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WO1997020675A1 - Procede et systeme de moulage par injection utilisant une zone de coulee a volume variable dans une cavite de moule definissant un article, et article ainsi produit - Google Patents

Procede et systeme de moulage par injection utilisant une zone de coulee a volume variable dans une cavite de moule definissant un article, et article ainsi produit Download PDF

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Publication number
WO1997020675A1
WO1997020675A1 PCT/EP1996/005433 EP9605433W WO9720675A1 WO 1997020675 A1 WO1997020675 A1 WO 1997020675A1 EP 9605433 W EP9605433 W EP 9605433W WO 9720675 A1 WO9720675 A1 WO 9720675A1
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WO
WIPO (PCT)
Prior art keywords
mold cavity
core
plastic
article
spill area
Prior art date
Application number
PCT/EP1996/005433
Other languages
English (en)
Other versions
WO1997020675B1 (fr
Inventor
James Watson Hendry
Original Assignee
Melea Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Melea Limited filed Critical Melea Limited
Priority to AU11905/97A priority Critical patent/AU1190597A/en
Publication of WO1997020675A1 publication Critical patent/WO1997020675A1/fr
Publication of WO1997020675B1 publication Critical patent/WO1997020675B1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/1703—Introducing an auxiliary fluid into the mould
    • B29C45/1704—Introducing an auxiliary fluid into the mould the fluid being introduced into the interior of the injected material which is still in a molten state, e.g. for producing hollow articles
    • B29C45/1705—Introducing an auxiliary fluid into the mould the fluid being introduced into the interior of the injected material which is still in a molten state, e.g. for producing hollow articles using movable mould parts

Definitions

  • This invention relates to plastic injection molding and, more particularly, to plastic injection molding which includes a spill area.
  • the pressurized fluid is typically nitrogen gas which is introduced into the mold cavity at or near the completion of the plastic injection.
  • the pressurized fluid serves several purposes. First, it allows the article so formed to have hollow interior portions which correspond to weight and material sav ⁇ ings. Second, the pressurized fluid withm the mold cavity applies outward pressure to force the plastic against the mold surfaces while the article solidifies Third, the cycle time is reduced as the gas migrates through the most fluent inner volume of the plastic and replaces the plastic in these areas which would other ⁇ wise require an extended cooling cycle. Fourth, the gas pressure pushes the plastic against the mold surfaces, thereby obtaining the maximum coolant effect from the mold.
  • another ap ⁇ proach is to use a fixed volume spill cavity 24 with a block pin 20 and shims 26 to control the volume of plastic going into the spill cavity 24.
  • the pin 20 is in its up position blocking plastic flow from the molding in the article- defining cavity 12, through a runner 23 and into the spill cavity 24.
  • the pin 20 is m its down position allowing plastic to go to the spill cavity 24 by the pressure of the gas.
  • Figure 2 illustrates blow out in the spill cavity 24 causing a loss of gas pressure in the molding in the article defining cavity 21.
  • One result of this is a possible shrinkage due to loss of gas pressure m the molding in the article defining cavity 21.
  • a lso, gas leakage may occur at the mold parting line.
  • Figure 3 illustrates the use of too much plastic which would result m sink marks at reference numeral 26.
  • Figure 4 illustrates the addition of the shims 26. However, overpackmg and blow out as illustrated in Figures 3 and 2, respectively, can still occur.
  • An object of the present invention is to provide a method and system for injection molding utilizing a variable volume spill area which: (1) eliminates the need for a shut off pin in a fixed volume shut off situation; (2) eliminates blow out in a spill over area that causes loss of gas pressure in the gas channel and resulting collapsing of the walls of the gas channels; (3) eliminates inaccuracies in the screw ram to deliver the same quantity of plastic shot after shot; and (4) allows positive displacement of plastic into a spill area within the article-defining mold cavity to insure no blow out as in Figure 2 or solid as in Figure 3, and a strain-free molding (i.e., no overpacking) .
  • a method for injection molding a hollow plastic article.
  • the method includes the steps of injecting a quantity of fluid plastic mto a rrold cavity having a shape defining at least a portion of the article; displacing a portion of the plastic from the mold cavity mto a spill area by introduction of a charge of pressurized gas into the mold cavity; permitting the injected plastic to solidi ⁇ fy, venting the gas from the mold cavity; and removing the plastic article from the mold.
  • the improvement of the method includes tne step of allowing the volume of the spill area to increase during the step of displacing to produce a substantially strain-free hollow plastic article wherein the spill area is withm the mold cavity.
  • the volume of the mold cavity is partially defined by an end face of a core reciprocally mounted the mold cavity.
  • the method further includes the step of increasing pressure on the core to move the core to an extended position with the mold cavity and wherein the step of allowing includes the step of reducing the pressure on the core to allow the core to move to a retracted position.
  • the method includes the steps of injecting a quantity of fluid plastic into a mold cavity having a shape defining at least a portion of the article; allowing a portion of the plastic from the mold cavity in flow into a spill area during the step of in j ecting by introduction of a charge of pressurized gas into the mold cavity; permitting the injected plastic to solidi- fy; and removing the plastic article from the mold
  • the improvement of the method includes the step of allowing the volume of the spill area to increase during the step of injecting to produce a substantially strain-free plastic article wherein the spill area is withm the mold cavity.
  • the method and system of the present invention preferably utilize a pneumatic spring coupled to the core so that when the pressure of the plastic being injected by a screw ram overcomes the pressure on the core, the core will move out of the mold cavity making sure that the molding will not see more pressure than the fill pressure Therefore, the hollow plastic part will be substantially strain-free. In this way, the inaccuracy of the screw ram to deliver the same quantity of plastic shot after shot is compensated for.
  • the present invention admits to molding of structural articles for use in diverse product fields, such as a bumper having a pair of end wings for an automobile .
  • FIGURE 1 is a schematic cross-sectional view, partially broken away, of a prior art injection molding method utilizing a pin to prevent plastic flow into a fixed volume spill cavity;
  • FIGURE 2 is a view similar to Figure 1 with a pin in its down position and illustrating blow out in the spill cavity due to the lack of sufficient amount of plastic in the article defining cavity;
  • FIGURE 3 is a view similar to Figure 2 except too much plastic has been utilized with resulting sink marks;
  • FIGURE 4 is a view similar to the views of Figures 2 and 3 with the addition of shims located at the bottom of the spill cavity;
  • FIGURE 5 is a flow chart indicating the basic steps involved in the practice of the method of the present invention.
  • FIGURE 6 is a schematic cross-sectional view, partially broken away, illustrating the method and system of the present invention including a core coupled to a pneumatic spring after the step of plastic injec ⁇ tion;
  • FIGURE 7 is a view similar to Figure 6 after the introduction of pressurized gas into the mold cavity to form the hollow part;
  • FIGURE 8 is a schematic cross-sectional view, partially broken away, of a second embodiment of a core of the present invention.
  • FIGURE 9 is a schematic cross-sectional view, partially broken away, of a third embodiment of a core of the present invention.
  • FIGS 6 and 7 broadly illustrate the method and system cf the present mvention wherein a variable volume spill area 28 is located wl hln a gas channel of a mold cavity 29 of a mold core side 35 of a mold.
  • the volume of the area 28 is controlled and is varied by the position of a core 30, the end face 32 of which is exposed to a pressure from plastic 33 withm the mold cavity 29.
  • the core 30 is coupled at its opposite face 37 by a rod 39 to a pneumatic spring 41.
  • the core 30 may be square, round, rectangular or odd shaped to suit the gas channel with the cavity 29.
  • Figure 6 illustrates the core 30 its extended position within the mold cavity 29 with the mold closed during injection of the plastic mto the gas channel within an article-defining cavity 29
  • the spring 41 has a preset pressure which causes the core 3D to extend into the cavity 29.
  • Figure 6 illustrates the location of the plastic after it has been injected into the article- defining cavity 29 wherein inaccuracies in shot weight delivered by the screw ram are taken up by a lower portion of the spill area 28 (i.e., the core 30 moves up slightly) . If the injection pressure of the plastic to fill the mold is, for example, 1000 psi then ts lower portion of the spill area 28 will take up the 1000 psi and not allow the screw ram to go into a packing phase at a pressure much higher than 1000 psi. If such a pressure over 1000 psi was reached, this would strain the molding in the article defining cavity 29.
  • the pneumatic pressure of the spring 41 must be equal to the plastic injection pressure to fill the cavity 29 completely.
  • the spill area 28 takes care of excess plastic injection.
  • Figure 7 illustrates gas injected mto the molding m the article defining cavity 29 by a gas pin 42 to create a void 43. Excess plastic is passed into the spill area 28 vacated by the core 30 within the cavity 29. In other words, the core 30 moves to create the spill area 28 in the cavity 29 when the gas pressure through the pin 42 in the cavity 29 overcomes the preset gas pressure of the air spring 41.
  • An end face 32' of the core 30' is cham ⁇ fered to create more volume between the end face 32' and the mold core side 35' . This ensures that sufficient molten plastic is at this location to permit the gas injection pressure to be felt at the end face 32' .
  • FIG 9 there is illustrat ⁇ ed yet another embodiment of a core 30" of the present invention where parts which are the same or perform substantially the same function as the parts of Figures 6 and 7 have the same reference numeral but a double prime designation.
  • An end face 32" of the odd-shaped core 30" is curved. While faces 44" and 46" of the mold core side 35" may touch sides 48" and 50", respectively, of the core 30" during plastic injection, the end face 32" must have room between it and a facing surface of the mold core side 35" to allow a sufficient amount of plastic to flow therein so that the gas pressure can reach the end face 32" with enough pressure to move the core 30" before the plastic at the end face 32" hardens.
  • Figure 5 is a flow chart of the steps involved in practicing the process of the present invention.
  • a quantity of molten plastic is injected from an injection molding machine into the channel of the article-defining mold cavity 29 with the core 30 fully extended (i.e., Figure 6) .
  • the plastic may be most thermoplastics and the invention works particularly well with glass or mineral filled thermo ⁇ plastic polyester, commonly known by the trademark Valox of General Electric Co.
  • the quantity is sufficient to fill the mold cavity 29 not occupied by the core 30 and may partially move the core 30 upward to partially fill the spill area 28.
  • the core 30 Prior to plastic injection, the core 30 is in its fully extended position as illustrated in Figure 6 due to the preset gas pressure of the spring 41.
  • step 112 i.e., Figure 7
  • a charge of pressurized gas is introduced into the mold by the gas pin 42 upon substantial completion of the injection of the quantity of molten plastic.
  • gas pin 42 upon substantial completion of the injection of the quantity of molten plastic.
  • other ways of introducing gas into the mold are possible such as through a nozzle as illustrated in U.S. Patent No. 4,101,617 to Friederich.
  • step 114 the gas flow into the mold is maintained in pressure and duration in amount and time sufficient to displace a controlled quantity of plastic from the article defining mold cavity 29 into the spill area 28 defined by the end face 32 and side surfaces of the core 30. Movement of the core 30 due to the pres ⁇ sure of the gas causes an additional amount of plastic to flow into the spill area 28.
  • the gas tends to displace the hottest, most fluent plastic in the central portion of the mold cavity. Consequently, the molded plastic article has a hollow interior where the least viscous plastic has been displaced.
  • the presence of the gas affords savings in weight and material usage. Added benefits include enhanced surface quality due to the outward pressure exerted by the gas, and reduced cycle ti e due to displacement of the relatively hot plastic from the central portion of the article.
  • step 116 the article is permitted to solidify within the mold cavity 29 including the spill area 28 vacated by the core 30 while the internal gas pressure is maintained.
  • step 118 the pressurized gas is vented from the interior of the molded article preparatory to opening the mold.
  • Numerous ways of venting are possible such as described in the U.S. Patent No. 4,101,617 to
  • step 120 the plastic article is removed from the mold.
  • Core 30 is held in its extended position by the preset pressure of the spring 41 when the mold closes.
  • Pressure on the core 30 is equal to the plas- tic injection pressure.
  • This design eliminates the need for a shut-off pin between the article defining cavity and the spill over. This design further eliminates overpacking of the mold cavity and takes care of the inaccuracies of the screw to deliver precise shot weights on each cycle.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Injection Moulding Of Plastics Or The Like (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)

Abstract

Procédé et système permettant de mouler par injection des articles en plastique, qui font appel à une zone de coulée (28) dont le volume varie à l'intérieur d'une cavité de moule (29) définissant un article. Dans un mode de réalisation, le volume augmente durant l'introduction de gaz sous pression dans la cavité du moule. Dans un autre mode de réalisation, le volume de la zone de coulée (28) varie durant une injection de plastique remplissant la cavité du moule. Un noyau (30) monté réciproquement dans la cavité du moule définit partiellement le volume variable de la zone de coulée (28). Un ressort pneumatique (41) permet de commander la pression sur le noyau (30), qui s'oppose à la pression du plastique sur la surface terminale (32) du noyau (30). Dans un mode de réalisation, cette surface n'est pas plane, de façon à créer une zone où le plastique fluide peut exercer une pression contre la surface terminale à l'intérieur de la cavité du moule durant l'injection de plastique et/ou durant l'introduction de gaz sous pression.
PCT/EP1996/005433 1995-12-07 1996-12-05 Procede et systeme de moulage par injection utilisant une zone de coulee a volume variable dans une cavite de moule definissant un article, et article ainsi produit WO1997020675A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU11905/97A AU1190597A (en) 1995-12-07 1996-12-05 Method and system for injection molding utilizing a variable volume spill area within an article-defining mold cavity and article produced thereby

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US56896295A 1995-12-07 1995-12-07
US08/568,962 1995-12-07

Publications (2)

Publication Number Publication Date
WO1997020675A1 true WO1997020675A1 (fr) 1997-06-12
WO1997020675B1 WO1997020675B1 (fr) 1997-08-07

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AU (1) AU1190597A (fr)
WO (1) WO1997020675A1 (fr)

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4414167A (en) * 1982-02-18 1983-11-08 Rca Corporation Method for molding an article
DE4002503C1 (en) * 1990-01-29 1991-05-29 Schade Kg, 5970 Plettenberg, De Hollow injection moulded plastic mouldings prodn. - comprising injecting plastic melt into mould and applying pressurised gas to melt, using variable cross=sectioned mould
JPH06143318A (ja) * 1992-11-09 1994-05-24 Mitsubishi Kasei Corp 中空部に補強リブを有する射出成形品の製造方法
DE4334012C1 (de) * 1993-10-06 1994-10-27 Webasto Karosseriesysteme Deckel eines Schiebe-/Hebedaches für Fahrzeuge
EP0628395A1 (fr) * 1993-06-11 1994-12-14 Battenfeld GmbH Procédé de moulage par injection d'articles en matière thermoplastique et moule pour sa mise en oeuvre
JPH07148768A (ja) * 1993-12-01 1995-06-13 Asahi Chem Ind Co Ltd 厚肉ファンの成形方法
WO1995020477A1 (fr) * 1994-01-28 1995-08-03 Perstorp Ab Procede de production d'un article moule a bord creux
EP0692360A1 (fr) * 1994-07-15 1996-01-17 Cinpres Limited Dispositif de moule et procédé de moulage par injection

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4414167A (en) * 1982-02-18 1983-11-08 Rca Corporation Method for molding an article
DE4002503C1 (en) * 1990-01-29 1991-05-29 Schade Kg, 5970 Plettenberg, De Hollow injection moulded plastic mouldings prodn. - comprising injecting plastic melt into mould and applying pressurised gas to melt, using variable cross=sectioned mould
JPH06143318A (ja) * 1992-11-09 1994-05-24 Mitsubishi Kasei Corp 中空部に補強リブを有する射出成形品の製造方法
EP0628395A1 (fr) * 1993-06-11 1994-12-14 Battenfeld GmbH Procédé de moulage par injection d'articles en matière thermoplastique et moule pour sa mise en oeuvre
DE4334012C1 (de) * 1993-10-06 1994-10-27 Webasto Karosseriesysteme Deckel eines Schiebe-/Hebedaches für Fahrzeuge
JPH07148768A (ja) * 1993-12-01 1995-06-13 Asahi Chem Ind Co Ltd 厚肉ファンの成形方法
WO1995020477A1 (fr) * 1994-01-28 1995-08-03 Perstorp Ab Procede de production d'un article moule a bord creux
EP0692360A1 (fr) * 1994-07-15 1996-01-17 Cinpres Limited Dispositif de moule et procédé de moulage par injection

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
"Herstellung von Hohlkörpern durch Spritzgiessen", KUNSTSTOFFBERATER, vol. 28, no. 9, September 1983 (1983-09-01), ISERNHAGEN DE, pages 22, XP002029445 *
PATENT ABSTRACTS OF JAPAN vol. 18, no. 452 (M - 1661) 23 August 1994 (1994-08-23) *
PATENT ABSTRACTS OF JAPAN vol. 95, no. 9 31 October 1995 (1995-10-31) *

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Publication number Publication date
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