In steel structure manufacturing, shipbuilding, bridge engineering and heavy machinery industries, the quality of surface treatment directly affects coating adhesion, anti-corrosion performance and product service life. In order to standardize the quality of steel surface cleaning, international standards clearly classify the surface condition after blast cleaning. Common grades include Sa2, Sa2.5 and Sa3.
For many purchasers and engineering project managers, understanding the differences between these cleaning levels is helpful in selecting the appropriate surface treatment process and shot blasting machine to meet project quality requirements.
The Sa grade is derived from the international standard ISO 8501-1 "Surface treatment of steel before application of paint". Among them, "Sa" represents the quality level after surface cleaning using jet abrasives (such as steel shot, steel sand, etc.).
The different grades reflect the extent to which scale, rust, old coatings and other impurities have been removed from the steel surface.
In the actual production process, both shot blasting machines and sand blasting equipment can meet the corresponding Sa level requirements, but for large-volume industrial production, automated shot blasting equipment can usually provide more stable and consistent cleaning effects.
After treatment, the oxide scale, rust, oil stains and attachments on the steel surface are basically removed, but a small amount of firmly attached traces are still allowed.
Surface state characteristics
Most scale and rust removed
Minor spotting and areas of discoloration allowed
Overall surface is cleaner
Suitable for general industrial anti-corrosion requirements
Typical applications
Ordinary steel structural parts
Engineering machinery parts
General industrial equipment
Projects with low requirements on anti-corrosion life
Sa2.5 level is one of the most widely used surface treatment standards in the field of industrial manufacturing. It is also called "near white metal level cleaning".
After treatment, the surface of the steel is almost completely removed from scale, rust and other impurities, allowing only a very small amount of slight stains.
Surface state characteristics
The surface has a uniform metallic luster
Oxide scale and rust are basically completely removed
Only a very small amount of color difference is allowed to exist
Can significantly improve coating adhesion
Typical applications
shipbuilding
Marine engineering equipment
bridge steel structure
Wind power equipment
petrochemical facilities
Export steel structure project
At present, most international engineering projects and high-standard anti-corrosion projects require Sa2.5 level.
Sa3 level is the highest level in blast cleaning standards and is often referred to as "white metal level cleaning".
The surface of the treated steel should be metallic in color, without any visible scale, rust, oil or other contaminants.
Surface state characteristics
Exposed metal substrate
No visible contaminants
Uniform surface color
Meet surface cleanliness requirements
Typical applications
Nuclear power engineering
High-end marine engineering equipment
Special anti-corrosion project
Extremely corrosive environment facilities
High performance coating system
Since reaching the Sa3 level requires longer processing time and higher energy consumption, it is relatively rarely used in general industrial projects.
For steel plate, H-shaped steel and steel structure manufacturers, roller shot blasting machine is one of the most commonly used equipment to achieve Sa2.5 level.
In order to obtain stable cleaning results, it is necessary to focus on controlling the following factors:
The particle size, hardness and ratio of steel shot and steel grit will directly affect the surface cleaning quality and roughness.
The wear of the blades, directional sleeves and shot splitting wheels will affect the projectile projection angle and coverage, so they need to be inspected and replaced regularly.
The running speed of the workpiece and the shot blasting intensity need to maintain a reasonable match to ensure that the surface receives sufficient impact time.
A good dust removal system can reduce dust interference, improve surface cleanliness and equipment operation stability.
Sa2, Sa2.5 and Sa3 represent different grades of steel surface cleaning standards. The main differences are surface cleanliness and subsequent anti-corrosion performance requirements.
For the vast majority of steel structures, ships and construction machinery projects, Sa2.5 can already meet the requirements for high-quality anti-corrosion coating, and is therefore the most widely used standard in industrial production. By rationally selecting shot blasting equipment, abrasive types and process parameters, companies can stably achieve target cleaning levels, improve product quality and extend service life.
Today, as surface treatment processes continue to be upgraded, automated shot blasting equipment is helping more and more manufacturing companies achieve production goals of higher efficiency, more stable quality, and lower operating costs.
