Jump to content
 

Low melt soldering irons


Recommended Posts

 When both ways work that is fine for you.

But my post was specifically countering the argument proposal/claim that was being made where the blob of solder allegedly being carried would freeze on contact with a big lump of whitemetal. Something I do not disagree with as white metal has pretty poor conductivity properties. So though I do not disagree with it, it would not happen to me (or anyone following my soldering technique) as the blob is never carried in the first place.

Of course soldering brass is quite a different matter altogether and do not quite see the relevance of brass in this context?

I don't have too much of a problem with different techniques working except when the reasons for doing one over another are outnumbering. Although I can see several reasons for not carrying molten low melt solder on the tip of an iron, I can find no reason in its favour.

Works for me, and others.

 

My main reason for using it is that, as anybody who solders knows, five hands would sometimes not be enough. I find it much quicker to assemble the parts, hold them with several contorted fingers on one hand, quick wipe of flux and in with the iron, picking up solder on the way, and right into the joint. There's no extra step of placing cold solder there, and hoping it stays put whilst you bring the iron in. Same for brass and whitemetal. Not 'right' but it works.

 

As for solder somehow denaturing on the iron. Well, I've knocked excess blobs off the iron tip, which freeze into a little ball. I've subsequently picked up that ball on the iron and re-used it. It's exactly the same as the original solder in behaviour, low melt included.

 

In terms of soldering whitemetal, I could argue that carrying in solder on the tip has the benefit of improving heat transfer to the whitemetal (through the better surface area contact of the molten blob) and the extra heat energy in the blob itself, both contributing to getting heat in quickly, and the iron out faster.

 

However, I'm not here to convert anybody, just to provide balance for the newcomer.

Edited by Arthur
Link to post
Share on other sites

But, if you had tried it, you would know that it was nonsense, unless you use an underpowered iron or too small a tip. The molten solder boils the flux on contact and that starts the local heating necessary for the solder to bond. Provided the iron can maintain the tip temperature well above the solder melting point, there's no chance of 'freezing'.

 

Oh come on, they aren't really that different

 

I wish you'd tell us some believable reasons for not carrying solder on the iron! As to reasons in it's favour, how about speed, convenience, not needing to spend time cutting up and placing small pieces of solder, and being able to solder at any angle without the solder fragments moving from where you want them.

 

Nick

How about the antimony (present in most low melt solders) vaporises at approx. 300oC? Not nice stuff to breath in.

 

I can and have used convention irons for whitemetal, but prefer to use a 60W  Maplin soldering station at about 280C, usually 12% phosphoric, and slivers of solder along the joint. I find that a quick touch of tip cleaner wets the iron beautifully to start the soldering and a quick wipe of tip cleaner allows you to use the iron for brass etc with no fuss.

 

You will find as many opinions as facts on here, find a way that suits you and use it.

 

Richard Lane

Link to post
Share on other sites

Low melt solder is an alloy of various metals and is often referred to as "Wood's Metal" Many varieties exist but most contain either Zinc, Cadmium, Thalium, even Mercury has been used along with the principle ingredients of Tin and Lead. These compounds are added to reduce the melting point of the Tin/Lead alloy. They are all toxic but (ignoring Mercury as it is little used these days) Cadmium has the particular property of subliming at its own low temperature. Cadmium melts and evaporates at 310'C. In fact much of the cadmium that evaporates from the alloy in the presence of heat (up to 25% typical) is designed to do so and in doing so it "cures" the solder. So chasing balls of pre-melted solder around and re-using them is not a good idea. The properties of the solder have been changed along with its melting point. (In addition to all the dirt collection)

 

Now, this you will say doesn't apply to those using a TCU as the temperature is set at some very low point of 100-150'C - in part that is correct - however this evaporation/sublimation of Cadmium starts and is also influences by other salts/compounds present.

 

I do not find cutting of chips of solder a time consuming step or an inconvenience. Most chips stay exactly here they are put, especially when sitting in a pool of flux. I don't solder upside down so have no problem with them falling off, and they could be placed back easily enough if they did. My iron carries all the heat required to melt the solder and boil the flux without having to preheat the solder on the iron or risk dropping it on the journey.

 

This isn't an argument about the use of a TCU it is an argument about telling a newbie that using a TCU is the only way forward. Something that comes up time-and-time again and always seems to be followed up with "I cannot seem to solder whitemetal".

Edited by Kenton
Link to post
Share on other sites

I've never owned or used a TCU, and agree Kenton, that they are not essential for whitemetal, nor any kit building work.

 

There may be some theoretical 'problems' but the experiences I've shared, chasing balls of solder' for example, are all empirical, they work, I've never had any problems in thirty odd years of kit building.

 

Clean the work, right flux, right solder and an iron man enough for the job, that's about it.

 

As Richard says, find a way that suits and use it.

  • Agree 1
Link to post
Share on other sites

How about the antimony (present in most low melt solders) vaporises at approx. 300oC? Not nice stuff to breath in...

Well, I'm not a chemist and it's getting on for 50 years since I did A level chemistry and last thought about vapour pressures, so I could well be wrong. However, I'm wary of believing that significant levels of vapour are released at 330o below it's melting point. As to 'present in most low melt solders', the last time I looked into this I only found a few higher temperature lead-based solder alloys with, usually, less that 0.5% antimony. However, it is found in quantities up to around 5% to aid flow in some lead-free solders.

 

That said, I understand that some white metals used for casting may contain significant amounts of Antimony.

 

Low melt solder is an alloy of various metals and is often referred to as "Wood's Metal" Many varieties exist but most contain either Zinc, Cadmium, Thalium, even Mercury has been used along with the principle ingredients of Tin and Lead. These compounds are added to reduce the melting point of the Tin/Lead alloy. They are all toxic but (ignoring Mercury as it is little used these days) Cadmium has the particular property of subliming at its own low temperature. Cadmium melts and evaporates at 310'C. In fact much of the cadmium that evaporates from the alloy in the presence of heat (up to 25% typical) is designed to do so and in doing so it "cures" the solder. So chasing balls of pre-melted solder around and re-using them is not a good idea. The properties of the solder have been changed along with its melting point. (In addition to all the dirt collection)...

Yes, Carr's 70o solder does appear to be Wood's Metal, though I think you should check the ingredients. Wood's Metal is normally 50% Bismuth, 25% lead and 12.5% each of Tin and Cadmium. As to sublimation of Cadmium, I was aware of oxidation issues in the liquid state, but was under the impression (perhaps wrongly) that sublimation was really only significant at low pressures. Wood's metal is also a eutectic alloy which, IIRC, means that it remains an alloy, not a mixture of separate metals in the liquid phase.

 

Personally, I prefer to use C&L's 100o solder which is a Bismuth, Lead, Tin alloy with no Cadmium.

 

...This isn't an argument about the use of a TCU it is an argument about telling a newbie that using a TCU is the only way forward. Something that comes up time-and-time again and always seems to be followed up with "I cannot seem to solder whitemetal".

Like you and many others, I'm quite happy to use a normal iron on whitemetal, but I have been soldering for well over fifty years. I am, however, nervous about recommending this to a beginner, particularly if they don't have someone to show them how to do it. I still have some well-melted parts of a K's kit that was my first attempt at around 12 years old, though at that time I hadn't discovered low-melt solders :scratchhead:

 

Nick

Link to post
Share on other sites

  • RMweb Premium

So, how exactly does the notion that soldering a metal with a melting point of 200 degrees with a soldering iron in excess of 400 degrees can have possible problems indicate a lack of understanding of the difference between heat and temperature?

 

A spark from a firework sparkler has lots of temperature but little heat. A beach that has had the sun shining on it has lots of heat but little temperature.  A 65 watt iron set at 190 degrees has more heat and not as much temperature as a 15 watt iron at 450 degrees.

 

Am I doing OK?

 

When the tip of the iron is at a temperature that can melt the metal if you allow it to heat it up too much then there is a possibility of it melting if you do not have the skill and experience to know just how long you can leave the iron on the job. You are also limited in what you can solder and where. With a low temp iron you can tin the parts and sweat them together just as if they were brass. You can solder detail parts on the outside of a kit by applying the iron to the inside, making for far neater soldering.

 

That technique is highly dodgy with a high temp iron, if not impossible.

 

With a temperature controlled iron, you can leave the iron on the whitemetal all day and it won't melt. You can move parts around and you can be as hamfisted as you like and not melt any part of the kit.

 

I have built many kits using both techniques and there is no way I would ever go back to using a normal iron now but each to their own.

 

Breaking it down to basics, with a high temperature iron it is possible to put too much heat onto the job and melt the whitemetal. With a low temperature iron it is impossible.

 

Therefore there is more chance of getting it wrong with a high temperature iron, especially for an inexperienced modeller.

 

Tony

  • Agree 1
Link to post
Share on other sites

  • 6 years later...

I use Carrs green label flux for everything, it’s savage stuff but it works and the solder always follows the flux. I also discovered the brass wool tip cleaner recently and it woks better than any other method. 

  • Agree 1
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...