|Richard Fryer||01/03/2017 13:40:32|
|6 forum posts|
Good afternoon everyone,
I hope so of you will be able to help me, with my silver soldering task.
I am restoring a second world war Scammell Pioneer heavy recovery tractor, part of which is making a whole new windscreen frame from scratch.
I have welded up the 25mm x 25mm angle outer frame, but now I need to do two things:
Firstly, i need to solder some 1/2" x 1/2" brass channel into the bottom of the frame to hold a 6" deep pane of glass.
Secondly, I need to make the hinging inner frames from the same 1/2" x 1/2" brass channel.
I suspect the first task will be the most problematic, given that it involves long joints between dissimilar metals. I imagine I need to do it at as low a temperature as possible.
So, I have a few questions:
1) what solder and flux do you recommend?
2) Is the long joint between the brass channel and steel angle going to be possible / a nightmare / very problematic?
3) I'm assuming silver soldering is the best bet, but open to suggestions of other processes.
4) Does anyone want to come help? in somerset.
5) Any other advice / pointers / things to look out for etc.
Thankyou in advance for any help you can lend.
|Neil Wyatt||01/03/2017 13:55:57|
18992 forum posts
You may be better off getting someone to TIG it for you?
How were the originals made?
1675 forum posts
Wouldn't there be an issue with differing expansion rates, between steel and brass, causing distortion?
Neil, Can you TIG dissimilar metals?
|Ian P||01/03/2017 14:35:53|
2578 forum posts
Would love to help but distance rules it out.
Certainly silver soldering would be best for the frame made of brass channel. I presume the the corners would just be plain 45 degree mitre butt joints without any overlaps or stiffening.
I too think a long brass to steel soldered joint would be problematic, it would be easy to end up with a curve. Why not just drill and tap the steel angle at regular intervals and fix the channel to it with screws in slightly slotted holes. The screws would be hidden by the rubber strip or whatever holds the glass in place.
22584 forum posts
For 10ft of material over 100deg F temp change you would get about 1/32" difference in movement between brass and steel so say each half of your screen is 2ft long so maybe 0.006" so unlikely to see much distortion on the finished frame.
If silver soldering it I would start heating in the middle and chase the solder as it melts towards one end, then come back and chase it from the centre out to the other edge that way you keep the amount of movement during the higher soldering temperatures in one spot rather than trying to heat the whole 2ft length. I've done similar when soldering rings around the outside of discs with a similar circumference to your screen length.
Use Tenacity No5 solder sometimes sold as just "HT" as this will stay active for longer and the lowest melting point silver solder you can get.
Edited By JasonB on 01/03/2017 14:54:36
151 forum posts
Have you thought about pop rivets first then either silver solder or possible a high melting soft solder using the stitch method
|Speedy Builder5||01/03/2017 16:10:37|
|2593 forum posts|
If you are worried about distortion on cooling, perhaps put a slight bow in the steel before you silver solder so that it would straighten on cooling. Also, use step soldering; i.e.. solder a few inches, let it cool, miss a few inches and then solder some more. Once you have a series of steps, return and fill in the gaps.
|not done it yet||01/03/2017 17:57:08|
|6736 forum posts|
Glue it? Its not going to war any more, after all.
|Neil Wyatt||01/03/2017 18:47:52|
18992 forum posts
I was thinking that tig as a heat source for a compatible filler, which could be silver solder. the advantage with TIG being you could stitch it at intervals along the length, then fill in between (if required) to minimise distortion. I suppose you could do the same with an oxy actylene or oxy propane torch.
|Keith Hale||01/03/2017 20:39:43|
333 forum posts
Soft solder it with 60/40 tin lead soft solder> Melts at 187 deg
25% of the distortion problem compared to silversolder.
Joint strength I suspect will be adequate.
This is one of those occasions when silver solder is not the answer!
Edited By CuP Alloys 1 on 01/03/2017 20:45:17
468 forum posts
I would clean both parts and tin using solder paint. Then clamp it all up and soft solder the lot. I expect that was how the original was done. Don't worry about the strength of the joint being weak. Bugatti used to soft solder their propshafts together.
Its all based on the surface are of the joint.
|Andy Ash||01/03/2017 23:54:53|
|136 forum posts|
I reckon you're on the right track with that, but I've never made silver solder work with TIG. It's a bit expensive to be making a mess with silver solder anyway. I think the contamination issues and the low temperature of silver solder reflow would be the reasons. The trouble I find, is that I can't get silver solder close enough to the arc. If I lower the arc energy, then the steel isn't hot enough to accept the solder.
Silicon bronze (SIF do a good Silicon Bronze), is the route here I think.
Silicon bronze TIG brazing wouldn't be so susceptible to contamination as Silver solder would be.
I've never tried this particular combination but I might give it a go and report back.
I would offer to help but it's a bit distant and I imagine my skills would probably let me down anyway.
I imagine they would have used a special fluxed brazing spelter and an oxy torch back in the day.
Edited By Andy Ash on 01/03/2017 23:58:16
|Keith Hale||02/03/2017 07:19:12|
333 forum posts
You weld with TIG. You do not braze.
They are two totally different processes. Silver soldering is just one facet of the brazing process that is dependent on capillary flow to effect a joint. Heat from a TIG torch is more intense than oxy-acetylene, It is highly unlikely that you will be able to generate the heat in the right places to make a successful joint. It is bad enough with oxy-acetylene. This is the main reason model engineers have joint problems. At best you will simply melt the silver solder on top of the joint leaving a crack underneath!
You are not brazing You are not welding. You are simply using an expensive rod to block a hole! Probably the reason Andy didn't make it work.
48 years in this business and I've never seen TIG as a heat source for brazing work either! I can't even recall it being attempted.
It has nothing to do with contamination, nor the alloy used - special or not. Joints attempted using TIG will be inferior if made at all,
Going back to the original question, if there is still too much distortion when using tin-lead paint/paste/wire then glue it!
22584 forum posts
Keith, one of our motorcycle building members has shown TIG brazing in the past and very nice it was too. This is an example of the sort of thing. They tend to leave the weld textured rather than dress it as is common with fillet brazing done with a torch
Edited By JasonB on 02/03/2017 07:43:58
|Michael Gilligan||02/03/2017 07:52:16|
20090 forum posts
That's almost certainly what a modern vehicle manufactirer would do.
... I have no experience of specific adhesives for the job, but it I think it would be worth you [Richard] investigating.
|Alan Waddington 2||02/03/2017 07:56:27|
|522 forum posts|
I would consider bonding it on with sikaflex automotive windscreen adhesive. Key and degrease both surfaces and use the appropriate sikaflex primer.
22584 forum posts
Posted by peak4 on 01/03/2017 14:03:35:
Edited By JasonB on 02/03/2017 08:10:23
1843 forum posts
Hi Keith - good to chat with you at the show in Oldham, I even managed to sell one of my delux boilers there so a success for me. I have used TIG as a heat source for silver soldering copper and its not a great process. The heat is too localised and you cant see what you are doing with the rod. Ive also welded brass to steel with the tig, you get a good result but even with the right rod I found the joints to be quite brittle. If it were my job id be inclined as others have indicated and soft solder it. Best of luck Richard.
|Ian S C||02/03/2017 09:12:08|
7468 forum posts
For a military vehicle like that I'd tend to think that it would have been riveted after soft soldering. Tin both surfaces, then use brass rivets, heat with a torch/blow lamp.
Ian S C
|Ian P||02/03/2017 09:36:24|
2578 forum posts
WHY DO WE DO IT?
24 hours have not yet elapsed since Richard made the original post and asked several questions. There have now been about twenty replies covering lots of options and presumably there may be many more. Unless Richard comes back with some feedback (I think unlikely, with only one other posting in four years) what is the point in 'us' (me included) speculating and pontificating?
Actually all the replies do have a useful purpose in that it is good engineering discussion and may help spread useful tips. In the past some of these type of threads have run and run withe no real purpose though. OK it does no harm but as it increases website traffic so the adverts get seen more.
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