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    Home > Coatings News > Paints and Coatings Market > Common knowledge of coating: disadvantages of coating after coating of heavy-duty anticorrosive coating

    Common knowledge of coating: disadvantages of coating after coating of heavy-duty anticorrosive coating

    • Last Update: 2020-04-03
    • Source: Internet
    • Author: User
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    Core tip: after spraying of heavy-duty anticorrosive coating, all kinds of defects formed by the film will seriously affect the coating quality, even the product quality

    In addition to the quality of the coating itself, most of the defects of the coating are caused by incorrect coating construction

    "Three paint, seven paint." Therefore, in the coating construction, we must enhance the quality awareness, standardize the process and technical parameters, and improve the operation skills

    Once any abnormality is found, the construction shall be stopped immediately, the causes shall be analyzed, and corresponding measures shall be taken to reduce the occurrence of quality accidents

    This paper analyzes the main causes of film defects, and puts forward the corresponding Which is the price of Dajin diatom mud Recommended brief introduction: which is the price of Dajin diatom mud? How to buy genuine diatom mud? Guangdong diatom mud agent suggests placing a basin of cold water in the air conditioning room, so that the diatom mud wall can breathe effectively

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    When the indoor air is relatively dry, the wall of diatom mud will absorb the water Coating home news: after heavy-duty anticorrosive coating spraying, various defects of paint film formation will seriously affect coating quality, even product quality

    In addition to the quality of the coating itself, most of the defects of the coating are caused by incorrect coating construction

    "Three paint, seven paint." Therefore, in the coating construction, we must enhance the quality awareness, standardize the process and technical parameters, and improve the operation skills

    Once any abnormality is found, the construction shall be stopped immediately, the causes shall be analyzed, and corresponding measures shall be taken to reduce the occurrence of quality accidents

    This paper analyzes the main causes of paint film defects, and puts forward corresponding solutions, aiming to provide reference for coating construction

    1

    The main disadvantages of paint film 1.1 sagging refers to that after spraying, the paint film drops or flows vertically down the surface

    In severe cases, the coating moves downward like a tear

    The phenomenon that the upper part of the coating is exposed and the lower part of the coating is crowded together is formed at the defect place

    Because the driving force of the flow hitch is gravity, it usually occurs in the vertical plane, the corner, the edge of the intersection of the horizontal plane and the vertical plane, etc

    1.1.1 cause analysis from the perspective of coating process, the main causes of film sagging are as follows: (1) the dry film thickness of the film obtained by one spraying exceeds the specified value [1]

    (2) More diluents are added to the coating

    (3) Improper spraying operation

    Take airless spray painting technology as an example: the nozzle is too close to the steel surface (∠ 30 cm), the spray gun moves too slowly, and the nozzle aperture is too large

    (4) The substrate temperature of steel plate is too high

    After the coating is sprayed on, the bottom coating is dried immediately to make the coating on it flow

    (5) After the two-component coating is mixed according to the proportion, the mixing is uneven, or after adding diluent, the mixing is uneven and sufficient, which will form sagging

    (6) The temperature of the construction environment is too low, or the air exchange rate of the spraying room is not enough, so that the solvent in the coating cannot be discharged in time, the drying and curing are not timely, and the sagging is easy to form

    (7) After the two-component coating has exceeded the mixed service life, the operator attempts to use it by adding diluent

    At this time, the coating will also form sagging

    1.1.2 the main method to prevent the film from sagging is to operate according to the technical instructions provided by the coating manufacturer

    (1) When spraying based on the structure of the surface to be coated and the type of coating, the nozzle with proper aperture and fog amplitude shall be selected as the main part, and the pump pressure shall be adjusted as the auxiliary part to strictly control the amount of diluent added

    Frequently use the wet film tester to check the film thickness, control the wet film thickness or reduce the overspray

    (2) Improve incorrect spraying technique and operation skill

    (3) Two component coating mixing or diluent mixing shall be fully stirred

    (4) According to the environmental temperature and the characteristics of different coatings, the mixing and maturing time should be mastered correctly

    (5) If the two-component coating exceeds the mixed service life, it is strictly prohibited to continue to use

    (6) After coating, during the drying and curing period of the coating, continue to ensure that the temperature and air exchange in the spraying room are sufficient

    1.1.3 repair measures (1) the super thick coating deposited by sagging will eventually crack and fall off

    In the process of spraying construction, if any sagging is found, the coating shall be resumed immediately

    Remove sagging with a paintbrush and smooth the coating

    If there is film on the coating surface, it can not be treated with paint brush, otherwise, it will get worse and worse

    (2) After drying and curing, the coating can be modified as appropriate

    After flattening, or sanding with sanding paper or fine sanding paper, the original paint shall be used for repairing or recoating

    1.2 pinhole pinhole refers to the pinpoint like pinhole on the surface of paint film, which is the most taboo defect in painting

    It is formed because the air bubbles mixed in the paint film break and cannot flow flat before the paint film is dried and solidified

    The defect of pinhole is reflected in some parts without paint, which is the channel of corrosion

    After initial pitting, corrosion will gradually spread under the paint film, leading to early failure of the whole paint film

    1.2.1 causes (1) too thick paint film

    Under the condition of airless painting technology, the pressure of painting is high, the aperture of nozzle is too large, and after the film is too thick, air remains in the film and pinholes are produced

    (2) In the process of air spraying, the oil-water separator fails, the air is not filtered, or the moisture is brought into the paint during spraying, or it is stirred violently for a long time, which will cause pinholes

    (3) There are many voids on the surface of metal spraying zinc, aluminum layer or inorganic zinc rich primer

    If the epoxy micaceous iron intermediate coat is directly sprayed, the air in the voids will be intercepted, resulting in pinholes

    (4) In high temperature environment and steel surface temperature high painting construction

    (5) Excessive diluent or non matching diluent is added to the coating

    (6) In some automatic painting devices, the paint heater is not turned on as required

    1.2.2 preventive measures (1) avoid construction under high temperature environment, add appropriate diluent with slow volatilization (consult technical service personnel of relevant coating manufacturers), so as to slow down the solidification of paint film surface

    (2) When the surface temperature of the coated object is too high, it is not suitable for construction

    (3) In the case of high ambient temperature, it is not suitable to apply too thick at one time; it is not suitable to add excessive diluent or non matching diluent into the coating

    (4) When mixing the paint, try to avoid air mixing

    If there is air mixed in, it can be properly used for a period of time to let the mixed air out before use

    (5) For recoating on porous and rough base material or primer, pre spray the permeable sealing layer (also known as mist spray) first to drive out the air in the gap, i.e

    add 15% ~ 30% matching diluent to the original construction coating, or use the special "sealing coating" thin spray once, covering without omission

    After spraying, there will be a large number of small bubbles on the surface of the coating, but soon after the bubbles burst, the coating will make the small holes closed

    Wait for 10-20 minutes according to the ambient temperature, and then spray according to the process requirements

    1.2.3 repair measures (1) remove one layer of slightly small "half hole" pinhole with sandpaper, dilute it with original matching coating after cleaning, and repair one layer with paint brush thinly, so that the coating can easily fill the pinhole [2]

    (2) For the deep missed pinholes, they must be ground with sanding paper or fine sanding paper until they are basically flat

    If pinhole is serious, the coating should be removed basically

    After cleaning, repair or spray again according to the original matching coating

    (3) If it is a large area of deep pinhole, it is necessary to use fine sand paper to roughen, clean and then spray the sealing layer for construction

    1.3 when the spray particles of dry spraying [1] heavy-duty anticorrosive coating reach the surface of the coated steel, the liquid has become dry, unable to form a continuous coating film

    In serious cases, it is like sand particles

    The coating adhesion is poor, which will cause serious corrosion

    2.3.1 cause of formation (1) during construction, the temperature is too high (> 35 ° C), or the paint is painted outdoors, and the wind is strong

    (2) The distance between the spray gun and the steel plate is more than 40 cm

    The walking gesture of the workers is arc or tilt, and the moving speed is too fast

    (3) Painting pressure is too high, not matching with nozzle

    (4) The coating is too thin, or high temperature spray fast drying coating

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