Injection molding system and heating assembly for use in such a system

Abstract: Injection moulding system comprising an elongated manifold having a melt passage extending from a common inlet, branching to a number of outlets; each of which outlet is connected to a central bore (3) of a heated elongated nozzle (1) discharging into a gate (4) leading to a moulding cavity, which nozzle 1 is at least partly surrounded by a heating element (17); the heating element (17) is designed such that its diameter or cross-sectional shape is adjustable; said heating element (17) is encased by a mantle piece (21) of which the internal diameter or internal cross-sectional shape is adjustable too, and means are provided to clamp fit the heating element (17) with respect to the nozzle (1) under the action of the mantle piece (21).

Description: This invention relates to an injection moulding system comprising an elongated nozzle having a cylindrical body with a central bore which is in fluid communication with a gate leading to a moulding cavity and a cylindrical heating element, forming a jacket having a longitudinal slot and tightening means for adjusting the dimensions of the slot, the heating element being at least partly located around the nozzle. Such injection moulding systems comprising a nozzle and a heating element are well-known for instance from Japanese patent application JP-A-3176113. In this document a heating jacket or band heater is formed by a clamping plate, a cylindrical body and a clamping screw. When placed around the nozzle, a thermocouple can extend in the longitudinal gap of the band heater. From EP-A-0 444 748 a heating element is known comprising a coiled heating wire which is embedded in a solid metal body. The heating element is in close fitting contact with the outside of the nozzle circumference and is positioned by means of a clamping device. The known heating element has as a disadvantage that upon removal thereof, for instance for maintenance or replacement purposes, the nozzle assembly has to be disassembled and the heating element has to be slid along the nozzle in the axial direction. JP-A-0 7 142 157 describes a band-shaped heater which is clamped into close contact with an injection moulding nozzle by means of a clamping plate whithout the use of a tightenings screw. Furthermore, EP-A-0 653 283 describes a band-shaped heater which can be clamped around an injection moulding nozzle by means of a sheetlike clip formed into a diameter smaller than the diameter of the heater to exert a continuous tension. It is therefore a purpose of the present invention to provide an injection moulding system having a heating element which can be easily placed around the nozzle and removed therefrom. It is a further object of the present invention to provide a heating element which is cost-effective, which is of simple design and which allows for improved serviceability. Thereto the injection moulding system according to the present invention is defined by the features of claim 1. The heating assembly of the present invention is defined by the features of claim 6. By the longitudinal hinge, the cylindrical heating element according to the present invention can easily be replaced by releasing the tightening means. Preferably the heat conducting material is totally absent in the region of the hinge. Further objects and advantages of the invention will appear from the following description, taken together with the accompanying drawings, illustrating non-limiting preferred embodiments. Figure 1 is a sectional view of a portion of an injection moulding system, showing a heated nozzle seated in a socket holder according to one embodiment of the invention, partly cut away; Figure 2 is a cross-sectional view of the heated nozzle according to figure 1; Figure 3 is a view corresponding to figure 1 of a further embodiment; and Figure 4 is a cross-sectional view of the heated nozzle shown in figure 3. Reference is first made to figure 1, which shows a portion of a multi-cavity injection moulding system, showing a heated elongated nozzle 1. The nozzle 1 is secured to a common elongated manifold. As is common in the art, a melt passage 2 extends through the manifold from an inlet in a manifold extension for connection with the outlet of an injection moulding machine (not shown). The melt passage 2 extends from the manifold through a central bore 3 of the nozzle 1 and to a gate 4 leading to a cavity (not shown). The melt passage 2 also extends through a seal insert 5 which is seated in the nose portion of the nozzle 1 and forms an extension of the bore 3. The nozzle 1 is suspended from a supporting plate 6. For this purpose, the supporting plate 6 is provided with an internally threaded blind-hole 7 with a stepped portion. The socket 8 of the nozzle 1 is tightly toleranced received within the stepped portion of the hole 7. The socket 8 is clamped in place by an externally threaded nut 9, having a stepped portion bearing against a shoulder 10 on the socket 8. The supporting plate 6 and the socket 8 can be of relatively soft material, and the nut 9 of relatively hard material, such that damage will not occur to the screw thread of the nut. In this way, it is possible to insert the nozzle 1 in the supporting plate 6 from below too, such that it can e.g. easily be replaced, without the need for laborious disassembling the manifold-assembly in and above the supporting plate 6. Since the elongation part (11) is rather flexible compared to the rest of the construction, expansion of the manifold system has no influence on the position of the gate 4 at the end of the nozzle 1. And, by the use of the nut 9, positioning of the bore 3 is made less difficult. The manifold is heated by a heating element (not shown) which is integrally brazed in the manifold-assembly, and which is common in the art. Furthermore, the nozzle 1 is made up from an elongation part 11 with adaptable dimensions, and an end part 12 of standard dimensions. By virtue of this, for assembling nozzles 1 of different length, merely elongation parts 11 of different length must be kept in storage, reducing manufacturing and storage costs. The end part 12 is internally screw-threaded on the lower end of the elongation part 11. As is indicated in figure 1, the end part 12 is encircled by a helically wound electrically heating wire 13, or similar heating element. The wire 13 can be integrated with the end part 12. A connecting wire 14 is connected to the heating wire 13 and extends parallel to the nozzle 1 towards the supporting plate 6, for connection to a power supply (not shown). As shown in the drawing, the seal insert 5 is externally screw-threaded in the end part 12. The end part 12 also has two circumferential shoulders 15, spaced apart in the longitudinal direction, for clamp fit with a socket holder 16 which encircles a region of the nozzle 1 between its ends at a certain distance. The spacing between the socket holder 16 and the nozzle 1 is used to balance expansion due to temperature differences. The socket holder 16 aligns the seal insert with the central bore 3. Radial forces due to thermal expansion of the supporting plate are accommodated by the socket holder rather than by the seal insert 5. Furthermore, the socket holder provides for a thermal isolation between the hot nozzle part 11 and the colder cavity plate. Finally, the socket holder 16 forms a second seal against leakage of the melt along the insert 5. The elongation part 11 is encircled by a heating element 17. Unlike the end part 12, this heating element 17 is no integral part of the elongation part 11 of the nozzle 1. The heating element 17 is a separate cylindrical body. A hinge 18 is provided over the total height of the body 17, viewed in its longitudinal direction. Furthermore, the cylindrical body 17 defines an open slot 19 extending over the total height of the body 17, viewed in the longitudinal direction. The heating wire 20 embedded in the cylindrical body 17 follows a serpentine path, extending up and down parallel to the longitudinal direction of the nozzle 1, turning up or down at the lower or upper end, respectively, of the cylindrical body 17. The wire 20 is embedded in appropriate moudling or sintering material. At the hinge 18, there is no embedding material present, and the embedded parts of the cylindrical body 17 at both sides of the hinge 18 are joined by merely the exposed wire 20. The cylindrical body 17 is surrounded by a cylindrical mantle 21, with adjustable diameter. For this purpose, the cylindrical mantle 21 is slotted in its lengthwise direction, and the opposing slot edges can be brought together by tightening a nut, connected tot the one edge of the mantle 21 and screw threaded onto a screw threaded rod 23 connected to the opposing edge of the mantle. As is shown in figure 1, several bolt 23 and nut 22 assemblies are provided spaced apart in the longitudinal direction of the mantle 21. The mantle 21 is made from relatively thin sheet metal, and makes sure that the cylindrical body 17, comprising the heating wire 20, is reliably pressed against the elongation part 11 of the nozzle 1 in a relatively large contact area. With the cylindrical body 17 embedding the heating wire 20 in combination with the mantle 21, the heating element 17 for the elongation part 11 of the nozzle 1 can easily be replaced by untightening the nuts 22. Furthermore, a proper heating contact is provided between the heating wire 20 and the nozzle 1. Apart from that, the heating element 17 is a rather low cost and reliable piece of equipment. Of course, the heating element 17 according to the invention can be applied to other nozzle-types as well, apart from the combination of the elongation part 11 and the part 12. The supporting plate 6 is held in place by locating rings 24 (of which only one is shown in the drawing). Now referring to figure 3, an alternative embodiment of the invention is shown. Compared to figure 1, mainly the socket holder 16 and the heating element 17 differ. With respect to the heating element 17, the wire 20 now follows a zig-zag path extending between the opposite edges of the slot 19, encircling the nozzle 1, except for the width of the slot 19. Again, at the hinge 18, the embedding material of the heating element 17 is left out, such that a plurality of wire parts, present in succession in the longitudinal direction of the cylindrical body 17, are exposed here. Again, the heating element 17 is surrounded by a slotted mantle 21. Provided by an alternative design of the bolt 23 and nut 22 assembly, the diameter of the mantle 21 is adjustable such that the heating element 17 can be clamped around the nozzle 1. It is appreciated, that several modifications can be made without departing the scope of the present invention. For instance, the hinge 18 of the heating element 17 can be provided in a different way, e.g. by making the cylindrical body 17 thinner at that point, without exposing the wire 20. Apart from that, the slotted mantle piece can be dimensioned such that the edges of the slot overlap. Other designs for the adjustment of the diameter of the mantle 21 lie within the scope of the invention as well. It is even possible, to have a slotted mantle 21 with such high elastical properties under bending, that the cylindrical body 17 is spring-biassed around the nozzle 1 merely by the slotted mantle 21, without the need for additional tightening means, such as the bolt 23 and nut 22 assembly, if the internal diameter of the mantle 21, in its unstretched condition, is substantially smaller than the outer diameter of the cylindrical body 17 if firmly applied around the nozzle 1. There can be more than one layer of wire 20 over the thickness of the body 17.

Claims: Injection moulding system comprising an elongated nozzle (1) having a cylindrical body with a central bore (3) which is in fluid communication with a gate (4) leading to a moulding cavity and a cylindrical heating element (17), forming a jacket having a longitudinal slot (19), the heating element (17) being at least partly located around the nozzle, the heating element being surrounded by a concentric cylindrical mantle (21) comprising tightening means (22,23) for adjusting the width of the slot (19) and to clamp fit the heating element (17) around the nozzle under the action of the mantle (21), the heating element (17) comprising a heating wire (20) embedded in an embedding material (26), characterised in that the heating element (17) further comprises a longitudinal hinge (18), spaced away from the longitudinal slot (19), along which hinge (18) the thickness of the embedding material (26) is at least reduced. Injection moulding system according to claim 1, wherein the hinge (18) is located substantially diametrically opposite the longitudinal gap (19). Injection moulding system according to claim 1 or 2 wherein the heating wire (20) is exposed at the hinge (18). Injection moulding system according to any of the preceding claims, the tightening means (22,23) being spaced apart viewed in the longitudinal direction of the nozzle (1). Injection moulding system according to any of the preceding claims, the heating wire (20) of the heating element (17) (a) substantially extending parallel to the longitudinal direction of the nozzle (1) from the one longitudinal end to the other in an alternating serpentine path up and down; or (b) substantially extending perpendicular to the longitudinal direction of the nozzle (1) in a zig-zag-type path within the heating element (17) repeatedly from the one edge of the slot (19) towards the opposite edge covering at least almost completely the circumference of the body (17). Heating assembly comprising a heating element (17) forming a cylindrical body for clamping around a nozzle of an injection moulding system, the heating element having a longitudinal slot (19), the heating assembly comprising a cylindrical mantle (21) comprising tightening means (22,23) for adjusting the width of the slot (19), concentric with the heating element (17) the heating element having a heating wire (20) embedded in an embedding material (26), characterised in that the heating element (17) further comprises a longitudinal hinge (18), spaced away from the longitudinal slot (19), along which hinge (18) the thickness of the embedding material (26) is at least reduced. Heating assembly according to claim 6, wherein the hinge (18) is located substantially diametrically opposite the longitudinal gap (19).

Inventors: VAN BOEKEL FRANCISCUS ANTONIUS, VAN BOEKEL, FRANCISCUS ANTONIUS JOSEF
Applicants: EUROTOOL BEHEER B V, EUROTOOL BEHEER B.V.
Application year: 1996
Main classification: B29C45
IPC codes: B29C45