CA2593107C - Device for automatic control of blown film thickness - Google Patents
Device for automatic control of blown film thickness Download PDFInfo
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- CA2593107C CA2593107C CA2593107A CA2593107A CA2593107C CA 2593107 C CA2593107 C CA 2593107C CA 2593107 A CA2593107 A CA 2593107A CA 2593107 A CA2593107 A CA 2593107A CA 2593107 C CA2593107 C CA 2593107C
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- barrier
- blown film
- air flow
- servomotor
- controlling
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Abstract
In an improved system for controlling the thickness of a blown film, a controlled air flow is provided to the blown film as it exits from an extrusion die still in liquid form. The system has a cooling ring with an annular region through which the air is blown onto the blown film, after passage through one of a plurality of radial channels. The improvement is achieved by a plurality of adjustable barriers, one of which is inserted in each of the radial channels. A first and a second servomotor allow indexable selection and adjustment of any particular barrier. Each barrier has a head and a shank, the head adapted to engage a clamp associated with one of the servomotors. Rotating the barrier in one direction increases cross-sectional air flow area in the radial channel and rotating it in the opposite direction decreases the cross- sectional air flow area.
Description
, DEVICE FOR AUTOMATIC CONTROL OF BLOWN FILM THICKNESS
Field of the Invention The present invention relates to improving the quality of film produced in blown film extrusion lines. In particular the invention relates to a device for automatically controlling the thickness of film in blown film extrusion lines.
Background of the Invention Blown film extrusion is a known method of film manufacturing. The method consists of vertically extruding plastic melt through an annular die. After extrusion the plastic melt takes the shape of a tube. Air is introduced through a hole in the middle of the die, in order to expand the tube in a bubble-like shape. As the tube travels upward, it cools and solidifies. At the point of solidification the tube comprises a thin-walled film, which continues upward until it is collapsed by compression between two rolls, called nip rolls.
While continuously pulling the tube upward, the nip rolls collapse the tube into a two-layer film called a "lay-fiat". The lay-flat may continue down the line undergoing further processing, or it may be wound into rolls. In both alternatives variations in the thickness of the film cause problems in the further processing of the film. It is therefore desirable to produce film with consistent thickness.
One method for controlling the film thickness around the circumference of the film tube relies on an external air ring, called a cooling air ring, situated immediately on top of the die. The cooling air ring surrounds the exterior of the film tube and continuously blows air onto the exterior surface of the tube to cool it. The cooling air ring contains internal radially oriented channels through each of which air is blown onto adjacent areas of the film tube around its circumference. By controlling the air flow in each channel, the cooling of each adjacent area around the film tube circumference can be controlled. In this way the thickness of the film tube wall can be discretely controlled around the tube circumference.
, , One method for controlling the air flow in the radial channels of the air ring utilizes automatically controlled pistons, which slide in a vertical direction to measurably impede the flow of air through the channel. While the method generally achieves the goal of adequately controlling the thickness of the film tube wall, the control of the flow of air in the radial channels is not precise, because the pistons do not maintain their vertical positioning. It is desirable to have a more precise means of controlling the air flow in the radial channels.
It is therefore an unmet advantage of the prior art to provide an automatic and precise means for controlling the air flow in the radial channels of an air ring.
, Summary of the Invention Such a means for automatically and precisely controlling the air flow in the radial channels of an air ring is provided by the disclosed embodiments described in more detail below. These embodiments comprise a barrier inside each radial channel in the form of a threaded structure. The barrier is made of brass and consists of two parts: a lower threaded portion and an integrally attached upper flattened head portion.
The lower portion is cylindrical in shape, while the upper portion is flat shaped. The lower threaded portion is located inside the radial channel and portions of which form the barrier that controls the air flow inside the channel. The flat portion is situated exterior to the channel, generally on the topside of the channel.
By turning the flattened head portion in either direction, the threaded portion moves downward or upward inside the channel, thus varying the cross-section of the radial channel. This varies the air flow inside the channel in a precise and controlled manner, as each 180-degree turn lowers or raises the barrier by 0.030 inches.
In this way the thickness of the film tube is discretely controlled in the areas corresponding to each radial channel.
A controlling servomotor automatically controls the vertical position of the barrier. The servomotor is provided with a U-shaped clamp-like structure, which is complementary to, and fits precisely overtop the flattened head portion of the barrier.
By turning the barrier a desired number of turns, the controlling servomotor can precisely control the cross-section of the channel. The controlling servomotor is also provided with a means to read the height of the top of the brass flattened head. In this way, information is available about the state of each barrier in each radial channel in the system.
A positioning servomotor, located on top of the air ring controls the position of the controlling servomotor. Both servomotors are attached to an upper ring, which can rotate relative to the cooling air ring. The positioning servomotor controls the position , of the upper ring, thus controlling the position of the controlling servomotor overtop a particular barrier.
By continuously measuring the thickness of the film tube wall around the circumference of the tube feedback can be transmitted to the two servomotors.
When an adjustment in film thickness is required in a certain position around the circumference of the film tube, a signal is transmitted to the positioning servomotor to position the controlling servomotor overtop a particular barrier. When the controlling servomotor is in place, the sensor reads the height of the barrier's flattened head portion and the clamp is lowered correspondingly. Thereafter, the controlling servomotor turns the clamp together with the flattened head portion of the corresponding channel barrier by the required number of turns in either direction, thus increasing or decreasing the cross-section of the radial channel.
Further features of the foregoing will be described or will become apparent in the course of the following detailed description.
Brief Description of the Drawings In order that the disclosed embodiments may be more clearly understood, reference is now made to the accompanying drawings, wherein identical parts are identified by identical reference numbers and wherein:
FIGURE 1 is a perspective view of a cross-section of an embodiment of a cooling air ring;
FIGURE 2 is a perspective view of a portion of the Fig. 1 cooling air ring, showing the details of the barrier and the controlling servomotor;
FIGURE 3 is a cross-section of the controlling servomotor; and FIGURE 4 is a side sectional view of a portion of a radial channel of the cooling ring, with a barrier mounted therein.
Description of Preferred Embodiments United States published application 2006/0275,523 Al, published 7 December 2006, describes a melt distribution block that may be used to generate an annular film of a molten polymer in an extrusion die. The device described hereinafter is incorporated into the extrusion die above.
Referring now to FIGURE 1, a cooling air ring 10 is shown in a sectioned view that cuts through one of the radially positioned channels 100 therein. A
barrier 50 is seated inside each radial channel 100. The barrier 50 comprises a cylindrical shank 52 and a flattened head 54. More details of the barrier are provided below with reference to Figure 4. For the purposes of Fig. 1, it is noted that each barrier 50 is seated in a threaded opening 70 in one of the channels 100, with the flattened head 54 exposed and accessible to a control means that will now be described.
Also shown in Fig. 1 are a positioning servomotor 110 and a controlling servomotor 112. These servomotors are attached to an annular flange 12 of the cooling air ring 10. A film thickness sensor (not shown) detects the thickness of the blown film produced in the extrusion die and drawn through annulus 14, which is provided with a plurality of cooling air outlets 16. Air to the cooling air outlets 16 arrives at those outlets through the radial channels 100, so controlling the air flow through the channels also controls air flow through air outlets 16. Information from the film thickness sensor is processed and instructions for adjusting radial air flow in the channels are transmitted to the respective servomotors 110, 112. Of these, positioning servomotor 110 rotates the annular flange 12, along with controlling servomotor 112, in an indexing manner that can position controlling servomotor over any selected barrier 50.
Referring now to FIGURE 2, the controlling servomotor 112 comprises a sensor and a clamp 116. Sensor 114 detects the height of the top of flattened head 54 of the selected barrier 50. Based on the detected height, the controlling servomotor lowers clamp 116 until it is engaged around flattened head 54 in a manner that permits it to be turned. Once engagement, the servomotor 112 turns the clamp 116 either clockwise or counterclockwise by a required angular amount to move barrier 50 upwardly or downwardly with respect to the radial channel 100. In this way, the shank portion 52 of the barrier 50 is adjusted precisely, increasing or decreasing the cross-section flow area of the radial channel 100.
FIGURE 3 shows an enlarged cross-section of controlling servomotor 112, which is connected to the clamp 116 by means of shaft 118. The shaft 118 rotates horizontally by means of gear 120 and can also be raised and lowered in a vertical direction. The servomotor 112 in a preferred embodiment always turns the shaft 118 in integral multiples of 180-degrees. This ensures that the orientation of each flattened head 54 around the circumference of the cooling air ring will be the same. In turn, this enables the controlling servomotor 112 to lower the clamp 116 over any of the flattened head 54 in the cooling air ring in the same orientation, without the need to predetermine the orientation. By knowing the amount of cross-sectional change that a 180 degree turn of the flatted head will effect, the change in air flow can be precisely adjusted.
FIGURE 4 shows further detail of the barrier 50. As noted above, each barrier comprises a cylindrical shank 52 and a flattened head 54. The embodiment illustrated has the shank end 56 opposite the head that is unthreaded, with a medial portion 58 that has male threading. In such an embodiment, the unthreaded end will have a diameter smaller enough to pass in an unengaged manner through a female threading that will properly engage the male threading. In one embodiment of the barrier 50, the barrier is directly engaged in a threaded hole 70 in the radial channel 100;
in another embodiment, the barrier engages an internally-threaded sleeve 60 that is seated in the hole 70. In this latter embodiment, the sleeve's engagement in hole 70 is not affected by the turning of the barrier within the sleeve by the controlling servomotor.
Other advantages which are inherent to the structure are obvious to one skilled in the art. The embodiments are described herein illustratively and are not meant to limit the scope of the invention as claimed. Variations of the foregoing embodiments will be evident to a person of ordinary skill and are intended by the inventor to be encompassed by the following claims.
Field of the Invention The present invention relates to improving the quality of film produced in blown film extrusion lines. In particular the invention relates to a device for automatically controlling the thickness of film in blown film extrusion lines.
Background of the Invention Blown film extrusion is a known method of film manufacturing. The method consists of vertically extruding plastic melt through an annular die. After extrusion the plastic melt takes the shape of a tube. Air is introduced through a hole in the middle of the die, in order to expand the tube in a bubble-like shape. As the tube travels upward, it cools and solidifies. At the point of solidification the tube comprises a thin-walled film, which continues upward until it is collapsed by compression between two rolls, called nip rolls.
While continuously pulling the tube upward, the nip rolls collapse the tube into a two-layer film called a "lay-fiat". The lay-flat may continue down the line undergoing further processing, or it may be wound into rolls. In both alternatives variations in the thickness of the film cause problems in the further processing of the film. It is therefore desirable to produce film with consistent thickness.
One method for controlling the film thickness around the circumference of the film tube relies on an external air ring, called a cooling air ring, situated immediately on top of the die. The cooling air ring surrounds the exterior of the film tube and continuously blows air onto the exterior surface of the tube to cool it. The cooling air ring contains internal radially oriented channels through each of which air is blown onto adjacent areas of the film tube around its circumference. By controlling the air flow in each channel, the cooling of each adjacent area around the film tube circumference can be controlled. In this way the thickness of the film tube wall can be discretely controlled around the tube circumference.
, , One method for controlling the air flow in the radial channels of the air ring utilizes automatically controlled pistons, which slide in a vertical direction to measurably impede the flow of air through the channel. While the method generally achieves the goal of adequately controlling the thickness of the film tube wall, the control of the flow of air in the radial channels is not precise, because the pistons do not maintain their vertical positioning. It is desirable to have a more precise means of controlling the air flow in the radial channels.
It is therefore an unmet advantage of the prior art to provide an automatic and precise means for controlling the air flow in the radial channels of an air ring.
, Summary of the Invention Such a means for automatically and precisely controlling the air flow in the radial channels of an air ring is provided by the disclosed embodiments described in more detail below. These embodiments comprise a barrier inside each radial channel in the form of a threaded structure. The barrier is made of brass and consists of two parts: a lower threaded portion and an integrally attached upper flattened head portion.
The lower portion is cylindrical in shape, while the upper portion is flat shaped. The lower threaded portion is located inside the radial channel and portions of which form the barrier that controls the air flow inside the channel. The flat portion is situated exterior to the channel, generally on the topside of the channel.
By turning the flattened head portion in either direction, the threaded portion moves downward or upward inside the channel, thus varying the cross-section of the radial channel. This varies the air flow inside the channel in a precise and controlled manner, as each 180-degree turn lowers or raises the barrier by 0.030 inches.
In this way the thickness of the film tube is discretely controlled in the areas corresponding to each radial channel.
A controlling servomotor automatically controls the vertical position of the barrier. The servomotor is provided with a U-shaped clamp-like structure, which is complementary to, and fits precisely overtop the flattened head portion of the barrier.
By turning the barrier a desired number of turns, the controlling servomotor can precisely control the cross-section of the channel. The controlling servomotor is also provided with a means to read the height of the top of the brass flattened head. In this way, information is available about the state of each barrier in each radial channel in the system.
A positioning servomotor, located on top of the air ring controls the position of the controlling servomotor. Both servomotors are attached to an upper ring, which can rotate relative to the cooling air ring. The positioning servomotor controls the position , of the upper ring, thus controlling the position of the controlling servomotor overtop a particular barrier.
By continuously measuring the thickness of the film tube wall around the circumference of the tube feedback can be transmitted to the two servomotors.
When an adjustment in film thickness is required in a certain position around the circumference of the film tube, a signal is transmitted to the positioning servomotor to position the controlling servomotor overtop a particular barrier. When the controlling servomotor is in place, the sensor reads the height of the barrier's flattened head portion and the clamp is lowered correspondingly. Thereafter, the controlling servomotor turns the clamp together with the flattened head portion of the corresponding channel barrier by the required number of turns in either direction, thus increasing or decreasing the cross-section of the radial channel.
Further features of the foregoing will be described or will become apparent in the course of the following detailed description.
Brief Description of the Drawings In order that the disclosed embodiments may be more clearly understood, reference is now made to the accompanying drawings, wherein identical parts are identified by identical reference numbers and wherein:
FIGURE 1 is a perspective view of a cross-section of an embodiment of a cooling air ring;
FIGURE 2 is a perspective view of a portion of the Fig. 1 cooling air ring, showing the details of the barrier and the controlling servomotor;
FIGURE 3 is a cross-section of the controlling servomotor; and FIGURE 4 is a side sectional view of a portion of a radial channel of the cooling ring, with a barrier mounted therein.
Description of Preferred Embodiments United States published application 2006/0275,523 Al, published 7 December 2006, describes a melt distribution block that may be used to generate an annular film of a molten polymer in an extrusion die. The device described hereinafter is incorporated into the extrusion die above.
Referring now to FIGURE 1, a cooling air ring 10 is shown in a sectioned view that cuts through one of the radially positioned channels 100 therein. A
barrier 50 is seated inside each radial channel 100. The barrier 50 comprises a cylindrical shank 52 and a flattened head 54. More details of the barrier are provided below with reference to Figure 4. For the purposes of Fig. 1, it is noted that each barrier 50 is seated in a threaded opening 70 in one of the channels 100, with the flattened head 54 exposed and accessible to a control means that will now be described.
Also shown in Fig. 1 are a positioning servomotor 110 and a controlling servomotor 112. These servomotors are attached to an annular flange 12 of the cooling air ring 10. A film thickness sensor (not shown) detects the thickness of the blown film produced in the extrusion die and drawn through annulus 14, which is provided with a plurality of cooling air outlets 16. Air to the cooling air outlets 16 arrives at those outlets through the radial channels 100, so controlling the air flow through the channels also controls air flow through air outlets 16. Information from the film thickness sensor is processed and instructions for adjusting radial air flow in the channels are transmitted to the respective servomotors 110, 112. Of these, positioning servomotor 110 rotates the annular flange 12, along with controlling servomotor 112, in an indexing manner that can position controlling servomotor over any selected barrier 50.
Referring now to FIGURE 2, the controlling servomotor 112 comprises a sensor and a clamp 116. Sensor 114 detects the height of the top of flattened head 54 of the selected barrier 50. Based on the detected height, the controlling servomotor lowers clamp 116 until it is engaged around flattened head 54 in a manner that permits it to be turned. Once engagement, the servomotor 112 turns the clamp 116 either clockwise or counterclockwise by a required angular amount to move barrier 50 upwardly or downwardly with respect to the radial channel 100. In this way, the shank portion 52 of the barrier 50 is adjusted precisely, increasing or decreasing the cross-section flow area of the radial channel 100.
FIGURE 3 shows an enlarged cross-section of controlling servomotor 112, which is connected to the clamp 116 by means of shaft 118. The shaft 118 rotates horizontally by means of gear 120 and can also be raised and lowered in a vertical direction. The servomotor 112 in a preferred embodiment always turns the shaft 118 in integral multiples of 180-degrees. This ensures that the orientation of each flattened head 54 around the circumference of the cooling air ring will be the same. In turn, this enables the controlling servomotor 112 to lower the clamp 116 over any of the flattened head 54 in the cooling air ring in the same orientation, without the need to predetermine the orientation. By knowing the amount of cross-sectional change that a 180 degree turn of the flatted head will effect, the change in air flow can be precisely adjusted.
FIGURE 4 shows further detail of the barrier 50. As noted above, each barrier comprises a cylindrical shank 52 and a flattened head 54. The embodiment illustrated has the shank end 56 opposite the head that is unthreaded, with a medial portion 58 that has male threading. In such an embodiment, the unthreaded end will have a diameter smaller enough to pass in an unengaged manner through a female threading that will properly engage the male threading. In one embodiment of the barrier 50, the barrier is directly engaged in a threaded hole 70 in the radial channel 100;
in another embodiment, the barrier engages an internally-threaded sleeve 60 that is seated in the hole 70. In this latter embodiment, the sleeve's engagement in hole 70 is not affected by the turning of the barrier within the sleeve by the controlling servomotor.
Other advantages which are inherent to the structure are obvious to one skilled in the art. The embodiments are described herein illustratively and are not meant to limit the scope of the invention as claimed. Variations of the foregoing embodiments will be evident to a person of ordinary skill and are intended by the inventor to be encompassed by the following claims.
Claims (4)
1. A system for controlling the thickness of a blown film by providing air to the blown film exiting an extrusion die still in liquid form, the system comprising a cooling ring having an annular region through which the air is blown onto the blown film, the air being supplied to the annular region through a plurality of radial channels, wherein the system comprises:
a barrier inserted in each of the radial channels and adjustable therein to meter the air flow in the channel past the barrier;
an annular flange rotatingly mounted on the cooling ring for indexing rotation of the annular flange relative to the cooling ring by means of a first positioning servomotor;
a second controlling servomotor mounted on said annular flange having a barrier engagement mechanism;
a film thickness sensor for measuring the blown film thickness at a selected barrier and relaying the thickness information the first positioning servomotor operable in response to said thickness information to rotate the annular flange to operably connect the barrier engagement mechanism to the selected barrier the second controlling servomotor operable in response to said thickness information to adjust the barrier.
a barrier inserted in each of the radial channels and adjustable therein to meter the air flow in the channel past the barrier;
an annular flange rotatingly mounted on the cooling ring for indexing rotation of the annular flange relative to the cooling ring by means of a first positioning servomotor;
a second controlling servomotor mounted on said annular flange having a barrier engagement mechanism;
a film thickness sensor for measuring the blown film thickness at a selected barrier and relaying the thickness information the first positioning servomotor operable in response to said thickness information to rotate the annular flange to operably connect the barrier engagement mechanism to the selected barrier the second controlling servomotor operable in response to said thickness information to adjust the barrier.
2. The system of claim 1, wherein the barrier comprises a head and a shank which threadably connects to the cooling ring such that rotation of the head by the barrier engagement mechanism in one direction increases cross-sectional air flow area in the radial channel and rotation in the opposite direction decreases the cross-sectional air flow area.
3. The system of claim 1, wherein the barrier engagement mechanism comprises a clamping mechanism for engaging the head of the selected barrier and is operable to rotate the shank in either direction.
4. The system of claim 1, wherein the selected barrier is threadingly engaged in a sleeve that is seated in the cooling ring.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80618506P | 2006-06-29 | 2006-06-29 | |
| US60/806,185 | 2006-06-29 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2593107A1 CA2593107A1 (en) | 2007-12-29 |
| CA2593107C true CA2593107C (en) | 2014-02-04 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2593107A Active CA2593107C (en) | 2006-06-29 | 2007-06-29 | Device for automatic control of blown film thickness |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2593107C (en) |
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2007
- 2007-06-29 CA CA2593107A patent/CA2593107C/en active Active
Also Published As
| Publication number | Publication date |
|---|---|
| CA2593107A1 (en) | 2007-12-29 |
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