has been described what at present ;s considered to be the preferred method of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made thereto without depart;ng from the ;nvent;on. It is, therefore, ;ntended by the appended cla;ms to cover all such changes and modif;cat;ons as fall with;n the true sp;rit and scope of the ;nvention.
Vacuum forming by removing the air from between th;n plastic sheet and a mold is well known. Such a process is utflized in forming household refrigerator liners which are relatively larye. In the usual vacuum form;ng process the mold ;s made of aluminum and the plastic sheet ;s heated and blown into a bubble. The mold is then placed inside the bubble and a vacuum fs drawn so that the bubble collapses to conform to the shape of the mold. Upon coolfng the plastfc material solfd;fies and permanently assumes the shape of the mold. The air is pulled or vacuumed through small holes over most of the surface of the mold and sucked fnto a large vacuum storage tank by a vacuum pump. In such a process the plastfc materfal formfng areas of the back of the liner contact the mold and solidify first. As the remaining air is removed from the areas forming the top, sides and bottom of the lfner, the plastic materfal is stretched and thinned and as the th;n plast;c material ;s drawn down against the mold the rema;n;ng plast;c material has to str~tch further. In the final stage of the vacuum forming process the front flanges of the liner are-formed from very thin mater;al wh;ch ;s undes;rable as that port;on of the deep drawn plast;c article or liner is subject to high forming stresses and subject to stress cracking subsequently. It is desirable to have the front flanges the th;ckest port;on so that ;t can w;thstand handling and securfng the lfner to the outer case of a refr;gerator and prevent stress cracking. It is therefore desfrable to be able to form those areas of the plastfc article that are deep drawn wfth thfcker plast;c mater;al than the other areas of the art;cle. Thfs fs partfcularly advantageous as ft is desfrable to make plast;c l~ners for refrfgerators as thfn as possfble yet retafnfng desired thfckness ;n the areas that are deep drawn, thus savfng substantfal amounts of PATEIIT - ~D-HR-16813-Taylor et al material which of course reduces the cost of manufacturing such article5. By this invention a process is prov~ded that allows Forming a deep drawn plastic article wherein the deep drawn areas may be thickened relative to the rest of the areas of the article.
_UMMARY OF THE lNVENTION
An ~mproved process in a vacuum forming process for forming a deep drawn plastic article wherein a mold having a hollow cavity and a relatively thick outer shell mounted on a base forms the shape of the article. The shell has a plurality of small passageways through the outer surface and connected to relatively large passageways within the outer shell, the passageways being connected to a vacuum pump. A sheet of hot plastic mater;al ;s placed over the mold and a vacuum ;s drawn to form the plastic sheet ;nto the shape of the mold to form the article. The ;mprovement process provides for a first large passageway lS interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a first area of the mold outer shell that forms the deep drawn portion of the article and is connected in flow communication with a vacuum pump. A second large passageway is provided that interconnects to a plurality of small passsageways through the outer surface of the mold outer shell in a second area of the mold, which second large passageway ;s connected in flow communication with a vacuum pump. The sheet of hot plast;c material is placed over the mold and a vacuum is first drawn through the First large passageway to form the deep drawn portion of the article and then a vacuum is drzwn through the second large passageway. Th;s improved vacuum forming process provides for thicker mater~al in the deep drawn portion of the article than the rest of the article.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a mold used in the vacuum forming process of the present invention.
~.281~
PATENT - 9D-HR-16813-Taylor et al FIG. 2 is a side elevational cross-sectional view of vacuum forming process equipment showfng a first stage of a vacuum forming process in which hot plastic sheet material is formed into a bubble.
FIG. 3 is a side elevational cross-sectional view of vacuum forming process equipment showing a second stage of a vacuum forming process utilizing the mold of Fig. 1.
FIG. 4 is a side elevatfonal view partially in sectfon show;ng the third stage of a vacuum forming process utilfzfng the mold shown in Fig. 1 incorporating the present invention.
FIG. 5 is a side elevational view partially fn section showing the completion of forming the article utflizing the mold of Fig. 1 incorporat;ng the present invention.
FIG. 6 is a fragmentary vfew partially in section of a portion of the mold shown fn F;g. 1 incorporating the present invention.
DESCRIPTION OF THE PP~EFERRED EMBODIMENT
With reference to the drawing, there is shown a mold 10 used in a vacuum forming process for forming a deep drawn plastic article 11 (Fig. 5) such as liners for household ~efrigerators. In one type of vacuum forming process the sheet of plastic material 15 to be formed into the article 11 is held by clamps 17 on a carrier 19 having an opening 21 under the sheet. The material is heated to soften it, then blown into a bubble as shown in Fig. 2. The plastic material is then collapsed against the mold to conform to the shape of the mold. The mold is usually made from aluminum and has a hollow cavfty 12 surrounded by an outer shell 14 usually havfng a thickness of 4-6 fnches which is mounted on a base 16. The mold has a plurality of small passageways 18 over most of the outer surface 20 whfch small passageways extend part-way through the outer shell 14. The small passageways have a diameter of .06 to .08 fnches and they are spaced at ~8~87~
- PATENT - 9D-HR-16813-Tayl or et al an average of 2-4 inches apart. The small passageways 18 in the mold are for removal of the air between the mold 10 and the plastic material 15 to be formed into the article. As best seen in Figs. 3-6, the small passageways 18 are connected inside the outer shell 14 to large passageways 22 that have been formed through the center of the outer shell perpend;c~lar to the small passageways 18 as shown particularly in Fig. 6. The large passageways 22 have a d;ameter of .75 to 1.0 inches. It will be noted that the large passageways 22 have plugs 24 at the outer surface 20 of the outer shell 14 so that air being drawn between the mold Duter surface 20 and the plastic sheet mater~al 15 will be drawn in through the small passageways 18 only.
As can be seen particularly in Figs. 1, 4 and 5, the mold 10 has at the bottom thereof a flange portion 28 on all four sides of the - mold. The base 16 has a recess 30 also on all four sides of the mold and spaced outwardly of the flange portion 28. Between the flange portion 28 and the recess 30 ;n the base is a raised base portion 32, The deep drawn portion of the article 11 or liner is formed over the flange portion 28 and it is desirable that this flange 34 and the portion of the liner adjacent the flange 34 designated generally as sect;on 36 be thicker than the rest of the liner to withstand forces that cause stress cracking. In vacuum forming processes heretofore the flange 34 and section 36 were molded from thinner material as it was the last area drawn into the mold and the material was stretched to a thinner thickness by that time. By this invention there is provided in the outer shell 14 of the mold 10 a first large passageway 38 interconnected to a plurality of small passageways 18 which pass through the outer surface 20 of the mold outer shell in a first area designated A around the periphery of the outer shell 14 that forms the deep draw portion of the article 11 or liner. In the case of a refrigerator liner this would be an area extending from the flange 28 ~L~8~75 PATENT - 9D-HR-16813-Taylor et al upwardly for about 6 inches and there a plug 42 separates the first large passageway interconnected to the small passageways fronl a second area designated B wh;ch ;n the case of the preferred embod;ment ;s the rest of the outer shell 14. The small passageways 18 in the second 5 area B of the outer shell are interconnected through the outer surface of the mold outer shell in a second area of the mold by a second large passageway 46. With this arrangement then the mold outer shell 14 is divided ;nto two areas A and B. The first being area A that should have the pldstic material in the deep draw area thicker than the second 10 area B. Both the fir5t large passageway 38 and second large passageway 46 are connected to a vacuum pump 48 usually by means of an air hose 51. In the preferred embodiment there ;s sw;tching means such as a sw;tching valve assembly 50 located between the large passageways in the outer shell 14 an~ the vacuum pump 43. The vacuum switching valve 15 is arranged to connect the first large passageway 38 to the vacuum pump 48 in air flow commun;cat;on and stop the a;r flow from the second large passageway 46 to the pump unt;l the deep drawn port;ons 34 and 36 are formed in the liner 11 and the~n the sw;tching valve assembly 50 operates to connect the first large passageway 38 and second large 20 passageway 46 to the vacuun pump 48 in air flow communicat;on. If desired, the sw;tch;ng means may be arranged to close the a;r flow from the f;rst large passageway 38 and open the second large passageway 46 after the deep drawn portions 34 and 36 are formed in the l;ner 11.
W;th reference to F;g. 3, the sw;tch;ng valve 50 ;s shown in its first Z5 pos;tion where;n the f;rst large passageway 38 ;s connected through the swltch;ng valve assembly 50 to the vacuum pump v;a ~;r hose 51 whereas the second large passageway 46 ;s blocked by a plunger 52 and prevents air from be;ng drawn through the second large passageway and the small passageways 18 in the second area B of the outer shell connected ~.281~7~
PATENT - 9D-HR-16813-Taylor et al thereto. ~fter the deep drawn portions 34 and 36 of the article 11 have been formed by the mold, the switch;ng valve assembly 50 is arranged to withdraw the plunger 52 from the second large passageway 46 and allow the pump to draw a vacuum through both the first large passageway 38 and second large passageway 46 and the small passageways 18 connected thereto. The switching valve assembly 50 also includes a biasing means such as a spr;ng 54 which upon release of the vacuum will , , , automatically reclose the plunger 52 sealing off the second large passageway ready for the next molding cycle.
In the vacuum forming process of the present invention there is provided a flat sheet of plastic material 15 which is attached to a carrier 19 as by clamps 17 around the periphery of the sheet of material and the carrier 19 has an interior opening 21 inwardly of the clamps 17. The sheet of plastic material 15 is heated to an elevated temperature to soften it and then air is blown through the opening 21 underneath the plastic material and forms the bubble shown in Fig. 2.
The molding apparatus then moves the mold 10 including the base 16 upwardly through the opening 21 in the carrier 19 to the position shown in Fig. 3. It will be noted that the upper portions of the mold have engaged the bubble of heated plastic material 15 and there is some sl;ght forming of the plastic material over the mold 10 at this point.
An upper vacuum chamber wall 64 is shown in Fig. 3 in a position spaced above the carrier 19 and then it is moved downwardly to engage the carrier 19 outboard of the clamps 17. At this point it is desirable to Z5 form the deep draw portion of the article 11 or liner and the vacuum ! pump evacuates the first large passageway and the plurality of small passageways interconnected to the first large passageway to draw the bubhle of plastic material 15 into the first area A of the mold as shown in Fig. 4. It will be noted that as shown in Fig. 4 the flange ~28~87~
PATENT - 9D-HR-16813-Taylor et al 34 and section 36 of the liner have been pulled in against the outer surface of the outer shell 14 in the first area of the mold designated A. Once that forming has taken place and the a;r has been w;thdrawn between the plastic material 15 and the mold ;n the f;rst area A, the vacuum is suff;c;ent to overcome the bias force of spring 54 ;n the switching valve assembly 50 and move the plunger 52 away from plugging the second large passageway 46, thus allowing air to be drawn by the vacuum pump from between the plastic mater~al 15 and thè second area B
of the outer shell 14 of the mold. After the vacuum form;ng has been complete the sheet of plastic material 15 has now taken the shape of the outer surface of the mold 10 as shown in Fig. 5. With all of the air removed the plastic material forming the liner sol;d;fies into the shape of the mold. The air flow is then reversed so that the liner can be blown away from the mold and the mold removed from the now formed liner. The liner may then be removed from the molding apparatus for further processing. Once the vacuum operation is complete the sw;tch;ng valve assembl~ ~0 ;s reset by spr;ng 54 clos;ng plunger 52 and sealing off air flow from the second large passageway 46 to the vacuum pump 48 and is ready for another vacuum forming cycle.
While, in accordance with the Patent Statute, there has been described what at present ;s considered to be the preferred method of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made thereto without depart;ng from the ;nvent;on. It is, therefore, ;ntended by the appended cla;ms to cover all such changes and modif;cat;ons as fall with;n the true sp;rit and scope of the ;nvention.
Claims (7)
1. In a vacuum forming process for forming a deep drawn plastic article wherein a male mold having a hollow cavity and a relatively thick outer shell mounted on a base forms the shape of the article, said shell having a plurality of small passageways through the outer surface and connected to relatively large passageways within the outer shell, the passageways being connected to a vacuum pump, a sheet of hot plastic material is placed over the mold and a vacuum is drawn to form the plastic sheet into the shape of the mold to form the article, the improvement comprising:
providing a first large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a first area of the mold outer shell that forms the deep draw portion of the article and said first large passageway is connected in flow communication with the vacuum pump, providing a second large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a second area of the mold which second large passageway is connected in flow communication with the vacuum pump, heating a sheet of plastic material to soften it, blowing the softened sheet of plastic material into a bubble, placing the bubble of hot plastic material over the mold to trap air between the first area of the mold outer shell and the plastic material, first drawing a vacuum through the first large passageway to form the deep draw portion of the article, and then drawing a vacuum through the second large passageway.
providing a first large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a first area of the mold outer shell that forms the deep draw portion of the article and said first large passageway is connected in flow communication with the vacuum pump, providing a second large passageway interconnected to a plurality of small passageways through the outer surface of the mold outer shell in a second area of the mold which second large passageway is connected in flow communication with the vacuum pump, heating a sheet of plastic material to soften it, blowing the softened sheet of plastic material into a bubble, placing the bubble of hot plastic material over the mold to trap air between the first area of the mold outer shell and the plastic material, first drawing a vacuum through the first large passageway to form the deep draw portion of the article, and then drawing a vacuum through the second large passageway.
2. In the vacuum forming process of Claim 1 wherein a vacuum switching valve is located between the vacuum pump and the first and second large passageways which valve operates to connect the first large passageway to the pump in air flow communication and stop the air PATENT - 9D-HR-16813-Taylor et al flow from the second large passageway to the pump until the deep drawn portions are formed in the article and then operates to connect the second large passageway to the pump.
3. In the vacuum forming process of Claim 1 wherein a vacuum valve is located between the vacuum pump and the first and second large passageways and operates to connect the first large passageway to the vacuum pump in air flow communication and stop the air flow from the second large passageway to the pump until the deep drawn portions are formed in the article and then operates to connect the first large passageway and second large passageway to the pump in air flow communication.
4. In the vacuum forming process of Claim 1 wherein the plastic article formed is a refrigerator liner with an open front end having a flanged periphery and the deep drawn portion of the article is located in the area adjacent the flanged periphery.
5. In the vacuum forming process of Claim 4 wherein the first area of the mold outer shell having the first large passageway interconnected to a plurality of small passageways is located between the flanged periphery of the article and 6 inches above the flanged periphery.
6. In the vacuum forming process of Claim 1 wherein the small passageways have a diameter of from .06 to .08 inches and are spaced from each other an average of from between 2 to 4 inches.
7. In the vacuum forming process of Claim 1 wherein the large passageways have a diameter of between 3/4 and 1 inch diameter.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US90278786A | 1986-09-02 | 1986-09-02 | |
| US902,787 | 1986-09-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1281875C true CA1281875C (en) | 1991-03-26 |
Family
ID=25416392
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000545574A Expired - Fee Related CA1281875C (en) | 1986-09-02 | 1987-08-27 | Vacuum forming process for deep drawn plastic articles |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1281875C (en) |
-
1987
- 1987-08-27 CA CA000545574A patent/CA1281875C/en not_active Expired - Fee Related
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| Date | Code | Title | Description |
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| MKLA | Lapsed |