Assistance in identifying material composition of some wire

I have some 'wire' which comes from the tip of a Metcal induction heated soldering iron. This wire forms the induction coil around the nickel/copper soldering tip. I wish to use this wire type for induction heating of a 3D printer hotend - for a number of reasons - Metcal use it, so it must be OK - It obviously withstands the heat and shows no tarnish or corrosion at all

I am attempting to 'copy' the operation of the Metcal RF power source to get things working initially. The RF source runs at 13.56MHz, around 50 or so watts.

Now to the wire...

the wire is around 600mm long, is 0.2mm diameter ( vernier, not micrometer), as best as I can measure is 0.4 Ohms. This measured by placing a current through the wire till 1 volt drop across it ( Fluke 6digit multimeters), with another Fluke as ammeter in series - the amps was 2.5A.

The wire is bright silver. Scraping it gently under a microscope reveals NO copper colour at all. Bending it back and forth in a small bend seems to harden that section - sort of work hardened. It solders with plain tin/lead solder, 'tins' very easily, without cleaning or scraping.

From metal resistivity tables the resistance seems to low for aluminium, to high for silver and it ain't copper..

I suspect it may be silver or a silver alloy and trying to use resistivity comparisons probably leaves the path open to large errors - if I had a 100meters of it, maybe the resistance value would be useful, but 600mm...

Any Chemists with some bright ideas as to some basic chemical tests that may divulge the wires prime makeup?

Joe

Maybe a nickel alloy. Have a look at Espacenet patents search and put in Metcal and browse the results.

Tungsten?

pgk

Sorry, Joe ... I think it might be Platinum

**LINK**

https://www.sigmaaldrich.com/catalog/product/aldrich/357359?lang=en&region=GB

.

10.6 microOhms per centimetre isn’t all that far off what you are reading

MichaelG.

Thanks Chaps..

I don't believe it could be tungsten - resistance to low for that.

Dick, thanks for the reference to Patents - I have about 15 to go through now!

Michael, as usual, a trove if information...

You may just be correct. Ticks most of the boxes - very high temp performance, so that's probably why there is no sign of tarnishing or corrosion. Ohm's are valid withing my measurement capabilities. Just the price, from your reference, is an outlier. That site indicates 448 Euro for 1meter - the tip used 680mm, so around 300 Euro for the wire - The complete tip ( from which this wire was extracted) from Metcal costs 16 Euro. If it is platinum, maybe its nor pure and so costs less..

Going to dig in the patents and will report back!

Joe

Joe

Sigma Aldrich prices are ‘reassuringly high’ ... but if you can buy 680mm in a 16€ product, I would be very surprised if it’s Platinum.

The mystery deepens

MichaelG.

.

https://www.bullionbypost.co.uk/scrap-platinum-prices/

Edited By Michael Gilligan on 17/07/2020 09:19:21

Given RF at 13.56MHz gut feel is the metal must be silver, copper, or a silver-copper alloy. As RF tends to flow on the skin of a conductor, it's usually very important for RF coils to have the lowest possible resistivity. Except I don't know about inductively heated solder tips - possibly the coil in a soldering iron is designed to get hot itself as well as induce heating in the tip. Dunno.

May not help without a laboratory, but.

1. Heat the wire fiercely in pure Oxygen. (Copper will Oxidize, silver won't.)
2. Dissolve residue in dilute Sulphuric Acid. Should produce blue Copper Sulphate solution leaving a Silver as a residue. (Silver doesn't react with dilute Sulphuric Acid). Filter.
3. Confirm for Copper in the solution by adding Ammonium Hydroxide solution. If Copper is present, it will produce a blue precipitate, dissolving in excess Hydroxide to a deep blue solution.
4. Add dilute Nitric Acid to the filter residue. Silver dissolves in dilute Nitric Acid.
5. Confirm Silver by adding Ammonium Hydroxide solution. If Silver is present it should produce a white precipitate.

Classical chemical analysis involved the very disciplined application of many different tests to identify all the elements present in a compound. Even more difficult and time-consuming when the amounts of each element present were required, this needed many careful weight measurements with an accurate Chemical Balance. Nowadays it's mostly automated - a bunch of clever machines detect stuff in seconds that men in White Coats once took days or even years to unpick.

If there's an accurate scale available, the wire's density or specific gravity will be revealing. Metals like Tungsten and Platinum are characteristically heavy, Aluminium and Magnesium characteristically light. Knowing the density should eliminate a large number of possibilities.

The presence of metals can often be shown simply by heating them in a clear blue flame, though the results can be subtle. Try a flame test - Wikepedia is Helpful.

Dave

I'd agree with Michael, platinum is way too expensive. Fair point by SoD about skin depth, although silver does tarnish in the atmosphere so the wire may not be simply plated. From a simplistic viewpoint the intent of induction heating is to transfer energy to the workpiece to heat it up. Any heating of the primary coil is wasted energy, so I would have thought that the primary coil wouldn't be designed to get hot?

Andrew

Is this a genuine Metcal tip?

Last time I took one apart it used Litz wire. That was several years ago though. Has th bit been used? migh seem obvious but if it's not been used much it won't have oxidised much.

Robert G8RPI.

Either (a) you are going o use this element in which case it doesn't matter; or (b) you want to make your own.

If (b) why worry about what wire was used originally? Just use somewhat thicker copper, possibly silver plated, but frankly at 13 MHz it won't make much difference given that you want most of the loss to be in the thing you heat.

From John:

Either (a) you are going o use this element in which case it doesn't matter; or (b) you want to make your own.

If (b) why worry about what wire was used originally? Just use somewhat thicker copper, possibly silver plated, but frankly at 13 MHz it won't make much difference given that you want most of the loss to be in the thing you heat.

John, I would use it but its a little short for what I am trying to do. Point is that Metcal by induction generate 40 to 50 watts into the tip, without cooking the wire , no tarnish, no oxidation. The wire is insulated with a very open weave fibreglass sleeve when coiled around the nickel/copper slug at the tip, so that would lessen oxidation to some extent, but the weave is rather open so is exposed to hot air. I have been playing with peralin coated copper wire, as well as kapton coated copper - it cooks.... I tested this by winding an identical copper wire coil in place of the Metcal wire and running it on the metcal tip and power source.

From Robert :

Is this a genuine Metcal tip?

Well,... Yes - since its my Metcal iron and the tips I purchased from OKI International - Tip in the photos is a STTC-135

Last time I took one apart it used Litz wire. That was several years ago though. Has th bit been used? migh seem obvious but if it's not been used much it won't have oxidised much.

That must have been long ago - Litz wire was used in the SP-200 system ( over 15 years ago..), which ran at 475KHz - quite different,

From Andrew:

I'd agree with Michael, platinum is way too expensive. Fair point by SoD about skin depth, although silver does tarnish in the atmosphere so the wire may not be simply plated. From a simplistic viewpoint the intent of induction heating is to transfer energy to the workpiece to heat it up. Any heating of the primary coil is wasted energy, so I would have thought that the primary coil wouldn't be designed to get hot?

Andrew, that is the key here, and exactly what I am trying to discover how its achieved - The tip gets hot, but the wire is never hotter than the tip - Measuring the AC current in the coil while heating the tip ( using an old, good, HP current probe..) I read around 1.2amps RMS. The voltage across the coil is around 200volts PP. That magnetic field then generates eddy currents in the nickel mix cladding on the copper tip and heats it. But the wire does not cook. If I replace with copper wire, the current actually drops to 1.05amps, but the coil cooks after a while - I suspect the skin effect is killing the coil.

I begin to think the wire is silver - Pricing also reflects that - around 18 Euro for a meter...

And last, in one of the Patents I read, It is indicated that the wire can be Silver, copper, or nickel/copper....

Reading patents - to do much of that requires a special kind of person...

'said means of multiple claimed pluralities causing substantial crossing of the glazzies'..

Joe

Photo shows the coil in its glassfibre insulation, the tip heating slug right, and the bare wire on left.

Coil zoomed in

Bare Wire from a VERY used hot grade tip

When we had a induction heated setup up for melting metal the coil was thick wall copper pipe with cooling water flowing down the inside. That's not terribly helpful in your case, but we did have (heat) radiation shield in the form of a ceramic tube which reduced the heat radiated back into the coil from the crucible, this might be helpful. The only issue we had was the ceramic tube kept cracking because of differential expansion, middle got a lot hotter then the ends, cured by slicing it into relatively short lengths. I doubt you'd have that problem as your temperatures a lot lower.

Friend of mine tried to make an induction heated arrangement for silver soldering boiler fittings, less messy than getting the gas bottle set up, so if you get this running perhaps someone will develop it further. Way out of my pay grade!

Apparently it's a coating of 'Alloy 42' over copper driven at several megahertz, and when it passes it's curie point eth electron flow is forced into the copper beneath raising the resistance.

Should be easy to do in the workshop...

patents.justia.com/patent/5329085

My worry would be that metcal irons are all designed to work as specific, rather higher temperatures than you need for 3D printing.

I suspect the greater thermal inertia of a block of aluminium may be useful to ensure even heating and induction may offer no practical advantage over a cartridge heater.

.

Strange, that ^^^

Joe seemed quite explicit when he wrote:

“The wire is bright silver. Scraping it gently under a microscope reveals NO copper colour at all. ”

MichaelG.

From Michael:

Strange, that ^^^

Joe seemed quite explicit when he wrote:

“The wire is bright silver. Scraping it gently under a microscope reveals NO copper colour at all. ”

You observe correctly Michael..

Neil is a little confused.. Understandably so, if he spent time inside a Patent...

What Neil is referring to is the actual heated tip - it is a copper slug, covered ( plated in some cases) with a nickel ferrous mix ( alloy 42) ( Area 52..??) . When inductively excited at 13MHz, the eddy current which travels mainly on the surface due to skin effect, travels in the 'high' resistance alloy 42. heating it up. It heats till its Curie temp, when the resistivity drops, and the eddy currents travel in the alloy and copper below. The heating then stops, till the alloy cools below Curie, and the loop stabilizes. There are some electronics monitoring the reflected energy from the coil - when cool the reflected energy is low so max power is applied to the coil - when curie is passed, the reflected energy is high and the power is shut down till the reflected signal is good again.

The temp that the irons work at, ie, the tip temp, is purely a function of the Curie point of the cladding material on the tip - in my case the hotend is a stainless steel nozzle, with the coil around it ( basically). The coil inductance changes as the nozzle heats, changing the reflected energy ( higher SWR) and the my electronics would reduce power to the coil, etc. There is no Curie effect in my intended application, so I make the temp whatever I want-

IF I can get it to work - at the moment coils of copper are no good! The copper gets too hot, and could probably be used to heat the nozzle directly, making the whole induction thing somewhat moot..!

Neil, you are quite correct - heating with a resistor cartridge is the best solution - less wiring, less electronics, less fuss, but also, much less fun..

There are -so far- no less than 31 patents by METCAL on this subject!

Joe