What is Steel Pickling?

Metal manufacturers producing steel and other metal parts need to ensure that the surface they work on is free from impurities and residues, such as rust, metal oxides (scale), and stains. These contaminants can create defects when the parts go through further processing, or can weaken surfaces. Surface finishing is often a requirement for metal parts, as one such finishing method is called steel pickling.

What is Steel Pickling & What Processes Does It Apply To

Steel pickling refers to a process where chemicals are applied to a metal surface to remove contaminants. The chemicals used will depend on the type of contaminants that are encountered as well as the metal that is being worked. Pickled steel is often done during hot working and cold working production applications due to the increased amount of scaling that occurs.

Key Benefits of Steel Pickling

Steel pickling is often chosen over other methods such as abrasive blasting, grinding, or wire brushing as it provides more accurate results. Pickled steel also experiences less metal removal that may typically occur during grinding and abrasive processes. The pickling "liquor" can reach all surfaces evenly to remove impurities. This process can also improve the surface appearance and provide corrosion resistance.

What Are the Types of Acids Used in Steel Pickling

The acids chosen for the pickling will depend on the process, desired temperatures, the types of contaminants that need to be removed, and the price. Two of the most common acids used within immersion baths and spray nozzle applications are hydrochloric acid and sulfuric acid. When selecting spray nozzles to perform the acid application for steel pickling, consider how the acid will impact the nozzle's materials and components. Lechler offers specially designed and engineered spray nozzles that can handle the abrasive and corrosive nature of acid liquids while completely coating steel surfaces.

Hydrochloric Acid

Hydrochloric acid is the most currently used acid when wanting to reduce heating costs. This acid can be used for pickled steel at room temperatures. This acid will deposit less iron salts on the metal's surface and doesn't penetrate as deeply with its hydrogen due to its diffusion properties. Hydrochloric acid can more extensively remove scaling versus other acids yet can be more expensive.

Sulfuric Acid

Sulfuric acid offers affordability for the pickling process as it is often used when wanting to recover iron sulfate easily. The rate of the picking process for sulfuric acid can be controlled by changing the temperature, as you can use lower acid concentrations when raising the temperature. Sulphuric acid can be renewed more frequently yet cannot be used for fast steel making processes as it needs more surface contact time.

How is Steel Pickled?

The pickling process begins by degreasing and cleaning the surface of oil, dirt, and other contaminants. While the pre-cleaning process is performed, the chosen acid becomes diluted as it is added into the water. The level of dilution will be based on the type of metal and how much pickling will be done to the surface.

Next, the acid solution is applied to the steel. This process may involve an immersion bath, wire brushing, or an even application from spray nozzles. The steel surface is now rinsed off to remove the acid solution until all of the acid is removed. A neutralizer and rust inhibitor may be applied in certain circumstances before the product is dried.

Safety Considerations

When the acid is applied to the steel and later rinsed off, it becomes pickling sludge. This sludge is considered hazardous waste. The amount of sludge generated is limited by the EPA under their waste material limit regulations. Customers should also be careful when using hydrochloric acid as the pickling liquor. Hydrochloric acid can generate fumes during the process. Safety policies need to be generated and put into place when handling any acids at high quantities, as workers should be trained on the proper application, rinsing, and retrieval of acids.

There are also other limitations to the pickling process. When using acid baths, the acid in the vat can weaken over time which can cause varying results regarding the removal of metal and impurities. Customers should also be careful of steel embrittlement that can be caused by hydrogen diffusion.

Products for Your Steel Pickling Process

Lechler offers a large line of spray nozzle products that can be used for the steel pickling process. The type of nozzle used will depend on the spray pattern and liquids used. Two nozzle designs include flat fan, axial hollow cone, educator nozzles, and multi-channel jet nozzles. These steel pickling nozzles can be used for the application of the acid, for pre-cleaning, for rinsing off metal surfaces of the acid solution, and for air drying of the metal after the pickling process.

Flat fan nozzles used for cleaning, pickling, and rinsing include Series 632/633, Series 621, and Series 625. These flat fan nozzles provide a parabolic distribution of liquids for a uniform distribution. If looking for flat fan spray nozzles with retaining nuts, Series 652, dove-tail nozzle Series 660, dove-tail Series 664/664, and dovetail Series 669 provide a simple jet alignment for total liquid distribution.

We also offer tongue-type nozzle Series 686, Series 688/689, dovetail series 686.XXX.WW.08, dovetail series 686.XXX.WW.15, dovetail series 686.XXX.WW.09 with a flat fan spray pattern design. These nozzles are non-clogging as the dovetail series offer automatic jet alignment.

Axial full cone nozzles Series 490/491 and Series 460/461 are ideal for pickling, surface treatments, and rinsing along with acid fume scrubbing. Obtain large cross-free sections and stable spray angles.

When using air to blow off metal surfaces for drying purposes, the Whisperblast Series 600.130/ 600.493/ 600.582 multi-channel flat fan, Series 679 flat fan, and multichannel round jet Series 600.325 spray nozzles can be used at the end of the rinsing process. The nozzles can lower air consumption and noise levels while effectively drying off pickled steels.

When it comes to spray nozzles for pickling steel that is used for automotive and other metal products, Lechler has the spray equipment and systems that work for your manufacturing operations. Reach out to us today for a quote.