Factors Influencing Pelletizing Effect of Underwater Pelletizer And Its Treatment Measures

Aiming at the problem of the abnormal underwater pelletizer state, we will analyze the three factors of pelletizing trolley, three simultaneous and cutter life. And put forward the corresponding countermeasures to ensure that the device can operate safely, smoothly, and long-term.

2 Operation status of the pelletizing trolley

2.1 The centering deviation of the pelletizing trolley and the template

Failure conditions

After installing the template for the first time for alignment, it was found that the pelletizing system trolley was separated from the template within a short time and the alignment was good, but after 2 hours, the 4 guide keys were offset in the template keyway and the mold could not be closed.

Cause analysis

Re-test the flatness and perpendicularity of the template and the basic parallelism and flatness of the pelletizing trolley, and eliminate the foundation of the template and the guide rail. Loosen the flange of the metal hose at the inlet of the pelletizing water chamber and find that the alignment state is automatically improved. The length of the retested water inlet hose is 5 347mm, and the design length is 6 050mm. The pipe stress caused the deflection of the pelletizing trolley.

2.2 Three simultaneous

Three simultaneous, it means that the cutting water, molten material, and cutting knife reach the template at the same time. If the water flows into the template too early, some of the template holes will "freeze and block"; if the water reaches the template too late, a lot of lumps or flakes will be formed when the granulator starts. If the knife arrives later than the material, it will cause a pad knife.

Symptoms

After the trolley is closed and locked, the pelletizer will automatically start, and the underwater strand pelletizer will be manually stopped for the first time with the pad knife. The second test drive will stop due to the pad knife.

Cause analysis

First, eliminate the cause of the backing pad knife caused by the template, cutter, and knife pressure. At the same time of retest three, the material arrived 0.5s earlier than the knife, which is the key reason for the pad knife. The water arrived 1s later than the knife, and the particles cut by the cutter could not be washed away in time, which intensified the pad knife. Add a delay to the three simultaneous through the instrument control program. After the three simultaneous is adjusted to water (8.5s), knife (9.5s), and material (10.5s), the pellets are cut successfully.

3 Cutter life

3.1 Cutter wear

Problem description

The pelletizer model UG725, the cutter wear is required to be within 1.5mm, and adopts the "contact" pelletizing mode. After starting the production, running continuously for 2 days, the wear of the knife was 1.44mm, and the cutter was replaced three times within a week. With ZSK350 unit, the feed pressure is 45kg, the retreat pressure is 40kg, and the knife pressure difference is 5kg, but the feed and retreat pressure fluctuates unstable in actual operation.

Cause analysis

First, the Flowserve Renosafe\DU 46 flame-retardant and anti-wear hydraulic oil is analyzed, and the water content exceeds the standard by 3.8%-4.1%. After replacing qualified oil, the inlet pressure is stable, but the retract pressure is still unstable. The pressure tends to be stable after replacing the solenoid valve that controls the retract. Keep the other operating parameters unchanged, and reduce the pressure by 0.1MPa each time. When the feed pressure is 4.1MPa, the wear volume stabilizes. After adjustment, the cutter wears 0.3mm after continuous operation for 50 days, and the service life is estimated to be 5 months based on the wear.

3.2 Cutter pad knife

Fault description

The unit was stopped with a knife during the three starts. The three simultaneous, the flatness of the template, the perpendicularity of the template and the cutter shaft, and the parallelism of the cutter head all met the requirements.

Cause analysis

An important factor that affects the pad knife when driving is the distance between the initial position of the cutter and the template, which is required to be 1~1.5mm. The actual distance between the initial position of the cutter and the template is 0.7mm. When the cutting knife is attached to the template, a small amount of molten material has already covered the pelletizing belt, and the material sticks to the cutting knife to cause a cushion knife.

Through the analysis and improvement of the pelleting trolley, three simultaneous, and cutter life factors that affect the underwater pelletizing state, the underwater pelletizing state is greatly improved. Effectively improve the operating efficiency of the extruder and the production efficiency of polypropylene, reduce production costs to a certain extent, and create good economic benefits for the branch.

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