Note: Descriptions are shown in the official language in which they were submitted.
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
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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.
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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
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- 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
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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
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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
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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.
