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Underwater Pelletizer Problems

Views:98     Author:Site Editor     Publish Time: 2019-04-10      Origin:Site

underwater pelletizer

In the extrusion granulation unit, the Resulting in the friction cleavage of the underwater pelletizer system during operation, and the reasons for the unit interlocking parking can be divided into four categories:

 

Main motor system failure:

1. The main motor torque is too high or too low;

2. The main motor speed is too low;

3. The main motor bearing temperature is too high;

4. The main motor winding temperature is too high;

5. The main motor water-cooled cooler inlet and outlet temperature is too high;

6, the main motor bearing lubricant pump outlet flow is too low;

7, the main motor bearing lubricant pump outlet pressure is too low;

8, the main motor water-cooled cooler water leakage is too high.

 

Transmission system failure:

1. The gearbox shift lever position is deviated;

2. The instrument wind pressure of the friction clutch is too high;

3. The friction clutch speed difference is too large;

4. The gearbox lubricating oil pump outlet pressure is too low;

5. The gearbox lubricating oil pump outlet oil temperature is too high. High;

6, internal friction clutch failure.

 

Extruder screw process section failure:

1. The melt pressure before and after the throttle valve is too high;

2. The melt pressure of the machine head is too high;

3. The melt pressure difference before and after the change of the screen is too large;

4. The rotation of the driving valve is faulty.

 

Underwater pelletizing system failure:

1. The temperature of the grain-cutting motor winding is too high;

2. The speed of the pelletizer is too low;

3. The torque of the pelletizer is too high;

4. The automatic switching of the particle water bypass is faulty;

5. The water pressure of the pellet is too high or too low;

6. The flow rate of the granule water is too low;

7. The clamping bolt of the granulator is not tight;

8. The bypass valve of the granulating chamber is not closed;

9. The hydraulic clamping pressure of the granulator is too low;

10. The granulating motor is faulty;

11. The axial cutting pressure of the hydraulic cutter is too low.

 

Among the above-mentioned fault causes, the frequency of occurrence is more: the main motor torque of the main motor system is too high or too low; the friction clutch of the transmission system is faulty; the melt pressure of the system of the extrusion granulator screw process section is high; Granulator system failure, etc. The following is a detailed analysis of these common causes of failure, and the corresponding solutions are given.

 

Analysis of common causes and solutions

 

Main motor torque is too high

Cause Analysis:

If the oil lubrication system is faulty, the main motor output shaft and the gearbox's access shaft are poorly aligned, and the motor and clutch vibration will damage the main motor bearing, resulting in excessive torque. In addition, too much feed load or poor material melting can cause excessive torque in the main motor.

solution:

The lubricating oil system is inspected and cleaned regularly, and the main motor bearing is measured with a vibration measuring instrument and an infrared thermometer to form a trend graph. If the trend value is exceeded, determine whether the main motor idle current value or power value exceeds the specified value and determine whether the bearing should be replaced. Regularly check the alignment between the main motor output shaft and the gearbox input shaft. The alignment must be checked after three months of initial or replacement bearing operation. Perform electrical test checks to determine the cause of the rotor imbalance; perform a vibration speed test on the clutch and re-adjust the dynamic balance if the specified value is exceeded. Regularly check the heating and cooling system of the cylinder to ensure that the material is evenly melted by heat. If the extruder motor starts instantaneously, the main motor power curve and the melt pressure curve increase instantaneously, indicating that the feeding amount of the feeding system is too large, and the feeding amount should be reduced.

 

Main motor torque is too low

Cause Analysis:

Failure of the feed system causes the twin-screw idle to cause the main motor torque to be too low.

solution:

Check to see if the additive system or main material blanking system is faulty and clean up the plugging point.

 

Friction clutch failure

Cause Analysis:

The instantaneous starting voltage of the main motor is too low, the friction disc and the friction plate are overheated, the friction disc and the friction disc are aging, and the air pressure of the friction disc is too low, which can cause the clutch to disengage.

solution:

When the main motor starts, avoid the peak of power consumption and reduce the feeding load. The interval between restarts is as short as 30 minutes. In the summer, when the main motor is restarted more than twice, the interval should be extended or forced by the fan. Cool down. Use the instrument wind to sweep and wipe the surface of the friction plate and the friction plate with a rag. If the wear is heavy or the surface is “vitrified”, the friction plate and friction plate should be replaced. Check if the air pressure value matches the friction disc to the friction plate.

 

High melt pressure

Cause Analysis:

The filter mesh has a high mesh number, the polypropylene powder has a low melt index and a large feed amount, and the low temperature of each cylinder causes the material to be incompletely melted, and the template opening ratio is low, so that the extrusion of the head material is hindered, etc., which can cause melt pressure. Too high.

solution:

When producing low melt index products, use a low mesh filter to increase the throttle opening to reduce back pressure; replace the filter in time, monitor the quality of various additives and the ash content of the polypropylene powder. Reduce the feed load. Under the condition that the quality of the extruded product is not affected, the temperature of each section of the cylinder is increased, the temperature of the polypropylene melt is increased, and the fluidity of the material is increased. After the extruder has stopped, increase the temperature of the head and keep it constant for a period of time, then rinse the template thoroughly.

 

Underwater pelletizing system failure

Cause Analysis:

Excessive cutter wear or cutting edge damage, particle water flow is too low, the pelletizer vibration is too large, the cutter is not tightly attached to the template, the material melt index fluctuates greatly, the discharge flow rate is inconsistent, the particle water temperature is too high, etc. It can cause the underwater pelletizing system to stop and cause the entire unit to interlock and stop.

solution:

After parking, visually inspect the cutting edge for excessive wear or damage, and if so, replace the cutter. Check and confirm whether the particulate water leaks inside, whether the particulate water tank filter and the cooler are blocked. If the blockage should be cleaned manually; check whether the inlet and outlet pressure of the pellet pump is normal. If it is not normal, check the valve on the pellet pump and pump line. Check if the alignment between the cutter shaft and the pelletizing motor is out of tolerance, whether the bearing assembly of the cutter shaft is damaged, and whether the rotor balance of the cutter rotor is out of balance. During operation, check whether there is a gap between the four moving wheels of the pelletizing cart and the guide rail. Controls the volatiles in the polypropylene powder to eliminate vibrations on the cutter and cutter shaft as it flows through the die orifice. Reduce the temperature of the hot oil at the template, check the temperature distribution of the cylinder and the template, whether the flow, pressure and temperature of the cooling water of the cylinder are normal; confirm the time setting of “water, knife and material” reaching the template to prevent the pellet water from prematurely Arriving the template freezes the template holes. After the pelletizer is closed, the feed should be quickly increased to the set load of the extruder.

 

If the above fault cause points can be combined with the logical relationship of the interlock to be assembled into fault diagnosis software, it can provide quick and intuitive reference and help for the operation, maintenance and management of the unit.


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