Daily maintenance and common faults of high-temperature unloaders

A complete high-temperature discharger consists of several parts such as a motor, a reducer, a coupling, and a housing. The head part is composed of a shell, front and rear side covers, a main shaft, a sliding bearing, and a shaft seal. The high-temperature discharger belongs to positive displacement. During operation, it relies on the meshing of the driving and driven wheels to cause changes in the working volume to convey the melt. The working volume is composed of the body, the grooves of the sheave, and the bearing with the function of a side plate. When rotating, the melt enters the tooth grooves of the two wheels in the suction chamber. As the wheels rotate, the melt is carried from both sides into the discharge chamber. The re-meshing of the wheels extrudes the melt in the tooth grooves out of the discharge chamber and presses it into the outlet pipeline. As long as the pump shaft rotates, the wheels will press the melt towards the outlet side. Therefore, a very high pressure can be achieved at the outlet, and the flow rate is basically independent of the discharge pressure.

### I. Operation Management of High-temperature Discharger

#### 1. Routine Maintenance

(1) The disassembly, cleaning, heating, cooling, startup, and shutdown of the high-temperature discharger should be strictly operated in accordance with the regulations to avoid unnecessary losses.

(2) Attention should be paid to maintaining the stability of the pressure at the supercharging inlet to ensure a stable volumetric efficiency, which is beneficial to its own operation and the stability of the downstream spinning quality.

(3) For a stuffing box shaft seal pump with a negative inlet pressure, the pressure at the stuffing box should be maintained higher than the external atmospheric pressure. When the back pressure decreases, the pressure of the stuffing box should be adjusted in a timely manner. Otherwise, the pump will suck in air, causing the casting strip to break, affecting pelletizing, and resulting in the discharge of the pelletizer.

(4) Regularly check the temperature of the heat medium jacket. The heat medium temperatures of the main body, front cover, and rear cover should be kept consistent.

(5) Each time the output is increased, record the output, rotation speed, inlet and outlet pressures, and current values at that time. Compare the data before and after, and analyze them carefully to detect abnormalities as early as possible and handle them in a timely manner.

#### 2. Common Faults and Countermeasures of High-temperature Discharger are as follows:

(1) Fault Phenomenon: Unable to discharge materials

Fault Reasons: a. Reverse rotation direction; b. Inlet or outlet valve is closed; c. No material at the inlet or too low pressure; d. Excessively high viscosity, the pump cannot bite the material

Countermeasures: a. Confirm the rotation direction; b. Confirm whether the valve is closed; c. Check the valve and pressure gauge; d. Check the liquid viscosity. Check whether the flow rate according to the rotation speed ratio appears when operating at low speed. If there is a flow rate, it means insufficient inflow.

(2) Fault Phenomenon: Insufficient conveying capacity

Fault Reasons: a. Inlet or outlet valve is closed; b. Low inlet pressure; c. Outlet pipeline is blocked; d. Stuffing box leaks; e. Too low rotation speed

Countermeasures: a. Confirm whether the valve is closed; b. Check whether the valve is opened; c. Confirm whether the discharge amount is normal; d. Tighten; when a large amount of leakage affects production, stop the operation and disassemble for inspection; e. Check the actual rotation speed of the pump shaft.

(3) Fault Phenomenon: Abnormal sound

Fault Reasons: a. The coupling has a large eccentricity or poor lubrication; b. Motor failure; c. Abnormality of the reducer; d. Improper installation at the shaft seal; e. Shaft deformation or wear

Countermeasures: a. Align or fill with lubricating grease; b. Check the motor; c. Check the bearings and gears; d. Check the shaft seal; e. Stop the machine and disassemble for inspection.

(4) Fault Phenomenon: Excessive current

Fault Reasons: a. Excessively high outlet pressure; b. Excessively high melt viscosity; c. Improper shaft seal assembly; d. Shaft or bearing wear; e. Motor failure

Countermeasures: a. Check the downstream equipment and pipelines; b. Test the viscosity; c. Check the shaft seal and adjust appropriately; d. Check after stopping the machine. Check if it is too heavy to turn the handwheel; e. Check the motor.

(5) Fault Phenomenon: Suddenly stops

Fault Reasons: a. Power outage; b. Motor overload protection; c. Coupling damage; d. Excessively high outlet pressure, chain reaction; e. Abnormal bite in the pump; f. Shaft and bearing stick and jam

Countermeasures: a. Check the power supply; b. Check the motor; c. Open the safety cover and check by turning the handwheel; d. Check the instrument interlocking system; e. After stopping, confirm by turning the handwheel in both forward and reverse directions; f. Confirm by turning the handwheel.

Note: The above fault phenomena and countermeasures are in one-to-one correspondence.

### II. Measures to Improve the Operating Life of High-temperature Discharger

Since the body operates at high temperatures, a hinge support should be installed on the pipeline during cold installation to prevent pipeline displacement after heating up.