graphite electrode with nipples
Research on UHP graphite electrode with nipples joint bolt
Since the invention of the electric arc furnace steelmaking method in 1899, after more than one hundred years of development, the electric arc furnace steelmaking has become the main process for smelting special steel. Graphite electrode with nipples has the advantages of good electrical and thermal conductivity, good toughness, strong current impact resistance, high temperature non-softening and melting, easy processing, convenient production and use, etc. It is an irreplaceable high-temperature conductive material for electric arc furnace steelmaking. In recent years, with the rapid economic development, the demand for special steel has become more and more extensive, resulting in the rapid development of electric arc furnace steelmaking technology. Large-capacity and high-power electric arc furnaces and large-scale out-of-furnace refining technologies have become the modern iron and steel industry. Sign. According to the rated capacity of electric arc furnace transformers, the International Iron and Steel Institute (IISI) recommends 100-200 kVA/t for low-power electric arc furnaces, 201-400 kVA/t for medium-power electric arc furnaces, and 401-700 kVA/t for high-power electric arc furnaces. 701～1 000 kVA/t are ultra-high power arcs. The electrodes that match the above electric furnace are RP (normal power) graphite electrode with nipples, HP (high power) graphite electrode with nipples and UHP (ultra high power) graphite electrode with nipples.
In the use of graphite electrode with nipples, usually several electrodes are connected to form an electrode column through a joint. The graphite electrode with nipples joint adopts a conical joint, and the thread is a triangular thread. Such a thread has a large contact area to use the friction between the threads to achieve a firm connection. Different specifications of electrodes have corresponding connection tightening torques. However, compared with cylindrical joints, tapered joints have more serious back-offs. In particular, the ultra-high power arc furnace has the characteristics of low voltage, large current and high energy density. Due to the strong vibration induced by the continuous arc, considerable force is periodically applied to the electrode column, which can easily cause the joint to pull back. Moreover, during smelting, the swing of the electrode column up and down, the impact of the charge, etc., will aggravate the loosening and back-out of the threaded connection between the electrode and the joint, and cause the electrode column to fall off or break, as shown in Figure 1. graphite electrode with nipples products
In order to prevent the loosening and withdrawal of the electrode during use, the main measures taken by the electrode manufacturer are joint bolts (pressing or potting), joint paste (disc-shaped), joint pins, joint powder, glue, etc. Currently, joints are commonly used. Tie form. In recent years, China Pingmei Shenma Group Kaifeng Carbon Co., Ltd. has been purchasing joint bolts outsourcing, and the use effect is very unsatisfactory. The joint bolts hardly flow out from the bolt holes, and the effect of consolidating joints and electrodes is not achieved, as shown in Figure 2. Inside the round frame.
The joint bolt must meet the following conditions during use: first, it must have good fluidity, foam expansion performance, and be quickly distributed between the electrode and the thread of the joint at 150~250 ℃; second, it must be able to form sufficient bonding The coke must have sufficient strength; the third is that it can be transformed into a material with good electrical conductivity as the temperature rises. To this end, by analyzing the actual use of the joint bolt in the steel plant and consulting the literature, then formulating the test plan, implementation plan, test result comparison, and plan optimization, the UHP graphite electrode with nipples joint bolt was developed, and the sample was tracked at 150 t The use of ultra-high power electric stove.
Raw material selection
Traditional joint bolts often use ordinary petroleum coke as the main raw material. Compared with needle coke, ordinary petroleum coke has the disadvantages of poor electrical conductivity, large oxidation loss at 600-800 ℃, and easy peeling of particles. According to the ultra-high power graphite electrode with nipples joint bolt should have good fluidity and expansion at lower temperature, good consolidation and conductivity at higher temperature, graphite powder and calcined coal series needle are selected. Coke powder, hard pitch and expansion agent are used as raw materials.
1) Graphite powder and coke powder
Graphite powder and calcined coal-based needle coke powder have lower resistivity, higher conductivity, and have certain strength after being carbonized with pitch. The physical and chemical indexes of graphite powder and coke powder are shown in Table 1.
2) Hard pitch
Coal tar pitch is a thermoplastic substance, which has good fluidity within 140-250 ℃, and is a lipophilic and hydrophobic substance. It has properties similar to artificial graphite and needle coke. It can form high-strength coke at high temperatures. Hard pitch is relatively medium temperature. Asphalt has a high coking value and is suitable for the production and application of joint bolts. See Table 2 for the physical and chemical indexes of hard coal pitch.
3) Expansion agent
The expansion agent can produce a lot of gas when the asphalt is low in viscosity, so that the joint paste can quickly flow out of the plug hole and fill the space between the threads. The index requirements of the expansion agent are shown in Table 3.