Patent GB-1047703-A (GB)
Title: Surface finishing in high speed gyrating barrels
IPC: B24B31/02
Filed: 1963-05-17
Abstract: 1,047,703. Surface finishing. H. KOBAYASHI. May 17, 1963 [May 19, 1962], No. 19670/63. Heading B3D. A method of surface finishing small workpieces comprises loading a mixture of the workpieces and substantially spherical grains of abrasive into at least one elongated barrel having an internal cross-section in the shape of an equilateral polygon with five to eight sides and with the diameter of a circle inscribed in the polygonal cross-section at least eight times greater than one dimension of each workpiece, the mixture being loaded into the barrel in such a manner that a substantial free space is left in the barrel, and causing the barrel to gyrate about a fixed axis parallel to the axis of the barrel but not passing through the interior of the barrel whilst maintaining the barrel in a fixed orientation, at such a speed that the centrifugal force on the mixture in the barrel is greater than the force of gravity thereon so that relative movement occurs between the workpieces and the grains of abrasive in the surface layer only of the mixture in the barrel and successive portions of the mixture are brought into and removed from the surface layer by the gyration of the barrel. A surface finishing machine has a housing comprising a lower portion 12, a horizontal mounting 16 and an upper portion covered by a dome-shaped cover 14 provided on its top with a door openable by a handle 18 for access to the housing interior. Two spaced vertical discs 20 are secured to a horizontal shaft 26 rotatably supported by bearings 28 mounted on the mounting 16 and rotated through multiple belts 32 by an electric motor 36 in the lower housing portion 12. Barrel cages 22-1, 22-2, 22-3 and 22-4 are equally spaced circumferentially of the discs and have trunnions journalled in the discs. One trunnion of each barrel cage extends beyond its associated disc 20 and carries a sprocket 38 connected by an endless chain 40 to one sprocket of a multiple sprocket 42 loosely fitted on the shaft 26 and supported by a block 44 mounted on the mounting 16. The chains 40 are tensioned by sprockets 46. The sprockets 38 and 42 have the same diameter and number of teeth, so that while the discs make one revolution in one direction each barrel cage makes one revolution in the opposite direction, whereby the orientation of the barrel cage remains unaltered. The barrel cages include barrels B1, B2, B3, B4 having as internal cross-section a regular polygon. The internal cross-section may be hexagonal with parallel sides spaced by less than 200 mm. or octagonal with parallel sides spaced by more than 200 mm. The exterior of the barrel may be cylindrical. The barrels, removed from the barrel cages, are each loaded, preferably to 50-60% by volume of the barrel, with a mixture of workpieces, such as needle rollers, diaphragm sectors for photographic cameras or seconds hands of wrist watches, and of substantially spherical abrasive medium, such as bonded stone chips. The mixture preferably comprises one part by weight of workpieces and from one to two parts by weight of abrasive medium. The mixture may include water and a lubricant or surface activator. The barrels are replaced in the barrel cages and the shaft 26 rotated at a speed of the order of 165#D r.p.m., where D is approximately 3À3 times the diameter of the circle inscribed in the internal polygonal cross-section of the barrel.