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Cleaning Aluminum

Knowledge about the best ways to clean aluminum has come a long way since the first wave of used aluminum parts began to show up at the doors of rebuilding shops.

By Tom Glover

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"Ten years ago, when there wasn’t that much aluminum, people were scared," said Mike Wigert, sales manager of spraywasher manufacturer LS Industries. "They didn’t know how to regulate their ovens, they didn’t know which chemicals to use, and they were tarnishing their aluminum parts, and probably ended up hand cleaning a lot of them," he said.

Cleaning used automotive parts was a lot more straightforward back in the days when cast iron parts were the rule rather than the exception. Aside from the fact that petroleum-based solvents were the cleaning fluids of choice, engine bearings were softer and the oil was thicker. So while cleaning up an engine block or cylinder head prior to using it as a rebuilt engine component was important, it didn’t take on the critical aspect that it does today.

"Engine tolerances and clearances between bearings, pistons and cylinder walls is way less today, and it’s an absolute death knell for an engine to have dirt in it," said Lyle Haley, sales manager at Peterson Machine Tool in Shawnee Mission, KS. Dick Schaffner, owner of Aluminum Head Services in Belton, MO, puts an historical perspective on it. "In the 1940s, they didn’t even put oil filters on cars; look at where engine technology is today," he commented.

Although there are some interesting new methods being tried – bio-remediation comes to mind – the basic technology that the great majority of rebuilders use to clean parts, which are increasingly aluminum, still centers around heating, washing and blasting. Shops we talked to are all over the map about which combination of these three they use. Not surprisingly, the manufacturers of the machines that heat, spray and blast aluminum parts are also all over the map about why their methods are superior.

Cleaning aluminum parts is more time consuming on several levels. John Edie, a service technician at oven maker Winona Van Norman of Black River Falls, WI, pointed out that a cast iron version of a part can be cleaned in a 650°-700° F oven in a period of 20 to 30 minutes, whereas the same part in aluminum needs four to five hours at 350°-400° F.

But a comparatively longer time in the oven is not the only consideration. Peterson Machine Tool makes both spray washers and parts ovens. "I’m a strong advocate of heat cleaning aluminum, even though it takes longer to do it because you can’t use higher temperatures," Peterson’s Lyle Haley said. "Our experience is that you can safely clean aluminum in 500° F, but beyond that, you’re going to soften or anneal it," He also acknowledged that the time factor to heat clean aluminum is seen by some as a problem.

"Thermal cleaning, if you do it properly, isn’t really quick. But even though a cylinder head, for example, may spend more time in a rebuilder’s place of business, thermal cleaning reduces the number of man hours needed to get it clean," he observed, referring to the labor involved in loading and unloading parts from a spray washer and/or a glass beading machine.

Ric Havel, a consultant to Sunnen Products Company, acts as a spokesperson for Sunnen’s line of metal cleaning machines, which run the gamut from spray washers to ovens to airless blasters. But Havel favors thermal cleaning followed by airless blasting, as the preferred way to go for several reasons, one of them being energy efficiency. "An oven takes the primary source of energy, whether that be electric, natural gas, L.P. or fuel oil, and applies it directly to the cleaning job," he pointed out. Other machines take the energy constituents and utilize them to heat a liquid that’s being driven by an electric pump, where the liquid loses it’s heat within moments after it’s sprayed, and needs to constantly draw more energy to keep it hot."

Thermal cleaning alone is not common, primarily because its function is to drive the liquids out of the oils and greases that are on used automobile components. What’s left is usually easy to knock off through some mechanical means. Depending on what the part is, this takes the form of spray washing, and/or blasting with glass beads, plastic beads or steel shot. Occasionally all three methods – heating, washing and blasting, are employed.

Some rebuilders, like Grooms Engines of Nashville, TN, skip the spray wash cleaning sequence altogether. "We bake our aluminum components in an oven at 440° F for eight hours. Then we glass bead them in a "pressure pot" type of beading cabinet, which gives them a very saleable look," said Groom’s vice president, Doug Anderson. "But no washing," he said. "We used to put them in a jet spray booth with a silicone-based soap before glass beading the parts, but we found that doing that just increased the chance of trapping glass beads."

Anderson later said that he does use a spray washer on aluminum parts as a final rinse, but spray washing is not a part of the heavy-duty cleaning process. He feels that the effectiveness of the "pressure pot" type of glass bead machine (as opposed to machines that siphon the beads into the air stream) is a large part of the reason his company has been able to bypass a spray wash cleaning cycle for aluminum parts. "The siphon technology uses a considerable amount of air to create the siphon, so the impact of the glass bead on the part is reduced accordingly," he said. "The net result is that with a pressure pot type of machine, you can clean a head in about half the time."

Aluminum parts are more typically blasted with glass beads or plastic beads than with some other metal. But like everything else in this business, hard and fast rules don’t apply, and there are always manufacturers or users promoting products that overcome the common obstacles.

Sunnen Products’ Havel, for example, pointed out that Sunnen has gone to great lengths to develop a steel media that’s aggressive enough to clean iron, but not overly aggressive to the point that it harms aluminum. He calls it the most copied media in the industry, and claims that its service life is superior to other blast media.

"It’s a stainless steel media, but unlike stainless steel shot or cast steel, which is created through a refractory process, our stainless media is cut on a diagonal from wrought stainless wire," explained Havel. "Wrought stainless has no porosity, so it won’t trap oxide from the iron parts, which can cross-contaminate the aluminum parts," he said. "What’s more, it’s not brittle, so it doesn’t break down as fast. It gives the shop years of useful life, rather than months, without reclamation."

For those that do make spray washers a part of their aluminum parts washing strategy, one question that often comes up is whether to use a different wash solution on aluminum than is used with cast iron.

It’s almost a given that the old petroleum-based solvents are on their way out of most shops, if they haven’t already been banned from the premises. Instead, an aqueous or water-based solution is added to water. A typical concentration would be four to 12-ounces of a chemical mixture per gallon of water to make the water more effective in breaking down petroleum residue, flushing out complex cavities and, in general, cleaning more effectively.

In the not so distant past, when just about everything that got loaded into a spray washer was ferrous, the chemicals added to the water contained a strong concentration of caustic soda, with a pH of around 13.5. But that’s had to change with the increasing use of aluminum parts, which the caustic soda tends to etch and corrode. Consequently, one of the biggest pitfalls in cleaning aluminum is making sure the chemical formulation you’re using is "aluminum safe."

A spokesman for Memphis-based International Chemical Corporation, a manufacturer of chemical formulations used in spray washers, reported that very few shops opt to have two separate cleaning systems – one for aluminum and one for iron and steel parts – although that would seem to be a more efficient strategy. Most of his customers, he said, use dual-purpose cleaners that work reasonably well on cast iron, and do a good job on aluminum. To overcome some of the drawbacks inherent in using a less aggressive chemical on aluminum parts, some spray washer cabinet makers, such as AXE Equipment in Council Grove, KS, urge their customers to begin by soaking parts in the spry wash liquid before loading them into the spray wash cabinet.