Blowing devices

Abstract

Blowing device (1) for providing pressurized air against the surface of an object. The blowing device comprises an enclosure (3) having a pressurized gaseous fluid inlet (17), said enclosure having an outlet surface (9) comprising a plurality of primary and secondary exhaust passages (19, 21) wherein the secondary exhaust passages are angled away from the primary exhaust passages at an angle β in order to obtain an even pressure distribution on the surface of the object.

Description

[0001]Blowing devices Field of the invention The present invention relates to blowing devices, such as air knives and air manifolds, for providing pressurized air against the surface of an object. Background information For many years blowing devices, often called air knives, air manifolds and air (nozzle) manifolds, have been used in many industries and manufacturing processes to deliver pressurized air against the surface of stationary or moving objects to blow off, i.e., remove, liquid or debris from, or to cool or to heat the surface of those objects. A typical air knife consists of a manifold or plenum with an elongated narrow air slot, either continuous or segmented so as to more a plurality of small openings, from which pressurized air can exit along the length of the air slot. The slot is intended to provide a continuous air flow or jet along the length of the slot. Air knives are generally placed in close proximity to the part being blown off and any interruption in the continuous air flow may be detrimental to the blow off effect An air nozzle or air manifold consists of a manifold or plenum from which multiple air outlet nozzles, with round or elongated openings, are placed at various intervals along the length of the manifold. The air nozzle / manifold does not provide a continuous air flow along its length as does an air knife. Instead the orifice of each outlet nozzle usually delivers a much larger air flow in a concentrated area in the form of a high velocity air stream from each outlet nozzle. A problem may occur where two adjacent air streams impact a surface at the same spot but from different angles as the resulting combined airflow may form a “blind spot” which lacks the desired cleaning effect and fails to remove liquid or debris. Properties that are important for a compressed air blowing device are noise level, consumption, power and blowing pattern. These four parameters are dependent on the pressure in the blowing device and are usually specified at different pressures. In many air applications today, a rectangular cross-sectional area of the jet is required where the width of the air stream should be maximized, and the height minimized. Preferably the noise level and air consumption should also be minimized. One way of achieving this is use several smaller outlet nozzles instead of using one large outlet nozzle. The size and centre-to-centre spacing of the outlet nozzles are carefully calculated to minimize the sound level at a given pressure. The outlet nozzles can be placed in different patterns to obtain a specific blowing pattern. The cross-sectional areas of the outlet openings in the nozzles and the distance between them together determine the cross- sectional area of the nozzle. To determine the blowing pattern, the relative pressure that occurs on a flat surface from a manifold which is facing the surface at 90° can be measured. With a given design of the pattern of the outlet channels, if it is desired to increase the relative pressure across the width of the blowing pattern then this can only be achieved by adjusting the input pressure. The disadvantage of increasing the pressure is that it tends to result in a disproportionately high pressure increase in the centre of the air jet, which is rarely required for this type of nozzle, instead of a proportionate increase across the whole width of the blowing pattern. This means that, in practice, you use an unnecessary amount of energy to get an increase in the relative pressure over the whole surface covered by the air stream. Therefore, there exists a need for air blowing arrangements which can provide more equal coverage on a surface for a given pressure and a given cross-sectional area of the nozzles of the arrangement. Summary of the invention It is an object of the invention to overcome or at least minimize the problem mentioned above by means of a blowing device having the features of claim 1. Such a blowing device is characterised by having a group of at least two adjacent central exhaust passages which direct a pressurised gaseous fluid at a first angle from the blowing device wherein said group of central exhaust passages are surrounded on each side by at least one exhaust passage orientated at an angle away from the closest central exhaust passage. Owing to the presence of the at least two adjacent central exhaust passages directed in the same direction and the presence of further exhaust passages directed away from this direction, the resulting jet of co-mingled gas formed from the pressurized gas leaving these exhaust passages surprisingly exhibits a smaller central peak pressure than blowing devices with a single central exhaust passage directed in a first direction and arranged between further exhaust passages orientated at an angle away from the central exhaust passage. Description of the figures Figures 1a) to 1c) show schematically lateral, plan and end-on views of a first embodiment of a blowing device in accordance with the present invention. Figures 2a) to 2c) show schematically side, plan and end-on views of a first embodiment of a blowing device in accordance with the present invention. Figure 3 shows an example of the relative pressures measured at positions across a surface using different angles for exhaust passages. Detailed description of the invention Figures 1a)-1c) shows schematically and not to scale lateral, plan and end views of a blowing device 1 according to a first embodiment of the invention. Blowing device 1 comprises an enclosure 3 with an exterior wall 5 which encloses a chamber 7. The enclosure is in the form of a box, which in this example is shown as being substantially rectangular but which could be of any other suitable shape, and the box has an outlet surface 9 which is intended to face towards the item which it blows air onto as shown by the arrow 11. Preferably outlet surface 9 is flat and elongated with a major centre line 13 extending in a first direction X and a minor centreline 15 extending perpendicular to the major centre line in the direction Y. The external wall 5 has a pressurized gas supply inlet 17 which is adapted be connected to a supply of pressurised gas (not shown). The outlet surface 9 is provided with a plurality of primary exhaust passages 19 and a plurality of secondary exhaust passages 21 each of which extend from the chamber 7 through the exterior wall 5 and open out with openings 22 on the outlet surface 9. The primary and secondary exhaust passages are shown arranged in a straight line along the major centreline of the outlet surface to order to give this embodiment of the invention symmetry, but they may be arranged in any other fashion such as parallel to the major centreline or at an angle to the centreline. A plurality of primary exhaust passages form a group of primary exhaust passages 23 comprising at least two adjacent primary exhaust passages 19 which are arranged to direct pressurised gaseous fluid at a first angle α from the outlet surface. Preferably this angle is perpendicular to the outlet surface. If the blowing device is intended to provide a jet of air which is substantially symmetrical along the major centreline then the centre of the group of primary exhaust passages can coincide with the midway point of the major centreline as shown in the figures. If the blowing device is intended to produce a stream of air which is not symmetrical then the centre of the primary exhaust passages can be placed to one side of the midway point of the major centreline. The group of primary exhaust passages form a line, preferably a straight line, and which is followed on each end in the direction of the major centreline by at least one secondary exhaust passage 21 which is directed at an angle β away from angle α in the direction along the major centreline. As shown in figure 1a), the central group 23 of two primary exhaust passages 19 has three secondary exhaust passages 21 arranged to the left of it which direct pressurized gas at the angle β to the left, and three secondary exhaust passages 21 arranged to the right of it which direct pressurized gas at the angle β to the right. In this embodiment of the invention there are two primary exhaust passages in the group of primary exhaust passages and there are a total of six secondary exhaust passages arranged in groups of three secondary exhaust passages on either side the group of primary exhaust passage, but there could be more than two primary exhaust passages in the group of primary exhaust passages, and the number of secondary exhaust passages on each side of the group for primary exhaust passages could be any number equal to or greater than 1. The centre-to- centre distances between adjacent exhaust passages may be equal for all the exhaust passages or it may be different for some adjacent exhaust passages. For example, it may be greater for adjacent exhaust passages which are further away from the primary exhaust than adjacent exhaust passages near to the primary exhaust passages, or vice versa. The cross-sectional areas of the exhaust passages may be the same for every exhaust passage or they may be different. Figures 2a)-2c) show schematically and not to scale a lateral, plan and end view of a blowing device 1 according to a second embodiment of the invention where the same reference numbers used in figures 1a)-1c) are used for similar elements in these figures. Thus, blowing device 1 comprises an enclosure 3 with an exterior wall 5 which encloses a chamber 7. The enclosure is in the form of a box, which in this example is shown as being substantially rectangular but which could be of any other suitable shape, and the box has an outlet surface 9 which is intended to face towards the item which it blows air onto as shown by the arrow 11. Preferably outlet surface 9 is flat and elongated with a major centre line 13 extending in a first direction X and a minor centreline 15 extending perpendicular to the major centre line in the direction Y. The external wall 5 has a pressurized gas supply inlet 17 which is adapted be connected to a supply of pressurised gas (not shown). The outlet surface 9 is provided with a plurality of primary exhaust passages 19 and a plurality of secondary exhaust passages 21, each of which extend from the chamber 7 through the exterior wall 5 and open out with an outlet 22 on the outlet surface 9. The primary and secondary exhaust passages are shown arranged in a straight line along the major centreline of the outlet surface to order to give this embodiment of the invention symmetry, but they may be arranged in any other fashion such as parallel to said major centreline or at an angle to the centreline. A plurality of primary exhaust passages forms a group of primary exhaust passages 23 comprising at least two adjacent primary exhaust passages 19 which are arranged to direct pressurised gaseous fluid at a first angle α from the outlet surface. This angle may be perpendicular to the outlet surface or at an angle less than or equal to 10°. If the blowing device is intended to provide a jet of air which is substantially symmetrical along the major centreline then the centre of the group of primary exhaust passages can coincide with the midway point of the major centreline as shown in the figures. If the blowing device is intended to produce a stream of air which is not symmetrical then the centre of the primary exhaust passages can be placed to one side of the midway point of the major centreline. The group of primary exhaust passages forms a preferably straight line which is followed on each end in the direction of the major centreline by at least one secondary exhaust passage 21 which is directed at an angle β away from angle α in the direction along the major centreline. As shown in figure 2b), the central group 23 comprises two primary exhaust passages 19 and immediately outside this group of primary exhaust passages, on each side thereof, a pair 25 of secondary exhaust has been positioned, said secondary exhaust passages being arranged parallel to the minor centreline 15. Further outside each group of two secondary exhaust passages a single secondary exhaust passage is arranged on the major centreline. This single secondary exhaust passage is followed by a further pair of secondary exhaust passages parallel with the minor centreline 15. Figure 3 shows experimental results from a blowing device which comprised a row of exhaust passages arranged in a straight line. The blowing device comprised two central primary exhaust passages which pointed straight towards a flat pressure measuring surface. A plurality of secondary exhaust passages of the same cross-sectional area was positioned on either side of the pair of primary exhaust passages. The inlet pressure was 0.5 MPa, the distance to the pressure measuring surface was 200 mm, the face of the surface was 290 mm x 310 mm. The face of the blowing device that faced the pressure measuring surface was 43 mm x 7 mm. It had two central primary exhaust passages and 14 secondary exhaust passages (seven to either side of the central primary exhaust passages) arranged at centre-to-centre intervals of 2.7 mm. All exhaust passages were circular with an opening diameter (D) of 0.9 mm. Using two central primary exhaust passages minimizes the turbulence and therefore the noise level compared to using one single bigger exhaust with the same cross-section area as the sum of the two smaller exhausts. Furthermore, using a single central primary exhaust may lead to a pressure drop in the centre when blowing air onto a flat surface. A series of experiments were made using the same inlet pressure but with the secondary passages angled away at different angles from the first exhaust passages. The angles that were tested were 0⁰, 1.5⁰, 2.5⁰, 4⁰, and 6⁰. As can be seen in figure 3, increasing the angle of inclination of the secondary exhaust passages leads to a desirable lower but wider distinct peak which gives a good coverage of the surface without an excessively high peak pressure in the centre which only wastes energy. Surprisingly, at an angle of around 6⁰ the peak not only becomes wide but forms a plateau which gives an almost constant pressure over a wide range of positions. This is desirable as it gives a good cleaning or cooling effect over a wide area without requiring an increased inlet pressure. In all embodiments of the present invention the secondary exhaust passages can be inclined at the same angle β away from the nearest primary exhaust passage. Preferably angle β is greater or equal to 1 degree and less than or equal to 10 degrees in the direction away from the closest primary exhaust passage, more preferably angle β is greater or equal to 2 degrees and less than or equal to 9 degrees, even more preferably angle β is greater or equal to 3 degrees and less than or equal to 8 degrees, yet more preferably angle β is greater or equal to 4 degrees and less than or equal to 7.5 degrees and most preferably angle β is greater or equal to 5 degrees unless than or equal to 7 degrees. It is also conceivable that the angle β changes as the distance of a secondary exhaust passage from the closest primary exhaust passage increases. For example, the second exhaust passage closest to a primary exhaust passage may be inclined at an angle β away from the primary exhaust passage, the next secondary exhaust passage may be inclined at an angle β + x degrees, the next secondary exhaust passage may be inclined at β + y degrees, the following secondary exhaust passage may be inclined at an angle of β + z degrees and so on, where z> y > x. Preferably the maximum diameter or width (D) of the opening (22) of any exhaust passage is equal to or less than 1.0 mm and greater than or equal to 0.5 mm, and more preferably it is less than or equal to 0.9 mm and greater than or equal to 0.6 mm. Preferably, the openings of all primary exhausts are of substantially the same cross-sectional area as each other, and / or the openings of all secondary exhausts are of substantially the same cross-sectional area as each other, or the openings of all exhaust passages have substantially the same cross-sectional area. Preferably the minimum centre-to-centre distance between adjacent exhaust passages is equal to or greater than three times and less than or equal to five times the maximum diameter or width (D) of the opening of the widest of the adjacent exhaust passages.

Claims

Claims 1. Blowing device (1), for providing pressurized air against the surface of an object, comprising an enclosure (3) having a pressurized gaseous fluid inlet (17) and a plurality of primary and secondary exhaust passages (19, 21), leading to and opening out onto an outlet surface (9) of said enclosure, wherein said exhaust passages jointly exhaust said fluid from said enclosure (3) characterised in that said plurality of exhaust passages comprises a group (23) of at least two adjacent primary exhaust passages (19) arranged in a line which direct said pressurised gaseous fluid at a first angle α from said outlet surface (9) wherein said group of adjacent primary exhaust passages (23) are followed on each end of said line by at least one secondary exhaust passage (21) orientated at an angle β away from the closest primary exhaust passage.

2. Blowing device according to claim 1 characterised in that said at least one secondary exhaust passage (21) is arranged at an angle β which is greater or equal to 1 and less than or equal to 10 degrees away from the closest primary exhaust passage (19).

3. Blowing device according to claim 1 characterised in that said angle β is greater or equal to 2 and less than or equal to 9 degrees.

4. Blowing device according to claim 3 characterised in that preferably said angle β is greater or equal to 3 degrees and less than or equal to 8 degrees, more preferably said angle β is greater or equal to 4 degrees and less than or equal to 7.5 degrees and most preferably angle β is greater or equal to 5 degrees and less than or equal to 7 degrees.

5. Blowing device according to any of the previous claims characterised in that the number of primary exhaust passages (19) in said group of at least two primary exhaust passages is equal to or greater than two and less than or equal to six.

6. Blowing device according to any of the previous claims characterised in that the openings (22) of all primary exhaust passages (19) are of substantially the same cross-sectional area as each other, and / or the openings (22) of all secondary exhaust passages (21) are of substantially the same cross- sectional area as each other, or the openings (22) of all exhaust passages (19, 21) have substantially the same cross-sectional area.

7. Blowing device according to any of the previous claims characterised in that the maximum diameter or width (D) of the opening (22) of any exhaust passage (19, 21) is equal to or less than 1.0 mm and greater than or equal to 0.5 mm.

8. Blowing device according to any of the previous claims characterised in that the maximum diameter or width (D) of the opening (22) of any exhaust passage (19, 21) is equal to or less than 0.9 mm and greater than or equal to 0.6 mm.

9. Blowing device according to any of the previous claims characterised in that the centre-to-centre distance between adjacent exhaust passages (19, 21) is substantially the same.

10. Blowing device according to any of the previous claims characterised in that the centre-to-centre distance between adjacent exhaust passages (19, 21) is equal to or greater than three times and less than or equal to five times the maximum diameter or width (D) of the opening (22) of the widest of the adjacent exhaust passages (19, 21).

11. Blowing device according to any of the previous claims characterised in that said exhaust passages (19, 21) are arranged in a straight line.

12. Blowing device according to any of the previous claims characterised in that said exhaust passages (19, 21) are arranged in a first group comprising a plurality of exhaust passages (19, 21) in a first line wherein at least one further group of at least two exhaust passages (19, 21) is arranged in a second line which crosses said first line.

13. Blowing device according to claim 12 characterised in that each said further group of exhaust passages comprises two exhaust passages (19, 21) and is placed symmetrically between a pair of said exhaust passages (19, 21) of said first group of exhaust passages and symmetrically to said first line.

14. Blowing device according to any of the previous claims characterised in that said first angle α is substantially 90°.

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