During the graphitization process, the internal factor of cracks in the product is the low quality of the product itself and poor heat resistance; the external factor is that the temperature of the furnace core rises too fast during the graphitization process, and the temperature difference between the top and bottom of the product or around the product is also With the increase, the thermal stress also increases correspondingly, which is the main reason for the cracking of the product.

1. The graphitization process system is unreasonable

① Furnace loading method

Graphitization furnace products are usually installed in a vertical installation method, and the vertical installation method has two forms: normal installation and wrong installation. When the furnace core product is being installed, for any product, there is only one high-density current heating belt. The wider the heating belt, the more uniform the heating of the product. When wrongly installed, there are two high-density current heating belts for each product, and the heating of the product is more uniform than that of the formal installation. Therefore, the loading method of graphitization furnace products is not properly selected. During the process of graphitization and power transmission, the temperature rise rate around the product varies greatly, and the thermal stress generated by the product exceeds the thermal stress that the body can withstand, which is very easy to cause cracks in the product. 

②The power-on system is unreasonable

The temperature change curve of the graphitization furnace core is controlled by the power curve of constant power distribution. If the energization system of the graphitization furnace is unreasonable, the starting power of the determined graphitization furnace energization curve is too large and the rising power is too fast, so that the product is energized. During the process, the temperature gradient inside and outside is too large, and the thermal stress generated greatly exceeds the resistance of the product, resulting in cracks. Especially when the furnace temperature is 1300-1800 degrees, in order to strictly control the furnace temperature rise stage, the physical structure and chemical composition of the product begin to change greatly at this stage, and the graphitization of amorphous carbon does not start. In fact, the chemical reaction is Mainly, the elements such as hydrogen, oxygen, nitrogen, sulfur and other elements bound in the microcrystalline structure of amorphous carbon continue to escape. As a result of the escape, the impurity elements in the edge part of the microcrystalline structure of amorphous carbon continue to decrease, and some lattice defects remain. At the same time, the thermal stress is relatively concentrated, and it is very easy to cause cracks in the product.

③The resistance of the resistance material

The resistance of the graphitization furnace core is composed of the resistance of the product and the resistance of the resistance material in series. When the graphitization furnace starts to energize, the resistance of the resistance material accounts for about 99% of the resistance of the furnace core. About 97%, it can be seen that in the whole graphitization process, it is mainly the heat generated by the current passing through the resistance material to heat the product. When the resistance of the resistance material is quite different from the resistance of the product, the heat generated by the resistance material is far away during the graphitization and electrification process. It is far greater than the heat of the product itself, causing the temperature difference between the inside and outside of the product to be too large, which will cause excessive thermal stress to cause cracks in the product.

2. The quality of roasted products

①Internal cracks in roasted products

According to information, the temperature range of 350-500 degrees and 700 degrees and above is the most dangerous temperature range where carbon materials may be damaged during the roasting process. When the outer surface temperature of the product is 800 degrees and the maximum radial temperature difference is 10.7 degrees, the area with a radius of 50-65mm determines the strength of the material, and a dangerous tensile stress area is formed within the radius of 65mm from the center of the blank. When the temperature is 700 degrees or higher, the stress in this area is far greater than the limit of the breaking strength of the material, which is why the product produces longitudinal straight cracks, which generally do not extend to the outer surface of the product, that is, the product of internal cracks.

②The homogeneity of the product

The uniformity of the density distribution of carbon-graphite products, the uniformity of the radial density and the axial density distribution of the products is closely related to the quality of the products during the graphitization heat treatment process. Where the density distribution of the product is uneven, in the process of graphitization heat treatment, due to the thermal stress, the product is prone to internal stress, and the internal stress distribution of the product is also uneven. This uneven internal stress is easy to cause cracks in the product. As a result, cracked waste products appear during the graphitization process.

③The bulk density of the product is high

The bulk density of carbon-graphite products mainly varies with the production raw materials and technological conditions. The flexural strength, elastic modulus and thermal conductivity of the products increase with the increase of bulk density. When the bulk density is high, the elastic modulus of the product increases and the brittleness increases, resulting in poor thermal shock resistance of the product. During the graphitization heat treatment process, the thermal stress generated by the high temperature greatly exceeds the stress that the product itself can withstand. , There is a large difference between the internal and external stress, and the product produces cracked waste.

④The production of the previous process is unstable

Since graphitization is the last heat treatment process in the production of carbon-graphite products, it is also the heat treatment process with the highest temperature. It is generally believed that when the production of the current process is unstable or the quality fluctuates, it will be exposed intensively during the graphitization process. If the temperature of the calcined material is low, the softening point of the asphalt is unqualified, the roasting temperature is low, and the weight gain rate of the impregnation is unqualified, etc., the product will cause secondary shrinkage or uneven shrinkage during the high temperature graphitization treatment, and it is very easy to produce cracked waste products.

⑤Bloat phenomenon

A certain degree of irreversible volume expansion occurs during the graphitization process of the product. The main reason is that the product is caused by the rapid escape of sulfur concentration during the graphitization process. The degree of this irreversible expansion increases with the increase of sulfur content and The increase in the heat treatment rate increases, and this irreversible expansion behavior is called "blowing phenomenon".

It is well known that the content of non-carbon elements such as hydrogen, oxygen, nitrogen, etc., is generally less than 0.1% in petroleum coke after calcination at 1350 temperature; The bond begins to break above 1400 degrees, and sulfur and sulfur-carbon compounds are formed; at higher temperatures, mainly at 1500-1800 degrees, the generated sulfur and sulfur-carbon compounds are rapidly released from the product in the form of gas When the sulfur content reaches a certain level, it often leads to cracks in the products during the graphitization process.