Spraying is a common process for surface treatment of stainless steel products. Stainless steel products are commonly used in industrial, architectural and home decoration fields, and their surface coating can improve their appearance, increase wear resistance and corrosion resistance. This article will introduce the process and key steps of spraying stainless steel products.
1. Scope of application
Sand blasting process of stainless steel parts.
To ensure product quality, remove grease, other dirt, rust, oxide skin, welding fused particles, welding oxide layer, and roughen the sprayed surface to meet product quality, safe use and occupational health requirements.
3. Equipment and tools
Air compressors, air dryers, spray guns, sandblasting rooms, vacuum cleaners, gloves, glasses, gas masks, work clothes, work caps and other labor protection products.
4. Selection of sandblasting abrasives for different surface treatment products
Surface paint products: Surface roughness directly affects the adhesion of the paint surface. The rougher the surface, the better the adhesion, and the denser the pill pits, the better. Experience has proved that the surface roughness parameters of stainless steel products are Ra3.2～Ra6.3um, and the surface paint film Good adhesion, you can choose abrasives such as stainless steel shot or corundum (iron sand is prohibited).
1). Carefully read the drawings and process documents, and clarify the sequence of sandblasting in combination with the product.
2). According to the material of the workpiece to be sprayed, the purpose of sandblasting and customer requirements, select the type of abrasive with a suitable mesh number. The higher the mesh number, the smoother the surface to be sprayed.
3). The compressed air used for sandblasting must be dry and oil-free.
4). Wear protective equipment for labor protection.
5). Before sandblasting, use masking tape, metal sheet, collar, hard wood board, or rubber to shield and protect the non-effective surface.
6). Sandblasting abrasives must be kept clean and dry. Abrasives contaminated by old coatings, scale, or grease are not permitted.
- Sand blasting
1). Work on the workpiece according to the requirements.
2). The angle of the nozzle to the surface when spraying should be close to 90°, but slightly smaller so that the abrasive does not bounce right back to the operator. The distance between the spray gun and the workpiece is generally 50-150mm.
3). The sandblasting sequence should cover the entire surface to be cleaned. The nozzle should move in a straight line at a constant speed. The last one overlaps the previous one and exposes the clean metal without discoloration.
4). To adjust the appropriate pressure, if the spray force is too large and coarse abrasives are used, the jet flow will easily damage the surface of the workpiece. The low pressure produces a small jet stream impact force, and the polishing effect is good; the high pressure produces a large jet stream impact force, the sandblasting efficiency is high, and the polishing effect is reduced. If the compressed air pressure is too high, it may interfere with the mortar flow and reduce the processing efficiency. Compressed air pressure can be adjusted with the manual pressure regulator valve and should be adjusted with the spray gun open. Customer-approved samples can be used for testing to determine the most suitable compressed air pressure. Once set, it does not need to be adjusted frequently.
5). The moving speed of the sandblasting gun should be uniform, and the moving speed should be adjusted according to the surface corrosion and scale removal of the workpiece at any time. Do not overblast to prevent deformation of the workpiece. Especially where the plate thickness is ≤ 2mm.
6). Spray all the required places, the coverage rate is > 99%, and the surface roughness of the workpiece should be uniform after sandblasting.
7). Remove the sand everywhere, and blow off the dust on the surface of the workpiece with dry compressed air.
- Inspection: inspect the quality of the work and confirm the qualification.
1). Cleanliness: When observed without magnification, there should be no visible oil, grease, dirt, scale and foreign impurities, and no residual abrasives are allowed in the product.
2). Roughness: Visually compare the roughness template with the workpiece. Roughness sample should be checked by optical section microscope, RZ value should comply with GB1031
3). Sandblasting protection: the specific measures shall be implemented according to GB11375.
The workpiece after sand blasting should be protected during transportation, the surface is not allowed to be scratched or bumped, and it should be transported to the coating place in time.
- In rainy and foggy days and air humidity > 75%, sandblasting and workpiece transportation are not allowed.
- The workpiece must not be stained with water and oil during the process of sandblasting and painting, otherwise it needs to be reprocessed.
- Before painting, use sandpaper to polish or chemically treat unprotected but rusty or polluted parts to eliminate rust and pollution.
- In principle, paint the workpiece within 4 hours according to the requirements of the painting process after sandblasting. If it exceeds 4 hours, it depends on the material, environmental conditions and surface conditions. reprocessing.
8. Paint coating method and sequence
- Coating method:
The construction method of paint manual brushing:
The metal surface treatment standard before manual brushing should reach St3 level.
The interval between derusting and painting should not exceed 4 hours.
After the paint is mixed according to the weight ratio provided by the supplier, the prepared paint needs to be cured for 5-10 minutes before use, and the service life of the paint at room temperature is 1 hour.
When painting with a brush, you should first rub it back and forth on a certain object surface for many times, then pat it with your hands, and pull off the easy-to-fall sideburns of the brush several times in advance. The 1/3 end of the brush should be immersed in the paint bucket, and all the brushes should not be immersed in the paint solution, and the paint brush after moistening should scrape off the excess paint on the wall of the bucket, and then paint in order.
The paint used for brushing has a high viscosity, usually controlled at 25°C, apply -4 cups for 30-60S. Each time the paint brush is dipped in paint, it should be applied within one process. The general rule is to start from the upper left of the object to be painted, first spread the paint evenly on the surface of the object, and then spread it with the brush. The flattened coating film is uniform, and finally use a brush to gently brush according to the shape of the surface to be coated to help the coating film level.
The brushing sequence should be first up and then down, first left and then right, first inside and then outside, first and then second and then segmented. Vertical surfaces should be painted top to bottom one last time, and horizontal surfaces should be painted one last time in the direction the light hits.
Regardless of manual or mechanical spraying, the process connection must wait until the paint film is cured to ensure that the interval between curing time is sufficient before the next process can be carried out. After painting, the paint film layer must be uniform, tightly covered, tightly bonded between layers, and well adhered.
The number of coats should meet the design requirements, and the painted surface should be smooth without traces, with consistent color, no pinholes, no rust, falling, pulverization, cracking, falling off, damage and other phenomena. The minimum interval between coatings of each paint is surface dry (not sticky), generally no more than 3 hours, and the coating must be fully cured (24 hours after coating) before use.
When painting, use corresponding tools or equipment to protect the workpiece to avoid mutual contamination of paint.
According to the supporting requirements, apply various paints.
4. Quality control
5. Coating environmental requirements
- Before painting, in addition to cleaning and drying the surface of the substrate or the previous coating, it is also necessary to pay attention to the temperature of the substrate being 3°C higher than the dew point temperature.
- Generally speaking, when the relative humidity is lower than 85%, the construction temperature of the substrate is basically the same as the ambient temperature, so construction can be carried out when the relative humidity is lower than 85%.In addition, for two-component epoxy paints, if the temperature is lower than 5°C, the curing reaction will slow down or stop, so winter paints can be used in this case.
- Epoxy or polyurethane paint should not be exposed to rain and snow immediately after painting, as this will cause whitening of the epoxy paint film and pinholes or foaming of the polyurethane topcoat paint film. Be careful to avoid it! The coating is cured During this period, good ventilation should be maintained to accelerate the good film formation of the coating.Preparation and use of paint
- Generally, after a period of time, the paint will have different degrees of precipitation and layering. Therefore, after opening the can, use a power mixer or stir bar to stir it completely before using it, otherwise, it will affect the film-forming quality of the paint.
- Once the main paint and curing agent of the two-component paint are mixed at a certain temperature, there is a corresponding service time. Over time, the paint will gradually become difficult to apply, until it cannot be applied at all. Therefore, pay attention to mixing as much as you use, so as not to cause waste.
- The ratio of main paint and curing agent is the best ratio obtained through calculation and experience, and must be strictly followed. Now the mixing ratio of each related variety of paint and the use time after mixing.
* After the paint and curing agent are mixed, be sure to stir until completely mixed before use.
- Painting interval
- After one coat of paint is finished and before the next coat of paint is painted, it is necessary to confirm whether the specified painting interval has been reached, otherwise the painting cannot be carried out. For two-component paints, in addition to ensuring the shortest painting interval, pay attention to painting within the longest painting interval. It is best to apply the undercoat immediately after the minimum coating interval to ensure good intercoat adhesion.
- If the painting is carried out after the longest painting interval, the previous paint should be roughened with fine sandpaper, and the impurities should be removed before painting.
- After the epoxy paint is painted, the paint film will be whitened when encountering high humidity conditions such as wind, snow, rainfall, and condensation during the curing stage. In this case, the overcoating should be wiped with solvent or polished with sandpaper to remove the whitening film, so as to ensure good adhesion between layers.
- Complete curing of the paint film: After the paint film is surface-dried and hard-dried, the two-component paint is not the final formation of the paint film, and it must be placed at room temperature for more than 7 days. After the paint film is completely cured, it can be formally put into use use.
- Detection of coating film thickness
A.a. When applying various layers of paint, pay attention to the uniformity of the paint film and reach the specified thickness of the paint film to ensure the quality of the coating and the guarantee period.
- Testing tools: wet film thickness gauge, dry film thickness gauge
- Detection method: Immediately after the paint is sprayed, use a wet film thickness gauge to press the wet film vertically until it touches the substrate, and then take out the thickness gauge to read the value.
- Corresponding values of wet film thickness and dry film thickness
- Film thickness control principle:
The control of film thickness should comply with two 90% regulations, that is, 90% of the measuring points should be above the specified film thickness, and the remaining 10% of the measuring points should reach 90% of the specified film thickness. The density of measuring points should be determined according to the size of the construction area.
- Storage of paint
The storage of paint should pay attention to the following points:
- The storage environment should be cool and dry
- The storage site should be kept ventilated
- Store away from fire sources
- Paint packaging should be sealed and placed indoors
- Storage period of paint:
* If the paint is stored beyond its storage period, it should be checked, and if it meets the standards, it can still be used.
Through the above content of the article, we also understand the main steps of the detailed spraying process of stainless steel, which is convenient for us to further understand.To learn more about Stainless Steel Products, contact an Easiahome representative.