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LMM GROUP main products focus on the cold and hot plate & wide strip mill rolls and heavy section mill rolls and big casting & forging pieces.

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Common Surface Defects and Causes of Cold Rolled Sheet



Common surface defects of cold-rolled plates include pitting defects, cracks in the middle of the chilled plate, edge cracks of the chilled plate, band-shaped peeling, discontinuous point line-shaped defects, black (gray) line (band) defects, etc


Rolling rolls: Mill rolls, Cold rolled,Cold rolled sheet

Related product: Rolling mill rolls

1.pitting defect. The single pits are distributed irregularly, and the overall distribution is banded. Pockmarks are microscopically composed of many tiny pits, and many fine particles can be seen inside the pits. The impurity elements in the pits are basically the same as those of the mold powder, indicating that these inclusions mainly come from the mold powder.

2.The central part of the chilled plate is cracked. There are many scaly fragments hanging in the middle part of the crack. The edges of the large scaly fragments contain many small particles, and the fractures are brittle. The fine particles are similar in composition to the mold powder, and it is determined that these inclusions mainly come from the mold powder.

3.The edges of the cold hard board are cracked. The edge cracks are zigzag-shaped. The cracks contain a large number of particles of different sizes. There is no obvious gap between the particles and the matrix. Some particles are distributed in a line parallel to the direction of the crack. These particles also come from mold powder.

4.Ribbon-shaped warped skin. There is an obvious thin layer near the surface of the slab, which is separated or semi-separated from the substrate, and there is a large amount of powdery substances under the skin at the surface of the plate. Energy spectrum analysis shows that these substances are mainly derived from the denatured mold powder.

5.Discontinuous points and linear defects. The thickness of the plate is less than 1mm, and this defect is easy to occur. Linear defects mostly appeared in clusters, and silicate composite inclusions remained at the bottom of the defects. It is mainly the inclusions enriched in the slab shell and subcutaneous and central parts of the CSP cast slab, which gradually appear as the thickness becomes thinner during the hot rolling process.

6.Black (gray) line (band) defects. The macro morphology after pickling has strips, strips, blocks or multiple points, with a particularly clear outline.

Due to

1) The quality of the roll is poor, mainly due to peeling of oxide film, rough aging, peeling, adhesion of foreign matter, etc.

2) The descaling is not clean, mainly due to factors such as nozzle clogging and low nozzle pressure.

3) Process factors, non-standard cooling water control between racks, etc.

4) Scratches on the conveyor roller table before continuous casting to F7, mainly due to furnace roller nodules, foreign matter adhesion, dead rollers, etc.

The above factors cause the oxide scale to be pressed in, thereby forming black (gray) line (band) defects on the chilled plate.

Generally it is 5-10 days if the goods are in stock. or it is 15-20 days if the goods are not in stock, it is according to quantity.

A: Payment<=1000USD, 100% in advance. Payment>=1000USD, 30% T/T in advance ,balance before shippment.

Always a pre-production sample before mass production;
Always final Inspection before shipment;
During the epidemic, provide remote detection technical support

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Rolling mill rolls product

Classification by roll material:

Cast iron mill rolls

  • Alloy indefinite chilled cast iron rolls
  • Alloy chilled cast iron rolls
  • Alloy SG ductile cast iron roll
  • Pearlitic ductile cast iron roll
  • Bainite ductile cast iron roll
  • Centrifugal cast iron roll

Cast steel mill rolls   

  • Alloy cast steel rolls
  • Semi-steel roller
  • Graphite steel rolls
  • High-chromium steel roll
  • High-speed steel roll

Forging mill rolls

Sort by position on the rolling mill:

Work rolls
backup rolls

Intermediate roll

Product advantage

The world No. 1 in crude steel production steel plant, over 70% of the HSS for bar and wire are from us.

LMM high-speed steel rolls have higher steel passing per groove (times) due to their good wear resistance, which saves roll changing time, improves rolling mill operation rate, reduces roll consumption, and improve the overall efficiency of the factory.
Generally, the amount of steel passing in a single groove (times) is 3 to 5 times that of cast iron rolls.

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