Rough rolling process for medium and heavy plates
Rough rolling processing technology
The main task in the rough rolling stage is to stretch the slab or flat ingot to the required width and perform a large compression extension. According to the raw material conditions and product requirements, there are various rolling methods to choose from. These methods are the full longitudinal rolling method, the comprehensive rolling method, the full transverse rolling method, and the corner-longitudinal rolling method.
A full longitudinal rolling method
Longitudinal rolling refers to a rolling method in which the extension direction of the steel plate is consistent with the longitudinal axis direction of the raw material (steel ingot or billet). When the width of the raw material is slightly greater than or equal to the width of the finished steel plate, there is no need for widening rolling, and it can be directly rolled into the finished product through longitudinal rolling. Therefore, it is called the full longitudinal rolling method. The full longitudinal rolling method has a high output due to its simple operation. When rolling steel ingots, the defects at the head of the steel ingot will not spread to the entire length of the steel plate. However, in the full longitudinal rolling method, due to the fact that the rolled piece always extends along one direction during the rolling process (including at the initial rolling billet opening), segregation and inclusions in the steel are distributed in obvious bands, resulting in anisotropy of the steel plate's microstructure and properties, and reducing its transverse properties (especially impact properties). The full longitudinal rolling method is not widely used in actual production because it cannot adjust the width of raw materials and the anisotropy of the microstructure and properties of steel plates through rolling methods.
B Comprehensive rolling method
The comprehensive rolling method is the transverse rolling - longitudinal rolling method. Cross-rolling refers to the rolling process where the extension direction of the steel plate is perpendicular to the longitudinal axis of the raw material. The comprehensive rolling method is generally divided into three steps; First, the slabs are leveled through longitudinal rolling for 1 to 2 passes, which is called forming rolling. Then, rotate 900 degrees for transverse rolling and widening to extend the width of the slab to the required width, which is called widening rolling. Finally, it is rotated to 900 degrees for longitudinal rolling to form the product, which is called extended rolling. The comprehensive rolling method is the most commonly used method in the production of medium and heavy plates. Its advantages are as follows: The width of the slab is not restricted by the width of the steel plate and can be freely selected according to the raw material conditions, which is relatively flexible. Due to the certain extension of the rolled piece in the transverse direction, the transverse performance of the steel plate is improved. Generally, the specifications and dimensions of continuous casting billets are relatively few, so it is more suitable to adopt a comprehensive approach
Rolling method. However, in this method, the rolled piece undergoes two 90-degree rotations from raw material to cross-rolling and from cross-rolling to longitudinal rolling during operation. As a result, the output is reduced, and the steel plate is prone to becoming barrel-shaped, increasing edge loss and lowering the yield rate. In addition, due to the relatively small lateral elongation of the slab, the anisotropy improvement of the steel plate's microstructure and properties is not yet obvious, and the lateral performance is still prone to be low.
C full transverse rolling method
The full cross-rolling method involves cross-rolling the slab until it becomes a finished product. This method can only be used when the length of the slab is greater than or equal to the width of the steel plate. When continuous casting slabs are used as raw materials, the full transverse rolling method, like the full longitudinal rolling method, will cause obvious anisotropy in the microstructure and properties of the steel plate. However, if the initial rolled slab is used as the raw material, since the extension direction of the rolled piece during the initial rolling is perpendicular to that during the thick plate rolling, the anisotropy of the steel plate is greatly improved, and the transverse performance of the steel plate is significantly enhanced. To ensure the uniform performance of the steel plate, the reduction rates in the longitudinal and transverse directions should be equal in the total deformation calculated from the steel ingot. Based on this principle, the thickness of the slab required for medium and heavy plate rolling can be determined. That is, the thickness of the slab is selected based on the principle of H0/h1=h1+h1, with h1=(H0 - H2)1/2
(In the formula, H0 represents the average thickness of the steel ingot;h1 represents the thickness of the slab; h2 represents the thickness of the steel plate). In addition, compared with the comprehensive rolling method, the full transverse rolling method can achieve neater edges, and the steel plate is less likely to form a barrel shape, thus reducing cutting losses. Also, due to the fact that the full cross-rolling method reduces the time for one steel transfer compared to the comprehensive rolling method, the output has increased. Therefore, the full cross-rolling method is often used in the production of medium and heavy plates using primary rolled billets as raw materials. However, due to the limitation of the length specification and quantity of the steel billet, the flexibility to adjust the width of the steel plate is small.
D-corner rolling - longitudinal rolling method
Angle rolling is a method in which the longitudinal axis of the rolled piece is fed into the roll at a certain Angle to the roll's axis for rolling. The feed Angle varies within the range of 150 to 450. After rolling 1 to 2 passes along each diagonal, it is switched to the other diagonal for rolling. Each time a rolled piece is rolled at an Angle, it will be extended to a certain extent in the original width direction, thereby increasing its width. At the same time, the rolled piece will become a parallelogram. When the rolled piece turns to the other diagonal for rolling, the width of the rolled piece continues to increase, and the rolled piece returns from a parallelogram to a rectangle. The width of each rolled piece after rolling can be calculated by the following formula:
The advantages of corner rolling are that it can improve the biting conditions, reduce the huge impact force generated during biting, and the contact width between the rolled piece and the roll during corner rolling is smaller than that in cross rolling, which also reduces the rolling pressure, thereby improving the plate shape and increasing the output. For overly narrow slabs, the corner rolling method can prevent the rolled piece from "resting horizontally" on the guide plate. The corner rolling - longitudinal rolling method can improve the anisotropy of the rolled piece by deforming it in both the longitudinal and transverse directions. The disadvantages are that steel needs to be pulled, which prolongs the rolling cycle and reduces the output. Moreover, the feeding Angle and the shape of the steel plate are difficult to control, increasing the cutting loss, lowering the yield rate, increasing the labor intensity, making the operation complex and difficult to achieve automation. Therefore, the Angle rolling - longitudinal rolling method is only used in three-high Lauter mills that use steel ingots as raw materials.
Safety Operating Procedures for Rough Rolling Workbenches
Before taking up the post, it is necessary to check the safety devices of the equipment and whether the work site is clean and tidy. Only after confirming that the equipment is normal can operation be carried out.
(2) It is strictly prohibited to bring any items unrelated to work onto the operation console.
(3) Before starting the equipment or conducting a simulated test run, the horn should be sounded first to inform the dispatcher, and the dispatcher should be informed to broadcast through a loudspeaker. The dispatcher should be contacted for on-site confirmation. The equipment can only be started when there is no one beside the machine.
(4) During production, the rolling status should be constantly monitored. When any abnormality is detected, the alarm should be activated. If necessary, measures such as stopping the machine or emergency stop should be taken. Avoid human-machine injury.
(5) Operators should always be aware of the misoperation of the shearing machine caused by the surrounding electric welding and other light sources. They have the responsibility to remind or warn the electric welding operators to avoid direct light exposure to components such as thermal metal detectors as much as possible and take corresponding measures at all times to prevent human-machine injury accidents.
(6) In the event of an accident, steel should be fed in accordance with the main control instructions. It is strictly prohibited to feed the rolled piece into the medium rolling bar without authorization.
(7) Strictly enforce the operation card system.
Rough rolling process
Detailed production process and technology of hot-rolled strip steel
Heating furnace - descaling machine - roughing mill - descaling machine - finishing mill - surface quality inspection instrument - layer cooling - coiler - baling machine - marking machine - coil warehouse. The slab is first heated to the required rolling temperature in the heating furnace, and then enters the roughing descaling machine through the roller conveyor to treat the iron oxide scale produced on the slab. Then, it enters the rough rolling mill to roll the width and thickness of the steel strip. After that, it is conveyed by the roller conveyor to the finishing rolling descaling machine to treat the iron oxide scale produced on the surface of the steel strip. Then, it enters the finishing rolling mill for more precise rolling of the thickness and width of the steel strip. The surface temperature of the steel strip is strictly controlled before coiling by the roller conveyor through layer cooling. After entering the coiler to become steel coils, they are finally bundled, marked and sent to the coil storage for packaging.
The hot working process flow of steel rolling
Strip steel: Continuous casting billet - heating furnace - high-pressure water dephosphorization - rough rolling - dephosphorization before finishing rolling (high-pressure water) - finishing rolling - laminar flow cooling - coiling seamless steel pipe: round billet - heating furnace - fixed-length flame cutting - cross-rolling piercing - finishing rolling - fixed-length cutting - cooling bed - straightening bar and plate and strip are similar. Generally, there is a medium rolling. All are completely continuous.
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