Analysis and control method of common appearance defects of section steel

What is section steel?

Section steel is a kind of strip steel with a certain section shape and size. It is one of the four major varieties of steel (plate, tube, profile and wire). According to the section shape, the section steel is divided into simple section steel and complex section steel (special section steel). The former refers to square steel, round steel, flat steel, angle bar, six angle steel, etc.; the latter refers to I-beam, channel steel, rail, window frame steel, curved steel, etc.


20200305134449 25074 - Analysis and control method of common appearance defects of section steel

According to the different smelting quality of steel, section steel is divided into ordinary section steel and high quality section steel.
Large section steel: in large section steel, I-beam, channel steel, angle bar and flat steel are all hot-rolled. In addition to hot rolling, round steel, square steel and six angle steel are also forged and cold drawn.
I-beam, channel steel and angle bar are widely used in industrial buildings and metal structures, such as factory buildings, bridges, ships, agricultural machinery vehicle manufacturing, transmission towers, transportation machinery, and often used together. Flat steel is used in construction site as bridge, house frame, fence, power transmission ship, vehicle, etc. Round steel and square steel are used as various mechanical parts, agricultural machinery parts, tools, etc.
Medium section steel: medium section steel, medium section steel, groove, angle, circle, flat steel, similar to large section steel.
Small section steel: small section steel medium angle, round, square, flat steel, processing and use are similar to large section steel, small diameter round steel is commonly used as building steel.

Common surface defects of section steel

The common surface defects of section steel are: fold, scratch, scab, pockmark (pockmark), pit, delamination, bump and bubble, surface crack, crack, burning crack, surface inclusion, ear and torsion, bending, incorrect section shape, angle dissatisfaction (collapse angle, obtuse angle, fillet), pull through, tolerance out of standard, short ruler, etc.

Insufficient angle filling of section steel

Defect characteristics
Due to the insufficient filling of finished holes, the lack of metal at the edge of section steel is called insufficient filling of section steel angle. Its surface is rough, mostly along the whole length, but also partly or intermittently.
Causes
Because of the inherent characteristics of pass, the edge and corner of rolled piece can not be processed; the adjustment and operation of rolling mill are improper, and the distribution of reduction amount is unreasonable. Small amount of corner reduction, or excessive drawing and contraction phenomenon due to inconsistent extension of each part of the rolled piece; serious wear of pass or guide plate, too wide guide plate or incorrect installation; low temperature of rolled piece, poor metal plasticity, and difficult filling at the corner of pass; serious local bending of rolled piece, easy to produce local corner filling dissatisfaction after rolling.
Control method
Improve the pass design, strengthen the adjustment operation of the rolling mill, reasonably distribute the reduction; correctly install the guide device, timely replace the seriously worn pass and guide plate; adjust the reduction according to the high and low temperature of the rolling piece, so that the edges and corners are filled well.

Section steel size out of tolerance

Defect characteristics
General designation for section geometry of section steel that does not meet the requirements of the standard. When there is too much difference from the standard size, it presents deformity. There are many kinds of defects, most of which are named after the location and the degree of out of tolerance. Such as out of roundness, length out of tolerance, etc.
Causes
The pass design is unreasonable; the wear of the pass is uneven, and the new and old holes are not matched properly; the installation of each part of the rolling mill (including the guide and guard device) is poor, and the safety mortar is broken; the rolling mill is not adjusted properly; the billet temperature is uneven, and the temperature of a single piece of steel is uneven, resulting in the partial specification is inconsistent, and the whole low-temperature steel has the overall specification is inconsistent, which is too large.
Control method
Correctly install all parts of the rolling mill; improve the pass design and strengthen the adjustment operation of the rolling mill; pay attention to the wear condition of the pass; when replacing the finished hole, consider replacing the front hole of the finished product at the same time according to the specific situation; improve the heating quality of the billet to reach the uniform temperature of the billet; some special-shaped materials may affect a certain dimension due to the change of the section shape after straightening, which may not meet the requirements At this time, the defect can be eliminated by re straightening.

Rolling scar of section steel

Defect characteristics
A metal block bonded to the surface of a section steel as a result of rolling. Its shape is similar to scarring, and the main difference with scarring is that the shape of the rolling scar and its distribution on the profile steel surface have certain regularity. There is usually no non-metallic oxide inclusion under the defect.
Causes
The pass of roughing mill is seriously worn, There are intermittent live rolling scars on the fixed surface of the section steel; the external metal (or the metal scraped by the guide device) is pressed into the surface of the rolling piece to form the rolling scars; the periodic bump or pit is generated on the surface of a certain rolling piece in front of the finished hole, and the periodic rolling scars are formed after rolling, the specific reasons are: the groove is not well scored; the groove has sand hole or meat; the groove is rolled by “black head” Bumps such as bumps or scabs are stuck on the workpiece; the rolled workpiece slips in the pass, causing metal to pile up on the surface of the deformation area, forming rolling scars after rolling; the rolled workpiece is partially scratched or bent by mechanical equipment such as apron, roller table, steel tipper, etc., forming rolling scars after rolling.
Control method
Replace the groove which is seriously worn or stuck with foreign matters in time; check the groove surface carefully before changing the roll, and do not use the groove which has sand holes or bad marks; do not roll black head steel to prevent the groove from falling flesh or bumping; pay attention not to damage the groove when handling the steel clamp accident; keep the mechanical equipment before and after the rolling mill smooth and level, and correctly install and operate to avoid damaging the rolled piece; pay attention to rolling It is not allowed to press foreign matters into the surface of the rolled piece; the heating temperature of the billet should not be too high to prevent the rolled piece from slipping in the pass.

Lack of meat in section steel

Defect characteristics
There is a lack of metal along the length direction on one side of the section. There is no hot rolling mark of the finished rolling groove at the defect, which is darker and rougher than the normal surface. Most of them are full length, but some are partial.
Causes
If the rolling groove is staggered or the guide guard is installed improperly, a certain section of the rolled piece is lack of metal, and the pass filling is not enough when rolling again; if the pass design is poor or the turning is wrong, and the rolling mill is adjusted improperly, the amount of metal entering the finished hole is insufficient, so that the finished hole is not filled; if the front and rear passes are worn to different degrees, it will also cause the lack of meat; if the rolled piece is twisted or bent locally, the local lack of meat will occur after rolling again.
Control method
Improve the pass design, strengthen the adjustment and operation of the rolling mill to make the finished hole well filled; fasten all parts of the rolling mill to prevent the roll from axial movement, and install the guide device correctly; timely replace the worn pass.

Scratch of section steel

Defect characteristics
In the process of hot rolling and transportation, the groove marks formed by the sharp edges of equipment and tools. Its depth is not equal, visible ditch bottom, have sharp edge angle commonly, common straight line shape, some also show curve shape. Single or multiple, full length or locally distributed on the surface of profile steel.
Causes
The floor, roller table, steel moving and turning equipment in the hot rolling area have sharp edges, and the rolled piece is scratched when passing through; the surface of the rolled piece is scratched due to the poor processing of the guide plate, unsmooth mouth edge, or the guide plate is seriously worn, with iron oxide scale and other foreign matters; the surface of the rolled piece is scratched due to the improper installation and adjustment of the guide plate, and the pressure on the rolled piece is too large; the edge of the surrounding plate is not smooth, and it is scratched when the rolled piece jumps over the sleeve.
Control method
Equipment such as guide device, apron, floor and ground roll shall be kept smooth and flat without sharp edges and corners; installation and adjustment of guide plate shall be strengthened without deflection or over tightening to avoid excessive pressure on rolled piece.

Wave of section steel

Defect characteristics
Because of the uneven rolling deformation, the wave undulation along the length of the local section of the section steel is called wave. Some are partial and some are long. Among them, the longitudinal undulation of I-beam and channel steel waist is called waist wave; the longitudinal undulation of I-beam, channel steel and angle steel leg edge is called leg wave. The longitudinal thickness of I-beam and channel steel with waist wave is not uniform. In serious cases, there are metal overlaps and tongue shaped cavities.
Causes
The main reason for the wave is that the elongation coefficient of each part of the rolled piece is not consistent, and there is a serious shrinkage phenomenon. Generally, it occurs in the parts with larger extension. The main factors that cause the change of the extension of each part of the rolled piece are as follows. Improper distribution of reduction amount; roller movement in series, wrong teeth of rolling groove; serious wear of groove in front of the finished product or re front hole; uneven temperature of rolled piece.
Control method
When replacing the finished hole in the middle stage of rolling, the front hole of the finished product and the front hole of the finished product shall be replaced at the same time according to the characteristics of the product and the specific conditions; the rolling adjustment operation shall be strengthened, the reduction amount shall be reasonably distributed, and all parts of the rolling mill shall be fastened at the same time to prevent the rolling groove from malocclusion. Make all parts of the rolled piece extend evenly.

Torsion of section steel

Defect characteristics
Along the length direction, the different angle of each section around its longitudinal axis is called torsion. Place the twisted steel on the horizontal inspection bench. It can be seen that one side of one end is raised, and sometimes the other side of the other end is also raised, forming an angle with the table. When the torsion is very serious, the whole steel is even in the shape of “twist”.
Causes
Improper installation and adjustment of rolling mill, roller center line not on the same vertical or horizontal plane, axial movement of roller, dislocation of rolling groove; improper installation or serious wear of guide plate; uneven temperature of rolled piece or uneven reduction, resulting in uneven extension of each part; improper adjustment of straightener; turning of steel at one end of the cooling bed, especially in the hot state of large-scale materials, is easy to cause end torsion.
Control method
Strengthen the installation and adjustment of rolling mill and guide plate. Do not use the guide plate with serious wear to eliminate the torsional moment on the rolled piece; strengthen the adjustment of the straightener to remove the torsional moment added to the steel during straightening; do not turn the steel at one end of the cooling bed as far as possible in the hot state to avoid the end torsion.

Bending of section steel

Defect characteristics
Longitudinal irregularity is called bending. Named after the bending shape of steel, the uniform bending in the shape of sickle is called sickle bending; the repeated bending in the shape of wave is called wave bending; the overall bending at the end is called elbow; one side of the end angle is warped inward or outward (rolled up when serious) is called bending angle.
Causes
Before straightening: improper adjustment of steel rolling operation or uneven temperature of the rolled piece may cause different extension of each part of the rolled piece, resulting in sickle bend or elbow; the difference between the upper and lower roll diameters is too large, and the guide plate at the exit of the finished product is improperly designed and installed, resulting in elbow, sickle bend or wave bend; uneven cooling bed, inconsistent rotation speed of each roll of the roller cooling bed or wave bend after rolling; inherent product section The metal distribution of each part of is uneven, and the natural cooling speed is inconsistent. Even if the rolled steel is flat, there will be a fixed direction of sickle bend after cooling. When hot sawing steel, the saw blade is seriously worn, the saw is too fast or the hot steel collides with the baffle plate at high speed on the roller table, as well as the end of the steel collides with some protrusions in the process of transverse movement, which can produce elbows or corners. The steel is being lifted, Improper storage in the middle, especially in the red hot state of operation, can produce a variety of bends. After straightening: in addition to corners and elbows, the straightening process shall be able to achieve the effect of straightness for the normal wave bending and sickle bending of steel.
Control method
Strengthen the adjustment operation of the rolling mill, correctly install the guide and guard device, and control the rolling piece from excessive bending during rolling; strengthen the operation of hot sawing and cold bed processes to ensure the length of the cutting head and prevent the bending of the steel; strengthen the adjustment operation of the straightener, and timely replace the seriously worn straightening roller or roller shaft; in order to prevent the bending during transportation, install the spring baffle in front of the roller table of the cold bed; strictly follow the The regulation stipulates that the temperature of straightened steel shall be controlled. When the temperature is too high, straightening shall be stopped; the storage of steel in intermediate warehouse and finished product warehouse shall be strengthened to prevent steel bending or hanging by crane steel rope.

The shape of section steel is not correct

Defect characteristics
There is no metal defect on the surface of section steel, and the section shape does not meet the requirements. There are many names of such defects, which vary with varieties. For example, the ellipse of round steel, the diamond of square steel, the leg skew, waist wave and leg flesh shortage of channel steel, the angle of angle bar’s top angle is large, small and leg inequality, the leg skew and waist inequality of I-beam, the shoulder collapse, waist convex, waist concave, leg expansion and leg combination of channel steel.
Causes
The design, installation and adjustment of straightening roller are improper or seriously worn; the pass design of straightening roller is unreasonable; the wear of straightening roller is serious; the pass and guide device of steel rolling are improperly designed, worn or the guide device of finished hole is poorly installed.
Control method
The pass design of the straightening roller shall be improved, and the straightening roller shall be selected properly according to the actual size of the rolled product; when channel steel and automobile wheel network are bent for rolling, the second (or third) lower straightening roller in the forward direction of the straightener can be made into a convex shape (the convex height is 0.5-1.0mm), It is beneficial to eliminate the concave defect; the section steel which needs to ensure the unevenness of working face should be controlled from rolling; the adjustment operation of straightener should be strengthened.

Cutting defect of section steel

Defect characteristics
All kinds of defects caused by bad cutting are collectively referred to as cutting defects. When the small steel is cut by flying shear in hot state, the surface of steel will be cut with different depth and irregular shape; when the surface is damaged by saw blade in hot state, it is cut; when the cutting surface is not perpendicular to the longitudinal axis, it is cut or sawed; when the hot rolled and drawn part at the end of the rolled piece is not cut, it is cut short; when the cold shear is finished, it is cut After sawing (shearing), the metal flash left on the steel end face is called burr.
Causes
The sawing steel is not perpendicular to the saw blade (cutting edge) or the head of the rolled piece is bent too much; in terms of equipment, the saw blade has a large curvature, the saw blade is worn out or improperly installed, the gap between the upper and lower cutting edges is too large; the flying shear is out of alignment; in terms of operation, too many steel pieces are cut (sawing), too few ends are cut, the hot-rolled stretch part is not cut completely, and various misoperations.
Control method
Improve the condition of incoming materials, take measures to avoid excessive bending of the head of the rolled piece, keep the direction of incoming materials perpendicular to the cutting plane of the shear (SAW); improve the condition of the equipment, take the saw blade without or with small curvature, properly select the thickness of the saw blade, timely replace the worn saw blade (cutting edge), correctly install and adjust the shear (SAW) cutting equipment; strengthen the operation, and at the same time, do not cut (SAW) too many pieces More, to avoid steel ups and downs, bending. It is necessary to ensure the necessary cutting amount of the end, cut the hot rolling drawing part clean, and avoid all kinds of misoperation.

Correction mark of section steel

Defect characteristics
Surface scars caused during cold straightening. This kind of defect has no trace of hot working and has certain regularity. There are mainly three types. Pit type (or straightening pit), fish scale type and damaged type.
Causes
The pass of straightening roller is too shallow, the steel before straightening is bent seriously, the feeding of steel during straightening is not correct or the adjustment and operation of straightening machine is improper, which may cause the damaged straightening marks; the straightening roller is partially damaged or bonded with metal blocks, the roller surface is locally raised, the straightening roller is severely worn or the roller surface temperature is high, and the bonded metal can produce fish scale straightening marks on the steel surface.
Control method

When the straightening roll is severely worn and the straightening marks are serious, do not continue to use it; when the straightening roll is partially damaged or the metal block is adhered, polish it in time; when straightening the angle steel and other steel sections, because the relative movement between the straightening roll and the steel contact surface is large (caused by the linear speed difference), it is easy to make the temperature of the straightening roll rise and scrape the tumors, and produce the straightening marks on the steel surface, so the surface of the straightening roll should be poured with cooling water Cooling; improve the material of straightening roller or quench the straightening surface to improve the surface hardness and wear resistance.

Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry (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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Summary
what is section steel - Analysis and control method of common appearance defects of section steel
Article Name
Analysis and control method of common appearance defects of section steel
Description
The common surface defects of section steel are: fold, scratch, scab, pockmark (pockmark), pit, delamination, bump and bubble, surface crack, crack, burning crack, surface inclusion, ear and torsion, bending, incorrect section shape, angle dissatisfaction (collapse angle, obtuse angle, fillet), pull through, tolerance out of standard, short ruler, etc.
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www.steeljrv.com
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