# Hammer mill troubleshooting

URL: https://moinhosvieira.com.br/en/hammer-mill-troubleshooting/  
Updated on: 2026-11-03  
Other languages: Español: https://moinhosvieira.com.br/es/diagnostico-de-problemas-molino-de-martillos/ · Português: https://moinhosvieira.com.br/diagnostico-de-problemas-moinho-de-martelo/

> 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.

### The mill is producing less than usual

Probable causes:
- 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](https://moinhosvieira.com.br/en/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

Probable causes:
- 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

Probable causes:
- 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

Probable causes:
- 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.

Call technical assistance.

### Metal knocking noise inside the mill

Probable causes:
- 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

Probable causes:
- Worn screen guide sealing rubber
- Damaged screen

What to do:
- Replace the rubber ([see the guide](https://moinhosvieira.com.br/en/replacement-of-screen-guide-sealing-rubbers/)).
- Check the screen and replace it if it is damaged.

### Product leaks through the grinding chamber door

Probable causes:
- Worn door sealing rubber

What to do:
- Replace the door rubber ([see the guide](https://moinhosvieira.com.br/en/replacement-of-door-sealing-rubbers-grinding-box/)).

### Noise from the grinding chamber

Probable causes:
- Grinding rotor turning without its key

What to do:
- Switch the mill off and call technical assistance.

Call technical assistance.

### Bearing noise or seized shaft

Probable causes:
- 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](https://moinhosvieira.com.br/en/6-1-5-bearing-replacement/)).
- Keep [lubrication](https://moinhosvieira.com.br/en/bearing-lubrication/) up to date.

Call technical assistance.

### Belt noise

Probable causes:
- Loose belts

What to do:
- Check the belt tension and the pulley alignment ([see the guide](https://moinhosvieira.com.br/en/belt-replacement/)).

### The motor hums but does not turn

Probable causes:
- 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.

Call technical assistance.

### The rotor will not come off the shaft

Probable causes:
- Lack of grease on the coupling between shaft and rotor

What to do:
- Do not force the parts: call technical assistance.

Call technical assistance.