Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Reexamination Certificate
2002-05-10
2004-11-30
Davis, Robert B. (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
C264S536000, C425S525000, C425S527000, C425S535000
Reexamination Certificate
active
06824732
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention relates to assemblies, such as blow pin assemblies, which are used in blow molding machinery for inflating parisons and forming the necks of containers manufactured by such machinery.
2. Brief Discussion of the Prior Art
The blow molding of plastic containers is well known and practiced worldwide. Blow molding offers many advantages over other forms of container manufacturing.
These advantages include the ability to produce containers at minimal cost and with minimal waste; the low start-up costs and mold making lead times in comparison to other manufacturing methods, such as injection molding; the ability to produce irregular shaped and hollow containers; the ability to produce containers quickly and automatically; the ability to produce containers from a variety of materials having qualities suited to the specific application.
Blown containers having specially formed neck finishes are commonly employed for use with container closures. Neck finishes may be threaded for use with threaded closures, adapted for mating with snap-on closures, etc. It is common within a container blow mold system to employ a main mold to form the container reservoir, and a neck block, or top block, to form the neck finish. Top blocks are also made to standard dimensions so that the parting face of the top block and main mold properly match. The main mold is usually adapted to interchangeably accept any standard top block for a particular container size or style.
The first pair of components mounted to the top block are the neck finish blocks. Each neck finish block is usually made of aluminum, and may originally be formed as a circular body. The circular body is cut in half to form the neck finish block for each half of the mold. The neck finish blocks are machined to provide threads, ratchet teeth, shoulders or other surface features on the container which are used to engage or otherwise accommodate a closure.
During blow molding, a parison of molten plastic is extruded between the open mold halves, then the mold system closes to entrap the parison within the mold cavity. A hollow blow pin, which is ordinarily made of tool steel, is inserted through the neck opening, and into the parison where it inflates the parison with pressurized air to cause the parison to form to the shape of the container and neck finish cavity. The blow pin includes a hardened steel bushing, or shear bushing, having an annular blade, and each top block half includes a semi-circular hardened steel blade, or shear steel.
The shear steel shapes and trims flash from the top end of the bottle neck. By providing various degrees of precision ground undercut to the bottom surfaces of the shear steels, a distinct radius can be formed at the upper edge of the bottle neck area. This can improve the strength of the bottle neck in this critical area. Shear steels are made of precision ground and hardened steel.
When the mold is closed, the semi-circular blades and seals form annular orifices around the shear bushing. During molding, portions of the parison extending beyond the mold cavity are trapped between the parting faces of the mold halves and become unwanted flash. After the container is formed within the cavity and before the mold system reopens to release the blow molded container, the shear bushing is retracted through the shear steel orifice. The shear bushing and shear steels are sized and shaped so that the retraction causes a shearing of the container opening through the neck, whose diameter is that of the shear bushing blade and shear steel orifice. After the molded container is removed from the mold, flash is removed by trimming in an automated process.
The last set of components which are mounted to the top block are the master seals, which are sometimes referred to as masters. These components provide a seal for the blow pin, thereby preventing air from escaping from the mold when the parison is inflated to form the container. They also form a “flash pocket” which pinches and seals the parison when the molds close at the start of the production cycle. When all neck finish components, i.e. the neck finish block, the shear steel and the master seal, have been mounted to the top block halves, they are then secured thereto with four Allen cap screws or the like. Failure to do so can prevent the mold from closing properly, leading to damage or even destruction of the neck finish components and/or blow pin. U.S. Pat. No. 5,589,204, the disclosure of which is incorporated by reference herein, discloses a mold assembly including a top block assembly which facilitates alignment of the neck finish components with the mold parting line.
The slightest misalignment of the blow pin assembly within the mold will impose undue wear upon the blow pin assembly shearing edge and/or the shear steel as they cooperate to shear the container, thereby causing frequent replacement and sharpening. Such wear occurring at the blow pin assembly shear edge and/or the shear steel is a primary reason for blow molding process down-time and maintenance. Additionally, the dulling of the shear edge and the shear steel will result in uneven formation of the neck edges which will prevent proper release of the container from the mold, and cause ineffective sealing of the container cap. Therefore, it is of the utmost importance that effective and clean shearing of the container neck occur as the blow pin assembly is withdrawn from the mold cavity.
Alignment of the blow pin assembly during the shearing operation of the molding process is important in reducing the maintenance required for the blow pin assembly and the down-time of the machinery. Such alignment has traditionally been accomplished by employing a blow pin having a beveled F surface or chamfer that adjoins the shear edge thereof. More recently, a blow pin has been developed that includes a beveled surface or chamfer closer to its upper end. This surface will be guided by the master.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a blow pin assembly which effectively shears the plastic in the neck portion of a container formed in a blow molding machine, and which reduces the amount of maintenance; required using most existing assemblies.
It is another object of the invention to provide a blow pin assembly that effectively forces plastic to the sealing lip area of the molded bottle.
In accordance with the above objects of the invention, a blow pin and an assembly including a blow pin are provided for inflating a parison and forming the neck portion of a plastic container in a blow molding apparatus. The assembly includes a blow pin which is mountable to a blow rod. The blow pin includes a blow pin body including an exterior surface having a tapered portion and a cutting edge beneath the tapered portion. The tapered portion cooperates with the master seal of the mold to automatically center the blow pin before the cutting edge engages the shear steels to sever the blow molded article from the mold. The cutting edge of the blow pin forms substantially a ninety degree angle with the longitudinal axis of the blow pin. Such a configuration provides effective cutting as well as allowing the cutting edge to be resharpened one or more times. The frequency of blow pin replacement is accordingly reduced.
In the preferred embodiment, the blow pin includes a heat sink for removing heat from the blow pin body. As described in U.S. Pat. No. 5,795,598, the heat sink is preferably positioned within an internal cavity of the blow pin body and includes a plurality of flow passages therein to facilitate heat dissipation. Preferably, the blow pin body is made from a durable material, such as tool steel, and the heat sink is made from a material having high heat transfer properties, such as aluminum.
In order to force plastic to the sealing lip area of a molded bottle, a blow pin body is provided that includes upper and lower portions and a groove or recess between these portions. A plurality of air passages extend thr
Cobiski Richard J.
Wohlgemuth Emanuel E.
Davis Robert B.
Hoffmann & Baron , LLP
Ultraseal Technologies Corporation
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