Keyword：rough rolling, mill rolls
Desicription：This article lists the key items in the process control of the rough rolling process. Rough rolling operators must firmly grasp and implement carefully.
1. Precautions for width control
The rough rolling stand should ensure the normal input of the short-stroke function of the side press and the vertical roll.
Width control requires the cooperation of rough and finish rolling personnel. Although rough rolling is the main post for width control, the finish rolling personnel are also responsible for monitoring the width of finished products, and timely feedback problems to the rough rolling post.
The rough rolling stand often needs to input the function of modifying value inheritance when performing width compensation. Operators should pay close attention to width changes after modification. Because in the first few blocks of changing specifications, the width difference may be caused by inaccurate learning coefficients, but this deviation will gradually decrease with the progress of learning, so the compensation coefficient also needs to be modified in time. In the past, our factory had several quality accidents caused by a large number of continuous width overshoots due to the failure to modify the width compensation coefficient in time. This kind of human error must be eliminated.
2. RT2 temperature control principle
The control of RT2 temperature is mainly guaranteed by adjusting the firing of the heating furnace. 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 and check:
1. Whether the tapping rhythm is too fast, and there is steel swing somewhere in the rolling line;
2. Whether the working status of descaling water, cooling water, reverse spray water, etc. is abnormal;
3. Whether the temperature curve is normal, 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, etc.
If it is confirmed that the above conditions of the rolling line are normal, then contact the heating furnace personnel and process personnel, and the professionals will determine whether to take adjustment measures on the rolling line.
On the contrary, if the above conditions of the rolling line are abnormal, please contact the instrument professional in time for instrument problems, and contact the process professional for process problems in time. If the tapping rhythm is too fast or too slow, the operator should contact the heating furnace to heat up or cool down. However, since it takes a certain amount of time to heat up or cool down the heating furnace, before the furnace temperature is adjusted, the temperature of RT2 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 intervene in the rolling speed with load.
When the temperature of RT2 is too high, the R2 operator can reduce the temperature of RT2 by limiting the upper limit of the speed, increasing the number of descaling passes or placing steel appropriately.
Under normal production conditions, the setting of descaling passes shall not be modified. The modification of the descaling pass by the workers at the operating table is only a temporary measure to prevent the occurrence of rolling waste accidents under abnormal circumstances. For example, descaling can be appropriately reduced when the slab is placed on steel for a short 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. If the situation is serious and it is necessary to adjust the descaling pass, the process personnel must be contacted. The setting of the descaling pass shall not be modified without the consent of the craftsman.
When the temperature of RT2 is too low, the operator should inform the heating furnace to slow down or stop tapping and increase the heating temperature. At the same time, the RT2 temperature should be reported to the finish rolling in time, so that the finish rolling can be prepared accordingly. If necessary, the operator of R2 can close a descaling water under the premise of ensuring the surface quality of the strip. To ensure the stability of subsequent rolling and avoid scrap steel.
As the thickness of the slab decreases with each pass, the effect of limiting the rolling speed and adjusting the descaling passes on the temperature will gradually become stronger with the increase of passes. The operator can choose the modified pass according to the actual temperature situation. In addition, when increasing the number of descaling passes, the influence of descaling at the R2 outlet on the measuring instrument must be considered, especially the last pass, and the outlet descaling cannot be arranged. If the temperature of the incoming material is too low, the operator should stop and give up rolling decisively to prevent accidents.
The R2 operating platform should monitor the Raytek thermometer screen on the operating platform at any time, and 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 temperature distribution of the intermediate billet should be monitored. Inform the actual temperature deviation of the heating furnace in time, adjust it by the heating furnace, and write down the slab number, heating furnace number and temperature deviation value of the intermediate slab in the shift record book.
3. Sickle control
When rolling difficult-to-roll specifications, an operator needs to be on site to observe the situation of the camber, and direct and coordinate the deviation correction operation of R1 and R2. In addition, the R2 station can also use the center line curve of the intermediate billet and the head and tail shapes displayed on the optimized cutting screen to grasp the shape of the camber.
When the R1 station finds obvious side bending after the slab leaves R1, it should promptly notify other links of the rolling line to control the rolling rhythm, and switch to the manual state to adjust the Swivel value. The shape of the intermediate slab rolled out by R1 is controlled in a reasonable state.
R2 station should adjust the Swivel value of the pass in time when it finds obvious side bending after a certain pass of rolling, and eliminate the side bending at this pass to ensure that the slab rolled out of each pass has a good shape.
The reduction amount of each pass of R2 is gradually reduced. In the swivel adjustment process of R2 one to five passes (sometimes seven passes), the swivel value adjustment in the first few passes should be strengthened according to the principle of “changing from large to small” with the reduction amount. At the same time, it should be clear that the swivel value can not only be pre-adjusted, but also can be adjusted inching during the rolling process.
R2 The operator needs to make adjustments for each pass. It is forbidden to make small or no adjustments in the first four passes, and only adjust the last pass.
The operators of each station should promptly notify the upstream and downstream processes of the sickle bend in the area, so as to provide a basis for the adjustment and control of the upstream and downstream processes.
The swivel value adjustment range of R2 rolling mill is -2～+2.
4. Buckle warping head control
Under normal circumstances, the ski value in the rough rolling area should be controlled within ±4. If the control is still not effective 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 any difference in the surface conditions of the work rolls, or whether there is an obvious difference in the temperature of the upper and lower surface of the slab. At the same time, relevant personnel should be notified of the on-site situation in a timely manner, and records should be made.
Abnormal large-scale warping of the slab is generally caused by abnormal temperature of the slab. If the slab is placed on the 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 burner billet and reverse charging billet are heated abnormally, which is easy to buckle and warp. When encountering the above situation, the operator should predict in time and adjust the SKI value accordingly. If the situation is serious, the rolling should be terminated decisively.
The production personnel should communicate with the heating furnace in time to strengthen the temperature difference control of the upper and lower surfaces of the slab according to the different buckle warping rules of the slabs produced by several furnaces. When it is difficult to adjust the buckle head by the size of the ski value, the effective distance of the ski value can be appropriately increased, such as increasing the effective distance from 0.5m to 0.7m.
In addition, it needs to be pointed out that the R1 inlet descaling header has no anti-collision guard plate, and it should be avoided as much as possible to prevent the equipment from being damaged during even-numbered passes.
5. Measures to avoid thermal cracks of R2 work rolls
In the early production process, it was found that when returning and pushing the waste long intermediate billet, in order to quickly reduce the temperature of the intermediate billet, the cutting and pushing time of scrap steel was accelerated. The operator sometimes parks the intermediate billet in the R2 rolling mill and opens the mill to enter and exit the descaling water to cool the intermediate billet. Although the scrap steel processing time has been accelerated like this, serious thermal cracks are produced on the roll body due to the long-term contact of the roll part with the slab. This will increase the grinding amount of the roll and reduce the service life. In severe cases, it is easy to cause the roll to drop meat accidents. Therefore, the following requirements are put forward for rough rolling operators:
1. It is strictly forbidden to artificially stay the hot billet 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 roll room personnel in time, and pull out the rolls to check the damage of the rolls.
2. During manual stripping, in order to prevent the work rolls from cracking in the state of rapid cooling and rapid heating, the cooling water of the work rolls must be closed when the hot blank passes through the roll gap. That is to say, the operator cannot click the “Fault Ackn” button to cancel the quick stop signal after shooting the quick stop and before manually reversing the steel. If you click the “Fault Ackn” button, the quick stop signal will be eliminated, and the work roll cooling water will be automatically turned on).
3. When manually stripping steel, if it is necessary to use descaling water to lower the temperature of the slab, the operator needs to manually place the steel in the rolling mill when turning on the descaling water. But at the same time, it is necessary to pay attention to changes in the water level and pressure of the descaling water to ensure the normal operation of the descaling equipment.
6. Precautions for thin gauge rolling
(1) In the rough rolling area, the deviation correction operation should be strengthened when rolling thin and narrow specifications, and the deviation correction operation must be strengthened in the last two or three passes of R2, including the first few passes of R1 and R2. Ensure that the offset of the rough rolling intermediate billet is ≤20mm
(2) Rough rolling operators are responsible for monitoring and feeding back the RT2 temperature. Especially when rolling thin specifications, 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 properly adjust the descaling pass to ensure the temperature of RT2.
(3) When the rolling is found to be unstable, the rolling rhythm must be slowed down, contact the biotechnology room and other related professionals, 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 the rolls, nozzles, roller wipers, etc. Do not continue fast-paced production in the event of continuous instability of multiple blocks, which may lead to rolling waste and long-term rolling shutdown accidents.
7. Inspection and confirmation work during rough rolling and roll change
In order to ensure that the roll change work is carried out in a timely and orderly manner during the rough rolling roll change process, the operator should do the following work:
1. Before changing the rolls, the rough rolling operators should remove the foreign matter such as the oxide scale accumulated in the R2 work roll operating side bearing seat, locking baffle, and track. Ensure that the bearing seat and locking baffle are not blocked by foreign objects such as iron sheets when the roller is pulled out.
2. After the roll is pulled out, the operator cleans up foreign objects such as iron sheets and iron slides accumulated in the roll bearing housing and the like.
3. The production preparer prepares the spare nozzles and water hanging plates in time before changing the rolls, and checks the nozzles, water hanging plates and other process parts on the rolling mill after the rolls are pulled out. Immediately organize operators to replace if any missing, blocked, damaged, etc. are found.
4. The operator must record the exact time of loading and unloading of each pair of rolls and each accident of steel jamming in the rough rolling mill during the service life of the rolls on the roll list. And return the roll sheet of the old roll to the grinding roll room personnel when replacing the new roll.
5. Operators in each shift must keep the roll list and hand it over to the next shift together with the shift record. The roll list must also be confirmed when the next shift takes over. If the roll sheet is found to be lost during the shift, you must ask to go to work and indicate it on the shift record so that you can confirm the responsibility in the future.
8. Matters needing attention when the R1 rolling mill is empty
When the R1 rolling mill cannot be put into production due to some reasons, the operator needs to set R1 to the idle mode. The specific operation can be found in the part of “Modification of Rough Rolling Process Parameters and Control of Process Elements” in this regulation. However, attention should be paid to the distribution of the reduction of R2 after passing R1. Because R1 is empty, the first pass of R2 actually becomes the first pass of rolling, and the thickness of the biting slab is much larger than the thickness of the slab under normal conditions. Especially when the SSP width reduction is large, the average thickness of the R2 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 slipping or serious buckling of the first pass of R2.
In addition, if the load of the R2 rolling mill is too large, it should be considered to increase the rolling passes of R2 or reduce the thickness of the intermediate billet to ensure the safe rolling of R2.
9. Other precautions
Operators must control the production rhythm to avoid steel swing due to too fast rhythm. If there is steel balance in a certain area due to accidental failure or specification change, the operator in this area should notify the whole line to adjust the steel tapping rhythm as soon as possible. Therefore, the continuous pendulum steel shall not exceed three pieces.
When rough rolling operators encounter various abnormal process conditions, they should first contact the professional to deal with it in time, and in an emergency, the set value can be temporarily modified with the professional consent. However, it is not possible to use temporary measures to roll steel for a long time, and the setting of manual intervention should be canceled in time after returning to normal. In addition, operators should develop good recording habits. When an abnormal situation occurs, the process, phenomenon, temporary measures, and professional advice should be written on the shift handover record. It is convenient for other operators to understand the situation and sum up experience, it is convenient for professionals to analyze problems afterwards, and it is also convenient for judging responsibility when problems occur (proving that the relevant adjustments made by operators have been approved by professionals).