CA2061731A1

CA2061731A1 - Nozzle for use on a plasticizing cylinder of an injection molding machine

Info

Publication number: CA2061731A1
Application number: CA 2061731
Authority: CA
Inventors: Karl Hehl
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-03-20
Filing date: 1992-02-24
Publication date: 1992-09-21
Also published as: JPH05116180A; EP0504553A3; EP0504553A2; DE4109122C1; JPH0655394B2

Abstract

ABSTRACT
INJECTION NOZZLE FOR USE ON A PLASTICIZING CYLINDER OF AN
INJECTION UNIT OF AN INJECTION MOLDING MACHINE
The outlet portion of the nozzle passage of the injection nozzle is defined by the inside peripheral sur-face of a mouthpiece, which is adapted to be axially for-ced against the nozzle body by means of a clamping ring, which engages the mouthpiece and surrounds the nozzle body around a forward portion thereof, which is smaller in dia-meter than the rear portion of the nozzle body. The contact pressure between the mouthpiece and the nozzle body is adapted to be controlled by screw means, which are screw-threadedly connected to screw threads of the nozzle body.
The mouthpiece is made of a material which has a higher abrasion resistance than the material of the nozzle body.

Description

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rl~CK~R00~ F T~E IN~IErlTI0 1, fielrl af the Invention -This inventian relatos to an injection nozzle fcr use on a olasticizino cylinder of an axially reciorocable injectinn unit of an injection moldinn machine, which nozzle comorises a nozzle borly, which is ~er,!e of steel and adaote~ tn be cnaxiall\! ~ounted on the olasticizinq cv-linr!er an~ rJefines a nozzle passaqe havino a forward end Dortion includino a forwar~ly taDerino outlet nortion, which nozzle al90 comorises 3 valvo nee~le, which includes an acute anole ~ith the axis of the nozzle and is slidably mounterl in a neeole-gui~ino bore of the nozzle bo~v anrl is ~ovable betl~een open an~ closed oositions relative to the nozzle passage under the control of a oronram, which ~ore opens inta the forwarrl en~ portion of the nozzle ,nas-sa~e at a r!istance behind the outlet portian.

~` 7. ~escriDtion of the Prior ~rt `~ U.~. Patent 4,a~,439 discloses an injection nozzle Illhich is of the kinrl rlescribe~ hereinbefore and in which .
the nozzle bor!v is ~irectly engageable with the inJeCtion molrl of the in~e~tion moldinq machine.

~ u,~, Patent 4,595,55? r'iscloses an injertion mcl~-`~ inn anoaratus l~hich serves to make Dlaqtic articles, Darti-sularlv containers, anrl in which the means For Dlasticizinn the plastic matzrial ano the injection mol~ are structurally ,~ ~
combined in a unit. The Dlasticize~ plastic material is fed into the mald cavity through an angled passaqe and a ra-dially symmetrical injection nozzle, which exten~s into the sprue channel of the injection mold. ~y the extremely small ~; nozzle, the injectinn passage 30, which consists of a bore in a stEel block, is connectzd to the mol~ cavity. In its - :

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closed oosition t~e valve needle extends into the outlet orificz of the nozzle and thus defines a bnundary cf tbe mold cavity. That known injection moldinn aDoaratus, which is used to nrocess homooeneous olastics, can be exoecte~
S to ensure a relatively tiqht seal at the nozzle for rela-tivelv lonn operatina times. Put in recznt times, it has increasingly beco~e usual to admix abrasive substances, such as olass fibers, carbon and mineral substances, to the olastic material in the ma'~ino of moldinos which can be use~, e.q., in mechanical enoineerinn or in orecision ~echanics because SIIC~ ~ol~inos will resist, e.n., extre~e-V hioh mechanical stresses or extremely hinh temDeraturos.
In ~anV cases the moIdinns are also reauired to hav_ son-cial orooerties as renards electrical conducti\/itv.
Lnnn-term tests have shown that the processino of ;~ olastic materials containino suc~ abr~lsive a~ turos will ~` ni\/e ri3e after a relatively lonn nDe,ratinq ti~e tn serious -~ oroblzms re~ardinq the tiqht seal of the nozzle. This will ~ainly ~e the case if that surface oortion of the nozzle assaqe which constitutes a seat for thz valve needle an~
the free end portion of the valve ne_dle are subjected to abrasion by which the~radial symmetry of that seat and of ~` the needle end portion is disturbed so that leakaoe occurs there.

AYY aF THE I~!vE~lTIo~l -It is an obj~ect of the invention to orovide an in-3C jection nozzle which is of the kind dzscribed first herein-before and which is~so desione~ that~the occurrence of such leakaae at the injection nozzle l~lill be minimized or even avoided after relatively lono ooeratino times z\/en in the oroc2ssino of olastic ~aterials which contain abrasi\/e ad-~ixtures.

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That object is acco~olished in accordance with the in~/ention in that thr outlet portion of the nozzle passane is defined bv the inside oeripheral Purface of a seoarate ~outhDie_o, which is substantially radiallv sym-metrical an~ consists of a material which is harder thanthe ~aterial of the nozzlP body, and said ~outhoiece is adoated to be axially forced against the nozzle body by means of 3 clamoinn rino, which surrounds the nozzle bo~v around an end portlcn thereof which is smaller in diameter than the rear oortion of the nozzle body, wherein said clampi~q rinn also ennaoPs said mouthnirce and the contart pressure betwee:~ the mouthpiece and the nozzle body is a~apted to be controlled by menas of at least one screw-threade~ element, which is screw- threadedly ccnnected to screw threa~s of the nozzle 5ndy.

In such an injection nozzle the extre~e ~ardness of the ~outhniece ensures that the radial svm~etry of the valve needle and af the associated seat will substantially ~0 be oreserved for relati~/elv lona times even under hioh ; ooeratinn stresses. The same result will be obtained by the use of mouthpieces ha\/ing a relatively low hardness and made of sintered ~aterials which have an e~tremely high abrasion resistance and contain, e.a., carbides. P mouth-oizce ma~e of cera~ic material will desirably have a low ther~al cDn~uctivity because 5UC~ mouthpiece will effect a substantial thermal insulation between the injection nozzle and the injection mOlD.
' ~esides, it will be ensured, on principle, that in eash closinn operation the valve needle can be centered on the associated valve seat either automatically, for in-stance, in the embodiment shown in Figures 1 and Z, or bV
a manual adjLIstment, as in the embodiment shown in Ficures } and 4. For such manual adjustment the screw-threaded ~: . : . :: . .: : , - ~- . ~ . .:: i........... ::

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element is initially untiqhtened. Thereafter the valve needle is move~ to its slosed position so that the valve needle will imoart a slig~t radial disnlacement to the mouthDiece to center the latter on the valve needle. ~Ihen the mouthpiece has been centered, the mouthoiece can again axially be forced aoainst the nozzle body in a cen-tered position bV means of the screw-threaded element.

It has also been found that some leaks o~ the needle valve which are due to abrasion can be eliminated in that the clampinn ring is relieved from its initial axial stress and the mouthoiece is then rotated to a laraer o,~ smaller extent. As a result, any deviation of the valve ~' ,, seat and the seat-engaoina end portion of the valve needle from ra~ial symmetry can be eliminated by a defor~ation of the contactinq surfaces or such deviations can be caused to compensate each other if they are mutuall,y oppositely di--~ rected.

~0 RPIEF DESCRIPTICN OF THE ~FAWI~I~

Fioures 1 and 2 are sectional views taken on a vertical plane throuqh the nozzle axis a-a and show the nozzle with the vaIve needle in its closed and open posi-Z5 tons, respectively, andr ioures 3 and 4 are views wnich are similar to Fi~ures 1 and ?, respecti\/ely, an~ show a mo~ification of : i the nozzle.

; 30 nETAILED DESCRIPTIO~I OF THE PFEFEFRED EM~ODIME~TS
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,~ Two illustrative embodiments of the invention will now be described more in detail with reference to the dra-wino.
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The followinq descriotion is common to both embodi~ents:

The injection nozzle is intende~ to be detachab-ly mounted on the plasticizinq cylinder o~ an axially re-ciprocable injectinq unit of an injection moldinn machino.
As the injecting unit is axially reciprocated, the plasti-.: cizing cylinder together with tbe injection nozzle can be advanced until the injection nozzle engages the injection mold and can subsequently be retracted from the mold in each moldinn cycle. The injection nozzle comorises 2 no7zle body 10 or 11D, which is made of steel and is coaxially ~oun-;,;~ ted on the olasticizing clyinder, and a mouthpiece 17 or 11?, which is made of:ceramic material or of hard metal. The nozzle body 10, 110 is formed with a nozzle passaoe 11 or : 111, which has a forward end portion 11a or 111a, whic~
co~prises a Forwardly taoerinq outlet portion 11b or 111b leadina to a nozzle orifice 11c or 111c.~P valve needlo 13 or 113 is lonaitudinally slidably mounted in a needlo-ouid-0 ina bore 14 or 114, ~hich is for~ed in the nozzle body 10 or ~ 110 and extends at an acute anole to the axis a-a of the ` :~ nozzle passaqe 11 or 111. The vaIve needle 13 or 11~ can be ~ voe~ to predetermined~ooan and closed positions under pro-:~ ~ gram control.The bore 14 or 114 opens into the fnrward end :~
oortion 11a or 111a of the nozzle passane 11 or 111 at a ~ :
distance benind the outlet oortion 11b oF 111b. The outlet oortion 11b or 111b of thn nozzle passage 11 or ~11 is de-fine~ by the inside~ peripheral surface of the radially sym- :~
: metrica:l~mouthpiece 1~: or 117.~That~mouthpiece is adapted to be Forced against the noz~zle bod~y 10 ar 110 by ~eans of a cIamping ring 16 or~116 which surrounds the mouthpiece 17 or 112 and has behind~the~mouthpiece an axial flange 16a or 116a, which surraunds a forward Portion of the nozzle body:
:~ 10 or 110. That forward portion of the nozzle body 10 or 110 is smaller in diameter than the rear portion of the nozzle :' ~
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badv 1Q or 110. The mouthpiece 17 or 117 has a finish-~achined planar annular surface "~hich is at right anoles to the axis a-a of the nozzle oassaoe and is in sealinq cont3st with a mating annular surface of the nozzle body.
The clampinn rino 16 or 116 bears axiallv on the forward end fase 1?b or 117b Df a radial flanoe 17a or 11~a of the mouthoiece 1Z or 117.
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The features by which the twn illustrated embodi-ments di~fer from each other will now be ~escribed.
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`~ In the illustrative e~bodi~ent shown in Finures 1 and 7 a plurality of screw fasteners 17 extend throuoh and are screwed in tapped bores formed in an axial flange 10a, -;
with which the nozzle body 1~ surrounds the axial flanoe 16a of the clamping ring 16. The screw fasteners 17 have inner end faces 17a, which bear on peripherally spaced aoart abutment surfaces of the clamoino rinq 16 under ini-tial stress to axially force the ~outhpiece against the nozzle body 10. T~e valve nee~le 13 is composed of two sections, which are articulatedly connected to each other. The ro~like rear section 13a is slidably ouided in the bnre 1~ of the ~ ~ ;
nozzle body 10. The forward section 13c of the valve needle 13 is connected to the rear section 13a by a ball joint 13b ?5 and has a soherical \lalve me~ber 13d, which in the closed ousi~ion oF tlle valve needie 13 is in seaiino oressure con-tact with a valvo seat, which is constitute~ by the inside eripheral surface de~fining the outlet ~section 11b of the nozzle passaoe 11.;The forward needle section 13c is termi- ~ ~
` 30 nated at its fQrward end by the valve member 13d and at its ~ -rear end by a ball of the ball joint 13b and between said ends is cylindrical and has a ~iameter which is about one-half the ~iameter o$ the clyindrical rear needle section 13a.
As a result, the forward needle section 13c will be contac-ted by teih ~olten Plastic ~aterial on all sides so that the , : :: ~ :
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- ~ -radial pressures on said forward section will be balanced and the forward needle section will not be subjected to unilateral ra~ial pressures as the olastic ~aterial is injected.

In the embodiment shown i n Finures 3 and 4 the axial flan~e 116a of the clamping ring 116 has internal ~ screw threads 116b in mesh with external screw threads of :~ the Forward portion 110a of the nozzle body 110. That for-~:: 10 ward portion 110a is smaIler in diameter than the rezr ~: oortion of the noz2le bodv 110. Pnnular qaos 1~5 and 115l :~: are defineo by the cylindrical outside peripheral surfaces of the ~uthoiece 11~ and the opposite inside peripheral ~`~ surfaces of the clamping rin~ 116 and determine the extent :~
::~ 15 to which a radial displzce~ent of the ~outhpiece 11? will : .
be permitted when the clampinn rinq 116 has sufficiently ~ been untightene~. The valve needle 113 consists of two :~ ri~idly connected needle sectiDns 113a and 113b. The rear needle section 113a is slidably guided in the bore 11~.
~: 20 The forward needle section 113b has a spherical end face, which when the valve needle 113 is in its closed position ~ ~:
is in sealino pressure contact with a valve seat, which is - constituted hy the i~nside perioheral surface defininn the ~; forwar~ly taperinq outlet portion 11b of the nozzle passage:
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Claims

1. In an injection nozzle adapted to be mounted on a plasticizing cylinder of an axially reciorocable inject-ing unit of an injection molding machine, which nozzle comprises nozzle passage-defining means defining a nozzle passage, which defines a nozzle axis and comprises a for-ward end portion, which includes a forwardly tapering out-let portion, which nozzle passage-defining means comprise a nozzle body, which is adapted to be coaxially mounted on said plasticizing cylinder and has an inside peripheral surface defining said nozzle passage and at least on said inside peripheral surface consist of a first material, which extends at an acute angle to said nozzle axis and opens into said forward end portion of said nozzle axis and at a distance behind said outlet portion, end a valve needle, which is slidably mounted in said needle-guiding bore for a movement between open and closed positions for opening and closing said forward end portion of said nozzle passage.
the improvement residing in that said nozzle passage-defining means comprises an approximately radially symmetrical mouthpiece, which has an inside peripheral surface that defines said outlet por-tion of said forward end portion of said nozzle passage and at least on said inside peripheral surface consist of a second material, which has a higher abrasion resistance than said first material.
said nozzle body is formed with screw threads and has a rear portion and a forward end portion which is smaller in diameter than said rear portion.
a clamping ring is provided, which surrounds said forward portion of said nozzle body and surrounds and engages said mouthpiece, and screw-threaded means are provided on said clamp-ing ring and ] connected to said screw threads and are operable to force said clamping ring rear-wardly so as to clamp said mouthpiece axially rearwardly against said forward portion of said nozzle body under ini-tial stress.

2. The improvement set forth in claim 1, wherein said nozzle body consist of said first material and said mouthpiece consists of said second material.

3. The improvement set forth in claim 1, wherein said first material is steel and said second material is harder than steel.

4. The improvement set forth in claim 3, wherein said second material is selected from a material of the group consisting of sintered carbides.

5. The improvement set forth in claim 4, wherein said hard metal consist of sintered carbides.

6. The improvement set forth in claim 4, wherein said forward portion of said nozzle body has a for-wardly facing, finish-machined first planar annular surface, said mouthpiece has a rearwardly facing, finish-machined second planar annular surface in sealing contact with said first annular surface, and said first and second annular surface extend at right angles to said nozzle axis.

7. The improvement set forth in claim 1, wherein said clamping ring comprises an axial flange sur-rounding said forward portion of said nozzle body behind said mouthpiece and formed on the outside with peripheral-ly soaced apart and abutment surfaces, said nozzle body comprise an axial flange, which surrounds said forward portion of said nozzle body and said first axial flange and is formed with tapped bores formed with said threads and registering with said abutment faces, and said screw-threaded means comprise a plurality of screws, which are screwed in and extend through said bores and have end faces bearing on said abutment surfaces,

8. The improvement set forth in claim 7, wherein said valve needle comprises a rodlike rear sec-tion, which is slidably mounted in said needle-guiding bore, and a second section, which is articulatedly connected to said rear section.

9. The improvement set forth in claim 8, wherein said second needle section is connected to said rear section by a ball joint.

10. The improvement set forth in claim 9, wherein said inside peripheral surface of said mouthpiece defines a valve seat and said second needle section comprises a spherical end portion arranged to be in sealing pressure contact with said valve seat when said valve needle is in said closed portion.

11. The improvement set forth in claim 9, wherein said rear needle section is cylindrical, said ball joint comprises a ball formed on said second needle section and said second needle section has between said ball and said spherical end portion a cylindrical portion, which has a diameter that is one-half the diameter of said rear needle section.

12. The improvement set forth in claim 1, wherein said screw threads consist of external screw threads of said forward portion of said nozzle body and said clamping ring comprises an axial flange, which surrounds said forward portion of said nozzle body behind said mouthpiece and is formed with internal screw threads, which constitute said screw means and are screwed on said external screw threads.

13. The improvement set forth in claim 1, wherein said mouthpiece comprises a radial flange having a forward end face and said clamping ring engages said forward end face.

14. The improvement set forth in claim 13, wherein said mouthpiece has at least one clyindrical out-side peripheral surface, said clamping ring has at least one cylindrical inside peripheral surface facing said at least one cylindri-cal outside peripheral surface and radially spaced therefrom to define at least one annular gap therewith, said screw-threaded means are operable to suf-ficiently untighten said clamping ring from said nozzle body to permit nozzle body to an extent defined by said at least one radial gap.

15. The improvement set forth in claim 1, wherein said inside peripheral surface of said mouthpiece is formed at said forwardly tapering outlet portion with a valve seat, said valve needle comprises a rear section and a forward section, which are rigidly interconnected, said rear section is slidably guided in said needle-guiding bore, said forward needle section has a spherical forward end face, which is arranged to be in sealing pres-sure contact with said valve seat when said valve needle is in said closed position.