Intro and request for advice

General Composites Discussions Equipment Talk
#1

Hey all,

I am new to composites and want to start experimenting with infusion. I’ll be in an aerospace prepreg class this fall, but want to learn other techniques as well. I could go for some preliminary guidance as to my vacuum setup. I’ve done a lot of reading, but haven’t found the following details yet.

I have two Copeland semi hermetic HVAC pumps that pull ~27Hg. I know I need to change the oil, but I am having a tough time finding out how and what oil to use.

[ul]
[li]Does anyone have experience in trying to use these pumps for this application?[/li][li]Should I sell them and get something else?[/li][li]I could post photos if it would help ID them for someone, I do have the part #s.[/li][/ul]

I want a switch to control vacuum, I think I want to keep the vacuum pretty constant (25 - 27 Hg). I’ve seen mention of the Danfoss rt121, but it won’t work on 120 vac.

[ul]
[li]What do folks use stateside that is as accurate as the Danfoss?[/li][li]I’ve found the veneering site, but their suggestion for control seems to have too much differential variance to suit infusion.[/li][/ul]
HF paint pot w/ thick acrylic lid in the works

I’m really just looking to start trying layups and learn about vacuum and consumable placement etc. before trying to build anything.

Any info will help,
Thanks

#2

I changed the oil in the compressors to 10-30Wt engine oil for now. I suppose I’ll find that there are better choices available, but I think the point is to change it often to remove the styrene. One of them only had about an ounce of oil, so we’ll see how long it lasts.

I am considering plumbing them in parallel or series for reliability.

I’m leaning toward using an SMC vacuum switch with a relay and transformer if I can find the right combination for a reasonable price.

#3

The RT121 is pretty much independent from voltage, it is a mechanical switch. For small pumps you can hook them up without relais, although I do recommend using one to protect the switch.

The SMC switch is great as well, needs a little more thought to setup. I mounted one in a small box, together with relais and power supply, and even found place to install 2 wall outlets on it. One switched, one always on. That way I do not lose a power connection. You never know… This can switch all 220 volt pumps.

On oil: find a supplier for vacuum pumps, and use their oil. they probably know which viscosity to use.

#4

What I have so far is this:

Two Copeland cast iron piston pumps- one easily pulls 27.5 Hg and the other 26Hg. The second one appears to have a leak somewhere as it cycles regularly to keep vacuum. I hope its just a gasket or seal and there isn’t scoring or worn valves… Still don’t know the ins and outs of the pump valve design and rebuild kits look expensive. The 10-30w oil I’m using should work for the short term, according to my research, the pumps need a 10w viscosity.

smc zse-40 digital vacuum switch. This thing is great, I can control both pumps individually with very low hysteresis. Very programmable little switch, but I don’t have the experience to rave about it yet.

Two solid state relays , two switched AC outlets and a DC power source to supply power to the smc and the pumps. I can use pump 1, pump 2 or both.

Two vacuum reservoirs that are not set up yet. I’m still exploring my plumbing options regarding the flexibility to do CAPRI, SCRIMP, double bag… One is a Harbor Freight paint pot, one is a stainless pot with a 1" acrylic lid for degassing.

I’m excited to get started with troubleshooting and experimentation, but the project has been a bit slow to get going. As usual, I’ve gotten a bit carried away with the details considering the amount of experience I have. The problem (if you can call it a problem) is that I am attending an aerospace composites program and need to concentrate on what I’m being taught there and lack spare time. I begin the final quarter of the course today, which will concentrate solely on composite manufacture and repair.:amuse: I’m sure I’ll find things in my vacuum system to improve on during this course.

Please feel free to pick apart my setup if you have experience with this.

#5

If it’s regular compressor oil they sell it at advance.

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_1-qt-a-c-premium-high-vacuum-pump-oil-robinair_17630648-p?searchTerm=vacuum+pump+oil

#6

If you are preparing for infusion why are you shooting for 25-27 inHg instead of the full 29.9 inHG? I can see possibly using a slightly lower vacuum level for degassing your resin but for the infusion part the higher the vacuum the better.

#7

Hey Ben,
I’ll check out regular compressor oil viscosities, thank you.

Infusible,
I guess I’m not really sure yet. I’m new to this stuff still (haven’t even made an attempt yet). I got the pumps for free, so I’m giving them a shot. I was under the impression that at 29.92 Hg you potentially risk boiling the volatiles in the matrix at elevated temperatures. Maybe I’m getting polyester resin mixed up with epoxy ( I mainly want to do epoxy I think). I’ve read that 27 Hg is pretty good for infusion. I suppose time and experience will tell. Should I be really concerned, or just not be surprised if it doesn’t turn out well? If this doesn’t work, I’ll be on the lookout for different pumps directly. Initially, with the number of variables in this process, I think vacuum may be the least of my worries.

In this class I am taking, we are building a prepreg oven. The pump we are planning to use is only rated for ~25 Hg. I realize there are plenty of differences between prepreg and infusion and in a classroom setting we may not have the ideal setup due to cost constraints etc.

I don’t know, am I way off with the 25-27Hg thing?

I guess one thing I’m not considering is the actual vacuum the part sees. I’ve only tested at the pump itself so far.
Thanks

#8

1: the part sees what the pump does (barring any issues of leaks)
2: while 25"-27" isn’t ideal for infusion, it IS doable, and if they were free…that is what you start with. Upgrade to a better pump later.
3: high vacuum will degas the resin. This is a good thing most of the time. However, I have never had an issue with the resin boiling in my part, even with 29" pump.
4: prepreg is about the same for pumps, it likes more vacuum! The differences are, is mostly processing materials, and how you bag it.
5: get vacuum pump oil!!! Many HVAC shops would sell it, and maybe hardware stores? Online as well.

#9

Thanks riff,

I’ll quit screwing around and get the pump oil :o

Will probably start looking for a good deal on a dual rocking piston or diaphragm pump to replace the weak one I have- suggestions? I did see the thread on 29 Hg pumps, I’ll watch that

I may be mistaken on our school pump. I didn’t have time to check the model, but it looks like a single stage Gast diaphragm. We have a Harbor Freight backup.

The instructor mentioned the cost of the woven PTFE fabric- OOOF!

Thanks everyone, now I just need to start messing around with stuff

#10

Craigslist has a few. I found mine for half price. It was used one time for school and then the guy changed careers.

#11

Let me know if your school is interested in any bonders. I have a few spare hot bonders that include blankets thermocouples portable vacuum pumps and controllers. They are mainly used in aircraft advanced composite repairs in the field and on aircraft repairs.

They bond prepreg and titanium patches flawlessly as we’ll as water extract extremely well. I have one that the calibration date is expired but works great that I could cut a deal on.

Anyways sorry to spam your post but… I’ve used everything from Venturi vacuum generators to vane pumps. Rocker diaphragms work the best IMO… But… Use what you got. In the field with a crazy bag 25 hg is a gift.

What kind of program are you in… I wonder what actual hands on lab work they will be teaching. Believe it or not a lot of composite technique is used for many forms of work that doesn’t necessarily deal with fiberglass and graphite. I use vacuum bags all the time for … Stuff.:wink:

#12

Thanks hey ben. yeah, I’m influenced easily…I already bought a gast saa off of ebay. its a parallel pump, so it ought to be good to ~27Hg. I think if I get a rebuild kit for a staged pump I can convert it to ~29Hg for about $70 and some minor work. That, or maybe just reconfigure the valve plate.

dallas 84, I’ll check with my instructor on the hot bonders. We have heat con dual zone bonders. I think they are all currently working, but he may want a spare. We will be much less reliant on the hot bonders once we get the oven up and running. If he does, I’ll PM you. Thank you.

Also, the instructor was trained at Abaris, so I imagine that our class will follow what he learned there to some degree. He may have experience beyond that and he is very open to trying new stuff out. The course will cover repair and fabrication using prepreg carbon and glass with one wet layup lab. We will build a sandwich panel, unidirectional tape layup, unidirectional I beam, an aileron type structure and a project of our own choosing.

#13

The pressure differential between 27" and 29" is not that much if I understand correctly. We are only talking 14.7 psi or 1 bar max and I only understand it as linear, not exponential. I could be wrong and probably am but that’s why I am here.

#14

The difference between 29.0" and 29.92" is not much either…however one is considered a rough vacuum, the other ultimate, only achievable with highly expensive turbo and diffusion pumps. 27" and 29" is a world of difference in the long run. Both work, but one is better :slight_smile:

#15

difference in pressure between 27" and 29" would ~1PSI of compaction on your laminate. Could be the difference between getting the FVF you want or not. Also depending on your process you will have higher void content.