What is a Brake?

Industrial Brakes
"A brake is a frictional device that absorbs the kinetic energy of moving bodies and thus controls their motion."

A brake is a frictional device that is used to stop a rotating inertia load or to hold a component in a specific position without motion. The inertia load is usually the result of several rotating components that need to be stopped.

Holding Brakes vs. Dynamic Brakes

Type Function Example
Holding Brake Holds a component in stopped position Parking brake
Dynamic Brake Brings rotating load to a stop Drum or disc brakes

A holding brake is used to hold a component in position once it is stopped. A dynamic brake is used to bring a rotating load to a stop. Why the distinction between these two types? Consider the brakes on a vehicle. The stopping or dynamic brakes must be sized considerably larger than the parking or holding brake, the latter of which needs to be only large enough to hold the weight of the vehicle when at rest. This example applies to industrial rotating equipment in the same way.

Frequently, applications are encountered where the brake must perform both holding and dynamic braking functions. The brakes are usually attached to a stationary body in the drive line and a shaft passing through the brake is keyed or splined to the brake hub.

In addition, there are subtypes of dynamic and holding brakes. The subtypes are spring applied (energy release) and Energy Applied. These are distinguished by the way a brake is engaged. A brake is "engaged" when it is holding or stopping a load. It is "disengaged" when the device is free to rotate.

Methods of Brake Actuation

Dynamic and holding brakes are generally classified by the method of actuation. These include mechanical, electric, hydraulic and pneumatic (air).The last two are frequently combined when discussing brake actuation, since many brake models suitable for hydraulic actuation can also be used with pneumatic actuation.

View an actuation method comparison.

Spring Applied vs. Energy Applied Brakes

Type Function Example
Spring Applied Requires energy to disengage Learn more
Energy Applied Requires energy to engage Learn more

A spring applied dynamic or holding brake is said to be "normally engaged", requiring the application of actuation energy to disengage it. An energy applied dynamic or holding brake is "normally disengaged", and will not act as a dynamic or a holding brake unless actuation energy is applied.

A further breakdown describes the process by which the engagement method arrests the rotating mechanical energy. These "power transfer" methods include friction and positive engagement.

Friction Brakes vs. Positive Engagement Brakes

Type Function Example
Friction Gradual dynamic braking Vehicle brake
Positive Engagement Backlash-free holding brake Medical imaging equipment

In friction power transfers, single or multi-disc friction plates are brought together to stop or hold a rotating load by friction. Positive engagement power transfers involve jaw or tooth brakes which positively lock when engaged.

Generally, dynamic braking is accomplished with friction type devices, since the load can be brought to a controlled stop at a gradual rate defined by the equipment designer, and consistent with the inertia load being arrested. Friction brakes work well as holding brakes, but lack the precise control possible with a positive locking brake. Nevertheless, in many applications where the brake must perform both dynamic and holding functions, accurate positioning can be accomplished through careful design.

Positive Engagement brakes are best suited for holding brakes, particularly where extremely accurate control of the held device is necessary and backlash is not tolerable, as in medical imaging equipment, azimuth and elevation holding brakes for weapon systems, and the like. However a tooth or jaw brake used as a dynamic brake will cause immediate and violent stopping action, and may result in damage to both the brake and the rotating equipment being stopped.

Braking Considerations

The various classification and subtypes of dynamic and holding brakes offers designers a wide array of options. Each type of brake has its unique advantages and disadvantages. Carlyle Johnson can provide a full line of standard brakes at modest cost. We can also provide engineering expertise to solve the most difficult control problems where specially engineered solutions are required.

Classification Overview
Industrial Brakes

Brake Type

  • Holding Brake
  • Dynamic Brake

Method of Actuation

Brake Actuation Subtypes

  • Spring Applied (Energy Release)
  • Energy Applied

Power Transfer Method

  • Friction
  • Positive Engagement

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