Maintenance of nozzles during the coating pre-treatment process
1 Causes of nozzle failure
1.1 Erosion. When the high flow rate of liquid passing through the nozzle hole at the metal surface, it will produce erosion of the nozzle hole, resulting in lower nozzle pressure, spray state becomes irregular. The chance of erosion of the nozzle depends on the hardness of the liquid, spray pressure, the type of chemical material used and its dosage. In addition, the particles in the liquid impurities will also make the nozzle is severely punished erosion.
1.2 Accidental damage. Incorrect use and failure to perform timely maintenance is the main cause of accidental damage to the nozzle. Although the nozzle mouth is usually designed to concave, but the fan-shaped nozzle offset structure is vulnerable to damage.
1.3 Corrosion. When using chemical materials to spray and wash the workpiece, these chemical materials can also cause corrosion of the nozzle material.
1.4 Clogging. The accumulation of chemical materials and impurities inside the nozzle or on the external edges can cause clogging of the nozzle. This will affect the spray shape of the nozzle, which affects the spray pressure.
1.5 Temperature. Nozzles working at high or abnormal temperatures for long periods of time can cause damage to the nozzle due to material softening.
2 Nozzle problem identification
When the spray pump is operated at its rated capacity, the spray pressure of the nozzle will decrease with the expansion of the nozzle aperture. For damaged nozzles, even if the actual flow rate of the nozzle exceeds 30% of its rated flow rate, the change in its atomization state is difficult to identify with the naked eye.
The best way to identify nozzle problems is to observe the pressure changes in the spray pipe. The location and accuracy of the pressure gauge is critical when comparing different nozzles in the same pretreatment system. Typically the pressure gauge should be placed at the front end in the shower line. To determine the pressure changes in the spray line, the spray pressure of the intact nozzle should be used as a benchmark to determine whether there is a problem with the nozzle by the difference between the actual pressure and the benchmark pressure.
3 nozzle problem elimination
Because it is difficult to directly perceive the nozzle problem with the naked eye, so the first must pay attention to the selection of nozzles. After choosing the right nozzle, there is also a complete set of maintenance and replacement program.
3.1 Regular inspection of the nozzle. Including regular cleaning of the nozzle and regular inspection of the nozzle appearance for damage. General pre-treatment line in the first few processes (such as pre-degreasing, degreasing) of the nozzle every shift to check and clean, after the process of spraying the frequency of inspection and cleaning can be appropriately long.
3.2 Regular replacement of nozzles. The frequency of nozzle replacement depends on the environment in which it is located, the composition of the spraying liquid and the material of the nozzle. If the temperature is high, the spraying liquid contains impurities, the number of nozzle replacement is relatively frequent.