Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BINDER FOR BINDING BRAZE ALLOY AND OTHER METALLIC
PARTICLES IN JOINING AND REPAIR OF JET ENGINE COMPONENTS
BACKGROUND OF THE INVENTION
This invention relates to a binder for braze
alloys and other metallic particles for use in jet engine
component repair and joining applications.
Binders are used in connection with metallic
braze alloy powders to form viscous slurries which are
applied to damaged jet engine components during repair
operations. Such slurries are also used in conventional
brazing joining operations. Such binders often contain
agents such as acetone, 111' trichloroethane, and toluene.
These agents are selected because they form a flowable,
workable slurry with metal powders, because they burn off
at braze temperatures, and because they do not have
intolerable negative effects on the braze alloy structure
and properties. However, these and similar agents have
certain disadvantages, in particular, they are volatile and
present potential disposal difficulties and health hazards
if not handled according to established guidelines.
Furthermore, they typically have an unpleasant,
objectionable, and even noxious odor. There is a need,
therefore, for binders which are water soluble, have burn-
off properties which are equal to or better than current
binders, have no detrimental effects on braze alloy
structure and properties, and are odorless.
SUMMARY OF THE INVENTION
Briefly, therefore, the invention is directed to
a binder for binding braze alloy particles in jet engine
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component brazing operations, the binder comprising from
about 60% by weight to about 90% by weight water and from
about 10% by weight to about 40% by weight polyethylene
oxide.
The invention is also directed to a binder for
binding braze alloy particles in jet engine component
brazing operations, the binder being solvent-free and
comprising from about 60% by weight to about 90% by weight
water and from about 10% by weight to about 40% by weight
polyethylene oxide.
DETAILED DESCRIPTION OF THE INVENTION
The binder according to this invention employs
polyethylene oxide (PEO), which is a fine, water-soluble,
white powder having a chemical formula of (-CHZCH20-)n. PEO
is available from, for example, Aldrich Chemical Company of
Milwaukee, Wisconsin. The preferred PEO is 100 to 100,000
molecular weight. When PEO is mixed with deionized water,
the resulting mixture is a viscous fluid. This fluid
serves as a binder which is then mixed with superalloy
powder or other metallic powder to form a slurry.
The binder contains from about 10% to about 40%
by weight PEO and from about 60% to about 90% by weight
water. In one particularly preferred embodiment, the PEO
constitutes about 20% by weight, and the water constitutes
about 80% by weight. In forming the binder, these
components are weighed out, and the water is added to the
PEO, or the PEO is added to the water. The water is
preferably moderately heated to a temperature of about 150°F
(65°C) before adding the PEO. These two components are then
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mixed thoroughly using a spatula or other mixing device
such as a variable speed electric blender. Mixing is
continued until the mixture becomes a viscous fluid
constituting a binder, with no evidence of PEO powder
clumps in the mixture. Mixing time is typically less than
about 10 minutes.
After mixing the binder is allowed to cool,
preferably for about 2 hours, and then to settle,
preferably for at least about 24 hours, prior to use. It
is important that the binder be cool and free of air
bubbles prior to use.
The binder is then added to a superalloy powder
or other metallic powder to form a slurry. The ratio of
binder to metallic powder is dictated by the particular
function of the resulting slurry.
In an alternative preferred embodiment of the
invention, xanthan gum is added to the water/PEO mixture.
It has been discovered that xanthan gum additions increase
shelf life by decreasing the tendency for separation
between PEO and water. Xanthan gum is preferably added in
an amount of from 0.1% to about 5% by weight of the total
binder. In one particularly preferred embodiment, the
xanthan gum constitutes from about 0.2% to about 0.3% by
weight, more preferably about 0.25% by weight, water
constitutes about 79.75% by weight, and PEO constitutes the
remaining about 20% by weight . Xanthan gum is available
from, for example, the Nutrasweet Kelco Company of San
Diego, California. Mixing is carried out as described
above, with the xanthan gum added to the water
simultaneously with or after the PEO.
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The binder of the invention has the advantage
that it is solvent-free, defined herein as containing
essentially no organic solvents such as acetone, 111'
trichloroethane, and toluene. The binder has the
advantages that it is environmentally safe, that it
contains no harmful solvents, that it is water-based rather
than solvent-based, that it is easy to clean up when
spilled, that it is odorless, that it has a longer shelf
life than previous binders, that both PEO and xanthan gum
raw materials are in easy-to-handle powder form, that it
exhibits burn-off properties roughly equal to or better
than previous binders, that its raw materials are abundant
and relatively inexpensive, and that it is useful for
conventional brazing joining applications as well as
repair. A further advantage is that it exhibits loading
capabilities which are roughly equal to or better than the
capabilities of current binders, which reduces the risk of
voiding in braze repairs. This corresponds to decreased
porosity in the braze, decreased rates of rejection, and
increased process yields.
As various changes could be made in the above
constructions without departing from the scope of the
invention, it is intended that all matter contained in the
above description or shown in the accompanying drawings
shall be interpreted as illustrative and not in a limiting
sense.
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