Closure assembly for an injection unit of plastic material with micrometrical regulation of the closure rod, and corresponding device for regulating micrometrically and fixing a threaded element

Closure assembly (10), for an injection unit (11) of plastic material (MP), comprising: a closing rod (16); a driving piston (15) adapted to drive an axial movement (f1) of the closing rod (16) between an open position (P1), in which the closing rod (16) opens an injection hole (13′) of a mold (13), and a closed position (P2), in which the closing rod (16) closes the injection hole (13′); an adjustment element or nut (20, 21), provided of a fine-pitch threading (21a), that is adapted to be screwed or unscrewed in one sense or the other (f2) in a corresponding threaded portion (22b) of an internal seat (22), formed in the driving piston (15), in order to regulate axially, in a micrometric way, the closing rod (16) in the closed position (P2); and an elastic washer (30, 31) that is provided for cooperating with a plurality of projections and notches (23a, 23b), formed in such internal seat (22, 22a), in order to fix the adjustment element (21) with respect to the body (15a) of the driving piston (15), once the closing rod (16) has been exactly regulated in the desired closed position (P2). Advantageously the adjustment element (21) is entirely housed in the internal seat (22) formed in the driving piston (15), whereby it does not protrude from the body (15a) of the latter.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is the US national stage of International Application PCT/EP2010/000477 filed on Dec. 1, 2010, which in turn claims priority to Italian Patent Application B109A000015 filed on Dec. 2, 2009.

TECHNICAL FIELD

The present invention generally concerns the sector of the injection moulding of plastic material, and more particularly it refers to a closure assembly which is associated with an injection unit for the moulding of plastic material and is adapted to regulate in a micrometric way and to fix the axial position, closed, of a respective closure/cling rod or pin.

The present invention also concerns a corresponding and more general regulation device or system for regulating in a fine and micrometric way the axial position of a threaded element, like a screw, and to firmly fix it at the end of such regulation.

BACKGROUND ART

In the machines for the injection moulding of plastic material, the injection units are provided for receiving the plastic material, in a molten or fluid state, from a feeding unit and for injecting it at high pressure into the hollow of a mould.

These injection units can be of various type and, for instance, they can be associated with a closure group or assembly, in turn comprising a closing rod or stem or pin which is adapted to selectively open or close, by the respective tip, an injection hole, often called also “gate”, in order to control the duration of the injection stage and hence the quantity of the fluid plastic material injected into the mould.

More in detail, in the injection units of this type, the closing rod is driven to move alternately, along its axis, between an open position, in which the tip of the closing rod set free and opens the injection hole, whereby the molten plastic material can freely flow into the hollow of the mould, and a closed position, in which such tip closes the injection hole so as to interrupt the flow of the molten plastic material from the injection unit toward the hollow of the mould.

This axial alternate movement of the closing rod is for instance driven and controlled by a hydraulic or pneumatic piston, which is associated with an end of the closing rod and is subject to the pushing action, along the two directions, of a fluid in pressure, as compressed air, in turn controlled, in the flow towards and from the pneumatic piston, by a valve system of known type.

The open position of the closing rod, in correspondence of which the injection hole is, as said, open and adapted to allow the free flow of the molten plastic material towards the mould, usually does not need to be accurately regulated.

By contrast, it is instead very important, in order to optimize and to obtain the maximum outcome of the operation of injection, to control and adjust with extreme care and precision the closing rod in the respective closed position, in which, as said, the tip of the closing rod closes the injection hole and thereby interrupts the flow of the molten plastic material towards the hollow of the mould.

At present there are in use a lot of different solutions, systems and devices, to adjust the closing rod in the respective closed position.

For instance, a known solution adopts a threaded nut, that is mounted on the pneumatic piston which drives the axial motion of the closing rod, with this being associated with a click mechanism comprising a ratchet or pawl, in turn adapted to be triggered elastically in a plurality of seats, whereby, by rotating this threaded nut, between a click and the other of the ratchet in these seats, it is possible to vary and to adjust the axial position of the closing rod with respect to the body of the injection unit.

This solution has, however, the drawback that it is constructively very complex because of the presence of the click mechanism, and moreover that it is cumbersome, since the threaded nut constitutes an additional piece which protrudes from the body of the piston that drives the closing rod.

Also it is known to adjust the closing rod in the respective closed position by using one or more elements of a determined thickness, i.e. by interposing them between the piston, movable axially, which drives the closing rod, and the area, of the fixed body of the injection unit, against which the same piston is pushed and enters into contact in correspondence of the closed position of closing rod.

This other solution is clearly uncomfortable and of complex actuation.

DISCLOSURE OF THE INVENTION

Therefore a first object that the present invention aims to achieve is to provide a closure assembly, for an injection unit of plastic material, that is adapted to regulate exactly and in a fine and micrometric way, in particular by rotating a threaded element like for instance a nut or a screw, a closing rod of the closure assembly in a determined axial position, corresponding to a closed position in which the closing rod closes an injection hole of the injection unit, without being affected by the drawbacks of the actual technique, as above outlined.

A more general object, however linked to the previous one, of the present invention is also to provide a corresponding regulation device or system, suitable for regulating in a micrometric way a threaded element, as for instance a nut or a screw, in one determined axial position, which device and system innovate in comparison to those at present known, and in particular combine the capability of performing such micrometric regulation in an axial sense also with the capability of fixing in a sure and stable way the threaded element in the determined axial position that is reached at the end of the regulation.

The aforesaid objects appear to be fully achieved by the closure assembly, for an injection unit of plastic material, and by the device, for the micrometric regulation and the fixing of a threaded element, having the characteristics recited by the independent claims.

Particular embodiments of the closure assembly and of the micrometric regulation and fixing device of the invention are defined by the dependent claims.

DESCRIPTION OF A CLOSURE ASSEMBLY CORRESPONDING TO A FIRST PREFERRED EMBODIMENT OF THE INVENTION

With reference to the drawings, a closure assembly, having the characteristics of the present invention, is indicated in the whole with10.

The closure assembly is associated with an injection unit, generally indicate with11and schematically represented inFIG. 1, for the injection of plastic material MP into a mould, indicated with13, in the framework of a more general system or machine MS for the moulding of plastic material.

The injection unit11in turn includes an injection nozzle12adapted to directly inject the plastic material MP into the hollow or matrix13aof the mould13, through an injection hole13′, defined by the same mould13.

To this purpose, the injection nozzle12is generally housed in a respective seat13b, formed in a nozzle-bearing plate13cof the mould13, and usually comprises an internal body12c, that defines a flow channel12badapted to convey the flow of the plastic material MP toward the injection hole13′; heating means12d, of known type, as an electric resistance, that are associated with the internal body12cin order to hold in temperature the injection nozzle12; and still an external shell12f, having a form corresponding to that of the seat13b, of the mould13, in which the injection nozzle12is housed.

In this configuration the closure assembly10is supported on the upper part by a fixed support plate13d, also called bottom plate, of the mould13, and in detail comprises:a driving piston15adapted to move axially along a respective axis X;a closure/closing rod or stem or pin16extending coaxially to the driving piston15and having a respective first end or head16a, suitable for being driven by the driving piston15, and a respective second end or tip16b, opposite to the first end16a, suitable for cooperating with the injection hole13′, defined by the mould13, through which the plastic material MP, at the molten state, is injected by the injection nozzle12into the hollow13aof the mould13.

The head16a, preferably of cylindrical form, exhibits greater radial dimensions, whereby it protrudes from the adjacent remaining part, also cylindrical and extending in axial sense, of the closing rod16.

The driving piston in turn15includes a respective body15a, cylindrical, that is provided for translating in the two senses, along the axis X, in a cylindrical room17aformed in a body17fixed and integrated in the support plate13d, in order to drive a corresponding alternate axial movement of the closing rod16, as schematized inFIG. 3by a double arrow f1, between an open position, indicated with P1, in which the closing rod16sets free and opens by the respective tip16bthe injection hole13′, so as to allow the molten plastic material MP to flow from the injection unit11to the hollow13aof the mould13, and a closed position, indicated with P2, in which the closing rod16closes by the respective tip16bthe injection hole13′, so as to interrupt and to prevent the flow of the plastic material MP from the injection nozzle12to the hollow13aof the mould13.

The axial stroke of the driving piston15, corresponding to the stroke of the tip16bof the closing rod16between the positions P1and P2, is indicated with C and is for instance about 10 mms.

It is specified that inFIG. 1the closure assembly10is represented with the respective closing rod16arranged in the open position P1, while the closed position P2of the closing rod16is represented by dot-dash line.

For clarity, insteadFIG. 1arepresents by continuous line and in enlarged scale the zone of the tip16bof the closure rod16, when arranged in the respective closed position P2.

A cover28is fixed on the support plate13dand exhibits a surface28aagainst which an upper side15a′ of the body15aof the driving piston15is pushed into contact, at an end of the alternate motion of the driving piston15, in turn corresponding to the open position P1of the closing rod16.

The body15aof the driving piston15exhibits moreover a respective lower side15a″, that is arranged on the side of the closing rod16and is adapted to enter into contact with a surface17b, defined by the body17, at the other end of the alternate motion of the driving piston15, corresponding to the closed position P2of the closing rod16.

In turn the fixed support plate13dinternally defines a hydraulic or pneumatic circuit, of known characteristics, schematically represented and indicated generally with13d′, which is configured to convey, under the control of a valve system, also of known characteristics, a fluid in pressure toward and from the cylindrical vane17a, so as to selectively exert a pressure on the side15a′ or15a″ of the driving piston15, slidable in the cylindrical vane17a, and thereby to alternately move the driving piston15along the axis X between the two end positions, corresponding, as said, to the contact of the sides15a′ and15a″ respectively against the surface28aof the cover28and the surface17bof the body17.

Moreover the driving piston15is shaped with a cylindrical portion15b, adjacent to the cylindrical body15abut of smaller diameter, which extend axially from the lower side15a″ and in which inside the head16aof the closing rod16is housed.

Suitable sealing means, indicated with29and in particular comprising rings of the “O-ring” type, are provided for sealing the space between the various portions, either fixed or relatively movable, which define the closure assembly10, so as to allow its correct operation and also to ensure the sealing, against any leakage toward the outside, of the fluid in pressure that is used for driving by means of the piston15the alternate motion of the closing rod16.

The closing rod16extends axially, along the axis X, from the zone of the driving piston15toward the zone of the injection nozzle12, while crossing a distribution plate13e, also usually called hot distribution plate, of the mould13, which internally defines a distribution network, indicated with13e′, formed by a plurality of channels, for the distribution of the plastic material MP, in the molten state, to the injection nozzle12of each injection unit11.

Still, suitable coupling, guide and sealing elements, generally indicated with14(FIG. 14), are interposed in the space between the closing rod16and the body of the hot distribution plate13e, in order to couple these parts, to properly guide the closing rod16in its axial motion, and at the same time to seal such space against any leakage toward the outside of the molten plastic material MP which flows at the inside of the distribution network13e′.

The closing rod16, after having crossed the hot distribution plate13e, extends axially inside the flow channel12b, which is formed along the axis X of the injection nozzle12and is adapted to convey the plastic material MP, coming from the hot distribution plate13e, toward the injection hole13′, in order to inject the plastic material MP into the mould13.

Still, the closing rod16is guided in the tip zone, adjacent to the injection hole13′, of the injection nozzle12, by a guide hole12athat is defined by the latter.

Moreover the closure assembly10includes micrometric regulation means, indicated generally with20, for adjusting and regulating in a micrometric way the closing rod16in the respective closed position P2.

In detail, according to a characteristic of the present invention, the micrometric regulation means20include at least one adjustment element or nut21, of substantially cylindrical shape and provided along its external cylindrical surface of a threading21a, of fine pitch, wherein this adjustment element21is adapted to be screwed or unscrewed in a corresponding internal seat22, threaded, formed along the axis X at the interior of the driving piston15, in order to adjust in a micrometric way, along such axis X, the relative position of the head16aof the closure rod16with respect to the body15aof the driving piston15and thereby to regulate axially the closing rod16in the closed position P2.

Conveniently the adjustment element21has at one end a notch21bfor the application of a tool, like a screwdriver, to be used for rotating, i.e. screwing or unscrewing, the adjustment element21, during the regulation of the closing rod16in the closed position P2.

The internal seat22, formed inside the driving piston15, and the adjustment element21are so configured that the latter is entirely housed in the internal seat22, whereby the adjustment element21does not project from the upper side15a′ that is defined by the body15aof the driving piston15and is arranged in the opposite area to the closing rod16.

More in detail, the internal seat22, threaded, in which the adjustment element21is housed, comprises:a first upper portion22a, substantially cylindrical, which is formed adjacently to the upper side15a′, spaced from the closing rod16, of the body15aof the driving piston15, and which is provided along its internal cylindrical surface with a plurality of projections and notches, respectively23aand23b;a second threaded portion22b, intermediate, formed substantially at the inside of the body15aof the driving piston15, in which second portion22bthe adjustment element21is housed, and with respect to which it is adapted to be screwed or unscrewed, in the two senses, in order to adjust the closing rod16in the closed position P2; anda third lower portion22c, formed substantially inside the cylindrical portion15b, of smaller diameter, of the driving piston15, which third portion22chouses the head16aof the closing rod16.

More in detail, this third portion22cof the internal seat22is delimited by a surface15b′, defining a stair inside the portion15bof the driving piston15, wherein this surface15b′ is provided for cooperating with the head16a, radially projecting, of the closing rod16, in order to push and drag the closing rod16in its axial movement from the closed position P2to the open position P1.

Conveniently an intermediate element24, not threaded, is interposed between the adjustment element21and the head16aof the closing rod16, in order to cooperate into contact with the head16aand thereby transmit to the closing rod16the axial regulation that is set up by rotating the adjustment element21, as in the following more clearly described.

In detail the intermediate element24is housed in the same seat, as defined by the third portion22cof the seat22, which houses the head16aof the closing rod16, with a sealing ring29′ being interposed between such intermediate element24and the surface22cof the seat22, in order to ensure the sealing against any leakage of the fluid in pressure that is used to drive the closing rod16.

Therefore, in this configuration, the intermediate element24is provided for staying substantially still, so as to avoid any relative sliding between the sealing ring29′ and the surfaces coupled and into contact with it, i.e. the surface22cof the seat22and that of the groove of the intermediate element24in which the same sealing ring29′ is housed, when the adjustment element21is screwed or unscrewed in the second threaded portion22bof the seat22in order to regulate the closing rod16in the closed position P2.

A certain light L (FIG. 3), suitable for assuring a sufficient range of the regulation in axial sense of the adjustment element21and hence of the closing rod16, is provided between the head16a, protruding in a radial way, of the closing rod16, and the surface15b′, of the stair defined by the lower portion15bof the driving piston15, that is pushed against the head16a, during the axial movement of the closing rod16from the closed position P2to the open position P1.

Indicatively this light L is selected so as to assure a range of regulation of the closing rod16, in the closed position P2, equal to at least 0.5 mm.

Besides, according to a further characteristic of the present invention, there are provided fixing means, associated with the micrometric regulation means20and indicated generally with30, which have the function of firmly fixing the adjustment element21with respect to the body15aof the driving piston15, once the closing rod16has been exactly regulated in the closed position P2.

In detail the fixing means30include an elastic washer31, which is coupled integrally in the rotation to the adjustment element21and is externally provided with two protrusions or protruding portions31a, in turn adapted to cooperate elastically with the projections and the notches, respectively23aand23b, that are defined in the upper portion22aof the internal seat22formed at the interior of the driving piston15.

In detail, with reference toFIGS. 7 and 7a, the elastic washer31has an external edge31bwhich exhibits an approximately elliptic form in the non deformed configuration of the same elastic washer31, as shown inFIG. 7, and along which the two protrusions31aare defined.

Further, the elastic washer31exhibits a central hole31c, for instance of rectangular form, that, at the mounting of the elastic washer31on the adjustment element21, is adapted to be couple with a corresponding throat or groove21c, formed in an end portion, of rectangular section, of the adjustment element21.

In this way the adjustment element21and the elastic washer31are coupled together and made integral each other in the rotation around the axis X and in the axial movement along it.

Still, the elastic washer31exhibits a special configuration comprising two semi-circular cuts31d′ that extend respectively along two opposite portions31eof the external edge31b, in the zone of the protrusions31a; two linear cuts31d″ each extending in a radial sense between a corresponding cut31d′ and the central hole31b; and moreover two holes31ffor the application of a special tool for the assembling of the elastic washer31on the adjustment element21.

This special configuration, including a plurality of cuts, has the function of giving the washer31a certain capability of getting deformed elastically, both in the zone of the central hole31c, so as to allow the elastic assembling of the washer31in the groove21c, by surmounting the stair defined by the latter, and also in the zone of the two portions31e, of the external edge31b, with the protrusions31a, so as to allow these two protrusions31ato cooperate with and to elastically follow the projections23aand the notches23b, during the rotation of the adjustment element21while regulating the closing rod16in the closed position P2.

It is noted that the elastic washer31has a configuration which allow it to get deformed and thereby to acquire, in comparison to the original elliptic profile of the edge31b, an approximately circular external profile31b′, as represented with a dot-dash line inFIG. 7, when the protruding portions31aof the elastic washer31step over the projections23athat are formed in the internal seat22, during the rotation of the adjustment element21relatively to the body15aof the driving piston15.

Therefore, owing to this configuration, the elastic washer31, during the regulation of the closing rod16, i.e. with the elastic washer31rotating jointly with the adjustment element21, is adapted to get deformed along its external profile without interfering with the portion22aof the seat22.

In the use, with the cover28disassembled from the fixed support13d, the operator places the driving piston15with the respective lower side15a″ into contact with the surface17b, so that the position assumed by the closing rod16corresponds to the closed position P2.

Then the operator, by screwing or unscrewing the adjustment element21in the respective seat22, as indicated by a double arrow f2, regulates and exactly positions the closing rod16in the determine closed position P2, desired.

For instance, to this purpose, the operator can use a special tool suitable for measuring in some way the protrusion H (FIGS. 1 and 1a) of the tip16bof the closing rod16from the tip portion of the injection nozzle12, and then rotates the adjustment element21up to when such protrusion H corresponds to a predetermined value, in turn defining the exact closed position P2, as desired, of the closing rod16.

Therefore, in this way, i.e. by screwing or unscrewing in a sense or in the other the adjustment element21in the respective internal seat22, the closing rod16is regulated micrometrically in the determined closed position P2, that is requested.

While making this regulation, the protruding portions31aof the elastic washer31elastically cooperate with the projections23aand the notches23bof the internal seat (22), whereby, once the closing rod16has been regulated in the closed position P2, i.e. at the end of its regulation, each of these two protruding portions31aare housed and blocked in a respective notch23a(FIG. 7a), so as to firmly fix the adjustment element21and hence also the closing rod16in such closed position P2.

Then the cover is reassembled28, whereby the injection unit11is ready to operate, with the closure assembly10being opportunely regulated so as to position, during working of the injection unit11, the closing rod16in the determined closed position P2, as requested, and thereby to close in an optimal way the injection hole13′ by means of the closing rod16.

In detail, in the operation of the injection unit11, when the driving piston15drives the axial movement of the closing rod16from the open position P1to the closed position P2, the intermediate element24presses directly into contact with the upper surface of the head16a, so as to push the closing rod16from the position P1to that P2.

Instead, when the driving piston15drives the movement of the closing rod16from the closed position P2to the open position P1, the stair15b′, that is formed in the portion15bof the driving piston15, cooperates, by recovering the light L, with the lower and protruding zone, of the head16a, opposite to that provided for cooperating with the intermediate element24, so as to move and drag the closing rod16from the position P2to the position P1.

It is therefore clear, from the preceding description, that the present invention fully achieves the objects to which it was intended, and in particular provides a closure assembly which is capable of allowing a precise and micrometric regulation of a respective closing rod in the closed position, in order to close an injection hole, and which moreover is capable of firmly fixing the same closing rod in the determined closed position that is set by such micrometric regulation.

It is also clear, from the same description, that the elastic washer, included in the closure assembly of the invention and provided for rotating jointly with the adjustment element which controls and regulates the closed position of the closing rod, appears capable of performing a double function, i.e. both the function of allowing a micrometric axial regulation, defined by discrete steps, of the same adjustment element, and the function of firmly fixing it in an automatic way, once the closing rod has been regulated and positioned in the requested axial position.

Of course, without prejudice to the basic principle and concepts of the present invention, the embodiments and construction details of the closure assembly, proposed here, may be abundantly varied with respect to what has been described and illustrated up to here, without departing from the scope of the invention itself.

For instance, according to a variant represented inFIG. 8, a further washer33in combination with an additional “seeger” ring34can be provided, in comparison to the embodiment10ofFIGS. 1 and 3, in order to block in a sure way, along the axis X, the elastic washer31that is provided for fixing the adjustment element21, at the end of its axial regulation.

Description of a Device According to the Invention for the Micrometric Regulation and the Fixing of a Threaded Element in One Determined Axial Position

The invention has been described up to here with reference, even if in the form of a preferred and not exclusive way, to a closure assembly, indicated with10, that is associated with an injection unit11for the injection moulding of plastic material into a mould13and is adapted to open and to selectively close an injection hole13′ of the same mould13.

However the essential concept of the present invention cannot be confined and goes well beyond the use and application of the closure assembly10to close and open this injection hole, so as to appear as comprising a more general regulation device or system for the micrometric regulation and the fixing of a generic threaded element or organ, as in particular a screw.

Such micrometric regulation device, indicated generally with110and with the respective parts marked by numerical references increased of 100 in comparison to the corresponding parts of the closure assembly10, is schematically represented inFIGS. 9aand9b.

In detail the regulation device110includes a support part or body115, fixed, that exhibits an external surface115′, and a threaded element121that is provided with a threading121aof fine pitch, wherein, as shown by double arrow f2, the threaded element121is adapted to be screwed or unscrewed in a corresponding threaded portion122bof an internal seat122, in turn extending along a respective axis X at the interior of the fixed part115, in order to regulate axially along the axis X the threaded element121in one determined axial position PA with respect to the fixed part115, and wherein the internal seat122and the threaded element121are so configured that the latter does nor projects from the external surface115.′

Moreover, an elastic fixing element or washer131, having substantially the same configuration of the elastic washer31, is integrally coupled in the rotation and in the axial translation to the threaded element121and is provided along the external perimeter of two protrusions131aprovided for cooperating elastically with a plurality of projections and notches, respectively123aand123b, formed in a portion122a, substantially cylindrical and adjacent to the external surface115′, of the internal seat122, in order to firmly fix the threaded element121, at the end of the regulation, that is once the threaded element121has been positioned micrometrically in the axial position PA, desired, along the axis X.

In the use of the device110, i.e. during the rotation, in the seat122, in one sense or the other of the threaded element121in order to regulate in a micrometric way its axial position with respect to the fixed part115, the elastic fixing element131rotates and moves along the axis X jointly with the threaded element121.

Besides, during such regulation, the elastic fixing element131externally gets deformed and assumes from an initial elliptic profile131b, corresponding to its non deformed configuration, an approximately circular profile, that however is such as to not interfere with the profile of the portion122a, every time the protrusions131aof the fixing element131step over the projections123a.

Then, at the end of the regulation, i.e. when the threaded element121is finally regulated in the axial position PA, desired, the elastic fixing element131assumes a stable position in which the respective two protruding portions131aare housed and blocked in two corresponding notches123bof the internal seat122, so as to firmly fix the threaded element121in such final axial position PA.

Therefore, by summarising, the fixing element131, owing to its special configuration, fit to get deformed when cooperating with the projections123aand the notches123bof the internal seat122, is adapted, other than to allow the micrometric regulation, as defined by discrete steps, of the axial position of the threaded element121with respect to the fixed part115, also to stop and firmly fix in an automatic way the same threaded element121, once it has been regulated in the requested axial position PA.