Polymer concrete electrical insulator and method and apparatus for making

An improved electrical insulator for high voltage transmission lines is formed from certain polymer-based concrete compositions. An apparatus provides for the molding of the polymer-based mixture to form a highly degassed product. The method and apparatus include the ability to combine the constituents of the mixture in a mixer. A vacuum is applied to the mixture to degas the mixture. A mold is filled with the degassed mixture without introducing air thereinto in the absence of a vacuum. The resulting insulator has highly reduced air entrainment.

FIELD OF THE INVENTION 
The present invention relates to polymer concrete electrical insulators and 
methods and apparatus for making the same and, more particularly, to an 
improved insulator having reduced air entrainment and an improved method 
and apparatus for molding products from degassed compositions. 
BACKGROUND OF THE INVENTION: 
For many years, electrical insulators intended for usage on high voltage 
transmission lines were made of porcelain. In recent years, it has been 
discovered that such insulators may be formed from certain polymer-based 
concrete compositions to provide significant advantages in cost and 
performance. U.S. Pat. No. 4,210,774, issued Jul. 1, 1980, for example, 
discloses such a polymer filled concrete composition used to produce 
insulators having dielectric and mechanical characteristics far superior 
to those of porcelain insulators. The '774 patent discloses that polymer 
concrete insulators may be formed by generally conventional casting or 
molding techniques, wherein the mold is simultaneously vibrated and 
subjected to a vacuum during the curing process to extract entrained air 
from the composition. It is well known that increased porosity through air 
entrainment adversely affects the dielectric and mechanical strength of 
the insulator, encouraging the formation of electrically charged areas 
within the body of the insulator which may eventually lead to failure. 
The use of a vacuum to degas products during the molding process is well 
known in the art. U.S. Pat. Nos. 3,154,618, issued Oct. 27, 1964, and 
4,256,444, issued Mar. 17, 1981, illustrate typical examples of casting 
and injection molding methods and apparatus known in the art, wherein the 
mold itself is maintained under a vacuum during at least part of the 
curing process. Each time the mold is removed from conventional apparatus, 
the vacuum must be broken and re-established for the next molding cycle. 
No known method or apparatus allows multiple molding cycles to be carried 
out without repeatedly subjecting the mold to alternating cycles of vacuum 
and atmospheric pressure. It has been recognized that substantial amounts 
of time and energy are required in order to repeatedly subject a mold to a 
vacuum suitable for degassing each production cycle. 
Polymer concrete typically comprises the combination of one or more 
aggregate materials, a polymer resin, and a catalyst which, when combined 
with the polymer resin, forms a catalyzed composition hardenable at room 
temperature. It is known in the art that casting methods and apparatus for 
use with such compositions must be specially adapted to avoid undesirable 
clogging caused by premature hardening of the composition. U.S. Pat. No. 
2,862,239, issued Dec. 2, 1958, for example, discloses injection molding 
processes and apparatus wherein catalyst and resin are combined 
immediately prior to entering an injection pipe leading to a mold, with 
solvent tanks operatively connected to clean the system of the rapidly 
setting composition after each injection. The mixing means disclosed in 
the '239 patent, however, is suitable only for combining relatively low 
viscosity constituents, and is inadequate for thoroughly combining the 
high viscosity resin/aggregate mixture with a low viscosity catalyst used 
to produce polymer concrete. 
It is also well known in the art of casting and molding to employ a mold 
having a generally rigid outer structure, with a generally pliable liner 
forming the interior cavity configured to receive the molding composition. 
Room temperature vulcanizing silicone rubber (RTV) is commonly used for 
creating molds, as disclosed in U.S. Pat. Nos. 4,098,856, issued Jul. 4, 
1978, and 3,989,790, issued Nov. 2, 1976. Conventional RTV-lined molds 
used for casting concrete polymer insulators typically comprise two 
substantially identical halves, having essentially planar mating surfaces 
which allow an unacceptable amount of flash to form on the finished 
product. The unusually high degree of flash formed on concrete polymer 
insulators requires a significant amount of hand finishing to remove, a 
time consuming process which frequently increases the cost of the end 
product. Numerous solutions to this problem have been attempted, but none 
found to be commercially feasible. 
BRIEF SUMMARY OF THE INVENTION 
It is a principal object of the present invention to provide an improved 
polymer concrete electrical insulator, and method and apparatus for 
producing the same, correcting the aforementioned deficiencies in the 
prior art. More particularly, it is an object of this invention to provide 
polymer concrete electrical insulators having consistently lower porosity 
(i.e., proportional air entrainment) than conventionally made polymer 
concrete insulators, and a method and apparatus for making the same. 
It is another object of this invention to provide a mold for significantly 
reducing the amount of flash formed on polymer concrete insulators, or 
other molded products. 
Another object of this invention is to eliminate the need for exposing the 
mold to the vacuum at any time during the process of degassed constituents 
molding. 
A still further object of this invention is to provide a method and 
apparatus for producing a homogenous catalyzed composition suitable for 
molding. 
Another object is to provide such apparatus adapted for use with high 
viscosity constituents as used to produce polymer concretes. 
In accordance with the teachings of the present invention, there is 
disclosed herein a polymer concrete electrical insulator having 
substantially reduced air entrainment over conventional products. A method 
and apparatus for molding the improved insulator is disclosed, comprising 
a mixing chamber for combining the resin and aggregate constituents for a 
polymer concrete, with a vacuum pump communicating therewith to degas the 
mixed constituents. A pair of double diaphragm pumps are utilized to 
transfer the degassed mixture from the mixer to the top portion of a 
vertically oriented static mixer, at which point catalyst is added to the 
mixture by means of a poppet valve-operated injector. The combined 
catalyst and resin proceed through the static mixer to form a 
substantially uniform catalyzed mixture, which is then discharged into a 
rotating mold through a discharge nozzle which is gradually withdrawn from 
the mold as it fills. The unique mold comprises an outer canister having 
an RTV silicone rubber liner formed therein, the interior cavity formed by 
the liner defining the configuration of the molded insulator. The RTV 
liner is composed of two mating halves, the concave mating surface of one 
such half being defined by a naturally forming meniscus of the RTV 
compound, and the other half comprising a corresponding convex surface, 
such that the mating of the two halves minimizes the formation of flash on 
the resulting insulator. A recirculation system is in fluid communication 
with the mixer, whereby the resin/aggregate mixture may be recirculated 
through the evacuated portion of the mixer to ensure adequate degassing 
thereof, and continuously recirculated thereafter in its degassed state 
without allowing air to become entrained therein. A directional control 
valve selectively directs the flow of degassed mixture from the 
recirculating system to the top of the static mixer whenever desired.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIG. 1, molding apparatus 10 is shown 
diagrammatically to illustrate the unique molding method and apparatus 
provided by the present invention which produces a higher quality polymer 
concrete electrical insulator than is available with conventional methods 
and devices. Apparatus 10 comprises generally conventional tank 12 and 
hopper 14 serving as reservoirs for supplying resin and aggregate, 
respectively. While the advantages provided by apparatus 10 and the 
underlying molding method may be equally applicable to a wide range of 
molded products, apparatus 10 was designed for use with combined resins 
and aggregates typically used to produce polymer-based concretes. For 
purposes of this disclosure, it is to be understood that the resin 
supplied by tank 12 may be a mixture of polymers, monomers, and other 
suitable resins, while the aggregate supplied by hopper 14 may be a 
suitable commercially available treated filler, comprising a combination 
of various mineral compounds and other components. Accordingly, the terms 
"resin" and "aggregate", as used herein, are not to be limited to any 
single resin or aggregate, and the term "resin mixture" shall refer to the 
combination of resins and aggregates suitable for the purpose of making 
polymer concrete. 
Resin from tank 12 and aggregate from hopper 14 are combined within mixer 
16 in predetermined proportions to yield a suitable resin mixture. The 
nature of mixer 16 is generally not critical, provided that an adequate 
resin mixture may be obtained, but a conventional orbital type vertical 
cone screw mixer has been found particularly well suited for the purposes 
and advantages described herein. As will be recognized by those skilled in 
the art, the top section 18 of mixer 16 is adapted to receive resin and 
aggregate, middle section 20 is adapted to contain the resin and aggregate 
during thorough mixing and degassing thereof, and lower section 22 is 
adapted to contain and discharge the uniform resin mixture through 
conventional means. 
Vacuum pump 24 is operatively connected to the top section 18 of mixer 16 
through conventional plumbing and valving. Vacuum pump 24 serves to draw a 
vacuum within the interior of mixer 16, thereby suitably degassing the 
resin mixture contained therein. In the preferred embodiment shown, an 
initial vacuum is drawn within mixer 16 by means of vacuum receiver tank 
26, which is maintained in a substantially continuous evacuated state by 
vacuum pump 24. Subsequently, vacuum pump 24 may communicate directly with 
tank 16 through vacuum line 28 to maintain the desired reduction of 
pressure within mixer 16. A significant advantage over conventional 
methods and apparatus is that, by selecting mixer 16 having an appropriate 
capacity depending upon anticipated production schedules, a sufficient 
quantity of resin mixture may be degassed through a single operation of 
vacuum pump 24 to fulfill one or more complete production shifts. Once the 
resin mixture within mixer 16 is suitably degassed, vacuum pump 24 may 
remain idle for several hours or days, thereby conserving time and energy 
and significantly increasing the life of vacuum pump 24. 
Conduit 30 interconnects lower section 22 of mixer 16 with lower pressure 
pump 32 and high pressure pump 34, which cooperate to provide a steady of 
flow of degassed resin mixture through valve 36. Pumps 32 and 34 are of 
generally conventional double diaphragm design, the details of high 
pressure pump 34 being set forth in U.S. Pat. No. 4,543,044, issued Sep. 
24, 1985. The use of a rolling diaphragm piston pump as described in the 
'044 patent for pump 34 ensures a non-pulsating, constant-flow polymer 
concrete delivery system with precision metering capability. Such pumps 
further ensure that no unwanted air will be inadvertently introduced into 
the flow of degassed resin mixture. Other pumps may also be well-suited 
for these purposes. 
Valve 36 is selectively switchable to route the flow of degassed resin 
through either recirculating line 38 or discharge line 40. When switched 
to the former setting, valve 36 completes a recirculating loop wherein 
degassed resin mixture exiting conduit 30 is continuously reintroduced 
into mixer 16 through recirculating line 38. With all relevant components 
being properly sealed, the recirculation circuit may be utilized to 
continuously recirculate degassed resin mixture between molding cycles 
without the introduction of air, thereby ensuring a constant supply of 
flowable, degassed resin mixture. 
In the preferred embodiment of this invention, it is only necessary to 
evacuate mixer 16 temporarily to obtain an adequately degassed mixture. 
Thereafter, mixer 16 need not be sealed in order to maintain the mixture 
in its degassed state, provided that no air is introduced during 
recirculation. In this regard, it is preferred that the level of mixture 
within mixer 16 be maintained above the point of attachment of line 38, so 
that the recirculating mixture is always reintroduced into mixer 16 at a 
point below the surface of the mixture within mixer 16, thereby avoiding 
air entrainment. If recirculation is performed at a sufficiently low flow 
rate, such an arrangement is not essential to the successful operation of 
this invention; the flow of mixture being reintroduced into mixer 16 may 
be low enough to avoid air entrainment, even if it is at a point above the 
level of the mixture within mixer 16. 
With valve 36 in its second position, resin mixture flows through discharge 
line 40 and valve 41 to the top portion 42 of static mixer 44, which is of 
generally conventional design. A suitable catalyst, provided by catalyst 
tank 46, is then injected into the flow of resin mixture and uniformly 
combined therewith as the flow passes through the intermediate body 
portion 48 of static mixer 44. Pump 50, preferably a microprocessor 
controlled gear-styled metering pump, introduces the proper amount of 
catalyst depending upon the resin mixture flow rate through catalyst 
injector 52 described in more detail below. The uniform combination of 
catalyst and resin mixture forms a readily hardenable catalyzed 
composition which passes through fill tube 54 secured to the outlet end 56 
of static mixer 44, for ultimate discharge into a mold 58 as described 
more fully hereinbelow. 
FIGS. 2A through 2C illustrate, in some detail, the preferred embodiment of 
the mold fill station of the apparatus depicted diagrammatically in FIG. 
1. Discharge line 40 leading from high pressure pump 34 communicates 
through flexible hose 60 and coupling 62 with the inlet end 42 of static 
mixer 44. A pair of purge valves 64 (only one is shown for the sake of 
clarity) are operatively disposed between fluid lines connecting coupling 
62 with conventional supplies of solvent and air. Activating purge valves 
64 serves to alternatingly direct a suitable cleaning solvent and/or air 
through static mixer 44 and fill tube 54, discharged through nozzle 66. 
The purging operation effectively cleans the system between valve 41 and 
the distal end 144 of nozzle 66, thereby removing all unused catalyzed 
composition remaining therein. Valve 41, maintained in its closed position 
during purging, prevents air and solvent from being introduced in the 
resin mixture upstream of purge valves 64. 
As discussed more fully below, nozzle 66 is preferably withdrawn from the 
interior cavity 68 of mold 58 during discharge of the catalyzed 
composition. Therefore, the assembly comprising coupling 62, static mixer 
44, and fill tube 54 are longitudinally movable as a unit, by means of a 
generally conventional linear actuator. While a number of linear actuators 
may be suitable for this purpose, the embodiment disclosed herein utilizes 
bracket 72 to rigidly secure static mixer 44 to nut 74 which is 
threadingly engaged with threaded rod 76. Rotation of threaded rod 76 by 
means of a suitable motor (not shown) engaging either end thereof moves 
nut 74 vertically, with the static mixer 44 and fill tube 54 moving 
therewith. FIG. 2A demonstrates nozzle 66 in its fully inserted position 
within interior cavity 68, FIG. 2B demonstrates nozzle 66 in an 
intermediate position, and FIG. 2C demonstrates nozzle 66 in a fully 
retracted position. 
FIGS. 3A and 3B disclose more fully the preferred embodiment of catalyst 
injector 52, representing a superior method for combining catalyst with a 
resin mixture for purposes of molding. Body 78 of catalyst injector 52 
preferably includes four bores 80 -86 formed therein, with ports 82 and 86 
normally plugged during operation. While port 86 is formed in conjunction 
with bore 88 and provides access thereto, port 82 may serve as a 
connection to a second supply of catalyst in the event that hardening of 
the particular mixture is optimized by the addition of a plurality of 
catalysts. 
Nozzle member 90 is welded or otherwise rigidly secured to the face of body 
78 and threaded into the side of top portion 42, such that the interior 
bore 92 is in fluid communication with passageway 94 formed within body 
78. Stem 96 is disposed longitudinally through nozzle 90 and body 78, 
having longitudinally opposed threaded ends 98 and 100. Valve member 102 
is threaded onto end 98 of stem 96, and is configured to sealingly engage 
seat 104 formed in the distal end of nozzle member 90. Disposed within 
bore 88, nut 106 is threaded onto end 100 of stem 96, thereby securing 
compression spring 112 between washers 108 and 110. 
When assembled as shown, compression spring 112 serves to bias catalyst 
injector 54 in its closed position, as illustrated in FIG. 3A. Upon 
operation of catalyst pump 114, the tension provided by compression spring 
112 is overcome by the pressure of the catalyst, thereby unseating valve 
member 102 from seat 104 to allow catalyst to be injected into the flow of 
resin mixture. The catalyst and resin mixture are then substantially 
uniformly combined by the continuous flow through static mixer 44, thereby 
forming a fully catalyzed hardenable composition suitable for molding. 
Valve 41, preferably a pneumatically-activated ball valve, selectively 
controls the passage of resin mixture from discharge hose 60 into coupling 
62, where resin is introduced through injector 52 as described above. In 
the preferred embodiment illustrated, valve 41 is synchronized with valve 
36, so that both valves are simultaneously moved to either the open or 
closed position. Additionally, catalyst pump 114 is operated briefly prior 
to the opening of valve 41 during initial operation of molding apparatus 
10, and valve 41 is closed just prior to stopping catalyst pump 114, to 
ensure that all resin mixture is fully catalyzed. The pressure of the 
resin mixture created by pump 34 effectively prevents backflow of 
catalyzed composition during the filling operation, while valve 41, in its 
closed position, prevents backflow between filling cycles. 
FIGS. 4A-4D illustrate yet another unique feature of the molding method and 
apparatus taught by the present invention. Outlet end 56 of static mixer 
44 is secured to fill tube 54 by means of collar 116 threadingly engaging 
the upper threaded portion of fill tube 54. Actuator 118 is attached 
exteriorly to outlet end 56 by clamps, screws, or other suitable means. 
Actuator 118 may be operated hydraulically, pneumatically, or in any other 
manner suitable for the purposes described herein. Actuator 118 
selectively allows the hardenable polymer concrete composition to be 
discharged into mold 58 in a controlled manner. The distal end of piston 
120 is secured to rocker arm 122 inserted through tube 124 which is 
attached to the upper end of fill tube 54 and provides access to the 
interior thereof. Rocker arm 122 passes through ball mechanism 126, which 
sealingly engages the interior passageway of tube 124 while allowing free 
rotation of rocker arm 122 about its transverse horizontal axis. 
The opposite end of rocker arm 122 is operatively attached to the upper end 
of the stem 128, the lower end of stem 128 being secured to valve member 
130. The lower end 132 of fill tube 54 has valve seat 134 formed therein, 
with the upper, frustro-conical outer side surface of valve member 130 
being configured to form a seal therein. As shown in FIG. 4A, the downward 
position of piston 120 corresponds to the closed position for valve member 
30, wherein the hardenable concrete composition is prevented from being 
discharged through nozzle 66 which is threadingly engaged to lower end 132 
of fill tube 54. Activation of actuator 118 moves piston 120 to its upper 
position, as shown in FIGS. 4B-4D, whereupon valve member 130 is moved 
downwardly to its open position to allow the free discharge of the 
catalyzed composition. 
FIG. 4B illustrates nozzle 66 in its fully inserted position within 
interior cavity 68 of mold 58, during the initial discharge stage of 
catalyzed concrete composition. Just prior to the discharge of concrete 
composition, or substantially simultaneously therewith, table 136 is 
rotated about its vertical axis by operation of motor 138 (see FIGS. 
2A-2C). Rotation of table 136 effects corresponding rotation of mold 58, 
as mold 58 is anchored to table 136 by bolts 140 and nuts 142 or other 
suitable means. It may be preferable to utilize a quick coupling system to 
secure mold 58 to table 136, such as a plurality of centrifugally operable 
latches which automatically engage upon rotation of table 136. 
As discussed above, selective rotation of threaded rod 76 causes vertical, 
longitudinal movement of static mixer 44 and fill tube 54, from coupling 
62 through the distal end 144 of nozzle 66. This feature, particularly 
when used in conjunction with the rotation of table 136, greatly improves 
the ability of the present invention to mold solid objects without 
undesirable air entrainment over molding methods and apparatus known in 
the industry. The rotation of table 136 at an appropriate speed causes the 
concrete composition to flow radially outwardly from nozzle 66, thereby 
avoiding the formation of air pockets within the concrete composition. The 
rotation of table 136 and mold 58 causes a vortex to form within the 
concrete composition with distal end 144 being slightly submerged in the 
center. As the concrete composition is discharged, nozzle 66 is gradually 
withdrawn from cavity 68, with the concrete discharge rate and actuation 
of threaded rod 76 being synchronized such that distal end 144 of nozzle 
66 remains in contact with the top surface 146 of the polymer concrete 
composition and, preferably submerged slightly therein. It has been found 
that, by maintaining distal end 144 slightly submerged beneath the top 
surface 146, it is possible to avoid the entrainment of air about the 
longitudinal axis of the insulator which could otherwise result from the 
naturally occurring turbulence in the vicinity of the nozzle caused by the 
rotation of mold 58. 
It has been found preferable to inject a small quantity of a suitable 
monomer into mold cavity 68 prior to the injection of concrete composition 
as discussed above. For this purpose, monomer supply tank 180 and pump 182 
are provided to initially inject the desired amount of monomer into cavity 
68 through auxiliary tube 184. Pump 182 may be of purely conventional 
design, such as a piston pump, and may be secured to static mixer 44 and 
moveable therewith, communicating with tank 180 through a flexible hose. 
It will be appreciated that the manner of injecting monomer into cavity 68 
is largely inconsequential for purposes of this invention, and the 
apparatus disclosed herein is by way of example only and not to be deemed 
a limitation. 
The monomer initially injected into cavity 68, identified by reference 
numeral 147 in FIGS. 4A-4D, is displaced during the filling process by the 
concrete mixture, and is maintained in contact with the interior surface 
of the mold cavity 68 by the centrifugal force generated upon rotation of 
mold 58, thereby pre-wetting the surface of the mold. Such pre-wetting 
allows the concrete composition to more effectively wet the mold surface, 
thereby yielding a superior insulator having greatly reduced surface 
porosity over those produced by other known methods. Both styrene and 
methyl-methacrylate monomers have been found suitable for this purpose, 
and it is expected that other monomers may also yield acceptable results. 
Typically, the quantity of monomer used will be approximately 50 ml but 
may be varied as necessary according to the size of cavity 68, and other 
variables as appropriate. 
As also shown in FIGS. 4A-4D and in FIG. 6, the top portion of collar 166 
is flared outwardly and serves as an overfill reservoir to retain the 
unused monomer 147 upon completion of the mold filling process. Collar 166 
further serves to retain a certain volume of the concrete material 
displaced upwardly during high speed spinning of mold 58. It will be 
appreciated that mold 58 must be slightly overfilled during the initial 
filling process to ensure that sufficient material is present to fill the 
void created by the vortex once rotation of the mold has stopped. Collar 
166 serves to contain such overfill. 
At least two techniques for synchronizing the withdrawal of nozzle 66 with 
the rotation of table 136 have been found suitable for the production of 
polymer concrete electrical insulators. With the first technique, a 
relatively high initial rotational speed is attained with nozzle 66 in its 
fully inserted position, the speed decreasing gradually as nozzle 66 is 
withdrawn to its retracted position. Initial rotational speeds of 
approximately 600-700 rpm have been found successful. With the second 
technique, the rotational speed is maintained constant, with speeds of 250 
to 450 rpm providing acceptable results. With either technique, withdrawal 
of nozzle 66 is carefully controlled to track the top surface 146, as 
mentioned above. The cross sectional area of cavity 68 typically 
fluctuates at various points along its longitudinal axis due to the 
radially finned configuration of most such electrical insulators. It is 
therefore necessary for the withdrawal rate of nozzle 66 to fluctuate 
inversely according to the cross sectional area of cavity 68 corresponding 
to the location of nozzle 66. 
With the preferred molding method of this invention, a post spin operation 
is also employed after retraction of nozzle 66 to remove any air trapped 
within the top of cavity 68. Post spin speeds of 450 to 600 rpm maintained 
for a duration of thirty to sixty seconds, for example, have been found 
appropriate for the removal of air trapped therein. 
As those skilled in the art will fully understand, the preferred method 
described herein requires reasonably precise control of the discharge rate 
of resin mixture and catalyst, rotation rate of table 136, and withdrawal 
rate of nozzle 66. Similarly, the operation of catalyst injector 52 and 
actuator 118 must be carefully controlled to ensure consistent results and 
minimize waste. Accordingly, it will be appreciated that generally 
conventional microprocessor means have been employed to control the 
various pumps, valves, and actuators described herein. Those skilled in 
the art will further appreciate that considerable variation in the 
controlling parameters is necessary to accommodate a wide range of molded 
products. Since the catalyst and resin discharge rates, rotational speed 
for table 136, and withdrawal rate for nozzle 66 will vary considerably 
depending upon the size, configuration, and composition of the insulator 
or other product being molded, a detailed explanation of the controlling 
and programming apparatus has been omitted from this specification. 
FIGS. 5-8 illustrate in more detail the unique structure of mold 58 which 
substantially reduces the amount of flash formed at the parting line with 
conventional molds. Referring initially to FIGS. 5 and 6, mold 58 is of a 
two-part "clam shell" variety, having an outer housing comprising mating 
halves 148 and 150. Each mating half 148 and 150 includes a generally 
cylindrical body portion 152, with radial flanges 154 and longitudinal 
flanges 156 fixedly secured thereto. Flanges 156 of body member 148 
include locator posts 158 configured to engage corresponding holes 160 in 
body member 150, with remaining holes 162 serving to receive bolts or 
other fastening devices. End cap 164 is press fit into the central opening 
formed upon assembly of body members 148 and 150, and has collar 166 
secured thereto for guiding nozzle 66 into interior cavity 68. Threaded 
inserts 168 may be secured by bolts through holes 170 in end cap 164 to be 
molded in place. (Not shown for the sake of clarity is a bottom end cap 
similarly installed to enclose the lower opening of mold 58 and secure 
threaded inserts 168, without the need for a corresponding collar 166). 
Finally, holes 170 in radial flanges 154 are located to receive studs 140 
protruding from plate 136 for anchoring mold 58. 
The outer housing of mold 58 is preferably formed of aluminum or other 
suitably rigid material. The configuration of cavity 68, however, is 
defined by liner 172 formed within body members 148 and 150. As 
illustrated in FIGS. 7 and 8, the two halves of liner 172, designated by 
reference numerals 172A and 172B, are formed as mating pairs. As shown, 
surface 174 of member 172B is essentially concave, while surface 176 of 
member of 172A is correspondingly convex. The cooperative mating 
relationship between surfaces 174 and 176, upon assembly of mold 58, 
substantially reduces the amount of flash formed at the parting line when 
compared to products made with conventional molds. 
Liners 172A and 172B are preferably formed from a suitable room temperature 
vulcanizing silicon rubber (RTV) that is easily cast around a conventional 
pattern plug to form cavity 68. In order to obtain the unique 
configuration of surfaces 174 and 176, 172B is first cast within housing 
150, with a suitable pattern plug held in position by conventional means. 
With housing member 150 maintained in a horizontal position, the surface 
tension properties of the curing RTV create a concave meniscus which, upon 
final curing, forms surface 174. After the application of a release agent 
on surface 174, suitable for use with RTV rubber, housing member 148 is 
placed in position and a second quantity of RTV poured therein, with 
surface 174 being used as the molding pattern to produce mating surface 
176 in member 172A. When formed in this manner, a substantially perfect 
fit is obtained between surfaces 174 and 176. 
FIG. 9 illustrates a cross sectional view of an electrical insulator 178 
produced in accordance with the teachings of the present invention. 
Insulator 178 includes a plurality of threaded inserts 168 molded therein, 
as described generally herein. Typically, insulator 178 will include four 
inserts 168 in each end thereof, but those skilled in the art will readily 
understand that any number of inserts 168, or similar fastening means, may 
be utilized with insulator 178. By incorporating the principles of the 
method and apparatus described herein, insulator 178 has a significantly 
lower percentage of air inclusion than conventional insulators. While a 
wide variety of polymers, monomers, aggregates, and catalysts may be 
employed with the improved method and apparatus disclosed herein to obtain 
superior insulators, it has been found that polymer concrete compositions 
composed of the constituents combined pursuant to the example set forth 
below yield exceptional results. 
Polymer concrete is essentially composed of an aggregate mixture and a 
polymer resin, which are uniformly combined and mixed with a suitable 
catalyst prior to casting. For the purposes of this invention, the 
following aggregate mixtures have been found particularly well-suited: 
______________________________________ 
Material Approximate Weight % 
______________________________________ 
EXAMPLE 1 
Silica 12-28 33.00% 
Silica 20-40 23.98% 
Silica 40-60 13.32% 
Silica M-70 5.33% 
Daper Novacite 3.99% 
200 Novacite 10.65% 
Alumina Trihydrate 
7.99% 
Titanium Dioxide 
1.33% 
Ebony Novacite 0.41% 
100.0% 
EXAMPLE 2 
Silica 20-40 35.79% 
Silica 40-60 19.88% 
Silica M-70 7.95% 
Daper Novacite 5.96% 
200 Novacite 15.90% 
Alumina Trihydrate 
11.93% 
Titanium Dioxide 
1.99% 
Ebony Novacite 0.60% 
100.0% 
______________________________________ 
Each of the aggregate blends set forth in Examples 1 and 2 above should be 
treated with gamma methacryloxypropyltrimethoxysilane (silane), an organo 
functional coupling agent providing a mechanism for chemically coupling 
inorganic substrates with organic polymers. The aggregate ingredients and 
silane should be combined by a low shear blending method, such as a 
baffled rotating drum similar to that of a conventional cement mixer. 
Silane may be applied by a sprayer operating at 35 psi during mixing. 
Silane treatments comprising from 0.05% to 0.3% of the total aggregate 
mixture weight have been found to be successful. 
The preferred polymer resin for use with either of the above described 
aggregate mixtures is a formulation of dicyclopentadiene (DCPD) polyester. 
The formulation also includes 40% to 50% styrene or other suitable monomer 
to improve viscosity of the mixture. The preferred resin mixture 
formulation is as follows: 
______________________________________ 
Composition Approximate Weight % 
______________________________________ 
Polyester Resin/Monomer Mixture 
99.2-99.8% 
Cobalt Naphthenate (12%) 
0.1-0.4% 
Dimethyl Analine 0.1-0.4% 
Methyltertiarybutylhydroquinone 
.005-.050% 
______________________________________ 
After the preferred constituents have been combined in mixer 16 and 
properly degassed, as set forth more fully below, the preferred catalyst 
employed to initiate the polymerization reaction for curing is 
Methylethylketone peroxide (MEKP). 
A homogenized, degassed resin mixture is obtained by first providing a 
sufficient quantity of aggregate ingredients within mixer 16, mixer 16 
preferably being of the orbital, vertical cone screw mixture type. Polymer 
resin ingredients are then added, and the auger within mixer 16 activated 
in the reverse (counter clockwise) direction for approximately thirty 
minutes. The auger is then reversed to operate in the forward (clockwise) 
director for another thirty minutes, at which point the resin mixture is 
sufficiently homogenized. As those skilled in the art will understand, 
clockwise rotation of the auger serves to move material from the top of 
the mixer to the bottom, and counter-clockwise rotation serves to move 
material from the bottom to the top. Vacuum receiver tank 26 and vacuum 
pump 24 are then utilized as described above to expose the homogenized 
resin mixture to a vacuum approaching 25 in. Hg for approximately fifteen 
minutes, after which continued evacuation is unnecessary. The combination 
of the forward (clockwise) operation of the auger to direct resin mixture 
from the lower section 22 to the top section 18 of mixer 16, and the 
evacuated environment of mixer 16, suitably degasses the resin mixture. 
The principles of the present invention as applied to the production of 
polymer concrete electrical insulators will be fully appreciated by those 
skilled in the art upon reviewing the specification, claims, and drawings 
contained herein. Many principles of the present invention, however, are 
not limited to production of polymer concrete electrical insulators, and 
are more generally applicable to a variety of molding/casting methods and 
apparatus. Accordingly, it is expressly understood that the following 
claims are intended to cover and embrace not only the specific embodiment 
disclosed herein, but also such modifications and applications within the 
spirit and scope of this invention.