Sealable chamber extrusion apparatus and method with process controls

An extrusion system utilizes single or tandem extruders and a mixer-cooler to extrude a foamable extrudate through a die in a sealable chamber. The foamable extrudate is shaped and calibrated within the chamber. The die is mounted on the end of a gel tube projecting through a gland seal in a fixed bulkhead forming the upstream end of the chamber. The gel tube and mixer-cooler are mounted on a movable carriage, movement of which may be used to adjust the die with respect to shaping and calibrating equipment inside the chamber. The mixer-cooler achieves a selected narrow range of uniform viscosity of the melt at the die depending on the size of the product and density. The chamber is preferably a vacuum chamber producing low density foams. The product exits the chamber to atmosphere on a continuous basis through a submerged orifice in a water baffle immersion seal. The mixer-cooler enables a large size low density product to be produced with uniform cellular structure without cell collapse or density gradients, as the product is subjected to the pressure and temperature transformations passing from the chamber to atmosphere through the water. The seal includes the submerged orifice with a free wheeling guiding system upstream of the orifice. Immediately ahead of the guiding system, the parameters of the foam extrudate are sensed to control the configuration of the orifice on a continuous basis. Before the extrudate passes into the water baffle seal it moves over a floating dancer roll, the position of which controls a haul-off such as a vacuum belt at the tail end of the system. This avoids pushing on the extrudate.

BACKGROUND OF THE INVENTION 
Vacuum extrusion of high quality, low density polystyrene foam board sold 
under the well known color PINK.RTM. and FOAMULAR.RTM. trademarks by Owens 
Corning of Toledo, Ohio, USA, has been accomplished in inclined barometric 
leg vacuum extrusion lines. In such systems, the vacuum chamber is 
somewhat inclined. The die is positioned at the upper end along with 
shaping or calibration equipment. At the lower end, the chamber is closed 
by a hood extension and immersed in a pond of water. The pond seals the 
lower end of the chamber and provides an immersion cooling bath for the 
extrudate as it leaves the vacuum chamber. The buoyant extrudate may be 
supported beneath a continuously moving belt which moves through the pond 
through a large radius of curvature. When the extrudate surfaces to 
atmosphere, it is cut and processed further. Such installations are costly 
and present many operating problems, particularly since the upper end of 
the chamber may be a number of meters above and a substantial distance 
from the lower end. Anything dropped at the upper end of the inclined 
chamber where all of the relatively complex shaping and calibrating 
equipment is located may literally have to be fished out of the lower pond 
many meters away. 
In U.S. Pat. No. 4,783,291, a horizontal vacuum chamber system is employed 
which seals the exit end of the chamber with a water baffle seal. The 
extrudate exits through an underwater orifice which connects the vacuum 
section and atmospheric section of an immersion cooling pond. The 
extrudate is conveyed through the orifice by a curved belt conveyor, and 
the top of the orifice has a movable shutter which restricts the orifice 
in response to vacuum level. The shutter acts as a gross flow control 
valve for water moving from the lower level atmospheric section of the 
pond to the higher level vacuum section of the pond. During vacuum 
operation, the level of the pond inside the chamber is maintained by 
circulating excess water back to the atmospheric section. 
For sizable or complex extrudates, relatively complex power driven and 
adjustable equipment is required downstream of the die. For a fan shape 
die, where the die lips are curved, the equipment may literally surround 
the die. Typical of such equipment is an apparatus known as a "slinky" 
which includes upper and lower sets or assemblies of power driven disks 
which are mounted for rotation on arcuate or curved axles which extend at 
different radii from essentially the same center as the curvature of the 
fan shape of the die lips. All of such shaping and calibration equipment 
is complex and requires access and servicing, particularly during start 
up. 
A foaming, moving, hot extrudate under vacuum is an amorphous object and 
does not become substantially fixed until it passes through the cooling 
immersion pond of the water baffle seal to atmosphere. If the shaping or 
calibration machinery is not functioning properly, the amorphous extrudate 
may become deviant, expanding or diverting from the machine line. When 
this happens, more often during startup, the problem needs to be corrected 
promptly to avoid shutting down the line. If the line is shut down for any 
significant length of time, equipment may have to be removed and replaced 
or throughly cleaned before the line can be restarted. Downtime versus 
operating time, and rate is the economic measure of any production 
facility. It is accordingly important that the equipment be quickly 
accessible, and that the extrudate be drawn through the system without 
being pushed or shoved with inconsistent or excessive force. It is also 
important that the underwater exit orifice closely match the size of the 
extrudate which may vary in width and thickness. Too large an opening 
creates inefficiencies, while too small an opening can create hangups, 
deviations, pull-aparts, and other problems. 
In the extrusion production of foam boards, such as the noted insulation 
boards, the size and thickness may be substantial, such as 10 to 12 
centimeters (3.94 inches to 4.72 inches) in thickness and up to a meter or 
more wide. Such board may have a cross-sectional area of in excess of 
about 1000 cm.sup.2 (155 in.sup.2). To make such board in economic 
quantities, such as more than 450 kg/hour (1000.0 lb/hour) to about 1360 
kg/hour (3000.0 lb/hour) or more, the system must have substantial 
throughput and achieve a uniformity of the melt. To achieve proper uniform 
cell size and structure for low density, large size product such as those 
having a cross sectional area of at least 80 cm.sup.2 (12.4 in.sup.2) and 
preferably from about 200 cm.sup.2 (31 in.sup.2) to about 1000 cm.sup.2 
(155 in.sup.2) or more, the proper uniform melt must be formed. 
The melt is formed from pellets and reclaim scrap and other additives by 
the extruder under heat and high pressure. The other additives may include 
fire retardant and UV inhibitors, for example. A blowing agent is also 
added which does not expand in the melt under pressure, but does so as the 
melt exits the die into the vacuum chamber. The vacuum increases the 
pressure difference, promotes the expansion and enables the production of 
low density foam. 
As is known, the melt has to achieve certain elevated temperatures for 
thorough mixing and formation of the melt, but to achieve uniform quality 
foam product, particularly in a low density vacuum foam system, a critical 
uniform viscosity range must be achieved. The particular viscosity range 
is dependent on product size and density. A higher viscosity is required 
for larger size product. If the product is not viscose enough or too 
fluid, the cells will rupture or collapse during foaming. If the melt is 
too viscous, homogeneous cell grown is difficult to impossible. Although 
cells may collapse in atmospheric systems, in a vacuum foam system, 
problems such as cell collapse or less than prime quality product may be 
more pronounced. A vacuum foam system is different from normal 
atomospheric foam systems. Not only is there an increased pressure drop at 
the die lips, but the reversion to atmospheric pressure, especially when 
emerging from an immersion seal, can result in cell collapse or 
non-uniformity actually distorting or shrinking the product, resulting in 
irregularities or density gradients, and less than quality product. In 
vacuum foaming, not only must the proper viscosity be achieved, it must be 
maintained uniform throughout the melt. Viscosity is controlled in part by 
controlling the temperature of the melt. 
The problem with many heat exchangers employed for such purposes is several 
fold. One set of problems is complexity and cost. Another set is 
effectiveness and efficiency. To move the polymer melt through elbows or 
right angle turns at high pressure and temperature, or through divergent 
flow paths is energy inefficient and raises the costs involved. Moreover, 
niches or potential dead space should be avoided or minimized. These do 
not contribute to homogeneity of the melt and require more frequent 
cleaning and downtime for such purposes. Such dead space is simply 
inefficient. A complex form of heat exchanger is shown, for example, in 
U.S. Pat. No. 4,423,767. 
The flow path of the melt should be as close to or aligned with the machine 
axis as possible, and the heat exchanger should be as compact as possible. 
Any excess increase in dimension between the extruders and the die can be 
self defeating, since any thermal or viscosity homogeneity achieved by the 
heat exchanger may be lost if the melt has to travel too far. This is 
further complicated if the die is inside a vacuum chamber to achieve a 
good low density foam, and if adjustments or thermal expansion or other 
minor movements need to be accommodated. 
While static mixers have been employed to attempt to achieve homogeneity of 
melts, they do not, nor have the capacity or efficiency necessary for the 
large throughputs noted above, and the production of quality foam products 
subject to the pressure changes of vacuum extrusion. 
To achieve both extrusion throughput rates and product quality, it is 
important to have a mixer which can also precisely control the temperature 
and thus the viscosity of the melt and maintain the thermal homogeneity to 
the die. Only in this manner can the benefits of high quality low density 
foam formed under vacuum be achieved, reducing density gradients in the 
foam, which gradients may result in or from cell or board collapse 
particularly as the board moves from the vacuum chamber to the pressure of 
atmosphere. To achieve this improved product quality for a range of 
products which may vary in cross section (from relatively thin to thick) 
and vary in density, the heat exchanger must be able to control the melt 
temperature very precisely, and maintain homogeneity of temperature all at 
varying throughputs, and most difficultly at high throughputs for large 
extrudates. 
SUMMARY OF THE INVENTION 
A horizontal vacuum extrusion line includes one or more extruders which may 
be single screw or twin screw forming a hot plastic melt which may include 
a number of additives such as fire retardants, lubricants, ultraviolet 
(UV) inhibitors, and blowing agents. Where the product is foam board, 
which may be of substantial size such as 1000 cm.sup.2 (15.5 in.sup.2) or 
more, the melt has to be brought to critical range uniform viscosity 
before exiting the die. This is particularly true if the die is in a 
sealed vacuum chamber and the product is low density foam board such as 
the type used in insulation. To achieve this uniform viscosity, the hot 
melt is passed through a high capacity mixer-cooler which brings the melt 
temperature to a melt uniformity to achieve the desired homogeneous 
viscosity within a narrow range, which range is dependent on the size and 
density of the foam board being produced. 
The hot melt exits the extruders on the machine or line axis, and the 
mixer-cooler is on that axis immediately downstream of the extruders. The 
mixer-cooler is a relatively axially short pressure vessel which has 
upstream and downstream tube sheets, between which extend closely spaced, 
relatively small mixing tubes, each of which may contain an axially 
continuous series of deflecting blades thoroughly to rotate and mix the 
melt, as individual static mixers. Connected to each tube sheet are heads 
which have large flaring conical chambers overlying the inlet and outlet 
ends of the large number or bundle of smaller mixing tubes. The heads 
provide an expanding and contracting flow path, without elbows, notches, 
niches or corners creating significant dead spaces which would adversely 
affect the melt. The inlet head has an inlet on the machine axis which is 
axially aligned with the outlet in the opposite or downstream head. The 
outlet is slightly smaller than the inlet, creating a back pressure. 
Connections to the inlet and outlet may be made by standard ANSI high 
pressure flange connections. The bundle of mixing tubes is substantially 
symmetrical to the machine axis, and each tube is parallel to that axis. 
The overall diameter of the unit is only slightly less than the axial 
length. The unit is quite compact and can readily be inserted in and 
removed from the line. 
The large number of tubes in the bundle, which may range from about 50 to 
about 300, depending on throughput required, substantially increases the 
cross sectional area of the melt flow path, which slows down the flow of 
the melt through the mixing tube bundle. The ratio is well more than two 
to one, and for large volumes the ratio may be in excess of twenty to one, 
even when considering only the larger diameter inlet. 
The melt passing through the individual mixing tubes is moving 
substantially slower than the melt entering or leaving the mixer-cooler. A 
cooling medium is circulated through the shell of the pressure vessel. 
Each tube is fully immersed in the circulating medium. A series of baffles 
are provided within the shell so that the coolant flow passes over the 
majority of the tubes several times before leaving the vessel shell. The 
coolant in substantial volume moves through a heat exchanger extracting 
heat. The amount of heat extracted is closely controlled, and in this 
manner the temperature of the melt moving through the mixer-cooler can be 
set within a range of about.sub.-- 1.degree. F. (.sub.-- about 0.5.degree. 
C.). 
The mixer-cooler is connected to the extruder output by a short gel tube 
and to the die by a somewhat smaller yet longer gel tube. The longer gel 
tube from the mixer-cooler to the die preferably incorporates a static 
mixer breaking up any residual insulating film layer resulting from 
laminar fluid flow and maintaining the homogeneity of the melt. The 
upstream gel tube may also incorporate the blades and fins of a static 
mixer. The upstream gel tube may, however, be illuminated depending on the 
system throughput rate. 
The die is positioned inside a sealable vacuum chamber, and the longer 
smaller gel tubes extends from atmosphere into the vacuum chamber through 
a fixed bulkhead of substantial size or diameter. The die is positioned 
substantially near or on the center of the bulkhead and supported by a 
movable carriage outside the bulkhead. 
The die, gel tube, and cooler-mixer are mounted on such die carriage, and 
the extruder or extruders are also on a separate carriage supported for 
movement axially of the line, both for intentional adjustments or 
replacements, and for movements resulting from thermal or pressure 
expansions and contractions. The carriages are linked or coupled. A 
hydraulic actuator or traverse assembly is provided between the extruder 
carriage and the floor. This actuator is relatively small in diameter yet 
provides a substantial travel such as on the order of about 370 cm (145.67 
in) to 450 cm (177.17 in). To move the die axially for adjustment within 
the vacuum chamber with respect to shaping or calibrating mechanisms, for 
example, a larger yet shorter actuator is provided between the die 
carriage supporting the mixer-cooler, gel tube and die, and the fixed 
bulkhead. This larger yet shorter hydraulic cylinder may have a movement 
of about 5 cm (1.97 in). Both cylinder actuators may include a valve 
having a neutral position permitting yet restricting very slight movements 
such as those encountered with thermal or pressure expansions. 
The mixer-cooler, even though having significant throughput capacity, is so 
compact that it is supported a substantial distance off the floor, 
although this is in part may be due to the size of the fixed bulkhead, 
which may be several meters in diameter. The traveling die carriage for 
the mixer-cooler supports in cantilever fashion the downstream gel tube 
and die, all for axial movement on the machine or line axis. 
Where the shaping mechanism is fixed with respect to the machine axis, such 
as the noted "slinky", die-shaping mechanism, adjustment may then be 
obtained by axial movement of the die. If the die is adjustably attached 
to a shaping mechanism such as shown in copending application Ser. No. 
08/696,718, filed Aug. 14, 1996, and entitled "Vacuum Extrusion Apparatus 
and Method", then the axial movement of the die is primarily for 
adjustment of the combination, or for heat or pressure caused movements. 
The sealable vacuum chamber includes one or more large movable sections 
which surround a beam or truss extending between the fixed bulkhead 
through which the die extends and a downstream bulkhead. The shaping and 
calibrating equipment may be mounted on this beam or truss for movement 
axially of the line. The movable sections permit quick access to this 
equipment with adequate space or environment, which is especially 
important on start up. The telescoping sections quickly seal against the 
fixed upstream bulkhead and each other or fixed sections by inflatable 
seals and quick acting toggle clamps. 
The shaping and calibrating equipment controls the shaping and expansion of 
the foaming extrudate and may be of substantial length. After the 
extrudate leaves such equipment and has been subject to sufficient 
expansion under vacuum, it passes over a dam, the edge of which is just 
below the machine axis, and the foaming extrudate is deflected downwardly 
into an immersion pond of water. The pond has an interior section and an 
atmospheric section and acts as a water baffle seal to permit the foamed 
extrudate to exit the vacuum chamber on a continuous basis. Just before 
the extrudate is deflected downwardly, it passes over a dancer roll which 
literally lifts the extrudate from adjacent supports, but not far enough 
to make difficult or excessive the downward deflection of the extrudate 
into the pond. The dancer roll is fairly large and extends completely 
across the underside of the extrudate. It is supported on an arm frame, 
pivoted and offset beneath the extrudate either upstream or downstream of 
the roll. The arm frame pivot may be provided on a bulkhead or internal 
frame portion of the chamber on the upstream side of the dam, or the dam 
itself. An encoder in the pivot measures the angle position of the arm 
frame and thus the roll. The arm frame is supported by a low pressure 
pneumatic piston-cylinder assembly so that the dancer roll floats against 
the bottom of the extrudate. The encoder is, of course, a measure of the 
position of the arm and roll, and this is a measure of the extrudate 
deflection at a given upward pressure. This is in turn an analog control 
of the tension on the extrudate within the chamber between the steps of 
shaping and calibrating upstream, and a tractor device downstream. 
The indirectly measured tension is used to control the tractive effort of a 
haul-off which is at the tail end of the line some distance away. A 
preferred tractor device is a vacuum belt haul-off. It is believed 
apparent that too much tension on the extrudate would tend to pull it 
apart in or just downstream of the shaping and calibrating equipment. Too 
little tension may cause the extrudate to push itself causing deviations 
or deflections and adversely affecting the natural growth of the product 
and a uniform cellular structure. Either case can bring the line to a 
halt, requiring the opening of the chamber, making required corrections or 
adjustments, and rethreading or restarting the system. 
Another reason for maintaining the proper tension on the extrudate is the 
under water hole or orifice through which the extrudate moves to pass 
through the water baffle seal from the vacuum chamber section of the 
immersion pond to the lower level atmospheric section of the pond. Since 
the chamber under vacuum will draw water from the atmospheric section into 
the vacuum chamber only to be forcibly ejected by a circulation pump, the 
clearance between the extrudate and edges of the orifice should be close 
and uniform. Otherwise energy inefficiency, control surges, and attendant 
control problems result. If the clearance is too close, the extrudate may 
hang up or deviate from its intended path. Complicating the problem is 
that the extrudate is continuing to grow. Although the extrudate has 
achieved its primary "board" shape, it may still be growing somewhat 
axially, in width, and in thickness. 
To facilitate the movement of the extrudate through the orifice, a guide 
system is provided immediately upstream of the orifice. The guide system 
is provided in a projecting hood with the orifice being provided at a 
lower shallower portion. 
The guide system at the orifice includes upper and lower close-pack guide 
roller sets. Each set includes a larger diameter powered end rolls, with a 
series of closely packed smaller idler rolls tangent to a tangent line 
connecting the interior of the two larger end rolls. The larger rolls are 
powered only for start-up or threading, and all rolls free wheel or idle 
when the system is in operation and operating continuously. The larger 
rolls may have a urethane or rubber type coating. 
Since the foaming board will float, the upper guide roll set is aimed at 
the fixed upper horizontal edge of the orifice. The lower roll set is 
movable toward and away from the upper roll set, and a bottom shutter or 
gate for the orifice is mounted on the downstream end of the lower roller 
set. Accordingly, the lower orifice edge shutter and the bottom close-pack 
roll set move as a unit. 
Immediately upstream of the upper roll set is a fixed platen or plate 
beneath which the board extrudate slides. On the lower side of the 
extrudate opposite the platen is a thickness sensing roll which extends 
between the distal end of a pair of arms of a pivoting arm frame. The 
platen is a reference plane or back stop for the underslung thickness 
measuring roll, the roll being held against the bottom of the board 
extrudate by a low pressure pneumatic cylinder or actuator assembly. The 
thickness or (y) dimension measuring roller extends transversely beneath 
the product underwater while the arm frame pivot is above the water. A 
rotary encoder in the pivot senses the position of the roller and is an 
analog measurement of the thickness of the product. The generated signal 
operates a PID (Proportional Integral Derivative) motion controller which 
may include an adjustable compensating factor for known growth rate of the 
product in the (y) dimension. The PID controller operates a motor above 
the water level which vertically moves or controls the position not only 
of the bottom shutter, but also the bottom set of close-pack guide rollers 
always aligned with the upper edge of the shutter. 
The width or (x) dimension is sensed by two edge rollers having vertical 
rolling axes mounted on the distal ends of swing arms each proximally 
pivoted on vertical axes on a bulkhead above the water level. Respective 
pneumatic cylinder assemblies urge the respective edge rollers into 
engagement with the respective edge of the extrudate. A rotary encoder in 
each arm pivot senses the position of the roller sensing the position of 
the edge of the product. This becomes a measure of the width or (x) 
dimension of the product. The information is passed to respective PID 
motion controllers operating respective lateral or edge gates for the 
orifice. 
Each edge gate, while having a vertical inner edge, is mounted on inclined 
parallel tracks. The inclination may be about 30.degree. to about 
45.degree., and the gate has the angled configuration to fit. This then 
positions the operating drive for the gates in an elevated position out of 
the water. Each gate may be actuated by a motor on an inclined bracket 
extending from the hood. A rotary screw drive, for example, reciprocates a 
rod connected to the submerged gate, the rod extending parallel to the 
tracks. The edge rollers may also sense through a summing calculation the 
centerline of the product. If the centerline is out of tolerance, 
corrective action can be taken, but it does not normally affect the 
operation of the control of the orifice on a continuous basis. 
After the extrudate passes through the orifice, it enters the lower level 
atmospheric section of the pond, still fully immersed or submerged. The 
lower level pond may extend for some length axially of the line. The foam 
product is held submerged by a series of idler rollers above the product 
arranged on a large radius arc with the center of curvature well above the 
product. The buoyancy deflects the product upwardly out of the water in a 
controlled gradual fashion, where it is supported on top of idler rollers. 
The product moves through a blow-off where excess moisture is removed much 
like a car wash. The product at the tail end of the line passes through a 
vacuum table or pull stand tractor haul-off which grips and pulls the 
extrudate. Beyond the pull stand the extrudate or board may be trimmed, 
cut to length, or otherwise treated. 
The pull stand is preferably a vacuum table or tractor which has a power 
driven foraminous or open belt which moves across a vacuum chamber. The 
vacuum holds the extrudate to the belt, and the belt linear speed is 
powered by a motor drive and controlled by the angular position of the 
dancer roll and a dancer roll controller. The vacuum level in the table or 
pull stand may be controlled to achieve the proper vacuum or grip, while 
the degree of pull is controlled by the dancer roll and controller. 
In this manner, the foaming extrudate is not pushed or shoved during 
continuous operation at any point between the shaping and calibrating 
equipment within the vacuum chamber, and the pull stand at the tail end in 
atmosphere. In this manner, high quality foam products of a variety of 
sizes can be made economically and efficiently. 
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.

DETAILED DESCRIPTION OF THE ILLUSTRATED PREFERRED EMBODIMENTS 
Referring now to the drawings and more particularly to FIGS. 1A and 1B, it 
will be seen that the extrusion line or system starts at the upstream end 
with an extruder 30. The extruder is mounted on stand 31 and includes 
hoppers 32 by which raw materials are fed to the extruder barrel 33 to be 
formed under heat and pressure into a foamable polymer melt. 
An extension of the extruder indicated at 35 projects through a large 
diameter fixed bulkhead seen at 36. A die 37 is mounted on the end of the 
extruder extension within a chamber shown generally at 40. The fixed 
bulkhead 36 forms the upstream or entry end of the chamber 40. The 
downstream end is formed by a fixed bulkhead 42 and a water baffle seal is 
shown generally at 44. The seal permits the product to exit the chamber on 
a continuous basis. 
In FIG. 1A, the chamber includes a movable section 46 which may telescope 
over the upstream end of fixed section 47. The fixed section is mounted on 
stanchions 48 on the floor 49, while the movable section is mounted on 
rollers 50 on rails 51. The movable section may be powered by a motor 
shown schematically at 52, much like a garage door. 
Within the upstream end of the vacuum chamber is shaping and calibration 
equipment which may comprise a shaper 54 and calibration equipment as seen 
at 55 and 56. The particular equipment illustrated in FIG. 1A may be of 
the type manufactured by LMP IMPIANTI of Turino, Italy. The extrudate is 
plasticised in the extruder 33 from recycled and virgin material to which 
additives such as fire retardants, ultraviolet stabilizers, and blowing 
agents are added. This is formed into the melt which is then extruded 
through the shaper 54 forming it into a generally flat plate or board 
shape. As the extrudate continues to foam and passes through the equipment 
55 and 56, it is calibrated in thickness and flatness. When the chamber is 
closed and sealed, the expansion and shaping of the extrudate when forming 
low density material is accomplished under vacuum to obtain a low density 
foam product. 
It is noted that the shaper and calibration equipment are each mounted on 
respective carriages seen at 58, 59 and 60, which are mounted for movement 
axially of the line or parallel to the machine direction on a truss 61. 
The truss 61 extends from the fixed upstream bulkhead 36 and an interior 
support 62. 
The foaming extrudate shown generally at 64 passes from the die through the 
shaping and calibration equipment and then passes over a dancer roll 65 
mounted on a pivoting arm assembly 66 pivoted on the support 62. The arm 
assembly 66 is urged upwardly by a pneumatic cylinder assembly 67 causing 
the roller to lift and deflect upwardly the extrudate to some extent. The 
pressure in the pneumatic cylinder assembly is controlled to cause the 
roller to float or dance beneath the extrudate. The position of the dancer 
roll controls the tractor haul-off as hereinafter described. 
After the extrudate passes over the dancer roll 65, it is deflected 
downwardly by a roller conveyor system 69. The conveyor system may have a 
number of more closely spaced rollers on top and relatively more widely 
spaced rollers beneath the extrudate. The rollers are positioned and 
mounted so that the extrudate is deflected downwardly into the upper level 
section 70 of a pond of water 71 which is contained in the downstream end 
of the vacuum chamber by a dam 72. The gradual curvature of the conveyor 
system 69 causes the extrudate to become fully immersed in the pond 71. 
The extrudate 64 moves through a window in the bulkhead 42 and into a hood 
74 which projects into an elongated containment 75 for the atmospheric 
lower level portion 76 of the pond 71. The end of the hood indicated at 78 
is well below the atmospheric level section 76 of the pond 71. Positioned 
above the pond section 70 are spray nobles 79 which are connected to the 
atmospheric section 76 of the pond. When the chamber is evacuated, water 
will be drawn into the chamber spraying the extrudate before it submerges 
into the pond section 70 to facilitate cooling. 
From the conveyor section 69, the extrudate passes through a guide roller 
assembly shown generally at 80, directed toward a generally rectangular 
window or orifice 82 which is the demarcation between the vacuum upper 
level pond section 70 and the atmospheric lower level pond section 76. 
Under vacuum, water will tend to flow from the atmospheric section to the 
upper level vacuum section, and the level of the vacuum section may be 
controlled by the recirculating pump as described, for example, in the 
noted prior application of Roger Lightle et al., Ser. No. 08/696,472, 
filed Aug. 14, 1996, and entitled "Vacuum Extrusion System and Method". 
It will be appreciated that if the chamber is used as a pressure chamber, 
the pond levels will be reversed, and the circulation to maintain the seal 
or orifice 82 submerged will be in the opposite direction. 
When the extrudate exits the lower downstream end of the hood at 78, it is 
kept from floating to the surface by a conveyor system 84, seen primarily 
in FIG. 1B, which is positioned above the extrudate. The conveyor system 
may be a series of relatively closely spaced transverse idler rollers 
which simply keep the moving continuous extrudate submerged. The conveyor 
is formed in a relatively large radius arc which maintains the extrudate 
under water for a substantial distance and time in the atmospheric portion 
76 of the pond. 
As the extrudate approaches the level 76, the conveyor system 84 terminates 
as seen at 85, and a second curved conveyor system 86 supports the 
underside of the extrudate to lift it above the end wall 87 of the 
containment 75 and out of the water. The entrance of the conveyor 86 
indicated at 88 is flared or spaced from the tail 85 of the conveyor 84 so 
that the extrudate will move freely from beneath one to the top of the 
other. 
After the extrudate clears the containment wall 87, it passes through a 
blow-off indicated at 90. Jets of air passing through nozzles 91 simply 
remove excess moisture from the extrudate much as the equipment commonly 
used in car washes. From the blow-off, the extrudate passes into a tractor 
haul-off 93. The tractor haul-off 93 is mounted on a stand 94 and may 
comprise a plurality of power driven upper and lower rollers 96 and 97 
which grip and pull the extrudate from the calibration equipment seen in 
FIG. 1A over the top of the dancer roller 65 and through the water baffle 
seal to atmosphere. During continuous operation, there is no pulling or 
pushing on the extrudate from the calibration equipment to the tractor 
haul-off. The large number of rollers may be coated with a rubber material 
such as urethane, and the squeezing pressure on the extrudate is 
minimized. As hereinafter described, the position of the dancer roll may 
be employed to control the pull of the tractor haul-off and thus the 
tension on the foaming extrudate from the calibration equipment through 
the water baffle seal. 
After exiting the haul-off, the extrudate passes through a cutoff and 
trimming unit indicated at 99. The unit 99 may cut the extrudate to length 
and also trim or treat the lateral edges. Any scrap produced by the 
operation is treated and recycled. 
After passing through the cutting and trimming operation 99, the extrudate 
is in the form of sizable panels or boards which may then may be stacked 
and packaged for shipment, or be further processed to form lamination or 
sandwich panels, for example. The stacks may be formed at the final 
station 100 for such packaging or further treatment. After exiting the 
containment 75, the extrudate is processed at table height, which is the 
approximate height of the containment 75 for the atmospheric portion of 
the pond. For this reason, the cutoff and trim station as well as the 
stacking station are supported on stands at such table height. 
Referring now to FIGS. 2, 3 and 4, it will be seen that the configuration 
and equipment employed in the vacuum system may be modified in a number of 
ways designed to enhance the quality of the product while achieving large 
throughputs and extrudates of substantial size. 
Referring initially to FIG. 2, there is illustrated a system which employs 
tandem extruders shown generally at 102 and 103. Connected to the polymer 
melt output of the secondary extruder 103 is a mixer-cooler 104 and a 
"slinky" shaping mechanism 105 mounted on the inside of a large fixed 
bulkhead 106. The raw materials are fed through the hoppers 107 and 108 to 
the primary extruder 102. The output of the primary extruder may pass 
directly or through a gear pump to the secondary extruder 103. Both the 
primary and secondary extruders are mounted on stands seen at 110 and 111, 
respectively, in turn mounted on rollers 112 and 113, respectively, and 
connected or coupled at 114. The mixer-cooler 104 is also mounted on a 
stand seen at 116 which includes roller supports 117. The stand 116 is 
connected to the stand 111 at the coupling 118. 
Also supported by the stand 116 is a gel tube 120 which extends through a 
gland seal shown in more detail at 121 in FIG. 6 in the fixed bulkhead 
106. The extrusion die 122 is on the end thereof within the vacuum chamber 
which is shown generally at 125. The vacuum chamber is, however, shown 
open in FIG. 2. 
The gel tube projecting from the mixer-cooler 104 to the die 122 is 
supported on the carriage 116 by an angular strut 126. Movement of the die 
with respect to the fixed bulkhead 106 is obtained by a piston-cylinder 
assembly or actuator 127 connected between the carriage 116 and the fixed 
bulkhead. In this manner, the die 122 may be adjusted axially of the line 
with respect to the axially fixed "slinky" shaping mechanism 105. 
The vacuum chamber 125 of FIG. 2 may include a fixed section 47 like that 
of FIG. 1A, but includes two substantially larger movable sections seen at 
130 and 131. The larger sections are substantially larger than the fixed 
section 47, as is the fixed upstream bulkhead 106. The vacuum chamber 
includes a truss or beam 133 which extends between the larger upstream 
fixed bulkhead 106 and a downstream bulkhead 134 within the fixed section 
47 of the vacuum chamber. After the extrudate indicated at 136 leaves the 
shaping mechanism 105, it proceeds on top of a conveyor table 137 
supported on top of the truss or beam 133 by frame 138. Positioned along 
the conveyor table may be additional measuring and/or calibrating 
equipment such as those which may be employed for forming or texturing the 
major surface skins. In any event, after leaving the shaping mechanism, 
the foaming extrudate will continue to grow and may continue to do so 
under the beneficial influence of the vacuum within the chamber, when 
closed. After the extrudate leaves the table 137, it moves over the top of 
dancer roll 65 and enters the conveyor system 69 to be downwardly 
deflected into the water baffle seal through which the extrudate exits to 
atmosphere. The immersion cooling pond at the exit end of the vacuum 
chamber substantially concludes the growing or forming process of the 
large cross section area extrudate or board. The tandem extruder 
arrangement of FIG. 2, together with the mixer-cooler 104 and the large 
volume vacuum chamber, enable the production of high quality uniform foam 
boards having substantial cross sectional areas. For example, the 
extrusion system of FIG. 2 will produce high quality foam extrudate of 
about 1000 cm.sup.2 (155 in.sup.2) or larger and at throughputs of in 
excess of about 1000-1400 kg/hour (2000-3000 lb/hour). 
FIG. 3 represents a system like FIG. 2 but showing only a single twin screw 
extruder indicated at 142. The raw materials are fed to the twin screw 
extruder through the hoppers indicated at 143 and 144. The extruder is 
mounted on a stand 145 in turn mounted on guided rollers 146. 
A transaxial view of the extruder is seen in FIG. 5 where the twin meshing 
screws are indicated at 148 and 149. The meshing twin screws run in a 
figure eight barrel seen at 150 surrounded by suitable heating jackets 
151. The twin screw extruder may be of the type manufactured by the noted 
LMP IMPIANTI of Turino, Italy. 
It is noted that the stand 145 is connected to the stand 116 by the 
coupling 118 which may be the same as that shown in FIG. 2. The extruder 
142 is movable through a substantial distance by the actuator seen at 153 
in FIG. 3. The actuator is mounted on a bracket 154 projecting from the 
stand 145 and is anchored to the floor 49 at 155. The actuator 153, 
described in more detail subsequently, enables a substantial amount of 
movement of the extruder for placement in the line or removal from the 
line, and also enables the line quickly to be opened for removal or 
replacement of the mixer-cooler, or for a adjustment or die change. The 
details of the actuator are shown and described in connection with FIG. 7. 
In comparing FIGS. 2 and 3, it will be seen that the two large diameter 
sections 130 and 131 of the chamber 125 have been moved to the closed 
position and locked and sealed as hereinafter described. In FIG. 3, the 
"slinky" shaping mechanism 105 and the internal conveyor system is the 
same as that seen in FIG. 2. 
In FIG. 4, there is employed a large capacity single screw extruder 160 
mounted on stand 145 supported on guide rollers 146. The stand 145 is 
connected to the die supporting stand 116 through the coupling 118. The 
actuator 153 may be employed with the single screw extruder 160, the twin 
screw extruder 142, or the tandem extruders 102 and 103 of FIG. 2. The raw 
materials and reclaim scrap are fed to the extruder through the hoppers 
161 and 162, and the high temperature melt is fed through the mixer-cooler 
104 and the die 122 which is surrounded by the shaping mechanism 105. The 
telescoping vacuum chamber enlarged sections 130 and 131 are shown closed, 
locked and sealed in FIG. 4. 
After the extrudate 165 leaves the shaping mechanism 105, it passes onto 
the conveyor table 166 supported on stand 167 on top of the beam or truss 
133. However, unlike the conveyor system of FIG. 3, the conveyor table 166 
ramps downwardly slightly to its downstream end 168 which terminates short 
of the bulkhead 134. The dancer roll 65 and the arm assembly supporting 
the dancer roll are on the upstream side of the bulkhead 134, and the 
dancer roll literally lifts the extrudate off the lower end 168 of the 
ramped conveyor table 166. The bulkhead 134 may then serve as the dam for 
the water baffle seal, and the conveyor system 69 for diverting the 
extrudate downwardly into the vacuum chamber section of the pond may be 
shortened somewhat and moved upstream. This then shortens the fixed 
section of the vacuum chamber. The upstream end of the diverting conveyor 
section 69 includes a lower guide ramp indicated at 169 to facilitate the 
threading of the extrudate beneath the upper portion of conveyor section 
69 and into the vacuum chamber section of the pond. 
Referring now to FIG. 6, it will be seen that the "slinky" mechanism is 
mounted on the interior of the fixed bulkhead 106 to surround the die 122. 
The "slinky" mechanism 105 is similar to that mechanism shown in prior 
U.S. Pat. No. 4,234,529, but is driven from the exterior of the fixed 
bulkhead 106 in a manner similar to that shown in prior U.S. Pat. No. 
4,469,652. The die 122 has a semi-circular or fan-shape die face 172. The 
shaping mechanism includes a series of equally radially spaced paired 
upper and lower semi-circular polished rods shown at 173 and 174 which 
extend around the semi-circular die face 172. Mounted on the respective 
polished rods or axels are a series of relatively thin wafers or rollers 
seen at 175 and 176 which are oppositely driven for rotation during 
extrusion as indicated by the arrows 177 and 178. The wafers or rollers 
interfit with each other so that driving one for rotation drives all. 
The arcuate segmented driving rollers are paired top and bottom to be 
driven at the same speed and torque, but the speed and torque may vary as 
the extrudate moves radially of the die face. The drive for the paired 
upper and lower arcuate rollers comes through the bulkhead 106 as 
indicated by the shaft 180 on which is mounted pulley 181 driven by cog 
belt 182. The shaft is mounted for rotation in sealed bearings in the 
bulkhead. Inside the bulkhead the shaft 180 drives cog belt 183, in turn 
driving pulleys 184 and 185 in opposite directions. Such pulleys drive 
universally jointed or flexible drive shafts 186 and 187, respectively, in 
turn rotating drive sprockets 189 and 190, in turn driving through 
transmissions 192 and 193 a paired set of arcuate rollers in the opposite 
directions noted. A driving transmission for each paired roller set is 
provided so that the roller sets may be controlled as to speed and torque. 
While only five paired roller sets are illustrated, it will be appreciated 
that fewer or more may be employed depending upon the size of the foaming 
product. 
Each roller set is mounted on a pair of vertically extending rods as 
indicated at 195 and 196 through brackets such as seen at 197 and 198. The 
brackets are supported by respective pneumatic piston-cylinder assemblies 
200 for adjustment and for floating movement. Controlled air pressure 
compensates for the tare or dead weight of each roll set to achieve 
floating. A slight additional pressure is then employed to control the 
force exerted by the rolls on the foaming extrudate. The pressure is quite 
gentle but quite effective to confine the foaming extrudate radiating from 
the fan-shape die face into a board-shape which may be of substantial 
width and thickness. 
The various aspects of the "slinky" shaping mechanism are supported on the 
interior of the bulkhead 106 by various brackets seen at 203. While the 
array of shaping rollers above and below the die and its axis or line have 
a substantial amount of vertical adjustment or movement, there is no 
significant adjustment of the shaping mechanism axially of the line. 
In order to achieve adjustment of the die axially of the line with respect 
to the shaping mechanism, the mechanism 127 seen in FIG. 8 is employed to 
move not only the carriage 116, but the mixer-cooler 104 and the tube 120 
which supports the die 122 on the end thereof inside the vacuum chamber. 
Such die adjustment need not be very extensive. The traveling die carriage 
is seen at 116 and supports a relatively short stroke hydraulic 
piston-cylinder assembly 208. The piston-cylinder assembly or actuator may 
include its own motor 209, pump 210 and operating valve 211. The cylinder 
of the assembly 208 is mounted on a pad 212 on the frame 116. The rod 213 
projects through a bushing 214 in the carriage upright frame member 215 
and is anchored at 216 to a frame portion 217 of the stationary bulkhead 
106. The stroke of the actuator 208 is relatively short such as on the 
order of approximately 5 cm. In this manner, relative movement of the 
carriage with respect to the fixed bulkhead is obtained with the gel tube 
120 supporting the die 122 sliding in gland seal 121 seen in FIG. 6. The 
gland seal may be of the type shown in the above noted co-pending 
application of Robert L. Sadinski, Ser. No. 08/696,718, filed Aug. 14, 
1996, for VACUUM EXTRUSION APATUS AND METHOD. 
The traversing unit for the one or more extruders utilizes a significantly 
longer hydraulic piston-cylinder assembly actuator seen at 220 in FIG. 7. 
The cylinder of the piston-cylinder assembly is mounted through a pivot at 
221 to bracket 222 secured to the extruder carriage base 154. The rod 224 
of the actuator 220 is pivoted at 225 to compensating link 226 in turn 
pivoted at 227 to the stationary anchor 155 secured to the floor 49. The 
stroke of the piston-cylinder assembly 220 is substantially longer than 
the stroke of the die adjustment cylinder actuator 208. For example, the 
stroke of the cylinder assembly 220 may be on the order from about 370 cm 
(145.67 in) to about 450 cm (177.17 in) and will move the extruders a 
substantial distance. However, in operation, the piston-cylinder assembly 
208 of the die adjustment will normally override the piston-cylinder 
assembly 220, and the valve 211 may include a neutral position permitting 
slight axial movements of the die carriage and thus the die with respect 
to the fixed bulkhead to compensate for temperature and pressure 
variations. 
Referring now to FIGS. 9 and 10, there is illustrated a preferred form of 
locking mechanism 230 for the chamber, the location of which is shown by 
the arrow at the top of FIG. 1A. The locking mechanism may comprise a 
series of relatively low profile piston-cylinder assemblies 231 mounted on 
fixed brackets 232 on the exterior of the fixed section 47 of the vacuum 
chamber. Each piston-cylinder assembly is pivoted to its bracket at 233. 
The rod 234 of the assembly 231 is pivoted at 235 to triangular crank link 
236 pivoted at 237 to the bracket 232. Also pivoted to the crank link 236 
at 238 is a toggle link 239 pivoted also at 240 to dog leg link 241 which 
is in turn pivoted at 242 to the bracket 232. The bent distal end 243 of 
the link 241 is adapted to engage a pad 244 on the end of the moving or 
telescoping vacuum chamber section 46. 
In FIG. 9, the toggle locking mechanism is shown retracted, and the link 
241 is clear of the telescoping section 46, so that it may then move to 
the right as seen in FIG. 9. In FIG. 10, the toggle lock mechanism is 
shown in the locked position. The piston-cylinder assembly has extended to 
pivot the crank link 236 about the pivot 237 moving the pivot 238 causing 
the dog leg link 241 to pivot to the position shown so that the end 243 of 
the link 241 is against the pad. The three pivots 240, 238 and 237 form 
the toggle lock with the middle pivot slightly over center. When in the 
locked position seen in FIG. 10, the seal shown generally at 246 may then 
be inflated sealing the vacuum chamber for evacuation or pressurization. 
The details of the seal are seen more clearly in FIG. 11. 
The seal 246 in FIG. 11 is shown between the fixed bulkhead 36 and the 
opposite end of the traveling vacuum chamber section 46. The traveling 
section 46 includes a flange 247 with rings 248 and 249 projecting axially 
toward the fixed bulkhead 36 and forming an axially facing channel form 
groove. Seated between the rings is a seat 250 for the inflatable gasket 
shown at 251. The seat 250 snugly fits in the axially facing channel-form 
groove, and the gasket may include two snap-in ears seen at 252 and 253 
allowing the gasket easily to be inserted and replaced. The gasket is in 
the form of an inflatable O-ring which includes an axially facing ridge 
255 which compresses against the interior of the fixed bulkhead when the 
seal is inflated. In the FIG. 1A embodiment, the seal shown in FIG. 11 
will be provided at the left hand end of the traveling section 46. The 
seal at the right hand end will be as shown in FIGS. 9 and 10. 
In the FIG. 2, 3 and 4 embodiments, the seal between the traveling section 
130 and the fixed bulkhead 106 will be as shown in FIG. 11. The seal 
between the two traveling sections 130 and 131 will be the same as shown 
except that the seal will expand against a flange on the opposite 
traveling section. The seal between the fixed section 47 and the traveling 
section 131 will be as shown in FIGS. 9 and 10. The flange or plate 
closing the end of the traveling section 131 will, however, include an 
eccentric opening for the smaller diameter fixed section 47. 
With reference to FIG. 12, it will be seen that the dancer roll 65 is 
positioned between the outer end of the arms of arm assembly 66. The roll 
65 may be provided with a urethane covering. The arm assembly is pivoted 
at 260 to bracket 261. The pneumatic piston-cylinder assembly 67 which 
will cause the arm assembly to pivot upwardly or float to the phantom line 
position seen at 262. The assembly 67 is pivoted at its blind end at 263 
to vertically adjustable bracket 264 which may be mounted on the bulkhead 
62 or 134, for example. The rod of the piston-cylinder assembly is pivoted 
at 265. As is apparent from the several embodiments illustrated, the 
dancer roll assembly may be mounted on the bulkhead to face in either an 
upstream or downstream direction. In any event, the piston-cylinder 
assembly will urge the roller 65 upwardly into a floating position beneath 
the extrudate passing thereover. The pivot 260 includes a rotary encoder 
267 which is used to sense the position of the roller 65, and this becomes 
an analog control of the tension on the extrudate as it passes over the 
bulkhead on which the roller is mounted and begins its decent into the 
vacuum chamber section of the water baffle seal to be immersed and to exit 
the chamber to atmosphere. 
Referring now to FIGS. 13-15, it will be seen that the mixer-cooler unit 
104 includes a shell 270 extending between axially spaced tube sheets or 
plates 271 and 272. The shell 270 is seated on slight shoulders on the 
interior of the tube sheets and welded as indicated at 273. Extending 
through the tube sheets within the shell 270 are a large number or bundle 
of mixing tubes shown generally at 275. Each tube within the shell is 
provided with the sets of curved mixing elements 276 so that each tube is 
a static mixer. The blades 276 are curved and cause the melt moving 
through the tube to move or rotate around the tube axis. The static mixers 
of each tube may be of the type made and sold by Cemineer-Kenics of North 
Andover, Mass., USA. Although not shown, each of the tubes within the 
bundle is provided with the curved elements of a static mixer. In the 
illustrated embodiment there may be in excess of 90. For large volume 
throughputs, the number of mixing tubes in the bundle may be as many as 
225 to 300 or more. 
The tubes of the bundle are slightly spaced as indicated at 278. The bundle 
of tubes, regardless of the number, is arranged so that the bundle is 
symmetrical with the mixer and machine axis shown at 280. The tubes are 
all parallel to such axis and the transverse dimension of the bundle is as 
close to circular as possible and centered on the axis 280. In this 
manner, the tube bundle faces projecting through the tube sheets may be 
covered by conical heads or plenums seen at 282 and 283 connected to the 
tube sheets by the ring of bolt fasteners shown generally at 284. Each 
head is provided with a widely flaring conical recess as seen at 286 and 
287. The outer or wider end of each conical recess closely circumscribes 
the projecting ends of the tube bundles. A filler indicated at 289 
circumscribes the bundle and minimizes dead space in the melt flow path. 
The inlet head 282 is provided with an axial inlet passage 290 provided 
with a shoulder 291 and surrounded by tapped holes 292. In this manner, a 
standard ANSI flange connection may be secured to the inlet head. 
The outlet head is provided with an aligned axial outlet 294 which is 
somewhat smaller in diameter than the inlet 290. Secured to the downstream 
face of the head 283 is a flange adaptor 295. The gel tube 120 has a ring 
296 threaded on the end thereof held to the head by the fasteners 297. 
Alignment rings 298, 299 and 300 having mating conical surfaces are 
interposed between the gel tube and the flange 295. The interior of the 
gel tube is provided with static mixer elements indicated at 302 which 
continually rotate the melt about the axis 280. The tube may be provided 
with an outer shell 303 enclosing insulation 304. 
The mixer-cooler is provided with an inlet indicated at 306 and an outlet 
307. In addition, the shell is provided with a vent 308 and a drain 309. 
In the illustrated embodiment, the inlet 306 is on the bottom, while the 
outlet 307 is on the top. Situated between the inlet and the outlet are a 
series of baffles seen at 312, 313, 314 and 315. The baffles 312 and 314 
extend from the top of the shell, while the baffles 313 and 315 extend 
from the bottom of the shell, requiring the coolant circulated through the 
shell to move in a sinuous or sinusoidal path through the tube bundle. In 
the illustrated embodiment, the coolant will pass the majority of the 
tubes of the bundle five times. 
As indicated in FIGS. 13 and 14, the heads 282 and 283 may be provided with 
radial ports 317 enabling the mounting of pressure or temperature sensors 
at the inlet and outlet, respectively. The tube sheets 271 and 272 are 
provided with downwardly projecting supports 318 and 319 which support the 
mixer-cooler on the stand 116. 
With reference to FIG. 15, it will be seen that the coolant leaving the 
outlet 307 passes through a heat exchanger 322 where heat is extracted. 
The coolant then passes through the circulating pump 333, a control valve 
334, filter 335, and finally through temperature regulator 336 before 
moving back into the shell 270 through the inlet 306. The circulating 
coolant may be water with appropriate additives. 
Regardless of the number of tubes in a bundle, the mixing tubes in each 
bundle may be approximately 3.17 cm (1.25 in) in diameter. The doubling or 
even tripling of the number of tubes in a bundle does not significantly 
change the overall dimension of the mixer-cooler. For example, the overall 
height of a mixer-cooler with about 90 bundles is 84 cm (33.07 in), while 
one with about 229 tubes in a bundle is approximately 120 cm (47.24 in) in 
height. The varying dimension mixer-coolers can be accommodated simply by 
tailoring the height of the carriage 116. To achieve the noted throughput, 
number of tubes in the bundle is approximately 229. 
It is noted that the size of the inlet to the mixer-cooler is substantially 
larger than the outlet. The inlet may be on the order of 15.2 cm (5.98 in) 
in diameter, while the outlet is approximately 13.7 cm (5.39 in). If the 
individual mixing tubes of the bundle each have an inside diameter (ID) of 
about 2.54 cm (1 in), the ratio of the transverse area of the interior of 
the tube bundle to the inlet area is approximately 6.36, while the 
transverse area to the outlet may be approximately 11.31, both of which 
are well more than a ratio of about 2 to 1. 
It will be appreciated that these ratios considerably slow the movement of 
the melt through the mixing tubes enabling the efficient and uniform 
extraction of heat. With the mixer-cooler of the present system, the melt 
temperature may be controlled to within.sub.-- 1.degree. F. (0.5.degree. 
C.). 
In this manner, the viscosity of the melt at the die can be closely 
controlled to be within certain ranges necessary to produce quality and 
uniform product. For example, a board 122 cm (48.03 in) wide and 10.16 cm 
(4 in) thick has a cross-sectional area of approximately 1,240 square cm 
(192.2 square inches). To produce this type of product avoiding cell 
collapse, non-uniform cell structure, or less than prime production, a 
critical viscosity range of from about 25,000,000 to about 30,000,000 
centipoise would be desirable. For a similar product but only 2.5 cm (1 
in) thick and as small as about 80 cm.sup.2 (12.4 in.sup.2), a lower 
viscosity range of from about 15,000,000 to about 20,000,000 centipoise 
would provide the optimum foam quality. 
In this manner, the mixer-cooler can be operated as a viscosity control 
device, as the melt viscosity through the mixer-cooler is a function of 
the rheological properties of the melt which is proportional to the shear 
rate and foaming temperature. Also, the viscosity is affected by the 
amount of blowing agent in the melt and, to a lesser degree, by extrusion 
additives. Therefore, for any given extrusion rate, control of the 
required critical viscosity range is obtained by controlling the melt 
temperature in the mixer-cooler. The critical viscosity for a given 
product can be established by measuring the overall pressure drop through 
the mixer-cooler and calculating the absolute viscosity which is then used 
to establish the optimum product performance. These ranges may vary 
considerably depending on operating conditions, and once achieved 
empirically can be repeated with precision. 
Shear rate is proportional to the rate at which the polymer melt 
experiences shear stress, and this is normally measured in inverse seconds 
(sec .sup.-1). In the operation of the system, it is important that the 
tubes and mixing elements of the mixer-cooler be sized to place the 
overall shear rate at an operating range which will not induce additional 
melt shear from the mixing elements. A shear rate range for each 
individual tube at the length and diameter ranges given below should be 
from about 1 to about 10 sec .sup.-1. Maintaining the shear rate along 
with the temperature permits the proper control of the polymer melt 
viscosity which is important to produce uniform cellular structures at 
large throughputs, without cell collapse, excessive cell size or open 
cells. 
The design parameter ranges for the mixer-cooler which enable the 
production of such high quality low density foam board in the sealed 
chamber system illustrated are: 
______________________________________ 
Approximate Minimum 
Approximate Maximum 
______________________________________ 
Extrusion Rate 
453.59 kg/hr (1000.0 
1360.78 kg/hr (3000.0 
lb/hr) lb/hr) 
Melt Temperature 
123.88.degree. C. (250.degree. F.) 
135.degree. C. (280.degree. F.) 
Melt Viscosity (CP) 
15,000,000 30,000,000 
SC Pressure Drop 
25857.45 mm-mg 77572.35 mm-mg 
.DELTA.P (500.0 psig) (1500.0 psig) 
Tube Size - ID 
2.54 cm (1.0") 3.81 cm (1.5") 
Tube Length 
60.96 cm (24.0") 
152.4 cm (60.0") 
No. of Tubes with 
96 300 
Mixing Elements 
Shear Rate/Tube 
1 sec.sup.-1 10 sec.sup.-1 
______________________________________ 
It is also noted that the static mixer incorporated in the gel tube 120 
between the mixer and die helps to alleviate any tendency for the thermal 
gradients to reappear between the mixer and the die. It is also of some 
benefit to incorporate a static mixer in the relatively short section of 
piping indicated at 338 in FIG. 15, having the elements of the static 
mixer seen at 302 in FIG. 13. A static mixer at such location will reduce 
or minimize the thermal gradients going into the unit 104. 
Although as indicated, the parameters are to some extent empirical, the 
mixer-cooler and its ability to achieve the appropriate critical viscosity 
ranges for the various size boards or extrudates being produced are very 
important in the production of both large and small quality product with 
the sealed chamber system. The transformation of the product from the 
vacuum chamber, where the product is in an amorphous state and continuing 
to grow, to the atmosphere through the immersion water baffle seal cooler, 
makes the narrow range viscosity controls particularly beneficial. It 
avoids such problems as cell collapse and non-uniformity of cell 
structure, particularly with the low density ranges which are achievable 
with vacuum foaming. For example, low density foams in the range of 
approximately 0.016 grams per cubic centimeter (1 pound per cubic foot) to 
0.096 grams per cubic centimeter (6 pounds per cubic foot) may be made 
with proper viscosity range control with uniform cellular structure and 
without cell collapse as the extrudate moves through the water baffle seal 
and to atmosphere. 
The window or orifice 82 through which the extrudate passes from the vacuum 
chamber portion of the pond indicated at 70 to the atmospheric portion 
indicated at 76 is shown and described in more detail in FIGS. 16-18. The 
down stream end of the vacuum chamber 40 includes the bulkhead 42 which 
has a sizeable window 342 which communicates with the interior of the hood 
74. The hood 74 projects from the downstream side of bulkhead into the 
pond containment 75. The extrudate 64 seen in FIG. 17 moves downwardly at 
an angle beneath the water level 70 as guided by the conveyor system 69. 
The floating extrudate passes beneath a platen 344 positioned at the 
appropriate inclination in the upper portion of the window 342. From 
beneath the platen the extrudate enters between the guide rollers of the 
close-pack roller set 80. The guide roller set includes a top roll set and 
a bottom roll set with each journaled in frames 345 and 346. Each 
close-pack roller set includes larger end rolls seen at 348 and 349 which 
may be provided with urethane covers. Positioned between such rolls are a 
closely spaced or packed set of idler rolls indicated at 350. The idler 
rolls are tangent to a line also tangent to the interior of the end rolls. 
The opposed major end rolls of each set may be power driven, but only on 
start up. The opposed rolls on the opposite side of the extrudate may be 
driven to advance the extrudate by the transmission shown generally at 352 
in FIG. 16. When the line is operating on a continuous basis on the 
vacuum, all the rolls of each set will free wheel or idle. 
The two frames are mounted on four corner guide posts seen at 354, 355, 356 
and 357. The upper frame is normally fixed on such posts, although it may 
be moved for adjustment purposes only during initial set-up. The upper 
frame includes a fixed gate or shutter indicated at 359 forming the top 
edge of the underwater orifice 82. All of the other edges of the orifice 
are adjustable on a continuous basis. 
The bottom edge of the orifice is formed by the shutter or gate 361 which 
is mounted on the front of the frame 346 for the lower close-pack guide 
roll set. Movement of the lower gate or shutter 361 is obtained by 
rotating the posts in common directions with a nut follower element being 
provided in the bosses 363 through which an appropriate screw portion of 
the posts extend. The posts may be rotated through the drive seen at 364 
and the motor 365 seen schematically in FIG. 19. Thus not only does the 
bottom gate 361 of the orifice move up and down, so does the entire bottom 
close-pack guide roll set. 
The two lateral shutters or gates are shown at 367 and 368 in FIG. 18. 
These shutters each have a vertical edge which may be suitably rounded as 
indicated at 369 and 370, respectively. The gate 367 is mounted on 
parallel tracks 372 and 373, while the lateral gate 368 is mounted on 
parallel tracks 374 and 375. The tracks are inclined at about 30.degree. 
to about 45.degree. and are symmetrical with each other. 
Projecting from the exterior of the hood are brackets 378 and 379 which 
accommodate reversible motors 380 and 381, respectively. The motors 380 
and 381 drive screw jacks 382 and 383 projecting from housings 384 and 
385, respectively. The screw actuators are connected to links 387 and 388 
pivotally connected to the respective gates at 389 and 390. It is noted 
that for illustrative purposes only, the gate 369 is shown fully 
retracted, while the gate 368 is shown nearly fully extended. Movement of 
the lateral gates controls the width of the orifice 82. Movement of the 
bottom shutter 361 controls the height or thickness of the orifice. Also, 
for range illustrative purposes only, the extrudate in FIG. 18 is shown 
considerably smaller than that of FIG. 17. 
Referring now additionally to FIGS. 19-20, it will be seen that the gates 
or shutters are moved continuously in response to the geometric parameters 
such as the dimensions or positions of the extrudate as it moves through 
the pond and into the hood. Immediately upstream of the hood and mounted 
on the bulkhead 42 are extrudate edge sensing rollers 393 and 394, each 
mounted on a swing arm 395 and 396, respectively. Cylinder actuator 
assemblies 397 and 398 urge the rollers toward each other or toward the 
edges of the extrudate passing therebetween. The vertically elongated 
rollers are on a vertical axis as are the proximal pivots for the 
respective arms. At such proximal pivots there is provided rotary encoders 
401 and 402, respectively. It is noted that the rollers 393 and 394 are 
axially underwater, while the supporting arms 395 and 396 as well as the 
pneumatic piston-cylinder assemblies and the rotary encoders are above the 
waterline. 
The thickness of the extrudate is measured by an underslung roller 405 
mounted between the distal ends of arms of arm frame 406. A cylinder 
assembly 407 urges the arm frame in a counterclockwise direction as viewed 
in FIG. 17 about its upper pivot 408 which includes a rotary encoder 409. 
In this manner, the platen 344 above the extrudate acts as a backstop for 
the roller 405, and the position of the encoder is an analog measurement 
of the thickness of the extrudate. Again, the rotary encoder is above the 
water level, while the roller 405 is beneath the water level. 
As seen in FIG. 19, each of the three motors 380 and 381 for the lateral 
gates, and 365 for the bottom shutter or gate, is controlled by a 
respective motion controller seen at 412, 413 and 414. The motion 
controllers are preferably of the digital PID (proportional 
integral-derivative) type and take into account a programmed factor of 
product change from the position of the sensor rolls to the orifice. The 
rotary encoders on the pivots of the arms illustrated are connected to the 
respective PID controllers. The encoder 402 is connected to the controller 
412 by the line 416. The encoder 401 is connected to the controller 413 by 
the line 417, while the encoder 409 is connected to the controller 414 by 
the line 418. The controllers are also connected to the main process 
controls through the line 420. 
FIG. 19 also illustrates the dancer roll 65 supported on the arm frame 66 
and operating the encoder 267. In the embodiment of FIG. 19, the encoder 
267 operates a PID controller 422 which controls drive 423 for a 
foraminous belt 424 in a vacuum table shown generally at 425. The vacuum 
table may be employed in place of the tractor drive illustrated in FIG. 
1B. A vacuum in chamber 427 is created by the vacuum pump or blower 428, 
and the level of vacuum may be controlled by the blower or pump speed. The 
level of vacuum is sufficient to hold the extrudate 64 to the vacuum 
foraminous belt without damage, and the drive 423 pulls the extrudate to 
the right as seen in FIG. 19. The controller 422 is also controlled from 
the central process controls through the line 420. Again, the position of 
the dancer roll, over which the extrudate passes, controls the belt drive 
423 to control the tension on the extrudate from the shaping or 
calibrating equipment in the vacuum chamber through the immersion pond, 
through the submerged orifice, through the blow off, and into the cutting 
and processing equipment at the tail end of the process. 
Spray nozzles 79 are also shown in FIG. 19. The nozzles are supplied by one 
or more lines 430 which extend to the atmospheric pond section 76. When 
the sealed chamber is evacuated as by the vacuum pump 432 water will be 
drawn into the chamber to be sprayed on the extrudate or foam board 64 
before it enters the pond section so the water will be recirculated to the 
atmospheric section 76 by the circulating pump 434. If not above the pond 
a special sump may be provided. 
It can now be seen that there is provided a process and apparatus for 
producing high quality foams at low density, and for producing such foams 
with high and efficient throughput. 
To the accomplishment of the foregoing and related ends, the invention then 
comprises the features particularly pointed out in the claims, these being 
indicative, however, of but a few of the various ways in which the 
principles of the invention may be employed.