Features and Working Principle of Grab Cranes

Grab crane, commonly known as grab bucket crane. Grab crane refers to a lifting equipment machinery equipped with a grab bucket. It is widely used in port terminals, station freight yards, mines, etc. to load various bulk cargoes, logs, minerals, coal, sand and gravel, earthwork, etc. The grab crane is a kind of automatic picking up machinery, its grabbing and unloading of materials is controlled by the ship operator and does not require auxiliary personnel, thus eliminating the heavy labor of workers, saving auxiliary work time, and greatly improving the loading and unloading efficiency. Grab cranes are generally divided into bridge-type grab cranes, gantry grab cranes, and folding-type grab cranes. Usually, the grab crane that people often refer to refers to a knuckle-type grab crane, such as a log crane.

Features of grab cranes

1. Improve production efficiency

For example: before the birth of the grab crane, when loading and unloading mineral powder at the dock, 12 to 16 workers were used in the ship's warehouse, each with a shovel. Two people worked in groups. Each group took a large leather net bag and shoveled each shovel into the big leather net bag. For spade or powder, one net bag can net up to 4 tons of cargo. After the net bag is full, use a crane to lift it up. A warehouse can only handle a maximum of 200 tons of cargo in 8 hours. Nowadays, large ship unloaders can unload more than 2,000 tons of ore per hour, which greatly improves production efficiency.

2. Improve production safety

For example: before the birth of the grab crane, 4-6 workers were used in the dock to load and unload logs. They first used small wire ropes to pass through the cross-section joints of the log piles to form an estimated area, and then connected the two ends of the small wire ropes. Hang the end on the hook of the crane and lift it 1 to 2 meters away to tilt one end of the log. Then the worker takes a 16-28 wire rope. There is a heavy hook at the front end of the wire rope. From the lifted end, it is connected to the wood pile. Throw it over in neutral, and the worker on the other side can catch it quickly, otherwise the wire rope with the hook will slip into the groove of the wood pile. The worker who throws the wire rope has to pull up the wire rope and throw it again, or the worker on the other side uses a long wooden stick with a hook. Use the tool to pick up the wire rope, and then hang the hook on the wire rope to tie the logs together... During this process, the logs may roll and crush the workers' hands and feet. It is also possible that the workers may have overloaded the logs and the wires may have been interrupted in the air. A dozen or dozens of logs falling from the air will kill people. Later, Bao Qifan invented the wood grab, which greatly reduced personal injury accidents.

Working principle of grab cranes

The grab bucket is a spreader that grabs and unloads bulk materials by opening and closing the jaw plate. According to the operating characteristics, grabs can generally be divided into double rope grabs, single rope grabs and motor grabs. The most commonly used is the double rope grab. Grab buckets are divided into 3 categories according to the packing density of the material to be grabbed: light (such as grabbing grain), medium (such as grabbing gravel) and heavy duty (such as grabbing iron ore). According to the number of forehead plates, they are divided into double forehead plate grabs. Bucket and multi-jaw plate grab, the most commonly used is the double-jaw plate grab. For large pieces of ore, iron filings, scrap steel, etc., a multi-plate grab should be used because it has the characteristics of multiple claws and sharp cuts, making it easy to insert into the material pile and achieve better grabbing effects. There is also a scissor grab that imitates the scissor structure principle. Its grabbing force can gradually increase as the jaw plate closes, reaching the maximum value at the end of the closure. The opening of the bucket mouth and the area of covering materials are also larger than ordinary ones. The larger grab bucket improves the grabbing capacity and is helpful for cleaning the material yard and ship cabin. However, the initial grabbing force for large pieces of material is small and the effect is poor. The pick-up device is a double-roller four-rope grab with a simple structure and reliable operation. The grab can be opened and closed at any height. When grabbing material particles larger than 200mm, a cargo grab is required. The grab bucket is used for bulk materials in a natural accumulation state.

Classification of grab cranes

Grab cranes can be classified according to crane type, grab type, and driving method. 

According to crane classification, it is divided into bridge type grab crane, gantry type grab crane and knuckle arm type grab crane. It can also be divided into single-girder grab crane and double-girder grab crane. This kind of crane unloads bulk cargo such as coal, ore and phosphate from the cargo hold into the hopper, and then unloads it to the storage yard or loading platform via the conveyor belt.

Bridge grab crane

Lifting equipment bridge grab crane is specially designed for bulk and granular materials.

Conventional configuration of bridge grab crane: it adopts driver's cab control, and there are two types of driver's cab: separated type and closed type. Each mechanism adopts a wire-wound lifting motor and resistor speed regulation. Lifting equipment grab bridge crane working level: A6, A7, working environment 20~+40C. This model is not recommended for use in working environments with explosion-proof and insulation requirements. Lifting equipment grab bridge crane other configurations available for users to choose:

1. The grab opening and closing directions include parallel and vertical main beams.

2. The lifting capacity includes the grab's own weight.

3. When the trolley is equipped with a rain cover, the maximum size of the top surface is H+h.

4. The total capacity and maximum wheel load of outdoor cranes should be increased by 5% accordingly.

5. There are two types of trolley conductors to choose from: angle steel and safety sliding contact wires.

6. This crane has two options: standard trolley and trolley with weighing.

7. It can be equipped with sugar cane grabs, garbage grabs, wood grabs and other types of grabs as needed.

8. Grabs are divided into: single rope grab, double rope grab, electric grab, target set grab.

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