24-08-2012, 04:51 PM
A Project Report on Stretch Blow Moulding
final stetch blow.pdf (Size: 1.96 MB / Downloads: 174)
Introduction
Blow moulding is a technique that was invented thousands of
years ago for the production of glass containers, e.g. bottles and
jars. The automated blow moulding process as it is known today
has seen rapid development during the last century, while at the
same time the range of applications and diversity of materials has
considerably increased. In spite of the fact that blow moulding has
been used for many years, manufacturers still experience
difficulties in optimizing and controlling the process.
In polymer container manufacture three main blow moulding
techniques can be distinguished: injection blow moulding,
extrusion blow moulding and stretch blow moulding. In injection
blow moulding first a polymer preform is formed by injecting a
polymer melt into a tube-shaped mould and subsequently it is
brought into another mould, where the final container is blown by
inflating the perform with air. Injection blow moulding is usually
used to manufacture small or wide-mouthed containers. In
extrusion blow moulding the polymer melt is extruded in a preform
shape before blowing it into the container shape. Extrusion blow
moulding can be used for a wide variety of container shapes and
has in general a high production rate.
IMPORTANCE OF STRETCH BLOW MOULDING
The importance of molecular orientation is widely recognized. By
biaxially stretching the extrudate before it is chilled in the mould,
real improvements to the finished bottles can be obtained, this
technique allows the use of lower material grades or thinner wall
thicknesses; both approaches reduce material cost.
PROCESS OF BLOW MOULDING.
Blow Molding (BM) process makes it possible to manufacture
molded products economically, in unlimited quantities, with virtually
no finishing required. The basic process of blow molding involves
a softened thermoplastic hollow form which is inflated against the
cooled surface of a closed mold. The expanded plastic form
solidifies into a hollow product.
Blow molded components are now seen all over the markets and
industries for traditional materials, particularly in liquid packaging
applications. The last few decades saw the introduction of Poly
Ethylene (PE) squeeze bottles for washing liquids, Poly Vinyl
Chloride (PVC) for cooking oil and fruits squash bottles, and Poly
Ethylene Terephthalate (PET) for carbonated beverage
bottles. Nowadays, it is also used for the production of toys,
automobile parts, accessories and many engineering components.
STRETCH BLOW MOULDING
Stretch blow molding is perhaps best known for producing P.E.T.
bottles commonly used for water, juice and a variety of other
products. There are two processes for stretch blow molded P.E.T.
containers. In one process, the machinery involved injection molds
a preform, which is then transferred within the machine to another
station where it is blown and then ejected from the machine. This
type of machinery is generally called injection stretch blow molding
(ISBM) and usually requires large runs to justify the very large
expense for the injection molds to create the preform and then the
blow molds to finish the blowing of the container. This process is
used for extremely high volume (multi-million) runs of items such
as wide mouth peanut butter jars, narrow mouth water bottles,
liquor bottles etc.
WHY PET AND WHY STRETCH - BLOW?
The problem with polymers for carbonated drinks is to contain the
carbon dioxide pressure, and this depends on the gas permeability
of the polymers. Among the polymers commonly used for bottles,
PET is relatively impermeable. However, to make a satisfactory
article from PET, or any crystallisable polymer, requires. the
crystalline structure to be realized. This is the function of the
stretch-blow method of making bottles in PET. The same principles
can be utilized in e.g. PVC or P.P., PET is a prime example of a
Polymer whose crystallinity can be controlled by processing some
other crystalline polymer e.g. actual, nylon crystalline room
tenuously and so cannot be dry good in this way.
WHY PET IN PACKAGING.
Due to its excellent clarity, transparent like glass, Unbreakable,
light weight, Recyclable to granules for lower end market & High
speed, noise pollution free production on filling line & Eco-friendly
property it is going to replace almost all usage of glass in the field
of packaging.
What is PET?
PET stands for polyethylene terephthalate, a plastic resin and a
form of polyester. Polyethylene terephthalate is a polymer that is
formed by combining two monomers: modified ethylene glycol and
purified terephthalic acid.