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john robert bould said:
How many cast iron parts have you repaired, and whats the best way to test the finished job?
71 Brake Drum to Cush Hub- Pin Fix
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How many cast iron parts have you repaired, and whats the best way to test the finished job?
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JimC said:
If a microfusion repair process is used, then the amount of heat required does not result in carbon migration into the HAZ, so there is no need whatsoever to pre-heat or post cool the part to be repaired!
Parts such as a brake/drum sprocket in cast iron or steel are easily repaired, and using the correct grade of powder its quite possible to rebuild sprocket teeth if OE part is worn and replacement not available.
In terms of the success of this type of repair, powder type microfusion process is often used to rebuild cast iron locomotive and rolling stock wheels, and if there were any need to pre-heat-post cool using a furnace, then obviously repair would not be economically viable.
Carbonfibre said:
What planet are you on ?
Although we diverge here, train wheels have been STEEL for a very long time. And a user of the highest quality of metal avaulable at the time, the forefront of technollogy.
These (wheels) would have been the major impetus for metallurgical developments for much of the early part of the 'industrial revolution' - wheels exploding was a constant hazard for early train travel. Solving that, and better rail quality was a large part of the story of developing the railways. Along with bridge building....
Cheers.
http://en.wikipedia.org/wiki/Railway_tires
http://www.trackmobile.com/ourtechnology.htm
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Rohan said:
Train wheels are Carbon manganese steel,as are the lines..made some wonderfull chisels from it.
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As stated only barrel fins, and some early triumph head fins, welding cast requires some special skills if the part is to be a high stress repair, i have never tested a repair. as this would result it a secondary fracture, Regarding this original post, repairing a broken drive "blade" IF THE ORIGINAL HOT RIVET METHOD FAILED ,then a electic weld will not be as strong ,,,if a ships rivet was removed and a weld in the hole was made..well that would be no where near as strong ...agree :?:Carbonfibre said:
Just for the record. i have been a fitter /fabricator for 20 years, and some brick transfer cars i have made carry aprox 60Tons..all welded with stick. inc vertical 1/4 OHV using 200 amps .
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Rohan, on the Titanic I the meant issues discussed were specific to the plates' carbon grade and manufacture and method of weld, not the universal issue of iron/steel brittleness with increasing cold. Do we know it drum is cast iron or cast steel yet? So T95, what's ya gonna do when they come for you?
http://www.muggyweld.com/?view=castiron
http://www.muggyweld.com/?view=castiron
The spare drum I have for an 850, original to the 1970s, is quite clearly steel.
I would have no hesitation in electric welding this - be it Mig, Tig or stick.
Welded steel is near bulletproof, you can't go wrong.
And if you don't like how its going, just grind it off and go again.
I would have no hesitation in electric welding this - be it Mig, Tig or stick.
Welded steel is near bulletproof, you can't go wrong.
And if you don't like how its going, just grind it off and go again.
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john robert bould said:
How do you find powder welding or TIG brazing works on cast iron repairs?
T95 said:
There is a pretty good chance a lot of welders do not understand the science behind it but then again it doesnt really matter to them either as long as they are good at doing what they do. That said i find it interesting.....
When heating steel or cast iron to welding temperature there is a significant volume change at around 727 degC due to the change form BCC (ferritic) to FCC (austenitic) crystal structure, the best way to visualise these is to search for some pictures on the net but basically it is how the iron atoms (nothing to do with carbon yet) are arranged in a unit cell (cube). So before we consider the changes in microstructure we already have a large volume change, now because this is somewhat localised (due to the heat input from welding) it will introduce stress into the structure as the volume change is not consistent throughout.
Now if we consider the microstructural changes, cast iron has a high carbon content and can have pre-existing cracks (on a microscopic level as carbon flakes in the matrix... depending on the grade). The high carbon is significant in that it allows the formation of some very hard and brittle phases, martensite and cementite, the formation of these phases is dependent on the ability of the carbon atoms to diffuse (or not as the case may be) through the iron matrix (the carbon atoms are smaller and fit in the spaces between the iron atoms causing distortion of the unit cube FCC and BCC units also have different solubility limits of carbon). Because this is a diffusion process it is dictated by temperature. In the case of welding, or any heat treatment for that matter the rate of cooling becomes very important (google TTT diagrams), with any significant carbon content the metal can be cooled fast enough to form martensite. Now in the case of welding the cooling rate of the weld and the metal in the immediate vicinity can be (is) much higher than expected because you essentially have a very large heat sink and a relatively low temperature so you can easily cool at a fast enough rate to form martensite, this is commonly referred to the heat affected zone (in addition to the change to martensite there will also be grain growth here which is also not really a good thing).
This is where preheating comes into it, now specifically for welding the preheat may help remove some surface contaminants depending on how it is done, however the two main reasons are related to the points above. If we deal with the large localised volume change first, the change from FCC to BCC is not gradual so we cant reduce any of the stress associated with this volume change by by slowing it, what does happen though is that at the higher temperature (after preheating and welding) the yield strength of the material is reduced and the ductility is increased, this will allow some localised plastic deformation which has the effect of stress reliving the part without causing cracking.
Now by preheating the part we have also removed the large heat sink that is attached to the weld, well we havent removed it but made it significantly smaller, this reduces the cooling rate of the weld and surrounding material so we do not form the very hard and brittle phases. This is why I said preheating wasnt so much preheat but to control the cooling rate... which it is.
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The way very large cast iron parts are repaired, involves building a furnace type enclosure round the item to be repaired using fire bricks, and then introducing heat via multiple gas flames, which are often left burning overnight so the required temperatures are reached. When the part to be repaired is to the right temperature, it will be gas welded using cast iron rods. Things as large as ships engine blocks are often repaired in this way, and while the process is obviously very costly, its nowhere near as expensive as a new casting.
For small bike parts, one of the microfusion processes is much easier than heating the part to be repaired to cherry red heat, gas welding, and then carefully and slowly letting the repaired part cool down. In most cases anything cast thats been machined, will need to be re-machined after its been heated to cherry red, and without proper pre-heat and post cooling, failure of MMA or gas welded cast parts is very likely, as carbon tends to migrate into the HAZ adjacent to the weld, and will make this area very weak.
For small bike parts, one of the microfusion processes is much easier than heating the part to be repaired to cherry red heat, gas welding, and then carefully and slowly letting the repaired part cool down. In most cases anything cast thats been machined, will need to be re-machined after its been heated to cherry red, and without proper pre-heat and post cooling, failure of MMA or gas welded cast parts is very likely, as carbon tends to migrate into the HAZ adjacent to the weld, and will make this area very weak.
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Mr Cardonfibre,
Back to the original post. As the paddle is loose, and at worst the riveted flange as broken...would you advise a weld repair, bearing in mind these are available new, and if the repair was to give way it could cause an a crash, just a yes or no please :?: Repair, we all know some would,,but would you for someone else :?:
Back to the original post. As the paddle is loose, and at worst the riveted flange as broken...would you advise a weld repair, bearing in mind these are available new, and if the repair was to give way it could cause an a crash, just a yes or no please :?: Repair, we all know some would,,but would you for someone else :?:
Guido
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A new drum from Burton Bike parts is $83 US or 48 pounds Sterling.
I do find all this welding talk amusing but comparing a repair to just buying a new part is like comparing apples to lemons.
A failure of a repaired part would suck, waiting for the part to be repaired would suck, worrying if the part might fail while riding would suck, having a brand new part,,,,pricless.
But please,,, more welding talk. :roll:
I do find all this welding talk amusing but comparing a repair to just buying a new part is like comparing apples to lemons.
A failure of a repaired part would suck, waiting for the part to be repaired would suck, worrying if the part might fail while riding would suck, having a brand new part,,,,pricless.
But please,,, more welding talk. :roll:
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Guido said:
That might be a repro part of unknown quality. The factory part is only £67 which is a great deal.
Lets not forget that at some points in time some factory drums had welded in pins in them...
And in the good old days, when money was short and the factory was far distant, it was extremely common to machine off worn teeth and weld a new set there.
You still see this on surviving factory specials and race bikes.
This expertise has been around for a very long time.
P.S. And maybe you should examine that new spare on the shelf carefully, for who knows how it may have been made ??
And in the good old days, when money was short and the factory was far distant, it was extremely common to machine off worn teeth and weld a new set there.
You still see this on surviving factory specials and race bikes.
This expertise has been around for a very long time.
P.S. And maybe you should examine that new spare on the shelf carefully, for who knows how it may have been made ??
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john robert bould said:
It would obviously be ridiculous to carry out a repair if a new part is easily and cheaply available, and in the case of a repair to cast iron I wouldnt think a weld repair was the best possible method in any case, unless the repairer had a furnace and was able to properly pre-heat and post cool the part being repaired.
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