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Solution to Corrosion Defects of Decanter Centrifuge

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After the warranty period, the decanter centrifuge corrosion defects and their treatment methods are as follows:

1. Pitting corrosion, the following three conditions are minor, so they can not be dealt with temporarily.

1) Large pitting corrosion zone, but no cracks;

2) For scattered corrosion pits, the maximum corrosion depth has not exceeded half of the wall thickness value (not including the calculated thickness of the corrosion margin) required for the calculation of the strength of the vessel;

3) There is no serious chain pitting in the scattered pitting area.

2. There are three treatment methods for single corrosion defects under the skin of the decanter centrifuge and individual pit corrosion defects with an area less than 40mm.

1) When it is shallow, you can leave it alone

2) When it is deeper, the sanding method can be adopted, but the wall thickness should meet the strength requirements after sanding;

3) If the strength requirements cannot be met after grinding, surfacing treatment should be used.

3. When several large pits with a single area diameter of not more than 40mm exist at the same time, there are two situations.

1) When the distance between two adjacent defects is greater than 120mm, they can be treated as individual pit corrosion defects;

2) When the distance between two adjacent defects is less than 120mm and greater than 50mm, and the corrosion depth does not exceed 60% of the wall thickness, surfacing treatment can be used.

4. When the local corrosion defect of the centrifuge does not affect the strength requirement and the area is large (such as large area spots or ulcerative corrosion), it can be treated with metal spraying.

5. The local uniform corrosion defects of the centrifuge can be dealt with according to the following three conditions.

1) The corrosion area can be large or small, as long as the depth of the defect does not exceed 40% of the original thickness of the wall, surfacing can be used;

2) When several uniformly corroded defects exist at the same time, the area of ​​a single piece is not greater than 50mm*50mm, and the distance between two adjacent corrosion areas is greater than 50mm, and the depth of the defect does not exceed 60% of the original thickness of the wall, it can be surfacing;

3) When there are too many corroded pieces or the distribution is too wide, cut and repair or replace the defective tube section or tube body can be used.

6. The overall uniform corrosion defect of the centrifuge is the least dangerous kind of corrosion defects. Generally, only anti-corrosion measures are used and no other treatments are performed.

7. The intergranular corrosion defect is one of the most dangerous defects. For this type of defect, preventive measures are mainly taken. Otherwise, this type of defect can only be replaced as a whole.

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The necessity of periodic inspection of decanter centrifuge

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The necessity of periodic inspection of decanter centrifuge

 

1. Regular inspection of decanter centrifuge

(1) Regularly inspect the gap between the pusher plate, the scraper and the drum filter. The gap between the scraper and the screen should be within 5~7mm, and the axial clearance of the scraper blade from the bottom of the drum and the liquid blocking plate is about 4mm. (2) Check the vibration of the machine body every 7~15 days. (3) Check whether the safety interlocking device is sensitive and easy to use every 3 months. (4) Check and clean the oil filter every 3 months to ensure that there is no grease, water scale, and sand. (5) Analyze the quality of lubricating oil every 3-6 months to ensure that the quality of lubricating oil meets the standard. (6) Check and verify whether the instrument device meets the performance parameter requirements every 12 months to ensure that the instrument device is accurate, sensitive and easy to use.

 

2. Adjustment of decanter centrifuge

Checking and adjusting in time before operation or during the shutdown time is an important guarantee for keeping the machine in good running condition, and it is also an important part of machine maintenance.

(1) Adjustment of working pressure of oil pump

Adjust the relief valve to keep the output pressure of the oil pump at 1.6MPa (gauge pressure).

(2) Adjustment of the working position of the scraper

When the piston rod in the scraper cylinder descends and hits the bottom cover of the cylinder (that is, when the piston is at the bottom dead center position), the roller on the crank of the scraper device should touch the travel switch, and the scraper blade and the inner screen of the drum ( The distance between the surface meshes should be kept at 5~7mm. This distance is achieved by adjusting the travel switch on the door cover and the nut on the piston rod in the scraper cylinder. Adjust the fastening screw connecting the scraper blade to the blade holder so that the axial gap between the two ends of the blade and the bottom of the drum and the liquid blocking plate is approximately the same, about 4mm.

(3) The amount of drum loading

The thickness of the material layer is determined by different materials, but it should not exceed 120mm.

(4) Adjustment of process duration

In automatic operation, the time relay knob in the electrical console can be adjusted according to different materials and corresponding process requirements to realize the duration of each process and the total time to complete a working cycle.

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Correct operation process of decanter centrifuge

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Correct operation process of decanter centrifuge

 

1. Do not use decanter centrifuges for the separation of highly corrosive materials; in addition, operate strictly in accordance with equipment requirements and regulations. Non-explosion-proof centrifuges must not be used in flammable and explosive situations.

2. Before running the decanter centrifuge, cut off the power and release the brake first. You can try rotating the drum by hand to see if there is any seizure. Check whether other parts are loose and abnormal. Turn on the power and start in a clockwise direction (usually it takes about 40-60 seconds from static state to normal operation). Generally, each equipment must run empty for about 3 hours after arriving at the factory, and it can work without abnormal conditions.

3. The materials should be placed as evenly as possible. Must be operated by a dedicated person, and the capacity must not exceed the rated capacity. It is strictly forbidden to run the machine over speed, so as not to affect the service life of the decanter centrifuge.

4. After the decanter centrifuge is started, if there is any abnormality, it must be stopped for inspection, and it must be disassembled, washed and repaired if necessary.

5. The decanter centrifuge runs at high speed when it is working, so you must not touch the drum with your body to prevent accidents.

6. To ensure the normal operation of the decanter centrifuge, the rotating parts should be refueled and maintained every 6 months. At the same time, check the lubrication of the bearing and see if there is any wear; if the parts in the brake device are worn, replace it seriously; if there is oil leakage in the bearing cover.

7. After using the decanter centrifuge, clean it up and keep the machine tidy. The daily maintenance and repair of the centrifuge, such as daily lubrication, bolt tightening, etc., shall be carried out by personnel trained in the use of the centrifuge.

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No-load test run of decanter centrifuge

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For no-load test run of decanter centrifuge, we need to know some key factors below:

1. Commissioning of the speed regulating motor (remove the drive belt) Set the speed regulating potentiometer to the zero position, close the power brake, and turn on the power switch of the speed regulating motor controller. Press the start button to start the asynchronous motor, and immediately press the stop button to observe the motor rotation. Looking forward from the rear end of the motor, the counterclockwise rotation of the fan blades of the motor is correct. If the asynchronous motor turns correctly, you can press the start button again to make the asynchronous motor run. After 1min, start to adjust the multi-turn potentiometer to start the speed-regulated motor. The speed control knob is required to rotate slowly, and the speed increase time of the speed control motor from 0 to 1350r/min is not less than 2min to ensure a smooth start. Observe the operation of the motor. If it is normal, you can press the work button to read the no-load motor current. Measure the speed of the speed regulating motor, when the multi-turn potentiometer is rotated to the maximum position (about 10 turns), the speed of the speed regulating motor is 1350r/min (obtained by adjusting the feedback potentiometer on the speed motor controller), and the speed is corrected accordingly table.

 2. After the adjustment of the speed regulating motor is completed, install the driving triangle belt to start the no-load operation of the host. Reset the speed potentiometer to zero position (this should be the case before each drive). Press the start button, after the asynchronous motor reaches full speed (about 1min), start to slowly rotate the multi-turn potentiometer, requiring the speed of the motor to increase from 0 to 1350r/min, the speed-up time is not less than 2min. When the host is started, the operation should be observed. If there is excessive vibration or there is a noise of collision, you should immediately press the stop button, stop the decanter centrifuge to check the cause and eliminate it. If everything is normal, increase the speed of the host to 3200r/min (at this time the speed motor is 1350r/min), press the work button (the ammeter starts to indicate, the overload protection circuit is put into operation), watch the no-load current, it should be less than 18A (380v) After the empty car runs normally for 1~2h, stop to check all fasteners and parts once and confirm that they are normal. Check the temperature of each bearing, it should not be greater than 30 degrees at room temperature, and the temperature of the differential case is less than 70 degrees.

 

Check before decommissioning of decanter centrifuge:

1. Check the tightening of all bolts for looseness, breakage, shortage, etc.

2. Check whether the electric steering is correct, the belt tension is appropriate, and the pulley is intact

3. Check whether the oil level of the bearing housing meets the requirements

4. Rotate the drum with the hand wheel, it should be easy and flexible without rubbing.

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How to adjust and control the vibration of decanter centrifuge

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How to adjust and control the vibration of decanter centrifuge

Processing any equipment will definitely produce tolerances. The higher the processing accuracy, the smaller the tolerances, but the processing cost is greatly increased. The decanter centrifuge is designed to use a variety of knowledge to achieve a certain processing error, so that the decanter centrifuge's vibration is controlled within the normal range. However, if the user uses it improperly, it will destroy this design balance and cause serious accidents. Only when the working speed of the decanter centrifuge is not the critical speed, the rotor can move smoothly. For low-speed decanter centrifuges with a low working speed, the critical speed is generally increased as much as possible, so that the decanter centrifuge operates below the critical speed. The shaft of this decanter centrifuge is very thick and has high rigidity, which is called a rigid shaft. When the speed requirement is very high, reduce the critical speed as much as possible. The shaft is made thinner and the rigidity is small. It is called a flexible shaft. Modern decanter centrifuges all use flexible shafts.

The critical speed is related to the decanter centrifuge and the rotor used. A decanter centrifuge can be equipped with several kinds of rotors, so when designing a decanter centrifuge, the tolerance of the decanter centrifuge's vibration reduction design to various rotors should be considered. The working range of the decanter centrifuge is very wide, from several thousand revolutions/minute to tens of thousands revolutions/minute. The higher the rotation speed at which the decanter centrifuge vibration occurs, the greater the danger. Once the vibration occurs at high speed, the decanter centrifuge should be stopped at the fastest speed down gear, and all personnel should leave the scene quickly to avoid personal injury in the event of shaft breakage. Never cut off the power. Once the power is cut off, the brake (rapid deceleration) will be gone and the rotor will stall very slowly. Accidents are generally caused by improper operation of the decanter centrifuge, such as the rotor is not placed on the main shaft, the rotor cover is not covered, the swinging basket of the rotor is not placed, etc. Modern decanter centrifuges generally have unbalanced protection functions. That is, once the vibration of the rotor is greater than a certain size when the decanter centrifuge is started, the decanter centrifuge will automatically slow down and stop. The decanter centrifuge with this performance sometimes misses the report and cannot ensure that no accidents will occur.

Decanter centrifuge rotor machining errors and decanter centrifuge installation errors will cause the rotor centroid to deviate from the decanter centrifuge main shaft to varying degrees, therefore, vibrations will occur when the rotor rotates, and these vibrations will be inherent to the decanter centrifuge drive system at certain specific speeds The frequency resonates, causing strong vibration of the entire system. The speed at which this phenomenon occurs is called the critical speed. The rotor will cause vibration when rotating at high speed, but the flexible shaft has an "self-aligning effect". The principle of action is that the rotor produces a disk effect when rotating at high speed, and the elastic reaction force when the flexible shaft bends pulls the rotor that deviates from the geometric centerline of the main shaft back to the geometric centerline of the main shaft, and the vibration disappears. Of course, the amount of unbalance existing in the rotor at this time must also have a certain limit, beyond which the vibration will not disappear.