Different Iron Tips for 145/179/188 and Low-Melt Solders?

[Brian T]

Hi all,
I've heard conflicting reports that it's best not to use the same Soldering Iron Tips on both Low-Melt (70 degree whitemetal) and "normal" solders (such as 145/179/188 degree). Is this correct, and if so then why?

Many thanks,

Brian

[David B]

For many years, I have used the same tips with all my solders from low melt to 188 with no problems at all. I do clean the tips so when changing from one solder to another, I am not contaminating one with another. I also use the same flux with all the solders whether soldering white metal, brass and nickel silver. I have not soldered steel or other metals.

[Brian T]

Many thanks David - that's good enough for me!!
Kind Regards,
Brian

[Will L]

Hi all,
I've heard conflicting reports that it's best not to use the same Soldering Iron Tips on both Low-Melt (70 degree whitemetal) and "normal" solders (such as 145/179/188 degree). Is this correct, and if so then why?

Anybody who believes this should consider that, In years gone by, soldering irons came with plain copper bits. Before you could use them, you needed to tin the bit. This you could not do with low melt solder, so you had little choice.

While it is true that melting different solders together on a joint is undesirable and can theoretically produce metal mixtures with undefined and even unexpected properties. Experience suggest that a clean tinned bit has insufficient quantities of the tinning solder to materially affect the properties of the solder actually being applied. So, as long as you keep the bit nice and clean and properly tinned you should not need to change the bit when you change solders.

In case you’re wondering, on those occasions when you are using solders of different melting points to produce complex assemblies, the objective is not to melt the higher melting point solders when applying the lower melting point ones, so they don’t mix.

There are reasons why you may want to change bits as you go along, but that would be because you want to match the size of the bit to the job to be done. This is primarily to do with amount of heat you need to apply to the job and was the way we used to manage before heat controlled soldering irons came along.

[David B]

So, as long as you keep the bit nice and clean and properly tinned you should not need to change the bit when you change solders.

I have not tinned my bits for years and managed very well. In our hobby, we sometimes solder small parts and other bits we want to move where very small amounts of solder are needed. I found that having a tinned bit meant I had far too much solder on my iron, even a pointed bit.

There is a tendency for many people to put on too much solder and then spend a lot of time cleaning it off. To my 'mean git' mind, this seems to me a waste of both time and solder. I have advocated elsewhere on this forum and many times when demonstrating, chopping up solder in to small pieces (and then chopping the small pieces into even smaller pieces) and picking up just that small piece of solder on a clean iron. This helps to avoid swamping a joint with surplus solder.

[Re6/6]

I have advocated elsewhere on this forum and many times when demonstrating, chopping up solder in to small pieces (and then chopping the small pieces into even smaller pieces) and picking up just that small piece of solder on a clean iron. This helps to avoid swamping a joint with surplus solder.

After David showed me the method of chopping up the solder into pinhead sizes, I've never had to scrape off any excess afterwards. Highly recommended!

A very delicate Judith Edge pan for SR Raworth loco soldered for me by David which I subsequently bent!

20230316_120511.jpg

[Will L]

So, as long as you keep the bit nice and clean and properly tinned you should not need to change the bit when you change solders.

I have not tinned my bits for years and managed very well. In our hobby, we sometimes solder small parts and other bits we want to move where very small amounts of solder are needed. I found that having a tinned bit meant I had far too much solder on my iron, even a pointed bit.
There is a tendency for many people to put on too much solder and then spend a lot of time cleaning it off. To my 'mean git' mind, this seems to me a waste of both time and solder. I have advocated elsewhere on this forum and many times when demonstrating, chopping up solder in to small pieces (and then chopping the small pieces into even smaller pieces) and picking up just that small piece of solder on a clean iron. This helps to avoid swamping a joint with surplus solder.

Entirly agree the small bits of solder idea and I'm also a take the solder to the job on the iron man.
I learned my soldering in the days before pre-tinned/iron coated bits, and cleaning and retinning l was a necessary part of the job. Particularly when the copper surface started to erode and you needed to file it flat. Not something that happens much with modern coated bits. As I would include wiping way any excess solder as part of the cleaning /tinning process and you probably keep your bits scrupulously clean (or they wouldn't pick up the solder or transfer enough heat to the job to work), I'm not convinced there is much practical difference in technique between us.

[Joe Newman]

In the early days of my attempts to build white metal kits I learnt of the need to tin brass with 145 deg C solder before using low melt (70 deg C) solder to attach white metal castings.

I also was advised - by someone at an exhibition somewhere - to use two irons for this purpose. Until the advent of 100 deg C low melt solder I followed these suggestions.

I always understood that the reason for using a separate iron for use with low melt solder (70 deg C) was because this solder contains cadmium which is extremely toxic.

I currently use Carr's 100 deg C low melt solder which is described as 'a cadmium free tin/lead/bismuth solder'.

My older sample of Carr's 70 deg C low melt solder carries the warning 'Contains cadmium. Dangerous fumes can be formed during use.'

Cadmium has a low melting point of 321 deg C and boiling point of 767 deg C. However, the liquid metal has a relatively high vapour pressure which means that there will be atoms of cadmium in the vapour above the metal below its boiling point.

What can happen with single iron use is that when used with 70 deg C low melt solder some of this solder remains on the tip. The iron is then heated to a higher temperature for use with 145 deg C solder and the iron could be at, say, 360 deg C, i.e. above the melting point of any cadmium on the iron's tip.

This could in turn lead to very small quantities of cadmium vapour above the iron. And this could be ingested by the modeller.

Like most heavy metals, cadmium is toxic and a cumulative poison. It is approximately 15 times more toxic than lead.

So I would suggest either use 100 deg C solder and one iron or 70 deg C solder and two irons. Working in a well ventilated room is sensible as is washing your hands when finished.

I have found the 100 deg C solder to be excellent for soldering white metal to brass.

As ever, I hope this helps.

Joe