Is 25" Hg at sea level enough? part 2

[MesquiteMan]

A while back I took some pictures of some blanks being stabilized. I took the pics at 25" Hg, 27" Hg, and 28.5" Hg at 1,000+/- feet above sea level to show the difference in the amount of bubbles from each vac level. Some folks say that 25" Hg at sea level is enough for good stabilization. I disagree.

The idea behind vacuum stabilizing is to remove as much air from the blank as possible, thus making room for the stabilizing resin to be "sucked" back into the blank when the vacuum is released. At sea level, a 25" Hg vacuum is only removing 85% of the air from the blank. Is that enough? Most likely it will do a descent job but higher vacuum will remove more air, thus allowing more room for additional resin to be infused into the blank.

Here are some pictures I took this evening from an interesting experiment to show just how much difference there is between an 85% vacuum and a 99% vacuum. I took a regular nitrile shop glove and tied it off with no apparent air in the glove. I then placed it in my vacuum chamber and took pictures at different vacuum levels. I held the vacuum at the particular level for 15 minutes BEFORE I took the picture to make sure it had "inflated" as much as it was going to. Remember, I am at around 1,000' above sea level so my maximum theoretical vacuum is 28.92" Hg since you loose 1" of mercury on the gauge for every 1,000' above sea level.

Here is the glove at atmospheric pressure:

Here is the same glove at 20" Hg:

25" Hg:

26" Hg:

27" Hg:

28" Hg:

28.5" Hg:

And finally, an animated gif with all of the photos in sequence to show what is happening:

If course if this was a pen blank, the air would be coming out of the blank as bubbles and rising to the surface. You can see there is a huge difference in the amount of air expansion between 25" Hg and 28.5" Hg. Remember, the more air you can get out of the blank, the more resin you can get in!

 

[bensoelberg]

I've never done any casting, vacuum stabilization, or built a pressure pot. Heck, I don't even know what an Hg is, but you completely sold me with that animated gif! :biggrin:

 

[firewhatfire]

what he said. Is that how you do your cactus blanks or is that different?

I've never done any casting, vacuum stabilization, or built a pressure pot. Heck, I don't even know what an Hg is, but you completely sold me with that animated gif! :biggrin:

 

[el_d]

Very cool experiment Mr. Wizard. :biggrin:

Really like the gif putting it all together :good:

Thiers a BIG difference between the 27"Hg and the 28"Hg would you happen to know why?

 

[Justturnin]

I totally agree w/ what you are finding. Your experiments are really helping with mine. I placed a Buckeye Burl in some Polycrilic yesterday and added some Transtint Bourdoux dye. I was going to shut it off after an hour at 28+Hg, at this time the liquid had dropped close to 1/2". I decided to keep it in because I kept getting stray bubbles popping up every 15 secs or so. I eneded up letting it run for 3 hours solid and the liquid ended up dropping another 1/4". I am sure some of that total of 3/4" drop could be attibuted to evaporation and thickening but I feel I got better penetration becasue of it. I figure it will take a week or more for the blank to dry out totally but when it does I will turn it and see what I get out of it. Weighing it to make sure it is dry.

Thanks Curtis!!!

 

[MesquiteMan]

Very cool experiment Mr. Wizard. :biggrin:

Really like the gif putting it all together :good:

Thiers a BIG difference between the 27"Hg and the 28"Hg would you happen to know why?

I really do not know why the big difference but I have run this experiment at least 20 times with similar results every time. I actually demo'd it at SWAT this past weekend a number of times.

 

[seamus7227]

I actually demo'd it at SWAT this past weekend a number of times.

Yeah, i got to see it first hand! Thanks for sharing Curtis! It was truly a pleasure to have you as a Superb chauffeur to and from dinner! Me and Don are grateful:biggrin:

 

[penhead]

Very interesting Curtis...have to admit that I had to think about that for a minute or two to unnerstan' why the glove inflated....vewy intewesting..!

 

[its_virgil]

We were!! Thanks Curtis for hauling us around. A really good friend would have changed the flat tire for this old man:biggrin::biggrin::biggrin: I kept watiing the the glove to pop and blow off the top of the chamber....it was interesting to see the glove grow inside the chamber.
Do a good turn daily!
Don

I actually demo'd it at SWAT this past weekend a number of times.

Yeah, i got to see it first hand! Thanks for sharing Curtis! It was truly a pleasure to have you as a Superb chauffeur to and from dinner! Me and Don are grateful:biggrin:

 

[Fibonacci]

Very cool experiment Mr. Wizard. :biggrin:

Really like the gif putting it all together :good:

Thiers a BIG difference between the 27"Hg and the 28"Hg would you happen to know why?

edit: Pardon all the periods, the forum software keeps removing my spacing

If you don't mind a bit of math, here is the reason:

The ideal gas law describes the relationship between pressure, temperature, volume, and number of molecules. It is an idealized case, but is very commonly used for thermodynamic calculations.

PV = nRT

P = Pressure (measured from vacuum)
V = Volume
n = Number of molecules
R = Constant (not going into this here)
T = Temperature

Assuming for the moment that Curtis is maintaining a constant number of molecules (sealed in the glove) and a constant temperature, then the variables are Pressure and Volume.

As you increase pressure from 0 (decrease vacuum from 28.92), the volume will fall off dramatically. For comparison sake, you can set the right side of the equation to anything you want and adjust P and V to compare. For the purpose of this example, let's set it to 1.

So, if you start at a pressure of 1, then volume is 1. When you reduce the pressure to .5, the volume becomes 2. If we follow this along to increasingly smaller pressures, you see that the volume increases exponentially as the pressure goes down.

Pressure...... Volume
1................... 1
.5.................. 2
.25 ................4
.125 ...............8
.1 ..................10
.01 ............... 100

So, lets extend this to the pressures Curtis is talking about.

We can assume that atmospheric pressure is our steady state condition, so we will say that a pressure of 1 corresponds to atmospheric pressure. We cannot have negative numbers for this, so we will measure from the theoretical maximum vacuum toward atmospheric.

Under this method, atmospheric is 28.92" hg and a perfect vacuum is 0" hg.

So, the pressures he gives are below, along with relative volume:
in hg ..........vacuum equivalent pressure ......relative volume
0 ...........................28.92 .............................. 1
20 ......................... 8.92 ..............................3.24
25 ..........................3.92 ..............................7.38
26 ..........................2.92 ..............................9.904
27 ..........................1.92 .............................15.06
28 .......................... 0.92 ............................ 31.435
28.5 ....................... 0.42 ..............................68.857

So as you can see, the difference between 27" hg and 28" hg is almost 5x the difference between 0" hg and 20" hg. The closer you get to a full vacuum, the more significant every change is.

Make sense?

 

[msvoma44]

You gotta love it when a science guy gets involved.......lol

 

[theidlemind]

Okay, I'm a believer.
So what is the least expensive pump that will do the job?
I'm ready to buy a pump and some cactus juice.
I've got some curly maple I'd love to stabilize and dye.