Custom/Hybrid Casting Plastic/Urethane

speedysprocket

speedysprocket

Alex
Location
Chesapeake, VA
Just wondering if anyone making stuff out of plastic or urethane can or wants to speak to the process. I want to make some pump cones, and while I learned some things to speed up the process on my first attempt last night, it still will take me longer than I want to turn them on my lathe out of a solid piece of delrin. So I'm interested in simpler and cleaner methods...
Can anyone recommend a good material for a cone? Would I be able to mold the whole thing at once, or mold the cone solid and then machine the inside out...?
 
DAG

DAG

Yes, my balls tickled from that landing
Location
Charlotte, NC
I done quite a bit of research on Devcons Castable Urethane mold. It looks very promising for a project I’m working on. Looks like we have a space race ;)
 
speedysprocket

speedysprocket

Alex
Location
Chesapeake, VA
DAG said:
I done quite a bit of research on Devcons Castable Urethane mold. It looks very promising for a project I’m working on. Looks like we have a space race ;)
Click to expand...
Space race? I really am only trying to make some cone options for my pump. No intentions of stealing whatever you're working on.
 
DAG

DAG

Yes, my balls tickled from that landing
Location
Charlotte, NC
Castable urathans are nothing new in our sport. I think your idea is great. Lots of info on youtube showing step by step processes.
 
OCD Solutions

OCD Solutions

Original, Clean and Dependable Solutions
Location
Rentz, GA
I have played with quite a few urethanes. There's quite a bit to the process such as degassing using vacuum and then casting under pressure to ensure no air bubbles. It's an expensive endeavor to develop a new product as well. I spent over $450 in trials and testing before I made my first usable ebox grommet. I never did find a suitable material to cast my flame arrestor adapters out of and bailed after $150 of R&D. Everything either had too much flex or was just too brittle. The only items I am still successfully casting with urethanes are my grommets and switch mounts.

I purchased my lathe and mill with the intention of making molds to cast urethanes but once I get them automated and running off CNC, I think I will be better off skipping the urethanes altogether and just producing the parts out of aluminum, Delrin, etc. It wouldn't make sense doing it manually but CNC is a game changer, even with small equipment.

I briefly looked into injection molding as well. There are so many options if you have the time, money and space to operate in. I'm home based and severely limited for space.
 
OCD Solutions

OCD Solutions

Original, Clean and Dependable Solutions
Location
Rentz, GA
I went through 4 different designs of vacuum/degassing chambers before finally building exactly what I needed. The best ended up being the cheapest too I might add.

I also use silicone molds which begin to degrade as soon as you make them. They have a shelf life of a couple years but they begin to degrade within about 6 months to the point where they need to be recast. Thus the need for keeping good "masters" to remake your molds every so often.

The other hard learned lesson is ambient temperature. Successful casting drops to less than 20% if you can't keep the ambient above 75F. The material just doesn't flow and air entrapment causes a ton of blems and outright failures.
 
OCD Solutions

OCD Solutions

Original, Clean and Dependable Solutions
Location
Rentz, GA
They say to vacuum before and after mixing but I find that most of the time, before is more than adequate and you aren't eating into pot life. Nothing like trying to pull a vacuum for 5 minutes on a product with a 7 minute pot life and then trying to pour it into a mold with fine features.
 
speedysprocket

speedysprocket

Alex
Location
Chesapeake, VA
This stuff had a "20 minute pot life" and I found myself wanting more... With the amount of mixing I had to do, I can't imagine vacuuming before mixing would be worth anything.
 
OCD Solutions

OCD Solutions

Original, Clean and Dependable Solutions
Location
Rentz, GA
That will depend greatly on the specific product, viscosity, ambient temp, size of batch and mixing method. I typically do very small batches (1-2 ounces) of a low viscosity material so I stir slowly and fold the material rather than mixing. If your product requires a mechanical mixer, you would be introducing a lot of air and moisture and so degassing afterwards would be very important as well.

Degassing removes any and all moisture from the compounds so it doesn't release and expand while curing. if you perform this prior to mixing, you can do it for as long as it takes to reduce every little bit. This greatly reduces and possibly even eliminates the need to degass afterwards as all you need to do is purge whatever was introduced during mixing.

EDIT: Degass in a glass vessel so you can see the reaction. You will be amazed and learn so much faster if you see exactly how it reacts under vacuum. This is how I learned that doubling my pre-mixing vacuum time, dropped my post-mixing vacuum requirement to almost nothing.

Seeing the process also lets you adapt to the material taking on moisture as it sits. The material starts taking on moisture as soon as you crack the seal on the container and even a few weeks makes a huge difference on how long you have to degass. I had read about all these points but didn't believe it until I experienced it first hand.
 
Last edited:
You must log in or register to reply here.
Top Bottom