GB2254808A - "air knife" - Google Patents

Abstract

An air knife 1 has a housing 2 defining a duct 6 receiving pressurised air. A longitudinal slot 18 communicates with the duct for dispensing an elongate jet of air. The housing has first and second blades 3, 4 and spacer means 21 determining the width of the slot. Each blade is formed as an extrusion of uniform cross-sectional profile. Preferably, at least one blade is pivotally movable about a longitudinal axis to adjust the slot width. The air knife is useful in wiping surfaces and spreading viscose liquids. <IMAGE>

Description

"AIR KNIFE" This invention relates to apparatus for use as an air knife.

Conventional air knife systems consist of a medium pressure air blower connected by ducting to a housing having an accurately formed outlet slot from which an elongate jet of air emerges. Such systems are used to remove moisture or solid particles from work surfaces or for spreading viscous liquids. In order to produce satisfactory operation, particularly when spreading liquids, it is essential that the width of the slot is uniform over the entire length of the air knife.

According to the present invention there is disclosed apparatus for use as an air knife comprising a housing defining a duct for receiving pressurised air in use and defining a longitudinally extending slot communicating with the duct for dispensing an elongate jet of air, the housing comprising first and second blades and being provided with spacer means maintaining the blades in spaced apart relationship to define the slot therebetween, wherein each blade is formed as an extrusion of uniform cross-sectional profile.

An advantage of this arrangement is that a slot of any desired length can be formed by cutting to length extrusions forming the blades. By forming the extrusions of rigid materials it is then possible to ensure that the blades are sufficiently rigid to avoid flexure thereby ensuring that the slot width is uniform over its entire length.

Preferably the housing comprises pivot means facilitating pivotal movement of at least one of the blades about a longitudinal axis to thereby adjust the width of the slot.

An advantage of such an arrangement is that the adjustment of the width of the slot to be uniform along its entire length becomes a relatively straightforward task compared with the operation of prior art apparatus in which relative motion between blades is provided by sliding action.

Preferably at least one of the first and second blades includes an integral hinge formation engageable with a cooperating integral hinge formation of the housing thereby constituting pivot means to facilitate pivotal adjustment of the blade to thereby adjust the width of the slot.

Preferably the housing comprises a tubular member defining a longitudinally extending aperture, the tubular member comprising longitudinally extending flanges projecting radially at locations on each side of the aperture, the respective flanges being engageable with cooperating formations of respective blades to facilitate airtight connection in use.

Conveniently the tubular member is formed as an extrusion of uniform cross-sectional profile.

The tubular member can thereby readily be formed of any required length by cutting the extrusion to a length and joining end-to-end further extrusions if required.

Alternatively at least the first blade is formed integrally with a first part-tubular portion of the housing defining a side wall of the duct. The number of components in the apparatus may thereby be reduced.

Conveniently the first part-tubular portion of the housing is connected to a second part-tubular portion of the housing formed integrally with the second blade by means of a longitudinal hinge constituting pivot means facilitating relative pivotal movement of the blades about an axis defined by the hinge.

Preferably the hinge comprises a hinge pin received in respective recesses formed in respective hinge portions of the first and second part-tubular portions and clamping means operable to clamp the hinge portions in fixed and sealed relationship to the hinge pin.

Conveniently the first and second blades are formed unitarily with the respective first and second part-tubular portions of the housing.

Conveniently at least one extrusion defines a longitudinal bore engageable by a screw fitting. An advantage of this arrangement is that end connection to each extrusion is simplified so that for example a blanking plate can be readily screwed at one end of the housing or further lengths of extrusion can be added.

Preferably the blades project transversely with respect to the duct in spaced apart relationship to define a channel therebetween of narrower cross-section than the duct and communicating between the duct and the slot wherein the spacer means comprises at least one fastening member traversing the channel.

The spacer means may comprise a bolt carrying a spacer sleeve determining the separation of the blades or alternatively may comprise a continuously adjustable spacer mechanism. Such an adjustable spacer mechanism may for example comprise a spring mounted on the bolt and operable to urge apart the blades against clamping action of the bolt, the separation of the blades thereby being continuously adjustable by screw action of the bolt.

A particular embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings of which: Figure 1 is a perspective view of apparatus in accordance with the present invention; Figure 2 is a transverse section of the apparatus of Figure 1; Figure 3 is a transverse section of an alternative apparatus in accordance with the present invention; Figure 4 is a perspective view of the apparatus of Figure 3; Figure 5 is a perspective view showing use of the apparatus of Figures 3 and 4; and Figure 6 is a transverse section of part of a further alternative apparatus.

Apparatus 1 of Figure 1 comprises a housing 2 consisting of first and second blades 3 and 4 and a generally tubular member 5.

The tubular member 5 as seen more clearly in Figure 2 is an aluminium extrusion of uniform cross-sectional profile defining a cylindrical duct 6. The tubular member 5 defines a longitudinally extending aperture 7 and includes radially projecting flanges 8 and 9 disposed on either side of the aperture 7.

The first and second blades 3 and 4 comprise aluminium extrusions of uniform cross-section and of equal length to the tubular member 5. The first blade 3 consists of a generally planar portion 10 which projects outwardly of the tubular member 5 and is coupled to the tubular member by means of a longitudinally extending groove 11 which receives flange 8. The second blade 4 similarly includes a planar portion 12 with a groove 13 receiving flange 9. The planar portions 10 and 12 extend in parallel spaced relationship to define a channel 14 therebetween which is narrow compared with the diameter of the duct 6.

The first and second blades 3 and 4 include respective lips 15 and 16 which are inclined to their respective flat portions 10 and 12 so as to converge and thereby define a tapered portion 17 of the channel 14 and are narrowly spaced apart to define a slot 18 communicating with the channel 14.

A number of bolts 19 distributed along the length of the housing 2 provide connection between the blades 3 and 4 and are received in transverse bores 20 in the respective blades. Each of the bolts 19 traverses the channel 14 and receives a respective cylindrical sleeve 21 which serves to space apart the flat portions 10 and 12 by a predetermined distance.

The blades 3 and 4 each include longitudinally extending rib formations 22 defining longitudinal bores 23 and similar ribs 24 are provided on the external surface of the tubular member 5 to define respective bores 25. A blanking plate 26 is secured to the housing 2 at a first end 27 of the housing by means of self-tapping screws which engage the bores 23 and 25. The duct 6 is thereby closed at the first end 27. A pipe coupling 28 is connected to a second end 29 of the housing 2 by means of a flange 30 through which self-tapping screws engage the bores 23 and 25.

In use the pipe coupling 28 is connected to a supply of compressed air and pressurised air fills the duct 6 and the channel 14. A jet of pressurised air exits the slot 18 and is directed in use at a work surface.

Air knife apparatus of any required length can be formed by cutting to length the extrusions forming the blades 3 and 4 and the tubular member 5. Lengths of these extrusions can be joined end-to-end by suitable fittings engaging the bores 23 and 25.

Apparatus as described above can achieve a slot width of lmm to a tolerance of better than 10% over the entire length of a 2m slot.

The sleeve 21 may alternatively be replaced by a continuously adjustable spacer mechanism in order to provide a continuously adjustable slot width. During such adjustment the blades 3 and 4 are pivotal about the flanges 8 and 9 which in combination with the grooves 11 and 13 constitute individual hinge formations of the apparatus.

An alternative apparatus 40 is shown in Figure 3 and will be described using corresponding reference numerals to those of Figures 1 and 2 where appropriate for corresponding elements.

Apparatus 40 has a housing 2 comprising first and second portions 41 and 42 which are part-tubular in that they fit together to enclose a generally cylindrical duct 6 and are symmetrically disposed about a plane 43 extending through the cylindrical axis of the duct.

The respective portions 41 and 42 include planar portions 10 and 12 which project outwardly from the duct 6 parallel to the plane 43 and in turn are unitarily formed with first and second blades 3 and 4 which converge to define a narrow slot 18 in a manner similar to that described above with reference to Figures 1 and 2.

The first and second blades 3 and 4 have external surfaces 44 and 45 which are smooth and which converge at an angle of 150 towards the slot 18 apart from a localised surface area 46 immediately adjacent to the slot where the angle of convergence increases to 450.

The portions 41 and 42 are also provided with respective first and second hinge portions 47 and 48 which are located on the opposite side of the duct 6 from the location of the slot 18. The hinge portions 47 and 48 each comprise a longitudinally extending and outwardly projecting flange 49, 50, the flanges being provided with semi-cylindrical recesses 51, 52 which are a sliding fit on opposite sides of a cylindrical hinge pin 53. The hinge portions 47 and 48 and the hinge pin 53 together constitute a hinge 57 defining a pivot axis 60.

Longitudinally spaced bolts 54 extend through apertures in both the flanges 49, 50 and the hinge pin 53 such that when the bolts are tightened the flanges are urged into contact with the hinge pin thereby forming an airtight seal and frictionally locking the first and second portions in position.

Longitudinally spaced bolts 55 provide connection between the blades 3 and 4 and each bolt 55 carries a helical compression spring 56 held in compression between the blades so as to urge the blades apart in opposition to the clamping action of the bolts, this arrangement constituting a mechanism for continuously adjusting by screw action the separation of the blades and hence the width of the slot 18.

Each of the portions 41 and 42 is formed as an aluminium extrusion of uniform cross-sectional profile.

In Figure 4 the apparatus 40 is shown connected to a pipe coupling 28 which in turn is connected in use to a supply of compressed air (not shown). A blanking plate 26 closes the opposite end of the duct 6.

In use the apparatus is constructed from a pair of opposite handed extrusions constituting the first and second portions 41 and 42, these portions being cut to a suitable length and loosely coupled by assembling hinge portions 47 and 48 with the hinge pin 53 and loosely fitting the bolts 54. The further bolts 55 and springs 56 are assembled and the position of the blades 3 and 4 adjusted by screw adjustment of the bolts 55 to provide a suitable size slot 18.

Movement of the blades 3 and 4 is accommodated by pivotal movement of the portions 41 and 42 about the pivot axis 60. The bolts 54 are then tightened such that the hinge portions 47 are firmly clamped around the hinge pin 53 to both form an airtight seal and lock the hinge 57 in a fixed position. A blanking plate 26 and pipe coupling 28 are then fitted and the apparatus 40 can then be mounted for use.

A typical application of the apparatus 40 in use is shown in Figure 5 where the apparatus 40 constitutes an air knife suspended over a conveyor belt 58 on which is conveyed a workpiece 59 from which a liquid film is to be removed. The air knife provides a concentrated downwardly inclined jet of air which is evenly distributed along the length of the slot 18.

The smooth external shape provided by the external surfaces 44 and 45 of the blades 2 and 3 assists in providing a smooth flow of air externally of the blades 3 and 4 which is relatively free from turbulence effects. The effect of air streaming from the slot 18 is to entrain ambient air in the region of the slot so that there is a net flow of air over the external surfaces 44 and 45. It is therefore preferable for the external surfaces to be relatively free of protuberances and irregularities so as to minimise turbulence which would otherwise disrupt the uniformity of the air jet produced.

A further alternative apparatus 70 shown in Figure 6 will now be described using corresponding reference numerals to those of preceding Figures where appropriate for corresponding elements.

The apparatus 70 is similar to the apparatus 40 of Figures 3, 4 and 5 in that it includes first and second part-tubular portions 41 and 42 formed as aluminium extrusions of uniform cross-sectional profile. The second portion 42 however includes a side entry air inlet 71 in the form of a tubular connector 72 defining a bore 73 communicating with the duct 6 and of comparable diameter.

The connector 72 is formed integrally with the second portion 42 by cutting a hole in the extruded second portion and bonding the connector in place.

Such a T-piece arrangement allows air from a compressor to be introduced midway along the length of the apparatus and this is particularly useful where exceptionally long slots are to be supplied with compressed air. A number of lengths of the apparatus 70 may be joined end-to-end so as to have a corresponding number of air inlets 71 to ensure an even longitudinal distribution of air pressure.

An air inlet 71 of the type shown in Figure 6 may be used instead of or in addition to the pipe coupling 28 of preceding Figures.

Apparatus in accordance with any of the above embodiments may be externally coated with coatings suitable for use in specific environments, for example polytetrafluroethylene coatings may be applied for use in the food industry.

Apparatus in accordance with the present invention may be used in a variety of applications such as removing surface moisture from printed circuit boards, extrusions, cans, castings, glass sheets etc., or for spreading substances such as glue, foodstuffs and other viscous films. The apparatus may also be used for removing surface contamination such as dust, swarf or coolant or for drying fabrics or carpets.

The apparatus of Figures 1 and 2 may be modified to include an adjustable spacer by replacing the sleeve 21 with a spring which may be a coil spring or stack of spring washers for example. The apparatus of Figures 3 to 6 may similarly include alternative spacing means which may include a stack of spring washers or a rigid spacer sleeve of the type shown in Figure 2.

Claims (13)

CLAIMS:

1. Apparatus for use as an air knife comprising a housing defining a duct for receiving pressurised air in use and defining a longitudinally extending slot communicating with the duct for dispensing an elongate jet of air, the housing comprising first and second blades and being provided with spacer means maintaining the blades in spaced apart relationship to define the slot therebetween, wherein each blade is formed as an extrusion of uniform cross-sectional profile.

2. Apparatus as claimed in claim 1 wherein the housing comprises pivot means facilitating pivotal movement of at least one of the blades about a longitudinal axis to thereby adjust the width of the slot.

3 Apparatus as claimed in claim 2 wherein at least one of the first and second blades includes an integral hinge formation engageable with a cooperating integral hinge formation of the housing thereby constituting pivot means facilitating pivotal adjustment of the blade to thereby adjust the width of the slot.

4. Apparatus as claimed in claim 3 wherein the housing comprises a tubular member defining a longitudinally extending aperture, the housing having integral hinge formations comprising longitudinally extending flanges projecting radially from the tubular member at locations on each side of the aperture, the respective flanges being engageable with cooperating hinge formations of respective blades to facilitate airtight connection in use.

5. Apparatus as claimed in claim 4 wherein the tubular member is formed as an extrusion of uniform cross-sectional profile.

6. Apparatus as claimed in claim 2 wherein at least the first blade is formed integrally with a first part-tubular portion of the housing defining a side wall of the duct.

7. Apparatus as claimed in claim 6 wherein the first part-tubular portion of the housing is connected to a second part-tubular portion of the housing formed integrally with the second blade by means of a longitudinal hinge constituting pivot means facilitating relative pivotal movement of the blades about an axis defined by the hinge.

8. Apparatus as claimed in claim 7 wherein the hinge comprises a hinge pin received in respective recesses formed in respective hinge portions of the first and second part-tubular portions and clamping means operable to clamp the hinge portions in fixed and sealed relationship to the hinge pin.

9. Apparatus as claimed in any of claims 6, 7 and 8 wherein the first and second blades are formed unitarily with the respective first and second part-tubular portions of the housing.

10. Apparatus as claimed in any preceding claim wherein at least one extrusion defines a longitudinal bore engageable by a screw fitting.

11. Apparatus as claimed in any preceding claim wherein the blades project transversely with respect to the duct in spaced apart relationship to define a channel therebetween of narrower cross-section than the duct and communicating between the duct and the slot wherein the spacer means comprises at least one fastening member traversing the channel.

12. Apparatus as claimed in claim 11 wherein the spacer means comprises a continuously adjustable spacer mechanism.

13. Apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.