GB1166864A - Improvements in or relating to The Surface Treatment of Workpieces - Google Patents

Abstract

1,166,864. Finishing. ROTO-FINISH Ltd. 26 Jan., 1967 [7 Feb., 1966], No. 5227/66. Heading B3D. A method of finishing workpieces by immersing them in a mass of particulate abrasive media and causing relative movement between workpieces and media, is characterized in that the media is maintained in motion (a) by imparting to it a rapid rotation about a substantially vertical axis so that under the influence of centrifugal force the media flows outwardly and upwardly, and (b) by returning the media inwardly and downwardly above the outwardly flowing stream, so that the mass of media assumes a toroidal form with individual particles of the media travelling helically around the toroid. A motor 2, Fig. 1, drives, through belt 3 and worm reduction gearing 4, a vertical shaft 5 having secured to its upper end a dished bowl 6 having a rubber or like lining 7. The bowl fits within and substantially closes the circular lower end of a stationary octagonal tub 8 having a rubber or like lining 10, preferably removable. The periphery of the bowl 6 is bevelled and the extreme edge of the bowl lining 7 lies very close to the tub lining 10 but spaced from it by a small gap; a brush 16 having bristles of nylon or like secured to and extending around the bowl seals the gap against the passage of anything but liquids and very finely divided solids. The tub 8 is charged with solid processing media, such as stone fragments or ceramic or plastic chips and the workpieces added. A pump 13 immersed in a tank 14 supplies liquid to a sprinkler 11. Liquid escaping from the tub past the bowl is collected in a chamber 15 and drains back into the tank 14 which may have baffles and/or filters. Alternatively, fresh liquid may be supplied to the sprinkler pipe 11, liquid collected in the chamber being discharged to waste or to separate recovery plant. For removal of treated workpieces an opentopped circular basket 32 whose side wall at least is formed of wire mesh or perforated sheet metal or otherwise provided with numerous apertures, is secured to the lower end of a sleeve 27 having at its upper and lower ends square openings fitting with clearance around a tubular shaft 18 of square crosssection surrounding a shaft 17 connected to the shaft 5. A clutch 23, operated by a lever 24, allows the shaft 18 to be disengaged from or coupled to the shaft 17 and a band brake 25, operated by a lever 26, allows the shaft 18 to be brought to rest after disengagement of the clutch 23. A non-rotating arm 29 connected to the upper end of the sleeve 27 by a bearing 28 is slidably mounted on a column 30 and is moved vertically by hydraulic cylinder 31. When a batch of workpieces has been treated, the clutch 23 is operated to connect the shafts 17, 18 so that the basket rotates at the same speed as the bowl and cylinder 31 is operated to lower the basket. The diameter of the basket is greater than the internal diameter of the toroidal mass so that the material returning inwardly is received in the basket; the media continues to circulate through the openings in the basket wall but workpieces are retained in the basket. After a short interval, the basket is raised clear of the mass, rotation being continued so that media lifted with the basket is discharged centrifugally. The basket is then brought to rest and the workpieces removed, the sequence of operations being repeated as often as necessary to extract all the workpieces of the batch. Instead of positively driving the basket through clutch 23 the basket may be left free to rotate. A deflector blade 38 is mounted on arm 29 so that when the basket is lowered the blade projects into the mass between the tub wall and the basket to ensure complete recovery of the workpieces; alternatively, a part of the tub wall may be formed as a hinged panel which can be swung inwards to form a deflector, or a deflector plate can be mounted for radial movement through a slot in the tub wall. For discharge of media the tub wall has an opening with a door 39 which can be opened to allow media to escape under the influence of centrifugal force generated by rotation of the bowl; the door may open inwardly to assist in deflecting media through the opening and may be constituted by one wall of a shoot. The door may be used for discharging the whole contents of the tub, separation of workpieces from media being effected after discharge. Various alternative ways of sealing the gap between the edge of the rotating bowl and the surrounding tub wall at least sufficiently closely to prevent the escape of media or workpieces are described. Instead of mixing the workpieces with the media they may be secured to fixtures mounted on the wall of the tub or other fixed part or on the arm 29 or sleeve 27. The fixture may be held stationary or permitted or caused to rotate. In a modification, Fig. 6 the bowl 6 is mounted directly on the shaft of an hydraulic motor 43. An extension 44 of the shaft is supported at its upper end in a bearing 45 carried by a fixed frame 46 and carries a slidable sleeve 47 having a clamp 48. A vertical column 49 outside the tub is capable of rotation about its own axis and can be moved vertically by a screw jack 50 driven by a motor (51). Column 49 carries a cross-bar 52 having at each end an arcuate plate 53 adapted to be gripped by the clamp 48. Adjacent each end of the cross-bar is a spindle assembly 54 adjustable along the, length of the cross-bar and includes a vertical workholding spindle 55 rotatable by a motor 56. A workpiece is secured to the spindle 55 which is outside the tub; jack 50 is operated to lift column 49; clamp 48 is released, cross-bar 52 is turned through approximately 180 degrees and the clamp retightened; jack 50 is operated to lower the workpiece into the media. The workpiece is continuously or intermittently rotated by the motor 56. The tub walls may be incurved, and instead of being stationary may be rotated at a speed different from that of the bowl or in the opposite direction. Liquid may be forced upwardly into the tub through the gap between the rim of the bowl and the tub wall; the bowl may have pump vanes on its underside, a reservoir being provided below the bowl. The treatment may be performed dry, the tub wall being perforated to permit the escape of powder produced in the treatment.