Injection molding is a commonly employed manufacturing technique for forming articles. An example of an article that is typically formed using injection molding is a plastic preform. A plastic preform can then be subsequently blow-molded into a plastic bottle.
An injection mold for making preforms (and other molded articles) typically includes one or more molding cavities for receiving molten resin and forming the preforms. To increase the flexibility of the molding assembly, interchangeable inserts can be inserted into bores in a cavity plate. FIG. 1 shows a portion of a prior art injection molding machine 10. One or more mold cavities 12 are usually defined between complementary shaped, generally cylindrical cavity inserts 14 and core inserts 15 that are arranged within bores in a cavity plate 16. The mold cavities 12 are aligned generally parallel to the direction of mold-clamping action (i.e., the mold-clamping axis).
For mold articles that have threaded neck portions, a split neck ring (not shown) cooperates with the core insert 15 to create the neck. A taper is typically provided at an end of the cavity insert 14 (also not shown) to help align the neck ring.
A hot runner assembly 18 communicates a flow of molten resin to melt channels 19 in one or more nozzle assemblies 20. A gate insert 22 is seated within the mold cavity inserts 14. A first profiled surface 24 on gate insert 22 defines a receptacle to house the tip of the nozzle assembly 20. A second profiled surface 26 on the gate insert 22 defines a portion of the mold cavity 12. A gate 28 is provided in gate insert 22 which provides fluid communication between the nozzle assemblies 20 and each of the mold cavities 12. Gate 28 is open or closed by a piston valve 29. Other types of gating, such as slide valves or thermal gating can also be used
The molten resin that is injected into the cavities must be cooled to solidify the resin so that the molded preform can be removed from the mold. It is desirable to cool the preform as quickly as possible so the preforms can be removed and a next injection cycle initiated with minimal time delay. To this effect, cooling channels 30 are typically provided in the cavity and gate inserts 14 and 22. A cooling fluid, such as water, is circulated through the cooling channels 30.
The use of mold cavity inserts 14 and gate inserts 22 increases the machine's flexibility, as the inserts can be switched to produce a different molded object without the need to remove the cavity plate 16 from the molding assembly 10. However, before the cavity inserts 14 and gate inserts 22 can be safely removed, the nozzle assemblies 20, which may contain still-hot molten resin, must be allowed to cool.
Efforts have been made to improve mold assemblies. U.S. Pat. No. 6,398,542 to Romanski et al. teaches a valve gating apparatus for injection molding including at least one shutter disposed between the gate and the cavity melt channel into a mold cavity. The shutter is removably fastened to a rail member. When the rail member is moved laterally, the shutter moves between a closed position wherein flow of melt from the nozzle into the cavity is inhibited, and an open position wherein flow of melt into the cavity is unimpeded by the shutter. In a preferred embodiment, a sliding gate valve with inserts that includes a hot runner insert around the injection nozzle and a gate insert which defines a portion of the mold cavity. The gate between the injection nozzle and the mold cavity is defined and split between the hot runner insert and the gate insert. The hot runner insert is retained by the manifold plate of the hot runner assembly, and the gate insert is retained by the cavity plate.
U.S. patent application 2006/0099295 to Elliot teaches a gate insert for a stack assembly in an injection molding machine having a gate through which a melt of thermoplastics material enters a mold cavity. The gate insert has a cooling channel surrounding, and substantially uniformly spaced from, the gate. The cooling channel has an inner surface with a profile substantially parallel to the gate. The cooling channel is further defined by a two-piece gate insert having interconnecting surfaces.
U.S. patent application 2005/0236725 to Niewels et al. teaches a method and apparatus for controlling an injection mold having a first surface and a second surface includes an active material element configured to be disposed between the first surface and a second surface. The active material element may be configured to sense a force between the first surface and the second surface, and to generate corresponding sense signals. Transmission structure is coupled to the active material element and is configured to carry the sense signals. Preferably, an active material element actuator is also disposed between the first surface and a second surface, and is configured to provide an expansive force between the first surface and a second surface in accordance with the sense signals. The method and apparatus may be used to counter undesired deflection and/or misalignment in an injection mold. The active material actuator is operable to “tilt” a core element when misalignment occurs.
U.S. Pat. No. 5,736,173 to Wright et al. teaches a preform injection mould includes an elongate mould core cooperating with a female mould and a neck ring in a manner to define a mould cavity therebetween. An injection nozzle in the female mould allows molten plastic to be injected into the mould cavity so that a preform molded article may be formed. The neck ring is constituted by a pair of mating halves which can be separated laterally with respect to the longitudinal axis of the mould core. A taper sleeve surrounds the mould core beneath the neck ring. The neck ring halves are secured to diametrically opposed slides to facilitate lateral separation of the neck ring. A pair of slide taper locks contact a respective one of the slides to inhibit lateral movement of the slides and to back up the neck ring when injection mould is in a mould closed position. An annular formation is formed on the upper surface of the neck ring and is accommodated by a complementary recess formed in the bottom of the female mould. The mating inclined surfaces of the female mould and the annular formation constitute an upper taper lock which is backed up by a cavity plate. An annular formation is provided on the upper surface of the taper sleeve and is accommodated by a complimentary recess formed in the bottom of the neck ring. The mating inclined surfaces of the taper sleeve and neck ring constitute a lower taper lock. Since a portion of the neck ring constitutes the female taper of the lower taper lock, the lower taper lock is backed up by the slide taper locks through the slides allowing the cross-sectional area of the neck ring to be reduced.
U.S. Pat. No. 6,569,370 to Amin et al. teaches an injection molding system for molding a molded article and method for forming same, including a mold cavity for forming the molded article, wherein the mold cavity is defined at least in part by a mold core defining inner walls of the molded article, a first insert defining at least outer side walls of the molded article, and a second insert defining an outer wall of a neck of the molded article. In addition, a cavity plate at least partly surrounds the first insert and a cavity flange retains the first insert in the cavity plate.