The technological development of modern electric furnaces also has commonalities. The most obvious one is that the electric furnace hydraulic control system is developing towards high pressure, large flow, high integration, and strengthening the auxiliary functions of accessories.

Optimization of pump source

Most modern large-scale ultra-high-power electric furnace hydraulic systems use high-pressure large-flow pumps as the main working pump. The maximum working pressure of the system has been increased to 18 MPa, and flame-retardant water-glycol or synthetic organic esters are used as the working medium. The increase in the working pressure of the system can better meet the structural needs of large-scale electric furnace equipment, and can effectively reduce the diameter of the hydraulic cylinder, reflecting the transmission characteristics of hydraulic control; and the use of large-flow hydraulic pumps reduces the number of working pumps, so The area of the hydraulic station room can be greatly reduced, which is more conducive to the process layout of the electric furnace steelmaking zone.

Improvement of energy storage device

The electric furnace hydraulic system must be equipped with emergency measures to deal with accidents, and setting up a hydraulic energy storage device is a common method. This is the safety technical requirement of the electric furnace steelmaking process for the hydraulic system. The purpose is to release the pressure oil in an emergency situation to ensure the completion of the hydraulic action of some important mechanisms of the electric furnace (such as: the rapid lifting of the electrode, the safe reset of the furnace body Wait). Due to the large demand for liquid motor volume, the previous energy storage devices mostly use energy storage tanks. The structure of the energy storage tank is that the gas and liquid are in direct contact. In actual use, if the operation is improper, the high-pressure gas in the tank will infiltrate Air bubbles are generated in the pipeline, which seriously affects the normal operation of the system. Therefore, most current systems use piston accumulators.

In contrast, piston accumulators have many advantages. It not only has large energy storage, but also can isolate the contact between gas and liquid by virtue of its own structural characteristics, and at the same time can pressurize the gas in the tank to complete its own high-pressure inflation.

Table 1 shows that: only one electric furnace hydraulic system uses an accumulator tank, and the other three systems have used piston accumulators. Obviously, the latter configuration is better.

Compact valve control device

The hydraulic valve preferentially selects the superimposed valve supplied in a complete set. Even if there are non-standard processed hydraulic manifold blocks, the hydraulic valves are arranged tightly around the geometric plane of the manifold block to achieve a high degree of integration of the valve block. See Figure 1 for details. .

图1　150 t电炉倾动控制液压集成块

Strengthen the auxiliary function of the accessory parts

Specifically:

a) Increase the damping device to reduce the noise of the high-pressure pump set. In the current electric furnace hydraulic system, the transmission power of each hydraulic pump is often 75 kW or 90 kW. In order to reduce the mechanical noise of the transmission, the entire hydraulic pump device is flexibly connected to the outside, that is, the suction pipe of the hydraulic pump is connected to the outside through a rubber tube. The oil tank is connected, the oil outlet pipe of the hydraulic pump is connected with the valve block by a high-pressure hose, and the elastic shock-absorbing pad set under the transmission base can make the whole set of hydraulic pump device be placed on the foundation;

b) The pipeline is equipped with additional pressure measurement and venting points, which is convenient for system debugging and daily maintenance. In electric furnace machinery, the positioning elevation of most hydraulic cylinders is significantly higher than that of the hydraulic valve table. Therefore, adding pressure measurement and air release points at the highest part of the pipeline is more conducive to the air release of each oil pipe;

c) Set up a filter to ensure that clean cooling water enters the cooler. This is mainly set for the winter cooler may not be involved in the work, to ensure that the cooling water pipe can input clean cooling water to the cooler after being idle for a period of time;

d) Set the pressure gauge and temperature gauge to display the actual working condition of the cooling water. In order to understand more intuitively whether the cooling water meets the requirements and how the cooling effect is, it is necessary to set the above two tables on the cooling water pipe.

Important controls:

Emphasize the cooperation with the main equipment to improve system safety

An important sign of modern electric furnace steelmaking is a significant improvement in the degree of process automation control. The safe operation and interlocking of each control subsystem is an important guarantee for the normal production of electric furnace steelmaking. Therefore, the modern electric furnace hydraulic system not only pays attention to its own reliability, but also emphasizes the safety cooperation with the main equipment.

The most obvious is that there are more hydraulic valve control devices installed on the hydraulic cylinder. There are some very important hydraulic control mechanisms on the electric furnace body, such as: electrode lifting, furnace body tilting, and the hydraulic cylinders of the EBT tap hole opening and closing mechanism need to be specially designed for machine-liquid integration. Since the cylinders of these hydraulic cylinders are in motion, and hoses are used when connecting the pipelines to the hydraulic cylinders, additional consideration should be given to the safety of the use of the hoses, in order to ensure that the above-mentioned mechanisms can be used in unexpected situations (such as sudden bursts of hoses or hydraulic system failure). (Press) can be positioned immediately without falling, some special hydraulic devices need to be separated from the original valve table and directly installed on the hydraulic cylinder. This requires a combination of system design and equipment design to jointly solve installation problems. This is a typical example of the cooperation between the hydraulic system and the main equipment. The hydraulic system is no longer designed in isolation.

Figure 2 is a hydraulic valve control device installed on the furnace body tilting hydraulic cylinder.

图2　炉体倾动液压缸上的阀控装置

Application of hydraulic proportional control technology

With the development of hydraulic technology and the needs of large-scale electric furnace equipment, other important mechanisms of modern electric furnaces, such as: electric furnace body tilting, furnace cover rotation, furnace cover lifting, etc., all adopt hydraulic proportional control like electrode lifting control. The application of hydraulic proportional control technology better realizes the soft switching of the operating speed of the mechanism, overcomes the adverse effects of the huge mechanical inertia on the transmission mechanism, and makes the mechanism run more smoothly.

For example, the tilting of the furnace body of an electric furnace. The use of EBT (ie eccentric bottom tapping) technology is an important symbol of modern electric furnace steelmaking technology. In EBT technology, the tilting angle, tilting speed, and back tilting speed of the electric furnace body have become very important. For the furnace body, during the tapping or slagging process, due to the continuous change of the tilting angle and the fact that it is at a certain angle Restarting after locking puts forward speed control requirements for its hydraulic transmission. Figure 3 is a schematic diagram of the furnace body tilting of a large eccentric hearth type ultra-high power DC electric arc furnace introduced by a domestic steel plant. The hydraulic control uses a proportional directional control valve.

a)冶练　　　　　　　　　b)出钢

图3　偏心炉底式直流电弧炉的炉体倾动示意图

The EBT tapping process is as follows:

a) First, the furnace body is tilted to 6° at a speed of 62 mm/s (1°/s) and locked. After confirming that the tapping conditions are met, the tapping opening baffle opens to realize the first tapping of the electric furnace.

b) During the subsequent tapping process, the furnace body is still tilting forward at a speed of 62 mm/s (1°/s) (the maximum inclination angle is 25°). When the furnace is tilted to 12°, the furnace body is locked and a confirmation during the tapping process is completed; afterwards, the furnace continues to be tilted. When the molten steel contained in the ladle reaches the calibrated tonnage, the ladle weighing device sends a message, instructing the furnace body to be 186 mm/s (I.e. 3°/s), the speed quickly tilts back to +3° to achieve deceleration, and completely stops at 0°. Obviously, if the tilting speed of the furnace body is too slow, it may cause tapping with slag, affect the quality of molten steel, and increase the burden of secondary smelting.

Because the tilting furnace adopts hydraulic proportional control, the function of "slow start-constant speed operation-slow stop" can be realized every time the furnace body moves to ensure smooth switching of the operating speed. Proportional control is very suitable for super-large operation equipment such as body protection, and the actual operation effect is also the same.

Feature control

Charging technology of high pressure accumulator

The modern electric furnace hydraulic system uses a piston accumulator, so its structural characteristics can be used when charging it with nitrogen. With the help of a special valve control device, the charging can be completed. The charging pressure can reach up to 21 MPa. 4 Explain its specific inflation principle.

1. Accumulator unit 　 2. Working pump 　 3. Nitrogen source 　 4. Stop valve 　 5. Check valve 　 6, 9. Safety valve 　 7. Piston accumulator 　 8. Gas cylinder 　 10. Pressure gauge

Figure 4 　 Piston type accumulator charging principle

Author unit: Shanghai Metallurgical Design and Research Institute