The presence of foreign impurities in the repair coating is a common phenomenon in painting. Even if spraying in a very clean environment, impurities will be found in the coating film. The reasons for this phenomenon can be analyzed from the following aspects.
1. The coated workpiece is unclean
In order to avoid impurities in the coating caused by this reason, the following points should be noted:
①Before the workpiece is transported to the painting work area, dust removal treatment is required, that is, blown off with steam or compressed air, and then wiped with a rag. Cleaning up before painting is better than repainting due to poor quality after painting The cost is much lower.
② When it is necessary to cover a certain part of the workpiece during repair, the workpiece should be wiped again after the cover is completed to remove paper dust, dust, fibers and other debris.
③ Fixtures, hangers, and brackets on the conveyor need to be kept clean. If there is a lot of flying paint on these objects, it will fall on the workpiece after drying, causing coating pollution.
④Drying equipment may also be the source of impurities, so the walls and roof of the baking furnace should be cleaned frequently to avoid contamination of the painted workpiece after entering the baking furnace.
2. The paint itself is not clean
①The paint is easily contaminated by external impurities during the process of mixing, diluting and filtering before use. If the container used to mix the paint is covered with dust, the paint will be seriously contaminated. In order to prevent paint pollution, the paint cups and paint tanks filled with paint should also be kept clean. For example, the paint cups used for suction Spray Guns are better made of non-stick paint polytetrafluoroethylene. Disposable lining at any time.
②The paint contains fillers that cannot be mixed evenly. If these paint skins and solid particles are not filtered out, the coating film will contain impurities. Therefore, the paint should be filtered with a metal or nylon mesh before use and the filter must be clean, and do not use Gauze or cotton cloth is used to filter the paint to prevent the introduction of fiber impurities.
③When the paint is diluted, if the thinner is used improperly, it will not only fail to achieve the effect of dissolving and thinning, but even reduce the solubility of the paint and cause sinking. Therefore, the designated thinner (solvent) must be used in the solution station.
④Do not use expired paint, because the paint has a certain shelf life, and the expired paint itself will deteriorate, and it will contain rust caused by the corrosion of the container.
3. The atomizing air is unclean
There may be several reasons for the unclean atomization air.
① When cleaning the Spray Gun, immerse the whole Spray Gun in the solvent. This cleaning method is easy to bring the dirty solvent with paint into the air path of the Spray Gun, and the dirty paint will be deposited in the air path of the Spray Gun and brought into the atomized air during spraying, so the Spray Gun cannot be completely submerged during cleaning into the solvent.
②The compressed air may contain moisture, oil and other impurities, and the rust and corrosion of the gas pipeline will attract impurities. The iron workpieces in the gas pipeline will rust and corrode due to the moisture contained in the compressed air. Moisture, grease and other impurities in compressed air are removed. A simple way to check the cleanliness of the atomized air is to put a white towel in front of the Spray Gun, remove the air cap, turn off the paint supply channel, trigger the gun for 1 minute, let the air flow through the hands, and observe whether the hands are dirty. Dirty, indicating that the atomizing air is not clean.
4. The spraying construction area is not clean
The construction area for repair painting should be dust-free and clean. In order to maintain a high degree of cleanliness, the walls, ceilings, floors, lamps, etc. of the painting area such as the spray booth should be cleaned regularly. Moreover, the pre-spraying work area such as grinding, sandblasting, polishing, etc. should be as far away from the spraying work area as possible. The painting area requires idlers not to enter to prevent dust carriers from entering.
5. Improper operation of the spray booth
① The air entering the spray booth is not clean. If the air sent into the spray booth is unfiltered or poorly filtered, it will inevitably contain dust and other impurities.
② There is a problem with the filter material in the filter device. The type of filter material used needs to meet the requirements and be clean. If the filter material is not cleaned and replaced frequently, the filter element will be blocked by impurities, which will affect the filtration efficiency.
③ The air inlet pressure of the spray booth should be greater than the pressure outside the spray booth, otherwise the impurities outside the spray booth will enter the spray booth from the cracks and cracks in the door and wall.
6. Improper operation of spraying method
①If an excessively high air atomization pressure is used during spraying, the dust and flying paint accumulated in the spraying room will fall on the Spray Gun and the workpiece, which will eventually pollute the coating, so try to use a lower suitable air when spraying Atmospheric pressure.
② During the spraying process, pay attention to the flow direction of the ventilation, and start spraying from the direction away from the exhaust outlet, so that the generated flying paint and rebound paint will move along the direction of the airflow, and will not pollute the sprayed parts.
7. Pollution caused by cloth fibers
Fibrous impurities such as fine cloth and wool often cause coating film pollution, so workers should wear clean work clothes that will not produce fiber debris when spraying, and work clothes, hats, gloves and other utensils should also be cleaned.
8. Pollution caused by static electricity
Static electricity attracts dust particles, especially when humidity is low. In order to eliminate the pollution of the coating film by the dust generated by static electricity, a device for eliminating static electricity should be equipped, and the workpiece, equipment and operators should be well grounded if possible.
As long as the above-mentioned aspects are carefully checked, it is possible to avoid introducing impurities into the coating film during repair coating.
