Sealing the flame spray layer is perforated structure, which is advantageous in many applications.
The pores of the coating help to store the lubricating oil, which can improve the lubrication between the workpiece and the surface.
In some cases, however, pore seals are required to prevent corrosive media from penetrating the coating, causing corrosion to the substrate.
Therefore, the coating and anticorrosion coating for working under the corrosion conditions shall be sealed to protect the substrate.
In addition, the sealing treatment can obviously improve the abrasion resistance of the spray coating.
1. Performance requirements of the sealing agent.
In order to achieve good sealing effect, the sealing agent must satisfy the following requirements:
1.
It's permeable.
Because the pores are bent and small, they are not sufficiently permeable to fill the required degree.
2.
Chemical resistance.
Because the coating itself is in the corrosive medium of some kind of chemical and solvent, the sealant can not be subjected to the erosion of these media, the sealing hole is invalid.
3.
Can withstand certain mechanical action.
That is, the sealant is not broken off or broken by mechanical action.
4.
Stable performance at work temperature.
The sealant cannot be dissolved, evaporated or decomposed in the operating temperature.
5.
Cannot react with coating or substrate.
Maintain chemical stability in working environment with coating and substrate.
6.
Does not 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.
2. Selection of sealing agent and key construction 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.
The sealant used for anticorrosion coating must be fully cured before being put into use.
The general sealing agent is not dangerous, but some are volatile and flammable, in storage and use, should be careful, not near open fire or heat.
The use should be fully ventilated, so as not to interfere with normal breathing.
There are two main types of sealant: organic and inorganic.
The main basis for selecting the sealing agent is the corrosion condition 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, generally following the following points:
1.
Many of the sealants need to be diluted with diluent to ensure good permeability.
2.
Before the coating is sealed, it is better to preprocess the coating (usually phosphoric acid) to form a composite phosphate compound film, which helps to seal the hole agent.
3.
A lot of sealant is mixed with flake aluminum powder to improve the temperature resistance and corrosion resistance of the sealant.
4.
The sealant can be sprayed with a spray gun, coated with a brush or submerged, some of which can be used in either of the above three, some of which can only be used in one or two of them.
Depending on the need, sometimes just one, sometimes two or more.
5.
In order to increase permeability, some use vacuum osmosis operation.
6.
The sealant is divided into two parts, two parts, air drying and curing. It is necessary to master each step correctly in use.
Main types and properties of sealant.
The world's first product to market a series of sealants to the market is the us METCO (now SULZER METCO), which has been successfully used for many years.
Our country has not yet formed a series, large-scale sealant product.
This work is urgently needed to be developed and promoted due to the important link in thermal spraying technology.
Referring to foreign related products, several important sealing agents are introduced as follows:
1.
Air dry type glyceride resin.
Characteristic: the resin content is up to 95%, the penetration and filling capacity is very high, the sealing hole can be directly processed, and the machining performance is obviously improved.
Working temperature: 145 ° C for continuous work.
Dosage of sealant: 11.
6 m2 / l / 0.
6 mm
Construction method: soak, brush or spray.
The surface of the coating should be dry and clean.
According to the need, after the implementation of the first, after 15 minutes, can be implemented second.
Curing procedure: the air is dry at room temperature, and it needs to be completely cured by one week.
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 a lot of organic matter.
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.
When spraying, the diluent should be diluted with ketone, aromatic hydrocarbon and anhydrous ethanol, and the dosage is 1/2 ~ 1/3.
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.
It only takes 15 to 30 minutes to bake at about 135 degrees Celsius.
Typical application: suitable for hot water, salt mist, acid, oil, gasoline and grease.
3.
Aluminium vinyl resin
Characteristic: an anticorrosive, air - drying, aluminium-ethylene copolymer, often used in zinc and aluminum finish, and its relative primer is passivate chromate.
Dosage of sealant: 5.5m2/L.
Working temperature: no more than 80 ° C.
Construction method: pressure spraying or painting.
Curing procedure: dry for 30 minutes, the thinner is xylene or ketone.
4.
Passivate zinc chromate.
Specificity: primer for aluminum vinyl resin finish.
Air drying type, because it can produce porous membrane, the surface layer sealing agent provides strong bond.
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 metal and ceramic coatings is a baking type of synthetic phenolic slurry.
In terms of protection performance, the baking type is higher than the air drying type.
In many organic materials, good chemical stability (but not alkali), 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.
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, grease and other media.
6.
Asphalt base aluminium paste
Characteristic: it is a kind of high melting point and bituminous paint, mainly composed of flake aluminum 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.
When spraying, dilute with mineral alcohol, and take 2.
Typical application: when the substrate is steel, nickel or nickel chromium alloy, the coating is aluminum, and it is in the environment of high temperature oxidation, high temperature and sulfur gas corrosion, this kind of sealing agent is the first choice.
7.
Aluminum silicon resin
Characteristic: it is a kind of silicon resin containing flaky aluminum powder, which has a high temperature resistance in the oxidation atmosphere.
Dosage of sealing agent: 3.6m2/L.
Working temperature: 480 ° C.
Construction method: brush or spray, each thickness 0.018-0.02mm.
The brush should not be diluted, and the spray should be washed with ethanol, aromatic and methyl ketone, and the dosage of diluent is 1/3.
8.
Air drying silicone.
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%.
Sealing agent dosage: 5.0-11.6m2 /L(related to 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: a baked polyimide resin used for weak or moderate corrosive environment.
Solid content of up to 30%, low viscosity, good permeability, film solid.
It is very stable for water, solvent, organic matter, inorganic oil, fuel, liquid flow and dilute acid.
Dosage of sealing agent: 5.3-9.5m2 /L/0.6mm.
Working temperature: long-term working temperature of 260 ° C.
Construction method: soak, spray or brush.
Operate at room temperature until the surface of the coating is not absorbed. After 15 minutes,
One more time.
Room temperature curing time of 8 hours, 180 ° C is 2 hours.
Typical application: it is suitable for conveying pump 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 inert, petroleum based microcrystalline stone, 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 corrosion of materials, especially for high pressure lubricating environment.
It provides effective dry lubrication when lubricants cannot be applied.
Amount of sealant: 10m2/kg.
Working temperature: no more than 80 ° C.
Method: after the workpiece preheat to 95 ° C, on the surface directly.
Typical application: it is usually used to seal the shaft or other workpiece to ensure the turning or grinding, prevent sand from entering the pores, and also have good anti-corrosion ability.