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Патент USA US2411254

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Nov. 19,‘ 1946.
2,411,254
G. H. FRANK
MOLDING DEVICE
Filed Sept. ‘29', 1942
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BY ?lm? I; M HrTOKNE-Y
2,411,254
Patented Nov. 19, 1946
UNITED STATES PATENT OFFICE
MOLDING DEVICE
George 11. Frank, Oak Park, Ill., asslgnor to
WesternElectric Company, Incorporated, New
York, N. Y., a corporation of New York
Application September 29, 1942, Serial No. 460,066
6 Claims. (Cl. 18-30)
2
This invention relates to molding and more par
ticularly toan apparatus for injection molding
of thermo-setting materials.
.
In the manufacture of molded articles from
thermo-setting molding vcompounds, such as cer
.
from the preheating chamber to the molding die. _
Other objects and advantages of this inven-l '
tion will be apparent from the following detailed
description taken in conjunction with the fol
lowing drawing, wherein:
'
'
tain phenol aldehydes, the molding, compound
Fig. 1 is a front elevation, partly in section,
of a molding apparatus constructed in accordance
' may be preheated prior to injection into the mold.
Heat is applied to plastify the compound and
with one embodiment of this invention, and
Fig. 2 is a. fragmentary sectional view along
render it soft enough to be injectable. Pressure
is then applied to inject the compound into the 10 the line 2-2 of Fig. 1.
-- mold. With some phenol aldehyde compounds,
This invention will be described in connection
with the molding of phenol aldehydes. However,
the period of heat treatment prior to injection
it will be understood that the invention is appli
of the compound may be relatively short. For
cable to any plastiflable materials exhibiting an
example, with certain phenol formaldehyde com
pounds, it may be a matter of only a few seconds 15 appreciable dielectric loss angle when subjected
to a high frequency, high voltage field, such, for
of heat treatment before the compound will set
or cure and become impossible to inject. Thus,
example, as rubber and the like.
the heat treating should preferably be done by
While most phenol aldehydes are excellent in
a means that permits rapid and uniform preheat
sulating materials for direct current or for "low
ing and quick transfer of the compound to the 20 frequency alternating current, they‘ are gener
ally poor insulators for high frequency use, be
molding die when the optimum condition for
plastic ?ow has been attained.
'
Since the heat is usually transferred to the I
. .cause the power factor of such materials increases
‘with increases in applied frequency. Thus, if
compound from the walls of the steam or elec-' ' 'a high frequency current of from .1 to 100 mega
trlcally heated container, and since most phenol 25 cycles, and of su?lcient energy, be applied. to
. aldehydes are poor conductors of heat, that por
tion of the molding compound which contacts the
walls of the container is heated more quickly than
that portion of the compound in the middle and
such an insulating material, considerable heat
will be generated. The percentage of electrical
current transformed into heat will be, in general,
proportional to the power factor of the insulating
not contacting the walls of the container. Thus, 30 material and will increase with increases in fre
quency. This heat is developed internally within
the insulating material and may be regulated
tainer may set before the remainder has been
precisely by controlling either the strength or the
plasti?ed. If, however, the compound is trans
frequency, or both, of the imposed current.
ferred to the mold as soon as this outer portion
has been properly preheated, the inner portion 35 For a given power factor, that material which
is likely to be so inadequately plasti?ed that an
has the highest dielectric. constant will produce
incompletely cured part may result.
the greatest heating effect. In other words, the
generation of heat is proportional to the product
It is an object of the present invention to pro
. the portion which contacts the walls of the. con
'vide an efficient and effective apparatus for in
of the dielectric constant and the power factor.
jection molding thermo-setting materials.
40 Certain types of Pyrex glass are obtainable which
have a power factor of approximately .2 and a
In accordance with one embodiment of this in
vention, .a molding apparatus may be provided
" dielectric constant of approximately 5 at 18 mega
comprising a, molding die having an inlet to ad
cycles, giving a product of 1. Phenol formal
mit molding compound. A Pyrex preheater is
dehyde, which is a commonly used phenol alde
positioned adjacent this aperture and is pro 45 hyde compound,‘ has a power factor of approxi
mately 6 and a dielectric constant of approxi
vided with a pair of electrodes which are con- .
mately 5 at 18 megacycles, the product of these
nected to a source of high-frequency current.
The transformation of high frequency energy into
being approximately‘ 30. Comparing these prod
heat in the dielectric molding material causes
ucts, an energy loss ratio of about -1 to 30 may be
the material to plastify uniformly and permit 50 seen to obtain between Pyrex and phenol form
quick injection. The dielectric losses in the mold
aldehyde. This indicates that per unit'volume of
ing compound produced by the high frequency glass and phenol formaldehyde, the transmission
electrostatic field cause the compound to heat
suil‘lciently for injection. A ram is provided for.
of high‘ frequency current through each at the
proper energy level would cause the heating of
transferring the plasti?ed molding compound 55 the ‘phenol formaldehyde through a range of 150°
3
2,411,254
4 .
0., while the temperature of the glass would be
raised only 5° C. Thus. if a heating chamber be
made of this type of Pyrex glass, it becomes pos
sible to heat treat the phenol formaldehyde with
out substantially increasing the temperature of
the heating chamber. Because the heat is gen
erated internally within the phenol formaldehyde
is attached to the bottom of the plate 42 by a
number of bolts 22 and associated clamps 23,
which engage a projecting portion 24 at the base
of the section 2I. A funnel shaped aperture 44 is
formed through the middle of the supporting
plate 4.2 to admit heated molding compound from
the heating chamber 5 to the molding die. An
resin, the preheating is uniform throughout the
aperture 25 extends through the mid-portion of
charge in the heating chamber.
the upper section 2I of the molding die to permit
The present invention contemplates heating the 10 passage of the molding compound to the molding
molding compound through the heat generated in
die. A replaceable sleeve 26 of hardened metal
the compound by the presence of a high fre
is inserted in this aperture and extends into the
quency, high voltage electrostatic ?eld. Fig. 1
funnel-shaped aperture 44 of the cross plate 42.
illustrates an article molding apparatus con
By employing a replaceable sleeve of hardened
structed in accordance with this invention. Es 15 metal, the maintenance cost, due to scoring of the
sentially, this apparatus comprises a preheater
die by the ram, is kept at a minimum.
5 for heating the molding compound prior to
A relatively thin, removable wedge-shaped plate
transfer of the compound by a ram ll to a mold
45 is positioned on the upper surface of the plate
ing die 20. The preheater 5 is formed by a thick
42 so as to contact the lower end of the preheater
walled shell 5 of Pyrex type glass having as low 20 5 and thereby to prevent the molding compound
a dielectric constant, loss angle and power factor
from moving downward out of the heating cham
as feasible in order to keep heating of the pre
ber before the period of heat treatment is com
heater during the operation of the apparatus at
plete. A number of guides 46 are attached to
a minimum. As may be seen in Fig. 2, a pair of
the upper surface of the plate 42 in which the
electrodes 1 are embedded in the wall of the pre 25 plate 45 is slidable, and serve to position the plate
heater and oppose each other. It is desirable
45 properly with respect to the aperture 44..
that these electrodes be made of a conducting
A lower section 30 of the die 20 is mounted on
material having a temperature coeillcient of ex
a vertically movable cross plate 36 which is similar
pansiomas near that of the glass used for the
in size and appearance to the supporting plates
heating chamber as possible in order to prevent 30 42 and I4. This section of the die is attached to
strain and possible breakage of the glass due to
the plate 36 by a number of clamps 31 and asso
uneven expansion of the two materials during
ciated T-bolts 38 which engage the plate 38, the
base of the lower section 30 having a projecting
heating.
A properly terminated coaxial cable 9 is con- I
portion 40 which is engaged by the clamps 31.
nected to each electrode and may, in turn, be 35 The supporting plate 36 has an aperture in each
connected to a suitable high frequencq, high volt
corner and each aperture is provided with a sleeve
age current. With a material such as phenol
bearing 39. The posts II extend through these
formaldehyde, it has been found that by employ
sleeve bearings and, thus, serve as guide posts for
ing a current of approximately 2000 volts at a
the plate and lower section of the die as they are
frequency of approximately 18 megacycles, the 40 raised and lowered by the ram 48.
material will reach molding temperature in a
A pair of feeders 3I are formed in the lower
very few seconds. In order to obtain maximum
surface of the upper section of the die to permit
eiiiciehcy of the heating apparatus, a current fre
the molding compound to be injected into mold
quency is employed to which the heatingv appa
cavities 21, also formed therein. The lower sec
ratus is resonant, the apparatus in e?ect being a
tion is provided with cavities 32 and the mold cav
condenser: the electrodes ‘I serve as the conduct
ities are shaped in accordance with the shape of
ing plates while the molding compound, inter
the articles to be molded. In operating position,
posed therebetween, serves as the dielectric body.
the lower section is held tightly against the up
Once the resonant frequency is determined, ade
per section by the ram 48 which presses against
quate control of the heating is had by varying the
the base of the plate 36 and raises or lowers it as
voltage.
may be required. When these two sections are in
As shown in Fig. 1, the base of the preheater is
closed or operating position, the cavities of the
in a recessed portion of the under-side of a heavy,
two sections of the die form a pair of enclosed
supporting, cross plate I4 which is supported by
mold cavities into which the molding compound
four vertical posts II, two being shown in Fig. 1. 55 may be injected by the ram I1. A number of
A number of bolts I3 and associated clamps I2
apertures 28 are formed in both sections of the
“ serve to hold the heating chamber in place. Holes
die to permit heating thereof, either by steam or
are provided in each of the corners of the plate
hot air, to complete the curing of the compound.
I4 through which the posts extend and the plate
The high injection pressures required for mold‘
is ?xed in position on the posts by a number of 60 ing thermosetting materials are such that even
nuts I5 which are threaded to the posts. An aper
the hardest metals may be scored or deformed.
ture ‘I5 is provided in the middle of the plate I4
Thus, a removable insert 33 of hardened metal is
to permit an operator to place molding compound
positioned in the upper surface of the lower sec
in the heating chamber. This aperture is made
tion of the die to receive the brunt of the pres
65
somewhat larger in diameter than the inner diam
sure exerted by the ram I ‘I in forcing the molding
eter of the heating chamber in order to facilitate
compound into the mold cavity. This insert may
easy insertion of the molding compound. The
be replaced by inserting a suitable tool in an aper
four posts together with'a base plate 50 form a
ture 34, which extends from the base of the lower
frame for the whole apparatus. The apparatus
‘section of the base of the insert, and knocking it
may be supported on a table 5i.
out. The lower section of the die, of course, must
The lower end of the ‘preheater‘ is tapered and
be removed from the plate 36 in order to do this;
is positioned slightly ‘above a second heavy cross
its removal is facilitated- by the use of the T-bolts
plate 42 which is ?xed to the posts I I by nuts 43.
38 and clamps 31.
This plate serves as a ?xed support for summer
In the operation of this apparatus, a quantity
section 2| of the molding die 20. This section 2!
of molding compound to which a small percentage .
75
2,411,254
of carbon black may be added to accelerate the
heating, may be placed in the preheating cham
ber. Among other materials that‘ accelerate the
rate of heating, zinc sulphide and zinc oxide may
also be cited. The presence of moisture in 5
amounts up to 6% also has a de?nite accelerative
effect on the heating. The compound may be
previously compacted to form a‘cylindrical block
'6
said stationary mold section to form a mold cav
ity, means for moving said movable mold section
to open and close the mold, means for heating
said mold sections, said stationary moldl section
having an extrusion cylinder for ?lling said mold
cavity, a preheating chamber in alignment with
said extrusion cylinder, removable means for clos
ing one end of said chamber means for electro-‘
of substantially the same size as the inside of the
statically heating molding material in said cham
heating chamber. Due to heating and the appli
ber to a plastic ?ow condition, and a plunger in
cation of pressure, the molding compound will or
dinarily be reduced’to one-third of its original vol
ume, and by compacting the compound in advance
as much as possible, the required size or the heat
ing chamber is kept at a minimum. The ram 11, 15
a which is supported by a cross plate It ?xed to
the upper ends of the posts II by a number of
nuts I9, is then caused to move downward to
compact the compound in the heating chamber
alignment with said preheating chamber. and said
extrusion cylinder for compressing the molding
material in said preheating chamber and for
transferring the plasticized molding material
from said preheating chamber to the extrusion
cylinder and then to the mold cavity.
2. A molding apparatus for molding thermo
setting material comprising a stationary mold
section, a movable mold section cooperating with
by actuating a suitable driving means (not 20 said stationary mold section to form a mold cav
ity, means for moving said movable mold section
shown). A pressure on the order of 150 pounds
to open and close the mold, said stationary mold
per square inch may be used in the preheating
section having anextrusion cylinder for ?lling
chamber. Compacting the compound is desir
said mold cavity, means for heating said mold
able to obtain maximum e?lciency ofthe electro
static ?eld applied to the compound by the elec 25 and extrusion cylinder, a preheating chamber in
alignment with said extrusion cylinder, means for
electrostatically heating molding material in said
The ram, being metal, is withdrawn so as not
chamber to a plastic ?ow condition, and a plunger
to be in the electrode ?eld and the high’frequency
in alignment with said preheating chamber and
current is then applied. when the compound
has become sumciently heated and plasti?ed, the 30 said extrusion cylinder for transferring the plas
ticized molding material from said preheating
retaining plate 45 is withdrawn and the driving
chamber to the extrusion cylinder and then to
means for the mm H is again actuated toforce
the mold cavity.
the compound out of the heating chamber,
3. In a molding apparatus for molding thermo
through the funnel-shaped aperture 44 in the
plate 42, through the aperture“ in the upper sec 35 setting material. a preheating chamber, a pair of
electrodes associated with said chamber, means
tion of the die 20 and toinject it into the mold
for supplying current to said electrodes, said elec
cavities. The ram continues its downward move
trodes comprising substantially ?at plates of con
ment until the die cavities 21 and 32 have been
ducting material, said plates being spaced from
?lled. An injection‘pressure as great as 30,000
pounds per squareinch may be employed in order 40 and parallel to each other so as to create a sub
trodes.
‘
,
.
‘
‘
to force the compound into the mold cavities.
The molded articles are permitted to cure in
the mold cavities and then the driving means for
the ram 48 is actuated to lower the ram and cross
plate 30 so as to separate the two sections of the
molding die, thus permitting removal of the
molded articles by means such as ejector pins ‘
‘ stantially uniform electrostatic ?eld therebe
tween. a mold chamber having an extrusion cyl
inder in alignment with said preheating chamber,
means for heating said molding chamber and
extrusion cylinder. means including'a ram in
alignment with said preheating chamber and said
extrusion cylinder for transferring the plasti
cized molding compound from said preheating
commonly employed in the art. ‘The sections are
chamber to said extrusion cylinder and then to
then brought together again by the ram 48 and
50 said , mold chamber, and means for retaining
the cycle or operation is ready for repetition.
molding compound in said preheating chamber
Since for most phenol aldehyde compounds,
both the power factor and dielectric constant in
crease at a much faster rate with increases in
temperature than is the case for glass, while the
during preheating.
4. A molding apparatus for molding thermo
setting material comprising a stationary mold
heating of the molding compound may be rela 55 section, a movable mold section cooperating with
said stationary mold section to ‘form a mold cav
tively slow at ?rst application thereto of the high
ity, means for heating said mold sections, means
frequency ?eld, the percentage of energy in the
for moving said movable mold section to open and
circuit transformed into heat will continuously
close the mold, said stationary mold section hav
increase at a rapidly accelerated rate as the tem- ,
ing an extrusion cylinder for ?lling said mold
perature of the molding compound increases. In ,
cavity, a preheatingr chamber in alignment with
short, the higher the temperature of the com
said extrusion cylinder, means for electrostati~ “
pound, the greater is the speed of heating. Since
cally heating molding material to a plastic ?ow
this heating characteristic is many times greater
condition in said chamber, a removable member
for the phenol formaldehyde than for glass, the
for retaining the molding material in said cham
glass remains relatively cool throughout the op
ber, a feeder groove extending laterally from the
eration of the apparatus.
‘
‘base of said extrusion cylinder to the mold cav
While but one embodiment of the present in
ity, said groove being formed in the surface of one
vention has beenshown and described, it will be
' understood that many changes and modi?cations
vof said mold sections, and a means including a
may be made therein without departing from the 70 plunger in alignment with said preheating cham
ber for compressing the molding material in said
spirit or scope of the present invention.
preheating chamber and for transferring molding
What is claimed is:
material from said preheating chamber to the
1. A molding apparatus for molding thermo
extrusion cylinder and then to the mold. cavity.
. setting material comprising a stationary mold
5. A molding apparatus for molding thermo
‘ section, a movable mold section cooperating with 75
7
2,411,254
setting compound comprising a preheating cham
ber, means for electrostatically heating molding
ing chamber being made of a Pyrex type glass,
means for electrostatically heating said molding
compound in said preheating chamber to a plas
material in said chamber including a pair of »
tic ?ow condition, means for retaining said mold
spaced electrodes imbedded in the walls of said
ing compound in said preheating chamber until
chamber, a removable member for closing one end
heated, a mold having an extrusion chamber in
or said chamber, a mold having an extrusion cyl
alignment with said preheating chamber, and a
inder in alignment with said preheating chamber,
plunger in alignment with said preheating and
means for heating said mold and extrusion cylin
extrusion chambers for compression the mold
der to a temperature to maintain said plastic flow
ing compound in the preheating chamber and for 10 condition, and a plunger in alignment with said
transferring the plasticized molding compound
preheating chamber and extrusion cylinder for
from the preheating chamber to the extrusion
compressing said molding material in. said pre
chamber and then to the mold.
heating chamber and for transferring the plasti
6. A molding apparatus for molding thermo
‘cized molding material from the preheating
setting material comprising a cylindrical pre
chamber to the extrusion cylinder and then
heating chamber for heating a charge of molding
extruding it into the mold.
material to a plastic ?ow condition, said preheat
GEORGE H. FRANK.
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