Click on a thumbnail to see the full-size image
Newer techniques allow the use of water with vari...
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
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
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.
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
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.
Page 2 of 2