Nipple pins for UHP graphite electrodes discussion

In order to adjust the resistivity of the nipple pin, a mixture of coal-based needle coke and graphite powder are used. Due to the different surface properties of coal-based needle coke and graphite powder, the adsorption of asphalt is different, resulting in differences in the flow and expansion properties of the nipple pin at higher temperatures, which will affect the spread of the nipple pin between the threads after melting. Experiments show that different ratios of needle coke and graphite powder have different coking strengths, as shown in Table 6. Choosing an appropriate ratio is conducive to improving the consolidation strength.

The particle size of the aggregate also has a great influence on the fluidity of the nipple plug paste. For the electrode and connector with a pitch of 6.350 mm, the contact side is attached after connection, and the non-contact side gap is about 0.25 mm, as shown in Figure 4 . Considering the deviation of processing accuracy and the paste must maintain good fluidity (to ensure that the paste fully fills between the threads before the asphalt is coked), it is appropriate to actually choose a particle size below 200 mesh (0.074 mm).

Foaming performance of expansion agent

The expansion agent plays a vital role in the application of the nipple pin. When the electrode is smelted in an electric furnace, the molten nipple pin must be able to quickly flow out of the nipple pin hole and be distributed between the threads to the greatest extent to ensure that the nipple pin is effectively coking and consolidate electrodes and nipples. The selection of the expansion agent for the nipple plug follows the following principles: First, the expansion agent has good compatibility with asphalt, crosslinking with the saturated and aromatic components in the asphalt, reducing the viscosity of the asphalt, and interacting with coke powder and graphite. The powder should also have good adhesion; Second, a large amount of gas is generated at 140-160 ℃, and foaming makes the paste-like nipple plug rapidly expand. The expansion rate of the nipple plug increases with the increase in the amount of expansion agent. Comparing different experiments, it is best when the added amount of expansion agent meets the expansion rate of 200% to 300%. The nipple pin can firmly consolidate the nipple and the electrode, and the nipple pin is coked and consolidated, as shown in Figure 5 for the consolidation test effect of the nipple pin. If the usage of expansion agent used is too high, the expansion effect is not obvious, and the cost increases more.

Conclusion

UHP graphite electrode nipple plug is specially developed for graphite electrodes for large-capacity and ultra-high power electric arc furnaces. Compared with traditional nipple pins, it has good flow, expansion and coking properties, making the electrode and nipple tightly connected, effectively preventing electrode nipples loosen, buckled, disconnected, broken, and other accidents during usage, and can effectively reduce electrode consumption by about 10%. At present, this product has been applied in ultra-high power electric arc furnaces in many steel plants at home and abroad.