|Title of Invention||
A VALVE GATE MECHANISM AND A SYSTEM FOR GAS ASSISTED INJECTION MOULDING
|Abstract||Apparatus and methods for fluid-assisted injection molding systems or co-injection molding systems. A pair of concentric movable pin members are positioned in a mold bushing and selectively controlled to facilitate or prevent the passage of molten plastic material and a fluid into the mold cavity. An inner pin member is positioned within a hollow pin member and both pin members are controlled by piston members which are selectively moved in a block member by selective pres- surization from a hydraulic or pneumatic source. Movements of the piston members selectively controls the operation of the pin members and thus the operation of the fluid-assisted injection molding system.|
The present invention relates to pin-type valve-gate bushing devices for use with fluid-assisted injection molded systems.
Background of tin
unheated) into the cavities of hollow molds. Often, two or more sprue bushings attached to a common manifold are used. In this instance, the plastic melt coming from the injection molding machine through runners is distributed by a heated distributor block (a/k/a manifold) to the individual sprue bushings. One conventional method used to control the melt flow utilizes one or more pin or needle valves, also known as valve-gate bushings.
With these systems, a needle valve is inserted through the manifold into the sprue bushing and controlled for axial movement by a hydraulic, electric or pneumatic control device or mechanism. The needle vaive has an elongated pin which is moved axially by the control mechanism and is adapted to fit within an orifice in the end of the sprue bushing in order to open and close the passageway of plastic molt from 1.1 LO 8prue bushing into the mold cavity. One of the MO nym.(Miif:; I u shown, for example, in U.S. Patent No. 4,27 9,½H2.
Another type of plastic injection mo.) '1 i ng method and system utilizes a co-injection appa tatiuu. This apparatus injects two different plastic ma tot ia In, typically an inner core material and an ouroj nh‹›.l 1 material, into a single mold cavity, A oo ■ inject. Ion manifold receives material from two ciitf:erent UIJIH'I ion machines and combines the two materials into a single stream that flows into a mold or die,
Co-injection processes create a product which is less expensive. A smaller amount of the more expensive outer plastic material is used for the f-;lnal part, since it only is used for the outer fc..uiri;ace or shell of
the product. The second material which is co-extruded is typically a less expensive plastic material and forms the inner non-visible core of the product. A co-injection manifold and process are shown, for example, in U.S. Patent No. 4,376,625.
Summary Of The Invention
It is an object of the present invention to provide an improved valve-gate bushing for use with a fluid-assisted injection molding process. It is also an object of the present invention to provide an improved valve-gate bushing which can be alternately u,‹;;ed toi a co-injection apparatus and system.
It is another object of the present: i nvtMit i on to provide an improved valve-gate bushing or nozzle with a movable gate pin which can close off the ent:ry of" piastic material into the mold, and at the same t i me allow entry of pressurized fluid (liquid or gas) therein. It is a still further object of 1 In* present inveii tion to provide a valve-gate bushing which h The present invention overcomes the prior difficulties with valve-gate-type bushingB or nozz3es used with fluid-assisted systems, and fulfills the objects and purposes noted above. The present invention provides a pin-type valve-gate device which easily and
effectively opens and closes the flow of plastic material into the mold as desired, and also equally easily and effectively opens and closes the entry of fluid (gas or liquid) into the mold cavity.
In particular, the bushing has a movable shut-off mechanism which operates a dual pin mechanism to selectively open and close the bushing orifice as well-as the orifice formed in the ends of the pin members. A first movable elongated pin member is positioned inside a second movable elongated pin member. A p.iston•-type control mechanism, which is operated elthet hy‹:b:,tu lically, electrically, pneumatically, or the 1 ike, selectively moves the two pin members longitudina I .1 y either together, or relatively to one anoi: he i, to selectively open and close the two valve members (ori-fices) . The end of the outer pin member nwiteei wit h i he orifice in the end of the bushing ot tioz/, le uuMiil›et creating a valve or "gate" for entry of p'l aui:i ‹* neu.ee hi I. into a mold cavity. The end of the JIU'H•L j›iu UIMMIIK. , creates a second valve mechanism with the inner: end of the outer pin member. This valve mechanism is used to regulate the flow of the second fluid material, such as a liquid or gas, into the mold cavity.
In a preferred embodiment:, each ot t he pin members is secured to stacked separately movable piston members which are positioned in a control, mechanism. The two pistons are moved together or independently, thus resulting in the desired movement of the two pins relative to each other and relative to the sprue bushing.
In a second embodiment, one piston member is positioned inside the other piston member and the two piston members are again adapted to move in the same direction or in opposite directions, thus regulating the valve mechanism at the end of the two pin members, as well as the valve mechanism at the gate in the sprue bushing.
These and other objects, features and benefits of the invention will become apparent from the following description of the invention, when taken together in view of the accompanying drawings and appended claims.
Brief Description Of The Drawings
FIGURES 1-3 and 3 A illustrate a preferred embodiment of the present invention, and also depict the operation thereof; and
FIGURES 4-6 illustrate an alternate embodiment of the present invention, as well as depicting the operation thereof.
Best Mode(s) For Carrying Out The invention
Figures 1-3 and 3 A illustrate a preferred embodiment of the present invention and show its use in a fluid-assisted injection molding £jyBt:em. ] n t.h:i s regard, the present invention is part: h'n I ‹i i l,y ,i«.la|>t ed t .-. be used in a gas-assisted injection moldi n‹f pn.H.'VM:UJ or system. However, the present invention :lti ,IIBO adapirJ to be used with fluids other than gas, such as a gas .In a liquid state (e.g. liquid nitrogen) or other liquids under pressure. Moreover, it is possible to u.oe the
present invention in a co-injection molding system which injects two different plastic materials, one for an inner core and the other for an outer ,r=jhel 1 , i nt:o a single mold cavity.
Since the preferred use of the present: invention relates to gas-assisted injection molding systems, it will be referred to herein in that manner. However, for the reasons set forth above, it is to be understood that the use of the term "gas" herein LB not nu•aiu. to be limiting relative to the invention.
Also, the present invention is preferably adapted for use with sprue bushings or nozzles, 1M this regard, the invention is shown in 111in app 1 icat; i o11 Iur use with one type of sprue bushing 12, Of course, other sizes, shapes and types of sprue bushings, machine nozzles, and the like can be used with tin- present invention and fall within the spirit; and t¾oopc thereof. In addition, the present invention can be t^sed without a sprue bushing.
The valve-gate system is generally referred to by the reference numeral 10 in the drawings. The system 10 includes a bushing or nozzle 12, a manifold 14, and a cylinder member or block member 16, The mold bushing 12, which is also commonly referred to as a "nozzle," is mounted in a cavity 18 in a mold 20. The mold 2 0 can be of any conventional type and has a first plate member 22 which houses the bushing 12, as well as a second plate member 24 which has a mold cavity 26 therein. The mold cavity 26 is formed or machined in the size and shape of the final part to be produced, as is well known in the art.
The sprue bushing or nozzle l.2 * 'an I >«* ut .my conventional type, such as those available from In roe Corp., Troy, Michigan. In this regard, the sprue bushing 12 has a metal body or shank member 30, an internal elongated passageway 32, a m.:rew• -i›n \ ip MHNUU-M. 34, and an annular resistance heater niembfn 3r. The I i\.> member 34 has a forward end 40 which in adaptod to til within the end of the recess 18. The Up M h‹m ..iu I .-1»e M i end 42 through which plastic materla 1 i o stvl tu.a iv, j y allowed to flow into the mold cavity 26.
A movable central pin mechanism 50 is positioned in the sprue bushing 12. The pin mechanism SO has an outer hollow pin member 52 and a central pin member 54 which preferably is sol. id, 1 tut could be tubular. The pin member 54 is movab.ly positioned inside elongated passageway 53 in the outer pin member 52. As explained in more detail below, the two pin members 52 and 54 are adapted to be moved longitudinally (axially) and separately, together or relative to one another. The pin members are movable in the direction shown by arrows 55 in the drawings.
Outer pin 52 is secured to first piston member 60 while inner pin member 52 is connected to second piston member 62, Preferably, the pin members are releasably threadedly connected tc the piston members so they can be adjusted where necessary, although the pin members could also be fixedly secured to the piston members.
The piston members 60 and 62 are posit ioiied in block member 16 and held in position by cov‹-;t pl,iie 17. The two piston members 60 and 62 an a/ldpl nrl n› bt mwod separately or together in the block U›, aJ i-v› in i lu-¾ direction of the arrows 55. The piston membeiu (›n ,IK:J 62 are adapted to be moved in the cylinder block 16 by any conventional means, preferably hydraulically or pneumatically. Also, it is possible, in accordance with the present invention, to provide an electrical system for moving the two piston members e;u and 6';;i in the desired manner and sequence, For example, t;h«* pistons could be mounted in Acme threads and either the pistons could be rotated or the surrounding housifig could be rotated by an electric motor.
Molten plastic material is introduced to the system through passageway 64 in the manifold 14. The plastic material is introduced into the passageway by a conventional injection molding machine (shown schematically by box rIM") . The manifold 14 is heated by any conventional means, such as cartridge or tubular heaters (not shown). The passageway 64 allows the plastic material from the injection molding machine IM to be introduced into passageway 32 in the bushing and into the mold cavity 26. In this regard, the direction of flow of the plastic material is indicated by the arrow 65. Pillars or spacers 66 (a/k/a "risers") are positioned between the manifold 14 and block member 16. The block member, manifold and mold are typically secured or fastened together by any appropriate means, such as clamps, machine bolts, or the like, conventionally known in the art♦
The bushing or nozzle 1.2 C.III 1'*:' u,.td(• ^ mi. more pieces as desired. For example, a.s shown in i he-embodiment of Figuies 1-3, the bushing 12 can have a head portion 31 which is produced integral with, ur threadedly attached to, the body or shank member 30, The heater member 36 is positioned on the outer surface of the shank 30* The heater member, which pre I «.: rubly \ b a resistant-type heater, such aa a coll heatei: ur a Lnnd heater of any conventional type, is electrified through lead 38 connected to an appropriate power source (not shown) . The heater member can be of any conventional type. In some situations, it may be possible co provide a bushing without a heater.
As indicated, the bushing can be a one piece or multi-piece component device. The heater member also can be positioned internally or externally relative to the body or shank member 3 0. The bushing further can have any convenient or conventional shape or cross-section, and can be provided without a head portion. The bushing further can be of a type which is chreacfedly attached to the mold or manifold. All of these types of bushings and heater members are well known in the art.
The "plastic material is heated and initially converted into a molten state in the barrel of an injection molding machine IM. The plastic material is then forced into the bushing, or, if a manifold is utilized such as shown in Figures 1-3, into and through the manifold and then into one or more bushings. In this regard, the heaters in the manifold 14 keep the plastic material in the manifold pantJcujewayn o'i m ,i molten condition and the heater membe r (or ineml.›‹ •in) in the bushing maintains the plastic material in t.l H-J
bushing passageway 32 in a molten condition. In this manner, after the injection cycle injects a quantity of.' plastic material into the mold cav I ty, t he remaining plastic material in the buwhing n.nd imniit old does not harden or solidify, but ia retained in a liquid or molten condition ready for the next injection cycle.
The fluid (gas) is introduced into the mold cavity 26 through passageway 53 in the pin mechanism 50, The gas is introduced into the system 10 from a conventional pressure source "gas" to the coupling 72. An appropriate conduit 73 is used to supply the gas to the coupling 72 from the pressure source. The direction of entry of the gas into the system 10 is shown by the arrow 75. The gas is introduced to the coupling 72 and, in turn, to the pin mechanism 5 0 and into the mold cavity 26.
As shown by comparison of Figures 1 and 2, the inner pin member 54 can be moved longitudinally or axially relative to the outer pin member 52. The lower or distal end 56 of the inner pin member 54 is adapted to mate with the inner lower end 58 of the passageway 53 in the pin member 52. The lower ends 56 and 58 form a valve or gate which controls the flow of gas from the passageway 53 into the mold cavity 26.
The inner pin member 54 is Ljec:unVl y ›d tcu./liei.n manlier vi is preferably threadedly secured to the piston member (›2 by a threaded joint or connector mechanism 68. Similarly, the outer pin member 52 is connected to µ:Lui.on member 60 by an appropriate coupling 70.
The piston members 6 0 and 62 arc ›jlidably positioned in chamber cavity 80 in tho bloc}%, member 16. Fluids, such as liquids or gases, are introduced into the cavity 80 by channels 82, 84 and 86 as desired, and provide movement of the pistons 60 and 62.
A plurality of seals are provided between the piston members 60 and 62 and the block member 16 in order to separate and isolate the fluids or gases being introduced into the cavity 80 by the passageways 82, 84 and 86. These seals can be of any conventional type, such as rubber or elastomer O-rings. In this regard, piston member 62 is sealed by seals 88 and 89. Seal 88 is positioned on cover plate 17, while seal S9 is positioned in annular cavity 90 in piston member 62. Piston member 60 is sealed by sealing members 92 and 93, Sealing member 92 is positioned in block member 16, while seal 93 is positioned in cavity 94 in piston member 60,
The hydraulic or pneumatic fluid or gas is supplied to the passageways 82, 84 and 8 6 by conduits 83, 85 and 87, respectively, from one or more conventional hydraulic or pneumatic power sourc'en "KPS". The passageways can all be connected to the name µi utimu e source and selectively utilized by ,m aµµrwµi i ni e valving and control system. The conduits are connect.e,d to the block member 16 and cover plate 17 by any appropriate connectors or fasteners. The passageways 82, 84 and 86 are machined or provided in the. cylinder block and cover plate in the posi tions shown i n K.iqu i›?u 1 ;'*, although it is understood that they can be pi ( ›VI‹,U:MI :t.n other locations within the skill, of µninoun in i h‹ aH
The lower end 57 of outer pin member 52 is adapted to mate with the opening (orifice) end 42 of the bushing 12 and form a valve mechanism. The members 5 7 and 42 mate together to form a valve which regulates the flow, of plastic material into the mold cavity 26 from the passageway 32.
When the system 10 as shown in Figures "13 is used, the valve or gate formed by members 4 2 and 5 7 is initially opened, as shown in Figure l. In this condition, plastic material which is present in the manifold 14 and bushing 12 is allowed to enter into the mold cavity 26. During this stage of the process, the two pin members 52 and 54 are positioned in the manner shown in Figure 1 which prevents plastic from being introduced into the passageway 53, For this part of the process, the two piston members 60 and 62 are forced into the upper part of chamber 80 by entry of pressurized gas or fluid through passageway 86 into the chamber SO. This forces the two pistons together and t:o the potji tion shown in Figure 1.
Once the requisite amount of plastic material 100 is introduced into the mold cavity 26, the pron.isur-ized gas in chamber 80 from passageway 86 is removed or relieved, and liquid or gas is introduced undoi; µr^Mt-swie into cavity 80 through passageway 84, When pn ›nrn.i i- i ved fluid is introduced into cavity 80 t Innugh p.nm/.iqt'Wc-*y 84, the piston members 60 and 62 are divided or a‹var‹.d ed and forced into the positions in cavity 8u shown .in Figure 2. This caupes the end 57 of outer pin 52 to be seated in the opening in end 4 2 and thereby clo›se the entry of plastic material from bushing 12 into the moid cavity 26, At the same time, this procedure also openu
the gate or valve between end ¾6 and .UUH•O .Lowm' tan I M› of pin 52 allowing gas under pressure to U; im I'‹‹hi‹oi through connector 72 into annular patauayeway '. .* aim :i n turn into the mold cavity 26. The gas or fluid introduced into the mold cavity 26 pushes the plastic material 100 into all areas of the mold cavity, completely filling it, as shown in Figure 2.
The specific pressures uti 1l/ea and process steps for the gas-assisted injection molding process- are well-known in the art and any conventional process can be utilized. The present invention is adapted to be used with any type of conventional gas-assisted injection molding processes. In this regard, the gas or fluid can be introduced into the mold cavity during the flow of plastic into the cavity, after the plastic material 100 has been deposited in the cavity, or in any combination thereof* For example, as shown in Figures 1 and 2, an initial amount of plastic material 100 can t5¾ introduced into the mold cavity, then gas or fluid at a first pressure can be introduced into the cavity, and, if desired, the same or different gas or fluid can be introduced at the same or at a different pressure - also through connector 72. The introduction of the gas or fluid(s) into the mold cavity along with or subsequent to the plastic material, pushes the plastic material into all areas of the mold, completely filling the cavity.
Although the present invention is described herein with reference to the particular system shown in Figures 1 and 2 whereby all of the plastic: mri t::ei i z\ I \ r, introduced first into the mold cavity and t.lv* M;-H; or fluid introduced thereafter, it is aluo underiH oo.| rliat
the operation of the pistons 60 and 62 could be regulated such that the gas or fluid could be introduced along with a portion of the plastic material into the mold cavity. Figure 3A depicts one step in the operation of the invention in this manner. For this purpose, a control system could be devised which would regulate the positioning of the piston members 60 and 62 in order to satisfy those processing parameters.
Once the requisite amount of plastic material 100 and gas are introduced into the mold cavity 26, both of the valve members are closed at the entrance into the mold cavity. This is shown in Figure 3. For t:.his step, the pressurized fluid or gaa is removed or re h-ea^ed from cavity 80 through conduit 84, and pret3tfur\ zed i:.luid or gas is introduced into cavity 80 through passageway M2. This moves piston member 62 into contact with piston member 60 and at the same time moves the end ,[>b ot pin member 54 into engagement with the inner end '›ß of pin member 54, closing the gas valve or gate.
In accordance with standard gas an )i BI t-/•d injection molding techniques, after t: \u\ i uqui‹‹ 11 t amounts of gas and plastic are introduced into a mold, the pressure of the gas is maintained, to compensate ioi any volumetric shrinkage of the plastic as it cools and solidifies* The positions of the members of the system 10, as shown in Figure 3, can be utilized t‹i natisty this step. Also, for cooling, the uudd mumberu 22 and 24 are typically cooled by circulation of a coolant through appropriate channels or passageways (not shown) which assist in solidifying the plastic.
Once the plastic part, in the mold 2 6 has solidified sufficiently, the gas within the molded part is vented to atmosphere in any conventional manner, ‹xwd the part is ejected from the mold cavity. In accordance with the present invention, the gas could be vented from the molded part by reversing the processing step shown in Figure 2 which opens the valve between members 1JG and 58, Other conventional methods could be used to vent the gas in the mold part, however, such as a vent pin mechanism in the mold.
The gas which preferably is utilized wit h t he present invention is nitrogen, but it can be any other gas or fluid utilized with conventional gas assisted injection molding processes- Also, if desired, the qas which is removed or vented tirom the moid nlt;ei_ t he molding cycle, can be collected, r ec ! a ;.m.:-d and i en. ■ d. In this regard, it; is preferable to pjnvi.de i I i he r¾echanism in the gas return or exhaust passageway ;i n order to remove any foreign or plastic particles.
Virtually all of the members ot the system 10, with the exception of the seals, are made from a metaj material, such as steel. 01: course, any other i nnveit-tional materials used in injection molding syntems or gas-assisted injection molding uy steins can be vitili-/eci so long as they meet the requirements of ‹the present invention.
Although a particular sequence of processing steps are described above with reference to Figures 1, 2 and 3, it is also understood that the invention can be utilized with processing or method steps in a different sequence. In one preferred process, the system 10 is
shown in Figure 6. At the same time, sufficient pressure is maintained in passageway 14 2 and In tin upp^r portion of chamber 80' in order to maintain the piston 112 in its lowermost position.
The operation of the system 10' shown in Figures 4-6 with gas-assisted systems is siiniiar to t he operation of the system 10 in Figures 1-3 and 3A. The sequence of processing steps can also be modified in the same manner in order to meet the npv‹ei I i. cni en;; I:M requirements of the particular gaa ann.ini eci i i ■. j ■ ••i ^ n molding system preferred to be ut i ( i zed . [n t t.e; regard, regulation of the pressurized IJuids in i›nn:ete‹ ways 142 and 144, in combination with eid; i y eil j e,ieM^ material through passageway 5 3 and pannage o i • in‹i assisted fluid or materials through eonnect ‹ a '/,■'. ,u e coordinated and regulated t:o IIII‹H. t It- d.-ni j'tui ti i|ai i ^ ments.
While the above deneript e.‹n dt.;ser. i ben i he preferred embodiments of the invention, those nl.i. I led :ia the art will realize that changes and mod it. re a t ie•n;-i itue/ be made thereto without departing 1: J;OIII the spirit ,(nd scope of the invent l.on. The :i nvent I.* ›n iu ini ended i.t claim all such changes and modi f t eat i oi \(:\ \ \ ia i fa1.1 within the true scope of the invent i,.:n w... d‹.. 1 ined and covered by the following eiaimn.
What Is Claimed Is:
1. A valve-gate mechanism for use in a fluid-assisted injection molding process, said mechanism
3, The valve-gate mechanism of CLAIMS l wherein said first and second piston member a are adjust ably connected to said hollow pin member and sand tower pin member, respectively.
a second pressurized fluid source for apply ing pressurized fluid into said second µassageway in said first pin member; and
12 . A valve-gate mechanism for use in a fluid-assisted injection
|Indian Patent Application Number||3010/MAS/1997|
|PG Journal Number||07/2008|
|Date of Filing||29-Dec-1997|
|Name of Patentee||INCOE CORPORATION|
|Applicant Address||1740 E.MAPLE ROAD, TROY, MICHIGAN 48099-0485,|
|PCT International Classification Number||B 29 C 45/17|
|PCT International Application Number||N/A|
|PCT International Filing date|