Sep 19

Decanter centrifuge is abbreviated of Horizontal screw centrifuge, which is a kind of efficient centrifuge equipment. Decanter centrifuges can generally be divided into two types: horizontal spiral filter centrifuge and horizontal spiral sedimentation centrifuge. According to some users, in the process of using the decanter centrifuge, they encountered the problem of the slow dehydration power of the centrifuge. The specific phenomenon is: as the fixed image material in the drum increases, the centrifuge dehydration time is prolonged, and the dehydration is not dry. The emergence of, now I will deal with this phenomenon for you one by one and attribute it to a common phenomenon.

   To understand this problem, users should first understand the concept of filtration rate and the factors that affect filtration rate of decanter centrifuge.

   Therefore, in response to this problem, the following three points are available for reference:

   1. The rotating drum of the horizontal spiral sedimentation centrifuge moves forward. (Within the scope of safety promise, and the material is non-corrosive or less corrosive)

  2. The filtering area in the drum of the forward decanter centrifuge (horizontal spiral sedimentation centrifuge). The method is:

   (1) Add a lining net to keep a tiny gap between the filter bag and the centrifuge drum to advance the water permeability.

   (2) Add cross-sectional area, such as adding a V-shaped filter baffle.

  3, a small amount of multiple dehydration method, to reduce the amount of dewatering and filtering material each time the centrifuge, more, less discharge method.

   4. Assuming that the material is viscous, wash it within the scope of the process.

  5. The size of the solid phase material particles in the decanter centrifuge (horizontal spiral sedimentation centrifuge). Under the condition of the same process, if you want to increase the speed, you can consider adding, such as flocculant.

   The above is the method that affects the dehydration power processing of the decanter centrifuge.

written by Decanter Centrifuge

Sep 13

The environment of the manufacturers producing fake and inferior decanter centrifuges is extremely irregular, resulting in poor manufacturing process and product quality. This situation can be seen from the manufacturing process of the decanter centrifuge.

Also, for the outer packaging products used for the decanter centrifuge products, it can be seen whether the centrifuge products are fake and inferior products, whether the manufacturer logo on the centrifuge is clear and complete, and whether the machine is clean and tidy; finally, pay attention to whether the centrifuge is in terms of sales channels. If there is a problem, if you buy a centrifuge produced by a regular manufacturer, you will basically not buy a centrifuge with a problem. If you buy it in some second-hand markets or irregular places, you may buy fake products.

  Because the production environment of the fake and inferior decanter centrifuges is extremely irregular, its production process and product quality are not good enough. This situation can be seen from the production process of the fully automatic centrifuge. Secondly, with regard to the outer packaging products used in the automatic centrifuge product, it can be seen whether the automatic centrifuge product is a fake or inferior product, and whether the manufacturer’s logo on the automatic centrifuge is clear and intact, and it is clear whether the product is clean and tidy.

  Secondly, in the outer packaging products used in the decanter centrifuge product, it can be seen whether the centrifuge product is a fake or inferior product, and whether the manufacturer’s logo on the centrifuge is clear and complete shows whether the machine is clean and tidy.

Finally, pay attention to whether there are any problems with the sales channels of the decanter centrifuge. If you buy from the centrifuge produced by a regular manufacturer, you will basically not buy the problematic centrifuge, but buy it in some wholesale markets. It is possible to buy fake and shoddy products;

   Pay attention to whether the manufacturer’s decanter centrifuge technology is mature. If the technology is not mature, the material requirements of the centrifuge must not meet the standard. Centrifuge products cannot win the market by reducing costs. In this case, inferior centrifuge raw materials are usually used for production, while regular centrifuge products use high-quality centrifuge raw materials. Only in this way can the centrifuge lifespan can be guaranteed.

written by Decanter Centrifuge

Sep 05

The structure of common DC bus VFD system:

   The decanter centrifuge is driven by the main motor, and the differential shaft and the auxiliary motor are coaxially connected. The speed of the main and auxiliary motors is controlled by the inverter, and the DC bus of the two are connected in parallel, and the three-phase power is input to the main inverter.

   Features:

   (1) Excellent energy-saving performance When the spiral lag, the regenerated energy is sent to the DC bus of the auxiliary inverter. Since the DC bus of the main and auxiliary inverters are connected in parallel, the energy is used by the main motor through the main inverter.

For the sake of simplicity, suppose the decanter centrifuge is running at constant torque and constant differential speed in steady state (not counting the influence of acceleration torque and deceleration torque during speed regulation), then the recovered energy is: P=0.8M n/9550, In the formula: P-power (KW); M-small shaft torque (Nm); n-small shaft speed (r/min); 0.8 times before M is due to regenerative braking, even if the discharged braking resistor is not added , 20% of the internal motor is also converted into braking torque.

   (2) Fast dynamic response: Some PID regulation systems tend to have overshoots, and the transition process takes a long time. For example, the eddy current brake speed regulation system has a stable period sometimes as long as several minutes. The torque response time of the frequency conversion speed regulation system is only 150~200ms, and the dynamic characteristics are obviously improved.

(3) It is easy to deal with the accumulation of materials in the drum of decanter centrifuge caused by emergencies. The auxiliary motor runs in the first quadrant (motor state) when it reverses. At this time, the differential speed is very large: Δn=(nl+n)/i, (nl -Drum speed r/min; i-differential speed ratio). Because the inverter has a static starting torque of 2 times the rated torque, the materials accumulated in the drum are easily discharged.

(4) It is conducive to realize constant torque control. Certain materials, such as urban sewage, contain 60% to 70% of organic matter. The sediment is compressible, and the solid content is constantly changing, which makes the screw pushing torque. With the fluctuation of the feed flow rate and solid content rate, the electrical system is required to control the feed rate or differential speed in time according to the torque change, otherwise, it is easy to block the material.

written by Decanter Centrifuge

Aug 29

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

1. Pitting corrosion, the following three cases are minor ones, 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 vessel strength;

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 can be used.

4. When the local corrosion defect of the Decanter 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 Decanter 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, the digging treatment or the replacement of the defective tube section or 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 should be mainly adopted. Otherwise, the defect can only be replaced as a whole.

written by Decanter Centrifuge

Aug 20

When the decanter centrifuge is working, it is inevitable that there will be gyro and friction phenomena with the limit, which will lead to work efficiency. So how to prevent similar phenomena from happening, analyze the solutions for you as follows:

Some decanter centrifuges are designed with friction reducing parts and stabilizer sleeves in the transmission system, and electric fast brakes, so that the centrifuge can greatly increase the acceleration when the speed is raised and lowered, and smoothly pass the critical speed of the rotor to make the rotor critical System resonance caused by rotating speed is minimized. The motor buffer base or suspension frame, elastic coupling, and sound suppression system are used to reduce noise and make the working environment more quiet and comfortable.

   Decanter centrifuge vibration isolation measures: Although the design, manufacture, assembly, operation, maintenance, and repair of the rotor of a centrifuge consider the elimination of unbalance problems, it cannot completely eliminate the unbalanced force and torque. This is because the original balance of the centrifuge is destroyed by the partial wear of the ten rotors during operation. At the same time, due to the operation of the centrifuge, such as continuous feeding of materials, uneven cloth, and material leakage, it often causes problems. The unbalance of the rotating drum causes the vibration of the decanter centrifuge. For this reason, in addition to minimizing vibration in design and manufacturing, effective measures are often taken to isolate vibration. This type of vibration isolation is called vibration isolation. Vibration isolation is the use of damping elements (such as springs, rubber pads, etc.) to isolate the source of vibration from the foundation ground or other instruments and equipment to avoid expansion of the impact of vibration; or to isolate the instruments, equipment and vibration ground that need to be protected to avoid damage . In engineering, the former method is often used to isolate the centrifuge, that is, to install vibration isolation elements at or under the bearing seat of the centrifuge to prevent the vibration of the centrifuge from being transmitted to the foundation and surrounding buildings to achieve The purpose of vibration isolation.

(1) The machining interference of the original planetary gear is small. Now use the wheel tile material, process it into bad parts, and process and install it by yourself to ensure the installation interference.

(2) The original bearing inner ring, outer ring, and the cage are bearing steel of the same material. Now it is changed to imported bearings, and the cage is made of copper alloy, which improves the wear resistance of the bearing and does not damage the bearing due to cage wear.

written by Decanter Centrifuge

Aug 16

 Before starting the decanter centrifuge, check in advance: whether the overload protection device is in normal working condition; whether the fastening bolts everywhere are loose; whether the decanter drum can rotate normally; whether the moving parts and static parts are rubbed.

   When the density of the solid and liquid phases of the suspension is relatively high, the solids are easy to settle. In order to prevent the uneven distribution of sediment in the drum at the beginning of the start-up, which may cause the decanter centrifuge to vibrate, the auxiliary liquid (water or other liquid) can be added to the decanter drum before the suspension is added. The temperature of the auxiliary liquid should be the same as the temperature of the suspension; After the drum is filled with auxiliary liquid, the suspension is gradually added to gradually increase the load of the centrifuge to the normal load.

   Stop adding suspension before stopping the decanter centrifuge, and then add flushing fluid to rinse the inside of the decanter centrifuge, and all the sediment in the drum needs to be rinsed. If there is sediment in the decanter drum, it will cause strong vibration when the decanter centrifuge is restarted, or jam the conveying screw and overload the differential. If the centrifuge bearings are forcibly lubricated by the lubricating oil pump, the centrifuge should be stopped when the machine is stopped, and the oil pump should be turned off after the centrifuge drum stops rotating.

   When the feed rate is too large or the concentration of the suspension is too high, the decanter centrifuge may be blocked and forced to stop. The method to eliminate the clogging of the centrifuge is to introduce the flushing liquid from the feed pipe, and at the same time slowly rotate the drum by hand along the direction of rotation of the drum, so that the sediment blocked in the drum is gradually discharged from the slag discharge port of the drum. If the blockage is serious and the above method cannot be used, the decanter centrifuge needs to be disassembled, the conveying screw is taken out of the drum, and then the blockage is removed.

written by Decanter Centrifuge

Aug 08

The number of gears on the decanter centrifuge is relatively large. If one of them has a problem, it will affect the use of the entire decanter centrifuge. According to the experience analysis of the decanter centrifuge manufacturer, several common faults in the decanter centrifuge gear can be Basically summarized as the following.

     Usually, the common faults of decanter centrifuge gears include tooth surface wear, tooth surface gluing and scratches, tooth surface contact fatigue, bending fatigue and broken teeth. The causes include manufacturing errors, poor assembly, poor lubrication, overload, and operating errors. Due to the characteristics of the structure and working principle of the gear, the vibration signal is very complicated, and the vibration fault diagnosis of it needs to be analyzed in the time domain and frequency domain at the same time. Regardless of whether the gear is in a normal or abnormal state, the change frequency of the gear meshing stiffness always exists. Therefore, the gearbox should be diagnosed according to the gear meshing frequency component. Because the gear signal is more complex, the fault has a lot of influence on the vibration signal, especially due to the effect of amplitude modulation and frequency modulation, there are many sideband structures in the gear vibration spectrum, which requires specific analysis of it during analysis and diagnosis. The components of the gearbox can accurately diagnose the fault of the gearbox.

The fault characteristic frequency of the decanter centrifuge gear is as follows:

1. The normal frequency spectrum shows the 1X and meshing frequencies of all rotating shafts. There are speed sidebands on both sides of the gear meshing frequency, and the peak value is small.

2, gear wear. The natural frequency of the gear appears, and there is a sideband of the rotational speed of the shaft where the worn gear is located. When the wear is obvious, a sideband with a higher peak will appear near the meshing frequency.

3. The centrifuge gear is eccentric. There are sidebands with higher amplitude near the meshing frequency, indicating that the gear is eccentric or the shaft is not parallel, and the peak meshing frequency increases with the increase of the load.

4. Misalignment of centrifuge gears. Almost always arouse the vibration of the second or higher harmonics of the meshing frequency, and the peak of the 2X or 3X meshing frequency spectrum is larger, and there are side frequencies separated by the speed frequency.

written by Decanter Centrifuge

Aug 01

The thermal cracks generated in the decanter centrifuge all occur and develop along the junction of the dendrites in the weld metal. The most common situation is that cracks in the middle of the weld along the length of the weld are sometimes distributed between two dendritic grains inside the weld.

VFD Control Panel for Centrifuge
VFD Control Panel for Centrifuge

Decanter centrifuge hot cracks are all produced at the grain boundary, which shows that the grain boundary is a “weak zone” during the crystallization process of the weld.

The reason for the formation of this weak zone is because in the metal crystallization process, there are more brittle impurities enriched in the grain boundary, and these impurities have a lower melting temperature. For example, FeS can be formed when the metal to be welded contains high sulfur content, and FeS and iron form a low-melting eutectic with a melting point of only 988 degrees. For example, in the later stage of the solidification process of the welded metal, the low melting point eutectic is pushed to the grain boundary to form a so-called “liquid interlayer.” In the process of metal transition from liquid to solid, the weld is subjected to tensile stress due to volume shrinkage. Under the action of tensile stress, cracks may be formed in this liquid interlayer, that is, thermal cracks.

Therefore, the reason for the thermal cracking of the decanter centrifuge is that the weld is subjected to the existence of a liquid interlayer, and the weld is subjected to tensile stress during the crystallization process. The existence of a liquid interlayer is the root cause of thermal cracks, and tensile stress is a necessary condition for thermal cracks. From the above analysis, it can be seen that not the entire crystallization process will produce hot cracks, but only in the later stage of the crystallization process, near the solidus line is the dangerous temperature zone for hot cracks.

written by Decanter Centrifuge

Jul 26

  1. When abnormal noise or other abnormal phenomena occur during the operation of the decanter centrifuge, it should be shut down immediately for inspection. It is not allowed to adjust, maintain and troubleshoot the centrifuge while it is running. Use it when adjusting, maintaining and troubleshooting The necessary protective measures.

    2. Rotating parts such as the centrifuge drum, main shaft and other important parts should be replaced or repaired in time when the corrosion is severe or the drum is obviously unbalanced. Unsafe emergency measures such as surface repair welding shall not be used; centrifuge parts are damaged It needs to be replaced in time. As soon as important parts such as transmission parts, load-bearing parts and safety-related parts are found to have cracks, serious corrosion, and unsafe factors that affect strength and reliability, stop operation immediately.

    3. The technical conditions of the decanter centrifuge during operation must ensure that its main technical parameters (vibration, noise, temperature rise indicators) meet the relevant standards.

    4. In view of the corrosiveness and use environment of the centrifuge separated by the medium, the centrifuge scrapping cycle shall be formulated in accordance with relevant regulations; if cracks or severe corrosion of key components such as the drum, main shaft, base, scraper, etc. are found, there is no repair value. Mandatory scrap immediately.

    5. Monitor and record the operation of the centrifuge, describe in detail the fault conditions, causes and solutions during the operation of the centrifuge; and make a record of shifts.

    6. The key parts of the decanter centrifuge: drum parts, base parts, casing parts, scraper parts, electrical control, etc. must be adjusted and maintained by personnel with professional technical knowledge and special skills.

7. 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.

written by Decanter Centrifuge

Jul 18

After the no-load test run of decanter centrifuge is qualified, the load test can be carried out according to the operating regulations, and the load test time is not less than 8h.

1. Start-up sequence

Speed ​​control potentiometer reset to zero position (if not reset to zero, the potentiometer is interlocked with the main motor control switch, the motor cannot start) Close the power brake, press the start button, the asynchronous motor starts, and observe whether the stabilizer oil mark comes Turn on the power switch of the speed controller, slowly turn the speed potentiometer knob to start the host, increase the speed from 0 to the working speed of no less than 2min Press the work button, the overload protection circuit is put into operation, and the motor appears Current indication. The empty vehicle current is less than 18A when not feeding.

2. Feeding operation

After the empty decanter centrifuge runs at normal speed, it is rinsed with clean water for 5 minutes, and then fed to the continuous production. For example, after stopping the feed, rinse with clean water for 10 minutes, and then stop the host. The feeding speed should be strictly controlled. It is one of the important factors that determine the solid content of the filtrate and the moisture content of the slag. The motor current during feeding is the empty vehicle current plus 5~6A. There should be no leakage at the seals. After the operation, measure the temperature of the two main bearings. The temperature of the main bearing of the feed end is allowed to be +25 degrees of the feed temperature, the temperature of the main bearing of the other end is 65 degrees, and the temperature of the differential case is 70 degrees (both measured at the position of the case). Measure the vibration and vibration at the two main bearing seats. The strength is not more than 11.2mm/s. Measure whether the production capacity meets the requirements and carefully make test drive records.

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.

written by Decanter Centrifuge