Patent Application
20190283297
The present invention refers to apparatus for injection molding of plastic materials of the type comprising a mold having a cavity and including at least one plate, a hot runner distributor of the fluid plastic material, at least one injector for the introduction of the plastic material from the distributor into the mold cavity, and an actuator for controlling the opening and closing of the injector.
More in particular, the invention refers to molding apparatus thus made wherein the actuator which actuates the injector, typically provided with a valve pin axially displaceable between a full closing position and a maximum opening position of the injector, consists in a fluid jack or in an electric motor supported by the distributor.
During the operation of the molding apparatus the actuator, whether pneumatic or hydraulic or electric, is subjected to heating by means of the heat of the distributor, and it is conventionally cooled by means of an autonomous cooling hydraulic circuit. In some applications, even characterised by high temperatures of the mold, there arises the desire that the actuator, particularly in the case of the fluid jack, be without a cooling circuit so as to simplify the molding apparatus further. The heat of the hydraulic jack must however be dissipated, and solutions in which the cooling of the hydraulic jack occurs by means of thermal exchange with the aforementioned at least one mold plate were proposed for this purpose. As concerns this, it should be observed that the expression “mold plate” is used to indicate, in the description and in the claims that follow, the so-called mold clamping plate, as a whole or in relation with a component thereof in that it can consist of several adjacent plates, the die i.e. the fixed part of the mold, a plate of the distributor, as well as the plane of the press of the injection apparatus.
Solutions in which the cooling of the fluid jack occurs by means of the thermal exchange with a metal plate of the apparatus are for example disclosed by documents WO-2009/052611 on behalf of Mold Masters and documents WO-2011/119791 and US-2014041192, U.S. Pat. No. 8,349,244, U.S. Pat. No. 8,562,336, U.S. Pat. No. 8,728,378, EP-2550144, EP-2631059, WO-2015/183332, U.S. Pat. No. 9,682,504, US-2017/0246784, EP-3240666, US-2016/0361856, WO-2016/153608, WO-2016/153632, WO-2016/153703, WO-2016/153704 and WO-2016/153705 on behalf of Synventive Molding Solutions.
Provided in all these prior art solutions is an elastic thrust member, typically consisting of or including a metal spring, interposed between the cylinder of the hydraulic jack and the plate with the aim of guaranteeing the thermal exchange contact irrespective of the thermal dilation phenomena of the hot runner which supports the hydraulic jack directly or indirectly. The use of plastic thrust members is also considered necessary by the prior art so as not to have to demand high precision machining of the mold plate/s against which the cylinder of the actuator must be kept at thermal exchange contact.
The use of such elastic members entails construction complications and thus considerable costs, and the thermal exchange surface between the hydraulic jack and the plate made available by such elastic members is generally limited and thus scarcely efficient.
The object of the present invention is to overcome the aforementioned drawbacks and provide an apparatus for injection molding of plastic materials of the type defined above that allows to obtain an efficient thermal exchange cooling between the actuator and the mold plate in a more simple, economic and functional manner.
With the aim of attaining subject object, the main and peculiar characteristic of the invention resides in the fact that for the cooling of the actuator provided for is at least one body made of thermally conductive material that at least partly surrounds the actuator in an axially slidable manner and is kept in thermal exchange contact with the said at least one plate by at least one from among a magnetic force, a pressurised fluid thrust, an electrical drive force.
Should the actuator consist of a fluid jack, such hollow body conveniently has a radial wall faced to the cylinder of the hydraulic jack and defining a flat surface at contact with said at least one plate. Such radial wall may be restrained against the plate by a magnetic attractive or repulsive force, by a pressurised fluid or by a pneumatic or hydraulic thrust, or still by an electrical drive force, or the combination thereof.
The invention applies both to the case where the actuator is directly fixed to the hot runner, and in such case the aforementioned at least one plate may consist in the mold clamping plate or in the hot runner plate, or it can be indirectly fixed to the hot runner, laterally thereto, and in such case the aforementioned at least one plate consists of the die plate or hot runner plate. Alternatively, the aforementioned at least one plate may consist in an element of the press of the molding apparatus.
The invention will now be described in detail with reference to the attached drawings, provided purely by way of non-limiting example, wherein:
An apparatus for injection molding of plastic materials conventionally comprises a press (not illustrated) for sending the fluid plastic material to a distributor or hot runner 1 from which the plastic material is injected into the mold cavity (not illustrated) through one or more injectors. Each injector comprises a displaceable valve pin 2, relatively to a mold gate, between a full closing position and a maximum opening position. The displacement of the valve pin 2, and thus the opening and closing of the injector, occur through an actuator which, in the case of the present invention, consists of a fluid jack indicated in its entirety with 3, pneumatic or hydraulic. Alternatively, the actuator could consist in an electric motor.
The hydraulic jack 3 comprises a cylinder 4 and a plunger 20 directly or indirectly connected to which is the valve pin 2 for example as shown in
The cylinder 4 of the hydraulic jack 3 is supported by the distributor 1: in the case of the embodiments represented in
The cylinder 4 is without an autonomous cooling circuit that conventionally uses a cooling liquid, and the cooling thereof occurs by means of thermal exchange contact with a plate of the molding apparatus. Such plate may include any mold plate and in particular, like in the case of
It should be observed that the clamping plate 6 or other plates (not shown) can be provided with a liquid cooling circuit, indicated with 12, or it can be without one.
In order to guarantee the thermal exchange contact between the cylinder 4 of the hydraulic jack 3 and the clamping plate 6 the invention provides for, in place of a thrust spring member like in the case of the prior art, at least the body 7 made of thermally conductive material that at least partly, and preferably for a substantial and almost full perimeter width, surrounds the cylinder 4. This body 7, made of thermally conductive material, is axially slidable against the outer surface of the cylinder 4 for a stroke of limited degree by means of one or more C-shaped lateral bands 8 engaged—at one end—with the cylinder 4 and—at the opposite end—an axial clearance in a groove 9 of the body 7, as better observable in
The body 7 may have a generally L-shaped or C-shaped section with an end radial wall 10 facing the bottom plate 11 of the cylinder 4 and defining a flat surface at planar contact with the clamping plate 6. The lateral wall of the body 7, indicated with 22, is in sliding thermal exchange contact with the cylinder 4 of the hydraulic jack 3.
The bottom plate 11 may consist in an element separated from the body of the cylinder 4, or it can be made of a single piece with the cylinder 4.
In order to constantly maintain the wall 10 of the body 7 in thermal exchange contact with the clamping plate 6, the invention provides for different alternative solutions among which the preferred one, represented in
As observable hereinafter, the magnetic force may also be a repulsive force instead of an attractive force.
In the case of
The same arrangement of
According to a further alternative solution not represented in the drawings, the thermal exchange contact between the body 7 and the clamping plate 6 can be obtained by means of an electrical drive force, or through an electric actuator configured for pushing, by means of a transmission known to a man skilled in the art, the transversal wall 10 against the plate 6.
It should be observed that the various alternatives described above could be combined with each other: so that the pneumatic thrust, the hydraulic thrust and the electrical drive force could be combined with each other and/or with the magnetic attraction.
As previously mentioned, the fluid jack 3 can be fixed, instead of directly onto the hot runner 1, laterally thereto for example as represented in
According to a further alternative not represented in the drawings, the plate against which the body 7 is in thermal exchange contact can consist in the plane or another element—magnetic or non-magnetic—of the molding apparatus and the relative press to which the mold is associated.
In the further variant of the invention schematically represented in
The auxiliary element 23 is kept at constant contact with the bottom plate 11 for example by means of the attraction force obtained by the permanent magnets 24. Furthermore, there can be further provided for permanent magnets 25, 26 respectively carried by the auxiliary element 23 and by the plate 6 and configured so as to obtain a magnetic repulsive force suitable to press the radial wall 10 of the body 7 against the plate 6.
The magnets 26 can also be directly applied to the bottom plate 11 of the cylinder 4 should the auxiliary element 23 not be present, and the magnetic repulsive force can also be combined with a pressurised fluid thrust and/or with an electrical drive force, as described previously.
Lastly, it should be observed that the thermal exchange contact between the body 7 and the plate 6 can be obtained not only by the radial wall 10 but also by the lateral wall 22. This lateral contact can be obtained directly, and in this case the lateral wall 22 will be at least partly inserted into a recess or complementary seat of the plate 6 or of an element of the mold, or indirectly by means of an intermediate element fixed to the plate.
In light of the above it will be clear that the invention is capable of ensuring, during the operation of the molding apparatus, an efficient heat dissipation of the hydraulic jack 3 in a constructively easy and economic manner.
Obviously, the construction details and the embodiments may widely vary with respect to what has been described and illustrated, without departing from the scope of protection of the invention as described in the claims that follow. Thus, for example, the invention also applies to the case where the actuator of the injector consists of an electric motor instead of a fluid jack.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102018000003490 | Mar 2018 | IT | national |
