Continuous casting machine cooling water system characteristics and water quality requirements. The characteristics of the butterfly valve and the ball valve are mainly described, and the role of the valve in the cooling water system of the continuous casting machine is analyzed, and the selection method is given.
1 Introduction
Valves are used in a wide range of applications and are very useful. In the continuous casting machine cooling water system (hereinafter referred to as the water system), the valve regulates the flow; opening, closing, overhaul, etc., which can ensure the normal operation of the continuous casting machine equipment, extend the service life of the equipment, and ensure that the continuous casting machine can produce qualified. Slab.
However, the valve is often neglected compared to other equipment in the continuous casting machine. If the valve is improperly selected, the entire cooling system will have insufficient adjustment capability, low production efficiency or cause other accidents. Therefore, the water system valve should be reasonably selected according to the special requirements of the continuous casting machine.
2, continuous casting machine cooling water system
The cooling water system is divided into four systems: (1) Crystallizer cooling water system, the water quality is soft water, the inlet water pressure is about 1.0 MPa, and the temperature is 35-55 °C. (2) Equipment indirect cooling water system, the water quality is net circulating water, the inlet water pressure is 0.6-0.8 MPa, and the temperature is 40-55 °C. (3) Secondary cooling water system, the water quality is turbid circulating water, the inlet pressure is constant pressure of 1.0 MPa, and the temperature is about 40 °C. (4) The equipment directly cools the water system, the water quality is turbid circulating water, the inlet pressure is not less than 0.4 MPa, and the temperature is about 40 °C. Table 1 shows the water quality requirements of each system.
3. Selection of water system valves
According to the requirements of the continuous casting machine cooling water system, the system should use metal material valves with low pressure PN≤1.6MPa, normal temperature -40°C≤t≤120°C, and non-extra large diameter DN≤1400mm. The water system valve must meet the general performance requirements, but also meet the special performance requirements of the continuous casting machine. The following is the analysis of the butterfly valve and ball valve commonly used in the water system.
3.1, the choice of butterfly valve
The butterfly valve is a valve that opens, closes and adjusts the fluid passage by reciprocating the disc type opening and closing member by 0°~90°.
(1) Commonly used midline butterfly valve and double eccentric sealing butterfly valve for water system
When the double eccentric butterfly valve plate is opened from 0° to 90°, the valve plate can be completely separated from the seat sealing surface from 0° to 8° to 12°, so that the mechanical wear between the valve plate and the sealing surface of the valve seat is relatively mechanical. The squeezing angle is shorter, which improves the life of the valve. Figure 1 shows the principle of opening and closing the double eccentric butterfly valve. Since the filter of the water system pipeline (the pipeline above DN100) often needs to be repaired and cleaned, the double eccentric butterfly valve is especially suitable for the inlet, outlet and bypass of the filter, and the other selection of the midline butterfly valve can meet the life requirement of the water system.
(2) has good sealing
The valve sealing material has a synthetic rubber seat and a composite valve seat made of polytetrafluoroethylene and synthetic rubber. Because the synthetic rubber is easy to age, wear and fall off, it may block the water seal of the crystallizer copper plate, the nozzle of the fan segment, the bearing block of the segment, etc. Therefore, the composite valve seat made of PTFE and synthetic rubber is more suitable for continuous casting equipment. Fig. 2 is a composite valve seat center line butterfly valve composed of polytetrafluoroethylene and synthetic rubber.
(3) has good flow regulation characteristics
When the butterfly valve is opened between 15° and 70°, it can perform sensitive flow control, especially for the crystallizer copper plate cooling circuit, and the pneumatic regulating valve and electromagnetic flowmeter on the circuit can effectively compensate the adjustment range of the pneumatic regulating valve. Figure 3 shows the application of the butterfly valve in the mold copper plate cooling circuit.
(4) The pressure loss of the butterfly valve in the pipeline is relatively large, about three times that of the gate valve. Therefore, the influence of the pressure loss of the pipeline system should be fully considered when selecting the butterfly valve.
Figure 3 Butterfly valve in the mold copper plate cooling circuit application
The pressure loss caused by the valve in the pipeline can be expressed as:
In the middle
ΔP is the pressure loss caused by the valve in the pipeline, MPa; K is the pressure loss coefficient of the valve; K1 is the pressure loss coefficient caused by the partial opening of the valve. When the valve is fully open, K1=1; v is the average velocity of the water flow, m/ s; ρ is the density of water, kg/m 3 .
The pressure loss coefficient K of the butterfly valve is about 0.2 to 1.5 depending on the thickness of the valve plate. Figure 4 is an approximate result of the butterfly valve K1.
3.2, ball valve selection
The ball valve is evolved from a plug valve. Its opening and closing member is a ball that is opened and closed by rotating the ball 90° around the axis of the valve stem.
(1) The ball valve of the floating ball valve and the V-shaped opening is often used in the water system, and is used on the pipeline whose pipeline is not larger than DN125. The floating ball valve mainly functions as opening and closing; the V-shaped open ball valve is used for flow adjustment. Figure 5 is a floating ball valve, and Figure 6 is a flanged V-shaped opening adjustment ball valve.
(2) It has good sealing properties. The commonly used sealing material for water system is polytetrafluoroethylene, which has small friction coefficient, stable performance and is not easy to age.
(3) Compared with the butterfly valve, the V-shaped open ball valve has better flow regulation characteristics. Turbine-driven V-shaped open ball valve has the function of precise adjustment and reliable positioning. The flow characteristics are approximately equal percentage, the adjustable range is large, and the large adjustable ratio of Zui is 100:1. Figure 7 shows the adjustment characteristic curve of the V-shaped open ball valve. This kind of ball valve is suitable for the branch of the secondary cooling system. It can compensate the adjustment range of the pneumatic regulating valve more accurately with the pneumatic regulating valve and electromagnetic flowmeter on the circuit. It is suitable for the indirect cooling backwater branch of the equipment and is matched with the local display. The flow meter precisely adjusts the amount of water dispensed to each segment.
(4) It has a low flow resistance of zui. For a full-bore ball valve, the flow resistance can be regarded as zero in the fully open state.
4 Conclusion
(1) Butterfly valve is suitable for pipelines above DN125 in water system; double eccentric sealing butterfly valve is used for inlet and outlet of filters that are frequently opened and closed; bypass valve is used for flow adjustment in the return line of crystallizer; Composite valve seat made of tetrafluoroethylene and synthetic rubber; pressure loss should be considered when selecting butterfly valve.
(2) The ball valve is suitable for pipelines below DN125; the turbine-driven V-shaped open ball valve is used for precise flow adjustment on the secondary cooling branch and the indirect cooling return branch of the equipment; the PTFE seat is used for the seal; The ball valve, in the fully open state, does not consider the pressure loss caused by the ball valve on the pipeline.
(3) For the requirements of the continuous casting machine cooling water system, the butterfly valve and the ball valve can completely meet the precise adjustment of the opening, closing and flow of the pipeline, and can replace the valves such as gate valves and globe valves.
