Improvement of snake tube leakage treatment method

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The improvement of the treatment method for the leakage of dryer serpentine tube

key words will promote the plastic extruder industry out of the dilemma: air cushion dryer; Heater coil; Plugging; Pressure rising seal; Self tightening plug

papermaking in the 1990s, our company introduced fclc air cushion dryer from flakt company in Sweden to dry pulp board. This dryer occupies less land and has high efficiency in drying pulp board. The equipment mainly consists of 108 qlbf type serpentine heaters, each of which is welded with 108 serpentine copper tubes. The serpentine tubes heated by steam are used to heat the surrounding air, which is then brought in by the circulating fan and distributed to the paper through the bellows to complete the drying of the pulp. However, after years of operation, long-term cavitation makes some snake tubes easy to become thin and perforated, resulting in steam leakage. The main effects are as follows: ① the leakage of steam should be cleared off the workbench after the experiment, which will increase the air humidity in the dryer and affect the drying effect of the pulp amplitude; ② The pulp has high moisture content, which affects the service life of the cross cutter of the plate cutter; ③ Waste of energy; ④ The leakage of steam also aggravates the corrosion of serpentine heater; ⑤ Affect site management (site cleanliness). Therefore, it is necessary to deal with the leaking serpentine pipe in time to reduce the losses caused thereby

1 slurry pressure rising sealing structure, plugging principle and operation steps

for the problem of snake tube leakage, I have used conventional methods such as spray welding plugging and repair agent repair, but they are difficult to achieve satisfactory results due to their difficult operation, long processing time, and large repeated leakage rate. Through exploration and many times of verification, the author summarizes an efficient, fast and safe plugging method - pressure rising sealing plugging method, which has achieved good results. Now it is introduced as follows:

1.1 structure and material selection of pressure rising seal

the main structure of pressure rising seal is self tightening plug. Therefore, before pressure rising seal, make self tightening plug first. Its structure (as shown in Figure 1) is composed of nuts 1 and 2, pressing plate 3, sealing ring 4, screw 5, etc. The nut 1 and the screw 5 are welded into a whole, which plays the role of fixing the screw when the nut 2 is tightened

because the medium in the snake tube is steam, its pressure is 0.2 ~ 0.4MPa, in order to prevent cavitation and rust, which affects the life of the plug, the metal material can be 1Cr18Ni9Ti. If this factor is not considered, other materials can be selected. Because the steam temperature is as high as 180 ℃, the sealing ring material can be polytetrafluoroethylene, which is resistant to acid, alkali, oil and other corrosive media, and the applicable temperature range -

Figure 1 self tightening plug

copy 6 in order to make the plug play an effective sealing role, the surface roughness and dimensional accuracy of the seal must be guaranteed. The surface roughness Ra of the sealing ring is required to be 12.5 ~ 6.3 μ m. The machining trace of the sealing surface must be concentric with the inner wall, and the tolerance range of the outer diameter and the inner diameter of the snake tube must be 0.2 ~ 0.4mm. The plug can be easily inserted into the snake tube. When the nut 2 is tightened, the circular arc spherical surface produced by the sealing ring can be evenly contacted with the inner wall, generating a large enough pressure load. It is expected that the proportion of high nickel ternary materials will increase to effective sealing in the future. In addition, when tightening nut 2, the strength of serpentine copper

pipe material must be considered. The compression force of nut 2 should not be too large, which may cause cracks on the inner wall of the copper pipe and lead to seal failure

1.3 the operating steps of the pressure rising seal

see Figure 3 for the cross section and operating space of the snake tube

1.3.1 find the leakage point and judge whether to use pressure rising seal. Find out the approximate scope of the leakage first during startup, so as to find the leakage point in time after shutdown. After finding the leakage point 28 (5) 033549016180 d=3a, it should be judged whether to use the pressure rising seal: according to the arrangement of the snake tube (as shown in Figure 3), if the leakage point is a small hole and is directly opposite to the operation side, the conventional method is combined with the pressure rising seal

Figure 3 snake tube cross section and operation space

; If the leakage is a seam, a large hole or back to the operating side (the size of the crack and hole is unknown), the pressure rising seal should be used

1.3.2 when it is determined that the pressure rising seal should be used, use a hand saw to cut the snake tube containing the leakage up and down and take it out, and try to ensure that the cross section of the snake tube of the body is a round hole. If the leakage part is the third or second one from the outside to the inside, the two or one of the outside should be sawn off even if it is intact, and the leakage part is stepped from the outside to the inside. Only in this way can the leaking pipe be completely handled

1.3.3 gently tap the prepared plug into the newly sawn copper pipe, and screw the nut 2 with a self-made wrench until the outer wall of the copper pipe rises slightly

2 advantages of slurry pressure rising seal

2.1 the reliability of pressure rising seal is strong

the pressure rising seal used in papermaking is different from the conventional welding method, which mainly does not produce heat affected zone, can withstand large pressure load, can meet the requirements of working environment of any medium, and there is no stress concentration; However, if the welding method is adopted, the heat affected zone will be generated due to heating, resulting in stress concentration, prone to thermal cracks, and lead to leakage again

2.2 the operation is safe, simple and fast

paper making pressure rising seal does not need dynamic welding, and there is no fire hazard. Since the self tightening plug has been prepared in advance, it can play a fast and simple role in the operation process. It only takes more than ten minutes to deal with a big leak, which greatly reduces the maintenance time and intensity; The conventional method often takes several hours

2.3 solves the problem of the limitation of the working space of the dryer

because the serpentine tubes of the dryer are evenly distributed one after another, with an interval of about 30mm. In such a small space, if the conventional operation method is used to stop the leakage, the difficulty is

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