Ray Litten Posted January 11, 2010 Share Posted January 11, 2010 I wish to make a dustbin muffler for my OS 91FX engine so that it fits within the cowl of my Piper arrow II. I have some 40mm diameter alloy tube which I thought would 'do the job' but welding alluminium seems to present some difficulties, that is, until I read about 'Durafix' rods. These melt at around 730 F. I'd be grateful if any one out there could advise me on what temperature the exhaust of my OS91FX is likely to reach as I don't want to buy this stuff, make the muffler and then find it out 'it falls to pieces' as soon as the engine has warmed up. Thanks for any help. Ray Litten Quote Link to comment Share on other sites More sharing options...
Allan Jordan Posted January 11, 2010 Share Posted January 11, 2010 Hi Raymond, Why not ask Brian Winch ( aka "WIZARD OF OZ ") Try this[email protected] Brian uses a pyrometer to carry out engine tests, perhaps he can help. I have made alluminium exhausts but I'm not familiar with "DURAFIX " rods. Give Brian a go, he's a mine of info. Regards Allan J Quote Link to comment Share on other sites More sharing options...
flytilbroke Posted January 11, 2010 Share Posted January 11, 2010 730F is very close to the melting point of aluminium. Our Alcohol base fuel glow engines do not normally get even close to that temperature. Consider the standard exhaust port and Muffler, Aluminium. our model materials would be at risk too if the temperature came anywhere near 730F Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 11, 2010 Share Posted January 11, 2010 Depending on the alloy (pure aluminium is very rarely used) it will melt at around 650 degrees C which is around 1200 F so there's even more margin! Quote Link to comment Share on other sites More sharing options...
Ray Litten Posted January 12, 2010 Author Share Posted January 12, 2010 Thanks for all your help concerning ic exhaust temperatures. I'll purchase the rods and use these to help construct dustbin muffler then post a thread giving the results. Thanks again for your help/suggestions. Ray Litten Quote Link to comment Share on other sites More sharing options...
Arceenut Posted January 12, 2010 Share Posted January 12, 2010 Durafix is great stuff but is a bit of a b1tch to work with. One cardinal rule for using this stuff is MAKE SURE THE ALUMINUM IS CLEAN. Also take care with the heat so that you don't melt the metal you are trying to weld Quote Link to comment Share on other sites More sharing options...
flytilbroke Posted January 12, 2010 Share Posted January 12, 2010 Doh, I should not post reply when tired.. 730F SLAP WRIST and me who worked in the Smelting industry for 43 years,,, Slap wrist again. The rest of my observation is ok though Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 12, 2010 Share Posted January 12, 2010 If Durafix is anything like the other (I think) zinc based aluminium brazing rods, the best technique seems to involve agitating the molten material with a thin piece of stainless steel until the base metal "tins" and teasing the flow around to follow the heat. You only need a minimum of 3 hands! Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 12, 2010 Share Posted January 12, 2010 Ray the Durafix works fine for exhausts...I've used in a couple of jobs with no problems....thr trick is getting the job hot enough without getting it too hot & melting the aluminium as the melting point of aluminium is pretty close to the melting point of the Durafix rod so I'd suggest a bit of practice first..... The trick is to get the job hot enough to melt the rod rather than using the flame to do it...a bit like soldering....you heat the job up & melt the solder on the work piece rather than the soldering iron.... Remember to give everything a good wire brushing with the (supplied) stainless wire brush first..... B&Q are a good source of aluminium tube & angles etc....get the non anodised stuff though.....Maplin are a good source of small aluminium boxes to make the muffler body from.... Hope this helps Quote Link to comment Share on other sites More sharing options...
Ray Litten Posted January 14, 2010 Author Share Posted January 14, 2010 To all who replied to my exhaust temperature enquiry. It seems that this is still not a straight forward process after all as care is required when applying heat to the relevant part(s). It's certainly a good idea to practice on some small pieces of aluminium first, just to get a feel for what's required, before attempting the main job. It's extremely handy having access to peoples experience on these matters, so again, thanks to all of you who gave me advice, it's now back to the workshop to start making the muffler. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 14, 2010 Share Posted January 14, 2010 I think most of the problems arise from us not being experienced welders.....lets face it, it takes years to become a skilled welder/brazer & how often do we do it? Once a year? Twice...?? If you look at the Durafix website theres a guy repairing a hole in an ally can...if I tried that the ally can would be a blob of molten metal!!!! When I made my muffler the problem I had was with the disparity in the size of the parts being welded. I was welding some nice 10mm ally tube into an ally box but found that the ally tube has much less mass than the box & so heats up/melts quicker.... & the box acts as a huge heatsink & conducts all the heat away from where its needed!!! Solution? concentrate the main part of the flame on the biggest part of the job & try & heat both parts up evenly & again this comes down to (that word again) experience & practice.... Remember that good judgement is the result of experience & experience is the result of bad judgement!!! Consider also your blow torch....you need a nice small pencil flame but one that is pretty hot.....a MAPP gas torch is probably best if you have access to one......I actually did mine with one of those cooks blow torches.....the sort you burn the sugar on yer creme brulee with...worked OK but took some time to get the job hot enough....if you have too big a flame it tends to melt the rod before you get it to the joint!!!!!! Practice a bit first & you'll be fine...... Quote Link to comment Share on other sites More sharing options...
Chris Channon Posted January 16, 2010 Share Posted January 16, 2010 Hi, you could of course use silver solder , clean the ally, coat the parts to be soldered in clean oil ! then just heat up and solder as normal. Been making exhaust systems like this for years, it works well. ( it was an article in RCM&E years ago ) Regards Chris. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 16, 2010 Share Posted January 16, 2010 Coated with oil? Tell us more (I assume you're being serious) - I've always understood the opposite! Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 17, 2010 Share Posted January 17, 2010 I don't know Durafix but I suspect it will be much the same as Techno-Weld. I've just found some excellent instructional videos here although the first one stops half way through - go to the button at the bottom left and you'll be able to move on. There are some more videos on the Durafix site but the Techno-Weld ones show the techniques a little better and with more explanation. You'll see the use of a stainless steel rod for agitation of the molten material and surface tinning in these as well. I've bought "aluminium repair rods" from B&Q in the past (can't remember if they were branded) and these seem identical in use to these other products and reasonably priced. Edited By Martin Harris on 17/01/2010 00:16:26 Quote Link to comment Share on other sites More sharing options...
mal brewer Posted January 17, 2010 Share Posted January 17, 2010 Posted by Chris Channon on 16/01/2010 17:50:23: Hi, you could of course use silver solder , clean the ally, coat the parts to be soldered in clean oil ! then just heat up and solder as normal. Been making exhaust systems like this for years, it works well. ( it was an article in RCM&E years ago ) Regards Chris. Hello Chris, this surely cannot be right.To melt silver-solder,the work piece has to be brought to red-heat,when soldering brass or mild steel,to allow the solder to fuse with the metal.Ally would be well melted before that temperature was reached...........Mal. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 17, 2010 Share Posted January 17, 2010 Some grades of silver solder melt below aluminium (not much margin though) e.g. CuP Alloys 840 Melting range 595 - 630 °C I'm more interested in the use of oil !?!? Quote Link to comment Share on other sites More sharing options...
Arceenut Posted January 17, 2010 Share Posted January 17, 2010 The oil keeps the air (oxygen) from the work surface so the aluminum does not oxidise and prevent the solder from sticking. I've not used this method myself but at one time hot peanut oil was used to melt and 'flow' solder on printed circuit traces to 'tin them. Peanut oil was used as it did had a very high 'smoke temperature'. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 17, 2010 Share Posted January 17, 2010 I guessed it would be something along those lines but I'd imagine only specific oils would work - usually any sign of oil is a no-no for soldering operations - maybe due to impurities rather than the oil itself? Aluminium oxidises extremely easily and aggressive fluxes are usually the order of the day... Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 18, 2010 Share Posted January 18, 2010 I was supprised by the silver solder bit too......needs too high a temperature I thought....didn't know about the lower temperature stuff!!! No flux used with the Durafix stuff although you have to give the surfaces a good wire brushing with a stainless steel wire brush (a normal steel wire brush will not do apparently ferrous metals being a big no no with this stuff!!!). I suppose with these rods you are actually melting the surface of the ally & fusing it that way...... Quote Link to comment Share on other sites More sharing options...
Chris Channon Posted January 20, 2010 Share Posted January 20, 2010 Hi all, sorry for the late reply, Yep it is correct, abrade the ally with a good clean wire brush or a "dremel" type rotary stainless steel brush, as soon as you have finished cleaning, coat straight away with a good clean oil, 3-in-1 works well or even cheapy ASDA engine oil. You can use a large soldering iron, i use a small modelling butane torch to heat up the work, then apply the solder just as you would when making a tank etc. The silver solder i use ( note, normal lead / tin solder will work for things like a tank but will melt on a silencer job ( unless it is for a diesel then it is ok ) i get from Sussex models, it is a cored solder used by the car racing boys for making battery packs ). Clean off the work when completed and if needed apply an etch primer and then paint with hammerite hi-temp ( exhaust ) paint . Hope this helps a bit, if anyone needs any help, then please feel free to give me a shout.Edited By Chris Channon on 20/01/2010 18:33:36 Quote Link to comment Share on other sites More sharing options...
Phil Claridge Posted January 22, 2010 Share Posted January 22, 2010 old step ladders are a good source of box section ally Quote Link to comment Share on other sites More sharing options...
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