Dirt
or soil is an inevitable part of manufacturing or maintaining all sorts
of manufactured objects including parts, components, and product. We
can think of soil as matter out of place. Cleaning is the removal of
soil, the removal of matter which is out of place. Some soils or contaminants
that are deposited on the product originate in the air or from people
involved in the manufacturing process.
On the other hand, many soils originally had a very useful part in the
process; once they have served their purpose, they have to be removed.
How much soil has to be removed depends on down-stream processes
and on required product performance.
Is it a cleaning step?
One unrecognized challenge is to recognize when cleaning is actually
occurring. Sometimes, steps are not referred to as cleaning, because
cleaning is not a particularly classy term. We hear references to surface
preparation (which can mean different things to metal fabricators and
wafer fabricators), deblocking (in optics), depainting, defluxing, vibratory
surface polishing, pickling, or “N” removal (where “N” is
whatever was added to the component at an earlier step). Even art restoration
often involves a component of cleaning; decades of build-up of soils
have to be removed to expose the colors, textures, and surface finish
that the artist originally intended. Sometimes, steps in the cleaning
processes that are not specifically thought of as cleaning may actually
contribute to soil removal. For example, rinsing an aqueous (water-based)
cleaning agent can act as a cleaning step for inorganic, polar materials
such as minerals. Sometimes, one organic (carbon-based) cleaning agent
that evaporates rapidly (for example, isopropyl alcohol or acetone) is
used as a rinsing or drying agent for another solvent with a high boiling
point (such as a soy-based or orange terpene cleaner). Rinsing and drying
agents may themselves contribute to cleanliness.
It’s very important to recognize these steps which are actually
cleaning by another name, because sometimes, when they are eliminated
or even modified, and unexpected soils are left on the part, and product
quality is compromised.
Examples of soils
Some examples of soils are indicated below. Defining a soil depends on
the situation. Very often, water is benign or even beneficial. Where
corrosion is an issue, residual water can be a problem. In some refrigeration
applications, even a trace of water can be devastating to product performance.
In the same way, sometimes, organic solvents can evaporate or out-gas
from the product with undesirable results; this is a particular problem
where the product contains or operates in an enclosed space. Whatever
the source, the challenge in cleaning is to remove the soils without
harming the worker, the environment, the digestive system of your group’s
accountant, or the product itself.
General and Precision Cleaning
Finally, people often try to distinguish between general cleaning and
precision or critical cleaning cleaning. Some say that precision cleaning
is cleaning objects that already look pretty clean (C. LeBlanc). Others,
try to relate the type of cleaning to the cost or the potential critical
application of the product. We think the terms form a continuum. In a
sense, all cleaning which might impact the bottom line is precision or
critical cleaning. You are the best judge of how critical your process
is. Whether you are working in a cleanroom or a shop, you may be doing
precision cleaning.
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