Controlled porous "Lotus" castings

MolaKule

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Member Trav, on another thread, suggested we comment on two referenced two papers regarding porosity in cast metals. His two very interesting references were: 1.) https://www.jim.or.jp/journal/e/pdf3/47/09/2259.pdf Tribological Behaviour of Lotus-Type Porous Cast Iron, by Takeshi Kato1, Takuji Nakahata and Hideo Nakajima, found in Materials Transactions, Vol. 47, No. 9 (2006) pp. 2259 to 2263 and 2.) http://www.google.com/patents/US4173500 a patent, Oxidation of flake graphite in atmosphere of carbon monoxide and dioxide, and water and hydrogen US 4173500 A. There are also other papers on this topic such as: 3.) Compressive properties of lotus-type porous iron, by Matej Vesenjak, Aljaz Kovac, Masakazu Tane, Matej Borovinšek, Hideo Nakajima, and Zoran Ren, in Computational Materials Science, Vol. 65, (2012) 37–43, 4.) Fabrication of lotus-type porous iron and its mechanical properties, by Soong-Keun Hyun, Teruyuki Ikeda, Hideo Nakajima in Science and Technology of Advanced Materials, Vol. 5, (2004) 201–205. 5.) Fabrication, properties, and applications of porous metals and directional pores, by Hideo Nakajim, in Proc Jpn Acad Ser B Phys Biol Sci. Nov 11, 2010; 86(9): 884–899. So let’s examine the two major forms of porosity for automobile engine castings. A. Internal porosity in metal castings can be modeled as little spheres or voids with solid boundaries and hollow internal spaces. B. Surface porosity in metal castings (such as in cylinder bores) can be modeled or idealized as little wells with three solid sides and an opening at the top which allow other metal particles and oil films, with dimensions smaller than themselves to enter, Ref. 1, Fig 7. In basic engine block finishing or refinishing, the cast iron block is first bored for cylinders and bearing saddles, then the cylinders are finished with a hone of approx. 280 grit in the usual cross-hatch pattern. In first machining the bore to basic dimensions, the bore surface is too smooth to trap oil films. The honing process produces an intersecting pattern of hills and valleys readily seen with the naked eye. This intersecting pattern of hills and valleys (cross-hatching) produces valleys which trap oil films, so when the piston ring passes by, there is a thick enough oil film for lubrication. Castings with large voids in them (casting defects) can lead to problems such as cracking and poor structural strength, poor heat conduction (less cooling), and even leakage, as in the case of poor aluminum transmission case castings in the past. In most of the papers referenced, Lotus means, “a new type of porous material which is distinguished by elongated pores resembling a lotus root.” The basic process of producing Lotus (unidirectional) pores is: 1.) controlling the alloying content, 2.) introducing various gases, and 3.) controlled heating and cooling cycles. Depending on the process, an elongated unidirectional pore can be produced, Ref. 1 and 3, or pores perpendicular to the solidification direction, Ref. 1. In reference 1, Figure 3, they show two porous surfaces, one elongated and one perpendicular. In the left photograph is an elongated pore, whereas the picture on the right is a perpendicular pore. For the picture on the left, the smallest pore “track” is about 0.02mm in width, and the largest is about 0.07mm in width. For the picture on the right, the smallest pore is about 0.005mm in diameter, and the largest pore is about 0.06mm in diameter. If one can produce a casting structure with directional pores to hold oil films, AND with the necessary structural strength, the production process can be simplified, the weight can be reduced, the friction coefficient is reduced, and wear resistance is increased. In one of the papers, it was suggested that the casting of porous bearings could entrain oil when heated to a specific temperature and under a specific pressure. This would be similar to the Oilite process where the sintered metals entrain oil because of their large inter-granular voids. Except here, the pores in the casting would entrain the oil. If used as engine bearings, the problem I see is this: When the oil in the pores become oxidized from continual heating and turn to sludge and then to solid carbon, what happens to the COF and the wear? The oil in those pores can never be “refreshed” with new oil. If you increased the porosity such that the pressurized oil supply could refresh it, then it appears the structural strength of the bearing would decrease and be unable to support the loads, which then takes us back to the old multi-layer, grooved, solid bearing.
 
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MolaKule, I know that they used an aluminum/silicone mix in the old Chevy Vega block (Gosh, I hate to bring up old nightmares) to achieve the same thing. But these failed, usually by 50,000 miles. Was the mode of failure in these blocks due to oil oxidation or was it simply wear and tear of the sides of the cylinder? I believe the aluminum was etched away leaving a porous silicone skeleton on the surface that was supposed to function as an oil trap.
 
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Originally Posted By: Boomer
MolaKule, I know that they used an aluminum/silicone mix in the old Chevy Vega block (Gosh, I hate to bring up old nightmares) to achieve the same thing. But these failed, usually by 50,000 miles. Was the mode of failure in these blocks due to oil oxidation or was it simply wear and tear of the sides of the cylinder? I believe the aluminum was etched away leaving a porous silicone skeleton on the surface that was supposed to function as an oil trap.
Boomer, I posted some links here on the SiAl processes, etching, and lubrication...alas I was on holidays, on a mobile device, and offended some a little.
 
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I appreciate the time you took doing this Mola. Thanks. This really raises some questions so i hope you don't mind if i pick your brain a little and get your opinions. Is this more beneficial to sliding surfaces like those found on cylinder walls as opposed to something like a rotating surface like a bearing? Is this advantageous to reducing friction on those surfaces therefore reducing heat and wear? Which would accomplish this better a lighter or heavier viscosity oil? Would a solid lubricant like MoS2 or Ceramic (hexagonal boron nitride) be of any benefit or counter productive by clogging the pores? Can this technology or similar processes be used in other materials eg aluminum? In your opinion is this improving or enhancing the lubrication properties of engine oil through metallurgy and will it benefit wear and frictional losses? Thats all i can think of at the moment, i am sure others will have some interesting questions. Again i sincerely thank you for your input, it could be a very educational and enlightning topic. With lower viscosity oils, variable displacement pumps and metallurgy we just may see an engine that is less prone to wear due to lower friction and maintain its level of performance. I hope this doesn't get sidetracked into a thick/ thin oil, additive/anti additive or additives soaking into metal thread. I want to lean something from this.
 
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Trav, my view is that the technology is most applicable in areas like cylinders than bearings. In IC engines that is. We tend to try to get bearing surfaces smooth as we can. Shaft surfaces smooth as they can in hydrodynamic lubrication, using smoothness and shape rather than roughness to achieve lubrication. (Have seen some bearings where people have put "crosshatching to hold oil" which has lasted, but made me scream when I found out, it turns a bearing into a lot of little bearings. Cylinders have crosshatching to hold oil, sintered bearings are porous to hold oil, they are more in the realms of boundary lubrication...which is my view on where this technology is most useful. Personally, I'm a bit suspicious of intentional porosity, as if you are intentionally eliminating it (the vacuum/inert gas partial pressure in the crucible is used even on 60 tonne turbine rotors these days), a little bit can be a minor issue. Intentionally introducing it means that there's more scope for a greater than desired amount of it more often...I have seen porosity crush when subject to hydraulic loading, and spall out through what's likely "intracellular" fatigue when subject to cyclic hydraulic loading. Not dissing it, as the ultra pure castings that we have today took decades of evolution to get where they are.
 
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I can see where it would be of no benefit on a rotating shaft. I was thinking more about the use on smooth bore engines with little or no crosshatch and low tension rings. .
 

MolaKule

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Originally Posted By: Boomer
MolaKule, I know that they used an aluminum/silicone mix in the old Chevy Vega block (Gosh, I hate to bring up old nightmares) to achieve the same thing. But these failed, usually by 50,000 miles. Was the mode of failure in these blocks due to oil oxidation or was it simply wear and tear of the sides of the cylinder? I believe the aluminum was etched away leaving a porous silicone skeleton on the surface that was supposed to function as an oil trap.
I know the Vega engine very well. I was a student at the U with 2 kids and a mortgage so the Vega was my putter and daily driver. I never had any engine mechanical problems. I did have problems with Le carburateur. I always carried an extra carb rebuild kit with me after being stalled in an intersection a couple of times. I could rebuild that thing in under 15 minutes, in any weather. shocked2 I did help some friends replace their Vega short blocks when their engines went caput. And then there was the rustbucket body. I was always patching up rust spots. The silicon/aluminum alloy engine block was supposed to be GM's savior during the oil distribution crisis. Most of the engine failures in my experience were due to overheating caused by head gasket failures, since the head was cast iron and the block was aluminum/silicon. Differences in COE usually nailed a decent short block.
 
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MolaKule

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Quote:
Is this more beneficial to sliding surfaces like those found on cylinder walls as opposed to something like a rotating surface like a bearing?
Cylinder walls. I fully agree with Shannow on this one.
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Is this advantageous to reducing friction on those surfaces therefore reducing heat and wear?
Yes.
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Which would accomplish this better a lighter or heavier viscosity oil?
A low viscosity oil since it would wash the pores better.
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Would a solid lubricant like MoS2 or Ceramic (hexagonal boron nitride) be of any benefit or counter productive by clogging the pores?
If the oil can be refreshed I don't think nano-particles would necessarily clog the pores.
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Can this technology or similar processes be used in other materials eg aluminum?
Yes it can. There is some research going on right now into aluminum blocks.
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In your opinion is this improving or enhancing the lubrication properties of engine oil through metallurgy and will it benefit wear and frictional losses?
Engine oil development has to necessarily track engine metallurgy. I do think the laser scribing method described by ElastoHydro,
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This looks similar to the laser-dimpling surface treatment Audi has been using to get micro oil reservoirs to set up at the surface of cylinder walls. http://www.coherent.com/Downloads/AE1204.pdf The lotus porous surface also sets up oil reservoirs.
seems to make more sense than developing a complex casting process. IE, leave the porosity alone and keep the metal matrix's structural strength, but only scribe where it is necessary to retain oil films. This also guarantees that no grit is left in the "valleys."
 
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Thanks for that Mola. I am digging around in my dads old reference books on metallurgy. He studied it and got a degree in it and business after he learned his trade as a machinist. He needed it to run the machine and tool manufacturing company, he was my reference for all things metal and machine shop stuff but he died. I can operate most of the machinery (not with a high degree of skill) and know little about the materials, hardening, expansion rates, flex and so on.
 

MolaKule

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I am digging around in my dads old reference books on metallurgy. He studied it and got a degree in it and business after he learned his trade as a machinist. He needed it to run the machine and tool manufacturing company, he was my reference for all things metal and machine shop stuff but he died. I can operate most of the machinery (not with a high degree of skill) and know little about the materials, hardening, expansion rates, flex and so on.
Cool, my dad was first a machinist and then a tool and die engineer in aereospace. One of my first jobs out of HS was as a machinist.
 
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Originally Posted By: OVERKILL
Fantastic information! Thank you for sharing. thumbsup
Times a dozen, greatly enjoyed the dissection as reading them was a bit out of my league...
 
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This looks similar to the laser-dimpling surface treatment Audi has been using to get micro oil reservoirs to set up at the surface of cylinder walls. http://www.coherent.com/Downloads/AE1204.pdf The lotus porous surface also sets up oil reservoirs.
seems to make more sense than developing a complex casting process. IE, leave the porosity alone and keep the metal matrix's structural strength, but only scribe where it is necessary to retain oil films. This also guarantees that no grit is left in the "valleys." [/quote] Could the pours be localized? Or would they exist through the whole casting? That would not work well in areas that needed to be threaded for fasteners. It also seems the pours are unidirectional. How would that work with regard cyl walls ? 'Pin holes' could be formed on Two sides of the cyl wall ie. 6 O'clock and 12 O'clock, but the voids would progress to Ovals then Slots at the 3 and 9 O'clock positions. Ideally the pours should be Radial to the axis of the bore. But I'm not sure that is possible. The Audi Laser method seems much better and more controllable. Heck, you could even have varying degrees of Dimples along the length of the bore depending on the degree of oil retention you needed.
 

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Quote:
Could the pours be localized? Or would they exist through the whole casting? That would not work well in areas that needed to be threaded for fasteners.
They would exist throughout the whole casting.
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It also seems the pours are unidirectional. How would that work with regard cyl walls ?
The pores that are elongated strips would have to be perpendicular to the axis of the bore.
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The Audi Laser method seems much better and more controllable. Heck, you could even have varying degrees of Dimples along the length of the bore depending on the degree of oil retention you needed.
I agree.
 
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I am looking for more information on whats refereed to as porous iron that is claimed to be the type used in old cast iron blocks. It had pores up to a certain size and anything greater was defective because it could crack easier or become too porous. Porosity it seems is considered a defect. The size of the pores apparently is what makes it acceptable for use or discarded. Interesting read here.. http://www.weber-automotive.com/fileadmi...nklassen_EN.pdf The Lotus iron appears to be a very controlled, deliberate and uniform process. It would seem the VW/Audi process is better but going through books and Google is about the limit for me the rest is a bit over my pay grade. I do know that engine block iron is generally gray iron, the cheapest there is, cranks are usually nodular iron. The more i look into this i began to realize that the castings on most of these cheap offshore tools and equipment are mostly stuff that should have been discarded.
 
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Trav, porosity is a fact of life in casting, and has been for as long as the technique has existed (my backyard cast Al perfect case in point). Porosity, as a lack of homogeneity has always been frowned upon, and requires an overdesign, invariably making things heavier and less reliable than they could have been. The spec that you linked to is the sort of industry spec for what's an acceptable amount of defective material, based through hard won experience, and more recently through finite element analysis, where they can calculate stresses,and how two defects near each other will push local stresses to the point of fatigue or cracking. Look at a cast part, and seemingly stupid stuff like a radius in a fillet can affect the flow of molten iron, and make the foot of an HF drillpress look like a sponge and break off while bolting it down. If you look at a turbine rotor (as an example), traditionally, they were cast vertically. As the metal cooled and solidified the impurities and gasses are forced to the centre, leaving a mess in the middle...which was then drilled out, and discrded, as the clean metal around it is better without the core than with it left in. Then an analysis is done on every single pore that is left... Industry has developed techniques to reduce porosity, latest is ultraclean metals, under inert gasses/vacuums. It's been ongoing over decades...now they don't need to bore rotors, there's not as much rubbish in the centre. That's why I'm suspicious of re-introducing controlled porosity.We'll get it right, but there might be lots of unhappy customers in the mean time. Not sure on the porous iron you mentioned, but some of the cast irons have a lot of graphite, porosity, and the like... e.g. http://machinedesign.com/basics-design/porous-metal-bearings There are some rail carriages for extremely heavy loads, in remote areas which use plain bearings exclusively as they can be jacked off, scraped, and re-inserted out in the field without rolling elements, heaters, pullers/pushers etc.
 
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Thanks for the info Shannow. I cant really comment on much because i don't know much about it but it is interesting. The more you read the more complex it becomes. I know a high quality vice cost a lot of money but its the iron and the casting that drives the cost up, they will last a lifetime and more. I remember seeing an old engine that had a high silver content iron block and nickel iron is common in high stress blocks. There is a new type iron casting that is claimed as light as aluminum and much stronger. Ford will be using it in the new 2.7 ecoboost and Hyundai uses it in their 3.0 as well as some other auto engine manufacturers. Graphite type and content seems to play an important role. http://www.sintercast.com/file/documents...der-heads-1.pdf Edit: Could this compacted graphite iron be the same as the "Lotus" iron?
 
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Vise. Although high quality vice costs a lot too, or at least so I'm told wink
Originally Posted By: Trav
I know a high quality vice cost a lot of money
 
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