1. Surface pretreatment (key foundation)
Degreasing and oil removal
Use organic solvents (gasoline/trichloroethylene) or metal degreasing agents to remove oil stains and ensure that there is no grease residue on the surface.
Rust removal
Light rust: manual sandpaper/wire brush grinding;
Severe rust: sandblasting/shot blasting (surface roughness Ra≤12.5μm).
Cleaning and dust removal
Blow dust with compressed air and wipe with solvent to ensure the surface is clean and dry.
Special part treatment : The cutting surface needs to be coated with special epoxy primer (to enhance the adhesion of the smooth surface).
2. Shielding protection
Sealing surface/thread/valve stem : Wrap with high temperature resistant tape to prevent paint from penetrating and affecting the function;
Flange surface : Cover with PP protective cover to avoid spraying pollution.
3. Coating process selection
| Method | Applicable scenarios | Technical points |
|---|---|---|
| Brush method | Small valves below DN50 | Dip the paint brush evenly, starting with the hard part and then moving on to the easy part, to avoid wrinkles (thickness ≤ 80μm) |
| Spraying method | DN50 and above or mass production | Air pressure 0.4-0.7MPa, spray gun 100-150mm away from workpiece, move at a constant speed to prevent dripping |
| Dip coating | Parts such as handwheels with low appearance requirements | Control the immersion time and vertical placement to ensure uniform coating |
4. Coating system design
Primer
Epoxy primer: suitable for all metal substrates, salt spray resistance ≥500 hours; Topcoat
Matching solution: epoxy primer + polyurethane topcoat (outdoor weathering), epoxy primer + fluorocarbon topcoat (anti-corrosion enhancement);
Total coating thickness: 120-200μm (according to ISO 12944 standard).
Environmental alternative: water-based industrial paint (VOC emissions reduced by 70%), which must meet corrosion resistance requirements.
5. Environment and quality control
Construction conditions: temperature ≥5℃, humidity ≤80%, avoid rain, fog and strong wind environment;
Drying and curing: 2 hours at room temperature, fully cured for 24 hours (or baked according to the paint instructions);
Test items:
Adhesion (cross-cut method ≥1 level);
Film thickness uniformity (error ≤±15%);
Appearance inspection (no missing coating, sagging, bubbles).
6. Packaging, storage and transportation specifications
The valve cavity is filled with anti-rust oil, and the flange is covered with a protective cover;
Frame wooden boxes are used to hang and fix above DN200 to prevent the coating from being damaged by transportation vibration;
Pressure level, flow direction arrow and "moisture-proof and shock-proof" label are marked.
Technical evolution: High-end valves use tungsten carbide spraying (HV≥900) instead of traditional paint, with a temperature resistance of 800℃ and a lifespan increased by 3 times.
