Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
  • B60R19/00—Wheel guards; Radiator guards, e.g. grilles; Obstruction removers; Fittings damping bouncing force in collisions
  • B60R19/52—Radiator or grille guards ; Radiator grilles
• • 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

Definitions

• the present invention relates to a gas injection moulded plastic article with at least one cavity enclosed in the same.
• the invention also relates to a method and an injection moulding device for manufacturing such a plastic article.
• Gas injection moulding is used, for example, when making plastic panels with hollow elongated reinforcing ribs, where the cavities in the ribs are made by injecting gas in the not yet hardened plastic in the mould cavities against the surfaces of which the external surfaces of the ribs are to be formed.
• US 5 204 051 describes and shows the manufacture of plastic articles with cavities by gas injection moulding.
• US 5 204 051 illustrates the use of either two gas injection needles inserted into the plastic melt in the vicinity of the opposite ends of the mould cavity or a single gas injection needle inserted centrally into the mould cavity. This latter alternative is limited to cavities or relatively small dimensions in relation to their cross-sectional area.
• the purpose of the present invention is to achieve a plastic article with at least one cavity enclosed in the same, which can be manufactured using a single gas injection needle for a given length of cavity, which required, with previously employed technology, at least two gas injection needles to achieve a result of comparable quality.
• This is achieved according to the invention by virtue of the fact that the cavity in areas remote from a gas injection location have a cross-sectional area which decreases with increasing distance from the gas injection location.
• the invention is based on the simple fact that a larger volume of fluent plastic melt can flow per unit of time through a larger flowthrough area than through a smaller flowthrough area. If the plastic melt on one side of the gas injection needle tends to flow out more rapidly than the plastic melt on the opposite side, the former will be slowed down when the flowthrough area decreases, so that a balance is achieved in relation to the latter which is still within a section of larger cross-section.
• a plastic article which can be injection moulded with advantage in the above mentioned manner is a radiator grill for motor vehicles, comprising a frame and a plurality of hollow mouldings surrounded by the frame and joined thereto. All of these mouldings are gas injection moulded in one piece with the frame and have end portions connected to the frame, the cavities of which have decreasing cross- sections towards the ends.
• the frame also has hollow frame portions with cavities which have end portions with decreasing cross-section towards the ends.
• An injection moulding device for manufacturing a plastic article according to the invention is characterized in that the mould cavity has substantially greater length than height and width and has end portions with decreasing cross-sectional area towards the ends, and that means are arranged for supplying fluent plastic under pressure and gas under pressure to the mould cavity midway between its two ends.
• Figure 1 shows a perspective view of the back of a plastic article in the form of a radiator grill for motor vehicles
• Figure 2 shows a section along the line II-II in Fig. 1
• Figure 3 shows a section along the line III-III in Fig. 3
• Figure 4 shows a section through a schematically represented moulding device.
• the radiator grill shown in Figs. 1-3 comprises a rectangular frame, generally desig- nated 1 , which consists of a horizontal upper frame member 2, a horizontal lower frame member 3 and two vertical side frame members 4, which should join the upper and lower frame members 2 and 3 to each other. Between the frame members 2 and 3 there also extend a pair of vertical mouldings 5, and between these vertical mouldings and the respective side frame member 4, a pair of horizontal mouldings 6 and 7 extend. Finally, a horizontal moulding 8 extends via the vertical mouldings 5 from one side frame member 4 to the other.
• All of the components 2-8 shown and described are made in one piece with each other in a gas injection moulding process in such a manner that cavities are formed in the frame members 2 and 3 and in the mouldings 6, 7 and 8. These cavities, which extend over the entire length of the frame members, are designated 9, 10, 11, 12 and 13 in Fig. 2. All of them have, as is illustrated in Fig. 3, end portions with gradually decreasing cross-section towards their ends which are joined to the side frame members 4. As is particularly evident in Fig. 2, the cavity 9 of the upper frame member has a larger depth "a " than height "b". This provides greater rigidity for the panel as a whole and in the upper frame member 2, so that it can be grasped when removing the panel.
• Fig. 4 shows schematically an injection moulding device which can be used for manufacturing the plastic article according to the invention and which comprises upper and lower mould halves 20 and 21, respectively, which define together a mould cavity 22 and which can be moved apart by means not shown in more detail here, from the position shown to open the mould cavity 22.
• the nozzle 24 of an injection moulding device opens into a channel 23 through the upper mould half 20.
• the injection moulding device has a cylinder 25 and a piston 26 axially displaceable in the cylinder, by means of which fluent plastic in the cylinder 25 can be pressed into the mould cavity 22.
• the mould halves 20 and 21 define, in addition to the mould cavity 22, a pair of so-called spill chambers 27, which corri riunicate with the mould cavity 22 via individual channels 28.
• a corresponding ejector pin 31 is disposed in a bore 32, opening into each spill chamber 27.
• a gas needle 33 extends directly opposite the channel 23 and has an opening 33a through which gas can be injected into the plastic material into the mould cavity 22.
• the gas needle 33 can be fixed in the position shown or be extractable from the mould cavity 4.
• Fig. 4 designates a control unit
• 35 designates a compressed gas source
• 36 and 37 are drive means for driving the piston 26 and the ejector pins 30, respectively.
• Fig. 4 is symmetrical relative to a center plane A, and to the left of the plane A there is illustrated the state after the piston 26 has reached the bottom of the cylinder 25, and the mould cavity 22 has been filled completely with fluent plastic b while air is purged and a small amount of plastic material c has entered the spill chamber 27.
• the control unit 34 keeps, via the drive means 37, the ejector pins 30 in the position shown to the left in Fig. 4, in which the upper end surface 30a of each ejector pin 30 leaves a narrow passage 28a open, through which first air and then plastic material can pass to the spill chamber 27.
• the control unit 34 activates the compressed gas source 35 so that gas under pressure (preferably nitrogen) is injected through the gas needle 33 and out through its opening 33a into the still not hardened plastic, which is pressed out through the channels 28 and into the spill chambers 27 until they are entirely filled, as illustrated in the right-hand half of Fig. 4.
• gas under pressure preferably nitrogen
• the control unit 34 keeps the ejector pins 30 in the position shown to the right in Fig. 4, in which their end surfaces 30a are at a lower level to free the entire flowthrough area of the channels 28.
• the mould cavity has end portions 22a with gradually decreasing cross-sectional area towards the ends, a more balanced filling of the cavity is achieved than if it had the same cross-sectional area along its entire length.
• the counter-pressure against the more rapidly flowing plastic will increase as it reaches the tapering portion of the mould cavity, so that the gas pressure will increase against the less rapidly flowing plastic material which still has not reached the corresponding opposite tapering portion of the mould cavity, until a balanced filling is achieved.
• the mould cavity 22 is opened and the control unit 34 activates the drive means 37 of the ejector pins 30 to move the pins 30 upwards to lift the plastic article from the lower mould half 21.
• the control unit 34 activates the drive means 37 of the ejector pins 30 to move the pins 30 upwards to lift the plastic article from the lower mould half 21.
• the pins 30 move up through the channel 29, the communication between the plastic in the mould cavity 22 and the plastic in the spill chamber 27 is cut off, so that the latter can thereafter be ejected by means of the ejector pin 31.
• 40 designates the holes left by the gas needles and 41 the remains of the plugs formed above the surfaces 30a of the ejector pins 30.
• Fig. 4 shows a plastic article 2 with a cavity 9, which means that the section through the mould is taken through the mould cavity in which the upper frame portion 2 of the radiator grill shown in Figs. 1-3 is moulded. It will be understood, of course, that for the sake of illustration, Fig. 4 is very simplified and that parts of the upper frame portion 2, revealed in Figs. 1 and 2 but which are of no interest for explaining the invention, have been left out.

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• 1996
  • 1996-12-04 SE SE9604474A patent/SE508096C2/sv not_active IP Right Cessation
• 1997
  • 1997-12-04 BR BR9713669-7A patent/BR9713669A/pt not_active IP Right Cessation
  • 1997-12-04 AU AU54219/98A patent/AU5421998A/en not_active Abandoned
  • 1997-12-04 EP EP97948077A patent/EP0954423A1/en not_active Withdrawn
  • 1997-12-04 JP JP52552198A patent/JP2001505148A/ja active Pending
  • 1997-12-04 WO PCT/SE1997/002027 patent/WO1998024610A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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