Balancing a Mulcher in the Field

Background

A mid-size agricultural holding in Germany operates twelve rotary mulchers for hedge and brush clearing. The machines run PTO-driven knife drums at 540 RPM. After 1,200 hours of service, the front bearing housing on one unit showed persistent elevated vibration — 12.4 mm/s RMS. ISO 10816-3 places this in Zone C (restricted operation), and bearing replacements had become a bi-monthly routine.

Sending the rotor to a balancing workshop required crane disassembly, transport, and a 3–5 day turnaround. With a clearing contract due in four days, in-field balancing with Balanset-1A was chosen instead.

Setup

The mulcher was parked on level ground with the implement lowered onto timber blocks to eliminate frame flex. Two piezoelectric vibration sensors were clamped to the front and rear bearing housings using magnetic holders. The optical tachometer reflective strip was applied to the PTO shaft coupling. Total sensor mounting time: 12 minutes.

Measurement Procedure

Run 1 — Reference
PTO engaged at 540 RPM. Both sensors logged for 15 seconds.

• Front bearing: 12.4 mm/s RMS
• Rear bearing: 9.7 mm/s RMS

The dominant frequency at 1× RPM on both channels confirmed mass imbalance. No 2× or higher harmonics, ruling out misalignment or structural looseness.

Run 2 — Trial weight
A 180 g trial weight was attached at the 0° reference mark on the front correction plane. The software calculated influence coefficients and determined correction weight vectors for both planes simultaneously.

Run 3 — Correction
Correction weights installed per software output:

• Front plane: 95 g at 147°
• Rear plane: 62 g at 213°

Final measurement:

• Front bearing: 1.4 mm/s RMS
• Rear bearing: 1.1 mm/s RMS

Both values fall within ISO 10816-3 Zone A. Balancing quality grade G 6.3 per ISO 21940 achieved.

Result

Total on-site time: 40 minutes from sensor mounting to final verification. No crane, no disassembly, no transport. The machine returned to service the same afternoon.