Mastering Material Surface Treatment: A Comprehensive Guide with Illustrations

Surface treatment is a method of artificially forming a surface layer with different mechanical, physical, and chemical properties from the substrate material on the surface of the substrate material.

The purpose of surface treatment is to meet the requirements of product corrosion resistance, wear resistance, decoration, or other special functions.

Commonly used surface treatment methods include mechanical polishing, chemical treatment, surface heat treatment, and surface coating. Surface treatment involves cleaning, sweeping, removing burrs, oil stains, oxide scales, etc., on the surface of the workpiece. Today, we will learn about surface treatment processes.

Commonly used surface treatment processes include vacuum plating, electroplating, anodizing, electropolishing, transfer printing, galvanizing, powder spraying, water transfer printing, screen printing, electrophoresis, and so on.

1. Vacuum Metalizing

Vacuum metalizing, also known as vacuum deposition, is a physical deposition process. In this process, argon gas is injected under vacuum conditions and strikes the target material. The target material separates into molecules and is adsorbed onto conductive goods to form a layer of uniformly smooth metallic surface.

Applicable materials:

  • Many materials can be subjected to vacuum metalizing, including metals, soft and hard plastics, composite materials, ceramics, and glass. Among them, aluminum is the most commonly used for electroplating surface treatment, followed by silver and copper.
  • Natural materials are not suitable for vacuum metalizing because the moisture in natural materials can affect the vacuum environment.

Process cost: During the vacuum metalizing process, the workpiece needs to be sprayed, loaded, unloaded, and then sprayed again, so the labor cost is relatively high, but it also depends on the complexity and quantity of the workpiece.

Environmental impact: Vacuum metalizing has minimal environmental pollution, similar to the impact of spraying on the environment.

2. Electropolishing

Electropolishing is an electrochemical process in which the atoms of a workpiece immersed in an electrolyte are converted into ions and removed from the surface due to the passage of electric current, achieving the effect of removing fine burrs and increasing brightness of the workpiece surface.

Applicable materials:

  • Most metals can be electropolished, with stainless steel being the most commonly used for surface polishing (especially austenitic grade stainless steel).
  • Different materials cannot be electropolished simultaneously, and they cannot even be placed in the same electrolytic solvent.

Process cost: The entire electropolishing process is basically automated, so labor costs are very low.

Environmental impact: Electropolishing uses less harmful chemicals, requires minimal water, and is easy to operate. Additionally, it can prolong the properties of stainless steel, delaying corrosion.

3. Pad Printing

Pad printing, which is capable of printing text, graphics, and images on irregularly shaped objects, is becoming an increasingly important specialty printing technique.

Applicable materials: Practically all materials can be printed using pad printing except for materials that are softer than silicone pads, such as PTFE.

Process cost: The cost of tooling and labor is low for pad printing.

Environmental impact: Because this process is limited to solvent-based inks (which contain harmful chemicals), it has a significant impact on the environment.

4. Galvanizing

Galvanizing is a surface treatment technique that involves coating the surface of steel alloy materials with a layer of zinc for aesthetic and anti-rust purposes. The zinc layer on the surface is an electrochemical protection layer that prevents metal corrosion. The main methods used are hot-dip galvanizing and electroplating.

Applicable materials: Since the galvanizing process relies on metallurgical bonding techniques, it is only suitable for surface treatment of steel and iron.

Process cost: There are no tooling costs, and the cycle is short. Labor costs are moderate because the surface quality of the workpiece depends largely on the manual surface treatment before galvanizing.

Environmental impact: Because the galvanizing process increases the service life of steel components by 40 to 100 years, effectively preventing rust and corrosion, it has a positive effect on environmental protection. Additionally, after the service life of a galvanized component expires, it can be returned to the galvanizing tank for reuse of liquid zinc without generating any chemical or physical waste.

5. Electroplating

Electroplating is a process that uses electrolysis to attach a layer of metallic film to the surface of a part, thereby preventing metal oxidation, improving wear resistance, conductivity, reflectivity, corrosion resistance, and enhancing appearance. The outer layer of many coins is also electroplated.

Applicable materials:

  • Most metals can be electroplated, but different metals have different levels of purity and electroplating efficiency. The most common metals used for electroplating are tin, chromium, nickel, silver, gold, and rhodium.
  • ABS is the most commonly used plastic for electroplating.
  • Nickel cannot be used for electroplating products that come into contact with skin since it is irritating to the skin and toxic.

Process cost: There are no tooling costs, but fixtures are needed to fix the parts, and time costs depend on temperature and metal type. Labor costs are moderate to high and depend on the specific electroplated item. For example, electroplating of silverware and jewelry requires highly skilled workers because they have high requirements for appearance and durability.

Environmental impact: A large number of toxic substances are used in the electroplating process, so professional diversion and extraction are necessary to ensure minimal environmental impact.

6. Hydro Transfer Printing

Water transfer printing, also known as hydrographics, is a process that uses water pressure to transfer colored patterns from transfer paper to the surface of a three-dimensional product. As people’s requirements for product packaging and surface decoration have increased, the use of water transfer printing has become more and more widespread.

Applicable materials: All hard materials are suitable for water transfer printing, and materials suitable for spraying are also suitable for water transfer printing. The most common materials are injection-molded parts and metal parts.

Process cost: There are no tooling costs, but fixtures are required to perform water transfer printing on multiple products simultaneously. Time costs generally do not exceed 10 minutes per cycle.

Environmental impact: Compared to product spraying, water transfer printing makes more extensive use of printing coatings, reducing the potential for waste leakage and material waste.

7. Screen Printing

Screen printing involves using a scraper to squeeze ink through the mesh of a graphic section and onto the substrate, creating the same graphics as the original. Screen printing equipment is simple and easy to operate, with simple printing and plate-making processes that are low-cost and highly adaptable.

Common printed materials include color oil paintings, posters, business cards, binding covers, product nameplates, and printed textiles.

Applicable materials: Almost all materials can be screen printed, including paper, plastic, metal, ceramics, and glass.

Process cost: Tooling costs are low, but still depend on the number of colors because each color requires separate plate-making. Labor costs are relatively high, especially when multi-color printing is involved.

Environmental impact: Light-colored screen printing inks have a relatively small environmental impact, but inks containing PVC and formaldehyde have harmful chemicals that need to be collected and treated in a timely manner to prevent water pollution.

8. Anodic Oxidation

Anodizing is mainly the anodic oxidation of aluminum, which uses the principle of electrochemistry to generate a layer of Al2O3 (aluminum oxide) film on the surface of aluminum and aluminum alloys. This oxide film has special properties such as protective, decorative, insulating, and wear resistance.

Applicable materials: Aluminum and aluminum alloy products.

Process cost: The consumption of water and electricity is significant during the production process, especially in the oxidation process. The machine itself generates heat, requiring continuous cooling with circulating water, resulting in electricity consumption of around 1000 degrees per ton.

Environmental impact: Anodizing is not particularly energy-efficient, and in aluminum electrolysis production, the anodic effect can also produce gases that have destructive effects on the atmospheric ozone layer.

9. Metal Wired

Metal wire drawing is a surface treatment method that creates line patterns on the surface of a workpiece through grinding to achieve a decorative effect. Depending on the different patterns after brushing, it can be divided into straight grain brushing, random pattern brushing, corrugated brushing, and spiral brushing.

Applicable materials: Almost all metal materials can be used with metal brushing technology.

Process cost: The process is simple, equipment is simple, and material consumption is minimal, resulting in relatively low costs and high economic benefits.

Environmental impact: Pure metal products have no paint or any chemicals on their surface, do not burn at 600 degrees Celsius, do not produce toxic gases, and meet composite fire protection and environmental protection requirements.

10. In-Mold Decoration-IMD

In-mold decoration involves placing a printed film with patterns into a metal mold, injecting resin into the metal mold to bond with the film, and solidifying it into a finished product. This is a molding method that integrates printing with the resin forming process.

Applicable materials: Plastic surfaces.

Process cost: Only one set of molds is needed, which can reduce costs and production time while simplifying the process. This is a one-time injection molding process that achieves both forming and decoration simultaneously.

Environmental impact: This technology is environmentally friendly and avoids the pollution caused by traditional painting and electroplating.

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