Ceramic coating, consisting of graphite, enameler's clay, and algin binder, applied to materials prior to salt bath brazing facilitates brazing process and results in superior joints. Alternate coating materials and their various proportions are given

Francisco, A. C.

Gyorgak, C. A.

English

NASA Technical Reports Server

October 1971	 Brief 71-10381 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a £ubscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Protective Coating for Salt-Bath Brazing 
[]
A protective coating applied to braze materials 
prior to salt-bath brazing facilitates the brazing 
process and results in superior brazed joints. The 
protective coating prevents deterioration of the - 
braze material between the time the work is inserted 
in the salt bath and the time the braze material 
melts and flows on the surfaces to be joined. 
In salt-bath brazing, metal parts are joined by 
fusing the contacting surfaces immersed in a molten-
salt bath. Usually, the braze material is applied as 
a paste, powder suspension, or preform. However, 
when a bonded powder is placed in the molten-salt 
bath, the binder is burned off at such a rapid rate 
that either the braze material is dislodged or, follow-
ing burnout of the binder, the movement of the 
dense molten salt erodes the braze material before 
it is fully melted. When solid preforms are used, the 
molten salt may erode the braze material as it melts 
but before it can wet the work and flow. The pro-
tective coating prevents these deficiencies and 
thereby ensures effective brazed joints.	 - 
One formulation for the coating consists of 90.1% 
graphite, 9.0% enameler's clay, and 0.9% algin binder. 
Other clays and binders common to the ceramic arts 
can also be used. For example, bentonite and 
kaolin may be used in lieu of enameler's clay, and 
carbowax, gum arabic and tragacanth may be sub-
stituted for the algin binder; While the indicated 
proportions of coating constituents are particularly 
effective, other proportions may be used, depending 
on the desired strength of the fired coating. Satis-
factory results are obtainable using 70-92% graphite, 
25-7.5% clay, and 5-0.5% binder. The coating con-
stituents are mixed together simultaneously so
that the binder coats all particles of the graphite 
and bodying clay.' When the mixture is applied to 
the braze-material surface, a tightly adherent coating 
is formed; the binder serves to bind together the 
coating constituents and the coating to the braze-
material surfaces. 
In use, the coating is thoroughly mixed with 
water, the amount of which depends on whether the 
coating is to be applied as a paste, in a bath, or 
as a spray. The mixture is then applied over the braze 
material which has been placed on the joint. The 
coating is dried to remove all moisture, and the 
work is immersed in the molten-salt bath. The coat-
ing acts as a sheath to keep the braze material 
intact during binder burnout. On completion of 
the brazing, the assembly is removed from the bath 
and cooled. Any salt and coating remaining on the 
surfaces are removed by washing. 
The use of this coating is not detrimental to 
the salt bath. To the contrary, there is no contamina-
tion of the salt, and the graphite reduces any metal 
oxides in the bath to pure metal. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B71-10381 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,008,229) and royalty-free license rights 
(continued overleaf) 
This documetct was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000379 2020-03-17T02:28:58+00:00Z
will be granted for its commercial development. In-
quiries about obtaining a license should be addressed 
to:
Patent Counsel 
Mail Code 500-311 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Source: C. A. Gyorgak and A. C. Francisco

Lewis Research Center

(LEW-90255)
. 
Brief 71-10381 Category 08


Protective coating for salt-bath brazing

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