WO2000034019A1

WO2000034019A1 - Device for cast-molding plastic materials

Info

Publication number: WO2000034019A1
Application number: PCT/EP1999/009514
Authority: WO
Inventors: Lorenzo Lorenzin
Original assignee: Main Group S.P.A.
Priority date: 1998-12-10
Filing date: 1999-12-06
Publication date: 2000-06-15
Also published as: IT1302527B1; ITPD980285A1; AU2280600A

Abstract

A device for cast-molding plastic materials, comprising a horizontal dispensing head (10), with a mixing chamber (11) and a mixing screw (12), associated with a vertical casting duct (13) with a shutter element (15) which controls the outlet (16) of the mixing chamber (11).

Description

DEVICE FOR CAST-MOLDING PLASTIC MATERIALS Technical Field

The present invention relates to a device for cast-molding plastic materials. Background Art

The device is particularly but not exclusively suitable for casting two- component polyurethane materials for manufacturing soles.

It is known that foamed polyurethane is the result of the rapid mixing of isocyanate and polyol, which react chemically with each other, The reaction occurs a few seconds after mixing, depending on the type of mixture, and develops almost instantaneously.

Accordingly, the mixed fluid must be deposited inside the mold rapidly before the reaction occurs.

It is also known that current molding units provide for injection with a horizontal screw while the mold is closed or provide for casting with a vertical screw while the mold is open.

After molding, the materials remaining inside the mixing head must be expelled; this occurs by means of a mechanical cleaning of the screw on the sleeve in which it is arranged or by washing with detergents such as chloride or trichloroethylene.

In the first case, the deposition of reagent material can occur with highly variable cycle times without any problem, since mechanical cleaning can be performed even after each injection.

In the second case, since the cleaning process is expensive, polluting and dangerous for the health of workers, it has to be performed less frequently and it is therefore necessary to work by casting almost continuously in order to prevent the reaction between two components of the polyurethane from occurring in the head before being fed into the mold.

From the practical point of view, open-mold casting with the mixing screw arranged vertically, using chemical cleaning when necessary, is preferable for sole manufacturing.

The existing machines are therefore provided with several mold holders on a rotating platform, so that the cycle allows to perform all the steps, including sole extraction, without problems in terms of residues inside the mixing head.

On the other hand, in order to be able to provide mechanical cleaning, which is evidently more convenient, it is currently necessary to have a mixing head provided with a horizontal screw.

A screw for mechanical cleaning in fact cannot work vertically, because it would cause dripping within the mold, with negative consequences for the quality of the molded item. Disclosure of the Invention

The aim of the present invention is to provide a device for cast-molding plastic materials which provides for a cleaning of the mixing chamber which is of the mechanical type, i.e., without using chemical additives.

Within the scope of this aim, a consequent primary object of the present invention is to reduce the amounts of waste polyurethane produced by machine downtimes, by washes and by color changes.

Another important object of the present invention is to provide a device which no longer requires the molding cycle times to be shorter than the material reaction time.

Another important object of the present invention is to provide cast- molding machines with multiple stations but with a small number of molds.

Another object of the present invention is to provide a device which in terms of operation does not increase the duration of the molding cycle, optimizing the output as much as possible.

This aim, these objects and others which will become apparent hereinafter are achieved by a device for cast-molding plastic materials, characterized in that it comprises a horizontal dispensing head, with a mixing chamber and a mixing screw, associated with a vertical casting duct 00/34019

3 with a shutter element which controls the outlet of said mixing chamber that leads into said duct.

Brief Description of the Drawings

Further characteristics and advantages of the present invention will become apparent from the following detailed description of an embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

Figure 1 is a schematic sectional view of a device according to the invention during cast-molding step; Figure 2 is a schematic sectional view of the device of Figure 1 during the cleaning of the mixing chamber;

Figure 3 is a schematic sectional view of the device of Figure 1 during the cleaning of the casting duct.

Ways of carrying out the Invention With reference to the above-cited figures, a device for cast-molding plastic materials comprises a dispensing head 10 which has a horizontal axis, with a conical mixing chamber 11 which contains a mixing screw 12 which rotates at a variable speed and is axially translatable.

The mixing chamber 11 leads at the front into a casting duct 13 which has a vertical axis, is conveniently fixed by means of screws 14 to the dispensing head 10, and in which a shutter element 15 which controls the outlet 16 is translatable.

In particular, the shutter element 15, conveniently having a cylindrical shape, has a free end 17 which controls said outlet 16, has a concave chamfer along its circumference and has an end 18 which is fixed to the stem 19, which is rigidly coupled to a plunger 20 which can slide inside a cylindrical chamber 21 of an actuation cylinder 22 which is fixed above the duct 13 and coaxially thereto.

The cylinder 22 is in fact provided with a flanged head 23 which is fixed by means of axial screws 24 and spacers 25 to a flange 26 of the duct 13. 00/34019

4

The cylinder 22 is also provided with a head 27 which closes it on the opposite side with respect to the head 23.

A partition 28 forms, inside the cylinder 22, another chamber 29 in which a plunger 30 can slide; said plunger is supported by a stem 31 which passes through the partition 28 and is suitable to abut against the plunger 20 at one end and against the head 27 at the other end, screwing by means of a threaded portion into an external ring nut 32.

Ducts 33, 34 and 35 are formed respectively in the head 23, in the partition 28 and in the head 27 of the cylinder 22 in order to feed and discharge working fluid.

As regards operation, the two components of the polyurethane (polyol and isocyanate) are made to enter the mixing chamber 11 and after being mixed they are cast into the mold, not shown for the sake of simplicity, due to the centrifugal thrust of the screw 12, which pushes them, through the outlet 16, into the casting duct 13.

The quality of the mixing of the material and therefore the best quality of the product, in addition to being adjusted by the variable speed of the screw 12 and by the tolerance between the screw and the wall of the mixing chamber 11, can be changed by the shutter element 15, which throttles the outlet 16, accordingly producing a counterpressure which affects the degree of mixing.

The degree of throttling is determined by the condition of the plunger 20 in the chamber 21 produced by the feeding/discharge of fluid into and from the ducts 33 and 35. The stem 31 carried by the plunger 30 provides a stop element which can be adjusted by means of the ring nut 32.

For the cleaning step of the mixing chamber 11 (Figure 2), the shutter element 15 is raised completely so as to clear the outlet 16 (this is possible by fully lifting the stem 31 by feeding fluid from the duct 33 and discharging fluid from the duct 35 until the plunger 20 reaches the end of its stroke).

This allows the screw 12 to reach a forward position in which it scrapes against the sleeve and, due to the centrifugal force produced by its high rotation rate, it expels the polyurethane residues that have remained inside. It is then possible to clean the casting duct 13 by translating fully downward the shutter element 15 by translatory motion of the plunger 20 by feeding fluid through the duct 34 (Figure 3).

In practice it has been observed that the intended aim and objects of the present invention have been achieved. The device in fact uses a horizontal injection screw in a vertical casting duct.

The shutter element arranged in the casting duct creates and adjusts a counterpressure which is capable of improving and optimizing the mixing of the materials. The shutter element cleans the casting duct directly after each casting, so that it is not necessary to resort to chemical cleaning.

In this manner, the operation of the casting head is rendered independent of the rigid cycle times linked to the reaction of the materials.

This leads to high flexibility in operation both in machines with a small number of stations and in machines with a large number of stations.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept.

All the details may also be replaced with other technically equivalent elements. In practice, the materials employed, so long as they are compatible with the contingent use, as well as the dimensions, may be any according to requirements.

The disclosures in Italian Patent Application No. PD98A000285 from which this application claims priority are incorporated herein by reference.

Claims

1. A device for cast-molding plastic materials, characterized in that it comprises a horizontal dispensing head, with a mixing chamber and a mixing screw, faced to a vertical casting duct with a shutter element which controls the outlet of said mixing chamber that leads into said duct.

2. The device according to claim 1, characterized in that said dispensing head having a horizontal axis is provided with said conical mixing chamber which contains said mixing screw, which rotates at a variable speed and is axially translatable, said mixing chamber leading at the front into said casting duct having a vertical axis, which is conveniently fixed by means of screws to said dispensing head.

3. The device according to claims 1 and 2, characterized in that said shutter element is cylindrical and has a free end, which controls said outlet and has a concave circumferential chamfer, and another end which is supported by an actuator.

4. The device according to claim 3, characterized in that said actuator is cylindrical and comprises a stem to which said end of said shutter element is fixed, said stem being rigidly coupled to a plunger which can slide inside a chamber provided with feed and discharge ducts.

5. The device according to claim 4, characterized in that a partition forms, in said cylindrical actuator, another chamber in which a plunger can slide, said plunger being supported by a stem which at one end passes through said partition and is suitable to abut against said plunger rigidly coupled to said shutter element and at the other end passes through a head of said actuator, screwing by means of a threaded part thereof into an outer ring nut, said other chamber being provided with a feed/discharge duct.