The Importance of Pulleys And Blocks In A Crane

In a crane, pulleys are mainly used to change the force direction of the wire rope. The pulley block composed of pulleys can achieve the purpose of saving effort or increasing speed.

1. Pulley

Commonly used pulleys are mostly made by forging. In order to reduce their own weight, they are often made into a structure with ribs and holes. Welded pulleys should be used for large pulleys. In addition, nylon pulleys are increasingly used in cranes due to their distinctive features such as light weight and good wear resistance. Pulley forgings are commonly used in cranes and their structural dimensions have been standardized.

The rope groove of the pulley is composed of an arc-shaped groove bottom and side walls. In order to ensure that the steel wire rope and the rope groove have sufficient contact area, there is usually a size relationship of R=(0.53~0.6)d. At the same time, in order to reduce the friction generated when the wire rope enters and exits the edge of the rope groove, the angle between the two should be about 45°. In addition, the rope groove should be of sufficient depth to prevent the wire rope from falling out of the groove.

2. Pulley block

A device consisting of a wire rope bypassing a number of movable and fixed pulleys in turn is called a pulley block.

(1) According to different functions, the block is divided into labor-saving block and growth block according to different functions. The labor-saving pulley block is widely used in the lifting mechanism of the crane and the ordinary boom amplitude changing mechanism, which can lift the material greater than several times its weight with a small steel wire rope tension. Speed block is mainly used in hydraulic or pneumatic drive mechanism, the use of oil cylinder or cylinder and other devices to obtain several times the speed or stroke of the piston, such as the boom telescopic mechanism of wheeled cranes.

(2) According to the different classification of structure, the block is divided into single block and double block according to the different structure. The single pulley block is characterized by one branch of the wire rope around the drum, and two branches of the wire rope around the drum of the double pulley block. The balancing pulley has the function of balancing the tension of the wire rope branch and adjusting the length of the wire rope. The double block is mostly used with the single winding double drum, and the single block is often used with the multi-layer winding drum.

The role of pulleys and blocks:

The pulley supports and guides the rope movement, which plays two roles of guidance and balance. Pulley block is composed of a certain number of movable pulley and fixed pulley through, it has the characteristics of movable and fixed pulley, pulley is divided into fixed pulley and dynamic pulley two. The fixed pulley only changes the direction of the force.

The pulley saves effort. Therefore, the pulley block can both change the direction of the force and save force. And can be used as a deceleration or acceleration device. When the lifting weight is large, it is appropriate to use a larger rate of pulley to reduce the tension of the wire rope; When the weight is light, it is appropriate to use a small rate of the pulley set, in order to reduce the number of wire rope winding, improve the work efficiency.

The pulley block composed of wire rope, fixed pulley and movable pulley is an important part of the lifting mechanism of crane. According to the role of the pulley is divided into two kinds of energy-saving pulley and speed pulley. The block is divided into two types: single block and double block.

The pulley shall be scrapped if any of the following conditions are met:

1. Cracks (no welding allowed);

2. Uneven wear of the wheel groove up to 3mm;

3. Wear of the wheel groove wall thickness up to 20% of the original size;

4. The reduction in the bottom diameter of the wheel groove due to wear reaches 50% of the wire rope diameter;

5. Other conditions that meet the scrapping conditions.

Pulley block inspection:

(1) Single-beam bridge crane dismantles and cleans the pulley block and inspects for cracks;

(2) Inspection of the pulley groove;

(3) Inspection of the shaft hole;

(4) Assembly;

(5) The pulley shaft shall not have cracks, the journal shall not be worn by 30% of the original diameter, and the taper shall not be greater than 5%. If it exceeds this value, it should be replaced;

(6) Use a template to check the pulley groove shape. The radial wear should not exceed 30% of the wall thickness, otherwise it should be scrapped. If it does not exceed the standard, it can be repaired. After overhaul, use a template to check that the bottom and lateral clearance should not be greater than 0.5mm, the deviation between the center line of the wheel groove and the center line of the pulley should not be greater than 0.2mm, and the deviation between the center of the rope groove and the contour end face should not be greater than 1mm;

(7) After overhaul of a single-beam bridge crane, the shaft hole is allowed to have defects of no more than 0.25CM2, and the depth should not exceed 4mm;

(8) After assembly, it should be able to be flexibly rotated by hand, and the lateral swing should not exceed D/1000. D-nominal diameter of the pulley.

GloryRail can supply kinds of pulleys, include welded pulley, cast steel pulley, cast iron pulley and rolled pulleys. Based on the crane track system, provides customers with one-stop solutions for the crane industry. Have any needs for crane constructions, welcome to contact us!