Actuating device for shut-off needles in injection molding devices comprising needle shut-off nozzles

A drive system (10) for shutoff needles in injection molds fitted with needle shutoff nozzles comprises an elevation drive element (20) to which can be affixed at least two shutoff needles (16) of two needle shutoff nozzles, said elevation drive element being displaceable—between two longitudinally supported control rails (30) that can be moved in a first direction (R1)—in a second direction (R2) perpendicular to the first direction (R1), at least two glide elements (50) being configured in grooves (40) oblique to said first and second directions (R1, R2) running between the elevation drive element (20) and the control rails (30), said glide elements converting the first motion of the control rails (30) in the direction (R1) into an elevation motion imparted by the elevation drive element (20) in the second direction (R2). In order to assure in particular substantially maintenance free and durably reliable operation of all valve needles, the invention provides that components which move relative to one another and hence are exposed to wear, in particular the control rails (30) and/or the glide elements (50), are made at least in part of a self-lubricating or a diamantine material or are coated at least in part with a self-lubricating or diamantine material.

FIELD OF THE INVENTION

The present invention relates to a shutoff-needle drive system in injection molds fitted with shutoff needle nozzles and to injection molds.

BACKGROUND ART

Needle shutoff nozzles are used in injection molds to feed a flowable material at a predetermined temperature and high pressure to a separable mold insert. Most commonly they are fitted with pneumatically or hydraulically driven shutoff needles which periodically open and close gates in the mold insert. For that purpose each shutoff needle is supported in axially displaceable manner in the mold-side region of the injection mold and, in the nozzle-side region, passes preferably centrally through a flow duct for the material to be processed. The flow duct terminates in a nozzle element subtending a nozzle discharge aperture. In the closed position, the lower end of the shutoff needle engages a sealing seat constituted in the nozzle end or in the mold insert.

SUMMARY OF THE INVENTION

Many applications require that all shutoff needles move synchronously and that they be loaded at the same closing pressure, in particular when several mold inserts are simultaneously injection-molded in one mold.

In this respect the European patent document EP 0 790 116 A1 proposes affixing the shutoff needles of one group of nozzles to a common support plate implementing an excursion in the longitudinal direction of the shutoff needles. For that purpose the support plate is configured at its front end between two stationary stops and laterally between two guide strips themselves supported in longitudinally displaceable manner within a clamping plate and are fitted at their side faces with obliquely mounted glide blocks or cams. The said glide blocks or cams laterally engage the support plate which is fitted with oblique grooves. When the guide strips are reciprocated longitudinally by a drive means, the support plate carries out an associated up and down displacement. In this manner all shutoff needles affixed to the support plate carry out the same elevation displacement.

This design occurs the drawback that the oblique grooves of the support plate and the sliders guided therein are subjected to comparatively high wear in particular in the case of high operational rates. As a result, and regardless of lubricants and the like, many maintenance procedures and hence shutdowns take place. Operational and maintenance costs are commensurately high.

As regards an injection mold known from the German patent document DE 196 11 880 A1, which comprises several needle shutoff nozzles, each shutoff needle is affixed to a separate needle support element. Such elements are fitted at two mutually opposite flat faces with oblique guide cams engaging oblique guide grooves of forked slider frame. A cylindrical element is subtended underneath the flat faces at each needle support element and is supported in the manner of an elevation plunger in axially displaceable manner in a guide bush. When the thrust frame is moved to and fro, the individual needle support elements will be moved up and down perpendicular to the motion of said frame.

This design is problematical in that due to dimensional tolerances, precisely synchronous entry of the shutoff needles in the particular associated sealing seat cannot be assured. For that reason each shutoff needle is affixed by means of a resilient intermediate element to its needle support element: this feature raises both the costs of assembly and those of manufacture. Again high frictional forces between the guide cams and the slider frame are a drawback in this instance too.

The German patent document DE 199 07 116 A1 discloses a drive mechanism situated between two mold plates and used for diecast valve elements. The individual valve pins of a group of nozzles are affixed to a common valve pin plate fitted near its edge with guide bushes and able to glide up and down on guide bolts running parallel to the valve pins. Two drive bars are mounted on the valve pin plate and support on their sides several glide blocks. These glide blocks engage oblique grooves of two cams supported in longitudinally displaceable manner between the upper mold plate and each holding plate.

Sets of roller bearings are provided at the top and bottom to reduce the cam bar friction. However the conversion of adjustment motions into elevation motions of the valve pin plate is carried out by commonplace glide blocks that are exposed to high wear in the oblique grooves of the cam elements. Moreover affixed drive bars and the additionally needed retention plates significantly increase the design height of the drive system, as a result of which this drive system may be used only to a limited extent in small molds.

The objective of the present invention is to avert the above discussed and other drawbacks of the state of the art and to create a compact drive system for injection molds with needle shutoff nozzles, said drive system always synchronously displacing the valve needles and loading them with the same closing pressure. In particular the objective of the present invention strives for maintenance-free and lastingly reliable operation of valve needles which moreover shall be individually adjustable within said system. Again this drive system shall be designed using simple, economic means and be easily operated.

Regarding a drive system for shutoff needles of injection molds fitted with needle shutoff nozzles, where said system comprises an elevation drive element to which may be affixed two shutoff needles of two needle shutoff nozzles, said element being displaceable between two longitudinally displaceable control rails in a second direction transverse to the first direction, grooves of at least two glide elements being configured between two glide elements and running obliquely to the first and to the second directions, said grooves converting a displacement of the control rails along the first direction into an elevation displacement by the elevation drive element in the second direction, the present invention provides that the mutually touching components that are displaced relative to each other, in particular the control rails and/or the glide elements, shall be made at least in part of a self-lubricating material or at least are partly coated with such. Alternatively the mutually touching components moving relative to one another, in particular the control rails and/or the glide elements, may be made at least in part of diamantine material or be coated with it. The term “diamantine” herein denotes a material of pronounced hardness, such as a diamond, which assures commensurately high component wear resistance.

By affixing the valve needles on a common elevation drive plate, all valve needles perforce will be displaced synchronously and be loaded by the same closing pressure. The glide elements made of a self-lubricating material and being guided in the oblique grooves of the control rails and loaded by transverse forces assure lastingly reliable operation of all valve needles because the friction is minimized within the grooves. The same feature is attained when the glide elements are coated at least partly, in particular in segments, with a self-lubricating material, or when, alternatively, they are made at least in part of a diamantine material or coated with one.

The present invention provides furthermore that the length of the glide elements shall exceed the thickness of the elevation drive element. Latter accordingly is always guided in accurate manner, no concentrated loads arising within the oblique grooves. The glide elements are inserted sideways into the elevation drive element to prevent them from rotating or tilting.

In the present invention, the elevation drive element is constrained to move in the second direction and preferably it is configured between two stops. These stops are made at least in part of a self-lubricating material or at least are coated with it, whereby the friction between the elevation drive element and the stops is significantly reduced. Alternatively the stops also may be made at least in part of a diamantine material or be coated with it.

In order to match the drive system and the valve needles individually to the mold, the valve needles are individually adjustable in the second direction relative to the elevation drive element. In order to furthermore always assure synchronous adjustment and simultaneous displacement compensation, a further feature of the present invention provides that the valve needles shall be axially fixed in position and floating relative to the excursion plate.

Between the valve needles, the elevation drive element comprises at least one recess passing a flow duct of a distributor arm or the like.

In another embodiment mode of the present invention, the control rails are linked to a drive, in particular by means of a common thrust element which together with said control rails constitutes a U-shaped frame. The control rails and the thrust element are connected in frictional and/or mechanically interlocking manner. Optionally, however, they also may be integral.

The accurate guidance of the control rails is attained by sliding them between guide elements. Illustratively these guide elements are guide rails affixed to or in a clamping plate. At their lateral surfaces facing the guide rails, the control rails are fitted with slide strips guided in sliding manner in the guide rail grooves. In order to reduce the friction between mutually displaceable components in this instance too, the glide strips are made at least in part of a self-lubricating material or at least are partly coated with it. Alternatively the mutually displaceable components also may be made of diamantine material or be coated with it in order to reduce wear due to relative, touching motion.

In another embodiment of the present invention, the guide elements are guide plates. These plates are affixed to the mold and to the control rails and are fitted with glide elements in the region of the slide surfaces. The guide plates and/or the glide elements are made at least in part of self-lubricating material or at least coated with it, resulting in advantageous glide properties.

In especially simple manner the self-lubricating material is a bearing material such as an alloy of tin, of lead, of aluminum or of copper or a sintered metal. Bronze or sintered bronze are especially preferred.

If a diamantine material is used instead of a self-lubricating material, the surfaces of the diamantine material advantageously shall be polished into a specular surface to attain low surface roughness and a low coefficient of friction. The wear due to relative, touching motions between the pertinent components may be reduced further thereby.

Also, the components incurring wear because of relative, touching motion and in particular the glide elements preferably shall be exchangeable so they be replaceable at will with new components.

In an especial embodiment mode of the present invention, the drive system is configured within an injection mold, in particular in or on a clamping plate. For that purpose said clamping plate is fitted with a recess receiving the drive system and thus simplifying assembly.

Significant advantages are attained when the drive system is flush with the clamping plate. In this manner the injection mold height is reduced. Where required, at least two drive systems may be configured in parallel next to each other, both being served by a common drive.

DETAILED DESCRIPTION OF THE INVENTION

The drive system denoted as a whole by10inFIG. 1is used to drive several shutoff needles16in injection molding equipment (not shown in further detail). Said equipment is used to manufacture molded parts from a flowable material, for instance a plastic melt. For that purpose, omitted needle shutoff nozzles are mounted underneath a manifold plate (omitted). Said needle shutoff nozzles move the plastic melt to be processed into a separable (omitted) mold insert of which the gates are periodically opened and closed by the shutoff needles16.

A clamping plate12is configured above the manifold plate and is fitted with a rectangular recess or aperture13to receive the drive system10. Hose or tube conduits of a flow medium moving in boreholes17through the clamping plate12can be connected to ports11. In this manner both said clamping plate and the driving system10are always optimally temperature controlled, in particular cooled, with advantageous results for operation.

An elevation drive element20is used so that the shutoff needles16may be operated simultaneously and is fitted with two shutoff needles16affixed to it in the embodiment ofFIG. 1. Preferably the elevation drive element20is a rectangular plate configured parallel to the clamping plate12and situated longitudinally between two displaceably supported control rails30. At its ends, the drive element20is configured between two stationary stops60,62affixed by screws63in the recess13of the clamping plate12. Two dowel pins66each assure accurate alignment of the preferably cross-sectionally rectangular stops60,62, the dowels66being firmly affixed in the base14of the clamping plate12and being received by (omitted) boreholes in snugly seated manner in the stops60,62.

The elevation drive plate20is fitted at each of its sides with two glide elements50guided parallel to one another in gliding manner in the control rails30(FIGS. 2 and 3). Said control rails are fitted at their lateral faces32facing the elevation drive plate20each with two grooves40running obliquely to the clamping plate12, said grooves40receiving the glide elements50to within a slight play in displacement.

The control rails30are longitudinally displaceably configured within the recess13between two stationary guide rails90in a first direction R1parallel to the clamping plate12and are connected by means of a common thrust plate82and an adapter86to a drive80. This drive is externally affixed for instance by screws86to the clamping plate12, the adapter86passing through a lateral (no further detail) borehole or aperture in the clamping plate12. The drive80may be an electric, pneumatic or hydraulic adjusting device or a motor preferably driven by an omitted control electronics.

The thrust plate82comprises two stepped ends83engaging the control rails30in a manner that there shall always be a tension-resistant connection in the first direction R1while being disengageable in the perpendicular direction thereto. For that purpose the control rails30are fitted with hooked ends33mechanically interlocking the stepped ends83of the thrust plate82by enclosing them. In this manner the elements30,82may be plugged into each other during assembly of the drive system10without resorting to tools; this feature simplifies handling and is advantageous regarding assembly costs. Also the components30,82always may be quickly exchanged, for instance when a long and/or wide elevation drive plate20is used. In the assembled state, however, the thrust plate82and the control rails30are always firmly linked in the drive direction R1.

The connection means between the thrust plate82and the adapter86constitutes a cross-sectionally T-shaped glide block88connected by a clamping pin87to the adapter86inserted—again without resort to tools—in mechanically interlocking manner into the thrust plate82. Appropriately said elevation drive plate82is fitted with a matching hollow89.

The guide rails90are laterally received in the recess13of the adapter plate12. These rails are affixed by screws91to the base14of the recess13and are fitted at their side faces92opposite the control rails30each with a continuous guide groove94running parallel to the adapter plate12. Each guide groove94receives—with little play—a glide strip35constituted at a side face39of the control rail30opposite the guide rails90. Dowels96assure the guide rails90shall be accurately aligned within the recess13. These dowels are firmly inserted into the base14of the clamping plate12as a tight fit into omitted boreholes in the guide rails90.

FIG. 1shows that the control rails30and the thrust plate82constitute a U-shaped frame laterally enclosing the elevation drive plate20and the stops60,62at little displacement play and being guided in sliding manner outside between the guide rails90. When the drive80periodically reciprocates the frame30,82in the first direction R1, then the elevation drive plate20constrained to move between the stops60,62will be periodically moved by the glide elements50guided in the oblique grooves40of the control rails30shall be moved up and down in a second direction R2perpendicular to the direction R1. Accordingly the elevation drive plate20, together with the shutoff needles16affixed to it, carries out an elevation motion in which all said shutoff needles16always are driven simultaneously and at the same closing power.

In order that the elevation drive plate20may carry out a defined and unfailingly reproducible elevation, the motion of the thrust element82in the first direction R1is limited by stops. A first stop is constituted by an end wall15of the recess13, whereas the stop60pointing toward the drive80constitutes a second stop. The separation “a” between the end wall15and the stop60predetermines the adjustment range of the thrust element82and hence for the control rails30which as a result may be reciprocated between at least two defined positions. Depending on the oblique position of the grooves40and the glide elements50, the elevation drive plate20carries out a correspondingly defined change in elevation, the drive80also controlling motions into intermediate positions when illustratively the shutoff needles16must be moved into various closed and open positions.

The plug-in connector means between the components30,82and82,86/89offer the advantage that the illustratively pre-mounted drive system is insertable in simple manner from above into the recess13of the stop plate12. Only the stops60,62already were inserted into the recess13. Accordingly the entire drive system10consists only of a few parts of simple geometry. Its installation is very simple. Vice-versa, the elevation drive element20, the control rails30, the thrust element82and the guide rails90always can be quickly and conveniently removed from the clamping plate12for instance to replace defective components, to change the shutoff needles16or to carry out other maintenance work.

The glide elements50of the elevation drive plate20preferably are elongated feather keys running at the same angle to the clamping plate12as the grooves40of the control rails30. Moreover they are received in the lateral faces22of the elevation drive plate20and are each secured therein by one or two screws52. For that purpose the elevation drive plate20is fitted with corresponding recesses23receiving the feather keys50in mechanically interlocking manner.

To assure appropriate guidance of the mutually parallel feather keys50in the grooves40of the control rails30and to enable high force transmission, the length of each feather key50exceeds the thickness D of the elevation drive plate20. As a result the control rails30are provided with a sufficiently large engagement surface to move the elevation drive element20into its up-and-down motions. This feature also favorably affects service life.

In order to furthermore reduce to a minimum the friction within the grooves40, the feather keys50of one embodiment mode of the invention are made of a self-lubricating material, preferably a bearing material, for instance bronze or sintered bronze. In addition or alternatively, the glide strips35of the control rail30and/or the stops60,62which make frictional contact with the elevation drive plate20also may be made of a self-lubricating material, the glide strips35being affixed by omitted screws to the control rails30.

As a result, the drive system10needs almost no lubricant and enjoys therefore lengthened intervals between maintenance. The drive system10assures a lastingly reliable elevation displacement of all valve needles16.

In another important embodiment mode, the present invention provides that the slide and guide elements35,50,60,62are made of steel and are coated (not shown in further detail) with a self-lubricating material. In this manner too the manufacturing costs may be reduced while simultaneously the drive system needs less maintenance. The components35,50,60,62may be coated in full with a self-lubricating material or merely in the areas of their contact/friction surfaces. The simple, plug-in design of the drive system10allows rapidly and conveniently exchanging components of which the coating has worn or was damaged.

Alternatively components that touch and are moving relative to each other may be made at least in part of a diamantine material or be at least partly coated with it. Because of this diamantine material, the pertinent components are made highly wear resistant and therefore offer long life. Preferably the slide surfaces along which said relative, touching motion takes place are additionally polished to lower the surface roughness and commensurately the coefficient of friction.

The embodiment mode ofFIG. 4provides that each guide rail30between three guide plates36,37,38be displaceably supported. Two of these plates36are affixed by screws46to the base14of the recess13whereas two upper plates37are affixed by screws47to cover plate19. Two further plates38each are inserted into the side face39of the guide rails30which for this purpose are fitted with grooves not further discussed. The side plates38and the guide rails30are firmly screwed into each other.

As furthermore shown inFIG. 4, the upper and lower plates36,37are fitted with glide elements56made of a self-lubricating material at their gliding respectively frictional surfaces facing the guide rail30. Such glide elements56also are inserted into the outer surfaces of the lateral guide plates38facing the clamping plate12. The guide plates36,37,38offer the advantage that the guide rails30shall always be guided accurately and reliably within the clamping plate12while the glide elements56assure low friction and commensurately low wear.

However, and just as are the glide and guide elements35,50,60,62, the glide faces of the plates36,37,38also may be fitted with a coating of a self-lubricating material. Or else, the plates36,37,38are entirely made of a self-lubricating material; and combinations of all such variations are applicable. Alternatively a diamantine material may be used for said components, the glide faces advantageously being polished for the reasons already discussed above.

The self-lubricating material used to make the elements35,50,56,60,62and/or used to coat them may be an alloy of lead, of tin, aluminum or copper or a sintered metal. The essential point is that the material offer self-lubricating properties in order to lower the comparatively high friction at the glide faces. At the same said material must be of adequate strength to preserve the benefits of long-term self-lubrication.

The shutoff needles16are inserted centrally to the longitudinal axis A from above into the elevation drive plate20which is fitted for this purpose with omitted boreholes. In the vicinity of the elevation drive plate20, each needle16is fitted at its end with a thread which is screwed into an omitted, substantially rectangular support plate. An adjusting nut18fastens the needle16in position relative to the support plate resting flat on the elevation drive plate20. In this manner the needles16are individually and longitudinally adjustable in the second direction R2relative to the elevation drive plate20.

Each support plate is situated in an omitted recess of which the height is nearly that of the holding plate and of which the outer dimensions exceed that of said plate, as a result of which this plate is able to move radially within said recess. A cover plate25affixed by screws26to the elevation drive plate20secures this support plate in said recess. Accordingly, within the least possible play in displacement in the axial direction of the shutoff needles16, the support plate is affixed between the elevation drive plate20and the cover plate25, and accordingly all the needles16always can be moved accurately into their closed positions and then be reopened again. On the other hand the support plates are floatingly supported in the radial direction, and as a result, position deviations of the needles16within the hot runner nozzles during excursion motions can be compensated. On account of the rectangular design of the support plate, the needles16moreover are irrotational relative to the elevation drive plate20.

The needles16project by their adjusting nuts18through the cover plates25. To preclude the needle ends from excessively protruding above the elevation drive plate20, the support plates and the cover plates25are configured in recesses24. In this manner the design height of the drive system10remains extremely low.

A central aperture70is constituted centrally between the recesses24in the elevation drive plate20and extends at the same inside diameter into the clamping plate12. The aperture70is crossed by a flow duct of a manifold arm or the like, in particular an omitted mold nozzle or a feed bush feeding the plastic to be processed to the manifold plate situated underneath the clamping plate12. The omitted inside diameter of the aperture70is selected in a manner to allow unhampered displacement of the elevation drive plate20.

The drive system10is closed by a cover plate19(FIG. 2) lying flat on the guide rails90to which it affixed by screws99. As indicated inFIG. 3, the cover plate19closes flush with the top side of the clamping plate12, as a result of which the drive system10does not project above said clamping plate12. Instead the system10is nearly fully integrated into the clamping plate12with very advantageous consequences regarding the mold's design height. Only the drive80is situated externally and on the side of the clamping plate12, without however affecting its height.

In the embodiment mode ofFIG. 1, two shutoff needles16of a group of needles are affixed to the elevation drive element20. However the number of shutoff needles16may be increased without difficulty by designing the elevation drive plate20to be commensurately longer or wider. The shutoff needles need not be mandatorily configured on the longitudinal axis A either. To most efficiently utilize the given mold surface, several mold inserts and hence several needle shutoff nozzles may be configured tightly near one another, and the nozzles where called for may be combined in groups of nozzles.

Conceivably too, two drive systems10may be configured side by side. For that purpose then the clamping plate12shall be fitted with two adjoining recesses13or with a common recess, as a result of which the control rails30and the guide rails90of the individual drive systems10shall be configured parallel to each other.

The present invention is not restricted to one of the above described embodiment modes, instead it may be varied in many ways. Illustratively the control rails30and the thrust element82also may be linked frictionally to one another, for instance using omitted snap-in elements. However the control rails30and the thrust element82also may be integral, as a result of which the U-shaped frame may be assembled/dismantled as one unit.

The glide and guide elements35,3637,38,50,60,62need not mandatorily be coated with the self-lubricant material or alternatively with diamantine material. The corresponding material also may be deposited on an intermediate support, for instance on a laminar substrate element which shall be affixed to the frictional surfaces of the glide and guide elements35,36,37,38,50,60,62, for instance by screws, interlocking or bonding.

All features and advantages implicit and explicit in the appended claims, the specification and the drawing, inclusive details, spatial configurations and method steps, may be viewed being inventive per se and also in arbitrary combinations.