why macula on the hot rolled pickling coils

September 27, 2022
Latest company news about why macula on the hot rolled pickling coils

The full name of pickling coil is "hot-rolled pickling coil", which usually refers to the product obtained by using hydrochloric acid (HCl) to remove the iron oxide scale on the hot-rolled surface.

The pickled substrate is in direct contact with the environment, unlike the surface of the cold-rolled and annealed sheet, which usually has a dense oxide layer to play a certain protective role, so the surface of the pickled product is very prone to oxidized macular defects.

In view of this characteristic of pickling products, there are special descriptions and reminders in the major standards. Taking Baosteel's enterprise standard Q/BQB 302 as an example, the description is as follows:

 

6.4.2 Steel sheets and strips with pickled surfaces can be delivered with or without oil. Under normal packaging, transportation, handling and storage conditions for pickled steel plates and steel strips that have been oiled, the supplier guarantees that no rust will occur within three months

from the date of completion of production. . If the party requires the supply of pickled steel plates and strips without oil, it should be specified in the contract. Pickling steel plates and strips without oil coating are prone to rust and scratches during transportation and processing, and the supplier does not guarantee this.

There are similar descriptions and hints for this in the various hot rolling standards.

The causes of macular degeneration on the surface of acid-washed products are very complex

Production, packaging, storage, transportation, and one-time processing may all occur in steel mills. Therefore, when analyzing macular defects, it is necessary to mobilize information from each link for comprehensive analysis in order to obtain accurate judgments. Many technicians like to analyze the elemental

composition of the macula, and judge the cause by whether there is Cl residue.

It has to be said that this method is simple and rude, and also has quantitative data, which is easily accepted by users. However, if you ignore the surface features of the macula, it is easy to ignore the real cause, resulting in a passive situation in the subsequent processing of abnormal materials.

 

Basic Routines About Quality Defect Analysis

Friends who are familiar with our official account know that Brother Chai has always insisted on such a point of view: "Quality defect analysis and criminal investigation have a lot in common. They are essentially a kind of retrospective after the fact, and the result to find the cause. a process".

Its reasoning mode is retrospective, and its method is the hypothesis verification and exclusion method that constantly approaches the target truth. The main difficulty it faces is how to discover the inner connection of things from the complicated appearance.

Therefore, it is the basic routine of quality defect analysis to understand the background information of defective products, collect and classify the regularity and appearance of defects, and then comprehensively analyze with experience, and finally form a complete chain of evidence and confirm it.

 

Analysis of typical cases of macula

 

The wide strip-shaped macular parallel to the rolling direction will occur in both high-speed production lines and low-speed production lines, but oblique water-striped macules usually only exist in low-speed production lines, that is, in cross-cutting processing lines. is more likely.

But why did the quality inspector not find the macula during the slitting process? Because the formation of macula requires an oxidation time, when the steel plate is contaminated by water traces, only the appearance of water traces appears, not the appearance of macular.

We have encountered a reason for a similar appearance in the processing plant, which is for your reference in actual operation:

During the high temperature season in summer, several blowers are placed on the side of the cross-cutting line to cool down, and one of them is facing the production line.

Due to its particularity, the acid-washed macula needs to collect various information during analysis. At the same time, it is also necessary to choose high-quality and standardized processing plants for shearing.