Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: METHOD AND APPARATUS FOR FORMING
AN EXTRUDED FOAM PRODUCT
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BACKGRQUND OF THE INVENTION
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The present invention relates to the extrusion of
polymer foan product and methods and apparatus for
improvîng the production of such product. Apparatus and
methods of the present invention provide greater
flexibility in the manufacture of different fuam products
and greater freedom with respect to the accuracy of the
product and the size of the product which are extruded.
The direct or free extrusion of polymer foam
product is well known and requires the mixing of a gas in
a liquid form with a suitable polymer and forcing the
mixture through a controlled orifice which contributes to
the final shape of the product. Once this product leaves
the orifice, the gas which was previously in a liquid form
expands to ~orm the various cells of the foam product and
the cross section of the product increases many times
until foaming of the product is substantially complete. A
TM
mixture of Freon ' in a liquid form and a hot plastic is
passed through a die ori-f'ice and foams at atmospheric
pressure beyond the orifice as the FreonTM changes to a
gas. The product is typically dischaxged into a llquicJ
filled, llquid sprayed or air cooled trough to ass.lst in
~orming a skin on the product and to cool the product.
In a direct or free extrusion process, the shape
of the orifice in -the dle is critical in determinlng the
final shape of the product and the density of the product
3û as it is being extruded also contrlbutes to the final size
of the product. Because of these factors and others, the
tolerance variation of the final cross section of the
product varies considerably and changes in density of the
product will greatly contribute to even wider tolerance
variations.
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The other aspect that is important with free or
direct extrusion is the ability to maintain a generally
consistent cell structure and this requires -the gas to
remain in a liquid form until it is extruded through the
die orifice. Thus, there must be a substantial pressure
maintained on the mixture of hot plastic and FreonT~
such that the FreonTM on the upstream side of the die
orifice is maintained ln a liquid state and evenly
distributed. This requirement to maintain a significant
pressure is not a problem where the die orifice is small,
however7 in the manufacture of larger dia~eter product or
larger cross sectional area product, the orifice becomes
larger and the ability to continuously maintain this high
pressure on the upstream side is much more difficult. In
order to accomplish this, for example, in the manu~acture
of a five or six inch diameter rod, the initial material
is placed in an accummulator and processed on a batch type
process. For example, a certain amount of pro~uct, say,
sufficient product to produce a ten foot length, would be
accummulated in an extruder and then a piston would urge
this raw material at the necessary operating pressure
through the large orifice and the piston would ensure that
the product is maintalned at a suFFiciently high pcessure
to avoid th~ FreonTM or other material chan~in~ to a g&l~
state within the extruder. Thus, wi1h such a system, it
is possible to produce product o~ larger ccoss sectional
area, say, in excess o~ 12 square inches and in length up
to about ten feet or more, depending upon the size of the
machine on a batch type basis. In order to produce such a
large cross sectional area product on a continuous basis,
substantial capital costs investment would be required
and, to justify this expenditure, the demand for the
product woul~ have to be large. Even with such capital
expenditure, product variation due to changes in density
of the raw material would render the process diFFicult and
contribute to substantial tolerance variations.
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According to the present :invention, it is
possible to use lower capacity extrusion apparatus for -the
manufacture of laryer diameter produc-t and also improving
the final tolerance variation on the product.
According to the method and apparatus of the
present invertion, it is possible to produce large cross
sectional area products using a low capacity extrusion
process on a continuous basis.
It is also possible by the present apparatus and
method to produce both large and small in cross section
products having better accuracy.
SUMMARY OF THE INVENTION
According to the present invention, immediately
after the extrusion of a polymer foam product, the
progress of the product is impeded to an extent that the
product foams to fill a shaping horn of a predetermined
cross sectional area, whereby the final cross section of
the product is essentially determined by -the shaping horn.
2~ According to an aspect of the inven-tion, a
resisting force is applied on the extruded foam as it is
foaming which impedes the axial advance of the extruded
foam and causes an increase in the cross sectional area of
the product as it is Foaming with khe shaping horn
lirniting thls lncrease in cross sectional area to -the
desired sectlon to be achieved. The shaping horn engages
the sides of the procluct and provides a physical
restriction to the cross section of the product un-til
foaming of the product is at least substantially complete.
According to a further aspect of the invention, a
friction reducing lubricant is applied to the exterior of`
the foam as it is extruded to reduce friction between the
shaping horn and khe product as the product passes through
the shaping horn.
Both a method and apparatus are taught which
allow manufacture of foam product of greater cross
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sectional area, foam product having more restrictive
tolerance variation7 as well as a simplified rnethod for
the manufacture of large cross sectional area product.
~
Preferred embodiments of the invention are shown
in the drawings, wherein:
Figure l is a partial perspective view of the
extruding apparatus;
Figure 2 is a sectional view of the shaping horn;
Figure 3 is a partial sectional view of the
shaping horn; and
Figure 4 is a cross section of a flat sided
product more accurately produced by the present method and
apparatus~
DETAILED DESCRIPTION OF THE RREFERRED EM~ûDIMENTS
The extruder 2 includes a die 4 having an orifice
6 through which hot plastic is extruded in the forming of
a polymer foam product. Immediately acljacent the orifice
6 is a transitional portion 8 having a smooth, curved
surface lO associaked wlth the final shaping horn 12. The
final shaping horn 12 has a constant cross section
generally shown as l4 which limits the extent to which the
product can Poam. Thus, the transit.lonal portion 8 and
the f`inal shapiny horn 12 make up what can be referred to
as the shaping horn o~ the extruder.
As the hot product passes through orifice 6, it
starts to foam and a back pressure or retarding force 17
is exerted on the foam to cause the foam to fill the
transitional portion and the finaI shaping horn as i-t
moves in the axial direction away from the orifice 6. The
product takeup or drive 30 beyond the shaping horn is
driven at a speed less than but coordinated with khe rate
of extrusion to ensure that the shaping horn is full while
also removing product at a rate sufficient to avoid
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blockage. In this way, -the system can operate on a
continuous hasis.
In addition to the resisting -force prcvided by
the product drive 30, there is a drag exerted on the
product as it passes through the shaping horn. In order
to ensure the foam does not become adhered to the shapiny
horn as it passes therethrough, a lubricant 7 is
introduced through a lubrication system 20 which surrounds
the orifice 6. The lubr;cation systern includes a circular
port 22 supplied by inlet 23 which surrounds the orifice 6
and applies a thin film of lubricant to the product as it
passes through orifice 6. This film of lubricant,
generally shown as 26, expands with the ~oam and becomes
thinner as the product continues to ~oam in the shaping
horn. The film of lubricant remains on the outside and
separates the foam from the shaping horn. The product
leaving the shaping horn enters a water trough (not shown)
where water i5 sprayed on the foam to cool the same and
ensure the product does not adhere to the trough.
Lubrication system 22 includes an outer reservoir
20 about orifice 6 which allows the lubricant to pass
khrouyh a circular port about the orifice 6. The
lubricant can be under pressure to ensu.re a continuous
flow to the product as it passes through the die. Othe
arrangements for introducing the lubricant a.re possihle
and the lubricant is important where the ~oaminy product
is likely to adhere to the shaplng horn. This parti.cular
arrangement effectively applies the film to the product as
it is extruded.
According to the method and apparatus described
above, the product 50 may be oversized relative to -the
product which would be freely extruded through the orifice
6 and the tolerance variation in the final product are
much closer, within 2-3%, as the shaping horn basically
determines the final dimensions. Thus, variations in
density of the product can be accommodated as the product
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foams in an area lirnited by the shaping horn. The
extruder, generally shown as 2, having a capacity of
200-300 lbs./hour can produce product having a cross
sectional area greater than 12 square inches ccntinuously
and the accuracy of this product and the ability to forrn
desired angles and flat walls on the cross section of the
product is much better than with free ex-trusion. The
product, when produced, also has a skin thereabout and, as
the process is continuous, it can be produced in great
lengths. Complicated shapes, such as the flat sided
product 52 of Figure 4, are possible by changing of the
shaping horn and normally pairing the shape of the orifice
with the shape of the shaping horn. Such complicated
product shapes were previously difficult to produce and
difficult to control the production thereof.
The apparatus and process allow existing
apparatus to be modified for production of product having
larger cross sectional area and/or improved accuracy. A
free extrusion machine which processes material at 200-300
lbs./hour can produce, for example, cylinder shaped rods
up to possibly a 2~1/2 or 3 inch diameter. ~y using the
present process and an appropriately shaped shaping horn,
the same machine can produce product, for example, rods
having a 4, 5 or 6 inch diametsr on a continuous basis.
The same apparatus could also be usecl f`or produclny more
compllcated shapes such as those involving fla~ sldes or
particular angles betweer1 sides, as bu-t two examples. In
addit;on, the accuracy of the die orifice is not as
critical as the shaping horn is the dominate factor in
determining the final size of the product. In free
extrusion, the shaping of the die orifice is critical.
Although various preferred embodiments of the
present invention have been described herein in detail, it
will be appreciated by those skilled in the art, that
variations may be made thereto without departing from the
spirit of the invention or the scope of the appended
claims.
