The process method of artificially forming a surface layer on the surface of the matrix material with different mechanical, physical and chemical properties from the matrix
Surface treatment refers to the mechanical, physical andChemical propertiesDifferent surface processing methods.The purpose of surface treatment is to meet the requirements of corrosion resistance, wear resistance, decoration or other special functions of products.For metal castings, our common surface treatment method is mechanical grinding,chemical treatment，Surface heat treatment, spraying surface, surface treatment is toworkpiece surface Clean, clean, deburr, degrease, scale, etc.
Generally speaking, there are two interpretations of surface treatment in China. One is the generalized surface treatment, which includesPretreatment、electroplate、Painting, chemical oxidationThermal sprayingAnd many other physical and chemical methods;The other is surface treatment in a narrow sense, which only includesSandblasting、polishingWhat is included is what we often call the pretreatment part.The following is mainly about surface treatment in a narrow sense.
In the process of processing, transportation, storage, etc., the surface of the workpiece is often covered with oxide skin, rust molding sandWelding slag, dust, oil and other dirt.The coating shall be firmly attached to theworkpiece surface Before painting, the surface of the workpiece must be cleaned. Otherwise, it will not only affect the bonding force and corrosion resistance of the coating and metal, but also make the base metal continue to corrode even with coating protection, so that the coating will peel off and affect theMechanical propertiesAnd service life.Therefore, the surface treatment of the workpiece before painting is an important guarantee and measure to obtain a high-quality protective layer and extend the service life of the product.
history
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Surface treatment is the oldest technology. Since there are humans on the earth, surface treatment is the earliest technology mastered by humans.Primitive humanTheir life is extremely hard and they live in groups. In order to survive, they make stone tools and use grinding technology to make stone tools have sharp edges, producing a "sharp wedge" effect.In the Neolithic Age, the stone tools used by the primitive people have become the mainstream of the times after their whole body has been ground, the surface is fine and smooth, and the decoration effect is emphasized.
In the primitive society, the original painting technology was as important as the grindstone.Primitive humans have a sense of beauty. In the late Paleolithic Age, they used mineral dyes to paint small personal entertainment items.In the Neolithic period, the invention of pottery brought the original color coating technology to the peak, forming the famous colored pottery art in history, and opening the prelude of surface treatment coating technology.
method
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Surface treatment before painting
In order to remove all kinds of foreign matters (such as oil stain, rust, dust, old paint film, etc.) attached to the object surface, provide a good substrate suitable for the coating requirements to ensure that the film has a goodAnticorrosionPerformance, decoration performance and some special functions must be pretreated before painting.People refer to the work done by such treatment as pre coating (surface) treatment or (surface) pretreatment.
Manual processing
Such as scraper, wire brush orgrinding wheelEtc.Rust and rust on the workpiece surface can be removed manuallyOxide scaleHowever, manual processing has high labor intensity, low production efficiency, poor quality and incomplete cleaning.
chemical treatment
It is mainly caused by acid or alkaline solution and oxide and oil stain on the workpiece surfacechemical reactionIt can be dissolved in acidic or alkaline solution to remove rust, oxide skin and oil stain on the surface of workpiece, and then it can be made of nylonBrush rollerOr 304 # stainless steel wire (the purpose can be achieved by cleaning the steel wire brush roll made of acid and alkali resistant solution.Chemical treatment is suitable for cleaning thin plates, but its disadvantage is that if the time is not properly controlled, even if corrosion inhibitor is added, the steel can also cause over corrosion. For more complex structural parts and parts with holes, it is difficult to thoroughly remove the residual acid immersed in the gaps or holes after acid pickling with acid solution. If the treatment is not proper, it will become a hidden danger of corrosion of the workpiece in the future, and the chemicals are volatile,The cost is high, and the chemical discharge after treatment is difficult. If the treatment is improper, it will cause serious pollution to the environment.With the improvement of people's awareness of environmental protection, this treatment method is being replaced by mechanical treatment.
Mechanical treatment
Nylon brush roller
It mainly includes wire brush roll polishing method, shot blasting method and shot blasting method.
The polishing method is that the brush roller, driven by the motor, rotates at high speed on the upper and lower surfaces of the plate and strip in the opposite direction to the movement of the rolled piece to brush off the scale.The iron oxide scale brushed off shall be washed off with closed circulating cooling water flushing system.
Shot blasting cleaning is to usecentrifugal forceThe method of accelerating the projectile and throwing it onto the workpiece for rust removal and cleaning.However, due to the poor flexibility of shot blasting and the limitation of the site, there is some blindness in cleaning the workpiece, and it is easy to produce dead corners on the inner surface of the workpiece that cannot be cleaned.The equipment structure is complex, and there are many vulnerable parts, especially the blades and other parts that wear quickly, with many maintenance hours, high costs and large one-time investment.
Surface treatment by shot peening has great impact and obvious cleaning effect.However, the treatment of shot peening on thin plate workpiece is easy to deform the workpiece, and the steel shot hitting the workpiece surface (no matter shot blasting or shot peening) will deform the metal substrate. Since there is noplasticityThe oil film and its material deform together, so shot blasting and shot peening cannot completely remove the oil stain on the workpiece with oil stain.
Spraying equipment
Among the existing surface treatment methods for workpieces, the one with the best cleaning effectSandblastingclear.Sand blasting is applicable to the cleaning of workpiece surface with high requirements.But it is currently used in ChinaSand blasting equipmentZhongduo is composed of original heavy sand conveying machinery such as hinge, scraper, No. 1 elevator, etc.Users need to build a deep pit and waterproof layer to install machinery. The construction cost is high, and the maintenance workload and maintenance cost are huge. A large amount of silica dust generated during sand blasting cannot be removed, which seriously affects the health of operators and pollutes the environment.
More used abroadSand suction machineAs a machine for conveying sand, the sand suction machine is actually a super large vacuum cleaner, which connects the hopper with the sand suction machine with a thicker conveying pipe to suck in sandStorage tankThe characteristics of the sand suction machine are that the construction difficulty and process are simpler than that of the bucket elevator, and it is convenient and easy to control, less maintenance is required, but the power consumption is large. At present, there are several manufacturers specialized in making sand suction machines in China, but the technology is relatively immature, so most surface treatment enterprises mainly use bucket elevators.
Need to doJetting processThe sand conveying equipment andDust removal equipmentWe must take full account of the actual situation of production, and try to choose equipment with more power than production needs. Since the equipment used in shot blasting generally consumes faster, this or that kind of problem will affect production after long-term use, and selecting equipment with more power will greatly reduce the time and cost wasted in future maintenance.Insufficient power of dust removal equipment not only damages workers' health, but also seriously affects the visibility of the sandblasting room. The inability to discharge dust also affects the quality of the sand itself, affecting the surface roughness of the workpiece.
The manual sand blasting room should be designed according to the actual situation, which is relatively spacious compared with the space for containing the workpiece. It should not be too timid, or it will affect the manual operation of workers. At the same time, the lighting conditions must be good. For dry areas, the sand blasting can be carried out outdoors.[1]
Plasma treatment
plasmaAlso known as plasma, it is composed ofPositive particle、Negative particle(includingPositive ion，anion, ElectronicFree radicalAnd various active groups, among whichpositive chargeIt is equal to the negative charge, so it is called plasmaGaseousThe fourth state of the existence of extraneous matter - plasma state.
The plasma surface processor is composed ofPlasma generatorIt is composed of gas transmission pipeline, plasma nozzle and other parts. The plasma generator generates high pressure and high frequency energy to generate low-temperature plasma in the glow discharge activated and controlled in the nozzle steel pipe. The plasma is sprayed to the surface of the workpiece with compressed air. When the plasma meets the surface of the object to be treated, object changes and chemical reactions occur.The surface has been cleaned, and hydrogen carbide dirt, such as grease and auxiliary additives, has been removed, or etched and rough, or dense cross-linked layer has been formed, or oxygen containing polar groups (hydroxyl, carboxyl) have been introduced, which can promote the adhesion of various coating materials, and have been optimized in adhesion and paint applications.Under the same effect, the application of plasma treatment can obtain very thin high tension coating surface, which is conducive to bonding, coating and printing.It does not need other machines, chemical treatment and other strong acting ingredients to increase the adhesion.
Plasma surface treatment in printing and packaging industry
1. Solve the problem of plastic peeling
2. Solve the problem of UV and varnish opening
3. Beverage bottles and jam bottles are stuck with labels to ensure firmness and reliability
Plasma surface treatment in the field of automobile and shipbuilding
1. The bonding surface of automobile sealing strip is treated to make it more compact, sound proof and dustproof
2. It is applied in the bonding process of automobile lamps, and the bonding is firm, dust-proof and moisture-proof
3. The interior surface of the car shall be sprayed and treated before printing, without fading or paint peeling
4. Car brake pads, oil seals and bumpers are treated before coating and bonded seamlessly
5. Pre bonding treatment of materials for shipbuilding, perfect bonding
Plasma surface treatment on ceramic surface
1. Ceramic coating pretreatment, no primer, and the coating is firm
2. Ceramic glazing pretreatment, with enhanced adhesion
Cable industrial plasma surface treatment
1. Special cable printing, good inkjet printing effect
2. Optical cable printing, with fastness comparable to that of laser logo
3. The cross fiber printing is clear and wear-resistant
Application of plasma in medical biomaterials
1. Surface treatment of human implant materials to meet compatibility
2. Hydrophilic treatment of medical consumables
3. Disinfection of medical equipment
4. The bonding of medical catheter after surface treatment is more firm
Application of Plasma in Textile Printing and Dyeing Industry
1. Cellulose fiber treatment to improve dyeing performance and dye uptake
2. Protein fiber treatment to increase hydrophilicity and adsorption
3. Synthetic fiber treatment to increase moisture absorption and remove static electricity
Plasma treatment on plastic surface
1. Pipe surface treatment to increase the adhesion of printing
2. Toy surface treatment, favorable for bonding, printing, etc
4. Plasma treatment of daily necessities and household appliances
5. The shoes shall be treated before bonding to ensure that they are firm without opening the glue
Plasma surface treatment of digital products
1. Mobile phone and notebook casings shall be bonded, and the paint on the casings shall not fall off, and the words shall not fade
2. Mobile phone keys and notebook keyboard are bonded, and the keyboard text does not fall off the paint
3. The coating of mobile phone case and notebook case shall not fall off
4. LCD flexible film circuit fits more firmly
5. Processing before binding components to ensure firm bonding
Rubber and plastic industry surface treatment
1. Capable of printing, bonding, coating and other operations
Plasma treatment of glass products before bonding
1. Windshield bonding pretreatment, bonding more moisture-proof, sound insulation
2. The laboratory bacteria culture dish is hydrophilic, with adhesion treatment, and the bacteria production is even
3. Pretreatment of display screen bonding
Plasma metal surface modification
1. Improve the adhesion of metal surface
2. Improve the corrosion resistance of metal surface
3. Improve the hardness and wear characteristics of metal
Plasma treatment of daily necessities and household appliances
1. Surface treatment before coating to make the coating more firm
2. Surface treatment before printing, printing will not fall off
3. Surface treatment before bonding, stable bonding
4. High grade furniture surface treatment, no polishing, direct painting, no paint falling[2]
Technical classification
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According to the different methods used, surface treatment technologies can be divided into the following categories.
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 a cathode. Under the action of external current, the process of forming a coating on its surface is called electroplating.The coating can be metal, alloy, semiconductor or contain various solid particles, such as copper plating, nickel plating, etc.
（2） Oxidation
In the electrolyte solution, the workpiece is an anode. Under the action of external current, the process of forming an oxide film on its surface is called anodic oxidation, such as the anodic oxidation of aluminum alloy.
Chemical or electrochemical methods can be used for oxidation treatment of steel.The chemical method is to put the workpiece into the oxidation solution and form an oxide film on the surface of the workpiece by chemical action, such as the blueing treatment of steel.
chemical method
This method is no current action, using the interaction of chemical substances to form a coating on the surface of the workpiece.The main methods are:
（1） Chemical conversion film treatment
In the electrolyte solution, the process that the chemical substances in the solution interact with the workpiece to form a coating on the surface of the metal workpiece without the action of external current is called chemical conversion coating treatment.Such as metal surface blueing, phosphating, passivation, chromate treatment, etc.
（2） Electroless plating
stayelectrolyteIn the solution, the workpiece surface is catalysed without external current. In the solution, due to the reduction of chemical substances, certain substances are deposited on the workpiece surface to form a coating, which is called electroless plating, such as electroless nickel plating, electroless copper plating, etc.
Hot working method
This method is to order material melting or thermal diffusion at high temperature to form a coating on the surface of the workpiece.The main methods are:
（1） 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, hot dip aluminizing, etc.
（2） Thermal spraying
The process of atomizing molten metal and spraying it on the workpiece surface to form a coating is called thermal spraying, such as thermal spraying zinc, thermal spraying aluminum, etc.
（3） Hot stamping
The process of heating and pressing the metal foil on the surface of the 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 chemicals and ordering certain elements to enter the workpiece surface at high temperature is calledChemical heat treatment, such as nitriding, carburizing, etc.
（5） Surfacing
The process of making the deposited metal accumulate on the surface of the workpiece to form a welding layer by welding is called surfacing, such as surfacing wear-resistant alloy.
Vacuum method
This method is the process of ordering the material to be vaporized or ionized and deposited on the surface of the workpiece in a high vacuum state to form a coating.The main method is.
（1） Physical vapor deposition (PVD)
Under vacuum conditions, the process of vaporizing metal into atoms or molecules, or ionizing it into ions, and directly depositing it on the surface of the workpiece to form a coating is called physical vapor deposition. The deposited particle beam comes from non chemical factors, such as evaporation plating, sputtering plating, ion plating, etc.
（2） Ion implantation
The process of implanting different ions into the workpiece surface under high voltage to modify its surface is called ion implantation, such as boron implantation.
（3） Chemical vapor deposition (CVD)
Under low pressure (sometimes also under normal pressure), the process of forming a solid deposition layer of gaseous substances on the workpiece surface due to chemical reaction is called chemical vapor plating, such as vapor deposition of silicon oxide, silicon nitride, etc.
Other methods
Mainly mechanical, chemical, electrochemical and physical methods.The main methods are:
（1） Painting
The process of coating (organic or inorganic) on the workpiece surface by idle spraying or brushing is calledPainting, such as painting, painting, etc.
（2） Impact plating
The process of forming a coating on the workpiece surface by mechanical impact is called impact plating, such as impact galvanizing.
（3） Laser surface treatment
The process of laser surface treatment, such as laser quenching, laser remelting, etc., which irradiates the workpiece surface to change its structure.
（4） Ultra hard film technology
The technology of preparing superhard film on the surface of workpiece by physical or chemical methods is called superhard film technology.Such as diamond film, cubic boron nitride film, etc.
The workpiece is put into the conductive water-soluble or water emulsified coating as an electrode to form a solution circuit with another electrode in the coating.Under the action of electric field, the paint solution has been dissociated into charged resin ions, the cations move to the cathode, and the anions move to the anode.These charged resin ions, together with the adsorbed pigment particles, electrophoresis to the surface of the workpiece to form a coating. This process is called electrophoresis.
Under the action of DC high-voltage electric field, the atomized paint particles with negative electricity will fly to the workpiece with positive electricity directionally to obtain the paint film, which is called static spraying.[3]
Development prospect
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At present, some traditional methods of surface treatment, such as surfacing, thermal spraying, brush coating and other processes, often cannot meet the needs of modern industry.For example, some metal parts that are particularly sensitive to temperature will make the surface of the parts reach very high temperature, causing deformation or cracks of the parts, affecting the dimensional accuracy and normal use of the parts, and even causing shaft fracture in serious cases;Although there is no thermal effect on the brush carrier, the thickness of the carrier layer should not be too thick, causing serious pollution, and its application has also been greatly limited.At present, Western countries have developed on-site surface treatment methods for polymer composites in view of the drawbacks of the above methods, of which the more mature is the ForsyBlue technology system.The comprehensive properties of materials and the advantages of machining at any time not only fully meet the use requirements and accuracy after repair, but also reduce the shock and vibration borne by the equipment in operation and extend the service life.Because the material is a "variable" relationship, when the external force impacts the material, the material will deform and absorb the external force, and expand and shrink with the expansion and contraction of the bearing or other parts. It always keeps a tight fit with the parts to reduce the probability of wear. For the wear of large equipment, the "mold" or "matching parts" can also be used to repair the damaged equipment on site to avoid the overall disassembly of the equipment,It can also maximize the matching size of components, meet the production and operation requirements of equipment, extend the service life of equipment, and ensure the safe and continuous production of enterprises.In the application of domestic surface treatmentcompound materialIt also plays an increasingly important role.[4]
Technical Term
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Terminology of surface treatment[5]
stayPaintingThe process of removing the attachments or generated foreign matters on the substrate surface to improve the adhesion between the substrate surface and the coating or give the surface a certain corrosion resistance is also called pretreatment.
1 Mechanical pretreatment
Before coating, the process of using manual tools, power tools or spraying, shot blasting, granulation, etc. to remove foreign matters on the substrate surface.
2 Chemical pretreatment
The process of removing foreign matters or forming conversion film on the substrate surface by chemical methods before coating.
3 Electrochemical pretreatment
The process of removing foreign matters or forming conversion film on the substrate surface by electrochemical method before coating.
4 Degreasing
The process of removing oil stains from the substrate surface.
5 Chemical degreasing
The process of removing oil stains on the substrate surface by chemical methods.
6 Electrochemical degreasing
The process of removing oil stains on the substrate surface by electrochemical method.
7 Soak degreasing
The workpiece is immersed in cleaning agent for cleaning without external current.
8 Spray degreasing
The process of spraying degreaser on the workpiece to remove oil stain.
9 Ultrasonic degreasing
The process of removing oil stains on the surface of the workpiece is accelerated by means of superfield vibration.
10 Derusting
The process of removing rust products from the surface of steel substrate.
11 Trim
Remove burrs, nodules, welding slag and sharp edges on the substrate to make it suitable for the coating process.
12 Pickling
The process of removing rust and skin on the substrate surface with acid solution.
13 Flame cleaning
The process of burning the steel structure with reducing flame briefly, and then cleaning it with power wire brush.
14 Hand tool cleaning
The process of removing foreign matters on the surface of the substrate with hand tools.
15 Power tool cleaning
The process of using power tools to remove foreign matters on the surface of the substrate.
16 Spraying
The process of cleaning and roughening the substrate surface by using the impact of high-speed abrasive flow.
17 Dry blasting
The process of cleaning and roughening the substrate surface by using the impact of high-speed dry abrasive flow.Using the vacuum system around the nozzle to remove waste abrasive or debris is called vacuum dry jet treatment.
18 Wet blasting
The process of cleaning and roughening the surface by using the impact of the high-speed flow of the 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 blasting
The process of cleaning and strengthening the substrate surface by the impact of high-speed shot flow.
21 Rusting grade
Classification of rust degree on steel surface.
22 Derusting grade
Classification of rust removal degree on steel surface.
23 Abrasive
Natural or synthetic solid materials used as spray treatment media.
24 angular sand grid
An abrasive with angular or irregularly shaped particles for jet cleaning.
25 shot
A spherical abrasive used for jet treatment.
26 Depainting
Remove the old damaged coating film to prepare for the process of repainting.
27 Surface conditioning
The process of converting a surface to an appropriate condition that can be successfully treated in subsequent processes.
28 Conversion treatment
A chemical or electrochemical process that produces a film consisting of a compound of metal on the surface of the substrate.
29 Phosphating
The process of forming an insoluble phosphate film on the surface of the base metal by using a solution containing phosphoric acid or phosphate.
30 chromating
The process of forming chromate conversion film on the surface of base metal by using the acid solution of hexavalent chromium or trivalent chromium compound.
31 Passivating
The process of making the surface of base metal dull.
32 Integrated treatment
The process of degreasing, derusting or degreasing, derusting and phosphating together.
33 Temporary protection
The temporary protection of the substrate surface after surface pretreatment when its cleanliness does not change before the specified coating is applied.
Related research
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Magnesium alloy is the lightest metal structural material known at present, which has the characteristics of high specific strength and specific stiffness, and excellent machinability.In recent years, magnesium alloys have attracted worldwide attention and become key lightweight materials. A series of technologies have been developed to promote their applications in transportation, aerospace, national defense and military industries.Although magnesium alloys have broad application prospects, their low standard electrode potential and loose porosity of oxide film make them prone to galvanic corrosion, environmental corrosion and other problems in most corrosive environments, which limits their wide application.The composite oxidation technology is a new magnesium alloy surface treatment process developed for the corrosion resistance, wear resistance, high temperature resistance and other performance problems of magnesium alloy materials. The process perfectly optimizes these problems. The composite oxidation technology is followed by chemical plating, conversion coating, anodic oxidation, organic coatingThe latest technologies developed after surface treatment of magnesium alloys, such as thermal spraying and vapor phase treatment.
