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In recent years, the complexity
of engineering decisions surrounding threaded fasteners has
heightened. The defining criteria for finishes have shifted
to include not only functionality and corrosion protection
but also environmental compliance.
The beginning of the engineering
decision is the cleaning methods employed to ensure that manufacturing
oils, miscellaneous soil and heat treat scale are removed
from the substrate. This is a vital component to good adhesion
to the substrate and ensuring quality performance of the finish.
Common methods are: acid pickling,
vapor degreasing, mechanical blasting and alkaline washes.
Just as finishes are required to be environmentally friendly,
these cleaning methods are also subject to regulations.
Acid
pickling uses an acid dip that attacks the surface
of the part and removes heat treat scale but does not emulsify
the oils and completely remove them. Pickling, while producing
a good surface for the finish to be applied to and promoting
adhesion, also generates wastewater emissions and has the
potential of causing Hydrogen Embrittlement.
Vapor
degreasing uses mostly chlorinated solvents to remove
oil and other contaminants from the part. This process does
not remove heat treat scale so it must be used in conjunction
with another method to provide a clean substrate. Due to the
highly regulated solvents used in this process, the number
of companies willing to use it has radically decreased.
Cleaning for DACROMET® (Environmentally
Friendly)
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| Typical
tumble blaster used to clean scale from heat-treated parts.
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Use of an
alkaline wash solution removes manufacturing oils and
other soils from the surface of parts. These alkaline cleaners
are typically environmentally friendly, but they do not remove
heat treat scale and a mechanical blast is required if the
part has been heat-treated.
Mechanical blasting
consists of steel shot, grit or glass beads blasting the surface
and as a result removing heat treat scale and rust. This is
a good cleaning method used to ensure that there are no remaining
contaminants on the surface. This method does not remove oils
from the surface and is to be used after alkaline cleaning.
The most popular cleaning method that provides the necessary
cleanliness while complying with environmental regulations is
the use of an Alkaline Wash followed by a Mechanical Blast.
A result of this is many finishers have chosen to employ both
means in their facility to ensure a quality finish is preceded
by a quality cleaning method. |
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