A crane motor lifts the load, but the brake ensures it stays there. If a hoist brake fails, the load drops. If a travel brake fails, the crane crashes into the end stops.
Correct brake sizing isn't just about matching the motor torque; it requires a safety factor to account for wear, dynamic loads, and emergency stops.
Quick Tool Access: Open Brake Torque Calculator
1. Hoist Brakes (Holding the Load)
The primary job of a hoist brake is to hold the suspended load against gravity when the motor is off. It must also be able to stop a lowering load safely.
Key Formula: Required Torque
T_brake = Safety_Factor × (T_load + T_inertia)
Where:
- T_load: The torque generated by the load pulling on the drum.
- T_inertia: The torque required to decelerate the spinning motor rotor and load mass.
- Safety Factor: Typically 1.5 to 2.0. A factor of 2.0 means the brake can hold 200% of the rated load torque.
Why Safety Factors Matter
FEM and ISO standards recommend a minimum safety factor of 1.5 for service brakes. For critical lifts (e.g., molten metal), this increases to 2.0 or even 2.5. Never size a brake exactly to the load torque—it will slip over time as linings wear.
2. Travel Brakes (Stopping Motion)
Travel brakes (Cross Travel & Long Travel) work differently. They don't fight gravity; they fight momentum. The goal is to stop the moving crane within a safe distance without causing excessive load swing.
The "Soft Stop" Principle
If a travel brake is too strong (high torque), the crane stops instantly, causing the load to swing violently. If it's too weak, the crane coasts too far.
We calculate travel brakes based on Deceleration Time. A typical stopping time is 3 to 5 seconds. This provides a controlled stop.
3. Using the Calculator Tool
Our Brake Torque Calculator handles both Hoist and Travel scenarios. Here is how to use it:
For Hoist Brakes:
- Select the Hoist Brake tab.
- Enter the SWL, Drum Diameter, and Gear Ratio.
- Input the Motor Speed (RPM) and Rotor Inertia (check your motor datasheet).
- Choose your Safety Factor (Standard is 2.0).
For Travel Brakes:
- Select the Travel Brake tab.
- Enter Total Moving Mass (Crane + Load).
- Set your desired Deceleration Time (e.g., 4 seconds).
- The tool calculates the required torque to stop smoothly in that time.
Conclusion
Brake sizing is a balance between safety and control. Always err on the side of a higher safety factor for hoists, and focus on smooth deceleration for travel motions. Use our calculator to get a baseline, then consult with brake manufacturers for specific model selection.