METHOD OF INTERMITTENTLY SPRAYING POWDER AND A GUN THEREFOR

Abstract: Method of intermittently spraying solid particulate powder and gun therefor. In the work of intermittently spraying powder, a mixture of the powder and air continuously and constantly supplied from a powder pump which is a solid particulate powder supply source is spouted from a gun nozzle and during the interruption of the work, the mixture of the powder and air is discharged out of a gun by an air ejector provided in the gun through a bypass branching off from the path from which the mixture is spouted, thereby interrupting the spout of the mixture from the gun nozzle and by the intermittent operation of the air ejector, intermittent spraying of the solid particulate powder spouted from the gun nozzle is effected.

Description: S P E C I F I C A T I O N Method of Intermittently Spraying Powder and a Gun Therefor This invention relates to a method of inter¬ mittently spraying solid particulate powder and a gun therefor. Methods heretofore used as methods of inter- mittently applying solid particulate powder are of the electrostatic application type, the screen printing type, the roll type, the sprinkling type, etc., but any of these has suffered from the following disadvantages: (1) unclear outline of the applied pattern; (2) adherence of the solid particulate powder to unnecessary portions; (3) the use of masking and adherence of the solid particulate powder onto the masking; (4) reduced productivity; and (5) cumbersomeness of maintenance. Even the electrostatic application type which is said to be most excellent of the above-mentioned types has not been free from the disadvantage (1), that is, unclear outline of the applied pattern. Particularly in cord-like or band-like intermittent application, unclear lines of dissection have been a fatal problem to the end products. Description will hereinafter be made of the reason why such unclearness occurs . The sequence of an electrostatic type apparatus for intermittently spraying solid particulate powder in accordance with the prior art is roughly shown in Figure 10 of the accompanying drawings. Solid particulate powder air- transported by a powder pump 93 mounted on a tank 92 which is a supply source of solid particulate powder passes through a transport pipe 94 and arrives at a gun 81 through a distributor 95. The solid particulate powder is spouted from a nozzle 85 on the gun 81 and effectively applied onto a surface P to be coated under the action of a corona pin 89. However, the application pattern thereof, particularly in the case of the intermittent spray application, as described above, has been unclear in lines of dissection. In the above case, intermittent spraying has been accomplished-by intermittent operation of the powder pump 93 mounted on the tank 92. Consequently, when the spraying is to be interrupted, the powder pump 93 is stopped. Accordingly, the air-transport of the solid particulate powder is also stopped and the solid particulate powder is deposited on the bottom of the transport pipe 94. In that state, when the spraying of the solid particulate powder from the nozzle 85 is to be re-started, the powder pump 93 is re- operated to air-transport fresh solid particulate powder from the tank. Thereupon, the old solid particulate powder deposited in the transport pipe 94 is air-transported with the fresh solid particulate powder, arrives at the gun 81 and is sprayed from the nozzle 85. As a matter of course, the density of the solid particulate powder sprayed becomes higher. Consequently, the application pattern fluctuates. When the spraying is to be interrupted, the powder pump 93 (which is usually an air ejector) is again stopped, but since the supply of the solid particulate powder is by way of the relatively long transport pipe (or hose) between the powder pump and the nozzle as seen in Figure 10, the response thereof is slow and the frequency of intermission is limited to 30 times/ min. at greatest and accordingly, clean cut cannot be accomplished and the breaks in the application pattern leave fine trails. In the above-described manner, the lines of dissection in cord-like or band-like inter¬ mittent application have become unclear. There is also a conventional method of effecting intermittent spraying by means of a pinch valve. Reference is had to Figure 11 of the accompanying drawings. On an air-transport pipe 114, a pinch valve 116 is provided immediately before a gun 101. The pinch valve 116 is such that the air pressure is increased or decreased from the outside of a resilient tube, that is, the resilient tube is pushed or released, to thereby open or close the interior thereof and open or close the path of the solid particulate powder passing through the tube. When this valve is closed, it is usual from the structure thereof that the valve is closed while holding some solid particulate powder therein. Accordingly, it is difficult for the valve to be fully closed and even when closed, some air may flow. When the spraying is re-started, the solid particulate powder held in the valve is forced out with newly fed solid particulate powder and is sprayed from the nozzle 105 and therefore, the density of the solid particulate powder sprayed becomes higher. That is, in the breaks in the intermittent spraying, the application pattern of the solid particulate powder fluctuates and it is difficult to obtain clear lines of dissection. As described above, in any of the prior-art systems, it is difficult to precisely accomplish the opening-closing of the air-transport of solid particulate powder, and the response time by the signal of inter- mission is slow and accordingly, unclear breaks in the cord-like or band-like application pattern by intermittent spraying has been unavoidable. As described above, in the intermittently coated cord or band produced by the prior-art method of intermittently spraying solid particulate powder and the gun therefor, the frequency of intermission has been small and lines of dissection have been unclear. It is the object of the present invention to provide a method of increasing the frequency of intermission and making lines of dissection clear in the cord-like and band-like intermittent spraying of solid particulate powder and to provide a gun therefor. The gist of the present invention resides in a method of intermittently spraying solid particulate powder wherein in the work of intermittently spraying solid particulate powder, a mixture of the solid particulate powder and gas continuously and constantly supplied from a powder pump which is a solid particulate powder supply source is spouted from a gun nozzle and during the interruption of the work, the continuously and constantly supplied mixture of the solid particulate powder and gas is discharged out of a gun by an air ejector provided in the gun through a bypass branching off from the path"from which the mixture is spouted, thereby interrupting the spout of the mixture from the gun nozzle and by the intermittent operation of the air ejector, intermittent spraying of the solid particulate powder spouted from the gun nozzle is effected, and a gun therefor. Figure 1 is a front cross-sectional view illustrating a gun unit according to the present invention. Figure 2 is a front cross-sectional view of a first Modification of the gun of Figure 1. I Figure 3A is a front cross-sectional view of a second Modification of the gun of Figure 1. Figure 3B is a side cross-sectional view of the second Modification. Figure 4 is a cross-sectional view of the electrostatic application nozzle of the Japanese utility model application as attached to the gun of the present invention. Figure 5 is a front view of the multi-gun nozzle unit of the present invention. Figure 6 is a block diagram of an apparatus using the gun of the present invention. Figures 7A and 7B are plan views showing the patterns of intermittent cord-like coating provided by the gun of the present invention. Figures 8A and 8B are plan views showing the patterns of intermittent band-like coating provided by the gun with a flat nozzle according to the present invention. Figures 9A and 9B are plan views showing two examples of the pattern of multi-streak coating provided by the multi-gun unit of the present invention. Figure 10 is a block diagram of an intermittent solid particulate powder application apparatus using the powder pump of the prior art. Figure 11 is a block diagram of an intermittent solid particulate powder application apparatus using the pinch valve of the prior art. The structure of a gun according to the present invention is shown in Figure 1. In the interior of the gun 1, there is provided a spout path 2 for a mixture PA of solid particulate powder and air (hereinafter simply referred to as the mixture) As is conventional, a connector 8 to a supply hose (or pipe) is attached to the entrance of the path 2 and a nozzle 5 is attached to the other end of the path 2. The differences from the prior art are that there is provided a bypass 3 branching off from the spout path 2, that the bypass 3 is connected to an eject path 4 which is also provided in the gun 1, that an air ejector nozzle 6 is provided on the eject path 4 and that the end 6T of the air ejector nozzle is located substantially at the point of intersection with the bypass 3. In Figure 1, the . spout path 2 and the eject path 4 are parallel to each other and the directions of these paths are opposite to each other, but alter¬ natively, as shown in Figure 2, the two paths may be parallel to each other and only the directions thereof may be opposite to each other (a first Modification), or as shown in Figures 3A and 3B, the two paths may be provided not in parallelism to each other, but with an angle "α" formed therebetween (a second Modification). In Figures 3A and 3B, the angle " " is 90 ° . Also, a nozzle provided with a charging electrode for electrostatic spraying may be used as the nozzle of the gun. Figure 4 shows a side cross- sectional view of a gun having attached thereto a nozzle for electrostatic spraying of solid particulate powder disclosed in the Japanese utility model application No. 12535/1986 filed on January 31, 1986. In this nozzle, a charging electrode 28 is embedded in the body of the nozzle 27 and therefore, it happens less frequently that as in the prior art , solid particulate powder adheres to the electrode 28 to thereby diminish the corona discharge current. Although the nozzle 5 is of the ordinary type, i.e., the circular nozzle hole type, a nozzle of the flat type (the .slit type) may also be used. Also, a plurality of such circular nozzles or flat type nozzles may be arranged in one or more rows as shown in Figure 5 to provide a so-called multi-gun nozzle unit and a transmitter device or a control unit for causing the plurality of nozzles to effect spraying operation discretely can be connected to the nozzle to thereby provide a multi-pattern applying apparatus. Figure 6 is a block diagram of a powder intermittently spraying apparatus using the gun according to the present invention. A solid particulate powder supply tank 62 is of the fluidizing type (the floating type) and is provided with a vibrating device 78 and a blower 79. An air ejector 63 is provided as a powder pump, and air is supplied to an air supply pipe 75 for the air ejector from a blower 77 through an air heating device 76. An air-transport pipe 64 for solid particulate powder is connected to a gr.n 51 through a distributor 65. An air generator 73 for the air supplied to the air ejector provided within the gun and an intermittent air opening-closing valve 72 for the supplied air are provided. The valve 72 is connected to a timer 74. The discharge side of the air ejector is connected to a powder recovery device 177 including an air bag filter by a transport pipe 175. A charging electrode 59 for electrostatic coating, and which is connected to a high voltage source 60, is provided on the gun nozzle 55. The operation of the gun will now be described. Reference is had to Figure 1. In the gun 1 for intermittently spraying the solid particulate powder, when the mixture PA of solid particulate powder and air is supplied to the spout path 2 in the gun 1, the mixture PA passes through the spout path 2 and is sprayed (PA- ) from the nozzle 5 attached to the distal end of the path 2. Subsequently, when air A is supplied into the gun 1 by the opening of the inter¬ mittent air opening-closing valve 72 through the air generator 73 provided outside the gun 1, the air is spouted (A' ) from the air ejector nozzle 6 and, since the end 6T of the air ejector nozzle 6 is located substantially at the point of intersection with the bypass 3 from the spout path 2, the air sucks the surrounding gas with the aid of the action of the air ejector and is sent in the direction of delivery of the ejector. Said sucking action also reaches the bypass 3 and the spout path 2 for solid particulate powder and thus, all the mixture PA_ of the passing solid particulate powder and air is sucked and discharged out of the gun 1. That is, the spout of the solid particulate powder from the nozzle 5 is interrupted. Subsequently, when the intermittent air opening-closing valve 72 is closed and the supply of the air A to the air ejector is interrupted, the aforementioned sucking action by the air -.ejector is interrupted and therefore, the aforedescribed original spout or spray of the solid particulate powder is restored and effected through the nozzle 5. That is, the intermission of the spout of the solid particulate powder from the nozzle 5 is accomplished by the intermission of the supply of the air to the air ejector. Where the nozzle 5 attached to the gun 1 is of the ordinary circular type, the discontinuous cord-like application pattern thereof is as indicated in Figures 7A and 7B. Also, the band-like discontinuous patterns in a case where a nozzle of the flat type (the slit type) is used are shown in Figures 8A and 8B. As seen in this figure, lines of dissection of inter- mission appear clearly. Where a multi-nozzle is used, each nozzle can be operated singly to cause various patterns to appear as shown at "G" and "H" in Figures 9A and 9B. Description will now be made of the operation of a solid particulate powder intermittent spray applying apparatus comprising chiefly the gun of the present invention having the various nozzles attached thereto. Reference is had to Figure 6. The solid particulate powder tank 62 is of the floating type and the vibrating device 78 is also added to achieve uniformity of the degree of dispersion of the solid particulate powder_ In Figure 6, the air supplied to the air ejector by the powder pump 63 attached to said tank is hot air heated by the air heating device 76. The mixture of solid particulate powder and gas pumped by the powder pump 63 is supplied continuously and constantly to the gun 51 of the present invention through the air transport pipe 64 and through the distributor 65 and is sprayed onto a substrate 80 from the nozzle 55. When the spray is to be interrupted, the intermittent air opening-closing valve 72 for the air ejector which supplies the air into the gun 51 - 12 - is opened to supply the air to the air ejector in the gun, and the mixture of solid particulate powder and gas passing through the gun is sucked by the action of the ejector and discharged out of the gun 51, and it is delivered into the recovery device 177 through the air transport pipe 175. Thus, the spraying of the solid particulate powder from the gun can be intermittently accomplished by the intermittent operation of the intermittent air opening-closing valve for the ejector in the gun. The data experimented by the above-described apparatus will be given below. Solid particulate powder Nylon 12, polyethylene handled and epoxy resin Powder pump Air ejector Air pressure of the powder 0.3 kg/cm 2 pump Transport pipe Powder hose 3/16 Length from distributor 2,000 mm to gun Gun nozzle diameter 2.4 mmø Gun ejector air pressure 0.7 kg/cm Applied electrostatic 17 KV voltage Conveyor speed 50 m/min. Frequency of intermission 1,500 times/min. (Note) The frequency of intermission by the prior-art powder pump (air ejector) on the solid particulate powder tank side was 30 times/min. Max. According to the method and gun of the present invention, in the intermittent solid particulate powder spray applying work, cord-like or band-like discontinuous coating of solid particulate powder having clear and uniform lines of dissection is obtained under high¬ speed intermittent application of 30 - 1,500 times/min., and band-like coating of solid particulate powder in a clear geometrical pattern is provided by the multi- type gun nozzle of the gun.

Claims: C L I M S 1. A gun for intermittently spraying solid particulate powder, comprising: a spout path for passing therethrough a mixture of powder and air to be sprayed; an ejector path having an air ejector therein, and a bypass connecting said two paths , whereby said air-ejector is intermittently operated to bypass said powder so that intermittent spraying may be effected. 2. A gun according to claim 1, further comprising a spray nozzle connected to said spout path. 3. A gun according to claim 1, wherein the nozzle is a flat spray nozzle. 4. A gun according to claim 1, wherein said gun is for electrostatic application. 5. A gun according to claim 1, further comprising a plurality of nozzles arranged in a framework. 6. A method of intermittently spraying solid particulate powder, characterized in that, when the solid particulate powder is to be sprayed from a spray nozzle, a mixture of the powder and air continuously and constantly supplied by powder pump is spouted through a spout path in a gun and a nozzle, and when spraying of the powder is to be interrupted, said continuously and constantly supplied mixture is discharged out of the gun through a bypass branching off from the spout path in the gun and an ejector path which is connected thereto and in which an air ejector nozzle is disposed, and by said air-ejector being inter¬ mittently operated, intermittent spraying of the powder from said nozzle is effected. 7. A method according to claim 6, characterized in that the frequency of intermission is 30 times/min. or more.

Inventors: WATANABE TAKASHI, WATANABE, TAKASHI
Applicants: NORDSON CORP, NORDSON CORPORATION
Application year: 1987
Main classification: B05B7
IPC codes: B05B5, B05B7, B05B12, B05D1