vacuum degassing silicone query

[tango'd fett]

this one qoutes 37hg and looks pretty small next to the pencil !! They do a few others as well but this is the cheapest
http://www.coleparmer.co.uk/catalog/product_view.asp?sku=7816540

I asked their technical department and they say 80psi is required for its operation, what is needed for the HF pump?

 

[robn1]

...what is needed for the HF pump?

75psi

 

[exoray]

this one qoutes 37hg

I think they are whacky, as in the description is says max vacuum 29.5"...

You can't pull more then a perfect vacuum...

 

[tango'd fett]

Ah yes see it now exoray :unsure , going back to the pond venturi's the actual nozzle that pulls the vacuum is a lot smaller than the air inlet and outlet and looks around 1/4 " so i was wondering if this would make a difference, are the HF inlets the same size as the vacuum inlet ? Just found another one they do that is only £15 and the air inlets are 1/2" .http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=400084521420&ssPageName=STRK:MEWAX:IT

 

[exoray]

Ah yes see it now exoray :unsure , going back to the pond venturi's the actual nozzle that pulls the vacuum is a lot smaller than the air inlet and outlet and looks around 1/4 " so i was wondering if this would make a difference, are the HF inlets the same size as the vacuum inlet ? Just found another one they do that is only £15 and the air inlets are 1/2" .http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=400084521420&ssPageName=STRK:MEWAX:IT

I don't know where my HF one is off hand, I started to use an electric pump several years ago as it's simply easier and I picked 2 of them up at garage sales for less then $20 a pop, the AC evacuation pumps (like the one pictured above in the video) are cheap in the US since they started to regulate most freons putting the average fix it guy out of the AC service business... So hopefully someone else will chime in about the hole sizes on the HF pump...

But I will say that new one you posted looks like it will work a lot better but still might not do the job, you will still need a good size air compressor to pump a full 1/2" bleed for any length of time...

 

[tango'd fett]

But I will say that new one you posted looks like it will work a lot better but still might not do the job, you will still need a good size air compressor to pump a full 1/2" bleed for any length of time...

have asked the seller a few questions about it but i think you are right , it also looks to be all plastic as well so i dont think it would last long even if it did work , thanks for the help :cool

 

[exoray]

One thing to consider with those bigger pumps, you might get very good results hooking them up to water vs air... Meaning push water from your faucet though them to create the vacuum, this is how many low scale laboratories create simple vacuums...

Kinda like this... Still over priced but you might be able to find one more reasonable in the UK...

http://cgi.ebay.co.uk/ws/eBayISAPI....Category=26415&_trkparms=algo=LVI&its=I&otn=2

 

[tango'd fett]

One thing to consider with those bigger pumps, you might get very good results hooking them up to water vs air... Meaning push water from your faucet though them to create the vacuum, this is how many low scale laboratories create simple vacuums...

Kinda like this... Still over priced but you might be able to find one more reasonable in the UK...

http://cgi.ebay.co.uk/ws/eBayISAPI....Category=26415&_trkparms=algo=LVI&its=I&otn=2

Thanks exoray that looks much stronger I will have a look round , they got back to me and the pond venturi is all plastic construction so i recon it would probably last about 10 minutes!!

 

[whaley2]

is there anyone in the miami, fort lauderdale area with a vacuum degassing system that would be willing to show me the ropes in return for a couple bucks or lunch on me..iv been prototyping for about 3 years now and want to step up with professional pieces with zero air bubbles in my finished products..just would like to go over the basics and possibly degass a small part of mine to determine the variance in quality..thanks so much will

 

[exoray]

is there anyone in the miami, fort lauderdale area with a vacuum degassing system that would be willing to show me the ropes in return for a couple bucks or lunch on me..iv been prototyping for about 3 years now and want to step up with professional pieces with zero air bubbles in my finished products..just would like to go over the basics and possibly degass a small part of mine to determine the variance in quality..thanks so much will

You generally pressure cast hard resin parts to remove bubbles not vacuum, unless you use a real slow resin there simply isn't enough time to degas most casting resins...

Now with a slow resin, you can degas, it prior to pouring this will remove most suspended bubbles, but won't help after you pour into the mold and introduce more suspended air or create air pocket voids, this is where the pressure casting comes into play...

Ideally if you are anal;

1. You create a mold with a top reservoir that can hold 3-4 times the volume of resin used for the mold...
2. You use a very, very slow setting resin...
3. You vacuum degas the resin after fully mixing...
4. You pour the degassed resin into the mold carefully, to about 5-10% overfill...
5. You again vacuum degas the resin while in the mold...
6. This causes the resin to expand about 3-4 times it's volume, thus the necessity to have the top reservoir to accommodate the expanding resin...
7. You then remove the vacuum in the tank, and return back to normal atmosphere, about 15-15 PSI... this alone squishes most bubbles to microscopic...
8. You then pressurize the tank to 50-80 PSI...
9. And hold that pressure in the tank until the resin has fully cured...
10. The 5-10% overfill of the mold will gives you a little buffer for resin that sticks to the sides of the reservoir, leaks or whatever so that you are not short when you slam in the air pressure...
11. Presto a near perfect air free casting...

Most people just skip to step 8...

Degassing for most is generally to remove entrapped air in mixed silicone prior to pouring... Not for casting purposes...

On a side note, if you are pressure casting you should ideally also cure the silicone at the same PSI when molding that you will use when you pressure cast, this way if there is any entrapped air it will be normalized and reduce any distortions in the mold... Hardly an issue if the silicone is degassed well, but if there is a big air bubble trapped in a mold while it's under 80 PSI iot will distort the surrounding area, as it's compressed smaller...

 

[SmokeDT]

hi,

I was reading exoray's post about vacuuming and then pressuring the silicone, and it made me thinking and want to ask your opinion about the solution I found.

So, normally this method would require a vacuum pump and an air compressor, buying both costs a lot.
Yesterday i found a converter, called Vacuum Generator. You just plug it to your air compressor, and the compressed air turns through this generator and it creates vacuum. Here is a link

It would be great to just buy a generator (I already have an air compressor :rolleyes). Anyone have experience using one of these?

Thank you!

smk

 

[exoray]

hi,

I was reading exoray's post about vacuuming and then pressuring the silicone, and it made me thinking and want to ask your opinion about the solution I found.

So, normally this method would require a vacuum pump and an air compressor, buying both costs a lot.
Yesterday i found a converter, called Vacuum Generator. You just plug it to your air compressor, and the compressed air turns through this generator and it creates vacuum. Here is a link

It would be great to just buy a generator (I already have an air compressor :rolleyes). Anyone have experience using one of these?

Thank you!

smk

They are called Venturi pumps and they work fine as long as you have a good supply of air to drive them... The cheapy Harbor Freight one is use by a lot of people and is even talked about on the first page of this thread...

 

[KaraZor-El]

I've been doing a little research in this area...sorry for bringing a dead thread back to life, but I have a question and don't necessarily want to start a new topic...

I already have the pressure pot, and now I need the harbor freight vacuum pump. Vacuum Pump - AC Vacuum Pump w/ R134A & R12 Connectors

Will I need any additional hoses when I buy this pump that may not be included, in order to hook it up to the pressure pot? Or is it something I can find easily at Lowe's or some other hardware store? Noticing the clear tubes from another member's set up earlier on in the thread, those seem simple enough, is that all I need? Thanks for your time!

 

[Rebelscum]

almost any hose will work, which is why you commonly see 1/4" ID clear hoses.

you don't even need much of a connection at the pot, nothing like you'd see when using compressed air. A connection with a hose barb is the most you need. on my vacuum chambers, I just have a slick piece of brass tube I stick the hose over.

 

[KaraZor-El]

Thank you so much! That helps a lot! This is kind of scary for me since I've never really worked with clear resin before... I've been reading a lot about making bubble free castings and even the smallest details (like wondering about the hose I should use) can kinda psych me out, so I'm trying to study and learn as much about this stuff before the trial and error phase begins... lol


Now I have one more question. I would like to find some sort of transparent lid or covering for my pressure pot that I can use while degassing silicone...

If I were to find some sort of clear covering that is the same size as the original lid, since the pot has its own clamps, would it be safe to switch to the clear plastic/acryllic/glass lid so that I can watch the silicone as it degasses? Would I only need to add a hole in the top, and some sort of connector for the tube? Or is it a little more complicated than that?

 

[Rebelscum]

You don't need clamps on the lid for vacuum. the vacuum will hold them together nicely.

You just need a seal between the pot and the lid. Generally, this is in the lid on the pot, so if you replace the lid with something like a 3/4" piece of cast acrylic, you'll need to put a seal in that lid, or have some sort of donut seal you can put between the two.

I cut a dado in the clear piece with a router and just fill it with molding silicone.

 

[KaraZor-El]

ah ha! Wow thank you so much. That is far less complicated than I originally thought! Phew! I appreciate the advice so much!

 

[zorg]

i bought some silicone sheet from ebay (2mm i think)

i cut a circle in it an use it as the seal between my pressure pot and clear top.

works perfect.

-z

p.s. none of my threads are dead, they are just getting on with their own **** and don't want to be disturbed thats all.

 

[KaraZor-El]

Thanks Zorg! That was the next question forming in my mind...lol. I knew I had seem someone's set up with a silicone rim, and was thinking how to go about doing that. Now that I know it can be found on ebay, I'm so on that! Thank you!