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Application Procedure For Castables

Installing Conventional Castables

Batch and mixing

Batching by fractions of a bag is not recommended. A whole bag or multiples•should be used for each batch. Mixing should be done in a concrete mixer using clean cold water. The mixing time should be less than 1 to 2 minutes for load up to 250 kg and should be 2 minutes for larger batches. In case, hand mixing the castables

Formwork and anchors

The wet mixed castable should be placed within 15 minutes. The shuttering of the formwork should be rigid, watertight and designed for the pressures induced by the wet mix. Whenever castables are to be placed as roofing material or as spanning material between supports or as short cantilevers, suitable anchors should be secured firmly to the supporting frame or shell. Metallic (stainless steel Y or V type) or ceramic-based anchoring devices are recommended. The cover of the castable over the tip of the anchors should be at least 40 to 50 mm. Anchors must be coated with a 2 to 3 mm thick layer of beeswax, paper or bitumen in advance of placement. Advice of SKG refractory engineer may be sought in the matter of providing anchors, their spacing, etc.

Joints

Thermal expansion of dense castables are in the range of 4 to 6 millionths per degree C. Expansion joints are provided using a thin piece of plywood or card board at desired distances. These burn out during the first healing and will provide the necessary opening.

Placement

Immediately after pouring, the castable should be rodded and / or vibrated to ensure effective consolidation. This should be done within 15 minutes after placing.

Pin Prick Holes

For easy expulsion of moisture and steam, pin prick holes 3 - 4 mm diameter should be provided to half the depth of lining at 150 to 200 mm spacing.

Gunning

Dense castables can be placed pneumatically using a shotgun. The moisture content should be adjusted at the nozzle of the gun to ensure minimum rebound losses. Gumming should be contracted to trained operators.

Curing

Dense castables have a hydraulic binder, which hardens in the presence of moisture. Once in place, the castable should not dry out due to exposure or due to the heart produced within the mass. Curing should start immediately after the final set of the castables is placed. Moist conditions can be maintained by covering the castables with wet sack or by frequent sprinkling of cold water on all exposed surfaces. Curing should continue up to 24 hours and preferably up to 72 hours, After the wet curing period, natural air drying for two to three days is desirable.

Initial Firing

The temperature should be raised gradually at a rate not exceeding 250°C per hour up to the temperature of 30-500°C. The heat must be maintained thereafter for four hours and then raised at 300°C up to 500°C. The heat must be maintained thereafter for 8 to 12 hours and later, the rate of heating could be raised to 1000 °C per hour up to the recommended service temperature.

Admixture

No admixtures, either for improving the workability or altering the time of set or the rate of gain of strength should be used. The castables should not be contaminated with alkalis, salts, lime, plaster of paris, sodium silicate or such other chemicals.

For water requirements for various castables, please refer to our product data sheets.

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