What is surface treatment?
Surface treatment is a process of artificially forming a surface layer with mechanical, physical and chemical properties different from the substrate on the surface of the substrate material. The purpose of surface treatment is to meet the corrosion resistance, wear resistance, decoration or other special functional requirements of the product.
For metal castings, the most commonly used surface treatment methods are mechanical polishing, chemical treatment, surface heat treatment and spray painting.
Surface treatment involves cleaning, sweeping, deburring, degreasing and removing the oxide layer from the surface of the part.
Surface Treatment History
Surface treatment is one of the oldest techniques, and for as long as humans have existed on Earth, it was one of the first technologies they mastered. The life of early humans was extremely difficult, they lived in groups and, to survive, they made stone tools. They used grinding techniques to give stone tools sharp edges, creating a “sharp split” effect. In Neolithic times, the stone tools used by early humans were meticulously ground, with a delicate and smooth surface, emphasizing decorative effects, and became the dominant trend of the time.
In primitive societies, equally important to sharpening stone tools was primitive painting technology. Early humans already had a sense of beauty, and in the late Paleolithic they used mineral pigments to paint small items for personal enjoyment. In the Neolithic period, the invention of pottery brought the primitive color painting technology to its peak, forming the famous color pottery art in history, marking the beginning of surface treatment painting technology.
Types of surface treatment
1. Microarc oxidation
Microarc oxidation (MAO), also known as microplasma oxidation, is a process that involves the combination of electrolyte and specific electrical parameters.
This process results in the growth of a ceramic film on the surface of aluminum, magnesium, titanium and their alloys. The film is mainly composed of base metal oxides and is produced by the instantaneous high-temperature, high-pressure effect of arc discharge.
2. Metal drawing
Metal wire drawing is a surface treatment technique that creates decorative lines on the surface of a part through the grinding process.
3. Blue
Bluing is a process in which the entire body is coated with a colored enamel and then fired in a blast furnace at a temperature of around 800°C.
The colored nail polish changes from a solid granular state to a liquid state as it melts and, after cooling, forms a beautiful colored nail polish that adheres to the body.
At this point, the height of the colored glaze is smaller than that of the copper wire, so the glaze must be refilled.
It is then sintered, typically four to five times in a continuous process, until the pattern is filled to match the level of the wire pattern.
4. Sandblasting
Sandblasting is a cold working method that involves bombarding the surface of a part with pellets. This results in the deployment of residual compressive stress, which increases the fatigue strength of the part.
5. Sand Blasting
Sandblasting is a process of removing impurities and roughing the surface of a substrate by the impact of a high-speed flow of sand.
This is achieved by using compressed air to create a high-speed jet beam that sprays the blasting material (such as copper ore sand, quartz sand, corundum, iron sand, or Hainan sand) onto the surface of the part at high speed. , changing its appearance or shape.
6. Engraving
Etching is a method of removing material through chemical reaction or physical impact.
Typically, this process is also known as Photochemical Etching, which involves removing the protective film from the area to be etched after exposure and development and then immersing it in a chemical solution that causes dissolution and corrosion. This results in the creation of uneven surfaces or hollow molding.
7. Decoration in the mold
IMD, or In-Mold Decoration, is also known as paint-free technology and is a widely used surface decoration technique.
The technology consists of a hardened transparent film on the surface, a printed pattern layer in the middle and an injection layer on the back. The core paint offers protection against friction and prevents scratches, while ensuring the color remains bright and does not fade over time.
8. External mold decoration
Out-Mold decoration is a combination of visual, tactile and functional elements in a display.
It is an extension of IMD (In-Mold Decoration) technology and involves a 3D surface decoration technique that combines printing, textural structure and metallization characteristics.
9. Laser Carving
Laser carving, also known as laser engraving or laser marking, is a surface treatment process that uses optical principles. In this method, laser beams are used to create permanent markings on the surface of objects or transparent materials.
10. EDM
Electrical discharge machining (EDM) is a specialized machining method that uses electrical discharge to remove conductive materials. It involves discharge pulses between two electrodes that are immersed in a working fluid.
Tool electrodes are generally made of corrosion-resistant materials with good conductivity, high melting points and easy to process, such as copper, graphite, copper-tungsten alloys and molybdenum.
During the machining process, the tool electrode experiences some wear, but it is significantly less than the amount of metal removed from the part and may even result in no loss.
11. Laser Texturing
Laser texturing is a process that uses a high-energy density laser to produce patterns on the surface of steel, such as snakeskin, etching, perlite or other forms of lines.
12. Pad printing
Pad printing is a specialized printing method that uses a curved pad made of silicone (or copper, thermoplastic) and a silicone rubber material. The process involves dipping engraving ink into the surface of the pad and then pressing it onto the surface of the desired object to print text, patterns, and other designs.
13. Screen printing
Screen printing is a printing method that involves using silk, synthetic fiber or metal screens stretched over a frame. The screen is made using hand-painted film or photochemical platemaking methods, with modern screen printing technology using a photosensitive material to create the screen plates through photogravure.
This process exposes the graphics part of the screen card to produce screen holes and blocks the screen holes in the non-text part.
During printing, ink is transferred to the substrate by pressing a blade against the screen, which squeezes the ink through the graphic portion of the screen and forms a graphic that matches the original.
14. Direct Thermal Printing
Direct Thermal Printing refers to the process of applying a heat-sensitive agent to paper to make it a heat-sensitive recording paper. Thermal recording paper changes the physical or chemical properties of a substance (developing agent) when exposed to heat, resulting in an image.
15. Heat transfer printing
The principle of heat transfer printing involves printing a digital pattern using a printer and special transfer ink on a transfer paper, and then using a transfer machine to transfer the pattern to the surface of the product with high temperature and pressure, thus completing the impression of the product.
16. Planography
Since the graphic and non-graphic parts of the planograph are on the same plane, in order to make the ink distinguish between the standard part and the non-standard part of the printing plate during printing, the principle of oil-water separation needs to be used.
First, the water supply device of the printing plate component supplies water to the non-graphic portion of the printing plate, thereby protecting the non-graphic portion of the printing plate from being wetted by ink.
Then, ink is supplied from the ink supply device of the printing component to the printing plate.
Since the non-graphic portion of the printing plate is protected by water, ink can only be supplied to the graphic portion of the printing plate.
Finally, the ink on the printing plate is transferred to the milk film, and the pressure between the rubber roller and the printing cylinder is used to transfer the ink from the milk film to the substrate to complete printing.
Therefore, planography is an indirect printing method.
17. Curved surface printing
For curved surface printing, ink is placed on an engraving engraved with characters or patterns. The characters or patterns are then transferred to the curved surface and subsequently to the surface of the molded product through the curved surface. The paint is finally cured through heat treatment or exposure to ultraviolet light.
18. Hot Stamping
Hot stamping refers to the process of applying text and patterns made from materials such as aluminum foil to the front or back cover of hardcover books, or engraving book names or patterns through hot pressing.
19. Water Transfer Printing
Water transfer printing is a type of printing that uses high pressure to transfer color patterns onto a substrate from hydrolyzed transfer paper or plastic film. The process includes producing printing paper by water transfer, soaking the decorative paper, transferring the pattern, and drying the finished product.
20. Flat Screen Printing
Flat screen printing mold consists of a polyester or nylon screen (also known as 'flower plate') that is mounted on a square frame and has a stencil pattern. The stencil pattern allows the colored paste to pass through the patterned part of the flower plate, while the non-printed part is sealed with a layer of polymer film.
During printing, the flower is pressed against the fabric and filled with colored paste. The paste is then scraped back and forth with a scraper, causing it to penetrate the pattern and reach the surface of the fabric.
21. Calendering
Calendering is a finishing process for heavy leather that uses heat and pressure to create a smooth, shiny surface. The process involves feeding the material into a machine where it is heated and melted, then formed into sheet or film and cooled before being rolled.
The calendering process takes advantage of the plasticity of fibers to flatten the surface of the fabric or produce thin, parallel oblique lines. The most commonly used material for calendering is polyvinyl chloride.
Surface Treatment Terms
Before painting, the process of removing adhered or generated foreign bodies from the base surface to improve the adhesion between the base surface and the coating or to provide the surface with certain corrosion resistance, may also be called pretreatment.
- Mechanical pretreatment: Before painting, using hand tools, power tools or spraying, sandblasting, gritting, etc., to remove foreign objects from the base surface.
- Chemical pretreatment: Before painting, use chemical methods to remove foreign materials from the base surface or form a conversion film.
- Electrochemical pretreatment: Before painting, use electrochemical methods to remove foreign materials from the base surface or form a conversion film.
- Degreaser: Removing oil stains from the base surface.
- Chemical degreasing: Using chemical methods to remove oil stains from the surface of the base.
- Electrochemical degreasing: Using electrochemical methods to remove oil stains from the base surface.
- Immersion degreasing: Cleaning by immersing the part in a cleaning agent without applying external current.
- Spray degreaser: Removing oil stains by spraying degreaser on the workpiece.
- Ultrasonic degreasing: Using ultrasonic vibration to accelerate the removal of oil stains from the surface of the part.
- Derusting: Removal of rust products from the surface of the steel base.
- Trimming: Remove burrs, nodules, welding slag and sharp edges from the base to make it suitable for painting.
- Pickling: Using acid to remove rust and scale from the base surface.
- Flame cleaning: Steel structure with brief burning with a reducing flame, followed by cleaning with an electric steel brush.
- Cleaning with hand tools: Use hand tools to remove foreign materials from the base surface.
- Power tool cleaning: Use power tools to remove foreign materials from the base surface.
- Sandblasting: Using high-speed abrasive flow impact to clean and roughen the base surface.
- Dry blasting: Using the impact of high-speed dry abrasive flow to clean and roughen the base surface. Dry vacuum blasting is done by removing abrasive residue or chips using a vacuum system around the nozzle.
- Wet blasting: Using the impact of a high-velocity stream of a mixture of abrasive and water to clean and roughen the surface.
- Sand blasting: Using the impact of high-speed sand flow to clean and roughen the surface of the base.
- Sandblasting: Using high-speed shot flow impact to clean and strengthen the base surface.
- Rust degree: Classification of the degree of rust on the steel surface.
- Rust removal degree: Classification of the degree of rust removal from the steel surface.
- Abrasive: Natural or synthetic solid material used as a blasting medium.
- Grit: Abrasive used for blast cleaning in the form of angular or irregular particles.
- Shot: Ball-shaped abrasive used for blasting treatment.
- Depainting: Removing old, damaged paint film in preparation for repainting.
- Surface Conditioning: Converting the surface to a state suitable for successful processing in later stages.
- Conversion treatment: Chemical or electrochemical process that produces a film composed of base surface metal compounds.
- Phosphating: Use of a solution containing phosphoric acid or phosphate to form an insoluble phosphate film on the surface of the base metal.
- Chromatization: Use of a hexavalent or trivalent chromium compound acid to form a chromate conversion film on the surface of the base metal.
- Passivation: Making the surface of the base metal passive.
