Potential problems caused by insufficient slushing can be:
1. Bigger parts of bales remaining in the pulper and giving capacity problems
2. Smaller undissolved fibre bundles giving coating, printing, colour absorption and run ability problems further on in the paper machine. When having these types of problems a visual control will give important information.
Reasons for poor slushing can be:
Duration of pulp in the pulper is too short/design capacity is too low
- A mixing time of at least 12-15 minutes should be maintained
Water temperature is too low
- The temperature should be at least 35ºC
Consistency is too high
- At consistencies higher than 8% the bales tend to swim around and not readily be suck into the vortex. Maintain a consistency of 5 – 7%
The rotor is worn/deflectances on the walls of the pulper are insufficient
- Replace the rotor with a more effective one or refurbish the rotor by welding small wings onto the props. Make sure that they don't unbalance the rotor. When causing higher turbulence it’s a good idea to valid the motor size. There should be at least 2 deflectance plates on the inner wall of the pulper. Besides the rotation force there should be a force making some pulp going in the direction of the rotor centre.
The pulp bales are added too fast in succession
- The number and sequence of bales entering the pulper is dependent on the pulper size.
- For a smaller pulper normally two bales can be added together. Then wait half a minute until the next two bales are added.
Still having poor slushing
- In some installations there is no possibility to run the pulper with recirculation. If still having fiber bundles a recirculation is a good way to improve slushing. Use the pump that is normally used for emptying the pulp, but add the recirculation pipe.