MXPA06010135A - Step air foil - Google Patents

Abstract

Step air foil particularly for one-sided flotation of a running web, and web dryer incorporating the same. The air foil includes two dischargeslots which allow for increased draw down force, which flattens machine direction wrinkles in a floating web. The air foil includes a primary discharge slot and a second discharge slot spaced from and stepped down from the primary discharge slot, a first web support surface between the primary discharge slot and the secondary discharge slot, and a second web support surface downstream of the secondary discharge slot in the direction of web travel. The air foil is in communication with an air supply which provides a supply of air that is uniformly distributed to the primary and secondary slots. Air discharged from the primary slot is gathered into the air stream of the secondary slot and creates an increased air cushion to provide greater support to the moving web and thereby remove machine direction web wrinkles caused by higher tension in light weight webs.

Description

GRADUAL AERODYNAMIC SURFACE FIELD OF THE INVENTION The present invention relates to non-contact drying and guide travel fabric devices, and more particularly, an improved fabric air flotation device that minimizes, eliminates or removes net wrinkles. BACKGROUND OF THE INVENTION In the operations of coating, printing and drying fabrics, it is often desirable for the fabric to have non-contact support, in order to avoid damage to the fabric itself or to the coating (such as ink) previously applied to one or more tissue surfaces. A conventional arrangement for non-contact supporting a fabric during drying includes upper and lower horizontal sets of air bars between which the fabric travels. The hot air emission from the dry air rods supports the fabric as it travels. The important characteristics of any flotation system are the amount of cushioning provided by the flotation device, and the stability of the fabric as it passes over it. device. Proper support removes wrinkles from the tissue that are typically caused by higher stresses in lightweight fabrics. The Ref..175304 instabilities of the airflow near the tissue can induce the vibration of the tissue and the subsequent contact of the tissue with the mechanical parts of the dryer, which results in alteration of the coating or tissue damage. The vibration of the tissue can manifest itself in a multitude of forms, ranging from a violent flapping of the fabric to a high frequency tapping. Single slot air bars are known in the art as aerodynamic surfaces. They differ from the double and triple slit air bars because they have a positive as well as negative pressure on the face of the air rod, while the double and triple slit bars have only positive pressure. As a result, double and triple slit air rods can be operated over a wider range of pressures and gaps; typical aerodynamic flotation gaps that are approximately 2.3 mm compared to 6.3 mm for double and triple air bars. The aerodynamic surfaces also have a dramatic drop in heat transfer and flotation stability as the gap increases, while heat transfers for double and triple air bars are relatively stable up to a clear 25 mm (size bar) simple) . A typical application for single slot air bars is where flotation must be performed with air on only one side of the fabric. Conventional aerodynamic surfaces discharge air at approximately 45 ° with the fabric, which pushes the fabric up and depends on the flatness of the fabric to trap the air and force it to follow the face of the aerodynamic surface. This creates a negative pressure to push the fabric down again and keep it in place on the aerodynamic surface. When lightweight fabrics are floated under medium to high stresses, undulations in the machine direction will form in the fabric. These undulations allow the air discharged from the 45 ° slot to escape and not trap the air between the face of the aerodynamic surface and the fabric, thus reducing or eliminating the speed created to draw the fabric down to the face of the aerodynamic surface. . This can result in poor flotation and can render the aerodynamic surface ineffective. It is therefore an object of the present invention to provide an aerodynamic surface for floating a fabric that provides excellent tissue support for a wide range of tissue weights, and provides excellent tissue stability. BRIEF DESCRIPTION OF THE INVENTION The problems of the prior art have been overcome by the present invention, which provides a stepped aerodynamic surface particularly for flotation on one side of a moving tissue., and a fabric dryer having one or more such aerodynamic surfaces. The design of the aerodynamic surface includes two discharge slots which allow an increased pull down force, which flattens the wrinkles in the machine direction in a floating fabric. The design does not depend on a flat weave to help create a velocity across the face to attract tissue to the face for proper floatation as in conventional designs. The air discharged from the main groove is gathered in the air stream of the secondary groove and creates an increased air cushion to provide greater support to the moving tissue and thereby remove wrinkles from the fabric in the direction of the machine caused by tension. greater in lightweight fabrics. The two air discharge slots blow gas (air) parallel to the fabric in a longer area than in conventional designs thereby increasing the force of attraction down against the tissue. The aerodynamic surface includes a main discharge slot and a secondary discharge slot separated from and staggered down the main discharge slot, a first tissue support surface between the main discharge slot and the secondary discharge slot, and a second tissue support surface downstream of the secondary discharge groove in the direction of tissue travel. The aerodynamic surface is in communication with an air supply that provides an air supply that is evenly distributed to the primary and secondary slots. The aerodynamic surface can be used primarily for floating on one side, but can also be used with two-sided arrangements for increased drying. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a cross-sectional view of an aerodynamic surface according to the present invention; Figure 2 is a cross-sectional view of the aerofoil head of Figure 1; Figure 3A is a top view of the drag bottom plate of the aerodynamic surface of the present invention; Figure 3B is a cross-sectional view of the bottom bottom plate taken along line A-A of Figure 3A; Figure 4 is a cross-sectional view of the upper drag plate of the aerodynamic surface of the present invention; Figure 5 is a cross-sectional view of a spacer for the aerodynamic surface of the present invention; Figure 6 is a perspective view of the aerodynamic surface of the present invention; Figure 7 is a cross-sectional view of a reinforcement for the aerodynamic surface of the present invention; and Figure 8 is a schematic view of a dryer having a plurality of aerodynamic surfaces on one side of the fabric according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION The aerodynamic surface of the present invention is a unique design incorporating a secondary groove that discharges air parallel to the fabric in order to maintain a constant downward pull force that is independent of a flat fabric. It is particularly useful for flotation applications on one side. Turning now to Figure 1, an aerodynamic surface according to the preferred embodiment of the invention is shown generally at 10. The airfoil 10 is defined in part by a head 1, which, in the embodiment shown, is generally rectangular in shape. cross section except for its upper portion. As seen in Figure 2, the opposite sides 11b, 11b of the head end in respective upper eye portions 12a, 12b. The upper brow portion 12a is angled, preferably at approximately 65 ° relative to the vertical, and ends at a bent portion 13. The upper brow portion 12b extends to the opposite side Ia in a substantially horizontal manner. The head 1 defines an interior space 5 that serves as a full chamber for the gas that is received via the one or more holes 36 in the base of the aerodynamic surface that are in gas receiving communication with a gas supply (not shown) . The head 1 is placed in suitable conduits by aligning the aligners 8 in each end plate of the head and are sealed by the seal gasket 7. A diffuser plate 6 (Figure 1), which has a plurality of spaced holes, can be placed in the head to help distribute the gas supply evenly as it flows into the slots. In the embodiment shown, the diffuser 6 has an inclination (approximately 15 °) with an apex at or near the center line CL of the head 1. The brow portions 12a, 12b and the bent portion 13 of the head 1, together with the upper trailing plate 2 and trailing bottom plate 3, define the primary and secondary grooves of the aerodynamic surface. Specifically, Figures 3A and 3B illustrate the bottom plate 3 in greater detail. The plate 3 includes a relatively short portion 31 having a plurality of spaced apart openings 32a to 32n formed therein. Preferably, the openings are circular and evenly spaced to allow uniform flow of gas from the plenum to the secondary slot stepped down from the aerofoil, as discussed in more detail below. In the embodiment shown, there are six such openings, each approximately 5.08 centimeters in diameter, although those skilled in the art will appreciate that the present invention is not limited to any particular number or size of openings. The plate 3 also includes a relatively long portion 33 extending from the short portion 31 at an angle therefrom. The relatively long portion 33 forms the wing of the aerodynamic surface, as best seen in Figure 6, and ending in an eyebrow 34 that extends downward. Preferably, the relatively long portion 33 of the plate 3 extends from the short portion 31 at an angle of approximately 28 °, doubles an additional 2 to 3 ° towards the mid-point of the portion 33, and then doubles an additional 5o about 2.54 centimeters from the eyebrow 34. Eyebrow 34 extends downward at a right angle of approximately 1.27 centimeters. The plate 3, together with the upper drag plate 2, defines the secondary slot S through which the air flowing from the openings 32a to 32n is emitted. That air then travels along the upper face of the wing in the direction of tissue travel.

Figure 4 illustrates the upper trailing plate 2 in cross section. The upper plate 2 includes an eyebrow 21 which connects to the end of the short portion 31 of the bottom plate 3, such as by welding (see Figure 1). Extending from the eye 21 there is a first planar portion 22, a second planar portion 23 extending from the planar portion 22 at an angle of approximately 90 °, and an elongated portion 24 extending from the second planar portion 23 at an angle of approximately 27 °. When properly positioned in the head 1, the second planar portion 23 of the upper pull plate 3 with the eyebrow 13 of the head 1, the main groove P and the elongated portion 24 define a tissue support face of the airfoil 10. (better seen in Figure 1) along which the air leaving the main slot P flows in the direction of tissue travel. Preferably, the discharge opening of the main P-slot is approximately 0.20 centimeters. The distance between the main P slot and the secondary S slot is important for the proper airflow and tissue flotation. If the distance is very small, the air leaving the main P-slot will not flow in parallel with the tissue. If the distance is too large, the air flow of the main slot will lose its speed. Preferably, the distance between the slots is from about 6.35 centimeters to about 16.51 centimeters, with 8.25 centimeters particularly preferred.

Turning now to Figure 5, a spacer 4 is shown in cross section. The spacer 4 is formed to be received within the space defined by the upper and bottom drag plate assemblies. Preferably, a plurality of spacers 4 are positioned along the length of the aerodynamic surface, and are positioned between the openings in the bottom plate 3 so as not to interfere with the flow of gas emanating from the openings 32a a 32n. The separation across the length of the aerodynamic surface is not critical, as they barely form a grid system for reinforcement. The shape of the cross section of the spacers 4 equals the cross section of the area defined by the upper and bottom plates 2 and 3, respectively. The spacers 4 can be secured in place by any suitable means, and preferably secured by welding the tongue 47a to the head 1, the tongue 47b to the upper drag plate 2, and the tongue 47c to the bottom plate 3 drag. The ends of the spacer establish the opening space or size for the secondary S-slot, which is preferably approximately 0.20 centimeters. The secondary S-slot discharges air parallel to the tissue and maintains a constant air velocity across the flat face for maximum force of downward attraction.

In order to adequately support the extension of the wing of the bottom plate, a plurality of reinforcements 60 (Figure 7) are placed under the wing, as shown in Figure 6. Each reinforcement 60 is attached to the head 1 by suitable means, such as by welding on the tongues 61a, 61b. Similarly, the upper part of the reinforcement 60 is joined to the underside of the wing via welding of the tongue 61c. The upper part of each reinforcement 60 is tapered to accommodate the wing slope. The number of reinforcements required depends on the length of the nozzle, and falls within the skill in the art. In the embodiment shown in Figure 6, three uniformly spaced reinforcements are provided. As shown in Figure 8, the two discharge slots allow effective flotation of tissue on one side of fabrics of all weights, from thin films to heavier paper and films. A portion 100 of a fabric dryer is shown, with a plurality of aerodynamic surfaces 10, each in communication with an air supply head 101 and positioned on one side of the running tissue 200. Positioned on the opposite side of the running tissue 200 is a plurality of nozzles 105, each preferably positioned in a staggered relationship relative to the location of each aerodynamic surface 10. In the embodiment shown, the opposite nozzles 105 in the region of the gradual aerodynamic surface of dryer 100 there are basic single-slot nozzles with low speed and high volume for dilution of solvent to keep LFL levels low. A constant velocity through the face attracts the fabric to the face of the aerodynamic surface to produce good flotation and weaving characteristics. The design of two grooves allows to double the force of attraction down, which in turn flattens the wrinkles in the direction of the machine in a floating fabric. The increased downforce of the aerodynamic surface creates a flat weave for a stable transition to opposite areas of air rods without fabric grooving, tissue inflation or marking problems. Thus, in operation, air flow is discharged through slots or primary and secondary orifices. The design allows the reclamation of air discharged from the primary groove to be gathered in the air stream of the secondary groove and create an increased air cushion to give greater support to the moving tissue, which in turn removes wrinkles from the fabric in The direction of the magma caused by higher stresses in tissues of lighter weight. A higher float height (for example, a positive float height of 0.3175 centimeters from the face of the aerodynamic surface regardless of the line speed) is possible for more stressed fabrics. Because the air is discharged below and parallel with the fabric, there is always a velocity through the face of the aerodynamic surface to draw the wavy fabric down to the face and hold it in place for controlled transport. The increased cushion pressure of the secondary groove stretches the fabric, removing any wrinkles in the machine direction that may have formed in the fabric, thus creating a glass-like appearance for the fabric. By incorporating two discharge slots in two different locations of the face and thus the supply of two large flat face areas, the attractive force downwards is doubled, which is a necessity when flattening the wrinkle wrinkles in the address of the machine. The range of fabric weights and tension conditions with which the present invention exhibits excellent flotation characteristics is more than twice that of conventional designs. The performance of the aerodynamic surface allows a greater separation between aerodynamic surfaces when installed in a dryer and allows a greater window of operation with different tissue weights and tissue tensions. It can be used as a tissue stabilizing device due to the strong tissue capture characteristics of the design. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (14)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. An aerodynamic surface for floating a fabric of material, characterized in that it comprises a main discharge slot and a secondary discharge slot separated from and stepped downstream of said main discharge slot, a first flat tissue support surface between said main discharge slot and said secondary discharge slot, and a second tissue support surface downstream of said secondary discharge slot in the direction of travel of the tissue.
2. 2. The aerodynamic surface according to claim 1, characterized in that said secondary discharge groove discharges air parallel to the fabric.
3. 3. The aerodynamic surface according to claim 1, characterized in that the air discharged from said main discharge slot meets in the air stream of said secondary discharge slot in a direction parallel to the direction of transport of the fabric.
4. 4. The aerodynamic surface according to claim 1, characterized in that said second tissue support surface comprises a wing portion that slopes downwardly as it extends away from said secondary discharge slot.
5. 5. The aerodynamic surface according to claim 1, characterized in that it further comprises a diffuser for uniformly distributing air to said main discharge slot and to said secondary discharge slot.
6. A fabric dryer, characterized in that it comprises a tissue inlet and a tissue outlet separated from said tissue inlet, a plurality of air discharge nozzles in said dryer for drying said tissue, and at least one airfoil in said dryer, said aerodynamic surface comprising a main discharge slot and a secondary discharge slot separated from and staggered down from said main discharge slot, a first flat tissue support surface between said main discharge slot and said slot secondary discharge, and a second tissue support surface downstream of said secondary discharge groove in the direction of tissue travel.
7. The fabric dryer according to claim 6, characterized in that there are a plurality of aerodynamic surfaces in said dryer, all placed on the same side of said fabric.
8. 8. The aerodynamic surface according to claim 1, characterized in that said second fabric surface is an elongated wing having a series of folds.
9. 9. The aerodynamic surface according to claim 8, characterized in that said elongate wing terminates in an eyebrow that extends downward.
10. 10. The aerodynamic surface according to claim 8, characterized in that one of said bends is at an angle of 3o.
11. An aerodynamic surface for floating a fabric of material, characterized in that it comprises a main discharge slot and a secondary discharge slot separated from and staggered downwardly of said main discharge slot, a first tissue support surface between said slot of main discharge and said secondary discharge groove, and a second tissue support surface downstream of said secondary discharge groove in the direction of travel of the fabric, said second fabric support surface comprising a folded plate, wherein said secondary discharge slot is defined by said first tissue support surface and said bent plate.
12. 12. The aerodynamic surface according to claim 11, characterized in that said bent plate comprises a plurality of openings to allow air flow to said secondary discharge slot.
13. 13. The aerodynamic surface according to claim 11, characterized in that said secondary discharge groove discharges air parallel to the fabric. The aerodynamic surface according to claim 11, characterized in that the air discharged from said main discharge slot meets in the air stream of said secondary discharge slot in a direction parallel to the direction of transport of the fabric.