A hoist is a small and light lifting equipment that uses a drum to wind a steel rope or a chain to lift or pull a heavy object, also known as a winch. So, what is the composition and type of the hoisting structure of the winch? Let's understand together with the editor.
1. Composition of lifting mechanism
The hoisting mechanism of the hoist is a mechanism for lifting and lowering heavy objects. It is an essential and most basic mechanism for any crane. The electric 5 ton winch designed this time is composed of motor, coupling, brake, speed reducer, drum, guide pulley, hoisting pulley block, fishing hook, etc. The mechanism distribution of each aspect can be referred to as shown in Figure 13 below.
Figure 1-3 Schematic diagram of lifting mechanism
1—Motor 2—Coupling 3—Reducer 4 —Reel
5—Guide pulley 6—Pulley group 7—Hook
When the motor rotates forward or reverse, the brake is released, the high-speed shaft of the speed reducer is driven by the coupling with the brake wheel, and the drum is rotated by the low-speed shaft after deceleration by the speed reducer, so that the steel wire rope is wound into or released on the drum To lift or lower heavy objects. When the motor stops rotating, the brake wheel of the high-speed shaft is braked by the brake to stop the suspended heavy objects in the air. Various auxiliary devices can be installed on the hoisting mechanism as needed, such as lifting weight limiter, lifting height limiter, speed limiter and steel wire rope for multi-layer winding, so that the steel wire rope is arranged in a row on the drum in order Rope device, etc.
B Typical drive type of lifting mechanism
A standard two-stage reducer with high efficiency is usually used between the motor and the drum. When low speed is required, a three-stage large gear ratio reducer can be used. In order to facilitate installation, an elastic pin coupling or gear coupling with compensation performance is often used between the motor and the reducer. The former is simple in structure and can play a buffering role, but the elastic rubber ring has a short service life; the latter is durable and the most widely used. The life of the gear coupling is related to the quality of the installation and requires frequent lubrication. Generally, the brakes are installed on the high-speed shaft, so the required braking torque is small, the corresponding brake size is small, and the weight is light. Often, half of the coupling is used as a brake wheel. The half body with brake wheel should be installed on the high speed shaft of the reducer. In this way, even if the coupling is damaged, the brake can still brake the drum to ensure the safety of the mechanism.
The brake of the lifting mechanism must be normally closed. The braking torque should ensure a sufficient braking safety factor. There are sometimes two brakes in the important lifting mechanism, and the second brake can be installed on the extension end of the high-speed shaft of the reducer or on the rear shaft of the motor. In order to facilitate the arrangement of the mechanism and increase the compensation capacity, a floating shaft can be used to connect the motor and the reducer, and the two ends of the floating shaft are half gear couplings. Because there are many types of connection between the reel and the low speed shaft of the reducer. The connection between the drum and the low-speed shaft of the hoisting machine is a structure type with a gear coupling disc. The left end of the drum shaft is supported by a self-aligning bearing in the inner cavity bearing seat of the output shaft of the reducer. The outer edge of the low-speed shaft is made into an external gear. It meshes with the connecting disc with internal gear fixed on the reel to form a gear coupling to transmit torque, and can compensate for certain installation errors. On the outer side of the gear coupling, that is, the side close to the reducer is equipped with a split sealing cover to prevent the lubricant in the coupling from flowing out and the dust from entering. The advantages of this connection type are compact structure, small axial size, good grouping, and can compensate the installation error between the reducer and the spool shaft. See figure 14 below.
Figure 1-4 Connection type with gear joint plate
The diameter of the reel is generally selected as small as possible, because with the increase of the diameter of the reel, the torque and deceleration transmission ratio also increase, causing the entire mechanism to be huge. But when the lifting height is large, the method of increasing the diameter of the drum is often used to reduce its length. The type of pulley block (single or double) and its magnification also have a great influence on the size of the lifting mechanism. In the bridge crane, the double pulley block is used, on the one hand, the force on the two supports of the drum is unchanged, that is, the rail wheel pressure on both sides of the running trolley is unchanged, which is beneficial to the stress of the bridge frame and the trolley frame; On the other hand, the heavy objects are not moved laterally during the lifting process. However, because the ratio of the double pulley block is double that of the single pulley block, the transmission ratio of the lifting mechanism also needs to be doubled, which increases the size of the mechanism, so other cranes use single pulley block. This design is The winch of the 5 ton bridge crane, so the double pulley block is selected, as shown in Figure 15 below.
Figure 1-5 Double pulley block
1. Moving pulley 2. Fixed pulley 3. Reel
The determination of the ratio of the pulley block has a great influence on the tensile force of the wire rope, the diameter and length of the drum, the transmission ratio of the speed reduction mechanism and the overall size of the mechanism. The large lifting weight adopts a large magnification, which can avoid the use of too thick steel wire rope. Sometimes using a larger pulley set ratio while reducing the lifting speed to increase the lifting weight can make the lifting mechanism reach universality, that is, the same lifting mechanism is used for different lifting weights, which is in the series design The method often used.
The calculation of the hoisting mechanism is carried out after the design parameters are given and the layout plan is determined. The standard components required in the mechanism are selected through the calculation, such as motors, brakes, reducers and couplings. Separate design is required for non-standard parts. This hoist is designed to lift the load by 5 tons and is mainly used on the 5 ton bridge crane of the steel mill. This hoist is made up of the existing equipment and materials of the steel mill, so it is slightly different from the standard 5 ton hoist design.
