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Cleaning Aluminum: What Are The Options?

By Brendan Baker

Engine rebuilding may be your career, but component cleaning may be one of your biggest jobs. Ever since the earliest days when engine builders had only a hot tank and a solvent sink to clean their parts they have been looking for better methods to get parts clean. Back then, most parts were cast iron and steel. Today aluminum heads represent a growing proportion of many shops' businesses. However, aluminum presents unique cleaning challenges to the rebuilder for many reasons and the equipment to clean older parts was not designed to handle today's alloys. The various composites inherent in aluminum make it more difficult to clean if you rely on cast iron cleaning methods.

One of the biggest issues surrounding aluminum cleaning is how to get it clean with as little involvement from your personnel as possible? This month, we will look at different methods of cleaning aluminum and talk to engine builders about what they use and what works for them.

Keep in mind that every shop is unique. One method of cleaning aluminum may work great for one shop and not at all for another. A small one-man shop is obviously going to have vastly different resources and priorities than a large remanufacturer. We are not endorsing or promoting any particular method of cleaning over another. No matter what system you use, finding something that works for you is the key.

Some rebuilders have been struggling to find effective ways to clean aluminum for years.

For Ault & James Engine Rebuilders, Dayton, OH, the volume of aluminum has become quite significant over the past few years. At least half of the heads Jerry Ault rebuilds are aluminum. While cylinder head work is not his primary business - his shop does build a lot of long blocks - he does sell heads individually. And the majority of the heads Ault sells individually are aluminum, too.

"We've tried cleaning aluminum several different ways, including the thermal method and it didn't really work for us," explains Jerry Ault.

"We faced so much shot retention that we ended up spending as many man-hours trying to clean up the piece afterwards as we did cleaning it."

Ault says he prefers to clean aluminum the old fashioned way: by dipping the part in a hot tank chemical bath and then removing whatever doesn't come off there using a glass bead machine. "It's less time consuming for us," says Ault. "And you don't have to spend a lot of time masking or blocking off passages to keep shot out. Of course, you still have deal with retention of glass bead, but it's the method that works for us."

According to rebuilders we spoke with, there's no shortcut to cleaning aluminum. "I've looked fairly hard over the last 10 years to find a better, faster way for our shop to clean aluminum and there's really nothing I've found that's better than the way we've been doing it," says Ault.

Put Some Heat In It
Using an oven to clean aluminum can be done successfully according to experts, but you must use plenty of caution when it comes to temperature. Aluminum will anneal at high temperatures and long exposure to high heat.

One of the keys to cleaning aluminum with a thermal system is to dry the oil deposits to a dried ash state. Some manufacturers offer ovens that use indirect flame in a convection process. Convection is considered a safe way to clean aluminum because it's an indirect flame that basically stirs hot air around the part, uniformly heating the aluminum so there's less chance of annealing the part.

According to some experts there is a lot of misinformation about what can and can't be done when it comes to heating aluminum. There are a couple of ways that aluminum becomes annealed. One way is if the aluminum part reaches 600° F or more for at least one minute. Another way is if the aluminum is exposed to 450° F temperature for two hours or more. However, some of the engine builders we spoke to said that they just aren't comfortable heating aluminum to temperatures higher than 300° F, which at that temperature may not dry the oil deposits completely. Most thermal ovens only reach peak temperature for the last few minutes of the cleaning cycle, and therefore annealing shouldn't be an issue.

"We've tried to use ovens sparingly," explains Scott Murray, Murray's Auto Parts, Lancaster, OH. "The biggest thing we worry about is some of these aluminum heads (like GM) that use a Styrofoam-alloy casting. I made the mistake once of putting one of these heads in an oven. It didn't leak when we put it in but it sure did when it came out! So we watch what we do with an oven."

One engine builder says that he worries about guides and seats coming loose in an oven, as well as the issue with shot retention. It really comes down to what an engine builder is most comfortable with. The advantage of using the thermal process is that it's a hands-off process. You put it in and walk away. And if you're careful with how you heat the aluminum, an oven will clean as well as anything else. Cosmetically, aluminum cleaned in an oven combined with an airless shot blaster will produce the best looking finish.

Jet Spray Washers and Hot Tanks
A jet spray washer remains one of the most integral steps in cleaning aluminum. Whether you use it for your complete cleaning solution or just for a final rinse off after you've done another process, it plays a vital role in today's shops.

One of the keys to cleaning with a jet spray washer is to make sure you have enough temperature in the tank. If you don't heat the chemical up enough it won't clean as well as it should. Manufacturers recommend temperatures of around 170°-180° F, and say that anything below that causes you to waste energy. If you heat the chemical bath too much the water will evaporate too quickly and you'll use more chemical than you really need. Some manufacturers offer digital controls to monitor temperature, and new high impact nozzle designs help make jet spray washers more efficient than ever.

"We clean all of our aluminum with a jet spray washer," says Murray. "We crank up the temperature and make sure the chemical is 'juiced up' to where it's supposed to be so we get most of the dirt and oil off."

Murray, like others we interviewed, also uses a glass bead machine for removing hard carbon deposits. "If we need to we will touch up with a glass bead machine, but we're able to get most of the heads clean with just the jet spray washer. We try to stay away from using the glass bead machine as much as we can. The biggest issue we're concerned about is that there are so many blind holes in today's aluminum heads. So glass beading is our last resort because I think it's difficult to get all the glass out if you get into any of the blind passages," says Murray.

Aluminum-Safe Chemicals
Because aluminum builds a protective coating when exposed to water, called an oxide, the oxide has to be torn down with a caustic chemical. Most aluminum-safe chemicals today contain inhibitors to protect the aluminum from oxidization, which turns it black.

Some chemical manufacturers recommend that engine builders use a chemical with a high pH so they can clean heavy contaminants and still protect the aluminum surface. A high pH solution has another benefit in that it enables shops to clean all types of metal with the same chemical solution.

"Basically, we just use the jet spray washer and rinse everything very well," Murray explains. "We also use an aluminum safe chemical that works very well. I don't worry about the cosmetics of the aluminum because my customers usually just want it fast. Speed is everything for us."

Soda Blasters
Experts and veteran users say some types of blast media are not very well suited for use on aluminum because it can become trapped in oil galleys or other hidden crevices making it difficult to remove. Soda blast media is water-soluble and therefore can be used at full strength without worrying about how to get it out. Soda media is actually made from a form of baking soda, called sodium bicarbonate. It is not a recyclable product so it can only be used one time.

"We get a lot of cylinder heads, especially Asian overhead cam heads, that are notorious for caked-on, baked-on sludge," says Mark Daniels, Precision Machine Service, Jacksonville, FL. "That's part of the challenge of cleaning aluminum: trying to get those deposits off without wasting a whole lot of time doing it."

According to Daniels, the soda blaster makes pre-washing unnecessary. "We're able to clean the oily, gooey stuff off with no problem. Of course, the less you pre-wash the more soda you will use," he acknowledges.

"We're not using the soda blaster to clean the entire head," explains Daniels. "We just want it for cleaning the hard to reach areas and the places that have the heaviest deposits, and leave the rest of the cylinder head for our normal cleaning routine.

By minimizing how much he uses the soda blaster Daniels is able to keep the cost down. "It's about $25 for a 40 lb bag, so if you let it get away from you it can offset what you're saving on labor," says Daniels.

Ultrasonic Machines
Another tool in his arsenal to clean aluminum is the ultrasonic machine. Some engine builders use an ultrasonic machine to remove shot or glass bead, feeling it is a good way to make sure they've removed all of the oil and shot before putting the part into a final wash.

An ultrasonic machine works by creating tiny vacuum bubbles. The vacuum pulls the dirt inside the bubble and away from the part. The bubbles implode, which in turn creates a small vortex and pulls everything in its path into it.

"Our ultrasonic machine made a big difference in what we were able to accomplish, cleaning-wise," says Daniels. "We've had it for several years now and it works great for us. Usually after the soda blaster we put the aluminum part in the ultrasonic machine. Heavy deposits don't come off well in the ultrasonic machine, so we use our hot tank to pre-wash and then hit it a little with the soda blaster to get the heavy deposits off. We use the ultrasonic machine for the lighter deposits and to get in areas that we can't get with the soda blaster."

A Multi-Level Approach
Equipment costs money and not all shops can afford to purchase several different cleaning systems. But for shops that can justify the expense, it can be well worth it. By using a multi-level approach to clean aluminum, you can cut down on the labor involved with some other systems.

"We use a multi-faceted approach on aluminum mainly to reduce the input with our techs as much as possible," says Daniels. "We start off with an aluminum-safe chemical in a hot tank and the we use a combination of ultrasonic machines and/or soda blasting. The type of equipment we use really depends on how heavy the deposits are and where. If the deposits are in hard to reach areas, then the soda blaster is a better choice because it can get into areas that you used to have to scrape and pick by hand."

Daniels says he uses the soda blast machine for the heavier deposits and then he switches to the ultrasonic machine for a finish wash before using the spray washer for the final rinse.

"The combination of ultrasonic and soda blasting works pretty well at cutting down the actual contact time with our technicians. Cleaning aluminum has always been a bit difficult for everyone in the industry. It eats up a lot of our time trying to get parts clean, so we're trying this new system to try and reduce our labor."

How has his approach worked? According to Daniels he has seen some savings in time and operator involvement. "We're still pretty early on with our new system incorporating the soda blaster," says Daniels. "We've only been using it for about six months to a year. It seems to be yielding some of the best results of anything we've used as far as cutting down on labor and getting into heavier deposits and areas that are hard to reach."

Aluminum cleaning is a big part of what machine shops do these days. There is still plenty of cast iron work around but it is becoming less frequent. Some shops still run two systems for cleaning cast iron and aluminum, and others prefer thermal cleaning, but mainly for cast iron. It is all a matter of what works best for your own situation. The best way to clean aluminum seems to be a combination of several systems. However, having four or five different machines to clean aluminum may not be feasible for all shops. The important thing to remember is: however you clean, you want the best result with the least amount of fuss.