05-02-2013, 12:33 PM
BLOW MOULDING
[attachment=49669]
INTRODUCTION
The basic blow moulding process has two fundamental phases. First, a parison (or a
preform) of hot plastic resin in a somewhat tubular shape is created. Second, compressed
air is used to expand the hot preform and press it against mould cavities. The pressure is
held until the plastic cools.
Extrusion Blow Moulding
Continuous Parison Type
This is the simplest and most common type of blow moulding. A hollow tube
called parison is continuously extruded from an annular die. When the desired
length of the parison is reached, the mould closes around the parison. The parison
is cut above the mould and the mould is transferred to a separate station where the
parison is blown by compressed air, cooled and finally the article is ejected out of
the mould.
Intermittent Type
The parison is extruded between the two halves of the open mould. When the
desired length of the parison is reached, the mould closes around the parison.
Compressed air is blown through a bore in the mandrel. At the same time, the
article is externally cooled by water circulating in the mould. The article is then
ejected by compressed air or metal stripper.
Injection Blow Moulding
In this process a parison is injection moulded directly on to a blow stick. The blow stick
is then transferred with the molten parison, to the blowing cavity. The parison is blown
to the shape of the cavity by compressed air which is passed through the blowing stick.
Injection Stretch Blow Moulding
In this process, the first stage is to produce an Injection Moulded Preform. The preforms
are then fed to a reheating device where it is heated to the thermoplastic temperature
range. The reheated preforms are transferred into the blowing cavity where biaxial
orientation of preform to the shape of mould takes place.
Extrusion Stretch Blow Moulding
In extrusion stretch blow moulding, the free extruded hot parison is blown to a
predetermined shape in a first station blow mould. This shape is then transferred to a
second station blow mould where the final biaxially oriented container is produced.
Requirements for Blow Moulding Materials
From a processing technology standpoint, all materials with melts that have the following
properties are suitable for blow moulding applications :
· Sufficient thermal stability for the processing temperature range and, if necessary, for
repeated processing
· Sufficient flowability of the homogenous, plasticated melt.
· Sufficient stretchability of the tube (parison) even at high stretching speeds.
· Excellent repeatability of parison weight and length
· A smooth parison surface.
· Compatibility with additives such as masterbatches, pigments etc.
· A sufficiently wide processing range for the required finished part properties.
· Excellent lot to lot consistency.
[attachment=49669]
INTRODUCTION
The basic blow moulding process has two fundamental phases. First, a parison (or a
preform) of hot plastic resin in a somewhat tubular shape is created. Second, compressed
air is used to expand the hot preform and press it against mould cavities. The pressure is
held until the plastic cools.
Extrusion Blow Moulding
Continuous Parison Type
This is the simplest and most common type of blow moulding. A hollow tube
called parison is continuously extruded from an annular die. When the desired
length of the parison is reached, the mould closes around the parison. The parison
is cut above the mould and the mould is transferred to a separate station where the
parison is blown by compressed air, cooled and finally the article is ejected out of
the mould.
Intermittent Type
The parison is extruded between the two halves of the open mould. When the
desired length of the parison is reached, the mould closes around the parison.
Compressed air is blown through a bore in the mandrel. At the same time, the
article is externally cooled by water circulating in the mould. The article is then
ejected by compressed air or metal stripper.
Injection Blow Moulding
In this process a parison is injection moulded directly on to a blow stick. The blow stick
is then transferred with the molten parison, to the blowing cavity. The parison is blown
to the shape of the cavity by compressed air which is passed through the blowing stick.
Injection Stretch Blow Moulding
In this process, the first stage is to produce an Injection Moulded Preform. The preforms
are then fed to a reheating device where it is heated to the thermoplastic temperature
range. The reheated preforms are transferred into the blowing cavity where biaxial
orientation of preform to the shape of mould takes place.
Extrusion Stretch Blow Moulding
In extrusion stretch blow moulding, the free extruded hot parison is blown to a
predetermined shape in a first station blow mould. This shape is then transferred to a
second station blow mould where the final biaxially oriented container is produced.
Requirements for Blow Moulding Materials
From a processing technology standpoint, all materials with melts that have the following
properties are suitable for blow moulding applications :
· Sufficient thermal stability for the processing temperature range and, if necessary, for
repeated processing
· Sufficient flowability of the homogenous, plasticated melt.
· Sufficient stretchability of the tube (parison) even at high stretching speeds.
· Excellent repeatability of parison weight and length
· A smooth parison surface.
· Compatibility with additives such as masterbatches, pigments etc.
· A sufficiently wide processing range for the required finished part properties.
· Excellent lot to lot consistency.