Hooks can be classified into two types according to their shapes: single hooks and double hooks. They can also be divided into three kinds based on the manufacturing process: laminated hooks, forged hooks, and cast hooks. Currently, the commonly seen hooks are forged single hooks. Cast hooks are not permitted for use on kraanas. Hooks are widely made of low-carbon steel and carbon alloy steel to address issues such as corrosion resistance and crack formation.
To ensure safety, hooks should be regularly inspected. Once any of the following situations is detected, the hook should be immediately scrapped:
Cracks appear.
For hooks manufactured according to GB10051.2, the wear amount at the dangerous section shall not exceed 5% of the original height; for hooks made according to the currently used industry standards, it shall not exceed 10% of the original size.
The opening degree increases by 15% compared to the original.
The torsional deformation exceeds 10 degrees.
Plastic deformation occurs at the dangerous section or the hook neck.
When the wear amount of the laminated hook bushing reaches 50% of the original size, the bushing should be scrapped.
When the wear amount of the laminated hook spindle reaches 5% of the original size, the spindle should be scrapped. It should also be noted that the above-mentioned defects of the hook must not be repaired by welding.
The main inspection methods generally involve visual inspection, that is, carefully observing with a magnifying glass. When necessary, the dye penetrant method can be used, or flaw detection can be carried out. The wear amount at the dangerous section can be measured with calipers or calipers; to inspect the opening degree, simply compare the size measured by the caliper with the original size or the opening degree of the standard hook. Here is a simple and practical method: when a newkraanahook is just put into use, drill a small hole on each side of the hook opening, measure the distance between the two holes, and record it. This can be used to compare with the size of the hook after deformation in the future to judge the change in the opening degree. Torsional deformation can be visually inspected, or measured with the side of a steel ruler. For more precise measurement, a scribing ruler can be used on a platform. Items 5, 6, and 7 can all be visually inspected or measured with calipers.
From my years of maintenance and supervision work on truck cranes, I have found that the wear of the hooks on truckkraanas during operation is quite severe (this kind of wear refers to the abrasion that occurs when the truck crane travels from the garage to the work site or between different work sites to complete various loading and unloading tasks). Among them, the hooks of 5t, 7t, 8t, and 10t truck cranes are more severely worn because when these-tonnage truck cranes are in operation, drivers always lock and hang the hooks with wire ropes in front of the cab. The two ends of the locking wire rope are respectively hung on the two front tow hooks on the front bumper of the crane chassis.
When the crane is moving, especially when running under poor road conditions at the work site, more relative friction will be generated between the wire rope and the hook, resulting in mutual wear between the hook and the wire rope. Since the two ends of the wire rope are hung on the tow hooks on both sides, the wire rope is like the string of a Chinese fiddle, severely wearing the vertical dangerous section of the hook. Under harsh road conditions, such as when the truck cranes of the power department are working in the wild, the hook wear is particularly serious. Sometimes, the wire rope for locking and hanging the hook needs to be replaced every few months. This kind of hook wear is non-operational wear. There are three ways to reduce and prevent this kind of wear:
Increase the number of wire ropes for locking and hanging the hook to three Take a wire rope about 4.2m long and fasten both ends with rope clips. In this way, the contact between the wire rope and the hook changes from one to three, increasing the contact area between the wire rope and the hook, reducing their mutual friction and wear, solving the problem that a single wire rope easily cuts into the hook surface, and prolonging the service lives of the hook, the rigging, and the wire rope for locking the hook.
Sheathe a steel pipe on a single wire rope Take a steel pipe with a length of 400mm and a diameter of 25.4mm and sleeve it on the wire rope. During the operation of the truck crane, since the wire rope does not directly contact the hook surface, the casing plays a role in protecting the hook. The casing can also be made of other materials, such as thick rubber tubes or high-pressure hoses with wire meshes.
Replace the wire rope with other materials Näiteks, using nylon ropes or nylon slings used on ocean-going ships to replace wire ropes has a very good effect. In addition, it is recommended that the length L of the wire rope for locking the hook be taken as 1.35 – 1.45m. Through multiple tests, we know that if the wire rope is too long, the hook will be hung high, affecting the driver’s vision; if it is too short, it will be inconvenient to hook, and it is easy to sprain the waist and wrists of the hooking person. Generally speaking, taller drivers can choose a larger value, and vice versa. This way, the operation is convenient and can also meet the driver’s vision needs.
In addition to these basic maintenance and anti-wear measures, with the continuous development of the truck crane industry, more advanced technologies and concepts are emerging. Näiteks, in the field of materials science, new composite materials with higher strength, better corrosion resistance, and lower friction coefficients are being developed for hook manufacturing. These materials can significantly improve the overall performance and service life of the hook. They not only withstand greater loads but also better resist environmental corrosion, whether it’s from moisture in the air, chemicals in industrial environments, or salt spray near the coast.
In terms of inspection technology, modern non-destructive testing methods are becoming more and more sophisticated. Ultrasonic testing, magnetic particle inspection, and eddy current testing can now detect the tiniest internal defects in hooks with higher precision. These advanced testing methods are no longer limited to large-scale maintenance workshops but are gradually being miniaturized and made portable, enabling on-site technicians to quickly and accurately assess the health of the hook without having to disassemble it.
Moreover, intelligent monitoring systems are starting to be integrated into truck cranes. Sensors can be installed on the hook to continuously monitor parameters such as load, vibration, and temperature in real-time. Once abnormal values are detected, the system can immediately send out alarms to the driver or the maintenance center, allowing for timely intervention. This intelligent monitoring not only improves the safety of the crane during operation but also helps to establish a more scientific maintenance plan, predicting potential failures in advance and reducing unplanned downtime.
The training of crane operators also plays a crucial role. In modern training programs, in addition to basic operation skills, more attention is paid to safety awareness and equipment maintenance knowledge. Operators are trained to recognize the early signs of hook wear and other component failures, and they are taught how to take simple preventive measures on site. This comprehensive training system ensures that operators become the first line of defense for crane safety, effectively reducing the occurrence rate of safety accidents.
As the application scenarios of truck cranes become more diversified, from traditional construction sites to emerging fields such as wind power installation and port logistics, the requirements for hook performance and maintenance are also constantly changing. Näiteks, in wind power projects, the hooks need to withstand extremely large and irregular loads, and special anti-fatigue and anti-impact designs are required. Maintenance intervals also need to be adjusted according to the actual working environment and load frequency, which requires more in-depth research and innovation in hook design, materials, and maintenance strategies.
