Vacuum-impregnation resin stabilization for balsa nosecones and such?

[Marc_G]

Hi folks,

I've often wondered if it would be practical to have a small chamber into which I could put a nosecone or other wood parts, cover them with some sort of hardening liquid, pull a vacuum on it to cause most of the air to leave the pores in the wood, release the vacuum and have the hardening liquid thoroughly impregnate the cone. Then take the cone out and either leave it to dry or put in a curing oven depending on what it takes to harden the liquid.

Watching some facebook videos I just found out this is actually a thing that exists, not a new idea at all. Oh well. The process was applied to the wood handle being prepared for a straight razor to harden it and make it more water stable.

The one I saw had a hand-pump to create the vacuum; chambers similar to what I saw are on amazon for not too much $ here:

https://www.amazon.com/Clear-Stabil...rds=resin+stabilization&qid=1617983811&sr=8-7
While it would certainly add weight, it would make nice tough nosecones too. Apparently stabilizing resins can have dyes added to them. Interesting!

I've never heard of this method being applied to rocketry wood parts. Has anyone done this, or heard of it being done?

Marc

 

[kuririn]

Don't know about toughening the nose cone, but I'll bet it'll lengthen your nose cone by a couple of inches!
(Sorry, couldn't resist).

 

[Kelly]

The poor man's approach to this is to just use a brush on wood hardener, such as Minwax's hardener. This is an acrylic (think plexiglass) resin that penetrates the wood and hardens. I guess the best approach depends on what exactly what you want to achieve. Why do you need a hard nosecone? Just to protect against the occasional dents from handling and snap-back?

 

[Marc_G]

I've used Minwax Wood Hardener plenty of times. I prefer hardening cones so they are less likely to deform in sanding (flat spots). These days I use CA.

But I always remembered the idea of vacuum impregnation and when I saw it was actually a thing today it brought it all back.

I don't have a specific project for this, just curious if someone used it.

 

[kuririn]

I'm wondering if the other way around might work as well? I know that mills pressure treat their lumber with chemicals to prevent termite and fungal infestation. Gets the chemicals deep into the wood.
Might work with, say, finishing resin.
(Or maybe it's not thin enough).
EDIT: Upon further research I found that pressure treated wood uses a vacuum in a chamber, not high pressure. The air is replaced with preservatives. So, never mind.

 

[heada]

Vacuum impregnate the resin and then compress any bubbles left via high pressure.

 

[Troy3003]

A relatively cheap way to get started would be to go buy an a/c vacuum pump. Would then need a chamber, I've seen old pressure cookers(I think) being used for that.

 

[shockie]

One of these might work

or one of those freezer sandwich baggers?

 

[Sandy H.]

The pen turning community has you covered. Search for 'worthless wood' and look into 'cactus juice' for some good information. I've never thought about doing it, but I bet it could be feasible. Not sure of the end value for rocketry vs time/money invested, though. CA, wood hardener etc., could very well get you 90% of where you want to be for little/no money.

Sandy.

 

[Marc_G]

Thanks guys. At this point it is mostly a thought exercise rather than a project, coupled with curiosity about if this is used in practice in our hobby.

Oh, and to the point of pressurization versus vacuum: I used similar techniques in my lab work as a grad student (wow, decades ago!), And pressurization doesn't work as well as vacuum. Imagine a (cheap) container that can withstand 1atm pressure differential. You pressurize it to a total of 2 atm (regular atmosphere plus 1 extra atm of pressure). The trapped air shrinks to 50% size, resin infiltrates. When you open up the vessel, the air expands again pushing the resin backout of the the material. Whereas with vacuum, if you evacuated just 90% of the air (easy to do with even a hand pump), you permanently pull that much air out of the material. No bounce back. So it's more effective.

Great discussion guys!

 

[Sandy H.]

My experience with vacuum matches your 100%. I did an RnD project for my company 3 years ago using vacuum casting methods vs pressure casting vs open air. If I recall correctly, the vacuum castings were about 15% stronger than open air and the pressure casting was only about 3%. Obviously very different process, material, method etc., but the idea of getting the bubbles out vs compressing the bubbles small has merit, IMO. Regretfully, we never went further. . .

Sandy.

 

[dhbarr]

The pen turning community has you covered. Search for 'worthless wood' and look into 'cactus juice' for some good information. I've never thought about doing it, but I bet it could be feasible. Not sure of the end value for rocketry vs time/money invested, though. CA, wood hardener etc., could very well get you 90% of where you want to be for little/no money.

Sandy.

Would love to see some pen turning / knife handle style exotic nosecones. On my list of things to try when the shop is done.

 

[John Kemker]

When you think about it, vacuum casting is a form of pressure casting. You're using the atmosphere's natural pressure to force the resin into the wood. You get the added benefit of pulling the bubbles out.

 

[augendoc]

I used MinWax hardening liquid once and was unimpressed. It soaked in ok but took weeks to harden adequately. I would think one of the two part epoxy wood preservatives would work better. However, I think a material that would penetrate only the first 2-3mm or so would still keep the weight down while hardening and strengthening the surface.

 

[Marc_G]

I once mixed wood hardener (Minwax) with 3M auto glazing putty (red stuff, lacquer based). Brushed it on, let it soak in. Worked well, but as you say takes a while to fully harden.

 

[Stefan2k4]

A while back I watched some videos on youtube regarding subject matter along these lines. As for vacuum versus pressure, the general consensus seem to be that for infusing porous materials like wood vacuum was used. The use of vacuum helped infuse more resin into the wood by pulling out air, but also by pulling out moisture. Pressure was typically used for making clear solid castings of resin. In those resins there would almost always be small air bubbles. The pressure would compress those bubbles to the point they were so tiny as to be unnoticeable to the naked eye. Of course the pressure had to be maintained until the resin completely solidified. So, it would seem that for infusing a wooden part vacuum would be the best route, or at least vacuum would be used first. Of course, you could perhaps use a combination of both, by using vacuum first followed by pressure. If you did both, I'd think you'd have to first place the part in the chamber submerged in a container of resin. Before switching from vacuum to pressure, youd likely have to remove the part from the container of resin because you'd want to maintain the pressure until the resin hardens and obviously if you left it submerged in the container of resin you'd have a part encased in a solid block of resin.

One thing I learned from some of those videos is that some people were using a pressurized paint tank sold by harbor freight to make a cheap pressure vessel. I suppose it could also be likewise used as a vacuum chamber.

 

[David Schwantz]

I have used this type of products for years to make grips for my bows out of. It is very tough, water proof and beautiful. The wood was both maple and elm. Never done the process, bought the wood blanks already to use.

 

[BABAR]

After reading the title i figured that was how new little BT-5 nose cones were produced.

 

[cbrarick]

I've done a fair amount of vaccum bagging. You'd run the real risk of significantly compressing the balsa so the nose cone is too small. I did a set of fins out of 9 ply baltic brich actual 1/2 inch, with 2 layers of 11.4 ounce 2x2 twill on both sides. They were successfully vacuum bagged and the width afterwards was 7/16. Prior to vacuum it was 3/4, I lost 5/16 which represented 42% of the thickness. I was using west systems epoxy, proper vacuum bagging techniques and a gast vacuum pump that was capable of holding 29 inches of mercury. Thee fins had vacuum applied to them for 4 hours in a very warm environment, then given a 24 hour post cure heat soak at 120-140 degrees before the bag was removed.

 

[shockie]

I wonder is you heated the wood nose cone up to say 150 F, prior to applying the resin would help any? Maybe also using a thin laminating epoxy resin?