I have been playing with a Miller induction heating unit for the past
week. it is a rental and we have received minimal information.
It looks like a welding machine .... the size of a millermatic 250,
however its and inverter and runs on 460 three phase. The business end is a
very flexible cable that is water cooled and about twenty feet long. You
cover the pipe with Kaowool then wrap the cable around the pipe.
Has anyone played around with this machine? Better still, anyone know how
to use it effectively? The Miller manual has minimal information.
Heating round objects is pretty straight forward however flat surfaces
like steel plate are another matter. I am sure there is a lot at play such
as reactance, inductive resistance, air gap distances. These are all terms
I heard of over thirty years ago in college physics but know little about.
Randy
i would love some info on this as well , we are looking at building some
custom induction heaters for some of the equipment we repair. the big
rosebud is getting costly
R. Zimmerman wrote:
For all but constant section parts, evenly sized the full length, it's
all a best guess on the part of the engineers who figure out how to make it
work, then they experiment until they get it right.
I recently got some good heating results on a metal I beam by resistance
heating down the length of the web for a test. The heating was uneven just
at the very ends where current density spread out, but the rest of the beam
had little temperature gradients. Ironically, I thought it would work good,
the ee who was running the numbers for me didn't think it would, funny how
that work sometimes. Having a 250 amp DC power supply helped a lot. Less
than two volts across a part that was passing over 200 amps. Would have
cranked the current up more, as the supply was good for 350amps, but the
circuit breaker wouldn't let me go any higher, so I stopped and called it
good.
This site is a beginning. We are using an Intellifire 250. It certainly
does heat things up fast when they are round.
formatting link
Getting a magnetic field pulsing at 10 to 15 kHz plus running 450 to 600
volts seems scary. I look at the display and keep my distance once the
switch is thrown. I was warned not to leave any loose metal articles near
the cables.
Randy
i would love some info on this as well , we are looking at building some
custom induction heaters for some of the equipment we repair. the big
rosebud is getting costly
Good writting .. The beam wasnt insulated was it ? Heat loss over
large area ...
I did the F-111 wing pivots ( yeah , all by myself ! ) .
Many passes with TIG and.035% carbon wire .
But induction heating w/ large cables over the 5 inch steel
"arms" . Even had to heat them "down" hours after welding ....
Political ? I had to grind out most of the weld ! And that was before
X-rays !!! Not after !
We never found any reason to grind out more , after vuing X-rays .
Magnetic fields heat iron by hysterisis , that will cause currents
because the switching magnetic fields will force electrons .
Its one or the other . If electrons are forced in iron , then the
stationary
mag fld will deflect the electron , but if the mag fld is moving , it
will acelerate an elctron from rest .
Its just a point of vu , if you are a stationary electron ,
or a mag fld , you see the other moving .
Plywood glue is cured by the "other" thing in an RF fld .
The electrostatic force on wood fibers will rub them , heating them .
Rambling along .... HF MIG wire will stop , arc distance increases
and noise goes down and power to weld goes down BIG !
You can MIG if the wire is not large diameter and almost touching
the work . The reasons :
MIG only has a low voltage , many arcs are 10 to 20 volts .
Stick welders can make a welding 'arc" anywhere in 5 to 25 volts
for the amps is mantained , the voltage increases to maintain the amps.
But MIG stops dead , for its voltage is clamped to 24 vdc .
So pull the wire away a bit too much and you STOP welding !
Your MIG box would work better if it had a sophisticated elect
control to speed up wire , for operator errors . You would maintain
the power at the work .
This is why i recommend to novices : Always speed up the wire
too fast , then reduce if it dont weld .
Too slow speed will baffle many ppl .
Since MIG has a too high resistance in the small wire , always use
the largest wire . I use .035 on ALL steel .
? Its intuitive to start on .030" steel with a small wire , it may
be a "match" .
It just complicates learning , covers up problems .
But the complainst will be , its too fast to burn thru !
Yes but isnt that the main complaint always ?
Basics of welding :
thin edges will need to burned back and form a
round bulb edge before you can begin to build up
and fill a hole , so burn the bulb quick
and move fast , dont linger .
The book says gring a perfect fit ???
OK , do it .
But ill burn a bulb
and do a 2nd pass and its over in seconds !
Since you have CO2 coverage , you can do many passes over a MIG
weld and get strong bond .
MIG is a quieter arc , very close , sometimes wire will touch
and push ya a little , its a lower ,, blue arc .
If you are too far away , quieter ,, whiter ,
brighter , you cant weld here .
Notice the split rollers on 151T 220vac HF MIG ? Better idea , less
force to grab wire .
i dont like small diameter rollers . Im workin on a wire
feed device , no rollers , 3 cams push 3 arms ,
wire grippers can be very fault tolerant ! They dont bite the wire ,
but
they dont need adjust force !
The same appears to be the case when an electronic ckt shows
a flyback , with a transistor pulling a coil to ground , then letting
it go .
The current thru the transistor looks like its wasted , a closed
"switch" to gnd , only a coil slowing amps .
But all those coils and transformers windings are actually very
effecient
and dont disapate what you'd think .
and steel can be heated with 1000 watts to a high temp using
induction .
The waste can be very low in a 60 hz system and modern switchers
are way up in the 80% and more eff .
I design switchers and theres some exciting things happening .
I opened a cheap Chineese 400 watt PS and found a power transformer
far smaller than the common IBMPC pow supplies .
it was about 1 cubic inch . I had a 200w load avail' ...
it worked ! it ran cool .
The secret is in the wire , flat , perfectly formed soft copper ,
run at optimum freq of about 150-200 khz .
All smaller switchers , as in Sony laptops only use 1 bipolar
and it is always oscillating to nix the control needed to keep
core from saturating .
Switchers can be series or paralleld without problems .
i got 10 ( thats 4000 watts ) i'll use for a 100% duty cycle MIG .
Its much easier to safe a switcher , it can soft start , it can sense
tiny overloads and shut down in mili seconds . Except
for ICOM PS-125 , most switchers are protected , and its so
inexpensive to do !
Im a Ham Radio Op and my 745PRO pow supply had a short
and burned out the expensive hybrid circuit ( cause it is NOT protected
)
But i have all the control circuits , so a LM431 and a few resistors
and it will be running again . It was hype . They think MOSFETS
are good !!
There is nothing better than the old MJE1300x ( C2335
is Jap version ) . ICOM claimed they use 2 expensive MOSFETs !!
If you see a simple , single transistor switcher with no I.C. ,
only a zener and Opto ...or..... a LM431/Optocoupler ,
dont put it down , this is the future .
They are more fault tolerant , simpler , cheaper , higher efficiency
.
You can even modulate and turn completly off , easier !
It is possible to build a small "lunch" box that runs cool , 100%
duty cyle
and 200 amps . and very low cost .
Since this is all square wave , all parts like diodes and
transistors
can be paralleld without problems .
The transistor base drive can vary , no problem , as it wont harm the
hotter
transistor , it absorbs the base drive w/o much change , the gain is
allready
so low !
Or the collector characteristics can be mismatched and
the power chnage will be so low compared to the load it drives , no
problems .
Its called fault tolerant , if something changes , it wont burn
up anything .
At these hi frequencies , a tiny coil will ballast and increase the
phase angle
of conducting diodes to lower the peak current . Not so on the
slower input diodes ,
they must take large over loads ! I use TRIACs to soft start these
diodes .
Or nix Triac/Diode with SCR's .
.
Everything is much easier in switch mode power supplies .
I would check out this book , its relatuvely old but aside from the
power source types, the rest of the book is probably still quite
current. I have found Abe Books a great way to find machining and
engineering references.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.