Causes of pinhole shrinkage defects in spray processing

       The reasons for pinhole shrinkage defects in spray processing - wococarbide.com will tell you:



1: The main reasons for the appearance of pinholes are:



①The board surface is rusted;



②The galvanized substrate contains hydrogen ions;



③ Yellowing after pre-phosphating treatment;



④After the workpiece is phosphated, it is not cleaned with water, especially around the workpiece, it appears as a circle pinhole;



⑤The anion and cation exchange resin desalinated water is acidic; ⑥Powder quality.



solution:  



①Dry in time after phosphating and spray immediately;



②Dehydrogenation treatment (about 200℃, 2h);



③Adjust the parameters of phosphating solution, pay attention that the concentration of free acid should not be too high;



④Change to fresh water, clean the nozzle, make the water pressure > 1.5bar;



⑤ Disable it, temporarily replace it with tap water, test the pH value, (stainless steel spray paint) requirements to reach 6 to 7;



⑥ Take fresh powder samples and solidify them according to standard conditions to check the powder quality.



Two: the main reasons for shrinkage:



①Water or oil enters the powder production process. The shrinkage cavities are evenly distributed, in the form of small round pits or large pinholes;



② Other powders are mixed in during the spraying process, resulting in shrinkage cavities due to incompatibility;



③ External interfering substances pollute the spraying system (including workpieces), especially the presence of silicon-containing release agents and water-repellent agents in the workshop;



④ There are large and deep holes on the surface of the casting;



⑤ The coating has round pits, which are larger, commonly known as "fish eyes";



⑥The compressed air has high oil content.



solution:  



①Contact the manufacturer to change the powder;



②The powder room must be the cleanest when changing the powder. First, the cleaning and inspection procedures should be sorted out;



③ Carefully inspect the dusting site, eliminate these interfering substances, and strictly prevent the introduction of these interfering substances;



④The sandblasting should be thorough, and the castings can be preheated. The preheating temperature and time depend on the material and thickness;



⑤ Adjust the parameters of the degreasing section, the drying and curing tunnel pollution must be cleaned, and check whether the elevator and the rubber belt pollute the powder;



⑥ Check the filter of the compressor, install an oil-water separator, and discharge it regularly every shift.