Hi all,
First of all thanks for all the response.
It seems alot of poeple are cofident that the differential crystalization (shrinkage) is the cause for the forward bending effect.
Some other questions. :)
What time do the polymers need to crystalize? (ns,ms,s?)
And do you expect the...
@Compositepro
The bend is formed in the horizontal plane so the inside is not on top. Inside and outside of the bend are at the same level, so cooling due free convection is the same for in- and outside of the bend.
I calculated the cooling time to less then 10 sec. This means that when i...
@patprimmer
I guess you mean plastic is a good thermal insulator.
Are you realy sure that at the tube dimensions (OD=1mm ID=0.3) I mensioned, the diffence in wall thickness can realy cause the substantial bend angle error of 30deg?
My second post states the bend is suspended in free air. Only...
@patprimmer
The bend hangs in free air so cooling should be the same for inside and outside of the bend, which means that the crystal density (and thus shrinkage) should also be the same for the in- and outside of the bend.
The crystal density is expected to be different for the ouside and...
I agree on the residual stress and relaxation through creep.
If the wall thickness stays the same on the inside and outside i dont realy know, havent measured this. Theoreticaly i would expect the outside to be thinner due tensile stress and inside to be thicker due to compressive strees...
Hi people,
I am trying to bend some PA11 tube material OD=1mm ID=0.3mm
Weird thing is that the bends are showing a forward bending relaxation behavior which continouse for 3 days. The mold angle is 90deg (inside angle). After thermoforimg for 10 mins at 160degC and rapid cooling (under 5 mins)...
