Abstract:
An electrostatic powder-depositing installation for depositing powder on hollow parts of large dimensions. It includes a powder-depositing cage (1) which is open at the top and a powder-depositing unit (41) placed beneath this opening (2) so that the hollow parts vertically fit over the powder-depositing unit as they pass through the opening of the powder-depositing cage. Application is to installations for coating parts and, in particular, metal parts.

Description:
The present invention relates to depositing powder on parts by an electrostatic powder-depositing method in accordance with which a cloud of electrified enamel powder is projected inside a cage containing the part to be covered. The powder adheres to the part by the effect of electrostatic forces. A subsequent heat treatment applied to the part transforms the layer of powder into an enamel coating. During powder-deposition, only some of the particles of powder become fixed to the part which is to be coated; the remainder of the particles of powder fall below the part or try to escape outside the powder-depositing cage. 
     BACKGROUND OF THE INVENTION 
     The applicant&#39;s French Pat. No. 7 833 945 discloses a powder-depositing installation of integrated type which includes at least a cage, a powder supply system, a powder-recovery tank, and recycling units which include a powder-filtering system placed inside the cage which simultaneously forms a powder storage and dosing tank and a powder-recovery tank. 
     The invention aims to produce an installation of this type which can be used to deposit powder on the inside of hollow parts. 
     While the cage in accordance with the above-mentioned patent allows powder to be deposited principally on flat parts, this requiring only one narrow opening for the insertion of the parts on which powder is to be deposited, the installation in accordance with the present application includes an opening of large dimensions which allows the insertion of hollow parts which are necessarily broader than a flat part. The increase in the dimensions of the opening increases the possibility of powder escaping towards the outside. 
     The invention aims in particular to prevent the powder from leaving via this large opening. 
     SUMMARY OF THE INVENTION 
     The invention provides an electrostatic powder-depositing installation for depositing powder in hollow parts of large dimensions, characterized in that it includes a powder-depositing cage which is open at the top and a powder-depositing unit placed beneath this opening so that the hollow parts vertically fit over the powder-depositing unit as they pass through the opening of the powder-depositing cage and in that the powder-depositing unit is rotatably mounted such that all the inside surfaces of the hollow part can be powder-covered. 
     The characteristics and advantages of the invention become apparent from the following description of one embodiment of the invention given by way of example with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a schematic elevation, partially in section of a powder-depositing cage in accordance with the invention. 
     FIG. 2 is a cross-section along line II--II of FIG. 1. 
     FIG. 3 is a schematic elevation, partially in section of a variant of a cage. 
     FIG. 4 is a cross-section along line IV--IV of FIG. 3. 
     FIGS. 5(a) through 5(d) are sectional views about line V--V of FIG. 3 showing the nozzle-holder rotation control unit in four positions with the powder-depositing gun in phantom lines. 
     FIGS. 6(a) through 6(d) are plan views illustrating schematically four positions of a part on which powder is to be deposited, said powder being inside the powder-depositing cage, with the powder-depositing nozzle in each of the four positions. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the embodiment illustrated in FIGS. 1 and 2, the installation includes a cage 1 provided with a wide, parallelepiped horizontal opening 2 in its upper end for inserting the parts to be treated. The cage has an outer wall 3 and an inner wall 4 which forms a parallelepiped powder-depositing chamber for the parts to be treated. Walls 3 and 4 form together an air recycling box or peripheral chamber. 
     The cage has e.g. two filtering elements 8, only one being shown, connected to an aspiration box 9 which contains an unclogging unit 10 to recondition the filtering elements. 
     Air laden with powder descends via the central portion of the powder-depositing chamber then rises up the sides between the walls 3 and 4 under the aspiration effect of the filtering elements 8. The aspiration box 9 is connected to a ventilator or blower 11 driven by a motor 12 which sets up a vacuum in the box 9 and returns the aspirated air into a box 15 which is open on the outside. Separation plates 17 disposed between the two partitions 3 and 4 serve to direct the air by means of deflectors 18, 19 towards the filtering elements 8. 
     The powder collected on the filtering elements 8 falls after reconditioning on an inclined fluidization element 21 then drops onto a sifter 22 for separating metal particles. The powder is conveyed to the bottom of the cage 1 in which powder is stored in a powder recovery tank 46. Said powder is fluidized by fluidizing elements 23 disposed on the bottom of the cage 1 and is drawn directly by a dipper 40 of a powder-depositing gun 41 installed on a nozzle holder 24 which is rotated by a unit 25 described hereinafter. The upper portion of the gun 41 ends in a projection nozzle 26. 
     When powder is aspirated into the cage by the filtering elements it is deflected downwards and prevented from escaping from the cabin via the horizontal opening 2 through which hollow parts to be treated are inserted. 
     The gun 41 may be of the type described in the Applicant&#39;s French Pat. No. 79 01 970. 
     The nozzle holder 24 rotates inside a sleeve 42 fixed to the floor of the cage e.g. by welding or soldering. Two seals 43 or sealed bearings seal the nozzle holder in the sleeve. The upper hole of the sleeve is preferably above the level of the powder. 
     A unit 25 illustrated in FIGS. 5(a), 5(b), 5(c) and 5(d) rotates the nozzle holder 24. 
     The nozzle holder 24 is fixed on a connecting rod 33 which is rotated by two jacks 34 and 35 through an axle 45. Each of the jacks has one of its ends fixed to a frame (not shown) and the nozzle holder can assume any one of four positions, FIGS. 5(a), 5(b), 5(c), 5(d), by rotating through a quarter of a turn each time as shown in FIGS. 5(a) to 5(d) according to whether the jacks are extended or retracted. In position 5a, both jacks 34,35 are retracted, in position 5b, jack 34 is pressurized; in position 5c, both jacks are pressurized; in position 5d, jack 35 is kept pressurized and a vacuum is set up in jack 34. A slot 36 facilitates the rotating movement of the parts. The nozzle holder can be returned to its initial position by performing the movements in the reverse order. 
     The invention may be embodied in the manner shown schematically in FIGS. 6(a), 6(b), 6(c), 6(d), in which nozzle 26 is in the same positions as in FIGS. 5(a), 5(b), 5(c), 5(d). A hollow part 37 to be treated is placed inside the cage 1 by a manipulator 38 (FIG. 1). Between the different positions, the part moves by translation without rotation and nozzle 26 rotates as illustrated in FIGS. 5a to 5d so as to bring all the inside surfaces of the part in front of the projection nozzle. Powder is spread up the whole height of the part by moving the part vertically. 
     In the variant illustrated in FIGS. 3 and 4, wherein like numerals identify like elements, the installation includes a cage 1 provided with a wide horizontal opening 2 at its upper end for inserting the hollow parts which are to be treated. The cage has an outer wall 3 and an inner wall 4 which forms a powder-depositing chamber for the parts to be treated. Walls 3 and 4 form together an air recycling box. The upper end of cage 1 has a blowing box 5 disposed around the opening 2. The blowing box is closed by a high-efficiency filter 6, here called an ultrafilter, which distributes the flux all around the periphery of the opening 2 so as to constitute an inlet air-lock 7. 
     Air laden with powder descends via the central portion of the powder-depositing chamber then rises up the sides between the walls 3 and 4 under the aspiration effect of the filtering elements 8. The aspiration box 9 is connected to a ventilator or blower 11 driven by a motor 12 which sets up a vacuum in the box 9 and returns the aspirated air into an air recycling circuit 13,14,15,16 which communicates with the blowing box 5. Separation plates 17 disposed between the two partitions 3 and 4 serve to direct the air by means of deflectors 18, 19 towards the filtering elements 8. 
     The powder collected on the filtering elements falls after reconditioning on an inclined fluidization element 21 then drops onto a sifter 22 for separating out metal particles. The powder is conveyed to the bottom of the cage 1 in which powder is stored. Said powder is fluidized by fluidizing elements 23 disposed on the bottom of the cage 1 and is drawn directly by the dipper 40 of the gun 41 installed on a nozzle holder 24 which is rotated by the unit 25. 
     When the powder is aspirated into the cage and recycled air is blown around the opening for inserting the parts to be treated, the powder is prevented from escaping from the cage via this opening. 
     The nozzle holder is assembled and rotated as in the case of FIGS. 1,2 and 5. 
     The invention can advantageously be applied to depositing powder on hollow parts such as muffles of cooking ovens. Only one powder depositing gun is illustrated, but the cage may contain several stationary or moving guns; in particular one gun can be placed at each angle of the powder depositing cage.