Common faults of granulators and troubleshooting approaches

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:hug: Analysis and Treatment of Common Faults in Compression Granulators 2007-10-29 Author unknown. Compression granulation units feature a high degree of integration of mechanical, electrical, and control systems, as well as advanced automated control capabilities. As a result, many difficult-to-diagnose faults occur during actual operation, leading to prolonged processing times and thereby affecting the proper functioning of the entire polypropylene plant, **which significantly reduces production efficiency. By combining theoretical knowledge of the extrusion granulation production process with over a decade of practical management experience in production, the author analyzed and identified the common causes of failures that occur during the operation of this unit, and formulated corresponding solutions and handling methods to ensure its stable operation over extended periods of time. Causes of failure: In extrusion granulation units, the reasons that lead to the disengagement of the friction clutch during operation and subsequent shutdown of the unit can be divided into four main categories: 1. Faults in the main motor system; 1.1 Excessively high or low torque in the main motor ； 2. The main motor speed is too low ； 3. Excessively high temperature of the main motor bearings ； 4. Excessively high temperature of the main motor windings ； 5. The inlet and outlet temperatures of the water-cooled cooler for the main motor are too high ； 6. The outlet flow rate of the lubricating oil pump for the main motor bearings is too low ； 7. The outlet pressure of the lubricating oil pump for the main motor bearings is too low ； 8. Excessive water leakage from the water cooler used for cooling the main motor, etc. II. Transmission system failures 1. The gearbox shift lever is in the wrong position ； 2. Excessively high instrument air pressure in the friction clutch ； 3. Excessive speed difference in the friction clutch ； 4. The outlet pressure of the gearbox lubricating oil pump is too low ； 5. Excessively high oil temperature at the outlet of the gearbox lubrication pump ； 6. Internal failures of the friction clutch, etc. III. Faults in the screw section of the extrusion granulator 1. Excessively high melt pressure before and after the throttle valve ； 2. Excessively high melt pressure at the nozzle ； 3. Excessive melt pressure difference before and after the mesh changer ； 4. Malfunctions such as rotating faults of the driving valve. IV. Faults in the underwater pelletizing system 1. Excessively high temperature of the pelletizing motor windings ； 2. The granulator speed is too low ； 3. Excess torque in the pelletizer ； 4. Fault in automatic switching of particle water bypass ； 5. The water pressure on the particles is too high or too low ； 6. The particle water flow rate is too low ； 7. The clamping bolts of the pelletizer are not tightened properly ； 8. The bypass water valve next to the granulation chamber is not closed ； 9. The hydraulic clamping pressure of the pelletizer is too low ； 10. Pelletizing motor failure ； 11. Low axial feed pressure of the hydraulic cutter, etc. Among the aforementioned causes of failure, those that occur most frequently are: excessive or insufficient torque in the main motor of the main motor system ； Fault in the friction clutch of the transmission system ； The melt pressure in the screw process section system of the extrusion granulator is high ； System failures of underwater pelletizing machines, etc. The following text will provide a detailed analysis of these common causes of failure, along with corresponding solutions. Analysis of common fault causes and solutions: Excess torque in the main motor. Cause analysis: Faults in the oil lubrication system, poor alignment between the output shaft of the main motor and the input/output shafts of the gearbox, as well as vibrations in the motor and clutch can all damage the bearings of the main motor, resulting in excess torque. Furthermore, an excessive feeding load or poor melting of the material can also lead to high torque in the main motor. Solution: Regularly inspect and clean the lubrication system, and use vibration meters and infrared thermometers to measure the bearings of the main motor, creating trend charts for these measurements. If it exceeds the trend value, then check whether the no-load current or power value of the main motor exceeds the specified values, to determine whether the bearings need to be replaced. Regularly check the alignment between the output shaft of the main motor and the input shaft of the gearbox; the alignment must be checked after the first start-up or three months of operation following bearing replacement. Conduct electrical tests to determine the cause of rotor imbalance ； Conduct a vibration speed test on the clutch; if it exceeds the specified value, its dynamic balance must be adjusted again. Regularly inspect the heating and cooling systems of the cylinder to ensure that the material is heated evenly and melts thoroughly. If, at the moment the extruder is started, the power curve of the main motor and the melt pressure curve increase instantly, it indicates that the feeding amount from the feeding system is too high at that moment; the feeding amount should be reduced. Low torque of the main motor: Cause analysis – A malfunction in the feeding system that causes the twin-screw mechanism to spin idly will result in low torque of the main motor. Solution: Check whether there are any faults in the additive system or the main material feeding system, and clear any blockages. Faults in friction clutches – Cause analysis: An excessively low starting voltage of the main motor, overheating of the friction disc and friction pads, aging of the friction disc and friction pads, as well as insufficient air pressure in the friction disc, can all lead to the clutch disengaging. Solution: When starting the main motor, it is necessary to avoid peak electricity usage times, reduce the feeding load, and ensure that the minimum interval between restarts is 30 minutes ； During the summer, when the main motor is started more than twice, the interval between starts should be increased further or forced cooling using a fan should be employed. Use an air blower to clean the surfaces of the friction pads and discs, and wipe away any dust from them with a cloth. If there is significant wear or if the surfaces show signs of \"vitrification\", the friction discs and pads should be replaced. Verify whether the air pressure value is sufficient to bring the friction disc and friction pads into contact. Reasons for high melt pressure: A high mesh size of the filter, a low melting index of the polypropylene powder along with a large feeding rate, low temperatures in various sections of the cylinder that prevent thorough melting of the material, and a low porosity of the die plates that hinder the extrusion of the material from the die – all these factors can lead to excessive melt pressure. Solution: When producing products with a low melt index, a filter screen with a lower mesh size should be used, and the opening of the throttle valve should be increased to reduce back pressure ； Replace the filter screens in a timely manner, and monitor the quality of various additives as well as the ash content in the polypropylene powder. Reduce the feeding load. Without compromising the quality of the extruded product, the temperature of each section of the cylinder is increased, thereby raising the temperature of the polypropylene melt and enhancing the fluidity of the material. After the extruder is stopped, raise the temperature of the die head and maintain it at that level for a while, then thoroughly rinse and clean the die plates. Fault analysis of the underwater granulation system: Excessive wear of the cutting blades or damage to their edges, too low water flow rate for the pellets, excessive vibration of the granulator, poor fit between the cutting blades and the template, large fluctuations in the material’s melt index leading to inconsistent discharge speeds, and too high temperature of the water used for the pellets – all these factors can cause the underwater granulation system to stop operating, thereby triggering a shutdown of the entire unit. Solution: After parking, visually inspect the cutting blade to check for excessive wear or damage; if any are found, all the cutting blades should be replaced. Check and confirm whether there is internal leakage of particle water, and whether the filters and coolers in the particle water tank are clogged; if they are clogged, they should be cleaned manually ； Check whether the inlet and outlet pressures of the granule water pump are normal; if not, the granule water pump and the valves on the pump pipeline should be repaired. Check whether the alignment between the knife shaft and the pelletizing motor is out of spec, whether there is any damage to the bearing assembly of the knife shaft, and whether the dynamic balance of the cutter rotor is compromised. During operation, check whether there is any gap between the four moving wheels of the pelletizing trolley and the guide rails. Control the volatiles in polypropylene powder to eliminate the vibration generated on the cutting blade and its shaft as it passes through the template holes. Reduce the temperature of the hot oil at the template, and check the temperature distribution in the cylinder and the template, as well as whether the flow rate, pressure, and temperature of the cooling water for the cylinder are normal ； Confirm the timing settings for the arrival of water, blades, and material at the template, to prevent particles of water from reaching the template too early and causing the holes in the template to become clogged. After the pelletizer’s head is closed, the feeding rate should be increased quickly to the set load of the extruder. This post was last edited by li*ngya on 2009-3-13 16:52]