GB1124585A - Improvements relating to methods of and apparatus for burnishing articles - Google Patents

Abstract

1,124,585. Burnishing. WORCESTER ROYAL PORCELAIN CO. Ltd. 31 May, 1966 [2 June, 1965], No. 23433/65. Heading B3D. A method of burnishing, polishing or smoothing one or more surface portions of an article, such surface portion or each of same, being a surface of revolution with respect to a reference axis afforded by the article comprises the steps of (1) Rotating the article by means of a powerdriven rotary head upon which the article is held and which serves to transmit rotation to the article about an axis coaxial with said reference axis; (2) Continuously or intermittently delivering a supply of abrasive material in the form of powder on to the article so that at least some of the powder traverses or lies on the surface portion, or each surface portion, required to be burnished &c., and (3) Applying pressure to such surface portion or each of same by means of a burnishing &o. member whilst present on the surface portion concerned. The method is particularly intended for ceramic ware such as flat ware (plates, saucers and shallow dishes) and hollow ware (bowls or deeper dishes, cups) having a coating, e.g. of metal (gold, silver or platinum) which becomes dull due to oxidation during firing. A rotary head 14 comprising a metal disc carrying a rubber or like pad 15 is mounted on a shaft 16 driven by an electric motor through a belt. The shaft 16 has a bore 19 connected, through a rotary coupling 20, a container 22 containing filter pads and a pedal-operated valve 23, to the suction side of an air pump, so that an article of ceramic ware can be held on the pad 15 by suction. A part cylindrical side wall 12a acts as a guard to retain any workpiece thrown centrifugally from the rotary head due to failure of the holding means. The workpieee is centred on the rotary head 14 by three elements 24 of vertical rod-like form having a resilient sleeve or covering, e.g. of rubber. Each element is carried on an arm 25 on a spindle 26 having a sprocket 27 ; a common chain passing round the three sprockets may be operated by a pedal or handle. Above the rotary head 14 are disposed containers 29 for burnishing medium, e.g. zirconium powder. The lower frusto -conical end 31 of each container is connected to a delivery duct 32 constituted by a length of pipe which can be flexed so that the medium is delivered at the desired location relative to the workpiece. A pipe 33 supports the container from a radius arm 34 secured at one end to a bracket (30). Medium is conveyed by an entraining airstream through the pipe 33 to the container 29, the pipe 33 being connected to the container adjacent its lower end in an approximately tangential direction so that the medium tends to collect against the side wall, affording a central cavity from which the entraining air is extracted by an outlet pipe 36 at the upper end of the container. Medium thrown off centrifugally from the workpiece in the main operating chamber 11 passes through a coarse mesh 13 into a collecting chamber 10 provided with two downwardly extending outlet pipes 37. Each pipe 37 is connected to a horizontal portion (38) at the lower end of one supply pipe 33, an air injector nozzle (39) in the portion (38) having its outlet (40) immediately below the lower end of the pipe 37, whereby medium is extracted from the collecting chamber 10 and propelled along the supply pipe 33. Air from an air pump is supplied, through a pedal-operated valve 42, to the nozzles (39) and to a jack (47) operating brake shoes 45 urged by a spring (46) in contact with a brake drum 44 connected to the pulley 43 on the shaft 16. A polishing member such as a chamois leather is held by finger pressure advantageously at two opposed surface portions. Alternatively one or more polishing members may be adjustably mounted on supports movable between inoperative and operative positions by pedal, handle or automatically by a pneumatic jack. If the workpiece has a protuberance, e.g. the handle of a cup, this is protected by a jig. Valves may be provided in the ducts 32 for controlling the flow of medium on to the workpiece.