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July 26, 1999

4 Min Read
Moulds that work, No. 3:  Four-Cavity Injection Mouldfor a Polyamide Joint Element

Editor´s note: This issue´s featured mould was designed by Plastor S.A., Oradea, Romania.

The injection mould described here is used for producing joint elements shaped like pipe fittings with four socket openings. This tubular frame, when covered with PE film, makes a mini-greenhouse for young plants. Two of the joint’s four socket openings form a through-hole. The other two openings are located in the plane perpendicular to this hole such that their axes enclose an angle of 84°. The 84° branch contains a rib with a hole, into which a string can be drawn to tension the assembled frame.

Mould Design

The mould, with external dimensions of 560 cm by 560 cm and a height of 345 cm (Figures 3 to 14), is designed as a four-cavity mould such that the cavities enclosing the 84° angle lie within the parting line, whereas the through-hole extends in the direction of the mould opening.

The four mould cavities formed in the mould insert plates (12, 13) are arranged in the parting line in such a way that each two mutually parallel cores of a pair of cavities can be actuated by a common core puller. Six slides are thus available for pulling eight cores.

The core slide-bars (24, 28) run on the mould plate (6) in guides (35, 38) and on slide rails (32, 36). The closed slide-bars are locked by locking wedges (21, 30). Angled rods (22, 29), which are fixed to the mould plate (5) on the feed side, engage in the slides and actuate them as the mould is opened and closed. Ball detents (33) secure the position of the opened slide-bar when the angled rods are moved out of the slides. The core inserts (18, 31) are fixed in the slides by means of cylindrical pins (40, 42).

Because of the large number of slides, the clamping area of the mould is very large compared with the closing area between the mould insert plates (12, 13), which is determined by the mould cavities. To ensure uniform loading of the parting line during closing, stop buffers (37) are mounted on both mould plates (5, 6).


The moulding compound is fed via a sprue gate in the sprue bushing (15) and via cruciform runners located in the parting line to the pin gates at the side walls of the four cavities.


To cool the cavities, cooling bores are incorporated into the mould insert plates (12, 13). All four cores of each mould cavity are efficiently cooled by means of a central bore containing an inserted separating wall (17, 39, 41). The seat surfaces of the core inserts are sealed by rubber rings. The cores inserted into the slides are supplied with water via connection pipes (23) and flexible hoses. The water for the fixed cores is fed and discharged via bores in the respective mould plates lying below the cores.


When the mould opens in the parting line C-D (Figure 4), the mouldings remain on the ejector side, where they are first held by the core slide bars. This pulls the mouldings off the cores (16) on the feed side and out of the cavity parts. The sprue gate is demoulded by the sprue puller.

During the opening action, the slides are pushed outwards by the effect of the angled rods and pull the cores located in the parting line. During this process, the mouldings are still held firmly by the cores (25) at the ejector side. Finally, cavity ejectors (4) (three per mould cavity) and the sprue ejector (9) eject the moulding completely.

As the mould closes, ejector-plate return pins (11), which strike against buffer pins (14), push back the ejector plates, and thus the cavity ejectors and sprue ejector. The core pullers are brought back into the injection position by the angled rods. The mould is operated semi-automatically.

The prime objective in describing this injection mould was to demonstrate the arrangement and operation of the core pullers. To save sprue material, it would, of course, be possible to use a hot runner nozzle instead of the spherical sprue bushing. It would then be possible to separate the mouldings from the cruciform sprue automatically by means of tunnel gates.

Contact Information
Plastor S.A.
Mr. Ion Seres
Calea Clujului 175
RO-3700 Oradea
Phone: (40) 59 418444
Fax: (40) 59 470048

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