The Methods of Cleaning Press Felt
The methods of cleaning press felt is mainly have two two, mechanical washing and chemical washing.
Mechanical Washing
① Ordinary Low-pressure Shower Pipe: It is a fixed small hole, full width washing, and is a long used method for washing press felt in China. The disadvantage is that it consumes a lot of water and the washing is not uniform enough.
② Felt Washing Tank: a water tank used for washing press felt. After passing through the pressure zone, the felt are soaked in the washing tank during the return journey. After being rinsed by a common low-pressure water spray pipe, whipped by a felt beater, and squeezed by a water squeezing roller, they enter the couch roller (circular screen machine) or press roller (long screen paper machine) in a relatively dry state.
③ Felt Beater: It consists of 2-3 pieces of wooden boards, stainless steel pipes, thick plastic plates, etc. with a length greater than the width of the felt fixed on a shaft. A transmission device is installed at one end of the shaft to drive the felt beater to rotate in the opposite direction to the felt, continuously pulling and beating the felt. The function of a felt beater is to use its suction to blow the felt, causing the dirt trapped in the felt holes to loosen and easily be rinsed clean by the water spray pipe after being subjected to strong vibration, keeping the felt clean.
④ Squeezing Roller: composed of two rollers, upper and lower. The main function is to dry the dirty water from the washed felt, keep the felt clean, reduce the moisture content entering the rolls (cylinder mould) or press rolls (fourdrinier paper machine), reduce paper embossing, and extend the service life of the felt. For needle punching, sewing, and water squeezing, the squeezing roller will squeeze the mesh tighter and affect the washing effect. Therefore, for paper machines with high speed, it is best to use a vacuum suction box and high-pressure moving water needle to wash the felt.
⑤ High Pressure Moveable Shower Pipe: Multiple nozzles are installed on a main pipe, which can move horizontally along the felt. The high-pressure moveable shower pipe is usually installed before the low-pressure fan-shaped shower pipe, and its function is to:
a、 Utilizing high water pressure impact force to disperse the fine fibers, fillers, and adhered dirt on the surface of the felt, loosening the dirt inside the felt mechanism to facilitate the removal of subsequent contributions;
b、 When high-pressure water penetrates the felt, the fiber layer in its structure will restore its loose thickness and elasticity, maintaining the effective water holding volume of the felt and restoring its permeability to a certain extent. The best washing efficiency is to set the reciprocating speed of the washer at a distance of one nozzle diameter per revolution of the press felt. Direction of water jet: When the vehicle speed is low, it can be perpendicular to the running direction of the felt. For paper machines with a speed of over 200m/min, the jet angle should be between 20 ° -45 ° and opposite to the running direction of the felt. This is beneficial for the water jet to directly penetrate the felt, effectively flushing and removing dirt in the gaps of the felt without causing damage to the surface of the press felt.
⑥ Low Pressure Fan-shaped Shower Pipe. Main function:
a、 Further flushing the dirt dispersed by high-pressure water, making it free in sparse water, is beneficial for being sucked away by the vacuum suction box;
b、 Form a uniform water film on the surface of the felt, providing lubrication between the felt and the vacuum suction box cover to reduce wear and tear;
c、 A sealing effect is generated on the surface of the vacuum suction box, thereby forming a stable and high vacuum degree, effectively removing moisture from the felt. The spacing between nozzles and the distance between the felt surface should be evenly sprayed on the horizontal surface of the felt without overlapping spraying surfaces, but no blind spots are allowed. The direction of water spraying should maintain a certain angle with the direction of the felt’s advance, usually 0 ° -30 °, to facilitate the flushing of dirt on the surface of the felt. The optimal amount of water spray is to keep the felt in a saturated moisture state. There are three methods to determine that the felt is in a saturated state: as the water pressure increases and the amount of water sprayed increases, the vacuum degree of the suction box also increases. When the vacuum degree of the suction box no longer increases and is in a stable state, the amount of water sprayed is equal to the saturated water capacity of the felt; Calculate the effective water holding volume of the felt, and then adjust the flow rate of low-pressure water based on the speed of the paper machine; After the low-pressure water spray, the felt passes through the vacuum suction box, and there is no trace of high-pressure water that has penetrated the felt. At this point, the amount of water sprayed makes the felt saturated with water.
⑦ Vacuum Suction Box. The function of the vacuum suction box for washing:
a、 Effectively removing moisture and dirt from the felt through vacuum suction, maximizing the cleanliness and dryness of the return felt, and maintaining good breathability and water filtration of the felt;
b、 The cover of the vacuum suction box usually uses a slit shaped opening, which can evenly and uniformly dehydrate the felt.
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