Safety
Guidelines
Storage
Store crucibles in a warm dry place. Stand crucibles on pallets and not directly on
the floor. Do not stack crucibles one inside the other.
Fluxes
When using fluxes care should be taken to see that these do not come in direct contact
with the crucible. The time of use should be kept at a minimum and the use of excessive
quantities should be avoided.
Charging of Metal
When the crucible has reached red heat, charge the metal by keeping the crucible in a
vertical position. First charge the light scrap to form a cushion for the heavier metal
that follows. Use tongs to charge the crucible. Do not pack the metal tightly as metal
expands sufficiently to damage the crucible.
Tongs
Lifting devices rely on their grip on the crucible, thus the grip should be of Good
Fit, Even and Low Down.
Bale Out Furnaces
As far as possible, Bale out furnaces should be kept full. If a half full crucible is
in use for long periods the upper part of the crucible burns out. This causes the thermal
conductivity to reduce, which may cause cracks among other problems.
Grip Bricks
It should be ensured that the crucible is not jammed by the grip brick, otherwise
stress may arise which could cause the formation of longitudinal cracks.
Cleaning
The crucible must be cleaned out with careful scraping between the melts, when it is
still red-hot.
Melting and Pouring
Melt as quickly as
possible. Avoid over heating the melt.
Always melt at the lowest
possible temperature compatible with casting.
Avoid stewing the molten
metal for long period /pour the metal immediately as it is ready.
Empty the crucible as
quickly as possible.
Avoid delays between
heats and use the crucible for as many melts a day as possible.
VARIOUS METHODS PECULIAR FOR CRUCIBLE
FURNACES FIRED WITH DIFFERENT FUELS
Coke Fired Furnaces
Care should be taken to use dry coke only. Lump size should be such that the coke
packs well together and leaves no cavities. The crucible should be packed right up to its
lip, in order to ensure uniform heating. The removal of slag should should be performed
carefully and conscientiously in order to ensure proper draught.
Oil Fired Furnaces and
Gas Fired Furnaces
Care should be taken that burners are properly set. The flame should impinge
tangentially on the crucible on all sides and enter the furnace chamber at one side
beneath the crucible. The blower should be shut off at the same time as the burner. Under
no circumstances should the crucible be subjected to a blast of cold air, since this cause
the cracking of the crucible.
Electric Resistance
Furnaces
Care should be taken in resistance heated furnaces to ensure that the furnace chamber
is well sealed to prevent the entrance of air, since the crucible could loose its thermal
conductivity, due to oxidation of graphite and other carboneaous materials. |
