Keyword：Rolling process, billets, mill rolls
Description：
Rolling is a process in which metal bars, plates, profiles, etc. are deformed through continuous stress to obtain the required shape and size. In this process, you should pay attention to the following places to ensure the quality and performance of metal materials
Strip steel (strip billet) warped head
1. Causes:
①The temperature difference between the upper and lower surfaces of the billet: when the temperature of the upper surface is higher than the temperature of the lower surface, it will cause buckle of the strip, otherwise it will cause warping of the strip;
②Elevation of the rolling line: If the elevation of the rolling line is too high, it will cause buckling of the strip, otherwise it will cause the strip to warp;
③Influence of friction factors: When the surface of the strip steel is not descaled or the roll is rough, the strip steel will bend to the side with the iron sheet or the rough surface of the roll surface, which will cause the strip steel to warp or buckle;
④Influence of the rolling pressure of the roller system: when the upper rolling is used, the strip will be buckled; if the lower rolling is used, the strip will be warped;
⑤ Influence of rolling speed: When the roll surface speed of the lower roll is greater than the speed of the upper roll, it will cause the warping of the strip, otherwise it will cause buckling;
⑥Unreasonable distribution of rolling load.
2. Preventive measures:
① Reasonably arrange the heating system to ensure the heating temperature of the billet, the temperature difference between the upper and lower surfaces, and the temperature difference between the core and the outer surface ≤ 30 ° C; the rolling process maintains a reasonable rolling rhythm, and at the same time ensures the uniform cooling of the roll system;
②Replace the backing plate in time according to the elevation of the rolling line and the technical requirements of the backing plate of the rolling mill;
③Guarantee the descaling effect of coarse descaling and fine descaling. Coarse descaling water pressure ≥ 16MPa, fine descaling water pressure ≥ 18MPa;
④Use the upper roller under the condition that the elevation of the rolling line meets the requirements.
3. Processing method:
①Slow down the rolling rhythm;
②Adjust the difference between the heating temperature of the upper and lower surfaces of the billet;
③ Check whether the cooling system of the roll is blocked;
④ Readjust the load current of each rack and each pass;
⑤When the head warping is serious, the roll should be replaced in time (adjust the roll pressure, rolling elevation and properly reduce the height of the upper guard plate at the exit.)
Scrap steel
1. Causes:
① The thickness of the slab is uneven, there are side bends, etc., or the incoming material of the rough-rolled strip is not straight, which leads to inconsistent extensions on both sides of the strip after entering the finishing mill;
②The accuracy of pressing and leveling after changing the rolls is not high, resulting in large deviations in the gap between the rolls on both sides;
③Depressing the hand did not make timely and correct adjustments to the change of the material shape of the strip;
④ The center line of the opening of the guide is not centered or the opening is too large, causing the strip to deviate;
⑤ The roll gap of the rolling mill is out of position, and the operator did not confirm this in place and did not adjust it in time, resulting in partial scrap steel;
⑥ The roll body loses meat, and the material is biased when pressed into the strip;
⑦ Insufficient roll turning accuracy, such as material deviation caused by roll taper, out-of-roundness or three-point difference exceeding the process index;
⑧ Debris left on the rolling line, such as wrenches and leveling discs, etc. affect the strip threading process and cause material deviation.
2. Preventive measures:
① The operator should observe the shape of the slab and the rough rolling material frequently, and adjust it in time if there is any change, so as to ensure the straightness of the finishing rolling material;
②Strengthen the sense of responsibility, and be meticulous and careful during the leveling process to ensure the quality of leveling;
③Depress the hand to improve its own operating skills, and quickly and accurately adjust the changes in the shape of the strip steel;
④ Use the time of succession inspection and roll changing time to measure the guides and guards to ensure that the guides and guards are centered and the size of the opening of the guides and guards on each rack meets the process requirements;
⑤If you find that the roll gap is out of position, you should contact the automation personnel and other relevant personnel in time. If you have not confirmed whether the roll gap is true or false, you should stop and check, and you should not have a fluke mentality of gambling to prevent unnecessary steel scrap;
⑥Strictly implement the process discipline to ensure uniform cooling of the roll body. And use the shift or waiting time to carefully check the roll surface;
⑦The rolling section must ensure the machining accuracy of the rolls, and at the same time, the steel rolling section must check and confirm the roll surface of the upper machine roll;
⑧ Strengthen the inspection of equipment and process.
3. Processing method:
①Turn off the cooling water of the rolls in time, and quickly lift the roll gap to prevent the rolls from being partially heated to cause cracking defects;
② After the scrap steel is processed, the roll surface should be inspected first to see if the scrap steel sticks to the roll, loses meat, etc.;
③ Re-level the rolling mill;
④Whether the measuring guide meets the requirements of the process;
⑤ If there is a problem with the roll, it should be replaced in time.
On the wall
1. Causes:
① The adjustment of the material shape of the strip steel by pressing down the hand is not in place, so that the strip steel deviates during the belt threading process, causing the head to hit the wall;
② The operation is not careful, the speed hand cannot observe the strip threading process in place, and does not cooperate with the pressing hand to adjust the speed in time, so that the amount of sheathing between the racks is too large, causing the middle part, especially the tail, to hit the wall.
2. Preventive measures:
① The rough rolling operator should adjust the strip in time to prevent the material shape of sickle bend and S-shaped bend, and ensure that the upstream plate shape is good;
②Finish rolling operators strengthen their sense of responsibility and make careful adjustments.
③ There must be a tacit cooperation between pressing and speed, especially when wearing the belt at the head and throwing steel at the tail, the speed hand must be cautious.
3. Processing method:
① Press down the hand to adjust the roll gap of the previous frame to make the strip straight;
② The speed hand cooperates with the lower hand to try to reduce the speed of the upper rack correspondingly, and a certain tension is generated between the two racks on the upper wall, so that the strip steel “goes down the wall”.
③Once the wall occurs, the scrap steel shall be cut and processed in time, and the production shall be resumed quickly.
Broken roll
1. Causes:
①Rolling low-temperature steel: The heating temperature system is unreasonable. After heating, the billet has black marks on the water pipe or the temperature is too low, and the head of the billet is poured with descaling water. And cause the roll to break;
②Foreign matter brought in: the wrench, block, etc. left on the rolling line during maintenance or daily maintenance are brought into the rolling mill by the strip steel for rolling, resulting in partial concentration of the rolling force, resulting in roll breakage;
③Strip deviation: the operator is not careful in seasoning, causing the strip to deviate to one side of the roll, causing the roll to be broken due to excessive local load;
④Unreasonable load arrangement of the rolling mill: the unreasonable load distribution among the rolling mills makes one of the rolling mills bear too much load, which exceeds the maximum torque of the rolling mill roll and causes fracture;
⑤ Backing plate displacement of the rolling mill: during the pressing or normal rolling process, the roll is broken due to the excessive deviation of the actual rolling force on both sides caused by the displacement of the backing plate;
⑥ Roll cooling is not in place: the cooling water is not opened or the water nozzle is blocked, which leads to the fracture of the thermal stress caused by the excessive temperature or uneven temperature of the roll along the length of the roll body;
⑦The quality of the roll itself: the defects of the casting structure and heat treatment structure of the roll, which cannot meet the normal rolling conditions during use, are fractured;
⑧ Influence of the fatigue layer of the roll: After the used roll is turned, there are still fatigue cracks that expand during use, and the fracture occurs when the load is heavy;
⑨The roll is broken due to the excessive rolling force caused by the overlapping rolling of the strip steel.
2. Preventive measures:
① Strictly implement the process discipline, and there should be no luck;
②Strengthen the point inspection of equipment, especially to thoroughly inspect various production process parts before maintenance and rolling;
③ The operator must operate carefully to ensure the straightness of the material shape. To prevent the steel strip from warping or sheathing, resulting in overlapping rolling of the steel.
④ Distribute the load of each rolling mill in strict accordance with the regulations;
⑤ Understand the usage degree and wear condition of the shim iron, and replace the matching shim iron in time when there is a problem;
⑥Intensify the inspection of equipment, and timely feedback and solve problems found;
⑦ Ensure that the cooling water nozzle is not blocked, and at the same time, understand the working conditions of the rolls used in the machine to prevent the phenomenon of skewed rolls, burnt boxes, burnt rolls and roll surface cracks.
3. Processing method:
① Notify the roll to prepare the roll;
②Organize on-site handling of broken rolls, and take corresponding measures to take out the broken rolls according to the site conditions such as the location of the broken rolls, the degree of breakage, etc.;
③Find the cause of the broken roll and solve it in time to prevent the roll from breaking again.
Bad shape
1. Cause: along the rolling direction, there are wavy bending defects with ups and downs.
①The reason for side waves: According to the different parts of the wave distribution on the steel belt deck, the waves distributed on one side of the deck are called unilateral waves; the waves distributed on both sides of the deck are called bilateral waves. The elongation of the strip along the width direction is inconsistent, mainly due to the thickness difference before rolling, the roll is not leveled, the degree of wear in the direction of the roll body is inconsistent, the deviation of the strip steel and the uneven cooling of the length of the roll body are all caused. Causes of strip edge waves;
②Cause of intermediate waves: The defects distributed in the middle of the plate surface along the rolling direction are called intermediate waves. The main reason is that the convexity produced by the thermal expansion of the roll is greater than the deflection value of the roll under the action of the rolling force during the rolling process; in addition, the load distribution between the stands is unreasonable, and the load of the last stand rolling mill is too small. To some extent, it caused an intermediate wave;
③Causes of side bending: thickness difference of strip steel, temperature difference and working status of pressing screws, etc.;
④ The reason for the serpentine bend: the main reason is that the strip difference of the strip is large, the degree of control of the heating temperature and the degree of wear and levelness of the roll system of the finishing mill are all influencing factors;
⑤ Defects in the equipment, such as: deformation of the transmission shaft, loose anchor bolts, unstable frame, etc. will affect the change of the plate shape.
⑥The roll shape of the roll is bad, and the roll is conical, drum-shaped, or spindle-shaped; the rolling volume of the roll is too large, and the roll cannot be changed in time;
⑦The suppression system is unreasonable. The rear frame, especially the finished frame, has too much or too little reduction;
⑧ The roll level is not good, or the cooling temperature is uneven;
⑨ The roll shape and the plate shape are inconsistent;
⑩ Improper operation adjustment or misoperation.
2. Preventive measures:
① To ensure the leveling accuracy of the rolling mill, the operator should adjust in time to ensure the flatness of the plate shape change of the strip when the operator finds it, and ensure that the cooling water of the roll is evenly distributed;
② Reduce the rolling rhythm, increase the speed of rolling, and minimize the pure rolling time, thereby reducing the temperature rise of the rolls and ensuring uniform cooling of the rolls; reasonably adjust the temperature of each stand according to the difference between the deflection of the rolls and the thermal crown of the rolls. load distribution;
③Operators should adjust the plate shape changes in a timely and correct manner; strengthen the spot inspection of equipment, and carry out technical reforms for unreasonable places;
④Strictly implement the process discipline, and burn steel according to the heating process system;
⑤ Guarantee the grinding accuracy of the rolls, strengthen the inspection of equipment, and timely feedback and deal with existing problems;
⑥Adjust the levelness of the roll to ensure that the cooling water of the roll is evenly distributed;
⑦Appropriate original roll shape can be selected, which can reduce the influence of bad shape defects to a certain extent.
3. Processing method:
① Check the material shape of the upstream rack and adjust it carefully;
② For the rolls that are seriously worn due to the long working period of the rolls, the rolls should be replaced as soon as possible;
③ Check various influencing factors on site, analyze the causes of defects, and reasonably select work rolls with convexity and concavity according to the actual situation to ensure the quality of the roll profile.
④Optimize the reduction system, and the distribution of the reduction amount of each frame should be reasonable;
⑤The operator should carefully observe the rolling situation, control and adjust in time, and operate finely.
Can’t pull out the roller
1. Causes:
① Press down the screw and it is not in place;
② The exit guard board is not removed;
③The removal of the entrance guide is not in place;
④ The water retaining plate is not removed;
⑤The thermal expansion of the roll and the thermal expansion of the flat head of the rolling mill rolls;
⑥Insufficient hydraulic cylinder pressure;
⑦ The two connecting shafts are unbalanced, or the flat head of the roll does not match the sleeve of the connecting shaft;
⑧ The gap between the roll and the rolling mill archway is full of sundries, such as iron oxide scale, round steel for leveling, disc circle, etc.;
⑨The roll is off the way or the work roll is tilted when the roll is drawn, causing the bearing box to be stuck;
⑩ The bending cylinder is not reset. The lifting track did not go up in place
2. Preventive measures:
① Strictly implement the operation rules for changing rolls, and resolutely put an end to illegal operations;
② When new rollers are installed, oil must be applied to the copper sliding plates of each bearing box;
③ Strengthen the inspection of the connecting shaft sleeve liner to prevent falling off.
3. Take measures:
① Make sure that the hydraulic cylinder is pressed down and lifted when changing rolls so that there is a certain gap between the upper support roll and the work roll;
③The hydraulic fitter should confirm the hydraulic system of the rolling mill before changing rolls;
④ When changing rolls, set the position of the two joint shafts to the state of “two joint shafts in balance”;
⑤ The sundries in the rolling mill archway should be cleaned up in time when changing rolls or overhauling;
The loading roller cannot be loaded
1. Causes:
①The roller head is not aligned with the flat head of the connecting shaft, the two connecting shafts are parallel, or the chuck is not tightened when the roller is pulled out, resulting in the falling of the connecting shaft;
② The flat head inner liners of the upper and lower connecting shafts fell off, causing the roller heads not to be installed in place;
③The thickness of the copper plates on both sides of the bearing box is too high, the position of the bearing box fat or the copper plate is not in line with the position of the lower balance beam of the frame, and the flat head fat causes the roller to not fit in;
④ The bevel angle of the backing plate of the machine seat is not enough or the backing plate is out of position so that it cannot be installed;
⑤ The roll is not put in place, causing the roll to tilt as a whole or the roll to fall off the track, so that the bearing box can not be installed against the frame;
⑥The entrance guide is not moved out in place or the position of pressing down the screw is not high enough;
⑦Rolls of different racks cannot be mixed.
2. Preventive measures:
① When changing the roll, confirm that the position of the chuck is tightened, and at the same time, ensure that the roll head of the upper machine roll is in the same position as the flat head of the two connecting shafts;
② Check whether the flat head inner lining is normal before installing the roller;
③Guarantee the dimensional accuracy and process requirements of the bearing box, flat head and inner lining of the archway;
④Replace the backing plates that are severely worn or cannot meet the normal use in time;
⑤ Check whether the four positioning pins under the roll bearing box are placed in place, the size of the positioning pin exceeds the standard, and whether the roll is off the road, etc.;
⑥ Confirm the various process parts when loading the roll, and determine the lifting height of the pressing screw according to the different roll diameters of the loaded roll;
⑦Execution of strict process discipline, install the machine according to the order of roller matching.
3. Treatment measures:
According to the on-site situation analysis and elimination of influencing factors, check whether there are obvious traces of friction on the copper slide plate and flat head of each bearing box, and then grind or replace another new roll immediately.
Pull steel
1. Causes:
① The unreasonable speed distribution between the racks leads to a large extension in the width direction of the strip, which makes the strip narrow;
② When the specification is changed, the adjustment operation is not timely, the speed and the pressing are inconsistent or misoperation, etc.;
③During the rolling process, when the material is biased or the wall is on the wall, the steel drawing caused by reducing the speed of the rolling mill is adopted;
④The setting of speed ratio, hysteresis setting of the unit and the tension and angle setting of the looper setting are unreasonable;
⑤ Steel drawing caused by equipment reasons, such as: looper failure, sudden reduction in rolling mill speed, etc.
2. Preventive measures:
① The parameters of the operating procedures must be memorized, and the load and speed of the grid rolling mill shall be reasonably distributed in strict accordance with the process system;
② When changing specifications, analyze the reduction of each frame to confirm the range of speed adjustment; when adjusting, notify each other and cooperate consistently;
③Strengthen the spot inspection of equipment and carefully operate to ensure the normal operation of the equipment;
④ Set various parameters according to the regulations.
3. Treatment measures:
The measurer should be notified in time to change the specification, wait for judgment or downgrade. For the head tension steel, the core can be pulled to minimize the loss.
Roll gap movement
1. Causes:
①Automatic magnetic scale problem, the reading is not accurate;
② There is a problem with the clutches on both sides of the pressed motor, the separation and separation are not flexible or the gap is large;
③The brakes of the pressing system on both sides are loose;
④ There is a problem with the brush of the vertical roller clutch;
⑤ The hydraulic pressure on both sides is unbalanced, causing the roll to tilt;
⑥ The bearing box of the upper support roll or the upper work roll is fat, causing certain jamming.
2. Preventive measures:
①Intensify inspections, communicate with automation personnel, and solve problems in a timely manner; ②Replace severely worn parts in a timely manner;
③Communicate with the fitter, and solve it in time when overhauling or changing rolls;
④Ensure the machining accuracy of the bearing housing.
3. Processing method:
① When the roll gap is found to be out of position, it must be confirmed first, and the material shape should be observed to see whether the data displayed by the computer is true;
② If there is a problem, stop the rolling as soon as possible, and contact the automation personnel at the same time to troubleshoot the fault.
Roll injury
1. Causes:
① The impact of the fish head and tongue tail of the steel strip on the low-temperature irregular shape of the roll will produce certain roll marks on the roll surface;
② The unreasonable position of the upper and lower guard plates causes excessive wear on the rolls, resulting in damage to the strip loading rolls in the longitudinal middle of the strip;
③Under the alternating stress and thermal stress, the expansion of micro-cracks on the roll surface causes the roll surface to partially fall off;
④ Roll damage caused by periodic changes in the transverse direction of the strip caused by longitudinal and transverse textures or meat loss on the roll surface due to poor cooling of the roll body during use;
⑤ The damage to the roll surface caused by the disc circle or iron bar pressed in during the leveling process causes the roll damage of the strip steel on the length of the pass bar, and the damage to the roll caused by the introduction of foreign matter during the rolling process;
⑥ The collision of the rolls during the hoisting process, and the scratches on the surface of the work rolls by the support rolls or the bearing boxes due to the failure of the roll changer to confirm the position of the rolls when the work rolls are installed, resulting in scratches on the surface of the strip steel Periodic transverse roll damage occurs on the surface;
⑦ There are defects in the back-up rolls, and roll damage caused by uneven wear on the work rolls during the rolling process;
⑧ Damage to the surface of the feed roller, free roller or pinch roller caused by some uncertain factors during maintenance or routine maintenance, and scratches on the strip by some dead rollers on the roller table;
⑨There are quality defects in the roller itself, such as trachoma defects in the casting process.
2. Preventive measures:
① Cut the head and tail of the low-temperature irregular head and tail of the strip;
② Ensure that the angles of the copper tips of the upper and lower guard plates are correct, and that they are in good contact with the roller surface, and that the tightness of the guard plate installation should be appropriate; excessively worn and worn out copper tips should be replaced in time;
③ When the roll is turned, the fatigue crack layer should be turned off as much as possible;
④ Turn off the cooling water of the rolls in time when parking to avoid fried lines on the rolls; ensure that the cooling water of the rolls is uniform during normal rolling;
⑤ When leveling and pressing into the disc or round steel, the amount of reduction should not be too large, otherwise groove marks will be pressed on the roll. In addition, under the condition of other normal conditions, the end must be adjusted before changing the roll and after leveling. Check the roll surface of the rack to see if there are any defects;
⑥ When installing the work roll, be sure to confirm the position of the upper support roll and the bearing box to avoid scratching and scratching the work roll;
⑦ Pay attention to the protection of the feed roller, free roller and pinch roller on the roller table during inspection and daily maintenance. Avoid some things such as: dripping of welding bump, damage of gas cutting, etc.;
⑧Guarantee the quality of new rolls, and reject or feedback the defective rolls.
3. Processing method:
① After the measuring worker discovers the roll damage, he should notify the operation desk in time.
② For roll damage beyond the standard range, measures to stop rolling should be taken immediately, and the roll damage should be checked one by one according to the characteristics of the form and cycle of the roll damage, and it should be replaced immediately after detection.
