By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

Silver solder or copper rod?

All Topics | Latest Posts

Search for:  in Thread Title in  
DAVID POWELL 411/11/2011 08:29:13
26 forum posts
Recently when buying silver solder from a local supplier he asked what I was going to use it for. I told him I ws making my first copper boiler for a locomotive. He said that if I was soldering copper to copper I could use a copper rod. A great deal cheaper and no flux needed. He gave me some rods (free) to try. He also added that if I were to solder copper to say phospher bronze I could still use these rods but use flux.
I was wondering if anyone had any experience of using these rods in boiler making and had any comments on their use. I know that airconditioning installers use them for joining copper pipes.
Ian S C11/11/2011 09:40:34
7468 forum posts
230 photos
I'v used copper to join steel, but using it on copper would be a welding prosess rather than brazing, on copper you might get away with brass, but NOT for a boiler, stick to silver solder. I don't build boilers, but someone will tell of using different silver solders of differing melting temperatures so that you can solder up one bit without melting the bit you did before. Ian S C
Richard Parsons11/11/2011 10:53:26
645 forum posts
33 photos

The copper rods you were offered were a copper phosphorous alloy which needs no flux. In the 70s there was quite a ‘flame war’ in ME (Letters to the Editor) about their use. It seems that at boiler temperatures the joints were affected by sulphur (from the coal). This made the joints brittle.

This might well spark a new discussion as there are now copper – phosphorous – silver rods which were not around in the in the seventies



Chris Trice11/11/2011 11:14:27
1375 forum posts
10 photos
I have no experience of the benefits of one over the other but my philosophy has always been, if in doubt, always go with what you know works. You have to live with the model and feel comfortable with it.
KWIL11/11/2011 12:17:47
3554 forum posts
70 photos
It does not like the environment to which it would be subjected in a loco boiler. Silver solder can be affected by sulphur as well BUT it is the accepted material for such uses.
The following extract is from the Johnson Matthey site
When selecting a copper-phosphorus brazing filler metal it is necessary to understand about their flow properties
and ductility. The level of phosphorus within the filler metal controls these two characteristics - the higher this is the
more free flowing the filler metal and the lower its ductility.
Copper-flo™ is the most free flowing copper-phosphorus filler metal. However, due to its high phosphorus content
it is one of the least ductile. The low ductility of the alloy imparts it with glass like properties, making it both ‘notch’
sensitive and sensitive to impact type loadings. This filler metal should therefore not be used in applications
involving exposure to strong vibration, impact loads or where some deformation of the joint might be expected in
service. In such circumstances the use of the more ductile Sil-fos™ or Sil-fos™5 filler metals should be considered.
Copper-flo™ is best suited for making copper joints that are of the true capillary type and where tight joint
clearances of 0.025-0.075 mm are used. The use of ‘bell mouthed’ type joints should be avoided. Copper-flo™ can
be used to braze copper alloys, but its lack of ductility can be exposed in such applications.
Composition: 92.2Cu, 7.8%P
Conforms to: EN 1044 1999 CP201, ISO 17672:2010 CuP 182
Melting range: 714-770°C*
*The flow point for this filler metal is approximately 720°C
Uses for This Product
Copper-flo™ is widely used in the refrigeration, heating and ventilating and air conditioning industries for the
brazing of copper pipe-work systems.
wotsit11/11/2011 16:56:22
188 forum posts
1 photos
I have some copper (coloured) rods made by the German company Rolot, numbered 607. The company advertises them for use in copper soldering, at a temperature of 710 degs C. I have used it to solder copper pipe with no problems, using no flux. The resultant joint appeared very good, but I have no real way of testing the integrity, etc. I have wondered whether it can be used for boiler work (silver solder is not available in Romania). So far I have not found much technical info (internet), so I will try contacting the company to see if they can provide more information.
There does seem to be conflicting info (and prices!) in the Internet for this stuff. Someone on Fleabay is selling it at 1 euro per stick (I bought mine at 20 Euros for 25 sticks). Another site calls it copper rod, then gives what seems to be the constituents (L-CuP6) - I'm no chemist, but maybe this implies phosphorus content?. Yet another site is selling it as kupfer-silberhaltige (copper - silver content), so guess that the Internet cannot be relied on this instance.
I would really like to know if this stuff can be used for boiler work, as it would solve the problem of obtaining a suitable solder.
Speedy Builder511/11/2011 21:13:55
2613 forum posts
212 photos
Use these copper phos rods on steel at your peril. The joint is extreemly brittle and will fail under minute loads. like I found out !!!!
Dusty12/11/2011 10:17:52
490 forum posts
9 photos
Basic rule guys, If you do not know what it is, do not use it. The same applies to silver solders, we have all been given lengths of 'silver solder' by friends. I have several lengths of the stuff which I have aquired over the years. I only use it for fabrications, it does not go anywhere near a boiler. the other problem with copper/phos brazing is that club boiler inspectors will be very wary of a boiler constructed by this method and may very well refuse to test a boiler. If you know what the copper/phos is and can obtain technical information from the manufacturer as to its suitability then I can see no problem. My advice is use it at your peril, silver solder might be more expensive, but it could be even more expensive if a boiler were to fail after being brazed with copper/phos rods.
Stub Mandrel12/11/2011 16:48:37
4315 forum posts
291 photos
1 articles
(L-CuP6) - I'm no chemist, but maybe this implies phosphorus
'P' is indeed phosphorus, I'd guess that means 6% phosphorus, so less than the JM rods.
wotsit12/11/2011 19:59:07
188 forum posts
1 photos
I cannot disagree with Dusty's basic rule, nor with Roberts stricture - but I would note that nowhere in the advertising literature for these 'copper' rods have I seen that it can be used on steel - it always says copper (no flux) or brass/phosphor bronze (with flux), so I have to question why it was used on steel, resulting in a brittle joint - there are appropriate materials to use for steel.
As Richard Parsons mentioned earlier on this thread, some of these materials did not exist in earlier years, so perhaps it is time to explore what is/is not possible with new or different materials - (Roberts experience probably comes under what is not possible) How did model makers 50 or 60 years ago arrive at the conclusion that silver solder was acceptable (and now seems to be the only material to use)? I have articles dating to the 1950's that take it for granted that soft solder will be used for caulking in boilers, and brass fittings used in steam circuits. I can guess that people will now tell me about all the catastrophic failures that resulted - my point is that it is not acceptable to take these risks, so how can we explore new materials and their limitations?
I would like to know if this CuP rod could be used in place of silver solder to build a copper boiler. To do this, it would be good to know exactly how it measures up against silver solder as regards physical strength, aging factors, etc. I have seen lots of discussion (for example) about 'de-zincification' in brass exposed to high temperature steam, and the consequent effects. I would like to know if there is a similar risk with this CuP material. As I noted earlier, I will try contacting the maker of the rods I have, but I was interested to see if anyone else had any useful input or ideas.
Looking at the current prices of silver solder, and the increasing prices of commercial boilers, it seems to me that this part of the hobby has already gone beyond the financial reach of many, Unfortunately not all of us are high income professional 'model-makers', and have to consider costs. There have been comments in ME about attracting beginners to the hobby - I think if I was just embarking on model engineering, I would think (more than) twice about the cost of buying or building a boiler - and it will NEVER become cheaper using current materials and techniques.

mgj12/11/2011 22:02:08
1017 forum posts
14 photos
Ithink most of the answers are in Tubal Cains Soldering and Brazing pp37/38 which list several of these alloys.
Basically it should NOT be used for anything other than copper, or tungsten and molybdenum.
Aslo the finished joints should not be subjected to hot suphur bearing gases, or where the service environment is oxidising over 200C.
And details of failures on a test boiler are included.
So can it be used on coal fired boilers - No.
Eric Lougheed13/11/2011 07:06:02
23 forum posts
Back in the 60's I used to attend a 'free-for-all' evening class that included gas and electric welding, investment casting and many other 'metal-working' activities. There was even a well-equipped blacksmith's forge.
We used a lot of 'bronze' welding rods for joining steel tubing and were told that it was the best process for fabricating or adapting car chassis. In later years I've learned that vehicle inspectors are not allowed to accept such joints and must require fusion welds.
When investment casting, with a home-made centrifugal machine, the instructor had a precious store of very brittle stuff he called 'Phosphor/copper': when working with silver or nickel=silver (welding rods) to make jewellery or other small components we would be allowed to chip a fragment off the phosphor-copper and add it to the melt immediately before releasing the centrifuge and making the cast. It was said to act as a de-gassing agent and had been made up for the instructor by a metallurgist friend in his laboratory.
Not sure that this adds a lot to the boiler issue, but if Vehicles Inspectorate don't allow it in cars because of brittle failure it might be inadvisable to use it in the vibrating stresses of a miniature railway engine.
Eric Lougheed
Richard Parsons13/11/2011 08:46:07
645 forum posts
33 photos

Eric you are right in both cases. The reasons why brazed joints were good was that if (and it is a big IF) they were properly designed and made the process did not disturb or change the metal structure. In many cases the joints were not well made. Any way the cheap MIG welder became available. Mind you I have seen MIG welds done on car bodies which were passed the Goblins of Elfin Safety. These gave me the ‘creeps’.

A well designed and executed brazed steel pressure vessel may well be better than a welded one.

mgj13/11/2011 09:02:06
1017 forum posts
14 photos
Richard - I believe you are right about the joint design issue. A lot of those joints were just butt brazed, so I was told. I actually saw that on an F750 racer as well. The scrutineer told the man to take his car away.
Some tubing of course you cannot weld without subsequent heat treatment, and you either braze or use so called manganese bronze "welding", but it is a form of brazing.
I believe they also ban riveted joints- when a properly designed riveted joint is IIRC as strong as and less prone to fatigue than a welded joint.
jomac13/11/2011 12:17:36
113 forum posts

Hi I need to solder/braze carbide tips on to tool holders and some times braze up brass sections, I have silver solder which can be used with a soldering iron, and some silver brazing rods, the trouble with these is they need to much heat, so they distort and as mentioned de zincify, Down here CIG (which is now owned by BOC) are not much help and the price of lower temp silver brazing rods is astronomical, All my welding/brazing books are out of date, So is there a solution or up to date data out there.

John H.

Stub Mandrel13/11/2011 18:28:19
4315 forum posts
291 photos
1 articles
Brazed joints are the creme de la creme of bicycvle frame buildinbg, or at least used to be.
NB Brazing isn't the same as silver soldering, it doesn't flow as well and you have to create the space for a fillet.
LBSC was very keen on brazing; I suspect that he was on a retainer for Sifbronze, or at least had a handy source of supply...
mgj13/11/2011 19:00:23
1017 forum posts
14 photos
That was because you used Reynolds tubing, like we did on the racers. If you elded it it went allbrittle and fell apart. Now I suppose, they MIG or TIG up bike frames in ali, and my last car was all honeycomb board stuck together with one of the 3M glues and an activator! .Mind you, it brought the chassis weight down from 40lbs to about 8 with a consideralbe increase in torsional rgidity, so it wasn't all bad! (Just added a bit of local strengthening around the hard points where suspension was mounted.

There is a specific SS alloy for silver soldering tips onto tools. .If you have a silver solder that can be used with a soldering iron, are you sure it isn't one of the Comsol types, which I think contain a bit of silver, but are nowhere near as strong as proper silver solder.
I would email CUP alloys because a lot is about to change with the move to Cd free alloys.
Eric Lougheed13/11/2011 19:31:40
23 forum posts
What sort of car did you have? 8lbs chassis weight? even 40lbs sounds a bit formula 1
Eric Lougheed
JasonB13/11/2011 19:44:53
22747 forum posts
2653 photos
1 articles
Stub is right about the art of "smooth fillet brazing" being the bees knees for steel cycle frames as if done correctly does not affect the steel and spreads the loads over a wider area than welding and unlike using lugs gives the frame builder the ability to use whatever geometry he wants. My Uncle was a well known South London frame builder and I have a mountain bike he built to my design that has smooth fillet brazed joints.
Its a real skill to build up the fillet without getting it too hot and having the lot drop on the floor
Alloy frames can be welded and done with smooth joints such as Canondale, most steel and titanium are tig welded and the more exotics stuck together
Jomac the silver solder you can use with a soldering iron is not the silver solder we are talking about hear it is soft solder and should not be used for a boiler. You should not have problems using a silver bearing alloy as they start to melt at just over 600degC so should not melt your brass.
mgj13/11/2011 23:49:17
1017 forum posts
14 photos
F750. The 8 lbs didn't include the bloody 2 2 x16 gauge rails that were forced on us by the rules, but were utterly useless in a monocoque. The 40 lbs did, and got there by very careful use of the rollover hoop, round not sq tube, and keeping it very thin, and the car very small. (Most of the body was less than the height of the wheels, and they were 20" in dia) And virtually no brackets - just threaded tubes brazed (no nuts and centre drilled out allen bolts sized to a maximum stress loading.
Thats not a rolling chassis - thats a basic coffin/spaceframe - you have to put engine gearbox fuel tank etc etc.
1/2" aerolam board - its a honeycomb of paper with very thin glass reinforced epoxy outers. You make it up in a series of diaphragm bulkheads - ie thick wall with big oval cutouts.Probably been superseded by something else now
40lbs Not F1 at all BTW. (And we were a lot smaller than even the present F1 cars) Easy to move about the workshop! Thats a steel spaceframe in 20g round steel tube. That wasn't the lightest chassis about - one or two others were lighter, but at the expense of rigidity, so they didn't handle so well. Which is why I went to the Aerolam board, and I lost quite a few lbs.
Keep the suspension bolts to 1/4" dia, turn down the starter motor casing, ali flywheel, ali disks, magnesium wheels -
How heavy did you think a racing car was? Most of them, without an engine, you can easily pick up the chassis/monocoque even pretty well fitted out. - or could. I'm a bit out of date now.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Support Our Partners
Rapid RC
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest