Hold backs, Sprags, Clutches

Low Speed Roller Ramp

BTS supply Marland and Stieber low speed roller ramp holdbacks or Backstops. They use a roller ramp mechanism. The safest place to mount a holdback is on the head pulley, as there is no drive train (couplings & gearbox) transferring torque that can fail between the head pulley shaft and holdback.

At this point in the drive train of a conveyor or bucket elevator, the regenerative torque is the highest. These holdbacks are lubricated, have a

uniformly high torque capacity and have good load carrying ability. They are normally anchored with a torque arm which must not be constrained in anyway.

Literature:
Marland BC
Marland Holdback service manual

Bibby High Speed.

BTS supply Bibby holdbacks or backstops, which are high speed, non-lubricated and fail-safe and designed to be safe for operational personnel. Backstops rotate in one direction only and give positive protection against reverse torque runaways of inclined conveyor or elevated installations.

Typically used on intermediate shafts of gearboxes and fan shafts of motors, that

drive fully loaded conveyors, kilns or bucket elevators to stop them running back for any reason.

These holdbacks use the centrifugal pawl system.

There are 3 types of high speed holdbacks:

Standard - a non-lubricated, high speed holdback that has a uniformly high torque capacity and is supplied with a torque arm.
Plate Controlled Release - a non-lubricated, high speed holdback that has a uniformly high torque capacity. The locking mechanism (known as the cassette) can be released from the torque arm (known as an adapter plate, which is bolted to the gearbox or motor), thus giving the facility that the shaft, the holdback is mounted on, can run in both directions. This cannot be done under load.
Torque limiter plate controlled release - a non-lubricated, high speed holdback that has a uniformly high torque capacity. The cassette can be released from the adaptor plate (torque arm), thus giving the shaft, the holdback is mounted on, the ability to rotate in both directions. This can be done under the regenerated torque on the holdback, created by load on the application (incline conveyor, bucket elevator, etc). A friction clutch has been built into the holdback which secures the cassette against the adaptor plate. The friction clutch gives the holdback load sharing capability, which is used on multi drive conveyors.

Advantages include :

The torque created on the holdback when there is a tail pulley jam on an incline conveyor or bucket elevator (stacked condition), can be released in a safe controlled manner.
In multi drive conveyors, 70% of the regenerative torque of the conveyor is taken up by the first drive (regenerative direction). With load sharing holdbacks, the first gearbox’s gears & bearings can be protected from carrying the 70% load in the stationary position, by setting the friction clutch to limit the torque it will hold and thus share the torque with the second and third drive.

Literature:
Bibby Holdbacks

Sprag Free Wheel Clutches

BTS supply Stieber freewheel clutches or backstops. They use a sprag mechanism. Sprag clutches are used in many applications and can handle high speeds.

The free wheel clutches are versatile and normally more cost effective than their roller ramp and centrifugal pawl counterparts.

Literature:
Cecon continuous operation clutch
Cecon service manual
Cebmag one-way backstops
Cebmag service manual

Holdbacks, Sprags and Clutches

Low Speed Roller Ramp

Bibby High Speed.

Sprag Free Wheel Clutches

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