Analysis and Improvement of Scratches on 1750 mm Hot Continuously Rolled Strip
[Abstract] The causes of strip scratches caused by hot rolling equipment are expounded. The strip scratch defect caused by the upper guide plate of the coiler is analyzed, and the problem of scratches on the strip surface is found because the upper guide plate part is worn and its position is lower than the design position and contacts the strip. Renovate the equipment for the corresponding problems, solve the problem of scratches on the upper surface of the strip, and improve the product quality and yield.
Key words hot continuous rolling scratch coiler upper guide plate modification
- foreword
Scratches in hot strip are a common product defect in the production process . After the steel strip is scratched, after the quality inspection process detects it, the production unit must downgrade the product for sale, or even reduce it to scrap or cut off part of the scratched steel strip, seriously affecting the company's economic benefits or delaying the delivery of orders, resulting in damage to the reputation . What's more serious is that if the scratch defect is not found in the quality inspection process, and it flows into the market, it will cause product defects in the next process, such as flattening and cold-rolling raw materials. impact . Therefore, the management and control of scratches has always been an important task of each hot rolling production unit .
- Scratch cause analysis and phenomenon
There are many factors that cause scratches on the surface of the strip steel, all of which are caused by equipment in contact with the strip steel . During the production process, the equipment in contact with the strip includes finishing work rolls , loopers , transition plates between finishing stands and exit , coiler upper and lower pinch rolls , layer cooling roller table , coiler inlet upper and lower guide plates , coil Take-up auxiliary roll and arc guide plate , roll unloading trolley roller, etc. The phenomenon of strip scratches caused by different equipment is different .
Generally, the transition plate between the finishing stands and the exit , the layer cooling roller table , the upper and lower pinch rollers for coiling , and the idler rollers for unloading trolley are the main causes of strip scratches, and they are easy to find and deal with . Strip scratches caused by the upper guide plate at the coiling entrance are not easy to find and solve, and it is difficult to deal with them .
The finished steel strip is coiled for transportation and storage . During the coiling process, it maintains a constant tension coiling with the pinch roller to ensure the coiling quality of the strip . By pinch roller , rack mount , 1 # Rolling arm and roller , 2 # Rolling arm and roller , 3 # rolling arm and roller , main transmission box , outer support , transmission device and reel device etc. The design parameters are as follows:
Coiled strip width: 730 mm ~ 1 600 mm Coiled strip thickness: 1.2 mm ~ 16 mm Unit coil weight (maximum): 21 kg/mm
Coil weight (maximum): 30.4 t
Steel coil outer diameter: ① 1 100 mm ~ O 2 030 mm Steel coil inner diameter: ~ Q 762 mm
Coiling temperature: 350 °C~850 °C Minimum coiling cycle: 80 s Coiling speed: Max.~20 m/s Tape threading speed: Max.~11 m/s Unit coiling tension: Max. 15 N/ mm2 _
from Figure 1 that the upper guide plate at the entrance of the coiler is in the position of the pinch roller
The rear part acts as a guide for the strip, so that the head of the steel coil smoothly passes through this channel and enters the coiling space composed of 3 coil-assisting rollers and arc-shaped guide plates for coiling . The upper guide plate , the roll-assisting arm and the connecting rod form a relatively complex linkage mechanism. The servo hydraulic cylinder drives the roll-assisting arm to move, so that the
The upper guide plate connected by the connecting rod moves accordingly, keeping 1 # at any time The winding-assisting roller moves in unison with the upper guide plate, avoiding steel stacking accidents caused by poor biting position of the strip head . The movement trajectory of the upper guide plate is determined by the size from the hinge point of the upper guide plate to the connection point of the connecting rod , the size from the hinge point of the rolling arm to the connection point of the connecting rod, and the size of the connecting rod. The three dimensions are related to each other. Biting in, but also to ensure that the upper guide plate does not touch the strip .
In April 2008 , when the tail pressure control was adopted, when rolling coils with a diameter of 1880 mm and above, non-periodic and intermittent scratches appeared on the upper surface, and there was no problem with small-diameter steel coils . Through the uncoiling inspection of the leveling unit, it was found that it only appeared in a few turns at the end .
4 Transformation of the guide plate on the coiler
According to the analysis of the above reasons, it can be solved by increasing the height of the upper guide plate and reserving the amount of wear . There are two ways to increase the height of the guide plate, which are introduced and compared as follows .
- the size of the distance L1 between the hinge point of the upper guide plate and the connecting point of the connecting rod and the distance L2 between the connecting point of the connecting rod and the hinge point of the rolling arm . It can be concluded from Figure 1 that the original design L1 = l 032 mm, L2 = 297 mm, and the hinge point of the upper guide plate to the connection point of the connecting rod and the rolling arm L3 = 1 330 mm, that is, when the rolling arm is opened to the limit position , the hinge point of the upper guide plate and the three points connecting the two ends of the connecting rod are basically in a straight line. If the size of L1 or L2 is changed separately, it will cause internal force when the roll-assisting arm hits the limit position, which will damage the connection of the equipment, which will intensify over time. wear at the connection points . Therefore, only by making L1+L2 three L3 can a balance be achieved . Use the diagram method shown in Figure 2 to analyze, and get the change L4 of the upper guide plate when L2=297 mm as the benchmark, see Table 1 .
Table 1
L1 |
L2 |
Coil diameter |
L4 |
|
|
1 |
1180 mm |
150 mm |
① 1 880mm |
+39mm |
|
2 |
1033 mm |
297 mm |
① 1 880 mm |
0mm |
|
3 |
930mm _ |
400 mm |
① 1 880mm |
-22.7mm |
from Table 1 that shortening the size of the connecting rod L2 can improve the position of the upper guide plate . The disadvantage is that when the roll-assist arm is fully opened to ①2250mm , the hinge point of the upper guide plate and the connection points at both ends of the connecting rod are basically on a straight line, and L4 is zero . It can be concluded that changing the size of L1 and L2 can increase the position of the upper guide plate, but as the diameter of the steel coil increases, the distance between the upper guide plate and the surface of the steel coil will gradually decrease, and because the coiling equipment is concentrated, the space is narrow , the size of changes L1 and L2 will be limited .
- L5 from the connecting point of the upper guide plate and the connecting rod to the upper guide plate . See Table 2 .
|
|
table 2 |
/mm |
|||
|
serial number |
L5 |
L1 |
L2 |
Coil diameter |
L6 |
|
1 |
228 |
1 032 |
298.1 |
① 1 880 |
+37.5 |
|
2 |
238 |
1 033 |
297 |
① 1 880 |
+26.6 |
|
3 |
228 |
1 032 |
298.2 |
① 2 250 |
+18.9 |
|
4 |
238 |
1 033 |
297 |
①2 250 |
+6.9 |
From Table 2 , it can be concluded that the vertical distance L5 from the connection point of the connecting rod to the upper guide plate is reduced from 238 mm to 228 mm , and when the diameter of the steel coil is 0.1880 mm , the distance L6 from the upper guide plate to the outer ring of the steel coil increases from 26.6 mm to 37.5 mm , the difference is 10.9 mm . Increased by 41% ; L5 decreased from 238 mm to 228 mm , and when the coil diameter was ①2250 mm , L6 increased from 6.9 mm to 18.9 mm , with a difference of 12 mm , an increase of 174% . It can be concluded that changing the vertical distance from the connection point of the connecting rod to the upper guide plate can not only increase the distance from the upper guide plate to the surface of the steel coil, but also increase the distance gradually with the increase of the size of the steel coil, and the effect is better .
5 Conclusion
- Through the above comparison, it can be concluded that changing the vertical distance from the connection point of the connecting rod to the upper guide plate to 228mm has a better effect. During transformation, at the same time, it is necessary to repair the part where the upper guide plate is raised and interferes with other equipment .
5,2 After the problem of the upper guide plate is solved, the previous scratches on the 9.75 mm thick strip steel, resulting in 50,000 tons of secondary products, a price reduction of 100 yuan per ton , and an economic loss of 5 million yuan in quality accidents will not occur .
-
- The finish rolling work rolls and the upper and lower pinch rolls of the coiler may be scratched on the upper or lower roll surface due to the tail of the strip steel or foreign objects during the rolling process, resulting in periodic scratches or scratches on the upper or lower surface of the subsequent strip steel. Continuous scratches .
- Scratches on the strips due to their own defects in the looper , the transition plate between the finishing stands and the exit , the layer cooling roller table , and the lower guide plate at the entrance of the coiler only appear on the lower surface of the strip .
- The upper guide plate at the entrance of the coiler , the winding auxiliary roller and the arc guide plate , and the idler roller of the unloading trolley will cause scratches on the upper surface of the strip . However, due to process control, the rollers of the unloading trolley will only cause scratches on the upper surface of the second half of the strip, because before coiling, the unloading trolley stops at the start and stop position on the side of the coiler and does not contact the strip. After the strip bites in and the 2 # assisting coil arm returns to the maximum opening position, the idler roller of the unloading trolley rises to the coil unloading waiting position (decided to stop at a high or low position according to the size of the steel coil). When the coiling is close to the end, When the coiler decelerates and coils, the idler roller of the unloading trolley rises slowly at a low pressure, supports the steel coil, and descends with the increase of the diameter of the steel coil. At this time, the idler roller contacts the steel coil and scratches occur . Therefore, according to the above strip scratch locations and phenomena, the cause of the scratch can be quickly analyzed and processed to avoid large-scale quality accidents .
- 3 Analysis of scratches on the guide plate on the coiler
- Coiler Configuration and Parameters The full hydraulic three-assist roll down coiler is for cooling to the coiling temperature
- Principle of upper guide plate mechanism
- Control Principle In order to make the tape tail tight and neat, the coiler can have two control modes for selection .
- Take advantage of 1 # Help roll or 1 # and 3 # The winding-assisting roller performs tail pressing control at the same time . When the roll-up roll is opened after the strip is wound on the reel for a few turns, the selected roll-up roll, such as 1 # The auxiliary winding roller opens to the tail pressing waiting position (the gap between the set value of the outer diameter of the steel coil at the end of coiling + 50 mm ) and waits for the tail pressing start command (when the tape tail is close to the pinch roller); the auxiliary winding that has not been selected for tail pressing Roller opens to limit position . When the tail pressing start command is issued, the selected tail pressing roll is closed, and the pressure control is carried out according to the set tail pressing pressure after detecting that it touches the strip steel; The roll end pressure control is opened to the limit position .
- When coiling steel with high strength and thick specifications, the whole process of pressing is adopted . Full pressure only for 1 # The helper roller is effective . 1 # When the roll-assisting roller is under the full-range pressing control, it does not participate in the tail pressing control . If the full-range pressing control is effective, when the strip is wound on the reel for a few rolls and the auxiliary roll is opened, 1 # The auxiliary winding roller does not open, but carries out pressure control according to the set value of the tail pressure, until the controller issues a command to start unloading, and opens to the limit position .
- Scratch phenomenon
- Cause Analysis
- In view of this phenomenon, the reasons caused by equipment such as finishing work rolls , finishing stands and exit transition plates , loopers , layer cooling roller tables , and coiling pinch rollers can be ruled out . It may be caused by the upper guide plate of the coiler , the 1 # auxiliary winding roller , and the idler roller of the unloading trolley . After replacing the winding auxiliary roller and the supporting roller of the unloading trolley, the scratch has not been resolved, so it can be judged that it is caused by the guide plate on the coiler .
- According to the mechanism principle and control principle of the upper guide plate, 1 # When the winding-assisting roller is under the tail-pressing control, it will press against the strip steel after the coiling control system issues a command. Due to the swing of the winding-assisting arm, the upper guide plate will follow the movement through the connecting rod, and the position will be lowered accordingly . At this time, due to the wear of the connecting pin shaft and copper sleeve of the upper guide plate, the increase in the gap and the deviation of equipment processing accuracy, etc., the position of the upper guide plate is lower than the design position and contacts the strip steel, causing scratches on the strip steel .
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