Posted by
Derunmachine on Thursday, March 04, 2010 12:42:04 AM
Blow molding
is a process commonly used to create plastic objects. In general, the
process consists of generating a tubular form, referred to as a
parison. The parison is placed into a mold and is injected with a gas.
This causes the parison to expand to the shape of the mold, while
leaving a hollow interior. The process is frequently used in the
production of plastic containers and bottles. There are three types of
blow molding: extrusion, injection and stretch.
Extrusion blow molding is the most basic and simplest form of blow
molding. In this process, molten plastic is extruded directly over a
mold in a tubular shape (parison). In blow molding, the mold is
typically water-cooled. The mold is then closed around the parison. Gas
is injected through the top of the parison. The gas fills the parison
in much the same way that a balloon is filled by blowing into it. When
the molten plastic touches the cooled walls of the mold, it solidifies
the plastic into its final form. The plastic container is then ejected
from the mold, and any excess is trimmed. This process allows for a
wide range of shapes and sizes, as well as neck sizes.
The injection blow molding process occurs in two stages. In the first
stage, thermoplastic is melted in a barrel, generally through a
combination of barrel heating and sheer force applied by a screw. The
molten plastic is then injected into a preform mold that contains a
mandrel or blow stem (a hollow component inside the die-head). In the
second stage, the mandrel shapes the parison. The preform mold is
typically heated to maintain the molten state of the thermoplastic
material. The parison is then extruded over a mold, which closes around
it. Gas is injected, and the parison expands to the shape of the mold.
The plastic solidifies on contact with the cooled mold walls. The piece
is ejected from the machine and is trimmed. Injection blow molding is
preferable for smaller containers.
Stretch
blow molding machine
can be achieved in two ways. The first, referred to as injection
stretch blow molding, begins with creating a preform through injection.
The preform is then heated to a specified temperature and placed in the
mold. In the mold, the preform will be mechanically stretched and then
inflated with gas.
The second method, called reheat and blow molding, involves the use of
premade preforms. The preforms are generated off site and purchased by
a factory, for example. The preforms are then placed into a machine to
reheat the plastic and to inflate the preforms in the molds.
Attempts have been made to incorporate integral handles in PET and like
injection blow moulded containers—for example see U.S. Pat. No.
4,629,598 to Thompson, assigned to Tri-Tech Systems International, Inc.
The parison or preform from which the handled bottles of U.S. Pat. No.
4,629,598 are produced is illustrated in FIG. 1. To date, however,
attempts to produce a practical, mass produced version of this
arrangement have been unsuccessful. Instead, the best that appears to
have been done in commercial practice is an arrangement whereby the
blown containers are arranged to accept a clip on or snap on handle in
a separate production step after the container itself is formed. See
for example WO82/02371 and WO82/02370, both to Thompson.
Injection-stretch
blow moulding machine manufacturer is a process in which the parison is stretched both axially and radially, resulting in biaxial orientation.
Biaxial orientation provides increased tensile strength (top load),
less permeation due to tighter alignment of the molecules, and improved
drop impact, clarity, and lightweighting of the container.
Not all thermoplastics can be oriented. The major thermoplastics used
are polyethylene terephthalate (PET), polyacrylonitrile (PAN),
polyvinyl chloride (PVC), and polypropylene (PP). PET is by far the
largest volume material, followed by PVC, PP, and PAN.
There are basically two types of processes for stretch- blow moulding:
1) single-stage in which preforms are made and bottles blown on the
same machine, and 2) two-stage in which preforms are made on one
machine and blown later on another machine.
Single-stage equipment is capable of processing PVC,
PET recycling line
, and PP. Once the parison is formed (either extruded or injection
moulded), it passes through conditioning stations which bring it to the
proper orientation temperature. The single-stage system allows the
process to proceed from raw material to finished product in one
machine, but since tooling cannot be easily changed, the process is
best suited for dedicated applications and low volumes.
Oriented PVC containers most commonly are made on single-stage,
extrusion-type machines. The parison is extruded on either single- or
double-head units Temperature conditioning, stretching, and thread
forming are done in a variety of ways depending on the design of the
machine. Many of the processes presently in use are proprietary.
Many oriented PET containers are produced on single-stage machines.
Preforms are first injection moulded, then transferred to a temperature
conditioning station, then to the blow moulding operation where the
preforms are stretch-blown into bottles, and finally to an eject
station.
With the two-stage process, processing parameters for both preform
manufacturing and bottle blowing can be optimized. A processor does not
have to make compromises for preform design and weight, production
rates, and
pet bottle washing line
quality as he does on single-stage equipment. He can either make or buy
preforms. And if he chooses to make them, he can do so in one or more
locations suitable to his market. Both high-output machines and low
output machines are available. Heretofor two stage extrusion-type
machines generally have been used to make oriented PP bottles. In a
typical process, preforms. are re-extruded, cooled, cut to length,
reheated, stretched while the neck finish is being trimmed, and ejected.
It is an object of the present invention to produce a practical,
readily implementable injection, stretch blow moulded container made
from an orientable plastics preform material incorporating a handle
joined in a loop at at least two points to the preform.