Analysis and Control of Collapsing Defects of Hot Rolled Wide Strip

Aiming at the problem of collapse defects in the production of some varieties and specifications in the 1500mm hot-rolled broadband production line, the coiling tension, strip section shape, coiling temperature, reel expansion and contraction, auxiliary coil spoke and spoke gap setting are analyzed. The impact, and put forward the corresponding control measures, and achieved good results. Key words: hot-rolled wide strip; collapse; coiling tension; torque; control measures

the 1500mm hot-rolled strip steel production line adopts 2 underground horizontal coilers, and is equipped with hydraulic step control function to assist coiling. The steel strip is wound into a coil by the reel. After the steel coil is moved out of the reel by the coil unloading trolley, if the entire coil gradually collapses and takes on an elliptical shape, it is called a collapsed coil or a flat coil. Such a steel coil cannot be opened normally, which affects the finished product. Rate and user use In production, collapsed coils are concentrated in steel types with high Mn alloy content and thin specifications ( A< 6.0mm) , such as low-alloy high-strength steel ( Q345B , Q345D, etc.), automobile frame steel ( LG510L , LG610L) , oil casing ( J55) , container board (SPA-H) , etc. In addition, the proportion of flat rolls of checkered plates is also higher. See Table 1 for statistics on the flat coil quantity of this production line in 2007 .

Table 1 Field measured value and temperature model calculated value of finish rolling temperature °C

serial number	1	2	3	4	5	6	7	8	9	10
On-site measurement	917	911.5 _	911. 3	915	901.2	890	901. 3	917. 8	917.5 _	916.5 _
Calculated value of temperature model	900. 1	880.4	890.6 _	900.7	880.6	878.8	881.8	893.4	880.3	883. 1
Calculated value of temperature model after optimization	910.5 _	915.1 _	905.6 _	906.9 _	895.9	989. 1	910.1 _	911.7	912. 3	915. 2

2 Analysis and Control
There are many factors that affect the coil shape. In addition to the quality of the strip itself (such as convexity, wedge shape, camber, thickness deviation, etc.), layer cooling temperature, coil

Volume 27 • Issue 4
The radial stress inside the steel coil is too small, which can easily lead to slippage between layers and cause collapse.
Therefore, a reasonable coiling tension should be selected. The tension setting values of low-alloy high-strength steels of different specifications are shown in Table 2. The tension setting values are generally increased by 20 ~ 30kN on the basis of ordinary carbon steel . In addition, a "tension correction" function button is added to the HMI screen, and the tension correction range is ± 20kN . On the basis of the coiling tension set by the secondary control system, the operator is allowed to adjust it according to the actual coil shape, and the tension can be increased appropriately when a flat coil occurs.
Table 2 Low-alloy high-strength steel coiling tension setting value

Strip thickness /nun	Tension /kN
	b> 1270mm	1050mmV6 W1270mm	wxya 1050mm
	Fo — 10	F. _	F 0 + 10
A>12.0	F. _	F° + 10	Fo+20
6. 0<A<12. 0	Fo + 10	Fo+20	Fo + 30
Note 4 is strip width ; F. is the tension reference value.

2.2 The shape of strip section is abnormal or the wedge shape is too large
The cross-sectional shape of the strip steel has a great influence on the coil shape. If the wedge shape of the strip steel is too large, although the side of the steel coil is relatively neat under the action of the side guide plate, due to the large deviation of the transverse thickness of the strip steel, the density at both ends of the steel coil is obviously inconsistent. . Under the pressure of the side guide plate and the pinch spoke, the strip steel still enters the reel in a relatively straight direction. Although both sides of the coil are flat, the thicker side of the coil is compact, and the thinner side has obvious gaps, and the side with larger gaps is prone to collapse after unloading.
The flat coil caused by the abnormal shape of the cross-section of the strip or the excessive wedge shape has obvious inconsistency in the short axis of the coil core on both sides , that is, the degree of flat coil at both ends is obviously uneven. For this kind of flat coil, the curve displayed on the shape meter should be compared to the wedge shape of the strip steel, and the steel rolling worker should be notified in time to adjust the unilateral. If the ability of manual adjustment and correction is insufficient, it is necessary to stop the rolling in time for inspection and treatment, and conduct a comprehensive inspection of the wear of the spokes, the lateral movement device of the spokes, and the cooling water nozzles of the spokes until the wedge is eliminated.
2.3 Influence of layer cold temperature
During the rolling process, the steel strip is in the high temperature deformation stage. At high temperature, due to the phase transformation process, factors such as the volume fraction of ferrite affect the deformation resistance very obviously, and the relationship between the deformation resistance and the deformation temperature is more complicated, and it does not simply decrease with the increase of the deformation temperature. Fluctuations appear around the phase transition point. In order to ensure the performance of hot-rolled wide-band steel, laminar flow cooling is usually used to control the coiling temperature, and the general control is 400 ~ 8009 . Coiling in this temperature range, the transformation from austenite to ferrite has been completed, and the influence of phase transformation on the deformation resistance has disappeared, so the relationship between deformation resistance and temperature is simpler and clearer at higher temperatures, and the deformation resistance increases with the coiling temperature. increases and decreases monotonically. This is because as the coiling temperature increases, the thermal vibration of metal atoms intensifies and the deformation resistance decreases.
For thinner specification (A<6.0mm) low-alloy high-strength steel, if there is still a slight flat coil after increasing the coiling tension, the interlayer cooling temperature can be appropriately reduced to increase the strength of the strip steel and increase the extrusion resistance of the coil core, thereby Effectively avoid flat rolls. However, the lower the layer cooling temperature and the greater the deformation resistance, the greater the clamping force required by the coiling side guide plate on the strip. Therefore, while reducing the layer cooling temperature, in order to ensure a neat coil shape and a good layer, it is necessary to adjust coiling parameters such as coiling tension, side guide plate pressure, and pinch spoke pressure. The side guide controls have been optimized also.

2.4 Slip between the reel and the strip
2. 4.1 The expansion and contraction system of the reel is abnormal
The reel of this production line adopts the structure of quadrangular pyramid column pin and connecting rod. The expansion and contraction cylinder pulls the cone mandrel, and the quadrangular cone surface on the cone mandrel pushes the pin along the hole of the hollow shaft to push the fan-shaped plate outwards, so that the reel expands. If the fan-shaped plate is loose or the pressure release causes abnormal expansion and contraction of the reel, the strip steel is prone to slipping during coiling, and when it is serious, it will lose its expansion. .
To this end, equipment spot inspection and maintenance should be strengthened, the reel replacement system should be standardized, and the surface quality, wear condition, and expansion and contraction of the reel should be inspected, and any abnormality should be replaced in time. In addition, the diameter of the reel needs to be calibrated regularly, and the size of the reel in the shrinking diameter, initial expansion, and final expansion state of the reel should be measured with a steel wire or an outer diameter micrometer, and the recorded card value should be corrected in time to avoid the deviation caused by the deviation of the reel diameter. The calculation error of coil diameter will affect the output of coil tension and the quality of coil shape.
2. 4.2 The spoke gap between the helper spoke and the reel is unreasonable
d between the auxiliary coiling spoke and the reel is adjustable, and the size of d directly affects the coiling quality. If the value of d is too large, the steel coil is not easy to be wound tightly, and it is easy to slip in the first few turns; if the value of d is too small, there will be impact when the strip bites in, causing the auxiliary coil to jump, and the steel coil is also not easy to be wound tightly, or even slipped. Usually, the value of the spoke gap d is set by the computer according to the thickness of the strip steel, its material and the pressure of the auxiliary spoke . At the same time, the radial seam of the auxiliary coil should be calibrated regularly to eliminate the deviation caused by the looseness of the fan plate of the drum in time.
2.5 Checkered plate diameter compensation
The coiler tension control adopts the maximum torque control method. In the case that the tension cannot be directly detected, in order to accurately control the coiling tension, the torque of the coiler motor must be accurately controlled:
M m = D a /2XT/ a
In the formula, D . is the outer diameter of the coil; D is the coil tension; a is the gear ratio.
It can be seen from the above formula that the winding diameter is directly proportional to the torque of the coiler, and the calculation accuracy of the winding diameter determines the accuracy of the tension given value. rolling flower
For corrugated plates, the calculation of the coil diameter in the coiling tension control system is based on the thickness of the substrate. The calculated coil diameter is smaller than the actual coil diameter, and the torque output value is also relatively small. Especially for thin-gauge checkered plates, the proportion of the pattern to the entire plate thickness If it is higher than the thick gauge checkered plate, the calculation deviation of the coil diameter is greater, and flat coils are more likely to occur.
For this reason, the coil diameter of the checkered plate should be tracked and measured, and the checkered plate with the same blank shape and the same substrate thickness should be statistically compared with the ordinary flat plate to calculate the coil diameter compensation coefficient of the checkered plate. In the program control, calculate the coil diameter of the checkered plate on the basis of the flat plate and multiply the coefficient kCL. 10~ 1. 15) .
2.6 Lifting and stacking management of steel coils
In the process of hoisting or stacking, if the steel coil is violently impacted or injured, it will cause a flat coil. For steel coils with loose cores, after being severely squeezed in stacking management, flat coils will be formed.
Therefore, for the finished product specification 0mm coil off-line
When stacking, the continuous stacking shall not exceed 2 layers. 24 hours behind the line
The temperature model is combined with the genetic algorithm to optimize it, and the calculation results of the strip temperature curve are shown in Figure 3 . It can be seen from Figure 3 that the temperature change of the strip steel from the exit of rough rolling to the end of finish rolling. Table 1 shows the comparison of the measured values of the strip finish rolling temperature, the calculated values of the finite difference temperature model, and the calculated values after the optimization of the model. It can be seen from Table 1 that after using the genetic algorithm to optimize the model, the calculated temperature of the strip steel is closer to the actual measured value, and the calculation accuracy is within 10t .
epilogue
Combining the characteristics of flat coils and the status of on-site process equipment, the causes of flat coils were analyzed, and corresponding control measures were proposed, so that the defects of flat coils were effectively controlled, the quality of coil shape was greatly improved, and the competitiveness of products was improved. .

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