The take-up device in a conveyor belt system has three major functions:
1. To establish and maintain a predetermined tension in the belt.
2. To remove the accumulation of slack in the belt at startup or during momentary overloads, in addition to maintaining the correct operating tension.
3. To provide sufficient reserve belt length to enable re-splicing, if necessary.
Screw Take-Up Devices
Manual, as well as automatic, take-up devices are normally used in a typical conveyor belt system. The manual or screw take-up consists of a tension pulley (frequently the tail pulley of conveyor) which can be moved to tighten the belt by means of threaded rods or by steel cables which can be wound on a winch. These give no indication of the tension they establish and are adjusted by trial methods until slippage is avoided. They are unable to compensate for any length changes in the belt between adjustments and thus, permit wide variation in belt tension. Use is generally restricted to short and/or lightly stressed conveyors.
The manual take-up must be such that when tension is applied to the pulley, the conveyor pulley remains at right angles to the direction of belt travel. Also the tension must be high enough to allow elastic recovery of elongation due to starting forces, load changes, etc.
Automatic take-ups depend upon suspending a predetermined weight (gravity), by activation of a torque motor, by hydraulic pressure, or by spring loading. These devices maintain a predetermined tension at the point of take-up regardless of length changes resulting from load change, start-up, stretch, etc. This permits running the belt at the minimum operating tension and should be used on all long length conveyors and moderate to highly stressed conveyors.
The automatic take-up alignment must be such that the pulley or belt conveyor pulleys are maintained at right angles to the direction of belt travel. In a gravity or spring-loaded take-up, the carriage must be guided to maintain the pulley axis on a line perpendicular to the belt center line.
Hydraulic Tensioner for Belt Conveyor
Adequate take-up is essential to satisfactory operation of a belt conveyor. The amount required depends on type of belting and on service conditions. Please refer to belt manufacturer for recommendations.
Normally, when a new belt has been properly installed and tensioned, the take-up roll or take up pulley (automatic take-up) will be initially set at a position of 30% along the line of travel, leaving 70% of the take-up area available for elongation.