New to model engineering – what solder / flux and annealing question

[Chris machinParticipant @chrismachin]

Hi All , I’m new to model engineering (although i am a maintenence engineer) so have experience of lathes , millers e.t.c. At the moment i’m in the market for a small lathe but meanwhile i’ve purchased the book ‘building simple model steam engines’ by Tubal Cain and am going to have a go at the ‘Polly’ model.

 

This involves making a small cylindrical boiler out of a sheet of either brass or copper and silver soldering the joint.I’m going to use brass sheet. My questions are :

 

1. Do i need to anneal the sheet or do i work it cold ?

2. What solder / flux combination do i need and where’ s the best place to get it online.

3. How do i clean up the joint after its been soldered – i have access to an ultrasonic bath – would this be suitable ?

 

Any help appreciated.

Thanks

Chris.

 

[Chris machinParticipant @chrismachin]

[JasonBModerator @jasonb]

Depending on the grade of brass its liekly to need annealing a few times during the flanging process

 

Silverflow55 or 455 solder and Easyflo or EF flux

 

 

Dip in dilute acid, citric is safest, I use dry crystals and mix with water

 

Personally I’d make the boiler from copper but I think the Polly can be done in either.

 

Also look at this recent post, some of the jewelry related stuff is not quite the same as model engineering practice but same sort of principal

 

J

 

Edited By JasonB on 16/01/2012 19:28:58

[CHARLES lipscombeParticipant @charleslipscombe16059]

What is the correct procedure for annealing brass? There is plenty of info on the webb but just about every piece of advice seems to be contradicted by the next article.

I am making some petrol filler necks for vintage motorcycles from CZ 26130 brass which is an arsenic containing cartridge brass.It is listed as good for cold working but only fair for hot working. I need to bend a small tab at right angles to the main axis and as-supplied tubing when bent cold, cracks on the outside of the bend. Wall thickness of the tube is 1.63 mms.

In particular, does the brass need cooling rapidly or slowly after heating?

Somehow I have a lot more confidence in the forum and its contributors than You-tube

[Thor 🇳🇴Participant @thor]

Hi Charles,

I anneal copper and brass by heating to dull red using a propane torch in a makeshift hearth. As for cooling, it depends. Cooling in water may cause the part to warp, so for more complicated shapes I let it cool slowly in air. Usually for simple parts I just dip the part in a bucket of water.

Thor

[Keith HaleParticipant @keithhale68713]

Hi Chris,

The concept of silver soldering is very simple.

But have no illusions, it is a skillful process. There is no shortcut to experience gained through practice.

Jason is partly right in his recommendations but what works for one person may not be suitable for another. Question why he has made this recommendation. I suspect that he has done so because it works for him and, more importantly, the way he uses it.

Like Jason, you will only be successful if you adopt and adhere to the underlying principle of the process – capillary flow. These forums are full of problems involving silver soldering. In every case the problem lay in one place – behind the torch!

Everything that you do to make your joints should promote capillary flow of the alloy. That statement holds for any alloy you use or from where you buy it.

Check on your joint design. Set the right length and gap

Check that your joint is clean and oxide free at 650 deg C. That is the role of the flux – not you! Your job is to pick the right one. EF flux is sold by a company CuP Alloys, with which I have strong connections, but it may not be the right one. They have others.

Check on your heating technique to ensure that there are no cold spots. It's a hot spot you require to get the alloy to flow where you want it – into the joint! Heat the joint not the rod. 50 years experience in this field has taught me that in the hands of an amateur an oxy-gas torch being used in isolation will create more problems (cracks, leaks) than it perceives to solve.

Ask yourself, what do I want from the alloy? Do I need to perform any other silver soldering operations subsequently? Do I have sufficient heat to make the joint? Propane is good for the vast majority of joints and more flexible and forgiving. 455 is sold by CuP Alloys, but it is not always the best alloy for every application. Others, perhaps more suitable and cheaper, ones are available.

Now make your alloy selection. One thing you can ignore with silver solder is joint strength. Braze properly and all silver soldered joints will have a greater strength than the parent materials.

Decide where you are going to apply the alloy. Do you want rod or wire? What size? These are all simple questions with simple answers as long as you apreciate what you want to achieve.

There are folks about who depend on giving sound technical advice, selling the right materials and ensuring you produce high quality joints in order to pay their mortgages and pension contributions.

But please beforehand, understand what you are doing and why. Then go and do it.

You will be successful

**LINK**

**LINK**

Keith

[GoCreateParticipant @gocreate]

Chris

I've a few video's on forming copper for my Lion boiler which may be of help. Some silver soldering videos to follow though there are quite a few silver soldering videos on silver soldering.

Here's one of my videos

It's challenging work but worth while in the end.

Nigel

[Norman BillinghamParticipant @normanbillingham91454]

I help to run the SMEE Polly course, where we teach the basics of model engineering by building the Polly engine. I'd guess we've seen approaching 150 of them built by students over the years we've run the course. Forming that boiler seam neatly in rolled sheet is pretty tricky and we've always avoided it for beginners by making the boiler from 1 3/4" copper tube. Stronger, and very much easier to get a neat and leak-tight boiler. We supply a piece of the tube to our students, but you can use 42 mm plumbers pipe which is a bit easier to find in short lengths – though you have to change quite a few other dimensions to avoid problems.

[CHARLES lipscombeParticipant @charleslipscombe16059]

Hi Thor,

Thanks for your reply which I found very helpful. It seems that the rate of cooling of brass after annealing does not affect the properties of the annealed brass very much.

I have transferred my original posting to a new thread so maybe I will get more replies. Hopefully they won't be contradictoryI still need to know the temperature to use and maybe this will come up in further replies

P.S. I'm most impressed by your forum name. A nice piece of imaginative thinking

Regards, Chas

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