The crane may appear to have a complex structure, but it is actually composed of some commonly used main components arranged in an orderly manner, each with its own unique function and indispensable.
This article disassembles the main components used in cranes from a design perspective, detailing the functions and design points of each component, and helping you build a complete design cognitive system.
Main components commonly used in cranes (Part 1)
The lifting hook is the most widely used type of lifting device in the first section. It has the characteristics of simple manufacturing and strong applicability. (1) The classification and construction of hooks can be divided into two types based on their shape: single hook and double hook (as shown in Figure 2-1).
The advantage of a single hook is that it is relatively easy to manufacture and use; The force of the double hook is more favorable. Single hooks are used for smaller lifting loads. When lifting larger loads, double hooks are often used to prevent the hook from becoming too heavy. Due to the requirement of matching with the casting bucket, even if the lifting capacity is large, a single hook is still used for the plate type hook of the casting crane.
Figure 2-1 Types of Hooks
(a) Forging a single hook; (b) Forging double hooks; (c) Single piece hook; (d) Flat double hook
When forging hooks, indelible marks should be printed in low stress areas, including rated lifting capacity, factory logo, inspection mark, date, and number. After surface inspection and load testing by the forging hook factory, provide qualification certification documents.
The laminated pieces of the sheet hook are fastened by riveting. After riveting, the front end and upper end of the hook should be welded to each laminated plate. To prevent wear of the hook at the ear shaft, there should be a metal wear-resistant plate on the upper side of the bent part of the hook, which should be easy to disassemble and assemble.
To prevent self detachment, a safety device should be installed on the hook to prevent accidental detachment of the lifting weight (see Figure 2-2)
Figure 2-2 Anti decoupling device
Left: Gravity type Right: Spring type
(2) Hook group
The hook group is the combination of the hook and the pulley of the pulley group. There are two types of hook groups: long and short (as shown in Figure 2-3). The long hook group adopts a common short hook with a shorter handle, supported on the hook crossbeam, and the pulley is supported on a separate pulley shaft. Its height is relatively large, which reduces the effective lifting height.
Figure 2-3 Hook group
(a) Long hook group (b) Short hook group
In the past, short hook groups used long hooks, and the pulleys of this hook group were directly mounted on the hook crossbeam, greatly reducing the height, but it can only be used for double rate pulley groups. Short hook groups can only be used for smaller pulley groups with high magnification. When the magnification is high, the number of pulleys increases, the hook crossbeam becomes too long, and the bending moment is too large, resulting in excessive self weight of the hook. Therefore, the short hook group is only used for smaller lifting weights. (3) Dangerous section of the hook
The dangerous section of the hook is an important part of daily inspections and safety checks. After analyzing the force on the hook, the following dangerous sections of the hook are identified. Refer to Figure (2-4)
Figure 2-4
The main function of the pulley in Section 2 is to change the direction of motion of the steel wire rope and achieve the goal of saving effort. It is also commonly used as a balancing pulley to balance the tension of two steel wire ropes.
1, The construction of pulleys is divided into movable pulleys and fixed pulleys based on whether their axis is in motion.
As shown in Figure 2-5, pulleys are generally composed of a rim with rope grooves, a wheel width, and a wheel hub. The groove shape of the pulley consists of a circular arc shape, a groove bottom, and two inclined side walls (Figure 2-5c).
Pulleys are usually supported on a fixed spindle, and most use rolling bearings. Sliding bearings can also be used for low-speed pulleys or balance pulleys.
Figure 2-5 Structure of Pulley
(1) Rolling pulley (a) Casting pulley (b) Welding pulley (C) Rope groove
2, The pulley system is composed of pulleys, bearings, pulley covers, and other components. The pulley system consists of fixed pulleys and movable pulleys. According to their functions, they can be divided into labor-saving pulley groups and speed increasing pulley groups. Effortless pulley systems are commonly used on cranes. It lifts larger loads with a smaller driving force.
According to the structure of the pulley system, there are single pulley system and double pulley system. Boom type cranes often use single pulley systems, while bridge type cranes often use double pulley systems.
The multiplier of the pulley system is the labor-saving multiplier.
