‘Parked-off’ Conveyor Braking
First published in the August 2015 issue of Quarry Management
Steve Powell, product manager for Twiflex Ltd, explains how ‘parked-off’ conveyor brakes can improve safety during maintenance
Heavy-duty conveyors used in quarries, mines, cement plants and many other processing and materials-handling applications can carry huge loads and are therefore potentially dangerous. Generally, they are operated safely and responsibly, and have a number of built-in safety systems.
One of the key elements in a conveyor system is the parking brake, which locks the conveyor in position when it is not in use, is being serviced or during a power outage. This reduces the possibility of the conveyor starting to move under its own load, a situation that can become very dangerous, very quickly.
To counter the risk of a total power failure, most parking brakes are spring-applied. When no external power is supplied, the pressure of the spring is applied to the pad and the brake clamps shut, thereby locking the conveyor in position.
However, a downside to this is that while the spring-applied brake offers protection in the event of a power failure, it also makes maintenance much harder. When a spring-applied brake is powered down ready for maintenance work, the brake is shut tight against the disc. The springs therefore need to be compressed to access the pads, leaving a lot of potential energy in the brake.
To address this issue, Twiflex Ltd, have incorporated a special feature into their conveyor brake products to address the risk of brakes clamping shut unexpectedly during maintenance, which can pose a hazard to personnel. The ‘parked-off’ feature can be applied quickly while the brake is in the field and allows for maintenance and pad removal without the risk of the brake clamping shut.
Conventional industrial brakes typically employ a mechanical lock-out concept in which a nut and centre bolt arrangement holds the spring force and prevents the disc from closing during maintenance. However, this only works as long as the nut maintains its integrity. If the nut fails, eg because its thread shears, the brake will close unexpectedly, which could injure maintenance personnel, or anyone else nearby.
The Twiflex ‘parked-off’ feature is different to other solutions in that it actively removes the spring force from the brake while it is powered off, which means that there is no force acting on the pad and therefore no potential for an unexpected closure when correctly applied. With hydraulic pressure applied, maintenance engineers can unwind an adjusting spindle, which releases the spring pack. When the hydraulic pressure is removed the spring is free to extend without acting on the brake. At this point, the spring load and hydraulic pressure are both zero and the brake has no stored energy.
The ‘parked-off’ feature, which is available on many of Twiflex’s conveyor brakes, including the recently released VKSD and VBS modular brakes, has several benefits. First, it allows basic maintenance, such as brake pad replacement, to be carried out quickly and with a reduced risk of harm from unexpected closure, compared with conventional brake designs. Secondly, the brake pressure can be adjusted easily by setting the brake to ‘parked off’ and adjusting the number of shims from the end cover. Finally, installation is easier and the brake can be fitted without needing hydraulic pressure.
For more information visit: www.twiflex.com
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