Print

Email

Making Dollars and Sense Cleaning Blocks, Heads

Page 2 of 2


Because aluminum is a much softer metal than cast iron, cleaning techniques and media that are used on cast iron may be overly aggressive on aluminum. Likewise, a softer media that doesn’t etch or remove metal on aluminum parts may not be aggressive enough if used to remove carbon and rust on iron castings.

The 650 to 750 degrees in a thermal cleaning oven are no problem for cast iron heads and blocks. These high temperatures can quickly turn greasy deposits into ash, which can later be removed by a variety of methods. But aluminum can anneal (soften) if it is subjected to 500 degrees F or higher for more than an hour or two.

These high temperatures inside a cleaning oven can loosen the seats and valve guides in aluminum heads – not a big deal if they’re being replaced anyway, but a concern if they’re still in good shape. For this reason, the temperature inside a cleaning oven must be limited if aluminum heads and blocks are being cleaned.

Hard carbon deposits in the combustion chambers and exhaust ports are probably the most difficult contaminants to remove. Chemical solvents can soften and remove carbon deposits, but as said, can’t be used universally. If a solvent cannot be used, some type of media blasting may be necessary to dislodge heavy carbon deposits. Combining the scrubbing action of ultrasonics with water-based cleaners can also provide an effective means of removing hard carbon deposits.

Restoring a Like-New Finish
Restoring a like-new appearance to aluminum heads, blocks and other parts can be a challenge because aluminum stains and discolors rather easily. While an oxide that forms on the surface of the metal as soon as it is exposed to air protects the metal against further corrosion (meaning aluminum does not have to be painted), certain chemicals may, over time, dull the finish or even turn it black.

Dry blasting aluminum with glass beads, aluminum oxide grit or steel shot (stainless works well but is expensive), can remove discoloration. But this requires an additional cleaning step to make sure no beads, grit or shot are left behind in any of the nooks and crannies of the casting.

Masking off the valve guide and cooling jacket openings prior to bead or grit blasting can reduce the risk of media being retained (but adds still another step). Bead, grit or shot blasting removes metal and etches the surface, giving the casting a matte and slightly dull appearance.

Depending on what your customer wants (or expects), this may require yet another step in the refinishing process if you have to spray the casting with aluminum or silver paint.

An alternative approach to cleaning aluminum and restoring a like-new appearance is to use baking soda media with either a wet or dry blast process. The advantages of baking soda compared to other blast media is that it is relatively soft, inexpensive and is water soluble (which distinguishes it from other soft media such as plastic beads or walnut shells).

Baking soda does not require a prewash, which can save time and labor and is a very effective cleaning agent that can blast away hard carbon deposits without damaging the metal underneath.

When dry baking soda hits the surface of the metal, it fractures as it knocks loose the surface contaminants. This creates a lot of dust, which must be contained and filtered within a blast cleaning cabinet. But there are no hard particles left behind to cause problems later on. The residual dust can be rinsed off the part with water, leaving a clean, bright surface that looks like a new casting.

When wet blasting, baking soda (or other media) is mixed with water it forms a slurry. The slurry is then mixed with air and directed at the part. The design of the nozzles, air flow and slurry mixture all affect the cleaning action and effectiveness of the slurry. In some cases, a small amount of aluminum oxide can be mixed in with the baking soda to create a more aggressive cleaning action.

The main advantage with wet blasting is that, as a closed-loop process, it eliminates the dust. The cleaning cabinet does not have to be located in a separate area to keep dust away from other machining or assembly operations in the shop – which can save time and labor depending on how the work flow is organized and positioned.

In addition, it dramatically reduces the amount of product used. A manufacturer of wet blasting equipment says that  by recirculating the media through its machine (including filtering before reuse) baking soda can be reused 5 to 6 times before it breaks down and goes out of filtration. The conservative estimate is that consumption is 25 percent that of the same media in a dry blasting environment.

Another cleaning process that works well on both aluminum and cast iron is ultrasonic cleaning. Adding an ultrasonic transducer to a hot tank multiplies its cleaning effectiveness. According to one manufacturer,  a heated tank equipped with both agitation and ultrasonics works – if not miracles – extremely well.

The transducer generates high frequency sound waves that bounce back and forth throughout the cleaning solution.

This creates tiny bubbles that implode against the surface of the metal, knocking loose and scrubbing away any contaminants on the metal. The ultrasonic bubbles work with the cleaning detergent and hot water to break the soil bond and the agitation sweeps the soil away.

Filtration devices trap particulates and surface sparge to clear floating soils prior to the removal of the cleaned parts.

The main advantage of ultrasonics is that the cleaning action reaches into hidden areas of the casting such as blind holes, crevices and internal passageways. It does an excellent job removing most contaminants, and it does not etch the metal.

Although one of the knocks on ultrasonic systems has been the method’s relative inefficiency on heavy soils, manufacturers say better living (or at least working) through chemistry is possible. Aqueous cleaners can be diluted as needed, depending on how heavy the soil that is being removed.

In addition, citric cleaners can also be effective in certain cleaning operations, as can sodium hydroxide cleaners (or rust strippers) for ferrous substrates (however, not for use on aluminum).

Environmentally friendly, non-toxic rust absorbing solutions that work through a process called “selective chelation” can actually remove rust from cast iron with little or no effort on your part. The active ingredient in the solution bonds to the iron in iron oxide (rust) but is too weak to remove iron from steel.

Once the chelating agent has removed the iron, a sulfur-bearing organic molecule pulls the iron away and forms a ferric sulfate complex, which remains water soluble.

Keeping Things Clean
Once dirt is removed, you don’t have to worry about it – at least for  awhile. Not so when it comes to rust. When a water-based cleaning process is used, some type of corrosion inhibitor should always be added to the solution to prevent rust from reappearing after the parts have been cleaned.

In most cases, iron heads and blocks will be painted or powder coated after they have been cleaned and machined. But if iron castings will be stored for some time prior to painting, and rust is a concern (especially in damp climates), sealing the parts inside plastic bags that have been treated with special rust inhibiting chemicals can preserve their appearance.

The air-tight bag seals out oxygen and moisture, while the chemicals inside form a barrier on the metal surface that inhibits oxidation.