WO2002090084A1

WO2002090084A1 - Magnetic ejector link in injection moulding machine

Info

Publication number: WO2002090084A1
Application number: PCT/GB2002/002140
Authority: WO
Inventors: Phil Bloomfield
Original assignee: Magnaforce Uk Ltd; Phil Bloomfield
Priority date: 2001-05-09
Filing date: 2002-05-09
Publication date: 2002-11-14
Also published as: GB0111260D0; EP1392487A1

Abstract

A magnetic link connectable in an injection moulding machine for plastics, between an ejector withdrawal system and ejectors for the moulded product, the link being switchable between a position giving an attractive magnetic force allowing normal withdrawal of the ejectors but yielding if the ejectors seize, and a free position without that force, allowing ready separation of the link for mould changes or other work on the machine.

Description

MAGNETIC EJECTOR LINK IN INJECTION MOULDING MACHINE

The invention relates to injection moulding machines.

An injection moulding machine basically holds an injection mould closed between two platens, under considerable pressure and lock. It then allows molten plastics to be injected, under high pressure, into the mould. The mould halves are kept together while the plastics cool to solid, then the mould opens and the machine ejects the part/s by means of ejectors moving in relation to the mould-half carrying the cooled moulding.

To enable the machine to perform the ejection operation, followed by withdrawal of the ejectors to their rest position, a mechanical link is made to the ejectors from an ejection system on the machine, often by a simple threaded rod with locknuts or alternatively with a "quick coupling" of the mechanical type. This coupling remains engaged during the moulding cycle, though it must be released each time the mould is changed, to be reconnected to the next mould.

From time to time the link or coupling fails. This failure can be caused by the ejectors beginning to seize up, preventing their withdrawal and causing the coupling itself to fail. The damage caused requires major work to the mould and extensive repairs to the ejection system.

In considering these points we have sought a "fail-safe" connection between ejectors and ejection system, firm but at the same time quickly operated, and have realized that "switchable" magnets, known in themselves, afford an ideal solution.

The invention therefore lies in a magnetic link connectable in an injection moulding machine for plastics, between an ejector withdrawal system and ejectors for the moulded product the link being switchable between a position giving an attractive magnetic force allowing normal withdrawal of the ejectors but yielding if the ejectors seize, and a free position without that force, allowing ready separation of the link for mould changes or other work on the machine.

A suitable link is provide by a permanent face-magnet in contact with a steel disc or end plate, connectable between the withdrawal system and the ejectors, the magnet being switchable between a weak attraction, conveniently one separable by hand, and a strong attraction, for example 100 kg separation-force at "break" point.

Also within the invention is the injection moulding machine when provided with such a link and a kit for making such a link. Such a kit comprises the magnet, an end plate for opposition to the magnet, and means for mounting magnet and end plate in the machine one to the withdrawal system and the other to the ejectors. In particular the kit may comprise one or more alternative end plates and, correspondingly, one or more alternative attachments for the rear of the magnet, to receive different threaded bars or other mounting means in different machines .

By using the "break" point as a safety feature-, whereby if the pulling force required to move the ejectors goes above a set limit the magnet pulls off the tool, extensive damage to the mould and ejectors in seizure is avoided and damage to the machine does not occur.

The link or coupling was developed at shop floor level primarily to eradicate expensive downtime on the machine when failures occur but also to speed up removal and installation of the mould at tool change. By connecting the mould to the machine ejection system via a magnetic field at a known pull off value the invention gives a "fuse" or fail-safe link. Should anything fail in the mould or the machine the link will part and stop the machine cycle, preventing any further damage. The pulling force or "break" point can be tailored to requirements and there is also the option of a built in sensor to detect failure in the connection should it occur.

When the mould is changed, often the next mould is a different size/shape. This means that the technician must find the necessary parts to connect the next mould. This can take some time, but by installing the new link or coupling it is possible to connect to any mould tool at the throw of a lever or switch. As moulds can weigh up to 20 tonnes or even more, a ready coupling to the system that provides for product ejection is important. Further, the links can readily be designed to allow some misalignment correction. Machines in the 40 to 350 tonnes size range and greater can for example readily be accommodated, when a few millimetres alignment tolerance makes all the difference. The system, which aids moulders by simplifying the linkage process has the following benefits for the moulder and setter:

*It reduces down time of the tool *Magnetic contact will break, not the tool *Easy to install/Locate on tools *No possibilities of injuries to operator ^Reduces Location/Coupling errors *Connects and locks at the flick of a switch

The link has been tested on an 'Instron' test rig for its optimum breaking load and for operating temperatures up to for example 260°C. Successful trials have also been carried out on a standard injection moulding machine (Battenfeld) left to run dry cycling and on a production run of test plaques for several days. The Hnk worked as a ram as well as a link mechanism, and performed very well.

A preferred embodiment of the invention is described with reference to the accompanying drawings in which:

FIGURE 1 shows the magnet, pull back force one hundred kg, and the pin and knob which switches it between on and off; The Figure includes side and. face elevations of one embodiment Mid a face elevation and section of a slightly different embodiment.

FIGURE 2 shows a fitting kit, with magnet;

FIGURE 3 shows the system fitted to the ejectors on an injection moulding machine;

FIGURE 4 shows a fitted system in slightly more detail; and

FIGURE 5 shows an overall view of a fitted system. Summary

The embodiment described comprises a switchable magnet, a fitting kit and a ejector bar. It is to replace a simple threaded bar, which joins the mould tool to the machine ejector system. The threaded bar has a history of breaking and damaging the machine and mould tool, costing money and time. The new system will part if the tool seizes up, stopping more damage to the mould tool, ejectors and the machine.

Fitting

Briefly, to fit the system the operator centres the mould on the fixed platen of the machine; the moving platen is closed on to the mould tool; the ejector bar of the mould tool meets the magnet; and the lever is moved to lock the ejector bar. The system is then ready to be used.

Before fitting the system the operator makes sure that the moulding machine ejector plate is at the back position, then he should:-

1. Ensure that all parts are in the fitting kit.

2 Check what injection moulding machine it is to be fitted to.

3. Check what size thread the ejector system is on the moulding machine and on the mould tool.

4. Check and fit the system to the machine.

5. Check and measure the ejector bar length as per standard setting procedure.

6. Fit the mould tool to the machine, ensuring the magnetic faces are free of oil and grease. 7. Close the moving platen until contact is made with the back plate of the mould tool.

8. Ensure that the two halves of the system are in contact.

9. Swing activation lever.

10. Unscrew activation lever and store for added security, if required. Detailed Description

lϊi the drawing of Fig. 1 is shown the magnet with body 1 and brass inserts at 2 at 90° spacing. The second drawing in the Figure shows the face view of the magnet, the third the face view with internal parts indicated. A removable operating knob 3 switches the magnet, by a simple mechanical movement on known principles, between an "off position (dotted knob-outline in the first drawing of the Figure) at which an end cap or plate can be readily slid off by hand or by a light pull in the assembled machine, and an "on" position in which it is immovable by hand, having a 100 kg straight-line pull back separation force. The movement of the knob 3 is over a 45° arc as shown, through a pin passing body slot 4 and moving a centrally pivoted "switch" plate (4a in the section) between the "on" position at which powerful rare-earth permanent magnets housed in the body exert a strong external attractive force and the "off position in which they do not. The switch plate magnets, seen in dotted outline in the third drawing of the Figure, are stronger than those in the body and cancel out their effect in the 'off position. Tapped holes 5 are provided for fixing a mounting collar. The dimensions for this 100 kg break-load magnet are overall diameter 75 mm, thickness 38.5 mm, with brass inserts of outside diameter at the contact face 25.5 mm, internal diameter 16.5 mm.

For fitting to most moulding machines a kit is suitably provided with 16 and 20 mm threaded ejector bars; 16 and 20 mm threaded end caps faced for magnetic contact; the magnet itself; and 16 and 20 mm threaded inserts for a universal fitting collar bolted in use to the back of the magnet. The parts are shown in Fig. 2, including the magnet with its body 1 and contact face 10. The magnet carries a cable 7 for a proximity sensor for warning of any separation of the link in service. End cap 8, threaded for the bar (not shown), is faced at 9 for good magnetic contact with contact face 10. At the rear of the magnet collar 11 is secured by four screws 12 entering tapped holes 5. This collar retains alternative inserts 13, threaded like end cap 8.

The link is shown in use in Figs. 3 to 5, mounted in injection moulding machines of known kind schematically drawn. Referring to Fig. 3 the machine platen is broadly referenced 14 and the mould tool at 15. The ejector system uses a hydraulic jack 16 acting on an ejector withdrawal bar 17 through a guide plate 18 running on slide bars 19.

In Figs. 4 and 5 the parts are similar but in Fig. 4 the tool or mould half 15 is shown more fully, with a guide plate 22 through which the withdrawal bar runs to pass through the mould half 15 to ejectors 20. In Fig. 5 the opposing half 21 of a mould is seen with the mould half 15 ommitted but the platen 14 in the position it reaches in the first stage of release of a finished moulding.

Claims

1. A magnetic link connectable in an injection moulding machine for plastics, between an ejector withdrawal system and ejectors for the moulded product, the link being switchable between a position giving an attractive magnetic force allowing normal withdrawal of the ejectors but yielding if the ejectors seize, and a free position without that force, allowing ready separation of the link for mould changes or other work on the machine.

2. A magnetic link as defined in claim 1, comprising a permanent face-magnet in contact with a steel disc or end plate, connectable between the withdrawal system and the ejectors, the magnet being switchable between a weak attraction, conveniently one separable by hand, and a strong attraction, for example 100 kg separation-force at "break" point.

3. A magnetic link as defined in claim 1 or 2 comprising a sensor to detect separation of the link.

4. An injection moulding machine provided with a link as defined in any preceding claim.

5. A kit for making a magnetic link as defined in claim 2 comprising said magnet and end plate and means for mounting the magnet and end plate in the machine one to the withdrawal system and the other to the ejectors.

6. A kit according to claim 5, comprising alterative end plates and, correspondingly, alternative attachments for the rear of the magnet, to receive different threaded bars or other mounting means in different machines.