UNIVERSITY INSTITUTE OF ENGINEERING
Bachelor of Engineering (Mechanical Engineering)
Manufacturing Techniques (MET-204)
By: Dr. Vinay Shah
Lecture no. 15
CASTING PROCESS DISCOVER . LEARN . EMPOWER
Topics of Presentation
Introduction to Blow moulding
Advantages and Disadvantages of Blow Moulding
Extrusion Blow Moulding
Continuous extrusion blow molding
Injection stretch blow molding
Introduction to Blow moulding
Blow molding moulding is a specific manufacturing process by which hollow plastic parts are formed
and can be joined together. It is also used for forming glass bottles or other hollow shapes.
Fig: Blow Moulding Process
Source: Imagegallary.com
Introduction to Blow moulding
The blow molding process begins with melting down the plastic and forming it into a parison or, in the
case of injection and injection stretch blow molding (ISB), a preform. The parison is a tube-like piece of
plastic with a hole in one end through which compressed air can pass.
Fig: Blow Moulding Process
Source: Imagegallary.com
Advantages and Disadvantages of Blow moulding
Advantages
Low tool and die cost
Fast production rates
Ability to mold complex parts
Handles can be incorporated in the design
Disadvantages
Limited to hollow parts
Low strength
Parisons are often made of mixed (multilayer) materials, to
increase their barrier properties, and are thus not recyclable
To make wide neck jars spin trimming is necessary.
Extrusion Blow Molding
In extrusion blow molding (EBM), plastic is melted and extruded into a hollow tube (a parison). This parison
is then captured by closing it into a cooled metal mold. Air is then blown into the parison, inflating it into the
shape of the hollow bottle, container, or part. After the plastic has cooled sufficiently, the mold is opened and
the part is ejected
Fig: Blow Moulding Process
Source: Imagegallary.com
Straight Extrusion Blow Molding
Straight EBM is a way of propelling material forward similar to injection molding whereby
an Archimedean screw turns, then stops and pushes the melt out.
Continuous extrusion blow molding
Continuous Extrusion Blow Molding is a variation of Extrusion Blow Molding. In continuous extrusion blow
molding, the parison is extruded continuously and the individual parts are cut off by a suitable knife.
Continuous extrusion equipment
Rotary wheel blow molding systems
Shuttle machinery
Continuous extrusion blow molding
Intermittent extrusion blow molding
Intermittent Extrusion Blow molding is a variation of Extrusion Blow Molding. Intermittent extrusion
machinery
Reciprocating screw machinery
Accumulator head machinery
Continuous extrusion blow molding
Spin trimming
Containers such as jars often have an excess of material due to the molding process. This is trimmed off by spinning a
knife around the container which cuts the material away. This excess plastic is then recycled to create new moldings. Spin
Trimmers are used on a number of materials, such as PVC, HDPE and PE+LDPE. Different types of the materials have
their own physical characteristics affecting trimming. For example, moldings produced from amorphous materials are
much more difficult to trim than crystalline materials. Titanium coated blades are often used rather than standard steel to
increase life by a factor of 30 times.
Injection blow molding
Continuous extrusion blow molding
Advantages
• It produces an injection molded neck for accuracy.
Disadvantages
• Only suits small capacity bottles as it is difficult to control the base centre during blowing.
• No increase in barrier strength as the material is not biaxially stretched.
• Handles can't be incorporated.
References
Text Books :
1. P.N.Rao, Manufacturing Technology ( Tata McGraw Hill )
2. P.C.Sharma, A text book of Production Technology ( S Chand Publication )
3. R.K. Rajput, A Text book of Manufacturing Technology ( Laxmi Publications )
Reference Books:
4. Heine ,RW , CR Loper and Rosenthal, Principles of Metal Casting ( McGraw Hill –NewYork)
5. Amitabha Ghosh &Asok Kumar Malik, Manufacturing Science (Affiliated East West Press Pvt.
Ltd.)
6. S. Kalpakjian & Steven R. Schmid, Manufacturing Engineering & Technology (Pearson)
THANK YOU
