Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the continuous forming
of thermoplastic material into a three dimensional sheet
from granular form in a continuous process and parti-
cularly to an apparatus therefor.
The use of vacuum forming on a moving belt has
been directed to embossing a preformed sheet of material
or to extruding a falling sheet or curtain of material
and then embossing such sheet of material.
The present invention is directed to the
formation of a sheet of material to be vacuum formed
on cooperative continuous moving belts. The raw
granular thermoplastic material is blended, plasti-
cized and thence extruded to roller die means which
accurately controls the dimension of the hot sheet
of thermoplastic material. The conveyor belt which
receives the sheet of material is a lower belt made of
flexible material and has a three dimensional mold formed
thereon, which lower belt is cooperative with a mating
upper belt of similar form so that upon pulling of a
vacuum on the lower belt, the sheet material is formed
precisely into the shaped lower mold along with the upper
belt to form a precise dimensional end product. Such
upper belt facilitates the product formation and helps
to control the thickness thereof to improve the efficiency
and quality of the vacuum formed product.
According to the invention there is provided an
apparatus for the continuous molding of sheet material into
a three dimensional design comprising an endless lower
flexible belt mold having a three dimensional irregular
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pattern, particularly a female pattern, with peaks and
valleys formed therein, an endless upper flexible belt mold,
particularly a male belt mold, complementary in design to or
cooperative with the lower flexible belt mold, means for
feeding hot thermoplastic material to the bite of said belt
molds, said lower belt mold having a plurality of spaced open-
ings to provide means for pulling a vacuum on the warm thermo-
plastic material located between said belt molds, means con-
nected to said lower belt mold for pulling a vacuum through
said openings of said lower belt mold.
In particular the upper and lower belt molds have
upper and lower runs, and the lower run of the upper belt is
operable to engage a portion of the upper run of the lower
belt mold. Means are operatively connected to the endless belt
molds for moving them through their endless path.
The means for pulling the vacuum also functions to
pull the belt molds into complementary engagement while the
endless belt molds are moving through their endless path of
movement.
In particular the invention in one embodiment pro-
vides a blender that processes granular thermoplastic material
for an extruder which in turn feeds the extrudate to a pair
of roller dies which processés the extrudate into a
thin sheet of film for passage onto a lower endless
conveyor belt and its mating upper endless conveyor
.
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belt. The belts have a molded design thereon that
cooperates with each other so that when a vacuum is
pulled a finished three dimensional p~oduct is provided
that does not require trimming but is precisely di-
5 mensioned. In lieu of the blender and extruder asupply roll of sheet material is heated and fed to
the cooperative conveyor belts for forming.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side elevational view of the
10 preferred embodiment of the continuous thermo orming
machine.
Fig. 2 is a plan view of the thermo forming
machine shown in Fig. 1.
Fig. 3 is an enlarged cross sectional of
15 the finished product on the cooperative upper and
lower belt molds.
Fig. 4 is a cross-sectional view of the
cooperative belt molds taken along line 4-4 of Fig. 1.
Fig. 5 is a fragmentary side elevational
20 view of a modified form of the continuous thermo
forming machine shown in Fig. 1.
DETAILED DESCRIPTION
Referring to the drawings, wherein like
reference character designate like or corresponding
25 parts throughout the several views, there is shown in
Fig. 1 a blender 10 having a hopper with suitable
mixing means therein. The mixed blend is conveyed by
a suitable pump means not shown via conduit 11 to
the hopper 12 of an extruder 13. The extruder 13
- 30 is provided with a die head 14 from which the extru-
date issues and is guided to a pair of roller dies 15
and 16. The roller dies 15 and 16 accurately control
the thickness of the formed sheet of thermoplastic
material which is directed downwardly onto a lower
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endless conveyor belt mold 17. The lower conveyor
belt mold 17 is made of a flexible material being con-
toured with the groove design as shown on the product
in Fig. 2 and Fig. 3. As seen in plan view in Fig. 2,
5 the product has a corrugated design with peaks and
valleys. The specific groove design is only one
specific example which the cooperative belt molds to
be described may take as other three dimensional
- designs are contemplated. The conveyor belt mold 17
10 is trained over drive roller 20 and idler roller 21,
which idler roller 21 is suitably adjustable to pro-
vide the required tension thereon. The conveyor belt
mold 17 has a plurality of holes 18 therethrough to
provide means for exerting a vacuum onto the thermo-
15 plastic material being fed onto the endless conveyorbelt mold 17. A vacuum box 25 located beneath the
forwardly disposed portion of the conveying run o
lower conveyor belt mold 17 provides the means which
exerts the suction on the thermoplastic material on
20 the belt mold 17 to shape such material into the
mold design of the belt mold 17. A suitable vacuum
pump is connected via conduit 26 to the vacuum box 25
to exert a vacuum thereon. Downstream from the con-
veyor belt mold 17 is a take-away conveyor 30 trained
25 about suitable pulleys 31 and 32. Suitable power means
are provided to move the conveyor belt. A guillotine
shear 33 suitably powered for intermittent cuts severs
the formed thermoplastic materialinto predetermined
lengths of corrugated product 42. The cut lengths of
30stock or product 42 are stacked onto a skid 37 for
packing.
Mounted above the conveying run of lower
belt mold 17 and directly in line with vacuum box 25
is a plurality of rollers 35-36-37. Such rollers are
35supported by suitable brackets which brackets are
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deleted to better illustrate the relationship of
the conveyor belt molds. An upper endless conveyor
belt mold 40 is suitably trained about rollers 35-36-
37 and is complimentary to the lower endless conveyor
5 belt mold 17 acting as a cooperative male mold sec-
tion operative to assist the formation of the plastic
product 42 with the lower female belt mold section 17
as depicted by Figs. 1 through 3. Upper conveyor
belt mold 40 has a pair of laterally spaced longitudin-
10 ally extending edge portions 41 and a downwardlyextending central mold section 42 that in effect is a
male mold section cooperative with the female mold
sections of the lower endless belt mold 17 to
facilitate the formation of the product and to assure
15 a mating of the respective belt molds 17 and ~0 to
seal a vacuum therebetween in the product formation.
As a vacuum is drawn through the holes 18 of belt mold
17 the thermoplastic material is drawn into the female
mold portion of the belt mold 17 along with the male
20 mold section of belt mold 40 since atmospheric
pressure is also acting downwardly on the upper belt
mold 40 with the respective spaced edges ~1 of belt
mold 40 acting as a seal as it engages the side
portions 43 of the lower belt mold 17. The upper con-
25 veyor belt 40 is made out of a suitable flexiblerubber compound and molded to the design of the pro-
duct to be com21imen~ary with lower conveyor belt 17.
Product 45 is shown corrugated with valleys 46 and peaks
47 in a zig-zag design as seen in Figs. 1 through 3.
In the operation, granular material such as
polyvinylchloride is fed into the hoppers of the
blender 10 which premixes the granular material with
additives to provide a warm-up and premixing of the
raw material. The premixed blend is then conveyed to
35 an extruder 13 which plasticates and works the material
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to form a homogeneous mass which is then conveyed to
a pair of roller dies 15 and 16 which shapes the
material into a thin sheet of thermoplastic material
for deposit onto the conveyor belt mold 17. The width
5Of the sheet material is accurately controlled by side
blades 50-50 so as to control the width of the material
being deposited onto belt 17. As the thermoplastic
sheet material is fed between conveyor belt molds 17
and 40, a vacuum is pulled in the vacuum box 25, the
10 sheet material is shaped precisely to the desired
mold since the sheet material and the upper belt molds
provide a positive seal of the mold and the product
is accurately reproduced. The molding operation is
performed continuously during the conveying of the
15hot thermoplastic material and as the molded product
leaves the conveyor 17 and deposited onto conveyor
30, the material is cut to precise lengths by a
guillotine shear 35.
A modification of the invention is shown in
20Fig. 5 wherein like parts are designated by like or
corresponding numerals as those designated on the first
déscribed embodiment. The only difference is that in
lieu of the blender 10, extruder 13 and roller dies
15 and 16 a suitable supply roll not shown supplies a
25suitable width plaster material to a heating unit 60
which is shown as having heating elements 61. A guide
roll 62 guides the sheet material 63 to the heating
unit 60 for delivery to the cooperative belt molds
17 and 40 which are identical to those described above.
30The supply roll and the heating unit 60 defines a
means for feeding hot thermoplastic material to the
bite of the belt molds as does the blender, extruder
and roller dies. The formed product is cut and
stacked as shown and described in the first embodiment.
35The operation is essentially identical to that described
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above except that in lieu of blending, extruding
and using roller dies on the hot sheet material a
supply roll of sheet material 63 is fed through a
heater to condition the plastic sheet material 63 for
5 forming by the belt molds 17 and 40 as described
above.
Various modifications are contemplated and
may obviously be resorted to by those skilled in the
art without aeparting from the described invention,
10 as hereinafter defined by the appended claims, as only
the preferred embodiments thereof have been disclosed.
,
