Abstract:
Apparatus and method for delivering single or multi-component material through a disposable delivery tube and atomizing the material into a spray pattern of substantially uniform dispersion. The apparatus includes a tubular manifold having an opening for receiving a disposable delivery tube with the exit end or nozzle of the delivery tube projecting out from the end of the manifold. A plurality of atomizer holes are formed in the end of the manifold surrounding the hole which receives the nozzle end of the delivery tube. A source of air under pressure is connected to direct air through the atomizer holes. An air cap is mounted to the manifold to direct air passing through the atomizer holes about the nozzle of the delivery tube to atomize the delivered material into a uniform spray pattern without the material coming into contact with either the manifold or the air cap.

Description:
This application is a continuation of Application Ser. No. 09/451,323, filed Nov. 30, 1999, now U.S. Pat. No. 6,250,567 the entire content of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of single and multi-component spray systems, and specifically to apparatus and methods for delivering a single component or a mixed multi-component material through a disposable delivery tube and atomizing the material into a spray pattern of substantially uniform dispersion where the atomization occurs without any contact between the material and the spray apparatus thereby preventing clogging of the spray apparatus. The invention also covers a method for introducing a single component material or a multi-component material through a disposable delivery tube and applying air pressure to the material as it exits the delivery tube to atomize the material into a spray pattern of substantially uniform dispersion. 
     2. Description of Related Art 
     Multi-component materials usually consist of two or more components. These components are shipped and stored separately until the time of application. Then the components must be mixed together at their specified proportion ratio. Once properly mixed, the material can be applied using conventional methods such as air spray, airless spray, dispensing or extrusion, or metering. Typically, multi-component material consist of a base material and a catalyst, or a resin and a hardener, and once mixed, these materials usually cure rapidly. Usually, it is important that the two or more materials be well mixed together in a specific proportion which is referred as a mix ratio. 
     In conventional systems, because the mixed material passes through the internal passageways in the spray apparatus when the spraying stops, the mixed material quickly cures within the internal passageways causing clogging. This necessitates that the user must remove the spray tip and clean the atomizer passageways and outlets or flush it with a cleaning solvent which generates potential disposal problems. In addition, in the prior art spraying apparatus and processes for spraying a single component material, the material passes through the internal passageways of the spray apparatus before it is atomized, thereby leaving the nozzle subject to clogging when the spraying is stopped. 
     SUMMARY OF THE INVENTION 
     This invention relates to an apparatus and methods for spraying a single component material or a multi-component material in a manner such that there is no physical contact between the material and the internal passageways of the spray assembly. The apparatus of this invention includes a tubular manifold having a first longitudinal opening partially therethrough of a first diameter for receiving a portion of a disposable material delivery tube having an inlet end of a first diameter and a stepped exit end of a plurality of decreasing diameters. The manifold has a smaller second longitudinal opening therein formed coaxially with the first longitudinal opening for receiving in a close fitting relationship one of the smaller stepped ends of a delivery tube so that the distal end or tip of the delivery tube projects a predetermined distance from the end of the manifold. A plurality of atomizer holes are formed in the distal end of the tubular manifold symmetrically about the second longitudinal opening. The manifold has an air passageway therethrough for connecting to a source of pressurized air. 
     An adjustable air cap is mounted to the distal end of said manifold for directing air passing through the atomizer holes toward the exit end of the delivery tube at a desired spray angle to atomize the material into a substantially uniform conical pattern for spraying onto a surface. The air cap is designed so that the tip of the delivery tube is substantially flush with the end of the air cap. The manifold guides and positions the delivery tube so that the tip is concentrically mounted within the air cap allowing air to uniformly flow past the tip. When the spraying of the material is concluded, the spray apparatus does not become clogged due to the fact that the sprayed material is not in contact with any internal passageways in the spray assembly. If the sprayed material sets, the disposable delivery tube can be discarded and a new one inserted for another spraying operation. Due to the elimination of the necessity to clean the spray nozzle after each material application, the need for cleaning solvents is eliminated. This makes the subject apparatus and method environmentally friendly. 
     The methods of this invention include introducing a material under pressure into an inlet end of a delivery tube and out through an outlet end or tip of the delivery tube. A symmetrical pattern of air under pressure is introduced into the material as it exits from the tip of the delivery tube. The air is introduced at a predetermined distance back from the tip of the delivery tube. The spray angle of the pressurized air is adjustable to atomize the material into a conical spray pattern of substantially uniform dispersion. 
     The subject invention is applicable to spraying any kind of material, but particularly those that are rapid curing and/or are difficult to clean upon drying or setting. The materials that can be sprayed in accordance with the principles of this invention include, without limitation, paint, glue, stucco, mastics, adhesives, sealants, foams, undercoating and other coatings. 
     It is the primary object of the present invention to provide a spray apparatus wherein the cleanup of the spray assembly is eliminated by using a disposable internal delivery tube and not having any spray assembly passageways to clean. 
     Another object of the present invention is to provide a more precisely controlled spray pattern providing a more uniform application. 
     Another object of the present invention is to provide improved transfer efficiency. 
     Further aspects of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. It should be understood, however, that the detailed description and the specific examples while representing the preferred embodiments are given by way of illustration only. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall view of a portion of spray apparatus illustrating the metering and mixing of two chemical components which are sprayed in accordance with the principles of this invention. 
     FIG. 2 is an exploded view of a material delivery tube and spray nozzle assembly including a tubular manifold and atomizer air cap in accordance with the principles of this invention. 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG. 1 illustrating the inside of the tubular manifold and air cap of the subject invention. 
     FIG. 4 is a cross-sectional view of a portion of the tubular manifold illustrating the combination of threads used to guide and secure the delivery tube to the manifold. 
     FIG. 5 is a perspective view of the air cap of the present invention. 
     FIG. 6 is a representation of the circular spray pattern illustrating the symmetrical shape and substantially uniform size and shape of the spray droplets achieved in accordance with the present invention. 
     FIG. 7 is a representation of the pattern of prior art spray apparatus showing the irregular, somewhat elliptical cross-section of the spray pattern and the non-symmetrical droplet size achieved by conventional methods and apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is of the best presently contemplated modes of carrying out the subject invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limited sense. 
     Referring to FIG. 1 there is shown a two chemical component spray system of the type typically used to spray a multi-component material such as polyurethane. This system introduces the resin and the hardener into a delivery or static mixing tube  14  having flights or elements therein which mix a plurality of chemical components under pressure. The exit end of the static mixing tube  14  passes through a spray assembly  16  described more fully hereinafter. An air line  17  provides air into the spray assembly  16  to atomize the mixed chemical components to form a uniform spray pattern  15 . The spray system is shown applying a polyurethane liner to a truck bed  20 . When a polyurethane elastomer is being sprayed, it becomes a solid in seconds after it leaves the spray assembly  16 . The delivery tube is disposable. Thus a new tube  14  can be inserted with minimal downtime and no cleanup of the spray assembly  16 . 
     Referring to FIG. 2 there is shown an exploded view of the spray assembly  16  and the static mixer  14  and air line  17 . The spray assembly  16  includes a tubular air manifold  18  having an internal longitudinal passageway  19  formed therein (FIG.  3 ). The diameter of the internal passageway  19  is partially threaded so that the outer diameter of the static mixer  14  can be threaded into the manifold forming an air tight fit. A plurality of holes  21  are symmetrically formed in the end of the tubular manifold  18  to provide air under pressure which is uniformly dispersed to atomize the mixed multi-component materials. An air inlet  22  is provided in the tubular manifold  18 . The size and positioning of the air inlet is critical as described hereinafter for optimum atomization and uniform dispersion. An elbow  23  has one end connected to the air inlet  22  and the other end connected through a coupler assembly  24  to a fitting  15  of an air line  17 . An atomizer air cap  26  is threaded onto the end of the manifold  18  to provide precise control of the spray pattern. 
     Referring to FIG. 3, there is shown a cross-sectional view of the air manifold  18  and the air cap  26 . The static mixer or delivery tube  14  has a stepped end with a plurality of steps which decrease in diameter down toward the outlet  30 . In FIG. 3, there are four steps  32 ,  33 ,  40  and  46  shown from the main diameter down toward the exit end  30 . The manifold  18  has a first longitudinal passageway  19  which is internally threaded at the inlet end  35  to engage the static mixing tube  14 . The first step  32  and second step  33  of the delivery tube  14  are each smaller in diameter than the diameter of the passageway  19  to provide an annular air chamber  36  through which air flows from the air inlet  22  which is connected to a source of pressurized air. The geometry of steps  32  and  33  of delivery tube  14  is used to create the desired air accumulation chamber  36  which helps maintain constant air pressure and volume at the ideal level. If desired, a delivery tube or static mixer tube may not be stepped but the manifold has to be designed to have the desired size and shape to provide the required air chamber to give the proper distribution of air therethrough. The end  37  of the manifold  18  has a plurality of holes  21  symmetrically formed about the opening  54  in the manifold  18 . The holes  21  communicate with the annular air chamber  36  so that air passing through the air inlet  22  into the annular chamber  36  is directed outwardly through holes  21 , where it is directed by the cap  26  at a prescribed angle toward the exit end  30  of the static mixer  14 . The size and positioning of the air inlet  22  is important. The ratio of the surface area of the air inlet hole  22  to the combined areas of the outlet holes  21  is predetermined for optimum performance. It has been found that a ratio of approximately 1:4 is the optimum for spraying polyurethane. Other materials may require a different ratio which has to be determined empirically. 
     The spray assembly  16  is designed so that when the flow of material is stopped there are no materials left within any of the spaces of the spray assembly. The air cap is designed so that the exit end  30  of the delivery tube is substantially flush with the end of the air cap  26  for optimum performance. However, the design can be modified so that tip  30  slightly projects or is slightly recessed from the end of the air cap in order to alter the spray pattern. The atomizer air cap is threaded internally at  41  to engage the complimentary threads  42  formed on the exterior of the manifold  18 . The atomizer air cap  26  has a spring loaded ball assembly  43  inserted into an opening  44  which bears against the end face of the manifold  18  which has a slight depression  50  (shown in FIG. 2) therein. This serves to hold the air cap  26  in the precise position to which it is rotated for maintaining the desired spray angle thereby assuring stability of the spraying geometry. If desired, by rotating the atomizer air cap,  26 , the spray angle can be changed. The spray pattern can also be changed by adjusting the air pressure. 
     Referring to FIG. 4, there is shown an enlarged view of the inlet end of the atomizer manifold  18 . A plurality of trapezoidal guide threads  51  are used to guide the delivery tube  14  coaxially into position within the manifold  18 . The flats  52  of the threads  51  are formed to close tolerance to hold the outer diameter of the delivery tube so that the tip  30  is precisely centered within the hole  45  in the air cap as shown in FIG.  3 . The guide threads  51  guide the tube  14  as it is inserted into the manifold  18  to center the tube properly. A plurality of sharp threads  53 , which are cutting threads, cut into the tube to form close fitting relationship between the manifold and the tube with the tip  30  being centered within the opening  45  in the air cap  26 . This unique arrangement of threads in the manifold  18  insures the precise positioning of the exit end  30  of the delivery tube within the center of the hole  45  in the air cap  26 . 
     Referring again to FIG.  3  and FIG. 5, the air cap  26  has an opening  45  which is rounded and which is precisely dimensioned to be spaced a predetermined distance away from the outer diameter of the fourth step  46  of the static mixer  14 . A conical surface  47  is formed on the inside of the air cap  26 . As the cap  26  is rotated, the spray angle will change thereby determining the pattern which is sprayed. The spacing between the opening  45  in the air cap  26  and the end  46  of the static mixer tube, in conjunction with the displacement between the end  30  of the static mixer  14  and the end surface  52  of the air cap  26 , controls air velocity and volume and provides the ideal spray pattern. The outside diameter  48  of the conical portion  47  of the air cap  26  is slightly larger than the outer diameter of the pattern of symmetrical holes  21  so as not to block the flow of air. The diameter of the opening  45  is selected to provide the optimum predetermined spacing between the tip  30  of the delivery tube  14  and the air cap  26 . 
     When the spray gun stops dispensing the mixed material, no material is left in any of the passageways in the spray assembly  16 . The only material left is in the static mixer tube  14 . Thus, when a new operation is started, the static mixer tube  14  may be replaced and no further cleaning of the spray assembly  16  is necessary. This saves a considerable amount of time in any kind of spraying operation. 
     Referring to FIG. 6, there is shown a spray pattern generally designated as  50 . The pattern shows a plurality of substantially uniform droplets  51  which are all substantially circular and symmetrically positioned within the circular spray pattern provided by the subject invention. This spray pattern allows the operator to provide a more uniform application. It also results in less over spray or waste material and improve ease of application. 
     Referring to FIG. 7, there is shown a conventional prior art pattern generally designated as  55  which is irregular in shape forming somewhat of an ellipse and having non-symmetrical droplets of different sizes  56  and  57 . 
     In use, once the application, of polyurethane or other multi-component material is started, the air atomizer cap  26  is rotated to achieve the desired spray angle. This rotation once set will be maintained by the spring loaded ball assembly  43 . When the application of the polyurethane to a truck bed or any other surface is completed, the spray gun trigger is released stopping the flow of air and the mixed material. Due to the quick curing times of the polyurethane, any mixed material within the static mixing tube becomes solid relatively quickly. However, because none of the mixed material is in any of the other passageways of the spray nozzle, the nozzle does not become clogged and it does not have to be cleaned or flushed with a cleaning solvent. Due to the elimination of the need to clean the spray assembly after each material application, it likewise eliminates the need for cleaning solvents used in the cleaning process thereby making the apparatus more environmentally friendly. The use of the subject invention also improves transfer efficiency resulting in less overspray and reduced air flow, again reducing waste and improving ease of application. Transfer efficiency has two components; the first is how much overspray you have, and the second is how much air do you need to atomize the material. Greater transfer efficiency requires a smaller size air compressor. Further, greater transfer efficiency results in more sprayed material going onto the work surface and less material being wasted. The subject invention requires less air flow in cubic feet per minute than prior art assemblies because of the transfer efficiency of the design of the subject invention. 
     The unique design of the atomizer manifold  18  and the atomizer spray cap  26  allows precise control over the sprayed material. The precision alignment between the static mixer tube  14  and the manifold  18  which typically are ±0.0015 inches provides very precise alignment of the end  30  of the static mixer  14  relative to the atomizer air cap  26 . This precise control between the static mixer tube and the air cap  26  helps determine the atomization and spray pattern. 
     While the invention has been described with respect to spraying a multi-component material, it is also applicable to spraying a single material with or without mixing. Although the present invention has been described in terms of certain preferred embodiments and exemplified with respect thereto, one skilled in the art will readily appreciate that various modifications, changes, omissions and substitutions may be made without departing from the spirit and scope thereof.