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  1. #16
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    It runs off a 15 Amp outlet.
    If you filled it brimful it would probably hold 12.5 kg Brass. The melt time was, (from memory) roughly the same regardless of how full the crucible was. It just took 3-4 hours to get to pouring temps.
    That kiln is about 220 mm dia ID and 300 mm deep.
    Most mechanics have to reclaim used oil and often pay to dispose of it. I have yet to meet 1 who wasnt happy for me to take it off his hands for nix.
    You can also run your oil burner on diesel, vegetable oil, (new and used), or even clean motor oil.

    BobL
    I am not going to get into an argument about the possible dangers of burning WMO, and I accept that it contains numerous toxins, carcinogens etc, but there are probably tens of thousands of mechanics in Aus alone handling WMO daily. It isnt difficult to be clean and hygenic. That report you link to raises some very ambiguous points. It doesnt mention the temperature of combustion at which points the emissions occur or cease. It states that ......"A four cylinder car of between 1 and 1.51 capacity loses from 0.2 to 0.31 of lubricating oil for each 1000 km of roadway. These losses are not always so small, a level of 0.5-1.01 per 1000km being more usual. In diesel engines with 9 or 10 cylinders, the oil losses are between 0.5 and 23 g h-~ according to the loading and the rotation speed......
    I doubt there are many 1-1.5 lt engines on the road, (in Aus at least) using 2 X their sump capacity between oil changes. I have driven trucks and coaches, long haul and local. And if I was adding between 2-80 lt of engine oil per Melb- Brissy return trip that truck would be off the road for an engine rebuild. My 6 cyl diesel landcruiser doesnt need any oil added between 5000 km changes. Sure it is down a smidge on where it was when it was refilled but never even close to the "Add" line. And that engine has 420 000 km on board. It goes further to state..... "Most of the 25-28 million tonnes of used motor oil produced yearly is spilled into the environment"..... I would think based on that figure then I am doing something positive for the environment. I accept that emissions occur and not all are visible, but I, at times, use the exhaust port to melt lead and there is never any residue, soot or otherwise on the steel crucible even after sitting in the exhaust gas flow for 30 - 60 minutes.

    Cheers Phil

  2. #17
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by 12bolts View Post
    BobL
    I am not going to get into an argument about the possible dangers of burning WMO, and I accept that it contains numerous toxins, carcinogens etc, but there are probably tens of thousands of mechanics in Aus alone handling WMO daily. It isnt difficult to be clean and hygenic. That report you link to raises some very ambiguous points. It doesnt mention the temperature of combustion at which points the emissions occur or cease.
    You are right about mechanics but they don't burn the stuff at high temps, and destroying the hydrocarbons is irrelevant in terms of the heavy metal emissions.

    To destroy elements like Co, Mo, Ni etc, temperatures are needed that are beyond thermonuclear (i.e. billions of degrees) - this happens to be an area I have also done some research on.

    In industrial high temperature incinerators most of the metals in the used oil are retained as ash because they mix the oil with other waste materials.
    They also monitor the emissions with very sophisticated gear and make adjustments to a burn to minimise emissions - something that a DIY is not really able to do.
    If no ash remains that means that all the metals are being emitted as nano oxides which are way too small to see so a DIYer would have no idea what they are breathing.
    To disperse these nano oxides away from a furnace, high flow ventilation with tall stacks are needed but all this does is transfer the problem elsewhere.

    Just because everyone else pees in the pool is no reason to do the same.
    Environmentally responsible oil disposal does not need to involved burning.
    Oil can be and is currently recycled and in the future our great grandkids will be more than that we destroyed such a valuable resource along with fouling their very small nest.

  3. #18
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    On the cost and durability of the element wire for an electric kiln-type melting furnace:

    I used the Kanthal handbooks (Kanthal 2003. "Kanthal Handbook: Heating alloys for electric household appliances". Catalogue 1-A-4-3, and Kanthal 2001."Kanthal handbook: Resistance heating alloys & systems for industrial furnaces". Catalogue 1-A-5B-3) along with empirical data I dug up on power required for different kiln sizes (for this I used a chart - Figure 7.3 - in the book by Harry Fraser 2006 "The Electric Kiln"; and also data for Cone-10 rated octagonal kilns by Tetlow Kilns and Furnaces in Melbourne), to do a full design of an electric kiln suited to an A6 crucible. The Kanthal literature basically guided me through the calculation process, with regard to suitable energy density within the kiln, i.e. wire diameter and spacing. Kanthal A1 is the right one to use for bronze melting as it is higher temperature rated than NiCr wire.

    Anyhow, I figured that I need 39m of 2mm diameter Kanthal A1 wire (that's 39 metres of straight wire before coiling) to suit the electrical loading specified by Kanthal when I input 2.8kW, which should be ample for a chamber volume of 6.7L (i.e. the space inside the furnace, which looks like a standard top-loading octagonal kiln as made by Tetlow in Australia, Paragon in the US, Skutt in US, or Rohde in Germany).

    I phoned the Kanthal distributor (Vulcan Stainless, who have an offices in most capital cities). It turns out the wire diameter sold is 2.05mm (close to the old AWG size of 12 gauge). The minimum quantity sold is 1kg, which for 2.05 mm A1 wire is 42 metres (how neat is that - just the right amount), and costs $98 (call ahead when ready to buy).

    As to longevity, he said there's no literature because "how long is a piece of string" - it depends on so many factors - but in vague and general terms, if the design is proper (i.e. use the Kanthal handbooks design procedure), thermal shock is avoided, no mechanical damage occurs (like dropping molten bronze on the elements), then with daily industrial use, one might expect 2 to 3 years life - even 8 years if well treated - or just 2 to 3 months life if abused. So I suppose if you extrapolate that to occasional home use, the life could be virtually unlimited. The obvious dangers for home melting are physical damage from spilling the bronze, and not having a controlled warm-up and cool down (I'm not sure about the criteria for that yet - would need a PID controller if it's an important factor). But assuming those abuses can be avoided, it doesn't look like the element wire has to be replaced often, if at all.

  4. #19
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    I've been toying with the idea of making a carbon arch furnace. Rods are cheap, buzzbox welders are cheap, but other than melting a few things and a little brazing, thats as far as I've got.


    Quote Originally Posted by BobL View Post
    You are right about mechanics but they don't burn the stuff at high temps, and destroying the hydrocarbons is irrelevant in terms of the heavy metal emissions.
    But is there any significant difference between driving a car burning 1L per 1000k for 10k and burning 10L of used oil in a furnace?(ok granted the average age of the oil in the car would be only 5k)
    At least one premium car manufacture feels that 1L per 1000k is "normal"

  5. #20
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    I've been toying with the idea of making a carbon arch furnace. Rods are cheap, buzzbox welders are cheap, but other than melting a few things and a little brazing, thats as far as I've got.

    But is there any significant difference between driving a car burning 1L per 1000k for 10k and burning 10L of used oil in a furnace?(ok granted the average age of the oil in the car would be only 5k)
    At least one premium car manufacture feels that 1L per 1000k is "normal"
    Probably not, but 1L per 1000 km is not exactly normal.
    A well maintained vehicle should not not require topping up between services.
    I cannot recall any time in the last decade or so "topping up" engine oil on either of our vehicles.
    One is new -3 year old Subaru and the other is a 4-8 year old Toyota diesel.

    The last time I was topping up engine oil was in the early naughties on our clapped out 1984 mitsubishi van and that was more like 100ml per 1000 km just before we got rid of it.

  6. #21
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    Quote Originally Posted by BobL View Post
    Used engine oil is well know to be mutagenic and carcinogenic so just handling it represents a risk and burning it makes things worse.
    The main effects are environmental but burnt engine oil vapours has been associated with skin, bladder, lung and scrota cancers.
    Even if you burn it away from anyone pregnant, a couple of times a year upwind in an isolated location I reckon its not worth the risk.

    EG See
    ENVIRONMENTAL IMPACT OF USED MOTOR OIL
    The Science of the Total Environment, 79 (1989), 1 23
    By RAFAELVAZQUEZ-DUHALT
    Centro de Investigaciones Bioldgicas de Baja California, ApartadoPostal 128, LaPazB.C.S.,23000 (Mexico)
    "...well known..." ? News to me.
    I'd be very sceptical of any so-called science written in the last 40 years. Most of it is poorly researched crap.

    With all the volcanoes and bush fires around the world I think yer get a load of heavy metal in the air w'er yer like it or not.

  7. #22
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    Quote Originally Posted by BobL View Post
    but 1L per 1000 km is not exactly normal.
    Agreed. I shouldn't have confused myself with it. "Normal" in the "we don't want to fix the motor under warranty" sense. I believe they have quite a few.

  8. #23
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    Quote Originally Posted by Gunnaduit View Post
    As to longevity, ..... it depends on so many factors -....... But assuming those abuses can be avoided, it doesn't look like the element wire has to be replaced often, if at all.
    Thermal shock is not the problem, nor is handling. Fluxing your melt and splashes of molten metal are the killers for the element. They create intense hot spots which rapidly burn through the element wire. That instantly ends your melt. Waiting for the element to cool down, then carefully heating to red hot with your oxy torch the broken ends so you can uncoil the wound element and twist the broken ends together to make a repair sure gets very old very fast. A new unused element is like a slinky. They come wound, but unstretched. You could play with the kids with it. 1st time you power them up they become like brittle fragile china. If you try to flex a section that isnt red hot it just snaps. The wire also oxidises during use. You would not get 8 years, or even 2-3 years with regular use in a home environment. I would be willing to bet that "industrial use" also incorporates the use of inert atmospheres to obtain that sort of life expectancy.
    Does that $98 also include winding?

    Cheers Phil

  9. #24
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    Whilst I wouldnt go so far as to say this
    Quote Originally Posted by YBAF View Post
    ....any so-called science written in the last 40 years. Most of it is poorly researched crap.
    On further reading of the article BobL posted I really think there are serious flaws in the figures quoted. Just on the oil consumption alone of popular common engines, petrol and diesel the figures are just wrong.
    Quote Originally Posted by BobL View Post
    Probably not, but 1L per 1000 km is not exactly normal.
    A well maintained vehicle should not not require topping up between services.
    I cannot recall any time in the last decade or so "topping up" engine oil on either of our vehicles.
    And if those simple figures are so wrong then just how accurate is the rest of the article?

    Cheers Phil

  10. #25
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    Forgot to ad a reference and link to my last post.

    “The case against science is straightforward: much of the scientific literature, perhaps half, may simply be untrue. Afflicted by studies with small sample sizes, tiny effects, invalid exploratory analyses, and flagrant conflicts of interest, together with an obsession for pursuing fashionable trends of dubious importance, science has taken a turn towards darkness.”

    http://www.thelancet.com/pdfs/journa...%2960696-1.pdf

  11. #26
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    Quote Originally Posted by 12bolts View Post
    You would not get 8 years, or even 2-3 years with regular use in a home environment.
    This post might be at risk of “Too Long Didn’t Read”, but anyway, I’m going to make a few notes on longevity from a Kanthal perspective. Hopefully some day I'll be able to report my personal experience and compare it to the 'textbook theory' here below, but that day has not arrived yet.

    I called back to Vulcan Stainless (i.e. Kanthal) in Dandenong this morning to ask a bit more about longevity. This time I spoke to their sales engineer Wayne Murphy who incidentally tweaked my design even further. I had used the design procedure in the Kanthal Handbook (ref below). He tweaked that design, which involved lowering the element wire diameter from my assumed 2.05mm down to 1.83mm diameter, increasing coil diameter and opening the pitch slightly. This is all to optimise the element surface loading, which is the main design factor in improving longevity. And this all assumes use of Kanthal A1 wire, as nichrome is not at all suited to the high temperatures of bronze melting and will bomb out quickly.

    He thought that barring mechanical destruction by splashing metal, etc. he "would be surprised" if I didn’t get at least 3 years life from properly designed A1 elements, when used to melt bronze in an ordinary atmosphere, if I’m running the furnace less than 20 times a year; but again stressed it really isn’t possible to put a figure on it. He did say though that elements do eventually wear out, so at some point they have to be thought of as consumables. For these small furnaces though, 1kg of wire is ample and that’s $109 inc GST. (That’s for a reel of wire; you make your own coils to your own length and diameter to suit your own design).

    Here are some notes relevant to longevity from “The Kanthal Handbook: resistance heating alloys and systems for industrial furnaces” (Catalogue 1-A-5B-3. Sweden: Kanthal AB, 2001) page 8.

    “Heating elements made of Kanthal alloys [e.g. A1] have 2-4 times longer life than heating elements made of nickel-chromium material. The higher the temperature, the greater the difference”

    “When heated, resistance heating alloys form an oxide layer on their surface, which prevents further oxidation of the material. To accomplish this function the oxide layer must be dense and resist the diffusion of gases. It must also be thin and adhere to the metal under temperature fluctuations. In these respects the oxide formed on Kanthal alloys is superior to that formed on Nicrothal alloys [nichrome], which contributes to the much longer operating life of Kanthal heating elements [e.g. Kanthal A1].”

    “The material thickness has a direct relationship to the element life, in that, as the wire diameter is increased, more alloying element is available per unit to form a new oxide. Thus, at a given temperature, thicker wires will give a longer life than thinner wires.” Note though that the sales engineer warned that there is a limit to this, where too low a load on the wire (too big a diameter) begins to be counterproductive. All this is quantitatively dealt with as design factors in the handbook design procedure.

    Table 3 in the Handbook indicates that the maximum permissible element temperature in a dry air oxidizing environment for Kathal A1 is 1400°C. Figure 5 shows the comparative element life. It indicates that when element temperature is 1250°C, element life reduced to about 62% of its life if operated at 1200°C, and when element temperature is 1300°C, life is reduced to about 40% of its life if operated at 1200°C. But as the sales engineer pointed out, that’s not to suggest a catastrophically short life, it depends on the element surface loading – and he noted that commercial kiln manufacturers, who Kanthal supply, are dealing with this all the time.

    Also, “The operating life of the heating elements will be reduced by rapid temperature fluctuations. It is therefore advisable to choose an electric control equipment, which gives as even a temperature as possible, e.g. thyristors.”

    From googling around it seems that a lot of people making an electric furnace at home (though there's very few, propane and oil burners are predominant) jump in and don't worry about element material and design - they just use whatever is at hand and 'make it look sorta right'. So I'm not too sure if short life wouldn't be a side effect of that. And yet, the design procedure is there for the taking, and is the same procedure that the manufacturers use for the kiln-furnace they sell to you for $4000. Well, if I go down this road, I'll be able to report back sometime and say what my own experience is.

  12. #27
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    Quote Originally Posted by BobL View Post
    I
    FWIW I made a turbocharged Twin torch mains gas forge that fair pumps heat.
    now i'm taking interest
    why not supercharged Bob

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