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Have you ever wondered about the process used by leading steel manufacturers like Sree Metaliks to ensure a pristine finish for their steel products? If yes, then the answer lies in a crucial process known as 'Steel Pickling'. It is used by us to remove the scales and impurities from the steel surface. In steel manufacturing, the pickling process is not an ordinary but a transformative step which enhances the quality, shine and durability of steel.
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If you are curious to know about 'Steel Pickling' and its intricacies, continue reading this comprehensive post by the Sree Metaliks team. It will introduce you to this method and guide you through all the requirements and steps of this process.
What is Steel Pickling?
Steel pickling is exactly what the word says i.e. it is a method of cleaning the steel in a pickling solution to remove impurities and rust from its surface. Pickling is typically done before moving to the other processing steps during steel manufacturing such as coating and welding. It, therefore acts as a crucial link between turning raw materials to high-quality products.
The science behind it is simply about the chemical reactions caused when steel is dipped into the pickling solution which is usually made up of Sulphuric acid or Hydrochloric acid. The acid solution dissolves the impurities from the steel surface.
With a brief idea about what this process is, let us move on to the next section of this guide which will explain the steps involved in steel pickling.
Steel Pickling Process
Steel pickling is a significant step involved in steel fabrication and it requires utmost precision and attention to detail. The steps followed are given below
Surface Preparation
The first step is to prepare the steel surface for pickling. It involves ensuring that the surface is clean and does not have any contaminants like grease or dirt.
Pickling Bath Preparation
The next step is to prepare the pickling solution, which usually contains either Hydrochloric acid or Sulphuric acid. The bath is prepared by diluting any one of these acids with water. Sree Metaliks believes that it is the concentration of the pickling solution which is responsible for efficient results. Our experts choose the acid type and its concentration based on the steel type and impurities present in it.
Immersion in Pickling Solution
After carefully preparing this acid bath, known as a 'Pickling Solution' or 'Liquor', the next step is to immerse the steel in it. This immersion results in acid reacting with the surface impurities like scale and rust to dissolve them into the solution, leaving the steel surface clean. The duration needed for immersion varies for different types of steel. It also depends on the amount of surface impurities and the steel’s thickness.
Rinsing
When the pickling is completed, the immersed steel is thoroughly rinsed with water to remove acid residue from its surface. If needed, some neutralising solutions are also applied to the steel at this step to eliminate acidic residues.
Drying
The steel product is dried thoroughly after rinsing as even the slightest moisture left on it can result in rusting. Only after ensuring complete dryness, we can move on to the next steps involved in fabrication such as coating or galvanising.
Waste Management and Environmental Controls
Sree Metaliks is committed to environmental safety and believes that the pickling process is not completed until the waste produced from it is disposed properly. Here, waste means the acid bath and impurities removed from the steel. We neutralise it and dispose it off responsibly to minimise environmental impact.
Acids Used for Preparing Pickling Liquor
The acids used for the pickling process are usually Hydrochloric or Sulphuric acids, both of which have their unique advantages and disadvantages. Let us take a look at these:
Hydrochloric Acid
Advantages
- Removes scale more extensively as compared to other acids.
- Decreases heating costs as it can be used in the acid bath at room temperature.
- Minimal iron salt deposition on the steel surface.
- Less hydrogen penetration by diffusion.
Disadvantages
- Disposal of Hydrochloric acid is higher than Sulfuric acid.
- Expensive acid recovery systems
- Forms fumes when the temperature goes above ambient temperature
- Intense corrosive nature towards equipment
Sulphuric Acid
Advantages
- Temperature can be raised for lower acid concentration to ensure efficient pickling.
- Iron sulphate can be recovered easily.
- Feasible to renew acid more frequently.
- The pickling rate can be controlled with temperature changes.
Disadvantages
- Sulphuric acid baths are required to be heated and do not work at room temperature.
- Residues formed are adherent.
- Acid attacks significantly on the base metal.
- Significant hydrogen diffusion into the steel.
Advantages of Steel Pickling
Surface cleanliness is not the only benefit of the pickling process used during steel manufacturing. It also offers the following additional advantages.
Uniform appearance
One of the many benefits of the pickling process is that it offers a uniform appearance to the steel by removing the heat stains that have been caused by previous operations. The elimination of these stains ensures an appealing appearance for the final product, reducing the need for finishing processes.
Enhanced Corrosion Resistance
The pickling process also increases the steel’s resistance towards corrosion. This is especially advantageous in pickling stainless steel as it makes it capable of withstanding harsh environments.
Decreased Surface Abrasion
Pickling is much gentler on the steel’s surface as compared to other mechanical methods. As a result, the risk of particle embedment is reduced.
Easy and Cost-Effective
Another benefit of the pickling process is that it is quite simple to carry out. Also, it is much more affordable than other methods making it very cost effective. Its simplicity and affordability make it suitable for use in a large number of applications.
Bottom Line
Steel pickling is a highly reliable method used for cleaning steel. Sree Metaliks firmly believes in the advantages of this process and uses it efficiently to ensure the premium quality of its products. We follow all the steps of this method appropriately and diligently till the end making it our responsibility to neutralise and dispose of the residue acid bath and impurities eliminated from the steel to ensure minimal or no negative environmental impacts.