Powder coating pre-treatment per needs, not competitor number/assumptions

A. Hi Anup. Whether most of your enclosures are for indoor use or not, that doesn't mean you can process them all for adequate indoor corrosion resistance and just let the ones installed outdoors fail -- you must design for real-world corrosion resistance. If you wish to not design based on competitor assumptions, then don't base your treatment system on salt spray hours, as that's not what corrosion resistance is really about, nor what salt spray testing is for ... and to try to NOT exceed 300 hours salt spray resistance is just plain silly :-)

Iron phosphate followed by powder coating will be adequate for indoor use and 200+ hours of salt spray resistance. It's hard to say whether it will be good enough for outdoors because conditions vary. If there is no substantial exposure to chemicals (acid rain, industrial atmospheres, lawn fertilizer, de-icing salt) it should be okay. Iron phosphate is cheaper and simpler than zinc phosphate, and 3 stages may be enough. Although we understand what nano technology means, all such pretreatments are proprietary, so it's difficult to say how complex/simple and expensive/cheap they are; but one thing is fairly sure: they are not going to sell them for less than they have to -- which means if they are simpler than iron phosphate, you can count on them being more expensive :-)

But I am a bit confused about your intentions as I understand that NEMA 4x enclosures are built of stainless steel, aluminum, or plastic -- not mild steel. A mild steel enclosure passing 200 hours of salt spray does not mean it meets the NEMA 4X "benchmark", and it certainly doesn't mean that it has equivalent corrosion resistance :-(

Regards,

Thanks for the kind thoughts, Anup.

2). Here's the thing. A properly designed and operated system of even simple design like a 3-stage iron phosphate pretreatment might, on a good day, deliver 300 hours of salt spray resistance with a competent powder coating. So what do you do then: operate it poorly and out of balance, so it won't exceed 300 hours? Rather, I think the answer is that you need a properly operated 3-stage iron phosphate system (unless you go with nano instead), and it must consistently deliver 200 hours salt spray resistance, but if it happens to deliver a lot more, good. Yet another factor is that there can be a large variation in salt spray performance from cabinet to cabinet, operator to operator, etc., so if you manage 400 hours it can just be extra insurance that you'll always get 200 hours.

Things may be a bit different in India than in the USA, but here we generally don't design a system based on theory and first principles. Rather, the phosphate process suppliers or powder coating material suppliers run test parts through their labs to identify a proper sequence and to get an early heads-up if something doesn't go as hoped because of poor rinse-ability, air pockets, Faraday cage effects, difficult to clean steel, etc.

5). The size of the phosphating cabinet is based on the treatment time, as implied in your first posting (length of cabinet divided by speed of conveyor = treatment time). But I don't know the treatment time for the proprietary nano chemistry and would prefer not to guess at a good treatment time for the iron phosphate.

As for 50% variation in cabinet size between vendors, it is difficult to say what size is truly "necessary". Although you understandably want to spend no more than necessary, the general fact remains that 'robustness' of the treatment cycle doesn't really fit a "go/no-go" model. The vendor who proposes a 50% larger cabinet is probably allowing more insurance against clogged nozzles, accidental temperature drop, occasional loads of dirtier steel, etc., causing a corrosion failure ... it's very hard to quantify the value of such robustness, let alone reduce the issue to necessary/unnecessary. A "perfect" design is unlikely on your hundredth process line, let alone the first :-)

Luck and Regards,