What Is A Overhead Crane Brake?

What Is A Overhead Crane Brake?
 

Due to the periodic and intermittent working characteristics of the 10 ton overhead crane, each working mechanism is often in a state of frequent starting and braking. The brake has become an indispensable part of each mechanism of the power-driven crane.

Work safety device. Whether the brake is intact and reliable is the focus of safety inspection.
 

The working essence of the brake is to generate the braking effect through the friction of the friction pair. According to the needs of the work, the kinetic energy of the movement is converted into frictional heat energy to consume, so that the mechanism stops moving; or the mechanism is kept in the original static state through the balance force of the static friction force.
 

Its structural features are: one group of friction pairs of the brake is connected with the fixed frame; the other group is connected with the rotating shaft of the mechanism. When the friction pair is in contact with each other, the braking effect is generated; when the friction pair is separated, the braking effect is released and the mechanism can move.
 

1. The role of the brake
 

(1) Support function: keep the original stationary object in a static state. For example, in the hoisting mechanism, keep the hoisting weight still in the air; in the luffing mechanism of the 5 ton jib crane, keep the jib at a certain position; it plays the role of windproof and anti-skid for outdoor cranes.
 

(2) Stop function: The kinetic energy of the moving part is consumed and converted into friction heat energy through the friction pair, so that the mechanism stops quickly within a certain time or within a certain stroke. For example, the braking of various mechanisms in motion.
 

(3) Falling weight effect: the braking force is balanced with the gravity, so that the moving body falls at a stable speed. For example, the downhill speed of a truck crane.
 

2. Types of brakes
 

(1) According to different structures, brakes can be divided into the following three categories:
 

①Band brake. The brake steel band encircles the brake wheel radially to generate braking torque.
 

② block brake. Two symmetrically arranged brake pads tightly hold the brake wheel in the radial direction to generate braking torque.
 

The block brake consists of a brake shoe, a brake arm, a brake wheel and a brake release device. The brake wheel is often installed on the rotating shaft of the mechanism as a half of the coupling, the symmetrically arranged brake arm is hinged with the fixed part of the frame, and the two brake shoes with friction materials on the inside are respectively hinged. On the two brake arms, under the action of the upper brake force of the brake release device, the paired brake pads hold the brake wheel radially to generate a braking torque.
 

Taking the short-stroke electromagnet block brake as an example, the working principle of the block brake is explained. When the power is turned on, the iron core of the electromagnetic brake release attracts the armature to press against the push rod, and the push rod pushes the left brake arm to swing to the left, and the main spring is compressed. Simultaneously, the auxiliary spring that relieves the pressure pushes the right brake arm to the right, and the two brake arms drive the brake shoe to separate from the brake wheel, so that the mechanism can move. When the power is cut off, the iron core loses its magnetism, and the attraction to the armature is eliminated, thus releasing the pressure of the armature on the push rod. Under the action of the main spring tension, the two brake arms swing inward together, driving the brake pads to hold tightly The brake wheel generates a braking torque; at the same time, the auxiliary spring is compressed. The braking torque is determined by the force of the main spring, and the auxiliary spring ensures the loose clearance. The braking performance of block brakes is largely determined by the performance of the brake releaser.
 

The block brake is characterized by simple structure, easy installation, and the pressure balance generated by the pair of pads, so that the brake wheel shaft is not affected by the bending load. Widely used in cranes.
 

③Disc and cone brakes. Disc and conical metal discs with friction linings are pressed against each other in the axial direction to generate braking torque.
 

(2) According to the operation situation, the brake can be divided into:
 

①Normally closed brake. As long as the mechanism is not working, the brake is in the closed state; when the driving energy of the mechanism is connected, the brake is first opened, and the mechanism can work normally.
 

②Normally open brake. The brake is always in a loose state, and the brake force can be applied at any time according to the need to generate a braking torque to make the brake brake.
 

③Comprehensive brake. It has a normally open type, which can use the control lever to brake at will when the brake is released, and also has a normally closed type, which has the function of reliable braking when the mechanism is not working.
 

3. Installation of the brake
 

The brake is usually installed on the high-speed shaft of the mechanism (the motor shaft or the input shaft of the reducer), and some brakes are installed on the low-speed shaft or drum to prevent objects from falling when the transmission system breaks the shaft. The former can reduce the size of the brake due to the small braking torque; the latter can increase safety and prevent the load-bearing parts of the transmission system from being damaged and causing objects to fall.

During the safety inspection of the starting machine, the following requirements must be confirmed:
 

(1) For power-driven cranes, the lifting, luffing, running, and rotating mechanisms must be equipped with brakes;
 

(2) The brakes of hoisting mechanism and luffing mechanism must be normally closed brakes;
 

(3) As for the hoisting mechanism for hoisting hot metal or other dangerous goods, as well as the hoisting mechanism for which an accident may cause major danger or loss, each independent driving device shall be equipped with two sets of supporting brakes.
 

(4) For human-driven cranes, the hoisting mechanism and luffing mechanism must be equipped with brakes or stoppers;