inches of mercury?

General Composites Discussions Equipment Talk
#1

How many inches of mercury should a vaccuum be able to hold to do infusion?

#2

ideally you’d want 30"
I perform infusions anywhere between 26-29" and it works just fine

heres a good site to read up on almost anything you’d need to know about it http://www.hydraulicspneumatics.com/200/TechZone/Vacuum/Article/True/6460/TechZone-Vacuum

#3

Nice link to a great site…thanks! I’ll add that to the list.

#4

the fridge pump I picked up will pull 20" no problem, will that be enough?

#5

as well, I am in calgary which is at an altitude of around 3500ft, which obiously reduces the max that can be pulled.

#6

can’t say for sure, you might have to thin the resin a little bit
is that the only pump you’ve tried?? see if you can get another one to test out.

#7

im trying to do this on a reasonable budget. I managed to get this pump for free from a wrecker. How thin would the resin need to be and will thinning the resin compromise strength?

#8

you can use up to 10% styrene or MEK (not MEKP) to thin, don’t use acetone either
The more thinner you add the more brittle the part will be which is the problem of thinning :smiley:
Also, the more thinner you add (particularly styrene) the longer the set time, and the stinkier it’ll be.

oh, I’ve also bought pumps at appliance repair places for no more than $10 bucks

#9

Im at 6000 feet and the most Ive ever seen my pump (a robinaire) pull is 26" indicated. Mind you though, due to atmospheric pressure loss I start at a -2 on the gauge as it is…so Im only getting a good 24" at best and I infuse no problem. I actually look to see that my gauge starts reading 20" before I start mixing my resin.

I think 20 will be fine…youll know soon enough if the resin moves way too slow. Use bigger lines and thinner resin and make sure it kees vac on it. After the part is fully infused you only need 10" to keep things compressed.

#10

I only infuse at 28.5-29. Anything less means I have a bag leak, and that’s always bad.
I have infused small parts with a bad pump at only 10hg, but there was no gauge on that system so I didn’t know at the time. Infused ok, but a bit slow.