Manufacturing Technology
1.
(a) why the injection molding required the reciprocating screw?
(b) why moving forward and backward
2....
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Mechanical Engineering
Manufacturing Technology
1. (a) why the injection molding required the reciprocating screw?
(b) why moving forward and backward
2. glass (a)melting point (b) process in producing glass
3. Thermoforming (at least 5) : (a) material (b) application (c) how its work
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1a In a reciprocating screw injection molding machine materialflows under gravity from the hopper onto a turning screw Themechanical energy supplied by the screw together with auxiliaryheaters converts the resin into a molten state At the same timethe screw retracts toward the hopper end When a sufficient amountof resin is melted the screw moves forward acting as a ram andforcing the polymer melt through a gate into the cooled mold Oncethe plastic has solidified in the mold the mold is unclamped andopened and the part is pushed from the mold by automatic ejectorpins The mold is then closed and clamped and the screw turns andretracts again to repeat the cycle of liquefying a new increment ofresin For small parts cycles can be as rapid as severalinjections per minuteReciprocatingscrews were developed in the mid1950s and by 1960 they quicklybegan to supplant the older systems in Europe and the UnitedStates The great advantage of the reciprocating screw design isthat it helped to manage temperature in three critical ways2a meltingpoint of glassBy its very definition glass does not have a meltingpoint A melting point is the temperature at which the atoms in acrystal gain enough thermal energy to break theircrystalline bonds Instead of being fixed in an orderedarrangement they become free to move about as a liquidGlass is not a crystal When it is cooled from a liquid theatoms do not line up into that ordered arrangement Instead as thetemperature is reduced they move past each other more and moresluggishly Eventually a temperature the glass transitiontemperature is reached at which no further movement or rotationof bonds is possible The atoms are fixed in position but in theirdisordered liquid positions not an ordered crystal This sort offrozeninplace liquid is what we call a glassWhen a glass is heated to its glass transition temperature theatoms
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