Product graphitization crack prevention

The graphitization process should be reasonable

(1) Selection of furnace loading method

In the production process of the Acheson graphitization furnace, a reasonable furnace loading method is the guarantee for the graphitization of the products. Whether the product adopts the vertical installation method or the horizontal installation method, whether it is a formal installation or a wrong installation, should be determined according to the variety, specifications, quality standards and process parameters of the equipment to ensure that the heating of the product in the furnace core is relatively uniform, so as to reduce the Thermal stress, reducing cracks in the product during graphitization. For large-sized products, the dislocation 1/2D furnace charging method can reduce product cracks and achieve good graphitization effect. For products with high graphitization crack rejection rate and unstable quality, furnace core flow equalization measures can also be taken.

(2) Determine a reasonable power-on system

The temperature of the graphitization furnace core is controlled by the power curve of the constant power distribution. The correct and reasonable formulation and application of the graphitization furnace power-on system are very important for improving the yield, saving energy and shortening the graphitization cycle of products. significance. The determination of the energization system of the graphitization furnace should not only take into account factors such as furnace structure, product variety and specifications, quality information, resistance materials, thermal insulation effect, parameters of the power distribution system, etc. Different stages have different requirements for the temperature rise rate.

A reasonable power-on system for the graphitization furnace should be a "fast-slow-fast three-stage power curve to meet the different requirements of the product in the three stages of the temperature rise process, and the furnace core should have a faster temperature rise speed. Reduce the heat dissipation loss of the graphitization furnace, and prevent the temperature gradient of the furnace core from being too large to cause cracks in the products. For products with unstable graphitization quality, it is necessary to strictly control the temperature rise rate of the furnace core in the temperature rise stage to avoid excessive temperature rise. To cause cracks in the product, the rising power of the power transmission curve should be adjusted appropriately to form a four-stage power transmission curve of "fast-slow-slow-fast".

(3) Determine the appropriate resistor material

The Acheson graphitization furnace mainly heats the product by the heat generated by the current passing through the resistance material. The resistance material is closely related to the temperature change of the furnace core. From the perspective of increasing the temperature of the graphitization furnace core, the resistance of the resistance material is required to be larger. Especially in the later stage of power transmission, the secondary output current of the transformer has reached the maximum value, and the furnace core resistance is large at this time, which can maintain a high electrical efficiency; but the resistance of the resistance material is too large, which is unreasonable. Therefore, when determining the resistance material, it is necessary to consider not only the performance of the equipment, but also the variety and specification of the product and the power transmission curve, so that the resistance of the product and the resistance of the resistance material cannot be too different. For small and medium-sized products, metallurgical coke can be used as resistance material. Even if higher starting power and faster rising power are used, cracks are generally not produced in the product; for large-sized products, mixed coke or graphitized coke is used as resistance material. It is more appropriate, so that the resistance difference between the product and the resistance material is small, and the temperature difference between the inside and outside of the product is also reduced. Even if a faster rising power is used, it will not cause cracks in the product.

Second, the quality of operation must meet the standard

In the process of graphitization production operation, the furnace loading operation is the key. Since the products loaded into the graphitization furnace are both heating resistors and objects to be heated, the furnace core resistance is formed together with suitable resistance materials. Core resistance is a necessary condition for graphitization of products. First of all, the condition of the furnace body of the graphitization furnace, the short bus network, and the equipment of the power supply system should be in good condition. When installing the furnace, the section of the furnace core should be symmetrical with the conductive section to prevent the furnace core from drifting. The furnace installation operation should meet the requirements of the process technical regulations. The products should be arranged horizontally and vertically in the furnace core, the group spacing of the products should be consistent, and the resistance material should be well filled to avoid the phenomenon of hanging, and ensure that the temperature distribution of the furnace core is balanced during the power transmission process of the graphitization furnace. Secondly, the ratio of resistance materials should meet the requirements of production process technical standards, and the quality should be stable and uniform, so as to avoid the uneven temperature distribution of the furnace core during the power transmission process of the graphitization furnace. Thirdly, the graphitization furnace should transmit power according to the given power transmission curve, and the power fluctuation should be controlled within the normal range to avoid abnormal fluctuation of the transmission power, so as to ensure that the temperature of the furnace core rises evenly.

3. Master the quality information of the previous process

It is necessary to grasp the production situation and quality information of the previous process in a timely manner, according to the production stability and quality technical indicators of the products in the previous process, combined with the actual production of this process, formulate feasible graphitization production process and technical conditions to prevent the products from being in the graphitization process. Cracked waste products appear to ensure stable graphitization quality. When the graphitization furnace is installed, the appearance and body quality of the products should be checked one by one. For products that do not meet the technical conditions of the graphitization process, they should not be loaded into the graphitization furnace for graphitization, and the materials should be returned to the upper process in time.

4. Add an appropriate amount of inflation inhibitor to the ingredients

The irreversible expansion cracking phenomenon caused by the presence of sulfur in the graphitization process cannot be completely eliminated, but it must be controlled. At present, the most effective way is to control the escape rate of sulfur during the graphitization process of the product. The most practical way is to add an appropriate amount of inflation inhibitor during batching, usually 1%-2% Fe2O3 powder.

Regarding the mechanism of adding a swelling inhibitor, the main reason is that the inhibitor can capture sulfur in the temperature range of graphitization and swelling of the product to generate sulfur compounds and form gas in a higher temperature range, thereby widening the sulfur content. The escaped temperature range prevents the product from cracking due to excessive internal stress caused by the concentrated and rapidly escaping gas. The most commonly used inflation inhibitor is Fe2O3 powder. Its mechanism of action is that at high temperatures above 1000 degrees, Fe2O3 powder is easily reduced to form iron or carbon-iron compounds, and carbon-iron compounds will be further decomposed into iron and iron at higher temperatures. Carbon, iron formed in this process reacts with the sulfur released from the decomposition of the product, and is slowly released in the form of iron sulfide, thereby slowing the escape rate of sulfur in the product and inhibiting sulfur. The relevant chemical reaction formula is:

• Fe203+3C=3C0+2Fe
• 2Fe203+9C=Fe4C+6CO
• Fe4C3=4Fe+3C (graphite)
• Fe+S=FeS

Since Fe2O3 powder not only has a high chemical affinity for sulfur in products, but also has a good effect of inhibiting sulfur, and has abundant resources and low price, it will not have any adverse effects in the process of electric furnace steelmaking. In addition, Fe2O3 powder also has a strong catalytic effect on the graphitization process of the product, and is an excellent graphitization catalyst. It can be seen that for petroleum coke with high sulfur content, adding an appropriate amount of inflation inhibitor Fe2O3 powder can play a multiple role in the production of carbon-graphite products.

In a word, the reasons for the generation of cracked waste products in the graphitization heat treatment process of carbon-graphite products are various and complicated. To prevent the generation of cracked waste products during the graphitization heat treatment of carbon-graphite products, it is necessary to take various technological improvement measures, and pay equal attention to the specimens. The most important thing is that the body quality of the product should be high, the heat resistance performance should be better, and the production should be homogenized. In the process of graphitization heat treatment, the product in the Atchison graphitization furnace core temperature rise speed should be strictly controlled, to avoid the core temperature rise speed too fast, the product internal temperature difference increases, causing thermal stress also increases correspondingly, and crack waste products.