Can you use a hotplate with a vac chamber like this?

[MrAwder]

I just want to verify that it should be okay to set this chamber on top of a hot plate when purging. http://www.ebay.com/itm/VACUUM-CHAM.../261215135687?pt=BI_Pumps&hash=item3cd1a2a7c7

Second question - under vac should I be aiming for a different temperature than a regular non-vac heat purge?

 

[CarefulGrower]

I vac mine at the same temp I heat bath it at (115-125f). You can change temperatures to get different consistencies. Lower for shatter, higher for honey, longer for wax. If you use a chamber test to see it's heat loss (infrared laser thermometers reflect off polished metals, inside your chamber can be a few degrees cooler than your hotplate), take a teaspoon of salt, put it in your chamber and check the salts temperature.

As for heating the chambers, "no" it isn't safe entirely from what the internet has told me. That being said mine is on the griddle at the moment @ 120f, -29.5hg. I have done countless purges in it, no sign of a problem. The one you posted is nice because it has no rivets, less chance of a leak. I'd put it in a safe area where if it were to implode/jump, nothing would be damaged, but... mine is next to a window lol.

 

[BullnAChinaShop]

Nice plug n play setup.

 

[Gray Wolf]

I just want to verify that it should be okay to set this chamber on top of a hot plate when purging. http://www.ebay.com/itm/VACUUM-CHAM.../261215135687?pt=BI_Pumps&hash=item3cd1a2a7c7

Second question - under vac should I be aiming for a different temperature than a regular non-vac heat purge?

It depends on how hot and how thick that acrylic lid is. It doesn't really say, only that it is extra thick, but 1" of acrylic on a pot that size, will still deflect over 1/16", so I would contact them and ask how thick it is.

The ones imploding typically have lids closer to 1/2" thick, so the one pictured is not as likely to do so, but will lose strength rapidly with heat.

Here are some properties copied from here:

http://www.kaysons.in/acrylic/physicalproperties.pdf

Although the tensile strength of Acrylic sheets used is 10,000 psi (69 MPa) at room temperature (ASTM D638), stress crazing can be caused by continuous loads below this value.

For most applications, continuously imposed design loads should not exceed 1,500 psi (10.4 MPa). Localized, concentrated stresses must be avoided.

All thermoplastic materials-including ACRYLIK will gradually lose tensile strength as the temperature approaches the maximum recommended for continuous service. For ACRYLIK, the maximum is 180°F (82°C).

A 48” panel will expand and contract approximately .002” for each degree fahrenheit change in temperature.

In outdoor use, where summer and winter temperatures differ as much as 100°F, a 48” sheet will expand and contract approximately 3/16”.

AKRYLIK also absorbs water when exposed to high relative humidities, resulting in expansion of the sheet. At relative humidities of 100%, 80%, and 60%, the dimensional changes are 0.6%, 0.4% and 0.2%, respectively.

ACRYLIK can be used at temperatures from -40°F (-40°C) up to +200°F (93°C), depending on the application.

It is recommended that temperatures not exceed 180°F for continuous service, or 200°F for short, intermittent use.

AKRYLIK should not be exposed to high heat sources such as high wattage incandescent lamps, unless the finished product is ventilated to permit the dissipation of heat.

 

[MrAwder]

thanks for the idea on the salt to get the temp in the chamber. any idea how i can get the temp of the top sheet with a laser thermometer? applying heat to it is kind of a concern but i'm kind of hoping i can dial the chamber to 160-175 and the top sheet maybe even a few degrees cooler.

ill make sure whatever i end up with is 1".

 

[Gray Wolf]

thanks for the idea on the salt to get the temp in the chamber. any idea how i can get the temp of the top sheet with a laser thermometer? applying heat to it is kind of a concern but i'm kind of hoping i can dial the chamber to 160-175 and the top sheet maybe even a few degrees cooler.

ill make sure whatever i end up with is 1".

The top sheet is easy to measure with a laser thermometer, but it does prevent you from shooting through it and measuring the process temperature. I measure the temperature of the heating surface, and the inside of the pot with the lid off, so as to know what the delta T temperature is. I just subtract the difference when measuring.

Running an acrylic sheet at 175F will most likely end up with it failing. We get good results at 85/125F, which is not a problem.

 

[MrAwder]

Great thanks for the info on temps. Can you explain how the delta T temp helps? You have the temp of the heating surface [Ts] and the temp of interior of container (measured from the bottom? or sides?) [Tc]. [Tdelta] = [Ts] - [Tc]. Just not clear on what you mean when you say "I just subtract the difference when measuring".

Sorry if I over-complicated that.....

 

[Gray Wolf]

If the heating element under the pot measures 107F, with a Delta T of 7 degrees, then the inside the pot would measure 7 degrees cooler, or 100F.

 

[frankenstein2]

This is kinda on the same topic as what I just started doing. I do bho runs and until recently I was doing the "purge over time method". Now I do this. I do my run and then do an initial purge with hot water. when all the liquid is gone, I dry the bottom give it a minute, then do another hot water bath. Then I scrape and put into my glass ashtray. I bought a candle jar warmer. I also have a food saver vac set-up with the little vac dishes from wally world. I put the candle jar warmer under the vac container and turn it on. After the oil becomes vicious again I start to vac under heat. It works awesome and i'm getting product that looks like what the "pro's " here are making. I looked up the candle warmer and it says that it gets between 120-140f . How does that sound?

 

[dickcorn]

I'd love gray wolfs opinion on this too, if it works I'll be trying it. Good idea.

 

[Gray Wolf]

I would love to see pictures, to enable me to better form an opinion, but we vacuum process most of our oil in the 85/115F range.

I know some folks process in the 120/140F range, so it would undoubtedly work and if you are monitoring the progress visually, you can always unplug the ceramic candle warmer for a bit and let it cool.

How much of a vacuum are you able to pull with a Food Saver?

 

[frankenstein2]

The food saver pulls the lid down tight and dents it in. The little rubber seal on the lid is only like 1/4" away from the oil itself. I don't have any measurements as far as vac pressure, because I don't have any of those cool toys. I'm gonna go take a pic of my set-up now.

 

[frankenstein2]

Here's what I use and what it makes.

 

[frankenstein2]

five pic limit....

 

[frankenstein2]

Thanks for your time graywolf. And yes I unplug it and even move the ashtray away when I think it is getting too hot.

 

[Gray Wolf]

Thanks for sharing your process bro! How long does the purge usually take?

 

[frankenstein2]

It usually is a two day process for me. I make the initial oil. Then after five to six runs of purging (approx. 30 secs), I stir it and vac it once more and leave it to sit under pressure for the night. The next day is when I stir it and put it on the candle warmer. Stays on the warmer for 10-15 and a few vacs and then it's done.