U.S. patent number RE32,032 [Application Number 06/545,481] was granted by the patent office on 1985-11-19 for method of densifying open-celled polyurethane material.
This patent grant is currently assigned to Foam Cutting Engineers, Inc.. Invention is credited to Winslow L. Pettingell.
United States Patent |
RE32,032 |
Pettingell |
November 19, 1985 |
Method of densifying open-celled polyurethane material
Abstract
A method of densifying open-celled polyurethane foam is provided
in which heated air at a temperature between about 425.degree. F.
and 460.degree. F. is circulated through a mass of the foam so as
to rapidly and uniformly raise the temperature of the mass to
between about 365.degree. F. and 435.degree. F., the mass is then
compressed to a desired thickness while its temperature is
maintained between 365.degree. F. and 435.degree. F., and the mass
is then immediately permitted to cool.
Inventors: |
Pettingell; Winslow L.
(Wooddale, IL) |
Assignee: |
Foam Cutting Engineers, Inc.
(Addison, IL)
|
Family
ID: |
27366429 |
Appl.
No.: |
06/545,481 |
Filed: |
October 26, 1983 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
876736 |
Feb 10, 1978 |
|
|
|
Reissue of: |
044042 |
May 31, 1979 |
04228076 |
Oct 14, 1980 |
|
|
Current U.S.
Class: |
264/101; 264/280;
264/321; 264/DIG.66 |
Current CPC
Class: |
B29C
44/5636 (20130101); B29K 2105/045 (20130101); B29K
2075/00 (20130101) |
Current International
Class: |
B29C
44/34 (20060101); B29C 44/56 (20060101); B29D
027/00 () |
Field of
Search: |
;264/101,321,280,DIG.66 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Anderson; Philip
Attorney, Agent or Firm: Wood, Dalton, Phillips, Mason &
Rowe
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of copending application
Ser. No. 876,736 filed Feb. 10, 1978, now abandoned entitled
"Method of Densifying Open-Celled Polyurethane Material".
Claims
I claim:
1. A method of densifying a mass of fully cured open-celled
polyurethane foam, said method comprising the consecutive steps
of:
.[.passing.]. .Iadd.creating a suction to pass .Iaddend.heated
gaseous material entirely through the mass, the temperature of said
gaseous material being in the range of about 425.degree. F. to
460.degree. F. and the velocity of said gaseous material being
insufficient to destroy the integrity of the cell walls of the
mass, said gaseous material being inert with respect to the
polyurethane, and the period of exposure of the mass to the gaseous
material being insufficient to allow charring of the mass, yet
sufficient to raise the entire mass substantially uniformly to a
temperature between about 365.degree. F. and 435.degree. F.;
compressing the mass while its temperature is between about
365.degree. F. and 435.degree. F. to reduce its thickness and thus
increase its density to a desired degree; and
permitting the mass to cool.
2. The method of claim 1 wherein the gaseous material is air.
3. The method of claim 1 wherein the gaseous material is
.[.circulated.]. .Iadd.sucked .Iaddend.downwardly through the
mass.
4. The method of claim 1 wherein the mass is maintained in the
temperature range of 365.degree. F. to 435.degree. F. for a time
not exceeding about one minute.
5. The method of claim 1 wherein the mass is moved into a zone at
ambient temperature immediately after it is compressed.
6. The method of claim 1 wherein the mass is moved continuously
endwise and is compressed between pinch rollers.
7. The method of claim 6 wherein the mass is maintained in the
temperature range of 365.degree. F. to 435.degree. F. for a time
not exceeding about one minute.
8. The method of claim 7 wherein the mass is permitted to cool by
moving it endwise out of the pinch rollers into a zone at ambient
temperature.
9. The method of claim 1 wherein the mass is moved in a
discontinuous fashion and is compressed between two flat parallel
surfaces.
10. The method of claim 9 wherein at least one of said flat
parallel surfaces comprises a movable platen.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods of densifying foamed plastic
material and, more particularly, to a method of densifying a mass
of open-celled polyether or polyester polyurethane foam. While the
method is advantageous for material of any thickness, it is
especially valuable in treating material which is several inches
thick.
2. Description of the Prior Art
Previous methods of densifying open-celled plastic foam articles
have relied on the extended application of heat and substantial
compressive forces to the surface of the article. This is often
carried out by means of large heated metal molds or platens between
which the foam is placed. Heat is transmitted to the foam by
conduction from the heated platens for a substantial period of
time. The low K-factors of air and of polyurethane make such
heating processes very time-consuming.
A commercially acceptable polyurethane foam requires a density and
other physical characteristics which are quite uniform throughout.
This can only be achieved by bringing all parts of a mass of such
foam into a predetermined temperature range during processing
because the material will return to its pre-treatment state if the
treatment temperature is too low, and this necessarily causes a
non-uniform product if some parts of the mass are sufficiently hot
during treatment and others are not. Prior art processes inherently
tend to produce non-uniform material, and are difficult to control
because of the very low K-factors previously mentioned.
U.S. Pat. No. 3,577,519 (Gambardella) describes a method of
densifying polyurethane foam buns wherein partially cured foam is
compressed while still at or near its exothermal reaction
temperature. This process may result in non-uniform temperatures
and uncontrollable densification, at least in part, due to the
relatively rapid cooling of the exterior of the mass and the
typically large size of polyurethane reaction buns. This problem is
only partially alleviated by the use of heated compression means.
Also, the process may not be used to densify fully cured foam.
Further, the heating of a mass of foam by conduction, as in the
above-described prior processes, is very inefficient, as great
amounts of heat are required to initially heat the compression
means, which are often massive, and then to maintain the
temperature of the compression means while they are in prolonged
contact with the foam.
Another source of inefficiency in previous compression methods is
the inability of those methods to adapt to continuous operating
conditions. The nature of the prior processes eliminates anything
but extremely thin material for densification on a continuous
system. Prior processes were generally operated on an intermittent
basis which would result in platen marks on continuous strips of
foam.
Another disadvantage of prior compression densification methods as
applied to cured polyurethane is that very high compressive forces
are required until the mass reaches the proper temperature. This
requires the use of massive compressive equipment, the cost of
which further detracts from the desirability of prior compression
methods.
U.S. Pat. No. 3,475,525 (Peters) describes a method of reticulating
open-celled polyurethane foam in which a stream of heated gas is
passed through the foam in order to heat the foam so as to melt or
thermally decompose membranous cell walls without melting the
network strands supporting the cell walls. The gas temperature must
be above about 480.degree. F. and is generally between about
750.degree. F. and 1470.degree. F., and the thickness of the foam
must be less than 0.75 inches to prevent degradation of the network
structure. Additionally, the gas velocity through the foam must be
in excess of about 31/4 ft./sec.
The method of the present invention preserves the cell integrity,
since gas temperature and velocity are substantially less than in
Peters. Further, the present invention may be effectively applied
to foams of thickness much greater than 0.75 inches, the upper
limit of the Peters method.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved method of
densifying open-celled foam and, more specifically, of densifying
fully cured open-celled polyurethane foam.
It is a further object of the invention to provide a method of
densifying open-celled polyurethane foam which may be carried out
so as to provide an end product of uniform density throughout.
Another object of the invention is to provide a method of
densifying fully cured open-celled polyurethane foam wherein
relatively small compressive forces are required to effect
densification.
It is a further object of the invention to provide a method of
rapidly densifying open-celled polyurethane foam which may be
carried out on continuous strips as well as on separate slabs.
Yet another object of the invention is to provide a method of using
circulating hot air to rapidly raise the foam into the proper
temperature range while so controlling temperature and air velocity
as to avoid breaking down the membranous and skeletal structure of
the material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal central sectional view of an apparatus for
practicing the method of the invention; and,
FIG. 2 is a transverse sectional view taken substantially as
indicated along line 2--2 of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates an apparatus, generally designated 10, to
permanently compress and thereby densify a mass 12 of fully cured
open-celled polyurethane foam. The apparatus 10 comprises a base
(not shown) which includes a planar horizontal support (not shown),
an upstanding support means (not shown), an endless conveyor means
14, gas heating and circulating means 16, and compressing means 18
which form an integral part of the heating and circulating means
16.
The purpose of the invention is to densify the mass 12 of
chemically stable, open-celled polyurethane foam, which is
preferably and illustratively a continuous strip 20, but which may
be in the form of separate slabs for batch treatment. The mass 12
is of any thickness, with about 1/2" to about 7" being typical, and
has a density as low as about 0.9 lb/ft.sup.3. The density of the
mass 12 will generally be between 1.3 lb/ft.sup.3 and 2.25
lb/ft.sup.3.
The conveyor 14 comprises an endless open mesh belt 22 which
travels about a drive drum 24 and a pair of idler drums 26 which
carry the belt 22 in the direction of the arrow 27 through a
horizontal working run 28 and a return run 30.
One portion 32 of the horizontal working run 28 traverses and is
effectively enclosed by a chamber 34 of the gas heating and
circulating means 16, said chamber 34 comprising an upper portion
36 and a lower portion 38 disposed above and below the horizontal
working run 28, respectively.
Referring to FIG. 2, the gas heating and circulating means 16
comprises an endless conduit system including both portions of said
chamber 34 and a housing 40 containing a blower 42 and heating
means 44. The upper portion 36 of the chamber 34 is defined by said
portion 32 of the horizontal working run 28, part of an upper wall
46, an inner wall 48, an outer wall 50, and parts of a front wall
52 and a rear wall 54, seen in FIG. 1.
The endless conduit system has a hood-like upper member which
includes the upper portion 36 of the chamber 34, an upper section
56 of the housing 40, and a trough-like lower member 37 which
provides the lower portion 38 of the chamber 34 and constitutes the
gas inlet for the blower 42.
The trough-like lower member 37 is defined by said portion 32 of
the horizontal run 28, an inner wall 58, an outer wall 60 and an
arcuate side and bottom wall 62 (FIG. 1). The lower section of the
housing 40 is formed by a section of an inner wall 66, an outer
wall 68, a transverse wall 70 extending between the walls 66 and
68, and a transverse wall (not shown) which is parallel to the wall
70.
The blower 42 is a conventional type powered by a motor 64. In
operation, the blower 42 circulates gas in the direction of the
arrows shown in FIG. 2. The heating means 44 is located above, and
thus downstream of, the blower 42 and illustratively comprises a
plurality of electric heating elements 72. The upper section 56 of
the housing 40 is defined by the upper margin of the heating means
44, the upper part of the inner wall 66, an outer wall 74, part of
the upper wall 46, and those parts of the front and rear walls 52
and 54 which extend transversely between the walls 66 and 68.
As noted above, it is necessary to raise the temperature of the
mass 12 to a uniformly high level in order to effect uniform
densification thereof. Therefore, it is necessary that the gas flow
velocity be uniform throughout the chamber 34.
In order to ensure uniform distribution of gas flow across the
chamber 34, a perforate baffle plate 75 having a plurality of holes
75a of various sizes is disposed across the chamber 34,
substantially perpendicular to the gas flow path, preferably and
illustratively in the lower chamber portion 38.
In the absence of a gas distributing means such as the baffle plate
75, gas flow velocities through a given cross-sectional area
perpendicular to the gas flow path would tend to be distributed
such that gas flowing near the walls 50, 52 and 54, i.e. relatively
far from the blower 42, flows at a lower velocity than gas near the
wall 48 and centrally between the walls 52 and 54. This effect is
especially marked in large ovens. The baffle plate provides
variable resistance to gas flow through the chamber 34, with
relatively great resistance applied at those points where gas
velocity is highest, by means of relatively small holes, with
larger holes at points of lower gas velocity. Such baffle plates
are well known in the art.
It is to be noted, however, that even the smallest of the holes 75a
are large enough to ensure low total resistance at normal flow
rates which are less than 1 ft/sec.
Referring to FIG. 1, it is to be noted that the horizontal run 28
of the conveyor 14 and the foam mass 12 carried thereon enters the
chamber 34 through an elongate slot 76 and that the bottom of the
horizontal run 28 contacts a pair of upstanding sealing walls 78,
seen in FIG. 2. The vertical dimension of the opening 76
corresponds closely to the vertical dimension of the combination of
the horizontal run 28 and the mass 12, thereby effecting a seal
about the mass 12 and the working run 28, and external upper and
lower lipped flanges 80 and 81, respectively, aid in reducing the
escape of the circulating gas. It is to be understood, however,
that the seal is intended only to contain most of the circulating
gas and not to provide absolute containment.
The compression means 18 adjoins the gas heating and circulating
means 16 at the rear wall 54 thereof, and encloses a section 82 of
the working run 28. As seen in FIG. 1, the compression means 18
comprises a housing 84, including a top wall 86, a bottom wall 88,
upper and lower rear walls 90 and 92, respectively, a front
upstanding wall 94 connected to the wall 88, a side wall 96
extending between the rear walls 90 and 92 and the wall 94, and a
second side wall (not shown) disposed opposite the side wall 96.
The housing 84 communicates with the chamber 34 through an opening
97 in the wall 54. A deflector plate 98 extends between the walls
48 and 50 of the heating chamber 34 to direct heated gas into the
opening 97.
The housing 84 contains compressing means 99, illustratively
comprising an opposed pair of driven steel pinch rollers 100. An
inclined plate 101 which receives and supports the mass 12 extends
between the sidewalls of the chamber 84 and terminates adjacent the
surface of the lower roller 100 at a point selected such that the
mass 12 is directed substantially centrally between the rollers 100
in order to ensure that equal compressing force is applied to each
side of the mass 12, to prevent distortion thereof. It may be
understood that other compressing means, such as platens, may be
used. Platens are suitable for batchwise compression of foam
slabs.
The section 82 of the working run 28 travels over a roller 102 then
under a roller 104 disposed below the roller 102, and then over a
roller 106 at the downstream end of the housing 84, whereby the
working run 28 is separated from the strip 20 of polyurethane foam
so as to facilitate the simultaneous application of pressure to
both sides of said strip.
If desired, the rollers 100 may be coated with a release agent
which facilitates separation of the strip 20 from the rollers 100
after compression of the foam. It has been found, however, that the
use of a release agent is generally not necessary in the practice
of the invention. The rollers 100 must be maintained at or very
near the temperature of the circulating gas and the strip 20 in
order to prevent premature cooling of the surface of the strip 20,
which would result in non-uniform densification. Deflection of
heated gas from the chamber 34 into the housing 84 by the
deflection plate 98 and suitable heating means, such as a pair of
high-intensity lamps 107 mounted on the walls 90 and 92 and focused
on the upper and lower rollers 100, respectively, maintain the
temperature of the rollers 100 and the strip 20 at a sufficiently
uniform, high level to result in uniform densification.
The strip 20 and the working run 28 exit the housing 84, preferably
into a zone at ambient temperature, through a shallow elongate
opening 108 between the walls 90 and 92. While the vertical
dimension of the opening 108 is not so small as to form an absolute
seal about the strip 20 and the working run 28, it is sufficiently
small to prevent the loss of any substantial amount of heated gas.
The slot 76 and the shallow opening 108 allow moderate escape of
heated gas from the system, and the entry of make-up gas.
In operation, the mass 12 is placed on the conveyor 14 and is
carried into the chamber 34 where it is contacted by the
circulating heated gas. The gas is commonly and illustratively air,
but may be another gas or mixture of gases in certain situations.
The circulating gas must be chemically inert with respect to the
polyurethane, and not otherwise have a tendency to impart
undersirable characteristics to the foam.
The circulating air is heated to a temperature between about
425.degree. F. and 460.degree. F. by the heating means 44, and is
directed into the chamber 34 where it is drawn downwardly through
the mass 12 and the working run 28 by the suction produced by the
blower 42, which creates a lower pressure in the lower portion 38
than in the upper portion 36 of the chamber 34.
The open-celled structure of the foam allows the heated air to
intimately contact the entire interior cell structure of the foam,
thereby rapidly heating the mass 12 to a temperature which is
substantially uniform throughout the mass, but which is generally
lower than the temperature of the circulating air, e.g. between
about 365.degree. F. and 435.degree. F. At gas velocities less than
about 1 ft/sec, uniform heating of the mass to the desired
temperature level is typically accomplished within 10-15 sec. It is
important that the mass 12 does not reach a temperature above
approximately 475.degree. F. nor remain at a temperature above
about 365.degree. F. for periods longer than about one minute, as
undesirable charring of polyurethane may begin under such
conditions.
After the temperature of the mass 12 is raised to a temperature
between 365.degree. F. and 435.degree. F., the mass 12 exits the
chamber 34 and enters the housing 84 via the opening 97, where the
mass 12 is maintained at the desired temperature, and is fed
between the steel pinch rollers 100 while separated from the
working run 28.
The internal resistance of the mass 12 to compressive force is
greatly reduced when the temperature of the mass is between about
365.degree. F. and 435.degree. F. In that temperature range, the
state of the mass approximates that of its exothermal reaction
stage, during which it has low resistance to compressive force and
little resilience. As a result, a permanently densified strip 20a
may be produced by the application of a relatively small
compressive force for a comparatively short time relative to those
necessary with previous compression methods. The pressure may be
less than 10% of that required by previous methods; and after a
brief period of compression, the compressive force may be removed
at once without fear of subsequent expansion.
Cooling of the mass to substantially below 365.degree. F.
immediately after compression insures permanence of the
densification. Cooling occurs very rapidly because of the low
specific heat and relatively low density of the mass even after
densification. This allows higher production rates than were
possible with older methods of densification. Also, the need for
heavy molds or platens is obviated, thereby allowing for decreased
capital cost. The relative vertical spacing of the rollers 100 is
adjustable, thereby allowing for different desired final
thicknesses and, therefore, different final densities of the
densified strip 20a. The final density of the strip 20a may be up
to about 30 lb/ft.sup.3.
As an alternative to pinch rollers, two movable platens, or one
movable platen and a stationary surface, may be employed as the
compressive means 99. If so employed, a first platen is disposed
above the mass 12 with its horizontal surface substantially
parallel to the upper surface of the mass, and a second platen (or
stationary surface) is disposed below the mass 12, with its surface
substantially parallel to the surface of the first platen. The
upper platen, or both platens, are moved vertically toward one
another so as to apply compressive forces to the upper and lower
surfaces of the mass.
It may be noted that certain aspects of the operation are different
if platens are used as the compressing means, rather than pinch
rollers. Operations with platens are necessarily performed in a
discontinuous manner, as it is necessary to stop the movement of
the conveyor when the platens are in their closed position around
the mass 12. The use of platens is especially suitable for use with
individual slabs of foam as opposed to continuous strips, although
platens may be used to successively densify portions of a strip,
thereby effecting densification of the entire strip.
The surfaces of the compressing means 99 may be smooth or embossed,
depending on the desired surface appearance of the finished
product.
After compression, the densified strip 20a and the working run 28
exit the housing 84 through the opening 108; and after the strip
20a has cooled, it may be further cut, shaped, etc.
It may be noted that due to the extremely rapid nature of the
cooling process, further operations may be undertaken almost
immediately after the strip 20 exits the housing 84.
The following specific examples will serve to more fully illustrate
the practice of the present invention.
A series of foam densification tests were conducted on an apparatus
such as shown in FIGS. 1 and 2. The rollers 100 were of steel and
were each 8" in diameter, with spacings of 0.14" and 0.125" in
successive series of tests. The rollers were heated by two 400 watt
quartz infra-red lamps focused on the roller surfaces, as shown in
FIG. 1.
The belt 22 was 93% open steel mesh and was chain driven by a 1/4
Hp. capacity D.C. gear head motor. The rollers 100 were driven by
the same motor, and were interconnected with the belt 93 through a
gear arrangement allowing independent variation of the speeds of
the rollers 100 and the belt 93, with a maximum belt speed greater
than 125"/min.
Air temperature was controlled by control of voltage to the finned
strip heaters 72 by a Variac.
The blower 42 had a capacity of 160 ft.sup.3 /min. The
cross-sectional area of the chamber 34 was about 2 ft.sup.2 giving
a maximum air flow velocity of about 1.3 ft/sec. The length of the
heating chamber 34 between the front and rear walls 52 and 54 was
about 20". Actual air velocity was believed to be about 0.5-0.7
ft/sec., due to resistance from the foam mass 12.
It was found that the conveyor and roller system was easily stalled
by feeding a 14" wide, 3/4" thick strip of unheated polyurethane
foam having a nominal density of 2 lb/ft.sup.3 and an ILD
(indentation load deflection) characteristic of 36 to the rollers
at about 96"/minute. However, there was negligible resistance when
an identical strip was heated to temperatures between about
365.degree. F. and 435.degree. F.
The results of the tests are summarized in Table I:
TABLE I
__________________________________________________________________________
Conveyor Entering Mass Roller Post Com- Test Material Entering
Speed Air Temp. Temp. Temp. % pression Product No. Designation
Thickness (in/min) (.degree.F.).sup.(3) (.degree.F.).sup.(4)
(.degree.F.) Stretch Thickness Quality
__________________________________________________________________________
1 4530.sup.(1) 1" 96 455 380 420 7% .135" Good 2 4530 1" 96 450 395
420 8% .135" Fair 3 4530 1" 100 455 365 415 7% .135" Fair 4 4530 1"
125 425 375 405.sup.(5) -- -- Poor 5 4530 1" 112 460 405
430.sup.(5) 5% .135" Good 6 Ester.sup.(2) 1/2" 100 450 430 410 4%
.135" Good 7 4530 1" 84 430 400 440 4.5% .13" Excellent 8
2555.sup.(1) 11/2" 84 450 375 400 -- -- Poor 9 2555 11/2" 96 460
435 460 -- .125" Excellent 10 4536.sup.(1) 13/8" 96 460 400 460 --
.125" Excellent
__________________________________________________________________________
.sup.(1) Flexible Foam 4530 2 lb/ft.sup.3 30 ILD Ether (Chattanooga
4536 2 lb/ft.sup.3 36 ILD Ether Tennesee) 2555 2 lb/ft.sup.3 55 ILD
Ether .sup.(2) Crest Foam (Moonachie, New Jersey) 2 lb/ft.sup.3
Charcoal Ester .sup.(3) Measured immediately above mass in chamber
36. .sup.(4) Measured as air temperature immediately below conveyor
belt at chamber exit 97. .sup.(5) Roller heat lamps not used.
All foam density values are nominal and, where a stretch or
thickness value is not given, no measurement was made.
The time required to bring the temperature of the circulating air
and the rollers to a desired level was about thirty minutes, as
opposed to the required start-up time of four hours or more
experienced with prior platen compression systems.
It was noted that when the roller temperature was reduced, the
surface of the product foam was fuzzy and not fully densified, thus
showing that, if desired, foam of nonuniform density may be
produced.
Exposure time of the foam to heated air varied between about 10
seconds at a conveyor speed of 125 in/min to about 15 seconds at a
conveyor speed of 84 in/min. It is not believed that exposure times
longer than 15 seconds give improved results, except when the
initial foam thickness is greater than about 7 in.
Of course, it will be apparent that required foam/gas contact time
is a function of foam thickness and gas temperature, with longer
contact times being required for very thick (i.e. greater than 7
in.) foams and in cases where the gas is heated only to relatively
low temperatures. However, it is believed that contact times
substantially greater than 15 seconds will rarely, if ever, be
required at adequate heat.
The 1/4 Hp. motor was more than sufficient to power the system when
the foam was heated before and during feeding to the rollers, thus
indicating that required pressure is negligible compared to prior
systems. It is believed that the required horsepower increases with
increased roller size, which in turn increases with the initial
thickness of the mass 12. It is also believed that horsepower
requirements increase with the desired degree of densification of a
given thickness of foam.
It is to be noted that the foam may be elongated if desired by
increasing the speed of the rollers relative to that of the
conveyor belt.
It is to be understood that the use of the subject invention is
limited to those foams which have an open-celled structure which
allows penetration of the foam by the flow of heated gaseous
material. It should also be noted that either open-celled polyester
or polyether urethane may be employed with equally good results. It
is believed that the process of the invention may be advantageously
applied to foams of synthetic resins other than polyurethane.
It will be readily apparent from the foregoing detailed description
and test results that the present invention provides a foam
densification process whereby capital and operating expenditures
are significantly decreased due to the absence of the requirement
of massive pressure and heat application equipment.
It is believed that the time required to effect foam densification
according to the present invention is only about 10% of that
required by prior methods, thus allowing significantly increased
production rates. The relatively short required start-up and
turn-around periods also contribute significantly to increased
production rates.
The foregoing detailed description is given for clearness of
understanding only, and no unnecessary limitations should be
understood therefrom as modifications will be obvious to those
skilled in the art.
* * * * *