Steel Surface Preparation: What’s Involved?
When it comes to steel treatment, surface preparation is the essential first step. Steel can be treated in a number of ways, depending on its intended application, but all steel sections need to be prepped to ensure that dirt, dust, rust, and grease doesn’t interfere with the surface when it is coated.
The steel surface preparation methods range from simple chemical cleaning to more abrasive methods such as abrasive grit blasting. Let’s take a look at the different types and what’s involved.
Surface preparation is the essential first step for steel treatment. Let’s take a look at the different types and what’s involved.
What Kind of Contaminants Need to Be Removed?
Rust – All steel is susceptible to corrosion if it is not treated beforehand. There are many different types, ranging from uniform attack corrosion, to pitting corrosion. The type of corrosion will dictate what rust grade the steel is. Some grades should be avoided, such as pitted steel, which can be very difficult to clean.
Mill Sale – Mill scale is the flaky surface of hot rolled steel, consisting of different iron oxides. It is a nuisance when the steel needs to be processed. Any paint applied over it is wasted, since it will come off with the scale as moisture-laden air gets under it. Hence it needs to be removed.
Grease, Oil, Dirt and Dust – When preparing steel, anything that might prevent the paint wetting out or adhering to the surface needs to be removed. This includes grease and oils, as well as dirt, dust and salts.
What Are The Common Methods of Steel Preparation?
Solvent Cleaning – Before any further cleaning or preparation, steel sections are first wiped down with acetone, a thinner, or another type of solvent. This helps remove mill scale, oxides, and some corrosion.
Abrasive Grit Blasting – Grit blasting is the most effective method for removal of particularly difficult dirt, mill scale, rust and old coatings and other impurities. This is achieved using a shot-blasting machine, which the raw steel is passed through.
Prior to blasting, steelwork needs to be cleaned of any oils or grease. It is then blasted with shot or another abrasive material, which bombardes the steel surface, removing any impurities. The machine then brushes off any debris. There are all different types of classifications for blast cleaning a steel section, which will depend on what it is being used for, and what is being done afterwards (such as painting, coating or welding).
Hand & Power Tool Cleaning – Scrapers, wire brushes and other hand held tools are relatively ineffective in removing mill scale or corrosion. However, power tools like rotary brushes, rotary grinders, and needle guns may be useful for cleaning hard-to-reach places where grit blasting is not possible.
Acid Pickling – This involves immersing the steel in a bath of suitable inhibited acids that dissolve or remove the mill scale and rust. This technique is normally only used for structural steel intended for hot-dip galvanising.
Flame Cleaning – This involves passing an oxy/gas flame over the steel surface. The heat causes rust scales to flake off, which can then be removed by scraping and wire brushing followed by dust removal. It is not he most efficient process and is rarely used.
Wet Abrasive Blast Cleaning – As the name implies, this is similar to the girt blasting technique, however, water is employed rather than shot. This contributes to the reduction of a dust hazard, particularly when removing lead-based paints and water-soluble contaminants. Ultra-high pressure water jetting is also used, which is favoured by some because it removes high percentages of soluble salts from the surface.
If you need quality steel that is fabricated to suit your unique needs, or steel surface treatment to protect your steel, contact Steel Fabrication Services today.
Our team of expert structural steel fabricators have the experience and knowledge to answer any of your questions and will ensure that you find the best solution to suit your needs.