Corrugation in foamed PS profiles

[Arcodes]

When trying to produce fairly large profiles in low-density XPS foam we are continually faced with corrugation. We thought memory effect interfered with the foaming when exiting the die but (greatly) increasing the land length of our die has had no effect at all. A tip, anyone?

 

[patprimmer]

Is part density a bit on the low side?

Regards
Pat
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[Arcodes]

Yes, part density is on the low side, about 80-85 kg/m³. Upping the density to about 110-120 kg/m³ solves the problem but this makes our profit margin rather too low.

We use pure CO2 as a blowing agent.

 

[patprimmer]

Can you increase temperature or pressure in the melt.

Regards
Pat
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[Arcodes]

Not both at once, no

I always look for the pressure ceiling when testing so I know increasing melt pressure does not have a positive effect on the corrugation.

Increasing the temperature is only possible when I decrease the amount of blowing agent, otherwise the pressure is insufficient to keep the CO2 dissolved in the melt.

Could replacing a small amount of the CO2 with an endothermic blowing agent be helpful? So as to decrease the foaming rate after exiting the die?

 

[patprimmer]

Would a colder mould do the same.

Could you spray them with cold water to keep the surface frozen.

I am shooting in the dark a bit here as I have minimal experience with EPS foam. What little I do have used I think isopentane as the blowing agent. My experience is with chemical blowing agents and density reductions in the order of 10 to 30% only. Corrugations then usually mean under packed and over blown usually has a blow out not a corrugation.

There is less than zero profit in reject parts so while 110kg per cubic meter makes for low profit, it seems 80kg per meter makes less than no profit at this stage.

Regards
Pat
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[Arcodes]

Yes, cooling down the mould helps by making the melt slightly tougher and so more resistant to deformation. Cooling down too far impedes proper foaming though, as the tensile strength of the outer layer then becomes too high.

I guess we'll have to make do with a more dense product. Thank you for your help in this matter.

 

[patprimmer]

Sorry I could not help more.

Regards
Pat
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