Hainan Steel Wholesale

01. Roll printing defect

Defect characteristics:It is a group of periodic, roughly consistent in size and shape concave convex defects, with an irregular appearance

Cause of occurrence:

(1) On the one hand, due to fatigue or insufficient hardness of the rollers, some of the surface may have fallen off and the edges may be concave. On the other hand, it may be due to foreign objects adhering to the surface of the rollers, causing the surface to appear protruding;

(2) During steel rolling or finishing, concave and convex defects are formed by pressing into the surface of the steel plate.

02. Surface inclusions

Defect characteristics:There are irregular non-metallic inclusions in the shape of dots, blocks, or strips on the surface of the steel plate, and their colors are generally reddish brown, yellow brown, gray white, or gray black.

Cause of occurrence:

(1) The subcutaneous inclusions in the slab are exposed after rolling, or the original surface inclusions of the slab remain on the surface of the steel plate after rolling;

(2) Refractory materials and non-metallic substances such as mud and sand from the heating furnace fall on the surface of the slab, and are pressed into the slab surface during rolling.

03. Iron oxide scale

Defect characteristics:Iron oxide scale generally adheres to the surface of the steel plate, distributed locally or entirely on the surface of the plate, appearing black or reddish brown; Some iron sheets are loose and fall off, while others are not easy to fall off when pressed into the board surface; According to the different appearance shapes, there are:red iron sheet, block iron sheet, strip iron sheet, linear iron sheet, wood grain iron sheet, meteor shaped iron sheet, spindle shaped iron sheet, drag shaped iron sheet, and scattered iron sheet, with different depths of pressing.

Cause of occurrence:

(1) The generation of pressed iron oxide scale depends on the heating conditions of the slab. If the heating time exceeds a certain time, the higher the heating temperature and the stronger the oxidation atmosphere, the more iron oxide scale will be generated, and it is not easy to fall off. The iron scale produced once is difficult to remove completely, and is pressed into the surface of the steel plate during rolling;

(2) The setting of the large vertical roller is unreasonable, and the iron sheet is not squeezed loose, making it difficult to remove;

(3) Due to the low water pressure of the high-pressure descaling water pipe, water blockage, incorrect water angle, and improper use, the iron sheet on the surface of the steel plate has not been completely removed and is pressed into the surface of the steel plate after rolling;

(4) Iron oxide scale occurs more frequently in boiling steel, and it is easy to produce red iron scale in steel with higher silicon content.

04. Uneven thickness

Defect characteristics:The uneven thickness of each part of the steel plate is called uneven thickness. For steel plates with uneven thickness, it is generally due to excessive deviation, with local steel plate thickness exceeding the specified allowable deviation.

Cause of occurrence:

(1) Improper adjustment of roller gaps and configuration of roller profiles;

(2) The wear of the bearing shells on both sides of the rolling mill is different;

(3) The heating temperature of the slab is uneven.

05. Pitting

Defect characteristics:The surface of the steel plate shows local or continuous pits called pits, which vary in size and depth.

Reason:During the heating process, the slab oxidizes severely, and during rolling, the iron sheet is pressed into the surface, forming small pits after falling off.

06. Bubbles

Defect characteristics:There are irregularly distributed circular convex bumps on the surface of the steel plate, sometimes in a worm like straight shape, with a relatively smooth outer edge and gas inside; After the bubbles are crushed, irregular fine cracks appear; Some bubbles do not protrude, but after being flattened, their surface becomes bright and their shear cross-section appears layered.

Cause of occurrence:

(1) Due to the presence of numerous defects such as bubbles and airbags on the slab, it did not heal after multiple rounds of rolling and remained on the steel plate;

(2) The slab has been in the furnace for a long time, and bubbles are exposed.

07. Tower shape (staggered rolling edges)

Defect feature:The upper and lower ends of the steel coil are uneven, and each circle is higher (or lower) than the other, which is called a tower shape. The up and down movement of the curling edge is called curling edge movement.

Cause of occurrence:

(1) Improper adjustment of the gap between the auxiliary rollers;

(2) The gap between the pinch roller is wedge-shaped;

(3) Poor alignment during steel strip feeding into the coiling machine;

(4) Inappropriate winding tension setting;

(5) Improper adjustment of the gap between the formed guide plates;

(6) The action time of the side guide plate in front of the coiling machine is not synchronized;

(7) There is a gap between the drum and the pushing roll;

(8) The transmission end of the drum is severely worn, and there is a significant centrifugal difference during rotation;

(9) The strip steel has large sickle bends or poor flatness


08. Folding (folding, wrinkling, folding edges, folding corners)

Defect characteristics:The surface of the steel plate has a locally folded double-layer metal called folding, which has a shape similar to the crack, varying in depth, and generally presents sharp angles on the cross-section. The straight folding along the rolling direction is called forward folding; The fold perpendicular to the rolling direction is called a transverse fold; A folded edge is called a folded edge; The main difference between folding, printing, and wrinkling lies in the shape of the defect. The degree varies, and the degree of edge folding and angle folding varies according to the size of the angle. Lateral folding often occurs in thin strip steel. In soft steel with a carbon content less than 0.08, wrinkles are prone to occur due to the lack of tension rollers installed in the flattening machine.

Cause of occurrence:

(1) Scratches on rolled parts, resulting in folding during rolling, often occur on the lower surface of the steel plate;

(2) Excessive compression of the vertical roller, causing the roller ring to gnaw on the lower surface of the rolled piece;

(3) The depth to width=100% ratio of slab defect cleaning is too large;

(4) Uneven temperature of the slab, unreasonable configuration of the precision rolling roller profile, and unreasonable distribution of rolling load, etc., result in the formation of large waves during rolling of the strip steel, which are then pressed in;

(5) Due to the squeezing of the vertical roller ring or severe scratches on the rolled piece, as well as significant sickle bends in the incoming material from dry rough rolling, poor alignment, etc., the frame is scraped and then rolled again into a press fit;

(6) The side guide plate in front of the coiling machine is severely worn and has grooves, with small openings and wedge-shaped gaps between the clamping rollers, which can easily cause the strip steel to deviate and be pressed in by the clamping rollers at the groove of the side guide spot;

(7) Due to unforeseen circumstances, the winding was not carried out in a timely manner, resulting in a low winding temperature or an inappropriate winding speed setting;

(8) Steel coil edge misalignment, or due to loose steel coil, when lifted on a crane and lowered to the ground, is prone to edge and corner bending, which often occurs on thinner steel coils.

09. Unwinding

Defect feature:The steel coil is not tightly wound and there is a gap between layers, which is called loose coil.

Cause of occurrence:

(1) Inappropriate winding tension setting;

(2) The strip steel has severe wave shape or deformation on the roller conveyor due to coiling failure;

(3) The yield strength of steel is high, and the coiling temperature is too low;

(4) After the coiling is completed, the reel is reversed due to unforeseen circumstances;

(5) The tie is not tightened or the tie is broken.