Hammer mill troubleshooting
Updated on By Moinhos Vieira – technical team
Most hammer mill problems have a simple cause: worn hammers or screen, overfeeding, product moisture, a blocked pipe or a worn sealing rubber. Find the symptom below, see the likely cause and what to do. When the fix involves the rotor, the bearings or the electrical connection, call technical assistance.
Need the part? Request hammers · Request screens
Before any check
Switch the mill off and wait for the rotor to stop completely. Never open the grinding chamber while the mill is running.
Applies to MCS and MCD Series mills. For the MCS 190, contact technical assistance. The MCO Series has its own troubleshooting guide.
The mill is producing less than usual
Likely cause
- Worn hammers
- Worn or clogged screen
- Mill running with the cyclone closed
- Blocked pipes
- Reversed direction of rotation
- Grinding rotor turning without its key
What to do
- Turn or replace the hammers.
- Replace the worn or clogged screen (screens for mills).
- Keep the cyclone open while grinding and close it only to change the bag.
- Check and clean the pipes.
- Reversed rotation: an industrial electrician must correct the motor connection.
- Rotor without its key: switch the mill off and call technical assistance.
The mill chokes or blows product out of the air vent
Likely cause
- Overfeeding
- Product too moist
- Worn hammers or screens
- Altered air flow in the pipe or cyclone
What to do
- Feed the mill gradually: the product must enter together with the air the mill draws in.
- Check the moisture of the product.
- Turn or replace the hammers and replace the screen if it is worn or clogged.
- Check and clean the pipe and the cyclone.
Product builds up in the grinding chamber
Likely cause
- Product too moist
- Loss of pressure in the air flow
What to do
- Check the moisture of the product.
- Check the air outlet at the cyclone and the bag filter.
The mill vibrates too much
Likely cause
- Rotor imbalance
What to do
- Check that the pairs of hammers, pins and spacers have the same weight.
- If strong vibration starts right after replacing or turning the hammers, switch the mill off and call technical assistance.
Metal knocking noise inside the mill
Likely cause
- Foreign object (metal, stone, etc.) inside the grinding chamber
What to do
- Switch the mill off as soon as possible.
- Open the grinding chamber only when the rotor has stopped completely, and remove the object.
- If the hammers, screen or rotor are damaged, call technical assistance.
The particle size of the ground product has changed
Likely cause
- Worn screen guide sealing rubber
- Damaged screen
What to do
- Replace the rubber (see the guide).
- Check the screen and replace it if it is damaged.
Product leaks through the grinding chamber door
Likely cause
- Worn door sealing rubber
What to do
- Replace the door rubber (see the guide).
Noise from the grinding chamber
Likely cause
- Grinding rotor turning without its key
What to do
- Switch the mill off and call technical assistance.
Bearing noise or seized shaft
Likely cause
- Bearing damaged by dirt or a foreign object
What to do
- The bearing must be replaced. This is work for a technician: call technical assistance (bearing replacement).
- Keep lubrication up to date.
Belt noise
Likely cause
- Loose belts
What to do
- Check the belt tension and the pulley alignment (see the guide).
The motor hums but does not turn
Likely cause
- Wrong electrical connection of the motor
- Supply voltage
What to do
- Switch the mill off and have an industrial electrician check the motor connection and the supply voltage.
The rotor will not come off the shaft
Likely cause
- Lack of grease on the coupling between shaft and rotor
What to do
- Do not force the parts: call technical assistance.
Support resources
- Guides and videosParts technical supportMoinhos Vieira technical support: 3D drawings of the MCS and MCD series, MCS and MCO Series guides and the MCS, MCD and MCO mill manuals.
- ManualMill manualsWhat each series manual covers and how to request your copy.
- Download centerMoinhos Vieira download center: technical data sheets (MSDS) for the conical screen oil and the marking ink.