Resin extrusion apparatus

Details Resin extrusion apparatus Resin extrusion apparatus

2000-10-06

2002-11-05

Silbaugh, Jan H. (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

C366S076200, C366S141000, C425S155000, C425S376100

Reexamination Certificate

active

06474972

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of supplying a powder to be added to a resin and a resin extrusion apparatus. More particularly, in the present invention, to produce a resin pellet containing a coloring powder and a resin mixed uniformly with each other, the powder is quantitatively supplied to an intermediate portion of the resin extruder.
2. Description of the Related Art
In producing a resin pellet by mixing coloring powder with a thermoplastic resin serving as the material of the resin pellet, two methods are known. In one method, after the resin and the powder are stirred, the mixture is supplied to a resin extruder. In the other method, after the resin is supplied to the resin extruder, the powder is added to the resin and the powder and resin are mixed with each other.
FIG. 8A
shows the case where the resin and the powder are stirred. In this case, after a thermoplastic resin X and a predetermined amount of a coloring powder Y are supplied to a stirrer
2
such as a tumbler and stirred, the resin X and the powder Y are supplied to a resin extruder
1
through a hopper
1
a.
The resin extruder
1
heats and kneads the resin X and the powder Y and extrudes the mixture from a die
3
disposed at the front end of the extruder
1
. After the mixture is cooled in a water tank
4
, it was cut to produce a resin pellet P.
FIG. 8B
shows the case in which the powder Y is added to the resin X after the resin X is supplied to the extruder. In this case, initially, the thermoplastic resin X is supplied to a resin extruder
1
′ from a hopper
1
a
′, whereas the powder Y is supplied to an intermediate portion of the resin extruder
1
′ through a screw
6
a
of a powder feeder
6
. Thereafter, the resin extruder
1
′ produces a resin pellet P in a manner similar to the above-described manner.
To produce a uniform resin pellet P having non-uniformity in color or the like, it is necessary to quantitatively supply the powder Y to a predetermined amount of the resin X and mix them with each other. In the case where the stirrer
2
is used, the powder Y having a larger weight than the resin X tends to concentrate in the lower part of a stirring chamber
2
a
when the stirred resin X and the powder Y are supplied to the resin extruder
1
. The tendency is conspicuous when a large amount of the powder Y is added to the resin X. Consequently, the amount of the powder Y to the resin extruder
1
is large in an early time period from the start of production and small in the neighborhood of the termination thereof. Thus, there is a variation in the content of the powder Y in the resin pellet P.
In the case where the powder feeder
6
is used, it is impossible to make compensation when there is a difference between a set supply amount of the powder Y and an actual supply amount. This is because the screw
6
a
of the powder feeder
6
is rotated at a constant speed. Consequently, there is a variation in the specific gravity of the produced resin pellet P and a defective dispersion of the powder Y. Such a disadvantage occurs frequently in the case where barium nitrate and tungsten having a high specific gravity, respectively are used as the powder Y.
As shown in
FIG. 9
, in Japanese Patent Application Laid-Open No. 60-110411, there is disclosed a powder feeder
6
′ which supplies powder to be added to resin quantitatively by using a measuring instrument. The powder feeder
6
′ has a storing hopper
7
′ provided with a supply mechanism
7
a′
of cut-gate type, a supply container
6
b′
installed on a measuring mechanism
8
′, a spring feeder
6
c′
whose one end is located inside the supply container
6
b
′, and a power
6
d
′ for the spring feeder
6
c
′. In the powder feeder
6
′, the opening and closing of the supply mechanism
7
a′
of cut-gate type and the rotation of the power
6
d′
are controlled according to a numerical value measured by the measuring mechanism
8
′.
To supply the powder Y to the resin extruder
1
″ by means of the powder feeder
6
′, the powder Y is supplied to the storing hopper
7
′, the supply mechanism
7
a′
of cut-gate type is opened and closed appropriately, a required amount of the powder Y is dropped to the supply container
6
b′
, and a predetermined amount of the powder Y is dropped to a pneumatic feeder
9
by the rotation of the spring feeder
6
c′
. The pneumatic feeder
9
supplies the resin extruder
1
″ with the predetermined amount of the powder Y. The resin X is supplied to the resin extruder
1
″ from a hopper
1
a″.
The measuring mechanism
8
′ measures the weight of the powder Y. Thus, the powder feeder
6
′ can supply the powder Y quantitatively to the resin extruder
1
″. However, depending on the control system in which the supply mechanism
7
a′
of cut-gate type and the spring feeder
6
c′
are used, there is a possibility that the control system is incapable of following an actual powder supply operation. Thus,there may be a difference between a set supply amount and the actual supply amount. Another disadvantage of the powder feeder
6
′ is that the powder Y is supplied quantitatively to the resin extruder
1
″, together with the resin X. Thus, the powder feeder
6
′ has a problem similar to that of the resin extrusion apparatus using the stirrer
2
.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described problems. Thus, it is an object of the present invention to produce a resin pellet containing resin and powder mixed uniformly with each other by adopting a system of not mixing the resin and the powder with each other beforehand but quantitatively supplying the powder to a resin extruder at an intermediate portion of the resin extruder.
To achieve the object, according to the present invention, there is provided a resin extrusion apparatus including a resin extruder for extruding a thermoplastic resin supplied thereto from one end thereof to the outside from the other end thereof; a screw, driven by a motor, for supplying powder from a powder container to the resin extruder at an intermediate portion thereof, an inverter for setting the number of rotations of the motor for driving the screw; a controller controlling a frequency of the inverter; a weighing device, connected to the controller, for measuring an actual supply amount of the powder in a predetermined time period; and a detector for transmitting a measured value to the controller. Supposing that a set supply amount (g) of the powder in the predetermined time period is A; a tolerance (g) of the set supply amount is B; the actual supply amount (g) of the powder, in the predetermined time period, measured by the weighing device is C; a frequency (Hz) of the inverter is D; a feedback coefficient is E; and a frequency (Hz) of the inverter after a feedback control is executed is F,
when |A−C|≦B, the feedback coefficient E is set in the range of 0.1≦E≦0.7 and
when |A−C|>B, the feedback coefficient E is set in the range of 0.8≦E≦1.2.
Thereby, the powder is quantitatively supplied to an intermediate portion of the resin extruder by means of a rotation of the screw, based on the feedback-controlled inverter frequency:
F=D+E×{
(
A−C
)×
D/C}.
It is possible to recognize the difference between the set supply amount of the powder and the actual supply amount thereof by detecting the actual supply amount thereof. It is possible to rotate the screw according to a powder supply state and thus supply the powder quantitatively to the resin extruder by making the feedback control such that the difference is compensated. More specifically, in the case where the actual supply amount of the powder becomes smaller than the set supply amount thereof owing to various situations, compensation is made t

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