Reaction injection moulding

Question 1

RIM principle

Answer 1

• Reactive liquids Polyol and Isocyante are metered, mixed and injected into a closed mould at low pressure
• involves simultaneous flow and exothermic curing reacitons, controlling resin morphology

Question 2

Rigid & elastomeric

Answer 2

Rigid: higher flexural modulus, good thermal resistance, chemical resistance, acoustical insulation

Elastomeric: good tougness, dimensional stability, excellent corrosion, abrasion and wear resistance

Question 3

RIM steps

Answer 3

1. preparation & mould connection
2. mixing stage and injection
3. mould filling
4. end of filling
5. switch off mixing system
6. curing stage
7. extraction
8. post-curing, complete solidification and improve mechanical properties

Question 4

Curing process

Answer 4

i) liquid-to-rubber gelation
ii) rubber-to-glass vitrification

• after gelation, no material flows due to huge viscosity increase
• vitrification: cross-linking density and molecular weight of polymer increase
• when glass transition temp reaches cure temp
• rate of reaction significantly decreases after vitrification

Question 5

Structural RIM (SRIM)

Answer 5

• involves placement of a preform inside the mould

- besides that very similar to standard RIM

Question 6

Reinforced RIM

Answer 6

• short fibres mixed with polyol
• 0.4 - 1.5mm max length
• max 5wt%

Question 7

Gas assisted RIM

Answer 7

• gas is injected as reaction takes place

- pressure is held for a time whilst reaction occurs