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Hi,Im having trouble with my silver soldering, im soldering a copper steam train boiler, 7inch diameter, join has a 1.5 inch wide strap running the length of the boiler for extra strength, 3 propane burner are placed under the boiler (heating the strap) once temp is close to melting the solder I start up the oxy acetylene torch for extra heat, feed solder in from the inside of the boiler so it gets no direct heat from the burners until it flows out from the sides of the strap, I am getting pitting in the solder, I guess caused from over heating it, I thought I was doing a good job not heating it up to much when solder.Will there likely be pitting under the strap and if yes then will it weaken the join?Thanks Attached Images
Reply:how clean was everything when you started.. clean is everything when it comes to silver soldering..Harris makes a silver solder/flux paste all in one thats just wonderful....oh by the way your lucky..this is your first post..glad you introduced yourself the proper way most likely i'd ignore it...but i'm in a good mood.. ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Hi,Thanks for your reply, everything was very clean, I am useing Harris black flux.Sorry didnt realize people intrduce themself before posting on a forum.Im Darren anyway Hi.
Reply:well from the last pic it looks ok from the start..then it goes downhill from there..too much heat..when the copper hints of blue its way too hot and then nothing likes to stick to it...anymore...you need to clean it off again and start over......zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Hi,Thanks for your reply.I dont think it goes blue? it goes a dull ish red when its up to soldering temp.I think the reason it has spread out just after the start in the bottom picture is I put to much flax on that area, the solder seems to flow where ever the flux is, the solder has fully penetrated the join and the strap, the main thing I was concerned about was the pits in the first picture.
Reply:how are you going to pressure test this thing before use?whats its operating P.S.I.?...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:The black flux is more for high temperature brazing and might not be completely active at the working temperature for the solder. I would suggest the white flux in this application.
Reply:Neat work Daz.Try an experiment. Make some coupons (sample similar to your boiler material) and cut it in several sections to see what it look like from the side. I suspect for your application the joint will be okay. What other setup did you use? Did you make an oven of some sort to aid in controlling the temperature? A fire brick hearth would work. How long did it take to get it to brazing Temp?Does Harris Black flux contain the Silver Brazing Alloy? You stated you added filler. I've also, heard of people filing the filler and adding it to flux, then brushing the mixture onto the part.
Reply:It will be hydro tested at 200psi that 2x working presure.The black flux was recommended to my by a train builder, apparently its the best stuff out there
well thats what I have been told.I tried many times to replicate my soldering on small bits of copper, I even got the copper so hot that it melted but I couldnt seem to get the same results as I did with the boiler, when I file the pitted solder it becomes nice shiny and smooth, dont know if that means anything?No other setup, dont have any fire bricks yet, maybe 1-2min to get to brazing temp.No the flux doesnt contain any silver, I brushed the flux all over the joints and in-between the strap and boiler before I started.
Reply:I tried many times to replicate my soldering on small bits of copper, I even got the copper so hot that it melted but I couldnt seem to get the same results as I did with the boiler, when I file the pitted solder it becomes nice shiny and smooth, dont know if that means anything?well there you have it..nice and shiney and smooth = you have it soldered nicely...the crap on top is just that....crap...thats why its on top.. oxidation and contaminates will rise to the top of a weld... and soldering is no diffrent than welding...it is "welding"......same thing but diffrent.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Originally Posted by zapsterI tried many times to replicate my soldering on small bits of copper, I even got the copper so hot that it melted but I couldnt seem to get the same results as I did with the boiler, when I file the pitted solder it becomes nice shiny and smooth, dont know if that means anything?well there you have it..nice and shiney and smooth = you have it soldered nicely...the crap on top is just that....crap...thats why its on top.. oxidation and contaminates will rise to the top of a weld... and soldering is no diffrent than welding...it is "welding"......same thing but diffrent.....zap!
Reply:I am wondering if your choice of "black flux" is correct for copper. You might try the Brazing book which is very helpful. http://www.handyharmancanada.com/The...Book/bbook.htm You joint looks like a belt and suspenders situation with rivets and silver brazing. The concept of silver brazing is that the alloy runs into a gap between the mating surfaces. The smaller the gap the stronger the joint generally. With the riveted sections there is a pretty good guarantee that the solder did not reach some areas. From my perspective the area of most concern would be around the rivets since the seal relies on the grabbing action of the rivets on the plate and the sides of the hole that the rivet goes through. A better joint design would have had a foil of silver solder set between the tube and the strap with flux applied before the rivets were installed. The folks at the Handy Harman site are very helpful if you drop them a line.
Reply:Another few cents worth.Porosity or bubbling of the silver solder indicates tht you have boiled off some of the components of the alloy by overheating - not a good thing. Quite frankly, I can't see enough detail in your photos to make a judgment of quality, but you say it is porous. Weakening of the alloy by overheating cannot be cured by polishing or filing. The alloy has been damaged. polishing it is only hiding the problem.How did you select your alloy? "Silver solder" covers a very wide range of alloys with a wide range of melting temperatures and gap-filling capabilities. The suggestion elsewhere to seek advice from the alloy manufacturers is very appropriate. You have three major considerations in your alloy selection: melting temperature, gap-filling, and capillary penetration. The latter two are not necessarily optimized in the same alloy. Advice from a pro or careful study of the numerous handbooks out there will be worthwhile.I would recommend NOT using an OA torch. It is much too hot for the task and a moment's inattention, too long a dwell at any location, or less than perfect torch control will easily boil your alloy. Using a torch that has plenty of heat output, but a temperature closer to that required to flow the alloy, like a MAPP torch, will help you avoid overheating the alloy or the copper. I'd be sure that your three propane burners are set up in such a manner that they cannot overheat the joint by themselves, no matter how long they heat it, then use a MAPP torch to get the joint up to flowing temperature locally and lead the flowing alloy along the length of the joint. It sounds like you have gotten appropriate preheating with your present propane burner setup.Your rivets may be weakening, rather than strengthening your joint by both causing stress concentrations around the rivet holes and by causing a non-uniform gap along the length of the joint. Each alloy has a specific range of gap thicknesses that it is optimum for and by squeezing the joint intimately together at the rivets and allowing it to bulge apart(?) between rivets, you may not be able to get optimum capillary penetration with any single alloy. You may also find that no alloy can penetrate into the tightly squeezed regions A properly silver soldered joint with adequate overlap has tremendous strength and I don't think your rivets are helping, except to hold things in place before soldering. Proper clamping and no rivets - not easy to do - would, I think, result in a stronger joint after proper soldering.Your rivets are along the outer edge of the strap. This results in having a fairly narrow soldered region between the rivets and the edge of the strap. I don't believe that the rivets provide anywhere near the strength of a properly silver soldered lap joint, so I would want to maximize the width of the undisturbed seam in from the edge of the strap by omitting the rivets.I'd also recommend getting advice from a pressure testing firm about test pressure. A steam boiler is much more dangerous than an air tank at the same pressure due to the energy it contains. I was advised by one testing firm to test a second-hand air tank at three times operating pressure. Ideally, you would also test at operating temperature - probably a practical impossibility, since you would lose all the safety aspects of hydrostatic testing by heating the water up to your operating temperature. If you look closely at some ASME pressure vessels, they give the operating pressure at a specific temperature, and it is lower at elevated temperature than at room temperature.Not trying to discourage you. Have fun.awright
Reply:I know, I know, why can't he stop rambling on? But I've got another question.Looking at your pictures, daz59, it's difficult to judge the thickness of your 1.5" strap but it doesn't look as thick as the tube wall. That strap is not just, as you say, "...running the length of the boiler for extra strength." That strap is ALL the strength of the boiler wall at the seam and it should be the same thickness as the tube to support the same hoop stress as the tube. You can't rely on getting much tensile strength out of the silver soldered butt joint of the tube walls in the absence of the strap, especially if the solder has been boiled.Stay safe.awright
Reply:Thanks for your repliesApparently the join is more than strong enough without the strap, boilers have been tested up to 600psi without the strap, the strap is only there for to provide extra strength for the novice brazer.I dont want to have to make another boiler, and I also dont want the thing to open up full of steam.Im not sure what to do about it now
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Reply:The strap and boiler are the same 3mm thick.
Reply:The solder I used was 35% silverloy, cadmium free.
Reply:after you get it done send it out for a pressure test..let them "blow it up" as to say..if it does come apart then everyone will be safe..it will be in a explosion proof container... better there than next to you... be safe!!...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:daz59, I was a little surprised at your statement (if I understood it correctly) that boilers have been made with silver soldered butt joints that pass 600 PSI hydro testing. A quick calculation of hoop stress at 600 PSI for a 7" boiler with 3 mm wall shows that the tensile stress on the joint would be 17,800 PSI. Superficially, for silver brazing alloys offering 35,000 PSI joint strength, that sounds OK, depending upon the quality of the soldered joint and the appropriate safety factor. I do not know the appropriate safety factor and I do not know if the 35,000 PSI cited is for shear stress or tensile stress. I, personally, would not feel good about a silver soldered butt joint on a homemade boiler. Are you sure they weren't talking about a scarf joint?In searching for the strength of silver brazed joints, I ran across an excellent source of information at:http://www.cupalloys.com/content.php?categoryId=100Much better information than I could find on the Harris site.A few random selections out of their very good discussion of joint strength:"Joints placed under pure tension should be avoided.""Too tight a joint fit, or the absence of a gap which might occur when a tube does not align itself properly through a plate will not have a consistent gap. There will be no flux, the alloy will not penetrate. The result is, at worst, a dry joint - at best a weak joint that could fail due to thermal stresses if reheated. ... If an assembly has to be clamped it should not be done so as to eliminate the joint gap. If there is not a gap, there can be no capillary flow and no joint." "Blow holes can result from overheating an alloy particularly one containing cadmium. Cadmium boils at 767 deg C, temperatures readily achieved locally, particularly if an oxy-acetylene torch is used."You obviously have the benefit of discussion with model makers who have done it before. A wondrful resource. I don't have that advantage, but want us all to be safe.Have fun.awrightOh, yeah. My 1943 copy of the ASME Boiler Construction Code, Section v., "Miniature Boilers," says that a FUSION WELDED boiler should be tested at 3 times maximum allowable working pressure. It also says that the joint should be hammered during the hydro test and specifies the size of the hammer and the manner of weilding it. Wow! Things have surely gotten much more sophisticated since then.Last edited by awright; 09-20-2006 at 02:15 PM.
Reply:Originally Posted by awrightOh, yeah. My 1943 copy of the ASME Boiler Construction Code, Section v., "Miniature Boilers," says that a FUSION WELDED boiler should be tested at 3 times maximum allowable working pressure. It also says that the joint should be hammered during the hydro test and specifies the size of the hammer and the manner of weilding it. Wow! Things have surely gotten much more sophisticated since then.
Reply:Awright, this butt soldering was only done as an experiment to see what it could handle, from what I have been told the sides of the boiler started to bulge out but the seam didnt come apart.The boilers are all designed with a factor of safety of 8 I think it would be quite safe standing next to a boiler under hydro test at 3x working pressure, if it does come apart there isnt going to be any rapid expansion, the water would just fall on the ground, or squirt you in the eye.I have talked to a few model makes, one who has made about 15 boilers, he said it would be fine (he didnt see it), but that still doesnt put my mind at ease when im sitting behind a boiler with 150 degrees celsius of steam at 100psi.The main thing I want to know is, if it does pass the hydro test at 2x working pressure is there any chance of the bad solder joint loosening up over time.
Reply:The main thing I want to know is, if it does pass the hydro test at 2x working pressure is there any chance of the bad solder joint loosening up over time.i would think it would be good for life...it must come with a certification tag after testing i would think... ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Awright, how do you work out the hoop stress? I was working it out all wrong, I thought you worked out the outside circumference of the boiler and times that by the pressure.I did a little test, butt soldered two bits of copper together and soldered another two bits with a bridge across them just like on my boiler, I heated them both up so the solder boiled way more than I did with the boiler, the copper was orange hot, I didnt clean the copper first, made the gaps big 30 thou, tried to do the worst of everything. I drilled a hole in each end of the bits of coper and chained them up to a hydraulic ram, the butt soldered one broke at the join, the bridge joined one broke the copper, the join is fine
see picture.Zapster, yes the boilers are stamped with a serial number and you have to re test every 3 years. Attached Images
Reply:Originally Posted by daz59Awright, how do you work out the hoop stress? I was working it out all wrong, I thought you worked out the outside circumference of the boiler and times that by the pressure.I did a little test, butt soldered two bits of copper together and soldered another two bits with a bridge across them just like on my boiler, I heated them both up so the solder boiled way more than I did with the boiler, the copper was orange hot, I didnt clean the copper first, made the gaps big 30 thou, tried to do the worst of everything. I drilled a hole in each end of the bits of coper and chained them up to a hydraulic ram, the butt soldered one broke at the join, the bridge joined one broke the copper, the join is fine
see picture.Zapster, yes the boilers are stamped with a serial number and you have to re test every 3 years.
Reply:daz59, hoop stress is one of the simpler stress calculations in Strength of Materials. If you think about what is happening and remember that it is very simple, you can think through the calculation without any references.You don't actually have to include a length of a segment of the tube you are analyzing, but considering a unit length of tube makes it easier to visualize. So let's think of a 1" long segment of a pressure vessel like your tube, and think of that ring being cut in half along a diameter, leaving two half-circles of tube wall 1" long.The effective area that the internal pressure in the tank is pushing against, trying to force the two halves of the tank apart is the internal DIAMETER of the tank times the unit length of the segment we are analyzing. For your tank, that is 7" x 1", or 7 square inches area (assuming the I.D. is 7").The force trying to push the two halves of the tank apart is the internal pressure times that area, 600 PSI x 7 square inches, or 4200 pounds force.The area of wall trying to resist that 4200 pound force is the thickness of the wall times 1" length of segment times two (one on each side of the tank), or 3mm./(25.4 mm./inch) x 1 inch x 2 = 0.236 square inches of metal resisting the force.The hoop stress, that is, the tensile stress in the wall due ONLY to the internal pressure, is 4200PSI/0.236square inches = 17,796.6 PSI.If you work through the calculation, you see that the length of the segment you are analyzing cancels out, so you don't really have to consider the length of the inaginary segment.Back to our discussion of safety:I'm not at all surprised at the results of your experiment. I'm certainly not trying to scare you or saying I expect your tank to blow. But I wouldn't bet my life or that of my grandchildren on the quality of the tank joint you described. Go back to the discussion I linked to and reread the discussion of a starved joint due to leaving insufficient gap for the alloy to penetrate into by capillary action.How about another experiment? Make up a joint between two coupons about 4" by 1", riveted at one end just as tightly as the rivets in your tank. Solder it up just as you did on the tank, but solder it only for an inch at the end around the rivet. Drill out the rivet and peel the joint apart (it won't be easy). See if you got penetration of alloy over 100 % of the area of the joint, especially right around the rivet. (This is a different use of the term, "penetration," than we usually use in welding.) Also, see if you find any bubbles or voids in the joint. I'm not saying you will see anything wrong, but I am saying that the riveted, then soldered joint creates the POSSIBILITY and increases the probability that voids could occur.I see that you are still thinking in terms of hydrotesting at 2 times operating pressure, rather than 3x or at 600 PSI.I agree with you about the relative safety of hydrotesting even while hammering on the joint (I'm not saying that hammering is advisable or a current requirement - it was just interesting, historically) except that water spurting out of a pinhole leak at 600 PSI could be dangerous to the eyes and might even penetrate flesh that is close by. Penetration of non-sterile water into the body is very dangerous.awrightLast edited by awright; 09-21-2006 at 03:50 AM.got any other pics of the boiler assy... Im afraid I can't contribute to the conversation, but.. Im interested in building my own boiler for heating. Granted not as high a pressure ( maybe 2 or 3 lb at most ) but i'd like to see the rest of the design. I can give my email address instead of cluttering up the thread.ThanksRobert
Reply:awright, I don’t think it would be possible to peel apart that sort of join, maybe grind the top layer of copper off?You dont think my boiler would be safe to use? Solder did come out all but one of the rivets, I think that’s a good sign the solder made its way through most of the join?Just a bit of quick calculation if my join was 100% sound then it would need 22,000 pounds of pull per inch wide of the strap to break the solder, the copper has a 25,000psi tensile strengh so at 3mm by 1 inch wide would take 2900 pounds to break the copper.So the join is 7.5 times strong than the copper, I would only need about 13%+- of the strap covered in solder to gain the same strength as the copper.Now the copper tensile strength will take 1000psi in the boiler before it starts to failAnd 7500psi in the boiler for the join to fail (assuming its 100% sound)So the copper has a factor of safety of 10x and the join 75x so I only need about 1.3% of the join covered in solder to handle 100psi in the boiler.I think it would nearly be imposable to stuff up the join so bad that it opens up with 100psi.??I am working on silver solder tensile strength of 40,000psi and shear of 20,000psi (figures I found online)Last edited by daz59; 09-21-2006 at 06:07 AM.
Reply:Originally Posted by slamdvwgot any other pics of the boiler assy... Im afraid I can't contribute to the conversation, but.. Im interested in building my own boiler for heating. Granted not as high a pressure ( maybe 2 or 3 lb at most ) but i'd like to see the rest of the design. I can give my email address instead of cluttering up the thread.ThanksRobert
Reply:The Scotch Boiler that I cut apart and scrapped out of my small apartment building operated at 3 PSI, but once went up to 15 PSI when the draft door came loose and fell against the gas valve arm, preventing it from turning the fire off. The walls of that 30" diameter fire-tube boiler were about 1/4" thick steel, as I recall.No, daz59, I am definitely NOT expressing the opinion that your boiler is unsafe. What I AM saying is that, when messing around with a potential bomb that you and guests will be sitting behind, you want all the factors affecting safety on your side and you want to have good quality control. That is, you want to KNOW that your silver solder job is good and that you did everything properly to assure that the joint was good. This is what I have been questioning because I don't think everything in the joint design and soldering were in your favor. If it was my boiler, I would test it at at least 3 times working pressure. But, as I have revealed elsewhere in this forum, I favor overkill.I'm not sure I understand or agree with your calculation of force required for a peel test. Where did the 22,000 pounds figure come from? Perhaps you are thinking of shear strength over 1 square inch of soldered joint? That's not how a peel test operates. All the force of a peel test is concentrated over the very small effective area of the bond line at the point of peeling. That area is the width of the coupons times the depth of the solder that is yielding and contributing to resisting the pull - perhaps a few thousandths of an inch, depending upon solder thickness and alloy properties such as ductility.It sounds like you are thinking of a test comparable to the lap joint test you showed in your 6:59 AM post. That is a shear strength test (if done with proper joint size). For a peel test, the two coupons are directly on top of each other, but only a region at the far end of the coupons is soldered. After soldering, you grip the two coupons at the unsoldered ends and peel them apart, like opening a magazine. This concentrates all the force on the almost 1-dimensional line of solder where the peeling is taking place. In a formal peel strength test you wrap the coupons around mandrels of a specific diameter as you peel. That helps prevent tearing of the coupons due to bending at the peel line.You want to avoid creating a fillet at the boundary between the soldered and unsoldered portions of the coupons, because a fillet would make it much more difficult to get the peel started. Not easy to accomplish while still feeding sufficient solder into the desired bonded area. Offhand, I can't think of a heat resistant material only a mil or two thick that could be used to stop the solder from bonding the region you want to remain unbonded. Maybe some spatter-shield or high-temperature anti-seize compound would prevent bonding where it is undesired. Don't forget our goal, or at least, my goal. It is not to measure peel strength, but to get a peek at the solder coverage and wetting action inside the joint at the rivet. The fact that you saw solder appear at all but one of the rivets on your boiler is a very good indication that you got penetration and wetting by the solder.Please be more cautious about your estimates of the quality of joint required for a safe boiler. There are assumptions embedded in your calculations of required soldered area that are not valid. One is to assume that the force trying to burst the seam is distributed uniformly to all the successfully soldered areas. This ignores issues of stress concentration, abrupt transitions in thickness, effective region of the soldered area that contributes to strength, etc. Here, again, I am NOT trying to scare you - just to make you aware of some of the important issues. And never, ever forget that I have never built a boiler, have never talked to a steam modeler, and have no expertise whatsoever beyond that of an opinionated, interested hobbiest who likes to play with hot metal and sit endlessly at a computer keyboard.awrightLast edited by awright; 09-21-2006 at 02:30 PM.
Reply:Awright, sorry I was talking about pulling the join in my boiler apart not the peel test.The strap on my boiler over hangs the seam by .8 of an inch each side so that gives us .8 of a square inch, 20,000psi being the shear of silver steel x by .8 is 16,000 pounds per inch wide of the strap + the butt soldered join, 40,000psi being the tensile of silver steel, 3mm by 1 inch is 0.12 of a square inch, that gives us about 4800 pounds per inch wide of the join so total is 20,800 pounds per inch of the join (not sure how I got 22,000 last time)Going by your hoop stress calculation 17,800psi tensile with 600psi in the boiler divide by 6 since im only running 100psi =2966psi now times that by 0.12 since 3mm x 1 inch is only 0.12 of a square inch = 356 pounds per inch wide of the join.356 pounds per inch wide of the join is not very much when you think about it, especially when considering the join will take 20.800 pounds to pull it apart (assuming its 100% sound)There is a lot of tolerance to allow for imperfections and extra stresses as you pointed Going back to the safety, you would feel safe sitting behind my train if the boiler was tested to 300psi? what about the test I did yesterday, didn’t that point out the the join is much stronger than the copper?Last edited by daz59; 09-21-2006 at 06:10 PM.
Reply:It seems to me that if you have solder in that large lapping joint and it is riveted according to plan then you should have good luck passing your hydro test. After all that is all you really need to do. The objective is to have a serviceable boiler. It does not have to be perfect. It just has to be serviceable. As a side note to reassure you: A "perfect" silver solder joint can exceed 100,000 psi strength, way beyond the strength of the metal joined. In welding school we did an exercise with regular easy flo 45. We filed the ends of two half inch square steel bars. They were fluxed then silver soldered end to end. When cool we put one end of the bar in a vise standing up with the joint about an inch above the jaw. A crescent wrench was put on the bar above the joint and the bar was twisted. You had to at least get a ninety degree turn to pass. The stuff is amazingly strong when properly applied.
Reply:Is this silver solder or a braze? I'm pretty sure the 45% stuff is a braze alloy.
Reply:Originally Posted by 76GMC1500Is this silver solder or a braze? I'm pretty sure the 45% stuff is a braze alloy.
Reply:Originally Posted by awrightThe Scotch Boiler that I cut apart and scrapped out of my small apartment building operated at 3 PSI, but once went up to 15 PSI when the draft door came loose and fell against the gas valve arm, preventing it from turning the fire off. The walls of that 30" diameter fire-tube boiler were about 1/4" thick steel, as I recall.awright
Reply:daz59: yes, pics would be awesome. hell, even before and after would be great. What book? What I'm planning on heating is my house and (in the future) a small garage. I'm in the middle of experimenting with oil burners (can get all the free used oil I want from several restruants around town.) Im guessing about 150k btu or better. I just chose 3psi as a random number, being pretty safe about it. My apologies for hyjackin the thread.
Reply:daz59, if by safety valve you mean a pressure relief valve, sure. It was set at 15 PSI, which I believe is pretty standard for low pressure heating boilers. It was venting continuously. Firing would have continued until the water in the boiler was lost, then the boiler would have been burned out. Fortunately, one of my tenants was an engineer, had the combination to the boiler room, recognized what was going on and corrected it with no damage done. All the safety devices were functional and had always been tested each time I entered the boiler room (several times a week), but when the draft door dropped down on top of the draft door operating lever on the gas valve the valve could not shut off, even though it had the correct electrical command.Fortunately, that boiler is history now courtesy of a OA cutting torch and I have a brand new Peerless cast iron boiler that has the same BTU rating and much greater efficiency in about 1/3 the volume and has all the latest safety devices. The gas valve has no external operating lever that can be jammed.Regarding the discussion of brazing vs. silver soldering: The following is from the introduction to Handy and Harman's very interesting, "The Brazing Book Online," (http://www.handyharmancanada.com/The...ook/bbook.htm). They ought to know, since they make a lot of the filler metals."Brazing is the joining of metals through the use of heat and a filler metal – one whose melting temperature is above 840°F(450°C) but below the melting point of the metals being joined. (A more exact name for the brazing process discussed in this book may be "silver brazing," since in most cases the filler metal used is a silver alloy. To remain brief, we'll use the term "brazing" throughout this book, with the understanding that we are referring to a torch brazing process with a silver-bearing filler metal." I don't think temperature is a useful distinguisher of "brazing" vs. "silver soldering," as both are applicable over similar temperature ranges. One descriptor that makes some sense to me is that "silver soldering" and "brazing" both involve capillary flow of filler metal, whereas "braze welding" does not. However, I'm not really sure that it is important to make any distinction between the processes unless you want to distinguish filler metals with silver from those without.Back to the discussion of joint strength, daz59 said, "The strap on my boiler over hangs the seam by .8 of an inch each side so that gives us .8 of a square inch, 20,000psi being the shear of silver steel x by .8 is 16,000 pounds per inch wide of the strap".This is an example of why intuition is not a good basis for design of boilers. If you refer back to the cupalloy literature in one of my older posts (http://www.cupalloys.com/content.php?categoryId=100), you will find the statement; "Another feature of joint strength in a brazed joint is the joint length or degree of overlap. Results show that increasing joint length do not produce greater joint strengths, more the opposite. The longer the joint gap increases the possibility of producing voids. Shear stresses (and hence strain) are highest at the edges of the joint. If the length of the joint increases beyond a figure dependent on material selection, there is filler metal within the joint that carries no stress. Its presence therefore serves no purpose and contributes nothing to joint strength.Generally speaking the highest joint strength is attained with a joint length 3x the thickness of the parent materials and the smallest gap possible commensurate with achieving good joint soundness." If we accept this rule of thumb, with 3 mm. walls the effective portion of the joint is 3(3mm./25.4mm./in.) = 0.35 inches back from the fillet at the edge of the strap. For 20,000 PSI shear strength alloy, this would give you a strength of 7000 pounds per inch of joint length. Plenty of strength, but not 16,000 pounds per inch or 20,800 pounds per inch. Since essentially all the strength you are going to get occurs in the first 0.35 inches, no additional strength can be attirbuted to the butt joint under the middle of the strap or the extra width of the strap. You still want a tight butt joint, however, to avoid corrosion in the joint.Actually, the greatest joint integrity would be attained with a strap that was a total of about 0.8" wide that had been tapered down to a fine edge over the outer 0.35 inches so you end up with a gradual transition from the tube wall to the double thickness at the middle of the strap. This avoids the stress concentration at the abrupt change in thickness thereby allowing the full 0.3inch width of the tapered edge to contribute equally to overall joint strength. Such a strap would also facilitate getting the best wetting and penetration of filler metal in the joint. And no rivets.Yes, I would definitely feel safer behind a boiler tested at 300 PSI, rather than 200 PSI, and no, I don't think the tests you performed prove anything particularly related to the safety of your boiler. Interesting, though.awrightLast edited by awright; 09-22-2006 at 04:21 AM.
Reply:Generally speaking the highest joint strength is attained with a joint length 3x the thickness of the parent materials and the smallest gap possible commensurate with achieving good joint soundness."Yeah I did read that, I went a little over board, the plans had it at 30mm wide I did it to 42mm wide.and no, I don't think the tests you performed prove anything particularly related to the safety of your boilerWhy not? The test pointed out that the crappiest of crappy solder joints is strong then the copper (well in my situation anyway).If we accept this rule of thumb, with 3 mm. walls the effective portion of the joint is 3(3mm./25.4mm./in.) = 0.35 inches back from the fillet at the edge of the strap. For 20,000 PSI shear strength alloy, this would give you a strength of 7000 pounds per inch of joint length. Plenty of strength, but not 16,000 pounds per inch or 20,800 pounds per inch. Since essentially all the strength you are going to get occurs in the first 0.35 inches, no additional strength can be attributed to the butt joint under the middle of the strap or the extra width of the strap. You still want a tight butt joint, however, to avoid corrosion in the joint.why can no additional strength be attributed to the butt joint? If that was the case then I could leave the butt joint empty with no solder and it would be just as strong as it would with solder..?Ok even if it does come down to 7000 pounds per inch of joint its still much higher than the strength of the copper which is 3000 pounds per inch wide.
Reply:Just thought I would give you guys an update on the boiler, Its about 2/3 done now, has been seen by 4 boiler inspectors, they are all very happy with the solder quality and workmanship.Here are a couple of pictures. Attached Images
Reply:That looks cool. what you going to fire it with? keep it up!!
Reply:that is way coolChuckASME Pressure Vessel welder
Reply:Originally Posted by slamdvwThat looks cool. what you going to fire it with? keep it up!!
Reply:There are few things the folks at the welding store may not have mentioned. First, the language here is pretty imprecise. What you did is commonly called silver soldering but it is actually brazing because of the temperatures. Soldering is low temp and brazing is high temp. What you call a silver solder is also called a braze filler metal. The big thing that bothers me is that he didnt tell you how to prepare the surface or test for cleanliness and he didnt tell you how to analyze the finished joint for quality. If it is a Silvaloy 35 without cadmium then it is a Bag-35 braze alloy and called Silvaloy A-35. (http://www.bellmanmelcor.com/silvaloy_A-35.htm)It is technically a braze filler metal and as such is good at filling gaps. http://www.brazealloy.com/choose.htmHowever this means that it will not flow all that well into very tight spaces. For flow into very tight spaces I would recommend something with Nickel in it. Even without the Cadmium you still have Zinc which has similar properties when it comes to pitting. Both Cadmium and Zinc have low melting points and both fume as they approach the melting points. (It may also be that the fuming starts at the melting point there are various opinions in the literature.) The zinc can fume out and cause the pitting.Black flux is good. Black flux is white flux with extra elemental Boron added. In theory it operates longer at higher temperatures (or a combination thereof) than white flux. In practice we have seen much better results with Black flux over White flux than the chemistry predicts. In the picture join the bubbles are possible an indication of overheating and the Zinc coming out.What concerns me a great deal more is that the edge of the braze alloy is very steep. A steep wetting angle such as this is highly indicative of an improperly prepared surface and consequently weak bonding. (http://cs4u.org/newsletters/2006/20063March.pdf - see the article on cleaning saw steel for brazing) I think I would take a thin wire of the braze alloy, dip it in flux, flux both sides of the joint and the lay the wire on the gap and heat it. Tom
Reply:Thanks for the info. Hardmetalbrazer. Good stuff, especially the news letter and demo. on cleaning.
Reply:Just a quick update,past the hydro test 240psi for 30min.engine has been up in steam and running for over 10 hours now, not finished yet but its running. Attached Images
Reply:That looks like fun..How long is the track?You have way too much time on your hands.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:That track is onle 1/4 mile long, some of them get up to 2 miles long. |
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发表于 2021-9-1 00:11:58