EP2024160A1

EP2024160A1 - Machine for molding rubber and plastics

Info

Publication number: EP2024160A1
Application number: EP07734709A
Authority: EP
Inventors: Daniele Dalla Guarda; Corrado Dalla Guarda
Original assignee: Main Group Corp SRL
Current assignee: Main Group Corp SRL
Priority date: 2006-05-19
Filing date: 2007-05-15
Publication date: 2009-02-18
Also published as: WO2007135559A8; ITVI20060155A1; WO2007135559A1

Abstract

A machine for molding rubber and plastics in general, of the type comprising at least one press body (29), which has at least one terminal reaction plane, at least one fixed plane (13) and at least one movable plane or press plane (14), which are mutually parallel and are connected by means of stems or posts (18) and contain at least one mold, and at least one plasticizing assembly (30), which comprises at least one screw- or piston- type injection element (12); a movable frame or head (21) is supported detachably on the posts (18) and includes the press plane (14) and the terminal reaction plane, and the head (21) is rigidly coupled to an integrated hood which is kept in vacuum, so as to perform pressing of the injected material and any degassing operations in an environment in vacuum.

Description

MACHINE FOR MOLDING RUBBER AND PLASTICS

Technical field

The present invention relates to a machine for molding rubber and plastics in general and in particular to an injection-molding machine. Background art

Molding is the technology used to manufacture articles which have a finished shape, with or without undercut parts; moreover, with this technology it is possible to obtain two-color parts, hollow parts, parts having a cellular structure, parts with metallic inserts and laminated articles. Molding provides for a step for heating and plasticizing the material, a step for filling the mold and a step for cooling and extracting the molded part.

The machines used (presses) are designed to open and close the mold, heat and plasticize the material, and load it into the mold. The three steps of molding can all be performed in the mold or only the last two can be provided within the mold while the first one is performed separately; in the first case, one speaks of compression or transfer molding, whereas in the second case one speaks of injection molding.

In particular, injection molding is used for thermoplastic resins, for thermosetting resins and for elastomers, while the press for injection molding (of the horizontal or vertical type, depending on its geometric shape) comprises mainly two planes onto which the mold is fixed and which move horizontally or vertically, opening and closing the mold, a piston and/or screw injection assembly, in which the material is heated and brought to the plastic state, so that the axial movement of the piston or screw causes the loading of the initial material and simultaneously the injection of the plasticized material into the mold, as well as circuits for operation, adjustment and control.

Injection presses are defined by the surface of the mold supporting planes, by the closure force, by the opening stroke and/or by the injection capacity, while the molding cycles can vary from a few seconds to a few minutes, depending on the material and on the dimensions of the parts.

As is known, the rubber or plastic material to be injected is processed by means of the screw and/or piston assembly, which has a rotary and axial movement.

If a screw assembly is used, in this movement the screw assembly preplasticizes and discharges the material onto the head of the screw by means of a one-way valve, so that the screw gradually moves backward; the retraction of the screw is controlled and contrasted by a counterpressure, which allows to compact the material adequately, while precise control of the dosage of the material to be injected is achieved by means of the control of the retraction of the screw.

During the injection step, the screw remains stationary, in that it does not rotate about itself, and acts as an injection plunger, since it is made to perform a translational motion; moreover, during the translational motion the material cannot retract, because it is contrasted by the one-way valve and is therefore injected into the mold.

Another technical solution, as already anticipated, provides for the use of an assembly constituted by a screw plus a piston, in which the screw can only turn and can make the injection piston or plunger enter during the plasticizing step; the one-way valve is arranged between the screw and the plunger and the injection cycle is performed as in the previously described case, according to which, once the mold has been closed in the press, the injector injects the previously plasticized and dosed material and then proceeds with the plasticizing of a new amount, which will be injected in the subsequent cycle, after opening the mold and unloading the parts.

It is further known to perform processes for degassing plastic materials during the operation of the press, in order to eliminate or at least limit the defects of the molded product caused by the presence of air in the molds, which cause rejects and production halting problems. For this purpose, variously degassing methods have been proposed so far, such as the ones provided by means of hollow extrusion screw feeders or by means of porous extrusion cylinders or by means of suitable methods for vacuum injection. In particular, certain plastic materials can be treated beforehand in dry booths, with an optional simultaneous application of vacuum, and then plasticized in the injection press.

However, experience shows that it is important for the degassing step to occur in vacuum, inside the molding press and simultaneously with respect to the plasticizing step.

Further, it is also important to maintain a high vacuum condition during molding, without having to use mechanical elements, such as borders or gaskets, which have a very short average lifespan and do not ensure, neither immediately nor over time, the ideal vacuum conditions that are sought.

Disclosure of the invention

The aim of the present invention is to provide a machine for molding rubber and plastics in general which allows to subject to vacuum, instantly and simultaneously with respect to the plasticizing operation, any mold, even one which is not prepared, in order to overcome easily the waste of time caused by sorting problems due to defects of the products obtained by molding due to the presence of air.

Within this aim, an object of the present invention is to provide a machine for molding rubber and plastics in general which allows to simplify the open-mold molding conditions so as to be able to apply them also to shapes with particularly challenging undercuts.

Another object of the present invention is to provide a machine for molding rubber and plastics in general which allows to maintain vacuum over time without using mechanical elements, such as vacuum gaskets, which are frequently damaged by the movement of the brushes for automatic extraction.

Another object of the invention is to provide a machine for molding rubber and plastics in general which is extremely reliable, simple to use and particularly interesting for the market in view of the achieved advantages. This aim and these and other objects which will become better apparent hereinafter are achieved by a machine for molding rubber and plastics in general as described, in a generic and preferred embodiment thereof, according to the accompanying claim 1.

The dependent claims also contain other detail characteristics of the invention.

Advantageously, the molding machine according to the invention is constituted by a horizontally or vertically arranged injection press, with a classic piston screw provided with a built-in vacuum hood, which also contains the posts and the optional third plate or mold supporting plane, which is adapted to subject instantly to vacuum any mold, even one which is not preset, thus overcoming the waste of time and the production stops caused by defects of products due to the presence of air within the molds.

The machine can work by simple injection, by injection and compression, or by compression alone, particularly for small runs and for parts which have difficult functional characteristics, shapes and volumes.

In particular, the invention solves effectively the problems related to the preparation and setup of the press and of the operators assigned to the machine, since it allows to load the rubber and/or plastics even very loosely (it is sufficient to load the rubber to the right weight so as to produce no flash), allowing to gain time during processing. Brief description of the drawings

Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of a molding machine according to the invention, illustrated merely by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a general perspective view of a machine for injection molding, rubber and plastics in general, provided according to the present invention; Figure 2 is a general perspective view of the injection-molding machine of Figure 1 according to the present invention, with the vacuum hood removed;

Figure 3 is an enlarged-scale detail view of the injection-molding machine of Figure 1 according to the present invention; Figure 4 is a partially cutout perspective view of the injection- molding machine of Figure 1 according to the present invention. Ways of carrying out the invention

With reference to the figures, a molding machine or (horizontal) press for injection-molding rubber and plastics in general, according to the invention, includes a supporting outer frame 5, on which one or more pairs of walls 10 and dividing posts 11 are formed and joined by an upper fixed supporting plate (not shown in the accompanying figures).

The dividing posts 11 form a piston-type injection assembly 12, which is constituted by a plasticizing cylinder and the corresponding piston, in which the material that arrives from a hopper 15 and from a dosage assembly 16 is heated and brought to the plastic state; two vertical planes, respectively a fixed plane 13 and a movable plane 14, on which an additional fixing plane 17 for a mold is fixed, and a terminal reaction plane, with which a closure toggle (not shown in the accompanying figures) is associated.

The fixed plane 13 is associated with the movable plane 14 by way of guiding posts 18, while the movable plane 14 is further provided with an actuation assembly 19, which faces the closure toggle of a reaction plane 20 and is suitable for the extraction of the mold from the fixing plane 17. The axial movement of the piston-type injection assembly 12 causes the loading of the initial material and the injection of the plasticizing material into the mold; further, the movable plane 14, by moving horizontally, opens and closes the mold.

A movable frame or head 21 is supported on the posts 18 so that it can slide and includes the press plane 14 and the terminal reaction plane, which are mutually parallel, as well as a lower plane (not visible in the accompanying figures) and an upper plate 22.

In the specific case, the structure of the machine is composed mainly of four high-quality steel cylinders 28, which are mounted directly onto the footing or fixed plane 13 of the mold of the press body 29, thus forming a single monolithic unit with the four post-like stems 18 and the stems 26 in order to achieve maximum rigidity against flexing and elongation; further, the press body 29, as well as the plasticizing assembly 30, can be mounted horizontally or vertically on the bench of the structure of the machine. In detail, the plasticizing assembly 30 comprises the piston-type injection assembly 12, which is supported by a structure which includes a thrust bearing, the corresponding injection cylinder, a temperature- controlled chamber, a temperature-controlled nozzle, a circuit for the inflow of the material to be molded and a hydraulic motor 31 for actuating the injection assembly 12; the sealing structure of the cylinder and the cylinder itself are sized so that they can support screws or pistons having different diameters and chambers having different volumes.

Further, the plasticizing assembly 30 is mounted on the base plane 13 by means of a rotating platform which is actuated manually and can slide toward the outside of the frame 5 of the molding machine so as to facilitate the cleaning of the injection nozzle.

Two temperature regulators are further provided which are mounted in the footing in a position which is easy to reach for the operator, are controlled by microchips and are adjustable from a video terminal 35 by the operator; the video terminal 35, which has maximum reliability and simplicity in use, can be used effectively for the visualized control of all the parameters of the machine, such as the temperature of the planes, the temperature of the forming chamber and of the nozzle, the time of the loading-injection-vacuum cycle, et cetera. Further, the press body 29 includes the head 21, which contains the sliders of the post-like stems 18, the vacuum chamber, the cylinders 27 of the press plane or intermediate plane 14, and the extraction assembly; the head 21 is made of high-quality cast iron and is generously sized in order to ensure excellent rigidity when loaded. Advantageously, according to the invention, the head 21 is rigidly coupled to an integrated hood, which is kept in vacuum and extends to the posts 18 and to the optional third plate, so as to perform the pressing of the injected material and any operations for degassing in an environment which is completely in vacuum. In particular, the press plane 14 and the reaction plane are supported by the walls 23 of the integrated hood, optionally provided with windows 24 which are made of transparent material and are adjacent to appropriately provided windows 25, which are arranged so as to be able to slide on the outer frame 5 in order to facilitate the view of the operator inside the head 21, and by the transverse walls 20, which are respectively rigidly coupled to the press plane 14, which can move and slide freely within the head 21, and to the terminal reaction plane of the machine.

In particular, the use of a transverse back wall 20, from which the couplings and the rear outputs, such as a cable carrying chain 33, protrude outside the integrated hood in vacuum, eliminates the need to have at least one vacuum sealing gasket and improves the tightness of the machine.

The vacuum system 32, which is completely autonomous and suitable to create and keep in vacuum the hood rigidly coupled to the head 21, is arranged in the footing 34 of the press body 29 and comprises a water pump, a water-air separation tank, control devices and a heat exchanger. The use of an integrated vacuum hood further allows to subject instantly to vacuum any mold, even one which is not preset, overcoming easily the waste of time related to sorting out problems due to defects caused by the presence of air. The open-mold molding method therefore becomes problem-free and applicable also to shapes with particularly challenging undercuts.

Finally, in this manner, the use of vacuum sealing gaskets is eliminated; said gaskets are usually damaged by the movement of the brushes of the machine for the automatic extraction of the molded product. The characteristics of the machine for molding rubber and plastics in general according to the present invention are evident from the description given and so are its advantages.

Finally, it is clear that many other variations may be made to the molding machine being considered without thereby abandoning the principles of novelty that are inherent in the appended claims, and it is likewise clear that in the practical embodiment of the invention the materials, shapes and dimensions of the details shown may be any according to requirements and may be replaced with other technically equivalent elements. For example, as already mentioned earlier, the machine can be arranged horizontally, as in the described embodiment (horizontal press) or vertically (vertical press), or can work by injection alone, by compression alone or in a mixed injection-compression mode.

The disclosures in Italian Patent Application No. VI2006A000155, from which this application claims priority, are incorporated herein by reference.

Claims

1. A machine for molding rubber and plastics in general, of the type comprising at least one press body (29), which has at least one terminal reaction plane, at least one fixed plane (13) and at least one movable plane or press plane (14), which are mutually parallel and are connected by means of stems or posts (18) and contain at least one mold, and at least one plasticizing assembly (30), which comprises at least one element or assembly (12) for feeding the rubber or plastics actuated by an actuation motor (31), characterized in that a head (21) is supported detachably on said posts (18) and includes the press plane (14) and the terminal reaction plane, said head (21) being rigidly coupled to an integrated containment element which is kept in vacuum, so as to perform pressing of the injected material and any degassing operations in an environment in vacuum.

2. The molding machine according to claim 1, characterized in that said feed assembly (12) is an injection assembly of the piston type and includes at least one plasticizing cylinder and at least one corresponding piston, in which the material that arrives from a hopper (15) and from a dosage assembly (16) is heated and brought to the plastic state.

3. The molding machine according to claim 1, characterized in that said movable plane (14) is provided with at least one actuation assembly

(19), which is suitable for the mold extraction operation.

4. The molding machine according to claim 1, characterized in that said head (21) is delimited by at least one lower plane and by at least one upper plate (22).

5. The molding machine according to claim 1, characterized in that said plasticizing assembly (30) is mounted on said base plane (13) by means of at least one rotary platform, which can slide toward the outside of the frame (5) of the molding machine, so as to facilitate operations for cleaning the injection elements.

6. The molding machine according to claim 1, characterized in that said containment element is constituted by an integrated hood which is kept in vacuum and extends to said posts (18) and to at least one of said fixed plane (13), said movable plane (14) and/or said terminal plane.

7. The molding machine according to claim 1, characterized in that said movable plane (14) and said terminal reaction plane are supported by transverse walls (2O)₅ which are rigidly coupled to said movable plane (14) and to said terminal reaction plane, and by lateral walls (23) of said integrated containment element.

8. The molding machine according to claim 7, characterized in that said walls (23) are provided with transparent windows (24, 25) in order to facilitate the view of the operator inside the head (21).

9. The molding machine according to claim 1, characterized in that said movable plane (14) can slide freely within the head (21).

10. The molding machine according to claim 7, characterized in that the couplings and the outputs (33) rigidly coupled to the cylinders (27) of said movable plane (14) protrude outside said integrated containment element from at least one of said transverse walls (20).

11. The molding machine according to claim 1, characterized in that said machine can be arranged horizontally or vertically.

12. The molding machine according to claim 1, characterized in that said machine can operate by injection alone, by compression alone or in a mixed injection-compression mode.