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EP-4308362-B1 - INJECTION NOZZLE

EP4308362B1EP 4308362 B1EP4308362 B1EP 4308362B1EP-4308362-B1

Inventors

  • SPULLER, SWEN

Dates

Publication Date
20260513
Application Date
20220315

Claims (16)

  1. An injection nozzle (1) suitable for injection molding of thermoplastic materials, in particular polyolefin materials, the injection nozzle (1) comprising a. a housing (2) comprising a sleeve-shaped rear section (3) and a thereto coaxially arranged sleeve-shaped front section (4) surrounding a central passage (5) extending in an axial direction (z) forming part of a melt channel (6) in which a needle (7) is arranged movable in the axial direction (z) between a retracted open position and an extended closed position in which a gate (8) at a tip (9) of the front section (4) is closed by a front end (10) of the needle (7) in a sealing manner; wherein b. a spacer (11) is arranged between the rear section (3) and the front section (4) defining a total length of the housing (2) in the axial direction (z); characterized in that c. wherein the injection nozzle (1) comprises a needle centering means (14) for centering the needle (7) in radial direction during operation when moved between the open and the closed position, wherein i. said needle centering means (14) being arranged in axial direction (z) between the spacer (11) and the gate (8) and/or ii. said needle centering means (14) being designed as a separate element inserted into the front section (4) of the housing (2) opposite to the gate (8).
  2. The injection nozzle (1) according to claim 1, wherein the spacer (11) comprises a ring and/or a bushing and/or a washer.
  3. The injection nozzle (1) according to claim 1 or 2, wherein the needle centering means (14) is arranged in a pocket (15) of the front section (4).
  4. The injection nozzle (1) according to claim 3, wherein the needle centering means (14) is clamped between a shoulder (16) of the pocket (15) and the spacer (11).
  5. The injection nozzle (1) according to at least one of the preceding claims 1 to 4, wherein the needle centering means (14) is ring shaped.
  6. The injection nozzle (1) according to at least one of the preceding claims 1 to 5, wherein the needle centering means (14) comprises at least one fin (17) extending in radial direction and comprising on the inside a guiding surface (18) during operation centering the needle (7) in radial direction.
  7. The injection nozzle (1) according to claim 3, wherein the needle centering means comprises at least two fins (17) in circumferential direction spaced apart from each other.
  8. The injection nozzle (1) according to at least one of the preceding claims, wherein the tip (9) of the front section (4) in combination with the front end (10) of the needle (7) form a molding contour (12) for embedment into a molding cavity contour (13) during operation.
  9. The injection nozzle (1) according to claim 8, wherein a length of the spacer (11) in the axial direction (z) is configurable to compensate thermal expansion of the housing (2) in the axial direction (z), such that with respect to a thermoplastic material specific operating temperature the molding contour (12) is embedded into a molding cavity contour (13) in an adjustable manner, in particular in a flush manner.
  10. The injection nozzle (1) according to at least one of the preceding claims, wherein the spacer (11) comprises a rear sealing surface (19) and a front sealing surface (10) in a mounted position interacting with the front section (4) and the rear section (3) preventing leakage of melted thermoplastic material from the central passage (5).
  11. The injection nozzle (1) according to at least one of the preceding claims, wherein the rear section (3) comprises an outer thread (21) and the front section (4) comprises an inner thread (22) engaging in a mounted position with the outer thread (21) for interconnecting the front section (4) to the rear section (3).
  12. The injection nozzle (1) according to at least one of the preceding claims, wherein the spacer (11) is arranged in the central passage (5) and forms part of the melt channel (6).
  13. The injection nozzle (1) according to at least one of the preceding claims, wherein the spacer (11) and/or the needle centering means (14) comprises an engagement contour for engaging with a corresponding tool for removal or replacement.
  14. The injection nozzle (1) according to at least one of the preceding claims, wherein the front section (4) comprises an outer part (30) and a tip element (28).
  15. The injection nozzle (1) according to claim 14, wherein the tip element (28) is interconnected from the inside or from the outside to the outer part (30).
  16. An injection molding tool (23) for injection molding of thermoplastic materials, in particular polyolefin materials, the injection molding tool (23) comprising a. at least one cavity (24) having a molding cavity contour (13) at least partially defining plastic part formed therein from melted thermoplastic material and b. at least one injection nozzle (1) according to the claims 1 to 13 arranged adjoining the cavity (24) for supplying melted thermoplastic material to the cavity, said injection nozzle (1) forming at least part of the molding cavity contour (13).

Description

FIELD OF THE DISCLOSURE The present disclosure is directed towards the field of injection nozzles for injection molding of thermoplastic materials, in particular Polyolefines. BACKGROUND OF THE DISCLOSURE EP0873841 A2 published in 1998 in the name of Mold Masters Itd. relates to valve gated injection molding apparatus having a valve member with a cylindrical front end portion. A one-piece insert mounted at the front end of a nozzle has both a gate and locating blades extending inwardly from an outer body into a central opening leading to the gate. The inner surfaces of the blades fit around the front end portion of the reciprocating valve pin to guide and very accurately locate it in alignment with the gate. Very accurately maintaining the front end portion of the reciprocating valve pin in alignment with the gate allows it to be cylindrical rather than tapered which produces a much cleaner gate mark. EP1990175A1 published in November 2008 in the name of Mold Masters ltd. relates to an injection molding apparatus that includes a valve-gated nozzle having a nozzle tip assembly and a valve pin slidably disposed therein. The nozzle tip assembly includes a nozzle liner having a first valve pin guiding portion, a valve pin guide having a second valve pin guiding portion upstream of the first valve pin guiding portion, and a transfer seal having a bore for receiving the nozzle liner and the valve pin guide therein. The transfer seal bore includes an alignment surface that surrounds the nozzle liner and the valve pin guide to align the first and second valve pin guiding portions with the mold gate, such that the valve pin is accurately aligned during operation. The transfer seal also includes means to couple the nozzle tip assembly to the nozzle body. DE102016219833A1 published in April 2017 in the name of Inglass SPA relates to a nozzle terminal of an injector. The injector comprises a tip and a ring nut having respective distal ends one of which is configured so as to be coupled with a gate of a molding cavity, it cooperates with the shutter terminal of the valve pin of the injector, and it has an overall thickness in cross-section which is equal to or less than that of the cross-section of the shutter terminal of the valve pin. US2014295014A1 published in 2014 in the name of HUSKY INJECTION MOLDING relates to a mold-tool system, comprising: a body assembly; and a stem-guidance assembly configured to maintain guiding movement of a valve-stem assembly through the body assembly. US2011129561A1 published in 2011 in the name of DME COMPANY LLC relates to a nozzle assembly for selectably conveying material in a flowable condition to a cavity of a mold assembly comprises a nozzle body, a removable nozzle tip, a valve pin member extending through the nozzle body and having a tip end for selectably forming a seal with a valve seat to selectably prevent passage of material into the mold cavity and a pin guide for guiding the valve pin member. SUMMARY OF THE DISCLOSURE Injection nozzles for injection molding thermoplastic materials, in particular polyolefin materials, are during operation arranged in an expensive and precisely manufactured molding tool in order to inject melted thermoplastic material into a cavity of the molding tool. The cavity having a molding cavity contour, defines the shape of plastic parts formed therein by the injected melted plastic material after curing. For an accurate injection of the melted material, the nozzles are fluidly interconnected to the cavity via a gate, open and closable by a movable needle of the respective nozzle. To avoid wear at the molding tool, each gate is formed as part of a tip of a nozzle facing the cavity; the nozzle being less expensive to repair or replace compared to the molding tool in case of damage to gate. To allow manufacturing of high quality plastic parts having an almost unrecognizable injection mark originating from the gate through which the melted material is injected into the cavity, the nozzle should form during operation a level, or slightly indented, finish with the cavity. Therefore, an injection nozzle is preferably designed to account for thermal expansion and in turn to achieve a good alignment with the cavity during operation. A preferred variation of an injection nozzle according to the disclosure comprises a housing, in particular suitable to be installed in a corresponding injection molding tool. The housing comprises a sleeve-shaped rear section and a thereto coaxially arranged sleeve-shaped front section surrounding a central passage extending in an axial direction. In the central passage a needle is arranged movable in the axial direction between a retracted open position and an extended closed position in which a gate at a tip of the front section is closed by a front end of the needle in a sealing manner. A spacer is arranged between the rear section and the front section defining a total length of the nozzle in the axial direction. The spac