64 pictures of common defects in strip steel
What is strip steel?
Strip steel is a kind of narrow and long steel plate produced by all kinds of steel rolling enterprises to meet the needs of industrial production of various metals or mechanical products in different industrial sectors. The strip, also known as steel strip, is within 1300mm in width and slightly different in length according to the size of each roll.
The strip steel is thin, narrow and long. Its width is generally 20 MM-200 mm. Coil supply, the specification of which is expressed in thickness × width. According to the quality of steel, it can be divided into high-quality strip and common strip; according to rolling method, it can be divided into hot rolling strip and cold rolling strip, which are called hot rolling strip and cold rolling strip respectively. The thickness of hot-rolled common strip is 2 mm-6 mm, and that of cold-rolled strip is 0.05 mm-3.60 mm. Steel strip can be made of ordinary carbon steel, carbon steel, spring steel, tool steel, stainless steel and other steel. It is widely used in manufacturing welded pipe, clamp, washer, spring blade, saw blade, etc.
Strip steel is generally supplied in coils, with the advantages of high dimensional accuracy, good surface quality, easy processing and material saving.
Technological process:
- The production process of cold rolled strip is: pickling – rolling – process lubrication – annealing – leveling – shearing – packaging.
- Cold rolling process: Pickling – rolling – annealing – rolling dimension synchronous lubrication – anti rust oil – leveling and sizing – polishing – packaging.
- Hot strip rolling process: heating furnace dephosphorization machine roughing mill dephosphorization machine finishing mill surface quality inspection instrument layer cooling coiler bundling machine spray number machine coiler slab.
Hot rolling strip production process: firstly, the temperature is raised to the required rolling temperature in the heating furnace, and then it enters the rough rolling dephosphorizing machine through the roller table to process the oxide scale produced by the slab, and then it enters the rough rolling machine to roll the width and thickness of the strip, and then it is transported by the roller table to the finish rolling dephosphorizing machine to process the oxide scale produced by the surface of the strip, and then it enters the finish rolling The rolling unit carries out more precise rolling on the thickness and width of the strip steel. After the surface temperature is strictly controlled before coiling by the roller table through layer cooling, the strip steel enters into the coiler and becomes the final steel coil to be bundled, and the spray number is sent to the coil warehouse for storage and packaging.
In the process of strip production, there will be a variety of defects. In order to facilitate the search of the causes of defects and promote the quality improvement in production. Based on the practical experience in daily work, this paper summarizes 64 common defects:
Common defects Atlas of 64 steel strips
Irregular Shells
Appearance features: the thin layer on the surface of the plate and strip is folded, and the defects are usually gray white, with different sizes and shapes, which are irregularly distributed on the surface of the plate and strip.
Cause: there are non-metallic inclusions on the surface or under the skin of slab, which are broken or exposed during rolling to form sandwich fold.
Inspection judgment: through visual inspection, there shall be no interlayer between steel plate and steel strip.
Band surface inclusion (sandwich)
Appearance features: the inclusions on the surface of the plate and strip are irregularly distributed along the rolling direction in the form of line or strip, and sometimes disappear gradually in the form of point or tongue.
Cause: the inclusion under the slab skin is caused by severe extension and fracture during rolling.
Inspection judgment: through visual inspection, there shall be no interlayer between steel plate and steel strip.
Blisters
Appearance features: there is gas in the convex surface of the strip steel, with irregular distribution. There are closed bubbles and open bubbles.
Cause: because a large amount of gas can not escape during the solidification process, slab is enclosed in the interior to form gas inclusion. During hot rolling, cavities and cavities are elongated and brought to the surface or edge of the product as the thickness of the rolled product decreases. Finally, the high gas pressure makes the product surface or edge appear dome like protrusion or extrusion.
Inspection judgment: the steel plate and steel strip shall be free of bubbles through visual inspection.
Scabs
Appearance features: irregular tongue, fish scale, strip or M-shaped metal flakes are distributed on the surface of strip steel. One is connected with the strip steel matrix; the other is not connected with the strip steel matrix, but is bonded to the surface, which is easy to fall off, forming a relatively smooth pit after falling off.
Cause: as there are scabs and burrs on the slab surface, they remain on the strip surface after rolling. Or the slab has residue after flame cleaning, which is pressed into the surface during rolling.
Inspection judgment: through visual inspection, the steel plate and steel strip shall be free of scabs.
Split layer
Appearance features: the section of the strip steel shows a gap that is not welded, sometimes there are inclusions visible to the naked eye in the gap of the separation layer. Serious stratification causes local splitting of the steel plate, and the parts produced by stratification are irregular.
Cause: there are too many gas or non-metallic inclusions in the slab, which can not be welded during rolling; the chemical composition segregation is serious, which can also form delamination.
Inspection judgment: through visual inspection, steel plate and steel strip shall not be layered.
Warping
Appearance features: the warped skin is usually tongue shaped, linear, layered or M-shaped folded (discontinuous, the thin material is often warped), and often appears on the edge of the upper surface of the strip steel.
Cause: the pinholes, bubbles and inclusions near the upper surface of the slab are easy to be exposed at the edge (weak part) of the upper surface of the strip steel during rolling. During the round-trip rolling process or coiling process, part of the surface is peeled and warped, resulting in warping defects.
Inspection judgment: according to different standards and use requirements.
Flying wing
Appearance features: small arched folds of different sizes are discontinuous on any surface, often on the edge of strip steel.
Cause: it is caused by tearing or cracking due to the infiltration of oxidation into the grain boundary during heating and hot rolling. It mainly occurs in stainless steel, acid resistant steel and heat-resistant steel, especially in unstable austenitic steel.
Inspection judgment: generally, steel plates and strips are allowed to have fins with depth or height not exceeding half of the thickness tolerance.
Edge cracks
Appearance features: the edge of the strip breaks along one or both sides of the length direction, with obvious metal fleshy and crack, and the severe one is serrated.
Cause: edge crack is easy to occur in slab rolling process. Due to poor roll adjustment, improper roll shape or low edge temperature, it will break due to poor extension during rolling, and it will also occur in cooling process. The further reason for the formation of such defects is that the local area of the material edge is under stress beyond its strength limit.
Inspection judgment: through visual inspection, the steel plate and steel strip shall be free of edge cracks.
Burnt edges
Appearance features: cracks and cracks along the edge of the strip, which may appear on one side or both sides of the strip in the whole length.
Causes: improper heating conditions, such as too high heating temperature, too long heating time, partial burning and so on, may cause such defects, and sometimes may be related to too high sulfur content.
Inspection judgment: through visual inspection, the steel plate and steel strip shall not be overburned.
Split strip edges
Appearance features: longitudinal cracks along the strip edge.
Cause: due to the edge crack of slab, sometimes it comes from the flame cutting edge of slab and appears in the central segregation area.
Inspection judgment: according to different standards and use requirements.
Pores
Appearance feature: it is a small gas inclusion near the surface of the billet. According to different deformation degrees, these small gas inclusions are elongated during rolling and exposed to the surface. In hot rolled strip, the pores usually appear in the form of bright stripes after descaling.
Cause: the steel is formed due to high gas content during casting and solidification. Sometimes the pores can be oxidized and filled with iron oxide scale. At this time, according to different steel grades, a certain degree of decarburization may be caused during billet heating.
Inspection judgment: according to different standards and use requirements.
Rolled-inscale
Appearance feature: it is a kind of defect that iron oxide scale is pressed into the surface of steel strip. It is usually distributed in all or part of the upper and lower surface of steel strip in small spots, fish scales, strips and blocks irregularly, often accompanied by rough pockmarked surface. Some of them are loose and easy to fall off, some of them are pressed into the plate surface, and after acid pickling or sandblasting treatment, there are pits of different degrees. According to the different processes of defects, it can be divided into primary scale pressing and secondary scale pressing.
Cause: the primary scale pressing is due to the serious scale of the slab itself or the serious scale generated during slab heating, which is not removed before rough rolling, and pressed into the plate surface during rolling. The second scale pressing is formed by pressing the second scale into the strip surface during finishing rolling. Because of the large unit pressure, the hot-rolled thin strip is more likely to produce this defect.
Inspection and judgment: the steel plate and strip shall not be pressed with oxide scale. Generally, it is allowed to have a thin layer of oxide scale which is not more than half of the thickness tolerance.
Rolling dust
Appearance features: the powdered iron oxide scale is pressed into the surface of strip steel, which is mainly produced on the upper surface of strip steel, with irregular distribution, and may also occur on the lower surface.
Cause: it mainly occurs at the rear of finishing rolling, which is caused by dispersion distribution attached to the surface of strip steel or pressing of agglomerated powdered iron oxide scale.
Inspection and judgment: the steel plate and strip shall not be pressed with oxide scale. Generally, it is allowed to have a thin layer of oxide scale which is not more than half of the thickness tolerance.
Pitting
Appearance features: there are local or continuous rough surfaces on the surface of the strip, which are orange peel in serious cases. It may appear on the upper and lower surfaces, and the density is uneven in the whole strip length direction.
Causes: when the roll temperature is relatively high, the scale adheres to the roll, and there are pockmarks on the surface of the pressed plate during rolling. Due to the poor material or high temperature of the roll, the surface of the plate may also have pockmarks during rolling.
Inspection judgment: according to different standards and use requirements.
Roll marks
Appearance features: there are periodic bulges and pits on the surface of the steel plate in the shape of dots, flakes or strips, which are distributed in the whole length of the steel strip or a section of it.
Causes: the periodic bulge is caused by the damage of the working roll or tension roll; the periodic pit is caused by the convex starting point formed by the sticking of foreign matters on the working roll or conveying roll. According to the cycle length of defects, the causes and positions of defects can be determined. Depending on their degree and cause, these defects may be flattened in subsequent processes, with or without oxide scale.
Inspection and judgment: according to different inspection and judgment standards and use requirements, it is generally allowed to have local defects with depth or height not exceeding half of thickness tolerance.
Extraneous matter rolled-in
Appearance features: the pressing of metal or non-metal foreign matters will cause various shapes and sizes of indentation on the surface of the strip steel, which is usually not distributed in the whole or part of the strip steel periodically. The flame cleaning burr and chips (chips) are mainly attached to the edge of the strip, while foreign matters can be pressed at any point of the full length and width of the strip.
Cause: press the same or different materials into the strip surface during rolling or finishing.
Inspection and judgment: according to different inspection and judgment standards and use requirements, it is generally allowed to have local defects with depth or height not exceeding half of thickness tolerance.
Longitudinal cracks
Appearance features: discontinuous cracks on the surface of rolled piece along the rolling direction, with different length and depth. Serious longitudinal crack will lead to fracture of rolled piece.
Cause: it is caused by local transverse stress exceeding the strength limit of the material during rolling.
Inspection judgment: through visual inspection, the steel plate and steel strip shall be free of longitudinal cracks.
Transverse cracks
Appearance features: irregular cracks on the surface of the rolled piece perpendicular to the rolling direction, sometimes in the shape of M or Z. Serious transverse crack will lead to fracture of rolled piece.
Cause: local tensile stress exceeding the strength limit of the material occurs during rolling.
Inspection judgment: through visual inspection, the steel plate and steel strip shall be free of transverse cracks.
Crazing
Appearance feature: a discontinuous crack on the surface of a rolled piece, which centers on a certain point and radiates outward in the form of lightning. Depending on the extent of extension and spread, the area it affects is usually elliptical (initially circular). Cracks may also exist in the form of very small microcracks or hairlines.
Cause: when the grain boundary is weakened by the low melting point phase (such as hot brittleness), crazing will occur.
Inspection judgment: through visual inspection, the steel plate and steel strip shall be free of cracks.
M-defects
Appearance features: M-shaped tongue like defects similar to interlayer appear in the form of ablation in hot rolled strip, and may appear on both upper and lower surfaces.
Causes: due to excessive grinding of rough slab or incomplete removal of oxide scale formed in the process of billet heating, grinding grooves are formed and M-shaped defects of different degrees are formed. M-shaped defects mainly appear in stainless steel, acid resistant steel and heat-resistant steel, especially in stable austenitic steel.
Inspection judgment: according to different standards and use requirements.
Massive ruptures
Appearance features: the local cracks running through the upper and lower surface of the strip steel are irregular and discontinuous.
Cause: it is caused by excessive plastic deformation and local stress of material. Excessive local stress in materials is usually caused by defects such as cracks, cavities, slag inclusions or rough inclusions. In addition, the change of the geometrical dimension of the rolled piece and the surface mechanical damage will also lead to the wear crack.
Inspection and judgment: through visual inspection, the steel plate and steel strip shall not be cracked.
Laps
Appearance features: irregular surface materials overlap, which may be linear, glossy or layered, or M-shaped, which may appear in different parts of the rolled material surface.
Cause: the initial defects such as slab surface crack, slab bottom scratch caused in pusher furnace or slab surface damage caused by other reasons will form fold in the subsequent rolling process. In addition, it may also be caused by the uneven flow of edge materials (which may overlap to the surface) or the improper deformation of slab edge, the unreasonable roll configuration and the loss of roll flesh.
Inspection judgment: through visual inspection, the steel plate and steel strip shall not be folded.
Fold
Appearance feature: an overlap similar to wrinkles, often occurring at the end of the strip.
Causes: due to the change of roll shape, too large bending of the sickle or too long irregular part at the end of the workpiece entering the finishing rolling, the tail of the strip is shaken during the rolling.
Inspection judgment: through visual inspection, the steel plate and steel strip shall be free of wrinkles and defects shall be removed.
Scratches，grooves and gouges
Appearance features: the mechanical damage on the surface of the rolled piece varies in length, width and depth. Mainly along the rolling direction or perpendicular to the rolling direction, may be slightly flattened, and may contain iron oxide scale or exposed inner metal. The scratches at high temperature have a thin layer of iron oxide, which is black gray; the scratches at normal temperature show metallic luster or gray white.
Cause: it is caused by friction between rolling piece and mechanical equipment parts. The longitudinal defect is produced when the steel strip is transported by roller or when the coiler and uncoiler are used; the transverse defect is mainly produced when the steel plate moves horizontally or the steel coil is unloaded from the coiler. The scratch may also be caused by the relative movement between uncoiled steel coils. If the rolled piece is damaged at high temperature, oxide scale will be generated in the damaged area and pressed in the subsequent process, depending on where it is generated. Scraps will be produced when abrading, or material accumulation will be formed near or at the tail of the abraded area.
Inspection judgment: according to the inspection judgment of standards and use requirements, generally no more than half of the thickness tolerance is allowed to exist.
Damaged strip edges
Appearance features: the rolled side of the belt is polished to varying degrees, sometimes accompanied by raised flash or fine chips.
Cause: it is caused by the strong contact between the edge of strip steel and the entrance guard during coiling.
Inspection and judgment: according to the inspection and judgment of standards and use requirements, the general transverse depth shall not exceed half of the width deviation.
Folded strip edges
Appearance feature: a defect in the form of edge thickening, curling or mechanical damage in some prominent bands.
Causes: due to the strong deviation correction or improper coiling of the side guide during coiling or conveying of the strip steel, some belt ring layers protrude, and contact damage occurs during the loading, unloading, transportation and storage of the strip steel.
Inspection and judgment: according to the inspection and judgment of standards and use requirements, the general transverse depth shall not exceed half of the width deviation.
Sheared edge defects
Appearance features: dart like material fracture from the cutting edge, cutting flash and shear crack, with an angle of about 45 ° with the plate.
Cause: it is caused by improper setting of the blade clearance, wear and tear of the blade or other damage. High strength steel and wear-resistant steel are particularly prone to such defects.
Check and judge: check and judge according to standards and use requirements.
Rough edges
Appearance features: the roughness of one side or upper and lower sides along the whole length of the strip increases in varying degrees, which is clearer after pickling or sandblasting.
Cause: due to the high roller load in the edge area of strip steel, the roughness of the roller increases, which leads to the roughness of the edge of strip steel. Such defects mainly appear in stainless steel and heat-resistant and acid resistant steel.
Check and judge: check and judge according to standards and use requirements.
Strip folds
Appearance feature: a fold or bend occurring over the entire width of the strip at right angles to the rolling direction or in a diagonal direction.
Causes: in the process of strip rolling, if there is excessive looper in the finishing mill, the looper will be rolled to overlap when the strip passes through the next stand; if the strip forms looper or fold on the output roller table, it will be flattened by the subsequent band in the coiler and brought into the coil.
Inspection and judgment: there shall be no overlap of strip steel, and local parts shall be cut off.
Coil breaks
Appearance features: the transverse crease in the vertical rolling direction crosses the strip steel with regular or irregular spacing, or is located at the edge of the strip steel.
Cause: the result of local yield along the moving direction of strip during uncoiling. The geometric design of the drum, bend roll or guide roll, as well as the thickness and temperature of the strip steel have an important influence on the formation of the cross folding. High yield extension, especially with low yield strength, will increase the tendency of transverse flexure. Because the yield and strain processes are time-dependent, the tendency to produce the transverse fold mark is reduced at a higher uncoiling speed. This defect usually occurs when the tension is too high to exceed the yield limit of the material, and there is no system for eliminating cross folding.
Check and judge: check and judge according to standards and use requirements.
Coil cone
Appearance features: one end of the steel coil is in the shape of pagoda and bread.
Cause: improper adjustment of rolling mill causes sickle bend of rolled strip or improper adjustment of coiler.
Inspection and judgment: measure the tower height, and judge according to the standard.
Loose coils
Appearance features: the coil is not tight, and there is a large gap or looseness between coils.
Causes: the coiling tension is small, the coiling temperature is low, the bundling belt is broken or the hardness of steel grade is high.
Inspection and judgment: according to the standards and use requirements.
Bright band (convex edge)
Appearance features: along the circumference of steel coil, there is obvious linear thickening, bright band is observed by naked eyes, and convex edge is felt by hand.
Causes: the cooling water nozzle of the working roll is blocked, which causes local roll shape problems; the roll surface is excessively worn due to unreasonable rolling plan or uneven hardness of the finishing roll; the local temperature of the strip is low.
Inspection and judgment: measure with naked eyes or micrometer, and conduct inspection and judgment according to standards and use requirements.
Landscape pattern
Definition and characteristics: after pickling, the strip surface presents irregular landscape pattern with clear boundary.
Cause: the dephosphorization effect of the strip in the dephosphorization section is not good during hot rolling.
Prevention and correction: ensure the flow and pressure of dephosphorization water in the hot rolling production process, so that the oxide scale on the surface can be completely removed.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Scars
Definition and characteristics: gravure printing caused by improper transportation or storage can penetrate several circles of steel strip, and the shape is similar with periodicity.
Cause: the steel coil is in contact with the hard objects in the environment during transportation and storage.
Prevention and correction: keep the environment clean during transportation and storage.
Identification and judgment: it can be judged by naked eyes. If the cycle is fixed, it is easy to be confused with roller printing.
Outside tower
Definition and characteristics: the inner diameter or outer diameter of the steel coil is not aligned with a layer of steel strip coiling, and it is offset to one side.
Cause: the tension of the strip steel is lost after the tail is thrown, and after the coil is rolled to the outer diameter of the coil, the pressure of the roller is not tight; when the coil is unloaded, the inner diameter core pulling or the outer diameter is relatively sliding with the coil unloading trolley.
Prevention and correction: before production, confirm the compaction degree of the pressing roller, and then carry out production after it meets the requirements; during coil unloading, strengthen the operation to reduce the frequency of inner diameter core pulling.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Rust
Definition and characteristics: damage caused by oxidation of metal surface in specific environment such as air and water. It diffuses from the edge of the steel strip to the middle, red, showing a point shape.
Cause analysis: this kind of corrosion will occur when the steel coil is stored in the storage yard beyond the time limit or when the humidity of the storage yard is large.
Prevention and correction: control the placing time of steel coil in the stock yard to ensure the temperature and humidity of the stock yard.
Identification and determination: it can be determined by naked eyes.
Support roller imprints
Definition and characteristics: are marks on the surface of steel plate that are invisible to the naked eye and visible after grinding.
Cause analysis: there are foreign matters stuck on each roller surface or guide plate in contact with the strip steel, and there are marks when the strip steel passes by.
Prevention and correction: regularly clean the contact roll system with the steel plate surface.
Identification and judgment: it is not easy to confuse with other defects in visual judgment or oilstone grinding inspection. Generally, visual judgment and grinding inspection are used.
Damage strip edges
Definition and characteristics: the edge of the steel strip is damaged, resulting in the lack of meat on the edge.
Cause analysis: damage during lifting due to collision between edge of strip steel and equipment or uneven coiling or stacking of strip steel.
Prevention and correction: control the tower shape and overflow edge during rolling, and control the strip deviation during production.
Identification and judgment: generally, visual inspection is used.
Bad tension reel
Definition and characteristics: the two sides of steel coil are uneven
Cause analysis: coiling tower shape will be caused by coiling fault or bad shape of incoming plate, as well as unstable tension.
Prevention and correction: adjust the coiling tension and ensure the tension is stable.
Identification and judgment: it is easy to judge with naked eyes. It is not easy to be confused with other defects.
Flat coil
Definition and features: the coil is obviously out of round in radial direction and elliptical in shape.
Cause analysis: when the coiling tension is small or the force is squeezed when the coiling is placed, flat coiling will occur, mostly in thin material.
Prevention and correction: increase the coiling tension; when placing the steel coil, implement the principle of thin on top, light on bottom, wide on bottom.
Identification and judgment: generally, visual inspection is used.
Under pickled
Definition and characteristics: there is residual oxide scale on the surface of the steel strip that has not been washed off by acid, which is in the form of horizontal black stripe (similar to the horizontal black fine grain of “lifting grain”), forming a strip or sheet distributed on the surface of the steel plate. Touch with your hand. There will be black dirt on your hand.
Cause: the oxide scale on the surface of the tropics is not removed after being pickled, and remains on the surface of the strip steel.
Prevention and correction:
- 1. Ensure that the acid shampoo tail does not overspeed.
- 2. Ensure that the temperature of acid solution is within the control range, and the acid spraying amount reaches more than 60% of the set value.
- 3. The tension leveler is put into normal operation.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Over pickled
Definition and characteristics: the surface of the steel strip is rougher than the normal pickled steel plate, and the color is not silver white, but dark black or brown black.
Cause analysis: in the pickling line, if the acid temperature is too high or the running speed of the strip is too low, the hot-rolled strip matrix reacts with the acid solution, resulting in over washing.
Prevention and correction:
- 1. Prevent the pickling speed from being too slow.
- 2. Reduce abnormal shutdown and shutdown time of process section.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Emulsionmarks
Definition and characteristics: is the residual cracking emulsion on the surface of steel strip, randomly distributed on the surface of steel strip, with irregular shape, dark color, yellow color after a long time, and black color after annealing.
Cause analysis: the emulsion cracked, because the residual emulsion was not completely evaporated in the annealing process, that is, the excess emulsion on the strip was not blown away.
Prevention and correction:
- 1. Reduce 5 blowing faults.
- 2, 5 export rack pipes wrapped with cloth to prevent condensation emulsion dripping onto the steel plate.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
The edge is fleshy and short of meat
Definition and characteristics: the edge of the steel strip is fleshy and short due to the poor edge cutting after the disc shear.
Cause: aging of the cutting edge of the disc shear or collapse of the cutting edge.
Prevention and correction: ensure the status of the cutting edge of the disc shear in the production process.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Surface blotch
Definition and characteristics: the surface of the strip steel shows flake or large area of spots, and in some cases, there are signs of outward radiation at a certain angle.
Causes: high temperature in pickling section and rinsing section and slow operation of strip steel.
Prevention and correction: the temperature and speed of the process section are well matched to avoid too slow speed and too high temperature.
Waves
Definition and characteristics: the steel plate is not straight, and it is wavy bending along the rolling direction. According to the different distribution, it can be divided into single side wave, double side wave, middle wave and two rib wave.
Cause analysis: along the strip width direction, the middle extension is inconsistent with the edge extension, resulting in wave shaped defects.
Prevention and correction:
- 1. Select the original crown of work roll correctly.
- 2. Use positive and negative bending rollers correctly.
- 3. Use roller coolant correctly.
- 4. Control the shape and convexity of the incoming material.
Shearededge defect
Definition and characteristics: the small serrated crack on the edge of the steel strip after the disc shear.
Cause analysis: the cutting edge of the disc shear is blunt or notched, or the gap and overlap of the cutting edge are not adjusted properly, and there is burr after cutting.
Prevention and correction:
- 1. Ensure good quality of cutting edge.
- 2. To prevent large errors in the clearance and overlap of the cutting edge.
Stoppagemarks
Definition and characteristics: when the pickling line is stopped, a large number of spots are formed on the surface of the steel strip due to the chemical substances. It can be distributed in any position of steel strip.
Cause analysis: in the pickling line, if the strip steel stays in the pickling tank and rinsing tank for too long due to shutdown, the shutdown trace may occur.
Prevention and correction: reduce the shutdown of acid pickling section, which can be eliminated after shutdown.
Chatter marks
Definition and characteristics: it is irregular wavy, distributed along the rolling direction on the whole width of the steel strip, and the thickness of the steel strip changes in the rolling direction.
Cause analysis: the characteristic of the vibration pattern is the thickness fluctuation, which is caused by the resonance of the frame.
Prevention and correction: it is forbidden for the unit to use eccentric and severely worn supporting roll to prevent frame vibration; when frame vibration is large, reduce rolling speed.
Identification and judgment: it is not easy to be confused with other defects by naked eyes or after grinding.
Grinding mark
Definitions and features: are regular stripes, which can be distributed along the rolling direction on the whole width of the steel strip and parallel to the rolling direction.
Cause analysis: during roll grinding, the feed marks generated in the circumferential direction of the roll form longitudinal stripes on the surface of the strip steel under the action of rolling force.
Prevention and correction: unify the roller grinding procedure, fix the z-axis speed of each grinder, control the roughness of the smooth roller, avoid ring and skew marks on the roller surface after grinding, and conduct grinding inspection and confirmation on the roller edge.
Identification and judgment: it is not easy to be confused with other defects by naked eyes or after grinding.
Emulsion marks
Definition and characteristics: is the residual cracking emulsion on the surface of the steel strip, randomly distributed on the surface of the steel strip, with irregular shape and dark color.
Cause analysis: the trace of emulsion is that the residual emulsion on the surface of the strip is cracked. Because the residual emulsion is completely evaporated during the annealing process, that is, the excess emulsion on the strip is not blown away.
precaution and correction: ensure the angle and pressure of the outlet of the mill to avoid the condensation and dripping of the emulsion at the outlet of the mill.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Black band
Definition and characteristics: the black film on the surface of the steel plate is distributed longitudinally in strips or flakes. The width of the strips is different and the color is different.
Cause analysis: after rolling, the residual emulsion on the surface of the steel strip is too high, and the rolling tension of the rolling mill is too large. The residual emulsion in the center part of the coil is not easy to volatilize, and oxidation or carburization occurs during the placement process.
Prevention and correction: control the viscosity of the emulsion and the viscosity of the emulsifiable concentrate, ensure the angle and pressure of the outlet of the mill, and avoid the excessive take-up tension of the rolling mill.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Oil stain
Definition and characteristics: there are black or brown spots of different sizes on the steel strip surface, generally with obvious contour lines.
Cause analysis: the rolling oil spot is caused by the high content of mixed oil in the emulsion left on the strip surface. During the placing process, a small amount of oil volatilization is taken away by air, and a large amount of oil infiltrates into the strip surface to form iron oxide, causing the spot.
Prevention and correction: control the leakage of oil between the shelves, timely and accurately adjust the oil leakage, ensure that the rack is clean, and prevent the condensation of the emulsion from falling.
Identification and judgment: can be judged by naked eyes, which is easy to be confused with rust.
Clean emulsion marks
Definition and characteristics: after the cleaning unit, the residual cleaning solution on the surface of the steel strip is in sheet or line state, which is not obvious before annealing, and presents white or black spots after annealing.
Cause analysis:
- 1. Brush roll or squeeze roll failure.
- 2. High conductivity in rinsing section.
- 3. Dryer temperature is low.
Prevention and correction:
- 1. When the brush roller fails to meet the requirements of the procedure, replace it in time.
- 2. In case of serious wear or peeling of the roll surface, replace it in time.
- 3. Ensure the conductivity of scrubbing tank and rinsing tank.
- 4. Ensure that the temperature of the dryer meets the requirements of the regulations.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Anneal-stained edges
Definition and characteristics: the yellow or blue trace on the surface of cold rolled steel strip after annealing, and the S shape on the edge of steel strip after annealing in bell type furnace,
Cause: gas leakage or water inflow occurs in the protective cover, or it is discharged in advance.
Prevention and correction:
- 1. Heating is allowed only after the inner cover is qualified in leakage test before ignition.
- 2. Process spot check shall be carried out in advance.
- 3. Reduction treatment after emergency purging.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Color aberration
Definition and characteristics: along the longitudinal direction, the brightness of one part of the steel strip surface is obviously different from that of other parts, with obvious boundaries.
Cause: chemical composition of raw materials, residual emulsion of rolling emulsion, annealing process and atmosphere in the furnace will cause uneven surface color of strip.
Prevention and correction:
- 1. Reduce the residue on the steel plate surface.
- 2. Improve roll grinding process.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Chattermarks
Definition and characteristics: it is irregular wavy, distributed along the rolling direction on the whole width of the steel strip, and the thickness of the steel strip changes in the rolling direction.
Cause: the characteristic of the vibration pattern is the thickness fluctuation, which is caused by the resonance of the frame.
Prevention and correction:
- 1. Strictly implement the roll change system.
- 2. Reduce rack clearance and vibration.
- 3. Improve rolling accuracy and reduce thickness fluctuation.
- 4. Improve the quality of roll grinding.
Identification and judgment: it is not easy to be confused with other defects by naked eyes or after grinding.
Feather after SPM
Definition and characteristics: feather like patterns produced in the process of flattening, distributed in part or the whole steel strip.
Cause: uneven extension of strip steel in roll gap.
Prevention and correction:
- 1. Increase the tension before and after.
- 2. Improve the shape of the incoming plate.
- 3. Add roll bending or roll curve.
- 4. Increase the height of Anti Wrinkle roll.
Identification and judgment: visual judgment, not easy to be confused with other defects.
Rustafter SPM
Definition and characteristics: damage caused by oxidation of metal surface in specific environment such as air and water. In the edge, there are continuous strips or intermittent small pieces of rust spots, which are yellow and feel, and there is obvious black boundary after wiping.
Cause: the concentration of leveling solution is not consistent or too much leveling solution remains at the edge.
Prevention and correction:
- 1. Improve storage conditions in the reservoir area.
- 2. Increase the concentration of leveling fluid to keep it within the process standard; check the quality of purging equipment and compressed air to keep it in good condition.
- 3. Check the nozzle of oiler regularly to keep it unblocked.
- 4. Improve packaging quality.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Feather
Definition and characteristics: feather like patterns produced in the process of flattening, distributed in part or the whole steel strip.
Cause: uneven extension of strip steel in roll gap.
Prevention and correction:
- 1. Reasonable adjustment and reduction, and timely adjustment in case of single-sided waves.
- 2. Put the anti wrinkle roll into operation in time to ensure back tension.
- 3. Reasonable selection of roll crown and correct use of positive and negative bending roll.
Identification and judgment: visual judgment, not easy to be confused with other defects.
Coilbreaks
Definition and characteristics: there are continuous broken lines like the equal sign at the edge of the steel strip (very few of them also occur at some part in the middle of the steel plate). A line with different lengths at the edge of the steel plate, perpendicular to or at an angle of 45 degrees with the rolling direction of the steel plate.
Cause: local yield occurs along the uncoiling direction during uncoiling. The thickness of drum and strip steel has a great influence on the production of cross folding. In the case of high elongation and low yield strength, it is most likely to have a cross print. Because the stress-strain process is time-dependent, high uncoiling speed can reduce the occurrence of cross folding.
Prevention and correction:
- 1. Reduce the post tension properly.
- 2. Reduce the original crown of the work roll.
- 3. Use positive and negative bending rollers correctly.
- 4. Adjust the plate shape.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
Oilcoating odd
Definition and characteristics: there are some parts of the steel plate surface that are not coated with anti rust oil, which are banded and consistent with the rolling direction.
Cause: the spray knife beam of oiler is partially blocked
Prevention and correction:
- 1. Clean the oiler.
- 2. Clean the spray knife.
- 3. Guarantee voltage.
- 4. Ensure the oil temperature.
- 5. The cleanliness of antirust oil is above grade 8.
Identification and judgment: it can be judged by naked eyes and is not easy to be confused with other defects.
The back up roll mark
Definition and characteristics: regular light and dark stripes along the rolling direction of the steel plate, generally no hand feeling visible visually, serious hand feeling.
Causes: due to the residual dirt on the surface of the steel plate, it will stick to the working roll when passing through the straightener; there will be mechanical residual oil when disassembling the straightener; when the straightening reduction is large, the dirt or oil stain on the working roll will be printed on the steel plate.
Prevention and correction:
- 1. Ensure that the steel plate surface is clean with less residue.
- 2. Add proper mechanical oil during mechanical assembly.
- 3. Clean the working roll of straightener frequently.
- 4. Reasonable pressure.
Identification and judgment: generally, visual inspection is used for judgment and inspection, and slight inspection can be combined with grinding inspection.
Source: China Strip Steel Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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