Surface Treatment Techniques: A Comprehensive Guide

Surface treatment refers to the process of artificially creating a surface layer on the substrate material with different mechanical, physical, and chemical properties than the base material. Surface treatment involves cleaning, scrubbing, deburring, degreasing, and removing oxide layers from the surface of the workpiece.The purpose of surface treatment is to meet the requirements of corrosion resistance, wear resistance, decoration, or other specialized functions of the product. The commonly used methods for surface treatment include mechanical polishing, chemical treatment, surface heat treatment, and surface coating. In this blog, let's learn more about surface treatment techniques.

Commonly used surface treatment techniques include:

1. Vacuum Metalizing

- Vacuum metalizing is a physical deposition phenomenon. It involves introducing argon gas in a vacuum state, which collides with the target material. The target material separates into molecules, which are then adsorbed onto the conductive substrate, forming a uniform and smooth metallic-like surface layer. Applicable materials: - Vacuum metalizing can be applied to various materials, including metals, both soft and hard plastics, composite materials, ceramics, and glass. The most commonly used materials for electroplating surface treatment are aluminum, followed by silver and copper. - Natural materials are not suitable for vacuum metalizing treatment as the moisture in natural materials can affect the vacuum environment.

Process cost:

- During the vacuum metalizing process, there is a significant labor cost involved in spraying, loading, unloading, and re-spraying the workpieces. However, the cost also depends on the complexity and quantity of the workpieces.

Environmental impact:

- Vacuum metalizing has minimal environmental pollution, similar to the impact of spray coating on the environment.

2. Electropolishing  

Electropolishing is an electrochemical process in which atoms of the immersed workpiece in an electrolyte are converted into ions and removed from the surface due to the passage of electric current. This process effectively eliminates fine burrs and increases the brightness of the workpiece surface. Applicable materials: 1. Most metals can undergo electropolishing, with stainless steel being the most commonly used for surface polishing (especially austenitic grade stainless steel). 2. Different materials cannot be electropolished simultaneously or even placed in the same electrolyte solution.

Process cost:

The entire electropolishing process is primarily automated, resulting in low labor costs.

Environmental impact:

Electropolishing utilizes relatively low-hazard chemicals, requires a minimal amount of water, and has a straightforward operation. Additionally, it can prolong the properties of stainless steel, effectively delaying corrosion.

3. Pad Printing

Pad printing, which allows printing of text, graphics, and images on irregular and non-planar surfaces, is now becoming an important specialized printing technique. Applicable materials: Pad printing can be used with nearly all materials, except for those that are softer than silicone pads, such as PTFE. Process cost: Pad printing involves low mold costs and low labor costs. Environmental impact: Due to the use of solvent-based inks (which contain harmful chemicals), this process has a significant environmental impact.

4. Galvanizing

Galvanizing is a surface treatment technique in which a layer of zinc is applied to the surface of steel or iron alloy materials for aesthetic and anti-corrosion purposes. The zinc coating on the surface acts as an electrochemical protective layer, preventing the metal from corroding. The main methods used are hot-dip galvanizing and electroplating. Applicable materials: Since galvanizing relies on metallurgical bonding techniques, it is only suitable for the surface treatment of steel and iron.

Process cost:

Galvanizing does not involve mold costs, and the process has a short turnaround time. The labor costs are moderate because the surface quality of the workpiece largely depends on the manual surface preparation before galvanizing.

Environmental impact:

Galvanizing significantly extends the lifespan of steel and iron components by 40-100 years, effectively preventing rust and corrosion. It has a positive impact on environmental protection. Additionally, galvanized components can be reprocessed in galvanizing baths after their service life ends, allowing for the reuse of liquid zinc without generating chemical or physical waste.

5. Electroplating  

Electroplating is a process that uses electrolysis to deposit a layer of metal film on the surface of parts, providing benefits such as preventing metal oxidation, improving wear resistance, conductivity, reflectivity, corrosion resistance, and enhancing aesthetics. The outer layer of many coins is also electroplated. Applicable materials: 1. Most metals can undergo electroplating, but different metals have varying levels of purity and plating efficiency. The most common ones include tin, chromium, nickel, silver, gold, and rhodium. 2. ABS plastic is commonly used for electroplating. 3. Nickel metal should not be used for products in contact with the skin due to its irritating and toxic nature.

Process cost:

Electroplating does not involve mold costs, but fixtures are needed to secure the parts. The time cost depends on the temperature and metal type. Labor costs range from moderate to high, depending on the specific electroplated items. For example, silverware and jewelry electroplating require highly skilled workers due to their high aesthetic and durability requirements.

Environmental impact:

Significant amounts of toxic substances are used in the electroplating process, requiring proper diversion and extraction to ensure minimal environmental impact.

6. Hydro Transfer Printing  

Hydro Transfer Printing is a method of transferring colored patterns from transfer paper to the surface of three-dimensional products using water pressure. As the demand for product packaging and surface decoration increases, hydro transfer printing is becoming increasingly popular. Applicable materials: Hydro Transfer Printing is suitable for all hard materials and materials that are suitable for spray painting. The most common applications are for injection-molded parts and metal components.

Process cost:

Hydro Transfer Printing does not involve mold costs, but multiple products can be simultaneously printed using fixtures. The time cost typically does not exceed 10 minutes per cycle.

Environmental impact:

Compared to product spray painting, Hydro Transfer Printing makes more efficient use of printing coatings, reducing the possibility of waste leakage and material waste.

7. Screen Printing  

Screen printing is a process in which ink is transferred through the mesh of a screen onto the substrate by the pressure of a squeegee, reproducing the graphics and text from the original artwork. Screen printing equipment is simple to operate, and the printing and plate-making processes are easy and cost-effective, making it highly adaptable.Common printed products include color oil paintings, posters, business cards, book covers, product labels, and printed textiles. Applicable materials: Almost all materials can be screen printed, including paper, plastic, metal, ceramics, and glass.

Process cost:

Screen printing has low mold costs, but it still depends on the number of colors since each color requires a separate screen. Labor costs are relatively high, especially when multiple color printing is involved.

Environmental impact:

Light-colored screen printing inks have minimal environmental impact. However, inks containing PVC and formaldehyde are harmful chemicals and require proper recycling and disposal to prevent water pollution.

8. Anodic Oxidation

Anodic oxidation primarily refers to the anodization of aluminum, which utilizes electrochemical principles to form a layer of aluminum oxide (Al2O3) film on the surface of aluminum and aluminum alloys. This oxide film possesses special characteristics such as protection, decoration, insulation, and wear resistance. Applicable materials: Aluminum and aluminum alloy products.

Process cost:

During the production process, there is significant consumption of water and electricity, especially during the oxidation process. The heat generated by the equipment requires continuous cooling with circulating water, and the electricity consumption is typically around 1000 degrees per ton.

Environmental impact:

Anodic oxidation is not particularly energy efficient. Additionally, during aluminum electrolysis production, the anodic effect can produce gases that have a detrimental impact on the ozone layer in the atmosphere.

9. Metal Wire Drawing

Metal wire drawing is a surface treatment method that creates linear patterns on the surface of a workpiece through grinding, achieving a decorative effect. Depending on the different patterns formed after wire drawing, it can be divided into straight-line wire drawing, random wire drawing, corrugated patterns, and spiral patterns. Applicable materials: Metal wire drawing can be applied to almost all metal materials.

Process cost:

The process is simple, the equipment is straightforward, and the material consumption is minimal, making it cost-effective and highly economically beneficial.

Environmental impact:

Pure metal products without paint or any chemical substances do not burn at 600 degrees Celsius and do not produce toxic gases, meeting the requirements of fire protection and environmental protection.

10. In-Mold Decoration (IMD)

In-Mold Decoration (IMD) is a molding method where pre-printed film sheets are placed inside a metal mold. The molding resin is injected into the metal mold, bonding with the film sheet. This results in the film sheet with printed patterns becoming an integral part of the cured product. Applicable materials: Plastic surfaces.

Process cost:

Only one set of molds is required, reducing costs and allowing for high automation and simplified processes. It achieves simultaneous molding and decoration in a single injection molding process.

Environmental impact:

This technology is environmentally friendly, avoiding the pollution caused by traditional spray painting and electroplating methods.

Conclusion

In conclusion, the comprehensive surface treatment techniques for materials offer a variety of options, including vacuum metalizing, electropolishing, pad printing, galvanizing, electroplating, hydro transfer printing , screen printing, anodic oxidation, metal wire drawing, and in-mold decoration. These processes cater to the diverse requirements of different materials, providing properties such as protection, decoration, wear resistance, and aesthetics. Choosing the appropriate surface treatment technique enables the desired functionality and visual effects, adding value and enhancing the quality of products.