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Clutches and Brakes by the Numbers
Loads, linings, plate, cone and centrifugal clutches, shoe, band, disc and motor brakes, on one slipway winch
How to size and check friction clutches and brakes: loads and inertia, linings, plate, cone and centrifugal clutches, shoe, band and disc brakes, and spring-applied motor brakes.
Start readingAbout this book
A clutch connects a load to its drive and a brake connects a load to the ground. Both do it through friction, and both turn motion into heat while they slip. That shared physics is why one book can cover them: the torque a lining can carry comes from the force pressing it and the friction coefficient, the slip time comes from inertia and the torque left over to accelerate or stop it, and the heat comes from the torque multiplied by the angle slipped.
This book shows how to size and check friction clutches and brakes with numbers. It starts with the loads a device must handle, measured on the shaft where it sits, and the friction linings that carry them. It then covers plate, cone and centrifugal clutches, shoe, band and disc brakes, and the spring-applied brakes built into motors, finishing with proof tests and records.
It is for mechanical design and maintenance engineers, fitters and machine builders. It assumes engineering or trade training and comfort with torque, speed and energy; the friction models are explained as they are used. Each chapter works the running case with real numbers, includes one plausible mistake and how it was found, links the KEVOS® tools that do the chapter’s calculations, and ends with an exercise and its worked answer.
The running case
Every chapter follows one machine. This is an illustration. A boatyard in Cairns, Queensland, is refitting the SW-25, the electric winch that hauls boats on a wheeled cradle up a 60 m slipway and lets them back down.
- Slipway and load: a slope of 1 in 12, a largest boat of 22 t on a 3 t cradle, 25 t in all, and a rolling resistance of 0.02 for the cradle wheels on the rails.
- Drive: a 5.5 kW, four-pole motor at 1,450 rpm with a spring-applied brake, a 20:1 helical gearbox, a friction clutch on the gearbox output shaft, and a 22.5:1 open gear pair to the drum: 450:1 in all.
- Drum and brakes: a rope drum of 600 mm diameter to the rope centre, a 700 mm brake rim carrying a band brake for lowering, and a caliper disc brake on the drum flange as an independent second brake.
- Auxiliaries: a warping capstan engaged by a cone clutch, and a petrol engine with a centrifugal clutch that can drive the winch through a belt when the power is off.
Masses, dimensions, speeds, friction coefficients, ratings, limits and test figures are the case yard’s working figures or are calculated from stated assumptions. They do not describe KEVOS® work or any real business, vessel or supplier’s data.
How to use the book
Read Chapter 1 first: it sets out the loads that every later chapter uses. Chapter 2 covers friction linings and measuring torque. Chapters 3 to 6 cover clutches, and Chapters 7 to 10 cover brakes; the brake chapters can be read without the clutch chapters. Chapter 10 also covers proof testing and records.
Every calculation in the book was checked by running it, and the KEVOS® tools linked from each chapter were checked against the calculations they perform. Friction coefficients and lining limits in the book are typical figures for illustration; a real design uses the lining maker’s values.
Source limits and professional responsibility
This book is educational. Winches, hoists and their brakes are plant whose design, inspection and maintenance are governed by the model WHS laws and by Australian standards such as AS 1418.2; their brakes are safety-critical, and a real design must be done or checked by a competent engineer against the applicable standard and the makers’ data. Work on a winch is done with the load secured, the machine isolated from all energy sources and locked out. Decisions about real machines remain with the competent people responsible for them.
Who this book is for
Mechanical design engineers, maintenance engineers, fitters and machine builders who specify, size, check or maintain friction clutches and brakes on winches, conveyors, hoists and other drives.
What you will learn
- Turn a machine's duty into the torques, speeds, inertias and energies that a clutch or brake must handle, on the shaft where the device sits.
- Calculate the torque capacity of plate, cone and centrifugal clutches and the slip time and heat of an engagement.
- Calculate the lever force, band tensions, clamp force and lining pressure of shoe, band and disc brakes, and recognise self-energising and self-locking geometry.
- Size a spring-applied motor brake for stop time, stop distance, energy and holding factor, including overhauling loads.
- Measure torque with a brake arm, plan a brake proof test and keep records that show a clutch or brake is fit for its duty.
Inside this book
Chapters
- 01Loads on a winch driveHow to turn a winch's duty into the forces, torques, speeds, inertias and energies that its clutch and brakes must handle, on the shaft where each one sits.
- 02Friction linings and measuring torqueHow friction linings behave, why a design uses a low friction coefficient for a brake and a high one for the parts behind a clutch, and how to measure torque with a brake arm.
- 03Plate clutch capacityHow a plate clutch carries torque: the uniform-wear and uniform-pressure models, friction radius, faces, spring force and lining pressure, checked against the torque the drive needs.
- 04Engaging a friction clutchWhat happens while a clutch slips: slip time, the energy that becomes heat, the snatch on the load, plate temperature rise and engagements per hour, on the shaft where the clutch sits.
- 05Cone clutchesHow a cone multiplies its axial force into friction torque, why engaging needs more force than holding, when a cone sticks, and how to check its torque, slip time and heat.
- 06Centrifugal clutchesHow a centrifugal clutch engages by speed alone: shoe force, spring force, engagement speed, torque against speed, idle clearance, and the heat of slipping at part throttle.
- 07Shoe brakesHow a shoe brake's lever, pivot and friction combine: normal and lever forces, self-energising and de-energising directions, self-locking, shoe pressure and the side load on the drum shaft.
- 08Band brakes and controlled loweringHow a band brake multiplies a small lever force by friction round the drum: band tensions, lever force, lining pressure, the direction that matters, stops, and the heat of a controlled lowering.
- 09Disc brakesHow to size a caliper disc brake to stop a load that drives through the stop or helps it: braking torque, friction radius, clamp force, pad pressure, energy and stopping angle.
- 10Motor brakes, holding and proofHow 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.
Apply This in Practice
Use these KEVOS® tools to try the method from this reading with your own numbers.
Applies this method
Band Brake Stopping Design
Designs a band brake to stop an inertia against a resisting or overhauling load: design torque, band tensions, lever force, pressure, stop time, energy and drum heating.
Applies this method
Band Brake Torque and Lever Force
Gives a simple band brake's tight and slack tensions, lever force and peak lining pressure from the braking torque, drum size, wrap angle and friction coefficient.
Applies this method
Caliper Disc Brake Design (Clamp Force, Pad Pressure, Heat)
Sizes a caliper disc brake to stop an inertia with a helping or overhauling load: braking torque, friction radius, clamp force, pad pressure, energy, heating and stop angle.
Used in Disc brakes
Applies this method
Centrifugal Clutch Check (Engagement Speed, Torque at Running Speed, Idle Clearance)
Checks a shoe-type centrifugal clutch: centrifugal force per shoe, engagement speed against idle, net shoe force and torque at running speed against the torque needed.
Used in Centrifugal clutches
Applies this method
Cone Clutch Engagement Check (Torque, Engaging Force, Slip Time, Heat)
Checks a cone clutch starting a load: torque and engaging force, slip time, slip energy against the load's kinetic energy, and the cone's temperature rise per engagement.
Used in Cone clutches
Applies this method
Cone Clutch Torque and Engaging Force
Gives a cone clutch's torque capacity by uniform wear, the higher axial force needed to engage it, and its capacity against the required torque, with a warning for small cone angles.
Used in Cone clutches
Applies this method
Friction Clutch Engagement Design
Sizes a clutch for an inertia start: design torque, clamp force, lining pressure, slip time, energy per engagement, plate temperature rise and average heat.
Used in Engaging a friction clutch
Applies this method
Plate Clutch and Disc Brake Torque
Gives a plate clutch's torque by the uniform-wear and uniform-pressure models, its peak lining pressure and its capacity against the required torque with a service factor.
Used in Plate clutch capacity
Applies this method
Prony Brake and Absorption Dynamometer Power
Turns a brake arm's length, scale reading and zero reading at a measured speed into torque, power absorbed and the heat to remove, as used to test the winch's backup engine.
Applies this method
Reflected Inertia and Motor Acceleration Torque
Reflects the boat, cradle and drum through the winch's 450:1 drive to the motor and gives the inertia ratio and the peak motor torque to start a haul against the load.
Used in Loads on a winch drive
Applies this method
Single Shoe (Block) Brake
Gives a short single-shoe brake's normal force, friction force, lever force and shoe pressure for either direction of rotation, and flags self-locking geometry.
Used in Shoe brakes
Applies this method
Spring-Applied Holding Brake Sizing (Stop Time, Energy and Holding)
Checks a spring-applied motor brake: net decelerating torque, slip and total stop time with the delay, stop angle, energy per stop and per hour, and the holding factor.
Used in Motor brakes, holding and proof
Applies this method
Torque to Accelerate a Rotating Load
Gives the accelerating torque, total torque, turns and kinetic energy for bringing the winch drum and its load from rest to hauling speed.
Used in Loads on a winch drive
Related Tools and Examples
Useful alongside
Winch Drum Brake Check (Load Torque at the Brake, Stop Time, Holding Factor, Brake Energy)
Checks a geared winch's motor brake from the rope load, drum and ratio; it treats the load as a hanging mass, so on a slipway it is used to confirm torques beside the full-inertia check.
Related to Motor brakes, holding and proof
References and source notes
The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 1 November 2026.
- C. J. Pethick and H. Smith, Cambridge University Press. Bose–Einstein Condensation in Dilute Gases (2002). In copyright. Used only as a map of ideas: rotation and angular momentum, energy held in motion, and the dissipation and relaxation that bring a moving system to rest, which this book applies to friction clutches and brakes. No text, equations, figures or problems are reproduced, and all cases and calculations are KEVOS® originals.
- R. G. Budynas and J. K. Nisbett, McGraw-Hill Education. Shigley's Mechanical Engineering Design, tenth edition (2015). Background for the uniform-wear and uniform-pressure models of plate and cone clutches, short-shoe and band brake analysis, self-energising and self-locking, and the energy and temperature rise of an engagement, used in Chapters 3 to 9.
- R. C. Juvinall and K. M. Marshek, John Wiley & Sons. Fundamentals of Machine Component Design, fifth edition (2012). Background for friction materials, clutch and brake types and their heat capacity, used in Chapters 2 to 6.
- W. C. Orthwein, Marcel Dekker. Clutches and Brakes: Design and Selection, second edition (2004). Background for centrifugal clutches, band and disc brakes and their thermal checks, used in Chapters 6, 8 and 9.
- Standards Australia. AS 1418.2 Cranes (including hoists and winches), Part 2: Serial hoists and winches (1997). Named by number and scope only in Chapters 1 and 10, as the Australian standard for the design of serial hoists and winches. No values are quoted from it; brake factors and test loads in this book are the case's working figures and are labelled as illustrations.
- Safe Work Australia. Model Code of Practice: Managing the risks of plant in the workplace (2022). Named in Chapters 1 and 10 for the duties to manage the risks of plant such as winches under the model WHS laws, including isolation and the inspection and maintenance of brakes.