In general, the lifting weight is below 50t, the span is within 35m, and there is no special use requirement, so the single beam type should be selected. If the portal is required to be large in width and high in working speed, or heavy and long workpieces are often hoisted, the double-beam portal crane should be selected.

(2) Span

The span of gantry crane is an important factor affecting the quality of crane itself. When selecting the type, the span should be reduced as much as possible under the premise of meeting the equipment use conditions and meeting the span series standards.

(3) Determination of wheel tracks

(a) It can meet the stability requirements of the gantry along the crane track direction.

(b) The overall dimensions of the goods should be able to smoothly pass through the plane steel frame of the leg.

(c) Note that there is a certain proportional relationship between the tread b and the span s, generally taking the tread b = (1/4—1/6) s.

(4) Spacing size

In work, there should be a certain space between the external dimensions of the gantry crane and the passage of goods and transport vehicles in the freight yard to facilitate loading and unloading operations. Generally, when loading and unloading vehicles within a span, the distance from the door leg should be kept above 0.7m, when the spreader is not working, the distance from the transport vehicle should be greater than 0.5m, and the time interval for goods to pass through the door leg should be greater than 0.5m..

(5) Electrical equipment

It shall comply with the relevant provisions of GB/T 14406- 1993 General Gantry Crane. Bridge crane is a widely used crane in industrial and mining enterprises. A locomotive depot is now equipped with several bridge cranes, which are frequently used every day and have a heavy workload. Whether the bridge crane can work normally directly affects the completion of locomotive maintenance tasks and the safety of personnel and equipment. The original traction system of bridge crane adopts wound AC asynchronous motor, and the rotor circuit is connected in series with multiple external resistors for speed regulation, which is controlled by cam controller and relay-contactor. The main disadvantages of this control system are: motor rotor series resistance speed regulation belongs to slip speed regulation with energy consumption, high energy consumption, soft mechanical characteristics, small speed regulation range and poor smoothness; Mechanical impact is large, which affects the service life; Therefore, only by completely changing the original speed regulation mode can the problem of high failure rate of bridge crane be fundamentally solved. With the rapid development of electronic technology, the performance and reliability of variable frequency governor have been greatly improved, which provides favorable conditions for its application in the transmission system of bridge crane. Firstly, the traction system and hook lifting system of 32-ton bridge crane, which is responsible for locomotive diesel engine assembly, are reformed by frequency conversion to improve its running performance and reduce the failure rate.

Reconstruction plan

1. Frequency conversion transformation scheme

The electric drive system of the bridge crane includes two cart motors, one trolley motor, one motor for lifting a 32-ton hook and one motor for lifting a 5-ton hook. The general idea of this transformation is to control five motors with four frequency converters to realize heavy load starting and frequency conversion speed regulation.

The schematic diagram of the main circuit is shown in figure 1.

Figure 1 Schematic diagram of main circuit of variable frequency speed regulation for bridge crane

In the transformation, except the original cam controller and motor, all control cabinets, relays and contactors were cancelled. The frequency converter adopts SAJ special frequency converter, and the configuration of each transmission mechanism is shown in figure 1.

2. Braking method

Through the frequency conversion speed regulation system, the braking resistor is connected to the DC circuit of the frequency converter, which consumes the regenerative electric energy of motor braking when heavy objects fall, so that the rotating speed of the running car, car and hook can be quickly and accurately reduced to zero. For hooks, it is often necessary for heavy objects to stay in mid-air for a period of time (for example, when heavy objects translate in the air). Although variable frequency speed regulation system can stop heavy objects, it is easily disturbed by external factors (such as frequent power failure during translation) and has poor reliability. Therefore, mechanical braking also requires the use of electromagnetic brakes.

3. Control points of frequency conversion control system

The control of the driving system of the bridge crane includes: the left and right walking of the cart and the speed gear; The forward and backward movement and speed gear of the car; Lifting and shifting devices of hook, etc. These can be controlled without contact through the programmable controller of the frequency converter.

What should be paid attention to in the control system of bridge crane is the control to prevent the hook from slipping. Before and after the electromagnetic brake is held and released, the heavy object is easy to slide down due to the stopped state.

(1) Control point for stopping lifting heavy objects

By setting the stopping and starting frequency and the maintenance time of the sum (which should be 0.6s longer than the braking time of the brake electromagnet), when the working frequency of the frequency converter drops, the frequency converter outputs a "frequency reaching signal" and gives a power-off instruction of the brake electromagnet, which is maintained at this time, and then the working frequency of the frequency converter drops to 0.

(2) Control points of lifting heavy objects

Set "Lifting Start Frequency" and "Detecting Current Time". When the frequency converter reaches it, the frequency converter starts to detect the current, and when it is confirmed that the current is large enough and the generated torque can offset the falling torque, it will issue a release instruction, so that the braking electromagnet will start to be energized to release the brake, which should be longer than the electromagnet release time.

(3) Automatic torque boost setting

Increasing the intermediate frequency voltage properly during debugging can improve the low frequency characteristics and increase the starting torque; Increasing the zero-frequency voltage can increase the strong DC excitation, keep the motor torque large enough and prevent the hook from slipping.

(4) Function parameter setting of frequency converter of each transmission mechanism

Application of SAJ series inverter in the transformation of transmission mechanism of bridge crane.

The effect after transformation

Judging from the operation after the transformation, the effect is very obvious. The main effects are as follows: the switching device operated by the motor is contactless and has a semi-permanent life; First of all: before the lifting equipment leaves the factory, it is necessary to make an identity record. Safety inspection and maintenance before equipment installation: check the integrity of the performance of the main mechanism of the equipment, check the visible defects of the main steel structure and connectors, pins and bolts, check the anti-corrosion situation of the equipment surface, form records and issue installation opinions.

Secondly, the lifting equipment should be maintained by special personnel. After the equipment is delivered for use, the daily maintenance shall be the responsibility of the equipment operating driver or full-time personnel of the using unit, and the installation and maintenance unit shall be obliged to supervise and inspect the daily maintenance contents. The main contents of daily maintenance are summarized as "cross operation method": cleaning, fastening, lubrication, adjustment and anticorrosion. Every day after work 10 ~ 30 minutes, check whether all parts and parts of the equipment are normal, refuel and lubricate according to regulations, pay attention to whether the mechanical operation sound is normal, and do a good job of cleaning and handover to achieve the purpose of neat appearance and normal operation of the equipment. Daily maintenance records and handover records should be made into fixed forms for file management.

Thirdly, professional physical examination should be carried out regularly for lifting equipment. Regular inspection and maintenance of equipment in use: maintain and repair mechanical equipment several times within the specified time, focusing on cleaning, lubrication, adjustment, disassembly and overhaul. Generally, it is completed by maintenance personnel and operators.

After the crane leaves the factory, it is generally stipulated that there is a running-in period of about 60 hours (some are called running-in period), which is stipulated by the manufacturer according to the technical characteristics of the crane at the initial stage of use. Running-in period is an important link to ensure the normal operation of crane, reduce the failure rate and prolong its service life. However, some users ignore the special technical requirements of the new machine running-in period because of lack of common sense in crane use or because of tight construction period or want to get benefits as soon as possible. Some users even think that the manufacturer has a warranty anyway, and the manufacturer is responsible for the maintenance when the machine breaks down, so the machine is overloaded for a long time during the running-in period, which leads to frequent early failures of the machine, which not only affects the normal use of the machine, shortens the service life of the machine, but also affects the project progress because of the damage of the machine. Therefore, we should pay full attention to the use and maintenance of crane running-in period. Characteristics of running-in period: 1. Wear speed is fast.

Due to the influence of processing, assembly and adjustment of new machine parts, the friction surface is rough, the contact area of the mating surface is small, and the surface stress is uneven. During the operation of the machine, the concave and convex parts on the surface of the parts are embedded in friction with each other, and the metal chips that have fallen off continue to participate in friction as abrasives, which further accelerates the wear of the mating surfaces of the parts. Therefore, parts (especially mating surfaces) are easy to wear during the running-in period and wear quickly. At this time, if the work is overloaded, it may lead to damage and early failure of parts.

2. Poor lubrication

Because the fit clearance of newly assembled parts is small, and because of assembly and other reasons, it is difficult to ensure the uniformity of fit clearance, and it is difficult for lubricating oil (grease) to form a uniform oil film on the friction surface to prevent wear. Thereby reducing the lubrication efficiency and leading to early abnormal wear of components. In severe cases, it will cause scratches or bite marks on the friction surface with precision, which will lead to failure.

3. There is looseness

There are deviations in the geometric shape and fitting size of the newly machined and assembled parts. At the initial stage of use, due to the impact, vibration and other alternating loads, as well as the influence of heating, deformation and other factors, as well as rapid wear and tear, it is easy to loosen the originally fastened parts.

4. There is a leak.

Due to the influence of loose parts, vibration and machine heating, the sealing surface and pipe joint of the machine will leak; Some casting, machining and other defects are difficult to find during assembly and debugging, but due to vibration and impact during operation, such defects are exposed, showing oil leakage (water). Therefore, leakage is easy to occur during the running-in period.

5. There are many operational errors.

Due to the lack of understanding of the structure and performance of the machine (especially for new operators), it is easy to cause failures or even mechanical accidents due to operational errors. Use and maintenance during running-in period 1. As the crane is a special vehicle, the operator should receive the training and guidance from the manufacturer, fully understand the structure and performance of the machine, and gain some operation and maintenance experience before operating the machine. The product operation and maintenance manual provided by the manufacturer is the necessary information for the operator to operate the equipment. Before operating the machine, you must read the operation and maintenance manual and operate and maintain it according to the requirements of the manual.

2. Pay attention to the workload during the running-in period. Under normal circumstances, the working load during the running-in period should not exceed 80% of the rated working load, and appropriate working load should be arranged to prevent the machine from overheating due to long-term continuous operation.

3. Pay attention to always observe the instructions of various instruments. If there is any abnormality, stop in time to eliminate it. Stop the operation before the cause is found and the fault is eliminated.

4. Pay attention to regularly check the level and quality of lubricating oil, hydraulic oil, coolant, brake fluid and fuel (water), and pay attention to check the sealing performance of the whole machine. During the inspection, it is found that there is too much oil and water shortage, so the reasons should be analyzed. At the same time, the lubrication of all lubricating points should be strengthened. It is recommended to add grease to each shift of lubricating points during running-in period (except for special requirements).

5. Keep the machine clean, adjust and tighten loose parts in time to prevent parts from being worn or lost due to looseness.

6. At the end of the running-in period, carry out compulsory maintenance on the machine, do a good job of inspection and adjustment, and pay attention to changing the oil.

In short, the requirements for crane maintenance during the running-in period can be summarized as: strengthening training, reducing load, paying attention to inspection and strengthening lubrication. As long as we pay attention to the maintenance of the crane during the running-in period as required, it will reduce the occurrence of early failures, prolong the service life, improve the work efficiency and bring more benefits to the machine. As a large lifting equipment, the cost of buying a crane is not a small sum. In order to prolong the life of the crane and make it more durable, we must understand the common situations that may occur in the use of the crane fuselage, such as cracks in the crane fuselage. At this time, in order to achieve the purpose of long-term use of cranes, what should be done? The influence of the wind. The crane may be working in the open air, and the whole weather, coupled with the role of wind, makes the crane blocked by some wind in the process. Once the wind is too strong, the crane will resist the action of the wind when working, and the load it bears will be aggravated, which will exceed the bearing capacity of the machinery. No matter how strong the machine is, it will shake in an instant. Once the machine body is overloaded, cracks and cracks may appear. Cracks may occur during manufacturing, because the design is not forward-looking and the durability of machinery is not considered, which also needs to be prevented. Strengthening the shape of the crane body can reduce the damage to the main beam of the bridge crane. Improper installation of bridge crane will also cause long-term corrosion and damage. Therefore, attention should also be paid to installation and peacetime inspection, and attention to mechanical maintenance is indispensable. Because the bridge crane will have different degrees of corrosion when it is used for a long time, cracks will appear if a certain impact force is added. Therefore, lubricating oil should be added during inspection to reduce friction and delay the service life of the crane.