# Fix for porosity in brass ?



## woffler (Dec 10, 2021)

I everyone hope you are doing well i, i am having a issue with a casting i purchased some time ago and the issue is porosity in the flywheel as you can see in the picture .
 Just thought i would see if anyone had any better ideas than trying to braze it .


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## Brian Rupnow (Dec 10, 2021)

I don't think there is any good fix for that. If you can't have the casting replaced by the vendor, you will be stuck with filling the holes with J.B. Weld or auto bodyfiller, sanding, and then painting.


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## woffler (Dec 10, 2021)

That's what i was afraid of , i thought about trying to drill and braze it but i think i would wind up with a bigger mess than i have already .
 I believe i will hunt around for a replacement of cast iron and see what i can find, it's kind of a odd ball size 4.1875 finish dia. and 9/16 width rim.
It goes to a Crater popcorn engine model i bought some time ago,thanks for getting back to me i appreciate it  And Merry Christmas .


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## Sprocket (Dec 10, 2021)

Could probably get this one down to size
//www.martinmodel.com/collections/fly-wheels/products/4-6-spoke-curved 
But it might be worth trying to braze that one and see what happens.
Doug


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## woffler (Dec 10, 2021)

Thanks, i believe that will work have not run across this sight before , i will place a order .


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## Jasonb (Dec 11, 2021)

You could always turn the rim away and then fit the spoked area into a ring turned from a slice of brass or iron, if it was not for a popcorn engine which is usually blinged up filling and painting the rim would be the other option as it is not used to drive a belt.


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## GreenTwin (Dec 11, 2021)

The problem with Cretors castings is that they were nickel plated, and the plating tends to peel off after a long period of time.
If it were just a raw unplated iron casting, it may be possible to flux it, heat it, and apply lead-free (or leaded if you perfer that) solder, which could then be machine or buffed off for a clean surface.

The nickel plating would probably create problems if you tried to fill it with solder.
The old car bodies were filled with soft solder back in the day, and there was an art to that.
I have not tried this method, but I think it could work with a clean fluxed casting.

Edit:
Note that original Cretors castings are worth a significant amount of money, even with the defects shown above, so I would hang onto that flywheel, or sell it.
.


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## Steamchick (Dec 11, 2021)

Large holes can be drilled, tapped and filed with a brass screw and machined off. Odd tiny holes can be filled with silver solder (cooler than brass brazing) and often colour when pickling, or touch-up paint, after machining smooth. But I live with out of balance flywheels by using  them to smooth the running of engines by ensuring the more massive side is opposite the crank.Makes a big difference to how slow an engine can idle... and at minimum air pressure at shows I have had small singles doing 40rpm... Very watchable! - when we'll balanced.
K2


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## rutzen (Dec 11, 2021)

Hi, I've made some castings in brass and they had porosity problems, I've learned since that the solution is to add some phosphorus in the form of a stick of copper/phosphorous brazing rod which is commonly used in brazing joints in refrigeration applications.  This stuff is cheap and I've got some but haven't tried it yet. It happens with bronze castings as well, I read in an old Model engineer magazine from the 1940's that porosity used to be considered inevitable in non - ferrous castings.


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## SmithDoor (Dec 11, 2021)

It can be brazed
You would see a different color were you brazed the casting. 
But biggest downside it is a flywheel and flying apart. 

Dave 



woffler said:


> I everyone hope you are doing well i, i am having a issue with a casting i purchased some time ago and the issue is porosity in the flywheel as you can see in the picture .
> Just thought i would see if anyone had any better ideas than trying to braze it .


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## GreenTwin (Dec 11, 2021)

rutzen said:


> Hi, I've made some castings in brass and they had porosity problems, I've learned since that the solution is to add some phosphorus in the form of a stick of copper/phosphorous brazing rod which is commonly used in brazing joints in refrigeration applications.  This stuff is cheap and I've got some but haven't tried it yet. It happens with bronze castings as well, I read in an old Model engineer magazine from the 1940's that porosity used to be considered inevitable in non - ferrous castings.


I have read a lot about how to make quality castings that don't have any significant defects, and so far I am having good luck with iron castings that do not have porosity or other defects.
I did get some defects in the first cast iron flywheel that I cast due to using the wrong sand type (Petrobond), and some of the sand erroded at iron temperatures.  I was able to salvage the flywheel luckily, but I changed to resin-bound sand after that, and have not had any more casting defects.

I believe most casting defects are cause by excessive velocity in the molten metal stream that is flowing into the mold cavity.
The excessive velocity often damages the sand mold, and it also creates turbulence in the metal, with entrains air and slag into the casting.
If you control metal velocity, and avoid metal turbulence by using the correct sprue/runner/gate arrangement, you can consistently make iron or other castings without defects.

With a slight amount of ferrosilicon, the iron is very machinable too.
Phosphorus is said to be the bane of iron castings, and while it can give extreme fluidity to an iron melt, it also supposedly gives the iron some very poor qualities that you generally want to avoid in engine castings.

For aluminum castings, one of the secrets to avoid porisity is to melt the metal as quickly as possible, and don't heat it above pour temperature, and pour immediately.
Once you get aluminum above pour temperature, it becomes like a giant sponge, and your castings will be filled with porosity due to hydrogen absorption.
For super critical aluminum castings, you can use a degasser like nitrogen or some other inert gas, but you can get good aluminum castings without porosity just by not overheating the melt.

.


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## abby (Dec 11, 2021)

Brass does not suffer with hydrogen absorption problems, the vapour pressure of zinc prevents gas absorption.
The porosity is caused by incorrect  feeding , in the case of brass casting keep the feeder liquid for as long as possible by agitating with a piece of brass rod , this should keep the shrinkage and porosity as low as possible.
I find zinc oxide entrainment the biggest problem , in investment moulds any carried over oxide will finish up in a casting .
I use a flux made from potash , borax and salt helps to refine the grain size and clean any crap from the melt , a little dry sand added to the crucible just before pouring will thicken the flux allowing it to be scraped off easily.
Dan.


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## woffler (Dec 11, 2021)

Thanks everyone for all the posts you gave me some great ideas on how to save the flywheel ,i especially liked the idea of turning down the rim and fitting a brass ring to the spokes here is a little picture of another mo


del i just finished .


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## woffler (Dec 11, 2021)

Sorry about the last post i just realized that picture came thru full size ,i ordered a cast iron flywheel but i am definitely going to turn the brass one down and fit a brass tire on it, that is as soon as i can find some brass that size for less than a hundred dollars ,man have prices shot up on metal!


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## Steamchick (Dec 11, 2021)

If you want to Burst test the flywheel for a proof of strength, Tthen determine the maximum overspeed of the engine, multiply by 5/2 to get the minimum burst speed, and then mount the flywheel on a sturdy mandrel that can be driven (electric motor? Lathe?) to 2 1/2 times the revs of the max the engine will attain. Actual;ly, if you go up in increments of (say) 500 rpm from (say) 4000 rpm (max overspeed of the engine??) to 10,000 rpm, measuring 2 dims at 90 degrees across the OD with a micrometer, ata the speed you get some "set" (distortion = difference in the micrometer readings) then the part has "failed". If no distortion (remained elastic) by the 2 1/2 times Max engine speed then you will not be bursting the flywheel in use. That's effectively the standard for routine (100%) proof testing of car engine flywheels. (6200 rpm red line of the engine became 1600rpm for the proof test...). (OK, a car engine can rev higher than 6200rpm red line if you are locked in full throttle and a mid-gear and going down a 1:6 gradient..!!! - but not achieve 16000rpm. The engine might go bang first! - or clutch slip, tyre slip, etc. ANd racers tune engines from 6200 to 8500 rpm, etc.... without checking if the flywheel will burst!).
K2


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## Steamchick (Dec 11, 2021)

Instead of a brass rim, you could bend a square mild-steel bar into a circle, weld it, then machine the tyre and shrink fit it like full size railway tyres or wagon wheel iron rims are fitted... 
K2


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## Steamchick (Dec 11, 2021)

Has anyone cast Mazac flywheels? It is cheap from scrap yards where they extract all the oddly shaped cast armatures from inside wing mirrors, etc...
K2


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## GreenTwin (Dec 11, 2021)

I have not heard of "Mazac".
I have tried Zamac27, and have seen others try it for flywheels (myfordboy I think).

Zamak comes in different grades and is very strong, and also much more dense than aluminum.


			Alloys - Zinc Die Casting
		


Zamak got a bad name when some poor alloys of it were used that crumbled over time.

Zamak is said to be much easier to melt and cast then aluminum, given it has a lower melting point, but I could not tell the difference between melting aluminum 356 and Zamak27.

The problem I had with Zamak27 is much the same that I had with untempered aluminum, but much worse, which was when I tried to drill it, it melted at the front of the drill bit.
Zamak won't withstand any significant heat elevation on cast parts either, unlike aluminum 356.

Some have said that coolant has to be used to drill Zamak, and have said coolant helps with aluminum.

I solved the problem by just casting things using gray iron.
I can drill and machine gray iron with no coolant and no cutting oils, and it drills, taps and machines like a dream.

.


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## ChazzC (Dec 12, 2021)

GreenTwin said:


> The problem with Cretors castings is that they were nickel plated, and the plating tends to peel off after a long period of time.
> If it were just a raw unplated iron casting, it may be possible to flux it, heat it, and apply lead-free (or leaded if you perfer that) solder, which could then be machine or buffed off for a clean surface.
> 
> The nickel plating would probably create problems if you tried to fill it with solder.
> ...



Before Fibgerglass/Acrylic Resin can into use, high lead content (70% lean/30% tin vs. 60%–70% tin/40%–30% lead that was used for plumbing & electronics [with different fluxes]) was used as body filler and routinely used during construction of new vehicles to level seams. Lead is still used today on accurate restorations of antique cars.


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## Ken I (Dec 13, 2021)

This is not the same thing but these flywheel spokes are soft soldered in :-




The one on the left was polished (but not lacquered) 2 years ago and has aged - but initially the solder annulus was all but invisible in spite of its colour - the finish has since aged and the spoke and solder have aged different to the rim.
The one on the right was polished and lacquered about a year ago.
So you could pickle and soft solder or silver (hard) solder which would give an even better colour match.
Personally I'd silver solder it - not braze (beware - English terminology).
Whatever - it would look better than the porosity.
Regards, Ken


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## Jasonb (Dec 13, 2021)

Slice of steel or CI bar will be cheaper than brass. 

Can you get hollow cast bearing bronze over there in short lengths, you can buy it by the inch (25mm) here, that way you are not paying for the material in the middle


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## woffler (Dec 13, 2021)

Thanks Ken ,i am looking at possibilities i intend to try a few experiments on some brass and see what i get , Happy Holidays to all and i hope and i mean really hope for a better new year because the last couple have been not so good !


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## Ken I (Dec 14, 2021)

Postscript - I would pickle the flywheel before soldering as the porosity is almost certainly badly oxidised.
Regards, Ken


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## woffler (Dec 14, 2021)

I got some A2 tool steel in a round 4.25 diameter and 4 inches in length for about $60.00 plus shipping best i could find at the time . 
 Turned down the flywheel and left .1875 it just cleaned up at that, and the porosity came all the way across to within a 1/8th of the other side. 

I have gotten some let' say less than favorable castings before but at least we can do a work around on this one, and still use it but i hate having to modify a model from the original parts, just kind of makes me not happy about the Model .

A little work and some heat with a torch and we should get a nice shrink fit on the wheel and be done with it except for clean up .


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