Stripping the finish off coated parts can be a real headache for most powder coaters. There are many ways to remove coating from a part prior to re-coating with powder, but we will focus on two of the most popular stripping methods: mechanical stripping using abrasive blasting and chemical stripping using dip tanks.
Mechanical stripping typically involves sanding, buffing, or blasting the old coating off.
Sanding or buffing is pretty straightforward, but it is usually the most labor-intensive way to remove a previously applied finish. For re-coating parts that have a powder coated finish, it can be a valuable technique. Unfortunately, taking the part down to bare metal requires a lot of care, effort, and time.
Blasting is a better option to strip parts when other methods are not available or allowed. Choosing the correct abrasive media is key. Most blasting operations are set up to clean and prepare raw metal for coating. It isn’t uncommon to see a blasting system used to remove scale and rust, as well as provide a bit of texture to the surface of the parts that need to be coated.
Stripping paint or powder coating from a part is a similar but slightly different process. When cleaning raw metal parts, less abrasive media like sand or glass may be used to help maintain the surface details of the parts and prevent accidental damage. Stripping parts usually calls for more aggressive media like steel shot, garnet, or aluminum oxide.
All these abrasive medias have different grits, which leave different mil profiles. Remember, if you leave a deep mil profile, it will require more powder to cover up the rough texture left by the aggressive blasting. If you choose the finer grits, you will spend more time blasting the part, but you can preserve fine surface details such as decorative scrolling. It really is a balancing act to figure out how much labor you want to invest versus how smooth you need the final appearance of the coated part to be. On one hand, more blasting time obviously means your costs will go up. On the other hand, using larger grits will require you to apply more powder to cover the part and you may have to address a more pronounced “orange peel” look on the surface of the finished part.
Chemical stripping can be a viable option for those coaters who re-finish a high number of parts on a daily or weekly basis, especially if they aren’t particularly large. If your customers bring in a lot of stripping work, dedicated strip tanks can remove previously applied coatings without damaging the profiles of the parts being refinished.
B17 by Benco (https://www.bencosales.com/metal-strippers/b17-procedures-best-practices-the-bomb-of-strippers), is a common strip solvent used by many powder coaters. Most powder coating shops tend to have a half drum of this on hand for the occasional strip job if their local environmental regulations allow it.
Warning! This solvent is very aggressive and all proper personal protection equipment should be used when dealing with it and similar stripping agents. Face shields and goggles, long chemical-resistant rubber gloves, a respirator appropriate for solvent fumes, and Tyvek suits are recommended when handling parts during stripping, as is thoroughly rinsing parts or areas of incidental contact with water to reduce the concentration of these chemicals and halt their effect.
If stripping parts is a regular occurrence, strip tanks like the ones offered by Greensolv (https://www.greensolv.com/rims-stripping) provide an easily repeatable process for removing old coatings and cleaning parts like wheels prior to refinishing. They usually recondition the stripping solvent and have a way to filter trash and old coating material out of the tank using a circulation system with filtration.
Whether stripping using mechanical or chemical methods, once the parts are taken down to bare metal, they no longer have any rust protection and can flash rust unless immediately sealed/treated and then coated.
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