Graphite crucible refers to a type of crucible made of graphite, clay, silica and wax stone. Graphite crucible is mainly used to smelt non-ferrous metals and their alloys such as copper, brass, gold, silver, zinc and lead.
Graphite crucible is made of natural flake graphite as the main raw material and plastic refractory clay or carbon as a binder. It has the characteristics of high temperature resistance, strong thermal conductivity, good corrosion resistance and long service life. During high-temperature use, the thermal expansion coefficient is small, and it has a certain strain resistance to rapid cooling and rapid heating. It has strong corrosion resistance to acidic and alkaline solutions, has excellent chemical stability, and does not participate in any chemical reaction during the smelting process. The inner wall of the graphite crucible is smooth, and the molten metal liquid is not easy to leak and adhere to the inner wall of the crucible, so that the metal liquid has good fluidity and castability, and is suitable for casting and molding in various molds. Due to the above excellent characteristics of graphite crucible, it is widely used in the smelting of alloy tool steel and non-ferrous metals and their alloys.

Raw material ratio

The main raw materials of graphite crucible are graphite, silicon carbide, silica, refractory clay, asphalt and tar.
Graphite is the main raw material for crucible production, accounting for 45-55% of the ingredients, with crystalline flake and needle (block) graphite being preferred. my country generally uses flake medium carbon graphite in the production of graphite crucibles, with a carbon content of 85-93%. Select graphite particle size according to the performance, use, model and specifications of the crucible. Usually, large crucibles with a volume of more than 100# use large flake graphite of more than 32 mesh; medium-sized crucibles with a volume of 60# to 80# use 80 mesh flake graphite; small crucibles with a volume of less than 50# use 100 mesh flake graphite; special-shaped crucibles for hand-molding use -100 mesh fine flake graphite.
Refractory clay mainly acts as an inorganic binder for plastic molding. It requires pure clay composition, strong plasticity, and stable physical and chemical properties. It also has high refractoriness and good thermal effect.
Due to the different materials and use conditions of crucible smelting, the proportions of various raw materials in the production ingredients are different. It should be reasonably determined according to the performance, purpose and use conditions of the crucible

Production process

The manufacturing process of graphite crucible can be divided into three types: hand molding, rotation molding and compression molding. The quality of the crucible is closely related to the process molding method. The molding method determines the structure, density, porosity and mechanical strength of the crucible blank.
Hand molding is used for special-purpose special-shaped crucibles that cannot be molded by rotation molding and compression molding. Some special-shaped crucibles can be molded by a combination of rotation molding and hand molding.
Rotation molding is to drive the mold to operate with a rotary can machine, and use the inner knife to extrude the clay to complete the crucible molding.
Compression molding is the use of pressure equipment such as oil pressure, water pressure or air pressure as kinetic energy, and steel molds as molds to form crucibles. Compared with rotational molding, it has the advantages of simple process, short production cycle, high yield and efficiency, low labor intensity, less molding moisture, low crucible shrinkage and porosity, high product quality and density.

Maintenance and preservation

Graphite crucibles should be kept moisture-proof. Graphite crucibles are most afraid of moisture, which has a great impact on quality. If a damp crucible is used, it will crack, burst, fall off the side and bottom, causing the loss of molten metal and even industrial accidents. Therefore, graphite crucibles must be kept moisture-proof during storage and use.
The warehouse where graphite crucibles are stored should be dry and ventilated, and the temperature should be kept between 5℃ and 25℃, and the relative humidity should be 50-60%. Crucibles must not be stored on brick soil or cement floors to avoid moisture. Bulk graphite crucibles should be placed on wooden racks, preferably 25 to 30 cm from the ground. For complete items packed in wooden boxes, wicker baskets or straw bags, sleepers should be placed under the stack, no less than 20 cm from the ground. A layer of tarpaulin should be placed on the sleepers to prevent moisture. After a period of stacking, the stack must be turned over, with the lower layer turned over on the upper layer. It is best to turn the upper and lower layers opposite each other. The time interval between turning over should not be too long. Generally, it should be turned over every two months. If the ground is not too humid, it can be turned over every three months. In short, frequent turning over of the stacks will achieve the best moisture-proof effect.