Rust prevention is a step that nearly every finishing operation should take, but it appears that a large percentage don’t.
Larry EnsleyLarry Ensley is the Director of Technical Applications at Hubbard-Hall, and FinishingAndCoating.com Editor-in-Chief Tim Pennington recently spoke with Ensley on a variety of topics related to rust prevention for the Hubbard-Hall “Seen and Solved” podcast, which can be viewed here.
Rust is the most basic of corrosion. Tell us how it starts.
Larry Ensley: Rust is a naturally occurring reaction between the air and moisture on the surface of the metal. With steel, it’s iron oxide. So, it’s a naturally occurring reaction that you can’t really stop, but you can prevent. Or we can put a different process on top of it, which is more permanent to keep the air away from the surface of the part.
What are the most common types?
LE: Typically, it’s atmospheric corrosion. That’s the most common type. It’s when metal is exposed to the elements, again, moisture and air, and it starts a reaction that occurs immediately. You want to put a barrier between the air in the surface of the metal to stop it from happening.
The minute it hits the air, you’re going to start seeing reaction because you’re talking about a chemical reaction, correct?
LE: And it’s a term that we refer to called flash rust.
We know that in different parts of the country, it’s more prevalent. When you have humid air in Florida and those types of places, they deal with this a lot more through the Midwest, where you’ve got that wet air, basically.
LE: Coastal and human environments, like the Deep South, America, and the Orient, much more humid environments are much more susceptible to rust. The dryer elements in the Southwest, Arizona, and such, are much less prevalent. But rust will occur if you have any moisture and oxygen in the air.
We’ve often heard some shops and finishers talk about when parts are shipped from one facility to another, which could be two, three hours away, or could be overnight; that’s when it’s occurring.
LE: Correct. There are different levels of rust preventatives that you would need in your process, given that you’re trying to prevent flash rust inside the facility. There are temporary RPs to get you from one process to the other. And if you’re shipping across the country, there are long-term rust preventatives that are easier to remove and go further processing and such.
What are some ways to reduce corrosion from occurring?
LE: We’ll do it in stages. Here, we call it classes of corrosion and preventatives. We have temporary rust inhibitors, which are typically your water-based rest preventatives that you apply to the surface of the part after manufacturing, plating, or phosphating you’re plating and paint customers, powder coating customers. They use a lot of in-process rust preventatives that are easily removed prior to powder coating, painting, or plating without contaminating the process. Those are water-based products. Typically, they last anywhere from two days to two weeks. Those are your typical short-term process products. Then you get into your next class of products, what we call our soluble oils or emulsified oils. And it’s where you mix oils with water, and you’re going against everything. The mechanics of oil, oil, and water typically split. So, you add emulsifiers to tie them together to make longer-term corrosion protection for, let’s say, 24 hours of salt spray protection to 72 hours of salt spray protection. That’s pretty typical for a soluble oil. People would use that because it’s cheaper or more economical, let’s call it economical. You would be able to apply this to the part in a diluted form. You dilute it. One part rust preventative to nine parts waters, 10%, up to 20%. And you can reduce your cost that way. The problem is its shorter life, shorter bath life, contamination causes the emulsion to split, and you have to replace the oil. So, there are some drawbacks. But for somebody that needs economical rust preventative, that’s a good common use. The third class of products is your water displacing, solvent-based rust preventatives. Gives you longer-term corrosion protection; anywhere from 100 to 200 hours is your average, what we’re seeing, and it’s used as received. And we call it water displacement because it does just that. If you put a wet part into a solution of water displacement rust preventative, it pushes the water away from the surface, displaces it to the bottom, and it can be drained from the tank. And that’s the only maintenance. You just constantly replenish what is carried out on the part. So those are the difference in the classes and what you can expect as far as performance.
Are all of those applied the same way, or are there variations of how these can be applied?
LE: Water displacing products can be brushed on or sprayed on. The most efficient method is immersion. You get 100% surface contact. You have 100% water displacement. If you spray it, you may not displace all the water or moisture. And if we look at soluble oils, typically those are always emergent because you’ve got to dilute them with water. You have to heat it. You have to have agitation to make sure it stays in the solution. So typically, those are immersion processes. And the water-based temporary inhibitors can be sprayed, immersion, or brushed on.
What would determine which one you’d pick? It sounds like most people shops would probably go for probably the most economical or easiest way to do it, especially. But what determines how these things should be applied?
LE: It’s determined by how much rust protection you require and what your subsequent processes are. If it’s a true in-process product line, for instance, let’s say a pre-paint line where you’re getting ready to powder code or paint a part, and you go through the iron phosphate process or the zirconium process, and you want to have protection until it gets to the paint line itself. They may add either a seal or a temporary RP after the part is made before it goes into that pre-paint process to keep it from rusting. And you don’t want oil on the surface because oil if it’s carried into the pre-paint line, it starts to build up in your cleaner, and then you start to apply it to your parts, and you have paint failures. So, the reason you would choose an in-process product based on a means is that it doesn’t cause any contamination issues on the surface of the part. It’s easily removed. If we use a long-term, for instance, if a customer is manufacturing tubing in Michigan and they ship it to Texas to be powder coated or painted, you’ve got to choose. You’ve got to find a way to give longer-term corrosion protection without contaminating that pre-paint line. So there has to be a better cleaning process in between. If it’s in-house, you can shorten that amount of protection needed.
If you’ve got down holes or enclosed parts, is that something that you really can’t see those, but-
LE: Part orientation or shape that lends to the type of number one process beforehand. If it’s a wet part coming out of an aqueous environment, we have to displace the water on the surface of that part. So, immersion is typically your best option. And if it’s a final finished product. If you want the longest protection possible, you would go into water displacing oil, displace the water, pull it out, let it dry, and you package it or store it. If it’s not finished, it’s coming out of an aqueous environment, and you want to go to a subsequent step, then you would use an in-process, a mean-based rust preventative that will give you temporary rust protection prior to that next step. You don’t want to use oil between process steps.
We spoke earlier about flash rust, and I know that there are probably people that can’t even tell that things are starting to rust, but it does occur very fast. As you said, it starts immediately, but what is flash rust? What’s occurring there?
LE: Flash rust; what’s happening on the surface of the metal? The iron on the surface of that metal is reacting with air and water, and it’s forming a layer. That’s what’s occurring.
And do some processes have a step where they’re trying to dry the parts right away or are they just air dried? Or if they bake some of them?
LE: Some parts, yes. I’ve seen ovens used. I’ve seen air knives. I’ve seen halo rinses with RPs sprayed on the surface of the part if they don’t have the ability to dry. There are other methods to try to get moisture away from the surface. But if the part is super clean, the moisture in the air can still cause corrosion on the surface of the part.
Is it the way they’re storing parts, or is it how they’re preparing them to be shipped that causes this rust? Where are the most prevalent errors that they’re making on this?
LE: Choosing the wrong rust preventative and trying to cut costs after the part is finished. You spend all this money making and preparing a part, and you try to save money on the rust preventative, and you create corrosion where you could have prevented it. I see this a lot with one of the customers; in particular, they were using a soluble oil, a 10% solution of oil in water, and they were putting it on a hot cast iron part. When it went in the rust preventative, it cooled, and it sealed water into the pores of the metal. It packaged the part, put it in plastic bags, and put it in a box on its own. It’s created a humidity cabinet. Opened the part; it’s flash rust. They forgot rust. And we corrected that by eliminating water from the process completely. We went to water displacing oil, which was more expensive. It was 10 times more expensive, but we have eliminated 100% of their rust. There are five-plus years of data to prove that we’ve eliminated their rest problem.
So you’re talking about the chemistry being more expensive, but you were eliminating a problem, right?
LE: Eliminating a problem, 100%.
Which was probably a cheaper solution than having to have parts reworked or other issues?
LE: I had a discussion with the customer. And when he told me, he said, “It’s 10 times more expensive,” I said, “But you’ve got 100% failure.” I said, “You cannot afford to continue to run parts over and over and never be comfortable putting in a package, and you have one time to make a first impression. And when the customers that box up, if he finds a rusty party, your odds of getting that customer back is not good.”
When you go say to a finisher who’s talking about rust issues, do you often have to go back to the maker of that part and address it with them? Or is it just putting it on when it’s leaving their facility? Do you also have to go up the food chain a little bit to talk to them, or how does that work?
LE: Yes. For lack of a better answer, yes. It is an uneasy conversation to have. But typically, if somebody’s having trouble after processing after a customer has received this and they have complaints, it’s much easier to convince them if they’re not seeing the rust if they’re not seeing the prevention upfront in the cost savings that we can provide by doing it the first time. And it’s a little harder conversation. But you do that with proof. We do that with case studies. We do that with salt spray testing. We try to prove it with data.
How many years ago did the Metal Guard line come out?
LE: Metal Guard’s been around 20-plus years now.
I know you have variations of the product. What determines what it is that you’re going to use?
LE: If the part is being manufactured in one area of the plant, assembled or manufactured, and being moved to a plating line, paint line, or a powder coating line, and they just need a few days of protection, we’re going to look at one of our 800 series Metal Guards for temporary rust inhibition that will not contaminate post-processing such as paint, plating, or powder coating. That’s how I would choose one. If the customer desires a soluble oil, they’re just cost-conscious, and they want to use a soluble oil on the surface of the part, and there are good reasons for this; some people do this, for lack of a better term, there’s a smoke test on certain parts on small engines. And a lot of people in small engine markets use soluble oils because the water evaporates and the film left behind doesn’t smoke when you start the engines up, which is very important. So, I would find out if that’s their driver. Why are they choosing a soluble oil? And I would recommend one of our products. If it’s final rust preventative, then you determine, for instance, our Metal Guard 400 and 500 series products, I would find out exactly what they are looking for. What film is it going to be drawn to touch? Is it going to be oily? Is it going to be the best corrosion prevention possible? Do you determine what their driving factor is? What do they want from this process? What finish do they want on a part afterward? And then we make the recommendations.
I’m sure you get this question a lot, well, which is the best one?
LE: If you want the very best corrosion possible from our product line, I’m going to recommend Metal Guard 560 because it gives you up to 200 hours of rust protection over black oxide. But if you want the best corrosion possible with the driest finish, if we start trying to find our happy medium, we go down to the 500 and Metal Guard 480. Suppose you want the very driest finish possible after our water displacing oil, Metal Guard 450. But the customer has to understand if they start reducing the film left on the part, you reduce the corrosion protection. So we have to find a happy medium.
I remembered a couple of years ago, you and I were talking about a customer of yours that was finishing the parts, then putting it in a plastic seal, then putting it in a box and shipping it out. So where was that rust? Where was it occurring?
LE: Yes, that’s the process we discussed with the water being trapped inside the part. It was an emulsifiable water oil, a soluble oil. And when the part cooled, it trapped the moisture inside the pores of the metal. And then you wrap it inside of a bag, and you seal this moisture in a bag, and so you’ve created a humidity chamber. You’ve sealed oxygen in the bag; you sealed moisture in the bag, and you’ve created a chamber that’s going to create corrosion. That’s what was happening.
Give me some examples of where you all have seen where rust will start.
LE: You think about the tooling industry; the sockets, the wrenches, they’re manufactured on one side of the plant, and they’re put in these large bins ready to go to the next step, which is typically a plating line. Plating lines are known to be acidic. The environment’s very acidic. You can only do so much with the ventilation and such an atmospheric exchange. You still have an acid environment at a plating line. Well, if you put a bare steel part besides a plating line and let it sit there for a few days, you’re going to create corrosion. And what we do to prevent that is we add a product called Metal Guard 800D, which is a water-based rust inhibitor based on a means, and it gives you up to 72 hours of protection stored next to a plating line.
You mentioned something earlier. You said you could apply rust preventative, and it won’t affect the application of the paint or the powder, or the finish. Is that right?
LE: If you choose the right product, correct. Correct. Now, I’ll preface that by saying it depends on where we apply the rust preventative. If we are using an in-process Metal Guard 800 series product prior to the pre-paint line where it goes through the P stage process with the cleaning line, the rinse, the phosphaters are calling in the rinse and the seal, if you apply the rust preventative before it goes there, your cleaner’s going to remove it, and there will be no adhesion issues. Some customers decide that they want to use a rust preventative after applying. Typically, it’s these large spray one processes where they’re doing these huge parts with a manual high-pressure one, and they apply either zirconium or iron phosphate. When they finish that, they will cover it with an in-process rust preventative called Metal Guard 850 at a reduced concentration, and you can paint over it and not lose adhesion.
What are some common mistakes that people make that you see that really cause them problems for causing rust? Is there a few that kind of stick out?
LE: There are a few. It’s hard. One of the biggest problems customers, if a little bit is good, more must be better. And that’s not always the truth. You see a lot of customers using your in-process products as too heavy and too concentrated. The people that are trying to reduce costs and run it more economically, especially on the soluble oils, will sacrifice rinse waters. They will reduce the amount of rinse in between your process steps and contaminate your soy oil with high alkaline or high acid product and cause the emulsion to split. That’s a common occurrence. And the other one is just failure to do maintenance on water displacing product, which is draining the water off the bottom. Just get the water out of the product, and it will last indefinitely. I have a customer with a bath that was over 15 years old, and they did maintenance daily, and it lasted for that reason. It paid for itself.
As we wrap up, let’s talk about just a few things we want people to remember about this rust prevention. The thing I heard from you was one, look at the ROI with this. You’re going to pay for rust prevention, but it sounds like it will save other costs and higher costs down the road.
LE: Much bigger, yes. Make sure you choose the correct rust preventative for the job. Just because you have an oil on hand beside you and you process these parts, and you’re going to store them in your warehouse prior to being painted, you’ve got to understand that if you continue to drag oil into a pre-paint line, it’s going to eventually be spraying oil on the parts that have cleaner, and then you’re going to have paint adhesion. So, choose the right product for the process. Don’t try to skimp on cost. You’ve done all the work upfront; make sure that you put the right rust preventative on it to give the right protection so that you don’t have to do this. You don’t want to create scrap, or you don’t have to do rework. But those are some of the biggest issues. And do the maintenance. The maintenance on rust preventative tanks is very simple, and it’s something that shouldn’t be skipped. It’s something that’s very important.
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