Maintenance and care of the hook of a truck crane

Let's discuss the hook of a truck crane from two cases.

[Case 1] A hook fell, resulting in the death of a worker

When a construction team of a building engineering company in Tieling City was working on a coal bunker site of a coal mine, they used a truck crane to lift concrete for continuous pouring operations. When working late into the night and the driver taking over the shift falls ill, with the temporary consent of the construction team leader, the non-crane driver is allowed to get on the vehicle to operate. The result was that after working for only about one hour, when lifting the lifting hopper, due to a lack of attention, the hook was raised beyond its limit position and got stuck at the fixed pulley at the end of the boom. The force on the lifting wire rope suddenly increased and it was pulled apart. When the hopper and the hook fell, a square piece of wood was smashed, causing the worker standing on it to fall onto the slope at the bottom of the silo. The worker was sent to the hospital but died despite rescue efforts.

The cause of the accident was: There was a malfunction in the crane itself. Not operated by a crane driver. The safety protection device of the truck crane hook, the lifting height limiter, malfunctioned and was not repaired in time, resulting in the equipment operating while faulty. The non-crane driver had not received safety and technical training from relevant departments, was on duty without a vehicle operation certificate, and was not familiar with the performance of the truck crane, resulting in this accident. The lesson was very serious.

[Case 2] The load fell out of the hook, resulting in one death or injury

The 9th Team of the 3rd Section of a certain engineering company under the Zhengzhou Railway Bureau of the Ministry of Railways is undertaking the construction task of bored piles for the 6th platform of the elevated waiting room at Zhengzhou Passenger Station. After the steel cage was lowered at the pile position of No. 21 bored pile on Platform 6, a truck crane was needed to lift the fir pole out of the well hole. When the small end of the pole fell to the ground and the large end was about to land, the crane commander left his post to prepare for lifting the second section of the steel cage. At this moment, the driver, without any guidance, turned the boom by himself (preparing to lower the hook to lift the second section of the steel cage), but unexpectedly, the wire rope buckle slipped out of the hook due to reduced force and looseness, causing the large end of the wooden pole to fall onto Platform 6, injuring the heads of workers Niu and Fan who were preparing to weld the steel cage. After being promptly sent to the hospital for emergency treatment, Fan was saved but seriously injured, and Niu died.

Analysis of the cause of the accident: After the accident, it was found through on-site investigation that although a hook locking device was installed on the crane hook, the spring plate on the device had been damaged but not yet repaired, thus losing the locking safety function to prevent the accidental detachment of the rigging. This is an accident case that occurred under specific conditions due to inadequate maintenance work, which failed to keep all parts of the entire machine in good condition.

The hook serves to connect the crane and the heavy object, and its maintenance and upkeep must be given due attention. For this reason, when the lifting height limiter of the hook or the hook locking device malfunctions or is damaged, it must not be used again under any circumstances. As for working without a license, the leaders should be held accountable.

Hooks can be classified into single hooks and double hooks according to their different shapes. According to the differences in their manufacturing processes, they can be classified into three types: sheet hooks, forged hooks and cast hooks. At present, the common type of hook is forged single hook. Cast hooks are not allowed to be used on cranes. Hooks are widely made of low-carbon steel and carbon alloy steel to solve the problems of resistance and cracking.

To ensure safety, the hook should be inspected. If any of the following conditions are found, it should be scrapped immediately.

① Cracks appear.

The wear of the dangerous section of the hook manufactured in accordance with GBl0051.2 shall not exceed 5% of the original height. Hooks manufactured in accordance with the line continuation standard should be 10% larger than the original size.

The opening degree has increased by 15% compared to before.

④ Torsional deformation exceeds 10 degrees.

⑤ Plastic deformation occurs at the dangerous section or the neck of the hook.

When the wear of the plate hook bushing reaches 50% of its original size, the core bushing should be scrapped.

When the wear of the core shaft of the plate hook reaches 5% of its original size, the core shaft should be scrapped.

One more point to note is that the above-mentioned defects of the hook shall not be welded for repair.

The main method of inspection is generally visual inspection, that is, careful observation with a magnifying glass. When necessary, the coloring method can be used or flaw detection can be carried out. The wear amount of the dangerous section can be measured by a caliper or a caliper. The inspection of the opening degree is simply to compare the size measured by the caliper with the original size or the opening degree of the standard hook. Here is a simple and applicable method: When a new crane hook is just put into use, drill a small hole on each side of the opening of the hook body, measure the distance between the two holes and record it. It is used to compare and contrast with the size of the hook after deformation in the future to determine the extent of the change in the opening degree. Torsional deformation can be visually inspected or measured with the side of a steel ruler. When precision is required, it can be detected on a platform using a scribing ruler. Items ⑤, ⑥ and ⑦ can all be inspected by visual inspection or with a caliper.

Maintenance and care of the hook of a truck crane

From years of maintenance and supervision of truck cranes, the author has found that the hook of a truck crane wears out very severely during operation (this kind of wear refers to the wear that occurs when the truck crane is transferred from the garage to the operation site or between different operation sites to complete various loading and unloading tasks). Among them, the hooks of 5t, 7t, 8t and 10t truck cranes are worn out more severely. This is because during operation, the drivers of these tonnage truck cranes always lock the hooks with steel wire ropes in front of the cab. The two ends of the locking steel wire ropes (see Figure 1a) are respectively hung in the two front traction hooks on the front bumper of the crane's chassis.

When the crane is being moved, especially when it operates under poor road conditions at the working site, it will cause a lot of friction between the steel wire rope and the hook, thereby resulting in mutual wear between the hook and the steel wire rope. As the two ends of the steel wire rope are hung on the traction hooks on both sides, the steel wire rope is like the strings of a huqin, causing severe wear on the vertical dangerous section of the hook. In poor road conditions, such as when the truck cranes of the power department are operating outdoors, their hooks wear out particularly severely. Some need to replace the steel wire rope that locks the hook every few months. This kind of wear on the hook is non-working wear. The three methods to reduce and prevent this kind of wear are as follows:

(1) Increase the number of wire ropes for the lock-hanging hook to three

Maintenance and care of the hook of a truck crane

Take a steel wire rope about 4.2 meters long and form it into the shape shown in Figure 1b. Secure both ends with rope clamps. This changes the contact area between the steel wire rope and the hook from one to three, increasing the contact area between the steel wire rope and the hook, reducing the friction and wear between them, solving the problem that one steel wire rope is prone to cut into the surface of the hook, extending the service life of the hook and rigging, as well as the service life of the steel wire rope that locks the hook.

(2) Install steel pipes on a single steel wire rope

Take a steel pipe with a length of 400mm and a diameter of 25.4mm, bend it into the shape shown in Figure 2, and then put it over the steel wire rope. During the operation of a truck crane, since the steel wire rope does not come into direct contact with the surface of the hook, the casing plays a protective role for the hook. The casing can also be made of other materials, such as thick rubber hoses, high-pressure hoses with steel wire mesh, etc.

(3) Replace the steel wire rope with other materials

If the nylon ropes or nylon lifting slings used on ocean ships are used instead of steel wires, the effect will also be very good. In addition, it is recommended that the length L of the wire rope used for the lock-hanging hook be 1.35-1.45 meters. After numerous experiments, we have found that if the steel wire rope is too long, the hook will be hung too high, which will affect the driver's field of vision. If the steel wire rope is too short, it will be inconvenient to hook, and it is easy to sprain the waist and wrist of the person hooking. Generally speaking, if the driver is tall, a larger value is taken; conversely, a smaller value is taken. This way of operation is convenient and can also take into account the driver's field of vision requirements.