What are the protective devices for belt conveyors?

Belt conveyors in industrial settings, such as coal handling plants, are equipped with various protective devices to ensure the safety of the system, protect the equipment, and safeguard personnel. These devices are designed to prevent accidents, detect malfunctions, and protect against damage to the belt and other system components. 

Belt conveyor protection device

1. Pull Cord Switch

Purpose: Emergency stop device.

Function: Pull cord switches are installed along the length of the conveyor belt. When pulled, they trigger an emergency stop of the conveyor, allowing personnel to immediately halt the belt in case of an emergency or malfunction.

Location: Typically mounted on the side of the conveyor.

2. Belt Sway (Misalignment) Switch

Purpose: Detects belt misalignment or sway.

Function: The belt sway switch detects the deviation of the belt from its normal path. If the belt starts to drift off-center, the switch signals an alert or shuts down the system to prevent damage or material spillage.

Location: Installed along the edge of the conveyor belt.

3. Belt Slip Switch

Purpose: Detects belt slippage.

Function: This device monitors the speed of the belt and compares it to the drive pulley speed. If the belt is slipping or moving slower than the drive pulley (which indicates belt slippage), the switch will trigger an alarm or stop the conveyor.

Location: Installed near the drive pulley.

4. Zero Speed Switch

Purpose: Detects belt stoppage or slowdown.

Function: Zero speed switches monitor the conveyor's movement and ensure the belt is running at its designated speed. If the belt stops or slows down unexpectedly, the switch will trigger an alert or stop the conveyor system.

Location: Typically mounted on the tail pulley or drive pulley.

5. Sequence Protection Switch

Purpose: Ensures proper startup and shutdown sequence.

Function: These switches ensure that conveyors start and stop in the correct sequence, preventing material build-up in one section while others are not running.

This is crucial in multi-stage conveyor systems.

Location: Installed at various points in the system, usually in conjunction with the control system.

6. Overload Protection (Current Overload Relay)

Purpose: Protects the motor and system from overload.

Function: An overload protection relay monitors the conveyor motor’s current. If the motor is overloaded (due to excess material, jammed equipment, etc.), the relay will shut off power to the motor to prevent damage.

Location: Installed in the motor control panel.

7. Belt Tear Detector

Purpose: Detects belt tears or punctures.

Function: Belt tear detectors sense physical damage to the conveyor belt (e.g., tears, punctures) and immediately stop the system to prevent further damage to the belt or other components.

Location: Installed beneath the conveyor belt in areas where material spillage or large tears could occur.

8. Speed Sensor

Purpose: Monitors conveyor speed.

Function: Speed sensors monitor the conveyor belt’s operating speed. If the belt speed deviates from its normal operational range (either too fast or too slow), the sensor triggers an alarm or stops the system.

Location: Installed on pulleys, usually near the drive unit.

9. Load Cells

Purpose: Monitors the material load on the belt.

Function: Load cells measure the weight of the material on the conveyor belt. If the material load exceeds the belt's design capacity, the system can trigger a shutdown to prevent overloading.

Location: Installed at strategic points under the belt where material is loaded or conveyed.

10. Chute Block Switch (Plugged Chute Detector)

Purpose: Detects blockages in conveyor chutes.

Function: These switches detect when material is blocked or backed up in the discharge chute. A plugged chute can lead to conveyor overloading and damage, so the switch stops the belt to prevent material overflow.

Location: Installed near discharge chutes or hoppers.

11. Fire Detection Systems

Purpose: Detects fires on or near the conveyor belt.

Function: Fire detection systems, such as infrared scanners or heat sensors, detect hot spots or fires on the conveyor belt. When detected, the system can trigger alarms or activate fire suppression systems (e.g., water sprays or foam) to extinguish the fire.

Location: Installed above or near the belt, especially in high-risk areas such as transfer points or drive stations.

12. Automatic Belt Cleaning Systems

Purpose: Prevent material build-up on the belt.

Function: Belt cleaning systems, including scrapers and plows, remove material buildup on the belt to prevent misalignment, wear, or other damage. Though primarily a maintenance device, they can prevent accidents related to material spillage.

Location: Installed at the discharge or return end of the conveyor.

13. Thermal Protection

Purpose: Protects against overheating.

Function: Thermal sensors monitor the temperature of key conveyor components, such as the drive motor or bearings. If overheating is detected, the system can trigger an alarm or stop the conveyor to prevent component failure.

Location: Installed near drive units and motor housings.

14. Anti-Rollback Device

Purpose: Prevents belt rollback on inclined conveyors.

Function: On inclined conveyor systems, this device prevents the conveyor from rolling backward when power is cut or during a shutdown, ensuring safety and preventing equipment damage.

Location: Installed near the drive unit on inclined sections.

Summary of Key Protective Devices:

Pull cord switch: Emergency stop.

Belt sway switch: Detects belt misalignment.

Belt slip switch: Detects belt slippage.

Zero speed switch: Detects stoppage or slowdown.

Overload protection: Prevents motor overload.

Belt tear detector: Detects physical damage to the belt.

Chute block switch: Detects chute blockages.

Fire detection: Detects fires or hot spots.