What Is Surface Finishing?

Surface treatment is a process of artificially forming a surface layer on the surface of the base material that is different from the mechanical, physical, and chemical properties of the base body. The purpose of surface treatment is to meet the requirements of corrosion resistance, wear resistance, decoration or other special functions of the product. For metal castings, the more commonly used surface treatment methods are mechanical grinding, chemical treatment, surface heat treatment, spray coating, and surface treatment is to clean, clean, deburr, degrease, and descale the surface of the workpiece.

Chinese name: Surface treatment
Foreign name: Surface treatment

Nature: Industrial process
Method: Plating, etc.

Introduction to surface treatment

Generally speaking, there are two interpretations of surface treatment in China. One is broad surface treatment.

Surface treatment agent That is, many physical and chemical methods including pre-treatment, electroplating, painting, chemical oxidation, thermal spraying, etc .; the other is a narrow surface treatment, that is, only sandblasting, polishing, etc. Pre-processing part. What we are talking about below is mainly narrow surface treatment.

During the processing, transportation, and storage of workpieces, the surface often has oxide scale, molding sand, welding slag, dust, oil, and other contaminants remaining from the mold molding. If the coating can be firmly adhered to the surface of the workpiece, the surface of the workpiece must be cleaned before painting. Otherwise, it will not only affect the bonding force and corrosion resistance of the coating to the metal, but also make the base metal even when coated. Under the protection of the layer, it can continue to corrode, causing the coating to peel off, affecting the mechanical properties and service life of the workpiece. Therefore, the surface treatment of the workpiece before painting is an important guarantee and measure to obtain a high-quality protective layer and prolong the service life of the product.

Surface treatment history

Surface treatment is the oldest technology. Since there are humans on the earth, surface treatment is the earliest technology that humans have mastered. Primitive humans lived extremely hard lives. They lived in gregarious communities. In order to survive, they made stone tools and applied grinding techniques to make the stone tools have sharp edges and produce "split" effects. In the Neolithic Age, the stoneware used by the primitive people was polished, the surface was delicate and smooth, and the decorative effect was emphasized. It has become the mainstream of the era.

In primitive society, as important as grinding stone tools is primitive painting technology. Primitive humans already have a sense of beauty. In the late Paleolithic period, they used mineral dyes to paint and paint personal self-entertainment small items. In the Neolithic period, the invention of pottery brought the original color painting technology to its peak, forming a well-known colored pottery art in history, which opened the prelude to the surface treatment and coating technology.

Surface treatment method

Surface treatment Surface treatment before painting

In order to remove various foreign matters (such as oil, rust, dust, old paint film, etc.) attached to the surface of the object, provide a good substrate suitable for coating requirements to ensure that the coating film has good anti-corrosion performance, decorative performance and some For some special functions, the surface of the object must be pre-treated before painting. The work done for this kind of treatment is collectively referred to as pre-painting (surface) treatment or (surface) pretreatment.

Surface treatment by hand

Such as scraper, wire brush or grinding wheel. The rust and oxide scale on the surface of the workpiece can be removed by hand, but the manual treatment has high labor intensity, low production efficiency, poor quality, and incomplete cleaning.

Surface treatment chemical treatment

It mainly uses an acidic or alkaline solution to chemically react with oxides and oil on the surface of the workpiece to dissolve it in an acidic or alkaline solution to remove the rust scale and oil on the surface of the workpiece, and then uses nylon to make it. The brush roller or 304 # stainless steel wire (steel wire brush roller made of acid and alkali resistant solution can be cleaned. The chemical treatment is suitable for cleaning thin plates, but the disadvantage is that if the time is not controlled properly, even if a corrosion inhibitor is added, It can also cause over-corrosion of steel. For more complicated structural parts and parts with holes, after acid washing with acid solution, the residual acid immersed in the gaps or holes is difficult to completely remove. If it is not handled properly, it will become a corrosion of the workpiece Hidden dangers, and the chemicals are volatile, the cost is high, the chemical discharge after treatment is difficult, if not handled properly, it will cause serious pollution to the environment. With the improvement of people's environmental protection awareness, this treatment method is being replaced by mechanical treatment methods .

Surface treatment mechanical treatment

Nylon brush roller Mainly include wire brush roller polishing, shot blasting and shot blasting.

The polishing method is that the brush roller is driven by a motor, and the brush roller rotates at a high speed on the upper and lower surfaces of the strip to remove the oxide scale in a direction opposite to the rolling motion. The brushed iron oxide scale is washed away by a closed-cycle cooling water flushing system.

Shot blast cleaning is a method that uses centrifugal force to accelerate the projectile and throw it to the workpiece for rust removal and cleaning. However, shot blasting has poor flexibility and is limited by the site. It is somewhat blind when cleaning the workpiece, and it is easy to produce dead angles that cannot be cleaned on the inner surface of the workpiece. The equipment structure is complex, with many wearing parts, especially the blades and other parts wear quickly, the maintenance time is high, the cost is high, and the one-time investment is large.

Surface treatment with shot blasting has a large impact force and a clear cleaning effect. However, the treatment of thin plate workpieces by shot peening easily deforms the workpiece, and the steel shot hits the surface of the workpiece (no matter shot blasting or shot peening), which deforms the metal substrate. After peeling, the oil film is deformed together with its material, so shot peening and shot peening cannot completely remove the oil stain on the workpiece with oil stain.

Among the existing surface treatment methods for workpieces, sandblasting is the best cleaning effect. Sand blasting is suitable for high-level cleaning of workpiece surfaces. However, most of the current general sand blasting equipment in China are composed of primitive and bulky sand conveying machinery such as hinge dragons, scrapers, and top-level elevators. The user needs to construct a deep pit and make a waterproof layer to install the machinery. The construction cost is high, the maintenance workload and maintenance cost are huge, and a large amount of silicon dust generated during the blasting process cannot be removed, which seriously affects the health of the operator and pollutes the environment. .

Spraying equipment

Abroad sand suction machines are often used as machinery for conveying sand volume. The sand suction machine is actually a very large vacuum cleaner. The thicker conveying pipe connects the hopper to the sand suction machine, and sucks the sand material into the storage tank and the sand suction machine. The characteristics are that the construction difficulty and technology are simpler than the bucket elevator, and it is convenient and easy to control. It requires less maintenance, but requires a lot of power. At present, there are several manufacturers specializing in sand suction machines in China, but the technology is relatively immature. Therefore, most surface treatment companies mainly use bucket elevators.

Factories that need to do blasting process must fully consider the actual situation of production when selecting sand conveying equipment and dust removal equipment, and try to choose equipment that requires greater power than production, because the equipment for shot blasting generally consumes faster. After long-term use, one or more of these problems will affect production a lot, and the selection of equipment with larger power will greatly reduce the time and cost wasted for future maintenance. Insufficient power of the dust removal equipment not only damages the health of the workers, but also seriously affects the visibility of the blasting room. Failure to discharge dust also affects the quality of the sand material itself and the surface roughness of the workpiece.

The manual blasting room should be designed to be relatively spacious relative to the workpieces according to the actual situation. It should not be too restrictive or it will affect the manual work of the workers. At the same time, the lighting conditions must be good. For dry areas, sandblasting can be carried out outdoors. ^[1]

Surface treatment plasma treatment

Plasma, also known as plasma, is an assembly of positively charged positive and negative particles (including positive ions, negative ions, electrons, free radicals and various active groups, etc.), where the positive and negative charges are equal Therefore, it is called plasma, which is the fourth stateplasma statein addition to solid, liquid, and gaseous states.

The plasma surface processor is composed of a plasma generator, a gas conveying pipeline and a plasma spray head. The plasma generator generates high-pressure and high-frequency energy to generate low-temperature plasma in a glow discharge that is activated and controlled in a nozzle steel pipe. Plasma is sprayed on the surface of the workpiece. When the plasma meets the surface of the object to be processed, object changes and chemical reactions occur. The surface has been cleaned, hydrocarbon-based contaminants such as grease, auxiliary additives, etc. have been removed, or etching and roughening have occurred, or a dense cross-linked layer has been formed, or oxygen-containing polar groups (hydroxyl, carboxyl) have been introduced. These The group has the effect of promoting the adhesion of various coating materials, and is optimized for adhesive and paint applications. Under the same effect, the application of plasma treatment on the surface can obtain a very thin high tension coating surface, which is conducive to bonding, coating and printing. No other mechanical or chemical treatment is required to increase the adhesion.

Plasma surface treatment in the printing and packaging industry

1. Solve the problem of film opening

2. Solve the problem of UV and varnish opening

3. Beverage bottles and jam bottles are affixed with seals to meet firmness and reliability

Plasma surface treatment in automotive and shipbuilding

1. Automotive sealing strip bonding surface treatment, tighter bonding, sound insulation, dustproof

2. Application in automotive lamp bonding process, strong bonding, dustproof and moisture-proof

3. Automotive interior surface spraying, pre-printing treatment, no fading, no paint off

4. Automotive brake pads, oil seals, and bumpers are pre-painted for seamless bonding

5. Shipbuilding materials are pre-bonded, bonding is perfect

Plasma surface treatment on ceramic surface

1. Ceramic coating pre-treatment, no primer coating, strong coating

2. Ceramic glazing pre-treatment for enhanced adhesion

Cable industry plasma surface treatment

1. Special cable printing, good printing effect

2. Optical cable printing, fastness comparable to laser marking

3. Cross fiber printing, clear and wear-resistant printing

Application of plasma in medical biological materials

1. Surface treatment of human implant materials to meet compatibility

2. Hydrophilic treatment of medical consumables

3. Disinfection of medical equipment

4. Adhesion after medical catheter surface treatment, the adhesion is stronger

Application of plasma in textile printing and dyeing industry

1. Cellulose fiber treatment, improve dyeing performance

2. Protein fiber treatment, increase hydrophilicity and adsorption

3. Synthetic fiber treatment, increase hygroscopicity, destatic

Plasma treatment on plastic surface

1. Surface treatment of pipe to increase the adhesion of printing

2. Toy surface treatment, good adhesion, printing, etc.

3. Drink bottle cap, cosmetic surface printing, bonding

4. Plasma treatment of daily necessities and household appliances

5. Pre-adhesive treatment of shoes to ensure firmness

Digital products plasma surface treatment

1. Adhesive for mobile phone and notebook case, the case does not fall off and the text does not fade

2. The keys of the mobile phone and the notebook keyboard are bonded, and the keyboard text does not fall off.

3. Painting of mobile phone case and notebook case, no paint off

4. LCD flexible film circuit bonding, stronger bonding

5. Pre-treatment of components to ensure strong adhesion

Surface treatment of rubber and plastic industry

1. Capable of printing, bonding, coating, etc.

Plasma treatment before bonding glass products

1. Windshield pre-adhesive treatment, bonding is more moisture-proof and sound-proof

2. The laboratory bacteria culture dish is hydrophilic and treated with adhesion, and the bacteria production is uniform

3. Display bonding before treatment

Plasma metal surface modification

Improve the adhesion of metal surfaces

2. Improve the corrosion resistance of metal surfaces

3. Improve metal hardness and wear characteristics

Daily necessities and household appliances plasma treatment

1. Surface treatment before coating, coating is stronger

2. Surface treatment before printing, printing will not fall off

3. Surface treatment before bonding, stable bonding

4. The surface treatment of high-end furniture, without polishing, directly paint, no paint drop ^[2]

Classification of surface treatment technology

Depending on the method used, surface treatment technologies can be classified into the following types.

Surface treatment electrochemical method

This method uses electrode reaction to form a coating on the surface of the workpiece. The main methods are:

(1) Electroplating

In the electrolyte solution, the workpiece is the cathode, and the process of forming a coating on its surface under the action of an external current is called electroplating. The coating can be metal, alloy, semiconductor or containing various solid particles, such as copper plating and nickel plating.

(Two) oxidation

In the electrolyte solution, the workpiece is the anode, and the process of forming an oxide film layer on the surface under the action of an external current is called anodization, such as anodization of aluminum alloy.

The oxidation treatment of steel can be chemical or electrochemical. The chemical method is to put the workpiece in an oxidizing solution and rely on chemical action to form an oxide film on the surface of the workpiece, such as the bluing treatment of steel.

Surface treatment chemical method

This method has no current effect, and uses chemical substances to form a plating layer on the surface of the workpiece. The main methods are:

(I) Chemical conversion film treatment

In an electrolyte solution, a metal workpiece has no external current, and the process in which a chemical substance in the solution interacts with the workpiece to form a coating on its surface is called a chemical conversion film treatment. Such as metal surface blue, phosphating, passivation, chromium salt treatment, etc.

(Two) chemical plating

In the electrolyte solution, the surface of the workpiece is catalyzed without external current. The process of depositing certain substances on the surface of the workpiece to form a coating due to the reduction of chemical substances in the solution is called electroless plating, such as chemical nickel plating, Electroless copper plating, etc.

Surface treatment hot working method

This method is to melt or thermally diffuse the material under high temperature conditions to form a coating on the surface of the workpiece. The main methods are:

(I) Hot Dip Plating

The process of putting a metal workpiece into molten metal to form a coating on its surface is called hot dip plating, such as hot-dip galvanizing and hot-dip aluminum.

(Two) thermal spraying

The process of atomizing and spraying molten metal on the surface of a workpiece to form a coating is called thermal spraying, such as thermal spraying zinc, thermal spraying aluminum, and the like.

(Three) hot stamping

The process of heating and pressing metal foil on the surface of a workpiece to form a coating is called hot stamping, such as hot stamping aluminum foil.

(4) Chemical heat treatment

The process of contacting and heating the workpiece with chemical substances, and allowing certain elements to enter the surface of the workpiece under high temperature conditions, is called chemical heat treatment, such as nitriding and carburizing.

(5) Surfacing

The process of depositing deposited metal on the surface of a workpiece by welding to form a welding layer is called surfacing, such as surfacing welding of wear-resistant alloys.

Surface treatment vacuum method

This method is a process in which a material is vaporized or ionized deposited on the surface of a workpiece under a high vacuum state to form a plating layer. The main method is.

(1) Physical Vapor Deposition (PVD)

Under vacuum conditions, the process of vaporizing a metal into atoms or molecules, or ionizing it into ions, and depositing it directly on the surface of a workpiece to form a coating is called physical vapor deposition, and its deposition particle beam comes from non-chemical factors, such as evaporation Sputter plating, ion plating, etc.

(Two) ion implantation

The process of injecting different ions into the surface of a workpiece under high voltage to modify its surface is called ion implantation, such as boron injection.

(Three) chemical vapor deposition (CVD)

Under low pressure (and sometimes atmospheric pressure), the process of gaseous substances forming solid deposited layers due to chemical reactions on the surface of the workpiece is called chemical vapor deposition, such as vapor deposition of silicon oxide, silicon nitride, etc.

Other methods of surface treatment

Mainly mechanical, chemical, electrochemical, physical methods. The main methods are:

(I) Painting

Idle spraying or brush coating method. The process of applying coating (organic or inorganic) on the surface of the workpiece to form a coating is called painting, such as spray painting, brush painting, etc.

(Two) impact plating

The process of forming a coating layer on the surface of a workpiece by mechanical impact is called impact plating, such as impact galvanizing.

(Three) laser surface treatment

The process of irradiating the surface of a workpiece with a laser to change its structure is called laser surface treatment, such as laser quenching and laser remelting.

(Four) super hard film technology

The technology of preparing superhard film on the surface of workpiece by physical or chemical method is called superhard film technology. Such as diamond film, cubic boron nitride film and so on.

(V) Electrophoresis and electrostatic spraying

1.Electrophoresis

The workpiece is placed as an electrode in a conductive water-soluble or water-emulsified paint, and forms a circuit with the other electrode in the paint. Under the action of an electric field, the coating solution has dissociated into charged resin ions, the cations move to the cathode, and the anions move to the anode. These charged resin ions, along with the adsorbed pigment particles, are electrophoresed to the surface of the workpiece to form a coating. This process is called electrophoresis.

2. Electrostatic spraying

Under the action of a DC high-voltage electric field, the atomized negatively charged paint particles are directed to the positively charged workpiece to obtain a paint film, which is called static spraying. ^[3]

Development prospects of surface treatment

At present, some traditional methods of surface treatment, such as surfacing, thermal spraying, and brushing, often cannot meet the needs of modern industries. For example, some metal parts that are particularly sensitive to temperature will cause the surface of the part to reach a very high temperature, which will cause the part to deform or crack, which will affect the dimensional accuracy and normal use of the part. Influence, but the thickness of the crossing layer cannot be too thick, the pollution is serious, and the application is also greatly restricted. At present, the western countries have developed on-site surface treatment methods of polymer composite materials for the disadvantages of the above methods. Among them, the relatively mature Blessing Blue technology system. The comprehensive properties of the material and the superiority of being machinable at any time not only fully meet the requirements and accuracy of repair after use, but also reduce the shock and vibration experienced by the equipment during operation and extend its service life. Because the material is a "variable" relationship, when an external force impacts the material, the material will deform and absorb the external force, and expand and contract with the expansion or contraction of the bearing or other components. It always maintains a tight fit with the components to reduce the probability of wear. Wear, you can also use the "mold" or "matching parts" to repair the damaged equipment on-site to avoid the overall disassembly of the equipment, but also to maximize the size of the components to meet the production and operation requirements of the equipment, extend the service life of the equipment, To ensure the safe and continuous production of enterprises. In domestic surface treatment applications, polymer composites have also played an increasingly important role. ^[4]

Terminology for surface treatment

Terminology for surface treatment ^[5]
Before coating, the process of removing attachments or generated foreign matters on the substrate surface to improve the adhesion between the substrate surface and the coating or to give the surface a certain degree of corrosion resistance can be called pretreatment.
1 mechanical pretreatment
Before painting, the process of removing foreign objects on the substrate surface using hand tools, power tools or spraying, shot blasting, granulating, etc.
2 chemical pretreatment
The process of removing foreign matter on the surface of a substrate or forming a conversion film using a chemical method before painting.
3 electrochemical pretreatment
The process of removing foreign matter on the surface of a substrate or forming a conversion film using an electrochemical method before painting.
4 skim degreasing
The process of removing oil on the surface of the substrate.
5 chemical degreasing
The process of removing oil on the surface of a substrate by chemical methods.
6 electrochemical degreasing
The process of removing oil on the surface of the substrate by electrochemical methods.
7 Soak degreasing
The workpiece is immersed in the cleaning agent without external current cleaning.
8 spray degreasing
The process of spraying degreasing agent on the workpiece to remove oil stains.
9 Ultrasonic degreasing
With the help of super-field vibration, the process of removing oil on the surface of the workpiece is accelerated.
10 derusting
The process of removing rust products on the surface of a steel substrate.
11 trim trim
Remove burrs, nodules, welding slag, sharp edges on the substrate to make it suitable for painting.
12 Pickling
The process of removing rust and skinning on the surface of the substrate with an acid solution.
13 fiamo cleaning
The steel structure is briefly burned with a reducing flame and then cleaned with a powered wire brush.
14 hand tool cleaning
The process of removing foreign matter on the surface of a substrate using a hand tool.
15 power tool cleaning
The process of removing foreign matter on the surface of a substrate using a power tool.
16 blasting
The process of cleaning and roughening the surface of a substrate using the impact of a high-speed abrasive stream.
17 dry blasting
The process of cleaning and roughening the substrate surface by the impact of a high-speed dry abrasive stream. The use of a vacuum system around the nozzle to remove waste abrasive or abrasive debris is called vacuum dry blasting.
18 wet blasting
The process of cleaning and roughening the surface by the impact of the high-speed flow of a mixture of abrasive and water.
19 sand blasting
The process of cleaning and roughening the substrate surface by the impact of high-speed sand flow.
20 shot blasing
The process of cleaning and strengthening the substrate surface by the impact of high-speed shot.
21 rusting grade
Classification of the degree of rust on the steel surface.
22 derusting grade
Classification of the degree of rust removal on steel surfaces.
23 Abrasive
Natural or synthetic solid materials used as spray treatment media.
24 angular sand grit
An abrasive that sprays angular or irregularly shaped particles for cleaning.
25 shot
A spherical abrasive used in spray processing.
26 depainting
The process of removing old, damaged coatings in preparation for repainting.
27 surface conditioning
The process of converting a surface into an appropriate state that can be successfully processed in subsequent processes.
28 conversion treatment
A chemical or electrochemical process that produces a film composed of a compound of a metal on the surface of a substrate.
29 phosphating
The process of forming an insoluble phosphate film on the surface of a base metal by using a solution containing phosphoric acid or a phosphate.
30 chromate passivation
A process of forming a chromate conversion film on the surface of a base metal by using an acid solution of a hexavalent chromium or a trivalent chromium compound.
31 passivating
The process of making the base metal surface passive.
32 all-in-one treatment
Degreasing, derusting or degreasing, derusting and phosphating together.
33 temporary protection
Temporary protection of the surface of a substrate that has been surface-pretreated before its prescribed cleanliness has not changed.