Question about Plastic Thermal stability

[ryandias]

I am designing a plastic enclosure for electronics. I selected a PBT with no glass fiber reinforcement for the prototype, since it should be very predictable dimensionally.

The process engineer has raised concerns about the part "moving" when heated to 90C for 10 minutes.

My thoughts are if the plastic was held in place it would not "move".

What properties in the data sheet should I be looking at to get it's thermal stability, and how high a temperature it is reliably able to survive?

I have a Valox 357 PBT;
it lists on the data sheet,
Melt Flow 250C
Deflection Temp @ 0.46MPa, 135C
Deflection Temp @ 1.8MPa, 98C
Vicat Softening point 134C
UL RTI, Mechanical without impact 140C

Are any of these numbers I should be looking at?

 

[MacGyverS2000]

The process engineer has raised concerns about the part "moving" when heated to 90C for 10 minutes.

My thoughts are if the plastic was held in place it would not "move".

I'm willing to bet good money the process engineer gave you a confused look when you replied with that...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[ryandias]

Ok,

Sorry my description was not amazing. By move, I meant that the internal stresses in our "prototype" tooling injection molded part, pulled the room temperature straight sides and left them slightly curved. Approximately 1mm over a 50 mm length.

I think the plastic in it's softened state (90C), let the internal stresses in the part alter it's shape slightly.

The process engineer thinks that the plastic is not suitable at all.

 

[patprimmer]

I think you annealed the part and also quite likely got some post moulding crystallization that caused extra shrinkage.

Regards
Pat
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[ryandias]

Thanks.

But back to the original question.

What properties on the datasheet would predict the dimensional stability of a part made of resin X?

I felt that the;
Melt Temperature,
Vicat Softening point,
Deflection Temperatures,
were good indications of how the part would mold. Is there a better specification? or am I looking at the correct properties?

 

[patprimmer]

The property you are after is not normally quoted in data sheets. It is more likely in technical bulletins or literature with extensive data on properties.

Regards
Pat
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