Pulper Troubleshooting: Causes & Fixes

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Problems on this page:

Slushing time too long Extraction plate blocking Ragger rope breaking or not forming Contaminants passing into the stock Stock consistency wrong Main drive overloading Gearbox or rotor bearing noise Junk trap or reject system blocked

Slushing time too long

Hits OEE: Performance

Symptoms: The paper or board takes longer than usual to break down into stock.

Rotor worn

Measure the rotor against its new dimensions and refurbish or replace it.

Consistency too high

Check the water addition so the consistency matches the setting for the furnish.

Raw material harder to slush

Check for wet-strength or coated grades in the furnish and set a recipe for them.

Stock temperature low

Check the heating of the dilution water if the process uses it.

Prevention: Slushing time recorded per batch or per furnish.

Extraction plate blocking

Hits OEE: Availability

Symptoms: Flow through the extraction plate drops and the pulper cannot keep up with demand.

Plastics and wet-strength flakes covering the plate

Check the rotor clearance to the plate, since the rotor keeps the plate clean.

Plate holes worn or damaged

Inspect the plate and replace it if the holes are worn or broken.

Consistency too high

Reduce the consistency to the setting for the furnish.

Reject removal not running often enough

Increase the reject removal frequency for dirty furnish.

Prevention: Extraction flow trended so plate blocking shows up early.

Ragger rope breaking or not forming

Hits OEE: Availability

Symptoms: The ragger rope breaks, or does not form, and strings and wire build up in the pulper.

Seed wire missing or too thin

Use a seed wire that suits the furnish to start the rope.

Winch speed wrong

Set the winch speed so the rope forms without breaking.

Too little stringy material in the furnish

Check the furnish mix and adjust the ragger cycle.

Rope cutter or winch worn

Service the winch and cutter.

Prevention: Ragger rope checked each shift.

Contaminants passing into the stock

Hits OEE: Quality

Symptoms: Plastics, stickies or metal turn up in the stock downstream of the pulper.

Extraction plate holes worn larger

Replace the plate when the holes are worn beyond the limit.

Junk trap full

Empty the junk trap at the set interval.

Raw material dirtier than usual

Check the incoming bales and agree the quality with the supplier.

Detrashing system not running

Check the drum or detrasher after the pulper.

Prevention: Stock after the pulper checked for contaminants each shift.

Stock consistency wrong

Hits OEE: Quality

Symptoms: Stock leaving the pulper is too thick or too thin for the next stage.

Consistency transmitter out of calibration

Check the transmitter reading against a lab sample and recalibrate it.

Dilution water valve sticking

Service the valve and check its actuator and positioner.

Bale or furnish feed uneven

Check the bale weighing or the conveyor feed to the pulper.

Pulper level control unstable

Check the level transmitter and tune the level loop.

Prevention: Consistency checked against a lab sample each shift.

Main drive overloading

Hits OEE: Availability

Symptoms: The rotor drive trips on overload or the motor current is high.

Consistency too high

Lower the consistency, since thick stock raises the load on the rotor.

Large objects jamming the rotor

Isolate and lock out the drive before clearing; never reach into a pulper that can start.

Gearbox or bearings failing

Check the gearbox oil and bearing temperatures and vibration.

Belts slipping on belt-driven rotors

Check belt tension and wear.

Prevention: Motor current trended so rising load shows before a trip.

Gearbox or rotor bearing noise

Hits OEE: Availability

Symptoms: Noise, vibration or heat comes from the rotor bearing housing or the gearbox.

Lubrication low or the wrong grade

Check the oil level and grade, and that greasing follows the schedule.

Stock or water entering the bearing housing

Check the shaft seal and its flushing water.

Rotor worn out of balance

Inspect the rotor for uneven wear and refurbish it.

Bearing at the end of its life

Plan the bearing replacement for the next planned stop before it fails.

Prevention: Vibration and bearing temperature checked on a route.

Junk trap or reject system blocked

Hits OEE: Availability

Symptoms: The junk trap or the reject handling blocks, and the pulper has to stop.

Junk trap valves sticking

Service the valves and check their actuators and limit switches.

Large rejects bridging in the trap

Clear the trap only with the system isolated and drained.

Flushing water pressure low

Check the flushing water supply to the trap.

Reject conveyor or container not cleared

Check the reject conveyor and the container change routine.

Prevention: Reject system cycles and blockages recorded.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: mixer / agitator · centrifugal pump · vibrating screen · gearbox · electric motor · paper machine · pulp moulding machine

Stop the same fault coming back

Recurring pulper stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover