Backing material for a one-shot mold?

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Discussion Overview

The discussion centers around finding a suitable backing material for a fragile metallic cylindrical mold used in injection molding thermoplastic polymer at high pressures. Participants explore potential solutions that can support the mold during the injection process and be removed afterward, considering temperature constraints and the properties of various materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Phil describes the challenge of using a fragile metallic mold with a wall thickness of approximately 1 micron, which cannot withstand the injection pressure of 150 MPa without support.
  • One participant suggests using a 2-part firm silicone, commonly used in dentistry, as it can provide temporary support and is easy to remove after use.
  • Another participant expresses concern about the high injection pressure, stating that it could damage even cement molds and questions the necessity of using the current mold, suggesting that stronger materials might be more appropriate.
  • A further inquiry is made regarding the use of a solvent to lower the viscosity of the melt, along with questions about the mold's radius and the specific thermoplastic being used.

Areas of Agreement / Disagreement

Participants present multiple competing views on the best approach to support the mold, with no consensus on a single solution. Concerns about the high pressure and material choices indicate ongoing debate.

Contextual Notes

Participants have not fully explored the implications of using different materials or the specific requirements of the thermoplastic, leaving some assumptions unaddressed.

PhilMeagher
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Hi,

I currently have a fragile metallic cylindrical mold (wall thickness ~1 micron) into which I want to injection mold a thermoplastic polymer at about 150 MPa (3.14 Mlb/sq.ft). The mold and polymer together will form the final part. However, such injection pressure far outstrips the rupture stress of the mould; so I'm looking for some sort of backing which I could use to support the mold while injecting; but which I can then remove afterwards - ideally via some kind of solvent.

Unfortunately, due to the nature of the mold material, I can not use anything which requires a temperature >150°C (>300°F) to remove it.

Initially I considered some sort of epoxy, but it seems the only way to remove a crosslinked thermoset is via heat; and that really doesn't suit at all.


Any suggestions?



All the best,

Phil
 
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How about a 2-part firm silicone? It's used in dentristry, is pretty inexpensive if you hunt around, and gives you a few minutes of very soft pliability (warm plasticine) before setting to the firmness of a shoe sole in under 10 mins. It'll provide 1-time support and slip off a treat when you're done.

http://www.amazon.com/dp/B007DKSH9Q/?tag=pfamazon01-20 for instance
 
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I don't know 150MPa is really high. As in you'd have to be careful even with cement.

http://www.theconcreteportal.com/images/constrelation/stressstrain2.JPG

21755 psi. That would break apart a cement mold. Is there a reason you have to use this mold? Sounds like recreating it out of stronger materials would be better.

Normally large volume plastic molds are made from machined steel.
 
Do u want to use a solvent to lower viscosity of melt ? what is the radius of the mold?
which is the thermoplastic ?