Tiny Induction melting furnace

[Ardent]

X-No-Archive: yes

Hi all

I have a need to make a very small laboratory type induction melting
furnace for melting about 100 grams of stainless steel pellets - I
cannot use any other device that uses oil for burning.

On searching I could find only details of large systems.

Can any of you please help me with a schematic or any other help,
maybe a URL for a site?

TIA

--
Sandy Archer
Reply to newsgroups only

 

[Mac]

On Thu, 21 Apr 2005 00:36:38 +0000, Ardent wrote:

X-No-Archive: yes

Hi all

I have a need to make a very small laboratory type induction melting
furnace for melting about 100 grams of stainless steel pellets - I
cannot use any other device that uses oil for burning.

On searching I could find only details of large systems.

Can any of you please help me with a schematic or any other help,
maybe a URL for a site?

TIA

It is possible to make a microwave oven crucible for melting many metals.
If this interests you, search using google with the following three words:
microwave oven crucible.

Here is the URL for the first hit, which should be enough to whet your
appetite:

http://home.c2i.net/metaphor/mvpage.html

Apart from that, I have no idea how to make an induction furnace, but I
suspect that the schematic is not the most difficult part of the job.

--Mac

 

[Tim Williams]

With a bit of work and watercooling, this'll do it.

http://webpages.charter.net/dawill/Images/Ind_Lmatch5.jpg
So far it has melted solder:
http://webpages.charter.net/dawill/Images/Soldermelt.jpg
With a little more work it'll do steels no problem.

Circuit is
http://webpages.charter.net/dawill/tmoranwms/Elec_SG3524Driver.gif
Running a simple half-bridge which drives a series inductor to a parallel
resonant tank.

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

"Ardent" <iam@here.com> wrote in message
news:1114043800.716fbe6add758d4f23147b6c424123ca@teranews...

X-No-Archive: yes

Hi all

I have a need to make a very small laboratory type induction melting
furnace for melting about 100 grams of stainless steel pellets - I
cannot use any other device that uses oil for burning.

On searching I could find only details of large systems.

Can any of you please help me with a schematic or any other help,
maybe a URL for a site?

TIA

--
Sandy Archer
Reply to newsgroups only

 

[Anthony Fremont]

"Tim Williams" wrote:

With a bit of work and watercooling, this'll do it.

http://webpages.charter.net/dawill/Images/Ind_Lmatch5.jpg
So far it has melted solder:
http://webpages.charter.net/dawill/Images/Soldermelt.jpg
With a little more work it'll do steels no problem.

Cool. Looks like the floor in my "play" room. ;-)

 

[Winfield Hill]

Tim Williams wrote...

With a bit of work and watercooling, this'll do it.

http://webpages.charter.net/dawill/Images/Ind_Lmatch5.jpg
So far it has melted solder:
http://webpages.charter.net/dawill/Images/Soldermelt.jpg
With a little more work it'll do steels no problem.

Circuit is
http://webpages.charter.net/dawill/tmoranwms/Elec_SG3524Driver.gif
Running a simple half-bridge which drives a series inductor to
a parallel resonant tank.

The photos are certainly nice, Tim, but give us some details
we can digest and provide feedback upon.

What frequency and duty cycle when under use, how much power
drawn from the +/-17V supplies, etc. Some details of the
half-bridge, transistor type, drive stuff (25V gate drive?),
any snubber, etc. Details about the resonant tank, please.


--
Thanks,
- Win

 

[j.b. miller]

LECO ( Labratory Equipment COmpany) makes ( made) just what you want......I
used to repair them for a local steel mill.
Consisted of a 304TL tube as a simple colpitts oscillator with the coil made
of 1/4" OD copper tubing. The crucible sat inside the coil. Don'y know if
LECO is still around but it's another avenue to try.
It was simple and reliable........not cheap though..
Jay

 

[John Popelish]

Tim Williams wrote:

With a bit of work and watercooling, this'll do it.

http://webpages.charter.net/dawill/Images/Ind_Lmatch5.jpg
So far it has melted solder:
http://webpages.charter.net/dawill/Images/Soldermelt.jpg
With a little more work it'll do steels no problem.

Circuit is
http://webpages.charter.net/dawill/tmoranwms/Elec_SG3524Driver.gif
Running a simple half-bridge which drives a series inductor to a parallel
resonant tank.

Shouldn't the resonating capacitors be soldered directly to the heavy
tubing of the tank inductor?

 

[Tim Williams]

"John Popelish" <jpopelish@rica.net> wrote in message
news:UPmdnTutBq9UKfrfRVn-1g@adelphia.com...

Shouldn't the resonating capacitors be soldered directly to the heavy
tubing of the tank inductor?

Yes, I replaced the 3uF saran wrap mega-ESR thing with some polypropylenes
soldered on, I don't have a picture of it currently. It handles 100-200A
reactive pretty easily.

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

 

[Tim Williams]

"Winfield Hill" <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in
message news:d480ar05sg@drn.newsguy.com...

What frequency and duty cycle when under use

Whatever's needed, it's probably at 30-40%. I haven't scoped the driver in
a while, since it's not as finicky as the tank. ;o)

F = tank, right now it's got 4uH + 6uF, you know the frequency.

how much power
drawn from the +/-17V supplies, etc.

Mmmm, haven't measured that, can't be more than an amp.

The bridge is powered by a 100V 10A transformer (the clamped MOT) so the
circuit gets somewhere around 110-130V at up to 5 or 10A; I haven't measured
current consumption there either (and it just so happens I'm out of a DMM,
so I'll have to dig out my VTVM I guess).

Some details of the
half-bridge, transistor type, drive stuff (25V gate drive?),

12V peak gate drive, looks something like this:
http://webpages.charter.net/dawill/tmoranwms/Elec_SG3524_Osc2.jpg
Except a bit higher duty cycle of course.
Transistors = 6 x STW11NB80, sooner or later I'll wind a larger adjustable
matching inductor so I can bring up the voltage to suit.

any snubber, etc.

Nope. Can't detect any dissipation at 200-500W output, so it must be
switching fast enough (maybe 90% effiency). You could add some C to the
bridge output to slow transitions if you want.

Details about the resonant tank, please.

30uH (I need variable 0-300uH to step up the voltage and power) series choke
to match bridge to tank. Uh 20uF or so coupling cap between the bridge and
Lmatch, since I don't have a bipolar supply.

Work coil is 1/4" Cu tubing either 2" dia. 2" tall 5T = 1uH = uh 65kHz IIRC,
or 3 1/2" dia 3" tall 7T = 4uH.
Cap bank made up mostly of 0.22uF 400V polypropylenes from Digi-Key (uh,
PF2224-ND).

Oh, and the hottest thing I've had so far is a titanium strip, with help
from a ferrite rod to concentrate flux. Was a good orange glow (using the
1uH coil).

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

 

[John Popelish]

Tim Williams wrote:

"John Popelish" <jpopelish@rica.net> wrote in message
news:UPmdnTutBq9UKfrfRVn-1g@adelphia.com...

Shouldn't the resonating capacitors be soldered directly to the heavy
tubing of the tank inductor?


Yes, I replaced the 3uF saran wrap mega-ESR thing with some polypropylenes
soldered on, I don't have a picture of it currently. It handles 100-200A
reactive pretty easily.

Ah, yes. I didn't recognize that wad of foil as a capacitor.

 

[Watson A.Name - \"Watt Su]

"John Popelish" <jpopelish@rica.net> wrote in message
news:Tbednajc5f7ag_XfRVn-2w@adelphia.com...

Tim Williams wrote:
"John Popelish" <jpopelish@rica.net> wrote in message
news:UPmdnTutBq9UKfrfRVn-1g@adelphia.com...

Shouldn't the resonating capacitors be soldered directly to the
heavy
tubing of the tank inductor?


Yes, I replaced the 3uF saran wrap mega-ESR thing with some
polypropylenes
soldered on, I don't have a picture of it currently. It handles
100-200A
reactive pretty easily.

Ah, yes. I didn't recognize that wad of foil as a capacitor.

I didn't recognize this one either. Scroll down 2/3s
http://www.scitoys.com/scitoys/scitoys/radio/homemade_radio.html

Maybe I should make one and put it on the LC meter...

 

[Tim Williams]

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote
in message news:116guvc2ablnc1e@corp.supernews.com...

I didn't recognize this one either. Scroll down 2/3s
http://www.scitoys.com/scitoys/scitoys/radio/homemade_radio.html

Maybe I should make one and put it on the LC meter...

His is much better, a noninductive wind. I just taped aluminum foil on for
the terminals, so you can imagine the ESR! ESL was negligible though, being
only six feet long and under 5 thou thick.

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

 

[Daniel Haude]

["Followup-To:" header set to sci.electronics.design.]

I want to horn in about this: A colleague of mine recently asked me if it
was possible to build a supersmall induction heater for heating organic
molecules in a UHV chamber. The crucible is about 5mm (dia) x 5mm.
Induction heating (to about 300 C) would be elegant because it would
permit easy transfer of the crucible into and out of the chamber wihout
having to bother about electrical or thermal contacts for resistive
heating.

The coil would be about pencil diameter. I don't know it if is possible to
build a working furnace with such a tiny inductance and haven't had time
to look into the matter yet.

Suggestions? --D.

 

[Ptaylor]

Daniel Haude wrote:

I want to horn in about this: A colleague of mine recently asked me if it
was possible to build a supersmall induction heater for heating organic
molecules in a UHV chamber. The crucible is about 5mm (dia) x 5mm.
Induction heating (to about 300 C) would be elegant because it would
permit easy transfer of the crucible into and out of the chamber wihout
having to bother about electrical or thermal contacts for resistive
heating.

The coil would be about pencil diameter. I don't know it if is possible to
build a working furnace with such a tiny inductance and haven't had time
to look into the matter yet.

Suggestions? --D.

Seems do-able to me,but i'm no expert here..
I'd think the two main problems would be to make a small enough
coil,that could handle enough current without melting..But I suppose you
won't need a whole lot of power for a small workload.
Maybe some solid copper house wire,or large gauge enameled magnet wire.

The other might be the frequency,The frequency will be higher with a
smaller coil..But perhaps that isn't much of a problem either.There are
plenty of SMPS circuits to get ideas from,etc. And they usually run at a
fairly high freq.

Humm..maybe there aren't any real 'problems',just 'differences'.
Go for it!

 

[John Woodgate]

I read in sci.electronics.design that Daniel Haude
<haude@kir.physnet.uni-hamburg.de> wrote (in
<slrnd6h8it.p9i.haude@kir.physnet.uni-hamburg.de&gt about 'REALLY Tiny
Induction furnace (was: Tiny Induction...)', on Fri, 22 Apr 2005:

I want to horn in about this: A colleague of mine recently asked me if it
was possible to build a supersmall induction heater for heating organic
molecules in a UHV chamber. The crucible is about 5mm (dia) x 5mm.
Induction heating (to about 300 C) would be elegant because it would
permit easy transfer of the crucible into and out of the chamber wihout
having to bother about electrical or thermal contacts for resistive
heating.

The coil would be about pencil diameter. I don't know it if is possible to
build a working furnace with such a tiny inductance and haven't had time
to look into the matter yet.

Suggestions? --D.

The heat losses are greater in proportion for small coils, so lag the
coil with rockwool or something more attractive. Embedding the coil in
compressed powdered magnesia (as used in MICS cable) is a possibility.
That would increase the self-capacitance of the coil; MgO has a
dielectric constant of around 7.

Overcome the small inductance by using a larger tuning capacitor, so
that you are not radiating outside the relevant ISM band. This
low-impedance solution minimises the Q (and maybe f) change when you
insert the load.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Tim Williams]

"Daniel Haude" <haude@kir.physnet.uni-hamburg.de> wrote in message
news:slrnd6h8it.p9i.haude@kir.physnet.uni-hamburg.de...
<Snippet>

The coil would be about pencil diameter. I don't know it if is possible
to build a working furnace with such a tiny inductance and haven't had
time to look into the matter yet.

Absolutely...mind that the crucible is conductive. Moderate resistivity is
best, I wouldn't go with ferromagnetic materials personally. Something like
titanium would be good. Maybe 300 series annealed stainless.

Just hook up a little power LC oscillator. Well, like how I started...look
on my website.

Tim
(re-redirecting replies to ABSE+SED since I'm not subscribed to the latter)

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

 

[R Adsett]

In article <slrnd6h8it.p9i.haude@kir.physnet.uni-hamburg.de>,
haude@kir.physnet.uni-hamburg.de says...

I want to horn in about this: A colleague of mine recently asked me if it
was possible to build a supersmall induction heater for heating organic
molecules in a UHV chamber. The crucible is about 5mm (dia) x 5mm.
Induction heating (to about 300 C) would be elegant because it would
permit easy transfer of the crucible into and out of the chamber wihout
having to bother about electrical or thermal contacts for resistive
heating.

The coil would be about pencil diameter. I don't know it if is possible to
build a working furnace with such a tiny inductance and haven't had time
to look into the matter yet.

It is possible, I saw such a beast as a graduate student. It was used
for evaporating all sorts of materials for investigation of thin film
semiconductors. The big RF cabinet looked as if it were a commercial
design but it's been a while so I may be mistaken.

The coil was perhaps twice the diameter of a pencil, maybe less. Ah, the
fraility of memory.

Robert

 

[Dirk Bruere at Neopax]

R Adsett wrote:

In article <slrnd6h8it.p9i.haude@kir.physnet.uni-hamburg.de>,
haude@kir.physnet.uni-hamburg.de says...

["Followup-To:" header set to sci.electronics.design.]

I want to horn in about this: A colleague of mine recently asked me if it
was possible to build a supersmall induction heater for heating organic
molecules in a UHV chamber. The crucible is about 5mm (dia) x 5mm.
Induction heating (to about 300 C) would be elegant because it would
permit easy transfer of the crucible into and out of the chamber wihout
having to bother about electrical or thermal contacts for resistive
heating.

The coil would be about pencil diameter. I don't know it if is possible to
build a working furnace with such a tiny inductance and haven't had time
to look into the matter yet.



It is possible, I saw such a beast as a graduate student. It was used
for evaporating all sorts of materials for investigation of thin film
semiconductors. The big RF cabinet looked as if it were a commercial
design but it's been a while so I may be mistaken.

The coil was perhaps twice the diameter of a pencil, maybe less. Ah, the
fraility of memory.

I once made an induction heater out of a 100W audio amp and a 20 turn coil (plus
caps etc) about 20mm dia. Worked fine - even heated a small screwdriver to red heat.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[Mac]

On Fri, 22 Apr 2005 07:04:55 +0000, Daniel Haude wrote:

I want to horn in about this: A colleague of mine recently asked me if it
was possible to build a supersmall induction heater for heating organic
molecules in a UHV chamber. The crucible is about 5mm (dia) x 5mm.
Induction heating (to about 300 C) would be elegant because it would
permit easy transfer of the crucible into and out of the chamber wihout
having to bother about electrical or thermal contacts for resistive
heating.

The coil would be about pencil diameter. I don't know it if is possible to
build a working furnace with such a tiny inductance and haven't had time
to look into the matter yet.

Suggestions? --D.

I wonder how hot the sample would get if you put it in a quartz
crucible and hit it with several IR laser diodes? I do know that quartz
doesn't absorb IR. Most organic molecules do.

Not my area of expertise for sure, so I may be talking complete nonsense.

--Mac

 

[Mike Monett]

Tim Williams wrote:

"Daniel Haude" <haude@kir.physnet.uni-hamburg.de> wrote in message
news:slrnd6h8it.p9i.haude@kir.physnet.uni-hamburg.de..
Snippet
The coil would be about pencil diameter. I don't know it if is possible
to build a working furnace with such a tiny inductance and haven't had
time to look into the matter yet.

Absolutely...mind that the crucible is conductive. Moderate resistivity is
best, I wouldn't go with ferromagnetic materials personally. Something like
titanium would be good. Maybe 300 series annealed stainless.

Just hook up a little power LC oscillator. Well, like how I started...look
on my website.

Tim

Tim et al,

Is there any reason to go to the trouble and complexity? Why not just
pass 100A at 5V to terminals on the crucible and make it act like an
electric stove?

Mike Monett