Method of removing extraneous matter from injection mold

Details Method of removing extraneous matter from injection mold Method of removing extraneous matter from injection mold

2002-05-31

2004-12-14

Ortiz, Angela (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With step of cleaning, polishing, or preconditioning...

C264S102000, C264S335000

Reexamination Certificate

active

06830716

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to injection molding, and particularly to a method of removing extraneous matter (e.g., a nonvolatile component of plastic substance) generated in a cavity of an injection mold comprised of a movable mold and an immovable mold, and a method of precisely and securely placing an insert in the injection mold.
In general, an injection-molding machine includes an injection mold comprised of a movable mold and an immovable mold, and moldably fluidized resins are injected into a mold cavity of the injection mold formed of the movable mold and the immovable mold, to form a casting. Between joint surfaces of the movable and immovable molds of a conventional injection mold is provided a small clearance through which air and gas in the cavity may be evacuated, and a gas vent is connected to the clearance. The clearance is configured to have such a small size that only air in the cavity and gas emitted from the fluidized resins (hereinafter referred to as “atmosphere in the cavity”) may pass through the clearance, thus distributing the fluidized resins throughout whole space in the cavity.
To attach a part to a casting, the part may be joined integrally by means of thermal caulking with the casting that has been formed through an injection-molding process, or the part may be inserted in a mold during the injection-molding process to get integrally molded. However, the method of joining the part by means of thermal caulking has rarely been used because of low productivity thereof.
When a metal insert made of iron or containing great amounts of iron is embedded in the casting through the process of inserting the part in the mold, a concave holding portion in which the insert is placed is provided in the mold cavity. The holding portion may be magnetized for the purpose of securely holding the insert in the mold cavity. Alternatively, a magnet may be embedded in the holding portion to bold the insert.
FIGS. 12A and 12B
illustrate a conventional handling device that places the insert in the holding portion. As shown in
FIGS. 12A and 12B
, the handling device
1
includes an attraction gripper
3
that attracts an insert
2
, and an arm that moves and places the insert
2
attracted to the attraction gripper
3
at an insert position in an injection mold (not shown). The handling device
1
moves and rotates the arm
4
with the insert
2
attracted thereto in frontward, rearward, left-hand, right-hand, upward, and downward directions, and thereby properly positions the insert
2
in the injection mold (not shown).
The arm
4
is constituted, for example, of a jointed-arm robot; the attraction gripper
3
, which is made of rubber in its entirety, is attached to a head
5
at a distal end of the arm
4
. At a bottom of the attraction gripper
3
is provided an annular groove
3
a
between concentric inner and outer annular sections
3
b
and
3
c
to exert negative pressure on the insert
2
. At a bottom of the annular groove
3
a
are provided a plurality of suction inlets
3
d
,
3
d
, . . . Each suction inlet
3
d
is connected to a negative pressure passage
3
e
in the head
5
, and the negative pressure passage
3
e
is connected via a control valve (not shown) to a vacuum pump or vacuum tank (not shown).
When the handling device
1
is employed to position an insert
2
in the injection mold, first, the arm
4
is actuated to move and rotate in frontward, rearward, left-hand, right-hand, upward, and downward directions, to move the head
5
to a position where the insert
2
is picked up, so that the outer annular section
3
b
and the inner annular section
3
c
face target spots on the insert
2
. This position being kept, the control valve is then switched to a position at which the negative pressure passage
3
e
opens connections to the vacuum pump or vacuum tank so that negative pressure is created in the annular groove
3
a
to exert an attraction.
The negative pressure attracts the insert
2
to the annular groove
3
a
. When the insert
2
is attracted to the annular groove
3
a
, the arm
4
is next operated to move and rotate in frontward, rearward, left-hand, right-hand, upward, and downward directions to move and attach the insert
2
to the holding portion in the injection mold. Subsequently, the control valve is switched to a position at which the negative pressure passage
3
e
opens connections to an atmosphere discharge port of the control valve to release the insert
2
from the attraction gripper
3
. Thereafter, the arm
4
is operated to move the head
5
back to the position where the insert
2
is picked up.
Accordingly, a series of operations from the step of picking up the insert
2
to the step of moving the head
3
back to a home position is repeatedly performed for one cycle of the injection-molding process, with the result that productivity in embedding an insert in the casting may be enhanced in comparison with that which may be achieved through a thermal caulking process. To control the position of the arm
4
and the positioning of the insert
2
, a contact sensor such as a microswitch, a relay, etc., or a noncontact sensor such as a magnetic sensor, an optical sensor, etc. may be used.
As described above, when the conventional injection mold is employed, fluidized resins are distributed throughout whole space in the cavity, and are solidified under such a condition as to allow entire inner surfaces of the cavity to be kept in full contact with the fluidized resins, so that castings without defect in outer surfaces or inner structures may be formed. However, nonvolatile components (e.g., flame retardant for suppressing propagation of a flame, additives for improving fluidity of resins, etc.) that exude from the fluidized resins may cool off and deposit on inner surfaces of the cavity, a land, and the like. The extraneous matters that deposit in the cavity may inhibit an atmosphere in the cavity from coming out, thus decreasing yields of the castings. In addition, the increased extraneous matters derived from nonvolatile components would disadvantageously adhere to the casting.
Accordingly, the extraneous matters derived from the nonvolatile components are removed once a day, or an evacuator circuit that evacuates the nonvolatile components outside by exerting negative pressure in the cavity is provided, so that the casting may be taken out of the cavity after the atmosphere in the cavity filled with fluidized resins is evacuated outside.
However, the former approach disadvantageously requires a temporal suspension of a line for a cleaning operation, and needs enormous manpower and time for dismantling the injection mold. On the other hand, the latter approach using an evacuator may fail to bring about sufficient cleaning effects by a scant one atmospheric pressure, thus decreasing reliability.
The use of the handling device
1
to locate the insert
2
at a holding portion in an injection mold where the insert
2
is held by a magnetic attraction of the holding portion, as described above, would make it possible to automate an insert positioning operation. However, if the insert
2
formed by performing a press-forming or stamping process assumes a curved or uneven shape as shown in
FIG. 13A
, the attraction gripper
3
may get into contact with a wrong spot on the insert
2
deviated from an appropriate spot to attract the insert
2
, or a gap may be generated between the outer annular section
3
b
or the inner annular section
3
c
and a surface of the insert
2
. Such a deviated spot of contact would require a delicate operation of correcting a position of the insert
2
by actuating the arm
4
to move and suspend in a finely modulated manner. Further, thus-generated gap would cause a negative pressure to decrease, and allow the insert
2
to fall off from the attraction gripper
3
, disadvantageously resulting in failure to place the insert
2
in the holding portion. Otherwise, wear-out generated in the outer annular section
3
b
and the inner annular section
3
c
due to normal wea

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