Anti-rollover switch: the patron saint of safety of lifting equipment, working principle and purchase guide

In the statistics of lifting machinery accidents, over-rolling accidents account for more than 23% of the total accident rate. Once they occur, they often cause serious consequences such as the hook group hitting the boom or the pulley being pulled off. As a key safety device to prevent such accidents, the anti-roll switch has become the standard safety equipment for bridge cranes, tower cranes and lifts. Behind this seemingly simple device, there is a sophisticated safety protection mechanism. Today we will fully analyze this important safety component.

What is the anti-roll switch? What is its working principle?

Anti-roll switch is essentially a kind of​​Position safety limit device​​, Specially used to limit the lifting height of lifting equipment. When the spreader rises to a preset limit position, the anti-roll switch will automatically cut off the lifting power supply and trigger the braking system to prevent the spreader from continuing to rise and cause accidents. Its working principle can be divided into two types: mechanical and electronic: the mechanical type triggers the micro switch through a mechanical structure such as a lever and a cam; the electronic type detects the number of revolutions of the reel through an encoder or a proximity sensor, and outputs a control signal when a preset value is reached. Modern high-end anti-rollover switches such as Siemens 3SE5 series have an accuracy of ±2mm and a response time of no more than 0.1 seconds, which far exceeds the ±50mm accuracy standard required by national standards.

Which devices and scenarios are the main applications of anti-rollover switches?

This kind of safety device is widely used in all kinds of vertical lifting equipment. The most common are​​Bridge gantry crane​​Lifting mechanisms, especially on heavy lifting equipment in steel mills, ports, docks, construction sites and other places. Both the luffing and lifting mechanisms of tower cranes must be equipped with anti-rollover switches, which are clearly required by the national compulsory standard GB/T 3811-2008. Construction lifts and mine hoists also need to be equipped with this kind of protection device. In the investigation of a coal mine accident last year, it was found that the failure to install a qualified anti-roll switch was one of the main causes of the tank accident. Even in the lifting mechanism of some automated production lines, although the lifting height is not large, a simple anti-roll switch will be installed to ensure the safety of the equipment.

What are the common types of anti-rollover switches? What is the difference between different types?

According to the trigger principle, it can be divided into​​Mechanical trigger​​and​​Electronic induction​​Two categories. The mechanical type is divided into heavy hammer type, cam type and lever type. Among them, the heavy hammer type has a simple structure and low cost, but has low accuracy. It is mostly used in small cranes; the cam type can accurately set the limit position by adjusting the cam angle, and it is widely used in medium-sized equipment. The electronic type mainly includes a rotary encoder and a magnetic proximity switch, which triggers the protection by detecting the number of turns of the reel or the position of the wire rope. It has high accuracy and can achieve multiple protections, but the cost is relatively high. The current mainstream trend is the integration of mechanical and electronic products. For example, the Schneider ZV series not only retains the reliability of mechanical triggering, but also adds the electronic early warning function, which will send a pre-warning signal before reaching the limit position.

How to properly install and debug the anti-roll switch?

The choice of installation location is crucial. The mechanical anti-rollover switch should be installed at the end of the reel shaft or on the drive shaft linked with the reel to ensure that it can accurately reflect the retracting and discharging situation of the wire rope. During debugging, you need to run the hook without load to the upper limit position, and then adjust the trigger mechanism so that the switch moves at this time. The electronic type needs to set the pulse parameters of the number of turns, and calculate the set value according to the formula: total number of pulses= maximum lifting height/(reel circumference × reduction ratio). It is recommended to set aside during actual debugging​​Safety margin​​, Usually reduce the pulse by 2-3 turns on the basis of the calculated value as the trigger point to ensure reliable protection under the influence of wire rope elongation or other factors. A port crane installation case shows that the correctly debugged anti-rollover switch can start to slow down when the spreader is still 10cm away from the limit point, and completely cut off the power when it reaches 5cm.

What are the common faults of anti-rollover switches? How to check and repair?

Common faults include​​Malfunction​​、​​Do not act​​and​​Abnormal signal​​Three categories. Malfunction is mostly caused by loose mechanical parts or offset position. Check the position of the fixing bolts and trigger rods to solve it; inactivity is usually caused by damage to the micro switch or oxidation of the contacts, which can be judged by detecting the on-off state with a multimeter; signal abnormalities are common in electronic switches, which may be caused by loose encoder connectors.Or the counting module fails. It is important to establish a regular inspection system. It is recommended to check the fastening of mechanical parts once a week, clean the contacts once a month, and calibrate the accuracy every six months. During maintenance, the total power supply of the equipment must be cut off first, and the safety procedures of ”power failure → power inspection → listing” must be followed. A maintenance unit has caused maintenance personnel to be squeezed by equipment that was suddenly activated due to non-power failure for maintenance.

What is the selection standard for anti-rollover switches? Which brands are trustworthy?

The first thing to look at when buying​​Certification​​, Must have a special equipment manufacturing license and CE certification; secondly, look at​​Technical parameters​​, including the protection level (at least IP65), contact capacity (AC-15 category) and mechanical life (more than 1 million times); the third depends on the protection level (at least IP65), contact capacity (AC-15 category) and mechanical life (more than 1 million times).​​Adaptive performance​​, Whether it can work stably in environments such as equipment vibration and temperature changes. International brands such as Schneider, Siemens, and Omron have reliable quality but higher prices; domestic brands such as Delixi and Chint are cost-effective. The WTM series of Micro-special electronics is designed for lifting equipment and has pre-warning and dual protection functions. It has performed well in many large-scale projects. It is recommended to avoid buying cheap products without identification or certification. A logistics center has caused 200,000 yuan worth of goods to fall and be damaged due to the use of inferior anti-roll switches.

What is the relationship between the anti-roll switch and other safety devices? Is it an alternative?

The anti-roll switch is a lifting device​​Multiple security protection systems​​An important part of it, but not the only protection device. It usually forms a complete safety protection chain together with overload limiters, height limiters, buffers, etc. These devices each have their own focus: overload limiters prevent overload, height limiters control travel, and anti-roll switches specifically prevent top roll. Although there is some overlap in functions, they cannot be replaced by each other. National standards clearly stipulate that cranes with a rated lifting weight greater than 20t must be equipped with overload limiters and anti-rollover switches at the same time. The most reasonable configuration scheme is layered protection: first, the height limiter performs the normal limit, and then the anti-roll switch provides the final protection when the limiter fails.

What should I pay attention to in the maintenance of the anti-roll switch?

Maintenance needs to be established​​Regular inspection system​​。 Daily inspections include visual inspections (for mechanical damage), motion tests (manual triggering to see if it is effective), and cleaning and dust removal; monthly inspections need to measure whether the trigger force and stroke meet the standards, and check whether the wiring is firm; annual inspections should be fully disassembled and inspected, worn parts replaced, and accuracy recalibrated. In particular, it should be noted that the anti-roll switch must be recalibrated every time the wire rope is replaced or rewound, because changes in rope length will directly affect the lifting height. It is also important to establish a maintenance file to record each inspection and maintenance record, which is not only a safety requirement, but also helps to analyze the law of failure. The maintenance records of a large logistics company show that the failure rate of the anti-roll switch has been reduced by more than 80% for equipment that insists on regular maintenance.

Choosing the right anti-rollover switch and maintaining it correctly can not only meet regulatory requirements, but also effectively ensure the safety of equipment and personnel. It is recommended to consult professional and technical personnel before purchasing, and choose the most suitable model and configuration according to the specific working conditions of the equipment. Organize regular professional training of operation and maintenance personnel to ensure that everyone understands the importance of safety devices and basic maintenance methods, and jointly build a safety line of defense for lifting operations.