Note: Descriptions are shown in the official language in which they were submitted.
~L07~J107~
The present invention resides in an improved method
and apparatus for the extrusion of expandable synthetic resi-
nous foams. More specifically, the present invention resides
in an improved method and apparatus for the extrusion of ex
pandable synthetic resinous foams which can support the ex-
panding extruded foam without the necessity of individual
shaping plates for each product extruded.
Foamed plastics are well known items of commerce.
Particularly desirable forms of foam plastics are those
having rectangular or other regular configurations which are
suitable for structural purposes such as insulation. Bene-
ficially such foamed plastics are employed as panel cores,
building insulation as well as for decorative purposes such
as for supports for floral arrangements. Many foams have
a relatively low density usually Erom 1.5 to 3 pounds per
cubic foot and are prepared by extruding a heat plastified
mixture of a thermoplastic resin and a blowing agent. Such
~oamable plastic systems are well known in the art and some
are set forth in the following U. S~ Patents: 2,387,730;
2,409,slO; 2,5~5,250; 2,537,977; 2,576,911; 2l6~0,515;
2,669,751; 2,774,991; 2,857,625; 2,884,386; 2,92~,130;
3,121,130; 3,121,911; 3,194,~54; 3,219,733; 3,299,192;
3,431,163; 3,431,164; 3,466,705 and 3,764,642.
The extrusion of plastic foams with the passage of time
has become more sophisticated in order that the extruded
product might have physical characteristics suitable for -~
a specific application. It is particularly desirable in
the extrusion of foamed plastics that the cooled foam
have a shape and size of the desired end product thus
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avoiding loss of material by trimming, shaping and the
like. Tnerefore, it is desirable to extrude foam in such a
way that such trim waste is minimized and to this end
various extrude shaping devices have been employed~ The
physical properties of the resultant foam can be varied
quite significantly by such factors as the relative speed
of extrusion and takeaway speed which affects cell orienta-
tion. For many applications it has be~n found desirable to
provide shaping plates generally adjacent the extrusion die~
Such shaping plates have varied from flat plates which are
hinged adjacent the di~ to e3aborately curved plates which
conform more or less to the natural configuration of the
expanding foam. In some instances such plates have been
replaced by a plurality of rolls. Such shaping aids axe
intended to provide a finished product having a generally
rectangular or other predetermined configuration and hope
fully a generally uniform densi~y throughout the extruded
shape. One can, with time and patience~ devise a curved -~
shaping plate which aids in obtaining the desired physical
~0 characteristics in the extruded product. However, such a
shaping plate generally is satisfactory for only a single
product and/or a narrow rancJe of operating conditions and
when a different product or different operating conditions
are desired two or more new shaping plates must be developed.
The present invention resides in a process for
the preparation of synthetic resinous thermoplastic foam,
comprising the s~eps of extruding a heat plastified syn-
thetic resinous thermoplastic extrudable foamable compo
sition through an extrusion orifice into a shaping channel, ;
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of lower pressure, said channel having internal walls with a
cross-sectional configuration generally corresponding to the
shape of the product desired, the extrudable composition
expanding to generally fill said shaping channel and contact
the internal walls of said channel at a location adjacent a
discharge opening thereof, withdrawing the foamed product
from said channel at the discharge opening remote from the
extrusion orifice, and providing within said channel, at a
location ajacent to the extrusion orifice, a gas unde:r pres-
sure, the gas pressure being sufficient to regulate the
shape of the expanding composition at a location between the
die and a location where the expanding composition contacts
said channel walls.
Further features and advantages of the present
invention will become more apparent from the following
specification taken in connection with the drawing wherein:
Figure 1 is a schematic representation of a side
view of apparatus in accordance with the invention.
Figure 2 is a partially cutaway fractional view
of a portion of the apparatus of Figure 2.
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Figure 3 is an alternate embodiment of a channel
for the apparatus of Figure 1.
Figure 4 shows a channel suitable for the prepara-
tion of a foam having a circular cross-section.
In Figure 1 there is schematically depicted an
appaxatus indicated by the reference numeral 10. The
apparatus 10 comprises in co~perative combination a source
11 such as a plastics extruder which provides a heat plasti-
fied stream of a synthetic resinous thermoplaskic extrudable
~oamable composition. The extruder 11 is operatively con-
nected with a die 12. The die 12 has an extrusion orifice
13 having a generally slot-like configuration. The slot 13
i~ in ull communication with a hollow housing 15,. The
housing 15 defines the~ein a space~ channel or shaping
passage 16. The housing 15 has a discharge opening 17
remot~ly disposed from the die orifice 13. As depicted in
Figure 1~ the spacs 16 within the housing 15 has a desired
configuration; that is, rectangular. A conduit 18 is in
operative communication with the space 16 at a location 19
generally adjacent the die 12. The conduit 18 is in com-
munication with a conduit 21 which in turn comm~micat~s with
a gas pressure regulating valve 23 and a discharge nozzle or
bleed 24. Disposed within the space 16 is an expanded
extruded syn~hetic re~inous composition or foam 26 which
fills the cross-section o the space 16 adjacent the dis-
charge opening 17 thereo~. The foam 26 is in contact with a
major portion of the internal walls of the housing 15 and is
shaped thereby. A gas space 27 surrounds an extruda~le
foamable composition 26a at a location where the composition
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is foaming which is generally adjacent to the extrusion
orifice 13. The gas space 27 is defined by the housing 15
and foam 26a and 26. The extrudable composition 26a expands
or foams to form foam 26. The foam 26 remoke from the
orifice 15 peripherally engages the inner wall of the
housing 15 which series retains gas in the space 27. Remote
from the chamber 15 generally adjacent the ope.ning 17 are
takeaway rolls or conveying means 27 and 28.
In F.igure ~ there is more clearly shown the ccn-
figuration of the extrude 26a as it leaves the extrus:ion
orifice 13 and expands into the foam 26. -
In operation~ the foamable composition is extruded
from the orifice 13, expands to form the foam 26 and is
removed by the takeaway means 27 and 28. The gas pressure : :
regulating assembly consisting of components 1~, 21, 23 and 24
is adjusted by means of the valve 23 to provide a gas pressure
within the space 27 sufficient ~o permit either rapid : .
expansion or delayed expansion of the composition 26a as
desixed and provide the desired characteristics in the
extruded foam. For example, if cells are desired which
are elongated generally in directions normal to the direction .~:
of extrusion, a relatively low gas pressure is employed,
whereas if orientation is desired in the direction of
extrusion, a higher gas pressure is used 9 The gas pressure
; 25 tends to advance ~he foam from the chamber and overcomes
frictional drag forces developed by contact of the foam with -
the chamber walls. The particular pressure in the chamber
will vary rom composition to composition and depends upon
~he charac~eristics desired in the foam~ The gas pressure
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usually will be within the range of fxom about 1 to 15
pounds per square inch gauge. The temp,erature of the supply
gas is usually immaterial as the hea~ capacity and volume of
the gas is small relative to the extrude and the volume.
In Figure 3 there is schematically depicted an
alternate chamber suitable for use in the present invention
designated by the reference numeral 35~ The chamber 35
comprises a housing 36 which has an open end 37~ a closed
end 38 having defined therein an extrusion ori~ica 39. A
gas conduit 41 provides communication between the inside of
the chamber and a source of gas under pressure. A side
shaped fillet 43 is positioned in a corner of the housing
genexally adjacent to the slot 39. An upper shapled fillet
44 and a lowex shaped fillet 45 are similarly disposed
within corners of the housing. A Eourth side shaped fillet
is disposed opposite the fillat 43 but is not shown. The
arrangements of the fillets within the chamber 35 adjacent
the extrusion slot provides a convenience in startup of
extrusion hy eliminating sharp corners in which ini~ially
extruded foam may adhere prior to the extrusion of sufi-
cient foam material into the chamher to provide a cell
which would permit gas pressure to increase to a su~ficient
extent to shape the expanding portion of the extrude. The
~illets 43, 44r 45 and the fouxth side fillet (not shown~
do not contact the foam when steady sta~e operation is
achieved. Optionally, the side fillets may, if desired~
be increased in size to contact the extruded foam at the
rearmost edge portion and gas pressure support applied to
only the major aces of the expanding composition.
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In Figure 4 there ls depicted a sectional view
of a chamber su.itable for the practice of the pr~sent invention
generally designated by the reference numeral 50O The
chamber 50 has a jacketed housing 51. The housing 51 has
an open end 52 7 an internal passageway 53 and a feed end or
slot 54 remotely disposed from the open end 52. The housing
51 has defined therein a generally cylindrical passage which
smoothly curves in a concave mannPr to the orifice 54. The
conduit 55 is in communication with a source o~ pressure
regulated gas~ not shown. Dotted lines indicated by ~he
reference numeral 57 depict the shape of an extruded foam
composition within the chamber when a cylindrical billet is
being extruded. The housing may be heated, cooled or
operated at ambient temperature depending upon the surface
effects-desired in accord with conventional foam extrusion
practices. :
Apparatus as depicted in Figures 1-4 is eminently
satisfactory for the preparation of extruded thermoplastic
foams including polystyrene, polyvinyl chloride, polyethylene,
polypropylene and the like. .Rectangular, hexagonal and cir- :
; cular shape~ are readily prepared in a manner to give sub-
stantial control of cell orientation
The foregoing description is intended to be il-
lustrati~e and is not to be cons trued or interpreted as
2S being restrictive or otherwise limiting o F the present
invention.
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