Products » Castables » Application Procedure For Castables
Application Procedure For Castables
Installing Conventional Castables
Batch and mixing
Batching by fractions of a bag is not recommended. A
whole bag or multiplesshould 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
- Spread on a non-absorptive platform (concrete or metallic) one or two
bags of the castable.
- Make a crater of the castable after thorough dry mixing by hand
- Pour the recommended dose of water all at one time and allow half
minute for absorption.
- Mix the castable and water within two to three minutes after addition
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.
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.
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.
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
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.
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.
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