Need help finding a vac degassing pump.

[Rook 3]

I'm looking to get a degassing rig made for silicone.

What I need is a pump that can pull a minimum of 28-30 inches of mercury vacuum.

The ones I see on eBay all list the rating in microns and not inches of mercury.

Can anyone offer any first hand experince and help/suggestions for decent quality, reasonably low cost pumps?

Thanks in advance,

Russ

 

[racprops]

Yes you really want one rated at 6 to 12 CFM and able to boil water at room temp.

The CFM is only realy at the start but that gets most of the air out first them you start to pump down to lower inches. 26 to 28 is fine...

I tried a A/C service vacuum pump and the rubber would be hard by the time it had pumped it down.

I have a big belt driven unit and added 20 gals of vacuum tanks as well.

Getting steel wrapped hoses at 1 inch and a good valve at 1 inch is not easy, but it works very well.

I got a 15 inch dia and 20inch high pipe faced in a BIG lathe and use 1 inch Lexan at both ends and modeling clay to get the finel seal.

You can still see the lexan bend under vacuum.

But it lets you watch the RTV foam and collapes, oh it will rise 4 to 6 times it size in the bucket so use big buckets.

Rich

 

[exoray]

Yes you really want one rated at 6 to 12 CFM and able to boil water at room temp.

Why so much volume for degassing? You are spitting hairs with seconds not minutes for the average persons vacuum chamber volume, and exponentially increasing the cost of the pump after 6 CFM to save literally a few seconds...

I tried a A/C service vacuum pump and the rubber would be hard by the time it had pumped it down.

What kind of pump did you try that was that damn slow, honestly it takes about 1 minute to pull down enough to get a good boil with a 2-3 CFM pump in the average paint pot size chamber, why is your silicone kicking so fast? Even a 1 CFM pump will only take 2 minutes to pull down the average chamber...

I got a 15 inch dia and 20inch high pipe faced in a BIG lathe and use 1 inch Lexan at both ends and modeling clay to get the finel seal.

That is only 2 cubic feet of volume, that is why I question why you need a 6-12 CFM pump, a 3 CFM pump will get almost all the air out of a 2 cubic foot tank in about 45 seconds...

The silicone I use has a 45 minute pot life at room temperature (as do many of them) , over an hour if I refrigerate it before use... Is saving 30 seconds really that important or necessary when you have 45 minutes of work time? I generally have plenty of time to double mix, degass and pour without even the slightest issues...

You can pick up a 3 CFM 110 volt HVAC service vacuum pump on Ebay that pulls in excess of 28" for about $100 plenty good for the average hobbiest IMO...

 

[racprops]

Why so much volume for degassing? You are spitting hairs with seconds not minutes for the average persons vacuum chamber volume, and exponentially increasing the cost of the pump after 6 CFM to save literally a few seconds...

I do molds that can take up to 1/2 gal mixed and poured, and molds that take a long time to pour due to their set up so found small pumps did not do the job. So in many cases I really need the extra time.


What kind of pump did you try that was that damn slow, honestly it takes about 1 minute to pull down enough to get a good boil with a 2-3 CFM pump in the average paint pot size chamber, why is your silicone kicking so fast? Even a 1 CFM pump will only take 2 minutes to pull down the average chamber...

The kind that I had for serviceing home A/C and car A/C units, and it was belt driven and pulled into the 28 inches. And it was too slow...

All your doing on these A/Cs is pulling out water, so they can take a houe to do the job, RTV will be well done by then.

That is only 2 cubic feet of volume, that is why I question why you need a 6-12 CFM pump, a 3 CFM pump will get almost all the air out of a 2 cubic foot tank in about 45 seconds...

My oversized system does not make that... real world vs theory??


The silicone I use has a 45 minute pot life at room temperature (as do many of them) , over an hour if I refrigerate it before use... Is saving 30 seconds really that important or necessary when you have 45 minutes of work time? I generally have plenty of time to double mix, degass and pour without even the slightest issues...

Mine said the same, but it is AZ...Again I have taken so long to work my molds that I have seen it start to gelly, so I did what I needed, and as I was buying used.. it worked out.

You can pick up a 3 CFM 110 volt HVAC service vacuum pump on Ebay that pulls in excess of 28" for about $100 plenty good for the average hobbiest IMO...

I am long no hobbiest so when pro sized. Those 3 CFM 110 volt HVAC service vacuum pump are like the Service pump I tried and failed.


Rich

 

[exoray]

I do molds that can take up to 1/2 gal mixed and poured, and molds that take a long time to pour due to their set up so found small pumps did not do the job. So in many cases I really need the extra time.

Well I have found the opposite, I just poured a 4 gallon mold Friday, I broke it into 1 quart mixes (as that fits in the chamber better) and didn't have any issues mixing and pouring all 4 gallons before it set... While one mix was degassing I poured the previous one and whipped up the next one, it was almost a seamless pour...

All your doing on these A/Cs is pulling out water, so they can take a houe to do the job, RTV will be well done by then.

Huh? They are 2 stage vacuum pumps no different then any other vacuum pump and they take minutes not hours to pull a vacuum... It's not pulling water out it's pulling 28" of vacuum thus removing the moisture contaminated air in the system, that is why they advertise them as moister removers they are not just removing moister they are creating a vacuum like any other vacuum pump the removal of moisture is the byproduct of the action...

Hell my little Harbor Frieght venturi pump can pull 25-27"" in about 3 minutes and it cost a whopping $10 and is basically a toy... I no longer use it because I have the electric ones but it served it's purpose for several years...

My advise is still to get one similar to this, more then enough for the casual user...

http://search.harborfreight.com/cpisearch/web/search.do?keyword=cfm+vacuum+pump&Submit=Go

Or try an Ebay search for "HVAC vacuum pump" , I'm not recommending any brands as I have not tried them, both of mine are used units that I purchased at garage sales for dirt cheap but very similar in design to the ones above...

Now if you are going into vacuum forming they the more CFM is needed or you need to degass large chambers so you have the initial CFM, but for degassing silicone in a small to moderate sized chamber, I really can't see why 30 seconds is a make or break point...

 

[00MrNotWrong00]

Yes you really want one rated at 6 to 12 CFM and able to boil water at room temp.

The CFM is only realy at the start but that gets most of the air out first them you start to pump down to lower inches. 26 to 28 is fine...

I tried a A/C service vacuum pump and the rubber would be hard by the time it had pumped it down.

I have a big belt driven unit and added 20 gals of vacuum tanks as well.

Getting steel wrapped hoses at 1 inch and a good valve at 1 inch is not easy, but it works very well.

I got a 15 inch dia and 20inch high pipe faced in a BIG lathe and use 1 inch Lexan at both ends and modeling clay to get the finel seal.

You can still see the lexan bend under vacuum.

But it lets you watch the RTV foam and collapes, oh it will rise 4 to 6 times it size in the bucket so use big buckets.

Rich

OMG post pictures, post pictures, post pictures, Please .

 

[exoray]

The ones I see on eBay all list the rating in microns and not inches of mercury.

FYI for all practical purposes it goes like this...

Regular atmosphere = 759,968 microns

28 inches of vacuum = 50,800 microns
29 inches of vacuum = 25,400 microns
30 inches of vacuum = 0 microns

So when you see a pump advertised at say 100 microns, it's pulling nearly 30" of mercury, even a 25,000 micron pump is still pulling 29"

 

[Rook 3]

Interesting. So smaller numbers equal greater pressure.
Odd. Guess that's why I'm not a math major.

Thanks for all the help/suggestions everyone.

Also, is there a recommended end plate thickness for acrylic/kydex? I was estimating 1.5-2" thick.

The chamber I plan on using is a 5 galleon paint pot. I have it on hand, and it's large enough I
believe for what I need it to do.

Another question: You mix your silicone, do your pour, vac the silicone... then what? Do you need
to leave it pressurized until it cures, or do you depressurize after a period of time?

Russ

FYI for all practical purposes it goes like this...

Regular atmosphere = 759,968 microns

28 inches of vacuum = 50,800 microns
29 inches of vacuum = 25,400 microns
30 inches of vacuum = 0 microns

So when you see a pump advertised at say 100 microns, it's pulling nearly 30" of mercury, even a 25,000 micron pump is still pulling 29"

 

[exoray]

Another question: You mix your silicone, do your pour, vac the silicone... then what? Do you need
to leave it pressurized until it cures, or do you depressurize after a period of time?

Two options here

1. Mix silicone
2. Put in vacuum chamber and boil until degassed
3. Carefully pour mold, taking care not to introduce more air

Then you can do one of two things

4a. Leave as is to sit and cure at normal atmosphere, this is a good option for castings that you will be making at normal atmosphere...

4b. Take the whole mold and place in a pressure chamber and leave under pressure until cured, this is a good option for castings that will be done under pressure like clear ones...

Basically you want to cure the silicone at the same pressure you will be casting, the reason for this is that if you don't do this there is the chance the any air bubbles left in the silicone could distort the mold under different pressures...

For example if you cure the silicone under pressure, basically all you are doing is squeezing the air bubble smaller, once brought back out from pressure because silicone is soft the air will again expand distorting the mold... No of course an air bubble deep inside the silicone won't cause much issue, but one by the surface will create "pimples" when the air expands... And if you cure under normal atmosphere and the put it in the pressure post to cast any bubble near the surface will be squished leaving a "dimple" in the surface... Now this all revolves around bubble size and how close to the mold surface it is, MOST of the time it won't be noticeable, but that one time it is, you will be cursing to high heaven...

Never cure silicone under vacuum, you will end up with fluffy soft silicone that will for the most part be useless for molds...

 

[TK648]

Here is some info on the set up I have

Vac pump is from Harbor Freight
Here is info on the Vac chamber I have

The vacuum chamber or Jar is about 9 inches high 6 1/2 inches wide
I got it years ago and I want to say, I ordered it from a Edmund Scientific catalog but I am not to sure.
This is the info on the jar Label
Nalge Company
Nalgene Multipurpose Jars Cat. No. 5300-0507, -0609
Nalgene Vacuum Chambers Cat.No. 5305-0609
Only use Nalgene vacuum plates Cat.No. 5306-0070
Telephone: 716-586-8800
Hope this info helps

Here is a pic of the gauge the vacuum chamber is empty

 

[DanTheSwine]

Looking for places in the UK or European Union that I can buy vac pumps. Trawling through Google yields little in the way of results so wondering if anyone knows a specific site I can visit?

 

[kid2000]

Can I ask a question please.

If I need to mould small items can I use a Manuel Brake Bleading kit would this draw enough PSI, to be able to get a nice clean mould.

just im struggling to get a cheap pump in the uk as well.

Thanks in advances