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In this paper, 7 surface treatment processes are introduced in detail. They are vacuum metalizing, electropolishing, photo etching, pad printing, galvanizing, electroplating, powder coating, water transfer printing, screen printing, anodic oxidation, electrophoresis, micro arc oxidation, metal drawing and in-mold decoration, which basically cover common surface treatment processes. It is well worth collecting and learning.
Vacuum Metalizing
Vacuum Metalizing: It is a physical deposition phenomenon. In other words, argon is injected under the vacuum state and hits the target material, and the target material is separated into molecules and adsorbed by the conductive goods to form a uniform and smooth imitation metal surface layer.
Typical products: the surface treatment of reflective coatings, consumer electronics products and heat insulation boards
Suitable output: single piece to large quantities
Quality: high quality, highlight and product surface protection
Speed: medium production speed, 6 hours/cycle (including paint spraying)
Applicable materials
1. Many materials can be vacuum metalized, including metals, hard and soft plastics, composites, ceramics and glass. The most common material used in electroplating surface treatment is aluminum, followed by silver and copper.
2. Natural materials are not suitable for vacuum metalizing, because the moisture of natural materials will affect the vacuum environment.
Process cost
Vacuum metalizing relies heavily on manual operation. In the process of vacuum metalizing, the workpiece needs to be sprayed, loaded, unloaded and resprayed, so the labor cost is quite high, but it also depends on the complexity and number of the workpieces.
Environmental impact
Vacuum metalizing has little environmental pollution, which is similar to spraying.
Electropolishing
Electropolishing: With polished workpiece as anode and insoluble metal as cathode, both poles can be immersed into electrolytic cell at the same time, producing selective anodic dissolution by direct current ionization, thereby achieving the effect of removing fine burrs and increasing the brightness of the workpiece surface.
Typical products: building structures, food handling and storage as well as medical pharmacy
Suitable output: single piece to large quantities
Quality: the surface is highly bright, smooth and sanitary
Speed: medium production speed, 5-30 min/cycle
Applicable materials
1. Most metals can be electropolished, and it is mostly used for the surface polishing of stainless steel (especially austenitic nuclear grade stainless steel).
2. Different materials cannot be electropolished at the same time, or even put in the same electrolytic solvent.
Process cost
The whole process of electropolishing is basically completed automatically, so the labor cost is very low.
Environmental impact
Electropolishing uses less harmful chemicals, the whole process requires a small amount of water and the operation is simple, in addition it can extend the properties of stainless steel and retard the corrosion of stainless steel.
Photo Etching
Photo Etching: It makes anticorrosive film image by photographic means to protect the surface; with the aid of a chemical etchant, it etches the surface and produces surface textures on metal, plastic, etc.
Typical products: for the surface treatment of jewelry, nameplates and trophies
Suitable output: single piece to large quantities
Quality: Prolonged exposure and chemicals can realize photo etching surface treatment
Speed: medium production speed (50-100 microns /5 min)
Applicable materials
1. Most metals are suitable for photo etching surface treatment. The most common ones are stainless steel, mild steel, aluminum, brass, nickel, tin, copper and silver. Among them, the photo etching speed of aluminum is the fastest, while that of stainless steel is the slowest.
2. Glass and ceramics are also suitable for photo etching surface treatment, but different photoresist and chemical substances are required.
Process cost
1. Low mold cost
2. Medium labor cost
Environmental impact
The metal scraps produced by photo etching shall be recovered in a controlled manner; ferric chloride makes up one third of the chemicals used in photo etching, and caustic soda is also used to treat discarded photographic film. Both of the chemicals are harmful, so operators need to wear protective clothing when handling them.
Pad Printing
Pad Printing: With the ability of printing texts, graphics and images on irregular surfaces, it is becoming an important specialty type of printing.
Typical products: surface printing of vehicle interiors, consumer electronics and sports equipment
Suitable output: single piece to large quantities
Quality: achieve clear print details, even on undulating surfaces
Speed: single printing time (1-5 seconds)
Applicable materials
Almost all materials can be pad printed, except those that are softer than silicone pads, such as PTFE.
Process cost
1. Low mold cost
2. Low labor cost, because most processes are completed by machining
Environmental impact
Because this process is limited to soluble inks (which contain harmful chemicals), it has a great impact on the environment.
Galvanizing
Galvanizing: It is a surface treatment technology to plate a layer of zinc on the surface of iron and steel alloy materials for the purposes of beautiful appearance and rust prevention. The zinc layer on the surface is an electrochemical protective layer that can prevent metal decay. The main methods used are hot-dip galvanizing and electrogalvanizing.
Typical products: surface treatment for buildings, Bridges, vehicles, furniture, etc
Suitable output: single piece to large quantities
Quality: a perfect protective coating; the appearance greatly depends on the quality of steel
Speed: fast speed, basically 10 min/cycle
Applicable materials
As the galvanizing process relies on metallurgical bonding technology, it is only suitable for surface treatment of steel and iron
Process cost
1. No mold cost, short cycle and low cost
2. The labor cost is moderate, because the surface quality of the workpiece greatly depends on the artificial surface treatment before galvanizing
Environmental impact
As the galvanizing process increases the service life of steel and iron parts for 40-100 years, it has a positive effect on protecting the environment by preventing the rust and decay of the workpiece. In addition, at the end of the service life, the galvanized workpiece can be returned to the galvanizing pot, and the repeated use of liquid zinc will not produce chemical and physical waste.
Electroplating
Electroplating: It makes a metal film attach on the surface of the parts by electrolysis thus prevent metal oxidation, improve the wear resistance, electrical conductivity, reflective property, corrosion resistance and enhance the aesthetic effect. Many coins are also plated on their outer layers.
Typical products: surface treatment of transportation, consumer electronics, furniture, jewelry, silverware finish, etc.
Suitable output: single piece to large quantities
Quality: high gloss, anti-oxidation corrosion
Speed: medium speed, depending on the type of material and coating thickness
Applicable materials
1. Most metals can be electroplated, but different metals have different levels of purity and electroplating efficiency. Among the most common metals such as tin, chromium, nickel, silver, gold and rhodium (rhodium: a type of platinum, which is extremely expensive and keeps high brightness for a long time, and is resistant to most chemicals and acids. It is most commonly used in products that require high surface gloss, such as trophies and medals).
2. ABS is the most commonly used plastic for electroplating, because ABS can withstand 60°C (140°F) of electroplating high temperature, and it has electroplating and non-electroplating high bonding strength.
3. Nickel metal should not be used in electroplating products that contact the skin because nickel is irritating and toxic to the skin.
Process cost
1. There is no mold cost, but fixtures are needed to fix the parts
2. The time cost depends on the temperature and the type of metal
3. The labor costs (medium to high) depends on the type of electroplated workpiece. For example, the anodizing and electroplating of silver and jewelry requires extremely skilled workers to operate because of the high requirements for appearance and durability.
Environmental impact
Large quantities of toxic substances are used in the plating process, so professional separation and extraction are required to ensure minimal environmental impact.
Powder Coating
Powder Coating: As a dry spray method, powder coating is used on some metal workpieces by spraying or fluidized bed. The powder can be adsorbed on the surface of the workpieces by static electricity, and there will form a protective film on the surface when the powder is completely dry.
Typical products: praying of transportation, construction and white goods
Suitable output: single piece to large quantities
Quality: smooth and even color on the surface
Speed: The speed depends on the size of the workpiece and the degree of automation; it will take at least 30 minutes to dry
Applicable materials
Although it is suitable for some metal parts, plastics and glass surface coating, industrial powder coating is mainly used to protect or color aluminum and steel.
Process cost
1. There is no mold cost, but the equipment cost is very high
2. The time cost is low, but the drying time should be at least half an hour
3. The labor cost is quite low
Environmental impact
Compared with wet spraying, powder spraying has a higher material utilization rate (due to the electrostatic absorption of powder particles), which can be up to 95%.