Iqra abdul rashid Polymer Engineering department Polymer Science

Iqra abdul rashid Polymer Engineering department

Polymer Science & Engineering TM-2052 Lecture # 04

Outline • • Polymer Processing Extrusion Compression molding Transfer molding

Polymer processing • Polymer melts and concentrated solutions exhibit both viscous and elastic properties • Viscous properties determine processing parameters as the form of the velocity profile, magnitude of the pressure drop and the amount of heat generation (viscous heating ) during extrusion through die

Polymer processing • Elastic behavior is responsible for such extrusion phenomena such as Ø Die swell Ø Melt fracture • Polymer processing operations are classified in five categories • Extrusion • Molding • Calendring • Wire coating

Extrusion • Two principal components of an extrusion operation are the extruder and the die • Extruder consists of a hopper that holds the resin stock (small pellets or powder) • Extruder barrel can be divided into three sections ØFeed ØCompression ØMetering section

Schematic diagram of an extruder

Single Screw Extruders • The SSE is a relatively poor mixing device, and specialized screw sections are needed to improve the mixing efficiency of this apparatus. Distributive mixing can be improved using static mixers or mixing heads such as the “pineapple” configuration shown here. Kenics Static Mixer Pineapple Mixing Section

Extrusion • Devolatilization In commercial polymer production powder from a polymerization reactor may be fed directly to an extruder that has an opening for venting volatiles • viscosity of polymer melts and concentrated polymer solutions decreases with increasing shear rate • Extruders equipped with twin screws that rotate in opposite directions • Used when higher shear rates are needed

Industrial rubber extruders

Molding • • Compression molding Transfer molding Blow molding Injection molding

Compression molding • Compression molding is the least expensive and simplest of all polymer processing operations • Used for molding thermosets such as phenolic resins, alkyds, unsaturated polyesters • Resin is placed in the bottom half of an open, heated mold, next the top half of the mold is placed over the bottom half and pressure is applied to cause the molten resin to completely fill the mold cavity • Excess resin is forced out of the mold as flash

Schematic diagram of compression molding

Transfer molding • The mold is closed prior to resin entry • Plunger is used to force a predetermined amount of molten resin from an open transfer pot through a small opening in the mold • The mold is opened, ejector pins push the molded part out of the mold • Cull The residual (uninjected molding resin) is called the cull • Molding cycles tend to be shorter than for compression molding because

Transfer molding ØMold temperature is higher ØPre-melted polymer flows more easily through the mold under low pressure • Transfer molding is used to mold parts with ØIntricate geometries ØMold fragile parts or ØWhen an insert is used in the mold

Transfer molding

Assignment topic • Thermal , electrical, mechanical and chemical testing techniques of the polymers • Submission date June 6, 2016