Super experiment! Thank you. When I was doing aluminum castings I would use charcoal powder (600 mesh) instead of talcum as a parting agent over me home made green sand. That also improved the finish over talc. Now I know why.
As always, your experiment is well thought out, superbly executed, and produces undeniable "real world" results! Can we expect a follow up with varying proportions of coal dust? Then perhaps an "idealized coal dust" petrobond side by side challenge? Your efforts make this my favorite ferrous casting channel by a great margin, thanks so much for sharing this wealth of knowledge!
Excellant demonstration 👍🏻, Coal dust ignites at contact with iron and creates a thin ribbon of carbon(soote) which serves as a refractory against the facing sand and keeps it from fusing to the iron.
Excellent video! When I first started out casting I used Petrobond and to this day still use it. I have had good success using 2 cycle outboard motor oil to rejuvenate the sand when it starts to dry out. I am at the point where I want to build a furnace capable of melting cast iron and this video assures me that I can have success using Petrobond. Thank You !
Very intetesting well thought out experiment, thankyou. Perhaps you could try another where the petrobond or coaldust sand half is fully on the side of the gate so that the pour flows fully over it before hitting the sand bentonite mix. Perhaps then there would be more time for the off gassing to have an effect on the "standard" sand.
Thank you! As always an interesting informative video! You say that a reducing atmosphere would migrate to the other half of the mold. In my opinion, the reducing effect is localised and contained in one area as the mold is full and thus unable to allow the oxygen starvation to circulate. regards, Matthew
I would like to see a test using petrobond on one half and coal on the other. From the title that's what I expected. I think, from what you've done that I know the results, but would like to see it first hand.
Is that bituminous coal or anthracite coal that Petrobond mixes in? I'm assuming bituminous but it does make me wonder what if we tried anthracite.. Anyway some sources say there is mercury in coal and since mercury vaporizes at quite a low temperature I'm thinking that would be good to keep in mind.Love the experiment and this will be a video people will watch decades from now..
Thanks again for a well presented and thoughtful video. I used Petrobond for aluminum casting 30 plus years ago. It was capable of making great surface finishes. Watching this video makes me think of the surface finish in your other cast iron work. It is pretty good. As you say you need to temper your mix with more coal dust to get that level of surface finish. Care to show us the results of a further experiment?
I disagree with your explanation at the end about the effect of coal dust and petrobond... I don't think it lifts the surface of the metal up..it fills in the the voids left by the large sand particles creating a smoother surface, that's why petrobond powder/binder is so fine...that's what makes it a precision casting, if it raised the surface it would not be precision it would just be a better surface finish.... I do precision dental castings and have noticed the same affect with different types of investment and we work to tolerances in the microns. Just out of curiosity you should try mixing good quality dental plaster(gypsum) as a filler as this is a major component in professional investments..
dusting talk on the molds acts as a mold release so to speak..surface finish is affected by the smoothness of the mold and the heat resistance of the mold material ... with sand the surface is fairly rough, with petrobond which is way finer than sand the surface finish is way smoother before you poor the metal in the mold that's why it's a smoother casting... if you ground your sand to a fine dust you would get smoother castings without changing anything else..try it.
@@electro1622 The finer the sand the less venting capacity the mold has and the greater likelihood of imperfections. The gasses produced from the burning of the oil or coal create a very thin gas front that prevents the iron 'burning' in and giving the slick finishes. Cam
Cam at Battler.. G'day Cam.. I don't think that is true..in fact t 1:49 he reads from the instructions which say it needs less if any venting..and petrobond is way finer than sand..also.. I use the lost wax technique when casting and the investment we use is very very dense compared to sand casting and we don't vent at all with no ill effect or miscasts...the surface finish we get is also very good... here is a video I made a while ago about casting one metal onto another with a forge weld effect but it gives you an idea about the sprue and surface finish of the casting.... ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pYasBe2sjFk.html
Great demonstration / experiment. 👍 (insert cool casting pour emoji icon here) Not into casting iron yet, but my aluminum tests & experiments have been very rewarding. 😊 Yours are always good. Thanks.
Cool video again. For an occasional home shop iron caster, would it be more efficient to use a little petrobond as facing sand in each nould, backed up with home made synthetic green sand, which will slowly get contaminated by the Petrobond, or would a better course of action be pure petrobond, discard the burnt stuff in contact with the part, and mull the rest?
Badly. I have been concentrating on my MAHO retrofit for the last year. forum.linuxcnc.org/12-milling/33035-retrofitting-a-1986-maho-mh400e I have nearly finished making a small muller, as stomp mulling gets really old.
The principles of iron founding archive.org/details/principlesironf01moldgoog/page/n6 The production of malleable castings archive.org/details/productionofmall00moldrich/page/n8
1 mol of liquid water volume at STP occupies 18cc 1 mol of any gas at STP occupies about 22.4 liters. Vol change at STP = (22400 cc/18cc) = 1244 But it only gets worse. Once the water becomes a gas at 100C, it also expands depending on how much heat the steam is heated according to gas law PV=nRTk. Just use the ratio of absolute temp k as a rule of thumb for expansion on a non condensing hot surface. So one volume of steam at 100 C (373.15k) will expand 2.87 times more at 800 C (1073.15k) giving a total expansion from liquid water to high temp gas at 800C of: 1244 x 2.87 = 3777 ...and a great reason to at least use safety glasses during a pour. I did some Al casting 45 years ago and I am just getting back into it now that I have a little spare time, hopefully with iron. Your channel is one of the best resources I've seen LG, keep em coming.
Yes you are right, the number I've seen is 1700 times but that is at 100C. Pouring molten cast iron into a sand mold it is certain that the steam will be superheated and so be a lot more than 1700 times.
@@luckygen1001 A bit off topic, but I noticed you use scrap microwave timers in some projects. Problem is the new inverter timers need a special feedback signal from the inverter PWB or they throw an H97 or H98 error, making them useless for timers outside the original application. The feedback signal (mini-3 wire plug) needed is just the PWM signal (yellow to black) from the computer divided by 2, with the orange held high when no PWM is on the orange. I threw together a simple 5 component one chip simulator using a 4027 to keep the computer happy. Total parts cost.. about a buck. Let me know if you want the schematic for your projects.
It seems that no one uses coal dust anymore in a foundry setting. If you can wait I will be making a video in about two weeks time showing how to make a substitute for coal dust.
Great experiment!. With respect to the improved surface finish that is obtained by adding coal dust to the sand, I think there might be more going on than just the evolution of some gas from the coal dust. After all, the plain green sand liberates steam which could “lift” the metal, but perhaps it does that too vigorously. Rather I suspect that when the hot metal contacts the coal dust on the surface of the mould, it is somehow forming a beneficial crust which isolates the metal from the mould material. Presumable when the hot iron contacts that coal dust it cracks the bitumen content of the coal into hydrocarbon gases. I wonder whether the gasses combine with one or other of the other materials present to form a crust. These questions suggest some other experiments. If it is the hydrocarbon in the coal that provides the benefit you could try using some “oiled” coke dust to prove the point. Also, you could try just adding oil to the green sand mix. Oil can be mixed into water with the aid of detergent. You could try making your green sand with “oily” water, although the effect of the detergent, which is to lower the surface tension of the water, may also alter the mechanical properties of the sand at any given moisture content. Adding some detergent to the water in the green sand mix would be an interesting experiment in itself. Even traces of detergent affect how water spreads and wets the surface of some materials.
A water based sand will not give a good finish on cast iron, that is why a hydrocarbon is used to burn in a mold to give a better finish on the surface of the casting. Oil mixed with a water based sand will prevent the bentonite working as a binder. Detergents let oil and water to mix but the same problem will happen, the sand will not hold together as well as using only water. A small amount of oil may give a better finish in a water based sand but that would need a lot experimenting to see if it can be done.
Luckygen, the intriguing question is what is it in the coal dust that provides the improvement to the cast surface when it mixed into an otherwise water-based moulding sand, and is it possible to supply that benefit in some better way? As you have explained in your reply to another poster, it is not just the carbon in the coal dust that helps, otherwise powdered coke or graphite would do the same as coal dust. A suggestion for another experiment would be to simply spray the finished mould surface with some oil. It would be hard to apply a thin coat of a more viscous “heavy” hydrocarbon such as tar. Could the benefit of coal dust simply be that the hot iron “cracks” the hydrocarbon content of the coal and drives off the hydrogen and thereby forms a skin of carbon on the surface of the mould, a bit like the skin of carbon that gets deposited in the chimney of my wood fired heater? Whatever is the action of the coal dust, it has to be arising in the thin layer of sand that is in contact with the iron. Interestingly, the Hazer process that is currently being developed in Western Australia, cracks natural gas into hydrogen and graphite at temperatures of around 1,200 C, using iron ore as a catalyst. So it is likely that the hot iron in a mould cracks any hydrocarbons in coal dust down to carbon and hydrogen. With respect to the effect of detergent, the detergent molecules do get “used up” in a sense when oil is added to the water. The oil loving ends of the detergent molecules stick to the microscopic oil droplets. So, it may be that the deleterious effect of the detergent on the moulding properties of the sand might not be so great if the detergent content is fully occupied in surrounding the added oil. But rather than trying mix oil all through the sand maybe a better approach is to apply it where it is needed, although you would think someone would have tried it before now. Here is a link to what is in the various types of coal www.purdue.edu/discoverypark/energy/assets/pdfs/cctr/outreach/Basics8-CoalCharacteristics-Oct08.pdf
I have thought about spaying oil onto the mold surface but how much do I spray on and how evenly. When is it too much or too little? When oil is mixed with sand a known amount can be mixed with it but spraying the internal surfaces with deep pockets and other hard to spray surfaces could lead to uneven amounts on the surface.
@@luckygen1001 I was thinking of the oil spraying more as an experiment in the first instance to test whether hydrocarbon present on a green sand mould surface can produce the sort of improvement in the cast surface that is obtained by adding coal dust to the sand mix. If not, there must be some other action provided by coal dust. With your disk-shaped test piece, you could perhaps try four different intensities of application of the oil by masking the mould with a piece of sheet material. That might answer the question as to whether spray applied oil works at any degree of application. Considering the small amount of coal dust dust that is added to the sand mix, the quantity of hydrocarbon provided by the the coal dust has to be smaller still. Bituminous coal contains around 30 to 40% hydrocarbon equivalent. The following is evidently from Principles of Foundry Technology By P. L. Jain. I found the quote in the discussion in the following link. The quote mentions using pitch dust and fuel oil as alternatives to coal dust. www.researchgate.net/post/Whats_the_impact_of_increase_in_the_amount_of_coal_dust_in_the_mixture_of_sand_molding_on_formation_ferrite_on_the_surface_grey_iron_parts "Coal Dust - It is commonly used in green sand and dry sand moulding for protecting mould surfaces against the action of molten metal and improving surface finish of cast iron castings. When the moulten metal come in contact with mould surfaces containing coal dust, a gaseous envelope is formed which resists the fusion of sand to metal. Use of coal dust increases both green and dry strength, reduces expansion, tendency to scabbing and metal penetration. It, however, tends to reduce the permeability of sand. Good quality coal dust suitable for foundry use should consist of finely crushed bituminous coal free from foreign material, and should have fineness about 150 mesh BS sieve, equivalent to 106 micron IS sieve. It should have a minimum 30% volatile matter, maximum 20% ash, 3% moisture, 1% sulpher and 0.2% phosphorus content. Specifications of coal dust for use in foundry are covered by IS: 1752-1973. Pitch and fuel oil are used as reducing agents and have similar effect as coal dust. IS13100-1991 give the specification of pitch powder for use in foundries."
How much water expands. Let's go. One mole of water is 18 grams which is almost exactly 18ml. One mole of gas in standard state (24C, 105kPa, basically the definition of room temp and sea level pressure) will be 22,5dm^3 or liters. We have expansion from 0,018l to 22,5l which means up to 1250 times expansion! That's pretty fightening honestly
I'm just getting into casting iron and I'm lucky to have some of my grandfather's notes. But I'm trying to figure out why he used to smoke the inside of some of his coal dust molds with a sooty acetylene smoke. Could there be another reason besides helping to part the molds.
@@luckygen1001 thank you, I assumed it was for the surface finish but didn't know for sure.......I spent a lot of time helping him when I was younger and wish I could have started sooner. But he passed away when I was in high school and life has a habit of getting in the way. But thankfully he took good notes on the work that he did.
Great video! Where do you find coal dust? Do you make it or buy it under some foundry supply name? Here in the US my local supplier says he's never heard of it and that I should just use Petrobond. Id really like to try making and using your coal dust sand for Iron. I've watyched your sand making videos so I have the recipe, but again just need to know where I an get some coal dust. Would crushed charcoal work? Thanks again!
I buy it from my foundry supplier. Crushed charcoal will fill in the gaps in the sand but does not burn. If you cannot get coal dust then use petrobond sand as it is much easier to get.
Of course and thanks for the reply. I've been asking my supplier for coal dust which he claims he never heard of. But today when I asked for "Sea Coal" he said oh of course he sell that! Blasted younger generation. I told him about your RU-vid videos and he later called me and thanked me for the referral. Much appreciated!
Leads one to wonder...if you used super dry sand mixed with bentonite mixed w coal dust wetted with an oil of some sort perhaps synthetic oil? Would be interesting to do test if it would be cheaper to concoct than Petra bond
@@luckygen1001 well your the man...lol already tried it. But that's good to know though. Thanks for the reply and handy info. Blessed days sirSir, Crawford out
Could somebody explain - What is the coal dust? and where I can get it or Can I make it ? Is is what lesft from burning coal (charcoal?) or grinding the coal into dust?
Very interesting results. I never would have thought that Petra bond would act that way. Actually figured it would burn and not produce a good finish. Boy was I wrong. Thank you for sharing this with us. Blessed days sirSir, Crawford out
Thank you for watching the video! I was really impressed on how your lost PLA castings turned out in iron, outstanding effort. I must try that method one day.
I had a quick look online and could not find anything, I got mine from the supplier of the petrobond powder but other than that I do not know where to get the petrobond manual.
Hi Thank you for the reply I actually manage to find it this is the link www.slideshare.net/FoundryJoe/petro-bond-foundry-sand-brochure Bentonite Corporation doesn't exist anymore. What is the name of the manufacture on your bag? Again I enjoy all your videos and I appreciate you sharing your knowledge.
On Sandrammer's channel he found a supplier that supports home foundries. It's still expensive but you can buy in smaller lots vice having to buy a large lots then have the wife yell at you because you're only use a third of it at a time.
What grit of sand a and type to use? Ive always just used silica sand 120 grit, but would like to improve my surface finish. My supplier has something called Olivine and recommending 120 grit for both AL and Iron. What does everyone think? Its twice the price of plain white silica and I have about 300 lbs to replace as I make my new coal dust sand. I primarily into AL but will be moving into iron this summer so am preparing new sand now. Id like to use the same sand for both.
Silica sand has one problem, it expands suddenly when hot iron flows over it. It cannot be rammed too tightly otherwise there will be large mold movements that look like there has been an earthquake. I would love to try olivine sand as it does not have this problem of sudden expansion. You answered me because I have wondered how pricy olivine sand was and would like to try it for myself. The surface finish on iron castings can be improved by dusting talc or graphite on the pattern or after the pattern has been removed from the sand. Very fine grained sands will give a better surface finish on iron castings but have less porosity for the steam to escape.
Some irons are harder so more ferrosilicon has to added so the iron can be drilled or machined. I start with a 0.25% addition and then work from there. If too much is added then it will make the iron go very hard.
Thank you I’m having a hard time finding a supplier for Ferro Silicon in Canada, I found this on EBay. m.ebay.com/sch/i.html?_sacat=182920&_from=R40&_trksid=p2499334.m4084.l1313.TR4.TRC0.A0.H0.Xferro+si.TRS0&_nkw=ferro+silicon If my math is right 1lb should do 400lbs at .25% I have been casting aluminum for years and looking to step up to iron. I use a siphon burner and diesel so the heat is no trouble. What do you recommend for a crucible?
I started watching your videos a while ago and I think they're very good - there's not too many videos going into details of casting. It's the first channel when I saw the wedge method for example. Thanks for sharing the title of the book that you've used. Btw, if anyone is interested, here's a scan of the book: babel.hathitrust.org/cgi/pt?id=wu.89088935192;view=1up;seq=7 (and there's also tons of other foundry, machining, woodworking and other interesting books out there). Could you recommend any other books that you were using when learning about casting?
This is the best one I have used and have a hard copy www.dymocks.com.au/book/foseco-foundrymans-handbook-by-ta-burns-9781483293233/?gclid=Cj0KCQiA-JXiBRCpARIsAGqF8wXC885RMwPz3Nv-Pi-ObHr3JmqVWH9jb3GbG25K_jDc8uOPY-s9nnwaAgCAEALw_wcB
Very nice and informative videos! Appreciated! May I ask your email address? I really need your help on cast iron porosity and defects I'm having. I need to send you the pictures. Thank you!
I see that you only melt aluminium, as I rarely melt aluminium so the best channel to see is olfoundryman channel ru-vid.com/show-UC90RoN_IjSRF18jAG0HIA6gvideos?disable_polymer=1
