Surface Preparation Standard

The surface preparation, as the name implies, is to use a shot blasting machine, sandblasting room, or other surface cleaning equipment to remove rust and oxide scale on the surface of the workpiece before the workpiece needs to be painted or sprayed to increase the adhesion of the paint on the surface of the workpiece and the service life.

1. What is Surface Preparation?

Surface preparation is a process of forming a surface layer on the surface of the basic material that is different from the body's mechanical, physical or chemical properties. The purpose of our Surface preparation of products is to make the products meet certain requirements of corrosion resistance, wear resistance, decoration, or other special functions. There are different Surface preparation methods and processes for different products. One of the most important functions that affect the performance of the coating is the quality of the Surface preparation. This can be done mechanically or chemically.

Surface preparation is an indispensable first-stage treatment for steel substrates before applying any coating and is generally considered to be the most important factor affecting the complete success of a corrosion protection system.  The performance of the coating is significantly affected by its ability to properly adhere to the substrate. The residual oxide scale on the steel surface is an unsatisfactory basis for the application of modern high-performance protective coatings, so it can be removed by sand blast room. Other surface contaminants on the rolled steel surface, such as oil and grease, are also undesirable and must be removed before the blast cleaning process.  The Surface preparation process not only cleans the steel but also introduces a suitable profile to receive the protective coating.

1.1 Stages of Surface Preparation

1.1.1 Surface deformation strengthening

Surface deformation strengthening refers to a surface strengthening process that plastically deforms steel parts at room temperature to increase the surface hardness and generate favorable residual compressive stress distribution.

(1) Shot blasting

Shot blasting is a technique in which a large number of high-speed moving projectiles are sprayed onto the surface of the part as if countless small hammers hit the metal surface to cause certain plastic deformation of the surface and subsurface of the part to achieve strengthening.

(2) Rolling treatment

Use freely rotating hardened steel rollers to roll the machined surface of the steel part to produce plastic deformation, flatten the rough peaks on the surface of the steel part, and form a favorable residual compressive stress, thereby improving the wear resistance and wear resistance of the workpiece. Anti-fatigue ability.

(3) Surface expansion (squeeze or squeeze)

Surface expansion is to squeeze a steel ball or other shape expansion tool with a diameter slightly larger than the aperture through the processed inner hole of the workpiece at room temperature to obtain an accurate, smooth, and strengthened surface.

1.1.2. Surface coating strengthening

(1) Surface coating strengthening

Surface coating strengthening is a surface strengthening process in which one or more layers of other metals or non-metals are coated on the metal surface by physical or chemical methods.

(2) Metal spraying technology

The process of heating metal powder to a molten or semi-melted state, atomizing it with a high-pressure airflow and spraying it on the surface of the workpiece to form a coating is called thermal spraying.

It is widely used in almost all fields including cutting-edge technologies such as aerospace, atomic energy, and electronics.

(3) Metal coating

Covering the surface of the base material with one or more layers of metal plating can significantly improve its wear resistance, corrosion resistance and heat resistance, or obtain other special properties. There are electroplating, chemical plating, composite plating, penetration plating, hot dip plating, vacuum evaporation, spray plating, ion plating, sputtering and other methods.

(4) Physical vapor deposition (PVD)

Physical vapor deposition refers to the use of physical methods to vaporize materials into atoms, molecules, or ionize into ions under vacuum conditions, and deposit a thin film on the surface of the material through a gas phase process.

The physical deposition technology mainly includes three basic methods: vacuum evaporation, sputtering and ion plating.

(5) Chemical vapor deposition (CVD)

Chemical vapor deposition refers to a method in which a mixed gas interacts with the surface of a substrate at a certain temperature to form a metal or compound film on the surface of the substrate.

Because the chemical vapor deposition film has good wear resistance, corrosion resistance, heat resistance, electrical, optical and other special properties, it has been widely used in machinery manufacturing, aerospace, transportation, coal chemical industry and other industrial fields.

1.1.3. Surface heat treatment

Surface hardening

Surface quenching refers to a heat treatment method in which the surface layer is austenitized by rapid heating without changing the chemical composition and core structure of the steel and then quenched to strengthen the surface of the part.

The main methods of surface heat treatment include flame quenching and induction heating heat treatment. Commonly used heat sources include flames such as oxygen-acetylene or oxy propane, induction current, laser, and electron beam.

Induction heating

A method of using alternating current to induce huge eddy currents on the surface of the workpiece to quickly heat the surface of the workpiece.

Flame heating

The method of using acetylene flame to directly heat the surface of the workpiece. The cost is low, but the quality is not easy to control.

Laser heating

A method of heating the surface of the workpiece with a high-energy-density laser. High efficiency and good quality.

Laser surface strengthening can be divided into laser phase change strengthening treatment, laser surface alloying treatment, and laser cladding treatment.

Bluing and phosphating


A process in which steel or steel parts are heated to an appropriate temperature in air-water vapor or chemical drugs to form a blue or black oxide film on the surface. Also called blackening.

Commonly used in precision instruments, optical instruments, tools, hardness blocks and standard parts in the machinery industry.


The process of immersing the workpiece (steel or aluminum, zinc) into the phosphating solution (some acid-based phosphate-based solutions), and depositing a layer of water-insoluble crystalline phosphate conversion film on the surface is called phosphating .

Phosphating is widely used in anti-corrosion technology, metal cold deformation processing industry.

1.1.4. Chemical surface heat treatment

Chemical heat treatment is a heat treatment process in which the workpiece is placed in a specific medium for heating and insulation, so that the active atoms in the medium can penetrate into the surface of the workpiece to change the chemical composition and structure of the surface of the workpiece, and then change its performance.

Commonly used chemical heat treatment:

Carburizing, nitriding (commonly known as nitriding), carbonitriding (commonly known as cyanidation and nitrocarburizing), etc. Sulfurizing, boronizing, aluminizing, vanadiumizing, chromizing, etc.

The bluing and phosphating can be classified as surface treatment, not chemical heat treatment.

1.1.5. Surface cleaning and decoration

(1) polishing

Polishing is a finishing method to modify the surface of parts. Generally, only a smooth surface can be obtained, and the original processing accuracy cannot be improved or even maintained. Depending on the pre-processing conditions, the Ra value after polishing can reach 1.6~0.008 mm .

(2) Mechanical polishing

Including wheel polishing, barrel polishing and vibration polishing.

1.2 Methods of Surface Preparation

1.2.1. Polishing

Polishing is a processing method that uses mechanical, chemical or electrochemical effects to reduce the surface roughness of the workpiece to obtain a bright and smooth surface. It is the use of polishing tools and abrasive particles or other polishing media to modify the surface of the workpiece. Polishing cannot improve the dimensional accuracy or geometric accuracy of the workpiece, but aims to obtain a smooth surface or mirror gloss, and sometimes it is also used to eliminate gloss (matting)

1.2.2. Sandblasting

Sandblasting is a process of cleaning and roughening the surface of the substrate by the impact of high-speed sand flow. Compressed air is used as power to form a high-speed jet beam to spray the spray material (copper ore, quartz sand, emery sand, iron sand, Hainan sand) at high speed to the surface of the workpiece to be treated so that the appearance or shape of the outer surface of the workpiece surface is changed, Due to the impact and cutting action of abrasives on the surface of the workpiece, the surface of the workpiece can obtain a certain degree of cleanliness and different roughness, and the mechanical properties of the surface of the workpiece are improved. Therefore, the fatigue resistance of the workpiece is improved, and it and the coating are increased. The adhesion between the layers extends the durability of the coating film and is also conducive to the leveling and decoration of the coating.

1.2.3. Drawing

It is a surface treatment method that forms lines on the surface of the workpiece by grinding products to achieve a decorative effect. According to the different lines after drawing, it can be divided into straight drawing, chaotic drawing, corrugation, and swirling. The surface drawing treatment is a surface treatment method that forms lines on the surface of the workpiece by grinding the product to achieve a decorative effect. Surface drawing treatment can reflect the texture of metal materials

1.2.4. Anodizing

An electrolytic oxidation process in which the surface of aluminum and aluminum alloys is usually transformed into a layer of oxide film, which has protective, decorative and other functional properties

1.2.5. Electrophoresis

The process is divided into anodic electrophoresis and cathodic electrophoresis. If the paint particles are negatively charged, the workpiece is the anode, and the coating particles deposited on the workpiece under the action of the electric field force is called anodic electrophoresis; on the contrary, if the paint particles are positively charged, the workpiece is the cathode, and the coating particles deposited on the workpiece to form a film is called anodic electrophoresis. Cathodic electrophoresis.

1.2.6. PVD

PVD is the abbreviation of Physical Vapor Deposition, which refers to the use of low-voltage, high-current arc discharge technology under vacuum conditions, using gas discharge to evaporate the target material and ionize the vaporized substance and gas and use the acceleration of the electric field. The evaporated substance and its reaction products are deposited on the workpiece. The physical vapor deposition technology has a simple process, improves the environment, has no pollution, fewer consumables, uniform, and dense film formation, and strong bonding with the substrate. This technology is widely used in aerospace, electronics, optics, machinery, construction, light industry, metallurgy, materials, and other fields. Superconducting and other characteristics of the film.

1.2.7. Electroplating

Electroplating is the process of plating a thin layer of other metals or alloys on the surface of some metals using the principle of electrolysis. It is the process of using electrolysis to attach a layer of the metal film to the surface of metal or other materials to prevent metal oxidation (Such as rust), improve wear resistance, electrical conductivity, reflectivity, corrosion resistance (copper sulfate, etc.), and enhance aesthetics.

1.2.8. Etching

Generally referred to as etching is also called photochemical etching, which refers to the removal of the protective film of the area to be etched after exposure to plate making and development, and contact with chemical solutions during etching to achieve the effect of dissolving and corroding, forming unevenness or hollowing out.

1.2.9. Spraying

Spraying is a coating method in which spray guns or disc atomizers are used to disperse into uniform and fine droplets by means of pressure or centrifugal force and apply to the surface of the object to be coated. It has a wide range of applications, mainly in the fields of hardware, plastics, furniture, military industry, and ships. It is the most common coating method used today;

1.2.10 Laser carving

Also called laser engraving or laser marking, it is a process of surface treatment using optical principles.

The high-intensity focused laser beam emitted by the laser is at the focal point. The material is oxidized and processed. The effect of marking is to expose the deep material through the evaporation of the surface material, or the chemical and physical changes of the surface material caused by light energy to show traces Either part of the material is burned off by light energy, and traces are "carved", or part of the material is burned off by light energy, showing the pattern and text that need to be etched.

2. Surface Preparation Standards

The surface preparation standards are set up by various institutions around the world, which specify the cleanliness conditions of the shot blasting before applying the protective coating. The suitable cleanliness conditions are requested by the manufacturer of the protective coating or the owner of the structure to be painted. As usual, the SSPC, NACE, and Swedish Standards are the most common surface preparation standards. Every standard has four different standard requests, customer can according to their requirements to make the judgment. At the same time, the machine which can meet those standards is mainly the shot blasting machine.

2.1 What is SSPC Standard?

SSPC is the American national standard formulated by the American Steel Structure Paint Council, and they are also the most authoritative and widely used steel structure paint standards in the world. With the process of economic globalization, many medium and large steel structure projects with high-standard coating protection requirements have adopted internationally accepted norms and standards. After being processed by shot blasting machine, the steel structure cleanliness can up to the lowest standard SSPC-SP10.

SSPC-SP7: Clean all debris except for closely adhered oxide scale, rust, and existing coatings, exposing a large number of evenly distributed spots on the underlying metal.

SSPC-SP6: Clean and remove at least 2/3 of visible rust, oxide scale, coating, and other debris.

SSPC-SP10: Clean to a metallic luster. Blast cleaning to at least 95% of the surface without visible residues, after shot blasting process close to white metal blast cleaning.

SSPC-SP5: After cleaning up to the metal surface, it shows a complete metallic luster. The shot blasting machinery can clean up all visible rust, oxide scale, coating, and other debris.

2.2 What is NACE Standard

NACE is the original national association of corrosion. The quality of the surface preparation and the matching paint system affect the life of the coating to the same extent. Therefore, we should give comprehensive consideration to surface preparation. The main function of surface treatment is to remove substances on the surface of the material that may shorten the life of the coating. In order to make the painting work easier, the minimum surface cleanliness should at least meet the requirements of the NACE No. 2 standard of the American Society of Anti-corrosion Engineers after the shot blasting machine is processed.

NACE No.4  Remove loose oxide scale, loose rust, and others

NACE No.3 Oxide scale, rust, and others are basically removed, gray metal is visible

NACE No.2  Oxide scale, rust, and others are removed to the extent that only traces in the form of spots or streaks are left. The cleaned surface will show different shades of gray.

NACE No.1 Visible scale, rust, and others are completely removed. The cleaned surface should have a uniform metallic color but may show different shades of gray when viewed from different angles.

2.3 What is Swedish Standards for Blasting?

There are two standards representing metal surface cleaning grades, one is the SSPC designated by the United States in 1985, and the other is the SA designated by Sweden in 1976. The SA is divided into four grades, SA1, SA2, SA2.5, and SA3.

2.3.1 SA 1 Surface Preparation

Sa1 is equivalent to American SSPC-SP7. Generally, simple manual brushing and emery cloth polishing methods are used. This is the lowest level of the four cleanliness, and the protection of the coating is only slightly better than that of the untreated workpiece. The technical standard of Sa1: oil stains, grease, residual oxide scale, rust spots, and residual paint should not be visible on the surface of the steel. Sa1 is also called manual scrubbing and cleaning level.

2.3.2 SA 2 Surface Preparation

Sa2 is equivalent to American SSPC-SP6. Using sandblasting cleaning method, which is the lowest level in sandblasting, that is, the general requirement, but the protection of the coating is much higher than that of manual brushing. Sa2 standard: the surface of the workpiece should not be visible greasy, dirt, scale, scale, paint, oxide, corrosive, and other foreign substances (except for defects), but the defects are limited to no more than 33% per square meter of surface, may include slight shadows; a small number of imperfections, slight discoloration caused by rust. If there are dents on the original surface of the workpiece, slight rust and paint will remain at the bottom of the dents. Sa2 level is also called commodity cleaning level (or industrial level).

2.3.3 SA 2.5 Surface Preparation

Sa2.5 is commonly used in the industry and can be used as the level of acceptance of technical requirements and standards. Sa2.5 level is also called near-white cleaning level (near-white level or out-of-white level). The standard of Sa2.5 grade treatment: the same as the first half of Sa2 requirement, but the defect is limited to no more than 5% of the surface per square meter, which may include slight shadow; slight discoloration caused by a small amount of rust.

2.3.4 SA 3 Surface Preparation

Sa3 is equivalent to the US SSPC-SP5, which is the highest processing level in the industry, also known as the white cleaning level (or white level). The technical standard of Sa3 processing: Same as Sa2.5, but 5% shadows, defects, rust, etc. must not exist.

Conclusion of Surface Preparation Standard

Based on the above, we can see that although there are many surface preparation standards, the content and the cleaning requirements for the surface of the workpiece are similar. The purpose is to ensure the surface cleaning effect of the metal workpiece to ensure the best coating adhesion, and to help mitigate against later problems, such as corrosion and mechanical damage.

As one of the leading blasting machine manufacturers, Qinggong Machinery provides high-quality shot blasting equipment and sand blasting equipment, offering clients the most suitable way to do the surface treatment.