Patent Publication Number: US-6990751-B2

Title: Rotatable air knife

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present intervention is an apparatus, such as an air knife or an air distribution manifold, for directing air under pressure at passing articles to dry or remove dust and debris from those articles. 
   2. Description of the Prior Art 
   Conventional air knives and air distribution manifolds are often formed as elongated structures that extend alongside or transverse to a conveyor belt or conveyor chain carrying articles to be dried or blown clean. Air knives are extensively used for drying a wide variety of articles of manufacture, such as plastic soft drink bottles prior to labeling, printed electronic circuit boards, food packaging, and many other products. Conventional pressure air delivery devices in the form of air knives and air nozzles have been used in a wide variety of industrial and commercial processes to remove or control the amount of liquids remaining on the surfaces of products after washing, rinsing, cooling, coating, or lubricating fluids have been applied. The same air delivery devices have also been used to blow dust and debris from products as well as to accelerate the heating or cooling of products. Applications for air knife and air nozzle blow off include printed circuit board assembly, machine parts, fabricated metals, plastic trays and totes, conveyor belts, electroplating, assorted textiles, food production and packaging, car and truck washing, and many other applications as well. 
   Conventional air knives and air distribution manifolds are usually mounted in a fixed orientation relative to a conveyor system past which articles to be dried or cleaned are carried. One disadvantage of conventional systems of this type is that the article to be dried or blown clean passes through the curtain of air being blown at it for only a very brief instant. Also, the flow of air of a conventional system is directed at the article to be treated from only a single direction. The configuration of the article is often such that “blind spots” are created on the portions of the article facing away from the oncoming airflow. These blind spots result from the fixed angle at which the airflow is directed against the product. Air velocity is much lower in these blind spots, thus reducing the drying or cleaning effect of the flowing air. As a consequence, the article is often inadequately dried or cleaned. 
   In order to achieve complete drying, multiple air knives, nozzles, and blowers have often been required. A conventional motor-driven rotary air knife must be coupled by a shaft, gear, chain, or belt to a drive motor. Such additional driving equipment increases both the cost and complexity of the air knife system. 
   Some conventional air knife systems have been designed to impart a rocking movement to the air knife duct or to otherwise vary the angle at which the air is directed toward the article. Other prior systems employ a motor to oscillate the air knife or nozzle in one plane so as to cause a lateral air blow off across the surface of a product. However, conventional devices of this type have been largely unsatisfactory. The effective area of coverage and the number of passes over the surface of products to be treated are quite limited as contrasted to the system of the present invention. Also, such conventional systems result in very slow product speeds of conveyance and sometimes even extended stationary product positioning to ensure adequate air blow off coverage of the product. 
   SUMMARY OF THE INVENTION 
   The present intervention involves an improved construction for an air knife or air delivery manifold having a plurality of primary pneumatic ejection nozzles for cleaning or blowing off articles of manufacture or other products. According to the present intervention the air knife or air jet manifold is constructed with laterally separated, opposing ends and mounted for rotation about a longitudinal axis equidistant from its opposing ends. Furthermore, the system requires no mechanical drive mechanism to rotate the air knife or air jet manifold. Rather, a small thrust nozzle is located at each of the opposing ends of the air knife or air distribution manifold and is directed so as to exert a tangential, rotational force on the opposing ends of the structure to rotate it about the longitudinal axis passing through its center. The thrust nozzles divert a small amount of the air flowing into the plenum of the air knife or air distribution manifold so that no externally powered drive system is required to rotate it. 
   By rotating the air knives and air distribution manifolds about a central, longitudinal axis, rather than positioning them in static, fixed orientations relative to the conveyor system, each passing article is exposed to the airflow for a considerably longer period of time and from varying directions than is the case with conventional air knife systems. Considered another way, the rotating air knife reaches out to the approaching article to direct an airflow at it, then delivers air at it from continuously varying directions, and then follows the article to a certain extent as it leaves the proximity of the air knife. 
   The advantage of this improvement is that by rotating an air knife over an article, such as a printed circuit board, for example, there is an increase in dwell time of the air knife over the article. Also, the article can be dried or blown off more effectively since the airflow impinges upon the article from different directions as the air knife rotates. This increase in effectiveness means that the articles can be dried or blown off in a shorter amount of time, thereby allowing the speed of the conveyor system to be increased. Furthermore, because the air knife or air distribution manifold is continuously rotating as the article passes it, airflow is directed at the passing article from constantly changing directions. This increases the drying effectiveness which also allows conveyor speed to be increased. 
   In one broad aspect the present invention may be considered to be an apparatus for directing air under pressure at passing articles. The apparatus of the invention is comprised of an air distribution enclosure, at least one thrust nozzle, a blower, and a rotatable coupling. The air distribution enclosure has opposing laterally separated ends. Air under pressure from these opposing ends is directed at the passing articles. A central inlet opening is located midway between the opposing ends. This central inlet opening defines an axis of rotation. 
   Thrust nozzles are located at one or both of the opposing ends of the distribution enclosure to receive air from within the enclosure. The thrust nozzles are directed to emit jets of air in a tangential direction relative to the longitudinal axis. The blower has an inlet duct leading to the inlet opening in the air distribution enclosure. A rotatable coupling joins the air distribution enclosure to the inlet duct and permits rotation of the air distribution enclosure relative to the inlet duct. 
   The air distribution enclosure may be an elongated air knife having a narrow air discharge slot extending between the opposing ends. Such an air knife expels air not only at its opposing ends, but rather it discharges air in a band that extends linearly between the opposing ends. The band of air flow is emitted through the narrow air discharge slot that is rotated over a circular area by the jets of air emitted from the thrust nozzles. These air jets rotate the air knife about the longitudinal axis and in a plane parallel to the direction of conveyor advancement. 
   The thrust nozzles may have a fixed configuration and a discharge orifice of fixed area and shape. With this configuration the thrust turning the air knife in rotation is determined solely by the pressure of air within the plenum. Preferably, however, each of the thrust nozzles is provided with an adjustment mechanism, such as an infinitely variable orifice valve, to vary the force of the jets of air. These adjustment mechanisms may be manipulated so as to direct a greater or smaller portion of the air in the plenum through the thrust nozzles. 
   While a variety of different kinds of couplings may be employed, the coupling system that joins the air knife to the blower duct is preferably a low friction device. A bearing ring may be interposed between the stationary and rotatable components of the coupling in order to reduce friction. However, it is also highly advisable to minimize any escape of air through the coupling components. This may be done by constructing the stationary and rotatable components of the coupling to define a tortuous path of resistance to the flow of air radially outwardly from the coupling with respect to the longitudinal axis. 
   In this connection the stationary and rotatable components of the coupling may respectively include stationary and rotatable tubular structures that define radially projecting flanges at their extremities. The flanges reside in mutually facing relationship. One or a plurality of annular grooves may be defined in one of the flanges while one or a plurality of raised rings may be defined in the other flange. The rings fit easily into the grooves to permit rotation of the rotatable tube relative to the stationary tube but the nonplanar configuration of the flanges provides the necessary tortuous path of resistance to radial airflow out through the walls of the coupling. 
   The invention is not necessarily limited to air knives in which air is emitted from a single, long, narrow slot. Sometimes a manifold having a plurality of separate primary drying or blowoff outlet nozzles is used instead of an air knife. These primary nozzles may be located only at the ends of the manifold, but are more typically spaced along its length between the ends as well as at the ends of the manifold. 
   In another aspect the invention may be considered to be an apparatus for directing a flow of air on passing articles. The apparatus is comprised of an air distribution structure having a longitudinal axis and opposing ends located equidistant from the longitudinal axis. The air distribution structure is configured with at least one primary outlet to emit a flow of air in a longitudinal direction along a laterally extending swath. The air distribution structure is equipped with thrusting air jet nozzles located at its opposing ends. The thrusting air jet nozzles are oriented tangentially relative to the longitudinal axis so as to deliver sufficient thrust to rotate the air distribution structure about the longitudinal axis. As a result, the swath is swept in a circle centered upon the longitudinal axis. 
   The air distribution structure may be either an air knife or an elongated air manifold having a plurality of primary outlet nozzles spaced along its length. The air distribution structure forms part of an overall system which additionally comprises a blower having an inlet duct leading to the air distribution structure and also a coupling. The coupling has a stationary tubular member oriented coaxially with the longitudinal axis. The air distribution structure has an inlet opening centered on the longitudinal axis and a rotatable tubular member projecting from the inlet opening in the air distribution structure to the stationary tubular member. The rotatable tubular member of the coupling is in coaxial alignment with the stationary tubular member of the coupling. A bearing ring is interposed between the stationary tubular member and the rotatable tubular member. 
   In still another aspect the invention may be considered to be an improvement in an air knife assembly for directing a flow of air at passing articles. The assembly includes an elongated air distribution enclosure having opposing ends. The air distribution enclosure has an inlet side having a longitudinally aligned inlet opening therein equidistant from the opposing ends. It also has an outlet side having an elongated outlet slot defined therein. As a result, the air distribution enclosure emits a flow of air through the outlet slot along an elongated linear band. 
   The air knife assembly also includes a blower supplying air under pressure to the elongated air distribution enclosure. The blower includes an air supply duct leading to the elongated air distribution enclosure. 
   The improvement of the invention is comprised of a coupling interposed between the inlet opening of the elongated air distribution enclosure and the air supply duct. The coupling joins the elongated air distribution enclosure to the air supply duct and permits rotation of the elongated air distribution enclosure relative to the air supply duct about a longitudinal axis of rotation perpendicular to the elongated air distribution enclosure and centered at the inlet opening. The improvement is also comprised of laterally directed thrust nozzles on the opposing ends of the elongated air distribution enclosure. The thrust nozzles are oriented to emit tangential jets of air at a radially spaced distance from the longitudinal axis. The thrust nozzles thereby rotate the elongated air distribution enclosure about the longitudinal axis relative to the supply duct. 
   The system of the invention supplies air from a blower at up to ten pounds per square inch air pressure. The blower air passes through both rotating and stationary components of the coupling assembly. The coupling assembly has very low air pressure loss and low rotational resistance. The system allows the same blower air pressure supplied for the primary object of drying and blow off to be used to also rotate an air delivery device. This device may be either an air knife or an air nozzle manifold. By rotating the air delivery device, greater effectiveness and efficiency of air drying and blow off is achieved. The air delivery device is rotated by thrust air jet nozzles that can be either adjustable or fixed structures. 
   The air delivery device is continuously rotated by means of the thrust nozzles that emit air from jets at the ends of the air delivery device. The orientation of these thrust nozzles is in a direction tangential to the axis of rotation. The air delivery device can be continuously rotated at variable speeds of from 1 to 200 rpm. The rotating force is supplied by the compressed air flow from an industrial blower at a maximum pressure of ten pounds per square inch through a low resistance, low pressure drop air coupling. The thrust nozzles on the ends of the air delivery device produce air jets that create a tangential, rotational thrust force, thereby eliminating the need for a separate, secondary drive mechanism to provide rotational force. Rather, the same air pressure that produces high velocity air blowoff and drying from the surface of parts during manufacturing or other products and other processes is used to rotate the air delivery device. 
   The invention may be described with greater clarity and particularity by reference to the accompanying drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an apparatus for supplying and directing air under pressure onto articles passing beneath it on a conveyor belt. 
       FIG. 2  is an exploded view of the air distribution enclosure and the coupling employed in the system of FIG.  1 . 
       FIG. 3  is a side elevational view of the coupling employed in the system of FIG.  1 . 
       FIG. 4  is a sectional elevational view taken along the lines  4 — 4  in FIG.  3 . 
       FIG. 4A  is an enlarged sectional detail of the region indicated at  4 A in FIG.  4 . 
       FIG. 5  is an exploded perspective view of the coupling shown in  FIGS. 3 and 4 . 
       FIG. 6  is a perspective view of an air nozzle manifold that may be used in place of the air knife shown in FIG.  1 . 
       FIG. 7  is a perspective view of another embodiment of an air nozzle manifold that may be used in place of the air knife shown in FIG.  1 . 
   

   DESCRIPTION OF THE EMBODIMENT 
     FIG. 1  illustrates an air knife assembly indicated generally at  10  which is used for directing a flow of air, indicated by the directional arrows  12  at passing articles  14 . In the illustration shown, the articles  14  are printed circuit boards which are carried on a conveyor belt  16  beneath the air knife  18 . 
   The air knife  18  is comprised of a hollow, elongated air distribution enclosure  20 . The enclosure  20  is a tubular structure having opposing closed ends  22  and  24  with an inlet side  26  having a longitudinally aligned inlet opening  28  therein. The longitudinally aligned opening  28  is equidistant from the opposing ends  22  and  24  and is a circular opening centered upon a longitudinal axis  30 . The air distribution enclosure  20  also has an outlet side  32  having a narrow, elongated slot  34  defined therein. The air distribution enclosure  20  emits a flow of air through the outlet slot  34  along an elongated linear band indicated in phantom at  36  in FIG.  2 . 
   The air knife assembly  10  is also comprised of a blower  38  which includes an air supply duct  40  that supplies air under pressure to the elongated air distribution enclosure  20 . One suitable blower that may be utilized as the blower  38  is the Sonic 70 centrifugal blower manufactured and sold by Sonic Air Systems, located at 4111 North Palm Street, Fullerton, Calif. 92835. 
   The aspects of the air knife assembly  10  described thus far are conventional, as air knives have been utilized for many years for drying and cleaning a wide variety of products. However, the air knife assembly  10  shown in  FIG. 1 , and elsewhere in the drawings, has several unique features. 
   The air knife assembly  10  includes a coupling  42  interposed between the inlet opening  28  of the elongated air distribution enclosure  20  and the air supply duct  40 . The coupling  42  joins the elongated air distribution enclosure  20  to the supply duct  40 . The coupling  42  is constructed to permit rotation of the elongated air distribution enclosure  20  relative to the supply duct  40  about the longitudinal axis of rotation  30  which is oriented perpendicular to the alignment of the elongated air distribution enclosure  20 . 
   The air knife assembly  10  also includes laterally directed thrust nozzles  44  that are located on both of the opposing ends  22  and  24  of the elongated air distribution enclosure  20 . The thrust nozzles  44  are oriented to emit tangential jets of air at a radially spaced distance from the longitudinal axis  30  to thereby rotate the elongated air distribution enclosure  20  about the longitudinal axis  30  relative to the supply duct  40 . The air jet thrust nozzles  44  are provided with adjustable valves controlled by manually operable valve levers  46  to selectively control the thrusting force of the air jets emitted by the thrust nozzles  44 . 
   The coupling  42  is illustrated in detail in  FIGS. 3 ,  4 ,  4 A and  5 . The coupling  42  is comprised of a mounting plate  48 , an annular, stationary coupling duct  50  which also serves as a bearing housing, an annular, greaseless ball bearing ring  52 , a rotatable outlet tube  54 , a bearing retainer cap  56 , a spacer ring  58 , and a retaining ring  60 . 
   The stationary coupling duct  50  has a cylindrical, annular neck  62  that extends upwardly through a circular, central opening  64  in the flat, generally square mounting plate  48 . Eight screws  65  pass through eight mounting holes  67  in the mounting plate  48  to attach the stationary coupling duct  50  to the mounting plate  48 . The neck  62  of the stationary tube  50  is joined with an airtight seal to the inlet duct  40  in coaxial alignment with the longitudinal axis  30 . The stationary coupling duct  50  also is provided with a radially projecting flange  64  that extends outwardly from the central opening of the neck  62  that is centered coaxially on the longitudinal axis  30 . The coupling duct  50  also has a cylindrical annular skirt  66  that extends downwardly from the periphery of the flange  64 . 
   As illustrated in  FIGS. 4 and 4A , an annular, concave recess is defined in the underside of the flange  64  at the inner margin thereof proximate the neck  62 . In this inner marginal region the downwardly facing surface of the flange  64  is configured to define a pair of circular, annular, downwardly facing raised rings  68  which are located at spaced radial distances from the longitudinal axis  30 . 
   The rotatable tube  54  has a downwardly depending neck  70  that extends through a central opening  72  in the retainer cap  14 . The neck  70  of the rotatable tube  54  fits within a rubber hose junction sleeve  74  and is secured thereto in airtight engagement therewith by a releaseable hose clamp  76 . The air distribution enclosure  20  is provided with a neck  78  that projects upwardly from the inlet surface  26  to form the inlet opening  28 . The neck  78  also fits into the lower end of the junction sleeve  74  and is secured thereto in airtight engagement therewith by another releaseable hose clamp  76 . The rotatable tube  54  is a thereby connected to the air distribution enclosure  20  in coaxial alignment with the longitudinal axis  30 . 
   The rotatable tube  54  also has an annular flange  80  at its upper end that extends radially outwardly from the neck  70 . The flange  80  is configured with a pair of circular, annular upwardly facing grooves  82  that are coaxial with respect to the longitudinal axis  30  and which reside in registration with the downwardly depending rings  68  of the flange  64  of the coupling duct  50 . 
   The greaseless bearing ring  52  is interposed between the rotatable tube  54  and the stationary coupling duct  50 . As illustrated in  FIG. 4 , the outer raceway  84  of the bearing ring  52  slips into the bore  86  of the skirt  66  of the coupling duct  50 . The outer raceway  84  of the bearing ring  52  is entrapped and secured in place between the outer, peripheral surface of the underside of the flange  64  and the bearing retainer cap  56  by means of eight screws  88  that extend upwardly through openings in the periphery of the bearing retainer cap  56  and into tapped bores in the skirt  66  of the coupling duct  50 . The inner bearing race  90  of the bearing ring  52  is held in position against the underside of the flange  80  of the rotatable tube  54  by the spacer ring  58  and the retaining ring  60 . 
   Within the coupling  42  the radially projecting flange  64  of the stationary coupling duct  50  and the radially projecting flange  80  of the rotatable tube  54  meet in a face-to-face interface. The raised rings  68  on the underside of the flange  64  project downwardly into the annular grooves  82  in the upwardly facing surface of the flange  80 . The rings  68  do not fit tightly into the grooves  82 , however, as the rotatable tube  54  must be free to rotate relative to the stationary coupling duct  50 . Rather, and as best illustrated in  FIG. 4A , the flanges  64  and  80  are configured to define a tortuous, radial path through which air must pass to escape across the face-to-face interface between the flanges  64  and  80 . As a consequence, very little pressure is lost and very little air flows radially outwardly between the stationary and rotatable parts of the coupling  42 . 
   As best illustrated with reference to  FIGS. 1 and 2  of the drawings, the thrust air jet nozzles  44  rotate the air knife  18  about the longitudinal axis  30  and sweep the linear band or swath  36  in a circular path over each of the printed circuit boards  14  passing therebeneath on the conveyor  16 . The rotation of the air knife  18  above the conveyor belt  16  provides an air flow  12  that does not merely impinge upon the printed circuit boards  14  in nearly a linear band  36 , but rather an air flow that is directed at the articles  14  from many different directions as they are carried past the location of the air knife  18 . The direction of air flow at the printed circuit boards  14  from multiple directions as the circuit boards  14  move past the air knife  18  results in far fewer blind spots and much more efficient cleaning and drying of parts moving past the air knife  18 . 
   The same principle of operation can be employed if an air nozzle manifold is substituted for the air knife  18 . For example,  FIG. 6  illustrates an air nozzle manifold system  118  that may be substituted for the air knife  18 . Like the air knife  18 , the air nozzle manifold system  118  has an elongated, tubular air distribution enclosure  120 , closed at both ends  122  and  124 . The air nozzle manifold system  118  also has an upwardly projecting neck  78  that defines a central inlet opening  28  equidistant from the ends  122  and  124  and which may be coupled to the rubber sleeve  74  and secured thereto by a hose clamp  76  in the manner illustrated in FIG.  2 . Unlike the air knife  18 , the air nozzle manifold system  118  does not emit air from a single, longitudinal slot but rather from a plurality of outlet nozzles  134 . At least one of the outlet nozzles  134  is located at each of the closed ends  122  and  124  of the air distribution enclosure  120  in the embodiment of FIG.  6 . There are also interior outlet nozzles  134  laterally spaced and located between the end outlet nozzles  134 . Thus, the air distribution enclosure  120  directs air onto passing articles  14  along a linear band, much like the band  36  shown in  FIG. 2 , that is rotated over a circular area by the thrust nozzles  44 . 
     FIG. 7  illustrates another embodiment of an air nozzle manifold system  218  that employs only a pair of outlet nozzles  234  at its laterally separated ends. Like the other embodiments of the invention, the air nozzle manifold system  218  includes a central, upwardly projecting neck  78  centered on the longitudinal axis  30  midway between the opposing ends  232  and  234  of the air distribution enclosure  220 . 
   Undoubtedly, numerous variations and modifications of the invention will become readily apparent to those familiar with air knives and air nozzle manifolds utilized to dry or clean passing parts or other objects. For example, while the thrust nozzles  44  illustrated have internal valves that may be adjusted to vary the force of the air jets emitted that rotate the air knife or air nozzle manifold, thrust nozzles of fixed dimensions and configurations can be utilized as well. In addition, many different types of coupling systems may be utilized to joined the rotatable air knife or air nozzle manifold to the stationary air supply duct  40 . Also, other systems for reducing air pressure loss through the coupling may be employed. Accordingly, the scope of the invention should not be construed as limited to the specific embodiments depicted and described, but rather is defined in the claims appended hereto.