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Cleaning: Different Methods for Different Needs

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Back in the late 1800s, the director of the U.S. Patent Office was said to remark “Everything that can be invented has been invented.” Charles Duell, U.S. Patent Commissioner in 1899 reportedly told the President of the United States that there was no more innovation and, therefore, no more need for the patent office.

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Except he didn’t. Although often quoted as one of those “stupid things that come back to haunt you,” episodes, this ridiculous comment never actually happened.

It’s just like that guy who claims “there’s only one way to clean an engine.” We all know a buddy who has a friend who heard from a cousin about this shop owner who believes that one method of cleaning is good for all the parts that come through his door. Pure and simple, it’s not true.

Because of the range of materials used in today’s engines, the restrictions placed on shop owners by local and federal governments and the rapid pace of development in cleaning technology, there is more variety than ever in the products available to clean engine parts. Consequently, there are more questions than ever, too, about what’s best for certain situations.

Strangely, perhaps, despite the advances in technology, it is estimated that up to 70 percent of shops use a manual cleaning system to hand clean engine components. This may seem slow and tedious to some, especially in the face of the rapid change in the machining industry, but it’s often necessary quality control in order to remove all of the hidden particles that can cause damage to an engine and eventually lead to a comeback. Plus, it allows you to see what you are cleaning and to inspect for any other damage or debris that may exist.

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To achieve the excellence for which you strive and your customers demand, there are a variety of cleaning methods employed by today’s engine building/rebuilding facility.

We are all familiar with the solvent cleaning systems that have been around for decades. These systems use a certain volume of chemical in which the part is either soaked or sprayed by a nozzle at low pressure. These systems, though not as prevalent as they used to be as newer environmentally friendly systems have become the norm, reinforce the fact that the need for manually cleaning parts has not gone away.

Heat Cleaning

Engine builders have used ovens to clean cast iron components for years. One of the biggest reasons for using a thermal cleaning system is that it’s relatively simple: a technician can put the piece in the oven and walk away for a while until it’s done baking. Then he takes the work piece out of the oven and puts it into the airless shot blaster and walks away again.

Thermal systems also produce a work piece that looks more aesthetically pleasing than with some other systems.

However, the use of aluminum has led to concerns about heat ruining the component. Cast iron is not as susceptible to heat damage as aluminum, so it can run through an oven cycle for longer without losing its strength. But some engine builders have the perception that using an oven to clean aluminum is unsafe. According to our experts this is a common misconception in the industry. You can safely clean aluminum with the oven method but it requires careful attention to temperature and procedures.

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Essentially what happens when you clean cast iron is the material has a tendency to adhere to the shot itself. In so doing, the shot will become coated by the cast iron piece you just cleaned. So when you introduce an aluminum component to the airless shot blaster after a cast iron piece has just been cleaned, the cast iron particles will smear or transfer onto the aluminum piece, causing it to become discolored. In addition, this will aesthetically challenge the end result.

The key to thermal cleaning – especially with aluminum parts, say experts – is to dry the oil and sludge to a dried ash state. There are various ways to do this and each manufacturer has its own unique system of heating the components. One way to do this is with an indirect heat as opposed to direct heat.

This is called a convection process and involves swirling the hot air around in the oven. It generally heats the component much quicker than conventional oven heating methods. The advantage to having this type of heating element is that the component is brought up to temperature more evenly, which our experts say is safer for aluminum. There are no temperature spikes, which may cause parts of the component to lose strength.

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Compared to aluminum, our experts say cast iron can be cleaned much quicker and with higher temperatures because there is not the same concern with annealing that you have with aluminum. Without a metallurgical lab, though, it may be difficult to tell what composites and heat treatments are involved with today’s aluminum components. Therefore some experts believe it is better to stay on the safe side of temperature and time exposure unless you’re certain the aluminum component can handle it.

Heat cleaning aluminum may take extra time and care compared to cast iron, but that doesn’t mean you can be carefree about cleaning cast iron. Attention still needs to be paid to proper procedures.

Blasting

Sometimes the only way to get a part clean is by using a manually operated blasting media to remove stubborn oils and hard, baked-on carbons. Manually operated blast systems such as a glass bead machine, for example, direct a high-pressure stream of glass media at the surface of the part. Bead media produces an attractive but it can be difficult to completely remove afterwards in some cases

You must be sure that you don’t leave anything behind in the cleaning process. Certain types of media are more prone to lodging in a cavity than others. Glass bead and steel shot (especially shapes that are more jagged) can become lodged in very tight, hidden areas and require extra attention to get them out. In addition, you may have to mask the area off to keep the media from getting in.

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Another note of caution with using a media blaster is that you may damage aluminum surfaces of by moving the metal, affecting tolerances or changing the texture of the surface.

One form of media that does neither of these is soda media. This media is essentially made from a form of baking soda. It is considered a “one pass” product. This means that it can only be used once and cannot be recycled, but it still can be efficient and affordable for shops.

Experts say soda is the softest of all media: it is rated at 2.5 on the Mohs hardness scale: plastic is 3.5, glass is 5-6, sand is 7 and aluminum oxide is 9. The soda media also comes in a variety of sizes to suit your particular cleaning situation. Yet even though it is soft, it is quite effective on aluminum.

It can remove carbon without damaging the aluminum and is completely water-soluble. This gives the peace of mind of knowing potentially damaging media won’t be left behind in oil galleys, water jackets, boltholes or other blind areas.

Because there is no need to prewash the aluminum or do extensive rinsing as with other types of blast media, soda blasting can save time for the rebuilder because you can clean in one step without damaging the substrate.

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However, because the soda media fractures upon impact, it can be dusty in the blasting cabinet, and the operator’s view of the in-process part may be obscured. New ventilation technology improves visibility inside the cabinet so the operator can monitor the blast process in progress rather than having to stop, let the chamber clear, and sometimes even open the door to check the part.

Wet Slurry Blasting

The aerospace industry uses a lot of aluminum components and other more exotic metals, so it is imperative to clean these components without damaging them, and to inspect for further damage. One system that has been introduced to the automotive industry is a wet slurry blaster which basically mixes water and an abrasive media together into one solution in a sump, which then sends the mixed solution to the nozzle.

The slurry solution can be either used in a manually operated blast cabinet or in an automated system with multiple nozzles. A more scaled down system has been introduced into the automotive industry, but it can be quite expensive and probably out of reach for most two man shops. However, with the amount of aluminum components in today’s engines, a wet slurry system may be a more attractive option for some of the larger production shops.

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Unlike a sandblast or dry-blast process that strikes the part once and ricochets away, the slurry scrubs the components clean. Because the water surrounds the media it protects it from becoming embedded in the surface itself. The system can do extremely fine cleaning as well as remove scale, carbon buildup and get into all the nooks and crannies. The system can also handle parts with oil and grease on them, eliminating the traditional steps of washing and drying the parts before putting them into a dry blast cabinet. With a wet slurry system you can do that all in one process.

One of the advantages wet slurry blasting has provided to the aerospace industry is its capability for exposing very fine cracks in a casting. Blasting a casting with a traditional media blaster might actually push the top edges of a microscopic crack together, making it impossible to see even with magnetic particle inspection. With slurry blasting the water gets in there and it will actually clean out that crack, leaving it exposed for inspection.

You still must rinse and thoroughly inspect the part afterwards to be sure all the abrasive media has been removed. One manufacturer says it is addressing this problem by adding a secondary rinse system, which will be tied to the machine as part of the filtration package. It’s a closed-loop system that includes a filter to separate the oil and waste.

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Jet Spray Washers

Today’s jet washers have evolved from little more than a dishwasher to a complete cleaning solution. Manufacturers 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 and rust-inhibiting solutions for use on ferrous 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.

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Some of the keys to remember when cleaning aluminum or any other metal in a jet spray washer is the importance of good heat. For water-based systems to clean effectively, they usually need heat. The recommended temperature range will vary according to the type of equipment and chemicals used, and may range from 105° up to 190° F. If the water temperature is too hot, though, water loss due to evaporation may become a problem requiring more make-up water to maintain the cleaning solution. 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.

Ultrasonic

Ultrasonic sound waves produced under water have been found to be an effective way to clean many automotive components, especially areas where it is difficult to reach with mechanical devices on complex parts such as automatic transmission parts. When sound wave vibrations rise above a frequency audible for humans (above 18 Kilohertz) in a chemical solution bath, the results are a high vacuum and high-pressure area at any given point in the solution as sound waves pass. The vacuum creates what is called cavitation, an air bubble that implodes, resulting in high-pressure shock waves that, in turn, do all the work of scrubbing the component free from contaminants. Ultrasonic cleaning systems work very well on baked-on carbons and oils and are particularly effective at cleaning blind holes and complex parts.

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According to various sources, ultrasonic parts washers will do as good of job cleaning the external surfaces as bead media without damaging ports and other critical surfaces. Ultrasonic cleaning also offers the convenience of being an automatic process: you can throw the part in, turn it on, and walk away to do something else.

According to manufacturers of ultrasonic systems, a combination of cleaning steps works best: many engine builders are using jet spray washers to pre-wash aluminum parts to get the heavy grease off and then using the ultrasonic system to do the precision cleaning.

Ultrasonic cleaning works well because you’re not using a high impact force to do the cleaning, so you’re not changing the tolerances of the aluminum.

Engine builders should review their cleaning procedures periodically to make sure they are working well and there is no debris left behind. You may find that you can save money or time or both by changing equipment, media or chemicals. But you must recognize the solution must fit the need.

Cleaning today’s bimetal engines creates special challenges for engine builders because of the difference compoonets used. 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 what you’re cleaning.

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There is an effective cleaning method out there for each of your shop operations – however, reports of a “one-size fits all” solution are, thus far, just an urban legend.To achieve the excellence for which you strive and your customers demand, there are a variety of cleaning methods employed by today
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