Blow Moulding Flashcards
1
Q
What does blow moulding produce?
A
Hollow products
2
Q
What is a parison?
A
Pre extruded length of plastic which is inserted into blow mould to be expanded
3
Q
What can cause die swell ratio (B) to increase?
A
Die dimensions are reduced
Melt die temp is decreased
Molecular weight increases
Output rate increases
4
Q
What is thermoforming?
A
Plastic sheet is heated just above Tg and laid over a forming station, vacuum reshapes sheet to form
5
Q
What flow mechanisms are responsible for die swell and parison sag?
A
Die swell - melt elasticity so it expands at die exit when stress is zero
Parison sag - gravimetric deformation under the die
