ES381156A1 - Apparatus for the electrostatic coating of objects with atomised solids particles - Google Patents

Abstract

In an electrostatic spray gun for spraying powders the gun includes within it a tube of electrically insulating material (e.g. plastics material) 7 within which is a plurality of electrodes 1, 1a, 2, 2a &c connected to different potentials for the production within the tube of corona discharges. These electrodes are, in the embodiment shown, disposed in two rows, 1 to 6 and 1a to 6a, and in a helix around the tube surface, supplied with voltage from taps on either a voltage multiplier cascade (Fig. 3, not shown) or a voltage divider circuit (Fig. 4, not shown) the capacitors and diodes or the resistors of the circuit used being positioned outside the tube 7 and encapsulated in the plastics material of the body 20 of the gun (Fig. 2, not shown). The supply to the voltage multiplier cascade is from a transformer 11 at the rear of the gun, this in turn supplied from a voltage convertor in the handle of the gun, the electrical supply to the gun being low voltage and d.c., via cable 34, the trigger 18 and switch 19 controlling this supply. The powder is supplied to the gun at inlet 33 entrained in a gas, and expelled from orifice 21 and atomised by collision with the baffle 23, which baffle is movable with rod 24 through cord 27 and rod 28. An annular auxiliary electrode 22 may be positioned at the outlet of the gun, connected to the final stage of the voltage multiplier (or divider), it being embedded completely in the atomiser part 35 of the gun if the powder is rather flammable, partially exposed to the powder stream if the powder is less flammable or dispensed with entirely if the powder is very inflammable. A further embodiment (Fig: 6, not shown) has the electrodes arranged in an annular array of 4 spaced at 90 from each other and positioned closer to the orifice 21 than the diameter of the orifice, the opposite electrodes being at the same potential and each of the two pairs connected to one side of a voltage amplifier cascade consisting of two columns of capacitors interlinked with diodes (Fig. 9, not shown) positioned around the insulated tube through which the material is fed. The supply to the multiplier is as in the previous embodiment, the supply of coating material here being through the handle of the gun. Another method here of supplying the voltage is to have two of the electrodes connected to the output of a high voltage generator and the other two earthed via a divertor resistor (Fig. 10, not shown). A yet further embodiment (Fig. 5) has a reservoir of powder mounted on the gun.