1. FIELD OF THE INVENTION
The invention relates to a method for the manufacture of refractory bricks containing CaO, comprising the steps of forming a mixture comprising a refractory composition consisting at least partly of a material containing CaO and a binder composition, and moulding bricks from the mixture.
The invention also provides refractory bricks manufactured by the method, and a refractory structure consisting at least partly of the refractory bricks.
2. DESCRIPTION OF THE PRIOR ART
Refractory bricks containing CaO known in practice are pitch-bound bricks based on burned dolomite. These have the following disadvantages:
(i) The bricks cannot be used after moulding without further treatment, as the refractory structure made from the brick would be damaged during heating up as a result of the softening of the pitch. Therefore, after moulding, the bricks must be subjected to a heat treatment, which usually consists thereof that the bricks are refined for several 24-hour periods at a temperature in the range of 280.degree. C. to 350.degree. C.; by this treatment a part of the volatile components is driven from the pitch, so that the bricks subsequently have sufficient strength during heating up of the refractory structure. This refinement treatment requires much energy and is expensive. In addition, there are bricks that are fired at a temperature in the range of 1600.degree.-2000.degree. C.; in this way, bricks with ceramic bonding are obtained. PA1 (ii) The use of pitch as a binder for refractory bricks has ergonomic disadvantages. PA1 (iii) After manufacture, and until use in a refractory structure, the bricks must be protected against hydration of the CaO to Ca(OH).sub.2 by the humidity of the air. For this purpose, the bricks stored on pallets are usually shut off from the air by an enclosure, e.g. a plastic shrink foil, and/or are kept in a space subject to air conditioning. This prevents the bricks from pulverising as a result of the increase in volume occurring on hydration.
For a magnesia carbon brick, the use of a solution of novolak resin is proposed in U.S. Pat. No. 4,248,638. The usual solvent for novolak resin is ethylene glycol, which as explained below is not suitable for use with CaO-containing mixtures because it causes hydration of CaO and premature hardening of the mixture. For this reason in JP-A-No. 79.161611 (extracted in Chemical Abstracts, Vol. 92, No. 26, June 1980, page 272, abstract no. 219825f) it is proposed to use a modified novolak resin with CaO containing refractory material. The modified resin is a liquid and does not require a solvent. However, this modified resin is expensive to manufacture.