Surface Defects and Control Measures of Hot Plate Coil

Abstract : Aiming at the common main surface quality defects in the hot coil rolling process of Hebei Jingye Group , the causes of pitting , mechanical damage , indentation , bulging , plate shape defects , folds , and coil shape defects were analyzed in detail , and proposed The control measures are instructive for improving the surface quality of hot plate coils and reducing the loss of waste products.

Key words : hot coil ; surface defect ; control ; measure
CLC number: TG335.5 Document identification code: B Article number: 1006 -5008 ( 2012 ) 05 -0039 -03

Hot-rolled steel strip is also called hot-rolled steel strip , hot plate , and hot-rolled coil . It generally refers to a steel plate with a width of M 600 mm and a thickness of 0.35 to 200 mm or a steel strip with a thickness of 1.2 to 25 mm . The hot-rolled steel plate has low hardness, easy processing and good ductility . This paper analyzes the rolling defects of Hebei Jingye Group's hot coil plate , and puts forward corresponding solutions .

1. Type of defect

The main quality defects of hot coiled boards are : pockmarked surface , contusion , indentation , scratch , hemming , folding , tower shape , wave shape , etc.

1. Causes and control measures

3.1 Hemp noodles

1. Cause

The pitted surface is brown and short in shape , which is pressed in by iron oxide . On-site tracking found that pockmarks mainly occurred on the lower surface of the strip , and the occurrence of pockmarks was related to improper roll change and cooling water consumption .

1. control measures
2. To establish a normal roll change system , hot roll materials should be used after new rolls are replaced , and materials with too high hardness should not be rolled . while ensuring the establishment of

Date received: 2012 -03 -16
About the author: Yang Haixi ( 1972 - ), male , senior engineer , graduated from Shanghai University majoring in iron and steel metallurgy in 2001 , and is now engaged in metallurgical melt, heat transfer and
Numerical simulation of mass transfer process, etc., E -mail : [email protected] Suitable thin finish roll layer oxide film , when starting to roll the first 5 plates, the roll cooling water of the first three stands should be fully opened , the water volume is 100% , the cooling water should be turned on to 80% when rolling the 5th to 20th strip , and then turned to 100% after the 20th strip to prevent further thickening of the oxide film on the roll layer .

1. The cooling water between the racks of the first three racks should be turned on as much as possible .
2. After the rolls of the first three stands of finishing rolling were replaced with high-speed rolls , the problem of pitting was greatly reduced .

3.2 Mechanical damage
3. 2. 1 Reasons for formation
Due to the friction between the rolling piece and the mechanical equipment parts , the length , width and depth of the defect are different , mainly appearing along the rolling direction or perpendicular to the rolling direction , some are slightly flattened , and the damage may contain oxidation Iron sheet or exposed inner metal .
Longitudinal defects are produced when the strip is conveyed by the roller table or during coiling and uncoiling , and transverse defects are mainly produced when the strip moves laterally or unloads from the coiler . Scratches and bruises are generally caused by the relative movement between the layers of unwound steel coils . The bruises are triangular in shape and bright in color . Mild bruises are in the shape of iron nails . The bruises on the surface of the strip start from the tip of the small triangle. in the other direction and produce varying degrees of crease accumulation .
3.2.2 Control measures

1. Remove foreign matter from output roller table or replace dead rollers .
2. Adjust the hysteresis rate of the output roller table .

( 3 ) Regularly replace , repair and repair the liner of the side guide plate of the coiler to ensure the normal input of water spray on the front side of the pinch roller and prevent steel slag from entering the coil layer being coiled .
( 4 ) optimize the uncoiling and coiling speed of the tempering machine .
( 5 ) Use a reasonable opening of the side guide plate .
3 . 3 indentation 3 . 3 . 1 Causes
Indentation is a periodic concave imprint on the surface of the strip . The main reasons for the indentation are as follows .
( 1 ) The pre-pressure is too small when the rolling mill is idling , which causes the point contact between the work roll and the middle roll and wears the middle roll along the circumferential direction . The damaged middle roll in turn forms an imprint on the surface of the newly replaced work roll , resulting Indentation on steel surface .
( 2 ) The indentation on the surface of the strip is caused by the indentation on the surface of the work roll due to the meat loss of the intermediate roll .
3 . 3 . 2 control measures
( 1 ) If there is a slight small area of indentation on the surface of the strip, the work roll can be ground ( with sand and stone ), and the work roll should be replaced if there is a serious indentation .
( 2 ) Give a certain rolling pressure or use bending rolls when the rolling mill is idling to avoid local damage to the rolls. If local damage to the intermediate roll and support roll is found in time , the work roll should be replaced frequently , and the intermediate roll or support roll should be replaced if necessary. 3 . 4 drum ribs 3 . 4 . 1 Causes
The drum rib is a protrusion parallel to the edge of the strip . The main reasons for the drum rib are as follows .
( 1 ) The descaling machine has relatively serious nozzle aging , clogging and nozzle dropout , or there is abnormal contact between the equipment and the surface of the finishing work roll , which makes the local wear of the finish work roll serious .
( 2 ) Individual cooling water nozzles of the work rolls are blocked or dropped during rolling , resulting in serious local wear of the finish rolling work rolls .
( 3 ) The pinch roller or winding helper roller is seriously aged , or the roller surface is partially worn .
( 4 ) The coil convexity is too small , and the point thickness of the coil cross section is much higher than the coil convexity .
( 5 ) The wedge shape of the coil is relatively large , and the wear of the roll is too heavy , and the edge of one side is thickened .
3 . 4 . 2 control measures
( 1 ) If it is found that the cooling nozzle of the finishing work roll is blocked or dropped , it must be replaced in time .
( 2 ) Check the surface of the coiling pinch roller or winding helper roller to avoid severe aging or severe wear on the part of the roller surface .
( 3 ) Use appropriate strip shape control means to increase the crown of the strip .
( 4 ) Arrange the rolling plan reasonably , avoid mixed rolling of steel types , strictly control the production tonnage of coils , and avoid excessive wear of the rolls .
3 . 5 shape defects
3 . 5 . 1 Causes
The internal stress is unevenly distributed along the width direction of the strip , and the internal stress of the strip is not enough to resist the change of the flatness of the strip , resulting in elastic warping deformation in local areas . According to the distribution of elongation in the width direction of the strip , the reasons for the formation of plate shape defects are as follows .
( 1 ) The slab itself has defects such as camber , wedge shape, groove , longitudinal scratch , uneven temperature on both sides , etc. , which exceed the shape control ability of the rolling mill , and the rolling mill cannot adjust the shape of the slab .
( 2 ) The heating temperature of the slab is not uniform , and the temperature is not uniform due to the insertion of the cold slab .
( 3 ) The setting of crown , bending force and horizontal value of finishing rolling work roll is unreasonable .
( 4 ) The tonnage of the rolls is too high, the roll shape is bad , the PC crossing angle of the finishing rolling drifts , and the roll profile curve of the finishing rolling work rolls does not meet the requirements. 3 . 5 . 2 control measures
( 1 ) Improve the quality of slabs , and reject slabs with defects such as camber , wedge , groove , longitudinal scratches , and uneven temperature on both sides .
( 2 ) Adjust the heating system , reasonably control the holding time , and strengthen the inspection of the heating furnace burner to ensure that the burner is in good condition .
( 3 ) Reasonably arrange the rolling plan , strictly implement the rolling tonnage of the rolls , and strictly prohibit the production of over-tonnage .
( 4 ) Reasonably set the crown , bending force and level of the finish rolling work rolls .
( 5 ) Strengthen spot checks to ensure that equipment functions are put into operation stably .
3 . 6 fold
3 . 6 . 1 cause
Plate folding is a kind of wrinkle or bending , which occurs on the entire width of the strip at right angles or obliquely to the rolling direction ; edge folding occurs at the edge of the coil , mainly including edge thickening , coil There are mainly the following reasons for the folding of the edge and other forms .
( 1 ) The clamping force of the side guide plate is too large , which causes the edge of the strip to bend , and folds when it enters the pinch roller .
( 2 ) due to the free width of the head and tail of the strip steel , which is larger than the actual opening of the side guide plate , the head and tail of the strip steel will be partially warped before reaching the area of the side guide plate . When this type of groove reaches a sufficient depth , it will cause misdirection to the strip rolled in the later stage , causing the edge of the strip to warp . In severe cases, the strip will bend continuously and fold when it enters the pinch roll .
3 . 6 . 2 control measures
( 1 ) optimize the force control parameters of the guide plate , properly reduce the clamping force of the guide plate on the strip during operation , so as to reduce the wear of the guide plate .
( 2 ) optimize the replacement cycle of the side guide plate , and replace it at any time according to its wear condition , so as to avoid excessive wear of the guide plate .
( 3 ) Choose suitable repair welding materials to increase the wear resistance of the guide plate .
( 4 ) Ensure the good head and tail shape of the strip steel .
3 . 7 roll defects
3 . 7 . 1 overflow edge
( 1 ) The performance of the overflow edge is that the edge of the steel coil is partially uneven , and the main reasons for the overflow edge are: the pickling incoming material overflows the edge , the shape of the hot-rolled plate is poor , the coiling tension is too small and the fluctuation is too large , the rolling pressure The control is unstable , and there is no deviation control device at the entrance .
( 2 ) Measures : When it is found that the raw material is seriously overflowing , first of all, the speed must be manually reduced , and the centering adjustment must be performed manually to strictly control the shape of the plate. Cut off the part with poor shape of the strip head , strictly control the coiling tension to ensure that the pressing is stable and normal , and once there is a serious overflow , it will be divided into coils at the last rack. 3 . 7 . 2 towers
( 1 ) The performance of the tower shape is that the edge of the steel coil is in the shape of an arc . The reasons for the tower shape are : the tower shape of the pickling coil , the shape of the head of the strip steel is bad or the core has a waste head , the coiling tension is too small , the core The movement between the coiler and the reel of the coiler , the gap between the side falling plates of each frame is too large , etc., can cause the tower shape of the steel coil during coiling .
( 2 ) Measures : The speed of rolling pickled tower-shaped coils should not be high , and the centering adjustment must be performed manually at any time . When it is really impossible to correct the deviation , the last rack rolling worker divides the rolls according to the situation , and controls the head of the threading head to fall . When the shape of the leading plate is not good , it should be cut off in time , and the waste leading can not be involved in the core . Ensure that the coiling tension is normal and meet the requirements of the process system . If the tower shape is found, it should be divided into coils immediately .
3 . 7 . 3 heart-shaped rolls
( 1 ) The performance of the heart-shaped coil is that the inner diameter of the steel coil is partially concave , and the main reason for the heart-shaped coil is that the coiling tension at the head of the coil is too small , and the rolling specification is too thin .
( 2 ) Measures : increase the coiling tension at the head of the coil , which should be greater than the set
20% ~ 30% of the tension ; appropriately increase the thickness of the tape head, and replace the small-diameter reel if necessary .
3 . 7 . 4 heart pumping
( 1 ) The performance of the centering is that the inner diameter of the steel coil overflows locally , and the main reasons for the centering are : the shape of the strip head is not good , the coiling tension of the core is too small , the displacement of the coiler drum or the tension on the steel coil trolley The plastic pad wears unevenly , causing the center of the steel coil to be inconsistent with the center of the reel .
( 2 ) Measures : ensure that the strip head is in good shape , and avoid rolling the waste strip head into the inner diameter ; manually increase the coiling tension of the head , and reset the offset coiler ; at the same time, replace the worn steel coil trolley Plastic chocks to keep the surface of the spreader free from abrasion .
3 . 7 . 5 rolls
( 1 ) The performance of the collapse is that the steel coil is elliptical when lying down , and the main reason for the collapse is that during the entire rolling process , the coiling tension is lower than the set tension , and the collapse defect is exposed after the coil is unloaded . This is most evident in thin-gauge products .
( 2 ) Measures : When the tension adjustment system or the tension setting is abnormal , the coiling tension should be increased by manual operation to ensure that the coiling tension of the strip head and the entire coil meets the process requirements and avoid collapse Volume defect .

1. Conclusion Aiming at various quality defects in the production of hot plate coils , after finding out the causes , the occurrence of various defects can be effectively controlled . Strengthen the quality control of hot plate coils , reduce waste products , increase machine-hour output and production level of hot plate coils , so as to create better economic benefits for Hebei Jingye Group .

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