Load test is an important indicator to test the quality and safety of lifting machinery products. Through the load test, not only the deformation of the metal structure of the crane, such as the deflection value of the bridge crane, but also the safety device of the crane can be detected. Effective conditions, such as overload limiter, action protection of the moment limiter of the tower crane under the rated load state, etc. In conclusion, load tests are extremely important for checking the structural bearing capacity of the crane and its components, the crane's welds, cracks, permanent deformation, loose connections, the effectiveness of safety devices, and damage that affects the performance and safety of the crane. .

During the inspection and inspection of lifting machinery, we found that at present, many installation and manufacturing units, as well as related users, blindly conducted overload tests without deep research on the conditions and procedures of the load test. Often, the test not only fails to achieve the expected purpose, but also damages the structure of the crane, resulting in new hidden dangers, economic disputes and so on. In this paper, several important links such as the conditions, procedures and judgments of the load test are expounded, so as to attract the attention of the relevant units.

1. When several important conditions of the load test are not met, it is very easy to cause accidents.

(1) Cranes whose product quality has not been demonstrated, especially the cranes whose main stress-bearing welds have not been inspected and have no quality certificate.

(2) The installation has not been completed, and the person in charge of the installation unit has not identified the handed over crane.

(3) Cranes with incomplete safety devices and not working.

(4) The oil level of the lubricating parts is insufficient, and the gears are prone to wear and damage, failure, and accidents.

(5) The connecting bolts of the main force-bearing components are not fastened to the ends of the wire ropes to fix the cranes that do not meet the requirements.

2 The procedure of the load test cannot be reversed, the safety judgment must be accurate, and the reliability index should be evaluated

(1) The load test shall be carried out on the basis of the implementation of relevant safety measures, and shall be carried out according to 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 state, and check the accuracy and stability of each mechanism when working. After the no-load test is qualified, the rated load test can be carried out.

(3) The rated load test must be carried out at the specified position. For example, the tower crane lifts the maximum rated lifting capacity and the maximum rated lifting capacity at the corresponding range respectively. When identifying the rated load of the crane, the maximum stress of the structure should be based on the type of the dangerous stress area as the basis for safety judgment.

(4) After the static load test, all parts of the crane shall not have any problems such as cracks and loose connections that affect the performance and safety quality. The dynamic load test can only be carried out after the static load test.

(5) After all the tests of tower cranes are completed, the reliability index of the crane should be determined.

3 Summary

In accordance with the requirements of national standards, the load test should formulate the test process and make detailed records of each step. Only when every link is strictly controlled can the test be successfully completed. The standards and requirements of the load test for the identification of cranes and normally produced products are different from the factory inspection and the inspection after installation and erection, as well as the inspection and acceptance of products in normal use, and should be distinguished.