GB2065018A - Manufacture of small plastics articles by injection moulding - Google Patents

Abstract

Small plastics articles, for example slide fastener components, are made on apparatus having an injection head, mould wheel 4 and mould band. This band is of composite construction and comprises a plurality of bands 7/8 or 5a/5b which move in parallel and incorporate moulding portions which serve as a mould core when they converge with mould cavities in the wheel 4. The plural bands are separable from each other subsequent to moulding to facilitate disengagement of the moulded articles and allow a greater variety of shapes to be moulded on such apparatus e.g. strip fasteners or their elements. <IMAGE>

Description

SPECIFICATION Manufacture of small plastics articles by injection moulding This invention relates to apparatus for and method of manufacturing small plastics articles by injection moulding with a thermoplastics injection head, a mould wheel and a mould band movable past the injection head and in which the mould wheel has mould cavities around its perimeterforthe small plastics articles, and the mould band partially embraces the mould wheel at least in the vicinity of the injection head. The invention is particularly but not exclusively concerned with moulding small plastics articles such as bottom and top stop components for slide fasteners which limit the movement of a slider during opening or closing of the fastener and also with slide fastener coupling members, stringers of coupling members, and with preliminary elements for forming into coupling members.

Apparatus is known for the manufacture of preliminary flat elements which are folded into U-shape to form slide fastener coupling members. The flat elements are united in the manner of a rope ladder by textile threads or cords introduced longitudinally through the mould cavities and consequently embedded in the flat elements. By means of these threads or cords the individual flat elements are connected into rows of elements which are lifted out of the mould cavities beyond the sector of mould wheel embraced by the mould bands. The mould band does not enter the mould cavities. The cavities are shaped without undercuts or the like, and form on the flat elements coupling head portions which are necessary in the slide fastener coupling members. This system does not permit the manufacture of individual articles not connected by threads or cords.

The invention is based on the problem of further developing apparatus of the type described to permit the manufacture of small plastics articles, eg slide fastener coupling members having undercuts or grooves, and of individual small plastics articles not connected by threads or cords. This does not preclude the provision of plastics bridges between the individual articles if the mould cavities are shaped accordingly, though such bridges merely define preferred breaking points when separating the articles.

According to one aspect of the present invention, apparatus for the manufacture of small plastics articles by injection moulding with a thermoplastics injection head, includes a mould wheel and a mould band movable past the injection head and in which the mould wheel has mould cavities around its perimeter for the small plastics articles, and the mould band partially embraces the mould wheel at least in the vicinity of the injection head and can converge on the wheel at a position before the injection head and depart from the wheel at a position after the injection head, the mould band comprising two or more partial mould bands movable in parallel and having mould portions which complement each other and engage in the manner of a mould core in the mould cavities of the mould wheel.

The mould band may be continuously rotatable.

The mould portions of the bands may combine to form ejection formations which have undercuts on their outer sides whereby the moulded plastics articles can be lifted out of the mould cavities when the mould wheel and mould bands are operating, and during their movement the partial bands are displaceable from each other and thereby releasable from the moulded articles.

The mould band may comprise two partial bands with ejection formations which are separable at inclined planes and thereby movable relatively to each other. Alternatively, the mould band may comprise three or more partial bands with ejection formations and meet at mating surfaces extending orthogonally to the plane of the mould band, or are disposed in wedge fashion relative thereto and are movable relatively to each other. This use of three or more partial bands allows greater scope in the design of moulded articles to be produced.

In order to displace the partial bands with respect to each other, the partial bands may be carried over different guide rollers.

The apparatus may also include a cover belt having injection apertures corresponding to the mould cavities and fed between the mould band and the injection head.

In one form of the invention, apparatus is used for producing a stringer of slide fastener coupling members, in which the mould wheel also has a peripheral groove which intersects the mould cavities and is open towards said mould cavities and one of the partial bands is disposed in the peripheral groove for rotation with the mould wheel with an edge portion of the band extending into the mould recesses to form an undercut in the mould members.

Preferably, the partial bands are made of the same material.

According to a second aspect of the invention a method of producing small plastics articles by injection moulding with a thermoplastics injection head includes moulding in a mould wheel and mould band assembly of which the mould band is of composite construction having two or more partial mould bands which embrace the mould wheel at least in the vicinity of the injection head and have mould portions which complement each other in the manner of a mould core in mould cavities of the wheel.

Embodiments of the invention will now be explained in more detail by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic side view of apparatus in accordance with a first embodiment of the invention; Figure 2, on much largerscale than Figure 1, shows part of a radial cross-section in direction A-A in Figure 1; Figure 3, on the same scale as Figure 2, shows part of a radial cross-section in direction B-B in Figure 1; Figure 4, on the same scale as Figures 2 and 3, shows a cross-section in direction C-C in Figure 1; Figure 5, on the same scale as Figures 2 to 4, show small plastics articles produced by apparatus in accordance with the invention and only joined together by frangible connections;; Figures 6, 7, 8 show other cross-sections of small articles similar to that of Figure 5 and produced by the present invention; Figure 9 is a cross-section, similar to Figure 3, of a second embodiment; Figures 10 and 11 are similar cross-sections at further stages in the apparatus; Figure 12 shows, on enlarged scale, a crosssection in direction D-D of Figure 2; Figure 13 is a schematic side view of alternative apparatus according to the invention; Figure 14 shows on much larger scale a crosssection in direction E-E in Figure 13; Figure 15 is similar to Figure 14 but illustrates another embodiment; Figure 16 is similar to Figure 14 but illustrates a further embodiment; and Figures 17, 18, 19 are perspective views of fastener coupling members made with apparatus shown in Figures 13 and 14: Figures 13 and 15: Figures 13 and 16 respectively.

Referring to Figures 1 to 4 and 12 apparatus of the first embodiment is used for the manufacture by injection moulding of small plastics articles 1, in this case the bottom and top end stops for slide fasteners. Basically the apparatus includes a plastics worm-extruder 2 having an injection head 3 and an assembly of a mould wheel 4, and a mould band 5.

This mould band forms a loop which embraces part of the periphery of the mould wheel 4. As shown in Figure 12 the mould wheel 4 has mould cavities 6 around its periphery for the small plastics articles 1.

The mould band 5 is provided with mould portions to register with the mould cavities 6 in the wheel.

The mould wheel 4togetherwith the embracing part of the mould bands move past the injection head 3 of the extruder 2 and the band 5 then departs from the mould wheel 4. The band subsequently returns by converging on the wheel at a position before the injection head. The mould band 5 is of composite construction and comprises two associated or partial bands 5a, Sb, which travel in parallel, pass over guide rollers 12, 13 and combine to form com- plementary mould portions as ejection formations 7 which extend in the manner of a mould core in the mould cavities 6 of the mould wheel 4.

Figures 3 and 4 show that the ejection formations 7 have undercuts 8 on their outer sides whereby when sufficiently cooled and hardened the plastics articles 1 can be lifted out of the mould cavities 6 when, in operation, the mould band departs from the mould wheel. These Figures also show that the two partial belts 5a, 5b are separable at inclined planes 9, 10 and thus during their circulation the partial bands 5a, Sb can be displaced from each other and hence released from the moulded plastics articles 1. A cover belt 14 having injection apertures 15 spaced to register or correspond to the mould cavities 6 is provided and fed between the mould band 5 and the injection head 3. This belt 14 passes around guide roller 14a. Details of the cover belt 14 are not shown in the drawings other than in Figure 3.

In the second embodiment in Figures 9 to 11 the mould band 5 consists of three partial bands 5a, Sb, 5c of which mould portions complement one another to assist in defining the moulded articles 1.

These partial bands meet at mating surfaces 11, 1 1a extending orthogonallytothe plane of the looped mould bands. Alternatively, the partial bands may be disposed in wedge fashion and movable with re specttosaid plane and relative to each other. In addition, in this second embodiment the individual partial bands 5a, Sb, 5c of mould band 5 pass over different guide rollers, during which they can be moved relative to each other.

In this second embodiment the guide rollers 12, 13 are grooved at their periphery to receive the plastics parts 1 and the partial belts 5a, Sb, 5c. A scraper blade 16 may also be provided for peeling off a projecting film of plastics material. This applies especially when a cover belt 14 is involved. As shown in Figure 9, at the guide roller 12 the partial band 5b is removed from the moulded articles and afterwards returned to the mould wheel 4. As shown in Figure 10, during embracing of guide roller 13 the externally running partial belt 5c remote from roller 12 is lifted away and runs over a deflector roller back to mould wheel 4.The plastics articles 1 remaining on the partial belt 5a are displaced laterally at position X (Figure 1) by conical wedges 17 (Figure 11) or may be held by a towing connecting cord and moved outwards from the mould band.

Apparatus shown in Figures 13 to 16 is used for the manufacture of plastics articles 1 which in this case form a stringer 18 of slide fastener coupling members connected by at least one textile carrier cord 19.

The embodiments in Figures 14 and 15 show the use of a single textile core 19 and Figure 16 shows an embodiment with two textile carrier cords 19. The apparatus is similar to that of Figure 1 and basically includes a plastics worm-extruder 2 having an injection head 3, a continuously rotating mould wheel 4 with mould cavities 6, and a composite mould band consisting of partial bands 5a, Sb, rotatable with mould wheel 4 along an engagement sector 20 and the band 5a having mould cavities 21.

The two partial bands move together in parallel around the sector 20 and have mould portions which complement each in the manner of a mould core in the mould cavities 6. The worm-extruder 2 has its injection head 3 in sliding contact with the mould band 5a at the start of the engagement sector 20.

Molten thermoplastics material can be injected through the mould cavities 21 into the mould cavities 6. To aid clarity, Figures 14 to 16 do not show the injected plastics material.

From Figures 13 and 14, or 13 and 15, or 13 and 16, it will be noted that the mould cavities 21 in the mould band 5a also contribute to shaping the coupling members 1 in the stringer 18. In effect they define the underside of the coupling members 1 with the upper side defined by the mould cavities 6. The textile carrier cords 19 are introduced between the mould band 5a and the mould wheel 4, as shown in Figure 13, and the mould wheel 4 can be appropriately shaped. Although not shown the fastener coupling members 1 may additionally be united by connecting bridge portions to form the stringer 18.

Figures 14, 15 and 16 show the mould wheel 4 having a peripheral annular groove 22 in addition to and intersecting the mould cavities 6. The groove 22 is therefore open to the mould cavities 6. A partial band 5b is in contact with and rotates with the mould band 5a and is disposed in the annular groove 22 so that an edge portion of the band 5b extends into the mould cavities 6 to define a recess or undercut 8 in each fastener coupling member. The undercut 8 may be open at the edge, as indicated in Figures 14 and 16 to produce a step 23 of depth Tin the coupling member, see Figure 17. Alternatively, the band 5b in Figure 15 may produce a slot 24 as shown in Figure 18.Whereas the arrangements shown in Figures 14 and 15 produce coupling members with one leg as illustrated in Figures 17 and 18 respectively, the arrangement shown in Figure 16 produces a preliminary flat fastener element having two legs each with an undercut8 (similarto Figure 14) and this flat element is folded to bring the legs together so that the two undercuts form a slot 25 in the coupling member as illustrated in Figure 19. The partial band Sb is preferably made of the same material as band 5a. Although not shown, the band may also include marginal recesses open to the mould cavities 6.

More than two partial bands may be used to form particular configurations of moulded components.

Figures 17 to 19 illustrate advantages achieved by the present invention. In a continuous moulding operation, the partial band Sb produces the step 23 or slot 24,25 on the individual coupling members which can be used for guiding a fastener slider. The number of shaping elements is greaterthan in known apparatus, and consequently the fastener components as small articles 1 can be formed with a greater variety of shapes within the field of slide fastener technology.

Also the moulding bands may fulfil the function of lifting the moulded articles from the mould cavities and obviate the need for connecting cords in some articles.

Claims (20)

1. Apparatus for the manufacture of small plastics articles by injection moulding with a thermoplastics injection head, includes a mould wheel and a mould band movable past the injection head and in which the mould wheel has mould cavities around its perimeter for the small plastic articles, and the mould band partially embraces the mould wheel at least in the vicinity of the injection head and can converge on the wheel at a position before the injection head and depart from the wheel at a position after the injection head, the mould band comprising two or more partial mould bands movable in parallel and having mould portions which complement each other and engage in the manner of a mould core in the mould cavities of the mould wheel.

2. Apparatus as claimed in Claim 1 in which the mould band is continuously rotatable.

3. Apparatus, according to Claim 2, in which the mould portions of the bands combine to form ejection formations which have undercuts on their outer sides whereby the moulded plastics articles can be lifted out of the mould cavities when the mould wheel and mould bands are operating, and during their movement the partial bands are displaceable from each other and thereby releasable from the moulded articles.

4. Apparatus, according to Claim 2 or 3, in which the mould band comprises two partial bands with ejection formations which are separatable at inclined planes and thereby movable relatively to each other.

5. Apparatus, according to Claim 2 or 3, in which the mould band comprises three or more partial bands with ejection formations and meet at mating surfaces extending orthogonally to the plane of the mould band, or are disposed in wedge fashion relative thereto and are movable relatively to each other.

6. Apparatus, according to any of Claims 2 to 5, in which the various partial bands of the mould band are carried over different guide rollers and are thereby movable relatively to each other.

7. Apparatus, according to any of Claims 2 to 6, including a cover belt with injection apertures corresponding to the mould cavities, and fed between the mould band and the injection head.

8. Apparatus, according to any preceding claim, when used for producing end stops for slide fasteners.

9. Apparatus, according to Claim 1 or 2 for producing a stringer of slide fastener coupling members, in which the mould wheel also has a peripheral groove which intersects the mould cavities and is open towards said mould cavities, and one of the partial bands is disposed in the peripheral groove for rotation with the mould wheel with an edge portion of the band extending into the mould recesses to form an undercut in the moulded members.

10. Apparatus according to any preceding claim, in which the partial bands are made of the same material.

11. Apparatus according to either of Claims 9 or 10 in which said one partial band also has marginal edge structures open towards the mould cavities.

12. Apparatus for the manufacture of small plastics articles by injection moulding, substantially as described herein, with reference to and as shown in Figures 1 to 4 and 12 of the accompanying drawings.

13. Apparatus for the manufacture of small plastics articles by injection moulding, substantially as described herein, with reference to and as shown in Figures 1 and 9 to 11 of the accompanying drawings.

14. Apparatus for the manufacture of small plastics articles by injection moulding, substantially as described herein, with reference to and as shown in Figures 13 and 14,13 and 15 or 13 and 16.

15. A method of producing small plastics articles by injection moulding with a thermoplastics injection head, including moulding in a mould wheel and mould band assembly of which the mould band is of composite construction having two or more partial mould bands which embrace the mould wheel at least in the vicinity of the injection head and have mould portions which complement each other in the manner of a mould core in mould cavities of the wheel.

16. A method, according to Claim 15 and subsequentto injection moulding, separating the partial mould bands to release the moulded articles.

17. A method of producing end stops for slide fasteners substantially as described herein.

18. A method of producing a stringer of slide fastener coupling members substantially as described herein.

19. End stops for slide fasteners produced with apparatus according to any of Claims 1 to 8 or by the method of Claims 15 or 16.

20. A stringer of slide fastener coupling members produced with apparatus according to any of Claims 1,9, 10,11 or 14, or by the method of Claims 15Or16.