Pressure Screen is a pulping equipment, which belongs to the category of equipment accessories. It has many types, but its basic structure and working process are generally similar. The difference is the way of generating pressure pulse, the strength of pulse and the use of positive and negative pulses. Then, let's take the external flow rotor screen as an example to introduce the screening process of the pressure screen.
Usually, when the pulp enters the screen drum along the tangential direction with a certain pressure, it will move from top to bottom, and the good pulp will pass through the screen hole under the pressure difference between the inside and outside of the screen drum.
There are generally 2-3 blades on the rotor of the vertical rotor screen, and the gap between the rotor blade rotor surface and the screen drum is very small. When the rotor moves along the surface of the screen drum, the pressure difference of the pulp near the head of the rotor increases, and as the gap between the tail and the screen drum gradually increases, local negative pressure appears in this area. When the negative pressure generated makes the absolute value of the pulp pressure inside and outside the screen drum equal, the pulp stops passing through the screen holes. When the negative pressure continues to increase, the good pulp outside the screen drum returns to the screen drum through the screen holes, playing the role of recoil the pulp mass and coarse fibers adhering to the screen holes. This ensures the normal operation of the pulp screen. The negative pressure caused at the trailing edge of the rotor is relatively large. After the rotor passes, the negative pressure gradually decreases, and the pulp flows out again relying on the pressure difference and the push of another rotor to start the next cycle.
The size of the negative pressure caused by the movement of the rotor depends on the cross-sectional shape of the rotor and its distance from the inner wall of the screen drum. The degree of unobstructedness of the screen hole is proportional to the size of the negative pressure, the square of the rotor movement speed and the number of times the rotor passes.
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