Several issues worthy of attention in the load test of lifting machinery

Load testing is a comprehensive and important indicator for inspecting the quality and safety performance of lifting machinery products. Through load testing, not only can the deformation of the crane's metal structure, such as the deflection value of bridge cranes, be detected, but also the effective condition of the crane's safety devices, such as overload limiters, can be examined. The action protection conditions of the moment limiter of the tower crane under rated load conditions, etc. In conclusion, load tests are of great significance for inspecting the structural load-bearing capacity of cranes and their components, the welding and crack conditions of cranes, permanent deformation, loose connections, the effectiveness of safety devices, and any damage that affects the performance and safety of cranes.

During the inspection and testing process of lifting machinery, we have found that many installation and manufacturing units, as well as relevant user units, blindly conduct overload tests without conducting in-depth research on the conditions and procedures of load tests. The result is often that the tests not only fail to achieve the expected goals but also cause damage to the structure of the crane. It leads to new accident hazards and brings about economic disputes, etc. This article elaborates on several important aspects such as the conditions, procedures and judgments of load tests, in order to draw the attention of relevant units.

When several important conditions for load tests are not met, it is very likely to cause accidents

(1) Cranes whose product quality has not been verified, especially those whose welds at the main force-bearing parts have not been inspected for defects and lack quality certificates.

(2) Cranes that have not been installed and have not been appraised and handed over by the person in charge of the installation unit.

(3) Cranes with incomplete safety devices that do not function properly.

(4) Insufficient oil level at lubrication points can easily lead to gear wear and damage, failure, and cause accidents.

(5) Cranes where the connecting bolts of the main load-bearing components are not tightened and the end fixation of the steel wire rope does not meet the requirements.

The procedure of the load test must not be reversed, safety judgments must be accurate, and reliability indicators should be evaluated

(1) Load tests should be conducted on the basis of the implementation of relevant safety measures, following the procedures of no-load test, rated load test, static load test and dynamic load test.

(2) No-load test: Check the operation of each mechanism under no-load conditions, and verify the accuracy and smoothness of each mechanism during operation. Only after the no-load test is qualified can the rated load test be conducted.

(3) The rated load test must be conducted at the designated position, such as for tower cranes, the maximum rated lifting capacity should be lifted at the corresponding amplitude and the maximum rated lifting capacity should be lifted at the maximum amplitude respectively. When determining the rated load of a crane, the maximum stress of the structure should be based on the type of dangerous stress zone as the basis for safety judgment.

(4) After the static load test, there must be no problems such as broken connections or loose connections in any part of the crane that affect its performance and safety quality. Only after the static load test can the dynamic load test be conducted.

(5) After all the tests of the tower crane are completed, the reliability indicators of the crane to be appraised should be determined.

3 Summary

Load tests should be conducted in accordance with the requirements of national standards. Test procedures should be formulated and detailed records of each step should be kept. Only by strictly controlling every link can the test be successfully completed. The standards and requirements for the factory inspection of cranes and products in normal production, the detection after installation and erection, as well as the inspection, acceptance and load test of products in normal use are different and should be distinguished.