Method of cryogenic stretch blow molding

Details Method of cryogenic stretch blow molding Method of cryogenic stretch blow molding

2000-09-07

2002-10-08

McDowell, Suzanne E. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With step of cooling to a temperature of zero degrees c. or...

C264S528000

Reexamination Certificate

active

06461547

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the field of stretch blow molding apparatus for producing plastic containers from parisons, and more particularly concerns stretch blow molding methods and apparatus utilizing cryogenic fluids to cool plastic containers stretch blow molded from parisons.
2. Description of the Prior Art
In biaxially stretch blow molding parisons into plastic containers, a parison may be placed within a blow mold cavity and mounted to a parison engagement assembly, with a stretching rod moved into and along the longitudinal axis of parison, stretching the parison longitudinally. Blow air is introduced into the parison, laterally stretching the parison transverse to the stretching rod. To provide such stretch blow molded containers with heat resistant characteristics, permitting filling with heated fluid, containers may be heat-set to favorably adjust the orientation of the polymers. In order to shorten the operational time required to heat-set stretch blow molded containers, cooling fluids may be introduced within the containers, quickly quenching and heat-setting the container to permit rapid removal from the blow mold.
The introduction of cryogenic liquids through a stretching rod into the interior of a container that has been stretch blow molded from a parison is known in the art, for instance, as disclosed in U.S. Pat. No. 5,182,122. Further, apparatus and method of making a partially crystalline container by stretch blow molding within a hot mold and then injecting a cooling fluid within the blown container is also known, as described in U.S. Pat. No. 4,883,631, and corresponding United Kingdom patent application No. 2,195,287. Introduction of liquid nitrogen within a container for purposes of cooling is disclosed in U.S. Pat. Nos. 5,290,506; 4,375,947 and 4,376,009. The use of U.S. Pat. Nos. 5,290,506; 4,375,947 and 4,376,009. The use of cryogenic gas is also known in extrusion blow molding, as described in U.S. Pat. No. 3,789,093.
Unfortunately, the use of cryogenic fluids with stretch blow molding apparatus may also cause certain components of the apparatus to cool to a temperature where the apparatus becomes inoperative. In particular, cryogenic fluids may lower the temperature of components in contact with blow air to a level where water vapor present in the blow air sublimates onto surfaces of such cryogenically cooled components, causing an accumulation of water ice on the surfaces. With continued accumulation of water ice, the apparatus may be rendered inoperable. In addition, when the temperature of the sealing surfaces of seals present in a stretch blow mold apparatus decreases below a certain level that is characteristic of the materials from which the seals are formed, the seals may fail catastrophically. As a result, there exists a need for methods and apparatus for preventing accumulation of water ice and seal failure during stretch blow molding using cryogenic fluid.
U.S. Pat. No. 5,182,122 has proposed a solution to problems created by utilizing cryogenic fluids which includes using a stretching rod having an inner tube for delivery of a cooling fluid and a concentric outer tube for delivery of a thermally insulating fluid. Despite the availability of such devices, there exist a need in the art for methods and apparatus which permit the introduction of cryogenic fluid within a stretch blow molded container for rapid cooling while preventing accumulation of water ice and maintaining the integrity of the seals, but without the necessity of providing for delivery of a thermally insulating fluid.
SUMMARY OF THE INVENTION
In order to aid in the understanding of the present invention, it can be stated in essentially summary form that it is directed to methods and apparatus for stretch blow molding a parison into a container including the introduction of a cryogenic fluid within the container for rapid cooling and providing a source of heat to prevent the cryogenic fluid from causing accumulation of water ice and failure of seals.
More specifically, the present invention includes an apparatus for stretch blow molding a plastic parison into a container, for use with a parison engagement assembly for engaging a parison for stretch blow molding within a blow mold. The apparatus includes a blow mold rod seal assembly having a thermally conducting blow manifold, a thermally conductive blow seal housing, and a thermally conductive base plate mounted to a top plate so that the blow seal housing is sandwiched between and in thermal contact with the blow manifold and the base plate.
A blow manifold defines a first stage blow air inlet port for connection to a source of blow air through a blow air fitting, and further defines a second stage blow air inlet port for connection to the source of blow air. The blow manifold also defines an interior cavity first portion disposed in fluid connection with the first and second stage blow air inlet ports, a chamfered countersink communicating with the interior cavity first portion, and a blow air outlet port.
The blow seal housing includes an upper end and a chamfered lower end, with dimensions of the lower end selected for the blow seal housing to be disposed proximate to the blow manifold with the lower end in mating engagement with the countersink. The blow seal housing defines an interior cavity second portion having a generally cylindrical smaller chamber and a coaxial generally cylindrical larger chamber separated from the smaller chamber by a step. The blow seal housing further defines a first low pressure air supply orifice, disposed through the blow seal housing and communicating with the interior cavity second portion. With the blow seal housing engaged with the blow manifold, the smaller chamber is disposed proximate to the interior cavity first portion.
The base plate is disposed proximate to the blow seal housing and defines an interior cavity third portion having a generally cylindrical first chamber and a generally cylindrical second chamber separated by a second step. The dimensions of the first chamber may be selected to correspond with the exterior dimensions of the upper end of the blow seal housing, so that the base plate and the blow seal housing may be mounted together with the upper end in mating engagement with the first chamber and bearing against a portion of the second step. The second chamber is smaller in radius than the larger chamber, and is disposed proximate to and coaxially aligned with the smaller chamber and the larger chamber. The base plate further defines a circumferential first seal slot at the second chamber, and also defines a second low pressure air supply orifice, disposed through the base plate and communicating with the interior cavity third portion.
The top plate defines a plate opening, and has generally planar plate upper and lower surfaces. The plate opening is disposed above the smaller chamber, the larger chamber, and the second chamber, with the plate lower surface proximate to the base plate.
A piston is provided and includes a piston first end, a piston second end, and a generally cylindrical exterior surface having an exterior surface first portion disposed proximate to the piston first end with diameter slightly smaller than the diameter defined by the smaller chamber of the blow seal housing. The exterior surface also has an exterior surface second portion defining a diameter slightly smaller than the diameter defined by the larger chamber of the blow seal housing and disposed intermediate to the piston first and second ends, and further includes an exterior surface third portion defining a diameter slightly smaller than the diameter defined by the second chamber of the base plate and disposed proximate to the piston second end. A circumferential first shoulder is defined between the exterior surface first and second portions, and a circumferential second shoulder is defined between the exterior surface second and third portions. The exterior surface second portion defines a circumferential second

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