Bath maintenance is crucial to any finishing operation’s cleaning process.
Mike ValentiMike Valenti, Hubbard-Hall’s Director of Technology, has lectured on this at numerous local, regional, and national conferences, and www.FinishingAndCoating.com spoke to him about how to properly maintain your baths.
Q: Regarding bath maintenance for cleaning, once you get a line dialed in, everything will run really well.
Mike Valenti: Comparing and contrasting the two types of cleaning, in solvent de-greasing, your bath maintenance is minimal. You're doing two things: looking at the solvent's acidity. Solvents can become acids depending on the types of lubricants and solids they contain. So, there's an acid acceptance test that typically gets done. And then, really, the only thing you're doing in a solvent system is watching the solvent's boiling point. If you start seeing it rise, then there's a lot of soil built up, and it's changing the solvent's boiling point.
Those things happen slowly over time and don't immediately have major impacts. We're talking months to years sometimes before people start seeing those things. In aqueous cleaning processes, a lot of times, a couple of things are going on. The chemistry itself is constantly being drug out of the tanks, so let's go back to our part with all these little geometry. So, all these little areas will carry the cleaner solution out of the tank or out of the chamber or whatever the type of equipment is in solvent degreasing, recycling that solvent all the time. We're losing very little.
In aqueous cleaning, we always pull cleaner out of the tank whenever we run a barrel of parts or a rack of parts. So, as the volume of cleaner gets reduced, you have to add volume back to the tank. And so, if you have to add water back to the tank, you also have to add cleaner back to the tank. So, maintaining that bath chemistry is very important to ensure that the chemistry is at the right level to ensure we have the right amount of constituents in the bath. Because if you don't, and the cleaning tanks get too lean, and the chemistry gets too dilute, then parts aren't going to get clean. There are a number of ways that we do bath maintenance, but they tend to require daily, at least daily, intervention, doing simple things like titrations, titrating samples, and doing conductivity tests.
A lot of these things can be automated. We can automate tank fillings, but that doesn't mean you can get away from doing these tests of the tank's chemistry to ensure the chemistry is where it's supposed to be. When you go to aqueous cleaning, realize there's a lot more you must pay attention to regarding the tanks. And then I talk about rinses, so the opposite happens in the rinses. Now we're looking for chemistry to build up in the rents tanks. You have to do maintenance on your rinse tanks. You have to check your rinse tanks. How much of the cleaner and the contaminants am I dragging into my rinses? And how long before my rinses are so dirty that I'm just putting clean parts back into dirty water? So, there's also maintenance you must do on the rinse tanks themselves to ensure your rinses stay. It's not just a cleaner bath, but it's the rinses, too, that you have to do maintenance on.
And you have to do this on an ongoing basis. You can't go for a week and not check your cleaning process line. Another major thing that happens in an aqueous cleaning bath that doesn't happen in the solvent is that in solvent cleaning, the soils dissolve into the solvent. They don't separate, incorporated in aqueous cleaning baths. Soils have basically three things that can happen to them. They can float to the top, sink to the bottom of the tank, or emulsify into the bath.
Those are the three mechanisms or the three things that can be in these soils. If soils float to the bath, if it's that type of soil or that type of cleaner soil system, you have to be able to remove that floating contamination off the tank. So, you may need to skim the tank. You may have to put separator systems to separate the oil. Because what happens if you have an oil sheen or a layer of oil on top of a tank with clean parts underneath it? When you draw them up, they're going to be dirty.
If it's an emulsifying system, it is formulated to hold a certain amount of oil. And once they hit saturation, they're saturated. If you don't remediate the bath or replace part of the bath or all the bath, the oil's going to start splitting. So, there are things we can do. We offer a filtration technology to filter oils out of emulsified cleaner baths. So, splitting and emulsifying oils are mechanical processes that you should consider and put in place to remove the contaminants from the bath, and that makes the bath last longer.
If the soils sink, that's a problem. Those are a lot more difficult to deal with, and there are certain lubricants that are known to sink to the bottom of an aqueous cleaning tank. And historically, those types of lubricants are cleaned and solvent systems. As people try to transition those types of systems to aqueous, they will run into the issue of those types of lubricants sinking to the bottom of the tank. So that's always a big challenge.
Impact on Wastewater Systems
Q: How does aqueous cleaning impact facilities — such as wastewater systems — versus solvent cleaning?
MV: Solvent cleaning is actually greener than aqueous cleaning, and the reason is whether you're doing vapor de-greasing, a lot more people are looking at vacuum de-greasing, constantly recirculating fresh solvent in the system. The most modern de-greasing machines lose very little solvent out of the system. Your waste only comes when that solvent bath finally becomes so saturated with oil that you have to call someone to come in, pump that out, and haul it away.
With aqueous cleaning, every gallon of a cleaner solution eventually becomes a gallon of waste. Because we're dragging the stuff out, it's going into the rinses, so people have two choices. They're either pumping all that spent cleaner solution or dirty rinse water to a waste treatment system and treating that as waste, or they're paying someone to come in and pump all that material out and haul it away.
That's a cost that people don't think about because you can't dump those things down the drain. In many municipalities now, you can't even dump the rinse water down the drain. We have customers who are in areas where they're told specifically they cannot dump. They cannot discharge anything without it being waste-treated.
If you're a facility that doesn't have a waste treatment system, and now all of a sudden, you're generating all this aqueous waste, your two choices are put in a system to treat the waste or pay to have someone haul this material away. And so that's a major added cost, and it's something that people don't think about because if they've been solvent de-greasing, it's been simple.
Someone comes and pumps it out every six months to a year, and outside of that, they really, really don't have to worry about their waste profile. As soon as you become a waste generator, you have to have someone on staff who is licensed to handle waste generation. It adds a lot of complexity. And the days of just dumping things down the drain are over. So, it's getting tighter and tighter. Some of the aqueous chemistries, in particular, are getting the regulations on how much can be discharged tighter and tighter. So, it makes the waste treatment process even more important that they aren't discharging these chemicals. That's where, sometimes, even the rinses can become problematic. If you're discharging too much of a particular — like a phosphate, for example — they keep tightening down these chemistries tighter, so that starts to limit the chemistries that can be used. So, you can see how it builds on itself. It makes things a lot more complex.
Waste is a big consideration if you don't have a system in place already. Now, if you're a big facility and you're already treating waste, then you have to start thinking about what's in these cleaners and how that's going to affect your waste treatment. Is there something in the cleaner that's going to cause me to have a problem? And this is where Robin will come in and ensure that's not a problem they can treat properly. But that also happens all the time. Somebody decides, okay, I'm going to put this cleaner in, and I'm just going to dump the dirty cleaner basket in my waste treatment. Next thing you know, they've got a treatment problem.
If someone's been solving de-greasing and they've been treating other things, and then one day, they decide, oh, it's no big deal. I'm going to dump my cleaner tanks and start treating those, and then all of a sudden, they can't treat the waste anymore. So that's another thing they have to think about: What's in this chemistry that I'm about to dump my waste treatment system, and how will that affect it?
Q: You mentioned equipment earlier and how important it was. What are some considerations when putting in an aqueous system?
MV: It really depends on the parts and throughput. Everybody thinks I'm just promoting solvent cleaning. Hubbard-Hall, in general, we are agnostic to it. But again, one of the things about solvent de-greasing is that the cycle times are much shorter because you're dealing with one chemistry and one black box, so to speak, so your cycle times are short compared to aqueous cleaning. Why? Because I'm literally doing everything in one step. I'm cleaning, rinsing, drying, everything's happening at once. Parts are done.
If you have really high throughput needs and you go from solvent to aqueous, you may need to have a bigger footprint of equipment, or you're typically going to have a bigger footprint of equipment for aqueous de-greasing than you would for solvent de-greasing Because you got to put so many parts through. And we know the throughput will drop because it takes more steps to aqueous clean than it does to solve it clean. We know the time in the process is going to take longer. If it's going to take longer, then I have to have a bigger piece, typically, a bigger piece of equipment.
I work with many different equipment manufacturers, and a lot of novel pieces of equipment are designed specifically for people going from solvent to aqueous cleaning. The equipment guys are doing a good job, but it really depends on throughputs, your biggest thing. And then the second thing is the types of parts. If I'm running a really complex part like this with all the geometries, then I may need a system that flushes parts a lot better and has better rinsing. I may want built-in drying capability so I can flash dry these parts fast and not have corrosion issues. That's the biggest thing: throughput and the types of parts you're running for equipment.
If someone's cleaning, for example, just basic rack parts, they may be able to put in tanks, put in water-based cleaning tanks, put their parts on racks, and go through and not be an issue. But we're seeing more and more that the equipment plays a bigger role in doing this successfully.
Critical Cleaning Considerations
Q: We often hear that solvent is the way to go with critical cleaning. If a plant switches to aqueous, is there a way to test to see if they're still getting that?
MV: The two big areas, of course, are aerospace and medical. They need residue-free cleaning. Aerospace has done aqueous cleaning for years, and there are some processes in place to do that. We're working with a customer now that does parts for Pratt & Whitney for jet engines, and they're moving from solvent to aqueous cleaning. And yet, they have a whole lot of testing, corrosion testing, and residue testing on the surface.
There are a lot of tools available. We have a tool available that we can use to look at contaminants on the surface of parts. But you have to test things like corrosion. The biggest issue for those critical cleaning applications is residues. You can't have residues on the surface. The cleaners themselves can leave residues. You can have the best process line there is and still have residues left behind from the cleaning chemistry. You have to have cleaners that are more residue-free and that are more free-rinsing for those applications, and there are a number of ways. We have some specialized equipment we use to test. Is there anything on the surface that is going to be problematic? And so that's what asking for, is it tells if there's anything left because, in solvent cleaning, you generally have zero residues.
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