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October 6, 1998

6 Min Read
Moulds That Work: Challenging Part Ejection


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Editor´s note: This issue's featured mould was designed by Ellersiek & Schaminsky, Bunde, Germany, and built by Friedrichs & Rath, Extertal, Germany. It is moulding baskets for Miele dishwashers at Friedrichs & Rath.

Multiple compartment walls with a flexible grid-like structure, coupled with the high shrinkage of polypropylene, pointed towards a high ejection force requirement to strip a cutlery basket off the mould core. The complex part release and ejection control sequence in this mould are worthy of special note.


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Figure 1. Polypropylene cutlery basket.

The basket (Figure 1), with dimensions of 287 mm by 157 mm by 140 mm, is used to hold cutlery in a dishwasher. It is divided into 16 compartments by three partitions running lengthwise and crosswise. The outer walls and the bottom have a grid-like structure. In addition, two of the partitions have two openings, each 10 mm square. Special measures were taken to assure that the part could be ejected without being damaged in spite of its flexible grid-like structure.


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Figure 2. View of the ejector side. Key to Figures 2 to 6:
(2) Mould plate; (3) Stripper plate; (4) Core retaining
plate; (6) Ejector plates; (7, 8) Leader pins; (12) Contour-
forming insert; (18, 19) Slides; (20, 21, 29, 30) Support
blocks; (23) Hot runner system; (24) Locating rail;
(25) Core pin; (27) Push pin; (31, 32) Support rail;
(33, 34) Gibs; (37) Roller guide; (38, 39) Angled rods;
(40) Return pins; (41) Stripper bolts; (42) Blade ejector;
(43) Inhibitor pin; (47) Compression spring; (54) Stripper bar;
(57) Ball detent.

The Mould

The mould (dimensions: 596 mm by 496 mm by 687 mm; Figures 2 to 6) was largely constructed using standardized mould plates and latch locking units from Strack Norma, Wuppertal, Germany. Steel grade 1.2767 (hardened to 54 Rockwell C) was used for the part-forming components. The side walls of the basket are formed by four slides (18, 19, Figure 2) that move laterally in gibs (33, 34) mounted on the stripper plate (3, Figure 4). The slides are supported by heel blocks (20, 21, 29) located in mould plate (2) and, when the mould is closed, are held by additional support blocks and rails (30 to 32) in the stripper plate (3). When the mould is in the open position, the slides are held by spring-loaded ball detents (57) to prevent any unintentional movement. The slides are actuated by angled rods (38, 39) set at angles of 15° and 20°. An angle of 20° is used for angled rods (38) for the following reason: support block (30) serves also as a safety stop for the lower slide 18/1. If the angled rods were set at an angle of 15°, a collision with stop (30) would have resulted. For this reason, an angle of 20° was specified, with the result that, for the same stroke as the other slides, the length of the angled rod could be reduced.


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Figure 3. View of the injection side.

The part is filled via a hot runner system (23) using two valve gates located in the bottom of the basket. Eight circuits, comprising cooling channels in the slides, cavity inserts, and cores, provide for mould cooling.





Part Release and Ejection

The part release and ejection sequence is controlled by latches (Figure 6). Step 1. The mould opens at the main parting line (I) for a distance of 13 mm, because parting line (II) is initially held closed by latch (A). This releases the part from the bottom of the cavity (12). The slides (19, Figure 2) that form the short sides of the basket move outwards. This releases the core pins (25), which, by the action of the springs (47), retract from the openings in the partitions. The two remaining slides (19) that form the long sides of the basket (Figure 4) do not move at first, because the bores for the angled rods (39) have 3.5 mm play.


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Figure 4. Section E-E.

Step 2. Latch (A) releases parting line (II), while latch (B) locks parting line (I) at an open position of 13 mm. As parting line (II) opens a distance of 10 mm, the slides retain their position with respect to the moulded basket. The as-yet unopened slides (19) firmly hold the long walls of the basket, so that it is now stripped 10 mm off the core. Simultaneously, the stripper bolts (41) attached to stripper plate (3, Figure 4) advance the ejector plates (6) by this same 10 mm, thereby bringing the blade ejectors (42) as well as the stripper bar (54) into contact with the basket and supporting the part release operation.

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Figure 5. Section D-D.


Step 3. Latch (B) locks parting line (II) at the 10-mm position and releases parting line (I) fully. All four slides separate, releasing the moulded part completely.


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Figure 6. Latch control mechanism.

Step 4. The ejector plates (6) are moved for the remaining distance by the machine's ejector. The blade ejectors (42) and the stripper bars (54) strip the basket entirely off the mould core. The positions of the ejector plates, and thus of the blade ejectors and stripper bars, are monitored by proximity switches. To prevent mould damage during setup or in the event of a malfunction of the ejector mechanism, a mechanical safety is also incorporated.

First, the ejector plates are not allowed to be actuated until the mould has opened far enough to permit the part to be stripped off the core completely. To this end, the ejector plates (6) have inhibitor pins attached to them (43, Figure 4) that prevent movement of the ejector system until the bores (S) in the slides (19) line up with the pins (43). Once the slides, and thus the mould, have opened sufficiently far, the pins (43) can enter the bores (S), and the ejectors can advance.

Then, in order to prevent the ejectors from damaging the bottom of the cavity and also to avoid jamming the stripper bars into the slides, the mould is not permitted to close until the ejectors are fully retracted. To this end, the inhibitor pins (43) that have entered the bores (S) in the slides (19) prevent closing of the slides as long as the ejector system is not retracted. As the mould closes, parting line (II) closes before parting line (I) is fully closed. This prevents the core pins (25) from scuffing the contour-forming cores as the slides (18) close completely. Return pins (40) assure that the ejectors are in the fully back position.

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Contact information
Ellersiek & Schaminsky
Mr. J. Ellersiek
Im Uhlenbrock 11
D-32257 Bunde, Germany
Tel: +49 (5223) 62782
Fax: +49 (5223) 64155

Friedrichs & Rath GmbH
Mr. Süllwold
Papenweg 6
D-32699 Extertal, Germany
Tel: +49 (5262) 403 0
Fax: +49 (5262) 403 59

Strack Norma GmbH
Mr. Wolfgang Markowski
Post Box 100280
D-42002 Wuppertal,
Germany
Tel: +49 (202) 385 140
Fax: +49 (202) 385 110

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