What are the requirements for painting process after welding for sheet metal cabinets?

Surface pretreatment requirements

Cleanliness: Before painting, the surface of the welded sheet metal cabinet must be free of oil, dust, rust, welding slag and other impurities. You can use a special metal cleaning agent for cleaning, or you can use an organic solvent to wipe. For example, using acetone or alcohol to wipe the welding parts can effectively remove oil stains and impurities and ensure the adhesion of spray painting. For welding slag, it needs to be completely removed by grinding to prevent it from affecting the appearance of the cabinet and coating quality after painting.

Smoothness: Welding may cause unevenness on the cabinet surface, such as protrusion or depression at the weld. These parts need to be polished to make the surface smoothness meet the requirements of painting. Generally speaking, the height difference of the surface should be controlled within ±0.5mm to ensure the uniformity of the coating after painting. You can use a hand-held sander or sandpaper to polish, and gradually polish from coarse sandpaper to fine sandpaper to make the surface smooth.

Primer spraying requirements

Primer selection: choose the appropriate primer according to the material and use environment of the sheet metal cabinet. For example, for cabinets made of ordinary carbon steel, epoxy primer can be used in general indoor environment, which has good adhesion and antirust performance; If the cabinet is used in outdoor environment, it may be necessary to choose zinc-rich primer with better weather resistance.

Spraying thickness: the spraying thickness of the primer should be uniform, and the general thickness should be controlled between 20-40μm m.. Too thin may not provide enough rust prevention and adhesion, and too thick may lead to problems such as too long drying time and easy cracking of the coating. A thickness gauge can be used to detect the thickness of the primer to ensure that it meets the requirements.

Drying and curing: the primer needs to be fully dried and cured after spraying, and the conditions of this process vary with the type of primer. For example, the epoxy primer may take about 24 hours to completely cure at room temperature, but it can be shortened to 2-3 hours when the temperature is appropriately increased (such as 60-80℃). During the curing process, it is necessary to ensure good ventilation so that the solvent can be fully volatilized.

Intermediate paint (if required) requirements

Function and selection: Intermediate paint is mainly used to increase the thickness and shielding performance of the coating and further improve the protective effect. For example, in some occasions that require high corrosion resistance, mica iron oxide intermediate paint can be selected. This intermediate paint can effectively block the penetration of moisture and corrosive media.

Thickness and uniformity: the thickness of intermediate paint is generally controlled between 40-60μm, and it is also necessary to ensure uniform spraying. Uneven spraying may cause local thickness to be too thin or too thick, which will affect the overall protective performance and appearance of the cabinet. After spraying the intermediate paint, it should also be dried and cured as required.

Top coat spraying requirements

Appearance requirements: the top coat is mainly used to provide the appearance color and gloss of the cabinet. For computer operating cabinets, it is usually required that the top paint has good decoration, uniform color and no sagging, orange peel, bubbles and other phenomena. For example, in some demanding computer room environments, the paint color of the cabinet needs to match the overall computer room decoration style, and it should have a certain gloss to improve the overall beauty of the computer room.

Thickness control: the thickness of top coat is generally between 40-80μm m.. Too thick topcoat may cause problems such as cracking and peeling, while too thin topcoat cannot achieve the expected appearance and protective effect. When spraying top coat, pay attention to the distance and angle between the spray gun and the cabinet surface to ensure uniform painting.

Drying and curing conditions: the drying and curing conditions of topcoat are also very important. Some topcoats need to be baked at a higher temperature before curing, such as some polyester powder topcoats. The baking temperature may be between 180℃ and 200℃ for 20-30 minutes. For some topcoats cured at room temperature, it may take several days to ensure good ventilation and avoid dust and other impurities polluting the paint surface, depending on the ambient temperature and humidity.

Quality inspection requirements

Adhesion test: the adhesion of the coating can be detected by methods such as grid test. Scribe the coating with a special tool, then paste the scribed parts with adhesive tape, and observe the peeling of the coating after tearing off the adhesive tape. Generally, it is required that the coating falls off less than 15% to be qualified.

Thickness detection: use a coating thickness gauge to detect at different parts of the cabinet to ensure that the thickness of each layer of paint and the total coating thickness meet the requirements. Inspection points shall include all surfaces, edges and welding parts of the cabinet.

Appearance inspection: visually inspect the appearance of the cabinet to see if there are any defects such as sagging, orange peel, pinholes and bubbles. For some minor defects, it can be repaired; For defects that seriously affect the appearance and quality, it needs to be repainted.