Clean and Machine Aluminum by Combining Processes By Doug Kaufman Steel may still be the big dog when it comes to the content of the world’s motor vehicles, but aluminum usage in cars and trucks continues to increase. Fueled by the desire to save weight, time and energy, aluminum is gaining ground with manu- facturers of parts and components. How does the use of aluminum in today’s engine components impact today’s engine builder/rebuilder? It’s certainly not a foreign material but understanding its properties makes good business sense. Cleaning aluminum creates special challenges for engine builders because of its corrosiveness and soft metal prop- erties. There are several effective ways to clean this non-ferrous metal but there is no magic solution. You will more than likely have to combine several processes to get the kind of clean that you demand. The methods that will work best will depend on the volume of aluminum youre cleaning. Jet Spray Washers Today’s jet washers have evolved from little more than a dishwasher to a complete cleaning solution. Manu- facturers have improved turntables, nozzle systems, pumps and _ heating systems, and jet spray washers are often the starting point for cleaning aluminum in many shops. The chemical makers have stepped up, too, offering aluminum-safe alkaline soaps. Some of the keys to remember when cleaning aluminum or any other metal in a jet spray washer is the importance of good heat. Too low a temperature may mean incomplete washing—and wasted electricity. For this reason many manufacturers have incorporated digital thermal controllers to monitor the washer’s temperature. In addition, some new machines have improved spray nozzles to deliver uniform high pressure along the entire nozzle profile. The manufacturers of jet spray and other aqueous equipment agree that the physical properties of cleaning are the same whether it is aluminum or cast iron. The biggest difference with cleaning aluminum is in the type of chemical you use. Cleaning aluminum with aqueous requires using a compatible chemical that won’t etch or discolor the metal. Aluminum builds an oxide on it and that oxide has to be torn down chemically with a caustic agent. Most manufac- turers offer a variety of chemicals for cleaning aluminum and other metals, so you should always consult your chemi- cal supplier to decide what is best for your shop. The type of chemical you use depends on various factors like how many parts you clean, what equipment you have (and how many units), what type of metals are cleaned primarily and how dirty are the parts. While aluminum often turns black when exposed to caustic chemicals, this coloration is just oxidation, which can be removed by a de-oxidizer, returning the metal to its attractive uni- form aluminum surface. Some chemical suppliers say a mod- erate to high pH (around 12 pH) is safe for aluminum and when combined with a caustic and oxidation inhibitor, can be a very effective solution to cleaning bimetal components. It’s possible to squeeze out as much cleaning power and still inhibit the attack on aluminum so that you can clean mixed metals without having to run two systems. Formulations are available that are very safe on aluminum surface and will provide a clean, bright aluminum surface but without brighteners in them. There are mixes of phosphoric and nitric acids or phosphoric and hydrofluoric acid— there’s usually an acid mix that goes beyond straight phosphoric to actually bring out brightness in aluminum. There are three types of aqueous chemicals that an engine builder needs to be aware of: 1) high caustic products that are safe on ferrous alloys only; 2) silicated, higher pH products that are multi-metal safe and provide the most cleaning and protection for aluminum; and 3) non-silicated products, which are used mainly in precision cleaning processes. It is aluminum compatible and thoroughly rinseable but may cause some discoloration of the aluminum. Thermal Cleaning Heat cleaning is an effective way to clean aluminum but you should err on the side of caution when it comes to the factors of time and temperature. Many aluminum heads are made from a composite of alloys. Unless you have access to a metallurgical lab it may be impossible to know exactly what its composition is. The key to thermal cleaning, espe- cially with aluminum parts, is having the ability to dry oil deposits to a dried ash state. One way to do this is by using indirect flame—in other words a non- contact, convection process. In this process, a flame heats the air, which flows around the part. This is safer for aluminum because the lack of direct flame eliminates the possibility of temperature spikes, which can cause annealing of the surface, where the aluminum loses some of its hardness. Therefore, keeping temperatures in check is critical with aluminum parts. Media Blasters For baked-on carbons, sometimes the only way to remove it is to blast it off with some sort of bead media. Bea