GB2179583A - Collapsible mould core - Google Patents

Abstract

The core comprises three relatively movable assemblies (10, 110 and 120). The first assembly carries a cone (14), the second assembly carries an inner set of fingers (116) which form part of the core surface and engage the cone and the third assembly (210) carries outer fingers (216) moved by inclined pins (118) on the second assembly. As the assemblies are moved together the outer fingers move radially outwards and the inner fingers move axially in between them. Then the inner fingers move radially outwards and the cone fills the centre of the core. On reversal of the movement, the core is collapsed to enable it to be withdrawn from the moulded article. <IMAGE>

Description

SPECIFICATION Collapsible mould core The present invention relates to a collapsible core for a mould.

When moulding an article such as a canister with an inwardly directed lip, if the lip is only small and the plastics material is stretchable then the moulded canister can be forced off the core. If however the lip is more pronounced or the plastics material cannot stretch without damage then it isnecessaryto reso rt to a col lapsi ble core.

There are known collapsible cores which when assembled present a cylindrical surface about which the article may be moulded but which can be collapsed for withdrawal from the moulded article. The known collapsible cores comprise three main components. Two of the components are rings of axially extending fingers, the fingers of one ring being interdigitated with those ofthe other. When interdigitated, the two sets of fingers define a continuous annulus and a centre component slidably disposed within the annulus completes the cylindrical shape ofthe core.The mating surfaces of the fingers ofthe two rings are inclined to radii of the cylinder in such a manner that when the cylindrical centre component is axially withdrawn, it is possible to move the fingers ofthe inner ring radially inwardly byasufficient amounttoenablethemtocleartheliponthe moulded article so that they may be withdrawn. After the innerfingers have been withdrawn, it becomes possible to move the outer ring of fingers radially inwards so that they too may be withdrawn.

The fingers of each ring are usually resiliently mounted atone end on a common support so that they may flex in order to clear the obstruction presented by the lip on the moulded article.

The above arrangement has several disadvantages which will now be considered. First, because the fingers are pivoted on a common support, the amount of movement permissible next to the support is minimal and this places a severe con straintonthedepth ofthe lip on the moulded article.

A second consideration, which seriously affects the cycle time ofthe moulding machine and the complexity of the mechanism necessary to operate an injection moulding machine automatically, is that the inner set of rings cannot be collapsed radially until the centre has been totallywith- drawn axially and furthermore the second set of fingers cannot be collapsed inwards until the first set of fingers has been fully withdrawn. The travel required therefore to permit the moulded article to be extracted from the mould amounts to twice the length ofthe article or, put differently, the length of the core mechanism when the moulded article can be withdrawn is three times its length when the core is in the mould.In the case of some articles, such as a five litre paint tin, this amount oftravel cannot readily be accommodated, but in any event the time taken towithdrawthecompo- nent parts ofthe collapsible core sequentially from theinteriorofthemouldedarticlewould be excessive and not commercially viable. Of course, if this withdrawal of the collapsible core is to be carried outautomaticallythen the control system must be designed to ensure thatthethree phases are carried out sequentially and this results in undue complexity which is reflected not only in increased cost but also in reduced reliability.

The present invention seeks to provide a collapsi blecorefora mould which mitigates at least some of the foregoing disadvantages.

According to the present invention, a collapsible core for a mould comprises an inner and an outer set of interdigitated fingers which togetherdefine a continuous annulus and a centre dis posedwithinthesaidannulustocompletethesurface of the collapsible core, the centre a nd the sets offingers being axially movable relative to one another, characterised in that the centre has a conical outer surface and in that the fingers are provided with guiding means for moving the fingers radially simultaneously with their axial movement relative to one another and relative to the centre.

Preferably, the collapsible core comprisesthree assemblies movable relative to one another in the direction of the axis of the core, the first assembly supporting the conical centre, the second supporting one set of fingers and the third supporting the second set of fingers, each set of fingers being mounted for radial sliding movement on a supporting plate and the guiding means serving to cause radial sliding ofthefingers in synchronism with relative movement of the assemblies.

Advantageously, the assemblies are connected to one another by a mechanical mechanism capable of ensuring correct synchronisation oftheir movement.

Conveniently, the mechanism for synchronising the movement of the assemblies comprises a cam supported by the centre assembly and cam followers on arms, pivotably arranged in the manner of lazy tongues, on the other two assemblies.

Because the radial movement and the axial movement of the fingers occur simultaneously, and because the centre is conical ratherthan cylindrical, it is not necessaryforthe centre to clearthe fingers before the latter can commence radial movement. The radial collapse of the core is there- fore no longer dependent upon the length of the core.

A much shorter stroke suffices to clearthe lip on the moulded article and the extent of movement necessary is determined solely by the depth ofthe lip to be cleared.

It can also be seen that by a simple mechanism linking the movements of the assemblies to one another all the correct synchronisation necessary can be achieved.

Because the fingers are guided for radial move mentand do not flex, the fingers need not be of spring material and no limitation is placed on the extent of their deflection to clear the obstruction presented by the lip on the moulded article. As the fingers move radially along their entire length, it is also of little consequence whether the lip on the article is nearthe open or closed end ofthe moulded article.

It is particularly preferred that the fingers should be moved by a mechanical interaction with the movement ofthe assemblies, for examplethrough gearing, cams or guides, so thatthe onlyforce required to collapse and expand the entire core is that required to move the assemblies apart and together.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure t is a partial exploded view of a collapsible mould core ofthe invention, Figure2showsdiagrammaticallythe linkagefor assuring synchronised movement of the three assemblies of Figure 1, and Figure 3 shows the end surface of the mould core.

In Figure 1 ,the collapsible mould core of the invention comprises three relatively movable assemblies which are generally designated 10,110 and 210. Each ofthe respective assemblies includes a plate 12,112 and 212,thethree plates being accurately guided for movement relative to one another in a synchronised manner to be described below. The plates are guided for axial movement by means of rods secured to the plate 12 and bores in the othertwo plates but these are omitted from the drawings in the interest of clarity.

The first plate 12 carries afixed cone 14 which is formed with threetenons 16 equallyspaced around the circumference of the cone 14. The tenons 16 are grooves of T-shaped cross-section so that a matching slider introduced into the tenons can slide along the tenons but cannot be withdrawn radially. A lead-in portion 16a is provided for introduction of such sliders into the tenons.

The axial end face 18 ofthe cone 14forms the central partofthe collapsible mould core surface.

The plate 112 of the assembly 110 has three radially extending guide slots 114symmetrically surrounding a central aperture 115 and aligned with the tenons 16. Only one such guide slot 114 is shown in the interest of clarity, the other two being identical and being represented only by dotted lines.

Each guide slot 114 has slidably received within it the base 116a of one ofthe innerfingers 116 which define part of the surface of the collapsible mould core. Each base 1 16a has a slider 1 16c received in the respective tenon 16 of the cone 14 of the assembly 10, and a T-section received in the slot 114. The result of moving the plate 12 towards the plate 112 isthatthe inner fingers 116 move radially outwards along their respective slots 1 14astheyslide along the tenons of the cone 14.

The surfaces of the fingers 116 which form part of the mould core are their axial end faces 11 6b andasurface 116which hastheform of a tapering segment of a cylinder, the angle subtended by the segment atthe axis becoming smallerwhen mov ingtowardsthefree axial end ofthefinger.

The radially inner surface of each innerfinger is a part conical surface matching the cone 14 when the two plates 12 and 112 are fully collapsed against one another.

The side faces 11 6e ofthe innerfingers 116 also taper radially outwards as can best be seen from Figure 3, so that once the cone is withdrawn they may collapse radiallywithout interference from the outer fingers to be described below.

Three angled guide pins 118 (again only one is shown) are provided one diametrically opposite each of the slots 114. The purpose ofthe guide pins 118 will be clear from the description of the third assembly210.

The third assembly 210 comprises two plates 212, 214secured to one another. The plate 212 has three slots 215 symmetrically surrounding a central aperture 217 and aligned with the guide pins 118. The slots 215 receive the bases 216a of three outer fingers 21 6 so thatthe latter may slide radially.

The bases 216a which slide along the slots 215 are formed with angled holes 219 receiving the angled pins 118 so thatthe radial movement of the outer fingers is effected by the axial movement ofthe plates 112 and 212 relative to one another.

Eachouterfihger2l6hasanendsurface2l6b which forms part of the end surface ofthe collapsible mould core (see Figure 3). The outercylindrical surface 216d is part-cylindrical and tapers towards the plate 212, that is to say its circumferential extent increases towards the free end in a manner complementaryto the tapering ofthe innerfingers 116. The inner cylindrical surface 216c matches the surface ofthe cone when the assemblies abut one another to complete the surface of the core in the manner shown in Figure 3.

Similarly, the side surfaces 216taper inwards as best shown in Figure 3 to perm it the inner fingerto collapse by moving inwards radially.

The plate 214forms one end surface of the mould and its thickness extends to a return portion 218 ofthe fingers 216, the return portion being responsiblefortheformation ofthe lip on the end ofthe moulded article.

Let it now be assumed that the three assemblies are collapsed into one another to the maximum possible extent with the sliders 11 6c received in the tenons 16 and the guide pins 118 received in the holes 219 in the bases 21 6a of the outerfingers 216. The lengths of the cone 14, the inner fingers 116 and the outerfingers 216 are such that in this position their end surfaces are flush with one another and mate accurately to define the end surface of the core as shown in Figure 3. The cylindrical surface ofthe core is formed by the outer cylindrical surfaces of the inner and outer fingers 116 and 216, respectively. At the end ofthe cylindrical outer surface of the core a small return or reduced diameter portion is formed bythe return portions of the fingers but such a reduced diameter portion may be formed wherever desired along hte length of the fingers and need not necessarily be at the end.

During use, the outer part of the mould (not shown) surrounds the collapsible core to form a mould cavity having inthecaseoftheexampleillus- trated the shape of a paint canister. After an article has been moulded the core must be collapsed so that the part of the article moulded into the return portion may clear the largerdiameterouter surface of the core. This operation is carried out by moving the three assemblies apart.

First, the assembly 10 is moved away from the other two assemblies without any movement between the assemblies 110 and 210. As the cone 14 is retracted, the sliders 116 slide along the tenons 16 and move radially inwards. Because the inner finger 116 taper outwards when viewed axially, they are unimpeded in their movement by the outer fingers. Thus it is seen thatthe inward movement of the innerfingers occurs simultaneously with the withdrawal of the central cone.

When the innerfingers have cleared the obstruction presented by the lip on the moulded article, they may be withdrawn axially, even though the cone has not yet been fully withdrawn from the centre. Thus, as soon as the innerfingers 116 have been radially moved in sufficiently, the two assemblies 110 and 210 are move apart. Because the inner fingers 116 taper lengthways these can now be withdrawn easily from the outer fingers 216.

Astheassemblies move apart,the pins 118 interact with the holes 219to move the outerfingers radially inwards and again it is noted thatthe inwards movement occurs simultaneously with the withdrawal ofthe innerfingers.

When the innerfingers have been fully withdrawn, the outerfingers will have collapsed radially sufficiently to allow the moulded article to be removed from the core without any obstruction.

The total amount of movement required is determined by the depth of the obstruction to be cleared, the angle ofthe cone 14andthe angle ofthe inclined pins 118. It is not dependent upon the axial length ofthe core. This is to be contrasted with the prior art arrangement wherein the centre was nearly cylindrical ratherthan conical and before the outerfingers could be collapsed firstthe centre had to be moved the full axial length of the core and then the innerfingers had to be moved by the same distance.

To effect the movement of the assemblies in the correct phase a linkage such as shown in Figure 2 may be employed. This linkage comprises a lazy tonguearrangementcomprisingfourlevers 310,312, 314 and 316. The levers 314 and 316 are connected by means of a common pin 315 to the plate 12. Similarly,the levers 310 and 312 are connected by a common pin 311 to the plate 212. The levers 310 and 314 are connected by means of a cam follower pin 313 and the levers 312 and 316 are connected by means of a second cam follower pin 317. The cam follower pins follow I-shaped cams320 and 322 carried bytheplate 112.

If the plate 12 is stationary and force is applied to the plate212, then firstthe pins 313,317 will followthe cams 320,322 so that little movement occurs between the plates 212 and 112 but these two plates are moved together away from the plate 12. When the pins reach the corners in the ca ms, the lazy tong ues col lapse inwards with no movement between the plates 12 and 112 but with the plates 112 and 212 being moved apart.

Thus by a single mechanism operating the lazy tongues, the assemblies are moved apart and together and the fingers are automatically moved in synchronism to assemble and collapse the core.

It will be noted that in the preferred embodiment described and illustrated in the drawings, each ofthefingers has a base intheform of sliderwhich is guided for radial I m ovement, th e end surface at the radially outer end of each slider being accessible in all positions ofthe mould. It is therefore possible to form in each finger passages for a coolant and flexible pipes may be attached to this surface ofthe fingers to act as supply and return pipes for cool ant. l n view of the I imited amount of movement of the parts of the core, there need not be excessive slack in the pipes and they do not risk becoming entangled in the mechanical parts ofthe mould.

It is further more possible to cool the cone 14 so that every surface in contact with the moulded article may be cooled by a circulating coolant.

It is therefore possible to increase the speed of cooling the moulded article and thereby reduce stillfurtherthecycletime requiredforthemoulding of each article.

Claims (7)

1. A collapsible core for a mould comprises an inner and an outer set of interdigitated fingers which together define a continuous annulus and a centre disposed within the said annulusto complete the surface of the collapsible core, the centre and the sets offingers being axially movable relative to one another, characterised in thatthe centre has a conical outer surface and in that thefingers are provided with guiding means for mov ing the fingers radially simultaneously with their axial movement relative to one another and relative to the centre.

2. A collapsible mould core as claimed in claim 1, wherein the core comprises three assemblies movable relative to one another in the direction of theaxisofthecore,thefirstassembly supporting the conical centre, the second supporting one set offingers and the third supporting the second set of fingers, each set of fingers being mounted for radial sliding movement on a supporting plate and the guiding means serving to cause radial sliding of the fingers in synchronism with relative movement ofthe assemblies.

3. Acollapsible mould core a claimed in claim 2, wherein the assemblies are connected to one another by a mechanical linkageforensuringcorrect synchronisation oftheir movement.

4. A collapsible mould core as claimed in claim 3, wherein the linkage for synchronising the movement of the assemblies comprises a cam supported by the centre assembly and cam fol lowers on arms, pivotablyarranged in the manner of lazy tongues, on the other two assemblies.

5. A collapsible mould core as claimed in claim 2 or any claim appended thereto, wherein the fingers ofthe second assembly engage in tenons in the conical centre of the first assembly and the fingersofthethird assembly engage inclined guide pins on the plate of the second assembly whereby the movement of the two sets offingers is automatically synchronised with the relative movement of the assemblies and wherebythe only force required to collapse and expand the core is that required to move the assemblies relative to one another.

6. A collapsible mould core as claimed in any preceding claim, wherein coolant passages are formed in the fingers and/or in the centre and wherein means are provided for circulating a coolant through the passages to cool the collapsible core.

7. A collapsible mould core substantially as herein described with reference to and as illustrated in the accompanying drawings.