What is an Overhead Crane?

Overhead cranes are lifting equipment for lifting materials horizontally in workshops, warehouses and storage yards. Because its ends sit on tall concrete pillars or metal supports, it looks like a bridge. The bridge frame of the bridge crane runs longitudinally along the tracks laid on the elevated sides on both sides, which can make full use of the space under the bridge frame to lift materials without being hindered by ground equipment. It is the most widely used and largest number of lifting appliances.

A bridge type running on an elevated track

Bridge cranes are generally made of bridges (also known as carts). It consists of lifting mechanism, trolley, trolley moving mechanism, control room, trolley conductive device (auxiliary slide line), and crane general power supply conductive device (main slide line).

The main technical parameters of bridge cranes are lifting capacity, span, lifting height, running speed, lifting speed, work type and electric motor's power continuity rate.

(1) The power source of the crane is three-phase AC (three-phase four-wire system), the frequency is 50Hz / 60Hz, and the voltage is 1000V (can also be 3kV, 6kV, or 10kV as required). The voltage fluctuation of the power supply system at the access point of the crane feeder should not exceed ± 10% of the rated voltage.

(2) The track installation of crane operation shall meet GB / T tolerance requirements.

The grounding resistance of the crane running track should not be greater than 4.

The altitude where the crane is installed and used does not exceed 1000m (if it exceeds 1000m, the capacity of the motor should be checked according to the provisions of GB 755, and when it exceeds 2000m, the capacity of the electrical components should be checked).

(3) The radiant heat temperature of the lifting articles to the hook part of the crane should not exceed 300 ° C.

(4) Climatic conditions when the crane is working indoors:

The ambient temperature does not exceed + 40 ° C, and the average temperature within 24h does not exceed + 35 ° C;

Ambient temperature is not lower than -5 ° C; relative humidity does not exceed 50% at + 40 ° C.

(5) Climatic conditions when the crane is working outdoors:

The ambient temperature does not exceed + 40 ° C, the average temperature within 24h does not exceed + 35 ° C, and the ambient temperature is not less than -20 ° C. The relative humidity when the ambient temperature does not exceed + 25 ° C is allowed to temporarily reach 100%.

(6) The working wind pressure should not be greater than: 150Pa inland (equivalent to class 5 wind) and 250Pa in coastal area (equivalent to class 6 wind); the maximum wind pressure in non-working state: generally 800Pa (equivalent to class 10 wind), It can also be agreed separately. ^[2]

Overhead cranes are important tools and equipment to realize the mechanization and automation of the production process in modern industrial production and lifting transportation. Therefore, bridge cranes have been widely used in departments and places such as indoor and outdoor industrial and mining enterprises, steel and chemical industries, railway transportation, ports and terminals, and logistics turnover.

The bridge crane in the workshop is not suitable for mechanized hoisting because the top of the rail is close to the lower chord of the roof truss and the volume and weight of the bridge crane are large. Small and medium-sized bridge cranes are often hoisted with a single mast, which can improve work efficiency, shorten the construction cycle, and reduce aerial work. The construction procedures are as follows.

(1) Erecting the mast

Mast height The maximum height of the mast is the height from the ground to the roof panel minus the operating space between the top of the mast and the roof panel and the height of the sleepers interrogated by the mast. The minimum height should meet the needs of lifting height.

The position of the mast due to

1. The weight should be able to move in the up, down, left, right, front, and back directions, and be able to move simultaneously in the three-dimensional direction. Except for downward movement, terminal protection in the other five directions should be provided.

2. Have a reliable braking device, even in the case of power failure, heavy objects will not fall due to their own weight.

3. There should be a large speed adjustment range. When starting from a stationary state, it should gradually accelerate from the lowest speed, and the acceleration cannot be too large.

4. In order to prevent the danger that may occur during overload or overspeed, there should be short-term overload protection measures. Overcurrent relays are generally used as overload protection for circuits.

5. There should be pressure loss protection.

6. Have security measures.

Check item

Safety inspection of bridge cranes In order to ensure the safe operation of bridge cranes, some safety routine inspections are required during crane operation. The inspection items and points are as follows:

(1) Lifting height limiter, stroke

Leak repair protection

Overhead crane trolley reducer is affected by vibration, wear, pressure, temperature and other factors.

1) Appearance of bridge crane: sweep the exterior completely to ensure no dust accumulation and no yellow robe. Check for cracks and welding.

2). Big and small cars: Check and tighten the drive shaft seat, gear box, coupling, shaft and keys for looseness; Check and adjust the brake wheel clearance to make it uniform, sensitive and reliable.

3) Check the reducer of the bridge crane to see if it leaks oil. There is an abnormal sound inside the box during operation, it is necessary to open the box cover for inspection. It is usually caused by bearing damage or excessive backlash of gear meshing, and serious tooth surface wear.

4) Lifting and hoisting: Check whether the steel wire rope, hook and pulley are safe and reliable. If the wear exceeds the specified value, it should be replaced. Check and adjust the brake to make it safe, sensitive and reliable.

5) Inspection of wire ropes of bridge cranes. Commonly used varieties are phosphate-coated steel wire rope, galvanized steel wire rope and smooth steel wire rope. Inspection of wire ropes should focus on observing broken wires, abrasion, kinks, and corrosion. For some places where the wear and broken wires are more serious but have not exceeded the standard, do Mark for easy follow-up review. Attention should be paid to check whether the safety limiter of the wire rope in the drum is effective, whether the wire rope pressing plate on the drum is pressed tightly and whether the number of pressing plates is appropriate.

6) Lubrication: Check the oil quality and quantity of all parts, and add or replace the lubricant as required.

7) Inspection of pulleys of bridge cranes. The focus is on whether the groove bottom wear exceeds the standard and whether there are cracks on the cast iron pulley. As for the balance wheel of the pulley block of the pitching mechanism, it does not move because of normal circumstances, and it is easy to be ignored. Therefore, it is necessary to check the rotation flexibility before installation, otherwise, the length and tension of the left and right steel wire ropes cannot be automatically adjusted by the balance wheel during installation, which makes it difficult and difficult to adjust the ropes at high altitude.

8) Electrical: Check whether the limit switches are sensitive and reliable; Check whether the electrical appliances in the electrical box are sensitive and reliable; Check whether the motor, bell and wires are safe and reliable; Check whether the signal lights are good.

9) Check whether the couplings of the bridge crane are loose or even "roll". Focus on checking the elastic rubber ring of the elastic pin coupling for abnormal wear. Pay special attention to the tooth ring coupling's wear condition of the gear ring. Due to the poor installation accuracy, when there is a large offset between the two axes, it appears that the entire ring gear will soon be bald in a short time. If this happens in the lifting mechanism, serious accidents are likely to occur.