Care And Use
 

Graphite Crucibles, Straight Shape Clay, Hot Rod Thermocouple Sheaths, Excel E Crucibles, Manufacturers Of Crucibles, Silicon Carbide Crucibles, Clay Graphite Crucibles, Crucible Stand Accessories

 

HANDLING CRUCIBLES
• Always handle crucibles with care.
• Damage to glaze could adversely affect its performance.
• Never roll a crucible on a hard floor.

 
STORING CRUCIBLES
• Store crucibles in a warm, dry place.
• Stand crucibles on pallets, never directly on the floor.
• Never stack crucibles inside one another.
• When stacking crucibles, separate the layers with hardboard.
EXAMINATION OF THE FURNACE
• Before installing the crucible and stand in the furnace, check the condition of the refractory lining and make any necessary repairs.
• Remove any loose debris from the bottom of the furnace chamber.
• Ensure that the drain hole is clear and that the drain hole flap can move freely.
• In electric resistance furnaces check the condition of elements. Because of the risk of oxidation in electric
  resistance furnaces it is particularly important to eliminate the entry of air into the furnace chamber. The drain hole should be sealed with a thin zinc plate and all other apertures made airtight.
INSTALLING THE CRUCIBLE
• The use of a stand made of the same material will help to ensure uniform heating of the base of the crucible and so reduce thermal strains.
• The stand should have the same diameter as the base of the
   crucible in order to provide adequate support.
• For optimum heat transfer and melting efficiency :
     •   The height of the stand should be such that the base of the Crucible is on level with the centre line of the burner.
     •   The stand and crucible should be installed centrally in the furnace.
LIFT OUT FURNACES
• Sprinkle a thin layer of coke or other carbonaceous material on top of the stand to prevent the crucible
   from sticking to it.
• Always place the crucible centrally on the stand.
• Rocking and levering to free a crucible which has stuck to the stand can cause fractures in the lower wall of   the crucible.
BALE OUT FURNACES
• Set the top cover bricks to leave a gap of 8 mm around the crucible to allow for expansion of the crucible and the furnace lining. Too small
   a gap can lead to cracking at the top of the crucible.
• Place a layer of insulating material, such as ceramic fibre over the top of the lining and the top edge of the crucible in order to insulate the metal top plate. Do not push the insulating material down between the cover bricks and the crucible.
• If the steel top ring is fitted, ensure that there is a gap of 12 mm between it and the inside of the crucible to allow for expansion.
   Too small a gap can lead to cracking at the top of the crucible.
TILTING FURNACES
• Set the stand on the metal stand in the recess at the base of the furnace. Ensure that it is firm, central and level.
• Spread cement evenly over the top of the stand excluding the spigot.
• Place the crucible centrally on to the stand.
• Cement the key/grip bricks on to their support bricks in the furnace lining, leaving 6-10 mm gap between crucible and key bricks.
• Insert cardboard or carbonaceous material in the gap.
• Place key bricks 75 mm below the top edge of the crucible.
• Leave a gap of about 40 mm below the spout, to avoid the crucible hanging up on the spout.
CHARGING
• As soon as the crucible becomes red hot all over, charge and melt immediately.
• Charge the crucible in a vertical position.
• Charge light scrap first to form a cushion for a heavier metal to follow.
• Use tongs to charge ingots.
• Place ingots and large pieces vertically.
• Do not pack the metal tightly in the crucible.
CRUCIBLE WARM UP PROCEDURE
• Crucible should be preheated empty.
• Do not charge ingot or scrap until the crucible is red hot.
• The burner flame should be controlled to ensure the crucible is brought up to red heat (950°C) as per the Heating Recommendations.
MELTING AND POURING
• Melt as quickly as possible.
• Avoid overheating the melt.
• Always melt to the lowest possible temperature compatible with the casting.
• Avoid stewing the molten metal for long periods.
• Avoid delay between heats and use the crucible for as many melts a day as possible.
FLUX ADDITIONS
• Ensure that the correct flux is used for:
     • The alloy being treated.
     • Temperature of the alloy.
• Use minimum quantity of flux to satisfy metallurgical requirements.
• Any unnecessary increase in melt temperature will result in accentuated attack on the crucible with a drastic reduction in crucible life.
CLEANING OUT
• Crucibles should be cleaned out by careful scraping when the crucible is red hot.
• Slag left in the crucible leads to rapid thinning of crucible wall in subsequent melts.
• Dross/Oxide left in the crucible leads to longer melt times,higher fuel consumption and shorter crucible life in subsequent melting.
 
 
 
 
CARE
 

• Store crucibles off the floor in a dry, warm place.
• Do not nest one inside another. Separate layers with hardboard.
• Do not roll crucibles. Move using a sack truck with padding.
• Check thoroughly for cracks or damage before use.
• Use the correct crucible stand which must central and support the whole base.
• Allow space for expansion between crucible and furnace lining/cover.

• Use correctly positioned grip bricks in tilting furnaces, leaving gaps for expansion. Do not hang crucible on spout.
• The flame path must be tangential to the crucible.
• Ingots should be loaded carefully into the crucible using tongs.
• First charge with light returns, as a cushion, then add ingots vertically.
• Only add flux after the metal is molten.
• Avoid ingress of cold air by ensuring that the drain hole is sealed.
• Lift-out tongs should hold crucible on it's lower third and fit evenly on both sides.
• The crucible must be emptied before switching off the furnace.
• The crucible should be cleaned out carefully every day while still red hot.