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Soldering Techniques

Please note - this article was previously published in the form of a 'Data Sheet' on the old web site. It was written some time ago by Mr Brian Lewis, whilst he was the owner of C&L. A new table replacing the list at the end of the article has been prepared and will be added shortly.

BASIC SOLDERING TECHNIQUES

You will need to practice. Nobody would buy a piano and expect to master the fundamentals
immediately. So is it with soldering. The concept is simple.
 
1. Take two pieces of metal. Position them exactly as you want them to be soldered. Ensure
you will still be able to do this, when both pieces are heated. There are various ways of doing
this. Hot Tape will bind work together. You may be able to hold them in a vice. In theory you
can use a steel base plate and place a magnet on top of the work. In practice however, the
steel acts as a heat sink, so making soldering difficult.

2. If soldering delicate electrical components, use a heat sink. Aluminium forceps, sold by
hobby shops, are ideal for this purpose. A piece of water soaked tissue will do if nothing else
is around.

3. Wet the work with your chosen flux.

4. Touch the area you want soldered with the tip of the iron. Ensure as far as is possible that
you heat both pieces of metal evenly, i.e.. so both are at approximately the same temperature.

5. When the flux starts ‘smoking’, touch the join between the two metals with a strip of solder.
Be sure to touch the metals - not the iron. The solder should flow through the joint.

6. How much solder? Just the minimum that will make a clean joint. Too little and the joint may
not form properly. Too much and you will have to spend time scraping the excess away.
Think of using ordinary glues. You know instinctively just how much to use. Practice and it
will soon be the same with solder.

7. Remove the iron and allow the work to cool - making sure that there is no movement between
the pieces of the work. This is important, for the slightest movement will seriously affect the
strength of the joint.

8. Replace the iron into its stand.

9. A quick, but not always fail-safe way to test for this is to inspect the joint visually. A good joint
will be bright with solder. If it is an electrical connection, testing with an ohmmeter will give a
guide to the effectiveness of the joint.

10. Carry out Post Soldering Treatment.
 
If there has been movement, the solder will often appear greyish in colour and exhibit stress ripples.
If the joint has moved or is otherwise unsound, it is tempting just to pop the soldering iron bit back
on the joint. Re-melt the solder; remove the bit and what usually happens? As you pull the iron away,
the solder tends to pull away with it. You have just had a good demonstration of ‘spiking’. Now add
some flux and try again. This time the solder should stay on the joint. And this is an important
lesson: Applying flux is not necessarily a once only act. Solder plus heat plus flux is the recipe for a
sound joint. Without the flux, solder will not flow.

Practice soldering a couple of pieces of electrical wire. Then move on to some scrap brass. With
these, practice soldering two pieces together at right angles. Use varying solders for this and see
how different solders produce different fillets at the junction of the two pieces. Now solder two
pieces of brass edge to edge, and then solder a small scrap near the soldered joint. Does the first
joint start to bubble and become un soldered? Probably, but later in this booklet we will show you
how to overcome this.

Try different combinations of flux and solder. A couple of hours spent doing this will not only give
you good practice, but will build up your knowledge base. Think about humming or whistling. You
may not be able to read music and probably have no real idea of how we produce the different notes.
But we do it and we do it instinctively. This is what you want to achieve with soldering. You look at
a piece of work to be soldered and without really thinking about it, you select a suitable iron, bit,
solder and flux. This is when soldering becomes ordinary and talk of it being a ‘black art’ is forgotten.

Tinning
Not your soldering iron tip, but the work. The theory goes like this. You tin each piece of the work,
fit them together, brush with flux - whereupon it creeps into the joint by capillary action, apply heat
and hey presto! You have a perfect joint.

In fact, the practice is not far removed from this. In industry, tinning is carried out by dipping the work
in Solder Paint. It is then brought together, fluxed and heated. For larger items this still holds good,
although the Solder paint can be applied with a brush. For smaller items, especially where you are
making up sandwiches of thin materials - Brass or Nickel Silver etches, etc. the easiest and cleanest
way, is to wipe the surfaces with the thinnest smear of Solder Cream. This material is slightly
adhesive and will hold small items ready for soldering - a typical example being spectacle rings on
brass locos. Hold in position, apply heat and you should have perfect joints that require little or no
cleaning up.

Post-Soldering Treatment
Have we finished? Well, not quite. The fluxes that were so essential to your perfect joint, leave
residues that must be removed. If you are using a ‘No Clean Solder’, such as Carr’s Solder Creams
or a resin cored flux and you are soldering electrical components and wires, then no further
treatment may be necessary. However, in all other circumstances it will be most unwise to leave
matters there. We have seen the importance of cleaning, in the section dealing with Metal Blackening.
Also, should you be painting over a soldered joint at a later stage, it is essential that all acidic
residues be removed, else your carefully applied layers of paint will begin to bubble and peel.
Fortunately the task is not arduous and the most effective way of removing them is also probably
the easiest. Simply brush or immerse in Neutralizing Rinse and then wash off with several changes
of water. If this is a brass kit, then painting over with Surface Conditioner, followed by rinsing with
water and allowing to dry, will not only clean it, but will etch the surface very slightly, which will give
you more of a key for paint.

De-Soldering
What can be soldered can be de-soldered. You need to equip yourself with some Solder Mop,
sometimes also called Solder Wick. This is a braided copper strip, not unlike the car battery
earth leads that were popular some years ago. The technique is simple. The end of the wick
is placed over the area to be de-soldered and the bit placed on top. Be aware that de-soldering
requires more heat than soldering, so you may need to dwell with the iron for longer. Or you
can increase the temperature setting if you have an adjustable iron. Copper has a high degree
of conductivity, so do not hold the braid with your bare fingers, too near to the iron - a distance
of at least six inches is probably about right. After use, cut off the used end of the braid.3
Now solder wicks themselves are subject to the same oxidation that affects brass and nickel
silver so, if your braid seems to be ineffective, you can dip it into the same flux you were using
to solder the metal in the first place. Some folk do this anyway, as they feel it helps the
de-soldering process, but it is not absolutely necessary and may involve more cleaning
afterwards.

SUGGESTED PRACTICES FOR SOLDERING SPECIFIC METALS.
We can almost hear you saying, “Well, the above is all very well, but I’ve got this metal, which I want
to solder to that metal. Which flux and which solder should I use”? The serious answer is, ‘it all
depends’. Not very helpful, but there is a world of difference in say, soldering a brass gear wheel to
a steel axle and a brass steam pipe to a steel boiler. For, as we are told in other fields, size is
important. The following is intended as a general guide.

Please note:
1. Although many modellers mainly use solder creams for nickel silver and brass, the table
below lists wire and strip solders as being preferred. This is because solder creams are more
expensive and you may prefer to become used to soldering using a cheaper alternative.
2. Many of our other solders will work perfectly in the circumstances listed below. However, to
list too many will clearly cause confusion.
3. If your own personal favourites are not listed, but they work for you, then by all means carry
on using them.

Material(s)/Process: Nickel Silver to Nickel Silver.
Best Flux: Yellow Label.
Other recommended fluxes: Green Label. Red Label. Black Label.
Best Solder: 145 deg.
Other recommended solders: 138/179 Solder Creams.
Material(s)/Process: Nickel Silver to Brass.
Best Flux: Yellow Label.
Other recommended fluxes: Green Label. Red Label. Black Label.
Best Solder: 145 deg..
Other recommended solders: 138/179 Solder Creams.
Material(s)/Process: Brass to Brass.
Best Flux: Yellow Label.
Other recommended fluxes: Green Label. Red Label. Black Label.
Best Solder: 145 deg
Other recommended solders: 138/179 Solder Creams.
Material(s)/Process: Whitemetal to Whitemetal
Best Flux: Yellow Label.
Other recommended fluxes: Red Label.
Best Solder: 70 Deg.
Other recommended solders: 138 Solder Cream.
Material(s)/Process: Whitemetal to Brass
Best Flux: Yellow Label
Other recommended fluxes: Red Label.
Best Solder: 7 0 Deg.
Other recommended solders: 138 Solder Cream.4
Material(s)/Process: Whitemetal to Nickel Silver
Best Flux: Yellow Label.
Other recommended fluxes: Red Label.
Best Solder: 70 Deg.
Other recommended solders: 138 Solder Cream.
Material(s)/Process: Steel to Steel.
Best Flux: Green Label.
Other recommended fluxes: Black Label.
Best Solder: 188 deg Solder.
Other recommended solders: 224 deg. 188 Solder paint.
Material(s)/Process: Fine Detailing - non ferrous
Best Flux: Yellow Label.
Other recommended fluxes: Red Label. Green Label.
Best Solder: 138 Solder Cream.
Other recommended solders: 145 deg.
Material(s)/Process: Fine Detailing - steel
Best Flux: Green Label
Other recommended fluxes: Black Label.
Best Solder: 145 Strip Solder.
Other recommended solders: 179 Solder Cream.
Material(s)/Process: Tinning
Best Flux: Green Label
Other recommended fluxes: Black Label.
Best Solder: 188 Solder Paste.
Other recommended solders: 188 Strip Solder.
Material(s)/Process: Aluminium & Mazak
Best Flux: Grey Label.
Other recommended fluxes:- None.
Best Solder: 179 Strip Solder.
Other recommended solders:- None.
Material(s)/Process: Gap Filling
Best Flux: Yellow Label.
Other recommended fluxes: Green label. Black Label
Best Solder: 224 Deg.
Other recommended solders:- None
Material(s) to be soldered: High Temperature Work.
Best Flux: Green Label.
Other recommended fluxes: Black Label.
Best Solder: 243 Strip Solder.
Other recommended solders: 224 Strip Solder.
Material(s) to be soldered: Electrical Soldering.
Best Flux: Orange Label..
Other recommended fluxes: Yellow Label.
Best Solder: 179 Solder Cream.
Other recommended solders: 179 Solder in Step Solder Kit.
Material(s) to be soldered: Lead Free Soldering
Best Flux: Yellow Label..
Other recommended fluxes: Green Label. Red Label.
Best Solder: 227 Solder in Step Solder Kit.
Other recommended solders:- None.

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