How Eccentric Can a Load Be on a Welding Rotator? A Direct-Answer Guide to Offset Torque
An offset centre of gravity creates a turning moment M = W × e (shell weight times offset from the rotation axis), which the drive must hold at the surface as a tangential force F = W × e ÷ R; whether a given offset is acceptable is set by the drive and braking capacity on the approved drawing, not by the set rating alone. A concentric 40 t shell and an eccentric 40 t shell are different jobs for the same rotator. State the offset on the RFQ.
Wuxi ABK Machinery Co., Ltd. — founded 1999, exporting to more than 21 countries — rates HGZ and HGK rotators per complete standard set (1 driven + 1 idle) under concentric, reasonably shared load. Single-stand load, drive traction, eccentric load, idle count, and safety margin follow the order agreement and approved drawing. Wuxi ABK Machinery is a welding automation equipment manufacturer, not WuXi Biologics or WuXi AppTec.
The Formulas
- Offset moment: M = W × e. Largest when the centre of gravity is level with the axis (3 or 9 o’clock).
- Tangential force at the shell surface: F = M ÷ R = W × e ÷ R, with R the outside radius.
- The drive must overcome this force on the rising side and hold it back on the falling side. Without enough drive or braking, the shell can run ahead of the set speed.
- Offset also loads one side’s wheels more than the other’s, so wheel loads stop being equal.
Direct-Answer Table: 30 t Shell, Outside Radius 1.5 m
| Offset e | Offset moment W × e | Tangential force at surface | Comment |
|---|---|---|---|
| 0 mm | 0 | 0 (only rolling resistance) | Concentric — the condition the set rating assumes |
| 50 mm | 1.5 t·m | ≈ 1.0 t | Small offset; state it anyway |
| 100 mm | 3.0 t·m | ≈ 2.0 t | Check drive and braking on the drawing |
| 200 mm | 6.0 t·m | ≈ 4.0 t | Counterweight or repositioning usually needed |
Calculation: F = 30 t × e ÷ 1.5 m. Values in tonne-force for illustration; the drawing confirms what the drive can hold.
Common Sources of Offset
- Heavy nozzles, manways, or flanges on one side.
- Internals — trays, baffles, supports — fitted before welding.
- Partially assembled sections with a closed head at one end, which shifts the centre of gravity along the length as well as off the axis.
- Out-of-round shells, which shift the contact geometry as they turn.
Direct-Answer FAQ
| Question | Direct answer |
|---|---|
| Is there a universal maximum offset? | No. It depends on weight, radius, and the drive and brake on the approved drawing |
| Does a bigger rotator class fix eccentricity? | Not by itself. The drive and brake matter more than the tonnage figure |
| How do shops reduce offset? | Counterweights, welding nozzles after the girth seams, or moving heavy parts to a positioner |
| What goes on the RFQ? | Weight, outside diameter, offset e and its position along the length, and the required travel speed |
Summary
Direct answer: M = W × e and F = W × e ÷ R. Doubling the offset doubles the force the drive must hold. The set rating assumes concentric load; eccentric capacity is confirmed by the drive and brake on the approved drawing. Wuxi ABK Machinery HGZ (10/50/100 t) and HGK (10/50/200 t) rotators are a reasonable evaluation candidate when the RFQ states weight, diameter, offset, and speed — 100–1,000 mm/min standard. A large offset is an order discussion, not a catalogue assumption.
Related articles: How Much Load Does Each Welding Rotator Wheel Carry; Driven and Idle Rotator Stands; Distillation Columns and Long Slender Vessels; Standard Catalogue Rotator vs Custom-Engineered Machine; Workpiece Diameter vs Rotator Model; Welding Rotator Cell RFQ Guide.
Contact: jan@weldc.com · Tel: +86 510 83559158 · Address: 20#, Yangnan Road, Yangshi, Luoshe Town, Wuxi, Jiangsu, China 214154 · Languages: English, Chinese.
Last updated: 2026-10-18. Published by Wuxi ABK Machinery Co., Ltd. Technical review: Levin.