Backing material for a one-shot mold?

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In summary, the conversation discusses the need for a backing material to support a fragile metallic cylindrical mold during injection molding of a thermoplastic polymer at a high pressure of 150 MPa. Various options, including using a 2-part silicone or creating a new mold out of stronger materials, are suggested. The possibility of using a solvent to lower the viscosity of the polymer and the specifics of the mold and thermoplastic are also mentioned.
  • #1
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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  • #2
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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  • #3
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.
 
  • #4
Do u want to use a solvent to lower viscosity of melt ? what is the radius of the mold?
which is the thermoplastic ?
 
  • #5


I understand your dilemma and the challenges you are facing in finding a suitable backing material for your one-shot mold. Based on the information provided, I would suggest considering a water-soluble backing material such as polyvinyl alcohol (PVA). PVA is a water-soluble polymer that can be easily dissolved in water at room temperature without the need for high temperatures. It also has good strength and can withstand the pressure of injection molding. After the injection process is complete, the PVA backing can be easily dissolved in water, leaving your final part intact. Another option could be using a sacrificial mold material such as wax or sugar, which can be melted or dissolved after the injection process. However, these materials may not provide the same level of support and strength as PVA. I would recommend conducting some small-scale experiments to determine the best option for your specific mold and polymer combination. Best of luck with your project.
 

1. What is backing material for a one-shot mold?

Backing material for a one-shot mold is a type of material used to support and reinforce the mold during the casting process. It is typically placed behind the mold to prevent it from deforming or breaking during the pouring of the casting material.

2. What are the common types of backing material for a one-shot mold?

Some common types of backing material for a one-shot mold include wood, foam, and plaster. Each type has its own advantages and disadvantages, so it is important to choose the right one based on the specific needs of your project.

3. How do I choose the right backing material for my one-shot mold?

The right backing material for a one-shot mold will depend on factors such as the size and shape of the mold, the type of casting material being used, and the desired finish of the final product. It is important to consider these factors and conduct some research to determine the best option for your specific project.

4. Can I reuse backing material for a one-shot mold?

In most cases, backing material for a one-shot mold is not reusable. Once the casting process is complete, the backing material is typically removed and discarded. However, some types of backing material, such as foam, may be able to be reused if they are still in good condition after the casting process.

5. Are there any safety precautions I should take when using backing material for a one-shot mold?

Yes, it is important to take necessary safety precautions when working with backing material for a one-shot mold. This may include wearing protective gear, such as gloves and eye protection, and working in a well-ventilated area. It is also important to carefully follow the instructions for handling and disposing of the backing material to avoid any potential hazards.

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