U.S. patent application number 10/567153 was filed with the patent office on 2008-11-06 for metal mold, and formed body molding method by the metal mold.
This patent application is currently assigned to COKI ENGINEERING INC. Invention is credited to Akira Yotsutsuji.
Application Number | 20080271870 10/567153 |
Document ID | / |
Family ID | 34113492 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080271870 |
Kind Code |
A1 |
Yotsutsuji; Akira |
November 6, 2008 |
Metal Mold, and Formed Body Molding Method by the Metal Mold
Abstract
A metal mold capable of preventing a nonuniform wall thickness
from occurring in a cylindrical formed product, wherein a gate (8)
for filling molding material is formed in alignment with the center
axis (CL) of a tubular mold cavity (4) so that metered resin can be
injected and filled from the tip side of a core (5) into the mold
cavity, whereby since the metered molding material injected from
the gate into the mold cavity uniformly flows around the core, a
force is uniformly applied to the side face of the core through all
the periphery thereof to prevent the core from falling in one
direction and to always position the core at the center of the mold
cavity, the molded formed product cannot cause the nonuniform wall
thickness.
Inventors: |
Yotsutsuji; Akira; (Osaka,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
COKI ENGINEERING INC
Osaka-shi
JP
|
Family ID: |
34113492 |
Appl. No.: |
10/567153 |
Filed: |
August 4, 2003 |
PCT Filed: |
August 4, 2003 |
PCT NO: |
PCT/JP2003/009904 |
371 Date: |
July 15, 2008 |
Current U.S.
Class: |
164/132 ;
249/63 |
Current CPC
Class: |
B29C 45/2806 20130101;
B29C 45/261 20130101; B29L 2031/7544 20130101; B29C 45/36 20130101;
B29C 2045/2879 20130101 |
Class at
Publication: |
164/132 ;
249/63 |
International
Class: |
B22D 29/00 20060101
B22D029/00 |
Claims
1. (canceled)
2. A metal mold, comprising: a cavity having a predetermined
internal shape; a molding material injection path communicated with
the cavity via a gate for supplying a metered fluid molding
material to the cavity; and a valve pin disposed within the molding
material injection path so as to be inserted into and pulled out
from the gate, wherein the cavity includes a cylindrical mold
cavity and a columnar core to be coaxially inserted into and pulled
out from the mold cavity, and the gate for injecting molding
material is formed in alignment with the center axis of the mold
cavity, wherein the core has a cone-shaped front end portion, and
when the core is inserted into the mold cavity, the front end
portion of the core is inserted into the gate, and a gap of an
identical width is formed all around the periphery between the core
and the gate, wherein, when the valve pin is parted from the gate,
the molding material flows uniformly into the cavity all around the
periphery thereof from the gap, wherein the valve pin is formed
with circular cone recesses on the end face at the cavity side, and
a communicating hole communicating the circular cone recess and the
molding material injection path is formed, wherein, when the valve
pin fit with the gate to perform gate-cut, the cone-shaped front
end portion of the core fits with the circular cone recess of the
valve pin, and surplus molding material caught between the circular
cone recess and the front end portion can escape to the molding
material injection path through the communicating hole.
3. The metal mold according to claim 2, wherein the mold cavity is
for forming the outer surface of a cylinder and the core is for
forming the cylinder inner surface.
4. (canceled)
5. A formed body molding method, comprising the steps of: (a)
injecting a metered molding material from the molding material
supply side into a cavity via a gate to fill the cavity therewith,
(b) after filling the cavity, applying and maintaining a
predetermined pressure to the molding material within the cavity,
(c) after completing the pressure applying and maintaining step,
cutting off the gate, (d) cooling the molding material within the
cavity to solidify into a molding, and then (e) taking out the
molding, wherein the cavity includes a cylindrical mold cavity and
a columnar core to be coaxially inserted into and pulled out from
the mold cavity, and the gate for injecting molding material is
formed in alignment with the center axis of the mold cavity, the
molding material is injected from the front end side of the core to
fill the mold cavity therewith, the core has a cone-shaped front
end portion, in the step (a), the front end portion of the core is
inserted into the gate, a gap of uniform width is formed all around
the periphery between the gate and the core, and the molding
material flows uniformly into all around the periphery of the
cavity from the gap, in the step (c), when the valve pin disposed
so as to be inserted into and pulled out from the gate at the
supply side of the molding material is inserted into the gate to
perform gate-cut, and when the cone-shaped front end portion of the
core is inserted into a circular cone recess formed on the end face
of the cavity of the valve pin, inescapable surplus molding
material caught between the circular cone recess and the front end
portion can escape to the molding material supply side through the
communicating hole.
6. The formed body molding method according to claim 5, wherein the
mold cavity is for forming the outer surface of a cylinder and the
core is for forming the cylinder inner surface.
7. (canceled)
8. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a resource-saving type
metal mold and a formed body molding method of a mold using the
metal mold, which is capable of molding, in a case of a cylindrical
molding, without causing nonuniform wall thickness using a molding
material such as a resin, a kneaded material of a sintering powder
and a resin binder or the like, and suitable for molding a molded
formed product such as a cylinder for a syringe which requires an
extremely high cleanliness and precision.
BACKGROUND ART
[0002] In a conventional metal mold (101) for cylinder molding, as
shown in FIG. 7, a hot runner (107) is disposed in the central area
of a female die (102) and a cold runner (108) is formed
perpendicular thereto, and a metered resin (109) is filled within a
cavity (106) with a high pressure through a flange portion (110c)
of a cylinder (110). In this method, when the metered resin (109)
is injected into the cavity (106) with a high pressure through the
flange portion (110c) of the cylinder (110), the metered resin
(109) is gradually filled therein from a portion closer to the gate
(111) of the flange portion (110c) as shown in FIG. 8.
[0003] The injection filling pressure to the metered resin (109)
reaches to a high pressure of 1,000-2,000 kg/cm.sup.2, and a force
(F) perpendicular to the center axis (CL) of the core (105) is
applied to the side face portion of the core (105) closer to the
gate (111), from which the resin (109) is filled first, a slight
sag is made on the core (105) in a direction away from the gate
(111). When, such sag is generated, a difference [(t1)>(t2)] is
generated between the width at the gate side (t1) and the width at
the opposite side (t2) of the cavity (106), which is formed by the
core (105) and the mold cavity (104) formed in the female die
(102), a nonuniform wall thickness is generated in the molded
cylinder (110) (U.S. Pat. No. 6,562,009B1).
[0004] An object of the present invention is to provide a hot
runner type metal mold, which does not cause nonuniform wall
thickness unlike the cold runner type which causes nonuniform wall
thickness, and a formed body molding method using the metal
mold.
DISCLOSURE OF THE INVENTION
[0005] An aspect of a metal mold (1) according to claim 1 of the
present invention is a metal mold (1), which includes:
[0006] a cavity (6) having a predetermined internal shape;
[0007] a molding material injection path (12) communicated with the
cavity (6) via a gate (8) for supplying a metered fluid molding
material (9) to the cavity (6); and
[0008] a valve pin (7) disposed within the molding material
injection path (12) so as to be inserted into and pulled out from
the gate (8),
[0009] wherein the cavity (6) is formed with a cylindrical mold
cavity (4) and a columnar core (5) to be coaxially inserted into
and pulled out from the mold cavity (4), and the gate (8) for
injecting the molding material is formed in alignment with the
center axis (CL) of the mold cavity (4) to inject a metered resin
from the front end side of the core (5) and fill the core (5)
therewith. Accordingly, the gate (8) is formed on the center axis
(CL) of the mold cavity (4) and the core (5), the metered molding
material (9) injected into the cavity (6) from the gate (8) flows
uniformly around the periphery of the core (5); no force is applied
to the side face of the core (5) from one direction; the core (5)
is prevented from falling in one direction but always positioned at
the center of the mold cavity (4) throughout the course of the
injection and filling of the molding material; as a result, a
nonuniform wall thickness is not generated in the molded formed
product (10).
[0010] As a particular shape of the cavity (6), there may be given
such an example that the mold cavity (4) forms the outer surface of
the cylinder, and the core (5) is for forming the cylinder inner
surface.
[0011] As for the molding material (9) in the present invention, in
addition to ordinary resins, a kneaded material of a sintering
powder and a resin binder may be used.
[0012] A molding method using the metal mold (1) is a formed body
molding method, which includes the steps of:
[0013] (a) injecting a metered molding material (9) from the
molding material supply side (12) into a cavity (6) via a gate (8)
to fill the cavity (6) therewith,
[0014] (b) after filling the cavity, applying and maintaining a
predetermined pressure to the filled material within the
cavity,
[0015] (c) after completing the pressure applying and maintaining
step and after gate cutoff, returning a surplus molding material
(9a) remaining at the gate (8) portion to the molding material
supply side (12), and
[0016] (d) cooling the molding material (9) within the cavity (6)
to solidify into a formed body (10), and then taking out the formed
body (10),
[0017] wherein the cavity (6) includes a cylindrical mold cavity
(4) and a columnar core (5) to be coaxially inserted into and
pulled out from the mold cavity (4), and the gate (8) for injecting
the molding material is formed in alignment with the center axis
(CL) of the mold cavity (4), a metered resin is injected from the
front end side of the core (5) to fill the core therewith.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a cross sectional view showing a state of a closed
metal mold according to a first embodiment of the present
invention,
[0019] FIG. 2 is a cross sectional view showing a state of gate-cut
performed by the valve pin in FIG. 1,
[0020] FIG. 3 is a cross sectional view showing a state that the
metal mold in accordance with the first embodiment of the present
invention is opened,
[0021] FIG. 4 is a cross sectional view showing a state that
products are ejected from the metal mold in accordance with the
first embodiment of the present invention,
[0022] FIG. 5 is an enlarged cross sectional view of a gate-cut
state in the metal mold in accordance with the first embodiment of
the present invention,
[0023] FIG. 6 is an enlarged cross sectional view of a gate-open
state in the metal mold in accordance with the first embodiment of
the present invention,
[0024] FIG. 7 is a cross sectional view of a conventional example,
and
[0025] FIG. 8 is an enlarged cross sectional view showing a state
where metered molding material is being filled in the conventional
example.
CL BEST MODE FOR CARRYING OUT THE INVENTION
[0026] Hereinafter, the present invention will be described in
detail in accordance with an embodiment with reference to the
drawings. The present invention is applicable to forming any
runner-less cylinder. As a typical example of the embodiment, a
case where a cylindrical molded formed product (10) is produced
using a columnar core (5) and a cylindrical mold cavity (4) will be
described. The description will be made mainly taking an example in
which an ordinary resin is used as a molding material. Other
materials such as a kneaded material of a sintering powder and a
resin binder may be used; and the following materials are
available.
[0027] The molding material (9) includes a sintering powder and a
binder resin including mainly two kinds of resins constituting a
uniform mixture of a solvent soluble resin and a solvent insoluble
resin. The sintering powder includes a metal material, an oxide, a
nitride, quartz or glass as a main material to be sintered and a
binder for binding the above.
[0028] As for the main sintering materials capable of being
sintered, metal materials (stainless powder, Ni, W, Mo, Fe),
carbides (WC, TiC, chromium carbide), nitrides (boron nitride,
silicon nitride, aluminum nitride), oxides (quartz, aluminum,
glass, zirconium) are available; and as the binder for binding
these main sintering materials, Co and Ni are available. The oxides
(quartz, aluminum, glass, zirconium) may be sintered with no
binder. As the sintering articles of these materials, carbide
material, cermet material, ceramic material, quartz glass material,
tungsten material, stainless material, nickel material, molybdenum
material, glass material or compound materials of the above are
available. The optimum average particle size of the main sintering
material depends on the usage. For example, in the case of the
carbide material, average particle size of 0.2-0.5 .mu.m or so is
preferred for ensuring the durability of the edge portion. Ordinary
average particle size is 2 .mu.m or so.
[0029] The binder resin for supporting the sintering powder
includes a solvent soluble resin, which is solved into one solvent
and solvent insoluble resin, which is not solved into the solvent,
as the main material and necessary additives such as plasticizer
and release agent. It is preferred that the solvent soluble resin
and the solvent insoluble resin are completely mixed and coexisting
with each other at operation temperature. In this embodiment, the
following resin is used; i.e., both are solved into a solvent at a
melting temperature (high temperature) and separated from each
other in a state that both are uniformly mixed with each other at
an operation temperature.
[0030] Further, in order to enhance the shape retaining performance
after degreasing and the uniform dispersion of the sintering
powder, it is preferred to use a resin, which becomes fibrous or
plumose in the solvent insoluble resin, rather than the case where
the solvent soluble resin and the solvent insoluble resin are
simply mixed. That is, in the case of a resin in which the solvent
insoluble resin becomes fibrous or plumose, both are completely
solved into the solvent soluble resin at a high temperature
(=melting temperature of both). When the above is cooled down, the
solvent insoluble resin is gradually separated out in a fibrous
state; and among the fibers, the solvent soluble resin and the
sintering powder are left in an entwined state; thus the solvent
soluble resin and the sintering powder are extremely finely and
uniformly dispersed into the fibrous solvent insoluble resin.
[0031] As an example of such solvent soluble resins, polystyrene,
acrylate resin, vinyl chloride, cyclic polyolefin resin,
polycarbonate and transient plastic are available. As an example of
the solvent insoluble resin, polypropylene, polyethylene,
polyacetal and the like are available. As for the solvent for
solving the above at a high temperature (solvent insoluble resin
separates at a room temperature), for example, aromatic solvents
such as xylene, toluene, benzene and chlorinated solvents such as
dichloromethane and dichloroethane are available. Further, as a
plasticizer, dioctylphthalate, dibutylphthalate or the like are
available. As a release agent, zinc stearate, stearic acid amide
are available. The mixture ratio between the solvent insoluble
resin and the solvent soluble resin is 1:0.5-4.0 in volume ratio.
The volume ratio between the binder resin and the sintering powder
is 40:60-65:35. The above materials are formed into an ordinary
pellet state and used in the same manner as the ordinary resin.
[0032] Now, descriptions will be made with reference to FIGS. 1-6.
A metal mold (1) comprises a female die (2) and a male die (3), and
the female die (2) and the male die (3) are attached to a fixed die
plate (15) and a moving die plate (16) respectively. The male die
(3) is arranged so as to open and close with respect to the female
die (2) (as a matter of course, although not shown in the figures,
a relationship therebetween may be opposite to the above).
[0033] The female die (2) includes a first female member (2a)
having a parting face (P2), a cavity member (30) formed with the
mold cavity (4) and attached to the first female member (2a), a
second female member (2b) formed in the rear side of the first
female member (2a), a pin drive section (25), which is
hydraulically or pneumatically driven for moving valve pins (7)
forward/backward via a hot runner bush (20) and a valve pin
operation rod (25a) and attached to the second female member (2b),
a sprue-mounting block (27) attached to the rear side of the second
female member (2b), a third female member (2d) constituting the
rear side of the female die (2) for fixing the female die (2) to
the fixed die plate (15), a spacer member (2c) disposed between the
second female member (2b) and the third female member (2d) for
forming a housing space (28) for the sprue-mounting block (27)
between the members (2b) and (2d), auxiliary springs (25d) disposed
between the third female member (2d) and the valve pin operation
rod (25a) for pressurizing the valve pins (7) in the gate-cut
direction to urge the gate-cut operation of the pin drive section
(25), and the valve pins (7).
[0034] The first female member (2a) is formed with one or a
plurality of recess (18) from the parting face (P2) thereof to the
rear face, and the recess (18) receives the cavity member (30)
formed with the mold cavity (4) having the opening at the parting
face (P2) side. Here, the recess of the mold cavity (4) is formed
in accordance with the outer periphery shape of the cylinder
(10').
[0035] The mold cavity (4) of the cavity member (30) will be
described in detail with reference to FIGS. 5 and 6. In the portion
where the cavity member (30) faces to the hot runner bush (20), a
thin gate (8), which communicates with the molding material
injection path (12) of the hot runner bush (20), is formed. Being
continued to the gate (8), an outer periphery portion of a thin
front-end portion (10a) of the cylinder (10'), to which a needle
for a syringe having a diameter slightly larger than the gate (8)
is attached, is formed. And further, being continued to the thin
front-end portion (10a), the outer periphery portion of the
cylinder body (10b) is formed. The outer periphery portion of a
flange portion (10c) having the largest diameter is formed in the
parting face side.
[0036] As shown in the enlarged view of the gate portion in FIG. 5,
a portion (8a) from the thin front end portion (10a) toward the
rear direction [molding material supply side (1)] in the gate (8)
is formed in a straight cylindrical shape; and a horn-like portion
(8b) is formed in a horn-like shape being widely opened toward the
rear direction from the cylindrical portion (8a). And it is
arranged so that the front-end portion of the valve pin (7), which
will be described later, is precisely engaged with the portion of
the gate (8). And it is arranged so that the front-end portion of
the valve pin (7), which will be described later, is inserted into
and pulled out from the gate (8) to open/close the gate (8).
[0037] In the hot runner bush (20), the molding material injection
path (12), which is inserted with the valve pin (7) and is
connected to the molding material communicating path (24), is
formed; the front-end portion thereof is connected to the gate (8),
and is formed being tapered the same as that of the horn-like
portion (8b) of the gate (8). In the hot runner bush (20), for
example, a heater (29) is disposed to heat the molding material (9)
within the molding material injection path (12) of the hot runner
bush (20) up to the gate (8) to keep the molten state thereof.
Reference numeral (19) denotes a receiving hole for the hot runner
bush (20).
[0038] As described above, the sprue-mounting block (27) is
attached with a sprue bush (22); and being communicated with the
sprue bush (22), one or plurality of the molding material
communicating paths (24), which is branched on its way and
connected to the molding material injection paths (12), are formed
through the sprue bush (22) and the sprue-mounting block (27).
Further, guide holes (21) for guiding the valve pins (7), which
will be described later, are formed in the sprue-mounting block
(27).
[0039] The valve pin (7) is a member having a rod-like shape of
which the front end portion is formed in a tapered shape, and the
rear end thereof is fixed to the valve pin operation rod (25a). The
valve pin (7) is slidably inserted through the guide hole (21), and
the portion protruding from the sprue-mounting block (27) is
inserted into the molding material injection path (12) of the hot
runner bush (20). The front-end portion of the valve pin (7) is
formed so as to precisely engaged with the gate (8). That is, as
shown in the enlarged cross sectional view in FIG. 6, the front-end
portion of the valve pin (7) includes a portion (7a), which
straightly extends from the cavity side end (11) toward the rear
direction in accordance with the cylindrical portion (8a) of the
gate (8), and a tapered portion (7b) of which the diameter
increases gradually toward the rear direction from the straightly
extending portion (7a). The taper angle of the tapered portion (7b)
is slightly smaller and obtuse than that of the horn-like portion
(8b). Accordingly, when the front-end portion is inserted into the
gate (8), the front end portion is guided by the horn-like portion
(8b), and the straightly extending portion (7a) of the front end
portion perfectly fits with the cylindrical portion (8a) of the
gate (8); thereby the gate-cut is reliably performed. In other
words, the straightly extending portion (7a) and the cylindrical
portion (8a) of the gate (8) are molded so that the diameter and
the inner diameter thereof fit with each other with nearly zero
error.
[0040] Further, on the cavity side end (11), a circular cone recess
(7c) is formed so that circular cone-like portion (5e) on the front
end of the core (5), which will be described later, precisely fits
therewith. The diameter (d) of the circular cone recess (7c) on the
cavity side end (11) is formed so as to be identical to the maximum
diameter (d) of the circular cone-like portion (5e) on the front
end of the core (5), but smaller than the inner diameter (D) of the
cylindrical portion (8a). Accordingly, a gap (K) is formed between
the cylindrical portion (8a) and the circular cone-like portion
(5e) as shown in FIG. 5. When the front-end portion of the valve
pin (7) is separated away from the gate (8), the molding material
(9) flows into the cavity (6) through the gap (K) as shown in FIG.
5. On the other hand, when the front-end portion of the valve pin
(7) is engaged with the gate (8), the gap (K) is closed by the
front ring portion (11a) of the cavity side end (11). As a matter
of course, at this time, since the straightly extending portion
(7a) is fitted with the cylindrical portion (8a) of the gate (8)
with no gap, the molding material (9) does not enter into the
cylindrical portion (8a). The front ring portion (11a) means a
plane ring face between the periphery of the cavity side end (11)
and the maximum inner diameter of the circular cone recess
(7c).
[0041] Further, in the front-end portion of the valve pin (7), a
front-end narrow hole (13a), which is drilled from the head portion
in the axial direction of the circular cone recess (7c), and a
perpendicular narrow hole (13b), which is perpendicular thereto and
communicates the front-end narrow hole (13a) and the outer surfaces
of the valve pin (7), are formed; and the front-end narrow hole
(13a) and the perpendicular narrow hole (13b) forms a communicating
hole (13).
[0042] The pin drive section (25) includes cylinder holes (25b)
formed in the second female member (2b) and piston members (25c),
and the valve pin operation rods (25a) are bridged onto the piston
members (25c). By activating the piston members (25c), the valve
pins (7) are driven to slide via the valve pin operation rods
(25a). Reference symbols (M) and (N) denote outlets and inlets of
the compressed oil/air for activating the piston members (25c).
Owing to the working of the auxiliary springs (25d), the dimensions
of the pin drive section (25) can be reduced, and thereby the
entire sizes of the metal mold (1) can be reduced.
[0043] The male die (3) includes a male die body (3a) attached to
the moving die plate (16), one or a plurality of cores (5) attached
inside of the male die body (3a) in alignment with the die cavities
(4) and an intermediate die (3b), which is disposed so as to be
brought into contact with and parted from the inside of the male
die body (3a) and the core (5) is inserted thereinto and pulled out
therefrom, and push-out members (26) that, after the metal mold is
opened, pushes the intermediate die (3b) in the separating
direction to separate the molded cylinders (10').
[0044] An embedded end portion (5d) of the core (5) is embedded in
the male die body (3a), and the core (5) includes a base portion
(5c) protruding from the inside of the male die body (3a), a
columnar portion (5b), which has the same shape as the inner
peripheral shape of the cylindrical portion of the mold cavity (4)
in the front end side from the base portion (5c) and forms the
inner shape of the flange portion (10c) of the cylinder (10') and
the cylinder portion (10b), and a projecting portion (5a) formed
being projected in the center of the front end of the columnar
portion (5b) to form the inner periphery surface of the needle
mounting portion (10a) of the cylinder (10'). The front-end portion
of the projecting portion (5a) has a circular cone-like shape as
described above, and the diameter of the circular cone-like portion
(5e) is (d).
[0045] The operation of the metal mold (1) according to the present
invention will be described below. First of all, the moving die
plate (16) is activated to press the male die (3) onto the female
die (2) and mold them. At this time, the state where the gate (8)
is closed by the front-end portion of the valve pin (7) and the
circular cone-like portion (5e) at the front end of the core (5) is
closely fitted with the circular cone recess (7c) of the valve pin
(7) is obtained as shown in FIG. 1.
[0046] Then, the pin drive section (25) is activated to pull out
the valve pin (7) to open the gate (8) as shown in FIG. 2. In this
state, an injection-molding machine is activated and the metered
molding material (9) is injected through a nozzle (23). The metered
molding material (9) is injected into the cavity (6) through the
gate (8) via the sprue bush (22), the molding material
communicating path (24) and the molding material injection path
(12) being applied with a high pressure (for example, 1,000-2,000
kg/cm.sup.2). The state at this time is illustrated in detail in
the enlarged drawing in FIG. 5.
[0047] As illustrated in FIG. 5, since the gate (8) is formed on
the center axis (CL) of the core (5), the gap (K) formed by the
cylindrical portion (8a) of the gate (8) and the projecting portion
(5a) of the core (5) is formed with an identical width [(D-d)/2]
all around the periphery thereof. Therefore, the metered molding
material (9), which flows into the cavity (6) through the gate (8)
being applied with a high pressure, flows into cavity (6) uniformly
all around the periphery thereof. Accordingly, the force is applied
uniformly onto the outer periphery of the core (5). Unlike the
conventional manner, the core (5) is not sagged to be inclined in
one direction. Therefore, the cavity (6) does not generate
nonuniform wall thickness from the beginning to the end of the
injection molding; and accordingly, nonuniform wall thickness is
not generated in the thickness of the molded cylinder (10').
[0048] When the cavity (6) has been filled with the metered molding
material (9) as described above, the pressure applying and
maintaining step starts to continuously apply a pressure to the
filled molding material (9) within the cavity (6) from the nozzle
(23) of the injection molding machine. When being cooled down,
although the filled molding material (9) gradually solidifies and
simultaneously deflates, owing to the pressure, the molding
material (9) is replenished from the gate (8); and thus, the
cylinder (10') is prevented from sagging due to the pressure above.
When the cylinder (10') is cooled down to a certain level and no
deflation is caused, the pressure applying and maintaining step is
terminated, the pin drive section (25) is activated to reverse to
make the valve pin (7) advance; thereby the gate (8) is closed with
the front-end portion of the valve pin (7) as illustrated in detail
in the enlarged view in FIG. 6.
[0049] At this time, in the gate (8) portion, the surplus molding
material (9a) caught between the cavity side end (11) of the valve
pin (7) and the front end (14) of the core (5) can escape to the
molding material injection path (12) through the communicating hole
(13). Therefore, the circular cone-like portion (5e) at the front
end of the valve pin (7) is closely fitted with circular cone
recess (7c) on the cavity side end (11) of the valve pin (7) to
close the front-end narrow hole (13a). Further, the straightly
extending portion (7a) of the valve pin (7) engages with the
cylindrical portion (8a) of the gate (8) with no clearance to close
the gate (8). Thus, the gap (K) is closed by the front ring portion
(11a) of the periphery portion on the cavity side end (11) of the
valve pin (7); and the gate-cut is reliably performed with a small
force. Accordingly, the cavity (6) is reliably blocked off from the
molding material injection path (12).
[0050] Through the following cooling step, the filled molding
material (9) within the cavity (6) is gradually cooled down and
solidified. When the molding material (9) has been solidified, the
moving die plate (16) is activated to separate the male die (3)
from the female die (2) to open the metal mold as shown in FIG. 3.
The molded formed product (10) is pulled out form the mold cavity
(4) of the female die (2) being mounted on the core (5).
[0051] At this time, as illustrated in detail in the enlarged view
in FIG. 6, the front end of the needle mounting portion (10a) of
the cylinder (10') is completely blocked off from the molding
material injection path (12). However, since the molding material
(9) within the molding material injection path (12) is maintained
in a molten state by the hot runner bush (20), the cylinder (10')
as the molded formed product is taken out from the mold cavity (4)
in a completely molded state, unlike the conventional manner, free
from a cold runner. Therefore, the cold runner, which is
conventionally disposed of uselessly, is not generated.
[0052] Last, the push-out member (26) is activated to separate the
intermediate die (3b) from the male die body (3a); the cylinder
(10') is pushed out being engaged with the flange portion (10c)
thereof to separate the cylinder (10') from the core (5). After
taking out the cylinder (10'), the parting face is cleaned, and the
metal mold is molded to repeat the above-described steps.
INDUSTRIAL APPLICABILITY
[0053] As described above, according to the present invention,
since the gate is formed on the center axis of the core, the
metered molding material injected into the cavity from the gate
flows uniformly around the peripheral surface of the core.
Therefore, since the force is uniformly applied to the side face of
the core all around the peripheral surface thereof, the core is
prevented from falling in one direction but always positioned at
the center of the mold cavity. Accordingly, the molded formed
product is free from the nonuniformwall thickness.
* * * * *