Patent GB-1092238-A (GB)
Title: Prestressed grinding wheel
IPC: B24D18/00
Filed: 1966-04-26
Abstract: 1,092,238. Grinding wheels. ITT INDUS TRIES Inc. April 26, 1966 [Aug. 25, 1965], No. 18287/66. Heading B3D. A method of making a reinforced prestressed grinding wheel comprises providing a reinforcing network of high tensile strength, positioning the -network symmetrically within a circular mould cavity, applying a tensile prestress to at least a portion of the network, filling the mould cavity with a mixture of abrasive grains and bonding agent to at least partially embed the network therein, curing the mixture to effect a mechanical interlock of the network with the resultant abrasive matrix formed, and thereafter releasing the prestress tension on the network and removing the grinding wheel from the mould whereupon the matrix incorporates a residual compressive stress of a magnitude below the ultimate compressive strength of the matrix. The reinforcing network may comprise a plurality of annular discs 32, Fig. 4, which are interconnected by bolts 40. Each disc, except the upper one, has recesses for receiving hairpin shaped reinforcing elements 34 disposed about the bolts 40. The assembly of discs has a tapered bore and a tapered plug can he inserted into the bore to stress the discs after which the assembly is placed in a mould having a base-plate 46 mounted on a vacuum chamber 48 a split outer member 56 being mounted on the base. An abrasive mixture is poured into the mould between the member 56 and annular discs 32. After curing, the plug is removed so that the discs tend to contract and effect a tensile stress on the elements 34 which, in turn, effect a compressive stress on the abrading material. The elements may consist of steel wire, fibreglass cord, bronze, beryllium, copper, nickel, molybdenum or plastics material and be braided or formed with projections for effecting engagement with the abrasive mixture. In another embodiment, the reinforcing network consists of an element 70, Fig. 5, threaded about pins 68 on a split ring 60, a tapered member 72 being forced into the split 64 in the ring to effect tensioning of the element before insertion in the mould. After the wheel has been moulded, the member 72 and pins 68 are removed; ease of removal may be achieved by coating with a release compound such as polytetrafluoroethylene. The interruptions on the surface of the wheel may be filled with an abrasive mixture. In a further embodiment, the reinforcing element is tensioned by bolts extending through a ring. In yet another embodiment for a wheel without a central hole, the elements 94, Fig. 9, extend radially of rings 86, 100 the outer ring being split and a wedge 92 being used to tension the elements. The wheel may be used for snagging billet up to a surface speed of 16,000 feet per minute. The abrasive grain may be silicon, boron, tantalum or tungsten carbide, or alumina, diamond, glass, quartz or garnet, and the bonding may be vitrified, resinoid, shellac, rubber, silicate, magnesium, oxychloride or metallic. Thermosetting resins or mixtures for bonding may include phenol aldehyde, cresol aldehyde, resorcinol aldehyde, urea aldehyde, melamine formaldehyde, furfuryl alcohol, epoxy, polyurethane, polyamide or like resins.