Hot runner device having an overload protection device

The invention relates to a hot runner device comprising at least one needle valve nozzle and a shut-off needle which is movable in the needle valve nozzle by means of a movement means, and comprising an overload protection device for the shut-off needle, characterized in that the overload protection device is implemented as follows: the shut-off needle is connected in at least a first movement direction directly or indirectly to the movement means by at least one frictional connection that can be released when a threshold force is exceeded.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. nationalization under 35 U.S.C. § 371 of International Application No. PCT/EP2018/054248, filed Feb. 21, 2018, which claims priority to German Patent Application No. 102017104000.5, filed Feb. 27, 2017. The disclosures set forth in the referenced applications are incorporated herein by reference in their entireties.

The present disclosure is directed to a hot runner device with an overload protection device for a shut-off needle.

It is known to provide hot runner devices with an overload protection device having a positive connection or a fracture mechanism, which automatically suspends the movable shut-off needle in the hot runner during the closing movement under overload from the power flow of a drive device to avoid damage to the shut-off needle. However, the known overload protection devices are structurally designed in a relatively complex manner and yet offer only limited functional reliability. Reference is made, for example, to DE 10 2015 216 059 A1 concerning known overload protection devices, which shows positive engagement in the manner of a coupling with radially movable ball bodies as overload protection device, wherein a relatively long travel of the shut-off needle must be covered in order to trigger or activate this overload protection device. If the shut-off needle is blocked during opening or closing and the distance is not sufficient to trigger the overload protection device, the shut-off needle may be damaged or be moved without notice to an inadmissible position.

The present disclosure is directed to a hot runner device with a simply designed and reliable overload protection device.

A hot runner device according to the present disclosure has at least one needle valve nozzle and a shut-off needle which is movable in the needle valve nozzle by a needle mover (preferably in one direction back and forth), and an overload protection device for the shut-off needle, wherein the overload protection device is realized as follows: the shut-off needle is connected in at least one first direction of movement directly or indirectly to the needle mover by a frictional connection which is releasable when exceeding a limit force.

The protective mechanism for overload protection may take place exclusively via a frictional connection and not via a positive connection or a fracture mechanism, as in the known solutions, since it has been found that the triggering limit force at which the overload protection device releases the shut-off needle is adjustable in a simple manner in a relatively precisely way via the frictional connection. In addition, a frictional connection can be realized with simple design means with only small spatial requirements. This will be explained in more detail below with reference to illustrative embodiments to which the invention is not to be limited. According to the present disclosure, the triggering limit force may approach zero.

In some embodiments, which can be combined, the frictional connection is realized either on the one hand as a shrink, stretch and/or stretch-shrink assembly, and/or on the other hand via self-locking.

In an embodiment, the overload protection device is based solely on a frictional principle, since in this way the triggering limit force is particularly well adjustable.

In an embodiment, only one single frictional connection is provided, which causes a release of the shut-off needle in only one single direction of movement when exceeding the triggering limit force, for example, when closing an outlet opening of the needle valve nozzle with the shut-off needle. However, it can also be provided that the shut-off needle is connected in two different—for example, opposite—directions of movement directly or indirectly to the needle mover by at least one frictional connection which is releasable upon exceeding a limit force in order to effectively protect the needle valve nozzle against damage during both opening movements and closing movements of the shut-off needle for opening or closing the outlet opening of the needle valve nozzle.

In an embodiment, one or both of the releasable frictional connections may be realized in each case as a releasable self-locking cone press-fit connection or through two detachable cone press-fit connections.

In an embodiment, the first releasable cone press-fit connection may be realized by an outer cone on the valve needle and corresponding inner cone in the needle mover or the abutment of the shut-off needle, in particular a pin, as the first friction partner, a sleeve with inner cone as the second friction partner and another sleeve in the needle mover.

In an embodiment, a second cone press-fit connection can be provided that is formed by an outer cone on a sleeve, which is penetrated by the shut-off needle, as the first friction partner, and an inner cone in the needle mover or in a further sleeve inserted into the needle mover as a second friction partner.

In an embodiment, the shut-off needle is exclusively linearly movable back and forth with the needle mover. It can also be provided that the shut-off needle is connected in and/or against this direction or these directions only frictionally engaged with the needle mover. In an embodiment, the frictional engagement can also be supplemented by a positive connection, for example by a small circumferential groove in the one part (shut-off needle or needle mover) which engages in a corresponding circumferential groove of the other part (needle mover or shut-off needle) by way of latching. In an embodiment, the triggering force is substantially determined by the frictional engagement, i.e. it is determined by more than 50% by the frictional engagement.

It is provided in this case that one or both of the frictional and self-locking connections is/are realized in such a way that the shut-off needle or the abutment of the shut-off needle is connected in a frictionally engaged and self-locking manner to the needle mover such that the shut-off needle exceeds self-locking and automatically disengages at an axial force introduction which is greater than the static friction of the frictional connection.

In an embodiment, no axial displacement of the shut-off needle relative to the needle mover can take place before the overload is reached, since the frictional engagement is chosen such that it does not permit any elastic deformation upon release.

In an embodiment, the limit force is less than an expended mounting force (for pressing the shut-off needle into the needle mover). In addition, it is advantageous to set the level of the limit force depending on the level of the mounting force. Preferably, a setting of the limit force further takes place in a simple manner via the mounting force.

In an embodiment wherein the overload protection device is formed as a shrink assembly, the shrink assembly may be designed as a cylindrical shrink assembly in which, for example, a heated sleeve is shrunk onto a cylindrical portion, in particular onto a drive end, of the shut-off needle by cooling.

With regard to an embodiment wherein the overload protection device is a stretch assembly, it may be provided that the stretch assembly is formed as a cylindrical stretch assembly in which, for example, a cooled shut-off needle is expanded in a cylindrical portion, the sleeve or the receptacle by heating to ambient temperature.

In an embodiment, the shrink assembly and the stretch assembly may be combined to form a shrink-stretch assembly. The assemblies produced by heating and/or cooling are also called cross-press assemblies.

In an embodiment, the overload protection device may have a sensor which detects the triggering of the overload protection device and forwards a signal to a controller of the injection molding machine.

Generally, the protective mechanism for overload protection takes place via a frictional connection and not via a positive connection or a fracture mechanism, as in the known solutions, so that the triggering force is easily adjustable and the triggering takes place directly when the force is reached, without any deformation taking place or without having to cover any reaction path.

As far as terms such as above and below or right and left are used in the following, these relate to the position shown in the respective drawings. The installation position may deviate from this, so that the terms are to be understood in a relative way.

FIG. 1shows in the interaction of parts A, B and D or A, C and D a respective sectional view of a portion of a hot runner device with a needle valve nozzle1. This device is designed for injection-molding plastic components. The plastic component is injection-molded in a mold, which is here indicated only by a line S as a mold plate with opening and is otherwise not shown (see, for example, DE 10 201 521 6 059 A1), which usually has a mold plate having a gate bore.

FIGS. 1A-1Dis divided here for the sake of simplicity into four parts which are arranged from each other spaced apart, wherein the parts A, B and D, in an imaginary juxtaposed state, represent the hot runner device in a closed position and wherein the parts A, C and D, in an imaginary juxtaposed state, represent the hot runner device in an open state.

The outflow end of the needle valve nozzle1, which is aligned towards the mold plate, can be closed in the closed position by a closure end2of a shut-off needle3, so that no more plastic can enter from the needle valve nozzle1or into the mold.

InFIG. 1B, the shut-off needle3has been moved accordingly in the direction of the mold (here in the downward direction), so that the needle valve nozzle1is closed. In contrast, in the open position ofFIG. 10, the shut-off needle has been moved away from the mold (here in the upward direction), so that the needle valve nozzle1is opened. In this condition, plastic can flow into the mold.

The needle valve nozzle1and the shut-off needle3have a main extension direction X. The shut-off needle3is moved in a limited manner when closing and opening the needle valve1in and against the direction X relative thereto.

The shut-off needle3is held for this purpose at its—driven—end facing away from the free end2(hereinafter also called drive end)4in a needle mover of a lifting device. This needle mover may be formed as a lifting plate5. The needle mover is movable by means of a drive device6in the direction X or is itself a part of the drive device (e.g. a piston).

The needle mover—here the lifting plate5—is movable back and forth in a stroke volume33of a hot runner injection mold with multiple plates8,9,10in the X direction relative to these, wherein in and on these plates a hot runner section11with hot runner flow elements12,13,14,15is formed. At the so-called distributor—flow element15—the needle valve nozzle1is attached here.

The hot runner flow elements12to15and the needle valve nozzle1each have a channel section, wherein these channel sections in their interaction form a melt guide channel16which opens into an annular space around the shut-off needle3between the closure end2of the needle valve1and the drive end4of the shut-off needle and which extends to the open outlet end of the needle valve nozzle1, so that by moving the shut-off needle3the melt flow into the mold plate (at S) can be released or closed. A gap is formed between the hot runner elements12,13,14,15and the rest of the tool7to separate the hot or warm area from a region which is relatively colder in relation thereto. In order for the plastic melt to remain flowable in the gate system, it can be designed in any case to be heatable in sections (see the heater17).

The movement of the shut-off needle3can take place, for example, with the aid of a fluid-actuatable drive cylinder18as a drive device6, which has a movable piston19with a piston rod20which is directly or indirectly (i.e. via intermediately connected means) fastened to the needle mover—here the lifting plate5. The drive device can also be realized differently, for example as an electric motor or electromagnet or as a hydraulic cylinder. It is also conceivable that the piston19itself forms the needle mover, to which the shut-off needle3is releasably attached.

It is readily possible to also attach a plurality of the shut-off needles3to the lifting plate5and still move the lifting plate5with only one drive device.

The shut-off needle3shown here is detachably fastened with its drive end4via an overload protection device, which is designed here as a (first) frictional connection or as a frictional connection21(see alsoFIGS. 2A-2B), in or on the needle mover, here the lifting plate5. It is provided in particular that the overload protection device is realized as follows: the shut-off needle3is connected in at least one first direction of movement directly or indirectly to the needle mover, in particular a lifting means, via at least one frictional connection21which is releasable when exceeding a limit force. In this case, the frictional connection21is formed here according to an advantageous variant as a self-locking connection.

For this purpose, the at least one frictional connection21is designed such that the shut-off needle is held securely and firmly in the needle mover in normal operation during the reciprocation of the needle mover for opening and closing the needle valve nozzle1. Only in an overload case at an excess of a limit force, the frictional force of the frictional connection21is overcome, so that the shut-off needle3and its end of movement4is released from its tight fit (e.g. formed by a pin23, sleeve24and second sleeve28) in the needle mover, here the lifting plate5, so that the needle mover can move relative to the shut-off needle3in the X direction. Thus, the overload protection function/device is implemented with simple design means.

Hereinafter, various embodiments of an overload protection device according to the present disclosure are considered in more detail, to which the invention is not limited.

In an embodiment, the needle mover, in this case the lifting plate5, are penetrated by a stepped bore22, which may partially have a thread (FIGS. 1A to 5C). The drive end4of the shut-off needle3engages in this bore22. In this case, a pin23is attached to the drive end4of the shut-off needle3in the axial extension of the same.

This pin23may alternatively—seeFIGS. 5A and 5B, for example—also be integrally formed on the drive end4of the shut-off needle3.

The pin23has a conical outer shape and is directly releasably held and fixed with frictional engagement in the conical bore22′. For this purpose, the pin23is pressed during its assembly with a predetermined force into the bore22′. The frictional connection21is thus formed here by the pin23with the outer cone A and the bore22′ with the at least partially provided inner cone I and the friction between pin23and bore22′ (seeFIGS. 5A-5C and 6A-6B).

The bore22′ may be formed at least in sections in an inner conically corresponding manner to the conical shape of the pin23(seeFIGS. 5A-5C and 6A-6B). Here the pin narrows from top to bottom, i.e. in the direction X, in which the shut-off needle3is moved in a closure movement into the position ofFIG. 10.

Alternatively, the pin23can also be inserted directly into a bore22of the needle mover, in particular the lifting plate5(similar toFIG. 5A, not shown here in the drawing), or into a component inserted into the needle mover, in particular the lifting plate5(FIGS. 2A to 4B).

In an embodiment, this component may be a sleeve24/31.The sleeve24is configured in a further preferred embodiment as a screw with an external thread, which is inserted into an internally threaded portion of the bore22and itself has an inner bore22′ which is concentric to the bore22. The term “bore” is to be understood here and throughout this application in the sense of an opening, in particular a through-hole, which need not necessarily be made by drilling.

The needle mover5presses in this case via the pin23during the closing movement on the needle valve head27and the free end4of the shut-off needle3to move the shut-off needle3in an axially linear manner in the X direction.

Both the pin23and either the bore22in the needle mover or the bore22′, which is preferably concentric thereto, in the component, in particular the sleeve24, respectively comprise a corresponding outer cone A and an inner cone I over their entire length in the X direction or at least in sections.

The pin23is or was pressed with a defined force during its assembly into the needle mover5or, in this case, into the sleeve24via its outer cone A into the inner cone I of the surrounding body—the sleeve24or directly the needle mover.

In an embodiment, it can be provided that the shut-off needle3has an outer cone A instead of a separate pin23directly at its one end and is thus directly frictionally connected to the needle mover5(or its sleeve24). The shut-off needle3then has no separate pin, but forms this pin with its end itself. This embodiment is shown inFIG. 5A, which shows in A the components of an embodiment according to the principle ofFIGS. 2A-2B, in which the bore22in the lifting plate5is formed in a directly conical manner and in which the drive end4of the shut-off needle3is formed in a corresponding manner conically as a pin.

Overall, the pin23is connected in a frictionally engaged and self-locking manner to the surrounding body—preferably the sleeve24or the mold plate5—so that a translatory movement of the needle mover5moves the pin and thus the shut-off needle3in the direction X or in the opposite direction −X. In this way, the connecting needle3can be moved back and forth between the closed position (see, for example,FIG. 1Band the open position (see, for example,FIG. 1C).

During the closing movement, in which the needle mover—here the lifting plate5—is moved in the direction −X, the closing needle3exerts an axial force on the pin23or on the frictional engagement region between the inner cone I and the outer cone A. If this axial force exceeds the static friction of the frictional connection, the pin23is released from the surrounding body—preferably the sleeve24or the lifting plate5—and the shut-off needle3is no longer moved by the body or the drive device in the closing direction −X.

In other words, this means that the pin23triggers and no longer serves as an abutment for the shut-off needle3. This can be seen, for example, inFIG. 2B. Here, the frictional connection21has released after moving the needle mover (this movement is not visible here) and the shut-off needle3was therefore able to move relative to the needle mover. Damage to the shut-off needle3can or could be avoided in this way.

As a result of a suitable adjustment of the mounting force, the limit force or critical force at which the pin23is to trigger can also be adjusted. In this way, the shut-off needle3is easily preserved from damage due to overload.

The needle mover can be configured differently. It can, for example, also directly be a piston or, for example, the previously described lifting plate5. A lifting plate5is preferably—but not only—then chosen if one or more of the shut-off needles are to be installed in it.

Optionally, a cover cap26may be placed on the sleeve24at its end facing away from the shut-off needle3(FIG. 2A, which advantageously covers the bore22and prevents the released pin23from falling out into the stroke volume of the lifting plate.

In an embodiment, the shut-off needle3has a head27at its end4with a diameter which is widened in relation to the other diameter of the shut-off needle3, with which it rests axially on the pin23and/or is fixed thereto, so that good power transmission between the pin23and the shut-off needle3may be provided, in particular if they are not formed integrally.

In an embodiment, a second sleeve28is inserted into the bore22below the sleeve24. This further sleeve28may be fixed between a shoulder of the stepped bore22of the needle mover and the first sleeve24—in particular as this sleeve24is formed as a screw. The second sleeve28preferably itself has a stepped inner bore29. In this case, the head of the needle27is movably guided in the inner bore29. In this case it strikes down against a collar of inner bore29so that it cannot escape from the inner bore29. Usually, the dimensional adjustment is chosen so that the head of the needle27between the pin23and the collar of the stepped bore29has a slight play, so that the needle3can move transversely to the main movement direction X in order to avoid thermal stresses.

It is clearly shown inFIG. 2Athat the pin23is pressed with its outer cone A into the inner cone of the sleeve24. The shut-off needle3is moved upward (see alsoFIG. 10, which here corresponds to an open position on the needle valve nozzle1. InFIG. 2Bit can be seen that the shut-off needle3and the pin23have moved relative to the lifting plate5(lifting movement, it can be seen in each case from the offset of the lifting plate5between theFIGS. 2A and 2Bof the respective stroke). The lifting plate5was moved in the downward direction. The shut-off needle3has not followed this movement because a disturbing force acts on it in an unrecognizable manner here, which is greater than the press-in force for mounting the pin3in the needle mover, in particular in the first sleeve24. The pin23has been released from its press fit/friction fit and has not followed the movement of the needle mover.

The embodiment ofFIGS. 3A-3B and 4A-4Bdiffers from the embodiment ofFIGS. 2A-2Bin that the overload protection device is designed such that it can trigger in two directions +X and −X.

For this purpose, the overload protection device may have two (here locally separate) frictional engagement connections21aand21b.

Constructively, this can be achieved in various ways. According to the embodiment shown inFIGS. 3 and 4, a (here second) screw sleeve30is inserted into a lower portion of the bore22, which is stepped in this case, in addition to the frictional connection21a. This screw sleeve30is mounted on the side of the lifting plate5which is opposite the first sleeve24. The screw sleeve30has an inner cone I. An inner sleeve31is pressed into said core, which sleeve has an outer cone A. At the same time, this cone press-fit connection21btapers in the opposite direction (here in the direction −x) like the first cone press-fit connection21a.

The shut-off needle3passes through the inner sleeve31. This is in turn is designed here such that the second sleeve28rests upwardly on it. The pin23and/or the head27cannot fall out of the lower sleeve28downwardly or exit therefrom, since the diameter of at least one or both of these elements is greater than the inner diameter of the bore32of the inner sleeve31.

The function of the second frictional connection21bas part of the overload protection device is as follows:

The shut-off needle3has been moved inFIG. 4Awith the needle mover in the downward direction, which here corresponds to a closed position on the needle valve nozzle1. If the shut-off needle3is now to be moved from the closed position to an open position, the head27bears against the lower annular collar of the second sleeve28, so that the shut-off needle3is co-lifted by the movement of the needle mover together with the sleeves and pins23,24,28,30,31, which are screwed and inserted therein.

InFIG. 4Bit can be seen that the shut-off needle3or the head27, the second sleeve28and the inner sleeve31have moved relative to the lifting plate5. The lifting plate5has been moved upwards. The shut-off needle3has not followed this movement since a disturbing force acts on it in a manner not recognizable here, which is greater than the pressing force for mounting the outer conical sleeve31in the needle mover, in particular in the screw sleeve30. The inner sleeve31, which is conical on the outside, has been released from its press fit/friction fit in the mounting means, particularly in the internally conical screw sleeve30, and has not followed the movement of the needle mover.

According toFIGS. 5B and 5C, two overload protection devices are also respectively realized as overload safeguards both during lifting and when lowering the shut-off needle3with two cone press-fit connections21a,21b, which act in different directions. However, the structural design is particularly simple, which is advantageous but not mandatory for the function of the invention.

Also according toFIGS. 5B and 5C, either the conical drive end4or a conical pin23is inserted into a sleeve31having a bore22′, which is formed correspondingly conical to the pin23. In this way, in turn, a cone press-fit connection21ais realized. The inner cone and the outer cone expand in a first direction “upwards” (direction −X). This corresponds to the first overload protection device according toFIG. 5A. The sleeve31thus corresponds here in each case also to the sleeve24ofFIGS. 2A to 4B.

In addition, however, the outer contour of the sleeve31and the inner contour of the bore22in the lifting plate5are designed correspondingly conical. The inner cone and outer cone expand in a second direction “down” (direction X). According toFIGS. 5B and 5C, the bore22thus conically widens in the lifting plate downwards in the direction X, so that the sleeve31can be released under overload from its friction fit inFIG. 5Bin the downward direction. This is the respective second overload protection device.

According toFIG. 5B, the drive end4of the shut-off needle3is integrally formed in a conical manner and thus forms the pin23per se. According toFIG. 5C, however, a pin23is placed on the drive end4(which in turn is formed here as a cylindrical head27).

These embodiments are structurally simple and still well functional.

As a result of the two friction connections according toFIGS. 3A to 5C, the overload protection device can be reliably triggered in each case in both possible directions of movement of the needle valve nozzle.

In the following, the mode of operation of an overload protection device will be described in more detail again with reference toFIGS. 6A-6B and 7, which shows a constructively simplified but nevertheless theoretically functional design.

During its initial mounting, the conical pin23is pressed by means of a suitable device (not visible here) with a force FM—seeFIG. 6A—into the conical bore22′ of the sleeve24. Consequently, a normal force FN is built up via the flanks (flank angle α) of the cone of the conical frictional connection. The friction (coefficient of friction μ=tanρ) acts against the mounting force FMand generates the frictional force FR. Thus, the theoretically achievable normal force FN(th)is reduced and the x-component of the resultant force FE is reduced to the remaining spreading force FS. As long as the y component FN(y)of the normal force FNis smaller than the y-component FR(y)of the frictional force FR, there is self-locking and the conical pin can be pushed out again only with a release force FL(seeFIG. 6B).

The force diagram ofFIG. 7shows that self-locking is present for:

The force relationships during a disassembly process are illustrated inFIG. 6B. The exact release force FLcan be seen inFIG. 7. For this, it must be noted that when the mounting force FMis removed, the direction of the frictional force FRis reversed and thus the normal force FN, with the same spreading force FS, becomes smaller because the x-component of the frictional force FR(x)now counteracts the spreading force FS. The necessary release force FLis mainly determined by the mounting force FMand, as the force diagrams show, depends on both the flank angle α and the coefficient of friction μ=tanρ.

How the factors affect the release force (qualitatively) is shown inFIG. 7. The following applies: