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The sealing flame spray coating has a hole structure, which is beneficial in many applications. The pores of the coating can help to store lubricating oil, which can improve the lubrication between the workpiece and the surface. However, in some cases, the pore seals need to be sealed to prevent corrosive medium from penetrating the coating and causing corrosion to the substrate. Therefore, the coating and anticorrosive coating for working under corrosive conditions should be sealed to protect the substrate. In addition, sealing hole treatment can obviously improve the wear resistance of spray coating.
The performance requirements of the sealing agent
In order to achieve good sealing effect, the sealing agent must meet the following requirements:
1. It's permeable
Because the pore is small and small, not high permeability, it is difficult to fill to the necessary degree.
2. The effect of chemical solvents
Because the coating itself is in the corrosive medium of some kind of chemical and solvent, if the sealing agent cannot withstand the erosion of these media, the sealing hole will be void.
3. Can undergo certain mechanical effects
That is, the sealant does not fall off or break apart due to mechanical action.
4. Stable performance at work temperature
The sealing agent cannot be dissolved, evaporated or decomposed in the operation temperature.
5. Can't react with a coating or substrate
Maintain chemical stability in the working environment with the coating and substrate.
6. Not to reduce the performance of the coating or substrate metal.
7. When the coating is used in the food industry, it is not toxic to food.
8. Ensure safety during construction.
Ii. Selection of sealing agent and construction key points
Generally, all sealing operations should be carried out prior to grinding. In addition to the microcrystalline wax hole sealing agent, all other hole sealing agent should be performed when the workpiece temperature below 80 ℃, prevent hardening of the solvent evaporated quickly or hole sealing agent. Air drying glyceryl ester resin, in the heat generated in its machining will make it early heterogeneity of curing, therefor, the hole sealing agent must be cured after grinding, besides all the hole sealing agent and should be cured before grinding. A sealant used for anticorrosive coating must be fully cured before it is put into use. The general sealing agent is not dangerous, but some are volatile and flammable. In the process of storage and use, you should be careful not to close the fire or heat. Use fully ventilated to avoid affecting normal breathing. The sealing agent is mostly organic and inorganic. The main basis for selecting the sealing agent is the corrosion and working temperature of the medium. Organic hole sealing agent mainly ethylene resin, phenolic resin, modified epoxy resin and polyurethane resin and so on, they are used in the steel substrate zinc or aluminium coating sealing hole, working temperature is not high, in the atmospheric oxidation, industrial atmosphere, sea water environment; The asphalt base is used for high temperature oxidation medium aluminum paste, silicone resin and some aluminum silicate, chromate, such as inorganic substances, the highest working temperature can reach 980 ° C. Different sealing agents have different requirements, and generally follow the following points:
1. Many of the sealants need to be diluted to ensure good permeability.
2. Before the coating is sealed, it is better to pretreat the coating (usually phosphoric acid) to form a compound phosphate compound which helps to seal the pore.
3. Several sealing agents are mixed with flake aluminum powder to improve the temperature resistance and corrosion resistance of the sealant.
4. The sealant can be sprayed with spray gun, brushed with a brush or submerged to soak, some of which can be used in either of the three, some of which can only be used in one or two of the above. Depending on the need, sometimes just one, sometimes two or more.
5. In order to increase permeability, some adopt vacuum penetration operation.
6. The sealing agent has a single component with double component, air drying and baking curing, and must master each step correctly in use.
The main types and properties of the sealing agent
The first in the world to launch a series of sealant products for the market is the us METCO (now SULZER METCO), which has been successfully used for many years. China has not yet formed a serialized, large-scale sealant product. Due to the coating sealing hole is an important part of thermal spray technology, this work is urgently needed to be developed and promoted. In the light of foreign products, several important sealing agents are introduced as follows:
1. Air dry type glycerol ester resin
Characteristic: the content of resin is as high as 95%, the penetration and filling capacity is very high, the sealing hole can be processed directly, and the machining performance is obviously improved.
Working temperature: 145 ° C for continuous work.
Dosage of sealing agent: 11. 6 m2 / l / 0. 6 mm
Construction method: soak, brush or spray. Normal temperature operation, coating surface shall be dry and clean. According to the need, after the implementation of the first, after 15 minutes, the second can be implemented.
Curing procedure: air drying under normal temperature requires a week to cure completely. If the baking at a 145 ° C, 1 hour can be cured.
Typical application: work environment for dilute acid, weak corrosive medium, such as solvent, oil and salt water temperature does not exceed 145 ° C.
2. Air dry phenolic resin
Characteristic: a modified air drying phenolic paint. Suitable for metal and ceramic coating, good wettability, strong bond, good chemical stability, strong corrosion resistance and impact resistance. It's stable in many organic compounds.
Continuous work work temperature: 145 ~ 205 ° C, continuous work of 205 ~ 260 ° C
Dosage of sealing agent: 7.4 ~ 8.0m2/ L.
Construction method: brush or spray can be. The spray should be diluted with ketone, aromatic hydrocarbon and anhydrous ethanol. The dosage is one/two to one third.
Curing procedure: the air is dry for 30 ~ 60 minutes, but the total curing takes 1 ~ 10 hours, depending on the thickness of the sealing agent. Bake at about 135 degrees Celsius for 15 to 30 minutes.
Typical application: suitable for hot water, salt fog, acid, oil, gasoline and grease, etc.
3. Aluminium vinyl resin
Characteristic: it is an anti-corrosive, air drying aluminum vinyl copolymer, often used in zinc and aluminum paint, and its relative primer is the passivation chromate zinc paste.
Dosage of sealing agent: 5.5m2/ L.
Working temperature: no more than 80 ° C.
Construction method: pressure spraying or painting.
Curing procedure: dry 30 minutes, the thinner is xylene or ketone.
4. Zinc passivation chromate
Special: primer for aluminum vinyl resin finish. Air drying type, because of its ability to generate porous membrane, it can provide strong adhesion to the surface sealing agent. The main ingredient is zinc chromate.
Dosage of sealing agent: 6.0 ~ 7.4m2/ L.
Typical applications: as a primer used with aluminum vinyl resin finish, the atmosphere in the industrial atmosphere, salt fog and the drinking water of the steel structure in the medium or device such as aluminum zinc coating with hole sealing protection.
5. Baking phenolic resin
Characteristic: the sealing hole used for the coating of metal and ceramic is a kind of baking synthetic phenolic slurry. In terms of protection performance, the roasting type is higher than air drying. In many organic materials, good chemical stability (but not alkali - resistant), good heat resistance. The main components are phenolic and aromatic.
Working temperature: continuous work of up to 145 ~ 205 ° C, continuous work for 205 ~ 260 ° C.
Dosage of sealing agent: 4.6m2/ L.
Construction method: brush and spray can be. The spray was diluted with 25% isopropanol. The single-channel coating baking at 230 ℃ for 10 minutes or 205 ° C bake for 20 minutes; For multichannel coating on the bottom at 145 ° C, bake for 10 minutes, the surface of 190 ° C bake 60 minutes.
Typical application: same as dry phenolic resin, suitable for boiling water, salt mist, acid, oil, gasoline and oil and other media.
6. Asphaltic aluminum slurry
Characteristic: it is a kind of high melting point, bituminous paint, the main component is flake aluminium powder, bituminous coal tar and corresponding solvent.
Dosage of sealing agent: 4.9 ~ 7.4m2/ L.
Working temperature: 870 ~ 980 ° C.
Construction method: spray or brush can be. Dilute with mineral alcohol when spraying, take 2.
Typical application: when the substrate is steel, nickel or nickel chromium alloy, the coating is aluminum, and in the environment of high temperature oxidation, high temperature and sulfur gas corrosion, the sealing agent is preferred.
7. Aluminum silicon resin
Characteristic: it is a kind of silicon resin that contains flake aluminum powder of air drying, and it is high temperature sealing agent in the antioxidant atmosphere.
Dosage of sealing agent: 3.6m2/ L.
Working temperature: 480 ° C.
Construction method: brush or spray, each thickness 0.018-0.02 mm. The brush should not be diluted, while the spray should be made with ethanol, aromatic and methyl ketone, and the dosage of diluent is 1/3.
8. Air drying silicon resin
Features: for a two-component silicone, recommended for medium corrosion or below 205 ° C temperature and long-term exposure to the air environment, resistance to dilute acid, alkali, oil, liquid flow, medium such as water and salt water corrosion. The solid content is 25%.
Dosage of sealing agent: 5.0-11.6m2 /L (related to the coating porosity).
Working temperature: long-term working temperature is 205 ° C.
Method: it's a two-component, spraying or soaking method are available, and the dry air at room temperature about 1 hour, but fully cured need 3 days, 2 hours at 145 ° C baking can accelerate the curing.
9. Baked polyimide resin
Characteristic: baked polyimide resin used for weak or moderate corrosive environment. The solid content is up to 30%, the viscosity is low, the permeability is good, the film is solid. It is very stable for water, solvent, organic matter, inorganic oil, fuel, liquid flow and dilute acid.
Dosage of sealing agent: 5.3-9.5 m2/L/ 0.6mm.
Working temperature: long-term working temperature of 260 ° C.
Construction method: soak, spray or brush. Operate at room temperature until the coating is not absorbed. 15 minutes later,
One more time. Room temperature curing time of 8 hours, 180 ° C is 2 hours.
Typical application: it is suitable for conveying pump type in petrochemical system and paper industry. It has corrosion resistance and abrasion resistance. These pumps operate in soda ash, calcium hydroxide, magnesium hydroxide and sodium hydroxide.
10. Microcrystalline wax
Characteristic: it is a kind of sui, petroleum based microcrystalline wax, which provides sealing and lubrication for coating. It is stable in fresh water, seawater and almost all acids and bases, but it is not resistant to solvent and the corrosion of the material, especially for high pressure lubricating environment. In the absence of lubricant, it can provide effective "dry lubrication".
Dosage of sealing agent: 10m2/ kg.
Working temperature: no more than 80 ° C.
Method: after the workpiece preheat to 95 ° C, on the surface directly.
Typical applications: usually used to seal the axles or other workpieces to ensure the turning or grinding of the car, preventing sand from entering the pores, and also having good anti-corrosion capability.
Shanghai, the new material co., LTD., founded in 2006, is a structure of composite material technology providers and product manufacturers, focusing on high performance requirements and large structural composites provides overall solutions, mold design and manufacturing, the overall assembly line a total package, raw material supply. Main operation: epoxy system deformable agent, polyester system mold release agent, sealant and so on.