WO2003055663A1

WO2003055663A1 - Process for injection-molding, in thermoplastic material, of the proformer for producing blown receptacles

Info

Publication number: WO2003055663A1
Application number: PCT/IT2002/000034
Authority: WO
Inventors: Pierluigi Molgora
Original assignee: Ommp S.A.S. Di Molgora Pierluigi & C.
Priority date: 2001-12-20
Filing date: 2002-01-21
Publication date: 2003-07-10
Also published as: ITMI20012705A1; AU2002232140A1

Abstract

Process for injection molding, in an injection press or in installations comprising an injection press and blower, of the preformer of thermoplastic material for producing blown receptacles, with an injection mold (40) that presents the part, necessarily movable to permit it to open on completion of molding, comprising two or more elements (41, 42) that may be constructed of aluminium alloys, light alloys in general, translating radially, when the die (40) opens, in relation to the XX axis of the preformer.

Description

Process for injection-molding, in thermoplastic material, of the proformer for producing blown receptacles. The invention concerns the processes and machinery used in making what are known as "preformers" of thermoplastic material for the production of blown receptacles.

It is well known that a large proportion of blown receptacles of various types and dimensions are made in two stages: - injection molding of a tubular "preformer" with a closed bottom, the opposite end corresponding to the position of the "neck" of the receptacle that will be subsequently produced;

- blowing, with drawing if needed, this being a mechanical process to lengthen the suitably heated preformer axially, for insertion of the softened thermoplastic material inside a die having the shape of the final receptacle. This process is carried out with a single installation or with two:

- the first comprises an injection press and the injection die,

- the second comprises a heater of the preformer, a blower and dies for blowing.

From the above it follows that, at present, the processes for making blown receptacles are liable to the following drawbacks: - the design of the receptacle is conditioned by preformers that have "lined surfaces" and are conic in the direction of extraction from the injection die. A "lined surface" defines any surface produced by the movement, according to any law, of an ideal line whose various positions in space lead to "generation" of the lined surface.

- An opening stroke of the injection die of not less than two lengths of the preformer make it necessary to have injection presses with a longer opening stroke, or which in any case are oversized.

- Complexity of the preformer, the thickness of its parts being so calculated and situated as to enable radial, circumferential and axial drawing to be carried out after blowing in order that the blowing process may produce receptacles of the desired shape. The above disclosure eliminates these drawbacks and offers considerable advantages besides, as will be explained hereafter.

Subject of the invention is a process for molding the preformer in an injection press, or in installations comprising such a press, and with a blower, for the production of blown receptacles. The part of the injection die that must move on opening, comprises two or more elements which, when the die opens, can translate radially in relation to the axis of the preformer.

The preformer presents all the thicknesses for producing all the shapes obtainable by blowing and permitted by the presence of the translating elements.

The opening stroke of the die is reduced to a length only slightly greater than that of the preformer.

According to requirements, the preformer can present:

- a surface that is lined and conic only or, at the most, cylindrical in the direction of extraction;

- a surface lined and conic only in the direction opposite to that of extraction; - an unlined surface;

- a surface with undercutting, projections and the like, in a direction radial to the axis of the preformer for purposes that are functional, such as making handgrips, hooks, handles and others, and decorative.

In one type of execution the mobile parts of the die, especially in those that can move radially in relation to the axis of the preformer, are constructed of aeronautical aluminium alloys or of other light alloys. The invention clearly offers the following advantages. In the preformers: the possibility of having preformers with outer walls of the following shapes:

- a surface lined and conic only in the direction of extraction, or cylindrical,

- a surface lined and conic only in the direction opposite that of extraction,

- an unlined surface with any type of undercutting, projection and external motif for effects both functional, such as a handgrip, and ornamental.

In the injection press: the possibility of drastically reducing the opening stroke of the die for extracting the preformer and therefore of being able to use a standard press instead of one with a longer opening stroke or one that is oversized. In the injection die: the possibility of reducing bulk and therefore the weight of the die by replacing parts in steel with others of an aluminium alloy. In the economy of production: benefits regarding speed of translation, less wear on the die and on the machine, and in operational economy by removal of shavings. The present invention therefore secures advantages regarding the preformer, and consequently the blown receptacle, by offering a greater variety of shapes both for functional and decorative purposes. These advantages are felt both when the preformers are made using an injection die in an injection press, and when a single installation is used for production of the preformer by injection and formation of the receptacle by blowing.

Characteristics and purposes of the disclosure will be made still clearer by the following examples of its execution illustrated by drawings some of which are diagrammatic.

Fig. 1 A known type of die for injection molding of preformers for making blown receptacles, perspective view showing the top end of the preformer. Fig. 2 A longitudinal section of the die in Figure 1.

Fig. 3 A diagrammatic drawing of the preformer being extracted from the die in Figure 1.

Fig. 4 Perspective view of the invented die showing the lower end of the preformer. Fig. 5 Perspective view from above of the preformer made with the die in Figure 1.

Fig, 6 Longitudinal section of the preformer.

Fig. 7 Male of the die for making the preformer in Figure 7.

Fig. 8 Diagram to show extraction of the preformer when the die, subject of the invention, is being opened.

Fig. 9 Perspective view from above of a preformer with projections for functional purposes.

Fig.10 A side view of Figure 9.

Fig.11 A longitudinal section of the view in Figure 9. Fig.12 Preformer with longitudinal ribbing, perpsective from above.

Fig.13 A longitudinal section of the preformer in Figure 12.

Fig.14 A side view of the preformer in Figure 12. Fig.15 Perspective view of a preformer from above, showing the circumferential ribbing.

Fig.16 A side view of the preformer in Figure 15.

Fig.17 A longitudinal section of the preformer in Figure 15. Fig.18 A preformer with handles at the top, perspective from above.

Fig.19 A side view of the preformer in Figure 18.

Fig.20 A longitudinal section of the preformer in Figure 18.

Fig,.21 A preformer made by the process subject of the invention inside a blowing die to produce the shape of the blown receptacle, a longitudinal section.

One half of a die 10 of the usual type presents the impression 11 with its bottom 12 and flange 13 fixed by screws 15 on the die, for injection molding of a preformer 20 with a lined surface 21 and semispherical bottom 22. On opening the die extraction of the preformer 20 is eased by the lined surface 21 slightly conic in the direction of extraction and by the absence of undercutting.

Figure 4 shows the die 40 subject of the invention.

The two halves 41 and 42 of the die can be seen, these being mobile in relation to the structure 30 and guided by the bars 43 of the half die 41 that slide into holes 44 in the half die 42.

The die impression comprises two half impressions 50 and 55 respectively provided with flanges 51 and 56 fixed by screws 57, and the male 58 with its end 59. The preformer 60 (Figure 5) presents a semicylindrical body with lined surface 61 and the top 63 with its annular projections 64, raised band 65, raised annular rim 66.

Wall thickness is generally variable (Figure 6); this in order to give greater thickness where, during blowing, the material undergoes a stronger radial and circumferential pull, and where it is desired to give greater thickness to the blown receptacle. The different wall thicknesses 66, 67, 69 are obtained by a male 70 having parts 72-74 of different diameters that increase from the bottom 71 to the top (Figure 7).

As will be seen from the diagram of the die in Figure 8, the stroke (A) made by the mobile die half 81 in relation to the base 82, is slightly greater than the length (B) of the preformer 60 due to radial movement, in the direction opposite to the preformer's axis XX, of the mobile parts 83, 84 of the die.

Figures 9-11 show a preformer 90 with radial projections 91-93 of differing diameters, the top 94 having an upper ring 95, band 96 and rim 97 made by undercutting.

Figures 12-14 show a proformer 100 which, compared with the previous one, presents longitudinal ribs 105 on a wall 106 of constant thickness. Figures 15-17 present a preformer 100 with annular ribbing, continuous 112 and set at intervals 113, on a wall 111 of constant thickness.

Figures 18-20 illustrate a preformer 120 having a wall 121 of constant thickness, and having handles made by undercutting 122 at the top.

Figure 21 is a diagram to show formation of a receptacle 135 by blowing a preformer 130 having undercutting at the top 131-133 produced by the die 40, subject of the invention, inside a mold 140.

Claims

1. Process for injection-molding, in thermoplastic material, a preformer for the production of blown receptacles, in an injection press or in an installation comprising an injection press and blower , characterized in that the injection die (40) presents a part, necessarily movable in order that the die may open on completion of molding, comprising two or more mobile elements (41 , 42) translating radially in relation to the axis XX of the preformer when the die (40) opens.

2. Process as in claim 1 , characterized in that the preformer (60) may present all the thicknesses needed for the shapes (61 , 90, 100, 120, 135) that it is desired to obtain by blowing, permitted by the presence in the die of the two or more elements (41 , 42) translating radially in relation to the XX axis of the preformer when the die opens.

3. Process as in claim 1 , characterized in that that stroke A for opening the die presents a length slightly greater than length B of the preformer.

4. Process as in claim 1 , characterized in that the preformer presents a surface only lined and conic or, at the most, cylindrical in the direction of extraction.

5. Process as in claim 1 , characterized in that the preformer presents a surface only lined and conic in the direction opposite to extraction.

6. Process as in claim 1 , characterized in that the preformer (60) presents an unlined surface

(63-66).

7. Process as in claim 1 , characterized in that the preformer (90, 100, 120) presents a surface with undercutting (64-66, 91-93 95-97, 105, 112, 113, 122,

131-133), projections (91-93) and the like, in a radial direction in relation to its axis, to obtain functional effects such as handgrips (22), hooks, handles and the like.

8. Process as in claim 1 , characterized in that the preformer (90, 100, 120) presents a surface with undercutting (64-66, 91-93, 95-97, 105, 112, 113, 122, 131-133), protuberances and the like, in a radial direction in relation to its axis, to obtain ornamental effects.

9. Process as in claim 1 , characterized in that the movable parts (41 , 42) of the die (40), especially those able to make a radial movement in relation to the axis of the preformer, are constructed of aeronautical aluminium alloys, light alloys in general.

10. Injection mold (40) with the part that is necessarily movable to permit it to open on completion of molding, characterized in that it comprises two or more elements (41 , 42) which, when the die opens, translate radially in relation fo the axis of the preformer.

11. Mold (40) as in claim 10, characterized in that its mobile parts, especially those (41 , 42) made so as to move radially in relation to the axis of the preformer, are constructed of aeronautical alloys, light alloys in general.