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Thread: Stovetops: Aluminium vs Stainless Steel

  1. #1
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    Stovetops: Aluminium vs Stainless Steel

    Hi,

    A newbie question.

    I want to purchase a stovetop maker and see that there are aluminium and stainless steel. I am averse to using aluminium for health reasons. However, do the SS stove tops work as well ?

    Also, any recommendations on brand ?

    I searched this forum but couldnt find any results for these questions.

    Thanks,
    Murray

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    Re: Stovetops: Aluminium vs Stainless Steel

    Murray,

    Hi and welcome to CoffeeSnobs.....

    Have a read of :

    http://coffeesnobs.com.au/YaBB.pl?num=1179533130

    Whilst the jury is still out on whether Aluminium is a health risk - Id avoid it also.

    In that thread you will find comments that all stovetops arent created equal, the cheap ones (generally aluminium) being just that - cheap and nasty.

    A decent quality SS stovetop will perform very well.

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    Re: Stovetops: Aluminium vs Stainless Steel

    Thanks for that !

    Murray

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    Re: Stovetops: Aluminium vs Stainless Steel

    Id think that SS would be better all around; not only for durability, but because it takes longer for the whole thing to heat up, so if you pour boiling water in the bottom the top should be cooler, which wont scorch the coffee as much. How much of an effect this have is anyones guess, though.

    Cheers,

    Luca

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    Re: Stovetops: Aluminium vs Stainless Steel

    I have a quality SS item.. and it is quality... Id refrain from Aluminium as JavaB has said.

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    Re: Stovetops: Aluminium vs Stainless Steel

    Luca is correct...

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    Re: Stovetops: Aluminium vs Stainless Steel

    Well the old aluminium terror is a subject for much debate elsewhere, but if it terrifies you then I advise you to stop using underarm deodorant as well.

    Quality moka pots are made by Bialetti, who I believe were the original designers of this brewing machine back around 1935.
    They make good pots in either aluminium or SS, however if going for SS then I advise the Musa pot over the Class pot as there have been some reported difficulties with the thread/seal of the Class pot due to the difficulties in forming the shape of the bottom piece. Have a look at a picture of both and you will understand.

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    Re: Stovetops: Aluminium vs Stainless Steel

    I have a Bialetti :)

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    Re: Stovetops: Aluminium vs Stainless Steel

    Putting aside any debae about aluminium and health.... Stainless steel is much better.

    Over time, aluminium will corrode, the surface will become pitted, and it will be harder and harder to remove coffee oil staining. Taste will thus become affected.

    None of those issues with good grade stainless steel.

    Many stove tops today are made of a very poor grade of aluminium --very thin, but highly polished to compensate for the structural shortcomings.

    Stay away from them. If you want a low-maintenance, easy to clean stove-top, SS is the way to go.

    Robusto

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    Re: Stovetops: Aluminium vs Stainless Steel

    For a good short read on the history of the Bialetti Moka pot and why they prefer aluminium try this link http://www.ineedcoffee.com/03/mokaexpress/

    Bialetti are mentioned in the Guiness book due to the number of the Moka Express pots they have sold, reputed to be around 300 million!

    Robusto, Italian friends of mine have an aluminium Bialetti Moka pot over 50 years old and still going strong, cant wait for mine to taste as good as theirs. ;)

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    Aluminium vs Inox


    I have mokas in both aluminium and stainless steel. I use stainless steel on a daily basis and aluminium weekly, when two cups/mugs are required at the same time. My flavour preference is for aluminium, but as aluminium mokas need to be cleaned and dried immediately after use the stainless is easier.


    As for corrosion, I have an aluminium Bialetti I have owned for over thirty years and it is still going strong. Stainless pots simply don't take rough use, that is overcooking. If you are making coffee in a moka pot daily (and more than once daily) you will eventually leave one on the hob too long. (FYI I cook on gas.) Stainless pots all burn and stain permanently if left on the hob too long. (Yes, of course that ruins the coffee too!) In the 1980s I treated myself to an Alessi La Conica which has (had) a lifetime warranty. First the copper base came off from overcooking and differential expansion/shrinkage (1980s), then the ball fell off the top (2000s), and finally, a few years ago, it had a blowout in the base from corrosion (the ultimate result of overcooking stainless), rendering in useless. The warranty paperwork was long gone. If a stainless pot is overcooked it will eventually corrode.


    The worst damage an aluminium pot gets from overcooking is a melted or burned gasket. They will always clean up fine, and polish up too if you so wish.


    As the cost of replacing the La Conica locally was prohibitive I bought a replacement online, along with a La Cupola and a Moka Alessi which all together shipped to NZ for less than the local price for the La Conica alone. I mention this here as together they formed the foundation for my moka collection, which has since increased to over thirty pots, old and new, including Bialettis, Atomics, Caffexpresses (my personal favourite), La Signoras, Nova Expresses and many more classic Italian pots.


    I try to buy old mokas NIB or at least in undented and unscratched condition, knowing that no matter how grubby it is an aluminium pot will always polish up, whereas once burned a stainless moka will never look nice again. My new unused La Conica is the only stainless moka in my collection. The daily use pot, also stainless, but never to be a display item, is an old burned Bialetti. For weekly (two mug) use I have the choice of a Caffexpress or a stainless Moka SEB, but my preference, for flavour, is for the Caffexpress, bought in NZ in clean used condition. I have no qualms about using my smaller Caffexpress for a daily jolt, knowing it will always polish up but I'm just too lazy.

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    Senior Member speleomike's Avatar
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    Hi

    I have SS and Al pots and the Al ones make better tasting coffee for me. I have mentioned this a few times in posts in this forum and it's a debatable point and depends on a users tastes. The Al does not corrode if cleaned after use, it stains a little bit on the bottom and sides with an electric stove and quite a bit with gas (don't use a campfire!) but that just gives them character. The Al ones are cheaper, I think some of the SS ones are over priced. I'd suggest get Al to start and then get a SS if you desire :-) You can't have too may coffee making implements.

    Mike

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    Aluminium and stainless steel.

    FWIW, all aluminiums are no more equal than all stainless steels. Poor quality ones of either will give you problems.

    If you want all your coffees to taste the same regardless of which beans you use, go aluminium. It is porous and the oils soak into the metal. After that it has its own unique "pot flavour". I prefer actual "bean in pot flavour". Tastes may differ on that one!

    If you can get a decent quality stainless, it will last forever. The early Bialetti stainless is utter crap hence the post above with problems. Why? A friend of mine burnt out three of them, my 316 stainless replacement is still going strong there since the early '80's - and yes, he has forgotten it at least 5 or 6 times that I know off and melted / burnt the seal into the joint. Every year or three I have the job of fixing it up again. Surprisingly, it still looks new, even though the handle is rather scorched as well as "a little loose" due to missing bits.

    TampIt

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    They recommend not to use aluminium on ceramic stove tops as it leaves a residue which can be hard, if not impossible to remove. A friend of mine used a Teflon BBQ sheet between his aluminium stove top coffee pot and the ceramic stove hoping that this would work, but it still marked it over time

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    Senior Member Erimus's Avatar
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    I have both types of bialetti and for me aluminum has the superior flavor.

    Much better to use gas than electric for these devices. A camping gas or BBQ ring is a much better alternative if you're all electric.

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    Although I haven't used them in years; the aluminium bialetti versions seem to make better coffee. Not a world of difference though.

    Not 100% sure, but I think that aluminium versions take slightly more coffee and is the reason for the flavour difference.

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    The Australian designed stovetop, The Little Guy, is almost all highly polished cast stainless steel with no moving parts. It should last forever and it makes great coffee with crema and has good steam.

    Externally it has the classic Italian style of the Atomic coffee maker from the 1950's, however internally it has been redesigned. It has won awards for design. It is extreemly well designed and built.

    Barry
    Last edited by Barry_Duncan; 11th February 2015 at 10:07 AM.

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    Senior Member Erimus's Avatar
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    ^
    The Little Guy price is a bit high to compare it with a basic bialatti, in fact you're well on the way to a decent machine price wise.

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    Hi

    OT but anyone watching Matthew Evans (Gourmet Farmer) last night on the yacht might have noticed that he had a "Little Guy" coffee machine on board. It was just a few seconds as the camera swung around to another shot when he asked if anyone wanted a "cuppa" and then they served tea.

    Mike

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    Quote Originally Posted by TampIt View Post
    .....regardless of which beans you use, go aluminium. It is porous and the oils soak into the metal. .
    TampIt
    .?? That's the first time I have heard that aluminium is porous !
    any evidence to substantiate that statement ?
    .NO ? ...I thought not!
    i suggest you go and rethink your theory.

  21. #21
    Mal Dimal's Avatar
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    In fact...

    Aluminium porosity is a sign of defective production and/or welding processes, and NOT something to be sought after...

    Mal.

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    Senior Member Vinitasse's Avatar
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    Quote Originally Posted by blend52 View Post
    .?? That's the first time I have heard that aluminium is porous !
    any evidence to substantiate that statement ?
    .NO ? ...I thought not!
    i suggest you go and rethink your theory.
    Hydrogen porosity in cast aluminium is indeed something that exists oh baffled one and is a very common problem in the production of cast aluminium. A simple google check would have quickly yielded the evidence you seek.

    In the future, remember the following:
    1) search
    2) substantiate
    3) formulate
    and then, and only then,
    4) pontificate
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    Quote Originally Posted by Vinitasse View Post
    Hydrogen porosity in cast aluminium is indeed something that exists
    ...as are punctures in tyres, or potholes in the road... but all are considered defects !
    You could make any material defective if you wanted.
    laminations in steel sheet,
    micro cracks in castings, Etc
    any half decently made aluminium product will not be porous.

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    Quote Originally Posted by blend52 View Post
    any half decently made aluminium product will not be porous.
    Pretty sure that's what Vinitasse was intimating b52...

    Mal.
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    Senior Member Vinitasse's Avatar
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    Quote Originally Posted by Dimal View Post
    Pretty sure that's what Vinitasse was intimating b52...

    Mal.
    Thanks Mal... I thought it was pretty obvious. Oh well... I tried
    sigh
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  26. #26
    TOK
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    Quote Originally Posted by blend52 View Post
    .?? That's the first time I have heard that aluminium is porous !
    any evidence to substantiate that statement ?
    .NO ? ...I thought not!
    i suggest you go and rethink your theory.
    Short memory? Alzheimers?

    You and I had a little spat about this very topic a year or 2 ago, so I am afraid you HAVE heard this one before.

    Rather than argue back and forth about who gets to sit on the moral high ground with respect to their knowledge of metallurgic details & properties, what about instead discussing the real world / well known phenomenon that aluminium stovetop esporesso machines ("Moka" pot, "Bialetti" et all) really do somehow "season" with coffee oils and therefore do result in different flavours in the brew when compared to stainless steel moka pots?

    Over the years I have used and sold many different brands and models and the build quality variation in the castings of alli moka pots is astounding, whatever that's worth in the discussion.

    So if you reckon the "seasoning" isnt because the aluminium is porous, what about telling us what you think the reason is?

    Reiterating... Fact: aluminium moka pots season with coffee oils while stainless steel ones dont, resulting in different brew characteristics.

    How about getting off the pulpit and telling us what you think the answer is, instead of restricting yourself to telling others they are wrong without contributing a useful opinion of your own?
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    Quote Originally Posted by TOK View Post
    Short memory? Alzheimers? ...
    So if you reckon the "seasoning" isnt because the aluminium is porous, what about telling us what you think the reason is?
    ?
    Sorry but i am not the one claiming the seasoning effects on Aluminium moka pots, so I don't intend to explain your statements.
    i just don't like to see incorrect/false explanations being spouted as fact.
    At least my memory is good enough to remember the basic physical qualities of "normal" aluminium.
    PS;- I have used a range of moka pots , Al and SS, and have never noticed a difference in flavours tween them. But then again I do make a point of cleaning them between brews, and maybe my palette is not as finely tuned as others, or just maybe I am not that anal about fine analysis of brew characteristics !.
    PPS :- oddly, I am able to taste a difference between cold water drunk from a ceramic cup, Aluminium cup and a SS cup ??

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    mds
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    This thread started in 2007 and we're still crapping on each other. WOW!
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    Senior Member Yelta's Avatar
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    Here's an interesting read on the subject.

    Cooking With Aluminum - Equipment & Gear - Cooking For Engineers

    Interesting remarks re cast aluminium, which I imagine would include most aluminium stove tops.

    "Cast Aluminum is made by pouring heated molten aluminum into a mold. During this process, microscopic air pockets form in the metal. This means that the resulting cookware items will hold their heat for longer than sheet cookware. It also makes them quick to heat up and they only need a low heat source.

    However, they are not so great at distributing the heat evenly and are also quite brittle. If they are dropped, they will probably crack. Cast aluminum cookware is porous and needs to be seasoned. "
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    Quote Originally Posted by blend52 View Post
    Sorry but i am not the one claiming the seasoning effects on Aluminium moka pots, so I don't intend to explain your statements.
    i just don't like to see incorrect/false explanations being spouted as fact.
    At least my memory is good enough to remember the basic physical qualities of "normal" aluminium.
    PS;- I have used a range of moka pots , Al and SS, and have never noticed a difference in flavours tween them. But then again I do make a point of cleaning them between brews, and maybe my palette is not as finely tuned as others, or just maybe I am not that anal about fine analysis of brew characteristics !.
    PPS :- oddly, I am able to taste a difference between cold water drunk from a ceramic cup, Aluminium cup and a SS cup ??
    Can you tell us a bit about basic physical qualities of "normal" aluminium? plenty of info on cast and sheet, a search for normal aluminium doesn't seem to turn much up.
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    Jeez... You need to be a little more selective with your info sources.!
    ..or do you actually believe that rubbish about " pockets of air" allowing it to hold the heat longer ?
    ..and have you ever seen a cast Al cook pot crack if dropped ?
    Those comments are typical of someone with little more than a passing knowledge of modern metallurgy .
    But, hey if you are comfortable with an impression of cook pots and moka pots with sponge like texture,... That's OK.

    "Normal Aluminium"= aluminium without defects.

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    Quote Originally Posted by blend52 View Post
    "Normal Aluminium"= aluminium without defects.
    There ain't such a thing as anything without defects. Everything on this planet, man-made or otherwise, has defects. It's all about degree.

    And... as for air pockets in cast aluminium... MOST cheaply cast aluminium suffers from hydrogen porosity to some degree and these porous air pockets are typically 0.04 to 0.5 mm in diameter in cast items of under 3kg in weight. These pockets of air in porous aluminium become even larger in size in cast items in excess of 3kgs. Numerous air pockets of up to half a millimeter in size can certainly add a thermos effect to cast aluminium and it doesn't take a rocket scientist to see that porous metal is, by necessity, more brittle and more subject to cracking.

    Sure... it is possible to cast aluminium in a way to minimize (but never completely eradicate) hydrogen porosity... but these methods are highly complex and costly and would not be applied to cheaper consumer goods... i.e. moka pots.

    Bottom line b52, just because you don't want to believe it don't mean it ain't true.

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    Quote Originally Posted by Vinitasse View Post
    There ain't such a thing as anything without defects. Everything on this planet, man-made or otherwise, has defects. It's all about degree..
    OK Mr pedantic,.... let's refer to it as Aluminium made to a recognised industry standard.

    Quote Originally Posted by Vinitasse View Post
    And... as for air pockets in cast aluminium... MOST cheaply cast aluminium suffers from hydrogen porosity to some degree and these porous air pockets are typically 0.04 to 0.5 mm in diameter in cast items of under 3kg in weight. These pockets of air in porous aluminium become even larger in size in cast items in excess of 3kgs. Numerous air pockets of up to half a millimeter in size can certainly add a thermos effect to cast aluminium and it doesn't take a rocket scientist to see that porous metal is, by necessity, more brittle and more subject to cracking..
    Air pockets, porosity , etc is a defect.
    As I said earlier, anything can be made with defects,.....it just would not meet any recognised standard, and would be rejected.
    Thermos effect !! .??
    You do realise the reason cast Al cook pots hold their heat longer than sheet one, is because they are much thicker !?

    Quote Originally Posted by Vinitasse View Post
    Sure... it is possible to cast aluminium in a way to minimize (but never completely eradicate) hydrogen porosity... but these methods are highly complex and costly and would not be applied to cheaper consumer goods... i.e. moka pots.
    .
    No, neither complex or costly, and i doubt any casting shop would not be using simple degassing flux tablets which have been developed over many years to allow easy control of H2 porosity.
    It is a standard practice to prevent defects and costly waste.
    Im sure Bailetti would not be best pleased at your implying their products are cheaply made .

  34. #34
    TOK
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    Quote Originally Posted by blend52 View Post
    ....I have used a range of moka pots , Al and SS, and have never noticed a difference in flavours tween them....maybe my palette is not as finely tuned as others, or just maybe I am not that anal about fine analysis of brew characteristics...
    Dunno too many that would be so quick to admit that. In the case of the difference between alli VS s/st moka pots, the cupping characteristics are not even close to a "...fine analysis of brew characteristics...". More like so different they're glaring.

    Fact: aluminium moka pots season with coffee oils while stainless steel ones dont, resulting in different brew characteristics.

    Is it possible that some time soon you might stop trying to impress us with how much theoretical stuff you are able to memorise from web "research", and actually enlighten us with some real world practical knowledge on the subject of the topic?
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    Quote Originally Posted by TOK View Post
    D
    Is it possible that some time soon you might stop trying to impress us with how much theoretical stuff you are able to memorise from web "research", and actually enlighten us with some real world practical knowledge on the subject of the topic?
    "Subject of the topic" ...choice of moka pot ?
    i have already stated, I cannot tell the difference, so I will leave any further debate on that to the established experts.

    and you really should not assume everyone needs the same information sources as you might use.

  36. #36
    TOK
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    Sigh....

    Taken from another topic but much more relevant here:

    Originally Posted by Yelta
    Your a very patient man TOK.



    Despite all this wonderful academic knowledge you seem to be able to spruke concerning the properties of aluminium, you have not been able to suggest why aluminium Stove tops "season" with coffee oils while stainless ones don't.

    I have personally seen lots of dodgy aluminium castings that are porous. On rare occasions those castings have been so porous that liquid actually seeped through, but in the great majority of cases outright leakage doesn't happen. That doesn't mean that the castings aren't porous to whatever degree, and all of these castings get through "quality control" and end up in the marketplace....simply put, the machines work and are fit for purpose.

    I didn't read this in internet research, I learned it first hand.

    Happy for you to stick your head in the sand and continue to split hairs and say that aluminium (presumably) under ideal conditions / grade unknown / on the moon / in a vacuum(?) isn't porous, without venturing an opinion as to why then aluminium moka pots "season" with coffee oils.

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    Why do you repeatedly suggest that I should explain an effect ( seasoning ) that I have never claimed to have experienced ?
    seasoning is your proposal not mine, all i have done is correct the false assumption that moka pots are made from porous Aluminium castings.
    I you cannot explain your theory without resorting to false thinking, find another theory !
    the suggestion that any commercial aluminium cast container would be so "porous" that liquid would leak through is just so ludicrous I cannot believe you posted the comment as truth !
    If you insist it's true, I challenge you to state what the casting was, it's use and where it was made .
    any commercial cast shop would simply throw such a piece back into the recycle scrap pile.

  38. #38
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    Quote Originally Posted by blend52 View Post
    Why do you repeatedly suggest that I should explain an effect ( seasoning ) that I have never claimed to have experienced ?
    seasoning is your proposal not mine, all i have done is correct the false assumption that moka pots are made from porous Aluminium castings.
    I you cannot explain your theory without resorting to false thinking, find another theory !
    .
    thanks Mr Popper. The obvious question is, why interject in a debate concerning the explanation for a phenomenon for which you believe no explanation is required (coz you are not convinced that the phenomenon occurs)? This is bound to descend to circularity.

    I may as well ask 'Why are all dogs green?', ridicule the pro-photosynthesists, then after a few minutes later point out that dogs aren't green anyway.

    Just sayin...
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    Not sure which pic is most appropriate here, so I'm going to attach both
    Dead Horse GIF.gifNit-Picking.jpg
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    Quote Originally Posted by Barry O'Speedwagon View Post
    ..... why interject in a debate concerning the explanation for a phenomenon for which you believe no explanation is required (coz you are not convinced that the phenomenon occurs)?
    Just sayin...
    When have I said no explanation is required ?
    where did I say I am not convinced it occurs ?
    If you followed the discussion you would realise that my "interjection" was only to correct the blatantly false statement by Tampit....." Aluminium is porous" ....which was proposed as the explanation .

  41. #41
    Mal Dimal's Avatar
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    This ongoing circular debate helps the OP how, exactly....

    Mal.

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    If the following does not settle the debate once and for all... nothing will:

    "A PROBLEM AS OLD AS METAL ITSELF Ever since metal casting was first discovered, porosity, an area of sponge-like internal structure in an otherwise sound metal part, has been a problem. Porosity may be caused by internal shrinkage, gas cavitation, oxide films, inclusions andcombinations thereof. It can be found in virtually any type of metal casting or part, and is a particular problem in castings made from aluminum, zinc, bronze, iron, magnesium, and other alloys. Porosity is always present in powdered or sintered metal parts because of their structural nature.
    Various methods have been used to attempt filling porous openings in parts designed to contain liquids or gases under pressure. One of the first materials used for impregnation was "water-glass" or sodium silicate. In addition to sodium silicate, tung oil, linseed oil, pitch gum and many other materials were used with little success. Shortly after World War II, the development of thermosetting plastics, to be used as impregnants, became an effective and economical means of sealing porosity within the walls of metal castings, especially when used in conjunction with vacuum pressure impregnation techniques.
    UNDERSTANDING IMPREGNATION TECHNOLOGY
    Impregnation in metal castings and powdered metal parts refer to the sealing of leaks resulting from porosity. The impregnating material, as a liquid, is introduced into the voids or porosity within the wall of the part usually using vacuum and pressure. The material is then solidified, filling the porous openings and making the part pressure tight.
    Impregnation of powdered metal parts not only seals parts for pressure applications, but also improves plating or finishing, since bleedout or spotting due to entrapment of plating solutions in the pores is eliminated. Extended tool life is another benefit when machining powdered metal parts.
    At left:
    Coated parts
    Part on left was impregnated prior to coating
    Part on right was not impregnated prior to coating.
    Note coating breakdown on part at right.

    When castings have blind or continuous porosity areas, impregnation prior to painting or plating improves and protects the final surface finish from bleedout and blistering.
    Impregnation technology seals leaks on all ferrous and nonferrous metals, including die castings, sand castings, investment castings, pressure castings, powdered metal parts as well as forgings or weldments. Iron, bronze, aluminum, zinc, magnesium, steel, sintered metal, as well as alloys of these metals can be impregnated. Other non-metallic materials, such as wood, plastic, and ceramics can also be impregnated.
    IMPREGNATION IMPROVES OVERALL PART QUALITY
    When porosity in a metal part causes leakage problems, "bad" parts are often sorted out by testing and inspection. The "good" parts that are sent to production are often as porous as the "bad" parts, but the porosity is blind and not completely interconnected. Subsequent machining, mechanical or thermal shock, or stress often breaks the thin membrane which keeps the blind porosity from being continuous, thus causing a "leaker". Impregnation fills porosity from both sides preventing leaks even if the membrane does break. Therefore, impregnation improves and enhances quality, while inspection only sorts out leakers.
    ECONOMIES OF IMPREGNATION
    The value added to metal parts by machining, handling, and assembly may range into the hundreds or even thousands of dollars. This value is lost when a metal part is scrapped because of porosity and leaking. Impregnation costs are small fractions of the costs of remelting, recasting, re-machining and part overruns. Impregnation allows the manufacturer to save time, money, energy and insure quality by salvaging parts which would otherwise have to be rejected. The elimination of scrap and rework substantially increases productivity. In addition, 100% impregnation of metal parts sometimes eliminates the need for expensive leak testing, and often results in a dramatic reduction of field rejects in products such as transmission cases, air-conditioners, pumps and other metal parts.
    Impregnation of powdered metal parts provides the added benefit of prolonged tool life (up to 100 times) because IMPCO resins serve as lubricants as well as supporting the individual powered metal particles. Lubricity eliminates the chatter effect during the machining process of unimpregnated powdered metal parts.
    Because of the proven effectiveness and economies of impregnation, many engineers specify its use for all types of metal parts that must contain liquids or gases under pressure. It is now common for impregnation processes to be incorporated directly into production schedules to insure quality, rather than to be used strictly as a salvage operation.
    MACRO- & MICRO-POROSITY
    There are two general classifications of porosity found in metal parts: macro-porosity in the form of large flaws in the part which may be visible to the naked eye; and micro-porosity in the form of very small, almost invisible voids. In powdered metal parts, the structure of the metal results in a condition similar to macro-porosity in castings having low density, and micro-porosity in high density castings.
    Porosity can be found as "continuous, blind or totally enclosed" (see diagram below). Continuous porosity stretches completely through the wall thickness of a metal part causing a leakage path. Blind porosity is connected only to one side of the part wall. Totally enclosed porosity is totally isolated within the wall thickness of a part. When castings are machined, both blind and totally enclosed porosity are often "opened up" becoming continuous porosity and causing leaks.
    Modern "Impregnation Technology" permanently seals porosity leaks caused by either micro- or macro-porosity.
    IMPREGNATION METHODS
    There are four common methods of impregnation consisting of dry vacuum-pressure, internal pressure, wet vacuum-pressure and wet vacuum only.
    The dry vacuum-pressure which IMPCO pioneered is accomplished as follows:
    1. within an autoclave a vacuum is drawn, the air in the pores is evacuated without
    an impregnating liquid present to impede the evacuation (Figure 1) to a level fo 15 to 35 torr.
    2. the liquid impregnant is introduced while the parts are still under vacuum (Figure 2)
    3. a pressure cycle, up to 80-90 psi of shop air pressure (or up to six atmospheres) forces the impregnant deep into the porous cavities of the part for more positive sealing (Figure 3).
    After the impregnation cycle the part is removed from the autoclave, the surface is then rinsed in plain water, leaving no evidence or film of the impregnating material on the part surface. Machined surfaces or tolerances are not affected. The liquid material in the pores is cured by the application of heat.
    Internal impregnation is accomplished by placing the impregnant inside the casting and applying hydraulic pressure. This procedure is utilized in extremely large castings, forcing the liquid impregnant through the leak paths in the casting wall.
    Wet vacuum-pressure and wet vacuum only differ in the application of pressure. They both introduce parts into an impregnant bath and evacuate the air above the bath and subsequently from the porosity of the parts through the surrounding liquid impregnant. Pressure, either atmospheric or shop air is then applied to aid in penetration of sealant.

    After internal or wet vacuum impregnation, parts are washed and heated to solidify the resin.



    REQUIREMENTS FOR IMPREGNANTS
    The United States Department of Defense has established various military specifications outlining the requirements for impregnating processes and impregnants. In order to meet the standards required to produce pressure-tight castings, the ideal impregnant must be capable of penetrating and filling the porosity and then solidifying completely within the porosity of the metal parts. The impregnant should be a polar, low viscosity liquid containing no inert solvents, no filterable solid materials in suspension and producing no gaseous or liquid by-products on curing or transforming into an impervious solid.* These properties allow the impregnant to penetrate the tiniest openings and deepest recesses of porosity by capillary action. That is, such an impregnant can be drawn in by capillary forces, where it may not be possible to push it using hydraulic pressure alone. In addition, an impregnant should be stable, have a long pot life, be easy to handle and test without introducing unacceptable health and safety hazards in the work environment.
    * NAVORD Report 6957"

  43. #43
    Senior Member Vinitasse's Avatar
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    I thought the pretty pictures might help ;-P

  44. #44
    mds
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    If this thread was/were a horse we'd shoot it.
    BTW Vinnitasse your previous thread was longer than 600 words 😉😉😉😉

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    Senior Member Vinitasse's Avatar
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    Quote Originally Posted by mds View Post
    If this thread was/were a horse we'd shoot it.
    BTW Vinnitasse your previous thread was longer than 600 words 
    Good thing I wasn't the one who wrote it then dontcha think? Just sharing the good word so feel free to read as much, or as little as you wish. And... there's always the pretty pics for those who really couldn't be bothered.

  46. #46
    mds
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    I forgot, how dare you use facts! 😄😄😊
    Vinitasse likes this.

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    Interesting piece of history. ....that report was published 50 years ago !
    casting processes and quality standards have advanced a little since then.

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    Senior Member Vinitasse's Avatar
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    Quote Originally Posted by blend52 View Post
    Interesting piece of history. ....that report was published 50 years ago !
    casting processes and quality standards have advanced a little since then.
    The Navord Report was merely a footnote at the bottom of the text. The text itself comes from the very current website of a firm involved in the casting of aluminium and other metals... as in... now... 2015

    Care to admit that you might have been mistaken?

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    Quote Originally Posted by Vinitasse View Post
    Care to admit that you might have been mistaken?
    About what ?
    The date of the report ?.... No. that was from 1964
    About porosity ?.... No, it has always been considered a defect in aluminium and can be avoided with sensible foundry practices.
    About " impregnation systems "..No, they exist as a "repair" or rectification process for defective castings.

    Just to be clear , the basic point i am making is that commercial Aluminium in its correctly produced state, is a solid homogeneous metal.
    Porosity is a DEFECT and not considered acceptable in commercial products.

    As a further comment ....( might as well whilst i am at it !)
    hypothetically.. Even if those moka pots did have some porosity, do you think the manufacturer can control the amount in each pot ? or how even it is in any one pot ?, the size of the bubbles ? etc etc
    Making bad product is not difficult, but making consistently bad product is quite an achievement !
    Also, why would stale, burnt coffee oils retained in the pot walls be considered beneficial when in other coffee equipment the very same stale, burnt coffee oils are religiously cleaned out on a regular basis ??
    Last edited by blend52; 3rd March 2015 at 02:10 PM.

  50. #50
    Senior Member Vinitasse's Avatar
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    Behmor Brazen - $249 - Free Freight
    Quote Originally Posted by blend52 View Post
    About what ?
    The date of the report ?.... No. that was from 1964
    About porosity ?.... No, it has always been considered a defect in aluminium and can be avoided with sensible foundry practices.
    About " impregnation systems "..No, they exist as a "repair" or rectification process for defective castings.
    Does the following sound familiar?:

    ".?? That's the first time I have heard that aluminium is porous !
    any evidence to substantiate that statement ?
    .NO ? ...I thought not!
    i suggest you go and rethink your theory."

    Well... you've now heard about aluminium porosity a few times since that post... eventually it just might sink in. Good luck with that.

    In any event... you're not alone. Climate change deniers are also very good at not being able to see either the forest or the trees.
    mds likes this.

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