Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
As an illustration, injection molding of PET material involves heating the PET material (or other suitable molding material for that matter) to a homogeneous molten state and injecting, under pressure, the so-melted PET material into a molding cavity defined, at least in part, by a female cavity piece and a male core piece mounted respectively on a cavity plate and a core plate of a mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient to keep the cavity and the core pieces together against the pressure of the injected PET material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected PET material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the molding cavity. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be subsequently demolded by ejecting it off the core piece.
FIG. 1 is a cross-sectional view through a portion of a typical injection mold 50 that has been reproduced from U.S. Pat. No. 7,381,049 to LI, Guoming, published on Jun. 3, 2008. The description of the injection mold 50 that follows will be greatly simplified, as it is expected that one skilled in the art will readily appreciate the structure and operation thereof.
The injection mold 50 includes a first mold portion 52 and a second mold portion 54 that are shown clamped together to define a molding cavity 7 therebetween within which a molded article, such as a preform of the type for blow molding into a container, is moldable. More particularly, the molding cavity 7 is definable between a first stack portion 8 and a second stack portion 16 of a mold stack 20 that are associated with a first mold shoe 30 and a second mold shoe 40 of the first mold portion 30 and a second mold portion 40, respectively.
The first stack portion 20 broadly includes a core insert 2, a lock ring 4, and a split insert 6 that are structured to define an inner body portion, a top portion and an encapsulated portion (e.g. for molding the neck region on the preform/container) of the molding cavity 7, respectively.
The first mold shoe 30 broadly includes a core plate 32 and a stripper assembly 34. The core insert 2 and the lock ring 4 are associated with the core plate 32, whereas the split mold insert 6 is associated with the stripper assembly 34. The lock ring 4 is structured to both retain the core insert 20 to the core plate 3 and to align and hold closed (i.e. keep the halves thereof in a closed configuration) the split mold insert 6 during a step of molding of the molded article. The stripper assembly 34 includes a stripper plate 35, a wear plate 36, and a pair of slides 38. The stripper plate 35 is operatively coupled to a stripper plate actuator, which is not depicted, but is well-known to those of skill in the art (for example, a hydraulic actuator, a servo-motor actuator and the like). The stripper plate actuator (not depicted) is configured to move the stripper plate, back and forth, along a longitudinal axis of the mold stack 20.
For the performance of a molded article ejection function, the halves of the split mold insert 6 are operatively coupled to a respective one of the pair of slides 38 by suitable means, such as bolts (not depicted), for movement therewith as will be described momentarily. The pair of slides 38 are coupled to slide actuators (not depicted), which can be implemented as cam(s), servo motor(s) and the like. The slide actuators are configured to move the pair of slides 38, back and forth, in a direction which is substantially perpendicular to a longitudinal axis of the mold stack 20. The wear plate 36 is provided between the stripper plate 35 and the pair of slides 38 to prevent substantial damage to the stripper plate 35 and/or pair of slides 38 during the movement of the pair of slides 38 relative to the stripper plate 35. The wear plate 36 is implemented according to known techniques and is coupled to the stripper plate 35 by suitable couplers, such as bolts (not depicted) and the like.
Turning attention briefly to the second mold portion 16, it may be appreciated that the second stack portion 16 broadly includes a cavity insert 12, a cavity mounting flange 10 and a gate insert 14. The cavity insert 12 and the gate insert 14 define an outer body portion of the molding cavity 7. The gate insert 60 is further configured to connect the molding cavity 7 to a melt distribution system (not shown). The cavity mounting flange 10 is configured to retain the cavity insert 14 to the second mold shoe 40 and to align and hold closed the split mold insert pair 40 during the step of molding.
In the quest for ever more efficient and productive molding system productivity, a common approach is to maximize a density of mold stacks within the injection mold. To do this, the mold stacks are generally designed to take as little space as possible, and as a consequence often experience, in use, stresses and strains that approach, and sometimes exceed, the strength of the associated materials. As such, many injection molds further incorporate one or more tonnage blocks 29 in between confronting faces of the first mold shoe 30 and the second mold shoe 40 through which excess clamping force may be channeled around the mold stacks, including the mold stack 20, and thus avoid damaging (i.e. crushing) weaker portions thereof—such as, for example, an annular top portion 5 of the lock ring 4.
Other examples of known injection molds may be referenced in any one of the publications that follow, including U.S. Pat. No. 7,645,132 to MCCREADY, Derek, published on Jan. 12, 2010, discloses a mold stack of a molding machine. A cavity insert is provided. The cavity insert comprises a body having: an internal surface defining, in use, at least a body portion of a molding cavity; an external surface defining, in use, at least a first portion of a cooling channel configured, in use, to direct a flow of coolant; and a mounting flange configured to support, in use, the body relative to a front face of a cavity plate, the mounting flange including a member configured to define, in use, a second portion of the cooling channel.
U.S. Pat. No. 7,128,865 to MAI, Arnold, published on May 11, 2010, discloses a split mold insert and a mold stack incorporating same. The split mold insert for defining, at least partially, a neck area of a preform suitable for blow molding into a final-shaped article, in particular, is provided. The split mold insert comprises a body having (i) a cavity defining portion for defining, in use, a portion of the neck area and (ii) a top promontory and a bottom promontory located at opposite sides of the body; a first female taper portion associated with the top promontory; a second female taper portion associated with the bottom promontory; the first female taper portion and the second female taper portion for cooperating, in use, with a first male taper of a first mold component and a second male taper of a second mold component, respectively, for aligning the body into an operational configuration.
PCT patent application publication 2010/051620 to MAI, Arnold et al., published on May 14, 2010, discloses a tonnage regulating structure and a mold incorporating same. For example, a tonnage regulating structure for use in a mold of a molding machine, the mold being associated with an opening clearance between mold faces in a mold closed and clamped configuration, is provided. The tonnage regulating structure comprises a body having a first height in a resting configuration, the first height selected to be larger than the opening clearance between the mold faces in a mold closed and clamped configuration; the body including a compensating structure, the compensating structure for regulating, in use under applied clamp tonnage, the body to a second height, the second height being smaller than the first height.