Nine times out of ten, I recommend blasting parts before powder coating them. I’ve blogged extensively about this in the past, and won’t reiterate my pro-blasting arguments here.
Instead, I want to talk about the occasions when blasting may not be advisable. They’re less rare than you may think.
The customer doesn’t want the added cost.
Blasting parts before coating them can, in some cases, double the cost of the project. I completely understand why that’s a dealbreaker for people. The best I can do is to be honest with them about the ramifications of not blasting, and then pretreat (and possibly sand) the part as well as I can before coating it.
The part is too flimsy.
Sometimes, the customer will request blasting, and I’ll realize upon the part’s arrival that it won’t survive the process. Blasting imparts friction (heat), which can cause thin, flimsy metal to warp. No one wants that. Or if the part is highly corroded, blasting can tear holes right through the substrate. After nearly a decade in the business, I can tell by looking at a part whether it will survive blasting. This is a big part of why I request photos during the quoting process.
The part has threads, hinges, and enclosed areas.
Some threads, hinges, and enclosed areas can be masked, in which case blasting remains an option. But if there’s a risk of the blast medium getting stuck in sensitive (i.e., sliding or bearing) areas, or if masking the part becomes laborious and cost-prohibitive, we may have to forego blasting. Cost is a factor for most customers, and there’s no sense in coating a part we’ve broken.
The powder film thickness.
Blasted parts require more powder coating film thickness than unblasted parts. Blasting creates tiny peaks and valleys in the substrate – we have to fill the valleys with powder, and build film thickness over the peaks in order to fully protect the part. This involves multiple coats, which increases cost and process time.
Like most topics, this one requires greater nuance than most people are willing to use on social media. While it’s generally true that blasting is beneficial, it’s also true that blasting can be detrimental – to budgets, to substrates, to powder coating, and to the part itself.
