particularly the temperature during Installation, has a profound influence on the ability to drive off the chemically combined water. The dry out process can be considerably retarded, and can even have disastrous results should much or most of the products of hydration from the traditional calcium aluminates cement develop into the CAH10 or (worse) AH3 gel instead of the more desirable C2AH8 and C3AH6. If there is insufficient water, the excess CA will have a free ride. This is well known and we talk about it, but the realities are that the practical application of the knowledge in the filed leaves a lot to be desired. Only a few compounds are formed within traditional cements. The same considerations are even more applicable to the newer castables in which there are myriad of complex compounds. CERAMIC BOND It is often that it is desirous to heat to 800 C – 900 C to form a ceramic bond. By definition: “ a ceramic bond is the mechanical strength developed by a heat treatment which cause the cohesion or fusion of adjacent particles”, usually meaning fusion. Some MOR curves have exhibited minor increases in this range due to the formation of possibly feldspathic phases. However, is this evidence for a ceramic
bond? I do not think so. It is also the case that the temperatures attained in the bulk of the material are much less than the 800 C even 1000 C DRY OUT Is the removal of sufficient quantities of moisture from the hot face to warrant it safe to either start the main burners or processes at a later date. It is dry out, pure and simple! Heat cure is being used. But I do not think that we are curing anything. BAKE OUT Is the elevation of temperature in a refractory lining to cause. Particularly in plastics, a chemical bond to be formed. HEAT UP Is to have either of the above initial phases continue so that the unit can be put into operation. This mode should be enocouraged whenever possible. Form a purely ceramic engineering standpoint, a cool down can be more detrimental to the lining than the heap. Therefore to cool a furnace to see if there are any cracks is ludicrous. You will inevitably see cracks after the lining is expanded and then cooled down again. The latter considerably improves the rate at which heat is transmitted into the lining. All heat exchangers work with this principal and it also applies with refractoriness. We try to make the bottom of the vessel of furnace under possessive of at least neutral pressure to flood this area with air as well as preventing the ingress of cold air. We strive to place the thermocouples in the expected hottest and coldest areas… Thermocouple placement has been exhaustively. The temperatures referred in dry out schedules should be the temperature of the hot gases in contact with hot face and not of the refractory itself.