Oven brazed Evaps

[PhilippF]

What would you use to heat an evap in a vacuum? A large inductor? Wonder if I could build a small vacuum oven for evaps for a decent price. Does anyone know of a nice informative website on this concept? Can't find anything but food ovens or product listings.



God I hope this is a joke from the last thread about the acrylic mounts?

Just search for ceramic ovens, they go up a little further to 1100C.

The way I put the brazing there is still a bit of a "production secret", as I am still on my way to improve it further, at the moment it is a little pain in the a** to put it there.

As far as I remember Gosmayr used also a ceramic oven, I think I remember a photo posted by him with a lot of evaps on a tray...

Regards,

Philipp

[wdrzal]

You can get vacuum ovens in all different temperature ranges,the hotter ones have refractory brick lining them like a Kiln.

I seen a guy selling ceramic refractory brick by the case pretty cheap on ebay a while back.

[[XC] 2long4u]

So a vacuum chamber and then high-temp electric coils like those found on an electric kitchen stove? Seal it in a steel box, insulate, have a pump-down port. Hrm..

I don't know if a stove element would do it. I love the idea. Vacuum ovens arn't cheap.
Sorry for the spam I couldn't help myself.

[wdrzal]

The way I put the brazing there is still a bit of a "production secret", as I am still on my way to improve it further, at the moment it is a little pain in the a** to put it there .

The paste DetriotAC mentioned works well, just cut a template where you want the paste applied. You control the amount by the Thickness of the template. You can use a .050 or if more paste is needed increase the template thickness say to .075 until you get the right amount. You just fill in the void and run a scraper over the top to remove the excess.

You may someday want try a CO2 blaster to clean with too . Dry ice pellates work great,they just sublimate away. You can combine the dry ice pellets with supercritical co2. I,m sure you know it's a great solvent.

[B]BTW Super job on what you already done.

[mytekcontrols]

Great idea and technique for applying precise amount of solder paste Walt

And very good execution on what you've done thus far Philipp

[wdrzal]

Great idea and technique for applying precise amount of solder paste Walt

Just to be clear,the paste DetriotAC mentioned is actually flux & powered brazing filler in a paste form. By controlling the width & height by using template slots you don't over or under apply the filler alloy.

[star882]

What about induction heating? Just use a vacuum jar and a coil carrying high frequency current around it.
http://www.richieburnett.co.uk/indheat.html

[wdrzal]

Star882, Hannah what happened to Britney?

[star882]

Star882, Hannah what happened to Britney?

That was just a funny quote from a HVAC friend of mine. Way too good to pass up. He has already built a chiller based on R134a (about 1/2 ton capacity) and is planning to build a "pseudo-cascade" using R410a that uses a water cooled condenser and connections to the chiller to reduce condensing pressures. Hannah is the "fridge girl" I have mentioned before, and she is currently in a relationship with the "HVAC guy" I got the quote from. Every once in a while, they would set up a public HVAC/R discussion and allow those interested in HVAC/R to participate. I have actually learned a lot about HVAC/R from them.

As for Britney, it was a nice CPU, although somewhat outdated today. A modern quad core can easily outperform a Britney in almost all real world applications (except those using lots of memory bandwidth), for lots cheaper too.

[godmod]

Don't you guys think that it's a little bit too much OFF TOPIC ?!

[star882]

To get back on topic, the "AC/R couple" agrees that induction brazing evaporator blocks sounds neat, although the costs are a little high to be justified just to make a few blocks. Maybe an induction kiln can be DIYed using common electronic parts. 400w was enough to get a small nut in air white hot in 45 seconds, so we'll probably want something like 1000w max for an evaporator block in vacuum. Design the power stage with variable power to allow for careful control of the block temperature.

[Tonic]

In few months I will finish H-bridge inverter, and, since I'm interested in how induction heating would work for brazing evaporators, I'm going to test. However, I have feeling that it will be more complicated than it seems, because copper is a great conductor and losses caused by eddy currents will be small. In worst scenario it might need a few kW's and high frequencies to get reasonable results. Also, alloy might melt before touching evaporator, since it has a small mass

But! It surely would be fun to just put evaporator inside heating coil and what you would have to do is only touching with brazing alloy

[gosmeyer]

Well done The oven is the only way to fly! No guess work and no cleaning

[godmod]

However, I have feeling that it will be more complicated than it seems, because copper is a great conductor and losses caused by eddy currents will be small. In worst scenario it might need a few kW's and high frequencies to get reasonable results.

Good Point.

Also, alloy might melt before touching evaporator, since it has a small mass

That could also be seen as an advantage. As the Alloy melts it transfers the heaat to the capillary joints of the evap and helps distributing heat...

edit:
The Problem is not the good electrical conductivity, it is the bad magnetic permeability.

Conventional built inductive heaters can heat materials with a bad magnetic conductivity with a very bad efficiency factor.

[PhilippF]

Well done The oven is the only way to fly! No guess work and no cleaning

Thanks for the compliments from the evap master *bowingmyhead* !

[AliG]

just wondering, what's the big issue with oxidation? Does it make the block weaker? Hamper performance/flow?

[n00b 0f l337]

Ruins the system internally

[Moc]

Most important point is that it cause bad heat transfer.

Ruins the system internally

If you blow the tinder after brazing out, there won't be a problem.
Simply use N2/Co2/Propane.... and you have no problems.

[n00b 0f l337]

No not at all, contamination like that can cause oil problems.

[PhilippF]

And it really looks ugly... I know, I know, form follows function... but I like clean builds so much...

[teyber]

oxidation is a insulator in a way, so it does hamper performance... I don't think your oxidation from leaving it out in the atmosphere is going to change your temps by 1c though alig, just saying if you braze without purging...

regards

[AliG]

that's good to know, since my torch isn't strong enough and I had to have my dad's friend braze my evap for me (he owns a car repair garage) and didn't purge.

[teyber]

o :P yeah that definately isn't good. you will problably need to soak it in a acid, and oven-bake it. Don't know of any chemicals off the top of my head though

[PhilippF]

Yesterday I made the evap for August123´s 4-stager. It didn´t turn out exactly as I wished as I used a new silver solder, but I think it´s ok...

[one_servant]

It didn´t turn out exactly as I wished as I used a new silver solder, but I think it´s ok...

Quality work nevertheless!! That's a good looking evap without a doubt!