Crucible is one of the important equipment for alloy melting. It is a container for melting and refining metal liquids, as well as for solid-liquid heating and reaction. It is the foundation for producing high-quality castings.

Handling and storage of crucibles

Special handling tools must be used to transport crucibles, and crucibles cannot be rolled directly on the ground. During transportation, collision should be avoided to prevent damage to the glaze layer, which may affect the service life of the crucible.

The crucible must be stored in a dry and ventilated place, preferably on a wooden rack. Avoid placing the crucible directly on a brick, soil, or cement floor. Moisture can damage the glaze layer of the crucible, reducing its melting efficiency and service life. In severe cases, the bottom may even fall off.

Characteristics of silicon carbide graphite crucible

(1) Fast thermal conductivity: With high thermal conductivity, it can significantly shorten smelting time and cycle, saving energy;

(2) High strength: formed by isostatic pressing, with no defects in the internal structure and high physical strength;

(3) Antioxidant: Unique antioxidant design and use of high-purity raw materials to protect graphite, high antioxidant performance;

(4) Corrosion resistance: low porosity, special additives, effectively resist the chronic effects of molten materials such as slag removers;

(5) Long lifespan: Compared with ordinary graphite clay crucibles, the lifespan can be extended by 3-5 times.

Preparation work before installation

(1) Check whether the inner wall and bottom of the crucible furnace are intact and undamaged.

(2) Check if there is any residual slag in the furnace, and if so, remove it promptly.

Choose the correct crucible base

(1) The crucible base should have the same shape as the bottom of the crucible and be slightly larger in size (about 2CM).

(2) Suitable height crucible bases should be selected for different types of crucible furnaces.

(3) Avoid using discarded crucible bases, as this will greatly shorten the lifespan of the crucible.

Installation and fixation of crucible

(1) To install a crucible for gas or oil furnaces, first place the crucible on the base and reserve a certain amount of crucible expansion space between the crucible and the top of the furnace wall. Use materials such as wooden blocks and cardboard to fix it. Adjust the position of the burner and nozzle to align the flame with the combustion chamber, not directly with the bottom of the crucible;

(2) When installing a crucible for a rotary furnace, support bricks should be used to fix the crucible on both sides of the pouring nozzle, avoiding wedging the crucible tightly. At the same time, 3-4mm cardboard or other materials should be placed between the support bricks and the crucible as a pre expansion space for the crucible;

(3) The crucible for installing the resistance furnace should be placed in the central part of the furnace, with the bottom of the crucible higher than the bottom row of heating elements. At the same time, insulation cotton should be used to seal the top and between the crucibles.

(4) Install the crucible for the induction furnace to ensure that it is placed in the center of the induction coil to prevent local overheating and cracking of the crucible.

Preheating/First use of crucible

Preheating the crucible in the correct way can greatly extend its service life.

(1) According to different types of crucible furnaces, when using the crucible for the first time, preheat it to around 200 ℃ for 60-120 minutes without adding any materials, and dry it for 60 minutes. The purpose is to evaporate the water absorbed on the surface of the crucible. Prevent bursting during initial use.

(2) After preheating, the crucible should be heated to 800 ℃ (about 2 hours) as soon as possible, and kept warm for 20-30 minutes, then raised or lowered to the working temperature. The purpose is to quickly pass through the easily oxidizable temperature range of the graphite crucible.

(3) After the first preheating, the crucible usually does not need to be preheated again unless it becomes damp again.

New crucible and crucible cooled for a long time

Note that if the silicon carbide graphite crucible is not properly preheated, it is easily subjected to thermal stress impact. For large capacity furnaces and/or furnaces with high output burners, the following crucible preheating procedures must be followed to avoid damage to the crucible due to thermal shock;

(1) Slowly heat the empty crucible at a heating rate of 200 ℃ for 2 hours to remove moisture;

(2) Heat the crucible at a rate of 600 ℃ for 2 hours;

(3) Heat the crucible to 800 ℃ at the normal heating rate. The crucible used for aluminum insulation must be kept at 800 ℃ for about 30 to 40 minutes to fully utilize the glaze layer on the surface of the crucible.

(4) After the above steps, the crucible can be safely put into normal use. During use, it is also necessary to follow the crucible safety operating procedures.

After the first use and normal use of the crucible

(1) Load the furnace.

(2) Heat slowly with low power to 600 ℃. When the crucible is not used for a long time, it should be preheated at a heating rate of 2 hours to 200 ℃ and relevant operating rules should be followed.

(3) Heat the crucible to the specified temperature with full power,

The heating program depends on the frequency of furnace use, coil size, and the resistivity of the molten metal. The furnace design and crucible material determine whether an empty crucible can be preheated. If conditions permit, preheating the crucible would be better. Silicon carbide graphite crucibles are more susceptible to thermal shock and must be heated slowly.

Note: For tilting furnaces, the furnace top cover must be air dried with an electric induction or flame heater before starting to use the crucible.

For furnaces with frequencies above 1kHz:

(1) Suggest preheating the empty crucible. Heat the crucible at 20% of maximum power until it turns red hot.

(2) After 30 minutes, the heating power can be adjusted to 50% of the maximum power.

(3) Maintain 50% of the maximum power and add a metal block until the metal liquid fills half of the crucible volume.

(4) Increase power.

Be careful not to overheat the crucible. After the metal melts and fills the crucible, reduce the electrical power to avoid crucible corrosion.

For furnaces with frequencies below 1kHz:

(1) The heating efficiency of an empty crucible is relatively low, so it is necessary to put some metal blocks into the preheating crucible to improve the preheating effect.

(2) Heat the crucible at 20% of maximum power until it turns red hot.

(3) If the crucible powder turns red hot within half an hour, please heat the crucible at 50% of its maximum power.

(4) Keep heating at 50% of maximum power until the metal liquid fills half of the crucible volume before increasing the heating power

Feeding

(1) Metal materials must be dried before being added.

(2) When adding materials, they should be gently placed down and the metal ingot should not be thrown or poured into the crucible to avoid damaging it.

(3) Place the metal ingot vertically into the crucible, leaving sufficient expansion space between the ingot and the crucible wall. Do not place the metal ingot horizontally inside the crucible to prevent it from expanding and damaging the crucible after heating.

(4) You can first add some small pieces of metal material into the crucible as a cushion for large ingots.

(5) During continuous melting, a portion of the molten metal can be retained in the crucible to accelerate the melting rate. But it is necessary to avoid adding large pieces of metal material to a small amount of molten metal, in order to prevent the molten metal from rapidly cooling or solidifying and damaging the crucible.

(6) When adding liquid metal, avoid overfilling and generally do not exceed 80% of the crucible capacity.

The use of additives

When using additives, it is necessary to strictly follow the instructions for using the additives.

(1) Additives can only be added after the metal material has completely melted. Do not put additives in empty crucibles or solid metal materials, otherwise it will directly damage the crucible.

(2) When using additives, it is necessary to strictly follow the prescribed dosage, as excessive use of additives can greatly shorten the lifespan of the crucible.