Analysis and control methods of common appearance defects of section steel

1. The shaped steel angle is not fully charged

① Defect characteristics of underfilled profiled steel angles: Due to insufficient filling of the finished hole, the lack of metal in the edges and corners of the profiled steel is called underfilled profiled steel angles. The surface is rough, mostly appearing along the entire length, and sometimes appearing partially or intermittently.

② The reasons for insufficient filling of the steel angle: due to the inherent characteristics of the pass, the edges and corners of the rolled piece cannot be processed; improper adjustment of the rolling mill and unreasonable distribution of reduction. The corner reduction amount is small, or the extension of various parts of the rolled piece is inconsistent, resulting in excessive contraction; the pass pattern or guide plate is severely worn, the guide plate is too wide or is installed incorrectly; the temperature of the rolled piece is low, and the metal plasticity is poor. It is difficult to fill the edges and corners of the pass; the rolled piece has serious local bending, and local corners are easily not filled after re-rolling.

③Control methods for underfilling of profiled steel angles: improve pass design, strengthen rolling mill adjustment operations, reasonably allocate reduction; correctly install guide devices, promptly replace severely worn pass profiles and guide plates; adjust according to the temperature of the rolled piece Depress the amount so that the edges and corners are well filled.

2. The size of the section steel is out of tolerance

①Defect characteristics of out-of-tolerance dimensions of section steel: a general term for the geometric dimensions of section steel that do not meet the requirements of the standard. When it differs too much from the standard size, it will appear deformed. There are many names for this kind of defect, most of which are named after the location of occurrence and the degree of out-of-tolerance. Such as out-of-roundness, length, etc.

②Causes for the abnormal size of section steel: unreasonable pass design; uneven wear of the pass, improper matching of old and new holes; poor installation of various parts of the rolling mill (including guide devices), cracked safety mortar; improper adjustment of the rolling mill; uneven temperature of the billet, Uneven temperature in a single piece causes local specification discrepancies, and the entire low-temperature steel causes full-length specification discrepancies, which are too large.

③Methods to control the size deviation of section steel: correctly install each component of the rolling mill; improve the pass design and strengthen the adjustment operation of the rolling mill; pay attention to the wear of the pass; when replacing the new product hole, consider replacing the front hole of the finished product at the same time according to the specific situation and other related pass shapes; improve the heating quality of the billet to achieve uniform billet temperature; some special-shaped materials may have a certain size that is out of compliance due to the change in cross-sectional shape after straightening. At this time, the defects can be eliminated by re-straightening.

3. Steel rolling scar

① Defect characteristics of steel rolling scars: metal lumps bonded to the surface of the steel caused by rolling. Its appearance is similar to a scar. The main difference from the scar is that the shape of the rolling scar and its distribution on the surface of the steel has a certain regularity. There are often non-metallic oxide inclusions under the defects.

② Causes of rolling scars on section steel: The passing pattern of the roughing mill is severely worn, and live rolling scars are produced intermittently on the fixed surface of the section steel; metal foreign objects (or metal scraped off by the guide device of the rolled piece itself) are pressed into the rolling mill. Rolling scars are formed on the surface of the piece; due to periodic bumps or pits on the surface of a certain rolling piece before the finished hole, periodic rolling scars are formed after rolling. The specific reasons are poor scoring of the rolling groove; blisters or chipping in the rolling groove. meat; the rolling groove is damaged by the "blackhead" rolled piece or has scars and other protrusions; the rolled piece slips in the past, causing the metal to accumulate on the surface of the deformation zone, and then forms rolling scars after rolling; the rolled piece is partially damaged Mechanical equipment such as enclosures, rollers, and steel turners are jammed (scratched) or bent, and rolling scars will also form after re-rolling.

③Methods to control rolling scars on section steel: timely replace rolling grooves that are severely worn or have foreign objects stuck on them; carefully check the surface of the rolling groove before changing the roll, and do not use rolling grooves with blisters or poor scoring; it is strictly prohibited to roll black-headed steel to prevent rolling. When dealing with steel clamping accidents, be careful not to damage the rolling groove; keep all 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 allow foreign objects to be pressed into the rolling mill during rolling. The heating temperature of the steel billet should not be too high to prevent the rolled piece from slipping in the past.

4. Shaped steel lacks meat

① Characteristics of the defective steel section with missing meat: There is a lack of metal along the length direction on one side of the section steel section. There is no hot-rolling imprint of the finished rolling groove in the defective area, which is dark in color and rougher than the normal surface. Most of them appear all over the body, and some appear locally.

② Causes of missing meat in sectioned steel: Wrong teeth in the rolling groove or improper installation of guides, resulting in a lack of metal in a certain section of the rolled piece, and the pass is not filled during re-rolling; poor pass design or turning errors and improper adjustment of the rolling mill, entering the finished hole The amount of metal in the rolled piece is insufficient, resulting in the finished hole not being filled; the different degree of wear of the front and rear pass patterns will also cause a lack of flesh; the rolled piece is twisted or locally bent, resulting in a partial lack of flesh after re-rolling.

③Methods to control the lack of meat in section steel: improve the pass design, strengthen the adjustment operation of the rolling mill, so that the finished holes are well filled; tighten the components of the rolling mill to prevent axial movement of the rolls, correctly install the guide device; promptly replace the severely worn pass.

5. Scratches on section steel

① Defect characteristics of steel scratches: groove marks caused by the sharp edges of equipment and tools during hot rolling and transportation of rolled parts. Their depths vary, and the bottom of the ditch can be seen. They generally have sharp edges and corners, are often linear, and some are also curved. Single or multiple strips, distributed throughout the length or partially on the surface of the section steel.

② Causes of scratches on section steel: The floor, roller table, steel moving, and steel turning equipment in the hot rolling area have sharp edges, and the rolled pieces are scratched when passing through; the guide plate is poorly processed, the edges are not smooth, or the guide plate is worn Seriously, foreign matter such as iron oxide scale is stuck on the surface of the rolled piece, which scratches the surface of the rolled piece; the guide plate is improperly installed and adjusted, exerting too much pressure on the rolled piece, and scratches the surface of the rolled piece; the edge of the enclosure is not rounded, and it will be damaged when the rolled piece jumps. scratches.

③Methods to control scratches on section steel: Guide devices, enclosures, floors, floor rollers, and other equipment must be kept smooth and flat without sharp edges and corners; strengthen the installation and adjustment of guide plates and should not be skewed or too tight to avoid rolling. The pressure on the parts is too high.

6. Steel corrugation

①Defect characteristics of corrugated steel: due to uneven rolling deformation, the undulations along the length of the local section of the steel are called waves. There are partial ones and full-length ones. Among them, the longitudinal wavy undulations at the waist of I-beam and channel steel are called waist waves; the longitudinal wavy undulations at the edges of the legs of I-beam, channel steel, and angle steel are called leg waves. I-beams and channel steels with waist waves have an uneven longitudinal thickness at the waist. In severe cases, there will be metal overlap and tongue-shaped hollows with one wave on top of another.

② Causes of waves in profiled steel: Waves are mainly caused by inconsistent elongation coefficients in various parts of the rolled piece, resulting in severe shrinkage, which generally occurs in parts with larger extensions. The main factors that cause changes in the extension of various parts of the rolled piece are as follows. The amount of reduction is improperly distributed; the rolls move in tandem and the rolling grooves have wrong teeth; the front hole or the rolling groove of the finished product is seriously worn; the temperature of the rolled piece is uneven.

③ Control method of steel wave: When replacing the finished hole in the middle of rolling, the front hole of the finished product and the front hole of the finished product should be replaced at the same time according to the characteristics of the product and the specific situation; strengthen the rolling adjustment operation, reasonably distribute the reduction amount, and tighten at the same time Each component of the rolling mill prevents misaligned teeth in the rolling groove. Make all parts of the rolled piece extend evenly.

7. Steel torsion

① Defect characteristics of section steel torsion: different angles of the cross-sections of each part along the length direction around its longitudinal axis are called torsion. When the twisted steel is placed on a horizontal inspection bench, 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. When the torsion is very serious, the entire steel may even become "twisted".

② Causes of steel torsion: Improper installation and adjustment of the rolling mill, the center lines of the rolls are not on the same vertical or horizontal plane, the rolls move axially, and the rolling grooves are misaligned; the guide plates are not installed correctly or are seriously worn; the temperature of the rolled piece is uneven or compressed The cutting amount is uneven, resulting in uneven extension of each part; the straightening machine is improperly adjusted; when steel, especially large steel, is in a hot state, turning one end of the steel on the cooling bed can easily cause the end to twist.

③Control method of section steel torsion: Strengthen the installation and adjustment of the rolling mill and guide plate. Do not use severely worn guide plates to eliminate the torsional moment on the rolled parts; strengthen the adjustment of the straightening machine to remove the torsional moment added to the steel during straightening; try not to turn the steel at one end of the cooling bed when the steel is hot. , to prevent the ends from twisting.

8. Steel bending

①Defect characteristics of steel bending: Longitudinal unevenness is collectively referred to as bending. It is named according to the bending shape of the steel. A uniform bend in the shape of a sickle is called a sickle bend; a wavy overall repeated bend is called a wavy bend; the overall bending of the end is called an elbow; one side of the end corner is warped inward or outward (serious bending). when rolled up) is called a corner.

② Causes of steel bending: Before straightening: Improper adjustment of the rolling operation or uneven temperature of the rolled piece, which causes inconsistent extension of each part of the rolled piece, which can produce sickle bends or elbows; the diameter of the upper and lower rollers is too different, and the design of the finished product exit guide plate Improper installation can also produce elbows, sickle bends or wavy bends; uneven cooling beds, inconsistent speeds of rollers on the rolling cooling bed or uneven post-rolling cooling can produce wavy bends; uneven metal distribution inherent in the product cross-section, naturally The cooling speed is inconsistent. Even if the steel is straight after rolling, it will produce a sickle bend in a fixed direction after cooling; when hot sawing steel, the saw blade is seriously worn, the saw is advanced too fast, or the hot steel hits the baffle at high speed on the roller table, and the steel During the traversing process, the end collides with certain protrusions, which can produce bends or angles; improper storage of steel during lifting and intermediate storage, especially when operating in a red-hot state, can produce various bending. After straightening: Except for corners and elbows, the normal corrugated and sickle bends of the steel should be straightened after the straightening process.

③Methods to control the bending of section steel: Strengthen the adjustment operation of the rolling mill, correctly install the guide device, and control that the rolled piece should not have excessive bending during rolling; strengthen the operation of hot sawing and cooling bed processes to ensure the length of the cutting head and prevent collisions. Bend steel; strengthen the adjustment operation of the straightening machine, and promptly replace seriously worn straightening rollers or rollers; to prevent them from being bent during transportation, a spring baffle can be installed in front of the cooling bed roller table; control straightening strictly by the regulations When the temperature of the steel is too high, stop straightening; strengthen the storage of steel in the intermediate warehouse and finished product warehouse to prevent the steel from being bent or being bent by the crane rope.

9. The shape of the section steel is incorrect

① Characteristics of defects in the irregular shape of section steel: There is no metal defect on the surface of the section steel, and the cross-sectional shape does not meet the specified requirements. There are many names for this defect, which vary from breed to breed. Such as the ellipse of round steel; and the rhombus of square steel; the legs of channel steel are slanted, the waist is wavy, and the legs lack flesh; the top angle of angle steel is large, the angle is small, and the legs are unequal; the legs of I-beam are slanted and the waist is uneven; channel steel Slumped shoulders, protruding waist, concave waist, enlarged legs, parallel legs, etc.

② Reasons for the abnormal shape of the steel: Improper design, installation, adjustment, or serious wear of the straightening roller; Unreasonable pass design of the straightening roll; Severe wear of the straightening roll; Improper design, wear or finished product of the pass and guide device of the rolled steel The hole guide device is poorly installed.

③Methods to control the irregular shape of section steel: improve the pass design of the straightening roller, and select the straightening roller appropriately according to the actual size of the rolled product; when the channel steel and automobile wheel mesh is bent over for rolling, the forward direction of the straightening machine can be moved to the second The first (or third) lower straightening roller is made into a convex shape (convexity height 0.5~1.0mm), which is beneficial to eliminating the concave waist defect; for steel sections that need to ensure the unevenness of the working surface, control should start from rolling; strengthen straightening Machine adjustment operation.

10. Section steel cutting defects

① Characteristics of defects in section steel cutting: Various defects caused by poor cutting are collectively called cutting defects. Among them, when flying shears are used to cut small steel in a hot state, scars of varying depths and irregular shapes are caused on the surface of the steel, which are called cuts; in a hot state, the surface is damaged by the saw blade, which is called a saw wound; after cutting, cutting If the surface is not perpendicular to the longitudinal axis, it is called beveling or sawing; if the hot-rolled shrinkage part of the end of the rolled piece is not cut, it is called short cutting; after cold shearing, local small cracks on the shearing surface are called tearing; sawing (shearing) ) After cutting, the metal flash left on the end surface of the steel is called burr.

②Causes of section steel cutting: the sawing steel and the saw blade (shearing edge) are not perpendicular or the head of the rolled piece is too bent; equipment: the saw blade has a large curvature, the saw blade is worn out or improperly installed, and the upper and lower shearing edges The gap is too large; the flying shear is out of balance; in terms of operation: too many pieces of steel are sheared (sawed) at the same time, too few ends are removed, the hot-rolled shrinkage part is not completely cut, and various misoperations.

③Control method for section steel cutting: 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 material perpendicular to the shearing (sawing) plane; improve the condition of the equipment, adopt no or small curvature For the saw blade, choose the thickness of the saw blade appropriately. The saw blade (shearing edge) should be replaced in time when it is worn. Correctly install and adjust the shearing (sawing) equipment; strengthen the operation, and do not cut (saw) too many pieces at the same time to avoid the rise and fall of the steel. , bending. The necessary amount of end removal must be ensured, and the hot-rolled shrinkage part must be cut cleanly to avoid various misoperations.

11. Steel straightening

① Defect characteristics of section steel straightening: surface scars caused during cold straightening. This kind of defect has no traces of thermal processing and has a certain regularity. There are three main types. Pit type (or pit correction), fish scale type, damaged type.

②Causes of straightening marks on profiled steel: The hole pattern of the straightening roller is too shallow, the steel is severely bent before straightening, the steel is fed incorrectly during straightening, or the straightening machine is adjusted improperly, which can cause damaging straightening marks; local damage to the straightening roller or Bonded metal blocks, local bulges on the roller surface, severe wear of the straightening roller or high roller surface temperature, and bonded metal can produce fish scale-shaped straightening marks on the surface of the steel.

③Methods to control the straightening marks of section steel: Do not continue to use the straightening roller if it is severely worn and the straightening marks are severe; when the straightening roller is partially damaged or the metal block is bonded, it must be polished and smooth in time; when straightening angle steel and other sections of steel, the straightening roller must be The relative movement of the contact surface between the roller and the steel material is large (caused by the difference in linear speed), which can easily cause the temperature of the straightening roller to rise and cause scratches, resulting in straightening marks on the surface of the steel material. Therefore, cooling water should be poured on the surface of the straightening roller for cooling; to improve straightening The straight roller material may be quenched on the straightening surface to increase surface hardness and wear resistance.