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machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment.

Tag: Bronze brazing

6″ Vertical Boiler.Spearhead Superheater

Some more progress on the 6″ vertical boiler.  Not much to show, but here it is.

Actually, I have been wondering whether to continue with this blog as a “what I have done today” type diary, or whether to post less often, but when a significant milestone has been passed.  Your feedback would be welcome on this decision.

The superheater is a copper item, which steam passes through, and is located in or just above the furnace.  As a result the steam becomes hotter and drier and more energetic before it is passed through the engine or whatever it is being used for.

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This is a lump of copper, 10mm thick which I have cut off a bar which I had in stock.  It will be machined into the superheater spearhead.

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The copper spearheads machines into shape.  Copper is soft, but it grabs the cutters.  Not nice to machine.  Expert Stuart said that I should have used lubricant.  Next time. 

The sperheads are bronze brazed to copper pipes, but the difficult bit was bending the 1/4″ copper pipe to fit.

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The spearhead is bronze brazed to the copper pipe.  Tricky, but seemed to go OK.  Don’t know yet whether the bronze join is steam tight.

The tricky bit is the 2 x 90º bends, really close to each other.   Does anyone have any good method for doing this?  I ended up with this result, but it is not pretty, and I am sure there must be a better method for creating the bends.

The silver soldered joins are yet to be done into the brass fittings shown.  I ran out of time in the workshop.

This is getting exciting!  I am not too far off firing up this boiler!

Then a visit to the boiler inspector.

Trevithick Dredger Engine. Making and brazing the boiler cylinder tube.

The boiler cylinder tube is the vertical cylinder which penetrates the boiler shell, and boiler end plate, and eventually houses the cylinder and piston within the boiler.

In the previous post I described cutting the hole which encloses the cylinder.

Today I made the cylinder, and brazed it in place.

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Reference lines accurately marked using machinists blue.

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It is 51mm diameter, and wall thickness 3.2mm.

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Bronze brazed into position.

And now that the brazing is completed I can cut the boiler tube to its final length.  This was left until all the brazing had been completed, in case there was a major stuff up and it had to be repeated.  That should be the last bronze brazing join on this engine.  I can return to the easier, and lower temperature silver brazed joins from on.  I must mention that working close to a workpiece which is close to 1000ºc, for 5-10 minutes at a stretch is fairly uncomfortable.  Now I know why the bronze brazing torch is a minimum of 450mm long.  Even so, I got skin burns from the metal buttons of my jacket when I touched them after a session.   A leather apron from now on.

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Measure twice, cut once.  Actually, I measured this 3 times.

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Cutting with the drop bandsaw.  Very slow feed rate so the blade does not grab this very soft copper.  This removed 3 of the remaining 4 unwanted holes.  Just one remains to be filled.

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Final length of the boiler.  All nicely square.

 

Trevithick Dredger Engine- bronze brazing and some milled parts.

 

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The copper tube which I am using for boiler shell has 6 holes, intended for another project by the previous owner.  Here I am trimming the length, so 2 of the holes will eventually be removed.  Using a drop bandsaw, with a wooden plug so the tube is not bent by vise pressure.

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Bronze brazing the domed boiler end to the boiler wrapper.  The assembly absorbs a huge amount of heat before it reaches brazing temperature.  Showing the temporary forge, and the torch head for the oxy-propane fuel.  The join has been completed in this photo.

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The join in progress.  Note the positioning copper rivets, and the tacking points.  At this point I ran out of oxygen and had to finish the braze on the following day.

And today I made some parts for the boiler’s removable flat end.  My CNC mill is out of action, so GSMEE President Brendan kindly allowed me to use his machine.

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CNC spotting 3.2mm brass plate.

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The almost completed firebox door base.  Spotting did not allow for the removed material in the rebate, and the drill ran out in one hole- some repair required.  I will plug and redrill that hole.

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The manhole cover.  It will eventually be painted.

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Sitting in intended positions.  Fastener holes spotted, yet to be drilled and threaded.

Oxy-acetylene or Oxy-propane for silver soldering (and bronze brazing)?

There has been a big learning curve for me in making the 6″ vertical boiler and the Trevithick dredger engine.  I have used silver solder for previous projects, and I thought that I had the method under control.

I have always used oxyacetylene for my earlier, smaller projects, presuming that the higher flame temperature would produce results more easily.  That is what I tried to do with the 6″ boiler project.  But I struggled.  In order to produce a broad flame, and not burn the copper, I used a big, number 26 nozzle.  Initially it produced a lovely big hot flame, but within minutes it started popping, and blowing out.  Faulty acetylene gauge?  Gun not up to the job?  Acetylene cylinder running low?  So I replaced the acetylene cylinder. Cost $AUD100.   Seemed to fix the problem temporarily, but then the popping resumed.   Faulty gauge?  A borrowed replacement gauge produced the same result.

So back to the welding and gas supplier.

“You cannot run a nozzle bigger than No 15 when using acetylene.  The acetylene does not come out of solution in the cylinder quickly enough”.

OK.  So what do I do?  “Use propane”.  “but you need different hoses, different gauge, different mixer and nozzle”.  OK, give me those….  cost $AUD 260.   And it worked!!!

Propane and oxygen burns at a lower temperature (~2820ºc) than acetylene and oxygen (~3420ºc) , but the gas volume delivery of the propane is MUCH greater than the acetylene.  So the delivery of the heat is much greater.

For me, I will be returning the acetylene cylinder and permanently switching to propane.  Much cheaper and much more heat.  But, that heat can lead to unintended consequences…So, here we are on the Trevithick dredger engine.  I needed to bronze braze the join between the firebox and the firetube. (a boiler inspector requirement).  Bronze melts at 836-1030ºc which is not far off the melting point of copper.  And my first attempt ended in disaster!  I melted the copper firetube!!!  An expensive blob of copper and bronze!!! (no photos.  I was too cross with myself).

The next effort was an improvement, but not pretty.

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Using a holesaw to cut a 38mm hole in the 64mm copper tube.

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The angle was not quite right, but fixed with some careful filing.

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Setup, ready for bronze brazing.  The firebricks are holding the pieces in position.

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After bronze brazing.  It is not pretty, but I am a beginner at this.

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The end plate was used as a jig.

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And then I accidentally dropped it. (#$#%&**#)  Restored to proper shape with some careful blacksmithing.

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My great great grandfather was a blacksmith.  

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OK.  It is not pretty.  But not bad for a gynaecologist.

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And to show you what Trevithick’s blacksmiths made to his design.  I count at least 19 individual iron pieces, riveted together.  This was the firebox and firetube of the first high pressure boiler.  Incredible!

 

 

 

 

 

Home Made Ring Roller, and first attempts at bronze brazing.

The two projects for which I am currently accumulating materials, will require rolling copper sheet and rod into circular shapes.

A few years back I made a ring roller to make components for steel gates, and it would have been perfect for rolling the copper foundation rings and fireboxes.

It is fairly heavy duty roller, powered by a 1/2 HP motor, geared down 1:40.  I have bent mild steel up to 1/2″ thick 4″ wide, but I founds its limits when I tried to bend some hardened rod.   It left some grooves in the rollers.   And those grooves would imprint marks into the soft copper, which would be totally unacceptable in the two boiler projects.

So yesterday I disassembled the machine, removed the rollers, and turned the rolling surfaces in the lathe until the grooves vanished.  The 31.75mm diameter finished at 30.4mm.  Nice and regular and smooth.  And working smoothly again.

Pretty mundane stuff eh?  But oddly satisfying.

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BRONZE BRAZING

And after that I tried my hand at bronze brazing joins in copper parts.   The boiler inspector requires that certain joins in the boilers use bronze brazing, instead of silver soldering.  I am now reasonably proficient with silver soldering, and had no experience with bronze brazing.  So, do I try to learn a new skill and use it on my expensive copper components of the boilers?   Or do I pay an expert to do the bronze brazing for me?

Well, I decided to buy some bronze rods and flux, and give the bronze brazing a try on some copper scrap.  The AMBSC boiler code requires the use of Tobin bronze.  Local welding suppliers had never heard of it, but I found a supplier on ebay.

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Tobin bronze is another name for Naval Bronze. (according to my quick Internet “research”).  It is relatively resistant to corrosion, and very strong.  Actually much stronger than silver solder and with a much higher melting point.  Silver solder is said to be as strong as the parent metal, so bronze must be awesome.  Bronze will fill gaps, indeed a V gap is desireable, wheras silver solder prefers an even, tiny space which the solder fills by capillary action.

The brazing rods are available in diameters 1.6, 2.4, and 3.2mm.  I had no idea which size would be best, so I bought 1.6 and 2.4mm.  I also bought some 303 flux powder, even though some experts say that flux is not necessary.  OK, lots to learn.  (p.s. flux IS necessary. )

So, onto YouTube, and watching multiple tutorials on bronze brazing copper.  I reckon that YouTube is fantastic for learning new skills.

With silver soldering, the solder goes to the areas which are fluxed.  But, it seems that when bronze brazing, the bronze follows the heat, so the application of heat is critical.  And not just where the heat is applied, but how much.  The thing is, that the parent metal is not melted in either process (unlike welding).   When bronze brazing copper the temperature range between succesful brazing and melting the parent metal (which means disaster) is quite narrow (about 100ºc), and the brazing temperature is about 950ºc, so it is tricky.

And copper is an excellent heat conductor, so the heat spreads rapidly through the parent metal, with result that the bronze filler spreads and it is difficult to get a good appearance.

Here are the results of my first efforts.

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The copper is 3mm thick.  The bronze filler is not pretty, but this is my first ever effort.  I discovered that you cannot actually see the molten puddle until you have moved on a bit, and by then it is easy to have applied too much filler.

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I cut across the join to check the adequacy of the brazed join.  I was quite pleased to see that there were no gaps or voids.  Also, although the bronze filler looks ugly on the surface, it is actually fairly flat, and should be insignificant when painted.   You can see the V which was prepared in the edges of the join.

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Next I tried an angle join.  Looks neater, but not enough bronze filler at one end.  USB for scale.

OK, looking promising, but what about thin copper?  Will that just melt away?  By the way, my heat source is oxy-acetylene.  I tried MAP gas with air, but got nowhere near enough heat.  Oxy-acetylene burns at 3500ºc and copper melts at 1083ºc so it is not difficult to end up with an ugly, expensive blob of copper and bronze.

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This is 1/4″ pipe with a 0.7mm wall.   No problemo.

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and the final test for the day was end joining the 1/4″ pipe.  The hardest aspect was holding them in position.  Quite happy with this.

I tried both 1.6 and 2.4mm bronze filler rod diameters, and for this scale job I preferred the 1.6mm.  The  joins were significantly lumpier with the 2.4mm.

So, with a bit more practice I think that I might be able to bronze braze where necessary on the vertical boiler and the Trevithic dredger engine.

P.S.  Those readers who know about brazing will get a laugh.  I did the brazing without dark glasses!  None of the tutorials mentioned that dark glasses allow you to see what is happening in the molten puddle.  I found out about dark glasses at my model engineering club club meeting last night.  John.

 

 

 

 

 

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