The production line equipment of the No. 1 Wire Rod Plant of Shougang Group. is imitating the design of the fifth-generation Morgan rolling mill and produced by domestic manufacturers. The maximum stable rolling speed of this production line is 88m/s. The whole line consists of 28 rolling mills, including 14 roughing and intermediate rolling mills, 4 pre-finishing mills, which are alternately arranged horizontally and vertically, and the 10 finishing mills are arranged at 45° at the top. Feed roll and laying machine. The product specification is φ5.5—φ16mm, the specification span is large, and the variety of production is wide. Judging from the current production situation, the steel stacking accident rate of small-sized wire rod products below φ6.5mm (including 6.5mm) is much higher than that of other specifications due to the fast rolling speed and small section size. According to the classification of different rolling areas, this paper introduces the causes and solutions.
Cause analysis and measures of steel stacking
1.Rough and medium rolling area (1-14 stand)
1.1 The rolled piece cannot be smoothly bited into the next pass, resulting in piled steel
The main reasons for such accidents are:
- The front of the rolled piece is tilted after coming out from the last pass.
- The rear end of the last one is poured to raise the exit guide.
- Inappropriate adjustment of the opening of the import guide.
- The guide and the pass are not aligned (the rolling line is not correct).
- The slot slips.
- The size of the rolled piece does not meet the process requirements.
- The front head is split due to the billet.
- For the warped head of the rolling piece, it is necessary to check the diameter and wear of the upper and lower rolls, the gap at the connection of the transmission parts, and the consistency of the import and export guides.
- Reasonably adjust the opening of the inlet guide and the distance between it and the roller.
- If the setting of the roll gap for the new slotted hole is too small, make appropriate adjustments to the roll gap of the rolling mill or re-grind the slotted hole.
- Make appropriate adjustments to the roll gap of the rolling mill.
- Check the blank carefully, lengthen the length of the front end with 1# shear.
1.2 tacked steel between the stands after the rolling stock bites
- Incorrect setting of parameters such as rolling speed and roll diameter caused by man-made reasons.
- The adjustment of the stack-pull relationship after changing the roller or slot is not appropriate.
- The billet temperature fluctuates too much.
- The speed of a rolling mill is suddenly increased or decreased due to electronic control.
- The operator of the main console adjusts the wrong number of revolutions or sorties when adjusting the speed of the rolling mill.
- Correctly set the rolling speed, roll diameter, and reasonably adjust the stack-pull relationship between the rolling mills. Do a good job of confirmation between the two.
- Notify the heating furnace to adjust the fire, and at the same time keep warm and wait for rolling.
- Professional electrical inspection, reverse the spare cabinet.
1.3 Tail stacking of steel after rolling
The main reason is that at the upstream stand, when the rolling stock pulls the steel, when the rear tail is separated from the upstream stand, the steel is stacked on the downstream stand.
Treatment measures: Reasonably adjust the stack-pull relationship and the size of the rolling mill.
2. Pre-finishing area (15-18 stands)
2.1 stacking steel between racks
- The parameters such as roll gap, roll diameter and rolling speed are set incorrectly.
- The installation of the guide is not suitable.
- The guide strikes iron.
- Coarse-medium rolling and drawing steel cause the rolled piece to be left behind in the pre-finishing rolling.
- The rotation speed of a rolling mill is abnormal due to the reasons of electric control.
- Recheck the setting parameters.
- Check, replace or adjust the import and export guides.
- Adjust the height of the inner looper in the pre-finishing rolling and strengthen the inspection.
- Reasonably adjust the stack-pull relationship of the continuous rolling mill.
- Electrical professional inspection and at the same time turn down the spare cabinet.
2.2 Pre-finishing a certain sort of jump
- Pre-finishing cooling water pressure and lubrication system failure.
- The motor trips.
- The role of the accident detection system.
- Check the cooling water pressure and the control water valve beside the machine.
- Professional equipment inspection and lubrication system.
- Check whether the pre-finished fishing line pendant is fastened, and check its proximity switch at the same time.
3. High speed area (finishing mill to laying head)
3.1 Steel stacking between stands in the finishing mill
- The guide wheel does not rotate or the bearing burns.
- The rolling piece is split.
- The guide or the roller ring is wrongly installed.
- Improper setting of roll gap or inappropriate size of incoming material.
- The roller ring is broken.
- The breaking of the fishing line will cause the rolling line to break automatically.
- Replace the guide guard, and at the same time strengthen the correctness of the guide guard installation.
- Strengthen the blank inspection and lengthen the length of the cutting head.
- Recheck and adjust the roll gap.
- Replace the roller ring and check the cooling water pipe at the same time.
- Check the proximity switch at the fishing line pendant, and check whether there is scrap steel at the guide in the finishing mill. If there is, it means that the front and rear tails are stacking steel in the finishing mill, and reset the roll gap in the finishing mill.
3.2 Steel stacking at the scrap box of the finishing mill
There are two cases, one is stacking steel without spinning, and the other is stacking steel after spinning several turns.
The main reasons are:
- The cooling water in the water cooling section cannot be closed normally or opened too early.
- There are foreign objects in the water cooling section.
- The installation of the water-cooled guide groove is dislocated.
- The water valve of the first water-cooling box after the finishing mill is too open or the water pressure is too large.
- The speed matching between the finishing mill, pinch roll and laying machine is not good.
- The electric control professional inspects the water valve control system and manually tests the water, and the main console adjusts the opening delay.
- Check whether the water-cooling nozzle and guide groove are installed correctly and whether there is looseness, and at the same time check whether there are foreign objects, and use a φ13mm round steel to pass through the water-cooling section.
- Check the speed matching between the three.
- The specifications of the water-cooled nozzles and guide grooves can be enlarged, such as replacing φ12mm with φ16mm.
3.3 Steel stacking at the pinch roll laying head
- The inlet and outlet conduits of the pinch rollers are not installed correctly, are severely worn or have foreign objects in the conduits.
- The detection signal before the pinch roller fails, so that the pinch roller cannot be opened/closed on time.
- The spinning tube is seriously worn.
- The setting of the delay time of the clip tail is too short, causing the tail to be lost.
- Speed mismatch between finishing mill and laying machine.
- Internal quality defects of wire rods (smelting defects) or rolling defects (severe folds or ears) cause piled steel.
- Check and replace the inlet and outlet conduits.
- Electrical professional inspection and detection signal.
- Replace the laying tube.
- Extend the delay time of the clip tail.
- Reasonably set the speed matching between the finishing mill and the laying machine.
4. Steel stacking at flying shears
- The shearing speed of the flying shear does not match the speed of the upstream rolling mill, and there is a bend in the front and back of the cutting, resulting in piled steel.
- The length of the tail after flying shearing is too short, so that the tail is not completely cut off and brought into the next rolling mill.
- The shearing blade and switch are seriously worn, resulting in incorrect shearing position.
- The flying shears malfunction in the middle, and the shearing is out of control.
- Reset the lead coefficient of the flying shear.
- Adjust the length of the cutting head and tail.
- Check the front guide groove of the cutting edge and flying shear.
- Check the photocell and thermal detection signal.
5. Steel stacking at looper
- The looper delay setting is incorrect.
- The height setting of the looper is inappropriate.
- The lifting roller, guide roller or guide plate of the looper is seriously worn.
- Looper scanner failure.
- The front thermal detection signal is blocked.
- Excessive water mist or sunlight will affect the inspection effect.
- Reset or adjust parameters.
- Replace the process spare parts, or repair the guide plate.
- Replace the looper scanner and re-adjust the zero position.
- Add a fog blower in the place where the water mist is large, and add a shielding plate at a suitable angle for sunlight exposure.
In the production process, when a steel stacking accident occurs, due to the limitation of time and indicators, it is necessary to quickly and accurately find the cause. This requires a comprehensive consideration of the accident that occurred, and a multi-faceted search for the cause. In this way, the processing time can be shortened and repeated accidents can be avoided. It is also required that the on-site operators continuously and regularly check the size of the rolling stock, the stacking relationship of the rolling mill, and the guide and guard conditions in daily production, so as to better reduce the frequency of accidents.