Polymers Flashcards

Question

Elastomer examples

Answer 1

Natural rubber Synthetic rubber Silicones

Answer 2

latex based good for high friction abrasive applications but has low resistance to oil, heat and sunlight. App: shoes

Answer 3

improved environmental resistance over nat.rubber and higher temperature range. Apps: Tires, seals, belts

Answer 4

Highes temperature range. but inferiour in other properties. App: Seals, gaskets, thermal insulation

Answer 5

Highes temperature range. but inferiour in other properties. App: Seals, gaskets, thermal insulation

Answer 6

Very similar to metals. Can be molded, cast, machined, joined with ease polymers require less energy to process but their properties are highly influenced by processes polymers start out in pellet form or as liquid for reinforced plastic parts

Answer 7

raw thermoplastic pellets are fed into the hopper and then a barrell. the barrel houses a screw that conveys the pellets down the barrel the shearing action as well as external heaters cause the pellets to melt in the last section of the screw the pressure builds up and a the polymer is extruded through a die

Answer 8

Once the melted plastic reached the end of the barrel, it is forced through a die and cooled uniform cooling helps minimize distortion. various die shapes produce different proviles or even thin sheets and films. the phenomena of die swell causes plastic to be shaped differently than the extrusion die

Answer 9

Once the melted plastic reached the end of the barrel, it is forced through a die and cooled uniform cooling helps minimize distortion. various die shapes produce different proviles or even thin sheets and films. the phenomena of die swell causes plastic to be shaped differently than the extrusion die

Answer 10

simultaneous extrusion of multiple polymers through a single die each material may have their own properties and funtions ie: barier to oil and water, electrical inslation and conduction, sealing and labelling plastic coated eletrcial wires are produced this way

Answer 11

simultaneous extrusion of multiple polymers through a single die each material may have their own properties and funtions ie: barier to oil and water, electrical inslation and conduction, sealing and labelling plastic coated eletrcial wires are produced this way

Answer 12

Similar to hot chamber die casting Polymer pellets are plasticized to create "the melt" the melt is forced through a nozzle into the mold Use a reciprocating screw type injector For thermoplastics - the mold is cooled to speed up processing. For thermosets -the mold is held got to promote polymerization and crossing linking shrinkage is a concern (1-7%) and molds are made oversized

Answer 13

``` Gate Mold Cavity Cavities Main runners Sprue Guide Pin ```

Answer 14

Cold Runner 2 plate Cold Runner 3 Plate Hot Runner Mold

Answer 15

simplest mold desprue and runners must be removed by hand

Answer 16

Runner system is removed from part via intermediate stripper plate Runners and parts are separate and solid

Answer 17

Runner system is kept in melted state after parts have solidified

Answer 18

Combines Extrusion and injection molding

Answer 19

``` A thin tube (parison) is extruded and clamped into a mold high presure( 350-700 MPa) then forces the parison outward t fill the cavity. Upon coling the part is injected ```

Answer 20

Instrad of extruded parison in injected molded then transferred to a blow mold and expanded using high pressure gas. Ex: milk containers

Answer 21

similar to extrusion molding but at a lower cost Thin walled metal mold is made and powdered plastic is placed inside the mold. The heat and rotatin is applied about 2 perpendicular axis. Long thin walled parts may be made from this process. Cycle times are longer but mold and equipment costs are lower

Answer 22

similar to extrusion molding but at a lower cost Thin walled metal mold is made and powdered plastic is placed inside the mold. The heat and rotatin is applied about 2 perpendicular axis. Long thin walled parts may be made from this process. Cycle times are longer but mold and equipment costs are lower

Answer 23

A family of processes where thermoplast sheet is formed over a mold via the application of heat and pressure or vacuum This plastic sheet is head until soft then placed over a mold and pressure is applied. Holld parts ma be made by forcing to plastic sheets together against the mold and applying force. Limitations: No parts with holes

Answer 24

A preshaped charge i placed into a heated mold cavity and held under pressure until cured. Flash is formed which mustbe removed in subsequent operations Thermosets are usually chosen for compression molding because of londer cycle times and heated die molds are less complex and cost less tha injection molding undercuts are possible because molds can be mad to open sideways aps: dishes, handles, pipe fittings

Answer 25

A preshaped charge i placed into a heated mold cavity and held under pressure until cured. Flash is formed which mustbe removed in subsequent operations Thermosets are usually chosen for compression molding because of londer cycle times and heated die molds are less complex and cost less tha injection molding undercuts are possible because molds can be mad to open sideways aps: dishes, handles, pipe fittings

Answer 26

Some thermoplastics and thermosets maybe cast into rigid or flexible molds. For thermoplasics a mixture of monomer and catalyst is poured into themold and allowe dto polymerize at ambient pressure Use flexible molds allow complex, intricate shapes to be formed inserts and other components may be cast into the patr allowing versatility form molding of cups, food containers and packing materials are made using this process