Description: The roll is one of the important parts of the rolling mill. In the rolling production process, the roll directly contacts the billet and deforms it with a certain pressure to roll various specifications of steel. The rolls work in the harsh environment of high temperature, high pressure, high speed accompanied by alternating cold and heat and iron oxide scale. The rolls of each stand are exposed to large mechanical stress, friction stress, thermal stress and large impact load, and they are prone to wear , Cracks, peeling and other phenomena that seriously affect the service life. This article summarizes and analyzes the relevant management measures during the use of rolls on the 1 450 mm production line of hot rolling.
Keyword: Talking about how to improve the service life of the rolls of the 1450 mm hot rolling production line, roll technology
Measures to improve roll life
(1) Daily management
Rolls are the main process components of rolling mills, and their purchase costs are relatively high. Roll consumption is one of the important economic indicators of steel rolling production costs. The soundness of the roll management system and the level of management are of great significance to reducing the production cost of the rolling line and increasing the service life of the roll. It is necessary to have a dedicated person to manage the rolls and establish a roll management system. The roll-in acceptance, paired use, crack soft spots, abnormal exits, etc., must be filed and recorded. In this way, the use trajectory of each roll and the status of the roll are clear at a glance, which is very necessary to reduce the consumption of the roll and increase the service life of the roll.
(1) After the arrival of the new rolls, the roll management personnel should check immediately as required to check whether the outer packaging of the roll is damaged, whether the roll has obvious appearance damage, carefully check the information of the delivered roll, and record it in the “Roll Management System” Enter its number and arrival time, etc. If any abnormal situation is found, report to the competent authority in time.
(2) Roll management personnel should conduct inspections in accordance with the requirements of the roll order drawings and technical agreements, and enter the inspection results into the “Roll Management System”, in which roll length, diameter, hardness, and ultrasonic flaw detection results must be entered. Rolls that have not been inspected must not be put into use.
(3) New rolls that have been unpacked and inspected are not allowed to be put into use immediately. They should be placed on a special roll stand, and anti-rust oil should be applied to the roll body and roll head to prevent corrosion on the surface of the roll.
- Handling of problems found in warehouse acceptance: If unqualified items are detected, the unqualified items shall be clearly marked, and the competent department shall promptly report back to the manufacturer and raise quality objections. Confirm the existence of unqualified roll quality items with the roll manufacturer, conduct a re-inspection if necessary, and require the roll manufacturer to sign the inspection sheet or make a written record. The roll manufacturer shall analyze whether the rolls with unqualified quality items will affect the use of the machine, and put forward written opinions on handling.
●Roll pairing and management of cracks and soft spots
(1) The pair of rolls should be paired according to the principle of the same material and close size of the rolls. The same material can make the wear of the rolls on the machine closer, and will not perform too much grinding due to the excessive difference between the rolls after the machine is off, and the close size can reduce the excessive pressure caused by the excessive roll pressure. Grinding waste.
- During the rolling process, cracks and soft spots are generated on the surface and inside of the roll due to factors such as impact, tail-flicking, and steel jamming. Cracks and soft spots will cause greater damage to the normal production of the rolling line and the service life of the rolls. Severe cracks will cause the rolls to peel off and end their service life prematurely. Therefore, non-destructive testing is particularly important. Each roll should be subjected to eddy current testing after grinding to detect whether there are cracks and soft spots on the roll surface. Only those with crack soft spot equivalents that meet the roll management regulations are allowed to be used. When the crack exceeds the limit, it needs to be re-examined with an ultrasonic detector. According to the results of the re-examination, the best crack grinding amount is calculated, and the grinding amount is reduced as much as possible to increase the service life of the roll. For the rough rolling work roll and the front end of the finishing rolling caused by card steel and other failures, the axial hot cracks are generated, and the grinding amount is determined according to the crack depth. After grinding, it can bring a slight and closed hot crack on the machine. It can be used and can be replaced according to the normal roll change cycle, but the roll management personnel must inspect the hot cracks after each stop to confirm whether the hot cracks have deepened and expanded, and can continue to be used if there is no expansion. If the crack condition deteriorates, the amount of grinding should be appropriately increased, and the depth of the crack should be reduced to ensure the safe use of the roll. The support roll plays a supporting role in the production process, and is not a roll that directly deforms the steel. The cracks produced by the support roller can be judged according to the ultrasonic inspection results whether it is a shallow crack and whether it is necessary to eliminate it. If the crack does not need to be eliminated, it can be polished and used on the machine. The depth of grinding can be calculated based on the results of ultrasonic flaw detection, and magnetic particles can be used to assist in checking whether the cracks are polished clean.
(2) Abnormal roll change
In the normal rolling process, in addition to changing the rolls regularly, the rolls may also be cracked due to the impact of the tail-flick of the steel strip or caused by the sticking of the steel on the roll surface, the broken roll caused by the melting of the bearing, the hot crack or the contact stress. Abnormal roll change conditions such as roll peeling. The occurrence of the above situations will cause excessive roll consumption, which will end the service life of the rolls in advance. Therefore, how to reduce or avoid the above situations during the rolling process is particularly important.
● Treatment of sticking steel roll after flicking
Flicking will cause the sticking of steel on the surface of the roll and cracks on the roll. For rolls that are removed from the machine due to sticking steel, first manually dispose of the steel sticking to the roll surface, and then check whether the roll surface has defects or visible cracks. If any, the roll management personnel need to be notified for further inspection. Then determine the amount of grinding; if not, use eddy current flaw detection after normal grinding, and cracks must be eliminated, because such impact cracks can easily cause the roll to fall off or peel off.
● Reduce roll bearing sintering
When the roll bearing is working, the load is heavy, the speed is high, the working environment is bad, the water ingress of the poor seal, the deterioration of the lubricating grease, the lack of the lubricating grease, etc. will cause the bearing to be damaged. Because the initial damage of the bearing in the bearing housing is difficult to find if it is not carefully inspected. It may melt after the machine is used, and the roll will also be broken when it is melted. Reducing the sintering of roll bearings can effectively reduce the occurrence of broken rolls. When the roll bearing is in use, measure whether the temperature of the bearing seat is normal every time it gets off the machine; observe whether the bearing seat shakes when rotating on the grinder; observe whether there is metal powder falling off the bearing seat when rotating. If one of these phenomena occurs, it indicates that the bearing may have been damaged, and it should be disassembled in time to check whether it can be used continuously to prevent the damage from getting worse until the roller is burnt. In addition, selecting suitable lubricating grease and establishing regular oil injection records can also effectively reduce bearing burning.
●Reduce roll thermal cracks and contact stress
When a steel jam or pile-up accident occurs in the rolling line, the high-temperature steel strip contacting the roll surface will cause the temperature of the contact part to rise sharply and cause thermal cracks. After the steel jam occurs, the cooling water should be turned off immediately to stop cooling, and the upper roll should be lifted to prevent the strip from contacting the upper roll to avoid thermal cracks on the upper roll. Do not water cooling after the roll is replaced to avoid thermal expansion and contraction. In addition, insufficient cooling during rolling will cause a large temperature difference between the inner and outer layers of the roll, and thermal stress will cause the roll to peel off. Therefore, it is necessary to ensure that sufficient cooling water is sprayed to ensure that the nozzle is not clogged. During rolling, due to the large load, the roll contact causes alternating shear contact stress on the roll surface, and these stresses will cause the roll to peel off. Choosing a reasonable work roll profile, support roll profile, and support roll chamfer can improve the load distribution of the roll body and avoid the accumulation of contact stress and the peeling of the roll surface.
(3) Roll grinding
The grinding of rolls is one of the main consumption forms of rolls. There is currently no uniform standard for the amount of rolls to be ground, and they are all formulated by various factories according to their usage. How to make the rolls that are off the machine reach the standard for re-use on the machine after being ground with the smallest amount of grinding is the main means to reduce roll consumption, increase the service life of the rolls and reduce production costs.
● Reduce the amount of roll grinding
The roughing work rolls of the 1 450 mm production line have been ground to 2 mm since they were normally shut down from the start of production to 2014. In 2014, both the workshop and the roll manufacturer proposed to reduce the amount of grinding after normal shutdown. After comparing the grinding amount with the roughing work rolls of the same material and the same rolling amount used by other manufacturers, and inquired about the relevant information, it was considered that the grinding The amount is high. The grinding amount of the high chromium steel roll is 0.5～1.0 mm, and it can be machined with a slight and uniform fatigue pattern. In 2014, we began to gradually implement the test of reducing the grinding amount. To ensure the safety of the roll, the initial plan is to reduce the grinding amount to 1.5 mm. If there is no abnormality after normal use, consider continuing the experiment to reduce the grinding amount to about 1 mm. The initial experiment is to pick a set of high chromium steel rough roll R1W3-X1401/X1402 from the rolls to carry out a 1.5 mm grinding test, and to track the eddy current flaw detection after grinding, the roll surface after grinding, the roll surface of the lower machine, The hardness after grinding is compared with the other 2.0 mm grinding rolls. The test results show that there is no difference between the grinding indexes of the rough roll of 1.5 mm and the grinding of 2.0 mm, which fully meets the requirements of the machine. Therefore, in 2014-03, the 1.5 mm grinding amount was applied to all high chromium steel rough rolls, and the conditions of the upper and lower machines and after grinding were continuously tracked and observed at random. After half a year of use, no abnormality occurred, and several experiments were done with the same comparative tracking experiment method, and finally the grinding amount was set at 0.8-1.0 mm. At the same time, experiments were also carried out on the work rolls in the front finishing mill to reduce the original 0.4 mm grinding volume to 0.3 mm.
●Reduce the influence of grinding interference factors
The specified grinding amount is an ideal minimum grinding value. In the actual grinding process, due to the operator’s human factors, the size of the head, roll shape, roll pressure, surface quality and other quality are not up to the standard, and the grinding is carried out again, thus increasing Consumption; at the same time, the operating factors of the equipment will also affect the grinding quality. For example, the height of the support shoe of the grinding machine and insufficient lubrication of the support shoe will cause the roller grinding quality to be unqualified. . Regularly summarize the problems that occur in the grinding process, and train operators to improve the level of operation, develop quantitative grinding procedures, and regularly maintain grinding and other measures can effectively reduce the influence of interference factors on the grinding volume. Reduce roller consumption and increase service life.
Roll is one of the expensive parts with high consumption in the rolling line, and it accounts for a large proportion of the production cost. By formulating a sound roll management system, you can clearly know the status and trajectory of each roll, which can make the rolls optimally paired and use the rolls to the fullest extent; formulating a reasonable amount of grinding can not only eliminate the fatigue of the rolls The layer enables the roll to meet the machine standard, and can reduce consumption and increase the life of the roll; reducing abnormal roll changes can improve the production efficiency of the rolling line and increase the production efficiency.