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Soldering is it a good idea


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Many years ago, a mere youngster, I asked my dad for help. Dad I need to solder these braces to the main under carriage of this model. I cried. Dad said is that really a good idea? The main part will never be the same he opinioned.

In that era possibly 60% of the male working population had some useful knowledge of metal working, their was a strong manufacturing base to the UK economy.

Years later when studying for my degree (no one else’s), I was let into the dark practical arts of the tradesman (who knew the answers, but not the why) at a theoretical level.

The first was that processing history was responsible for a significant part of the properties of a material/component. An example, why a bright flat bar will bend if machined on one surface only, processing history of course.

This brings me back to soldering undercarriage legs. The properties of the piano wire we use is very dependant on this processing history, introducing highly directional characteristics, that are useful to us modellers.

The point is, by heating up the wire we modify these properties. How you all cry (none engineers anyway), by modifying the structure of the parent material. That answers nothing you all cry again.

I answer. During processing the material is work hardened very directionally, producing a fine elongated grain structure. I now exclaim that by heating to solder, braze, or even weld, this structure becomes modified. The more heat put in, the greater the modification. Enough heat and the carbon steel becomes annealed. That is the softest, ductile etc condition at room temperature. What has happened, is that the grains have been provided with enough energy to adopt the most low energetically favoured shape (tending to spherical) that any individual grain can achieve, some of the grains will have formed a larger size. As the grains get larger the areas of disruption in the grain boundaries become greater. It is these areas which introduce weakness. Also our directional properties are disappearing.

It is for these reasons that the heat effected zone will often be the site of unanticipated bending etc. It is often to avoid bending that the soldering was done in the first place.

So it is often better to have a mechanical joint (in my opinion) of some type than to go pumping heat into a metal.

It is now time for you Metallurgists (or Engineers) to contribute, please.

Regards

Erfolg
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I am pretty sure that soldering as we know it has no effect on piano wire etc. Funnily enough I'm just in the process of fitting wheels to the undercart of my Piper cub having done a "tug" test which failed with the press- on clip type hubs supplied.Shall solder on washers as I usually do .How do I get a potato behind it to prevent melting the wheels & causing noxious fumes & causing global warming etc.etc.etc.
Grumpy Myron
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erm, I ain't no metal-lurgy-ist, but I would have thought that to alter the grain structure of metal significantly you would have to heat it considerably above the temperature needed for (normal soft) soldering.

Most of the (sensible) soft-soldered joints I've seen are usually bound with wire anyway, such that the joint is partly mechanical, partly soft soldered - a bit like glass fibre and resin, where neither resin nor glass fibre on it's own confers enough strength/flexibility, but the combination is top dollar.

Brazing is probably a different ball game, but I haven't got round to reading the online guide yet.

AlistairT
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Myron,
Seriously, I usually use a scrap piece of thin ali sheet (litho plate or foil meat tray) to act as the spacer and heat protector. What you really need is a high wattage soldering iron (I use an ancient Solon 125 watt) to get lots of heat to the joint quickly. This heat the piano wire quickly, where you need it, and makes the joint without having the iron in proximity to the wheel for any longer than neccessary.
This I think also amswers (in part) the original question. A very hot iron that heats the wire locally, and briefly, will make a good soldered joint without affecting the metalurgy all that much. Blowtorches are a different matter maybe.

David
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Erfolg,
If you are using true cold drawn piano wire you will not have any effect on the properties as long as you do not heat it above 300 degC but go above that and the strength properties drop (by about 50% by the time you get to 600 degC).
So soft soldering at less than 250 degC is ok but silver soldering, which needs in excess of 600 degC, is not.
Steve.
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I know that Myron was giving me a little tweak.

I was really considering attachments that are subject to forces or stress, (if you prefer).

Will soldering effect the grain structure? Absolutely. How much, depends on how much energy you put in. On undercarriages, could well be the cause of all those un-expected bends after landing.

What I would like people to do is consider what has happened, (in all events) and think why. I am sure that all the metallurgists out there, are often in despair at the lack of interest in a fascinating subject. Ask yourself this question what is a soldered joint? Are the two materials made as one? What is the nature of the joint? What is the difference between a soldered, Silver soldered and brazed joint?

I am not a Metallurgist but, if you really do not care or wonder what is happening at a theoretical and practical level I really think you are missing out, and will not be able to get the most out of your creativity. Metallurgy really is fun and is practically important to us modellers.

After that impassioned plea, I will go back to the bottle.

Non Metalurgist

Erfolg
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Thanks all!
Have fixed my wheel problem .Tinned the axle ends & two nuts screwed on with flux .Put one turn of wet string between the wheel & the nut & with 50 watt soldering iron sweated it together .Lovely job & done vertically have a smooth shiny hub blob.Can't pull the wheels off .
Sorry but I've been on the proper thread too long !!!
Grumpy Myron
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Steve

This is the sort of discussion required.

I would suggest that that +220C is the melting point of the Lead free soft solder and soft soldering is taken to be a process up to 450C. There after called Silver Soldering etc.

My point is, it is easy to exceed the temperatures where the structure of the material is changed. You suggest 300C, that is a margin of about 80C

The values you quote are not that dissimilar to those I recognise. What is important is that it is easy, using a blow torch, to get into the temperature range where you are changing the structure, in a way which you prefer not to.

I am trying to reach a group of modellers who are not aware of metallurgy, but modellers such as yourself could help by broadening there knowledge base. I use these forums to gain an understanding of science where my knowledge is less than I would like.

During my electrical and instrument and control lectures I used to think, what do I need to know to pass the next exam. I know regret, dismissing whole tracts of information as "that wont come up in the exam”. I now think, what happens if you increase the diameter/length/windings/number of magnets/number of teeth/number of poles/ in a brushless or other motor, I do not know the answer. If I had been more inquisitive I might.

I do despair, when I hear modellers (I am also probably guilty) hold forth, with total conviction, with half truths and down right superstitions, dressed up as fact.

Two way discussion can help understanding, help us establish the important issues and above all educate. I know that I am not always right, when I am, it is often under a specific set of criteria. In this post industrial Britain, there are far fewer people with both practical and scientific knowledge, I suspect that most aero modellers are both practical and theoretical people, who deep down want to understand.

When I stop asking why, what if, I hope I have died, not mearly brain dead.

Erfolg
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We used the softening effect of silver solder to advantage with falp joiners on stunters. The joiner would be a 'U' shape in 14 swg paino wire with a steel horn silver soldered in the middle. The heat used softened the wire at that point to the extent that you could bend the twos arms of the 'U' relative to one another to tweak the model's trim in roll.

Mike
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I would suggest that that +220C is the melting point of the Lead free soft solder and soft soldering is taken to be a process up to 450C. There after called Silver Soldering etc.

In railway modelling we often use a low melting point solder - 145 degrees which would give you a greater margin if needed.

Mike
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I think that I see a slight ommission here. Soft soldering is done at lower temperatures. It has been stated that even these can alter the properties of the piano wire that we are using. I believe that we should ask, Are they altered SIGNIFICANTLY?

Lets be quite honest about it. If we do a heavy landing we will bend an undercarriage. Now how much will soldering affect the wire. Would it fail to bend at 1 mile an hour more if it were not soldered, 2 mph? Would an extra 8 ounces weight on the model be supported in that landing if it were not soldered?

When someone comes up with a definitive answer as to exactly how much difference it makes (and assuming that all piano wires are the same which they are not) I shall continue to solder. And if they do come up with the answer...I shall still continue to solder ebcause it works so well and is so simple.

Now Myron is a man after my own heart. I never use anything but solder to hold my wheels on. Stupid clips, crumby collects, they all fall off be=ut properly soldered on wheels never do.
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Both Mikes

It is obvious that you both know and understand the opportunities and limitations of Soldering/brazing systems. You use your knowledge to your advantage.

You do read from time to time of modellers, particularly scale models in competition, where the undercarriage has failed by bending near a joint, attachment point. In these cases I suspect a number of them have inadvertently weaken the parent material.

As is known the soldering/brazing is a wetting process, where the oxide film ahs been removed from the surfaces to be joined. The flux prevents the reformation of oxides during joining. Thereafter the object is to use the solder to wet the surface (bring into intimate contact), so that there is no gap or film between solder and substrate. Where the sections are heavy i.e., two bars and binding, particularly where the oxides have not been removed totally and suface protected, there is a tendency to pump in the heat.

Many young modellers do not have a scientific or engineering background. They know lots of other things of which I am ignorant. Helping this group to know more about the materials and structures they use in this wonderful (or men playing with toys as the wife calls it) hobby, will I am sure enrich there lives and move some to successful building, rather than just ARTF models.

Regards

Erfolg
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Peter,
The reason I feel confident in saying that soft soldering will not degrade the properties of cold drawn piano wire is that some manufacturers have an additional heat treatment cycle AFTER the cold drawing; this is at around 300 to 350 degC. The evidence is that this produces a slight increase in tensile strength. The strength increase is not much (less than 5%) but in some instances you want might everything you can get.
40/60 or 50/50 lead/tin solders (by far the most common types, and the cheapest) are liquid above 230 degC and solid below 180 degC. If you want to prevent overheating the piano wire then use the solder as the temperature indicator and remove the heat as soon as the solder melts and 'wicks' into the joint.
Steve
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I think this is possibly a time to assemble what we generally can say we know.

Wave bath solder as used today in lead free soldering has a melting point of between
220-227C dependant on Silver content, less silver, higher the temperature, (extract ANSI/J-STD-006,).

Traditional Lead tin alloys have a Eutectic temperature of 183C, this is a minimum (Phase Diagram, Engineers Hand book, rev 13) .

Solders used for electrical work traditionally have more tin and a little silver to reduce both leeching from electrical components, reduce the melting point and give better wetting characteristics to about 180C. This is the 62% tin,36 lead and 2% silver (EABS, on line library).

Although many cored solders were actually, 60%, tin 40% lead with a melting point of 191C.

Tempering is normally defined as a process which starts at 230C to 500C. The beginning of the range considered to be light straw 230C. The effects are, time temperature and mass dependant ( as well as Prior Heat treatment etc.) ( "Foundations of Materials Science and Engineering", 4th ed., McGraw-Hill & Ward French).

Adiabatic (fancy word for complete combustion) temperature of gas air torch is quoted as 1995C, the true max is possibly 1500C (GAZ).

Soldering irons particularly the temperature controlled usually start at about 250C the max is 400C. Lead-based solder uses 250°C to 280°C or 300°C while lead-free soldering needs a higher temperature, about 350°C to 400°C. (catalogue Antex)

As can be seen it is entirely possible to affect the structure of the steel by use of a propane torch, or a high Wattage iron (30-100w) as the difference between the melting point of solder and beginning to heat treat can be as low as 230-227 = 3C or 230-183 = 47C (temp of a typical CH radiator). In the real world, we are potentially in the same ball park.

The important issue for me if deciding if I want to solder is:

a)Does it matter, if the properties of the wire change?.
Where stress or forces could be high, possibly yes. Washers holding on wheels probably not.
b)Do I have to solder or is there a viable alternative?
In my youth I have seen crimped joints that seemed to work. Maybe an increase wire size to avoid re-enforcing braces etc. Maybe increase the wire size to compensate for any reductions in strength.
c)If I have to solder, can I control the temperatures:
1)Use a low melting point solder
2)Minimise heat input, using a big tipped, high wattage soldering iron (to minimise soaking effects).
3)Avoid the use of a propane torch ( to difficult to control heat at the joint).

I have purposely avoided talking about austenite phase, pearlite, or the detailed composition of Piano wire, silver steel etc. As I do not think it would add anything.

I am now quite bored with it all, so I am going back to building.

Whats that I hear? a cry of good.

Regards

Erfolg
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Erfolg writes :-
"I have purposely avoided talking about austenite phase, pearlite, or the detailed composition of Piano wire, silver steel etc. As I do not think it would add anything."
.
Unfortunately you are confusing the processing of 'carbon tool steel' and 'piano wire' and the explanation why they behave differently depends on what you avoided referring to.
.
Both start by taking the steel above its transition temperature (approx 750 to 800 degC, depends on the steel).
.
With a carbon tool steel the rapid quench from above the transition temperature produces martensite. Try cold drawing that and two things will happen (a) it will crack because it has no ductility and (b) it will wreck the die because it is rock hard. The subsequent tempering (between 210 and 300 degC depending on what you want to use the tool for) gives the steel toughness and reduces its brittleness.
.
With piano wire the cooling from above the transition temperature is carefully controlled and held at a temperature to produce a very fine grained pearlite, this is very tough and has sufficient ductility to enable it to be cold drawn. The cold drawing work hardens the steel, the trick is knowing how much work hardening you can do and still leave sufficient ductility in the final product (otherwise it will snap when you bend it, hands up all those who have bought piano wire like that!).
.
I hope you can see that by starting with steels which may appear to be chemically similar, but giving them very different processing, you can end up with two products that will behave differently when you come to apply the levels of heat associated with soft soldering. The quenched tool steel will behave differently to the work hardened piano wire because its structure is completly different. So quoting what happens to a quenched tool steel if you were to temper it at the temperatures associated with soft soldering is irrelevant for piano wire. Test evidence shows that subseqently heating piano wire to 300 to 350 degC does not affect its strength; some manufacturers used to do this, it produces a nice blued finish, but few do now.
.
Production of good quality piano wire requires a lot of material processing know-how to end up with a suitable product which has the required strength and ductility and is the reason, I suspect, why there is so much foreign rubbish currently for sale to aeromodellers.
This is the last post I'm making on the topic.
Steve

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We both agree that the material has a pearlitic structure. The full text provides details of the effects of temperatiure on the lamella and cementite. But the following is the most pertinent to experience of high tensile hyperutectoid wire as used in armouring, where annealing due to jointing had effected the cable performance

The mechanical properties of the steel wires increased with increase of annealing temperature, and the increase was more significant with higher drawing strain. Also, as annealing temperature increased, the hardness and tensile strength gradually increased up to 200C and then dramatically decreased at above temperature. However, bending fatigue limit, including fatigue life, showed the some different phenomena with increase of annealing temperature. These different behaviors depending on annealing temperature were discussed in terms of microstructural parameter changes such as pearlite morphology, rearrangement and coalescence of the dislocations.

The annealing temperatures were from 200-450C

We both seem to have had different experience with similar products. Mine hyperutectoid cold drawn with silicon. Yours I guess is based on Piano wire and silver steel.

Regards

Erfolg
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