Where does the hydrogen come from, and if from the fuel, why not use electricity?

@olfoundryman8418

5 жыл бұрын

Jerry, Damn good question! There are many sources for the hydrogen but they all boil down to one thing - water - but there are many sources for the water - damp scrap, corroded scrap, damp furnace tools, damp fluxes, addition of chemicals that contain water of crystallisation (eg. washing soda) water absorbed by the furnace lining or by the crucible. water from the binder in the sand, mould washes, and the two biggies moisture in the air (humidity) and moisture from burning hydrocarbon fuels. Aluminium has an absolutely rapacious appetite for oxygen and it will pinch it from anywhere - notably water with which it reacts to form hydrogen that immediately dissolves in the aluminium and aluminium oxide which floats around in our metal as folded films constituting weakness all through the end product. Many foundries do indeed use electric melting in the form of resistance heated crucible furnaces and while it has the advantage of no moisture from burning a fuel it is slow and expensive. You still have the water from those other sources and while many can be eliminated with care the problem of humidity in the air is ever present and it is more than enough to cause problems. Best solution for the hobbyist - don't melt rubbish (swarf etc) throw all the thin rubbishy bits away do not constantly remelt the same metal, preferably use a dedicated casting alloy not cans or extruded stuff, clean and dry everything, melt quickly, do not overheat and pour without delay, avoid fluxes and in particular avoid washing soda.... Martin

@andycoombes

5 жыл бұрын

@@olfoundryman8418 "avoid washing soda" :)

@olfoundryman8418

5 жыл бұрын

@@andycoombes You betcha! All that bubbling you see when its done is not CO2 - its water! 😱 .. Martin

@tomharrell1954

5 жыл бұрын

Olfoundryman PRETTY DARN GOOD CHEMISTRY LESSON !!!!!!

@raschellesherwood6347

5 жыл бұрын

Even the atmospheric water plays a role. If it's humid castings will alsoays have hydrogen absorption. Don't skim till the very end with very hot pre heated tools and go easy on the superheat. Don't hold metal above pouring temp for tooooo long either.

You're sounding better! Good to hear. Highly informative as ever - thanks indeed.

@olfoundryman8418

5 жыл бұрын

Andy, Yes I think I am at last steadily improving... Martin

Sir you are a motivator in my pursuit of simple casting,

@olfoundryman8418

Жыл бұрын

Renegade, I am happy to have provided some incentive... Martin

Brilliant video Martin. A real eye opener for a problem most castors are unaware of and do not know how to look for.

@olfoundryman8418

5 жыл бұрын

Mark, Thank you - it sort of shows up what most people never see. But also it shows that many worry about gas porosity unnecessarily - This metal was very gassy as witness the fizzing I saw as it solidified and yet in the sections there is very little evidence of true gas porosity and what is there is so small as to be unobservable without the etching (But polishing with a mop might have showed it up too). The large shrinkage pores are of course another matter but they are easily avoided with proper feeding in an actual casting.. Martin

Awesome video Martin, I believe the best solution for us home castings is use good clean metal and use a correct basin, sprue and runner design and just forget about all the addictives of homemade fluxes and degassers. Always learn a lot from your videos thank you sir, hope your health gets better.

@olfoundryman8418

5 жыл бұрын

Ray, You got that dead right I would though add use a proper casting ally, melt quickly, don't get it too hot, and pour without delay - don't give that damn hydrogen a chance!. Health is improving - slowly.. Martin

Your lecture here is fantastic!! Very very good Sir!!!

@olfoundryman8418

5 жыл бұрын

Thomas, Glad that you liked it... Martin

Hard to argue with the results. Thanks for taking the time to make this video Martin. Get better. Missing seeing you in action! Mark

@olfoundryman8418

5 жыл бұрын

Mark, I am still here - just a bit slower for the moment, hope to be improving. As always the time id my pleasure... Martin

Thanks for the illustration, very informative as always👍🏻

@olfoundryman8418

5 жыл бұрын

Windy, My pleasure... Martin

Thank you, that was very educational. Hope you're feeling better.

@olfoundryman8418

5 жыл бұрын

Craig. Yes I am feeling a little better and thank you for asking, still need to get a lot of strength and endurance back but at the moment at least I am winning..Martin

Great video mate. Thanks for sharing

@olfoundryman8418

5 жыл бұрын

Rupert, Glad that you liked it... Martin

Very nice video about the problem of porosity.

@olfoundryman8418

5 жыл бұрын

Mister, Yes I think if some people tried this little test they would get a very rude shock! I have seen people on YT cut gates off a casting with an abrasive wheel - the greatest thing for smearing metal known to mankind and then looking at the "cut" declare their casting porosity free - Pigs A... Martin

Interesting, good video. You're one of the most meticulous KZread casters out there, from what I have seen and you seem to get great results. By the way, that slimy feeling when you get this on your skin isn't he Sodium Hydroxide solution, it's not very slick itself. It's your skin dissolving and forming a slick surface. The same thing occurs with bleach, as it's also a fairly strong base.

@olfoundryman8418

5 жыл бұрын

CJ, Thank you for the kind words. Slimy feeling is skin dissolving - not too sure I like the idea of that - skin dissolving - Yuck! In truth most alkalis will do it including sodium carbonate and the vinegar works with the bleach too even gets rid of the smell!... Martin

I am so impressed I am binge watching your channel, thank you vegoilguy for the recommendations. I have subscribed.

@olfoundryman8418

5 жыл бұрын

MItchell, Binge watch! your a glutton for punishment 😏 Thanks for the sub and if I run into Veg again I will thank him for the recommendation. Martin

@donniebrown2896

5 жыл бұрын

Martin and luckygen 1001 are my go to for true knowledge of their trade. Got hooked on Martin's presentation the first time I watched. You won't be disappointed by subbing .

@olfoundryman8418

5 жыл бұрын

@@donniebrown2896 Thanks for the good words I will pass them on to Lucky. I am sure he will be as happy as I am.. Martin

Good information, always enjoy your videos

@olfoundryman8418

5 жыл бұрын

Marty, Glad that you enjoyed it... Martin

Wow did not know a lot of things in the video...kepp posting videos...great job man.

@olfoundryman8418

5 жыл бұрын

Gasper, I intend to keep posting even as they nail the lid onto the box... Martin

Very interesting, thanks for doing this.

@olfoundryman8418

5 жыл бұрын

Tobho, No problems mate, glad to do it… Martin

What grit are you using for your fine sanding?

@olfoundryman8418

5 жыл бұрын

Andrew, The abrasive paper is not actually marked but I would judge it to be in the 400 to 600 range. Its really the caustic that does most of the work - all abrasive strategies regardless of how fine will flow the metal and thus tend to cover up defects. The caustic removes the flow but it also exaggerates the cavities a bit because it will eat them a little bigger so don't etch for too long. The final after etch sand is very light, just barely enough to remove the worst of the etch.... Martin

Is there a solid degassing substance that you recommend?

@olfoundryman8418

3 жыл бұрын

BFries, Sadly, No. In the good (bad) old days hexachlorethane tablets were available. When plunged into the molten aluminium these gave of chlorine gas which reacted with the aluminium to give aluminium chloride. This was a gas at the temperature of molten aluminium and bubbled up through it removing hydrogen as it did so. These tablets did seem to be reasonably effective. However the gases produced were quite toxic and very corrosive (the tin roof above my furnace is badly eaten away!). I believe that hexachlorethane has now been banned in most countries. There are tablets called "Nitral 10"made by Foseco these give off nitrogen when plunged into the molten aluminium. My experience with these was not good. They bubbled so viciously that they threw a lot of metal out of the crucible, they only bubbled for about 2 minutes and this is nowhere near long enough to remove much hydrogen. A local foundry did some tests and found that these tablets made things worse - most likely because of the violent turbulence of the rapid bubbling and large bubble size. I usually advise people not to bother with degassing. True gas porosity is very small as this video shows, what most people think is gas is most likely trapped air through bad pouring and gating techniques. Just use good clean metal that has been dried and is free from grease and oils - no paint and no printing. Don't endlessly recycle the same metal. Melt quickly, do not get too hot,(keep below 760 deg C) and pour without unnecessary delay using good gating and pouring methods.... Martin

Good video. Im having problems with porosity but it sounds like shrinkage voids, rather than gas. This was an engine casing, cast into a pre heated tube. I put a video showing it under microscope, any ideas how to improve for next time? Thanks

@olfoundryman8418

2 жыл бұрын

Mark, I watched your microscope video and the one before it that I assume was the pouring of the sample seen under the microscope. What magnification was the microscope video - a shot of a mm ruler against the casting surface would be a great help. There seems to be a lot going on i.e. several factors at play in creating all that porosity. Simply listening to the pour - all that plip plopping as air gets sucked in to the turbulent pour is perhaps the best clue to some of the problems. Come to me at olfoundryman@gmail.com and I will try to explain more.... Martin

Enlightening, thankyou. Here is my 5 cents worth. Having come from a polyurethane casting background, I know a bit about bubbles and gas porosity in castings, but was always a bit puzzled in metal casting why the "gas " didnt just go to the surface like it does in polyurethane. I now believe Campbell is correct in saying that the bubbles are actually voids caused by shrinkage pulling the bi-films apart as the metal solidifies. No amount of feeding will prevent these voids from forming. I think the term gas porosity is misleading. If you look at the shape of the voids, they are not round as you would expect , but pointy , backing up the oxide bi-film theory. I also believe that the reason bubbling inert gas through the melt works, is that the gas attaches itself to the oxide bi films, taking them to the surface where they are held there by surface tension. Aluminium oxide is denser than aluminium so it should sink but does not seem to. I think that is due to the variable thin layer of gas trapped between the aluminium oxide bi-films.

@olfoundryman8418

5 жыл бұрын

Greg, Thoughtful comment .Whether or not the bubbles go to the surface depends a lot on their size. The smaller the bubble the slower it rises and if slow enough it may get frozen in well below the top surface. Even if big enough it may get caught in an oxide bifilm trail that has become hooked on part of the mould. In this case it may be big enough to have enough buoyancy to keep rupturing the top of the oxide film and thus ascend or it may not and thus remain caught somewhere in the middle of the metal. When (and if) it gets to the surface only the larger of bubbles will actually Pop (you will have observed something similar in the polyurethane where bubbles rise to the surface but just sit there and hence the gas flame to Pop them). Often the oxide film prevents the bubble popping and also the oxide film on the metal surface is too strong for smaller bubbles to break through. Campbell is indeed correct - he states that the tensile strength of liquid metal (strange concept but true) is so great that the forces associated with liquid to solid metal shrinkage are too low to cause the spontaneous appearance of voids inside CLEAN metal. A bifilm is a defect, a crack, or we might think of it as a deflated bag easily pulled open by shrinkage forces. However gas porosity is certainly a real thing. Old timers often used to say that you could filter gas out - You can't of course - but what you can filter out are the bifilms (those deflated bags) that the hydrogen gas needs to nucleate on/in. Thus even in hydrogen saturated metal gas bubbles will not just spontaneously appear, they need those bifilms to form. Without them i.e. with truly clean metal the gas would simply remain in supersaturated solid solution and do no harm. Remembering that bubble formation whether gas or shrinkage (but not trapped air) happens late in solidification it is obvious that the Bifilms will be contorted (pushed) by advancing dendrites into all sorts of non round shapes that will be reflected in the eventual pore shape. Bubbling inert gas certainly does float out bifilms but it is said only films bigger than the bubble diameter - smaller and the film just slips off the bubble. I firmly believe that hydrogen from the metal does move into the lower hydrogen environment of the inert gas and is thus partially removed too - I understand that before and after analysis has indicate lower H levers afterwards. The oxide/metal density difference is not great and even the slightest bit of air or void or gas trapped within the "deflated bag" will over come this difference. convection currents will probably keep the films moving around too also some are spinel type lighter again I think. The addition of things like Tibor grain refiners can result in heavy particles attaching them selves to the films and thus weighing them down - this is I believe part of Bob Puhakka's float the boat sink the battleship practice of melt cleaning. But we should all be aware that this is an area where the truth is as yet only partially known.. Martin

@gregarmstrong4653

5 жыл бұрын

@@olfoundryman8418 Thanks for that info Martin, clearly I have a lot to learn, but as a result I may just ask the right question (due to my ignorance) , that leads to some new solution.

@olfoundryman8418

5 жыл бұрын

Greg, We all have a lot to learn and none of us will ever know anything like even a small part of it - never stop asking and thinking its the only way to move forward... Martin

Most interesting! I might have to get some real caustic soda after all.

@olfoundryman8418

5 жыл бұрын

Sw, Yep, I reckon its worth another try on your squares with some real caustic none of the comatose stuff - $0.98 indeed 😏.. Martin

@askquestionstrythings

5 жыл бұрын

lol, that "comatose stuff - $0.98 indeed"

@unclebobsbees4899

5 жыл бұрын

@swdweeb Perry again squandering your YT profits in the name of science! We already know the Earth is flat. 🤪🤪

@swdweeb

5 жыл бұрын

@@unclebobsbees4899 I know, someday I'll be sitting on my front porch wishing I had that money back ;-)

@askquestionstrythings

5 жыл бұрын

@@swdweeb I can just imagine you sitting on your front porch thirsty, begrudging the lost YT profits spent in the pursuit of knowledge and experience; and wishing you could get a cold drink.

very interesting cheers

@olfoundryman8418

5 жыл бұрын

Julian, Don't worry that bronze will not have holes like that - well maybe 😊...Martin

Outstanding demonstration. Very interesting to see how much hydrogen was picked up with the metal sitting for 7 hours. Makes me think it might be worth degassing the metal before pouring ingots if the metal has been sitting the crucible for a long time. (but then again degassing before pouring ingots might not do anything to improve the metal for the next pour since it will get degassed at that point)

@olfoundryman8418

5 жыл бұрын

Ask, As I mentioned in the video I have done this job a few times each year for close to 30 years and I have only ever had gas like this once before and on that occasion there was something strange with the batch of metal as it produced a strange iridescent colour on the solidified surface. On that occasion it picked up gas very fast, I had to degas every 30 minutes throughout the day. I would love to know what the impurity was but probably never will - I still have a sample but it would cost a fortune to have it analysed for all know possible contaminants! Hmm, I wonder if I can get Bob Puhakka to analyse it for me, sort of thing I think he would be interested in. Perhaps it was just a very humid day, perhaps the metal was a little contaminated perhaps I had it a bit hotter to compensate for the lad doing the casting being slower than I and the die ran colder thus needing hotter metal, perhaps we will never know. One of the ways of getting gas out of metal is to ingot it into moulds that will cool it only very slowly. That way most of the gas comes out of solution and hopeful escapes into the atmosphere. There seemed to be very little gas left in these slices so presumably that which came out of solution soon enough escaped completely with only the last getting caught under the steadily thickening oxide skin on the upper surface. On remelting I think it most likely that the hydrogen bubbles would escape into the atmosphere rather than redissolve in the metal as to do that it would have to travel (relatively slowly) through an oxide layer on the bubble / metal surface.... Martin

@olfoundryman8418

5 жыл бұрын

Ask, Something had been niggling in the back of my mind so I did a bit of checking and found that there is a further impediment to hydrogen bubbles getting back into solution when the metal is remelted, The hydrogen in the bubbles is molecular i.e. H2 to dissolve in the aluminium it needs to be atomic (sometimes referred to as "nascent") i.e. H To get from H2 to H is not impossible but it will slow the whole dissolution process down giving even more time for the H2 to waft of into the atmosphere rather than into the metal (as H). However for gas to have bubbled out on solidification the metal must have bee saturated as to what it can hold when solid and this will of course transfer to the liquid metal on remelting giving a perhaps higher H lever to start with and therefore probably a higher level when cast again. Incidentally Allen Hanford in a comment gave the following link - worth looking - at bit shocking really! kzread.info/dash/bejne/YqB6m8exlLHeeKg.html … Martin

@askquestionstrythings

5 жыл бұрын

​@@olfoundryman8418 wowzers, that is shocking that anyone would have shipped a casting looking like that. I'll come back to reread what you posted here again, I'm a little swamped with P-Q curves for fans and related research at the moment.

@olfoundryman8418

5 жыл бұрын

Ask, Yes, it is pretty awful. Cylinder heads are difficult and most cast are impregnated to seal them up but this one really was or at least should have been a throw out. Those gas bubbles were rather big too. Maybe they were experimenting with a new lightweight aluminium - foamed with hydrogen gas 😊.. Martin

And another excellent video Martin. As you know, I have a lot to blame you for at the moment. So I have just popped you off an email to show you how I am getting on. Speak soon mate.

@olfoundryman8418

5 жыл бұрын

Andy, Will reply to you email... Martin

Gloves and safety squints for certain with caustic soda. If it gets in your eyes, you get less eyes. The feeling on your skin is 'soapy' - it converts the fats from your skin into actual soap. This NaOH etch produces Hydrogen gas, so be sure to do it outside, well ventilated. I once blew up a car battery on charge. Hydrogen gas explodes really fast. A situation best avoided. Alternative etchants would be HCl/Hydrochoric acid/Muriatic acid (all the same thing) or FeCl3/Ferric Chloride. FeCl3 stains everything yellowy-brown. If it gets on your fingers you look like a seriously heavy smoker for a week.

@olfoundryman8418

4 жыл бұрын

aga, Yes, I am well aware of the dangers of caustic soda - another of its nasty little tricks is that its dissolution in water is an exothermic process - enough caustic in a small enough amount of water and it will boil possibly spitting saturated boiling caustic solution all over you. 50:50 caustic water will do it! And as you say H is very flammable and explosive, I too have had a battery blow up under my hands blew the top clean off a 72 amp hour 12 volt battery scared the crap out of me and did not do much for the battery either. There of course it was an H and O explosion a lot worse that H air. Not sure if HCL will do the same job on aluminium as the caustic and will generate H anyway (I think) and don't know about Fe chloride acidified or not its usually more used for copper base etching. I have both so I will try them - stay tuned. Thanks for the input… Martin

@aga5897

4 жыл бұрын

@@olfoundryman8418 Quite a few things will have a go at Al. It is an extremely reactive metal. It reacts so fast with oxygen in the air to form that oxide layer it disguises it's real character. HCl, H2SO4, NaOH, FeCl3 and many more chemicals will etch it. For some, e.g. H2SO4, it'll go faster if you add a pinch of salt. The chloride ions strip away the oxide, exposing the actual metal, making it go a lot faster. My battery blew up because i'm partly Idiot. Just wanted to angle-grind a chunk off a bar, right next to the on-charge battery. Had a full face mask on at the time, fortunately. Took several seconds to work out exactly what had exploded, then the tingly/stingy sensation started all over my head and back. Turned out that when the battery blew up, it sprayed acid upwards, which hit the shed roof and rained on me. I flushed all affected areas with water very quickly (jumped in the pool fully clothed). No angle-grinders were harmed in the process.

How much does a dye penetrant help with making voids visible? It's interesting how machining and sanding obscures the pores and etching cleans out the pores but can bring out other artifacts. There's a huge difference between textbook metallurgy and the realities of prepping and examining a sample; good to have such an accessible demonstration of both theory and practice.

@olfoundryman8418

5 жыл бұрын

aclight, Dye penetrant would be quite helpful, it would make these small pores much more easily seen and may well show up ones smaller that we could not see but probably exist in these samples. I have used it for crack detection on steering components and it is a good technique if a little messy - that red die, it gets everywhere. My Metallurgy student days (Oh so long ago!) were spent in a lot of sample preparation, we spent a lot of time eyes glued to microscopes and we got to pretty much know what a sample was an what had been done to it and what if anything was wrong with it just by looking down the microscope I wish I could affords a good scope!.. Martin

That could sure wake a person up really quick about the quality of his pours.

@olfoundryman8418

5 жыл бұрын

Icensis, Sometimes its better not to know, ignorance is bliss 😏 but I do suspect that most people would be shocked to see the true extent of porosity in their castings... Martin

Hi sir I want detailed procedure for caustic etching process for aluminum extruded rod to detect centre crack and porosity

@olfoundryman8418

4 жыл бұрын

Yogesh. I have never tried the procedure on extruded rod but it should work Ok I think. You will just have to try it. Start with a piece of rod that you know to have defect in it and cut it both square and diagonally to see which way shows the problem best. Etch it in a 20% caustic soda solution until a noticeable attack has occurred (again trial and error). Rinse off with water and see if the crack is evident it will probably be seen as a fizzy line as caustic seeping out of it continues to attack the rod - to stop all attack rinse in vinegar.... Martin

Never EVER do this without a mask people. This man just did irrepairable damage to his lungs

@olfoundryman8418

3 жыл бұрын

Hans, Did I not cover exactly this in the video? Try re-watching it (gives me another view😊) and pay particular attention at about 7.34. ..Martin

Wow Just wow! What an ungodly mess in this ingot. Would I be correct in assuming this was all caused by the extended time at molten temperature? Really glad to see and hear you again Martin. Bob

@olfoundryman8418

5 жыл бұрын

Bob, Your assumption is correct with respect to the hydrogen gas porosity. However 99.9% of the porosity in these ingots is shrinkage porosity. It's only those very small bubbles that are true gas porosity. Had this been a casting and provided with an adequate feeder the shrinkage would not be present. All we would see is the small gas bubbles although I suspect there would be quite a few more as no doubt a lot of the gas has gone into the shrinkage pores rathe than form its own little bubbles. I have now got to the stage where health wise I can manage a video like this a bit at a time but as yet I am not up to the longer rigours of casting. I hope that it will come in time, in the meantime I have some older video to get edited and quite a few non casting but foundry related videos to get done. There may be some time between videos but they won't stop. - well not yet at least.😏... Martin

@unclebobsbees4899

5 жыл бұрын

@@olfoundryman8418 See I am actually learning something! Light exercise always helps. I was just released from the plaster cast prison, pun intended. I had to design some exercises around the house that didn't involve crutches. Damn things made me have the coordination of a dead gazelle. I'm sure you have a few ingots handy that could be used. 😁

@olfoundryman8418

5 жыл бұрын

Bob, I have in fact embarked on an exercise regime it does seem to be helping - although I hate it... Martin

The only question I can't seem to get answered (or I haven't come across yet) and that is how does one prevent porosity in high humidity areas?

@olfoundryman8418

5 жыл бұрын

Amalgamous, I am mulling this difficult question over in my mind. I will come back to you in a day or three with what I hope will be some sort of sensible, and more importantly, useful answer. I have heard of foundries that just would not pour on especially humid days but that is not always an option . and I think it possible to do better.... Martin

@olfoundryman8418

5 жыл бұрын

Amalgamous, OK lets have a go at an answer. Firstly its not relative humidity on its own that we need to worry about but rather its combination with temperature, because together they determine just what percent of the air is water. Thus high humidity and high temps are bad while high humidity and low temps are nowhere near as bad. Now you can either find charts on the internet that relate the two to water content or you can simply use "dew point " as an indication the lower the dew point the less the water in the air and the safer it is to cast. Either way investigate this throughout the day week month year etc to determine when the lowest water content times are and perhaps cast only then - mould and get ready any time but cast only at lower water content times. But is all this bother really necessary? Even a high humidity day (90%) at 20 deg. C is going to have about 2% water in the air, raise the temp to 35 deg. C and you might have a bit more than 4 % but in my opinion anyone who casts on a 90% rH 35 deg. C day has got rocks in their head - way to damn uncomfortable for this little black duck! We all burn a hydrocarbon fuel, propane or vaporised oil. Taking propane C3H8 and assuming the right amount of air we get the exhaust gasses swirling around and into our crucible of metal of Approx. 75% nitrogen 17.5% CO2 and 9.5% water. The nitrogen is just a parasite doing nothing more than removing a lot of expensive and lovely heat out of our furnace by virtue of its much raised temperature as it leaves. The CO2 and water remove heat too but at least they contributed to it in the first place by their formation. My point here is that the 9.5% water in the furnace gasses is going to completely swamp the effect of the natural rH and any great worries about whether the day is 1% or 2% or even 3% water in the air pale into insignificance beside that 9.5% in the furnace gasses. Of course its an additive situation, that 1 or 2 or 3% will add (slightly diluted by the addition of a dry gas - the fuel) and will push that 9.5 % up to 10.5% or 11.5% or even 12.5%. But if you are doing things right is that relatively small increase going to have any great an effect - I don't think so - an effect sure but not large and if you are having severe gas problems I suggest you look elsewhere for the cause. High rH will make it a little (emphasis on "little") harder but attention to raw material, melting and pouring practices, and good gating together with if necessary good degassing procedures (NOT washing soda that just increases gas levels .. Grr..) should prevent any serious gas problems. Remember that hydrogen gas needs nucelli within the metal to form bubbles on without these even quite high levels of hydrogen will remain in the metal in the form of a harmless super saturated solid solution. Most commonly these nuclei are oxide films that come with dirty metal - clean metal = no gas bubble metal.. Martin

@AmalgmousProxy

5 жыл бұрын

@@olfoundryman8418 Thank you so very much for the reply. Since our climate here is subtropical with hot and humid summers are the norm, I definitely agree that hot and humid summers here has made casting during the winter months to me is almost a necessity. Otherwise, I risk having the floor smack me in the face. I have some homework to do and some experiments to try. Thanks!

Have you seen Mark Presling youtube channel? Watch his video (Brass Casting - Tragedy and Triumph) He is copying your methods but I think something is being lost in the translation.

@olfoundryman8418

5 жыл бұрын

Lucky, I had seen some of Mark's work - Hmm! I had not seen the particular video that you referenced but now I have and yes there is quite something lost in the translation - basin way to shallow and with a rounded bottom, parallel sprue, part down sprue etc at totally the wrong time - should be before striking off of course! Gating a bit strange and obviously on first try metal too cold, feeder not in best place and perhaps a little large. And why is it that people insist on poking their finger down the top of the sprue after they have finally closed the mould etc, etc. - Grr.... Martin

I've etched with caustic but was concerned it was selectively etching softer material potentially making good material look pitted. I've been polishing and seeing cavities as small as 0.0015".

@olfoundryman8418

5 жыл бұрын

Andrew, Yes, any etching will remove different phases in the structure at different rates and thus if carried out for too long could indeed produce a pitted appearance - note though, that's it not necessarily the "softer" phased that are eaten out most. Polishing sure does accentuate porosity because the "nap" of the buffs seems to eat into any small holes and not only enlarge them but also depress the surface around them, thus making them all the more obvious. One would need some decent magnification to see holes that small - my eyes are too old to see that sort of stuff unaided but having spent a lot of time in my metallurgy days looking down microscopes I can assure you that often materials are riddled with many holes way smaller than that... Martin

@andrewmartin4258

5 жыл бұрын

@@olfoundryman8418 Do you have any guidance as to whether there is porosity which is small enough to be ignored from a strength perspective? My question is around trying to avoid voids from hydrogen/bifilm. Even if you don't have hydrogen to expand the bifilm, is it true the bifilm present, but not expanded, is still a defect like a crack?

@olfoundryman8418

5 жыл бұрын

Andrew, As a general sort of rule it is reckoned that if a defect (of any sort) occupies, say 10% of the cross section of a sample then the strength will be reduced by about that 10% BUT the ductility (elongation) will be reduced by much more -quite possibly about 50%. Certainly my experience with tensile test results (357 T6 alloy) is that anything that gave a poor elongation result had a quite large defect usually in the form of what I now know thanks to John Campbell's work to be an oxide bifilm, almost invariably the defect showed a semi iridescent sort of shiny blue/grey colour - probably a relatively older and thus thicker bifilm. It may or may not have had gas (H) or trapped air associated with it. I don't think it matters how small the porosity is - I would guess that 10% porosity present as hundreds of small pores would have the same effect as 10% porosity present as, say, just 5 or 10 pores. No doubt though if the porosity is so small as to get down to interatomic spacing it would be a different story. I think its a case of a hole is a hole is a hole is a defect and it will have an effect. This analogy might well break down with the case of one very large hole as depending on where it is in the sample under test it may have strange effects and from that point of view of if one has to have porosity I would prefer it as lots of small holes rather than the one big one. If a bifilm is still "ravelled" it constitutes a much smaller defect than if has become unravelled and will thus have a smaller effect on properties. However it is still a defect and will still have an effect. Note that not only hydrogen can expand a bifilm air can do the same thing and so importantly can nasties like some iron aluminium silicon compounds and this is why you should NEVER melt aluminium in steel crucibles! The compounds seem to preferentially nucleate on the bifilms and as the growth orientation of many of them is acicular or plate like they grow in a straight line pulling the ravelled bifilm into a nice straight and much more extensive unravelled one. Iron cannot be economically removed from aluminium alloys and once thus contaminated they are at end of life and fit only for burying in a hole in the back yard. A bifilm is in effect always a crack - ravelled its a smaller crack, unravelled its a bigger crack. The effect on properties is proportionate.... Martin

@andrewmartin4258

5 жыл бұрын

@@olfoundryman8418 Thank you for the detailed response. If I may I have a couple of more questions. From a tensile specimen standpoint I understand a ravelled bifilm in the direction of tensile load is just as bad as an unravelled one (a tight crack still has no strength across it), but until it is unravelled, I can't see it. Is it wrong to think the hydrogen does me a favor? I have been using a stainless steel crucible with very little metal loss. Is stainless steel as damaging to aluminum as carbon steel?

@olfoundryman8418

5 жыл бұрын

Andrew, Re tensile point of view, I think its just a matter of the percentage of cross sectional area that the bifilm occupies. Ravelled or unravelled its a weakness but unravelled it will likely occupy a bigger percentage of the area. Hydrogen does no one any favours (actually that's not exactly correct but lets not get into that here as it does not apply to sand castings except very badly made sand castings - mind you a lot of those about on YT and elsewhere!) To my mind melting aluminium alloys in any type of metal crucible is a hanging offence (sorry) and those doing it should have their box of matches confiscated! The worst impurity that one can have in aluminium alloys is iron and once in you can NOT get it out - its the death of the metal. As regards relative resistance to attack grey cast iron is best (a bloody poor best!!!) followed by mild steel followed in last and worst place by stainless steel. The graphite in cast iron seems to give some slight protection, mild steel is slightly protected by the relatively thick oxide layer but stainless steel has such a thin oxide layer that it is easily scratched through and then once wetted by the aluminium it will eat through in seconds - stand by for wet boots as your SS crucible piddles molten aluminium all down you leg or ruins your furnace or burner PLEASE get a proper crucible! Rule one of making good castings - start with a high quality melt, one full of iron is NOT high quality - all else that follows then is a waste of time... Martin

Caustic soda reacts with Al When placed on a solid piece it's more likely to react along naturally occurring dislocations. That makes a "small hole."

@askquestionstrythings

5 жыл бұрын

Grain lines (naturally occurring dislocations) are going to be extremely small compared to gas porosity. orders of magnitude difference.

@olfoundryman8418

5 жыл бұрын

John, Ask, We have to be a bit careful here as dislocations are a very specific thing to do with local disruptions of the atomic structure. They are extremely important in the way metals deform( by dislocation movement) and the prevention or hindering of their movement is fundamental to various hardening /strengthening processes. I doubt this is the sort of dislocation that you mean. I am assuming that you mean local differences in the alloy that encourage local corrosion a local precipitate of another phase in the structure for example but more likely an oxide bifilm inclusion these are inevitably the site of gas and shrinkage porosity and of precipitation of other phases

@olfoundryman8418

5 жыл бұрын

Damn! clicked "reply" too soon had not finished. It is of course true that etching will increase the size of a defect because it is chemical removal of metal so it would make a hole a bit bigger - how much - I have no idea but don't think it much and there has to be a hole there first anyway for it to get bigger!. Not sure that I would call grain lines (boundries) naturally occurring dislocations I think the term is more specific than that. But it is true that at a grain boundary there are frequently dislocations of structure within the grain and that structure I different to that in the grain next door and a given dislocation is structure specific. For metal to deform across a grain boundary a new suitably orientated dislocation has to come into play at the edge of the second grain or deformation stops. This is all getting a bit complicated.😊.. Martin

@markfryer9880

5 жыл бұрын

@@olfoundryman8418 Martin there are a couple of videos floating around on KZread from WWII that show representations of Al at the molecular level and talk about slip planes and structures and the effects of forging and heat treatment as well as tempering.

Ok, I’m guessing Perry didn’t have a strong enough caustic soda solution. Nice!

@olfoundryman8418

5 жыл бұрын

John, Yep, that caustic Perry had was DOA... Martin

I've worked with sodium hydroxide and soap making in addition to the gloves and mask you should also have eye protection on if it gets in your eyes it will blind you

@olfoundryman8418

5 жыл бұрын

Brian, You are right it can be nasty stuff. At my age glasses are mandatory so my eyes did have some protection - perhaps I would have been better off with full visor but then my voice would have been muffled. Try it 50 50 with water it will boil for sure stand back though!... Martin

@tomharrell1954

5 жыл бұрын

Olfoundryman YOU SHOULD HAVE A RESPIRATOR ON WITH ACTIVATED charcoal TO ADSORB THE OH

@olfoundryman8418

5 жыл бұрын

Thomas, No dispute you are right! But you would not have been able to hear me through the respirator - I suffered (only a very little) for your benefit 😊… Martin

Nasty stuff that I know lol. Add some lithium to that and you will get purple spitting fireworks from your container lol .do not try at home. Ahhhh so the tiny holes I seem to be getting are infact porosity and maybe not the loose grains of sand I thought they were. Thanks again Martin and swdweeb

@olfoundryman8418

5 жыл бұрын

Raschelle, Loose sand is unlikely to be within the metal. it may be on the very surface and is then the result of not blowing the mould out properly with air. However, I have found it quite difficult to remover every little grain! You can get an idea by shining a torch at a steep angle along the cavity surface this will show up any little grains sitting above the surface. Really good moulders (way better than me!) used to solve the problem (in part) by "printing back" the pattern. This was the putting of the pattern back in the cavity after all the gates feeders etc were cut and thus any upstanding grains were pushed back into the mould by the pattern and the cavity thus much smoothed up. However this meant of course that you not only had to get the pattern out but back in again and then out again - you need damn steady hands to do this!… Martin

You might be interested in this video about a Ferrari casting: kzread.info/dash/bejne/YqB6m8exlLHeeKg.html

@olfoundryman8418

5 жыл бұрын

Allen, Very interesting, thanks for the link. It sure does look like gas porosity to me, all the same size and nice and round! Would have been interesting to see that after a caustic etch! To be honest cylinder heads are pigs of things to cast all that complexity of water passages ports etc make it hard to get a good casting and most are vacuum impregnated to seal them up, but even so I would expect better from a foundry supplying Ferrari!. Either way too high a gas lever or the metal is way too dirty or more probably both as dirty metal always shows more gas for the same true gas content as does clean metal. As John Campbell says "start with a good quality melt" they didn't .. Martin

@allenhanford

5 жыл бұрын

@@olfoundryman8418 anyone can make a mistake; the fact that quality control on an ultra-expensive car didn't catch it is shameful. A Harley-Davidson dealer near me once showed me a brand-new Sportster cylinder with a hole IN THE BORE that I could put my pinky into. Not sure what causes such problems in cast iron but the fact that it went out the door means that multiple people didn't even look at it.

@olfoundryman8418

5 жыл бұрын

Allen, Such a hole (assuming its smooth) is probably an air bubble caught in the liquid metal by bad gating practices it gives this sort of random defect. Where I last worked (for a boss) they did 100% inspection (brake components) but even that does miss things - people are human! But a hole that size, well that sure should have been picked up!... Martin

If you don't have sodium hydroxide, just heat some baking soda to above 1600F, and it will decompose to sodium oxide, which produces sodium hydroxide when added to water. Not sure if it would eat through a crucible though, just an idea.

@olfoundryman8418

4 жыл бұрын

Radster, I assume that your comment is based on Baking soda (NaHCO3) decomposing to Sodium carbonate (Na2CO3) at around 100 deg C and then the Na2CO3 breaking down as the temperature is raised further. This is an area that I am interested in as it relates to the useless preoccupation some amateur foundry types have in foolishly attempting to degas aluminium with washing soda (Na2CO3.10H2O) or even anhydrous sodium carbonate (Na2CO3). It is my hope to do a video rebuttal of this process in a scientific way and thus I have investigated the properties of the various sodium carbonates with respect to their behaviour with heat. One reference I have - Mellors Modern Inorganic chemistry - admittedly now a bit old, states that Anhydrous sodium carbonate melts at about 850 Deg C with “slight decomposition”. More modern information suggests that decomposition actually begins at about 400 deg C BUT that it is only very slight - perhaps about 1.5% at the melting point and is not complete until about 1500 deg C and is only about 5% complete at 1200 Deg C. Do you have information and a reference to suggest otherwise? If you do, I would be very appreciative to receive information about it. Incidentally sodium oxide is quite nasty stuff treat it with care and particularly when adding it to water….. Martin

@5thDragonDreamCaster

4 жыл бұрын

​@@olfoundryman8418 Thanks for the reply Martin. I read the Wikipedia article for sodium carbonate will decompose to sodium oxide above 850C, and I was planning on testing that, but I am unsure what it would do to a graphite crucible. I did say it was just an idea, never said it was a good idea. I was also curious if you knew anything about it, and I'm glad to see that you do. Even a low percentage sodium hydroxide could still be useful for something. I've also seen Cody's Lab make it from a salt solution. About the supposed 'degassing with carbonate', I never believed that would work. I only do small, decorative castings, so I don't bother degassing aluminum. When I melt copper, I never try to cast pure copper like a lot of people seem to do. I use a 98% Cu, 2% Sn alloy, and it's gas free enough for making coins. If I want to make a knife, I use ZA27. Silver I will spend the time to degas though, especially after I spent extra time adding a bit of germanium to it to make 'Argentium sterling silver'.

@olfoundryman8418

4 жыл бұрын

@@5thDragonDreamCaster, I would not try it in a graphite crucible as I strongly suspect that any of sodium carbonate sodium hydroxide or ether of the two sodium oxides (Na2O2 ,Na2O) will attack the non-graphite part of the crucible and flux it away. The behaviour of those two oxides of sodium is a bit of a mystery as at a quick look it seems as though either decomposes to the other at some elevated (but not that high) temperature weirdly the info I came across suggests a sort of merry-go-round between them! The problem with degassing with washing soda is that if you use anhydrous Na2CO3 you get no gas given off (Luckygen 1001 showed this) and if you use the true old-style washing soda Na2CO3.10H2O the only gas you get off would appear to be water (and perhaps a smidge of CO2), remembering that the hydrogen we are trying to get out of our aluminium got in there in the main by reaction of the aluminium with water, bubbling water (steam) through the aluminium would appear to be most counterproductive. I usually advise people that if they use good metal that is clean and dry and melt quickly cast without delay, they will not have a gas problem unless their castings are very thick - in other words do not bother with degassing. Copper is a bit difficult and everybody I have ever seen do it on YT has done it wrong! The use of a small amount of tin or zinc helps no end A knife from ZA27? I have used a fair bit of the ZA12 alloy but I would have thought that even a “hard” zinc alloy like ZA27 way to soft for a knife?? I assume that you stir it well as the ZA alloys are prone to segregate when liquid. I understand that Argentium silver is somewhat superior to sterling silver in many ways but I have never worked with either ($$$) 😱 and it postdates my metallurgy student days. Regards, Martin PS We need to see more videos from you!

@5thDragonDreamCaster

4 жыл бұрын

​@@olfoundryman8418 I do have some videos on Billy-Bobus Foundry. I haven't had a chance to do more videos for a few months, but I'm planning on making some more soon now that I've had a propane forge for the past 3 months, and it blows away my old electric one. The knives that I've made still aren't great; most of my experience is with casting coins and small engravings. I've recently come up with a copper based alloy that will scratch mild steel, but its fairly brittle. I might show that next time I make a video. My set-up doesn't get quite hot enough to do cast iron. It will melt it, but I can't get it hot enough to cast. Thanks, Mike

@olfoundryman8418

4 жыл бұрын

Mike, Electric while clean and quiet is very slow as you no doubt found. But if you can’t get enough heat to melt cast iron I would guess that you have a self-aspirating gas burner the problem with these is that they have difficulty pulling in enough air to get the slightly oxidizing flame that you need for maximum heat. IN another life (Oh so long ago) I briefly worked in the open-hearth department of a steel company. My job was to do furnace gas analysis to check for the oxygen level withing the furnace. They were aiming for 2% oxygen i.e. somewhat oxidising through excess air as this was the mixture that gave the greatest heat. With a self-aspirating gas burner your chances of getting this excess air are miniscule - you need to add a well controlled blower to push the air in - then you will melt iron but use a clay graphite crucible NOT a silicon carbide one. There are some very hard copper base alloys out there. One I use to make things like synchro rings for gearboxes is called CMA 1 and it has a higher hardness cousin CMA 2 www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwi1-8KznqrmAhXh4nMBHT76A3oQFjAAegQIAhAC&url=https%3A%2F%2Fcopperalliance.org.uk%2Fresources%2Faluminium-bronze-alloys-industry%2F%3Fdownload%3Dstart&usg=AOvVaw1Q1QhDR2sEhgtt6HSaW7Et I tried to paste a chart in here but It does not seem to want to work so try page 15 on the link above As you can see it is an aluminium bronze and it thus requires care in casting, in particular it is very prone to hot spot shrinkage. It will certainly scratch mild steel and it is not brittle. You need very sharp tools to machine it Incidentally the AB3 alloy also listed in the link is wonderful stuff, quite easy (relatively) to work with and it has a beautiful warm gold (not brassy yellow!) colour also it machines quite well although it is hard on tools ( the silicon content makes it a bit abrasive) I have used this alloy a lot but have had to make it up myself (not easy) as I cannot buy it here in Australia. It would be an excellent alloy for you coin sized work. Regards, Martin

Good test to try on critical parts before wasting time machining them.

@olfoundryman8418

5 жыл бұрын

Bob, Indeed, but the problem may be that you never find a porosity free casting - sometimes ignorance is bliss 😏… Martin

@MrEh5

5 жыл бұрын

@@olfoundryman8418 So very very true!

caustic soda??? throw it on your leaf pile in the garden and put the hosepipe on it, the plants in my garden grow the best where I dump chemicals that are safe to dump in the soil if you dilute with a hosepipe after. No oils or solvents but acids and alkalis are safe if diluted.

@olfoundryman8418

4 жыл бұрын

Paul, Within the limits of which plants like acid or alkaline conditions or have sensitivities to things like phosphorous (Aussie native plants abhor phosphorous) you are probably right,. Not too sure about effect on soil fauna though...Martin

@AirCrash1

4 жыл бұрын

@@olfoundryman8418 Gumtrees, sheep and flies are hardy bastards and most of the worlds uranium is mined in Australia, you will be fine....hahaha

Might want to add a warning during the etch about ventilation and ignition sources. That's hydrogen production and if she blows you could get a face full of caustic soda.

@olfoundryman8418

5 жыл бұрын

Daniel, Venting that spray would have been a good idea it sure does catch in one's throat. I think the hydrogen unlikely to blow the caustic around the room as it is above not under the caustic - I did though make sure there were no ignition sources nearby as hydrogen does ignite very easily over the widest range of hydrogen air mixtures....Martin

@danielrouw2593

5 жыл бұрын

@@olfoundryman8418 the hydrogen may be above, but the blast if ignited, can send some decent splashes out. Brings back memories of fun with sodium in high school. I bet the carpet still has bleached spots from the caustic soda.

@olfoundryman8418

5 жыл бұрын

Daniel, You have piqued my curiosity! I will just have to try. Full face visor long gloves get it bubbling hydrogen away and standing well back while wearing a plastic rain coat light it up. Carpet in the science block - must have been a pretty flash school I was sent to one of the local best and most expensive and no carpet - anywhere - I should put in for a refund. 😊.. Martin

@danielrouw2593

5 жыл бұрын

@@olfoundryman8418 the teacher decided to have to fun in the general purpose classroom instead of the lab, portable modular building outside in -30 C. He misjudged the amount of sodium. Woops.

@olfoundryman8418

5 жыл бұрын

Daniel, If he was anything like some of my teachers he "misjudged" it on purpose!. -30 deg C, boy you can have that lot on your own! On a very cold frosty morning we might dip to a brief low of -1 or -2 C but even that would be rare... Martin

So this alloy is a skin former, subject to porosity and it machines poorly......what are its bad qualities???😜

@olfoundryman8418

5 жыл бұрын

Rv4, It's a horses for courses thing! Every alloy has it good and bad points and thus each its particular uses. This alloy is very fluid and thus it is used for thin castings - lawnmower bases for example, lace work etc. Being a skin form is not necessarily a bad thing it just means that the metal tends to solidify in a line, solid one side liquid the other no mushy bit in between and sometimes this is an advantage, the gross shrinkage porosity is easily avoided by providing feeders and designing to avoid hot spots in the mould. I only use this alloy where I feel the excellent fluidity is a help. It has moderate but useful strength without heat treatment it can not in fact be heat-treated. Its high silicon content makes it abrasive to tooling HSS tools lose there very sharp edge quite quickly - carbide really is a must. Bandsaw blade dull quickly much quicker than with the more common 601 (356) alloy. It is perhaps most used in gravity die work, and should not really be used for thick castings by any method... Martin