Exploring the 21 Types of Surface Treatment Processes | MachineMFG

Exploring the 21 Types of Surface Treatment Processes

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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 product’s corrosion resistance, wear resistance, decoration, or other special functional requirements.

For metal castings, the more 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 workpiece surface.

Surface Treatment History

Surface treatment is one of the oldest techniques, and since there have been humans on Earth, it has been one of the first technologies they mastered. The life of primitive humans was extremely difficult, they lived in groups, and for survival, they made stone tools. They used grinding techniques to give the stone tools sharp edges, creating a “sharp-splitting” effect. By the time of the Neolithic Age, the stone tools used by primitive humans were thoroughly ground, with a delicate and smooth surface, emphasizing decorative effects, and had become the mainstream of the era.

In primitive societies, equally important to grinding stone tools was the primitive painting technology. Primitive humans already had a sense of beauty, and in the late Paleolithic Age, they used mineral pigments to paint small items for personal amusement. By the Neolithic period, the invention of pottery brought the primitive color painting technology to its peak, forming the famous colored pottery art in history, marking the beginning of surface treatment painting technology.

Types of Surface Treatment

1. Micro-arc Oxidation

Micro-arc Oxidation

Micro-Arc Oxidation (MAO), also referred to as Micro-Plasma 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 primarily composed of base metal oxides and is produced by the instantaneous high-temperature and high-pressure effect of arc discharge.

2. Metal Wire-drawing

Metal Wire-drawing

Metal Wire Drawing is a surface treatment technique that creates decorative lines on the surface of a workpiece through the process of grinding.

3. Bluing

Bluing
Bluing

Bluing is a process in which the entire body is coated with a color glaze and then fired in a blast furnace at a temperature of around 800°C.

The color glaze transforms from a granular solid into a liquid state as it melts, and after cooling, it forms a beautiful color glaze that is fixed to the body.

At this point, the height of the color glaze is lower than 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. Shot Blasting

Shot blasting
Shot blasting

Shot Blasting is a cold working method that involves bombarding the surface of a workpiece with pellets. This results in the implantation of residual compressive stress, which enhances the fatigue strength of the workpiece.

5. Sand Blasting

Sand blasting

Sand Blasting is a process of removing impurities and roughing up the surface of a substrate by the impact of a high-speed sand stream.

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 workpiece at a high speed, altering its appearance or shape.

6. Etching

Etching

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. In-Mold Decoration

In-Mold Decoration
In-Mold Decoration

IMD, or In-Mold Decoration, is also known as Painting-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 ink in the middle provides protection against friction and prevents scratches, while also ensuring the color remains bright and doesn’t fade over time.

8. Out Mold Decoration

Out 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

Laser Carving, also referred to as Laser Engraving or Laser Marking, is a surface treatment process that utilizes optical principles. In this method, laser beams are utilized to create permanent markings on the surface of objects or within transparent materials.

10. EDM

EDM

EDM

Electrical Discharge Machining (EDM) is a specialized machining method that utilizes electrical discharge to remove conductive materials. It involves pulses of discharge between two electrodes that are immersed in a working fluid.

Tool electrodes are usually 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 workpiece and may even result in no loss.

11. Laser Texturing

Laser texturing

Laser Texturing is a process that utilizes high-energy density laser to produce patterns on the surface of steel, such as snake skin, etching, pearlite, or other forms of lines.

12. Pad Printing

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 the ink from the gravure onto 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

Screen printing is a printing method that involves the use of silk, synthetic fiber, or metal screens that are stretched over a frame. The screen is made using hand-painted film or photochemical plate-making methods, with modern screen printing technology using a photosensitive material to create the screen plates through photoengraving.

This process exposes the graphic part of the screen plate 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 part of the screen and forms a graphic that matches the original.

14. Direct Thermal Printing

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. The 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

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 product surface with high temperature and pressure, thereby completing the product printing.

16. Planography

Planography
Planography

Since the graphic and non-graphic parts on the planography are on the same plane, in order to make the ink distinguish between the pattern part and the non-pattern 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 wet by the ink.

Then, the ink is supplied from the ink supply device of the printing component to the printing plate.

Because the non-graphic portion of the printing plate is protected by water, the 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 skin, and the pressure between the rubber roller and the impression cylinder is used to transfer the ink on the milk skin to the substrate to complete a printing.

Therefore, planography is an indirect printing method.

17. Curved Surface Printing

Curved surface printing

For curved surface printing, the ink is placed in a gravure engraved with characters or patterns. The characters or patterns are then transferred onto the curved surface, and subsequently to the surface of the molded product through the curved surface. The ink is finally cured through heat treatment or ultraviolet light exposure.

18. Hot Stamping

Hot stamping

Hot stamping refers to the process of applying text and patterns made from materials such as foil to the front or back cover of hardcover books, or embossing book names or patterns through hot pressing.

19. Water Transfer Printing

Water transfer printing

Water transfer printing is a type of printing that utilizes high pressure to transfer color patterns onto a substrate from a hydrolyzed transfer paper or plastic film. The process includes the production of water transfer printing paper, soaking of the decorative paper, transfer of the pattern, and drying of the finished product.

20. Flat Screen Printing

Flat screen printing

The flat screen printing mold consists of a polyester or nylon screen (also known as a ‘flower plate’) that is mounted on a square frame and has a stencil pattern. The stencil pattern allows the color paste to pass through the patterned part of the flower plate, while the non-patterned part is sealed with a polymer film layer.

During printing, the flower plate is pressed against the fabric and filled with color 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

Calendering is a finishing process for heavy leather that uses heat and pressure to create a smooth and glossy surface. The process involves feeding the material into a machine where it is heated and melted, then formed into a sheet or film and cooled before being rolled up.

The calendering process leverages the plasticity of fibers to flatten the fabric surface or produce fine, 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 matter from the base surface to improve the adhesion between the base surface and the coating or to provide the surface with certain corrosion resistance, can also be called pretreatment.

  1. Mechanical pretreatment: Before painting, using hand tools, power tools, or spraying, shot blasting, grains, etc., to remove foreign objects from the base surface.
  2. Chemical pretreatment: Before painting, using chemical methods to remove foreign matter from the base surface or form a conversion film.
  3. Electrochemical pretreatment: Before painting, using electrochemical methods to remove foreign matter from the base surface or form a conversion film.
  4. Degreasing: Removing oil stains from the base surface.
  5. Chemical degreasing: Using chemical methods to remove oil stains from the base surface.
  6. Electrochemical degreasing: Using electrochemical methods to remove oil stains from the base surface.
  7. Soak degreasing: Cleaning by immersing the workpiece in a cleaning agent without applying an external current.
  8. Spray degreasing: Removing oil stains by spraying the degreaser on the workpiece.
  9. Ultrasonic degreasing: Using ultrasonic vibration to accelerate the removal of oil stains from the workpiece surface.
  10. Derusting: Removing rust products from the surface of the steel base.
  11. Trimming: Removing burrs, nodules, welding slag, and sharp edges from the base to make it suitable for painting.
  12. Pickling: Using acid to remove rust and scale from the base surface.
  13. Flame cleaning: Briefly burning steel structure with a reducing flame, followed by cleaning with a power steel brush.
  14. Hand tool cleaning: Using hand tools to remove foreign matter from the base surface.
  15. Power tool cleaning: Using power tools to remove foreign matter from the base surface.
  16. Blasting: Using the impact of high-speed abrasive flow to clean and roughen the base surface.
  17. Dry blasting: Using the impact of high-speed dry abrasive flow to clean and roughen the base surface. Vacuum dry blasting is done by removing waste abrasive or chips using a vacuum system around the nozzle.
  18. Wet blasting: Using the impact of a high-speed flow of a mixture of abrasive and water to clean and roughen the surface.
  19. Sand blasting: Using the impact of high-speed sand flow to clean and roughen the base surface.
  20. Shot blasting: Using the impact of high-speed shot flow to clean and strengthen the base surface.
  21. Rusting grade: Grading the degree of rust on the steel surface.
  22. Derusting grade: Grading the degree of rust removal from the steel surface.
  23. Abrasive: Natural or synthetic solid material used as blasting medium.
  24. Grit: An abrasive used for blasting cleaning in the form of angular or irregular particles.
  25. Shot: An abrasive in the form of a sphere used for blasting treatment.
  26. Depainting: Removing old, damaged paint film to prepare for repainting.
  27. Surface conditioning: Converting the surface to a suitable state for successful processing in later stages.
  28. Conversion treatment: A chemical or electrochemical process that produces a film composed of compounds of the base surface metal.
  29. Phosphating: Using a solution containing phosphoric acid or phosphate to form an insoluble phosphate film on the base metal surface.
  30. Chromating: Using a hexavalent or trivalent chromium compound’s acid to form a chromate conversion film on the base metal surface.
  31. Passivating: Making the base metal surface passive.

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