U.S. patent application number 11/227827 was filed with the patent office on 2007-03-15 for circumferentially variable surface temperature roller.
This patent application is currently assigned to Eastman Kodak Company. Invention is credited to Richard D. Bomba, Jose L. Garcia.
Application Number | 20070060457 11/227827 |
Document ID | / |
Family ID | 37596284 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070060457 |
Kind Code |
A1 |
Bomba; Richard D. ; et
al. |
March 15, 2007 |
Circumferentially variable surface temperature roller
Abstract
A casting roller having a variable temperature surfaces
comprises a rotatable cylindrical shell (12). Axially aligned
heating electric elements (14) are equally spaced and internal to
an outer surface of the rotatable cylindrical shell. A brush
assembly (16) is in electrical contact with the heating elements
during a portion of the rotatable cylindrical shell rotation about
an axis. A stationary core (26) is internal to the rotatable
cylindrical shell. An annular space is between the stationary core
and the rotatable cylindrical shell. A cooling fluid fills (22) at
least a portion of the annular space.
Inventors: |
Bomba; Richard D.;
(Rochester, NY) ; Garcia; Jose L.; (Acworth,
GA) |
Correspondence
Address: |
Mark G. Bocchetti;Patent Legal Staff
Eastman Kodak Company
343 State Street
Rochester
NY
14650-2201
US
|
Assignee: |
Eastman Kodak Company
|
Family ID: |
37596284 |
Appl. No.: |
11/227827 |
Filed: |
September 15, 2005 |
Current U.S.
Class: |
492/46 |
Current CPC
Class: |
B29C 2043/023 20130101;
B29C 43/46 20130101; B29C 33/04 20130101; B29C 43/52 20130101; F28F
5/02 20130101; B29C 33/026 20130101; B29C 2043/522 20130101; B29C
33/08 20130101; B29C 33/044 20130101 |
Class at
Publication: |
492/046 |
International
Class: |
F28F 5/02 20060101
F28F005/02 |
Claims
1. A casting roller having a variable temperature surface
comprising: a rotatable cylindrical shell; axially aligned heating
electric elements equally spaced and internal to an outer surface
of said rotatable cylindrical shell; a brush assembly in electrical
contact with said heating elements during a portion of said
rotatable cylindrical shell rotation about an axis; a stationary
core internal to said rotatable cylindrical shell; an annular space
between said stationary core and said rotatable cylindrical shell;
and a cooling fluid filling at least a portion of said annular
space.
2. A casting roller as in claim 1 wherein a baffle confines said
cooling fluid to a portion of said annular space.
3. A casting roller as in claim 1 wherein said cooling fluid is
selected from a group comprising organic synthetic media that has
an operating temperature range of 60 C to 350 C (140 F-662 F).
4. A casting roller as in claim 3 wherein the viscosity of the
fluid varies from 8.2 centipoise to 0.26 centipoise.
5. A casting roller as in claim 3 wherein specific heat of said
media varies from 1.62 kJ/kg*K at 60 C to 2.82 kJ/kg*K at 360
C.
6. A casting roller as in claim 3 wherein thermal conductivity
varies from 0.125 W/m*K at 60 C to 0.086 W/m*K at 360 C.
7. A casting roller as in claim 3 wherein density of said media
varies from 1016 kg/m3 at 60 C to 801 kg/m3 at 360 C.
8. A casting roller as in claim 1 wherein said heating elements are
cartridge heaters.
9. A casting roller as in claim 8 wherein said heaters are 0.25
inch diameter with a heat flux output of approximately 60
W/in2.
10. A casting roller having a variable surface temperature
comprising: a rotatable cylindrical shell; a stationary core
internal to said rotatable cylindrical shell; an annular space
between said stationary core and said rotatable cylindrical shell;
baffles creating a first and second region in said annular space; a
first fluid at a first temperature circulating in said first
annular space; and a second fluid at a second temperature
circulating in said second annular space.
11. A casting roller as in claim 10 wherein said first fluid is a
cooling fluid and is selected from a group comprising organic
synthetic fluid has an operating temperature range of 60 C to 350 C
(140 F-662 F).
12. A casting roller as in claim 11 wherein a viscosity of the
fluid varies from 8.2 centipoise to 0.26 centipoise.
13. A casting roller as in claim 11 wherein a specific heat of said
fluid varies from 1.62 kJ/kg*K at 60 C to 2.82 kJ/kg*K at 360
C.
14. A casting roller as in claim 11 wherein thermal conductivity of
said fluid varies from 0.125 W/m*K at 60 C to 0.086 W/m*K at 360
C.
15. A casting roller as in claim 11 wherein a density of said fluid
varies from 1016 kg/m3 at 60 C to of 801 kg/m3 at 360 C.
16. A casting roller as in claim 10 wherein said first annular
space covers one third of the circumference of the shell at a
time.
17. A casting roller as in claim 10 wherein said second annular
space covers two thirds of said cylindrical shell at a time.
18. A casting roller as in claim 10 wherein: said rotatable
cylindrical shell is thin; and a shoe supports said rotatable
cylindrical shell at a nip.
19. A method of casting a web of material comprising: contacting
said web within a heating zone of said roller; raising said web to
a casting temperature; forming an impression on said web;
maintaining said web in contact with said roller through at least a
portion of a cooling zone on said roller; and stripping said web
from said roller after said web has cooled.
20. A method as in claim 19 wherein said roller surface temperature
is increased 30 degrees centigrade to 60 degrees centigrade greater
than a web glass transition temperature.
21. A method as in claim 19 wherein said roller surface temperature
is decreased to 3 degrees centigrade to 5 degrees centigrade less
than a web glass transition temperature.
22. A casting roller having a variable surface temperature
comprising: a rotatable cylindrical shell; a stationary core
internal to said rotatable cylindrical shell; an annular space
between said stationary core and said rotatable cylindrical shell;
baffles creating a first and second region in said annular space; a
first fluid at a first temperature circulating in said first
annular space; a second fluid at a second temperature circulating
in said second annular space; wherein said rotatable cylindrical
shell is thin; and a shoe which supports said rotatable cylindrical
shell at a nip.
23. A casting roller as in claim 22 wherein: a third region is
created by said buffer surrounding said shoe; and a third fluid at
a third temperature is in said third region.
24. A casting roller as in claim 23 wherein said third fluid
lubricates said shoe.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Reference is made to commonly-assigned copending U.S. patent
application Ser. No. 10/795,010, filed Mar. 5, 2004, entitled
COMPLIANT PRESSURE ROLLER WITH UNIFORM NIP PRESSURE, by Bomba et
al.; AND U.S. patent application Ser. No. 10/889,561, filed Jul.
12, 2004, entitled AXIALLY COMPLIANT PRESSURE ROLLER UTILIZING
NON-NEWTONIAN FLUID, by Richard D. Bomba; the disclosures of which
are incorporated herein.
FIELD OF THE INVENTION
[0002] This invention relates in general to casting rollers and in
particular to a casting roller having a radial variable surface
temperature.
BACKGROUND OF THE INVENTION
[0003] In extrusion and embossing operations the surface
temperature of the rollers contacting the molten material or web
material is an important process parameter. Typical roller designs
provide single roller bulk temperatures as established with
internal circulation of a fluid media. The maximum temperature is
normally limited to a value in which the material can be easily
stripped from the roller surface.
[0004] One attempt to solve this problem can be found in expired
prior art, U.S. Pat. No. 2,526,318, which vaguely describes a
configuration providing two regions of variable temperature but
provides no detail of design criteria or performance capabilities.
Subsequent prior art, U.S. Pat. Nos. 5,945,042; 6,260,887; and
6,568,931 similarly describe a method to provide more than one
temperature region around the circumference of a roller but provide
no detail of design criteria or performance capability. Prior art
U.S. Pat. No. 6,554,755 describes a roller design with the ability
to provide a localized region of temperature difference, but the
sole embodiment of this method is to create a means of compensating
for shell deflection.
[0005] At the contact point of either the molten material or web a
region of higher temperature is desirable to improve contact
between the materials and the roller surface and to improve
replication of the roller surface but this temperature is normally
too high to allow stripping the material from the roller surface.
Therefore, a lower surface temperature is required at the stripping
point, which limits the wetting of the roller surface and pattern
replication.
[0006] The purpose of this invention is to provide at least two
regions around the periphery of a roller with sufficient
temperature difference to provide improved wetting and replication
in one region and allow for uniform stripping of the material from
the second region.
SUMMARY OF THE INVENTION
[0007] Briefly, according to one aspect of the present invention a
casting roller having a variable temperature surfaces comprises a
rotatable cylindrical shell. Axially aligned heating electric
elements are equally spaced and internal to an outer surface of the
rotatable cylindrical shell. A brush assembly is in electrical
contact with the heating elements during a portion of the rotatable
cylindrical shell rotation about an axis. A stationary core is
internal to the rotatable cylindrical shell. An annular space is
between the stationary core and the rotatable cylindrical shell. A
cooling fluid fills at least a portion of the annular space.
[0008] The present invention provides detailed design criteria and
expected performance capabilities based on finite element analysis
to investigate the effect of roller diameter, shell thickness and
materials of construction
[0009] The invention and its objects and advantages will become
more apparent in the detailed description of the preferred
embodiment presented below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a cross-sectional view of a casting roller
according to the present invention.
[0011] FIG. 2 is a perspective view, partially in section, of
another embodiment of a casting roller according to the present
invention.
[0012] FIG. 3A is a cross-sectional view of yet another embodiment
of a casting roller according to the present invention.
[0013] FIG. 3B is a perspective view, partially in section, of the
embodiment shown in FIG. 3A.
[0014] FIG. 3C is an enlarged cross section view of the shell and
support shoe of the embodiment shown if FIG. 3A.
[0015] FIG. 4 is a chart showing the calculated cooling
efficiencies of various roller design configurations according to
the present invention.
[0016] FIG. 5 is a chart showing the calculated reheating
efficiencies of various roller design configurations according to
the present invention.
[0017] FIG. 6 is a cross-sectional view of a pattern on the surface
of a roller.
[0018] FIG. 7 is a chart of temperature versus pressure showing
pattern replication.
[0019] FIG. 8 is a chart showing calculated shell deformation at
maximum temperature.
[0020] FIG. 9 is a chart showing calculated shell deformation for
shell subject to a nip pressure and a supported by an internal
pressure gradient.
[0021] FIG. 10 is a cross section of an axially compliant pressure
roller forming a nip with at second roller.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention will be directed in particular to
elements forming part of, or in cooperation more directly with the
apparatus in accordance with the present invention. It is to be
understood that elements not specifically shown or described may
take various forms well known to those skilled in the art.
Embodiment 1
Electrically Heated Shell With Fluid Media Cooling
[0023] The outer shell 12 of the roller is machined to accommodate
a series of electrical heating elements 14 closely spaced, near the
outer surface of the shell. A brush assembly 16, mounted to the
roller, is utilized to provide electrical power only to heaters in
the desired heating zone 18. The internal surface 20 of the outer
shell 12 would be exposed to a fluid media 22 to remove the heat
added by the heating elements and to continue to remove heat from
the process material. The fluid media inlet 32 is attached to the
roller by a commercially available rotating joint. The diameter of
the shell is based on desired heating dwell time, final cooling
temperature, line speed, and materials of construction. The cooled
region 24 removes heat from the outer shell 12 and the cast
material 86, shown in FIG. 1 and FIG. 10. The fluid media 22 is
circulated in the annular region beneath the internal surface
20.
Embodiment 2
Roller With Two Surface Temperature Zones Created With Thermal
Fluid Media At Different Temperatures
[0024] Referring to FIG. 2, the outer shell 46 rotates about a
fixed inner shell (stator) 40 on carbon bearings 54. A carbon seal
52 is mounted adjacent to the bearings to prevent fluid leakage.
The stator is machined with at least two separate flow passages 42.
A close fitting baffle 44 between the stator 40 and the outer shell
46 creates a boundary between the fluid streams. Higher temperature
fluid 47 is circulated through one part of the stator 40. Contact
with the outer shell 46 as it passes over this region heats the
shell to the desired process temperature. The second region is
maintained at a lower temperature by circulating the low
temperature fluid 49. The stator 40 is designed to minimize contact
points between the higher and lower temperature zones.
Embodiment 3
Thin Shelled Roller With Internal Support And Two Different
Temperature Regions
[0025] This embodiment is similar to the embodiment above in that
the inner shell is fixed, outer shell rotates about inner shell and
two temperature zones are created by thermal medium circulation.
This embodiment utilizes a thin outer shell 70 supported internally
by a series of pivoting loading shoes 72. The loading shoes 72 are
independently adjustable to change the force exerted on the outer
shell 70 and to compensate for deformation of the outer shell due
to thermal and mechanical loads. The thermal medium circulates
within the region containing the shoes and is baffled at two points
by a first axial baffle 74 and a second axial baffle 76 to create a
higher temperature region and a cooling region. This heat transfer
medium may also serve as a hydrodynamic lubricant between the shoe
and the inner surface of the shell.
[0026] The thin outer shell 70 is an advantaged in this application
for it provides a more thermally responsive system that can heat
and cool more quickly. This can also be realized as a smaller
diameter for equivalent line speed. The smaller diameter translates
into less work to create patterned surface and a higher contact
stress in the nip for a given load.
[0027] Referring to FIGS. 3A, 3B, and 10, the roller consists of at
least three main regions. In this representation, the outer shell
70 rotates in a counter clockwise direction with respect to these
regions. The cooling region 41 creates a series of flow passages 42
exposed to the inner surface of the shell 25. High temperature
fluid 2 supply 60 impinges on the inner surface of the shell to
remove heat. High temperature fluid 2 return collects the fluid
from the flow passages 42 and directs the flow out of the roller. A
close fitting baffle 44 is positioned at the entrance to the
cooling region 41 to provide a separation of fluids between the
cooling region and the load shoe region 45. A first axial baffle 74
is located at the exit of the cooling region 41 to separate fluids
between the cooling region 41 and the reheating region 43. Similar
to the cooling sector 41, the reheating sector 43 is a flow
distribution sector in which high temperature fluid 1 supply 56
impinges fluid on the inner surface of the shell with fluid removal
through the high temperature fluid 1 return 58. A second axial
baffle 76 is mounted at the exit of this region to separate this
region from the loading shoe region 45. The purpose of this sector
is to increase the shell temperature prior to entering the nip
point 35.
[0028] The loading shoe region 45 consists of an axial member
machined to form pockets 29 along the length to accommodate each of
the loading shoes 72. The force applied to each loading shoe is
independently adjustable by means of the shoe loading mechanism 78.
A manually controlled worm screw adjusting mechanism has been shown
but is not limited to this implementation. High temperature fluid 3
supply 48 is located at the inlet of the loading shoe 72 to shell
interface to maintain continuous supply of fluid for the
hydrodynamic lubrication at this point. High temperature fluid 3
return 50 collects excess fluid for removal from the roller. Each
of these regions is arranged around the periphery of the fixed
inner shell 40 and constrained at a central point to accommodate
differential thermal expansion. The fixed inner shell 40 is rigidly
attached the machine structure through a support bracket 80 on each
end. The outer shell 70 is constrained to rotate about the fixed
inner shell 40 through bearings 28 mounted on each end. A seal 30
is adjacent to the bearings 28 to prevent leakage of the fluid from
the inner flow chambers. A drive sprocket 82 can be used to rotate
the shell to overcome nip forces and internal frictional
forces.
[0029] Each of these embodiments can be described in terms of
dimensionless parameters that are based on the physical properties
of the cast material to be processed, the desired process
conditions, the physical properties of the roller and the desired
manufacturing rates. Heat transfer textbooks describe transient
heat transfer using similar methods, but no direct method is taught
for a design considering a combination of cast materials and roller
design criteria subject to more than one heat transfer process.
[0030] A dimensionless temperature ratio, theta, can be formed
based on the following parameters; T.sub.infinity, which is
described as the bulk temperature of the heat transfer media.
T.sub.initial, which is defined as the initial temperature of the
roller shell or cast material depending on the particular process
function and T.sub.end, which is defined as the desired temperature
at the end of a given process operation. A smaller value of this
ratio indicates a higher efficiency in achieving desired process
goals. .theta. TR .times. : = T end - T infinite T initial - T
infinite ##EQU1##
[0031] Another dimensionless parameter can be formed, dimensionless
time, commonly referred to as tau in open literature. This
parameter normalizes the time dimension by utilizing the thermal
diffusivity of the material and the thickness. .tau. .times. : = t
dwell .alpha. ( t shell 2 ) 2 ##EQU2##
[0032] FIG. 4 shows a chart in which the dimensionless temperature
ratio, theta, is plotted on the ordinate and dimensionless time is
plotted on the abscissa. The family of curves is of the exponential
form as shown in the equation below: .THETA. t .function. ( x , k ,
h , t ) .times. : = P .times. .times. 1 .times. .times. s .times.
.times. 1 0 e - ( x - K mat k h t ) 1 - K mat k h t ##EQU3## The
coefficients shown in this equation are fitted to the finite
element results of various process simulations and related to
physical properties of the cast material, roller geometry and
physical properties of the roller. The subscripts of the fitted
curves end with the letters cl. The subscripts on the curves al,
steel, ag, and cu indicate shell materials of construction;
aluminum, steel, silver and copper respectively. In addition, the
subscript values of 0625 and 125 indicate shell thickness values of
one sixteenth of an inch (0.00158 m) and one eight of an inch
(0.0031 m) respectively. The calculations are based on a heat
transfer coefficient, h, of 350 Btu/(hr*ft.sup.2*.degree. F.) (1990
watt/(m.sup.2*.degree. C.) and cooling a commercially available
plastic material with a thermal diffusivity of 0.005 ft.sup.2/hr
(0.00000013 m.sup.2/s).
[0033] The roller design can be determined from these equations for
a particular set of requirements. Defining a dimensionless
temperature ratio based on the temperature of each zone, heat
transfer media temperatures and molten material temperature, the
chart of FIG. 4 can be use to either determine a process efficiency
for a given operating condition and roller configuration or for a
chosen process efficiency an operating speed can be determined for
a given roller diameter, shell thickness and material of
construction. FIG. 5 shows a chart plotting dimensionless
temperature ratio, theta, against dimensionless time, tau, for
shell reheating resulting from finite element calculations. The
subscripts follow the same convention as denoted for FIG. 4. The
calculations are based on an internal heat transfer coefficient, h,
of 350 Btu/(hr*ft.sup.2*.degree. F.) (1990 watt/(m.sup.2*.degree.
C.) and an external heat transfer coefficient of 3
Btu/(hr*ft.sup.2*.degree. F.) (17.03 watt/(m.sup.2*.degree.
C.).
[0034] Referring now to FIG. 10 an axially compliant pressure
roller is referred to in general by numeral 10. Axially compliant
pressure roller 10 is comprised in general of a stationary inner
core 26 and a plurality of loading shoes 72 which are pivotally
mounted to the stationary inner core 26. A series of non-magnetic
dividers create a plurality of annular chambers and each of the
loading shoes 72 occupies one of the annular chambers.
[0035] Referring to FIGS. 3A, 3B, and 3C loading shoe 72, which is
eccentrically mounted, is shown. A pivot point 15 and shoe
adjusting pin 17 are attached to loading shoe 72. A non-magnetic,
metallic material is used in the construction of the loading shoe
72, but the present invention is not limited to this embodiment.
The curved surface 33 of loading shoe 72, has a curvature that is
slightly smaller than the curvature of the inner surface of the
thin walled outer shell 70. This creates a converging cross section
at the interface between these components.
[0036] In FIG. 10, the axially compliant pressure roller 10
comprises a non-rotating stationary core 26, which is the main
support structure for the axially compliant pressure roller 10. A
non-magnetic, metallic material is used in the construction of the
stationary core 26, but the present invention is not limited to
this embodiment. The stationary core 26 has a cylindrical form in
which axial holes 27 have been provided. At least one of these
holes is used to house the magnetic field generator 37. In the
preferred embodiment one magnetic field generator 37 is associated
with each of the plurality of loading shoes 72. This allows for
local adjustments to the thin walled outer shell 70. In an
alternate embodiment a magnetic field generator 37 may be located
in each of the plurality of loading shoes 72 as shown in FIG.
3C.
[0037] Axial holes 27 are used for the circulation of heat transfer
media within the core. A series of pockets 29 are created in a
radial direction to serve as supports for the loading shoes 72.
Seats on the stationary core 26 enable mounting of bearings 28 and
fluid seals 30.
[0038] In operation, the hydrodynamic effect of a viscous fluid
subject to the shear stress created by the relative velocity of the
thin walled shell with respect to the loading shoe, develops a
pressure profile within the converging region of viscous fluid 11.
This pressure acts on the thin walled shell curved inner surface of
shell 25 and the curved surface of the shoe 33. The pressure acting
on the shoe results in a force normal to the curvature at the
center of pressure. This force is resisted by the spring preloading
force acting on the loading shoe 72. The pressure acting on the
rotating thin walled outer shell 70 creates an internal force on
the shell. The net difference in force acting on the shell from the
internal hydrodynamic action and the external nip force will result
in a localized deformation of the thin walled shell in this
region.
[0039] A thin walled shell of small shell diameter is possible with
this embodiment because the structural design of the shell is not
dictated by beam bending criteria or shell crushing criteria. The
wall thickness of the shell can be significantly thinner because
the surface of the shell subjected to the external nip force is
directly supported internally by the pressure created by the
interaction of the magneto-rheological fluid (not shown) and the
loading shoe 72.
[0040] The thin walled outer shell 70 is constrained with bearings
28 to rotate about the stationary core 26. The rotation of the
shell can be imparted by the friction force at the nip point 35,
shown in FIG. 10, or with an external drive mechanism as shown by
drive sprocket 82. Along the curved inner surface of shell 25, for
a given convergent interface, relative velocity, and fluid
viscosity a uniform pressure is developed. The annular chambers in
conjunction with the loading shoes 72, magneto-rheological fluid,
and axially variable magnetic field generator 37 can be subjected
to variable hydrodynamic pressure forces by changing the viscosity
of the fluid. The ability to exert axially variable pressure along
the thin walled shell results in localized deformation changes of
small magnitude and at a much higher frequency than possible by
other prior art.
[0041] FIG. 8 shows the results of finite element calculations used
to model the effect of the variable internal pressure capability of
this apparatus on the radial profile of the roller surface in the
nip point. The dimensions of the shell can be represented in terms
of the following quantities; a flexural rigidity of approximately
1800 lb-in (203 newton*m) and a shell thickness to diameter ratio
of 0.025. The flexural rigidity is defined as the quantity of the
product of the material elastic modulus and the shell thickness
cubed divided by the quantity of the product of a constant value 12
and the quantity of the difference of 1 and Poisson's ratio
squared. An average nip pressure of 250 psi, (1.724 MPa) placed on
the thin walled outer shell 24 along a localized region parallel to
the axis of rotation, has been used in this calculation. The
variable (UX) is the radial displacement in the x-direction, which
is also normal to the applied nip pressure region. A greater
positive value indicates further deformation toward the center of
the roller shell.
[0042] The curve with diamond shaped markers represents the
expected shell deformation under nip load but without internal
support. The curve with triangular shaped markers represents the
effect of applying a localized pressure on an area equivalent to
the curved surface of the loading shoe 72 acting at the center of
the shell with an average pressure of 50 psi. (0.344 MPa) The curve
with rectangular shaped markers represents the positive effect on
the radial deformation obtained by applying a gradient pressure
profile along the inner surface of the shell ranging from 15 psi to
20 psi (0.103 MPa to 0.137 MPa). Utilizing basic fluid dynamic
principles it has been calculated that a pressure of approximately
30 psi (0.206 MPa) can be developed in this region given a fluid of
viscosity of approximately 10 Pa-s sheared between the outer shell
and the curved surface of the shoe with an average shear rate of
250 l/s.
[0043] FIG. 10 shows a cross sectional view of a typical two roller
nip utilized in the extrusion cast web formation. An axially
compliant pressure roller 10 is loaded radially into the interface
of the molten resin 86 and a second roller 84. Utilizing a
non-contacting deformation detector 88 such as a laser
triangulation gage or an eddy current device, the resulting shell
surface deformation can be measured. This measurement data can be
utilized to control internal loading conditions along the axis of
the roller by sending a deformation signal 90 to microprocessor 92,
which alters the strength of one or more of the magnetic field
generators 37.
[0044] In addition to the magneto-rheological fluid described
previously, this apparatus can accommodate other fluids without
magneto-rheological properties but which exhibit non-Newtonian
characteristics (viscosity of fluid is dependent on shear rate
imposed). Localized pressure variations can be created through
adjustment of the gap between the outer shell and the curved
surface of the shoe. The average shear rate in this gap is
proportional to the surface velocity of the shell divided by the
gap height. Non-Newtonian fluids exhibit a logarithmic relationship
between viscosity and shear rate. External manipulation of the gap
combined with a fluid with desirable shear sensitive properties
provides an additional means of creating localized pressure
differences within each chamber.
[0045] A key advantage of this invention is the ability to
replicate a pattern with lower nip pressure due to the increased
surface temperature at the point of contact of the molten material
with the patterned roller surface. One example of this has been
modeled with computational fluid dynamics software, Polyflow, in
which a resin material, polycarbonate was subject to a pressure
boundary condition and the flow of the material into a fine
patterned geometry was studied. FIG. 6 shows the two dimensional
representation of the resin material and the patterned geometry.
FIG. 7 shows the improvement in pattern replication as mold surface
temperature increases. An equivalent level of replication can be
obtained for a given temperature as a significantly lower applied
pressure. An increase in patterned surface temperature of 10% can
result in a decrease in applied pressure of 67.5% for an equivalent
replication efficiency.
[0046] In one example, a finite element analysis has been performed
on the shell of six inch diameter by 20'' face with a wall
thickness of 0.125 inch, constructed of aluminum to determine the
effect of circumferentially variable heating on the mechanical
stresses and thermal deformation. FIG. 9 shows a plot of the
calculated shell deformation. The lower curve shows the resultant
effect of uniformly distributed pressure on the outer shell surface
at the point of maximum temperature. The upper curve shows the
resultant effect of the application of an internal compensation
pressure adjusted to minimize surface deformation. A greater
positive value indicates a greater deformation away from the center
of the shell.
[0047] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention.
PARTS LIST
[0048] 10 axially compliant pressure roller [0049] 11 converging
region of viscous fluid [0050] 12 outer shell [0051] 14 heating
elements [0052] 15 pivot [0053] 16 brush assembly [0054] 17
adjusting pin [0055] 18 heating zone [0056] 20 internal surface
[0057] 22 fluid media [0058] 24 cooled region [0059] 25 inner
surface of shell [0060] 26 stationary core [0061] 27 axial holes
[0062] 28 bearings [0063] 29 pockets [0064] 30 seal [0065] 32 inlet
for fluid media [0066] 33 curved surface of shoe [0067] 35 nip
point [0068] 37 magnetic field generator [0069] 40 fixed inner
shell (stator) [0070] 41 cooling region [0071] 42 flow passages
[0072] 43 reheating region [0073] 44 close fitting baffle [0074] 45
loading shoe region [0075] 46 outer shell [0076] 47 higher
temperature fluid [0077] 48 high temperature fluid 3 supply [0078]
49 lower temperature fluid [0079] 50 high temperature fluid 3
return [0080] 52 carbon seal [0081] 54 carbon bearings [0082] 56
high temperature fluid 1 supply [0083] 58 high temperature fluid 1
return [0084] 60 high temperature fluid 2 supply [0085] 62 high
temperature fluid 2 return [0086] 70 outer shell [0087] 72 loading
shoes [0088] 74 first axial baffle [0089] 76 second axial baffle
[0090] 78 shoe loading mechanism [0091] 80 support bracket [0092]
82 drive sprocket [0093] 84 second roller [0094] 86 material
entering nip [0095] 88 deformation detector [0096] 90 deformation
signal [0097] 92 microprocessor
* * * * *