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General technical conditions for surface coating of steel products

Views:170     Author:Near     Publish Time: 2019-01-02      Origin:Site Inquire

This standard is mainly applicable to the surface coating of steel products. Where there is no special requirement in the contract documents, the surface coating of the products shall comply with the provisions of this standard.


First, the surface treatment before painting


All steel raw materials used in equipment manufacturing require surface descaling before painting. And apply the primer (shop primer) within the specified time range.


1. Before the spray is derusted, the thick rust layer should be removed. And remove grease and dirt. After spraying or descaling, the surface of the steel must be cleaned of ash and debris.


2. Two descaling grades are specified for the surface of the steel for jet rust removal. The text is described as follows:


Sa2 thoroughly spray rust: no visible grease and dirt on the steel surface, and the deposits such as scale, rust and paint coating have been basically removed, and the residue should be firmly attached.


Sa21/2 is very thorough spray rust removal. There are no visible grease, dirt, iron oxide and paint layers on the surface of the steel. Any traces of residue should be only slight spots or streaks.


3, for the steel surface of the hand and power tools rust, rust has a predetermined level, the text described as follows:


St3 is very thorough with manual and power tools for rust removal. There are no visible greases and dirt on the steel surface, and there are no adhering oxide scales, rust and paint coating deposits. The surface of the exposed portion of the substrate after rust removal shall have a metallic luster.


4. The term "attachment" may include welding slag, weld spatter, soluble salts, and the like. When the scale, rust or paint layer can be peeled off from the steel surface with a metal putty scraper, it should be considered as poor adhesion.


5. The surface of the steel to be inspected should be visually compared with the corresponding photo. The photo should be close to the steel surface. The assessment should be carried out under well-scattered daylight or under artificial illumination with comparable illumination.


6. The film thickness and coating selection during pretreatment are as follows:


a) Paint film (dry film) thickness: 15 to 25 μm.


b) Coating varieties: inorganic zinc silicate (workshop) primer, epoxy primer, epoxy zinc-rich primer, zinc phosphate primer, iron red epoxy primer.


c) The primer used must be a variety in the product's matching paint system or a paint that is compatible with the primer in the matching paint system.



Second, technical requirements


1. Before painting, the coating must be allowed to reach the specified descaling level.


2. In the case of mildly corrosive environment, when the conventional coating is prepared, the surface descaling grade is Sa2.


3. When the chemical atmospheric corrosion, seawater erosion, high temperature oxidation and inorganic zinc-rich coating are used as primers, the surface descaling grade is Sa21/2.


4, before painting the surface roughness of the steel must be controlled, in addition to control the angle and speed of the abrasive jet, the abrasive recycled pellet diameter which is not greater than 1.2mm.


5. Spray or project the surface of the object to be coated after descaling. Immediately after cleaning, apply the first layer of primer. The interval should not exceed 6h.


If the surface is rusted again, it should be reprocessed to allow the coating to be applied after the specified standards are met.

6. The coatings or materials coated with the shop maintenance primer may cause secondary rust removal due to welding, correction, scratching, exposure, etc., and the grade after rust removal shall reach St3.



Third, preparation before painting


1. The paint used should have a product certificate, and retest according to the acceptance rules of the paint product. Paints that do not meet the product quality are not allowed to be used.


2, the same coating system, the choice of primer, putty, intermediate paint, topcoat, thinner, etc. must be used together.


3. Before the paint is opened, confirm its grade, variety, color, batch number, etc., and record. If the logo is ambiguous, it should be checked carefully. If there is crust after opening the barrel, the crust should be carefully removed. If the paint is found to be out of date, it should be identified and confirmed to be reliable in quality. In case the paint deteriorates, it should be discarded.


4. Some pigments in the paint have a high density and are easy to precipitate. It is necessary to use mechanical agitation to make the paint uniform. The two-component coating should be stirred first before the curing agent is added, and then stirred again after adding the curing agent.


5. Mix and mature two-component or three-component paints should be mixed according to the specified ratio. The normative approach is as follows:


1 The paint is evenly stirred;


2 pour half of the curing agent and mix well;


3 pour the remaining curing agent and mix well;


4 then add diluent if necessary;


5 Place a certain period of time for the ripening pre-reaction according to the regulations;


Be careful not to exceed the regulations. The curing time and mixing time are shortened as the temperature rises. Pay attention to the manufacturer's instructions. Avoid construction under the sun during the hot season.


6, diluted


Paints can usually be used in open barrels without dilution and must avoid habitual dilution. When using a thinner, be sure to use the correct thinner. Excessive dilution can result in coatings that do not reach the specified thickness, reduce drying and curing time, and cause sag problems. Thinners can be added in the following cases:


1 In the winter, when the temperature is low, an appropriate amount of diluent can be added to reduce the viscosity of the coating;


2 manual or air spraying requires the addition of thinner for easy construction;


3 Deliberately reduce the film thickness and add appropriate amount of thinner.


7, filter


In order to remove large particles, crusts or other foreign matter that are difficult to disperse in the coating, filtration must be carried out to ensure that the nozzle is not blocked. The norm is to pour into another empty bucket through the filter. When spraying, add 80-120 mesh screen or filter at the suction port of the paint pump. The filter must be clean and clean. Wash with solvent after use for reuse next time.



Fourth, painting


1. The construction area must maintain air circulation. There should be no dust or other foreign matter flying during the coating and curing process. During the painting process, it is necessary to ensure that the paint film is uniform and not leaky. For the edges, corners, cracks, welds, etc., first apply, then apply a large area.


2, the surface of the machine product needs to putty putty, should be carried out according to the process documents.


When scraping the putty, the primer should be applied first, and the primer should be dried before the putty operation. The putty is generally carried out 1~2 times, each time the thickness is about 0.5~1mm, and the local maximum total thickness should not exceed 5mm. After the putty is dried, the surface must be polished. The surface of the putty after polishing should be smooth, firm, firm and free from cracks.

3. Painting work should be carried out under the permitted climatic conditions. Do not paint when the following conditions occur


a. Generally, the ambient temperature is below 5 degrees Celsius or above 35 degrees Celsius.


b. When it is painted in the open air, it will rain, snow, fog, frost, and strong wind;


c. The surface temperature is lower than the dew point temperature plus 3 degrees Celsius; the dew point temperature value is checked for reference in the appendix.


d. The relative humidity of the surrounding environment is above 85 percent;


4. Defects such as pits, blisters and pores appear on the surface of the casting. Must be filled with putty. Do not fall off or crack under the putty layer.


5. The surface treatment quality should be checked before painting. Unsuitable for painting. In the process of painting, if there are defects such as sag, wrinkle, blistering, cracking, pinholes, etc. It must be repaired by appropriate technical measures.


6. When the construction cannot be carried out according to the specified coating conditions due to environmental or other reasons, it is necessary to take necessary technical measures and confirm that the coating quality can be ensured before construction, and the measures to be taken should be recorded.


7. The coating applied in several times must be carried out according to the coating interval specified in the paint product specification. If the specified coating interval is exceeded, the surface of the front coat should be roughened.


8. The coating that is not dry should be protected to prevent soiling and damage. The film that has been soiled and damaged should be repaired as required.


9, two kinds of coating color at a different phase, boundaries must be clearly, neat, specification.


10. The painted parts assembled on site, the last one of the top coats shall be painted after the equipment is installed and debugged.


11, painting construction methods, whether using brush or spray should strictly abide by the operating procedures. The thickness of the film should meet the design requirements.


12, any of the following circumstances are not painting


A.. High-strength bolt friction surface.


b. Buried concrete or parts in contact with refractory materials.


c. Machined surface that is closely attached or has relative motion.


d. Anchor bolts and their bottom plates.


e. Sealed box and valve body surface.


f. Stainless steel parts, plated parts, non-metallic parts and unpainted parts indicated in the drawings.


g. The part that needs to be processed on site.





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