Title：Precautions for control of rough rolling width, temperature, camber, hot cracking of work rolls, etc., hot rolling technology
Description: According to the problems that occurred in the rough rolling area in the past, the key items in the process control of rough rolling are proposed here. Rough rolling operators must firmly grasp and implement them carefully.
Keyword: rolling mill
- Precautions for width control
The rough rolling table should ensure the normal input of the short stroke function of the side press and vertical roll.
Width control requires the cooperation of roughing and finishing personnel. Although the rough rolling is the main position for width control, the finishing rolling personnel are also responsible for monitoring the width of the finished product and timely feedback the problem to the rough rolling position.
When the roughing table is used for width compensation, it is often necessary to invest in the function of modifying value inheritance. Operators should pay close attention to width changes after modification. Because in the first few blocks of variable specifications, the learning coefficient may be inaccurate, resulting in a wide gap, but this deviation will gradually decrease with the learning, so the compensation coefficient also needs to be modified in time. In the past, our factory has experienced a large number of quality accidents with continuous width exceeding due to the failure to modify the width compensation coefficient in time. Such human error must be avoided.
- RT2 temperature control principle
The control of RT2 temperature mainly depends on the adjustment of the heating furnace to ensure the fire. However, if necessary, the rolling line can also be adjusted in a small range by adjusting the rolling rhythm, modifying the rolling speed, and changing the descaling pass.
When the rolling line finds that the RT2 temperature exceeds the control target range, the operator should first confirm the cause of the abnormal RT2 temperature, check:
1. Whether the rhythm of tapping is too fast, and there is a steel swing somewhere in the rolling line;
2. Whether the working conditions of descaling water, cooling water, reverse water spraying, etc. are abnormal;
3. Whether the temperature curve is normal, and whether the instrument is not working properly due to the influence of the measurement environment;
4. Whether the process parameters such as rough rolling speed and reduction are normal and so on.
If it is confirmed that the above conditions of the rolling line are normal, contact the heating furnace personnel and the technical personnel, and the professionals will determine whether to take adjustment measures in the rolling line.
On the contrary, if the above conditions of the rolling line are abnormal, the instrument professional should be contacted in time for instrument problems, and the technology professional should be contacted in time for process problems. If the tapping rhythm is too fast or too slow, the operator should contact the heating furnace for heating or cooling. However, since it takes a certain time for the heating furnace to heat up or cool down, before the furnace temperature is adjusted, the RT2 temperature can be properly adjusted by adjusting the rolling rhythm, modifying the rolling speed, changing the descaling pass and other temporary measures. During the rolling process, it is strictly forbidden to manually interfere with the rolling speed under load.
When the RT2 temperature is too high, the R2 operator can lower the RT2 temperature by limiting the upper speed limit, increasing the descaling pass or properly swinging the steel.
The descaling pass setting cannot be modified under normal production conditions. The manual modification of the descaling pass on the operating table is only a temporary measure taken to prevent the occurrence of rolling scrap accidents under abnormal circumstances. For example, the descaling can be appropriately reduced when the slab is placed in a short period of time for some reason. If the RT2 temperature is abnormal under normal production conditions, the rough rolling operator should notify the heating furnace to adjust the temperature in time. Without the consent of the craftsman, the setting of the descaling pass shall not be modified.
When the RT2 temperature is too low, the operator should notify the heating furnace to slow down the tapping or stop tapping and increase the heating temperature. At the same time, the RT2 temperature should be notified to the finishing rolling in time, so that the finishing rolling can be prepared accordingly. If necessary, the R2 operator can turn off a descaling water under the premise of ensuring the surface quality of the strip. In order to ensure the stability of subsequent rolling and avoid scrap.
Since the slab thickness is reduced successively, the effect of limiting the rolling speed and adjusting the descaling pass on the temperature will gradually become stronger with the increase of the pass. The operator can choose the modified pass according to the actual temperature. In addition, when adding descaling passes, the influence of the R2 outlet descaling on the measuring instrument should be considered, especially the last pass, and the exit descaling cannot be arranged. If the incoming material temperature is too low, the operator should resolutely stop and give up rolling to prevent accidents.
The R2 console should monitor the Raytek thermometer screen on the console at any time to monitor the temperature distribution of the intermediate billet. In each pass of R2 rolling, once the temperature difference between the two sides of the intermediate billet along the width direction is greater than 15 °C The actual temperature deviation of the heating furnace shall be informed in time, and the heating furnace shall adjust it, and record the slab number, heating furnace number and temperature deviation value of the intermediate billet in the shift record book.
- Sickle control
When rolling hard-to-roll specifications, an operator is required to observe the sickle bend on site, and to direct and coordinate the rectification operations of the R1 and R2 units. In addition, the R2 station can also grasp the shape of the camber by using the centerline curve of the intermediate blank and the head and tail shapes displayed on the optimized cutting screen.
When the R1 station finds obvious side bending after the slab exits R1, it should notify other links of the rolling line to control the rolling rhythm in time, and switch to the manual state to adjust the Swivel value. The shape of the intermediate billet rolled by R1 is controlled in a relatively reasonable state.
R2 station should adjust the Swivel value of the pass in time when it finds that there is obvious side bending after a certain pass of rolling, and eliminate the side bending in this pass to ensure that the slabs rolled out in each pass have a good shape.
The reduction amount of each pass of R2 is gradually reduced. During the swivel adjustment process of R2 one to five passes (sometimes seven passes), the principle of “from large to small” with the reduction should be strengthened as much as possible in the first few passes. The swivel value of the pass is adjusted, and it should be clear that the swivel value can not only be pre-adjusted, but also can be adjusted by jog intervention during the rolling process.
R2 operators should adjust each pass, and it is forbidden to make small or no adjustments in the first four passes. Only the last pass is adjusted. Once a similar situation is found, a serious assessment will be made.
The operators of each station should notify the upstream and downstream processes in a timely manner of the occurrence of the camber in the area, so as to provide a basis for the adjustment and control of the upstream and downstream processes. The adjustment range of the swivel value of the R2 rolling mill is -2 to +2.
- Buckle head control
Under normal circumstances, the ski value of the rough rolling area should be controlled within ±4. If it can not be effectively controlled when adjusted to ±4, it is necessary to check whether the cooling water of the upper and lower work rolls is normal, whether there is a difference in the surface conditions of the work rolls, or whether there is a significant difference in the temperature of the upper and lower surfaces of the slab. At the same time, the relevant personnel should be notified of the on-site situation in a timely manner, and records should be kept.
The abnormal large-scale buckle head of the slab is generally caused by the abnormal temperature of the slab. If the slab swings steel for a long time and stays in the equipment for some reason, the temperature of the upper surface is likely to be low, causing warping. In addition, the furnace head blank and the reverse charging blank are abnormally heated, and it is easy to buckle the head. When encountering the above situation, the operator should make a judgment in time and adjust the SKI value accordingly. If the situation is serious, the rolling should be stopped decisively.
The production personnel should communicate with the heating furnace in time according to the different buckle and warping rules of the slabs produced by several furnaces, and strengthen the temperature difference control between the upper and lower surfaces of the slabs. When the buckle head is difficult to adjust by the size of the ski value, the action distance of the ski value can be appropriately increased, for example, the action distance of 0.5m can be increased to 0.7m.
In addition, it should be specially pointed out that the R1 inlet descaling header has no anti-collision guard plate. When the even-numbered passes are used, the head should be avoided as much as possible to prevent the equipment from being damaged.
- Measures to Avoid Thermal Cracking of R2 Work Rolls
In the early production process, it was found that when returning and pushing the scrap long intermediate billet, in order to quickly reduce the temperature of the intermediate billet and speed up the processing time of scrap cutting and pushing out, the operator sometimes stopped the intermediate billet in the R2 rolling mill and opened the rolling mill entry and exit to remove The scale water cools the intermediate billet. In this way, although the processing time of scrap steel is accelerated, serious thermal cracks are generated on the roll body due to the partial long-term contact of the roll with the slab. This results in increased roll grinding and reduced service life. In severe cases, it is easy to cause the accident of falling meat from the roll. Therefore, the following requirements are put forward to rough rolling operators:
- It is strictly forbidden to artificially stop the hot blank on the work roll at any time. If the steel is stuck in the rolling mill due to tripping or other reasons, the operator should notify the process and the grinding roll room personnel in time, and pull the rolls to check the damage of the rolls together.
- When the steel is withdrawn manually, in order to prevent cracks in the work rolls in the state of rapid cooling and rapid heating, the cooling water of the work rolls must be turned off when the hot billet passes through the roll gap. That is to say, the operator cannot click the “Fault Ackn” button to cancel the fast stop signal after the quick stop and before manually rewinding the steel (the cooling water of the work roll is turned off after the quick stop. If the “Fault Ackn” button is clicked, the The quick stop signal is eliminated, and the cooling water of the work roll will be automatically turned on).
- When removing the steel manually, if it is necessary to use the descaling water to reduce the temperature of the slab, the operator needs to manually swing the steel in the rolling mill when the descaling water is turned on. But at the same time, it is necessary to pay attention to the changes in the water level and pressure of the descaling water to ensure the normal operation of the descaling equipment.
- Thin Gauge Rolling Considerations
(1) When rolling thin and narrow gauges in the rough rolling area, the rectification operation should be strengthened, not only the last two or three passes of R2, including the first few passes of R1 and R2, must be strengthened. Make sure that the offset of the rough-rolled intermediate billet is ≤20mm.
(2) The rough rolling operator is responsible for monitoring and feeding back RT2 temperature. Especially when rolling thin gauges, it is necessary to assist and supervise the heating furnace to ensure that the RT2 temperature is at the upper limit of the regulations. If necessary, R2 can be properly adjusted for descaling pass to ensure RT2 temperature.
(3) When the rolling is found to be unstable, the rolling rhythm must be slowed down, contact the biotechnology room and other related majors, and at the same time confirm whether the heating furnace, rough rolling, and finishing rolling process points meet the requirements. If necessary, stop the machine to check rolls, nozzles, roll wipers, etc. Do not continue fast-paced production in the event of continuous multi-block instability, which is likely to lead to scrap and long-term outages.
- Inspection and confirmation work during roughing roll change
In the process of rough rolling roll change, the operator should do the following work in order to ensure the timely and orderly progress of the roll change:
1. Before the roll change, the rough rolling operator should clear the foreign matter such as iron oxide scale initially accumulated on the bearing seat, locking baffle, rail, etc. on the operating side of the R2 work roll, so as to ensure that the bearing seat and locking baffle are not free from foreign matter such as iron scale when the roll is drawn. Jamming.
2. After the roll is pulled out, the operator cleans the iron sheets, iron slips and other foreign objects accumulated on the roll bearing seat.
3. The production preparers prepare spare nozzles and water-hanging plates in time before changing the rolls, and check the nozzles, water-hanging plates and other process parts on the rolling mill after the rolls are drawn out. If it is found to be missing, blocked, damaged, etc., the operator is immediately organized to replace it.
4. The operator must record the exact time of loading and unloading of each pair of rolls and the accident of steel jamming in the roughing mill during the service cycle of the roll, and record the roll sheet of the old roll when replacing the new roll. Return to roll shop personnel.
5. Operators in each shift must keep the roll sheet and hand it over to the next shift together with the shift record. The roll order must also be confirmed when the next shift takes over. If it is found that the roll sheet is lost during the shift, it must be required to go to work and indicate it on the shift record so that the responsibility can be confirmed in the future.
- Precautions for R1 Mill Empty Obsolescence
When the R1 rolling mill cannot be put into production for some reason, the operator needs to set the R1 to the idle mode. The specific operation can be seen in the section “Rough Rolling Process Parameter Modification and Process Element Control” of this regulation. But after emptying R1, attention should be paid to the distribution of the reduction amount of R2. Because R1 is empty, the first pass of R2 actually becomes the first pass of rolling, and the thickness of the slab that bites into the slab is much larger than the slab thickness under normal conditions, especially when the SSP width is large, R2 The average thickness of the inlet slab can reach more than 250mm. Therefore, the reduction amount of the first pass of R2 should be reduced from a maximum of 48mm to 35-40mm to prevent the first pass of R2 from slipping or seriously buckled.
In addition, if the load of the R2 rolling mill is too large, it should be considered to increase the R2 rolling pass or reduce the thickness of the intermediate billet to ensure the safe rolling of the R2.
- Other considerations
Operators must control the production rhythm to avoid swinging steel due to too fast rhythm. If the steel swing occurs in a certain area due to accidental failure or change of specifications, the operator in that area should immediately notify the entire line to adjust the tapping rhythm. Therefore, the continuous pendulum steel shall not exceed three pieces.
The rough rolling operator should contact the professional to deal with it in time when encountering various abnormal process conditions. In emergency situations, the set value can be temporarily modified with professional consent. However, temporary measures cannot be used to roll steel for a long time, and the setting of manual intervention should be cancelled in time after returning to normal. In addition, operators should have to develop good recording habits. When an abnormal situation occurs, the process, phenomenon, temporary measures, and professional advice should be written on the shift record. It is convenient for other operators to understand the situation and sum up experience, and it is convenient for professionals to analyze the problem afterwards, and it is also convenient for determining responsibility when a problem occurs (to prove that the relevant adjustments made by the operator have been approved by professionals).