BIZOMAT MAKEOS · Power Transmission
Winch Drum Brake Check (Load Torque at the Brake, Stop Time, Holding Factor, Brake Energy)
For a geared winch or hoist with a brake on the motor shaft, can the brake hold and stop the descending load quickly enough, and how much heat does each stop put into it?
Check of the motor-shaft brake of a geared rope winch or hoist: the drum torque from the rope load, the load torque at the brake through the gear ratio with the gear efficiency helping the brake when lowering, the rope speed, the inertia at the brake including the load reflected through the drum and gears, then the stopping time, stop distance, holding factor and energy per stop and per hour (as the holding brake sizing tool, load overhauling), against your stop time and brake ratings.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Rope load | kN | Load on the rope at the drum, including hook and rope. |
| Drum diameter (to rope centre) | mm | Drum diameter to the rope centre (use the outer layer for a multi-layer drum). |
| Gear ratio (motor ÷ drum) | Total reduction from the motor to the drum. | |
| Gear efficiency | % | Efficiency of the gearing. |
| Motor speed | rpm | Motor speed when lowering. |
| Motor, brake and coupling inertia | kg·m² | Inertia of the motor rotor, brake disc and coupling. |
| Brake | ||
| Brake torque (dynamic rating) | N·m | Dynamic torque rating of the brake. |
| Engagement delay | s | Time from switching off to the brake gripping. |
| Required total stop time | s | Longest acceptable stop time. |
| Holding factor required | Brake torque as a multiple of the load torque needed for holding. | |
| Permissible energy per stop | kJ | Energy the brake may absorb in one stop. |
| Stops per hour | Stops per hour. | |
| Permissible energy per hour | kJ | Energy the brake may absorb per hour. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Rope load
- What it is
- The pull in the rope where it leaves the drum, including the load, hook block and hanging rope.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 10000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The load torque at the brake rises in direct proportion.
- Get it right
- Enter it in kN, not N or kg: divide a force in newtons by 1000.
What this means: Drum diameter (to rope centre)
- What it is
- The drum diameter measured to the centre of the rope, which sets the lever arm of the rope pull on the drum.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- For a multi-layer drum use the outer rope layer, where the torque is highest.
What this means: Gear ratio (motor ÷ drum)
- What it is
- The total speed reduction from motor to drum: motor speed divided by drum speed. The brake is on the motor shaft.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 10000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger ratio lowers the load torque at the brake.
- Get it right
- Multiply the ratios of all gear stages and any chain or belt drive.
What this means: Gear efficiency
- What it is
- The efficiency of the gearing between drum and brake. When the load drives the gears backwards, losses reduce the torque that reaches the brake.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 10% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 85% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the back-driving efficiency from the gearbox maker if it differs from the forward value.
What this means: Motor speed
- What it is
- The motor shaft speed when the brake is applied, normally the lowering speed.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1450 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The braking time after engagement rises in direct proportion to speed, and the energy per stop with its square.
- Get it right
- Use the actual lowering speed, which can exceed the rated speed with some drives.
What this means: Motor, brake and coupling inertia
- What it is
- The mass moment of inertia of everything on the motor shaft: rotor, brake disc, coupling and fan.
- Units and format
- Enter a number in kg·m²: kilogram square metres (mass moment of inertia). The form accepts 0 kg·m² to 10000 kg·m². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.02 kg·m² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the motor and brake data sheets and add them; it is in kg·m², not the GD² value.
Brake
What this means: Brake torque (dynamic rating)
- What it is
- The braking torque the brake gives while slipping, from the brake maker’s dynamic rating, acting at the motor shaft.
- Units and format
- Enter a number in N·m: newton-metres. The form accepts 0.000001 N·m to 10000000 N·m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 N·m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More brake torque shortens the stop and raises the holding factor.
- Get it right
- Use the dynamic (sliding) rating, which is lower than the static holding rating.
What this means: Engagement delay
- What it is
- The time from switching off to the brake gripping, during which the load keeps moving at full speed.
- Units and format
- Enter a number in s: seconds. The form accepts 0 s to 5 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.05 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the brake data; DC-side switching of the coil is much faster than AC-side switching.
What this means: Required total stop time
- What it is
- The longest total stop time you accept, from switch-off to standstill, including the engagement delay.
- Units and format
- Enter a number in s: seconds. The form accepts 0.000001 s to 600 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must be longer than the engagement delay; take it from the machine’s safety requirements.
What this means: Holding factor required
- What it is
- The multiple of the load torque at the brake that the brake torque must reach to hold the load stationary.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the standard or rules that apply to the hoist.
What this means: Permissible energy per stop
- What it is
- The energy the brake can absorb in a single stop without overheating, from the brake maker’s data.
- Units and format
- Enter a number in kJ: kilojoules. The form accepts 0.000001 kJ to 1000000 kJ. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 kJ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter kilojoules, not joules.
What this means: Stops per hour
- What it is
- How many times per hour the brake stops the load from speed, used to find energy per hour.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 100000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Energy per hour rises in direct proportion.
- Get it right
- Count only dynamic stops; brake applications at standstill add no friction energy.
What this means: Permissible energy per hour
- What it is
- The energy the brake can absorb per hour of operation, limited by how fast it sheds heat.
- Units and format
- Enter a number in kJ: kilojoules. The form accepts 0.000001 kJ to 100000000 kJ. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 kJ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the brake maker’s data; enter kilojoules.
Method and formulas
- Drum torque = F D ÷ 2; load torque at the brake when lowering = drum torque ÷ i × η; rope speed = π D n ÷ (60 i).
- Inertia at the brake = J_m + m (D ÷ 2i)² with m = F ÷ g.
- Stop time, angle, energy and holding factor with the load driving through the stop (as the holding brake sizing tool); stop distance = brake shaft angle × D ÷ 2i.
- Example: 15.938 N·m at the brake; the load stops in 0.22145 s after dropping 77.284 mm.
Limitations
- Rigid rope and gearing; rope stretch adds to the stop distance and softens the shock.
- Single brake on the motor shaft; a second (load) brake changes the duty.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check the brake on a hoist or winch
- Find the stop distance of a descending load
- Check a brake after a gearbox change
Who it is for
- Lifting engineers
- Maintenance engineers
- Machine designers
What you get
- Drum torque, load torque at the brake, rope speed
- Inertia, stop time and stop distance
- Holding factor and brake energy
Interpreting the result
- When lowering, gear losses help the brake; when the gearbox is efficient the brake must do more.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2455–2459, 165–168. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Useful alongside · BIZOMAT original book
Motor brakes, holding and proof
In Clutches and Brakes by the Numbers
What it covers: How to size a spring-applied motor brake for stop time, distance, energy and holding factor, why a hoist tool differs on a slipway, and how to prove and record a brake.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.