BLOW MOLDINGDepartment of Applied MechanicsSUBMITTED BYNivesh Pandya2008AMD3104SUBMITTED TOAssistant Prof. M.P.Gururajan

Historical Development

YearDevelopment1930The first applications for blow molding were for cellulose nitrate 1940Introduction of LDPE (Low Density Polyethylene ). With LDPE, the plastic industry growth rapidly1942The first polyethylene bottle was manufactured using the blow molding process1950The demand for blow moulding increases by the mass production of High Density Polyethylene (HDPE) and Polypropylene (PP) for various applications

The principle of blow moldingA simple explanation of the principle of blow molding is similar to inflating a balloon

IntroductionBlow molding : Definition There are several methods of blow molding plastic parts.They all have five stages in common :-

1. Plasticizing or melting the resin

2. Parison or preform production

3. Inflation of the parison or preform

4. Ejection of the part

5. Trimming and finishing of the part

Blow molding processes

Blow molding processes

Extrusion blow moldingInjection blow moldingStretch blow molding ( Classification based on parison/preform formation )

Extrusion blow molding

(Courtesy : http://www.et.byu.edu/groups/mfg355/pages/lectures/powerpoint_ppt/13%20blow%20molding.ppt)

Step 1 Step 2

Step 3 Step 4(Courtesy : http://www.et.byu.edu/groups/mfg355/pages/lectures/powerpoint_ppt/13%20blow%20molding.ppt)

Extrusion blow molding

Continuous extrusion blow molding Intermittent extrusion blow molding

Extrusion Blow Mold

(Courtesy : http://industrialblowmolding.com/?page_id=22)

Extrusion Blow MoldNeck-ring insert

Cooling water ports

Cut-off insert123132(Courtesy : http://industrialblowmolding.com/?page_id=22)

Injection-Blow Molding (IBM )(1) Parison is injected molded around a blowing rod(2) Injection mold is opened and parison is transferred to a blow mold(3) Soft polymer is inflated to conform to the blow mold(4) Blow mold is opened and blown product is removed(Courtesy :http://www.me.umn.edu/education/courses/me3221sum/Lab/BlowMolding/blowmolding.html)

AdvantagesEliminates the weld line

DisadvantagesExtra steps in manufacturing

Injection-Blow Molding (IBM )

Stretch blow molding(Courtesy :http://www.me.umn.edu/education/courses/me3221sum/Lab/BlowMolding/blowmolding.html)The biggest disadvantage of blow molding process (above all three) is that these are limited to hollow parts.

Material RequirementsGood melt strength ( i.e low melt index)

Melt index : Measures the rate of extrusion of thermoplastics through an orifice at a prescribed temperature and load. Melt index gives the processor a rough idea of what to expect from the flow behavior of a resin during processing.

Reasonable blow ratio capabilities

Most thermoplastics can be blow molded

Some typical applications are

HDPE : High Density Polyethylene (stiff bottle, toys, cases, drum)LDPE : Low Density Polyethylene (flexible bottle)PP : Polypropylene (higher temperature bottle)PVC : Polyvinyl Chloride (clear bottle, oil resistant containers)PET : Polyethylene terephthalate (soda pop bottle)

Application (Courtesy : http://industrialblowmolding.com/?page_id=22)

Process ParametersParison characteristicssize, shape, straightness, wall thickness, mechanical propertiesInflation pressureMold designcooling, ventingBlow ratio= Mold diameter/Parison Diameter (1.5 to 3 are common

Thank You

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