Dear Mr. Amit Dasgupta,

Please note that whether the brake is AC or DC or Thruster, the application of braking force is always by spring or counter weight (gravity). Thus, aforesaid brake types do not have different method for generation of braking force ! The above does not include disc brakes.

However, the difference arises in speediness or gradualness in application of the braking force. Plus operational reliability / durability of the item.

Certain applications demand quick action of brakes. In such applications, AC or DC brake is used. It is generally understood that DC brake is superior to AC brakes, and therefore, important application requiring speedy action of brake uses DC brakes.

The belt conveyor demands gradual action of brakes. The gradual action of brakes reduces the forces as well as tendency for longitudinal vibration along conveyor; as conveyor is high inertia machine (like train). The situation is more demanding than train as the inertia mass is resting on elastic tension members (belt). Therefore, thruster brakes are more suitable and are widely used for conveyors. Thruster brake creates braking torque to full value gradually, may be in about 2 - 3 seconds time, which makes the difference. Also, the gradual action time can be extended up to 6 - 7 seconds by incorporating additional inbuilt features, if need be.

As I remember, price wise AC, DC & Thruster brakes are in ascending order, i.e. thruster brake is probably costliest.

I hope the aforesaid information clarifies your query. You may also interact with brake manufacturers and investigate the issue further.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Dear Amit:

Your brake type enquiry is for smal to medium brake systems. The following response is with this understanding.

Johnson Industries, a leading supplier of brakes around the world, gives the following advice:

These types of brakes are normally applied to the high speeed shaft.

DCEM are sometimes used on low speed caliper disk applications where the disk might be of the 1200 mm diameter. The magnetic caliper can develop a release force of close to 90 kN.

1. Cheapest in the small brake sizes: thrustor

2. DCEM: magnet builds the strongest, but most costly, due to magnet winding cost. Don't have much control of the magnet release of the spring unless you use multiple calipers or drums and digitally control the indivdual release timing.

3. ACEM: Normally, the drum size is below 250mm and max.

torque to about 400 N-m

4. Thruster type is the only one to offer a regulated control and are generally preferred for the mdium small to intermediate sized conveyor.

Of course there are other types of brakes such as: hydraulic or pneumatic caliper disk, friction disk similar to clutch plates.......

Visit Johnson Brake website: www.jbrake.com or email them at:

www.johnson@jbrake.com

Lawrence Nordell

Conveyor Dynamics, Inc.

Specialist in Large Brake Systems

www.conveyor-dynamics.com ■