Injecting apparatus with check valve

Details Injecting apparatus with check valve Injecting apparatus with check valve

2001-06-14

2003-03-18

Heitbrink, Tim (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Control means responsive to or actuated by means sensing or...

Feed control of material en route to shaping area

C425S559000

Reexamination Certificate

active

06533567

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention relates to an improvement in an injecting apparatus equipped with a check valve for preventing the reverse flow of a melt of molding materials.
2. Description of the Related Art
A typical prior screw injecting apparatus is shown in cross section in
FIG. 7
hereof. The screw injecting apparatus
100
generally comprises a heating cylinder
101
, a screw
102
received in the heating cylinder
101
rotatably and movably back and forth, a check valve
103
mounted on the tip end of the screw
102
, an injecting cylinder
104
for moving the screw
102
back and forth, and a rotating means or device
106
for rotating the screw
102
via a piston rod
105
of the injecting cylinder
104
.
In the injecting apparatus
100
thus arranged, plasticizing-metering phase, waiting phase and injecting phase are carried out in a manner as described below.
Plasticizing-metering phase: Raw molding materials are fed from a hopper
107
into the heating cylinder
101
during rotation of the screw
102
and heated by the heating cylinder
101
while being transferred toward a discharge nozzle
108
by rotation of the screw
102
. By friction heat arising from the transfer and heat transmitted from the heating cylinder
101
, the molding materials are plasticized and kneaded.
During that time, the check valve
103
is in the open state and thus permits passage therethrough of a melt of molding materials.
The screw
102
is pushed back rightward in
FIG. 7
by a counter force of the melt accumulated around the tip end of the screw
102
(between the check valve
103
and the nozzle
108
). The amount of melt can be metered by measuring the retreating or backward stroke of the screw
102
.
Waiting phase: After completion of the metering, the screw
102
is held inactive until the melt becomes ripe for injection.
Injecting phase: By activating the injecting cylinder
104
, the screw
102
is rapidly advanced at one stroke to cause a metered amount of melt accumulated forward of the screw
102
to be injected through the nozzle
108
into a mold not shown. Advancing movement of the screw
102
causes the check valve
103
to close, so that the melt is prevented from flowing back toward the screw
102
.
FIGS. 8A and 8B
are views illustrative of the structure and operation of the check valve
103
of the conventional screw injecting apparatus
100
.
As shown in
FIG. 8A
, the check valve
103
is provided on the tip end of the screw
102
and includes a screw head
111
attached to the tip end of the screw
102
and a cylindrical check ring
112
slidably mounted on the screw head
111
.
In the metering phase, the check valve
103
is in the open state so that rotation of the screw
102
causes a melt of molding materials to pass through a passage
113
in the check valve
103
in the direction of the arrows {circle around (
1
)} and {circle around (
2
)} shown in FIG.
8
A.
In the injecting phase, as shown in
FIG. 8B
, the screw
102
is rapidly advanced as indicated by the profiled arrow {circle around (
3
)}. As the screw
102
advances, the check ring
112
is subjected to a force or pressure applied from a metered amount of melt
11
accumulated forward of the screw head
111
. This causes a backward movement of the check ring
112
as indicated by the arrow {circle around (
4
)}, which continues until the check ring
112
comes into abutment with a valve seat
115
formed on a shoulder of the screw
102
(S
1
shown in
FIG. 8A
is zero). The check valve
103
is thus closed so that the reverse flow of the melt
114
toward the screw
102
does not take place.
However, from the start of backward movement of the check ring
112
to the arrival of the check ring
112
at the valve closing position shown in
FIG. 8B
, the passage
113
is still in an open state. Accordingly, the melt
114
can flow backward through the passage
113
to the screw
102
side. Even though the amount of melt
114
flowing backward is very small, such backflow of the melt
114
deteriorates the metering accuracy.
In order to increase the injecting speed and metering accuracy, the amount of melt
114
flowing backward should be reduced to near zero.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide an injecting apparatus equipped with a check valve which is capable of reducing the amount of backflow of the melt to nearly zero.
To achieve the foregoing object, according to the present invention, there is provided a screw infecting apparatus comprising: a heating cylinder for heating a molding material being transferred therethrough, the heating cylinder having a nozzle at one end thereof; a screw received in the heating cylinder rotatably and movably back and forth and having a tip end portion spaced backward from the nozzle, the screw, when rotating in one direction, feeding a melt of molding material toward the nozzle while the screw is pushed back by a reaction of the melt accumulated around the tip end portion of the screw head; and a check valve for preventing the melt from flowing backward toward the screw. The check valve comprises a seat ring mounted on the tip end portion of the screw and movable in unison with the screw, the seat ring having an axial groove for the passage therethrough of the melt, and a check ring mounted on the tip end portion of the screw in tandem relation to the seat ring and rotatable relatively to the screw and the seat ring within a predetermined angular range, the check ring having an axial groove for the passage thererthrough of the melt, the axial groove of the check ring and the axial groove of the seat ring being phased such that rotation of the screw in said one direction causes the axial groove in the check to communicate with the axial groove in the seat ring, thereby permitting passage of the melt through the check valve, and rotation of the screw in the reverse direction causes the axial groove of the seat ring to be closed by a body of the check ring, thereby blocking passage of the melt through the check valve. The screw injecting apparatus further includes a control unit for controlling operation of the screw such that in a metering phase of molding process, the screw rotates in said one direction to feed a melt of molding material toward the nozzle, when a metered amount of melt is accumulated forward of the tip end portion of the screw, the screw moves backward by a predetermined distance to reduce the reaction from the metered melt and, thereafter, the screw rotates in the reverse direction to cause the screw to move forward until the amount of forward movement of the screw becomes substantially equal to said predetermined distance.
When the screw is rotating in one direction (normal direction), the check valve is open, so that a melt of molding material is fed toward the nozzle and accumulated forward of the tip end portion of the screw disposed backward of the nozzle. The screw while rotating in the normal direction is pushed back by a reaction of the meld accumulated around the tip end portion of the screw. By measuring the stroke of the screw in the backward direction, it is possible to meter the amount of melt accumulated forward of the tip end portion of the screw.
When the metered amount of melt is accumulated forward of the tip end portion of the screw, the check valve may be closed in preparation for the injecting process by rotating the screw in the reverse direction. In this instance, however, reverse rotation of the screw causes the screw to move forward as if the screw bits into the metered melt accumulated around the tip end portion of the screw. With this forward movement of the screw, the metered melt is forced to leak out from the nozzle.
To avoid this problem, according to the present invention, when the metered amount of melt is accumulated forward of the tip end portion of the screw, the screw is moved backward by a predetermined distance under the control of the control unit. With this backward movement of the screw, the pressure in a m

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