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

YUAN HUI
YUAN HUI
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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Research on the use and maintenance of cold rolling mill rolls

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Rollers are key contact process equipment in strip steel production. In view of the problems existing in the processing and use of cold rolls, we improve the surface quality during the production process, reduce production costs, and ensure efficient operation of continuous production from three aspects: roll grinding, roll non-destructive testing, and roll use.

Non-destructive testing of rolls is of great significance to the rolling of cold rolled plates, especially ultrasonic testing. Reduce rolling accidents during online operation of the rolls. Reasonable scheduling according to the attenuation of roll roughness, improving the chromium plating quality of the chrome-plated rolls and optimizing the edge chamfer design of the support rolls will help reduce roll consumption.

cold rolling mill rolls

Roll mill rolls processing

The rolls are subject to high rolling loads during operation. At the same time, there are frequent bending, torsion and friction between rollers. After a certain period of use, surface grinding is required to remove surface defects such as pits, roller marks, cracks, etc., and the fatigue layer is gradually removed while repairing the roller curve. The roll material is a polymer composed of iron-based solid solution and alloy carbide. Currently, Cr5 rollers are generally used, and the single grinding amount is 0.2-0.3mm. If the roller processing cannot be qualified at one time, the grinding amount will reach more than 0.1mm after repeated processing.

In addition to the mechanical equipment factors of the grinder, the most critical media and consumables for roll grinding are metal cutting fluid and grinding wheels, and the improvement of surface quality also puts forward higher requirements for metal cutting fluids and grinding wheels. Metal cutting fluid needs to have good chip settling properties, excellent cooling and cleaning properties, and reduce scratches on the roller surface. Select the appropriate grinding wheel model and grinding process parameters to ensure that roll shape problems, surface vibration lines, transverse thread lines, surface roughening, etc. do not occur during the grinding process. For hardened steel rolls, corundum grinding wheels are generally used. Only by selecting a matching corundum grinding wheel according to the material of the roll can high surface quality and grinding accuracy be achieved. Problems with roll shape are usually primarily caused by a grinding wheel that is too soft. Chattering defects on the roll surface will occur when the grinding wheel is too hard or the feed rate and lateral movement speed are too high. It needs to be solved by reducing the linear speed of the grinding wheel, reducing the feed amount, reducing the lateral movement speed, and increasing the roll speed. Transverse thread lines, also known as tool lines, will appear when the grinding wheel is not well corrected or the feed rate and lateral movement speed are too high. When the grinding wheel is too soft, the coolant filtration fails, and the abrasive grains float in the coolant, it will cause grinding point defects on the roll surface. It is necessary to check the coolant filtration, increase the grinding wheel speed, reduce the roll speed, and reduce the amount of feed. . The grinding wheel is too hard and has poor self-sharpening. The passivated sand grains are not easy to fall off, and the grinding roller surface is prone to roughening. It is necessary to increase the roller speed and reduce the grinding wheel linear speed.

The grinding feed of the roll and the cooling property of the cutting fluid not only affect the surface state of the roll, but excessive feed or insufficient cooling will also cause micro-cracks on the surface of the roll, which are small and fine. The use of non-destructive testing such as eddy current and ultrasonic testing requires high sensitivity to detect. Ultrasonic and magnetic particle testing results of micro-cracks on the roller surface burned by grinding. If such grinding micro-cracks are not discovered, use of the machine will cause serious accidents such as peeling and roller explosion.

In order to achieve good deep drawing properties and high coating adhesion, the surface condition of cold-rolled strips is usually pitted, and the work rolls need to be texturized. At present, the roll texturing method used for high-quality plate and strip production mainly uses electric spark texturing. The morphological parameters of EDM texturing, such as surface roughness Ra, peak density Pc value, etc., can be controlled by adjusting the pulse voltage, point spacing, current intensity, intermittent time, etc. Reducing the current or pulse width can reduce the Ra value and increase the PC value. The uniformity of texturing and the point defects of texturing are related to the quality of toner and electrodes. Uneven discharge and toner adhesion will cause texturing quality problems, leading to repeated grinding and texturing, resulting in increased costs. At the same time, watermarks often appear during the texturing process. The watermarks are wavy and curved, with a certain color difference on both sides. They are more obvious after chrome plating and have a serious impact on rolled high-end surface products.

Roll inspection

Non-destructive testing is required before the roll is put on the machine. Ultrasonic testing, eddy current testing, magnetic particle testing and penetrant testing are commonly used in daily production. Eddy current testing has the advantage of fast detection speed and can detect soft point defects, but it can only target surface opening defects, and is affected by many factors that interfere with it. Too high sensitivity can easily cause cluttered signals. Penetrant testing is only effective when dealing with local large opening defects. The use of ultrasonic waves combined with magnetic particle testing is more effective in ensuring the normal use of rolls.

The most convenient way to use ultrasonic surface waves is to use the bottom wave method, that is, place the probe at a position 1000mm in the middle of the roll body, adjust the water chestnut reflection wave at the end of the roll body to 20%, and then gain 32dB. When the roll is in good condition, no abnormal wave reflection will be caused by detecting the surface of the roll body in both circumferential and axial directions. However, due to the constraints of the smelting process, there are sometimes tiny pores and loose defects in the outer ring of the roller body. After forging, the elongated strips are called hair lines, which are randomly distributed along the length of the roll body, with a length of mostly 0.05-3mm, causing abnormal reflection in surface wave detection. These tiny hairline defects are generally within 1mm in length and will not affect product quality during use. However, it is difficult to distinguish the small cracks produced by the on-line rolling of the roll during ultrasonic testing. In this case, magnetic particle inspection and microscopic observation are required. If the edges of the defects are flat, they are generally defects in the roll manufacturing. If the edges have sharp corners, they are generally crack defects caused by rolling use. Surface crack defects will cause strip peeling on the roll surface, which can effectively detect the residual cracks on the roll surface that have not been ground to avoid roll belt damage during online operation. Magnetic particle and ultrasonic inspection results of hair lines and magnified images of residual cracks.

The sensitivity of direct ultrasonic flaw detection is based on the AVG method to determine the equivalent diameter of the flaw, and 20% of the first bottom wave reflection that is not full screen height is used as the reference height, and then the gain is adjusted according to the sensitivity increment of the flaw detection part according to the calculation formula.

After discovering the defect signal, use the gain of the instrument to detect the thickness of the workpiece into ten equal parts, with the principle of 12, 7, 5, 4, 3, 3, 2, 2, 2. Decrease the corresponding gain value according to the defect position, and use this as a basis to increase or decrease the height of the defect wave to 20% of the full amplitude scale of the screen. Generally, the outer surface of the work roll and the intermediate roll with a depth of 90mm from the roll surface is not allowed to have defect echoes, and the middle area is not allowed to have defects exceeding Φ2+15dB. The abnormal wave defect near the center of the work roll caused a certain decrease in the bottom wave, but the evaluation results did not exceed the standard. The abnormal wave comes from the loose superposition equivalent in the center, and there is no abnormality when the roll is put into use.

When using support rollers, the stress concentration location during use is 5-10mm deep. It is difficult to detect defects in this depth area through ultrasonic surface wave inspection after off-line. Using a straight probe to detect the formation of defects is relatively shallow, and it will be more difficult to detect if they have not reached a certain scale. In this case, the sensitivity of surface waves is increased, grass-like waves are screened, and the position of the beams that appear in clusters is focused on direct ultrasonic detection. Ultrasonic detection and internal and external conditions of damage under the roll skin. In the subsequent use, it is necessary to increase the detection and tracking of the accident roll to prevent the cracks from continuing to expand and cause the entire roll to be scrapped.

rolling mill rolls hs code

Roller use

In the case of acid continuous rolling with large reduction, the hardness of the roll body of the rolling mill work roll needs to be absolutely guaranteed, otherwise it will cause product thickness fluctuations and poor plate shape. The pursuit of roller height and hardness will lead to poor accident resistance of the rollers, which puts forward higher requirements for a low production line operation accident rate. A more serious belt breakage accident will directly cause the work roll worth 100,000 yuan to be scrapped. Downstream users such as automotive appliances have higher requirements on the shape of cold-rolled products. At the same time, the surface roughness requirements of automotive steel are very narrow. In order to obtain the strip surface roughness and surface quality that meets user requirements, it is necessary to reasonably arrange the production plan according to the attenuation of the roll roughness, extend the roll life cycle as long as possible, and reduce the frequency of roll replacement. Reduce roll consumption.

The roller replacement cycle of the support roller has relatively little relationship with the structure and specifications of the product. The abnormal consumption of the roll is in addition to the internal damage caused by the accident. At the position where the stress is greatest on the shoulder chamfering of the support roller, and when the chamfering form at the end of the roll body is a straight line, it is easy to form small micro-cracks with a depth of 2-3 mm. Grinding and removal will cause a lot of roll consumption. , if it is not handled in time during subsequent use, it will cause the roller side to peel off. Switching to arc chamfering can effectively reduce stress concentration at this location. Quality problems such as inclusions in the roll itself will also cause the fatigue resistance of the chamfered area to decrease. Even if the chamfering curve is optimized, the inclusion defects in this area will cause the initiation and expansion of cracks, affecting the service life of the roll.

The chromium-plated roller can reduce the friction coefficient during the rolling process. The amount of iron powder produced during the roll gap friction process is reduced, which greatly improves the cleanliness of the rolled strip. Increase the surface average reflectivity of the strip. It reduces the pressure in the subsequent continuous annealing and galvanizing cleaning sections, which is beneficial to improving the quality of the board surface.

①The manufacturing control of the roll itself and the optimization of subsequent grinding and texturing processing parameters are the key to ensuring the quality of the roll surface. The first pass rate of roll grinding increases by 5%, and the overall service life of the roll is extended by more than 2.5%, which plays an important role in improving product quality and reducing costs.

② Defect prevention through non-destructive testing and stable operation of online testing equipment, basically avoiding 1-2 roll peeling losses per year.

③The attenuation law of roll texture roughness, the quality of roll chromium plating and the design of the operating cycle can increase the output of products requiring high-quality surfaces by 80%. Basically, each roll cycle reduces the production of 3-5 rolls of strips per roll, which is an important factor in improving product quality and reducing costs.

Cold rolling mill rolls

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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