Causes and prevention methods of work roll failure in finishing rolling of hot-rolled plate and strip steel

In view of the relatively high risk of failure of the finishing rolling work rolls, in order to develop a scientific and reasonable solution, relevant technical personnel summarized the failures that have occurred in the past and analyzed the following main reasons for the failure of the work rolls.

KeywordWork roll

backup rolls
  • The problem and solution of high chromium centrifugal composite cast iron roll falling off

The high chromium centrifugal composite cast iron roller is made of high chromium white cast iron containing 12% to 22% chromium as the outer material of the roller body. High-strength ductile iron is used as the core and roll neck materials. High alloy composite cast iron roll produced by centrifugal composite casting process. Abnormal failures of rolls mainly include roll body peeling, roll body fracture, roll body cracks, etc.

The cause of the problem.

First of all, from the perspective of the shedding of the roll body, during the actual operation of the rolling mill, technicians often find that the surface metal material of the finishing rolling work roll has fallen off when inspecting the mechanical equipment. There are also many types of work roll shedding, which are mainly classified according to the location where they fall off. The common shedding locations are in the working layer and shoulder structure of the roll, where the situation is more serious. Analyze from the shedding of the working layer. The reason for this has a certain relationship with the standardization of the operator’s operations. In order to improve production efficiency, rolling mills are often operated for a long time without stopping, which causes the work rolls to bear relatively high pressure. Especially when using high Cr composite cast iron rolls, once the pressure increases during continuous operation, the corresponding temperature will be abnormal. These are the main reasons for the detachment failure of the finishing rolling machine of hot-rolled plate and strip steel when it is actually put into use.

As for the problem of the roller shoulder structure falling off, it is also related to the high pressure of equipment operation. At the same time, there are also deficiencies in the structural design and installation process of the roller shoulder by technicians in the early design stage, which makes it prone to falling off.

Preventive and solution measures.

In order to solve the problem of work roll shedding and failure in the finishing rolling of hot-rolled plate and strip steel, it is necessary to standardize the work behavior of operators, clearly standardize various work processes and operating precautions for production and processing, and focus on temperature control issues. At the same time, technicians should be arranged to regularly inspect, repair and maintain the internal operating status of the equipment. Based on the development and progress of science and technology, companies can purchase professional intelligent flaw detection equipment during the actual inspection process. Currently, the most common method is ultrasonic flaw detection, which can accurately detect internal flaws without disassembling the equipment, thereby ensuring that the inspection work will not have a negative impact on production efficiency.

In addition, preventive work also needs to start from the production of finishing work rolls, fundamentally eliminate adverse risks in operation, reasonably increase the service life of the rolls, and ensure the smooth operation of various tasks.

  • Problems and solutions to cracks in high-chromium centrifugal composite cast iron rolls

The cause of the problem.

The rolls are constantly subjected to contact fatigue and thermal fatigue during the periodic loading, unloading, heating, and cooling processes. When the cyclic stress exceeds the maximum bearing strength of the roll, cracks will occur on the surface of the roll body. This kind of crack is mainly caused by the excessively long roll replacement cycle. At the same time, excessive changes in working pressure and temperature difference between the inner and outer roller bodies will also affect the stability of the roller body, causing crack problems. The more common ones are trapezoidal cracks. Most of these cracks are intermittent cracks caused by insufficient internal coolant and high temperature. In addition, local cracks refer to cracks with irregular shapes. The cracks are concentrated in a certain local position of the roll body. Such cracks are usually accompanied by shedding. Once cracks occur, it will have a serious negative impact on the safety of the production process.

Preventive and solution measures.

In order to solve the problem of cracks in the work rolls, technicians must ensure the stable operation of the rolling mill and prevent sudden accidents that cause mechanical equipment to suddenly stop running. This has a certain relationship with the power supply situation, so backup circuits and power supplies need to be set up to prevent power outages. At the same time, it is necessary to take protective measures for temperature cooling of the rolling mill, check the use of coolant regularly, and replace it with clean coolant. Once crack failure is discovered, technicians must promptly disassemble the roll for inspection, and use appropriate grinding methods to repair the damaged parts of the roll. If it cannot be restored, the working equipment should be replaced with a new one.

  • High chromium centrifugal composite cast iron roll breakage problems and solutions

The cause of the problem

High Cr composite cast iron roll during pouring process. The inner surface of the outer layer will fuse with the molten iron in the core, and the Cr in the outer layer will diffuse to the core, and the graphite will be in the form of strip graphite, which will reduce the strength and toughness of the core, causing the performance of the core to deteriorate, thus causing a fracture accident. The fracture problem is the most dangerous type of accident among the entire work roll failure types. Relevant staff need to pay attention to it and actively study feasible prevention and solution strategies.

Preventive and solution measures

First of all, we should start from the production process of hot-rolled plate and strip steel finishing rolling work rolls, and choose metal materials with higher hardness to ensure that the quality of the materials meets the needs of the rolls. At the same time, protection should also be carried out from the aspects of transportation and installation, and protective measures should be taken to prevent the working machine from colliding during the process, which may cause cracks in the internal materials and cause fracture problems. The installation process must be standardized, and professional mechanical equipment should be used for installation to ensure that the entire process is handled with care. It also needs to be debugged before it is actually put into use to ensure that the overall structure is stressed evenly.

During the entire processing process, the company should establish a scientific management system and train employees on operational knowledge and skills to ensure the smooth operation of each work, so as to promptly detect abnormal conditions of the work rolls and effectively solve them. Improve the economic benefits of enterprise production and processing work.

Conclusion: At present, the common failure problems of high-chromium centrifugal composite cast iron rolls mainly include surface material falling off, crack generation, roll body fracture, etc. In the actual production and processing process, technicians must combine specific conditions and use scientific and technological means to study feasible methods to improve the safety of work operations. Enterprises should standardize employees’ operating behaviors, improve safety work awareness, and arrange for technical personnel to regularly repair and maintain equipment. We should also start from the production, transportation and installation of work rolls to comprehensively eliminate operational safety hazards and reduce the probability of work roll failure.

 

MM GROUP is one of the professional roll manufacturing base in China, which supply all kinds of large-size rolls for iron and steel enterprises with production capacity of 100,000 tons of all kinds of hot strip mill rolls, section mil rolls, rod mil rolls, cold rolling m rolls, casting and forging backup rolls.

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