Fluid molding system

An apparatus and method for forming components having one or more inner cavities wherein material forming the component is laid up about a number of eutectic salt mandrels corresponding to the inner cavities. The mandrels are melted and the laid up material compressed during the formation of the component by hydraulic pressure transmitted through the molten mandrels.

BACKGROUND OF THE INVENTION 
The present invention relates to the formation of hollow molded components, 
particularly by means of an apparatus in which uncured thermosetting 
material is laid up about one or more meltable mandrels formed from 
eutectic salts. 
Destructable molds made from low melting point, or eutectic, salts are 
known in the art. For example, U.S. Pat. No. 1,523,519, issued to Gibbons, 
addresses the suitability of various combinations of salts for use as mold 
forms for rubber tires and other vulcanized articles. U.S. Pat. No. 
1,554,697, issued to Alden, teaches the use of salt cores in the 
manufacture of hollow articles, which cores may be extracted from the 
molded article by dissolving the salt with water after completion of the 
molding process. Other methods of removing the core or interior mold, 
namely by breaking or melting same are discussed in U.S. Pat. No. 
2,217,743, issued to Dreyfus. 
Several advantages are realized by the foregoing schemes. Eutectic salt 
cores or mandrels may readily be cast in rather fine detail, allowing 
ample flexibility in the design of articles to be molded therefrom. 
Furthermore, the ease with which new cores may be recast from the melted, 
broken or dissolved material of previously used cores lends a desirable 
economy to the overall operation. 
With regard to the use of salt cores to form discrete, non-continuous 
hollow articles, however, one problem which has not been satisfactorily 
solved to date is the removal of the core from the finished article. 
Dissolving the core as in Adler is objectionable because it is time 
consuming. Hollow, frangible cores, as suggested by Dreyfus, may be more 
readily extracted, but are costlier and more difficult to produce than 
solid cores. Solid cores may be melted, but must then be drained by 
gravity. Regardless of what method of extraction is used, recasting has 
required collecting and repouring the used salt to form new mandrels, thus 
interrupting the continuity of the process. 
An apparatus for shaping and laminating thermoplastic sheets which includes 
means for continuously recycling the eutectic salt used in the process is 
shown in U.S. Pat. No. 2,608,720, issued to Meisner. U.S. Pat. No. 
4,056,596, issued to Pahl, discloses another continuous scheme wherein 
tubing is formed about a hollow mandrel which may be melted by an 
induction coil or broken up by ultrasonic waves and forced back through 
the mandrel by compressed air. Neither Meissner nor Pahl, however, is 
adaptable to recycling mandrels used in forming discrete, non-continuous 
hollow articles, their utility being limited respectively to the formation 
of continuous sheets and tubes. 
A further objection to present techniques is the lack of control over the 
compression of the material to be molded. The formation of high strength 
laminates having a thermosetting resin matrix depends on the uniform 
exertion of a precisely controlled pressure during the molding or curing 
process. In the prior art, layers of thermosetting material wrapped about 
a salt core and placed in a rigid outer die for curing were compressed 
almost exclusively by the expansion of the salt core due to heating to 
cure temperature. If instead of a rigid outer die, the uncured component 
is enclosed in a vacuum bag which is in turn placed in an autoclave, the 
surfaces exposed to the vacuum bag will usually be compacted sufficiently 
by the autoclave pressure to be free of voids due to air bubbles, but the 
inner surfaces must still rely on thermal expansion of the mandrels. 
Because the manufacturing tolerances of the mandrels, the thickness 
variation of the uncured material, and the manufacturing tolerance of the 
outer die, the final fit of the uncured component into the outer die will 
be difficult to control. This dimensional variation will have a direct 
effect on the pressure exerted by the thermally expanded mandrels on the 
component at cure temperature, which, in turn, will determine the strength 
and quality of a part. 
U.S. Pat. No. 2,739,350, issued to Lampman, discloses a reusable, 
thermoplastic inner mold which may be easily withdrawn from the molded 
article after completion of the molding process but before the mold cools 
to a rigid state. The mold includes an inner cavity which is pressurized 
during the molding operation, resulting in compression of the material to 
be molded against a rigid outer die. Still, however, a precisely 
controllable, uniform pressure cannot be applied using the Lampman inner 
mold because the pneumatic pressure must be transmitted through a rather 
thick layer of viscous thermoplastic. Another objection to the Lampman 
method is that the opening to the interior cavity of the article to be 
molded must be at least nearly as wide as the cavity itself. Furthermore, 
the cavity must not include any sharp recesses transverse to the direction 
of removal of the inner mold, thus limiting the shapes which may be formed 
by the Lampman process. 
SUMMARY OF THE INVENTION 
A principal object of the present invention is to provide a molding 
apparatus with which one may apply a controlled, uniform pressure to the 
interior surface of a hollow component to be cured. 
It is further desired, according to this invention, to supply such a 
molding apparatus wherein the material to be molded is laid up about one 
or more meltable mandrels formed from eutectic salts, the outer contours 
of said mandrels conforming to a desired inner contour of the articles to 
be molded. 
Yet another object of this invention is to furnish a molding apparatus, of 
the type employing eutectic salt mandrels, with means for automatically 
controlling the curing cycle, the extraction of used mandrels from the 
molded component, and the recasting of new mandrels. 
A still further object of the present invention is to furnish a molding 
apparatus with a molding fixture adaptable for use with either a rigid 
outer die or a flexible vacuum bag. 
It is yet another object of this invention to provide a molding apparatus 
employing eutectic salt mandrels with means by which the used mandrels may 
be quickly and completely extracted from the molded article upon 
completion of the molding process. 
One still further object of the present invention is to provide a molding 
apparatus employing eutectic salt mandrels with means by which the 
mandrels may be accurately recast in a hot mold to avoid the problems of 
chilling and shrinkage. 
The foregoing and other objects and advantages are realized, in brief, by 
the provision of a molding apparatus having a curing oven in which are 
enclosed a eutectic salt reservoir, a molding fixture and an appropriate 
die or dies for recasting eutectic salt mandrels. Pressurizing means are 
included which may be operated when the eutectic salt is in a molten state 
to control the hydraulic pressure within the reservoir. A hydraulic check 
valve allows this pressure to be directed to the molding fixture which 
contains the article to be cured, thus transmitting a uniform, 
controllable pressure to the article's interior surface. 
Removal of the mandrel is achieved with the salt in molten state, and may 
be commenced once the article being cured has set or reached the gel 
state. A valve directing pneumatic pressure to the molding fixture is 
opened, and a second valve interposed along a line from the molding 
fixture to the mandrel recast dies is opened. Air pressure thus forces the 
molten mandrels flow from the molding fixture to the recast dies. 
When the mandrel dies have been fully replenished, the oven temperature is 
reduced to below the melting point of the eutectic salt. Upon 
solidification of the mandrels, the molding fixture and mandrel dies are 
opened and the cured component and recast mandrels removed, where upon the 
molding process may be repeated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A. Construction 
Referring to FIG. 1, the novel features of an apparatus embodying the 
present invention are shown schematically. An oven 10 encloses a fluid 
loop 12 along which are interposed three major elements--a molding fixture 
14, a reservoir 16 and recast dies 18. Also interposed along loop 12 are a 
filler port 20, hydraulic check valves 22 and 24, a T fitting 26, a 
three-way two-position valve 28 and a window flow gauge 30. 
An auxilliary line 32 connects T fitting 26 to air compressor 34 located 
externally of oven 10. Interposed along line 32 are a pneumatic regulator 
valve 36, a hydraulic check valve 38 and a three-way, two-position valve 
40. A flush line 42 is connected to the third inlet 43 of valve 40, while 
a drain line 44 is connected to the third inlet 45 of valve 28. 
A quantity of eutectic salt 46 is partly contained in fixture 14 (during 
the formation of a component) or in the recast dies 18 (during the 
post-cure cycle) in the form of a number of molding cores or mandrels 48. 
The mandrels may also include an outer layer 49 of inert material, such as 
Teflon or Kapton (FIG. 6). Eutectic, or low melting point, salts are well 
known, and those skilled in the art would weigh a number of factors such 
as melting point, solubility, thermal expansion, etc., in selecting a 
particular salt in connection with this invention. 
In general, eutectic salt 46 exists in either a solid or a molten state 
depending on its temperature and, in its molten state, is characterized by 
fluid properties. Thus, when compressed, molten eutectic salt 46 will 
exhibit a uniform hydraulic pressure over a containing surface, and may be 
forced to flow through fluid loop 12 in the direction of check valves 22 
and 24. 
Compression means 50, located externally of oven 10, are arranged so as to 
allow control of the hydraulic pressure of molten eutectic salt 46 
contained in reservoir 16. Such means may include a hydraulic pressure 
cylinder 52 with a plunger 54 responsive to hydraulic fluid 55 entering 
fluid ports 56 and 58. A rod 60 may be used to connect plunger 54 to a 
second plunger 62 in the reservoir. Insulation 64 prevents heat from oven 
10 from affecting hydraulic fluid 55. Compression is controlled by a 
hydraulic pump 66 and a four-way, two-position valve 68 which are 
connected to a hydraulic fluid reservoir 70. 
A component 72 is contained within molding fixture 14 during formation. By 
way of example, component 72 in FIG. 1 includes three inner cavities, 72a, 
72b and 72c. According to one aspect of this invention, each inner cavity 
of a component in place within the molding fixture must be in fluid 
communication with the reservoir. According to a further aspect of the 
invention, each inner cavity of a component in place within the molding 
fixture must not only be in communication with the reservoir, but must 
itself be part of the fluid loop. That is, there must be a fluid path 
through each inner cavity from the reservoir to the recast dies. 
The molding fixture 14 of FIG. 1 provides a series path through inner 
cavities 72a, 72b, and 72c of component 72 by means of fluid inlet port 74 
connected to reservoir 16 by portion 82 of fluid loop 12, intermediate 
ports 75-78 and fluid outlet port 79 in registry with openings 74' and 
75'; 76' and 77'; and 78' and 79' in cavities 72a, 72b and 72c 
respectively. Ports 75 and 76 are connected by intermediate line 80, while 
ports 77 and 78 are similarly connected by intermediate line 81 and outlet 
port 79 is fluidly connected to the recast dies 18 by portion 84 of the 
loop. 
Recast dies 18 are equal in number to and shaped accordingly with the 
mandrels. As with the inner cavities of component 72 enclosed in molding 
fixture 14, the recast dies are interconnected such that a fluid path may 
be traced through each recast die from the molding fixture back to the 
reservoir. 
The foregoing scheme of ports and interconnections is only representative 
of the possible embodiments of the present invention. Numerous variations 
will be obvious. For instance, a parallel fluid path may be implemented by 
inserting four-way fittings at the inlet and outlet ports and replacing 
lines 80 and 81 with appropriate connections, or the flow in cavity 72b 
may be reversed by switching the connections of lines 80 and 81 to ports 
76 and 77. Or, for a two cavity component, ports 76 and 77 maybe blocked, 
and lines 80 and 81 replaced by a single interconnecting line between 
ports 75 and 78. 
For most changes in the configuration of a component, further adjustments 
beyond rearranging the interconnecting lines will be necessary. To form a 
component with more than three parallel cavities using the six port 
molding fixture 14 of FIG. 1 for instance, adapter plates may be inserted 
into the molding fixture between the fluid ports and the ends of the 
component. Adjacent to the component thin plates having holes in registry 
with the openings to each inner cavity would be used. Thicker plates 
having slots to provide fluid channels between holes in the thin plates 
and the fluid ports would be inserted between the thin plates and the 
molding fixture. Such adapter plates could be used to provide serial or 
parallel flow according to the arrangement of slots on the slotted plates. 
FIG. 2 shows a cross sectional view of molding fixture 14 enclosed by an 
external vacuum bag 86. Included on vacuum bag 86 are airtight grommets 88 
and 90 in registry with ports 76 and 77. Similar grommets provide airtight 
seals around ports 74, 75, 78 and 79. A lip 92 of vacuum bag 86 provides a 
vacuum seal against table 94 which supports the molding fixture. Suitable 
means may be provided to evacuate bag 86, such as grooves 96 in the 
underside of molding fixture 14, fitting 98 on the underside of table 92 
in communication with grooves 96, and vacuum line 100 connected to fitting 
98. 
To facilitate the formation of complex components, a modified molding 
fixture having an irregularly shaped molding surface may be used. 
Alternatively, rigid adaptor plates or outer dies having a shape conformed 
to a desired outer shape of the component may be inserted into molding 
fixture 14. In general, any complex outer die with plural displaceable 
individual portions may be adapted to the present invention by providing 
said die with holes in registry with the openings in the component, 
appropriate internal lines for interconnecting the holes in the die with 
the fluid ports in the molding fixture and adequate structure to hold the 
die in position in the fixture. 
In FIG. 3, molding fixture 14 is shown in cross section with a rigid die 
102 providing a molding surface for a reinforced airfoil component 72'. 
Die 102 comprises mutually displaceable portions 104 and 106 which may be 
separated to remove the cured component by lifting cover 108 from the 
molding fixture. As shown, two mandrels 48a and 48b lie in the fluid loop 
between ports 76 and 77, and die 102 includes internal lines 110 which 
interconnect the mandrels and the ports in the molding fixtures. Internal 
lines 110 are arranged so that molten salt flowing through airfoil 
component 72' exits each cavity at its lowest point. Thus, to insure 
"downward" flow between ports 76 and 77, i.e., flow parallel to that 
between ports 74 and 75 and between ports 78 and 79, the connections to 
ports 76 and 77 should be reversed from FIG. 1 by having interconnecting 
lines 80 and 81 connect port 76 to port 78 and port 77 to 75, as described 
above. 
A modified molding fixture 14' (FIG. 4) having an enclosed vacuum bag 86' 
may be used to form complex, multi-reinforced structures such as component 
72" (FIG. 5). Fixture 14' includes a rigid outer wall 112 with removeable 
cover 108' which may be assembled to define an airtight chamber 114. Cover 
108' is held in place as by braces 109 to enable pressurization of chamber 
114. Vacuum bag 86' divides chamber 114 into a pressure chamber 116 and a 
vacuum chamber 118 in which the component 72" is contained during 
formation. Extension lines 120 mounted in end plugs 122 serve to fluidly 
connect the vacuum chamber to the fluid ports in the molding fixture. 
The pressure chamber 116 may be pressurized by means of a pneumatic valve 
or fitting 124 mounted in cover 108' while the vacuum chamber 118 may be 
evacuated by means of fitting 126 in the bottom wall of the molding 
fixture. A molding surface within the fixture is provided by lower surface 
128 against which vacuum bag 86' is sealed. Salt mandrels 48' communicate 
with fluid loop 12, while forms 130 are segregated and removable after the 
cured component has been removed from the molding fixture. Forms 130 may 
be formed from eutectic salt, but are preferably made of a rigid material 
such as aluminum or Teflon. 
B. Operation 
FIG. 6 illustrates the lay-up of component 72 of FIG. 1. Mandrels 48, as 
formed in recast dies 18, are prepared by wrapping each with a layer of 
inert material, 49 such as Teflon or Kapton to prevent the molten eutectic 
salt 46 from permeating the component 72 during formation. The number of 
mandrels equals the number of inner cavities in the component to be 
formed, and each mandrel has a shape corresponding to a desired shape of 
its associated inner cavity. 
A desired thickness of material from which the component is to be formed is 
then laid up about the wrapped mandrels 48. The lay up procedure may 
comprise wrapping layers of material 132 about the individual mandrels, 
then draping additional layers of material 134 over the mandrels as they 
are fitted together to form the component. 
With regard to the type of material forming the component, the present 
invention finds its greatest utility in the formation of high strength 
laminited components. Typically such structures are formed from layers of 
fibrous material, such as glass or graphite, impregnated with a 
thermosetting resin. Various other materials and lay up procedures, 
however, will be obvious to one skilled in the art. 
The mandrels 48 and laid up material 132, are next put into molding fixture 
14. If a rigid outer die is to be used, the mandrels and laid up material 
would first be placed in the die, then the die inserted in the molding 
fixture. If an inner vacuum bag is to be used, the mandrels and laid up 
material are first seated on the molding surface in the molding fixture, 
the vacuum bag is placed over the mandrels and laid up material such that 
they are completely enclosed, then the extension lines are put in place 
and the cover to the molding fixture secured. 
The temperature of the reservoir 16, molding fixture 14 and recast dies 18, 
controlled by oven 10, is then raised to a point above the melting pont of 
eutectic salt 46. Since each inner cavity of the uncured component in the 
molding fixture is in fluid communication with the fluid inlet port, 
compression means 50, operable to control the hydraulic pressure of 
eutectic salt 46 while in the molten state, provides means for controlling 
the pressure exerted by mandrels 48, also molten, against the laid up 
material 132. To transmit hydraulic pressure from the reservoir 16 to this 
fluid inlet port 74 through the molten salt, fluid outlet port 79 is 
closed by means of valve 28. 
By appropriate control of compression means 50 and oven 10, the laid up 
material may be cured at a desired temperature and pressure for a desired 
length of time. If an external vacuum bag is used, evacuation of the bag 
may be performed at any time prior to the gel stage of the curing process. 
Similarly, if an internal vacuum bag is used, pressurization of the 
pressure chamber and evacuation of the vacuum chamber must be accomplished 
before the laid up material begins to gel. 
On completion of the curing process the used mandrels may be forced from 
the molding fixture 14 through the fluid outlet port 79 by applying 
pneumatic pressure to the fluid inlet port 74, since, with the component 
contained in the molding fixture, a fluid path may be traced, for each 
inner cavity in the component, from the fluid inlet port through the inner 
cavity to the fluid outlet port. Location of the exit openings to each 
cavity at the lowest point in the cavity facilitates complete removal of 
the mandrel. 
Valve 28 allows the fluid outlet port to be fluidly connected to the recast 
dies 18 such that the mandrels which are forced from the molding fixture 
14 will flow into the recast dies. Pneumatic pressure is applied to the 
fluid inlet port by means of air compressor 34 and valve 40. Additional 
salt to make up for traces remaining in the component may be added to the 
recast dies from reservoir 16 through portion 132 of fluid loop 12. Salt 
may be added to the loop through filler port 20, which may also serve to 
bleed off air from the recast dies. 
Sight gauge 30 provides an indication of when the mandrels have been 
completely removed. At this point, shown in FIG. 1, valve 40 positioned to 
allow a solvent, preferably water, to be injected into the fluid inlet 
port through flush line 42 such that any traces of eutectic salt remaining 
in the inner cavities of the component after the mandrels have been forced 
out by pneumatic pressure may be dissolved and carried out through the 
fluid outlet port by the solvent. The solvent is routed out of the oven 
through drain line by repositioning valve 28. 
After removing the completed component from the molding fixture, the entire 
process may be repeated, using the recast mandrels after allowing them to 
harden, until a desired number of components have been formed. 
The foregoing descriptions, while indicative of the presently preferred 
embodiments, are given by way of example only, the scope of the present 
invention being defined by the appended claims.