From 70 mm/s to 1.2 mm/s: balancing a worn-out Ferri mulcher in the field
This Ferri mulcher has had a hard life. According to the Vibromera team who filmed the job, it has been brought back more than once: bearings replaced, cracks welded, rotor rebalanced. Its owners keep it working with regular balancing and a lot of welding.
Before: 70 mm/s. After balancing with Balanset-1A: 1.2 mm/s. Smooth enough to stand a coin on its edge on the machine (video).
How far off was 70 mm/s?
For scale only: a mulcher isn't covered by ISO 20816-3, the vibration standard for industrial machines. In that standard, the zone where vibration can cause damage starts somewhere between 4.5 and 11 mm/s, depending on machine size and foundation. 70 mm/s is far beyond anything that standard would accept.
Why mulchers lose their balance
- Knives and hammers wear unevenly, break or get replaced one at a time.
- Welding repairs add metal that's rarely spread evenly around the rotor.
- Soil and wrapped material stick to the rotor unevenly.
- Cracks don't add mass, but they let the rotor flex and shift, and they have to be welded anyway.
So the balance you had last season can be gone after the next big repair.
Lessons
- Balance after major repairs: after welding or a knife change. After a bearing swap, measure and balance if the vibration came back.
- Fix the mechanics first: cracked welds and worn bearings come before weights.
- Use the same rpm every run. On a tractor-driven mulcher that means the same PTO speed.
- Save the influence coefficients. For a machine you balance every season, the next job is one run plus a correction.
Vibromera has a longer write-up on balancing flail mower and forestry mulcher rotors.
The full routine is in the step-by-step field balancing guide.