Thread Content
A belt conveyor is a type of material handling equipment widely used in manufacturing enterprises, and it mainly consists of a conveyor belt, a drive motor, as well as supporting equipment and control and protection devices. Typically, a complete conveying system is formed by several belt conveyors that are interconnected in a cascaded manner, enabling the long-distance transport of materials. The operating condition of belt conveyors is directly related to the safety of conveying equipment and personnel during the production process. It is of great practical significance to determine how to enable the belt conveyor protection devices to function efficiently, reliably, and stably during production operations. The main subjects discussed in this article are the primary protection devices for belt conveyors, such as deviation prevention switches, slipping prevention switches, and tearing prevention switches. Current application status and existing problems of belt conveyors: (1) Deviation prevention switch. The deviation prevention switch is a protective device used to detect the degree of belt deviation during the operation of the belt conveyor and to issue alerts; it is sometimes also used to trigger an emergency stop when the belt deviates significantly. The deviation switches that are widely used today are generally travel-switch type deviation prevention switches. The deviation prevention switches are fixedly installed at regular intervals (about 50m) on the supports on both sides of the belt conveyor. When the roller part of these switches is pressed by the edge of the conveyor belt that is operating off-center, it deflects; once the roller deflects by a certain angle, this triggers the switch contacts to activate. Typically, the normally closed contacts of all the deviation switches on a belt conveyor are connected in series and then integrated into the conveyor’s start/stop control circuit or alarm indication device. For very long belt conveyors, it is sometimes necessary to connect the deviation switches along the length of the conveyor in segments or groups. The main disadvantages of the deviation detection switches currently widely used in belt conveyors are as follows: ① Belt conveyors cannot display the operating status of each deviation detection switch remotely and independently, and they generally lack a function for self-locking after a contact is activated. When a deviation switch activates, it is difficult to determine which one specifically has triggered; an on-site inspection is required to identify the exact location where the conveyor belt has deviated. ②The mechanical roller structure of belt conveyors finds it difficult to withstand the impacts from the conveyor belt over a long period of time, requiring frequent maintenance and replacement of the deviation switches. (2) Belt conveyor anti-slip switch: The belt conveyor anti-slip switch is a protective device used to detect slipping between the conveyor belt and the drive drum and to issue an alarm; it can automatically trigger an emergency stop when slipping occurs on the conveyor belt. Slipping is a relatively serious fault condition; its causes may include overload, jammed conveyor belts, broken belts, stuck rollers, abnormal rotation speed of the drive motor, and so on. Failing to shut down the equipment in time can lead to severe damage to the equipment, fires, and other serious accidents that may cause injury to people. There are many types of slip switches, and their working principles as well as detection methods vary. For example, classified by detection method, there are roller-type slip switches that directly measure the conveyor belt speed and compare it with a set standard speed, there are slip switches that measure the speed of the driven wheel and compare it with a set standard speed, and there are comparative slip switches that simultaneously measure both the speed of the drum and the conveyor belt speed and compare them ； Based on their internal working principle, they include magnetoresistive, magnetoelectric, photosensitive, and so on. Some slip switch devices are also capable of providing real-time signal display and output of the conveyor belt linear speed or drum rotation speed. Common problems encountered in the installation and use of slip switches, which are widely used today, include: ① There are many different types of slip switch products for belt conveyors, and improper selection often occurs in practice. Some products struggle to cope with harsh on-site environmental conditions such as dust, humidity, and vibration. Some products are difficult to install on-site; for example, split-type products with a speed sensor and a control box separate from each other make on-site installation and wiring rather troublesome. ②In many belt conveyor systems, slippage is detected by comparing the actual speed of the conveyor belt with its rated standard speed; therefore, such systems need to have the capability to bypass the startup and shutdown processes of the conveyor belt, which makes it impossible to detect any slippage that occurs during these processes. However, during the startup of a belt conveyor, due to acceleration, the need to overcome significant static friction, and the possibility of jamming, slipping can occur very easily. 3. Belt conveyor tear prevention switch: The belt conveyor tear prevention switch is a protective device that detects longitudinal tears in the conveyor belt and triggers an alarm; it can be used to initiate an emergency shutdown automatically when a tear occurs in the conveyor belt. Most tears occur at the outlet of the discharge hopper at the tail end of the conveyor belt; large hard objects in the material get stuck at this outlet, causing scratches or even punctures in the conveyor belt. Some tears are caused by deformations in the conveyor belt supports and idlers. Based on different detection methods and working principles, there are photoelectric and conductive rubber type tear switches that are installed beneath the conveyor belt, as well as pull-cord type switches that are also installed beneath the conveyor belt ； There is a baffle-type tear switch installed at the outlet of the discharge hopper at the end of the conveyor belt ； In addition, there are also vibration-sensitive tear switches and the like. The main disadvantages of the tear switches used widely in belt conveyors at present are as follows: ① Most belt conveyor tear switches can only activate after the conveyor belt is torn and penetrated, which results in a very limited protective effect of these switches. Many products have poor reliability and stability; as a result, many users simply refrain from installing tear switches, relying instead on indirect methods such as increasing inspection frequency and minimizing large debris in the materials to reduce the likelihood of tearing occurring. ②Many products are prone to malfunctioning under slight disturbances, affecting the normal operation of the conveyor belt. ③Most products feature a modular design with several sensor probes and a control box, which makes on-site maintenance inconvenient. The above has briefly discussed the functions and disadvantages of belt conveyor protection devices from aspects such as function, structure, and performance. Overall, the belt conveyor protection devices we use currently have drawbacks such as single functionality, outdated performance, complex structure, rough appearance, and poor reliability. At present, manufacturing enterprises in our country are in the process of shifting from an extensive to an intensive model, and from a labor-intensive to a technology-intensive approach. How to ensure production safety while reducing labor input and increasing efficiency and productivity is an important challenge for every enterprise. Improvements to the condition monitoring devices, including those for belt conveyors, will surely enhance the reliability and stability of the operation of conveying equipment in manufacturing enterprises, which will ultimately result in a significant increase in production efficiency.