Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
1999-11-08
2002-06-25
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C425S589000
Reexamination Certificate
active
06409957
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an injection apparatus.
2. Description of the Related Art
Conventionally, in an injection molding machine, resin heated and melted in a heating cylinder is injected into a cavity of a mold apparatus under high pressure so that the cavity is filled with the resin. The molten resin is then cooled and solidified within the cavity so as to obtain a molded article.
The injection molding machine includes a mold clamping apparatus and an injection apparatus. The mold clamping apparatus is provided with a stationary platen and a movable platen. The movable platen is advanced and retracted by a mold clamping cylinder, to thereby perform mold closing, mold clamping, and mold opening.
The injection apparatus includes a heating cylinder for heating and melting resin supplied from a hopper, and an injection nozzle for injecting the molten resin. Further, a screw is disposed within the heating cylinder such that the screw can be rotated and can be advanced and retracted. When the screw is advanced by a drive section disposed at the rear,end of the screw, the resin is injected from the injection nozzle, and when the screw is retracted by the drive section, the resin is metered.
The drive section comprises a front plate for supporting the heating cylinder; a rear plate disposed a predetermined distance away from the front plate; guide bars disposed between and supported by the front plate and the rear plate; and a movable plate disposed to be slidable along the guide bars. The above-described screw is rotatably supported by the movable plate. A ball screw shaft and a ball nut are disposed between the front plate and the movable plate. When an injection motor is driven to rotate the ball screw shaft or the ball nut, the movable plate is advanced or retracted.
FIG. 1
is a sectional view of a drive section of a conventional injection apparatus;
FIG. 2
is a side view of the drive section of the conventional injection apparatus; and
FIG. 3
is a schematic diagram showing the concept of the drive section of the conventional injection apparatus.
In these drawings, reference numeral
12
denotes a heating cylinder,
22
denotes a screw,
31
denotes a slide table slidably disposed on an unillustrated frame, and
34
denotes a stationary plate fixed to the slide table
31
. The rear end (right end in
FIG. 1
) of the heating cylinder
12
is fixed to the stationary plate
34
. Further, a movable plate
36
is disposed such that the movable plate
36
can be advanced and retracted relative to the stationary plate
34
.
A screw support shaft
38
is disposed at the approximate center of the movable plate
36
and is rotatably supported thereby via bearings
41
and
42
. The rear end of the screw
22
is fixed to the screw support shaft
38
, and a driven pulley
43
is fixed to the rear end of the screw support shaft
38
.
An unillustrated metering motor is attached to one side surface S
1
of the movable plate
36
, and an unillustrated drive pulley is attached to the output shaft of the metering motor. An unillustrated timing belt extends between and is wound, under tension, around the drive pulley and the driven pulley
43
. The bearing
42
assumes the form of a thrust bearing in order to bear injection force that acts on the screw
22
upon injection.
Two parallel ball screw shafts
45
are disposed at positions in the vicinity of the circumferential edge of the movable plate
36
and are rotatably supported by the movable plate
36
via bearings
46
. Each of the ball screw shafts
45
has a screw portion
48
and a shaft portion
49
projecting from the rear end (right end in
FIG. 1
) of the screw portion
48
. The shaft portion
49
penetrates a hole
36
a
formed in the movable plate
36
and extends rearward (rightward in FIG.
1
), and a driven pulley
51
is attached to the rear end of the shaft portion
49
. The screw portion
48
penetrates a hole
34
a
formed in the stationary plate
34
and extends frontward (leftward in
FIG. 1
) to be screw-engaged with a ball nut
52
attached to the stationary plate
34
. The ball nut
52
has a flange portion
53
at its front end (left end in
FIG. 1
) and is fixed to the stationary plate
34
by use of unillustrated bolts that penetrate the flange portion
53
. Reference numeral
55
denotes a press plate for pressing the bearing
46
.
An injection motor
75
is attached to the approximate center of the other side surface S
2
of the movable plate
36
. A drive pulley
76
is attached to the output shaft
75
a
of the injection motor
75
, and a timing belt
77
extends between and is wound, under tension, around the drive pulley
76
and the driven pulley
51
.
Next, operation of the injection apparatus having the above-described structure will be described.
In a metering stage, when the screw
22
is rotated through driving of the metering motor, resin falls from an unillustrated hopper and enters the heating cylinder
12
, so that the resin is advanced (moved to leftward in
FIG. 1
) within the heating cylinder
12
. Subsequently, the screw
22
is retracted (moved to rightward in
FIG. 1
) while being rotated.
An unillustrated heater is disposed to surround the heating cylinder
12
and is adapted to heat the heating cylinder
12
to thereby melt the resin within the heating cylinder
12
. Therefore, when the screw
22
is retracted by a predetermined amount, while being rotated, molten resin for one shot is accumulated on the front side of an unillustrated screw head.
In a subsequent injection step, when the screw
22
is advanced through driving of the injection motor
75
, the resin accumulated on the front side of the screw head is injected from an unillustrated injection nozzle attached to the front end of the heating cylinder
12
and is charged into a cavity of an unillustrated mold apparatus.
In such a conventional injection apparatus, since the two ball screw shafts
45
are rotated at the same circumferential speed through driving of the single injection motor
75
, the diameters of the respective driven pulleys
51
must be made equal in order to make their reduction ratios equal. When the diameters of the driven pulleys
51
are increased in order to increase their reduction ratios, their inertia increases, with the result that the performance of the injection apparatus is lowered. Further, the timing belt
77
must have a longer length. When &thgr;
1
represents an effective angle of engagement of the drive pulley
76
which establishes meshing engagement for transmitting rotation from the injection motor
75
to the timing belt
77
, and &thgr;
2
and &thgr;
3
respectively represent effective angles of engagement of the driven pulleys
51
which establish meshing engagements for transmitting rotation from the timing belt
77
to the respective ball screw shafts
45
, the following equation is satisfied.
&thgr;
1
+&thgr;
2
+&thgr;
3
=360°
When the drive-side effective angle &thgr;
1
is small, as shown in
FIG. 3
, the rotation transmitted from the injection motor
75
cannot be transmitted to the timing belt
77
in a reliable manner. Therefore, rotation cannot be transmitted to the ball screw shafts
45
in a stable manner, resulting in a deterioration in the performance of the injection apparatus.
The inter-axis distance L
1
between the drive pulley
76
and the driven pulleys
51
or the widths of the driven pulleys
51
, the drive pulley
76
, and the timing belt
77
may be increased in order to increase the drive-side effective angle &thgr;
1
.
However, when the inter-axis distance L
1
is increased, the size of the injection machine increases, because the width of the movable plate
36
or the depth of the drive section must be increased. When the widths of the driven pulleys
51
, the drive pulley
76
, and the timing belt
77
are increased, noise generated when the injection motor
75
is driven at high speed increases.
SUMMARY OF THE INVENTION
An injection apparatus is provided which comprises a cylinder se
Hiraga Noritsugu
Nishio Okito
Arent Fox Kintner Plotkin & Kahn
Sumitomo Heavy Industrie's, Ltd.
Tentoni Leo B.
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