Patent GB-391858-A (GB)
Title: Improvements in refractory brick
IPC: C04B35/14
Filed: 1931-11-06
Abstract: A silica refractory furnace lining is produced from calcined quartz and a suitable binding material such as sodium silicate or lime by a method characterized in that more than 35 per cent of hard coarse particles of specific gravity not exceeding 2.38 and of screen size larger than 30 mesh per linear inch are mixed with less than 60 per cent of finer particles and with a binding material, bricks are made from the mix and used in a high temperature furnace without previous firing.  The coarse particles of which the preferred amount used in 55 per cent are composed of transformed and coalesced silica, i.e. silica which has been heated to 870-1470 DEG  C. to convert to the less dense crystalline form, and then coalesced, or both operations may result from the same heating.  Coalescence is the drawing together by the action of heat of the minute bits of silica which make up an individual silica fragment.  It may be due to the softening of the silicious binding material between the minute bits, or to actual fusing of the minute bits.  The object of coalescence is to eliminate porosity due to volume increase on the crystallographic transformation.  The finer particles, of which the preferred amount used is about 45 per cent, are such as to pass a screen of 50 mesh per linear inch.  Particles of size passing a screen of 30 and being retained on a screen of 50 mesh per linear inch are omitted.  The preferred binder is sodium silicate, used in a proportion of less than 3 per cent by weight of the brickmaking mix.  As raw material, any mineral containing quartz is suitable, rock mineral such as rock quartzite or ganister is treated to effect the polymorphous transformation and coalesce the grains and is then ground to the desired size.  Fine grain glass sand or other small grain raw material is heated to vitrification, cooled slowly to effect the transformation and then ground to the required size.  In this way raw material of initial particle size smaller than the particle size of which the brick is made can be used.  Smooth round particles are not at a disadvantage as raw materials as the subsequent vitrification stage and grinding process produce sharp particles which interfit closely.  The transformed, coalesced, ground particles are graded into the following sizes: (1) retained on screen having 30 mesh per linear inch, (2) retained on screen 50 mesh per linear inch and passing screen 30 mesh per linear inch.  Ternary diagrams in the Specification show curves of isodensity, from which the desired composition may be deduced for any desired density.  These curves are specific to ganister, curves of any particular ingredient have to be experimentally obtained.  The graded particles are formed into brick, by the use of high pressure such as 2,000 lbs. per square inch, which is applied fairly rapidly and maintained for 1/2 to 1 second.  The bricks thus formed after drying at 100 DEG  C. have a volume weight exceeding 1.80 grams per cubic centimetre.  To reduce cost, a small amount of untreated raw material may be added to the transformed coalesced silica prior to forming the brick, but where such addition is made it should always be less than 50 per cent and preferably less than 25 per cent, and should always be present as fine particles which pass a sieve of 50 mesh per linear inch.  It is also possible to mix transformed coalesced silica with transformed uncoalesced silica, the uncoalesced particles being of small size.