Anyone for Brazing?

I've just taken a bit of 1/4" plate ally from the scrap box and measured it with the sides of the meter probes gently applied. Reads a dead short. ;-)

Argon arc was the first common way. A MIG will work too.

There is also a very primitive form of welding which basically involves beating the living s*it out of two bits of metal until they have no alternative but to fuse together. You don't need a filler for this process; just arms like Popeye.

It's called 'Hammer Welding'. Heat to white heat, sprinkle silver sand on one piece as a flux, overlay them, then working from one end hammer them into fusion progressively working to the other end. This forces the slag out of the join keeping inclusions to a minimum.

I have a Blacksmiths Power Hammer, which is brilliant for this, and also drawing down large sections. However as part of my major clear out the Power Hammer will be featuring on eBay when I can get close enough to take photos :)

Another process that is largely similar is 'explosive welding'. The two metals are forced together literally by means of an explosion. Often used to fuse sheets of steel and aluminium as an interstitial layer between two parts of a structure to avoid electrolytic corrosion. Many modern warships have a steel lower hull and aluminium upper works, and use this bimetal to make the union.

Andrew

There is another welding process called Thermite welding. It is also known as exothermic welding

It is used in the railway industry to weld long sections of rail.

Basically you lay the two rails butting them up against each other.

You then build an empty "volcano with heat resistant putty.

You then fill this "volcano" with Iron oxide and aluminium powder.

You then ignite the powder mix.

The aluminium and iron oxide react very violently to then become Aluminium oxide and iron. The huge amount of heat also melts the two rail ends together.

Another powder combination can be used, copper oxide and aluminium. for the formation of electrical joints.

When the reaction is proceeding, it does look like a volcano.....

After its all cooled down, apply angle grinder till you have a continuous rail with no perceptible joint... and hence no clackety clack of train carriage wheels over the rail joint.....

Yes it's a very impressive process to watch 'up close and personal' :)

Thing that puzzles me is when a rail is joined to the next there is no allowance for thermal expansion. Rails joined by 'fishplates' deliberately leave an expansion gap to allow for this. Now unless the EU has banned thermal expansion it presumably still happens. I was told as one explanation that rails are 'stretched' before joining but have seen no evidence of this watching thermite welding being done and the forces involved would be immense. Maybe modern rails are made of Invar - I think not :)

Next welding topic : 'Electron Beam Welding' - not welding two beams of electrons together, but using a beam of electrons in a vacuum to fuse metals in (usually) very small components

Andrew

No, you just need a striker with arms like Popeye.

Colin Bignell

And laser welding. I had a detached retina re affixed by around 130 shots of an Argon laser over the space of three minutes a few years ago;!...

Suppose I'd be blind on one eye if that tech wasn't around:)...

Hopefully not so. When I had my retina refixed back in the early eighties it was cryogenic welding with a probe that was inserted through the white of the eye. My retina got "creased" in the process and it took some time before my brain learned that straight lines weren't wavey. Hopefully yours was refixed a little better than that though, to be fair, back in those days I was just grateful that I could see through that eye again.

Nick

In article , Nick Odell scribeth thus

Well I did think it odd that the insultant said "just go get some lunch and come back and we'll operate then" had visions of something like that;!..

Has worked very well, have a check-up every so often and thus far no problems:)..

Vision good enough corrected to be a commercial airline pilot so I'm told and uncorrected just scrapes by the road number plate as tested recently by a traffic policeman on a sight test demo..

And Do I always remember the glasses when cutting that bit of steel sometimes .. course it'll be alright won't it;()

Six weeks ago I couldn't even spell engineer - now I are one.

I haven't seen the welding being done but have worked in possessions where the rail clips are removed and every 5th one replaced by a roller which fits under the top "web" of the rail, it's an over centre device operated by rotating a square nut through 90 degrees so the rail is clear of the sleeper and free to roll on this "pandrol destresser". I have one on my desk picked up by a litter patrol.

As I have not noticed any expansion devices recently I assumed that all the expansion was taken up by the spring in the stressed rail.

AJH

I was under the impression they had a type of scarf joint ever so often that was not welded and this was to absorb the expansion...

They have extremely effective devices, effectively a form of jack, for applying tension to the rails - but that will be up or down the track a bit from the site of the thermite weld.

Can't now remember the temperature they aim for, think it is what the rails get to on a warm, sunny day (rather than extreme hot day). When that temperature is reached, the rail will have close to zero tension, if temperature continues to rise, they can and do end up in compression.

Buckling can occur if they get it wrong!

Did the same thing myself at the same age and was utterly euphoric at immediately picking up a stentorian voice conveying round the clock news with astounding clarity and no fading whatsoever. I was less chuffed when I eventually discovered that was *all* I could receive over the entire tuning range and it was in fact the BBC World Service (1MW DC input power) less than 3 miles away. Could have picked the damn thing up on a loose filling.

They start failing (buckle) at around 35C summer temperature. The rails themselves are probably hotter in the sun when this happens, but that's about the ambient temperature when lines start being closed. I only recall it happening a small number of times.

Are you sure about that? When I was at school (long, long, long time ago) and doing my O levels, we had to learn about something called the "coefficient of linear expansion" which states, if I recall correctly (maybe I don't, it was a LONG time ago (if I haven't already mentioned that)) that linear expansion is inevitable in certain materieals and is directly related to temperature (rails fall within that category of "materials").

I've seen it used for fairly sizable chunks of lithium-aluminium alloy, which is difficult to weld using conventional means :-)

Also friction welding, which will do fun things like let you weld[1] copper to steel.

Sure, plenty of *new* methods. Few of them applicable in a shed with basic equipment, though. And there's nothing wrong with the old methods, done properly.