Patent GB-831348-A (GB)
Title: Improvements in and relating to powder spray apparatus
Inventor: WHITE ALBERT ALEXANDER
IPC: B41F23/06
Filed: 1957-03-26
Abstract: 831,348. Set-off preventing. AEROSTYLE Ltd. March 17, 1958 [March 26, 1957], No. 9890/57. Class 100(2) Powder spray apparatus for spraying printed sheets to prevent set-off comprises a powder container 1 having a discharge orifice in its bottom, and means for agitating powder at the bottom of the container to cause a flow of powder from said orifice downwards into an air duct 33 through an inlet which is also open to atmosphere, air under pressure being directed along the duct 33 from a nozzle 35 and being discharged, together with entrained powder through a nozzle 36 having a flared inlet opening in line with the nozzle 35. The container 1 comprises a cylinder 2 which has a bottom formed by a diaphragm 4 of rubber or the like, the periphery of which is nipped between the bottom end of the cylinder 2 and a base element 5. A ring- shaped member 12 mounted on the top of the cylinder forms a seat for a lid 3 and also carries rods 14 the threaded lower ends of which pass through side lugs in the base element 5 and a cup-shaped member 34, shims 57 separating the parts 5, 34, and are engaged by nuts 13. Mounted centrally in the diaphragm 4 by means of a bush 22 washer 25 and nut 24 is the upper end of a tube 23 which passes through a central opening 31 in the base element 5. A guide duct 19 having a nipple 17 mounted in its upper end is secured in the tube 23 by a nut 27 and projects downwards from the lower end thereof. The nut 27 also engages the underside of a plate 20 which is pressed downwards by springs 21 mounted in blind bores in the base element 5. The downward pressure on the plate 20 urges the diaphrgm 4 into contact with an annular rib 15 formed on the base element 5 around the opening 31. An annular groove 50 in the top face of element 5 is connected by a connector 38 and passages 43, 44 (Fig. 4, not shown), 46, 47, 48 with a source of air under pressure which raises the diaphragm 4 clear of the rib 15, lets it fall back under the influence of the springs 21 as the air escapes through the opening 31 and then raises it again. The diaphragm is thus vibrated so long as air is fed beneath it and the powder at the bottom of the container is agitated so that it falls freely through the orifice of the nipple 17 and down guide duct 19 which is vibrated with the diaphragm. The interior of the cup shaped member 34 is vented to atmosphere through a gap 40 between the lip of the cup and the underside of the base element 5 and through slots 41, and communicates through an opening 37 with the air duct 33 in the bottom of the member. The lower end of the duct 19 is located in the opening 37 so that when air under pressure is fed via the connector 38 and the nozzle 35 into the air duct 33 the powder falling from the duct 19 is entrained in the air and carried out therewith through the second nozzle 36 to the distribution points. The flow of the powder through the opening 37 and the dissemination of it in the air is helped by air which escapes from under the diaphragm 4 through the opening 31 and air which is sucked in through the gap 40 and slots 41. The rate of vibration of the diaphragm 4 and hence of the flow of the powder through duct 19 may be varied by regulating the flow of air through the passages 47, 48 by means of a needle valve 45 in the passage 46, or by substituting springs of a different strength for the springs 21. The powder flow may also be regulated by changing the nipple 17 for one having an orifice of a different size.