Introduction.

 Blow molding is a process for producing hollow objects, primarily from thermoplastic materials.

 Bottles and packaging are the primary applications of blow molded parts, due to its least expensive & simplest process to manufacture.

 As an industry segment, approximately 80% of polyethylene (PE) and a major share of polyethylene terephthalate (PET) materials are used for bottles and packaging by the blow molding industry.

 It offers a number of processing advantages, such as moulding of irregular curves, low stresses, variable wall thickness, the use of polymers with high molecular weight & favorable moulding cost.

 Blow moulding is operated using low moulding pressure & hence result in Low Internal Stresses.

 Since the mould used for the process consists of female cavity, it is easy to vary wall thickness & weight of the part.

 This is done either by changing machine parts or melt conditions.

Blow molding process;

PRINCIPLE:

 Material is fed into a heated barrel of Extruder.

 With the help of screw rotation & heaters the plastic is melted and homogenised.

 Melted material is forced through a set of die to form a tube or parison (Hot Plastic tube)

 parison is introduced into a mould, The mould closes & pinches off.  Blow pin is inserted through the open end of the parison to form a neck.

 Finally air is introduced through the blow pin to inflate the parison inside the mould.

 By this, the molten Polymer copies the details of the Mould.

 Lastly the moulded product is cooled & ejected.

 In the finishing stage, the part undergoes, trimming, finishing, Printing- Labeling & decorating.

Process:

Process parameters:

 Melting temperature

 Cycle time

 Blow pressure

 component thickness

 Shape of component

Processing characteristics:

 Air pressure

 Cooling

 Clamping

 Shrinkage

Materials used:  Low-density polyethylene(LDPE), High-density polyethylene (HDPE), Polypropylene (PP), Polyolefins, Unplasticized (rigid) polyvinyl chloride (UPVC), Polyethylene terephthalate (PET) and the use of engineering plastics such as Nylon (PA) and Polycarbonate (PC) in blow-molded applications is also on the rise..

 Most thermoplastics can be blow molded

 High melt strength is necessary

 OPERATIONS & FUNCTIONS

Blow Mould Closing operations by:

 Pneumatic System

 Mechanical System &

 Hydraulic System.

Clamp Platen mechanism serves following functions :

 Hold & align the mould halves.

 Hold the mould closed against the pressure of blowing air.

Blow molding machines:

 Hand operated

 Automatic

BLOW MOULDING CYCLE: • As shown in Fig. 4.11, the cycle time is made off :- Blowing time + mould closing time + blow pin insert time + cooling time + ejection or removal time .

Blow Ratio :

• The blow ratio is the ratio of the outer diameter of the blown container divided by the outer diameter of the parison.

• The required die gap can be approximately calculated multiplying the desired wall thickness of a blown bottle by the blow ratio.

Requirements for blow molding materials :

 Sufficient thermal stability for processing temperature range.

 Sufficient flow ability of the homogeneous, plasticated melt.

 Sufficient stretch ability of the tube even at high stretching speeds.

 A smooth parison surface.

 Compatibility with additives such as master batches, pigments, etc.

 excellent lot to lot consistency. BLOW MOULDING MATERIALS

For Mould Parts:

 aluminum, aluminum alloys,

 Steel, Beryllium-Copper(Be/Cu) & Cast Zinc alloys.

For Pinch off section:

 Beryllium-Copper or Steel inserts.

 Be/Cu Provides high thermal conductivity.

 Steel Insert provides wear resistance & toughness.

Based on the method used to create the parison or perform:

1. Extrusion Blow Moulding that uses an extruded tube.

2. Injection Blow Moulding that uses an Injection Moulded preform.

Blow moulding methods commonly used in Industries are :-

 Extrusion Blow Molding

Continuous Blow Molding

Intermittent (Accumulator) Method

Co-extrusion Blow Molding

 Injection Blow Molding

 Stretch Blow Molding Process:

 The blow molding machine is based on a standard extruder barrel and screw assembly to plasticize the polymer. The molten polymer is fed through a right angle and through a die to emerge as a hollow (usually circular) pipe section called a parison.

 When the parison has reached a sufficient length a hollow mould is closed around it. The mould mates closely at its bottom edge thus forming a seal. The parison is cut at the top by a knife prior to the mould being moved sideways to a second position where air is blown into the parison to inflate it to the shape of the mould.

 After a cooling period the mould is opened and the final article is ejected. To speed production several identical moulds may be fed in cycle by the same extruder unit. The process is not unlike that used for producing glass bottles, in that the molten material is forced into a mould under air pressure

Continuous Blow Molding

 In the continuous method, the parison is extruded continuously from a head or die unit.  The extruder produces an endless parison, which subsequently is pinched and/or cut by the closing mold halves. injection Blow Moulding

Extrusion Blow Moulding

Typical Materials Used

Polypropylene-PP

Polyethylene-PE

Polyethylene Terephthalate-PET

Polyvinyl chloride-PVC

Typical Products Made Bottles and containers

Automotive fuel tanks

Venting ducts

Watering cans

Boat fenders etc APPLICATIONS OF BLOW MOULDED PARTS

 Packaging for Milk, Fluids, Medicines, Cosmetics etc.

 Automotive fuel tanks, Oil Bottles, Air-Ducts, Seat-Backs etc.

 Consumer Products like toys, house wares, sports goods etc.

 Drums for chemical industries.

 Bellow shaped shields & Double-Walled carrying cases.

FAULTS,CAUSES AND REMEDIES IN BLOW MOULDING PROCESS