Questions on using solid silver for a soldering iron tip

GopherT

Joined Nov 23, 2012
8,009
Not trying to start an argument but understand. Doesn't a higher thermal conductivity also mean it will loose it's heat faster? Once the correct temp is reached, won't it also cool down faster? I was always under the assumption that thermal conductivity just meant it would heat up faster from the heat source. Take at example of cookware, aluminum heats up faster than cast iron. But when taken off of the stove it also cools down faster. I know it's not the same as a soldering iron, but an example that I'm very familiar with and can be easily measured due to the larger size.
One is called thermal conductivity, the other is heat capacity. Metals with high thermal conductivity (and high electrical conductivity) tend to have unpaired electrons in the ground state (sodium, silver, gold, copper).

Heat capacity is generally reported in terms of heat transferred per unit mass. The least dense elements have the highest heat capacity. Once all elements are corrected for density differences, the heat capacity per unit co,home is much closer. So, in the case of soldering iron tips, the size (by volume) is not going to change much by a designer so assume all elements would be pretty close on this aspect.

Finally, touching a piece of steel at 300F can easily be done, grab and release. A hot spoon, the handle of a cast iron pan, for example. But, touch a thick piece of aluminum at 300F with the same pressure and time and you'll be sure to get a blister. Aluminum conducts very well and transfers that heat vey well.

Final note, aluminum has about 2.2x heat capacity of iron per pound. But slightly less than iron for a 1" X 1" cube of each.
 

ian field

Joined Oct 27, 2012
6,536
What do you mean? It will become tarnished? I expect it will be slower than copper, and I can just chuck it in the lathe and polish/sharpen when it gets dirty

Almost any metal will oxidise at soldering iron temperature - Antex save costs by not pre tinning the iron plating on their bits, you have to tin it during the first warm up or it oxidises. Its a PITA to clean it off without damaging the plating if you don't get it right first time.

Aluminium oxidises instantly in free air at room temperature. You can tin it with the right flux or an ultrasonically agitated solder dip - presumably that means its capable of alloying with solder, so it would also lose a bit of aluminium in every solder joint.
 

MrAl

Joined Jun 17, 2014
11,565
Not trying to start an argument but understand. Doesn't a higher thermal conductivity also mean it will loose it's heat faster? Once the correct temp is reached, won't it also cool down faster? I was always under the assumption that thermal conductivity just meant it would heat up faster from the heat source. Take at example of cookware, aluminum heats up faster than cast iron. But when taken off of the stove it also cools down faster. I know it's not the same as a soldering iron, but an example that I'm very familiar with and can be easily measured due to the larger size.
Hi there,

I dont take it as an argument, just as someone looking into this a little further that's all. We have to ask questions sometimes and i do that all the time too :)

In a way you are right that better thermal conductivity will lead to faster cooling, but who cares if we turn the iron off and it cools down faster. I happen to like that behavior dont you? While the iron is still plugged in however there's no chance it will cool down, and with the same size tips we have the same surface area so there will be very nearly the same cooling per unit length of the tip for any material, unless of course it has very different surface texture.

What does the iron actually do. It converts electrical energy into heat energy then has to conduct that energy to the joint. This action is very similar to how a wire transfers electrical energy to a node. If we have better conductance we have better energy transfer because we have less resistance to the flow of current. The heat travels to the tip and there is an analogy, and that is that the tip length represents a thermal resistance in series with the flow of heat (which would be current in the electrical circuit) and the less thermal resistance, the more energy transfers to the joint (or the node). If we use a resistor with less conductance then it must have higher resistance, and that means less energy transfer, if we use a tip with higher thermal resistance, less energy transfer again.

The heat 'circuit' could actually be simulated in a simulator like LT Spice if we just convert the thermal elements to electrical elements. For example, the iron heat coil temperature would be the voltage source, the tip would be a resistor (with some perpendicular capacitance), and the joint would be a capacitor in parallel with another resistor. So we end up with a voltage divider with the tip resistance on top, and as we all know the lower the resistor value the more voltage appears at the node.
It should be apparent that if we raise the resistance of the tip (make it longer or use less conductive material) it not only takes longer to heat up the joint, it also can not deliver as much energy to the joint because the temperature can not reach the higher level that it can with a lower resistance tip. We could set this up if you like and run some simulations, or just do a few calculations.
 
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Thread Starter

Eddy Current

Joined Jan 25, 2017
25
Almost any metal will oxidise at soldering iron temperature - Antex save costs by not pre tinning the iron plating on their bits, you have to tin it during the first warm up or it oxidises. Its a PITA to clean it off without damaging the plating if you don't get it right first time.

Aluminium oxidises instantly in free air at room temperature. You can tin it with the right flux or an ultrasonically agitated solder dip - presumably that means its capable of alloying with solder, so it would also lose a bit of aluminium in every solder joint.
Losing a bit of silver into the joint is better than a bit of aluminium, right?

And no coating = no PITA to clean
 

Thread Starter

Eddy Current

Joined Jan 25, 2017
25
Frequently is a relative term

I already said I am using bare copper, and there is no way I have to replace that "frequently"

And Alec_t isn't replacing his "frequently"
 

tranzz4md

Joined Apr 10, 2015
310
The use of sublime? Correct me if I'm wrong (which I'm sure someone will do) is when material from one surface vaporizes and migrates to a new......
Common enough language in parts of the USA that have cold icy winters. Our ice sublimes away quickly when it's windy and we have high barometric pressure. Sublimation is when our H2O changes from solid to vapor without passing through the liquid stage.
 

ian field

Joined Oct 27, 2012
6,536
THat's good for you, but you missed the part where I manage to dirty tips up easily
You can get Sandflex blocks - rubber blocks with particles of industrial diamond.

Its always best to avoid cleaning plated tips with anything abrasive, but most people think in terms of using a file or emery paper.

If you wipe off any solder then let the iron cool, a sandflex block can remove oxide and scale with a lot less risk to the plating.

If you don't look after your iron - replacement tips are simply the cost of doing business.
 
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