Role, Type and Safety Requirements of Overload Restrictor for Tower crane

15-08-2019

The "Safety Regulations for Tower Suspension" stipulates that tower cranes with a rated weight of more than 20 T, gate tower cranes, loading and unloading bridges, railway tower cranes, and gate tower cranes with a weight of more than 10 T should all be equipped with overload limiters. Rated gravity moment less than 250 KN? M Tower cranes and lifting equipment such as lifts and electric gourds should also be equipped with overload limiters as required by the user.

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The overloading operation of the tower crane will produce excessive stress. It can cause the cable cable to break, the transmission parts to be damaged, and the motor to be burned. Due to the relatively insufficient braking moment, braking failure will result. Overloading is very harmful to the structure of the tower crane, which will not only cause the deflection of the main beam of the tower crane, but also cause instability, cracks or weld welds on the upper cover and ventral plate of the main beam, and will cause the tower crane frame or the tower body. Break and other major accidents. Due to overloading the overall stability of the tower crane, it is possible to have a vicious accident disaster such as overturning and overturning.
(I) Type of overload limiter
The overload protection device can be divided into automatic stop type, alarm type and comprehensive type according to its function.
1. Automatic stop type overload limiter

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When the lifting weight exceeds the rated lifting weight, it can stop the tower lifting in an unsafe direction and allow the tower lifting to move in a safe direction. The safety direction refers to the drop of the suspension, the contraction of the arm frame, the reduction of the amplitude, and the combination of these actions. The automatic stop type is generally a mechanical overload limiter, which is mostly used for tower lifts.
2. Alarm overload limiter
It can display weight and can send out an alarm sound and light signal when the weight reaches 95 % to 100 % of the rated weight.
3. Integrated overload limiter
When the tower crane reaches 95 % to 100 % of the rated weight, an alarm sound and light signal can be issued. When the lifting weight exceeds the rated weight, the tower can be stopped from continuing in the unsafe direction.
The overload limiter can be divided into three types: mechanical, hydraulic and electronic. Mechanical overload limiters have levers and tactics.

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(II) Technical requirements for the safety of overload limiters
The comprehensive error of mechanical overload limiter should not be more than 8 %, and that of electronic overload limiter should not be more than 5 %.
When the load reaches 90 % of the rated weight, an indicative alarm signal should be issued.
3 After the tower crane is equipped with an overloaded limiter, it should be adjusted or calibrated according to its performance and accuracy. When the lifting weight exceeds the rated lifting weight, it can automatically cut off the lifting power source and issue a prohibitive alarm signal.
4 Bridge frame type tower hanging, railway tower hanging, door tower hanging, should be equipped with overload limiter; Tower cranes, lifts and electric gourds can also be installed according to actual needs.

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