Frequently asked questions

Select problem area in the table below. If you can’t find the right answer, your are always welcome to contact our help desk.

Dust in regrind

Possible reason

Solution

The knives are dull

Re-sharpen the knives

The knife gap is too wide

Check the gap using a feeler gauge. If it is too wide, you’ll need to take the knives out and properly pre-set them using the pre-setting jig provided with the granulator

The screen is worn out, showing more or less oval shaped holes with worn rounded edges

Turn the screen around if one side is still fresh. Otherwise, contact Rapid or your Rapid representative to get a replacement screen

The holes in the screen are too small for the application

If possible, change to a screen with larger holes or contact Rapid/your Rapid representative to get a screen with hole size better suited to the application


Flyback from hopper

Possible reason

Solution

The flaps are worn, damaged or incomplete. Normally there are two or even three rows of flaps to prevent flyback, the inner flaps being the most important.

Check the status of the flaps and contact Rapid if needed.


Higher than normal energy consumption

Possible reason

Solution

Dull knives

Re-sharpen the knives, pre-set them properly and reinstall in granulator.

Incorrect knife gap

Check the gap using a feeler gauge. If it is too wide, you’ll need to take the knives out and properly pre-set them using the pre-setting jig provided with the granulator.

The inertia is too low for the application

An extra flywheel might be a good solution. Contact Rapid or your Rapid representative to discuss what can be done.


Hopper/cutter house door are difficult or impossible to close

Possible reason

Solution

Regrind is left on the contact surfaces due to improper cleaning.

Open the granulator again and check for remaining regrind.


Knife coming loose

Possible reason

Solution

The bolts are of inadequate quality.

The bolts must be of 12.9 quality. Rapid provides high-quality bolts with a guaranteed quality of 12.9. We strongly recommend to change the bolts at least every second time the knives are changed, as bolts fatigue over time causing them to lose the clamping ability they had when new.

The bolts have not been tightened to the correct torques with a torque wrench.

A torque wrench is required when tightening the bolts. Otherwise it is not possible to achieve the specified torques.

The torque wrench shows values that are too high or too low due to improper calibration, resulting in bolts being over tightened or tightened too loosely.

Calibrate the torque wrench and tighten the bolts.

Rapid recommended special washers have not been used.

For knives held in place with a washer instead of a support ruler, it is crucial to make sure that the Rapid recommended special washers are used. Standard washers will neither withstand the force nor efficiently distribute the load of the bolt.


Knife lifespan is shorter than normal

Possible reason

Solution

The knives lack the correct angles due to improper re-sharpening.

Re-sharpen the knives according to the angles described in instruction manual.

Attempts to re-sharpen cassette knives for the Rapid 150-Series or the Rapid 200-Series with a staggered rotor.

These knives cannot be re-sharpened. Contact Rapid or your Rapid representative to order new set of knives.


Leaking regrind

Possible reason

Solution

The granule bin inside the granulator has not been properly closed or the pipe coupling is not properly fitted.

Carefully clean the granule bin before sliding it in place and fit the quick couplings between the granule bin and the evacuation pipe.


Low output from granulator

Possible reason

Solution

The knives are dull.

Re-sharpen the knives.

The knife gap is too wide.

Check the gap using a feeler gauge. If it is too wide, you’ll need to take the knives out and properly pre-set them using the pre-setting jig provided with the granulator.

The screen is worn out, showing more or less oval shaped holes with worn rounded edges.

Turn the screen around if one side is still fresh. Otherwise, contact Rapid or your Rapid representative to get a replacement screen.

The holes in the screen are too small for the application.

Contact Rapid or your Rapid representative to get a screen with hole size better suited to the application.

The blower wheel is worn out and not evacuating the regrind efficiently.

Contact Rapid or your Rapid representative to get a replacement blower wheel.

The granulator and/or evacuation blower is running backwards.

Check the rotation of the granulator/blower to verify. If necessary, have an electrician switch to two phases.

The transmission belts are slacking or the belts are worn/damaged.

Check belt tension and adjust if necessary. If worn/damaged contact Rapid or your Rapid representative to get replacement belts.

The filters are clogged, restricting airflow through granulator.

Clean the filters.

Transport piping has been modified, creating greater resistance for the blower (i.e. more bends, especially 90°-bends/higher transportation height. Bends should not be closer than 1 m to the blower).

Adjust the piping to get optimal airflow.


Noise levels are higher than normal

Possible reason

Solution

Dull knives.

Re-sharpen the knives, pre-set them properly and reinstall in granulator.

Incorrect knife gap.

Check the gap between rotating and fixed knives using a feeler gauge. If the gap is too wide, take the knives out, pre-set them properly using the provided jig and reinstall.

The inertia is too low for the application

An extra flywheel might be a good solution. Contact Rapid or your Rapid representative to discuss what can be done.


Regrind contains stitches

Possible reason

Solution

The application has changed and the configuration of the granulator is not meant for the recycled material.

Contact Rapid for a solution.


Rotor still rotates when hopper is opened

Possible reason

Solution

The transmission belts are worn out or improperly tensioned.

Check the safety equipment.

The safety equipment is not functioning.

Check the drive belt(s). Adjust the belt tension and replace drive belt(s) as necessary.


The granulator or any optional equipment fail to start or stop unexpectedly

Possible reason

Solution

The emergency stop is activated.

Reset the emergency stop(s).

The granulator/optional equipment are not connected to the mains.

Connect the granulator/optional equipment to the mains.

The main switch is in position “0”.

Put the main switch in position “1”.

The button “Reset safety relay” has not been pressed.

Press the button “Reset safety relay”.

Screen, screen box, granule bin, hopper, enclosure and/or optional equipment have not been not properly closed, or their safety switch(es) and star knob(s) are open.

Close the granulator. Check that all safety switches/star knobs are properly installed.

The granulator’s overload protection has tripped since the granulator has been overloaded.

Reset the overload protection. Before restarting: clean the granulator; check the drive belt(s), adjusting belt tension or replacing drive belts as necessary; check the sharpness and clearance of the knives.

Band conveyor (optional): The band conveyor’s overload protection has tripped since the band has stuck or the granulator has been overloaded.

Reset the overload protection. Before restarting: clean the granulator; check the drive belt(s), adjusting belt tension or replacing drive belts as necessary; check the sharpness and clearance of the knives.

Blower (optional): The blower’s overload protection has tripped since the blower has been overloaded.

Reset the overload protection. Before restarting: clean the granulator; check the drive belt(s), adjusting belt tension or replacing drive belts as necessary; check the sharpness and clearance of the knives.

A level switch (optional) has stopped the granulator/optional equipment.

Check the level switch. Make sure it can rotate freely and connect its mains plug.

The current relay has stopped the granulator/optional equipment.

Verify that granulator’s cutterhouse is not blocked by plastics and that the regrind bin is not filled with regrind.


Vibrations

Possible reason

Solution

The knives are unbalanced in the rotor, possibly due to incorrect re-sharpening.

Re-sharpen correctly so that all knives are the same width. Start by re-sharpening the most worn knife and sharpen the others to the same width.

The gap between knives is inconsistent due to improper pre-setting of the knives.

Pre-set the knives properly.

On granulators with friction couplings, the friction disks on the rotor pulley or rotor may be worn.

Check the friction coupling and disks according to the instruction manual. Contact Rapid or your Rapid representative if necessary.