GB394667A - Improvements in or relating to bonded articles such as abrasive wheels, and methods of making them - Google Patents

Abstract

394,667. Moulding grinding-wheels &c. CARBORUNDUM CO., Ltd., Trafford Park Road, Manchester.-(Carborundum Co.;: Niagara Falls, New York, U.S.A.) Dec. 28, 1931, No. 35836. [Class 87 (ii).] Relates to a process for securing uniformity in the structure of a bonded article such as a grinding-wheel. The mixture of grinding- material, bonding-material and water, is supplied to a mould, preferably a rotating mould, in small uniformly distributed portions, e.g. a volume not exceeding one cubic centimetre or fifteen times the average volume of the coarsest kind of grain in the mix. The division of the wet or damp mix into small portions may be effected by a shaking screen, the mesh of which does not exceed five times the average size of the grains. The uniformity of the grinding-wheel is further assured by making it under controlled humidity conditions in a chamber to which a spray is introduced by an injector. The control is effected by a wooden block which expands or contracts under varying humidity conditions and adjusts the injector valve accordingly. The mould is jolted, after charging, whilst subjected to a. light preliminary consolidating pressure, and the material is afterwards subjected to the heavier final compression. As shown, the mould 3, 4, 5 is carried on a turntable 10 positioned beneath a vibrating frame 7<1> carrying the screen 8 and, if desired, one or more additional screens 9. The screen 8 is larger in area than the mould to ensure uniformity of charging. The light preliminary pressure is applied by a single weight 43, Fig. 3, or by a number of nested smaller weights which accommodate themselves to surface irregularities, or an inflatable bag 27, Fig. 6, may be used for more perfect accommodation. The nested weights may be placed on a closed air cushion. The jolting may be effected pneumatically either in a vertical direction or in two horizontal directions at right-angles, or both vertical and horizontal jolting may be used. The mould 3 is placed on the shaking table 10 which has a central stem working in the pneumatic cylinder 13. The horizontal jolting is effected, in two directions at right - angles, by plungers 21 associated with cylinders 22 and guided by stops upstanding from the table 10. Spring buffers bear on the sides of the mould. Before the application of the final pressure, the ring 4 is removed from the mould and the material is strickled. A test for uniformity is described, comprising impregnating the wheel with the material known by the Registered Trade Mark " Bakelite," heating to harden the " Bakelite " and grinding and polishing the surface. Definite areas of the wheel are then examined by a reticulated microscope and estimates made of the spaces in each area occupied by grinding-particles, bonding-material and pores.