GB748696A - Process of making abrasive phenolic resin mixes - Google Patents

Abstract

Moulding powders for making shell moulds or abrasive articles, e.g. grinding-wheels, and comprising granules of sand &c. wetted with a plasticizer and coated with a partially cured phenolic resin are prvented from sticking together by fluidizing the granules in a current of air or other gas at temperatures from 40-200 DEG C. In making the mixture sufficient plasticizer, e.g. furfural or liquid reactive phenolic resin is added to pick up nearly all the abrasive powder leaving 1 per cent free powder and the powdered phenolic resin is then added. In examples mixtures comprising 22.4 lbs. 24-grit size alumina, 0.52 lb. liquid resin and 1.78 lbs. solid resin are specified. This mixture is fed successively through hoppers 1, 9 and thence, by means of pressure supplied by air fed through line 21, through glass tube 12 and heater 13 to the upper chamber 31 of the fluidizing apparatus comprising a steel cylinder 35 divided into upper and lower chambers 31, 39 by a porous plate 41 and provided with electric heating coils 36. The lower chamber is cone-shaped and has an inlet pipe for the fluidizing gas while above the chamber 31 is provided a glass tube 73 in which the extent of the fluidizing action may be observed and from which passes a pipe 89 to a centrifugal separator 93 in which any powder carried over by the fluidizing gas is separated, the gas being vented through a receiver 98 containing water. Fluidizing gas is supplied under pressure from the mains 29, the pressure being sufficient to give the required differential pressure for the feed at points 14 and 43 respectively. The air <PICT:0748696/IV(a)/1> is first dried by passage through a glass wool filled trap 26 and then passes to the T-piece 22 where the supply is divided to feed the lines 21 and 68. The latter supply passes through a cylinder 61 containing a dehydrator, e.g. calcium sulphate, and thence through a ceramic pipe 48 fitted with resistance heating wires into the base of a cylinder 47 from the top of which the dried air passes through an electrically heated tubular heater 55, 56 into the base of the cone-shaped chamber 39. A mercury pressure gauge 103 connected on the one side through pipes 105, 106 to the upper chamber 35 and on the other side through pipes 102, 101 and T-union 100 to the lower chamber 39 enables the pressure differential to be controlled in conjunction with the temperature limit specified read off at thermometers 111 and thermocouple 109 that the level of the fluidized mixture is controlled to rise to the level of the outlet 77 from which catalyst is continually withdrawn through line 78 to receiver 80.