Plastic molding machine

Details Plastic molding machine Plastic molding machine

1994-11-14

2001-07-03

Chiesa, Richard L. (Department: 1724)

Plastic article or earthenware shaping or treating: apparatus

Shaping orifice and downstream work contacting gaseous...

C264S040300, C425S140000, C425S145000, C425S326100, C425S387100

Reexamination Certificate

active

06254368

ABSTRACT:

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a plastic molding machine and more particularly a plastic molding machine which can maintain the frost line of a plastic product when molten plastic which is supplied from an extruding machine is emerged from a discharge opening to form plastic products having a predetermined film or the like.
BACKGROUND OF THE INVENTION
In general, in the conventional extruding machines, a plastic such as a thermoplastic resin is melted while being transported by a screw conveyor within a closed cylinder and the molten plastic is extruded toward a die having a predetermined opening and ejected through the opening to form a plastic product having a desired shape.
FIG. 3
shows a conventional plastic molding machine of the type described above. A hopper for feeding a predetermined plastic powder into the cylinder of an extrusion machine
1
is mounted thereon and with the interior of the extrusion machine
1
has a screw conveyor
4
for transporting the plastic powder supplied from the hopper
2
toward a head
3
and a heater (not shown) for melting the plastic powder being transported by the screw conveyor
4
toward the ejection opening of the head
3
.
The extrusion opening of the head
3
of the extrusion machine
1
is connected to an L-shaped feed pipe
5
and a feeding opening
7
of a die
6
for forming,for example, tubular plastic products is detachably connected to the leading end of the feed pipe
5
. An annular emerging opening
9
for emerging the molten plastic
8
so as to form a tubular plastic product is formed through the upper surface of the die
6
. Furthermore, defined at the lower portion of the die
6
is an air injection opening
11
for expanding and maintaining the shape of the molded product in the form of a tube. An annular cooling air supply device
12
is disposed upwardly of the ejection opening
9
of the die
6
adjacent to the upper portion of the die
6
. The cooling air supplied from a blower (not shown) is injected through the ejection opening
9
into the tubular plastic product
8
, thereby cooling the same.
A plurality of guide rollers
13
are disposed upwardly of the cooling air supply device
12
so that the cooled tubular plastic product can be gradually made into the form of a flat laminated sheet. Disposed upwardly of the uppermost guide roller pair is a pair of pinch rollers
14
for pulling up the flatly laminated plastic product
8
. A winding roller
15
for winding the flatly laminated plastic product
8
is disposed at the downstream side of the uppermost guide roller pair
13
.
With the conventional plastic forming machine with the above-described construction, the predetermined plastic powder
8
is fed into the extrusion machine
1
through the hopper
2
and is melted while being transported by the screw conveyor
4
. Thereafter, the molten plastic is forced to emerge through the opening of the head
3
and then fed into through the feed pipe
5
into the inlet opening
7
of the die
6
. The die
6
forms the molten plastic
8
into a tubular shape, which is discharged from the emerging opening
9
upwardly. In this case, the air is fed into the die
6
through the air supply opening
7
and injected at a predetermined pressure level through the air injection opening
11
into a tubular plastic product
8
so that the product
8
is expanded and maintained in a predetermined shape. The emerged plastic product
8
is cooled by the cooling air injected from the cooling air supply device
12
so that the plastic product
8
is cooled and then gradually laminated by the guide rollers
13
into a flat shape. The laminated plastic product
8
thus formed is pulled up by the pinch roller pair
14
and then wound around the winding roller
15
.
THE PROBLEMS WHICH THE PRESENT INVENTION CONTEMPLATES TO SOLVE
With the conventional plastic molding machine of the type described above, when the plastic product
8
emerged from the emerging opening
9
of the die
6
is cooled by the cooling air supply device
12
and becomes to have a maximum diameter at which a frost line
16
is formed. The temperature of the plastic product
8
below the frost line
16
ranges from 100 to 120° C. while the temperature of the plastic product
8
above the frost line
16
drops by 5-15° C. below the temperature of the plastic product
8
below the frost line
16
. Depending upon the position of the frost line
16
, the maximum diameter, the thickness and the like of the plastic product
8
vary so that it is desired that the position of the frost line
16
is maintained at a constant level.
However, there has been a problem that the position of the frost line
1
is moved upwardly or downwardly due to the variations in temperature between the day and night time and between summer and winter, More specifically, when the outside temperature is high, the rate of solidification or hardening of the plastic product
8
becomes low so that the frost line
16
moves upward. As a result, the thickness of the plastic product
88
is not uniform and furthermore the plastic product
8
swings between the die
6
and the guiderollers
13
so that it becomes instable and consequently the quality of the plastic products
8
are degraded. On the other hand, when the outside temperature is low, the rate of solidification or hardening of the plastic product
8
becomes higher so that the frost line moves downward, resulting the reduction of the diameter of the plastic product
8
and the degradation of quality there of as in the case of the low outside temperature.
In order to solve the above-described problems, so far the quantity of a plastic to be discharged is manually controlled and the flow rate of the cooling air supplied from the cooling air supply device
12
is also manually adjusted so that the frost line
16
can be moved upwardly or downwardly. The above and other problems, therefore, have been the obstructions when the automatic molding of the plastic products is desired.
BRIEF SUMMARY OF THE INVENTION
The present invention, therefore, was made to solve the above and other problems encountered in the conventional plastic molding machines and has for its object to provide a plastic molding machine which can always maintain the frost line at a predetermined level and which can automtically produce plastic products with the same quality.
According to the present invention, plastic powder is melted by an extrusion machine and transported the plastic thus melted toward a die. The melted plastic is molded into a desired shape and is forced out through an ejection opening of the die. Thereafter the molded plastic product is cooled by the cooling air supplied from a cooling air supply device. The level of the frost line is continuously detected by a frost line sensor and when the frost line is not maintained at a predetermined level, a control device controls the quantity of plastic powder to be supplied into the extrusion machine and/or the flow rate of the cooling air supplied from the cooling air supply device so as to move upwardly or downwardly the frost line, whereby the frost line can be always maintained at a predetermined level.
The plastic molding machine with the above-described construction in accordance with the present invention can automatically detect the frost line of a molded plastic semiproduct and can maintain the frost line always at a predetermined level without any manual control. Therefore the plastic products with the same quality can be automatically molded so that the quality of the plastic products can be remarkably improved.


REFERENCES:
patent: 4201741 (1980-05-01), Pannenbecker
patent: 4243363 (1981-01-01), Mulcahy
patent: 4246212 (1981-01-01), Upmeier et al.
patent: 4355966 (1982-10-01), Sweeney et al.
patent: 4402656 (1983-09-01), Schott, Jr.
patent: 4606879 (1986-08-01), Cerisano
patent: 4931003 (1990-06-01), Van Erden
patent: 4938903 (1990-07-01), Schaeffer et al.
patent: 5124094 (1992-06-01), Lenius et al.
patent: 5179521 (1993-01-01), Edge
patent: 5213725 (1993-05-01),

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