Patent GB-671150-A (GB)
Title: Improvements in or relating to segmental abrasive wheels
IPC: B24D5/06
Filed: 1950-02-17
Abstract: 671,150. Abrasive wheels. CARBORUNDUM CO. Feb. 17, 1950 [Feb. 19, 1949], No. 4197/50. Class 60. [Also in Group XXV] An abrasive wheel comprises a concrete core, a number of abrasive segments encircling the core, a number of fastening elements which are initially tensioned, reaction members associated with said elements so that a part of each abrasive segment is initially gripped between a reaction member and 'a part of its associated fastening element whereby the tension in the fastening elements is maintained, each of the fastening elements being provided with means disposed within the body of the core for anchoring the element to the core, the reaction members being adapted to be rendered yielding whereby the tension in the elements may draw the segments firmly and positively against the core. Abrasive segments 11 for a wood-pulping wheel are provided at each end with pockets 19 communicating by slots 20 with recesses 21 formed at the base of each segment. Each cavity 19 receives the head 24 of a bolt 23; to provide a smooth, even seat for the head 24 a suitable bearing metal 24<SP>1</SP> may be cast around it. The inner end of the bolt 23 carries a nut 25 and washer 27 ; a sleeve 26 loosely fitting on bolt 23 is retained between washer 27 at one end and washers 29, 30 at the other end. Alternatively, the nut 25 may be contained in the cavity 19 and the head 24 project inwardly from the segment 11. The washer 30 is deformable or disintegrable being made of thermoplastic materials such as cellulose nitrate or cellulose acetate which soften at moderately elevated temperatures, low melting metals such as tin or alloys thereof, or materials such as casein which soften by the action of water. Depending on the nature of the washer 30, one or both of the metal washers 29 may be omitted. The washer 30 is, held by sleeve 26 against well 22' of recess 21. Before assembling a wheel, nuts 25 are tightened until the shanks of bolts 23 are each under a predetermined tensile stress sufficient to ensure that the segments 11 will be firmly seated upon the concrete core when the deformable or disintegrable washers 30 have had their effectiveness removed; the sleeves 26 and the portions of abrasive segments 11 surrounding slots 20 are thus put under compressive stresses equal to the tension in bolts 23. The necessary number of abrasive segments 11 are assembled, on a fixture, to form an annulus or cylinder; the joints between the segments being filled with material 31 which is resilient to take up expansion and contraction of the segments and is also resistant to water. The sides and ends of the segments may be coated with adhesive to hold the joint filling material. A cylindrical form is inserted within the fixture and inside the annulus of segments to provide for the insertion of a shaft, and concrete is then poured between the form and abrasive segments so as to embed the shanks of bolts 23. sleeves 26, nuts 25 and washers 27, 29, 30. The bottoms, of the abrasive segments are preferably coated with waterproofing material to minimize the absorption of water from the wet concrete which would impair the quality of the concrete. Prior to or during the pouring of the concrete 12 reinforcing rings 14 and a hub are preferably inserted between the cylindrical form and the abrasive segments. After the concrete has set the completed wheel is removed from the fixture. The washers 30 are then acted upon so as to remove them as an effective operating part of the holding means, thus releasing the sleeves 26 from compression and permitting the tension in bolts 23 to draw the abrasive segments 11 positively, through the action of the bolt heads 24 against the bottoms of pockets 19, to a firm seat against the core. The concrete of the core between the washers 27 and abrasive segments 11 and also the abrasive surrounding slots 20 is under compression. The washers 30 may be rendered ineffective, e.g, by heat treatment before the wheel is placed in use ; alternatively, this action may be effected when the wheel is in use, e.g. when the washers are of cellulose nitrate composition by the rise in temperature of the wheel when used or when they are of casein by the hot water present during use.