Single molding process ensures that plastic parts /of a given mechanical design/ produced from a conventional thermosetting molding compound will have a maximum tensile strength. The process can also be used for other thermosetting compounds to produce parts with improved physical properties

Heier, W. C.

English

NASA Technical Reports Server

April 1968	 Brief 68-I () 132 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Improved Molding Process Ensures Plastic Parts of Higher 
Tensile Strength 
Steam Platen 
Steam Inlet	 Steam Outlet
Female Cavity Split-Ring

Assembly	 Insert 
.  Steam Outlet uI. 
Male Foe
Plug 
Core Post	 I	 I Ii
I 
Steam Chamber	 Conical Nozzle	 Graphite 
Cavity	 Nozzle-Throat 
Insert
f Steam Chamber 
Vacuum Orifice 
	
A single molding process has been developed to	 A steel compression mold of unique design, illus - 
ensure that plastic parts (of a given mechanical design) 	 Irated for molding the asbestos-phenolic rocket 
produced from a conventional thermosetting molding 	 motor nozzle, is employed in the improved heat 
compound will have a maximum tensile strength. 	 vacuum-compression molding process. The mold has 
The process, specially developed for molding an 	 chromium plated cavity surfaces which are arranged 
asbestos-phenolic rocket motor nozzle incorporating 	 to be heated from ambient temperature to 3001F 
a molded-in-place graphite insert, can also be used for 	 within 60 seconds. Heating is accomplished by 
other thermosetting compounds to produce parts with	 admitting steam into the mold assembly through three 
Improved physical properties. 	 separate inlets. Ducting within the mold components 
(continued ocerlerf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 Information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000132 2020-03-12T05:30:05+00:00Z
provides for rapid and thorough distribution of the 
steam. If for any reason, such as between mold load-
ings, it becomes necessary to cool the mold, water 
can be admitted to the system in place of the steam. 
The mold is prepared for use in a number of steps 
involving ultrasonic degreasing; application of a 
releasing agent to all cavity surfaces; baking the 
assembled, closed mold for 2 hours at maximum tem-
perature (300° F); and spray coating with a mold 
release. On completion of the preparatory steps, the 
mold is positioned on the press, and steam and 
vacuum lines are connected. 
The initial step in the loading procedure consists of 
coating the core post with wax. The preformed 
graphite nozzle-throat insert is positioned on the 
waxed core post and potted in place with an epoxy 
resin. The core post with graphite insert is then 
placed in the mold cavity and assembled to the steam 
platen. On completion of this step, the mold cavity 
is loaded, at room temperature, with the prescribed 
weight of asbestos-phenolic molding compound, 
which had previously been admixed with 1 percent by 
weight of zinc stearate. The latter salt keeps the mold-
ing compound from sticking to the cavity surfaces 
of the mold. (It had been noted that the untreated 
molding compound tends to stick even to cavity sur-
faces coated with a releasing agent.) The force plug is 
then carefully inserted into the cavity, and the press 
is "inched" so that the mold will close sufficiently to 
engage the force-plug 0-ring seal.
The filled, assembled mold is placed under vacuum 
(3 mm of mercury) for 30 minutes and checked for air 
leaks. If there is no leakage, steam at 50 psig is 
admitted into the mold until the mold temperature 
reaches 250°F, but no higher. The steam is then turned 
off, and the mold assembly is permitted to heat-
stabilize for 3 minutes. At the end of this period, the 
mold is closed under automatic compression, which 
for the asbestos-phenolic compound is between 2000 
and 3000 psi. Steam at 125 psig is admitted into the 
mold assembly, which is then permitted to dwell for 
1 hour at 325 0 F. At the end of the dwell, the press is 
switched to manual control and opened. The core post 
is then removed and the molded nozzle ejected. The 
split ring inserts are carefully separated from the 
ejected nozzle, which is then post-cured by baking in a 
circulating hot air oven in accordance with a pre-
scribed temperature cycle. 
Note: 
Complete details may be obtained from: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia 23365 
Reference: B68-10132 
Patent status: 
No patent action is contemplated by NASA. 
Source: W. C. Heier 
(LAR- 10033) 
Brief 68-10132	 Category 05


Improved molding process ensures plastic parts of higher tensile strength

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