Get -40C in my fillet weld tensile break tests

Ideas to get a controlled temperature of around -40C (also -40F) in a test sample?

The lowest setting on my Alpicool C20 DC-powered freezer is -40C. Temps below -20C are accessed with the E1 special setting.

It works well enough but isn't as rugged or hands-off reliable as a normal AC-powered freezer, and really should have thicker insulation.

Propane boils at -42 C at atmospheric pressure.

Joe Gwinn

..... Yup, I know that as a PhD level scientist I have to work as a welder because everyone already ensconced in "office engineering" jobs manicured in their white shirts sees me as a "Dennis Hopper like" (think eg. "Blue Velvet" (1986) film) character of the science and engineering world ;-) If you keep the office door closed to all but your own manicured kind, you can keep reality out. Who can blame them if no-one comes and hurls them out into the cold hard world their scheme avoids? :-)

Rich Smith

--------------------------------

The snobbery of "Two Cultures" exists in the US scientific community too. I first encountered it as a Chemistry undergrad, from professors who either worked with government and industry or shunned all but pure academic research, and tried to convince us theirs was the only ethical path.

As a lab manager in a government research facility I worked with both hands-on and hands-off engineers, and again the theoretical, hands-off ones could be somewhat intolerant of people who could be both. I also saw that in Mensa, mainly from mathematicians. It was fun to watch the confusion after someone who had binned me as a mere craftsman found I could and solve engineering math problems mentally faster than they could with a calculator.

Personally I've been glad to stay in the lab, designing and building hardware, and avoid boring meetings and report writing. Another lab tech made a bumper sticker "Techs can do what engineers only dream of".

Not all great theoreticians kept their hands clean:

Propane boils at -42 C at atmospheric pressure.

Joe Gwinn

------------------------------- I checked the weather on Spitzbergen to see if the experiment could be done at ambient temperature there.

Funny, New England USA was that cold over the weekend, and we are at the latitude of Spain.

Ideas to get a controlled temperature of around -40C (also -40F) in a test sample?

---------------------------- The lowest setting on my Alpicool C20 DC-powered freezer is -40C. Temps below -20C are accessed with the E1 special setting.

It works well enough but isn't as rugged or hands-off reliable as a normal AC-powered freezer, and really should have thicker insulation.

------------------------------------------ I confirmed it could be set to -40C but didn't leave it there, as it's full of food and would have taken a long time to settle.

My Alpi wouldn't quite cool to -20C in a hot car so I made an insulated enclosure for it, 1" foam lined inside with a yoga mat to catch and drain summer condensation. The exterior is thin birch plywood joined at the corners with sheet metal angles inside and truss head screws. The lid is a flap of Harbor Freight moving blanket, doubled.

Spitzbergen idea - LOL !

Thanks for suggestion. Well rooted in science. I fear that as the sample gets colder with propane evaporation, we could get a hair-trim if the evaporated gas ignites.

The sample halves hurl around on sample weld breaking, so putting on a "vent tube" with the propane burning at the outlet - a "flare" - doesn't seem a viable solution.

It might be that I have to do something with "cardice" - solid CO2. Throw-in bits until reaches -40C.

Or cool to lower temperature and pump the cylinder when weld area has is showing -40C by thermocouple.

Thanks for suggestions.

I just looked online and find

lowest melting point is -21.1C

Something you learn about experimenting - while you do make sure everything holds together as it should, you don't look for the n-th degree of accuracy of physical conditions in the proof-of-concept tries.

To think in planning that a particular exact temperature is important is the error of thinking that if you specify something enough, "God" has to conform. Not going to happen. Get a pretty cold temperature and observe what is there to observe.

Regards,

LOL ;-)

-------------------

That's the first method I would try, to check your assumptions and procedure and shrapnel containment.

This suggests that impurity levels might be a significant uncontrolled variable in your experiments:

Is -40C the lowest you expect in European service? Some industrial temperature controllers have a cooling option that can operate a solenoid valve to regulate the temperature with evaporating CO2 from a tank of room-temperature liquid. "Liquid carbon dioxide converts to solid carbon dioxide snow at –79ºC (–109ºF)."

If the test chamber is nearly sealed the escaping gas should reduce or prevent frost covering the sample. US regulations required an oxygen level sensor and alarm at the test station. The body's breathing mechanism responds to CO2 level (pH) in the blood, not oxygen level, so you may not realize you are about to pass out from anoxia, especially with liquid nitrogen.

There are lots of other things besides sodium chloride to make "salt" baths from :-). See

for one list, and look at reference 2 and the reference pdf in ref 2 for a bit more info. I'd try calcium chloride hexahydrate/water either at the ratio for -41C or a bit stronger since they say it is difficult to reach the listed temps. You could also precool your metal with dry ice and even add some dry ice to the salt bath while it is cooling down, or put the salt bath in a small tub in a larger tub with dry ice packed around it. I'd make the starting ice either from distilled water (cheap at grocery stores) or reverse osmosis water if you have a home system already. If having the metal dripping with wet calcium chloride is a problem during your test put the piece in a ziploc bag. Partially seal the bag so about an inch at one side is still open then slowly submerge the bag in plain water while holding that corner out of the water. The air will be forced out so you get good contact between bag and metal for good heat transfer. Finish sealing the bag when as much of the air as possible is removed. Just pretend it is a steak you are about to cook sous vide :-).

Stunningly good info. Thanks.

I could see what NaCl-brine-ice does for the test, knowing there's further I could go.

Dam the ends of the Rectangular Hollow Sections to hold the brine-ice internally = direct contact. Contained. Salt on the sample wouldn't matter anyway.

Many thanks again.

One dodge is to make a heat pipe using propane as the working fluid, dry ice as the coolant.

Have liquid propane in the sealed copper boiler with a tube going uphill to a copper condenser cooled by dry ice in alcohol. The dry ice boils at -109 C, well above the freezing point of propane, so what will happen is that the propane will boil at -42 C, with the vapor rising to the condenser, where the propane will liquefy, and run back down to the boiler. This process is self-regulating so long as things are well insulated. But do this outside, and a 2-meter flare tube is a good idea.

The copper stuff can be ordinary plumbing tubing and fixtures. For a one-off, plumbers solder is good enough. For a true seal, braze with phosphorus-copper brazing filler, as used for HVAC systems.

Joe Gwinn

---------------------

The pipe fitting that enables making a condenser or similar concentric tube structure is a pipe reducer with the smaller end bored through on a lathe. Brass is easier than copper to chuck and turn. A 6-jaw chuck helps hold the reducer without (much) distortion, or you can jam a fitted wood plug into the large end.

When I learned industrial refrigeration in the 1970's this is what we brazed joints with:

I could see what NaCl-brine-ice does for the test, knowing there's further I could go.

---------------------------------

During a winter power outage I found that a mix of snow and road salt (NaCl

• ?) fell to 5F, -15C.

I don't visualize this.

What I was thinking was a simple one-pipe system, with vapor going up and condensate running down. The propane inventory need not be large.

Yeah, that's the stuff.

If you braze all the joints, you can hermetically seal the propane inside the heat pipe. Make sure that the total volume is large enough to prevent overpressure damage at room temperature. Or provide a pressure releas valve and refill before each use.

Joe Gwinn

"Techs keep Engineers out of trouble!"

Real deal. Thanks for that.

BTW

Mind's been going crazy over this. Spent yesterday Finite Element Analysis modelling the "beam-configuration fillet-weld tensile test"

"FEA : beam-configuration fillet-weld tensile test" Just occurred to me - if kept tubes strictly straight in-line with a frame/guide - could make it a longitudinal tensile - which means you could fast-load by firing a weight into a "stopper-plate" in the line of the sample. etc. etc.

If this sounds fanciful - every step of one of these home-spun investigations seems fanciful, each "next summit" seeming barely likely to happen. I could say this about this series of mini-projects so far, my fatigue-resistant welds research, my Doctorate studying then-new TMCP steels from Germany and Japan (definitely!), etc.

Real deal. Thanks for that.

BTW

Mind's been going crazy over this. Spent yesterday Finite Element Analysis modelling the "beam-configuration fillet-weld tensile test"

"FEA : beam-configuration fillet-weld tensile test" Just occurred to me - if kept tubes strictly straight in-line with a frame/guide - could make it a longitudinal tensile - which means you could fast-load by firing a weight into a "stopper-plate" in the line of the sample. etc. etc.

----------------------

the metal permanently deforms some of the kinetic energy converts to heat.

Resilient design - make sure that in an extreme event, there's not-a-lot / no abrupt breaking (low energy and structure is lost) and a lot of distributed bending and deformation (high energy, and the structure is still there)... :-)

Job as a welder - repair a height-restriction barrier at a supermarket

"Insert plates" so knocking it over again would be a long energy consuming process.