FR2538299A1 - HOLLOW BODY OF PLASTIC MATERIAL AND INJECTION MOLDING MOLD - Google Patents

Abstract

The invention relates to a hollow body of plastic material consisting of a cylindrical casing part, an attached lowered bottom and an annular channel 7. The annular channel 7 is filled during the injection molding process and establishes the connection between the orifice of. injection of the bottom and the envelope part. This channel 7 is formed in such a way that it has alternately narrowed sections 10 and non-narrowed 8. Application to the manufacture of molded parts of uniform quality. (CF DRAWING IN BOPI)

Description

The present invention relates to cylindrical hollow bodies made of

plastic and molds

  injection molding in which they are produced.

  In the particularly important hollow bodies

  as a rotational symmetry, the plastic material is injected through a bottom opening of the mold located mostly in the center, the mold core in the tool then penetrating by an external edge protruding and

  annularly in a corresponding annular groove

  the outer fixed mold contour of the tool.

  When the annular channel which establishes the connection

  its sound between the injection port of the bottom and the envelope portion is everywhere the same width, it is not possible to obtain a problem-free centering of the mold core because of the unilateral curvature of the core that occurs sometimes during of the injection molding process and, therefore, because of the throttling of material flow on the other side This is however necessary to obtain parts having thicknesses

  wall thickness and regular tolerances, as it is necessary

  for example to be able to print round bodies without interference on chuck printers

  in the offset process or even in the serial process.

  graphy. It was therefore undertaken to maintain the width of the annular channel smaller than the width of the space

  ring created between the peripheral faces of the enve-

  mold lump and mold core (Swiss patent

N 471 662).

  During the reduction which took place

  above the width of the annular channel up to 2 to 2.5 times the circumferential width of the cavity of the mold, this large narrowing has easily caused a sudden local overheating of the plastic material penetrating under pressure high in the mold cavity and thus some fracture ability, as well as deviations from the permeability values

  to maintain for water vapor or gas.

  On several hollow bodies, for example on small tubes or other pharmacy containers, it is necessary to have on the opening of flanged edges for arranging and fixing plugs One must constantly take into account an extreme precision of measurement to obtain

  a good seal of the container with respect to the

  what we tried to achieve by

  "controlled by the injection molding machine

  and exerted on the injected plastic material

  Since the core of the mold and also its outline must be cooled, the material at the narrowing of the mold cavity hardens very easily after termination of the injection process, so that this subsequent necessary pressure can only act only in a limited way or in a

  unfavorable case, can not act at all.

  such a narrowing with sudden closing of the mold cavity circulation path which is, however, caused by the narrowed known annular channel.

  regularly, all around its width.

  The object of the present invention is thus to eliminate

  This is because the annular channel formed between the outer contour portion of the mold and the core of the mold which penetrates therein is alternately formed by narrowed and narrowed sections. it is true a centering action and a fixing action to a sufficient extent, but nevertheless ensures, due to the "normally" wide annular channel sections lying between the narrowing, a material flow that is never

  completely interrupted We never arrive at a farm

  Sudden temperature with overheating Normal thickness

  wall remains equal over the entire length.

  To this is added that with hollow bodies for a hygroscopic filler and using according to the present invention an annular molding channel formed alternately by wider sections and more

  narrow, unwanted values of permeability to-

  the location of the annular channel of a small tube is already regressing to half that obtained with the regularly narrow annular channels of previously known injection molding molds. The non-narrowed sections of the annular injection channel may easily correspond, with the embodiment according to the present invention, to

  minus the shell thickness of the hollow body

  channel can be determined by thickening of one or the other or both of the wall sections, ie the bottom part or the contour part of the mold, which constitute the channel.

  ring in the injection mold.

  The cylindrical hollow bodies improved according to the present invention can also present

  more than the usual circular base face, also-

  oval base or polygonal shape, In this case, although the improvement of printing in

  chuck printing machines do not have the

  with the rotationally symmetrical bodies, the points of view - for example relating to the maintenance of dimensions in the thickness of the walls and

  permeability, however, remain important.

  It is necessary to have a mutual and precise coincidence between the data of construction techniques, chemical and physical hollow bodies and those of the molding tools used to

  their production, given the very considerable length

  for example 17 cm on which the nucleus of

  mold of the tool penetrates freely into the

  loppe which has a diameter of about 3.5 cm, furthermore the small wall thicknesses of the hollow body, for example 1 mm or even less, and finally, the low permeability values required for water vapor or gases on the one hand and partially very narrow conditions for performing the injection of the material under high pressure at temperatures of 280-3000 C, and 2538 t 99 that the different properties of the plastics used, such as polystyrene, polyethylene and

  polypropylene at high pressure-and low, on the other hand.

  The distribution, length and number (e.g.

  to 8) differently-sized sections of the annular channel.

  Two exemplary embodiments of the present invention will now be described with reference to enlarged partial representations of a cylindrical hollow body and its mold tool, with 8 annular channel narrowing.

  FIG. 1 is a view of the lower part of

  a small plastic tube according to the present invention in its injection molding mold,

  the configuration of the annular channel being then determined

  mined by corresponding deformations of the bottom portion of the inner core of the mold;

  FIG. 2 is a partial view corresponding to

  However, the configuration of the annular channel is determined by deformations in the bottom portion of the outer side of the contour of the mold; FIG. 3 is a purely diagrammatic representation of the annular channel oblique approximately at the height of the layer designated in FIG. 1 by the small arrows a and b; and

  FIG. 4 is a representation corresponding to

  also purely schematic of the oblique annular channel approximately at the level of the layer designated

  Figure 2 by the small arrows a and b.

  The sectional representations of FIGS. 1 and 2 show on an enlarged scale by fine hatching the lower part of a hollow body H made of plastic material in its injection mold, the outer part of which is called the outline. of mold "is

  either in one piece or as in the example of

  2 parts, an upper part 1 forming the casing and a bottom bottom portion 3 forming the bottom portion of the hollow body These parts are assembled on the face designated by the thick line along the small arrow a La internal part of the injection molding mold is constituted by the mold core 2 which enters from above freely into the hollow mold The intermediate space between the two mold parts constitutes the hollow body whose wall thickness

is substantially 1 mm.

  The lower part 3 of the "mold contour" has an axial injection orifice 4 for the plastic material. All around, this bottom portion 3 of the mold contour has a recess 5 into which the beaded edge 6 of the mold core penetrates. 2 in

protruding ring down.

  The annular channel 7 extending obliquely downwards and connecting the central portion of the bottom of the blank to the envelope portion is traveled during the injection process by the plastic material since

  the middle outwards For center of the proces-

  which takes place with a high pressure and a tempera-

  The ring core is also high, the mold core first freely penetrating into the hollow mold and at the same time preventing any tendency to an oblique position, the annular channel alternately having "normally" and narrowed sections which are formed by sections of canal walls alternatively

salient and reentrant.

  The embodiment of Figures 1 and 3 shows the described formation of the annular channel 7 by the treatment of the peripheral wall of the tucked in bottom 18 of the mold core: while on the wall sections 9 projecting inwards are the narrowed sections of channel 10, the re-entrant intermediate wall sections constitute the sections of

channel 8 of width "normal".

  The embodiment of FIGS. 2 and 4 makes it possible to see the formation described above of the annular channel 7 by the treatment of the peripheral wall portion of the bottom bottom piece 3 of the mold contour. The narrowed channel sections 10 are in

  face of the wall sections 11 projecting from the outside.

  and the 8 "normal" width channel sections are

  face reentrant wall sections 12.

Claims (5)

  1 hollow plastic body, consisting of a cylindrical shell portion, a lowered bottom and an annular intermediate channel filled during the injection molding process and establishing the connection between the bottom injection port and the shell portion, characterized in that the annular channel (7)   consists alternately of narrowed sections (10) '- and not shrunken (8).   2 hollow body of plastic material according to claim 1, characterized in that the width of the non-shrunken sections (8) of the annular injection channel corresponds at least to the thickness of the casing of the hollow body. Injection molding mold for producing the plastics hollow body according to claim 1 or claim 2, characterized in that, to form the narrowed sections (10) of the annular injection channel (7), the recessed bottom (18) of the core (2) of the mold has thickened wall sections (9)   turned away from the central axis (Figures 1 and 3).   Injection molding mold for producing the plastic hollow body according to Claim 1 or Claim 2, characterized in that, to form the narrowed sections (10) of the annular injection channel (7), the bottom portion (3) surrounding the bottom injection port (4) and forming part of the mold contour (1) has thickened wall sections (11)   directed towards the central axis (Figures 2 and 4).   Injection molding mold according to the invention   3 or 4, characterized in that the two parts   of molds (1 and 2) assembled to form the annular canal.   (7) have thickened or recessed sections to form the alternately narrowed sections and   not shrunken of the annular injection channel (7).