Clutches and brakes

Clutches and brakes couple, decouple, accelerate, and decelerate rotating machine components and maintain them at proper speed. The functions of each are so similar that their rolls are often interchangeable. Whether the clutch/brakes are mechanically, electrically, or fluid power actuated, they are considered mechanical devices because they transmit mechanical power.

06/12/2003


Key Concepts
 
  • Types

  • Selection

Sections:
Selection
Oil-shear clutches and brakes
Sidebars:
Selection criteria
Application notes
Troublemakers

Clutches and brakes couple, decouple, accelerate, and decelerate rotating machine components and maintain them at proper speed. The functions of each are so similar that their rolls are often interchangeable. Whether the clutch/brakes are mechanically, electrically, or fluid power actuated, they are considered mechanical devices because they transmit mechanical power.


Clutches and brakes are generally used in rotary motion applications. The clutch or brake must be designed to convert mechanical energy absorbed during relative motion or slippage into heat energy. It must survive both mechanical and thermal steady-state and shock loads imposed by the system during the operational cycle without damage.




Selection

The first step in selecting a clutch or brake is to determine the configuration required, depending on performance characteristics.

After selecting a type to use, the required size must be determined. Selection charts are available for this purpose.

A typical chart is based on the horsepower and speed of the system, which should be the shaft speed at the clutch or brake, not motor speed.














For example, the clutch needed to drive a shaft powered by a 1-hp
motor rotating at 1750 rpm is Model A. If the shaft speed at the clutch is a 2:1 reduction, clutch speed would be 875 rpm, and Model B would be selected.

The relationship between system horsepower and speed is given by the following equation for determining the dynamic torque capability required from the clutch or brake:

D = 5252 x hp x SF

_____________

N

where:

D = dynamic torque, lb-ft

hp = horsepower

SF = service factor (ranges from 1-10)

N = speed of clutch/brake, rpm

As rpm decreases, torque increases. For this reason, the best location for a clutch or brake is on the high-speed shaft of a machine.

Speed should not be too low; below 300 rpm is not recommended for friction-driven units. At low speeds, burnishing or mating wear of the friction faces does not occur, and torque capacity may be reduced dramatically.













When a clutch or brake must be operated at very low speeds, it might be necessary to oversize the unit. In these cases, it is normally sufficient to use a unit with a static torque rating two times the calculated dynamic torque requirement.



Oil-shear clutches and brakes

In a basic oil-shear drive, torque is transmitted through shearing of an oil film between two disks. As the rotating input disk moves toward the stationary output disk, the oil shearing action forces the output disk to begin rotating. There is no friction material-to-metal contact until input and output disk speeds are nearly equal. Then the oil film breaks down, allowing full static engagement. Wear is greatly reduced by the oil film, which lubricates while transmitting most of the dynamic torque of engagement.



Selection criteria

Maximum operating torque

Maximum torque

Type of actuation

Type of engagement

Response time

Cycle rate

Thermal capacity

Space or weight restrictions

Environmental conditions

Acceptable service life

Amount of routine maintenance

Application notes

Pneumatic and hydraulic-powered clutches and brakes have higher torque ratings than electric-powered units.

Electromagnetic tooth clutches have higher torque ratings than electromagnetic disk clutches and don't slip.

Self-actuating clutches work best where motor speed is an adequate control, soft starts are acceptable, and energy savings are important.

Magnetic particle clutches and brakes are useful in tensioning and positioning when there are continuous speed changes.

Eddy current clutches are useful for providing drag loads needed in tensioning.

Multicaliper clutches, with ventilated disks, are designed for continuous duty.

Square jaw clutches are limited to running engagements under 10 rpm.

Spiral jaw clutches allow engagement speeds up to 150 rpm.

Multitooth clutches can have running engagement speeds up to 300 rpm.

Disk clutches and brakes are preferred over drum-style units for frequent start-stop applications.

Eddy current clutches are used primarily in adjustable speed drives.

Troublemakers

Environmental and service conditions that can cause trouble for clutches and brakes include:

Exposure to gritty dust

Poor ventilation

Operation in wet or damp environments

Exposure to:
— oil vapor
— salt air
— chemical fumes



Top Plant
The Top Plant program honors outstanding manufacturing facilities in North America.
Product of the Year
The Product of the Year program recognizes products newly released in the manufacturing industries.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
June 2018
2018 Lubrication Guide, Motor and maintenance management, Control system migration
May 2018
Electrical standards, robots and Lean manufacturing, and how an aluminum packaging plant is helping community growth.
April 2018
2017 Product of the Year winners, retrofitting a press, IMTS and Hannover Messe preview, natural refrigerants, testing steam traps
June 2018
Machine learning, produced water benefits, programming cavity pumps
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
February 2018
Focus on power systems, process safety, electrical and power systems, edge computing in the oil & gas industry
Spring 2018
Burners for heat-treating furnaces, CHP, dryers, gas humidification, and more
April 2018
Implementing a DCS, stepper motors, intelligent motion control, remote monitoring of irrigation systems
February 2018
Setting internal automation standards

Annual Salary Survey

After two years of economic concerns, manufacturing leaders once again have homed in on the single biggest issue facing their operations:

It's the workers—or more specifically, the lack of workers.

The 2017 Plant Engineering Salary Survey looks at not just what plant managers make, but what they think. As they look across their plants today, plant managers say they don’t have the operational depth to take on the new technologies and new challenges of global manufacturing.

Read more: 2017 Salary Survey

The Maintenance and Reliability Coach's blog
Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
One Voice for Manufacturing
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Maintenance and Reliability Professionals Blog
The Society for Maintenance and Reliability Professionals an organization devoted...
Machine Safety
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
Research Analyst Blog
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Marshall on Maintenance
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
Lachance on CMMS
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Electrical Safety Update
This digital report explains how plant engineers need to take greater care when it comes to electrical safety incidents on the plant floor.
Maintenance & Safety
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
IIoT: Machines, Equipment, & Asset Management
Articles in this digital report highlight technologies that enable Industrial Internet of Things, IIoT-related products and strategies.
Randy Steele
Maintenance Manager; California Oils Corp.
Matthew J. Woo, PE, RCDD, LEED AP BD+C
Associate, Electrical Engineering; Wood Harbinger
Randy Oliver
Control Systems Engineer; Robert Bosch Corp.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me