Technical Guidance and Development Trend Analysis of Metallurgical Cranes

As an indispensable key and important equipment for the safe and normal production of the metallurgical industry, the reliability, safety and advancement of metallurgical cranes have always been highly valued by people. However, due to the constraints of traditional metallurgical processes, in the three decades before the reform and opening up, domestic metallurgical cranes basically made some minor improvements and developments based on the model of the former Soviet Union. With the continuous deepening of reform and opening up and the introduction of a large number of advanced foreign technologies, modern metallurgical cranes have also undergone significant changes. This article, in light of the improvement of metallurgical processes in domestic metallurgical enterprises and the usage requirements of end users, offers some insights into the development trends of metallurgical cranes.

Metallurgical cranes generally refer to casting cranes, material box feeding cranes, slab handling cranes, steel coil clamp cranes, disk cranes and other bridge cranes with higher working levels serving metallurgical plants, which are mainly used in metallurgical enterprises. Due to the changes in steelmaking, billet (ingot) casting and steel rolling processes in metallurgical enterprises, traditional metallurgical cranes such as billet removal cranes, clamping cranes for soaking furnaces, rigid material raking cranes, bridge-type charging cranes for open hearth furnaces and lid lifting cranes for soaking furnaces have gradually been phased out. No further analysis is provided here. Just make some preliminary analysis and discussion on the development trends of the several types of cranes that are widely used in metallurgical enterprises at present.

1. General development trend

1.1 Large-scale lifting capacity and high-speed working speed One of the main trends in the development of modern metallurgical cranes is the large-scale lifting capacity and high-speed working speed. With the development of society, the requirements for metallurgical enterprises are gradually increasing. This is not only reflected in the quantity requirements for metallurgical products, but more importantly, in the quality and variety of metallurgical products The increase in social demand has driven and promoted the technological transformation and progress of metallurgical enterprises. The application of large-scale converters, continuous casting and continuous rolling technologies has put forward higher requirements for the large-scale and high-speed development of metallurgical cranes. Now, a simple statistics is made on the development of casting cranes in major domestic metallurgical crane manufacturing enterprises: As can be seen from the above table, both the lifting speed and the lifting capacity of the main hook have increased significantly over the past fifty years.

1.2 Both the lifting and traveling mechanisms adopt speed regulation systems. As early as the 1970s and 1980s, with the development and maturity of AC speed regulation technology, many renowned crane manufacturers abroad successively made commitments to speed regulate various mechanisms. The speed regulation range varies depending on the different speed regulation methods adopted. At present, stator voltage regulation and variable frequency speed control systems are widely used in design. The hoisting mechanism is mostly stator voltage regulation, while the running mechanism is mostly variable frequency.

After the mechanism adopts speed regulation, it has the following obvious advantages

a) Smooth starting and braking of the mechanism: When the mechanism starts or brakes at only 1/10 or 1/20 of the normal speed, the lifted object runs smoothly, which is particularly beneficial for casting cranes that lift steel ladles.

b) It can effectively reduce the wear of the brake block;

c) The lifted object can be accurately positioned;

d) Reduce the impact on metal structures (bridge frames or trolley frames) and transmission systems to extend their service life;

e) It can effectively improve the working environment of the operators;

f) Reduce the impact of starting on the power grid.

The use of the speed regulation system also brings the following problems:

a) The cost of cranes has increased;

b) It has relatively high requirements for the technical proficiency of maintenance electricians. Although the adoption of a speed regulation system will increase equipment costs and raise maintenance difficulties, with the advancement of technology, the cost of the speed regulation system is gradually decreasing, while its superiority is becoming increasingly evident. After the system was speed-regulated, the change in its working conditions laid a solid foundation for its development.

1.3 Monitoring, sensing and control technologies have been widely applied, significantly enhancing their performance and reliability. With the advancement of science and technology, various monitoring and sensing control technologies have been extensively utilized in metallurgical cranes, thereby greatly improving the performance of the cranes. Transform metallurgical cranes from simple material handling tools in the past into comprehensive transmission equipment for logistics and information flow at present.

1.3.1 Weighing device: A digital weighing device is installed on the casting crane. The small display screen is placed in the driver's cab, and the large display screen is set under the main end beam, facing the ground, so that the weight of molten steel in the steel ladles can be displayed at any time. This data is connected to the computer room. On the one hand, it can accumulate the daily output; on the other hand, it can determine the amount of molten steel to be held in the steel ladles according to the size and number of continuous slabs, reducing waste. With the application of various large and high-precision electronic scales, metallurgical cranes can not only handle items but also perform functions such as production statistics, power-off in case of overload, and alarm.

1.3.2 Fault Display, Recording and Printing Devices In continuous production steel enterprises, time is money. After the crane malfunctions, it is hoped that the maintenance time can be minimized. The fault display device can show the name of the faulty part or component on the display screen in the driver's cab. Maintenance personnel can immediately know the location where the fault occurs, which can greatly shorten the maintenance time. The electrical and mechanical components that are prone to failure shall be listed by the owner. The crane manufacturing factory shall set up fault display points as required by the owner. Once the monitored components fail, they will be displayed on the screen to prevent more serious faults from occurring. In addition to the display function, this device also has the functions of recording and printing, which are needed to find the cause of faults and implement the responsibility for verification.

1.3.3 The spatial position of the lifting gear of the two-dimensional and three-dimensional positioning device can be displayed on the screen in the driver's cab through this device. The positioning accuracy can be controlled below ±10mm, which can meet the process requirements of various automatic production lines. The driver can visually determine whether the lifting gear or object has reached the position it should reach through the numbers displayed on the screen, which greatly shortens the lifting time and avoids the shaking of the object, effectively improving production efficiency.

1.3.4 Anti-collision Devices: In the past, to prevent two cranes from colliding, only limit switches and buffers were installed. Currently, laser or radar anti-collision devices are available. A transmitting device is installed on one crane and a receiving or reflecting device on the other. When the pre-set distance is reached, an alarm will be triggered to prevent collisions.

1.3.5 Safety Brake: When lifting important objects such as nuclear materials, liquid metals, and the rotor of a generator in a large hydropower station, a safety brake is installed on the drum of the main hoisting mechanism of the crane. On the rim of the flange on one side of the drum, one pair, two pairs or even three pairs of bearing blocks can be set according to the braking torque requirements, and they are controlled by a specially designed hydraulic station. When starting, the safety brake is activated first, followed by the working brake installed on the high-speed shaft. When braking, the working brake applies the brakes first, and the safety brake applies the brakes a few seconds later. The function of the safety brake is to ensure that when any transmission component in all transmission chain links between the working brake and the safety brake is damaged or broken, the lifted object can be safely operated. The appropriate application of various monitoring and sensing technologies on cranes to achieve wired or wireless control of metallurgical cranes is not only the development direction of modern metallurgical cranes, but also should be the goal that every designer should strive for.

1.4 Programmatic control technology: The application of remote control technology in special environments. With the development and continuous improvement of computer software and hardware technologies, it has become possible to achieve programmatic control of cranes, and their control scope has become increasingly wide, with control functions becoming more and more perfect. It has become a reality for various metallurgical cranes to perform certain tasks according to the pre-agreed mode by people. In order to complete various tasks more accurately and promptly, various metallurgical cranes are linked with the main control equipment through wired or wireless means. Control in the main control room has become possible, and remote-controlled metallurgical cranes and program-controlled metallurgical cranes have been used in some metallurgical enterprises. Remote-controlled metallurgical cranes are generally used in some dangerous operation areas with high dust and pollution, such as the slag discharge span of Wuhan Iron and Steel Corporation's No.1 Steelmaking Plant, Zhujiang Steel Plant, and Bayi Steel Plant, all of which have remote-controlled cranes in use. Program-controlled metallurgical cranes are generally used in situations with relatively high operational efficiency. To enhance the service life of cranes, reduce shock, improve the accuracy of operation, operational efficiency and the working environment for drivers, the 1580 and dry quenching coke hoists in the third phase of Baosteel's project have been applied to a certain extent. Program-controlled cranes and remote-controlled cranes will develop to a certain extent and gradually be adopted by metallurgical enterprises.

1.5 Standardization of structural Forms and Internationalization of Production Modes The reason why we propose "standardization of structural forms and internationalization of production modes" as the main development trend of modern metallurgical cranes is mainly based on the following two considerations

a) The objective requirements of the market economy for metallurgical cranes: As the economic operation system has shifted from planning to the market, this provides powerful and favorable conditions for equipment purchasing units to select high-quality and low-priced products through bidding and tendering in a short period of time. Without the standardization of structural forms and the internationalization of production models, it is difficult for equipment manufacturers to meet the requirements of users.

b) The development of information and communication technologies has provided sufficient material and technical support for the standardization of product structural forms and the internationalization of production models. The standardization of structural forms can also apply the mature and reliable structural forms that have been tested in practice to new products, avoiding technical quality problems caused by unreasonable structural forms and thereby improving product quality.

1.6 Generalization of crane Types and Specialization of lifting gear Types The proposal of "generalization of crane types and specialization of lifting gear types" as a development trend of modern metallurgical cranes is mainly due to the renewal of billet rolling technology in metallurgical enterprises, that is, from the traditional ingot casting → ingot removal → steel ingot heating → primary rolling → hot rolling, to the current continuous casting → continuous rolling. When cooperating with traditional techniques, metallurgical enterprises need to have: Various types of cranes such as bridge-type feeding cranes, material box feeding cranes, casting cranes, ingot removal cranes, soaking furnace clamp cranes, soaking furnace cover lifting cranes, slab clamp cranes, rigid material rake cranes, and (including disk) steel coil clamp cranes are used to complete the process. When the continuous casting → continuous rolling process is adopted, As long as the metallurgical plant has several types of cranes such as material box feeding, casting, slab clamping, and steel coil clamping, it can complete the material handling in the entire process, greatly simplifying the type of crane. Due to the diverse demands for metallurgical products, various specialized lifting devices have emerged, such as horizontal coiling lifting devices, vertical coiling lifting devices, self-centering vertical coiling lifting devices, lid-lifting devices, L-shaped hook steel plate lifting devices, and C-shaped hooks. When used in conjunction with manually controllable rotating hooks, they can achieve multiple operation functions.

2. Analysis and Understanding of Typical Structures and Transmission Types 2.1 Development Trend of the Main Hoisting Mechanism of Foundry Cranes The adoption of star-shaped reducers in the main transmission of foundry cranes should become the development trend of modern foundry cranes. Most of the casting cranes currently in use adopt ratchet and pawl transmission. There are two reasons for using ratchet and pawl transmission. One is that ratchet and pawl do have their advantages in ensuring the safe operation of casting cranes. Secondly, when the star-shaped reducer was first used on the casting crane, it encountered several problems in a row. The Ministry of Metallurgy issued a special document to suspend the use of star-shaped transmission. After decades of reflection, as well as the proven excellent performance of star reducers in imported casting cranes and the development of control and monitoring technologies. We believe that the application of star drive in casting cranes will gradually expand for two reasons. First, star drive basically possesses the advantages of the original ratchet and pawl drive and can also achieve long-term continuous safe operation of a single motor. Secondly, the understanding of the causes of accidents caused by star drives in the past has gradually reached a consensus, that is, structural problems rather than fundamental ones. As long as the design is improved and perfected, they can be avoided. Coupled with the advancement of electrical control and monitoring technology, the safe operation of star drives can now be effectively guaranteed.

Among the three types of clamping devices for slab clamp cranes, namely gravity clamps, electrically opened and closed gravity clamps, and power clamps, the power clamp has been somewhat affected in its expansion and promotion due to its relatively high cost. However, it has superior working performance, especially the ability to achieve accurate three-dimensional tracking of the clamp mouth, reliable lifting of trapezoidal blanks, high working efficiency, and no loss of lifting height. It has incomparable advantages for realizing the automation of metallurgical enterprises. Therefore, we believe that the power-driven slab clamp crane will play an increasingly important role in the development of modern metallurgical cranes.

2.3 Overall processing of bridge frames and trolley frames: The overall processing of bridge frames and trolley frames, including some large structural components, is an important measure and effective way to ensure the quality of metallurgical cranes. Due to the particularity of the operation of metallurgical cranes, higher quality requirements are put forward. The overall processing of the trolley frame refers to the one-time marking and processing of the motor base, brake base, reducer support base, drum support base, and trolley wheel support base and other machine bases welded on the trolley frame. The shape, position, and dimensional tolerances among them are guaranteed by the machine tool, so the assembly work becomes particularly simple. Just position the motor, brake, reducer, drum and wheel in place. Unlike the old method, the shape, position and dimensional errors among them were not adjusted by inserting gaskets. In short, the shape and position tolerances between these components are guaranteed by the machine tool accuracy and are independent of the technical grade of the assembly workers, eliminating human factors. As a result, the assembly accuracy and performance in use are greatly improved, and the maintenance time for users is also significantly reduced.

2.4 Basic Drive and Control With the continuous production of the metallurgical industry, metallurgical cranes are required to have high reliability, good debugging and positioning performance, self-diagnosis of faults, and smooth and comfortable operation functions. Their control structure is: industrial PC +PLC+ basic drive. The basic drive adopts variable frequency speed regulation. The operation process will gradually transition from traditional manual speed control to precise PLC position control. Work information will be automatically transmitted to the upper computer (industrial PC), and eventually connected to the entire factory's management and control system. This is the main trend in the development of basic transmission and control for metallurgical cranes.

2.4.1 Basic Drive: The basic drive will be dominated by all-digital thyristor stator voltage regulation and speed control, as well as variable frequency speed control. The lifting mechanism will adopt voltage regulation speed control or inverterable variable frequency speed control without inverter failure (such as Siemens AFE), and the operation will mainly be based on variable frequency speed control.

2.4.2 Automatic Control: The PLC will perform all automatic control functions and achieve speed and positioning control of the speed regulation devices of each mechanism through fieldbus (such as PROFIBUS). This method has a large amount of communication information, simple wiring, and high reliability. For the continuous automatic stacking of billet clamps used in billet continuous casting and the continuous automatic stacking of steel coils after continuous rolling, the PLC will automatically complete the timed and positioned automatic billet clamping and automatic positioning stacking according to the Settings. The entire process will be automatically completed and repeated in a cycle. The system will have a self-diagnostic function to ensure operational reliability. In case of malfunction, it can be switched to manual operation by the driver, and the automatic process can be switched from any process flow point at any time. This will make the efficiency higher and the equipment operation more reasonable.

2.4.3 Fault Monitoring and Control The PC or touch screen human-machine interface installed in the driver's cab will be able to display the operation status and fault information of each mechanism, and process requirement instructions can be set on the PC and downloaded to the PLC. Activate the automatic control function to achieve the automatic control process as required by the technology. Industrial PCS can also be connected to the factory management network through communication, thereby achieving production management automation.