Should surface temperature be below ejection temperature?

aonotaka96 — Mon, 19 Aug 2024 21:01:54 GMT

"Temperature, part" needs to be below ejection temperature?

One of my cooling studies show Temperature. part = 112 °C - 98 °C at hot spots at the end of cooling.

The material is PP (Glass filled) whose ejection temperature is 102 °C
We need to have ejector pins at those hot spots.
We cannot increase a cycle time anymore.
Cooling line has been optimized.

I am concerned about ejector pins deforming those hot spots.

Is it better to use moldmax inserts to those hot spots? or should I proceed without moldmax?

Because the material is glass filled PP, glass fiber can damage moldmax inserts. So I want to avoid Be/Cu inserts if I could...

Re: Should surface temperature be below ejection temperature?

bernor_mf — Wed, 18 Sep 2024 10:33:06 GMT

@aonotaka96

Hi,

You posted this a while ago, and maybe already sorted out and resolved?

In general I would say yes, that Temperature, part result should be below ejection temperature.

And to use to find hot spots.

Temperature. part = 112°C - 98°C indicates high temperature also in temperature mold.

I believe PP+GF aim is around 30-60°C.

"The material is PP (Glass filled) whose ejection temperature is 102 °C"

You also need to consider the Transition Temperature, which many times can be close like 10°C difference,

So mold temperature needs to be lower, and hence longer time to cool.

But you "cannot increase cycle time anymore", so kind of locked in the design in seems.

If to use Moldmax inserts or not, I believe a Cool simulation with insert should be considered.

A Moldmax insert needs to be cooled well. If not it will hold the heat, and might make the issue worse.

I think some Moldmax has different hardness, but affects thermal conductivity. So need to review this.

The wear out and damage depends on the flow direction and how enters mold cavity, generally more wears out in gate region where higher velocity.

Also, if you are at 112°C in regions, the material softens and you are getting closer to transition temperature.

Ejection Temperature is when the temperature when part has cooled sufficiently to be removed from the mold.

The ejection temperature for Moldflow materials are derivated from DSC (Differential Scanning Calorimetry), in general. (Might be deviations.)

I think you should be at Ejection Temperature for the material at least, to be on the safe side.

Also, check the HDT temperature. It gives a hint of the “load-bearing” capability compared to Ejection Temperature for the material.

Note: specimen thickness 4mm

By using those two temperature it gives information on how to move forward.

If the HDT temperature is higher than ejection temperature, the material could bear a higher load at ejection.

Use with care, as this is pushing the limits somewhat.

HDT Heat Deflection Temperature under Load

Standards: ASTM D-648 ; ISO 75

The test for HDT closely represents what a part endures during ejection with an ejector pin pushing on a single side, while the opposite side is unsupported.

Note: specimen thickness 4mm

HDT test measures the temperature at which the specimen loses its “load-bearing” capability.

Not a clear cut answer to your questions, but some things to consider I think.

Hope this helps somewhat.

Regards,

Berndt

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Should surface temperature be below ejection temperature?

Re: Should surface temperature be below ejection temperature?