More finishing operations want to move from solvent to aqueous as part of their cleaning operations.
Mike Valenti, Hubbard-Hall’s Director of Technology, has lectured on this at numerous local, regional, and national conferences, and FinishingAndCoating.com spoke to him about the considerations shops should consider when planning to make the switch.
Q: I know you’ve done a couple of talks about this, but I want to get into some real specifics about it. Is that a talk you enjoy giving?
Mike Valenti: Yeah, it’s a good talk because one of the issues, I think, and we deal with this regularly as people call in and ask us to help them is people that solvent degrease today and have never done water-based cleaning. They believe they will call us and say, “Hey, what cleaner do I need?” And they’re just going to start going and cleaning parts when there are many other factors and variables that they have to think about or may not have thought about when they decide to make that transition.
And so, it’s our job not just to sell people chemicals but to make them understand that there are many other things they will have to do to make that conversion. And honestly, if we can teach people that, it makes it easier for us to help make that conversion and eventually sell them a product or a process. Don’t think about it until we tell them, and then they’re like, “Oh, yeah, I hadn’t thought about that.” So, trying to get the word out sooner than later.
Q: I know there are lots of considerations. Let’s talk about what you consider the top consideration when cleaning the parts that way.
MV: I break it down into different parts of the process. You have chemistry, you have equipment, and then you have other issues like waste. That’s the three big categories. So, we’ll talk about chemistry first. One of the unique benefits of solvent degreasing is that solvents tend to be universal for metals. In other words, it doesn’t matter if I have a ferrous metal like carbon steel, copper, or aluminum; whatever the alloy is, the solvents tend to be benign or inert to those particular metals.
I can run steel parts; I can run aluminum parts. Take, for example, TRICOR TCE, a standard degreasing solvent. I can clean all those metals in the same TRICOR bath without making any changes or adjustments to the system. When you go to water-based cleaning, these different alloys now because we’re introducing water and different chemicals to make a cleaner bath, all these metals react differently to different chemistries. So now, I may not be able to use a universal cleaner or a universal product to clean different alloys, or I may have to set up a separate line to run my aluminum parts versus my steel parts.
So, it’s a consideration that people realize that things are going to get a little more complex because now we have to worry about the metals reacting with the chemicals we’re putting in the tanks or the machine or whatever our cleaning equipment is, whereas, with solvents, we didn’t have to worry about that so much in the past.
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Q: Let’s talk about part geometry. Everything’s different: big, small, intricate, down holes. Why is that one of the most difficult challenges?
MV: Part geometry is really important. So, if you’re vapor or solvent degreasing, these parts sit in the vapor phase; the vapor penetrates all these areas and dissolves all the lubricants or soils. The solvent then condenses, and it pulls all those materials out. The surface tension of solvents is very low, so you get a clean, dry part. The geometry doesn’t impede the chemistry from removing the soil or itself from the part.
As soon as I start aqueous cleaning these, I have two issues. Number one, I’ve got to have an aqueous chemistry that now I can get the surface tension low enough to get into these areas, but then I’ve got to get the chemistry out. This is where rinsing becomes the most important part of the cleaning process because if I’m unable to rinse the cleaner out of all these blind areas, and then I’m unable to get the water that I use to rinse the parts out, I’m going to have problems with corrosion. I’m going to have problems with soil not being flushed out.
It comes down to the simplicity of the process. The solvent is much simpler for tight geometries of parts, whereas water makes it much more complicated to flush and dry the parts properly.
And then, over time, if I don’t get the oils and things out of these small areas, I could get bleed out further down the process line. In this example, these parts get plated and go through a plating line. And if we’re not able to rinse properly and flush all the stuff we cleaned out, that’s going to bleed out into the other tanks, and that’s going to cause problems down the process line.
Again, it’s a lot of physics and chemistry of solvent versus water. It’s not an issue. We don’t have to worry about these things like surface tension. We don’t have to worry about rinsing per se because the solvent will evaporate out of all these areas, whereas, with water, it’s very difficult to get rinse water out of these types of parts. And if these parts are steel, they will rust if I can’t get the water out of all these areas and get them dried properly.
So again, it comes down to the simplicity of the process. The solvent is much simpler for tight geometries of parts, whereas water makes it much more complicated to flush and dry the parts properly. If somebody puts these parts in a vapor degreaser, the door closes, they get degreased, they come out, they’re dry, they’re ready to go, whereas on an aqueous process, now you’re going to need cleaner tanks, rinse tanks, and probably a heated drying process. So, you’ve added two full steps to the process that you didn’t have to worry about before.
Q: So, do steps mean more complication?
MV: More complication. That’s more things that can go wrong. Rinsing in aqueous cleaning lines tends to be one of the most ignored steps. People let their rinse tanks get dirty; they don’t flow enough water or use the proper type of water. So, you can clean the parts all day, but if you don’t rinse them properly, you’ll never get good clean parts out of a water-based process if you don’t have your rinses. That whole introduction of being able to rinse and dry properly is an aspect of aqueous cleaning that someone who’s only ever solvent decreased has to learn to deal with.
Q: These are fixable problems, but you must know what you’re doing.
MV: One of the things I try to tell people is, are there some chemistries that are better than others? For some of these, yes, but chemistry is not the whole solution to this problem of part geometry; equipment is a bigger part of the solution than chemistry. So, the type of cleaning equipment, what that process is, how parts are flushed, how they’re dried.
Equipment plays a much bigger role in part geometry and getting the right part clean, like you want it, than chemistry. There’s only so much we can do with the cleaning chemistries. The rest of it does come to the equipment itself, and how does that equipment help you get to the final part that you need? Unfortunately, we can’t fix every problem with chemicals.
Q: Let’s talk about the soils that are on there. You can’t see some of them, or you just can’t see. Some of them you possibly can see.
MV: There are two types of soils you will generally deal with. You have lubricants and coolants, and both of these can be used independently of each other. And sometimes people use lubricants and coolants. So, what’s the difference?
A lubricant is designed to help; say, we’re machining out these parts; it’s part of the lubrication process to help cut properly. Those tend to be things like straight oils. They tend to be heavier; they tend to be highly hydrocarbon oil-type materials. Then, you have the coolants designed to keep the tooling cool so the tooling doesn’t overheat. Most people today are running; they use the term water-based, but they’re not so much water-based. They’re water-dispersible materials. They can incorporate them into the water, and that helps to keep the tooling cool. Those are easier to remove.
If somebody is using heavy oils to cut, we start getting into issues, especially in part geometry, if those heavy oils are down inside these parts. So, then you need more aggressive cleaners, you need more aggressive rinsing.
If someone uses a water-based coolant to do their parts, those are much easier to remove. They don’t leave a lot of residue behind. You can use very mild cleaners; they’re easier to rinse off. It’s a much easier process. But if somebody is using heavy oils to cut, we start getting into issues, especially in part geometry, if those heavy oils are down inside these parts. So, then you need more aggressive cleaners, you need more aggressive rinsing.
If you’re a job shop, the parts could be coming in with rust preventives, which must be removed. So yeah, really, you got the two types of soils. You got the heavy oily type materials and the coolants. So, like I tell people, coolants are generally not an issue. We can get those clean, but the heavier cutting fluids are more problematic for those parts. And again, this is where solvents, when you run the solvent system, the solvent just universally dissolves off everything, and you’re good to go. It’s not a consideration you must worry about when you’re cleaning solvent.
Q: I’m sure it’s always a good practice for these finishers to have good dialogue with their customers to know if anything’s been changed, if anything, any fluids have been added, changed, swapped out, or anything.
MV: I know I talk a lot of jobs; they often don’t know, though. They don’t get informed. They tend to not know until they have a problem. We’ve had many customers over the years who will call and say that we’ve run for years and years and years. And I’ll get a phone call and say, we can’t get the parts clean anymore. And so I first ask, “Well, what’s changed?” Well, nothing’s changed. And then when you start doing some research, and you start talking to them, you find out, oh, well, we found out this lubricant changed or the supplier of the metal of the actual part that they’re making the parts, the supplier changed, and that supplier may be using some different soil or lubricant on the part.
So yeah, it’s very difficult if you’re a job shop. If you’re a captive shop, you’re generally doing your parts anyway. I was talking to someone not too long ago who told us that nothing had changed. And then somebody else came in the room and said, “Oh yeah, we changed one of the coolants in one of the processes.” And nobody else in the room even knew that.
Q: Their customers should be letting them know, right?
MV: They should be, but sometimes they don’t know. But that’s our job. That’s why we ask all the questions. That’s why we always kind of press to try to get to the root cause. Because we do this enough, if I’m told nothing else has changed, we start looking at stuff that’s coming in and maybe looking for changes there.