Note: Descriptions are shown in the official language in which they were submitted.
1315056
Title: FOA~I EXTRUSION APPARATUS AND METHOD
DISCLOSURE
This invention relates generally as indicated to a foam extrusion
apparatus and method, and rnore particularly one such method and apparatus
utilizing a large horizontal vacuum chamber.
BACKGROUND OF THE INVENTION
It has been shown that extrusion of foamable plastic into a
vacuum chamber will produce a high quality low density foam, such as the
foam products sold under the trademark FOAMULAR by U.C. Industries of
Parsippany, New Jersey. Such products are produced commercially by
extruding the plastic melt into an inclined barometric leg which is in the
form of a large diameter pipe which forms a vacuum chamber. The lower
end of the pipe which is of substantial length projects into a pond of liquid
preferably water. When the chamber is under vacuum the water is drawn
from the pond at least partially to fill the chamber. The water serves to
seal the chamber and cool the extrudate. The inclined configuration permits
the extrudate to be extracted from the chamber on a continuous basis with
the aid of a belt conveyor. Examples of such installations may be seen in
the following U.S. patents: 3,704,083; 4,044,084; 4,199,310; 4,234,529;
4,247,276; and 4,271,107.
One of the principal problems of the inclined barometric leg
installations such as shown in such patents is the cost of construction.
Because of the length of the leg or chamber and its inclination, the die end
where the extruders are located must be at a substantial elevation above the
exit or pond end. Such difference in elevation not only creates construction
problems but also material handling problems during operation.
Attempts have been made to employ a horizontally extending
vacuum chamber and reference may be had to U.S. Patents 4,487,731 and
4,486,369 for an illustration of horizontal chamber vacuum extrusion
;systems. As seen such systems avoid a liquid pond or bafne but instead use
an exit chamber which must be cycled from atmospheric to vacuum. Also
the extrudate must be cut and/or stacked within the chamber which makes
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service and control of such equipment difficult. Also spray cooling of the
product within the chamber may be inadequate for a large cross sectional
size extrudate.
Other types of vacuum extrusion appa~atus may be seen in U.S.
Patents 3,82~,331; 1,990,434; and 2,987,768, but such are obviously not
suitable for continuous foam extrusion, particularly extrudates of large
cross sectional size.
It is accordingly desirable to employ a horizontal chamber which
nonetheless utilizes a water baffle or seal in which the extrudate is
immersed as it exits the vacuum chamber.
SUMMARY OF THE INVENTION
A foam extrusion system and method employs a horizontal
vacuum chamber with a bulkhead and extrusion die at one end OI the
chamber, the extrusion die being inside the chamber when the bulkhead is
closed. A liguid baffle, preferably water, is provided at the opposite end of
the chamber through which the extrudate passes from the chamber to
atmosphere. The bafne comprises a pond of liquid having a higher level in
the chamber and a lower level outside the chamber. The higher level of the
pond is formed between a dam plate and a seal plate, the latter forming the
opposite end of the chamber. The seal plate includes a size adjustable
window through which the extrudate passes, the extrudate being guided by a
conveyor to extend inclined downwardly into the pond and to exit through
the seal plate and pond with a large radius upwardly curved section. The
level of liguid in the chamber is controlled by circulating liquid from the
higher level of the pond within the chamber to the lower leYel of the pond
outside the chamber with the amount of liguid circulated being inversely
proportional to the absolute pressure in the vacuum chamber. Optionally
the oirculated liquid may pass through a cooler to control the liquid
temperature. The size adiustment of the window or exit orifice in the seal
plate may be used to control the flow of liquid from the lower level pond
portion outside the chamber to higher level pond portion inside the chamber,
particularly during start up.
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To the accomplishment of the foregoing and related ends the
invention, then, comprises the features hereinafter fully described and
particularly pointed out in the claims, the following description and the
annexed drawings setting forth in detail certain illustrative embodiments of
the invention, these being indicative, however, of but a few of the various
ways in which the principles of the invention may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed drawings:
Figure 1 is a side elevation of a vacuum foam extrusion system in
accordance with the present invention with the liquid circulation and level
controls shown schematically;
Figure 2 is a front view of the seal plate showing the variable
gate through which the submerged extrudate passes; and
Figure 3 is a somewhat enlarged side elevation of the system at
the seal plate separating the two levels of the liquid pond.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to Figure 1 there is illustrated a large elongated
horizontally extending vacuum chamber 10 which includes a bulkhead 11 at
one end and a seal plate 12 at the opposite end. The chamber is substantially
elongated and is horizontal throughout its length and is in the form of a
large diameter pipe. The chamber may be formed of interconnected and
sealed large diameter concrete pipe sections su¢h as shown in prior U-S.
Patent 4,199,310.
The bulkhead 11 may be mounted for movement on a carriage
indicated generally at 14 for movement toward and away from the end of the
vacuum chamber 10. On the exterior of the bulkhead there is provided one
or more extruders indicated at 15 while the extrusion die is on the interior of
the bulkhead as seen at 16. Also mounted on the interior of the bulkhead are
shaping rolls to control the configuration and shape of the extrudate exiting
the die. For more detail as to the configuration of the shaping rolls and the
manner o~ mounting both the die and shaping rolls on the bulkhead,
reference may be had to prior U.S. Patents 4,234,529; 4,247,a76 and
4,469,6sa. In any event the vacuum chamber may be opened and closed by
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moving the bulkhead 11 horizontally toward and away from the end of the
chamber.
Positioned in the chamber fairly close to the bulkhead 11 is a dam
plate 20, the upper edge 21 of which extends somewhat above a horizontal
centerline of the chamber.
Positioned outside the chamber beyond the seal plate 12 is a
containment structure 24 which includes side walls 25 and 26 and fln end
wall 27 remote from the chamber 10. The opposite end wall of the
containment structure indicated at 28 includes the seal plate 12.
The containment structure together with the vacuum chamber
forms a containment for a pond shown generally at 30 of liquid, preferably
water, extending from the dam plate to the containment structure plate 27.
As indicated, a portion 31 of the pond is outside the vacuum chamber 10
whiie a portion 32 is inside the vacuum chamber. Such portions are OI
course on opposite sides of the seal plate and communication between such
portions is obtained by a window illustrated generally at 34 in seal plate 12.
A vertically movable gate 36 mounted on the seal plate and driven vertically
by motor 37 controls the size of the opening of window 34.
The foam extrudate shown generally at 40 leaves the die 16 to
expand and be shaped and then passes under the end 42 or tail pulley of a
conveyor belt 43 which is inclined downwardly to bring the extrudate below
the level of the pond in the vacuum chamber. The foam extrudate will of
course float up against the conveyor belt and the speed of the conveyor belt
is closely controlled to draw the foam extrudate from the vacuum chamber.
The conveyor belt 43 passes through the window 34 and then curves
upwardly as indicated at 45 terminating in head pulley 46 driven from drive
47. The curvature of the conveyor belt need not necessarily be uniform but
in no case should the curvature be on a radius less than 150 feet. Reference
may be had to prior U.S. Patents 4,044,084 and 4,199,310 for disclosures of
such conveyors used in inclined barometric legs or vacuum chambers. After
the extrudate 40 exits the portion 31 of the pond outside of the vacuum
chamber it is of course exposed to atmosphere and the extrudate proceeds in
the direction of the arrow 48 for subsequent cutting and processing.
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When the gate 36 is in its most closed position it provides fairly
close clearance for the conveyor 43 and extrudate 40 and acts as a gross
flow control valve for water moving from a portion 31 of the pond 30 outside
of the chamber to the portion 32 inside the chamber, particularly during
start-up.
In order to control the level of the water within the vacuum
chamber 10 there is provided two water circulation pumps indicated at 50
and 51 which draw water from the bottom of the vacuum chamber as
indicated at 52 and 53, respectively, just inside the dam plate 20. The
outlet of the pumps passes through check valves 54 and 55, respectively, and
through power operated valves 56 and 57, also respectively. Such power
operated valves are in pump outlet lines 59 and 60, respectively, which
extend to cooling tower 61 through respective valves 62 and 63. The cooling
tower may be bypassed by closing the valves 62 and 63 and causing the
water to flow through lines 64 and 65 leading directly into the pond 31
outside of the vacuum chamber. Such lines may also include respective
valves 66 and 67 which are opened and closed alternately with valves 62 and
63. W&ter from the cooling tower 61 returns to the pond 31 through line 69,
again outside of the vacuum chamber.
Also, in addition to the outlet check valves 54 and 55 each pump
is provided with inlet and outlet shut off valves as seen at 72 and 73 as well
as a pressure gauge 74. The pumps may be utilized concurrently or
separately.
Vacuum is established in the vacuum chamber 10 by one or more
vacuum pumps indicated at 77. The vacuum level is controlled by vacuum
controller 78 through an air bleed valve 79.
The vacuum controller 78 is also electronically connected to
both level control 80 and motor 37, the latter controlling the position of
gate 36 on the seal plate. The level controller connection is by the set point
control connection illustrated at 81.
The level controller 80 is connected to both the vacuum and
water sides of the vacuum chamber through the valves indicated at 83 and
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84. The level controller in turn controls level control valves 56 and 57 in
the pump discharge lines 59 and 60, respectively.
The vacuum chamber just to the inside of the dam plate 20 is
provided with a sump and drain indicated at 86 in the event water splashes
over the top 21 of the dam plate.
During operation of the system the pumps 50 and 51 function to
draw water from the portion 32 of the pond within the vacuum chamber and
deliver that water either directly or through the cooling tower to the
portion 31 of the pond outside the vacuum chamber or exposed to atmos-
phere. The water thus flows from one end of the pond to the other and
circulates back through the adjustable window in the seal plate 12.
Before vacuum is established in the vacuum chamber the water
level on both sides of the seal plate will be at a common level. At this point
the pumps 50 and 51 are turned on but the level control valves 56 and 57 are
closed. When the vacuum chamber is closed, by moving the bulkhead 11
against the end of the chamber, the vacuum controller 78, being set to a
desired level, turns on the vacuum pumps 77. As the vacuum level goes up
(absolute pressure goes down) water will of course be drawn from the
exterior of the chamber into the interior of the chamber causing the water
level on the interior of the chamber to rise. During this process, the level
controller begins to open the level control valves 56 and 57 and the vacuum
controller begins to close gate 36 through motor 37. The control of the gate
36 reducing the size of the orifice acts as a gross flow control valve for
water moving into the vacuum chamber.
Both the vacuum controller 78 and the level controller 80 have
optimum adjustable set points. When the vacuum controller 78 reaches its
set point, it begins to maintain the desired vacuum level by actuating the
bleed valve 79. When the level controller 80 reaches its set point it will
begin to modulate the level control valves 56 and 57 maintaining the water
level within the vacuum chamber within a given narrow range simply by
increasing or decreasing the flow or circulation of water from the vacuum
chamber to the atmospheric portion of the pond 31. As the vacuum level
increases, the water level inside the vacuum chamber ~ncreases and in order
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to maintain the water level at an acceptable level the water flow through
the valves 56 and 57 also increases. During operation of the system the
vacuum controller resets the level controller 80 on a continuing basis which
in turn modulates the level control valves 56 and 57. In other words, the
vacuum controller is the master and the level controller is the slave. By
resetting the level controller constantly, the vacuum controller then can
anticipate changes in the water level thus maintaining a precise water level
inside the vacuum chamber in response to the vacuum level. However, the
gate 36, once in its final position, will normally stay in that position and is
used as such gross flow control valve only during start up or shut down of
the system. In any event the full system permits the water level inside the
vacuum chamber to be controlled in response to the vacuum level within the
chamber thus obviating the necessity for a long and inclined barometric leg.
The system may also operate with less total volume of water.
With the present invention there is provided a foam extrusion
line which includes an elongated horizontally extending chamber with the
chamber being horizontal throughout its length. The chamber is provided
with an extrusion die at one end forming a foam extrudate within the
chamber and a water baffle at the opposite end to enable the chamber to be
maintained under vacuum. The foam extrudate is guided through the bafne
to atmosphere for subsequent cutting and processing. In order to maintain
the liquid level within the vacuum the liquid is circulated from the higher
level of liquid within the vacuum chamber to the lower level of liquid
outside the chamber during extrusion. The amount of liquid circulated is of
course inversely proportional to the absolute pressure in the vacuum
chamber.
- Although the invention has been shown and described with
respect to certain preferred embodiments, it is obvious that equivalent
alterations and modifications will occur to others skilled in the art upon the
reading and understanding of this specification. The present invention
includes all such equivalent alterations and modifications, and is limited
only by the scope of the following claims.
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