Curing and Heating Schedule after installation, Precautions
Curing should start immediately after the final setting of the castable and in any case, not later than 8 hrs & this should continue up to 24 hrs minimum and preferably up to 72 hrs. After this wet curing, 2-3 days air drying is advised before heating up. During the first heat-up initially the temperature should be gradually raised (heating schedule to be followed) -
From time to time vapour must be removed with the help of an exhaust fan (or any other device) plus at every stage of intermittent temperatures, a soaking of minimum 5 hrs should be given. The shelf-life of these castables under its original packed conditions is generally 6-9 months (to be provided by the vendor/manufacturer) and they should be stored in a cool, dry place well-protected from sun & water. If stored longer then the castables should be tested and approved before use.
(by Industry.Guru research team)
These are packed dry for in-situ mixing with a recommended dose of water and are available generally in HDPE bags / packets. Here we will discuss exact amount of water to be mixed to obtain workable consistency, precautions that should be taken during mixing and also after installation of normal and low cement type castables such as - curing and what should be heating schedule of the furnace, etc.
The water requirement to obtain a workable consistency is in the range of 11–12 per cent (conventional type) & 5-7 per cent (LCC type) by weight of the refractory castable. The mixing time should not be less than 2–3 minutes while doing it in a concrete mixer. In case of hand mixing, first a thorough dry mixing before adding the water is advised. Then the wet mixed castable should be used as quickly as possible, preferably within 15 minutes. The shuttering or forma-work should be water tight & rigid enough to withstand the pressure induced by consolidating the wet castable. Metal anchors should be preferably either ‘Y’ or ‘V’ type firmly welded to the supporting shell. The cover of the castable over the tip of anchors must be at least 40-50mm. Metal anchors should be coated with 2-3 mm layer of wax or bitumen before placement of the castable. Immediately after pouring of the castable it should be rodded &/or vibrated to ensure proper compaction before consolidation. Internal vibrators of 25-50 mm diameter with operating frequency 7000 - 9000 vibrations/minute will give good compaction.
Refractory castables are ready mix materials made from high purity calcium aluminate binder and selected refractory aggregates. Both conventional and low cement refractory castables are hydraulic setting and can be cast to any shape or make furnace linings through gunning, pneumatic ramming, etc.