Comprehensive Guide to Conveyor Belt Safety Protection Devices

Belt conveyor systems are the "arteries" for material transportation in fields such as mining, ports, power plants, and chemical industries. Their operational stability is directly related to the efficiency and safety of the entire production line. However, conveyor belts are highly susceptible to faults like deviation, slipping, tearing, and overload during operation—minor issues may cause shutdowns and production halts, while severe ones can lead to significant equipment damage or even safety accidents. Therefore, a complete and reliable safety protection system is not only a "compliance requirement" but also an "essential measure" to ensure personal safety and economic benefits.

I. Belt Deviation Protection Devices

Belt deviation is the most common fault, which can cause wear, material spillage, and even jamming and shutdown.

Functions

• Monitoring and Alarm: Real-time detection of whether the belt deviates from the center line.
• Automatic Correction/Shutdown: Issue an alarm for minor deviation; automatically shut down or activate the deviation correction mechanism for severe deviation.

Types and Characteristics

• Deviation Switch (Limit Switch Type): Mechanical structure. When the belt edge touches the lever and deflects it by a certain angle, the internal microswitch is triggered. It is usually designed with two stages: first-stage alarm and second-stage shutdown. Characteristics: Simple structure, low cost, strong anti-interference ability, and requires direct contact.
• Self-Aligning Idlers: Adopt a unique idler bracket design. When the belt deviates, friction is generated between the belt and the idlers, causing the idler group to rotate automatically at an angle, thereby creating a correction force that pushes the belt back to the center. Characteristics: Purely mechanical, passive, no power required, maintenance-free, and is the preferred solution for preventing deviation.
• Photoelectric/Ultrasonic Deviation Switch: Detect the position of the belt edge in a non-contact manner. Characteristics: High precision, no wear, but prone to interference in high-dust and sticky material environments, requiring regular cleaning.

II. Belt Slip Detection Devices

Slip indicates insufficient friction between the drive drum and the belt, which can cause wear, high temperatures, and even fire.

Belt slip detection devices can real-time monitor the actual operating speed of the belt and compare it with the theoretical speed (usually derived from the drive drum speed). When the speed difference exceeds the set threshold (e.g., 70%-85% of the rated speed), an alarm or shutdown signal is sent.

Types and Characteristics

• Contact-Type Speed Measurement Sensor: Typically, a speed wheel is closely attached to the back of the belt, and the belt linear speed is calculated by measuring the rotational speed of the wheel. Characteristics: Easy to install, but the speed wheel will wear out and needs regular inspection and replacement.
• Non-Contact-Type Speed Measurement Sensor: Adopt magnetic induction or laser principle to measure the rotational speed of the gear or encoder installed on the driven drum shaft. Characteristics: No wear, high precision, long service life, and is the preferred choice for modern systems.

III. Belt Tear Detection Devices

Longitudinal belt tearing is a catastrophic fault with extremely high repair costs.

Belt tear detection devices can quickly detect tearing at an early stage and trigger an emergency shutdown to prevent the tear from expanding.

Types and Characteristics

• Material Leakage Detection Type/Cable Pull Switch: A "suspension beam" or reticulated steel cable is installed below the belt's load-bearing section. When the belt tears, material leakage or the cable being torn will immediately trigger a shutdown. Characteristics: Mechanical, high reliability, low cost, and is the most widely used anti-tearing device.
• Non-Contact Type (Ultrasonic/Electromagnetic): Detectors are installed below the belt to continuously detect the integrity of the belt's internal structure. Once abnormal cracks or fractures are detected, an alarm is issued immediately. Characteristics: Can provide early warning before tearing occurs, advanced technology, but relatively high cost.

IV. Emergency Shutdown Devices

In case of an emergency at any position along the line, personnel can manually trigger the device to stop the conveyor immediately.

Types and Characteristics

• Pull Rope Switch: Steel cables are installed along the entire length of both sides of the conveyor, in series with a series of switches. Pulling the steel cable at any position can trigger a full-line shutdown. Characteristics: Mandatorily require self-locking; manual on-site reset is necessary before restarting to prevent misoperation, and it is the core of safety assurance.
• Emergency Stop Button: Large mushroom-head buttons are installed at key positions such as the drive station, head, and tail of the conveyor, which are eye-catching and easy to operate.

V. Overload Protection Devices

Overload protection devices can prevent the motor from being burned due to overload or the belt from being damaged due to excessive tension.

Types and Characteristics

• Motor Overload Protection: Realized through thermal relays in the electrical circuit or electronic protection functions inside the frequency converter to monitor the motor current.
• Chute Blockage Switch: Paddle-type or diaphragm-type switches are installed at the discharge port and chute. Material accumulation will push the paddle, triggering a shutdown. Characteristics: Direct and effective, preventing the belt from being crushed by blocked materials.
• Weighing System Interlock: Real-time monitor the flow rate through an electronic belt scale; once the limit is exceeded, it can link to adjust the feeder or issue an alarm.

VI. Anti-Reversal Protection Devices

Anti-reversal protection devices can prevent the upward-conveying belt from reversing due to the gravity of materials after shutdown, which may cause material accumulation, belt blockage, and damage.

Types and Characteristics

• Roller Backstop: Installed on the high-speed shaft of the reducer. The rollers in the internal chute are in a relaxed state during forward operation and wedge tightly immediately during reversal to achieve mechanical locking. Characteristics: Small size, large torque, high reliability.
• Belt-Type Backstop: A brake belt is wrapped around the head drum shaft, which is loosened during forward operation and tightened during reversal. Characteristics: Suitable for belt conveyors with low power and small inclination angle.
• Non-Contact Type (Ultrasonic/Electromagnetic): Detectors are installed below the belt to continuously detect the integrity of the belt's internal structure. Once abnormal cracks or fractures are detected, an alarm is issued immediately. Characteristics: Can provide early warning before tearing occurs, advanced technology, but relatively high cost.

VII. Temperature and Smoke Monitoring Devices

Temperature and smoke monitoring devices can monitor abnormal temperatures at key parts and early fire smoke to prevent fire.

Types and Characteristics

• Temperature Sensor: PT100 thermal resistors are commonly used, installed at heat-prone parts such as the drive drum bearing housing and bend drum. Characteristics: Can real-time monitor the temperature curve and issue an alarm when the temperature exceeds the limit.
• Smoke Sensor: Installed at key areas such as the drive station to detect smoke particles generated by friction-induced overheating. Characteristics: Provides very early fire warning and is often interlocked with automatic fire extinguishing systems.

VIII. Speed-Related Protection

In addition to slip protection, it also includes:

• Over-Speed Protection: Mainly used for downward-conveying belt conveyors to prevent stall and "runaway".
• Chain Break/Belt Break Protection: Detect abnormal speed (zero or extremely fast) of the cleaner chain plate or belt, and is often used as the trigger signal for the belt break catcher.

IX. Position Limit Protection Devices

Limit the travel range of heavy-duty components such as tensioning trolleys and mobile tails to prevent mechanical collisions caused by exceeding the limit position.

Characteristics: Adopt heavy-duty limit switches with high protection class (IP67), resistance to vibration and impact, and the output signal is directly connected to the safety circuit.

X. Auxiliary Power Supply Protection Devices

Provide stable power for belt protection devices, sensors, and lighting in remote areas without external power supply (such as mine mining areas).

Characteristics: Usually adopt the method of kinetic energy recovery (obtaining power from belt operation) + storage battery to ensure the safety system works uninterruptedly under any circumstances.

Maintenance Recommendations

An effective safety protection system is not just a simple combination of equipment; it also requires reasonable selection, correct installation, and regular maintenance.

1. System Integration: Modern conveyor systems usually integrate all these protection devices through a PLC (Programmable Logic Controller) or a specialized safety relay to achieve intelligent interlocking (e.g., deviation alarm → delayed shutdown if it persists; slip early warning → emergency shutdown and activation of fire sprinkler if it persists).
2. Regular Inspection: A strict inspection and maintenance plan must be formulated. For example:

• Manually test the effectiveness of pull rope switches and emergency stop buttons once a month.
• Regularly clean the probes of photoelectric sensors to prevent dust coverage.
• Check the rotational flexibility and wear of mechanical devices (such as deviation switches and backstops).
• Calibrate the set values of monitoring parameters such as speed and temperature.

Appendix: Quick Reference Table for Conveyor Belt Safety Protection Devices

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