Lifting equipment is a type of machinery with relatively high risks at construction sites. Once an accident occurs, it often leads to severe consequences with multiple casualties. Therefore, the safety issues of lifting equipment have always been emphasized by relevant departments. The moment limiter is one of the most crucial safety protection devices for cranes. Practical experience has demonstrated that the correct selection and maintenance of crane moment limiters can reduce and even eliminate major liability accidents caused by overloading and overextending of lifting equipment, ensuring the safe operation of the equipment.
In China, the history of independently designing and manufacturing moment limiters is not long. Before 1990, most moment limiters were mechanical. Due to the lack of regulations and standards, their reliability was generally poor. Since 1990, when the State Bureau of Technical Supervision issued the “Safety Technical Specification for Crane Moment Limiters,” there have been relatively clear standards, norms, and methods for the design, appraisal, and acceptance of this device.
II. Development Trends and Characteristics of Moment Limiters
In recent years, moment limiters have developed rapidly and exhibited several characteristics. The integration and intelligence level of the main unit has become increasingly high. The display adopts multi-window and large-screen designs. The latest products have added a “black box” function, which can record the real-time operation status of the crane. The remote monitoring function based on the Internet of Things enables real-time remote monitoring of various working condition data of the crane. The appearance is more refined. The installation and adjustment are more convenient, and the reliability of the product has been significantly improved.
It is worth mentioning that the moment limiter products of Yichang Weite Electronic Equipment Co., Ltd. in the domestic market. Its WTL – A220 tower crane remote monitoring moment limiter comprehensively integrates the above-mentioned functions and has received excellent practical application feedback after being launched in the market.
III. Existing Problems and Improvement Directions of Moment Limiters
Despite the progress, the author believes that there are still many aspects of moment limiters in the current market that need improvement. Specifically, there are two main aspects. Firstly, the improvement of primary components of moment limiters, such as sensors, photoelectric encoders, and circuit connectors. Since most of these primary components are purchased or outsourced by manufacturers, and the quality of these products varies, it is easy for local deficiencies to affect the overall function of the system. The solution is for manufacturers to carefully select and conduct multiple tests and comparisons of primary components to achieve an optimized combination and meet the requirements of system performance to the greatest extent. Secondly, in the design of weight sensing devices of some manufacturers, long-term reliability has not been achieved. For example, the display of the instrument is very accurate during acceptance, but deviations occur after 2 – 3 months, which often leads to the failure of the entire moment limiter system and affects system reliability.
IV. Selection Principles of Moment Limiters
There are a wide variety of moment limiters in the current market. The author believes that when selecting a moment limiter, in addition to considering the characteristics of the crane type of the unit, the following basic principles should be followed: quality and performance first, price second, and mainly domestic products.
The quality and performance of moment limiters directly affect their use and are the fundamental principles for selection. The principle of “mainly domestic products” is due to the fast and considerate after-sales service provided by domestic manufacturers, which provides convenient channels for later use and modification.
V. Maintenance Precautions of Moment Limiters
When maintaining moment limiters, the following matters should be noted. Firstly, the power supply, overloading, and overextending connection lines are concentrated in the control box. When disassembling and assembling the connection lines in the control box, attention should be paid to the connector labels to avoid incorrect wiring and damage to the instrument output ports. Secondly, when off work, the power supply of the main unit should be turned off to prevent electronic components from aging faster under high temperature for a long time. It is necessary to avoid direct exposure of the display instrument to sunlight and rain. Non-maintenance personnel should not randomly adjust the buttons on the instrument panel and the adjusting bolts of the force-taking device. If abnormalities occur, professional technicians should handle the faults according to the methods provided in the manual. If the faults cannot be eliminated, consultation with the manufacturer should be carried out.
In conclusion, the selection and maintenance of crane moment limiters are of great significance for ensuring the safety and reliable operation of cranes. Although there have been certain developments and improvements in moment limiters, continuous efforts are still needed in aspects such as component quality improvement and system reliability enhancement. By following the correct selection principles and maintenance precautions, the effectiveness of moment limiters in crane safety protection can be maximized, reducing the occurrence of safety accidents and promoting the healthy development of the lifting equipment industry.
