Nipple pins for UHP graphite electrodes

1 Preparation process

The preparation process is shown in Figure 3.

(1) Grinding

Graphite, needle coke, and hard pitch are ground separately, and the purity is controlled above 70%.

(2) Mixing

Weigh the pitch, graphite powder, and needle coke powder into the mixer according to the formula ratio. After mixing for 5 minutes, weigh the expanding agent according to the formula and pour it into the mixer, and continue mixing for 40 minutes. There should be no agglomeration in the mixed material, if there is agglomeration, use a screen to remove it.

(3) Suppression

The fully mixed materials are measured and put into the mold. The size of the mold can be selected according to the size of the joint bolt produced. This test uses a Φ35 mm × 45 mm mold (a set of 6). Adjust the pressure of the molding press to 9～10 MPa for pressing, and keep the pressure for 20 s. The pressed joint bolts are placed in an iron plate covered with kraft paper.

(4) Baking and curing

Put the formed joint bolt into the oven, adjust the temperature at 90～95 ℃, the baking time is 1～1.5 h, and then take it out for cooling.

(5) Inspection, testing and packaging

After cooling, the joint bolts are subjected to visual inspection and physical and chemical index tests. Qualified connector bolts can be packaged and spared. The study of nipple pins for UHP graphite electrodes.

2 Physical and chemical indexes of joint bolt

The index of the joint bolt is shown in Table 4.

 Table 4 Indicator requirements of nipple pin

3 Practical application of joint bolt

The manufactured joint bolt was tested and applied on a 150 t ultra-high power electric furnace. The comparison of the joint bolt before and after use is shown in Table 5. A total of one and a half months of follow-up testing, totaling 150 t electrodes, the parameters of the electric furnace are as follows:

Nominal capacity: 150 t AC furnace; Transformer capacity: 100 MVA; Rated operating current: 65 kA; Maximum operating current: 100 kA; Secondary voltage: 550～900 V; Smelting time: 55 min; Electrode consumption: 1.10 kg/t Molten steel (assessment index).