Patent Publication Number: US-3875898-A

Title: Fluidized bed apparatus for coating elements

Description:
United States Patent [1 1 Braden l l FLUlDlZED BED APPARATUS FOR COATING ELEMENTS {75] Inventor: Denver Braden. San Diego. Califv [73] Assignee: lllinois Tool Works Inc.. Chicago.  
 lll.  
  221 Filed: Jan. 25. 1974 2| Appl.No.:436,412  
 [52] US. Cl 118/421; ll7/21 [51] Int. Cl. BOSc 3/00 [58] Field of Search ll8/42l; ll7/2l [56] References Cited UNlTED STATES PATENTS 3.039.432 bll&#39;JoZ Boutillicr et al.. ll8/42l 3.|o8.885 2/l965 Weiss [Hi/421 3.56639] 3/l&#39;-)7l Koch ll8/4Zl 3.827.400 X/l974 Grenfell ll8/4&#39;ll 3.834.927 9/1974 Putney ll&#39;l/Zi Primary E.\&#39;amincr-Louis K. Rimrodt AA&#39;ATA&#39;IHHI I-.&#39;.\&#39;zm|im&#39;rSteven Hawkins I57] ABSTRACT The present invention involves the application of a protective coating on an element. such as an electrical component having connection leads extending from it, wherein the element is preheated and is then passed to a fluidized bed stage in which a powder of coating material is applied to the heated surface of the component or element to be coated which causes the coating material to coalesce on the body of the component. In the present invention the component is located at a fixed position and a movable fluid bed reservoir is dipped into a larger supply reservoir to be replenished with powder. The movable reservoir is then brought to the heated component so as to bring the powder into contact with the component to be coated. In order to maintain a precise uniform height which will coat only a predetermined portion of the component and will not extend unnecessarily over the lead of an electrical component. the movable bed fluid reservoir is vibrated in a predetermined manner.  
 9 Claims. 4 Drawing Figures PATENTEUAPR 8l975 PATENTEDAPR BIBYS 1875,8953  
 O O O O saw 3 OF 3 0 OOO FLUIDlZED BED APPARATUS FOR COATING ELEMENTS BACKGROUND OF THE INVENTION In order to protect electrical components, such as capacitors. resistors. etc., and other elements from moisture and other destructive conditions it is often desirable to coat the element with a protective coating layer. In the coating of an electrical component in this manner it is desirable that the coating extend over the body of the component but not of the connection leads to any substantial extent since this could prevent proper electric assembly and connection of the electrical component.  
  The coating of an electrical component with a synthetic resin material in the form of pulverulent granules that coalesce on a preheated component is a known manner of achieving such a coating. The electrical component is first heated and is then brought into contact with a suspension ofa cloud&#34; of powder particles so that the heat from the component melts or sinters the resin granules that it comes into contact with thereby causing the surface of the component to be continuously coated with a layer of this material. The coated component may then be brought to a second heating stage where the coating can be cured. A general background on coating materials. operating parameters and other considerations that should be taken into account in the design of such a system can be found in US. Pat. No. 2.844.489 issued in the name of Erwin Gemmer. and in the references cited therein.  
  There have been several disadvantages of prior coating systems which limited their usefulness. In some prior systems the coating was formed by pouring the powder material downwardly onto the component. With this method an excess amount of material was used: and. in addition. the material could be blown around the machine thereby making for a messy and a possibly dangerous to health condition. Fluidized bed devices have also been constructed in which a gas inlet is connected to the bottom of a tank with the coating powder in the tank being separated from the gas inlet by a porous member which allows a distributed flow of gas to pass upwardly through a porous membrane to the powder. The distributed gas flow provides a suspended dense phase or cloud of particles which exhibit liquidlike characteristics and form a definable upper boundary zone. The particles are prevented from entering the gas inlet portion of the apparatus by the porous member. However. even in this type of coating machine special component handling devices were often required so that each component that was coated had to be specially handled in order to achieve a satisfactory coating on it.  
  In order to achieve maximum efficiency in the formation of a coating of resinous material on an element it is desirable that a number of components be brought to the coating station at one time. and that each component be held at a fixed location in the coating stage of the system so that they do not have to be subjected to a particular type of motion while suspended in the flu idized bed. This is particularly desirable when the component to be coated is extremely small. such as a capacitor of the ceramic chip type. and the handling of each individual component becomes extremely difficult and most of the time it is impractical.  
  The present invention is advantageous in that a coating process is achieved by utilization of a fluid bed apparatus which has a large supply reservoir which is separated from a first gas inlet by means of a first porous member and a smaller movable active reservoir which is immersed into the larger reservoir when replenishment of the amount of particles in the smaller reservoir is needed. The movable reservoir has its own gas inlet and porous separation member, and after it is refilled the movable reservoir is raised so that the cloud of suspended particles in the movable reservoir surrounds one or more electrical components that are suspended above the two reservoirs. An accurately located free upper surface level which overlies components that are to be coated is obtained by vibrating the movable reservoir in a manner such that both horizontal and vertical vibrator components are present.  
  It is. therefore, an object of the present invention to provide for the suspension of a mass of powder particles in a vibrated reservoir whereby the suspended particles coalesce on heated components that are immersed in the suspended particles so as to form an accurately controlled protective coating layer.  
  It is another object of the present invention to provide for coating an element with suspended powder material in an active reservoir that coalesces upon coming into contact with the heated element by immersing the active reservoir into a larger supply reservoir. wherein each of the reservoirs has its own gaseous input line and porous separation members. and the active reservoir is periodically replenished with a new supply of powder and is then transported adjacent the component to be coated and is preferably vibrated in a manner which maintains an accurate free upper surface level of powder particles which overlie the portion of the component that is to be coated so as to provide a precise coating boundary.  
  Other objects and advantages of the present invention will become apparent upon to those skilled in the art upon consideration of the disclosure found herein.  
 DESCRIPTION OF THE DRAWINGS The invention is shown by reference to the following drawings. in which:  
  FIG. 1 is a perspective view of an apparatus which is constructed in accordance with the principles of the present invention;  
  FIG. 2 is a side cross-sectional view of the fluidized bed apparatus of FIG. 1;  
  FIG. 3 is an end cross-sectional view of the fluidized bed apparatus of FIG. 1; and  
  FIG. 4 is a side view of an electrical capacitor coated with the apparatus of FIGS. 1 through 3.  
 TECHNICAL DESCRIPTION OF THE INVENTION The present invention is shown by reference to the figures in which components 10 are to be coated with a protective coating and are mounted on a support rack 12 which is secured at its opposite ends to a pair of drive chains l4, 16 by means of the links 18, 20, respectively. The invention achieves a coating preferably of a dielectric material on the body of the component which is precisely controlled and which. in the case of electrical components of the radial lead type. does not extend over the leads to any substantial extent.  
  The components 10 are first heated in a preheat oven 22. The temperature to which the components I0 are heated in the preheat oven 22 is below the temperature at which the components 10 will undergo deleterious affects for the application for which they are intended, but is above the coalescent temperature of the powder particles. After the components I are heated in the preheat oven 22 they are passed to the fluidized bed stage 24. at which the powdered resinous coating mate rial is supplied in a fluidized dense phase or cloud which contacts the heated components and causes a coating to be formed on the components 10. If curing of the coating deposited in the fluidized bed stage 24 is desired. the component It) may then be passed to a curing oven 26 where the coating is cared to a desired state.  
  Some of the materials which may be used to produce the coating include resins that may be selected based on requirements such as mechanical strength. adhesion. cost. etc. Suitable resins which may be used may include epoxies. polyesters. polypropylenes. nylons. acrylics, vinyls. cellulose acetate butyrates. A resin mesh size of 80 or less is preferred for the present invention.  
  Referring to FIGS. I through 3. an embodiment of the invention is shown in which a fluidized bed coating stage 24 includes an elongated fixed supply reservoir 30 and an elongated movable active reservoir 32. The rescnoir 32 is periodically immersed into the fixed bed supply reservoir 30 when it is to be replenished with a new supply of powder from the supply reservoir 30. The supply reservoir 30 is closed at its bottom by means of a closure plate 34 which is secured to a flange 36 of a sidewall 37 of the rescri oir 30 by means of the bolts 38. An aperture 40 in the closure plate 34 receiies a threaded end of a gas input tube 42 which is locked into place by the nut 44 so that low pressure gas or air may be directed through the space 46 which is located just above the closure plate 34. A porous mem brane 48 is secured in place above the space 46 to per mit a distributed flow of gas upwardly into the reservoir area 30. The pores of the membrane 48 are sufficiently fine so that gas can flow upwardly. but sufficiently small so that suspended powder 50 in the reservoir 30 cannot pass downwardly through the membrane 48.  
  In order to support the reservoir 30 the closure plate 34 is secured to four elongated braces 52 which extend outwardly to the mounting blocks 54. 56 on the opposite ends of the fluidized bed stage 24. The braces 52 are secured to the blocks 54, 56 by the bolts 58. 60. respectively. The bottoms of the blocks 54, 56 are in turn welded or secured by other means to the support bar 62 which extends across the fluidized bed stage 24. The support bar 62 is secured at its opposite end to the fixed frame members 64. 66 by the bolts 68. 70. respectively. In this manner the fixed supply reservoir 30 is secured in place with respect to a fixed frame.  
  A pair of solenoid vibrators 72. 74 may be utilized to agitate the reservoir 30 in order to help maintain a suspension of the powder 50 at a desired level in the resci= voir 30. The vibrators 72. 74 may each have a fixed stator 76. 78, respectively. which are secured to the su port plate 62 by the bolts 80, 82 and a movable armature 84. 86. respectively. which are secured to the bot tom ot&#39;the closure plate 34. It has been found. however. that for many applications the solenoid vibrators 74, 72  
 are unnecessary.  
  By use of the present invention a number of components 10. such as electrical ceramic chip capacitor may be coated at the same time. The components 10 are brought to the fluidized bed stage 24 where they may be held stationary during the coating operation. No special movement or handling of the components 10 is required at the fluidized bed stage 24, and they may thus remain on the same support rack 12 as they pass through the preheating oven 22, the fluidized bed stage 24 and the curing oven 26. Another advantage of the present invention is that the amount of coating that is to be applied is precisely controlled and when electrical components are coated. no coating of the leads of the component will occur.  
  The manner in which the upper free surface level or boundary zone of powder. across which a marked change in particles occurs, is controlled with respect to the location of the component 10 as shown by reference to the movable reservoir 32. In order to replenish the reservoir 32, it is periodically immersed into the fixed supply reservoir 30 as shown in FIG. 3. The top 85 of the reservoir 32 is below the boundary zone or free upper surface level 87 when the reservoir is at its immersed position A. After being filled the reservoir 32 may be transported adjacent the component 10. as shown by the dotted line position B in FIG. 3. by a mechanism which will be subsequently described. In addition to moving the reservoir 32 up adjacent the component It). the reservoir 32 is agitated or vibrated so that the dense phase of particles 88 in the reservoir 32 will be confined along a relatively stable free upper surface level 89 which is located along a line which preferably is adjacent the top 85 of the reservoir 30 so that the coating does not extend to any great extent over the leads 28 of the component 10 when its body is below the free upper surface level 89.  
  The details ofthc movable reservoir 32 and the transporting dri\e mechanism for the reservoir 32 are best shown by reference to FIGS. 2 and 3. The movable reservoir 32, like the fixed reservoir 30, also has a closure plate 90 on its bottom which leads an opening 92 which is connected by means of a channel 94 to a low pressure air or gas input line 96. After the gas passes through the channel 94 and the opening 92 it is distrib utcd upwardly through a porous membrane 98 which is located above the closure plate 90. The gas flow in the lines 96 and 44 may be supplied at a rate as low as l5 cubic feet per hour.  
  In order to allow excess powder in the reservoir 32 to be returned to the supply reservoir 30 with a minimum ofdisturbance when the reservoir 32 moves to the position B the movable reservoir 32 is formed with sidewalls 100, I02 and have sloped upper edges I04, 106 which direct the excess powder downwardly along the outside of the vertical sidewalls I00. 102. In addi tion. a pair of vertical deflection plates 108. III) are mounted to the sidewalls I00. 102 by means of the braces IIZ. Il4 to assist in keeping the powder that spills o\cr the upper edges 104, I06 confined between the deflectors 108, Ill) and the sidewalls 100. I02.  
  In order to pro\ide for vibration of the reservoir 32 the opposite ends I16. N8 of the elongated reservoir 32 are secured to the vibrator arms I20, 122. respectively The vibrator arms I20. I22 are formed with vertical lower sections I20n. 12211 which are mounted to the reservoir ends 116, I18 by the screws I24. The arms I20. 122 also ha\e horizontal upper sections I201). I221? which are each attached to one of the sole noid vibrators I26. I28. &#39;I he vibrators I26. I28 include stators 130, 132 and armatures 134, 136, respectively. The armatures 134, 136 of the vibrators 126, 128 are connected to the horizontal portions 120b, 1221; of the vibrator arms 120, 122 by the bolts 138, 140. In order to support the vibrators 126, 128 a pair of base plates 142, 144 are provided and a pair of coupling blocks 146, 148 are secured between the base plates 142, 144 and the vibrator arms 120, 122 by the bolts 150, 152.  
  For the purpose of raising the reservoir 32 from position A to position B a hydraulic actuator is employed. The hydraulic actuator includes a shaft 160 which has a threaded portion at its lower end on which is fastened a threaded collar which is used to limit the up stroke of the actuator for desired coverage of components. An elongated drive bar 166 extends parallel to the elongated reservoir 30, 32 and it has a yoke 168 which extends downwardly from the center ofthe drive bar 166. The shaft 160 has a pair offlat surfaces 162, 164 which extend upwardly. The yoke 168 has a pair of spacedapart yoke arms 169, 171 which receive the flat surfaces I62, 164 of the shaft 160. A pin 173 extends through the arms I69. 171 to secure the shaft 160 to the yoke 168.  
  A pair of drive shafts 170, 172 for driving the drive bar 166 are secured at their lower ends to the outer ends 178. 180 of the drive bar 166. The upper ends of the shafts 170. 172 are secured in the support cups 174, l76 which are respectively attached to the vibrator base plates 142, 144. The ends 178, 180 of the drive bar 166 are split to form two pairs of bifurcated arms 182, 184. A pair of threaded screws 188. 190 are employed to squeeze the bifurcated arms 182, 184 together so as to lock the lower ends of the shafts 170, 172 in place. lhe shafts 170. 172 are mounted to slide easily in the lower bearings I92. 194 in the bearing blocks 196, 198, which are secured to the support plate 62 by bolts 200. 202 and in the upper bearings 204, 206 in the bearing blocks 208. 210, which are secured to the support blocks 54, 56 by the bolts 212, 214, respectively.  
  With the pin 173 being removable and the ends 178, I80 of the drive bar 166 being removable from the lower ends of the shafts 170. 172. it is possible to completely remove the drive bar 166 from the apparatus thereby allowing for easy adjustment of the position of the coupling member 160 with respect to the drive shaft 156. The up and down actuation of the shaft 156 may be achieved periodically by conventional camming and hydraulic mechanisms (not shown).  
  In operation the components 10, such as electrical capacitors having radial leads, pass through the preheat to en 22 which may comprise a number of elongated electrical resistant heater elements. a gas fired heater or other suitable heating means. The components are next turned by the chains 14. 16 to the fluidized bed stage 24 where the powder 50 is suspended in a dense phase or cloutf in the reservoir due to the gas flow upwardly through the porous membrane 98. When the reservoir 32 is to be filled from the reservoir 30. the shaft 156 is positioned in a lowered position so that the mot able reservoir 32 is located at the position A as shown in FIG. 3. The gas or air input through the inlet tube 42, the space 46 and the porous membrane 48 in the reservoir 30 causes a suspension of particles to be formed in the reservoir 30 which has a free upper surface level 86 that is abme the top 85 ofthe reservoir 32; and. therefore. the reservoir 32 will become filled 6 with powder from the reservoir 30 when it is in position A.  
  After the reservoir 32 has become filled with powder particles the cylinder 156 is raised by means of the hydraulic pressure and the reservoir 32 will correspondingly be raised to position B of FIG. 3. At position B the vibrators 128, 126 cause the support arms 120, 122 to vibrate in such a manner that the free upper surface level 89 of the powder 88 in the reservoir 32 is maintained at a predetermined level which is located approximately at the top of the reservoir 32.  
  In order to achieve the desired vibration of the reservoir 32, the arms 120. 122 are preferably shaped to have a narrow width section 215 which causes the arms 120, 122 to impart horizontal vibration components to the reservoir 32. The ratio of the horizontal and vertical components of vibration of the reservoir 32 that is required may thus be controlled by fixing the width of the section 215 to a predetermined amount. By varying the width ofthe section 215 vibration may be achieved in a simple manner which will maintain the free upper surface level 89 along a relatively constant horizontal line. By making the narrow width section 215 narrower, the arms 120, 122 will impart more ofa horizontal component to the resultant vibration; and by making the section 215 wider, the arms 120, 122 will impart less of a horizontal component to the vibration.  
 The invention is claimed as follows:  
  1. An apparatus for coating a remotely positioned heated element with a coating formed from powder particles which are capable of coalescing to form said coating on said element when said element is heated to a temperature below a predetermined deleterious temperature for the element but above the coalescent temperature of said particles comprising a first reservoir for containing a relatively large amount of said parti cles, first gas distribution means for supplying a tllStt&#39;lh&#39; uted flow of gas upwardly from the bottom of said first reservoir so as to provide a fluidized dense phase of said particles in said first reservoir having a free upper surface level. a second reservoir initially immersed in said dense of said particles of said first reservoir for containing a relatively small amount of said powder particles, second gas distribution means for supplying a distributed flow of gas upwardly from the bottom of said second reservoir so as to provide a fluidized dense phase of said particles in said second reservoir while said second reservoir is immersed in said dense phase of said particles in said first reservoir, holding means for holding said element, transporting means for transporting said second reservoir between its initial position in said dense phase of particles in said first reservoir so that said second reservoir is thereby filled with particles frotn said first reservoir to a second position adjacent said element at which the free upper surface level of said second reservoir overlies the portion of said element which is to be coated and vibrating means for vibrating said second reservoir independently of said first reservoir when it is positioned adjacent said element. so as to maintain said free upper surface level of said second reservoir at a predetermined coating level.  
  2. An apparatus as claimed in claim 1 wherein said second reservoir has a pair of vertical outside sidewalls and a pair of upper walls each of which slope downwardly so as to intersect with said sidewalls at an acute angle.  
  3. An apparatus as claimed in claim 1 wherein said second reservoir has a pair of vertical sidewalls and a pair of vertical deflector plates each of which is secured to one of said vertical sidewalls and is spaced outwardly therefrom.  
  4. An apparatus as claimed in claim 1 wherein said holding means is located directly above said first reservoir and said transporting means comprises lift means for lifting said second reservoir vertically comprising a pair of spaced apart shafts coupled to said second reservoir at their top ends. an elongated member con nected to the bottom ends of said shaft adjacent the outer ends of said elongated member. a vertically driven cylinder located below and approximately at the center of said elongated member and connecting means interconnecting said cylinder and said elongated member.  
  5. An apparatus as claimed in claim I wherein said vibrating means comprises means for vibrating said second reservoir simultaneously in the vertical and the horizontal directions.  
  6. An apparatus as claimed in claim 5 wherein said second reservoir is of an elongated shape. said vibrating means comprises first and second vibrators located at opposite ends of the long dimension of said second reservoir and said first and second vibrators as coupled to said second reservoir by first and second coupling members respectively.  
  7. An apparatus as claimed in claim 6 wherein said first and second coupling members each have a vertical section and a horizontal section. each of said vertical sections being connected to one of the opposite ends of said elongated second reservoir and spaced apart from the other of said vertical sections by the long dimension of said second reservoir and each of said horizontal sections being connected to one of said vibrators.  
  8. An apparatus as claimed in claim 7 wherein each of said vibrators have a stator and an armature and each of said armatures is secured to one of said horizontal sections of said coupling members.  
  9. An apparatus as claimed in claim 8 wherein each of said vertical sections of said coupling members have a reduced width portion. the dimensions of which are predetermined so as to provide a predetermined ratio of horizontal to vertical vibration of components of said second reservoir.  
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