GB2134437A

GB2134437A - Moulding hollow bodies of plastics material

Info

Publication number: GB2134437A
Application number: GB08332303A
Authority: GB
Inventors: Herbert Jaeniche; Horst Meyer; Eduard Guzda
Original assignee: Jaeniche & Co KG Dr GmbH
Current assignee: Jaeniche & Co KG Dr GmbH
Priority date: 1982-12-02
Filing date: 1983-12-02
Publication date: 1984-08-15
Also published as: FR2538299A1; DE3244678A1; GB2134437B; AT383986B; ATA422683A; GB8332303D0; CH663570A5; FR2538299B1; DE3244678C2

Abstract

A hollow plastics body, Figures 1, 2 (not shown), has a recessed base including a frusto-conical portion having alternating segments of greater and smaller wall thickness in the circumferential direction. During injection moulding of the body, a frusto-conical mould portion distributes the plastics material through a channel 7 from a central opening to the cylindrical wall of the body, the segments of differing wall thickness 8, 9 being formed either by formations on the free end of the mould core 2 as shown, or by formations on the outer mould part 3 providing the floor of the mould cavity, Figure 4 (not shown). It is stated that the mould portions of differing roll thickness help to keep the core 2 centered. <IMAGE>

Description

SPECIFICATION Hollow bodies of plastics material and moulds therefor The invention relates to hollow bodies of plastics material and to injection moulds in which they can be formed.

In rotationally symmetrical hollow bodies, which are particularly important, the plastics material is injected through a generally centrally arranged opening in the base of the mould, and the mould core of the mould device has a projecting annular outer edge which extends into a corresponding annular groove of the fixed outer mould part of the device.

If the annular channel which connects between the injection opening in the base and the sleeve or casing portion is throughout so uniformly dimensioned, it is not possible to achieve an unobjectionable centering of the mould core because deflection to one side of the core takes place in consequence of the injection process, thereby throttling or restricting the flow of the material on the other side. It is however necessary to maintain such centering, in order to produce parts with uniform wall thickness and tolerances, as is necessary for example to permit round bodies to be correctly printed in mandrel printing machines by offset or screen printing processes.

It has therefore already been proposed to keep the width of the annular channel smaller than the width of the annular space appearing between the peripheral surfaces of the mould casing and the mould core (Swiss Patent Specification No. 471 662).

By the restriction of the annular channel width undertaken in accordance with these proposals to 2 to 25/2 times the peripheral width of the mould chamber, this sharp constriction readily leads to sudden local underheating of the plastics material flowing into the mould chamber under high pressure, and thus to brittleness or cracks as well as to variations in permeability values for seam or gases.

In many hollow bodies, for example in small tubes or the like containers for pharmaceutical use, there must be provided beads or enlarged rims at the opening for the reception and securement of stoppers or closures. At all times, in order to produce a tight fit of the container with the closure, for which extremely precisely measured dimensions are laid down, search was made to reach a stressing or an "after pressure" of the injected plastics material controlled by the injection device. Because however mould cores and also mould contours must be cooled, so the material solidifies very easily on contraction of the mould chamber at the end of the injection process, this required after pressure is limited or in unfavourable cases cannot be effective.

Precisely such a contraction with sudden closure of the access path of the mould chamber is however brought about by the known uniform annular contraction of the width of the annular channels.

The object of the invention is to remedy the deficiencies mentioned. This is achieved in that the annular channel formed between the outer mould contour part and the mould core extending into it consists of alternating restricted and not restricted segments or portions. Through the restricted portions, there is produced to a sufficient extent a centering and locating effect; at the same time however a never completely restricted flow of material is allowed through the "normally" dimensioned portions of the annular channel lying between the restrictions. There is never a sudden closure with overheating. The normal wall thickness remains preserved over the whole length.

In addition, there is obtained for hollow bodies for hygroscopic contents, by the provision, in accordance with the invention, of annular casting channels with alternating expanded and restricted sections, amelioration of the undesired permeability values at the annular channel position of a tube or tubular container, moreover with half of the uniformly narrowed channels of the prior art injection moulding.

The segments of the annular injection channel which are not narrowed in the structure in accordance with the invention can directly correspond at least to the sleeve or casing thickness of the hollow body. The narrowing of the channel can be effected in production by suitable thickenings or projections at one or other or both of the mould portions, that is, the base part or the mould outer or contour part, which forms the annular channel in the injection mould.

Cylindrical hollow bodies embodying the invention can have internally and externally the useful circular cross-section, also other cross-sections for example of oval or multisided or polygonal form, for which the improvement in printing in mandrel printing machines does not have the importance as for rotationally symmetrical bodies but which however maintain their importance from the point of view of regulation of wall thickness and permeability for example.

Considering the very substantial length, for example of 17 cm, over which the mould core of the moulding device projects freely into the casing part of about 3.5 cm diameter; further, the slight wall thickness of the hollow body, for example, 1 mm or even less; and finally the required low permeability for steam or gas obtained on the one hand and to some extent very strict conditions for injection of the material under high pressure at temperatures of 280-300 C; as well as the different properties of the plastics material used, such as polystyrene, heavy duty and normal duty polyethylene and polypropylene on the other hand, a very precisely interrelated co-ordination of the structural chemical and physical data of the moulded bodies and the moulding tools is needed for their production.The division length and number (for example 5 to 8) of the differently dimensioned segments of the annular channel can be selected in accordance with the material employed.

For a better understanding of the present invention reference may be made to the following illustrative description and the accompanying drawings, in which: Figure 1 is a sectional view through the lower part of a plastics tube according to the invention in its injection mould, in which the shape of an annular channel is obtained by corresponding formations in the base portion of the inner mould core; Figure2 is a corresponding sectional view in which however the moulding of the annular channel is effected by formations in the base portion of the outer contour side of the mould; Figure 3 is a schematic representation of the annular channels approximately in the region of the layer indicated in Figure 1 by the arrows a and b; and Figure 4 is a correspondingly schematic representations of the annular channel about in the region of the layer indicated in Figure 2 by the arrows a and b.

The sectional views of Figures 1 and 2 each show the lower part of respective hollow bodies H of plastics material, in a mould in which it has been injection moulded. The bodies H are of circular internal and external cross-section and are formed with appropriate openings (not shown) at their upper ends.

The outer portion of the mould is a so-called "form contour or form outline" and is either unitary or, as shown, in two portions comprising an upper portion 1 for forming a sleeve part of the body H and of an underneath base portion 3 for forming the base parts of the body H. The two mould portions 1 and 3 abut at surfaces in the plane indicated by the lines marked with the arrow a. The inner portion of the mould comprises a mould core 2 which extends freely from above into the moulding chamber provided bythe mould portions 1 and 3. The intermediate space between the two cores 2 and the other mould portions forms the hollow body H of which the wall thickness can approximate to 1 mm.

The lower portion 3 of the "mould contour" or female mould portion contains an axial injection opening 4for plastics material. This base portion 3 of the mould contour has annularly therearound a depression 5 into which a ring-shaped projecting edge 6 of the mould core 2 downwardly projects.

The upwardly recessed centre part of the base or floor of the moulded body 4 is connected with the cylindrical part by way of a tapered or frusto-conical annular channel 7. The channel 7 flares downwardly and outwardly to an annular base portion within the groove or the depression 5 in the mould portion 3, from which base portion the cylindrical wall of the body H upwardly extends. During the injection process, the plastic material flows from the opening 4through this channel 7.

The injection process takes place under intense pressure and high temperature and in order to centre the moulding core 2 which initially projects freely into the mould cavity and to counter immediately any fitting to an inclined position, the annular channel 7 has alternating portions or segments respectively of narrowed or restricted and of "normal" breadth, in the radial direction, which are constituted by alternate projecting and recessed portions of the channel wall.

The embodiment shown in Figures 1 and 3 has the described form of the annular channel 7 as a consequence of the elaboration of the recessed frusto-conical wall surface of the base 18 of the mould core 2. The channel portions 10 lie at the wall seciton 9 projecting outwardly, producing the intermediate stepped back wall sections as the channel sections 8 of "normal" width.

The embodiment illustrated in Figures 2 and 4 shows the formation of the annular channel 7 as described by extending out the surrounding wall part of the lower base portion 3 of the female mould portion or mould contour. There, the inwardly projecting wall portions 11 stand opposite the recessed channel portions 10 and the stepped back or recessed wall sections 12 opposed the channel sections 8 of"normal11width.

It will be evident that the invention can be embodied in a variety of ways other than as specifically described, for example, as to the number and the relative peripheral and radial dimensions of the channel portions.

Claims

1. A hollow moulded article having a wall portion through which plastics material flows outwardly to the periphery of the wall portion, the wall portion being divided generally along the flow direction into parts of greater and lesser thickness.

2. A hollow article of synthetic material comprising a cylindrical portion, a base portion and an intermediate portion, therebetween, the intermediate portion providing an annular channel for flow of the material from an injection inlet to the cylindrical portion during injection moulding of the article and having alternating parts of greater and lesser thickness.

3. An article as claimed in claim 1 or 2 wherein the portion having the parts of greater and lesser wall thickness is of generally frusto-conical, the base portion being recessed within an end of the cylindrical portion.

4. An article as claimed in claim 1,2 or 3 having the parts formed as recesses in the inner surface of the portion.

5. An article as claimed in claim 1,2,3 or 4 having the parts formed as recesses in the outer surface of the portion.

6. An article as claimed in any preceding claim wherein the thickness of the parts of greater thickness correspond at last approximately to the thickness of the main wall of the article.

7. An article as claimed in any preceding claim wherein the peripheral dimensions of the parts of greater and lesser thickness are substantially equal.

8. A hollow moulded article substantially as herein described with reference to Figures 1 and 3 or Figures 2 and 4 of the accompanying drawings.

9. A mould for injection moulding of a hollow article having a wall portion constituting an annular channel for the flow of material from an injection opening during the moulding process, the mould having spaced opposed surfaces shaped for forming the wall portion with parts of different thickness adjoining each other generally along the flow direction.

10. A mould as claimed in claim 9, wherein the opposed surfaces are shaped to form alternating channel parts respectively of greater and lesser thickness.

11. A mould as claimed in claim 9 or 10 comprising male and female mould elements, the male mould element having projecting formations shaped to define the narrowed channel parts.

12. A mould as claimed in claim 9, 10 or 11 comprising male and female elements, the female element having projecting formations shaped to define the narrowed channel parts.

13. A mould as claimed in claim 9, 10,11 or 12 wherein the opposed surfaces define main wall portions of the article of substantially the thickness of the thickest channel part.

14. A mould substantially as herein defined with reference to Figures 1 and 3 or Figures 2 and 4 of the accompanying drawings.