KR20080055847A - Cicumerentially variable surface temperature roller - Google Patents

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.

Description

Cylindrical variable surface temperature roller {CICUMERENTIALLY VARIABLE SURFACE TEMPERATURE ROLLER}

BACKGROUND OF THE INVENTION The present invention relates generally to casting rollers, and more particularly to casting rollers having a radially variable surface temperature.

In extrusion and embossing operations the surface temperature of the rollers contacting the molten or web material is an important process parameter. Typical roller designs provide single roller bulk temperatures as established by the internal circulation of the fluid medium. The maximum temperature is generally limited to a value at which the material can be easily stripped from the roller surface.

One attempt to solve this problem can be found in the expired prior art, US Pat. No. 2,526,318, which discloses a configuration that obscurely provides two variable temperature regions but with performance capabilities or design. It does not provide a detailed description of the criteria. Prior art, US Pat. No. 5,945,042; 6,260,887 and 6,568,931 similarly disclose methods for providing one or more temperature zones around the circumference of a roller but do not provide a detailed description of performance or design criteria. Prior art, US Pat. No. 6,554,755, discloses a roller design with the ability to provide localized areas with temperature differences, but the only embodiment of the method is to create means of correction for deflection of the shell. .

The higher temperature region at the point of contact of either the molten material or the web is desirable to improve the contact between the materials and the roller surface and to improve the replication of the roller surface, but this temperature is generally too high for the material from the roller surface. Allow stripping Thus, lower surface temperatures are required at the stripping point, which limits the wetting of the roller surface and pattern replication.

It is an object of the present invention to provide a sufficient temperature difference in at least two areas around the periphery of the roller to provide improved wetting and replication in one area and to allow uniform stripping of the material from the second area.

Briefly, according to one aspect of the invention, a casting roller having variable temperature surfaces comprises a rotatable cylindrical shell. The axially aligned heating electrical elements are present inside the outer surface of the equally spaced and rotatable cylindrical shell. The brush assembly is in electrical connection with the heating elements during part of the rotatable cylindrical shell rotation about the axis. The fixed core is present inside the rotatable cylindrical shell. An annular space exists between the fixed core and the rotatable cylindrical shell. The cooling fluid fills at least part of the annular space.

The present invention provides the expected performance and detailed design criteria based on finite element analysis to study the effects of roller diameter, shell thickness and construction materials.

The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiments disclosed below.

The invention relates in particular to elements which form part of the device according to the invention, or elements which cooperate more directly with the device according to the invention. It will be understood that elements that are not explicitly shown or described may implement various forms well known to those skilled in the art.

1 is a cross-sectional view of a casting roller according to the present invention.

2 is a perspective view, in partial area, of another embodiment of a casting roller according to the invention.

3A is a sectional view of another embodiment of a casting roller according to the present embodiment.

FIG. 3B is a perspective view, in partial area, of the embodiment shown in FIG. 3A.

3C is an enlarged cross-sectional view of the shell and support shoe of the embodiment shown in FIG. 3A.

4 is a chart showing the calculated cooling efficiencies of various roller design configurations according to the present invention.

5 is a chart showing the calculated reheating efficiencies of various roller design configurations according to the present invention.

6 is a cross-sectional view of the pattern on the surface of the roller.

7 is a chart of temperature versus pressure showing pattern replication.

8 is a chart showing the calculated shell deformation at maximum temperature.

FIG. 9 is a chart showing shell deformation calculated for a shell applied with nip pressure and supported by an internal pressure gradient.

10 is a cross-sectional view of the axial compliant pressure roller having a second roller to form a nip.

<Description of the symbols for the main parts of the drawings>

10: axially compliant pressuer roller

11: converging region of viscous fluid

12: outer shell

14: heating elements

15: pivot

16: brush assembly

17: adjusting pin

18: heating zone

20: internal surface

22: fluid media

24: cooled region

26: stationary core

27: axial holes

28: bearings

29: pockets

30: seal

32: inlet for fluid media

33: curved surface of shoe

35: nip point

37: magnetic field generator

40: fixed inner shell (stator)

41: cooling region

42: flow passages

43: reheating region

44; Close fitting baffle

45: loading shoe region

46: outer shell

47: higher temperature fluid

48: high temperature fluid 3 supply

49: lower temperature fluid

50: high temperature fluid 3 return

52: carbon seal

54: carbon bearings

56: high temperature fluid 1 supply

58: high temperature fluid 1 return

60: high temperature fluid 2 supply

62: high temperature fluid 2 return

70: outer shell

72: loading shoes

74: first axial baffle

76: second axial baffle

78: shoe loading mechanism

80: support bracket

82: drive sprocket

84: second roller

86: material entering nip

88: deformation detector

90: deformation signal

92: microprocessor

Example 1  Electrically heated shell with fluid medium cooling

The outer shell 12 of the roller is machined to receive a series of closely spaced electric heating elements 14, near the outer surface of the shell. Mounted on the roller, the brush assembly 16 is used to provide electrical power only to the heaters in the desired heating zone 18. The inner surface 20 of the outer shell 12 will be exposed to the fluid medium 12 to remove heat added by the heating elements and to continue to remove heat from the process material. The fluid medium inlet 32 is attached to the roller by a rotating joint that is commercially available. The diameter of the shell is based on the desired heating dwell time, final cooling temperature, line speed and materials of construction. 1 and 10, the cooled region 24 removes heat from the outer cell 12 and the cast material 86. Fluid medium 22 circulates in the annular region below the inner surface 20.

Example 2  A roller with two surface temperature regions created with the thermal fluid medium at different temperatures

Referring to FIG. 2, the outer cell 46 rotates relative to an inner shell (stator) 40 fixed on the carbon bearings 54. The carbon seal 52 is mounted adjacent to the bearings to prevent fluid leakage. The stator is machined into 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. The higher temperature fluid 47 circulates through a portion of the stator 40. Contact with the outer shell 46 heats the shell to the desired process temperature as it passes over this area. The second region is maintained at a lower temperature by circulating the lower temperature fluid 49. The stator 40 is designed to minimize contact points between higher and lower temperature regions.

Example  3-thin shell roller with inner support and two different temperature zones

This embodiment is similar to the above embodiment in that the inner shell is fixed, the outer shell rotates with respect to the inner shell, and two temperature zones are created by the heat medium circulation. This embodiment uses 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 heat medium circulates in the region containing the shoes, and the two points by the first axial baffle 74 and the second axial baffle 76 to create a higher temperature and cooling region. Baffled at This heat transfer medium can also act as a hydrodynamic lubricant between the inner surface of the shell and the shoe.

The thin outer shell 70 is advantageous in this application because it can provide a better thermal response system that can heat and cool faster. This may also be achieved with smaller diameters for the same line speed. Smaller diameters result in less work to create higher contact stresses and patterned surfaces in the nip for a given load.

3A, 3B and 10, the roller consists of at least three main areas. In the present description, the outer shell 70 rotates counterclockwise with respect to these areas. The cooling zone 41 creates a series of flow passages 42 exposed to the inner surface of the shell 25. The high temperature fluid (2) supply 60 impinges on the inner surface of the shell to remove heat. The high temperature fluid 2 circulation collects fluid from the flow passages 42 and directs the flow out of the rollers. A close fitting baffle 44 is located at the inlet to the cooling zone 41 to provide separation of flows between the cooling zone and the rod shoe zone 45. The first axial baffle 74 is located at the outlet of the cooling zone 41 to separate the fluids between the cooling zone 41 and the reheating zone 43. Similar to the cooling zone 41, the reheating zone 43 acts on the fluid on the inner surface of the shell with the high temperature fluid (1) supply 56 with fluid removal through the high temperature fluid (1) circulation 58. It is a flow distribution area. The second axial baffle 76 is mounted at the exit of this region to separate it from the loading shoe region 45. The purpose of this region is to increase the shell temperature before entering the nip point 35.

The loading shoe region 45 is composed of a shaft member machined to form pockets 29 along its length for receiving respective loading shoes 72. The force applied to each loading shoe is independently adjustable by the shoe loading mechanism 78. Manually controlled worm screw adjusting mechamisms have been shown, but are not limited to this embodiment. The high temperature fluid 3 supply 48 is located at the inlet of the loading shoe 72 to the shell interface to maintain a continuous supply of fluid to the hydrodynamic lubricant at this point. The high temperature fluid 3 circulation 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 different thermal expansions. The fixed inner shell 40 is rigidly attached to the mechanical structure via a support bracket 80 on each end. The outer shell 70 is constrained to rotate relative to the fixed inner shell 40 via bearings 28 mounted on each end. The seal 30 is adjacent to the bearings 28 to prevent leakage of fluid from the inner flow chambers. Drive sprocket 82 may be used to rotate the shell to overcome nip forces and internal friction forces.

Each of these embodiments may be disclosed by dimensionless parameters based on the physical properties of the cast material to be treated, the desired process conditions, the physical properties of the roller and the desired production rates. Heat transfer textbooks initiate transient heat transfer using similar methods, but the direct method does not teach designs that consider a combination of roller design criteria and cast materials for one or more heat transfer processes.

The dimensionless temperature ratio, theta (θ), can be formed based on the following parameters; T _infinty expressed as the bulk temperature of the heat transfer medium _. T _initial defined as the initial temperature of the cast material or roller shell depending on the particular process function. T _end defined as the desired temperature at the end of a given process operation. Smaller values of this ratio indicate higher efficiency in achieving the desired process targets.

Other dimensionless parameters can be formed with dimensionless time, generally referred to as tau (tau) in the published literature. This parameter normalizes the time dimension by using the thickness and heat spreadability of the material.

4 shows a chart in which the dimensionless temperature ratio, theta (θ), is output on the ordinate and the dimensionless time is output on the abscissa. The family of curves is in exponential form as shown in the equation below.

The coefficients shown in this equation are fitted to the finite element results of the various process simulations and relate to the physical properties of the cast material, the roller shape and the physical properties of the roller. Subscripts of the fitted curves end with the spelling cl. Subscripts al, steel, ag and cu on the curves represent the constituent materials; Aluminum, steel, silver and copper, respectively. In addition, subscript values of 0625 and 125 represent thickness values of 1/16 (0.00158 m) of one inch and 1/8 (0.0031 m) of one inch, respectively. The calculation are with ^{350Btu / (hr · ft 2 ·} ℉) Thermal diffusivity (thermal diffusivity) of (1990watt / (㎡ · ℃) ) the heat transfer coefficient (h) and 0.005ft ² /hr(0.00000013㎡/s) of Is based on cooling commercially available plastic materials.

The roller design can be determined from these equations for a particular set of requirements. By defining the dimensionless temperature ratio based on the temperature of each zone, heat transfer medium temperatures and molten material temperature, the chart of FIG. 4 shows the process efficiency or selected process efficiency for a given operating condition and roller configuration. Can be used to determine any of the process efficiencies for and the operating speed can be determined for a given roller diameter, shell thickness, and construction material. 5 shows a chart outputting dimensionless time, dimensional temperature ratio versus tau, for shell reheating obtained from finite element calculations. Subscripts follow the same prior art as shown in FIG. 4. The calculation are ^{350Btu / (hr · ft 2 ·} ℉) (1990watt / (㎡ · ℃)) internal heat transfer coefficient (h) and ^{3Btu / (hr · ft 2 ·} ℉) of (17.03watt / (㎡ · ℃) ) Is based on the external heat transfer coefficient of h.

Referring now to FIG. 10, an axially compliant pressuer roller is generally indicated by reference numeral 10. The axial compliant pressure roller 10 generally consists of a fixed inner core 26 and a plurality of loading shoes 72 pivotably mounted to the fixed inner core 26. A series of non-magnetic dividers create a plurality of annular chambers and respective loading shoes 72 that occupy one of the annular chambers.

3A, 3B and 3C, a loading shoe 72 is shown mounted eccentrically. Pivot point 15 and shoe adjustment pin 17 are attached to loading shoe 72. Non-magnetic, metallic materials are used in the structure of the loading shoe 72, but the present invention is not limited to this embodiment. The curved surface 33 of the loading shoe 72 has a curvature 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.

In FIG. 10, the axial compliant pressure roller 10 comprises a non-rotating fixed core 26, which is the main support structure for the axial compliant pressure roller 10. Non-magnetic, metallic materials are used in the structure of the fixed core 26, but the present invention is not limited to this embodiment. The fixed core 26 has the form of a cylinder in which the shaft holes 27 are provided. At least one of these holes is used to receive a magnetic field generator 37. In a preferred embodiment one magnetic field field generator 37 is associated with each of the plurality of loading shoes 72. This allows local adjustments to the thin walled outer shell 70. In alternative embodiments the magnetic field generator 37 may be located in each of the plurality of loading shoes 72 as shown in FIG. 3C.

Shaft holes 27 are used for circulation of the heat transfer medium in the core. A series of pockets 29 are created radially to act as supports for the loading shoe 72. Seats on the fixed core 26 allow mounting of the bearings 28 and the fluid seals 30.

In operation, the hydrodynamic effect of the viscous fluid, which is affected by the shear stress generated by the relative velocity of the thin-walled shell with respect to the loading shoe, is a pressure profile within the converging region of the viscous fluid 11. Develop. This pressure acts on the curved inner surface 25 of the shell of the thin wall of the shell and the curved surface 33 of the shoe. The pressure acting on the shoe causes a force perpendicular to the curvature at the center of the pressure. This force is resisted by a spring pre loaded 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 internal hydrodynamic action and force acting on the shell from the external nip forces will cause localized deformation of the thin-walled shell in this region.

Thin walled shells of small shell diameter are possible with this embodiment because the structural design of the shell is not dictated by beam bendig criteria or shell crushing criteria. The surface of the shell affected by the external nip forces is directly supported internally by the pressure generated by the interaction of the magneto-rheological fluid (not shown) and the loading shoe 72 so that the shell The wall thickness of can be significantly thinner.

The thin walled outer shell 70 is constrained with bearings 28 to rotate about the fixed core 26. Rotation of the shell may be imparted by frictional force at the nip point 35, shown in FIG. 10, or with an external drive mechanism as shown by the drive sprocket 82. Along the curved inner surface 25 of the shell, a uniform pressure develops for a given convergence interface, relative velocity and fluid viscosity. The annular chambers associated with the loading shoes 72, the magneto-fluidic fluid and the axial variable magnetic field generator 37 can be affected by variable hydrodynamic pressure forces by changing the viscosity of the fluid. The ability to apply axial variable pressure along a thin-walled shell results in small localized deformation changes at frequencies much higher than would be possible by other prior art.

FIG. 8 shows the results of infinite element calculations used to model the effect of the variable internal pressure capability of the device on the radial profile of the roller surface at the nip point. The dimensions of the shell can be represented by the following quantities; Flexural rigidity of approximately 1800 lb-in (203 newtonm) and shell thickness-diameter ratio of 0.025. Flexural strength is defined as 1 divided by the square of the Poisson's ratio multiplied by the constant 12, divided by the product of the modulus of elastic modulus and the cube of shell thickness. An average nip pressure of 250 psi, (1.724 MPa), located on a thin walled outer shell 24 over a localized area parallel to the axis of rotation, has been used in these calculations. The variable UX is the radial displacement in the x-direction, which is also perpendicular to the applied nip pressure region. Larger positive values indicate further deformation towards the center of the roller shell.

The curve with diamond shaped markers shows the expected shell deformation under nip load without internal support. The curve with triangular shaped markers shows the effect of applying localized pressure on the same area to the curved surface of the loading shoe 72 acting in the center of the shell with an average pressure of 50 psi (0.344 MPa). The curve with the rectangular shaped markers shows a desirable effect on the radial deformation obtained by applying a pressure gradient profile along the inner surface of the shell ranging from 15 psi to 20 psi (0.103 MPa to 0.137 MPa). . By using basic hydrodynamic theories, a fluid of about 10 μs-s sheared between the outer shell and the bent surface of the shoe with a pressure of approximately 30 psi (0.206 MPa) having an average shear rate of 250 1 / s It has been calculated that it can be developed in this area given to.

FIG. 10 shows the stage shaving of two typical roller nips used in extrusion casting web formation. The axial compliant pressure roller 10 is loaded into the interface of the radially melted resins 86 and the second roller 84. By using a non-contact 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 used to control internal load conditions along the axis of the roller by sending a strain signal 90 to the microprocessor 92, which changes the strength of one or more magnetic field generators 37.

In addition to the previously disclosed magnetic-fluidic fluids, the device can accommodate other fluids without magnetic-fluidic properties, but it shows the properties of non-Newtonian theories (the viscosity of the fluid depends on the shear rate applied). Localized pressure changes can be produced through adjustment of the gap between the curved surface of the shoe and the outer shell. The average shear rate in this gap is proportional to the surface velocity of the shell divided by the gap height. Non-Newtonian theorems show a logarithmic relationship between viscosity and shear rate. External manipulation of the gap coupled with the fluid having desirable shear sensitive properties provides additional means of generating localized pressure differences within each chamber.

An important advantage of the present invention is the ability to replicate patterns with lower nip pressures due to the increased surface temperature at the point of contact of the molten material with the patterned roller surface. One example has been modeled with computational fluid dynamics software, Polyflow, where pressure boundary conditions are applied to resin matirial and polycarbonate, and the flow of the material into a fine patterned shape is studied. It became. 6 shows a two-dimensional representation of a resin material and a patterned shape. 7 shows the improvement in pattern replication as the casting surface temperature increases. Equal levels of replication can be obtained for a given temperature with significantly lower applied pressure. An increase in the patterned surface temperature of 10% may cause a decrease in applied pressure of 67.5% for equivalent replication efficiency.

In one embodiment, finite element analysis is performed on a 6 inch diameter shell by a 20 "face with a wall thickness of 0.125 inch, constructed of aluminum to determine the effect of circumferentially variable heating on mechanical stresses and thermal deformation. Figure 9 shows a plot of the calculated shell deformation The lower curve shows the resulting effect of the pressure uniformly distributed on the outer shell surface at the point of maximum temperature. The resulting effect of the application of the internal correction pressure adjusted to minimize surface deformation is shown, with larger positive values representing larger deformation away from the center of the shell.

Claims (24)

In a casting roller having a variable temperature surface, Rotatable cylindrical shells; Axially arranged heating electrical elements that are internal to the outer surface of the rotatable cylindrical shell and are spaced apart from each other; A brush assembly in electrical connection with the heating elements during a portion of the rotation of the rotatable cylindrical shell about an axis; A stationary core internal to the rotatable cylindrical shell; An annular space between the fixed core and the rotatable cylindrical shell; And And a cooling fluid filling at least a portion of the annular space. The casting roller of claim 1, wherein a baffle defines the cooling fluid as part of the annular space. The casting roller of claim 1, wherein the cooling fluid is selected from the group comprising organic synthetic media having an operating temperature range of 60 ° C. to 350 ° C. (140 ° F. to 662 ° F.). 4. The casting roller of claim 3 wherein the viscosity of the fluid varies from 8.2 centipoises to 0.26 centipoises. 4. The casting roller according to claim 3, wherein the specific heat of the medium is changed from 1.62 KJ / kg · K at 60 ° C to 2.82 KJ / kg · K at 360 ° C. The casting roller according to claim 3, wherein the thermal conductivity is changed from 0.125 W / mK at 60 ° C to 0.086 W / mK at 360 ° C. 4. The casting roller according to claim 3, wherein the density of the medium is changed from 1016 kg / m 3 at 60 ° C. to 801 kg / m 3 at 360 ° C. The casting roller of claim 1, wherein the heating elements are cartridge heaters. 9. The casting roller of claim 8 wherein the heaters are 0.25 inch diameter with a heat flow output of about 60 W / in ² . In a casting roller having a variable temperature surface, Rotatable cylindrical shells; A stationary core internal to the rotatable cylindrical shell; An annular space between the fixed core and the rotatable cylindrical shell; Baffles for generating first and second regions in the annular space; A first fluid at a first temperature circulating in the first annular space; And And a second fluid at a second temperature circulating in the second annular space. The casting roller of claim 10, wherein the first fluid is selected from the group comprising organic synthetic fluid that is a cooling fluid and has an operating temperature range of 60 ° C. to 350 ° C. (140 ° F. to 662 ° F.). 12. The casting roller of claim 11 wherein the viscosity of the fluid varies from 8.2 centipoise to 0.26 centipoise. The casting roller according to claim 11, wherein the specific heat of the fluid is changed from 1.62 KJ / kg · K at 60 ° C to 2.82 KJ / kg · K at 360 ° C. The casting roller according to claim 11, wherein the thermal conductivity of the fluid is changed from 0.125 W / mK at 60 ° C to 0.086 W / mK at 360 ° C. The casting roller according to claim 11, wherein the density of the fluid is changed from 1016 kg / m 3 at 60 ° C to 801 kg / m 3 at 360 ° C. 11. The casting roller of claim 10 wherein the first annular space covers one third of the circumference of the shell at one time. 11. The casting roller of claim 10 wherein the second annular space covers two thirds of the cylindrical shell at one time. 11. The rotatable cylindrical shell of claim 10, wherein the rotatable cylindrical shell is thin; A shoe supporting the rotatable cylindrical shell in a nip. In a method of casting a web of materials, Contacting the web in the heating zone of the roller; Raising the web to a casting temperature; Forming an impression on the web; Maintaining the web in contact with the roller through at least a portion of a cooling region on the roller; And Stripping the web from the roller after the web is cooled. 20. The method of claim 19, wherein the roller surface temperature is increased to be 30 ° C to 60 ° C greater than the web glass transition temperature. 20. The method of claim 19, wherein the roller surface temperature is reduced to be 3 ° C to 5 ° C less than the web glass transition temperature. In a casting roller having a variable surface temperature, Rotatable cylindrical shells; A fixed core inside the rotatable cylindrical shell; An annular space between the fixed core and the rotatable cylindrical shell; Baffles for generating first and second regions in the annular space; A first fluid at a first temperature circulating in the first annular space; A second fluid at a second temperature circulating in the second annular space; And A shoe supporting said rotatable cylindrical shell in a nip, And said rotatable cylindrical shell is thin. The apparatus of claim 22, wherein a third region is created by the baffle surrounding the shoe, And a third fluid at a third temperature is present in the third region. 24. The casting roller of claim 23 wherein the third fluid lubricates the shoe.

Images