Troubleshooting the Workhorse

Monitor output, amp usage and vibration for indications of needed maintenance on hammermills, the workhorses of the pellet industry.
By Sue Retka Schill | December 22, 2013

Hammermills are the workhorses of the pellet industry. Across the biomass industry, that fact is sometimes overlooked. “We’ll get calls saying the capacity has dropped off, and the first thing we ask them to do is to check the hammers,” says Curtis Horinek, service manager for Bliss Industries LLC. Today, automation has been a big improvement at many plants, there is a tendency to rely too much on automated systems. Previously, an operator would stand next to a machine and physically start it with a push of a button or by flipping a lever. While that can be done from the control room, but it doesn’t replace being there. “Nothing takes the place of occasionally walking through the floor and just listening, putting a hand on the bearings to see if they’re warm,” Horinek says.

Hearing or seeing an increase in vibration is a key indicator of wear in a hammermill, according to Horinek. Another indicator that maintenance is needed is a drop in capacity. Operators should not rely solely on what the screens in the control room report, he adds, recommending that the hammermill output be physically measured and compared to specs. 


Another place to monitor hammermill performance is the amp load. “If you keep bringing those amps up, and one day you find there are 50 more amps than a week ago, that’s an indication you may have worn parts in the system,” he says. “Or your feedstock has changed.”  If a mill begins to over-amp and shuts off as it is designed to do, it is time to go back and first check the incoming product. “Check the moisture. Is there oversized material? If not, open the inspection doors and check the hammers, and go through the checklist,” he says. The accompanying guidelines from Bliss provide a troubleshooting checklist applicable to any hammermill, whether used for size reduction of wood, hay or grains.


Automated systems are available to help with such monitoring, adds Chad Cook, vice president of sales and marketing at Bliss, as sensors can be installed to monitor vibration and bearing temperatures from the control room. 


There is an industry-wide movement to add fire safety equipment, Cook adds, and new hammermill systems are now being equipped with spark detection and fire suppression systems.

Author: Susanne Retka Schill
Senior Editor, Biomass Magazine
[email protected]




Hammermill Troubleshooting Guidelines
Tips for locating vibration source, improving the life of replacement parts. 

Hammermills used for grinding wood chips into uniform sizes before pelleting are systems that must be maintained properly to operate at maximum efficiency. Excessive vibration, worn parts and failure to diagnose irregularities in the grinding process can lead to costly repairs and operational inefficiencies. Plants that try to cut corners end up paying for it for the entire life of the system. The following steps are suggested as ways to help mills prevent this from occurring.

Finding the Vibration Source
Excessive vibration is one of the most common problems in hammermills. To locate the vibration source:

• First, remove all hammers, hammer rods and spacers, then, start the hammermill and run it at operating speed. If the vibration disappears, then the source is your  hammers and/or rods.

• If the vibration still exists, stop the hammermill and check the tightness of the stabilizing bars and spanner nuts. Check the welds on the rotors, if applicable. Start the hammermill again, and run it at operating speed. 

• If the vibration still exists, have the rotor rebalanced.  Check for excessive wear, looking to see if the rotor plate hammer rod holes are worn and need replacing. If the  rotor is worn, it will have to be replaced.

Optimal Replacement Schedule
Replacing parts before they become too worn is another preventative measure that can be taken. Here’s a look at three critical components of a hammermill and when they should be replaced:

• Screens: When the perforated hole edges become  rounded.

• Hammers: When the corners become rounded and  main drive motor amperage has increased. 

• Wear Plates: When the thickness has been reduced by 50 percent.

Maximize Longevity
Once the replacement parts are installed, take the following steps to maximize their longevity:

Reverse the rotation of the hammermill rotor on at least a weekly basis, if not daily. Doing this will increase the life of both the hammers and screens.

Make sure product is being fed uniformly into the mill.      

Too little air flow will cause premature wear on the main rotor plates and force you to change hammers and screens before they normally would need to be changed.

Make sure adequate air volume is used. Air flow will help  uniform feeding and grinding.


The Grinding Process
Finally, it’s important to troubleshoot the grinding process on a regular basis, to make sure the system is operating properly. One way to accomplish this is by using the following checklist:

Confirm capacity.

Check hammers and screens.

Check temperature of the grinding chamber.

Check the air volume.

Check the feeding device.

Check for possible discharge obstructions.

Make sure you’re not using excessive horsepower.

SOURCE: Bliss Industries LLC