Standards for Scrapping Crane Parts and Components - Detailed Q&A

A crane is a type of mechanical equipment used for lifting and transporting heavy objects vertically and horizontally within a specific range, also known as a hoist or a lifting machine. It is categorized as a material handling machine. The operational characteristic of cranes is that they perform intermittent movements, meaning that during a work cycle, different mechanisms such as loading, transporting, and unloading work alternately. Due to these combined movements, crane components naturally experience significant wear and tear. Therefore, it is essential to understand the scrapping standards for each component to replace worn-out parts timely, ensuring safe and efficient crane operation.

What is the scrapping standard for a hook?

Answer: A hook should be scrapped and replaced if it has any of the following defects:

1. Surface cracks, breaks, or fractures.

2. Wear at the critical section exceeds 10% of the original size.

3. Plastic deformation at the critical section or hook neck.

4. The opening has increased by 15% compared to the original size.

5. Torsional deformation at the hook tip exceeds 10%.

What is the scrapping standard for forged crane hooks?

Answer: For forged crane hooks, the scrapping standards are as follows:

1. The hook surface has cracks or breaks. If cracks or breaks are found, the hook must be replaced immediately and cannot be repaired by welding.

2. The height of wear at the hook’s working section (where the rope hangs) reaches 10% of the original height.

3. Permanent deformation at the hook’s throat, neck, or critical section. If the hook opening exceeds 15% of the original size, it should be scrapped.

4. If the hook's tail or thread transition section shows tool marks or cracks, it should be scrapped.

What is the scrapping standard for a pulley?

Answer: The scrapping standards for pulleys are:

1. Wear of the pulley’s groove wall thickness exceeds 20% of the original thickness.

2. Radial wear at the bottom of the pulley groove exceeds 50% of the steel rope diameter, or uneven wear exceeds 3mm.

3. Severe cracks in cast iron pulleys.

4. Severe damage to the pulley flange.

What is the scrapping standard for a brake wheel?

Answer: The scrapping standards for a brake wheel are:

1. The working surface has deep claw marks or radial wear that reaches 1.5mm.

2. If the wear exceeds 40% of the original thickness for the lifting mechanism brake wheel, it should be scrapped.

3. If the wear exceeds 60% of the original thickness for the running mechanism brake wheel, it should be scrapped.

What does a major overhaul of a bridge crane include?

Answer: A major overhaul includes the following:

• Mechanical part: Disassembly of all mechanisms, including the reducer, couplings, drum group, wheel group, and load handling devices. Replace worn-out parts, clean, reassemble, and lubricate. Replace wire ropes and brakes.

• Electrical part: Disassemble and dry the motors, reassemble, and lubricate. Replace damaged motors, brake devices, control devices, and protective cabinets. Replace all wiring, rewire, and install new lighting and signaling systems.

• Metal structure: Correct and reinforce the main beams if sagging or side bending occurs. Clean the entire crane and apply two coats of anti-rust paint.

What are the scrapping standards for a crane's main beam?

Answer: After multiple overhauls, if the crane’s main beam suffers from severe sagging (even after two repairs) or repeated cracks, it signals the end of its safe operational life. After an assessment by the relevant safety authority and technical department, the crane can be considered for scrapping or replacement.

Main beam sagging and cracks are considered fatigue damage caused by alternating stresses, leading to local slip and yielding. If sagging or cracks continue to recur, it indicates that the main beam has reached the end of its safe life.

Typical service life estimates:

• Heavy-duty grab cranes, electromagnetic cranes, etc. – around 20 years.

• Bulk handling cranes – around 25 years.

• Forging or casting cranes – over 30 years.

• General bridge cranes – 40-50 years.

The actual service life depends on the specific operating conditions.

What is the scrapping standard for a wheel?

Answer: A wheel should be scrapped if it has any of the following conditions:

1. Cracks.

2. The flange thickness is worn down by 50% of the original thickness.

3. The tread thickness is worn down by 15% of the original thickness.

4. For wheels with a running speed of less than 50m/min, the profile deviation exceeds 1mm; for wheels running at over 50m/min, the profile deviation exceeds 0.5mm.

5. Pitting on the tread: if the wheel diameter is less than 500mm, the pitting diameter exceeds 1mm; if the wheel diameter is greater than 500mm, the pitting diameter exceeds 1.5mm and the depth exceeds 3mm, with more than 5 pitting spots.

When the hook is lowered to the minimum position, how many layers of wire rope should remain on each side of the drum? Why?

Answer: At least two layers of wire rope should remain on each side of the drum when the hook is lowered to its minimum position.

This is because the wire rope is fixed to the drum by a pressing plate. Only with at least two layers of wire rope can sufficient friction be generated between the wire rope and the drum, reducing the pull on the pressing plate and preventing the rope from being pulled out from under the plate or causing the pressing plate screws to break when carrying a load.

What are the causes of rapid wear in gear couplings, and how can the service life be extended?

Answer: Causes of rapid wear in gear couplings:

1. Poor installation accuracy: Misalignment of the shafts causes improper engagement of the inner and outer teeth, resulting in high local contact stress.

2. Poor lubrication: Since gear couplings are non-moving connections, grease may be squeezed out, leading to dry friction, accelerating wear.

3. High-temperature operation: Lubricating oil can dry out in high temperatures, worsening lubrication and accelerating wear.

4. Violation of operating procedures: Frequent reversing or braking can accelerate tooth damage.

To extend the service life of gear couplings:

1. Improve the installation accuracy of components.

2. Perform regular inspections and ensure proper lubrication.

3. Adhere to operational guidelines to reduce improper usage.

What are the causes of motor vibration?

Answer: Internal causes of motor vibration:

1. Rotor mass imbalance.

2. The stator core is improperly installed in the motor casing.

3. The motor shaft is bent, or the brake wheel on the motor shaft is eccentric.

4. Loose motor foot bolts.

5. Poor rotor circuit contact or short circuits between stator windings, causing unbalanced electromagnetic torque.

6. Worn bearings, with clearances exceeding the permissible range.

External causes of motor vibration:

1. Misalignment between the motor and the driven gear reducer.

2. Vibrations from the reducer are transmitted to the motor.

3. Insufficient rigidity in the motor base structure.

What are the scrapping standards for a brake wheel?

Answer: The scrapping standards for a brake wheel are:

1. Cracks in the brake wheel.

2. The surface has unevenness greater than 1mm or the friction surface has damage deeper than 2mm.

3. The lifting mechanism brake wheel's flange wear exceeds 40% of the original thickness.

4. The running mechanism brake wheel's flange wear exceeds 50% of the original thickness.

When should the gears in a reducer be scrapped?

Answer: The gears in a reducer should be scrapped if:

1. They have broken teeth or cracks.

2. For the first gear in the lifting mechanism reducer, if the wear exceeds 5% of the original tooth thickness, and for other gears, the wear exceeds 20%. For the first gear in the running mechanism reducer, if the wear exceeds 10%, and for other gears, the wear exceeds 30-40%.

3. If the pitting area on the tooth surface exceeds 60% of the tooth height and width.

What are the primary causes of rail wear?

Answer: The main causes of rail wear are:

1. Non-standard wheels.

2. Non-standard rails.

3. Errors in the transmission system or blockages.

4. Skewed or deformed chassis.

5. Cracks in the main beam metal structure.

What are the consequences of rail wear?

Answer: The consequences of rail wear are:

1. Reduced service life of wheels and rails.

2. Increased running resistance and energy consumption, potentially preventing movement.

3. Increased vibrations, causing loosening of fasteners and affecting the structural lifespan of the building.

4. Severe rail wear may cause derailment accidents.