Analysis and control methods of common appearance defects of steel sections

1. Insufficient filling of steel section corners
1.1 Defect characteristics: Insufficient filling of steel section corners caused by insufficient filling of finished product holes, resulting in a lack of metal at the edges and corners of steel sections. Its surface is rough, mostly along the entire length, and some appear locally or intermittently.
1.2 Causes: Due to the inherent characteristics of the hole type, the edges and corners of the rolled piece cannot be processed; the rolling mill is improperly adjusted and operated, and the reduction amount is not reasonably distributed. The reduction amount of the corners is small, or the extension of each part of the rolled piece is inconsistent, resulting in excessive shrinkage; the hole type or the guide plate is severely worn, the guide plate is too wide or installed incorrectly; the rolled piece temperature is low, the metal plasticity is poor, and the corners of the hole type are not easy to fill; the rolled piece has a serious local bending, and it is easy to produce local corners after rolling. Home of Steel Rolling
1.3 Control methods: Improve hole design, strengthen rolling mill adjustment operation, and reasonably distribute the amount of reduction; correctly install the guide device, and replace the severely worn hole and guide plate in time; adjust the reduction amount according to the temperature of the rolled piece to fill the edges and corners well.

2. Steel section size deviation
2.1 Defect characteristics: A general term for the geometric dimensions of the steel section that do not meet the requirements of the standard. When the difference from the standard size is too large, it will appear deformed. There are many names for this type of defect, most of which are named after the location and degree of deviation. Such as out-of-roundness deviation, length deviation, etc.
2.2 Causes: Unreasonable hole design; uneven hole wear, improper matching of new and old holes; poor installation of various parts of the rolling mill (including the guide device), safety mortar rupture; improper adjustment of the rolling mill; uneven temperature of the billet, uneven temperature of a single piece causes local specifications to be inconsistent, and the entire low-temperature steel produces full-length specifications that are inconsistent and too large.
2.3 Control method: correctly install all parts of the rolling mill; improve the hole design and strengthen the adjustment operation of the rolling mill; pay attention to the wear of the hole. When replacing the finished hole, consider replacing the finished front hole and other related hole types at the same time according to the specific situation; improve the heating quality of the steel billet to achieve uniform temperature of the steel billet; some special-shaped materials may affect a certain size due to the change of the cross-sectional shape after straightening, and the defect can be re-straightened to eliminate the defect.

3. Steel rolling scar
3.1 Defect characteristics: Metal blocks bonded to the surface of the steel due to rolling. Its appearance is similar to scarring. The main difference from scarring is that the shape of the rolling scar and its distribution on the surface of the steel has a certain regularity. There is often no non-metallic oxide inclusion under the defect.
3.2 Causes: The rough rolling mill has serious wear and tear, resulting in intermittently distributed active rolling scars on the fixed surface of the steel; foreign metal objects (or metal scraped off the workpiece by the guide device) are pressed into the surface of the workpiece to form rolling scars; periodic bumps or pits are generated on the surface of the workpiece before the finished hole, and periodic rolling scars are formed after rolling. The specific reasons are poor groove notching; sand holes or meat loss in the groove; the groove is hit by "black head" workpieces or has protrusions such as scars; the workpiece slips in the hole, causing the metal to accumulate on the surface of the deformation zone, and rolling scars are formed after rolling; the workpiece is partially stuck (scratched) or bent by mechanical equipment such as the surrounding plate, roller table, and steel turning machine, and rolling scars will also be formed after rolling.
3.3 Control methods: timely replace the grooves that are severely worn or have foreign objects on them; carefully check the surface of the grooves before changing the rolls, and do not use grooves with sand holes or bad marks; it is strictly forbidden to roll black steel to prevent the grooves from falling or being hit; when dealing with steel clamping accidents, be careful not to damage the grooves; keep the mechanical equipment before and after the rolling mill smooth and flat, and install and operate them correctly to avoid damaging the rolled pieces; be careful not to press foreign objects into the surface of the rolled pieces during rolling; the heating temperature of the steel billet should not be too high to avoid the rolled pieces from slipping in the hole.

4. Lack of meat in steel
4.1 Defect characteristics: metal is missing along the length of one side of the cross-section of the steel. There is no hot rolling mark of the finished groove at the defect, the color is dark, and the surface is rougher than the normal surface. It mostly appears throughout the length, and some appear locally.
4.2 Causes: The groove is misaligned or the guide is improperly installed, resulting in a lack of metal in a certain section of the rolled piece, and the hole is not filled during re-rolling; the hole design is poor or the turning is wrong and the rolling mill is improperly adjusted, the amount of rolled piece metal entering the finished hole is insufficient so that the finished hole is not filled; the different degrees of wear of the front and rear hole types can also cause lack of meat; the rolled piece is twisted or the local bending is large, and local meat is missing after re-rolling.
4.3 Control method: Improve the hole design, strengthen the adjustment operation of the rolling mill, so that the finished hole is well filled; tighten the various parts of the rolling mill to prevent the axial movement of the roller, correctly install the guide device; replace the severely worn hole in time.

5. Scratches on steel
5.1 Defect characteristics: The groove marks formed by the sharp edges of equipment and tools during hot rolling and transportation of the rolled piece. The depth varies, the bottom of the groove can be seen, generally with sharp edges and corners, often straight, and some are also curved. Single or multiple, distributed throughout or partially on the surface of the steel.
5.2 Causes: The floor, roller, steel transfer and steel turning equipment in the hot rolling area have sharp edges, which scratch the rolled piece when it passes; the guide plate is poorly processed, the edge is not smooth, or the guide plate is severely worn, and there are foreign objects such as iron oxide on the surface of the rolled piece; the guide plate is improperly installed and adjusted, and the pressure on the rolled piece is too large, which scratches the surface of the rolled piece; the edge of the surrounding plate is not smooth, and the rolled piece is scratched when it jumps.
5.3 Control method: The guide device, surrounding plate, floor, ground roller, and other equipment should be kept smooth and flat, without sharp edges; strengthen the installation and adjustment of the guide plate, which should not be skewed or too tight to avoid excessive pressure on the rolled piece.

6. Steel wave
6.1 Defect characteristics: The undulations along the length direction of the local section of the steel section due to uneven rolling deformation are called waves. There are local and full-length ones. Among them, the longitudinal wavy undulations of the waist of I-beams and channel steels are called waist waves; the longitudinal wavy undulations of the leg edges of I-beams, channel steels, and angle steels are called leg waves. I-beams and channel steels with waist waves have an uneven longitudinal thickness of the waist. In severe cases, metal overlap and tongue-shaped voids may occur.
6.2 Causes: The waves are mainly caused by inconsistent elongation coefficients of various parts of the rolled piece, resulting in serious shrinkage, which generally occurs in parts with larger elongation. The main factors causing changes in the elongation of various parts of the rolled piece are as follows. Improper distribution of reduction; roller stringing, groove misalignment; severe wear of the groove of the front hole or the second front hole of the finished product; uneven temperature of the rolled piece.
6.3 Control method: When replacing the finished hole in the middle of rolling, the front hole and the second front hole of the finished product should be replaced at the same time according to the product characteristics and considering the specific situation; strengthen the rolling adjustment operation, reasonably distribute the reduction, and tighten the various parts of the rolling mill to prevent the groove from misaligning. Make the extension of each part of the rolled piece uniform.

7. Steel torsion
7.1 Defect characteristics: Different angles of the cross-sections around the longitudinal axis of each part along the length direction are called torsion. When the twisted steel is placed on a horizontal inspection stand, it can be seen that one side of one end is tilted, and sometimes the other side of the other end is also tilted, forming a certain angle with the table surface. When the torsion is very serious, the whole steel even becomes "twisted".
7.2 Causes: Improper installation and adjustment of the rolling mill, the center line of the rollers is not on the same vertical or horizontal plane, the rollers move axially, and the grooves are misaligned; the guide plate is not installed correctly or are severely worn; the temperature of the rolled piece is uneven or the pressure is uneven, resulting in uneven extension of each part; the straightening machine is improperly adjusted; when the steel, especially the large material, is in a hot state, the steel is turned over at one end on the cooling bed, which is easy to cause end torsion.
7.3 Control method: Strengthen the installation and adjustment of the rolling mill and the guide plate. Do not use severely worn guide plates to eliminate the torsional moment on the rolled piece; strengthen the adjustment of the straightening machine to remove the torsional moment added to the steel during straightening; try not to turn the steel over at one end of the cooling bed when the steel is hot to avoid twisting of the end.

8. Bending of steel sections
8.1 Defect characteristics: Longitudinal unevenness is generally called bending. Named according to the bending shape of the steel, the uniform bending in the shape of a sickle is called a sickle bend; the overall repeated bending in the shape of a wave is called a wave bend; the overall bending at the end is called an elbow; one side of the end angle is warped inward or outward (rolled up in severe cases) is called an angle bend. Steel Rolling Home
8.2 Causes: Before straightening: Improper adjustment of steel rolling operation or uneven temperature of rolled pieces, which makes the extension of each part of the rolled piece inconsistent, can produce sickle bend or elbow; the difference between the upper and lower roller diameters is too large, and the finished product exit guide plate is improperly designed and installed, which can also produce elbows, sickle bends or wave bends; the cooling bed is uneven, the speed of each roller of the roller cooling bed is inconsistent, or the cooling after rolling is not uniform, which can produce wave bends; the metal distribution of each part of the product section is uneven, and the natural cooling speed is inconsistent. Even if the steel is straight after rolling, sickle bends in a fixed direction will be produced after cooling; when hot sawing steel, the saw blade is severely worn, the sawing is too fast, or the hot steel hits the baffle at high speed on the roller, and the end of the steel collides with some protrusions during the transverse movement, which can produce elbows or corners; improper storage of steel during lifting and intermediate storage, especially when operating in a red-hot state, can produce various bends. After straightening: In addition to corners and elbows, the wave bends and sickle bends in the normal state of steel should be able to achieve a straight effect after the straightening process.
8.3 Control method: Strengthen the adjustment operation of the rolling mill, correctly install the guide device, and control the rolled piece to not have excessive bending during rolling; strengthen the operation of the hot saw and cooling bed process to ensure the cutting length and prevent the steel from being hit and bent; strengthen the adjustment operation of the straightening machine, and replace the straightening roller or roller shaft with severe wear in time; to prevent it from being hit and bent during transportation, a spring baffle can be installed in front of the cooling bed roller; strictly control the temperature of the straightened steel according to the regulations, and stop straightening when the temperature is too high; strengthen the storage of steel in the intermediate warehouse and the finished product warehouse to prevent the steel from being pressed or bent by the crane rope.

9. The shape of the steel section is not correct
9.1 Defect characteristics: There is no metal defect on the surface of the steel section, and the cross-sectional shape does not meet the specified requirements. There are many names for this type of defect, which varies with different varieties. Such as the oval of round steel; the diamond of square steel; the oblique legs, the wavy waist, and the lack of leg meat of channel steel; the top angle of angle steel is large, the angle is small and the legs are unequal; the legs of I-beam are oblique and the waist is uneven; the shoulder of channel steel is collapsed, the waist is convex, the waist is concave, the legs are expanded and the legs are parallel.
9.2 Causes: Improper design, installation, and adjustment of straightening rollers or serious wear; unreasonable design of straightening roller hole type; serious wear of straightening rollers; improper design, wear, and tear of the hole type and guide device of rolled steel or poor installation of the finished hole guide device.
9.3 Control method: Improve the hole type design of straightening rollers, and select straightening rollers according to the actual size of rolled products; when bending and rolling channel steel and automobile wheel nets, the second (or third) lower straightening roller in the forward direction of the straightening machine can be made into a convex shape (convexity height 0.5~1.0mm), which is conducive to eliminating the concave waist defect; the steel section that needs to ensure the unevenness of the working surface should be controlled from the rolling; strengthen the adjustment operation of the straightening machine.

10. Cutting defects of steel
10.1 Defect characteristics: Various defects caused by poor cutting are collectively referred to as cutting defects. When using a flying shear to shear small steel in a hot state, the scars with different depths and irregular shapes on the surface of the steel are called cut wounds; in a hot state, the surface is damaged by the saw blade, which is called saw wounds; after cutting, the cutting surface is not perpendicular to the longitudinal axis, which is called bevel cutting or saw bevel; the hot-rolled shrinkage part at the end of the rolled piece is not cut cleanly, which is called short cut head; after cold shearing, a small local crack appears on the shear surface, which is called tearing; after sawing (shearing), the metal flash left on the end of the steel is called burr.
10.2 Causes: The sawed steel is not perpendicular to the saw blade (shear blade) or the head of the rolled piece is bent too much; equipment: the saw blade has a large curvature, the saw blade is worn out or improperly installed, and the gap between the upper and lower shear blades is too large; the flying shear is out of adjustment; operation: too many steel roots are sheared (sawn) at the same time, too little end is cut, the hot-rolled shrinkage part is not cut cleanly, and various misoperations.
10.3 Control method: Improve the condition of incoming materials, take measures to avoid excessive bending of the head of the rolled piece, and keep the direction of the incoming materials perpendicular to the shearing (sawing) plane; improve the condition of the equipment, use saw blades with no or small curvature, select the thickness of the saw blade appropriately, replace the saw blade (shear blade) in time when it is worn, and correctly install and adjust the shearing (sawing) equipment; strengthen the operation, and at the same time, do not cut too many roots to avoid the rise and fall of steel and bending. The necessary end removal amount must be guaranteed, and the hot-rolled shrinkage part must be cut cleanly to avoid various misoperations.

11. Steel correction marks
11.1 Defect characteristics: surface scars caused during the cold correction process. This defect has no traces of hot processing and has a certain regularity. There are three main types. Pit type (or correction pit), fish scale type, and damage type.
11.2 Causes: The hole of the straightening roller is too shallow, the steel is severely bent before straightening, the steel is not fed correctly during straightening, or the straightening machine is improperly adjusted, which may cause damage-type straightening marks; the straightening roller is partially damaged or adhered to metal blocks, the roller surface is partially raised, the straightening roller is severely worn or the roller surface temperature is high, and the metal is adhered, which may cause fish scale-shaped straightening marks on the steel surface.
11.3 Control method: Do not continue to use the straightening roller when it is severely worn and the straightening marks are serious; when the straightening roller is partially damaged or adhered to metal blocks, it should be polished in time; when straightening angle steel and other steel, the relative movement between the straightening roller and the steel contact surface is large (caused by the difference in linear speed), which can easily increase the temperature of the straightening roller and scrape the nodules, resulting in straightening marks on the steel surface, so cooling water should be poured on the surface of the straightening roller to cool it; improve the material of the straightening roller or quench the straightening surface to increase the surface hardness and increase wear resistance.