Applications & Industries
Cranes and hoists
A lifting drive adds three things a conveyor does not have: a stopping case that can exceed the drive case, a holding case where the load must not descend, and a duty cycle of starts and stops that wears the mesh faster than continuous running at the same power.
- Author
- Priyansh Thummar, Editor
- Dates
- Published · Last updated
- Reading time
- 3 minutes
1. The coupling is in a load path that must not release
On a horizontal drive a coupling failure stops production. On a hoist with a load suspended, the consequences are of a different kind — and the whole drive is treated accordingly: statutory requirement, documented inspection, and margins set by regulation rather than by an engineer's judgement.
This article is engineering context, not compliance guidance. The lifting regulations that apply in your jurisdiction take precedence over anything here.
2. Stopping can exceed driving
A brake on a lifting drive is not sized to match the motor. It is sized to stop a moving load in an acceptable distance, or hold a suspended one with a margin against slipping — and that margin comes from a safety requirement, not the drive rating.
So the braking torque routinely exceeds anything the motor produces in normal running, and the coupling carries whichever case is larger. Sizing from the motor nameplate alone produces a component adequate for the drive and short for the job. Where the brake acts on a drum machined into the coupling, its heat and overhung mass become coupling problems too.
3. Duty cycle, not running hours
A crane spends its life starting, stopping and reversing rather than running steadily. Each start works the mesh through the acceleration of a load; each stop puts energy into the brake and heat into the assembly.
A crane running a few hours a day can accumulate more mesh work and more thermal cycling than a machine running continuously at the same power. Running hours are a poor proxy for wear here — which is why starts per hour belongs on the enquiry.
4. Outdoor service
Cranes sit in weather: temperature swings that cycle the grease and the seals, water ingress at the lip, dust in yards and ports, and long idle periods.
Standing still is not neutral. A coupling parked under load for months has one set of flanks in contact and the lubricant draining away from the rest.
5. What the enquiry must state
| Input | What it decides | Without it |
|---|---|---|
| Lifting duty class | Load class and service factor | A conveyor's factor on a hoist |
| Braking torque, stopping or holding | Frequently the governing case | Sized for the drive case only |
| Starts per hour | Mesh work and thermal cycling | Interval set from running hours |
| Inertia accelerated and stopped | Dominates the stopping case | Braking torque understated |
| Brake drum, and its diameter | Whether the size can carry it; heat at the mesh | Drum specified after the coupling — backwards |
| Environment and idle periods | Seals, grease, standing load | Indoor assumptions outdoors |
Frequently asked
- Is a hoist coupling sized on the motor?
- Not on the motor alone. It has to pass the drive case like any coupling, and then the stopping case separately — and a brake sized to hold a suspended load with a margin against slipping routinely applies more torque than the motor produces in normal running. On lifting duty the stopping case is usually what decides the size.
- Why does duty cycle matter more than running hours on a crane?
- Because a lifting drive spends its life starting, stopping and reversing rather than running steadily. Each start works the tooth mesh through the acceleration of a load, and each stop puts energy into the brake and heat into the coupling. A crane that runs a few hours a day can accumulate more mesh work and more thermal cycling than a machine running continuously at the same power.
- What does the brake drum do to the coupling underneath it?
- Two things. It puts heat directly into a component whose mesh runs in grease, which shortens the re-lubrication interval and can outrun the grease's dropping point. And it adds mass at a distance from the nearest bearing, which is overhung moment that bearing was not sized for, plus inertia the motor must accelerate and the brake must then stop.
- Can I use a standard industrial coupling on a hoist?
- Only if the stopping and holding cases have been checked against it, and only within whatever the statutory requirement for that lifting duty allows. Lifting equipment carries legal obligations about load paths and inspection that a general industrial selection does not address, and this article does not either — treat it as the engineering context, not as compliance guidance.
References
- AGMA 922-A96 (reaffirmed 2025), Load Classification and Service Factors for Flexible Couplings, for hoisting load classes.
- AGMA 9008-B00, Flexible Couplings — Gear Type — Flange Dimensions, Inch Series.
- IS 3238, Gear couplings (Bureau of Indian Standards).
- Editorial note: lifting equipment is subject to statutory requirements covering load paths, margins and inspection which vary by jurisdiction and which this article does not address. Nothing here is a substitute for the applicable lifting regulation or for the brake manufacturer's own sizing. No duty classes, braking margins or interval figures are published. Crane and hoist selections and the failure evidence behind them are to be added from Super Mech Industries records and confirmed at technical review.
Related articles
Coupling Types
When braking duty governs
The drum, the heat it puts into the mesh, and the sizing consequence.
Selection & Sizing
Service factor guide
Duty cycle as one of the three things a service factor prices.
Maintenance
What shortens an inspection interval
Why frequent starting shortens it more than running hours suggest.