What are the precautions for spraying PTFE on the valve stem
Information summary：Valve stem spraying is a key process for improving valve stem performance and extending service life. There are many precautions to be taken during operation:
1. Pre processing
Surface cleaning: The surface of the valve stem needs to be degreased, degreased, and derusted. Any oil stains or rust residue will affect the adhesion of the coating. Organic solvents can be used to wipe the surfac
Valve stem spraying is a key process for improving valve stem performance and extending service life. There are many precautions to be taken during operation:
1. Pre processing
Surface cleaning: The surface of the valve stem needs to be degreased, degreased, and derusted. Any oil stains or rust residue will affect the adhesion of the coating. Organic solvents can be used to wipe the surface first, and then acid washing, alkali washing, or sandblasting treatment can be carried out until the surface presents a uniform and clean metallic luster. For example, sandblasting can remove oxide skin, make the surface roughness appropriate, and facilitate subsequent coating adhesion.
Dimensional accuracy protection: Some valve stems have strict requirements for dimensional accuracy. During the early stages of polishing, sandblasting, and other treatments, process parameters should be controlled to avoid excessive removal of materials causing dimensional deviations. If necessary, fixtures can be used for protection to correctly maintain the original dimensions of key parts of the valve stem.
2. Selection of spraying materials
Suitable operating conditions: Select according to the working environment of the valve stem. If it is in a high temperature, high pressure, and strong corrosion scenario, such as chemical pipeline valve stems, high-temperature resistant and corrosion-resistant ceramic coatings or nickel based alloy coatings must be selected; If it is in a normal fluid medium and room temperature environment, organic polymer coatings can meet the requirements.
Material quality control: The purchased spray powder, silk and other materials should have reliable quality, and their composition reports and performance parameter certificates should be checked to avoid poor spraying effect caused by impurities and uneven particle size in the raw materials.
3. Spray coating process
Correct parameter adjustment: During spraying, the distance between the spray gun and the valve stem, spraying speed, powder (wire) feeding amount, current and voltage, and other parameters should be adjusted correctly. For example, in plasma spraying, if the spray gun is too close, the coating is prone to overheating and cracking; The distance is too far, the powder melting is insufficient, and the coating is loose and porous. Multiple experiments are needed to find a better parameter combination.
Uniformity guarantee: Ensure that the coating is evenly distributed on the surface of the valve stem, whether in the circumferential or axial direction. Through mechanical or automated equipment, the movement trajectory of the spray gun is correctly controlled to prevent local coating from being too thick, too thin, or even leaking.
4. Post processing
Coating curing and heat treatment: Some coatings need to be heated and cured after spraying to improve performance. The heating rate, curing temperature, and duration must strictly follow the process requirements, otherwise the internal stress of the coating will be imbalanced, leading to peeling and cracking; Some metal coatings also require appropriate heat treatment to optimize their microstructure.
Quality inspection: Use hardness testing, ultrasonic testing, adhesion testing and other methods to inspect the quality of coatings. If coatings with substandard hardness, internal defects, or poor adhesion are found, they should be reworked and repaired in a timely manner to prevent problematic valve stems from entering the assembly process
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