CAPABILITIES
Blow molding is the process of forming a molten tube (referred to as the parison or preform) of thermoplastic
material (polymer or resin) and placing the parison or preform within a mold cavity and inflating the tube with
compressed air, to take the shape of the cavity and cool the part before removing from the mold.
Any hollow thermoplastic part can be blow molded.
Parts are not just limited to bottles, where there is one opening and it is usually smaller in diameter or size
than the overall body dimensions. These are some of the most common shapes used in consumer packaging, however
there are other typical types of blow molded parts, including, but not limited to:
• Industrial bulk containers
• Lawn, garden and household items
• Medical supplies and parts, toys
• Building industry products
• Automotive-under the hood parts
• Appliance components
History of Blow Molding
The basic concept of blow molding comes from the glassblowing process. As early as the 1880’s there was a
patented method of extruding a Celluloid polymer into a parison and blow molding a part. Early methods and
materials to blow plastics into shapes were very crude and not suitable for mass production. It wasn’t until the
late 1930’s that the first commercial machines and products were developed for the manufacturing of blow molded
bottles. The major event that triggered and fueled the early years of commercial blow molding was the
development of low and high density polyethylene suitable for blow molding and consumer packages. From this,
there was an explosion of blow molded products and equipment in both Europe and North America.
Blow Molding Manufacturing Processes
There are three main types of blow molding:
• Extrusion blow molding
• Injection blow molding
• Injection stretch blow molding
The main differences among them are the method of forming the parison; either by extrusion or injection molding,
the size of the parison and the method of movement between the parison and blow molds; either stationary,
shuttling, linear or rotary.
In Extrusion Blow Molding-(EBM) the polymer is melted and the solid extruded melt
is extruded through a die to form a hollow tube or parison. Two halves of a cooled mold are then closed around
the parison, pressurized air is introduced through a pin or needle, inflating it into the shape of mold, thus
producing a hollow part. After the hot plastic has cooled sufficiently, the mold is opened and the part is
removed.
In EBM there are two basic methods of extrusion, Continuous and Intermittent. In continuous, the parison is
extruded continuously and the mold moves to and away from the parison. In Intermittent, plastic is accumulated
by the extruder in a chamber, then forces through the die to form the parison. The molds are typically
stationary under or around the extruder.
Examples of the Continuous Process are Continuous Extrusion Shuttle machines and Rotary Wheel machines.
Intermittent extrusion machines can be Reciprocating Screw or Accumulator Head. Various factors are considered
when selecting between the processes and the size or models available.
Examples of parts made by the EBM process include many hollow products, such as bottles, industrial parts, toys,
automotive, appliance components and industrial packaging.
With respect to the Injection Blow Systems – (IBS) process, the polymer is
injection molded onto a core within a cavity to form a hollow tube called a preform. The preforms rotate on the
core rod to the blow mold or molds at the blowing station to be inflated and cooled. This process is typically
used to make small bottles, usually 16oz/500ml or less at very high outputs. The process is divided into three
steps: injection, blowing and ejection, all done in an integrated machine. Parts come out with accurate finished
dimensions and capable of holding tight tolerances—with no extra material in the formation it is highly
efficient.
Examples of IBS parts are pharmaceutical bottles, medical parts, and cosmetic and other consumer product
packages.
Injection Stretch Blow Molding- (ISBM) the Injection
Stretch Blow Molding- (ISBM) process is similar to the IBS process described above, in that the preform is
injection molded. The molded preform is then presented to the blow mold in a conditioned state, but before final
blowing of the shape, the preform is stretched in length as well as radially. The typical polymers used are PET
and PP, that have physical characteristics that are enhanced by the stretching part of the process. This
stretching gives the final part improved strength and barrier properties at much lighter weights and better wall
thicknesses than IBS or EBM—but, not without some limits such as handled containers, etc. ISBM can be divided
into the One Step and Two Step process.
In the One Step process both preform manufacture and bottle blowing are performed
in the same machine. This can be done in 3 or 4 station machines, (Injection, Conditioning, Blowing and
Ejection). This process and related equipment can handle small to high volumes of various shape and size
bottles.
In the Two Step process the plastic is first molded into the preform using an
injection molding machine separate from the blow molder. These are produced with the necks of the bottles,
including threads on the open end of the closed end hollow preform. These preforms are cooled, stored, and fed
later into a re-heat stretch blow molding machine. In the Two Step Reheat Blow process, the preforms are heated
(typically using infrared heaters) above their glass transition temperature, then stretched and blown using
high-pressure air in the blow molds.
The Two Step process is more suited to very high volumes of containers, 1 liter and under, with very
conservative use of resin providing great strength, gas barrier and other features.
Materials suitable for Blow Molding
Examples of Blow Molding Polymers in single layer or multiple layer structures or combinations include such
materials as:
(i) High Density Polyethylene,
(ii) Low density Polyethylene,
(iii) Polypropylene,
(iv) Co-polyester,
(v) PET,
(vi) PVC,
(vii) Nylon,
(viii) EVOH,
(ix) EVA,
(x) TPE,
(xi) COP and COC,
(xii) Polycarbonate,
(xiii) Polystyrene,
(ix) ABS, etc.
