Why the Load Curve Matters More Than Maximum Torque
In gearbox selection, maximum torque is often treated as the key safety reference. If the calculated peak torque is within the gearbox rating, the selection is generally considered acceptable. In reality, maximum torque describes only a single point; it does not describe how the load behaves over time.
What defines gearbox fatigue and long-term reliability is not the highest torque value, but the load curve—the way torque varies throughout the operating cycle. A load curve shows how long the gearbox operates under different load levels, how frequently loads change, and how often high or low torque conditions occur.
Two applications can share the same maximum torque and still have completely different load curves. One system may experience high torque briefly and rarely, while another may operate under moderate but constantly fluctuating torque for most of its cycle. From a mechanical perspective, these situations are not equivalent.
Repeated exposure to varying loads accelerates fatigue in gears, shafts, and bearings. Even when torque levels remain below rated limits, the accumulation of stress cycles gradually reduces service life. This is why gearboxes in applications such as indexing systems, processing lines, and variable-load conveyors often show wear patterns that cannot be explained by peak torque alone.
Maximum torque helps define mechanical limits, but the load curve defines mechanical reality. Without understanding how torque is distributed across time—how long loads persist, how frequently they change, and how often they repeat—gearbox selection is based on incomplete information. Load curves are not theoretical tools; they are practical indicators of how a gearbox will age in real operation.
