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Member postings for CuP Alloys 1

Here is a list of all the postings CuP Alloys 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: Rothenberger Rolot brazing rods
12/02/2014 23:53:54

Under no circumstances should an alloy containing phosphorus eg Rolot S2, S5, Silbralloy, Silfos be used to braze copper that may come in contact with hot sulphur bearing atmospheres. The sulphur will go through the joint like a hot knife through butter!

Equally these alloys should not be used to braze copper to steel or any non-ferrous alloy containing nickel.

The phosphorus forms a very brittle intermetallic compound with iron and nickel. For more information on this point investigate the disaster associated with the submarine USS Thresher.


PS in gas fired boilers - no problem. All copper/copper joints in your central heating boiler are made with these alloys.

Edited By CuP Alloys 1 on 12/02/2014 23:59:23

Thread: Silver Solderin
29/12/2013 10:47:09

Hi John

go to

Any further help? Call us or talk to us at Alexander Palace in January



Thread: copper pipe for model engines
24/12/2013 09:11:48

Hi Rodney,

Do not use any plumbing grade of copper. It may contain lead so affecting flow characteristics of your silver solder.

Do not use any copper that may contain dissolved oxygen that could cause cracking of the copper during the silver soldering operation (hydrogen embrittlement)

Use C103 or C106 grade copper with total confidence.

For more info go to **LINK**




and a Merry Christmas and Happy New Year to all

Thread: Silver soldering problems
17/11/2013 07:08:33
Posted by CuP Alloys 1 on 16/11/2013 17:59:30:

Hiya Mark

Try this **LINK**

Successful silver soldering explained. It covers joint design, fluxing, heating techniques and alloy application. It includes a video clip.

This will more than point you in the right direction.



Edited By CuP Alloys 1 on 16/11/2013 18:02:02

16/11/2013 17:59:30

Hiya Mark

Try this **LINK**

This will more than point you in the right direction.



Edited By CuP Alloys 1 on 16/11/2013 18:02:02

Thread: acid
04/11/2013 19:26:36


See Royal Mail website - Corrosive Substances

caustic soda, acids, dyes, metal cleaning products and other corrosive materials CANNOT legally be sent by post.

Acids include liquid soft solder fluxes.

Dry flux powders and salts are OK.

Other suppliers via ebay may think otherwise.


Thread: Minnie Traction Engine Boiler Silver Solvering
21/10/2013 16:02:05

Hi Mark,

That looks like a 7.7KW burner 2941, which is way too big. Seek advice re more appropriate burners.


Thread: silver soldering problem
24/09/2013 18:47:15

Hi Bob,

Log burner hearth bricks - fine!

The flux paste we use for brazing demos at exhibitions was made up 8-9 years ago! We just add a few drops of water on day one. It is getting a little low now so we will be making up a small batch soon to take us up to 2025.

Hi Gordon,

Spot on.

Meths = less bubbling and no need to add washing up liquid.



24/09/2013 07:49:55

Why add a few drops of washing up liquid to powder flux prior to mixing with water?

a) it aids mixing to a smooth paste

b) it makes the flux stick to the work

c) when the paste dries out (and it will) it can be remixed with a few drops of water - the alternative to throwing it away

Problem that can arise with "hot-rodding" include

a) insufficient flux leading to poor coverage -

b) it promotes a welding technique for heating - poor penetration of alloy

c) the flux is not active enough quickly enough for efficient oxide removal. Factory made flux coated rods have a modified flux to cope.

For more information see "Best Brazing Practice" on website









Edited By CuP Alloys 1 on 24/09/2013 07:52:18

22/09/2013 19:10:04

Hi Baldric,

The alloy should have melted looking at the pictures - but may not have flowed.

Two totally different problems!

One part looks very hot , one is not.

You may need to use a different flux or modify your heating technique.

Ring us on 01909 547248 and talk it through. Help is at hand. You have not been abandoned!



Thread: making a 3.5 inch boiler
20/09/2013 07:45:34

Hello Steve,

Good stuff from John.

The burners with the holes nearer the handle are called cyclone burners.

The key is keeping the heat in. Compliment the effect of the lightweight bricks with a ceramic blanket.

Use a long life flux like HT5.



19/09/2013 13:34:43

Hi Michael,

The mapp gas is a cylinder - not a canister.

Check your inbox again.



PS There is a clue in the pen name!

19/09/2013 11:56:59

Hi Terry,

Declared interest - I have recently retired from the company but a link still exists. I only provide technical information. See your private messages.


19/09/2013 07:38:58

Hi Terry

Have you considered oxy-mapp gas?

The kit has bottles that you own and exchange when empty.

No rental charges, no admin charges



Thread: Silver Soldering Tungsten Tig Electrodes to Mild Steel
11/09/2013 14:54:34

Hi Jason,

Proceed as you thought with your silver solder and flux.

Keep joint gaps small say 2-3 thou.

Use propane to heat so you get good all-round heating of the joint.

Allow to cool slowly.



PS Same approach when brazing/silver soldering of small pieces of carbide

Thread: Another silver solder question
09/08/2013 15:04:57

Hi Bill,

Use "hot rodding" as a means of adding extra flux to a joint already fluxed.

Home made flux coated rods are not recommended for the model engineer because

  • the amount of flux is limited,
  • the flux is not as active as a "factory made fluxed rod, and
  • it invariably pushes the engineer to using a heating technique more akin to welding.
  • Result lack of penetration onto the joint.

Heat the joint and let the silver solder get its heat from the joint - not the torch.

Use the thinnest rod practicable

More advice on


PS Thanks Matt for your comments

Thread: Silver soldering
09/08/2013 09:41:29

Hi Marinus,

Cadmium free alloys eg Ag40Sn are generally better for gap filling properties because of the wider melting range 650 - 710 degrees and require more heat. It won't cope with 0.8mm though! Max 0.2mm.

A cheaper option is to use 38% silver alloy Ag38Sn

The down side is they are not as free flowing and have higher melting temperatures. Ag40Cd is 595 - 630 degrees.

For good all round advice re silver soldering go to

Go to "Best Brazing Practice" under Introduction to Brazing. There are also tips which include how to make your rings to size first time! Download it for a handy reference file.

Re your firebricks. Do not use conventional bricks or those taken from storage heaters. They ABSORB heat making brazing more difficult. Use lightweight refractory bricks

Incidentally, in this instance, it is cheaper to buy the silver solder ex stock in the UK and pay postage!



Thread: cleaning steel bright after silver soldering.
06/08/2013 11:41:49

Hi Brian,

Most chemical cleaners seem to have this effect.

It's down to elbow grease and a file I'm afraid.

Is sand blasting a viable solution for you?



Thread: Silver solder ?
09/07/2013 08:08:24

The decision to use brazing as the metal joining process in preference to soldering or welding is based on technical reasons eg parent material combination, temperatures, strength, corrosion resistance.

Brazing defines the process not the alloy used.

There are several sorts of brazing alloy.

Nickel brazing alloys - marine, nuclear applications

gold and palladium brazing alloys - jet engines

copper brazing alloys (eg brass and silfos)

silver brazing alloys

If the basic principles of the process - correct joint design, heating technique and fluxing - are not followed no brazing alloy will not work satisfactorily.

Peter a word of caution re silfos.

It contains phosphorus which will produce very brittle joints on steel and nickel bearing materials. Such a material is thought to be the reason a submarine did not return from its' test dive

Phosphorus does not like hot sulphur containing atmospheres eg boilers. your technical reason for using a silver brazing alloy (silver solder!)

09/07/2013 07:49:34

Why silver solder? Please bear with me !

There are several types of brazing alloy.

nickel brazing alloys - marine

gold brazing alloys - jet engines

palladium brazing alloys - jet engines

copper brazing alloys (includes brass and copper-phosphorus alloys eg silfos)

silver brazing alloys (silver solders)

Brazing defines the metal joining process not the alloy

Copper alloys are the cheapest and very versatile. So there has to be a very good reason to move away from them . That is invariably due to a technical reason. These include melting temperature, parent material combination, corrosion resistance, even colour or a combination.

The success of the process depends on correct joint design, heating technique and fluxing. If these criteria are not met no brazing alloy will work.

Peter, a word of caution. Silfos contains phosphorus. It appears to work well but combines with iron (in all steels) and nickel to create a very brittle intermetallic compound that can lead to catastrophic joint failure when stressed.

Copper phosphorus brazing alloys used to join copper nickel pipes on a submarine is thought to be the reason a submarine did not return from its' test dive.


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