Non-Chemical Can't figure out why skillet and sand didn't work

[924T]

A while back I bought a new electric skillet, put 3/4 inches of sand in it, dialed it up to maximum heat, let it
heat for 45 minutes with the lid on, put some small circuit boards in it to melt the solder to depopulate them and let them
'cook' for 30 minutes (with the glass lid on),

And nothing happened-----all I got was the aroma of hot circuit boards, no melted solder at all.

I know some of the forum members have done this and it worked, so I'm trying to figure out where
I went wrong.

Cheers,

Mike

 

[rusty]

A while back I bought a new electric skillet, put 3/4 inches of sand in it, dialed it up to maximum heat, let it
heat for 45 minutes with the lid on, put some small circuit boards in it to melt the solder to depopulate them and let them
'cook' for 30 minutes (with the glass lid on),

And nothing happened-----all I got was the aroma of hot circuit boards, no melted solder at all.

I know some of the forum members have done this and it worked, so I'm trying to figure out where
I went wrong.

Cheers,

Mike

Did you expect that the melted solder would fall away on its own or did you pick the boards up turning them on edge giving each a quick bump on the edge.

 

[924T]

rusty,

I pulled the boards out with a pair of pliers and whacked them on the lip edge of an old galvanized
steel bucket so hard that I dented the bucket.

Cheers,

Mike

 

[rusty]

melt temp various solder alloys

 

[NobleMetalWorks]

The method you are attempting to use, is called heat transfer. The heat is transferred from your heat source, to the skillet, to the sand, to the solder. Each time heat is transferred, you loose some heat (entropy). So your electric skillet will have to get hot enough so that you can loose some heat during the transfer of energy, so that you are left with enough heat to melt the solder.

Also, you must make contact between the sand and the solder in order for the heat to be transferred properly.

This sand must be of a type that not only transfers heat, but also retain enough heat so that when it transfers at the point of contact, it still has enough heat to melt the solder.

Scott

 

[Geo]

an electric skillet only reaches the lower limit to melt solder. reduce the amount of sand to about a quarter of an inch and dont worry so much about covering the top. better to put aluminum foil around the outside from the top lip of the skillet all the way to the table top. this way, the wind and breezes can not blow under the skillet, cooling it from the bottom. a good tell for when the solder melts is all the exposed solder will suddenly go very shiny with a mirror like surface. heating the entire board slowly is dangerous on a couple of different points. besides the organic vapors, some of the components contain oil and resins and can explode when overheated sending hot material flying in all directions. its best to apply enough heat to heat the board quickly. enough time to melt the solder but not enough to heat the components. electrolytic capacitors will explode if overheated.

 

[924T]

Geo,

I've cleaned up the mess quite a few times from 'blown' electrolytic capacitors----I used to rent out
p.a. systems, and disc jockeys (dj's) were invariably the roughest on my equipment.

They'd return the rental system(s) on a Monday, complaining about the high-frequency horns having
quit about halfway through their job----I'd ask if they heard a 'pop' or any other unusual noise.
Usually they'd describe it as having thought they heard a firecracker go off.

That's what you get when you drive power amps into clipping-----the distortion overheats the speaker
voice coils and the crossovers, and something's got to give. I was always happier to find out it was the
crossover(s) that blew up, instead of the horn driver diaphragms......

So, I'll retry the electric skillet/sand process, this time with .25" of sand instead of .75", and I'll either
try your suggestion of the Al foil 'skirt' on the skillet, or try lining the exterior with fire bricks.

First, I'll have to attempt to find that bag of playground sand I bought last summer.......

Cheers,

Mike

 

[bswartzwelder]

The real fine, white play sand works exceptionally well for me. But instead of a skillet, I use my trusty, RUSTY, Walmart hotplate and a rusty cake pan. The exposed heating coils on the hotplate produce tons of heat and the temperature control needs to be turned down once the sand reaches a point where it will melt solder. Keep a fan nearby to blow away the nasties.

 

[resabed01]

I remember from my youth I would take electrolytic capacitors and hook them up to a power supply reverse polarity just to see them pop. Something I wouldn't recommend doing.
Hey, what can I say.... We weren't allowed to buy firecrackers so I had to do something... :lol:
Come to think of it, I used to subject all kinds of components to excess voltage or current as "what if" experiments.

How else does one learn these things?

 

[Geo]

play sand is what i use but i sift out the coarser material with a small kitchen strainer.

 

[924T]

bswartzwelder,

I'm thinking that my electric skillet just doesn't get hot enough (450 F).

How old is your hotplate?

I'm wondering if new hotplates have been dumbed down as far as their maximum temperature, too,
so that I might have to go looking for an older (and better built) hotplate?

Cheers,

Mike

 

[niteliteone]

924T,
Don't waste money on new household hot plates as they are designed for "Safe Cooking Temperatures" which are usually under 500*F.
I bought 2 "Laboratory Hot Plates"off of ebay and paid less than $90 USD for both with shipping included.

They both reach temperatures above 800*F in a matter of minutes and have never had a heating problem with the various loads I put on them.
I generally place a handful of sand on the hot plate to set my flasks or beakers on as an insulation against being directly on the hot surface of the hot plate and insure better contact area on my glass.

Hope this helps.

PS. Remember to put your hot plate in a large plastic pan to catch any liquid Values in case of a glass failure.

 

[Palladium]

PS. Remember to put your hot plate in a large plastic pan to catch any liquid Values in case of a glass failure.

Good point he made. As another alternate i place my beaker in a piece of pyroceram dish. Best safety catch you can have.

 

[Geo]

i also use two cast iron porcelain coated pots as catch pans. each is 5 quart capacity. i use them to heat solutions in gallon jugs.

 

[bswartzwelder]

Mike,

My hot plate (from WalMart) is at most 2 maybe 3 years old, although it looks like an antique from all the spills that have boiled over on it. It is made by HOSTESS INTERNATIONAL and is model THP-432. It is (was) white with an exposed heating coil on top and a heat control knob on the right front side of the base. It has a pair of indicator lights (one red and one green) on the left side of the base. I have seen ones similar to it at WalMart lately and have seen online that some of them will reach 1000 degrees. Well more than needed to melt solder in a sand bath. I just looked at the nameplate and didn't notice the wattage. Things from China sometimes don't have all the nice information in an easy to read format like most American things. I'm thinking iust be some kind of military secret.

 

[Marcel]

Some components are glued to the PCs, exsp. when it is a double-sided PCB (where ther are components on boths sides, top and bottom)
While this may not be problem here, it can occur. The glue is very hard to remove, if possible at all.

 

[924T]

Wow------a bunch of very informative responses----many thanks!

I'm going to hit fleabay in just a few minutes and take a peek at the laboratory hot plates, and then visit
WalMart later today, and get a hands-on look at their hotplates.

I wouldn't have thought of using a porcelain coated cast iron pan as a safety basin, much less a ceramic
dish-----I'm pretty certain I can come up with a cast iron pan relatively easily (plus, that would tend to
hold the heat very well).

I doubt that just washing out that electric skillet would make it safe for food use, after having mild circuit
board fumes in it------------maybe it would still be useful for drying out Gold powder after the powder has
been rinsed in water?

I very much appreciate everybody weighing in on my skillet defeat, because that was extremely frustrating,
and has prevented me from achieving some things. What's really aggravating is the 'dumbing down' of the
cooking appliances in an apparent bid to protect us from ourselves......

Cheers,

Mike

 

[Geo]

i found as a good heat source is a propane burner. i keep all the side burners from propane grills. if its from scrap, they are basically free. the control valve lets you turn it down very low to wide open which will melt aluminum. i like the gas burners because of its portability. i can move the burner to the back of the property without running 500' of cords.

 

[bswartzwelder]

Very good idea to put your hotplate in a large catch container. I too, have had glass breakage (a beaker) when placing it directly on the heating coil. I did buy a piece of 1/4 inch thick steel (6 inches by 6 inches) and put it on top of my burner to spread out the heat more evenly. Seems to work well.

Edited to clarify and correct spelling mistakes.

 

[AndyWilliams]

i found as a good heat source is a propane burner. i keep all the side burners from propane grills. if its from scrap, they are basically free. the control valve lets you turn it down very low to wide open which will melt aluminum. i like the gas burners because of its portability. i can move the burner to the back of the property without running 500' of cords.

Checking out my local craigslist and found this. But it's a 45 min. drive and I'm not gonna take the chance it's gone! Wish people who live so far from the CL page they post on, would provide a contact so people don't have to drive to their place to find the item is gone.


(EDIT: The link is broken, I didn't think about the owner deleting the post once the item was picked up. It was quite like the picture Geo posted in his next post.

http://greenbay.craigslist.org/zip/4009490570.html