Control Of Spot Defect On The Surface Of Cold Rolled Sheet

In steel products, the requirements of the surface quality of the cold rolled plate are very strict. The surface defect is the most important quality problem of the cold rolling plate. Once the cold rolling plate appears surface defects, it will seriously affect the quality and performance of the subsequent deep processed products. The cold rolled products of the first steel mill of the Ma'anshan iron and steel organization (Limited by Share Ltd) have been plagued by the defects of the surface stains for a period of time. It has brought a very negative impact on the image of a steel rolling product and even the products of Masteel in the market and caused huge economic losses. Only from June 2011 to April 2012, a steel rolling cold rolling finished product paid 21417 tons due to quality problems, of which the quality of surface spot defects accounted for nearly 1/3 of the total quality problems, and became a problem to be solved urgently.

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The spots on the surface of the cold rolled plate of Masteel are irregular, lump and strip-shaped, light yellow, yellow-brown or red, and dark brown and rough surface. Maanshan Iron and Steel Co., Ltd. cooperated with the Science College of Naval Engineering University to analyze the causes of stain formation of cold-rolled products. First, through the strengthening of monitoring and management, the problem of blocking the center of small steel rolls caused by unsuitable stacking of the stack when the material is put into the furnace is eliminated, and the steel curl after annealing is black, and the surface carbon residue cannot be removed. The surface corrosion caused by the leakage of air conditioning droplets on the surface of the steel coil is caused by the leakage of rain or the movement of vehicles. And the problem of uneven oil coating in the oil painting system; Then the influencing factors are analyzed in depth.


They found that most of the spot defects occurred in the finished product roll of the flat unit, reducing the output of the finished product, and changing the finished product into the finished product can greatly reduce the production of such defects. Among them, the flat blowing system and the whole liquid system are closely related to the occurrence of surface spot defects.


1. The Effect of the PH Value of the Leveling Fluid on the Spot Tracking


The acid and alkali of the liquid have a corrosive effect on the surface of the plate. It is easy to form a fine point corrosion pit on the plate surface and keep in the corrosion pit, and the oxidation reaction is formed to form a spot. The test shows that when the pH value is greater than 7 and less than 9, there is no correlation between the pH value and the production of the spot. Therefore, the standard of making the pH value of the leveling liquid is equal to 7 and less than 9.  

2. The Effect of the Concentration of the Leveling Liquid on the Spot  
The leveling liquid is directly contacted with the surface of the strip, and its purpose is to lubricate the rolling process of the coil. The experiment showed that the concentration of the leveling liquid had a great influence on the spot. 100% of the spots were produced in 100% of the leveling liquid. There were no spots produced in 2.94%, 3.36%, 3.77%, 4%, and four modes. According to the test results and cost considerations, the formulation of leveling liquid concentration control is greater than 2.4% to less than or equal to 4% as the operating standard.

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3. The Influence of Dynamic Sweep Pressure of the Flat Liquid on the Spot

The test results show that the dynamic blowing pressure of the leveling liquid has no effect on the spot track when it is above 5Kg. Therefore, the dynamic blowing pressure of the leveling liquid must be kept above 5Kg, and the downtime is lower than the standard value.


4. The Influence of the Temperature of the Mixing Tank on the Spots.


The test results show that the temperature of the mixing tank is closely related to the spot track. The temperature of the leveling liquid is above 50, the number of spot volume is the least, the temperature of the leveling solution is below 30, and the number of spot volume is the most. Therefore, the temperature of the mixing tank should be controlled above 50.


According to the results of the test and analysis, Ma steel has taken corresponding measures. The quality objection caused by the surface stain problem has decreased greatly and achieved good results, which is equivalent to an indirect increase of 79 thousand and 200 yuan per month.