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By Milacron
Extruder TroubleSHOOTING
When troubleshooting a machine problem, it is essential to completely understand how the system functions during normal operation. Review the operational description (Section IV), circuit drawings, and electric diagrams. Once the system operation is understood, it is usually best to start at the problem, (e.g. heater band or cooling coil), and work back to the source, (e.g. heat contactor or cooling pump).
Some common machine problems, their possible causes and solutions are listed in Table 7-1 below.
TABLE 7-1
Item
Problem
Possible Cause
Solution
7.1.1 Barrel Heat Zone will not reach the set point. 1. Heater band burned out. Replace heater band.
2. Pyrometer is not energized when the temperature drops below the set point.
Replace the pyrometer.
3. Mercury contactor in control cabinet not energized or faulty.
Replace mercury contactor.
4. Overload protection circuit breaker for the individual heater zone is not energized.
Energize circuit breaker for appropriate zone
Item
Problem
Possible Cause
Solution
7.1.1
(Cont’d) Barrel Heat Zone will not reach the set point. (Cont’d)
5. Thermocouple is not seated in the bottom of the thermocouple well.
Seat the thermocouple in the well again.
6. Thermocouple or heater bandsreversed at their zones. (Example: Zone #1 thermocouple sensing a low temperature in Zone #1 and adding heat to Zone #2. Switch thermocouple or heater band to the proper zone.
7. Cooling control solenoid stuck in the open position.
Replace control solenoid.
7.1.2 Heat zone overriding the set point.
1. Pyrometer does not de-energize when the temperature exceeds the set point.
Replace the pyrometer.
2. Pressure relief valve stuck in the open position.
Replace the relief valve.
3. Thermocouple or heater bands reversed at their zones. (Example: Zone #1 thermocouple sensing a low temperature in Zone #1 and adding heat to Zone #2
Switch thermocouple or heater band to the proper zone.
4. Insufficient water flow through the heat exchanger. Heat exchanger is clogged or the globe valve is closed.
Check hoses, unclog heat exchanger, or open globe valve. Replace heat exchanger.
5. Solenoid for that zone’s fluidcontrol not opening. Replace defective solenoid.
6. Defective pump, motor, thermal overload, or coupling.
Replace defective pump, motor, or coupling.
7. Oil system plugged or clogged. Change oil filter. Clean and flush oil system.
Item
Problem
Possible Cause
Solution
7.1.3 Screw temperature overriding the set point
1. Pyrometer does not deenergize when the temperature exceeds the set point.
Replace the pyrometer.
2. Thermocouple near the flow meter outlet is defective
Replace the thermocouple.
3. Insufficient water flow through the heat exchanger:
a) Heat exchanger is clogged.
b) Water solenoid supply not energized or stuck in the closed position.
Unclog or replace heat exchanger.
Replace solenoid
4. Cooling fluid solenoid valve stuck closed.
Replace solenoid valve.
5. No fluid flow to the screws:
a) Pressure relief valve stuck open
b) Filter clogged
c) Faulty pump, motor, thermal overload, or coupling.
Replace relief valve.
Change filter.
Replace pump, motor, or coupling.
7. Oil system plugged or clogged. Change oil filter. Clean and flush oil system.
Item
Problem
Possible Cause
Solution
7.1.4 Screw temperature will not reach the set point. 1. Heater band around the heater tube is burned out.
2. Thermocouple is defective.
3. Pyrometer is defective:
a) Not energizing the mercury
contactor
b) Cooling solenoid continuously
energized.
4. Mercury contactor is defective.
5. Cooling fluid solenoid valve is stuck open.
6. Insufficient fluid flow:
a) Clogged filter.
b) Faulty pump, motor, thermal overload, or coupling.
7. Oil system plugged or clogged. Replace the heater band.
Replace the thermocouple.
Replace the pyrometer.
Replace the solenoid.
Replace the mercury contactor.
Replace the solenoid valve.
Change the filter.
Replace pump, motor, or coupling.
Change oil filter. Clean and flush oil system.
7.1.5 Insufficient vacuum for venting. 1. Insufficient water flow due to:
a) Hose leaks.
b) Loose hose clamps or manifold bolts.
c) Damaged O-Rings in sight glass
d) Clogged gate valve.
e) Clogged filter.
f) Defective solenoid valve.
2. Defective pump, motor, thermal overload, or coupling. Water shut off.
Replace hose.
Check for tightness.
Replace O-Rings.
Clean out gate valve.
Change the filter.
Replace solenoid valve.
Replace defective pump, motor, or coupling.
Item
Problem
Possible Cause
Solution
7.1.6 Excessive vibration. 1. Poor coupling alignment at motor .
2. Defective bearing in the reduction gearbox.
3. Defective bearing in the motor. Realign coupling.
Replace the bearing.
Replace the bearing.
7.1.7 Thumping noise in he rear of the machine.
1. Defective bearing in the distributor gearbox.
2. Rough spot on gear inside distributor gearbox.
3. Poor coupling alignment between the reduction and distributor gearboxes
Replace defective bearing.
Deburr rough spot on gear.
Realign coupling.
7.1.8 Erratic drive RPM. 1. Faulty speed board in DC drive.
2. Faulty current board in DC drive.
3. Faulty input voltage to DC drive.
4. Excessive current being drawn from the drive, causing it to go into overcurrent mode. Replace speed board.
Replace current board.
Correct the voltage supply.
Check and/or replace the DC drive motor.
7.1.9 Extruder will not start after an emergency stop button has been pushed or electrical cabinet door has been opened. 1. Machine power is not available.
2. The shunt trips in the main breakers have been tripped.
Pull the emergency stop buttons out into the latched ready position or close the electrical cabinet doors.
Turn both electrical breakers fully OFF to reset the shunt trip mechanism, and then place them in the ON position.
7.1.10 Barrel cooling pump will not start. Alarm indicator light "COOL OIL PUMP STOPPED" is illuminated. 1. The motor overload has tripped.
2. The motor fuses have blown.
3. The motor contactor has failed. Note: Energizing the pyrometer for barrel Zones #2, #3, or #4 will automatically start the pump.
Replace fuses.
Replace contactor.
7.1.11 Screw cooling pump will not start. Alarm indicator light "SCREW OIL MOTOR STOPPED" is illuminated. 1. The motor overload has tripped.
2. The motor fuses have blown.
3. The motor contactor has failed.
4. Debris inside the ON/OFF switch. Note: One of the barrel Zones
(#2, #3, or #4) must be energized before the screw oil pump is permitted to operate.
Replace fuses.
Replace contactor.
Clean switch.
Item
Problem
Possible Cause
Solution
7.1.12 Starve feeder auger does not operate. 1. The reference potentiometer is set to zero.
2. The control is not receiving the start input due to debris in the start buttons.
3. The starting coil, 5-PC, has not received an output from the control or is faulty.
4. The drive fuses have blown.
5. The feeder drive is faulty.
6. The armature fuse has blown.
7. If so equipped, the optional signal conditioned card used for slaving the main extruder motor and the feed auger has failed.
Reset or replace the potentiometer.
Clean out control buttons.
Check the connection and/or replace the starting coil.
Replace the fuses.
Replace the motor.
Replace the fuse.
Replace the card.
7.1.13 Starve feeder auger operates but will not achieve full speed. See Note ŕ Note: If the extruder is equipped with the optional slave circuitry connecting the feeder motor to the main extruder motor, the extruder may be operating correctly. The feeder motor reference is derived from the main motor potentiometer. If this potentiometer is set low or to zero, there will not be a sufficient reference signal available for scaling by the feeder motor potentiometer.
Increase the setting of the main motor potentiometer to increase the feeder motor speed. Correct operation will allow 100% feed motor speed at 100% full main motor speed.
Item
Problem
Possible Cause
Solution
7.1.14 The drive will not latch when the extruder start button is pressed. (The start button will illuminate when pressed but does not remain illuminated when released). 1. The extruder motor potentiometer was not set to zero prior to starting.
2. The threshold detector board on the drive has failed.
3. The start button contacts have been contaminated by dirt, preventing the start signal from reaching the control.
4. The drive is in a fault condition. Reset or replace the potentiometer.
Replace the detector board.
Clean dirt from control buttons.
Verify the extruder speed selector dial is in the OFF position.
7.1.15 The entire extruder is overheating.
1. The water saver solenoid has failed in the closed position or blown the related fuse.
2. The cooling water supply to the extruder is dirty causing restricted flow or the supply pressure is insufficient.
Check the solenoid valve and/or replace the fuse.
Change the filter or check the supply line for leaks.
7.1.16 Power is ON but the extruder will not operate. (No alarm lights or indicator lights are illuminated).
1. The programmable control has failed.
2. The 24-volt power supply has failed or blown the fuse protecting the power supply.
Verify that the programmable control light is illuminated. If not, check the fuse supplying the programmable control. If the battery light on the programmable control is illuminated, replace the battery and it may be necessary to reload the program. Ensure the selector key on the programmable control is in the RUN position.
Check the power supply and/or replace the fuse
Item
Problem
Possible Cause
Solution
7.1.17 Vacuum pump chronically tripping the motor overload.
1. Too much water is being supplied to the vacuum pump.
2. The exhaust line has a restriction or is not connected to a vent open to the atmosphere.
Note: Proper water supply adjustment.
With plastic in the extruder, start the vacuum pump and adjust the water supply valve until maximum vacuum is achieved with minimum water supply. Check the current draw for the vacuum motor to ensure it does not exceed the value on the motor data tag. Verify the pump is not overheating.
Note: Water is used to create a vacuum seal in the pump to carry away excess heat. Too much water causes the motor to overload; too little water causes the pump to overheat and damage the seals. The performance of the pump is very dependent on the temperature of the water! Colder water produces more vacuum.
Unclog the line and/or connect it to an open vent.
