We paint aluminum sand castings for an exterior application. We want to switch to powder but we are torn between a spray washer and an immersion system. Some of our parts can get up to 24-inches wide x 15 feet long. It’s not the size that causes the confusion. We hear different opinions on what gives us a better clean / pretreat. Any thoughts? R.J.
First let’s sort out some issues. Spray washing can be performed using a batch method (spray wand) or using a conveyorized method (in-line washer). Immersion washing is normally only used in batch operations, since tank sizes for in-line processes are way too big. If you are thinking about using either of these methods, then I have to assume that you are looking at a batch operation. Given that reasoning and the size of your parts, read on.
Spray wand (batch spray) washing and pretreatment is a process where parts are cleaned and pretreated using a hot water pressure washer and containment system. The actual cleaning is performed by the impingement pressure, chemical concentration, cleaning time, and water temperature. The degree of cleanliness and quality of pretreatment is directly related to the operator doing the work and the sophistication of the chemical induction system on the power washer. A well-trained and qualified operator using good equipment can obtain good results consistently. If your mentally challenged brother-in-law is operating a homemade pressure washer, then “look out”.
Immersion (dip tank) washing and pretreatment is a process where parts are cleaned and pretreated using hot water and chemical in a tank with agitation. The cleaning is performed by the amount of agitation, chemical concentration, immersion time, and water temperature. The degree of cleanliness and quality of pretreatment is directly related to the design of the tank (i.e. agitation, heating, oil skimmer, etc.) and the control of the process (i.e. proper titration and temperature). Typically this process is easier to operate with good results and is less operator dependent. That means you can let your “brain-dead” brother-in-law run this with some training.
Choose which process you want based upon the factors discussed here. Both are very capable of providing good results with neither being “better” than the other. If you have to compensate for your “Dumb & Dumber” brother-in-law then choose the immersion system, as he will stand a better chance of correctly cleaning and pretreating your parts.
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