Aluminum electrolysis production of flue gas purification centrifugal boiler induced draft fan power generally up to 800KW, speed 730r / min, flow Q = 500000m3 / h, medium specific gravity 0.745kg / m3, the highest environmental working temperature 60 ° C, lubricating oil 32 # mechanical oil. The sealing structure between the original bearing housing gland and the rotating shaft is a packing seal, and the sealing performance is poor.
Due to the high rotation speed of the rotating shaft, under the action of centrifugal force, the lubricating oil in the bearing housing is pulled out from the end cover along the shaft. The oil leakage phenomenon is very common, causing the bearing box, the coupling and the surrounding ground to be stained with oil, for safety production. Bringing hidden dangers, causing waste of lubricating oil, polluting the production environment, and sometimes causing damage to the induced draft fan due to lack of oil. Therefore, it is necessary to improve the crude oil seal structure and replace the crude oil seal with a new oil seal structure with a long service life.
First, the original sealing structure problems
During the operation of the induced draft fan, the lower end of the oil ring is immersed in the oil pool, the lubricating oil is stirred up, and the inner surface of the gland is smashed down and directly dripped onto the rotating shaft. The oil on the shaft is a lot of oil, which is driven by the rotating shaft, and the oil crawls along the shaft and enters the disk. The gap between the root and the shaft is difficult to grasp due to the gap and pre-tightening force of the packing during installation. The packing may have been damaged during the installation. After the operation for a period of time, the packing is worn, resulting in a large gap between the packing and the rotating shaft. Therefore, the lubricating oil is continuously pulled out in the axial direction, that is, oil leakage occurs. It can be seen from the above analysis that the main problem of the packing structure is that the packing material is poor and the installation is difficult to grasp. After a period of operation, the gap becomes large and the effective sealing effect is not obtained.
According to the statistics of the leakage of 48 dynamic sealing points of 24 bearing housings of 12 boiler induced draft fans in 1 year, 70% of the service life is about 1 month, and the maintenance strength is very large.
Second, the selection of magnetic oil seal
1. The structure of the magnetic oil seal The magnetic mechanical oil seal consists of two parts: a part is a static ring, which is mainly made of wear-resistant alloy, and has a stable and smooth static sealing surface. A stainless steel joint cover is fixed on the end cover of the bearing box. The sealing cover or the end cover is sealed by a sealant or an O-ring; the other part is a moving ring containing a magnetic element, and the dynamic sealing surface is made of a carbon-containing composite material excellent in heat dissipation and wear resistance, and With floating design, it can be kept close to the static ring for a long time. In order to achieve long-term connection with the static ring, the magnetic component of the magnetic oil seal adopts permanent magnet which will not demagnetize under high temperature and high speed environment. Materials, and in order to meet the requirements of the floating design, the moving ring is fixed on the shaft by a special fluorine rubber O-ring, and the friction between the O-ring and the shaft is greater than the shear force between the moving rings.
The entire magnetic mechanical oil seal device is designed for long-life use. The design features and structure of the self-protection are made of special materials, which are the basis for durability in harsh environments and repeated changes. Magnetic mechanical oil seals can be operated in dry or lubricated conditions and do not matter in the presence of water. Suitable for turning gears such as reducers, gearboxes, fans, pumps and motors in vertical or horizontal, low or high speed, dry friction or lubrication conditions.
2, the selection of magnetic oil seal 1) equipment accuracy requirements radial run: maximum 0.5mm axial turbulence: maximum 0.35mm verticality: maximum 0.05% × shaft diameter (such as: diameter 50mm axis, verticality requirement 0.025mm. The seat is sucked on the shaft, and the hands refer to the maximum tolerance of the shaft on the surface of the stationary ring.
Shaft tolerance: max. ±0.04mm, recommended ±0.025mm
Axis finish: maximum 64Rms, 32Rms recommended
Static ring installation tolerance: H62) Applicable conditions Operating parameters: temperature 160 ° C; pressure 3.3 kg, line speed 60 m / s, general specifications 20 ~ 320 mm.
3. Installation steps of magnetic oil seal
1) Pry the static ring on the clean surface instead of scratching it, and put the moving ring back into the box.
2) Apply a layer of silicone oil to the static ring. Do not touch the sealing surface with grease. Apply a layer of sealant evenly on the back surface of the end cap.
3) Use a wooden rod or a copper rod (do not damage the static torus) to press the static ring into the housing until it rests flat on the step surface, and then wipe off the glue and impurities on the friction surface.
4) Apply lubricating oil to the moving ring O-ring, push the moving ring on the shaft, and do not push it into place.
5) Push the end cover sleeve on the shaft, and after moving the static ring contact, push it to the final position together.
6) After tightening the end cap, use the included card as a tool to push the O-ring inward to prevent it from deforming during installation.
Note: If the static ring and the end cap are too loose, pressurize the plate and keep the friction pairs clean during the entire installation.
4. Application The oil seal modified by an electrolytic aluminum plant in March 2004 was tested on the 1# fan, and then installed on 4# and 7#. After more than one year of operation, the bearing box gland There is no leakage at the seal and it fully meets the design requirements.
Prior to this, due to the frequent leakage of the original sealing structure, the workload of the purification station operator was very large, and the bearing housing oil was replenished during the daily inspection, and there was also a device hug caused by the oil leakage. The shaft accident caused the motor to burn down and the direct economic loss was 100,000 yuan. Due to the prevalence of oil spills, on-site hygiene has been difficult to solve, which has made it difficult to manage equipment on site.
After the transformation, the lubricating oil basically does not need to be replenished during the oil change period, which greatly reduces the labor intensity of the workers, and the situation on the site is obviously improved, which also creates favorable conditions for the smooth operation of the production.
The improved method of magnetic mechanical oil seal sealing only needs to modify the matching size between the bearing gland and the static ring, and the original structure is changed little. The sealing structure is simple, the installation is convenient, and the power consumption is small. The use of magnetic technology, the use of the machine seal concept of the new design of the full floating sealing surface structure, so that the dynamic and static ring joint surface is always in close contact, even in the case of a large shaft jump, can achieve effective sealing.
In addition, by adjusting the structural parameters, the oil seal was also successfully applied to other bearing housing shaft seals, and satisfactory results were obtained. Therefore, the magnetic mechanical oil seal is the future development direction of the shaft seal, which has great promotion value.
The sealing of the packing is obtained by the "enveloping force" of the bushing, and the resulting friction heat accumulation party causes the bearing to "lock". Therefore, it is necessary to rely on the leakage to dissipate heat, and the leakage will cause the bearing to be "dry-ground" due to lack of oil, resulting in serious equipment failure. In this paper, through the analysis of the common oil leakage of the bearing case of the boiler induced draft fan, the reform of the crude oil seal of the induced draft fan is proposed, and a new magnetic mechanical oil seal structure for preventing the leakage of the induced draft fan is applied.
August 01, 2018