Pratt

Knowing little about these, indeed, only learning a few days ago that they existed at all, I come asking the wrenchers; Is one of the plug into the wall types of them a nice thing to get a bike, and other things, builder?
Thanks advance.

FBinNY 

Induction heaters have been around for eons. Italians have been using them to braze frames for over sixty years.

They use the same principle as glass cook tops, and are extremely efficient, so a good choice for volume work, but may be too costly for low volume situations.

So, don't run out and buy one before doing research to see if it's suited to YOUR needs.

It's been years since we had one so things might have changed a bit.

BITD you need a water cooling system to keep the coils from overheating at brazing temps.

You need different custom made coils to evenly heat the various joints.

You might also need an inert atmosphere system, depending on your specifics.

Also make sure any plug in unit is powerful enough to heat frame joints to working temps.

Andrew R Stewart 

I use an immersion water heater to warm up the water tub that I use to soak off brazing flux. This is my third version, the previous two both crapped out. If this is what you are talking about I suggest you only have it plugged in when under water or the coil will overheat and fail.



However I don't think you're talking about this type of heater. I am uneducated about induction heating, only know of the stove top version. That the bike frame has so many curved surfaces I wonder about how evenly induction would heat it up (sauce pans have a nice flat and large bottom). The varying thicknesses of the tubes, lugs and such might also prove challenging to get evenly hot. Then there's the aspect of the filler/braze being able to be heated by other that the joint's warmth. Does induction work on bronze or silver? Getting the filler to melt by only the joint's heat might mean having the joint really hot (as in too much). If induction heating acts like a convection stove top burner there's a time delay between "adjusting" the temp and having the work piece change its temp. I would think this delay would cause frustration for the brazer and any overheating would last longer as the "system" time to cool a bit is slow. (With a torch one only needs to flick the flame off the joint and the cooling is rapid, flick back and temp control is quick and easy). The size of an induction device might be significant, as well as the cost as Francis suggested.

I think the closest the industry gets is electric resistance heating, as in welding. But the heat is very localized and the tig torch, like the OA flame, can heat and cool rapidly with much control. There's a thread on another forum currently about Tig torch brazing and the consensus is that the braze/filler doesn't wet out on the steel to the same degree as with a flame. There are questions about resulting joint strength.

But many smart people have been blinded by tradition and wanting to continue techniques they already have mastered so I say have a go and report back. When you do post a follow up consider doing so in this forum's framebuilding sub forum, not the general mechanics one. Andy

Andrew R Stewart 

Do you mean hearth brazing? If so it's the same as flame heating but with heated air instead of an open flame touching the joint. I was told an interesting story about this method when I attended a building class taught by Albert E. Andy

sch

I think that when they refer to induction heating, it is using a coil into which the object to be heated is placed and then a
high current low voltage is applied to the coil and the object in the coil gets hot. Basically a low turn transformer using
magnetic fields to heat, the coils get hot also but not as hot as the object within the coil. Kilowatts of power are needed
but 110v coils can heat small objects. A google on metals useful for induction heating will show a list, seems to
exclude Ti but includes all bicycle frame material and common brazing alloys. Induction stoves work the same way
but with some limitations in metals used in the pots for best results.

One image of induction heating: https://external-content.duckduckgo....bd3&ipo=images

Nothing to do with immersion heaters pictured in prior post.

unterhausen

There is definitely induction brazing being done every day. I am not sure anyone is brazing enough frames to make it worthwhile to use in bike construction. Seems like it would have to be a giant induction heater to even work on a bike frame, but possibly I'm suffering from a lack of imagination. Multi-head torches like were used in the Merckx factory seem to make more sense.

JohnDThompson 

Trek developed an induction heating system for brazing frames in the mid-80s. It required specially shaped copper blocks to fit around the joints; each joint and frame size needed its own set of blocks to ensure even heating. Automated wire-feed machines fed a pre-determined length of brass wire into the joint after it was heated for a pre-determined time. Shorelines were touched up by hand while the joint was still hot. The system was only used for a couple/few years, as it was developed just as non-steel frames started to become fashionable, and was scrapped when the market became almost exclusively aluminum and carbon fiber.

JohnDThompson 

Electromagnets are used to induce an electric current in the target object; electrical resistance to this current in the target creates heat that eventually gets to a point where it can melt brass.

squirtdad

induction forge in action (for knife making)

FBinNY 

There seems to be some confusion about induction heating here, so I'm linking an article explaining it. In an nutshell, an alternating current is run through a coil surrounding the part to be heated. That creates a fluctuating magnetic field which, in turn, induces electrical eddy currents within the part, causing it to heat up. The process offers excellent precision and control and is very clean. As those with induction stoves know, it can only heat conductive materials, so glass cookware will never heat.

As I said earlier, it's not at all new, and Italian bike factories have been using it since the sixties (if not earlier). If you own a vintage Italian production bike odds are it was brazed using induction rather than gas. Besides being economical in places where electricity is cheaper than gas, it also offers advantages in quality control, and post brazing clean up.

Pratt

Thanks all. It makes a lot more sense now. My sense is that the recipient in question (#1 son) will be using it to loosen frozen bolts, etc. on abused construction equipment he is tasked with repairing.

dedhed

https://youtu.be/f2A8no15Ep0


​​​​​​https://youtu.be/YJElT9xK3bk

dsbrantjr

What you are describing sounds more like resistance soldering/brazing, where electrical contact by a tweezer, clamp or block type of electrode arrangement causes electric current to flow through the workpiece, directly heating it. I have used the process in electronic soldering, where copper or graphite electrodes are used.
Inductive heating uses coils to "induce" currents in the workpiece without contacting it directly.
Both are quite efficient because they directly heat the work, rather than conducting heat into the work by flame or contact e.g. soldering iron/gun; virtually all of the heat produced is in the workpiece.

JohnDThompson 

No, it was definitely electromagnetic induction.

tcs

Fun fact: The seat tube to top tube joint on Schwinn Varsity frames was induction heated silver braze.