Tuesday, December 10, 2013

Postblogging November 19443: Technical Appendix: The Alliance of Thrust and Iron

Wikipedia: The trackless forest of Anderida, where the Royal Navy's gunmakers lived and worked: Unsized because it's so damned evocative.. Obviously it's a bit spoiled by the embedded blog material, but you can go to the original if you like.

Robert Constant opens The Origins of the Turbojet Revolution in the mountains, in the same place that Clint Eastwood opens Pale Rider, with the same powerful vision. Water, under human control, washing down the mountains.

We are in the middle of a mountainside industrial revolution. Not in the Weald, but rather in the Sierra Nevada, this Monitor operator is finding gold with high-pressure water.  In Eastwood's vision, hydraulic mining is an evil thing. The cinematic composition implicates environmental hazard, but the crime that brings the  ghost of death(?) to town to kill all the bad people with guns is that of putting old fashioned panners out of work. In the nostalgic old days, people panned gold in communities. Now the Monitors had come to make their labour obsolete. This part, except for the offensive framing, is hard to swallow at this distance. It is not like panning in hillside shantytowns is a lifestyle that should have been preserved. Worst, behind it, and lurking just below the in-itself-defensible environmental talk is a discussion about  flood control-related public policy in California, where noble, anti-hydraulic mining discourse hides a less benevolent objection to state flood control intervention on the grounds that it would be paid for by taxes on people not directly affected. As time goes on, Pale Rider will be remembered more for Eastwood lifting his story than with an argument over the evils of hydraulic mining that may actually have had more to do with resistance to a. 

Anyway, Constant's take is less the Monitor than the Pelton wheel that was another component of this mining-industrial complex, because if you squint at the facts in the right way, you get to Lester Pelton's invention being the introduction of the "impulse turbine." If you have heard of the Pelton wheel, you have no excuse for being surprised by "the turbojet revolution."

Now, as usual, it turns out that calling it a "Pelton wheel" turns out to make us complicit in patent trolling. I wouldn't push this too far. Lester Pelton might have been inspired by, for example, the Fourneyron turbines rather than by a sudden thought that struck him as he looked at a water turbine made by the Knight Foundry. Again, there does seem to be dark deeds done here. The point of Pelton's improvement was to take business share from Knight. It was in no-one's interest to stop tinkerers in the California gold fields with vexatious patent-infringement suits, and even one's sympathy for Knight ought be measured. Pelton was able to build up a corporate interest that made a great deal of perfectly good mining equipment.

If Constant had started with Fourneyron, or with Charles Parsons, we would have missed a chance to see the Sierra Nevada. That he could have started with them is beside the point. He could have started in a great many places. Arguably, he ought to have started with those poor, sad Brown-Boveri salesmen trying to stimulate interest in their promising, new "gas turbine" concept in 1939.   They are the guys who put the technology of the combustion gas turbine out there on the market in the last years before World War II so that, finally, inescapably, it was obvious that the very near future belonged to turbines rotated by jets of combustion gas driving electrical generators, or powershafts, or compressors. Here is an actual industrial combine working to establish first mover advantage in what it clearly perceives to be a growth technology. The reason that we don't is so obvious as to be uninteresting. Brown-Boveri was a Swiss firm, and had no access to the Air Ministries of the great belligerents in an imminent world war. It was those air ministries that would pioneer the combustion gas turbine, because while Brown-Boveri was thinking of locomotives and ships and power regeneration in oil refineries, they missed the most important technology, the one area where buyers might be interested in something other than economic rationality: fighter jets!

By now we understand the problem. In its earliest stages, a combustion gas turbine installation is not likely to be more efficient than one of the highly-polished precursor technologies it is  meant to replace. A great deal of money is required bring the new technology to the point where a gas turbine pushes a freighter around more efficiently than a steam turbine --and steam turbines have never been that popular in mercantile shipping, anyway. On the other hand, as the speed of objects through air reaches a band within about 20% of the speed of sound, the air that it pushes aside ceases to be compressible and becomes incompressible. The rules of aerodynamics change and, unless the shape of the object likewise changes, its effect on the air changes, too. In a propeller-driven aircraft, this happens first at the tip of the screw, and that is why, in spite of ever more powerful engines, the top speeds of the hottest fighters of World War II top out around 460mph. Propel an aircraft with reaction mass out of a nozzle, and you can go much faster, and the "transsonic" limit will be reached by the plane's lifting surfaces instead, at speeds much closer to the local speed of sound. Your fighter jet will comfortably go a hundred miles per hour faster than its propeller-driven rivals, and getting through the transsonic limit to the endless horizons of supersonic flight is a possibility. 

I am throwing a "Patent Troll" tag on this posting in honour of Lester Pelton, but my tergiversations above will suggest that I am a little uncomfortable with this. I am not an impulse turbine expert, to put it mildly. But he's dead, and I don't think that he would mind developing the context of the posting in this manner because I think that there's an important point here. As long as we look at the advance of technology within the framework of heroic inventors, we belong in a conceptual universe such that the public revelation of the existence of jet fighters in early 1944 (spoiler alert!) is all about Ohain or Whittle having a Big Idea. Now that I have set the context, however, it becomes a little more puzzling. Why these two, heroic innovators. Why not everyone?

Here, then, I take you up into those other mountains, the Wealden fastness, to the lands of the charcoal burners and the ironmasters (and the Anglo-Saxon anarcho-syndicalistic commune of swineherds). It is time to contemplate our oldest and greatest communal technological praxis, to talk about blood and rye and salt and iron

Iron has an interesting history, to say the least. You will have heard that cast iron was invented in Coalbrookdale in 1709 by Abraham Darby I; that steel was invented in Sheffield in 1740 by Benjamin Huntsman; that iron was invented by the Hittites at the end (obviously) of the Late Bronze Age; that prized damascene steel  made in India and Syria (obviously) and even Toledo, Spain, was imported into Europe in the old days and much appreciated there; that there is a pillar of wrought iron in Delhi, India, said to have been made over 1500 years ago, although possibly a little younger; and that in the early 1200s, China's cast-iron industry was on the verge of an Industrial Revolution-style "takeoff" before the Confucian-minded scholar-bureaucrats of the Sung dynasty choked it off, on account of reading the Analects making you objectively anti-science. 

I have, of course, strawmanned many of these claims. People obviously do not believe that steel was invented in 1740 and in ancient times. That Huntsman even chose to frame himself as an "inventor" says far more about patent laws than about the progress of technology. But I think that the range and variety of claims points us towards something more interesting: iron is complicated.

Iron should be complicated. It is the endpoint of matter, in the middle of the Table of Elements because it is the last product of exothermic fusion, the final fuel of supernovas. The sixth most common element in the universe, it makes up 35% of the Earth's mass and is the fourth most abundant element in its crust. Modern mining does not even consider extracting iron from deposits where it makes up less than about 40% of ore weight, but it was also formerly worked when conveniently found in workable ingots scattered through coal measures, the legacy of ancient bog iron formations. Its ubiquity should imply its chimeric chemistry. There is a reason that it is at the end of the fusion chain, and it is found in its electron shells, which give iron no less than 10 ionisation states, two crystalline structures, and five allotropic forms. But this does not exhaust its complexity, because iron in its natural state is not very mechanically useful, being quite soft. It gains its strength from dislocations in its crystalline structure, what aluminum chemists call "strain hardening." Moreover, although this was only understood at a fairly late date, the properties that give it its strength are also involved in its capacity to resist local increases in temperature. "Stronger" iron makes better engine cylinder walls and turbine blades, not because there is a mechanical strain on them, but precisely because they are being chemically and thermally attacked. 

A little more history, as usual, recursively told (also, mea culpa upfront, based on half-remembered articles not properly referenced): back in, I think the late 1950s, when anthropology was feeling its oats and the field workers were out and about (demographer: "What is the typical structure of a Navajo family;" census analyst: "A mother, a father, two children and an anthropology grad student") but not yet quite hip to the whole cultural sensitivity thing, African tribes were a very interesting field of study precisely on account of their being primitive. Or, if you wanted to be modern about it, "seemingly primitive." But one of the most prominent groups, and thus easiest to study, were the Igbo of southern Nigeria, who made iron. And that's not primitive at all!

...Or is it? I am imagining, quite in ignorance of how this actually unfolded, or even whether there might be a literature about it, iron-making-Ibo-studying anthropologists talking to historians of science in their post-Kuhnian turn and hearing about attempts to rehabilitate the scientificness of Aristotle and Paracelsus. What was supposed to be true about how the Igbo conceptualised the matter of making iron was remarkably similar to what was supposed to be true about the way that Paracelsus and his contemporaries conceptualised alchemy. There were fructifying spirits in the Earth, and what was going on in the blast furnace was a great deal like fermentation. Stuff like that. 

I am not going to even try to unravel this. You really need some cool cat to come along and come at this dialogue in multiple ways, tease out the national politics and the local politics and the gender relations that are embedded in these dialogues of praxis and make it all simultaneously clear and more mysterious than ever. I am not that cool cat, and never will be. What I do know is that I came across a paper on early Classical Greece and its Phrygian connections that tried to dissect early myths of the Phrygian dactyls, the mythological entities who supposedly gave iron to humanity in the same way. It left me wondering whether the idea of Hittite invention of iron might be part of some larger project in which the Classical Greeks attributed the origins of things to the Phrygians (over to you, archaeologists!). It also left me with the conclusion that we might be better off paying less attention to what Igbo ironmakers are saying and more to what they are doing.

Ah, well. That's the skepticism of a skeptical historian of technology again. The final nail, as it were, was a 1905 reminiscence by an English colonial civil servant who visited the Igbo from the perspective of an ironmaker. Published in The Engineer, the paper gives a far more compelling picture of "traditional" iron making than the bullshit that you will find in the links in the paragraph with which I started.

Put bluntly, you have iron ore, which will not melt until it reaches a temperature well above the combustion temperature of carbon. So you either find an exotic fuel (which, even to the extent that it is practical, has its own problems, as Bessemer was to discover) or you use a reverberatory furnace packed with iron ore and "blown" with air, such that the temperature within rises well above the temperature of the C+O2>CO+CO2>O-+CO step. The iron is now out of your hands. What is worse, the iron is never entirely pure. Entrained with the ore are silicates and aluminates, and there is phosphorus and manganese dissolved into the iron ore. Moreover, the melting temperature of iron will fall as carbon dissolves into it, so that carbon-free iron is practically impossible to make by this process. Since by "steel" we mean a carbon-iron ally well below the saturation point, it is furthermore impossible to make steel directly from iron ore in a blast furnace. 

The Engineer article does not, however, focus so much on this subject as on the "flux" added to the furnace. This, an amorphous silicate compound, melts and gradually flows through the packed mass of iron and coal, washing out the "slag" of silicates, aluminates and manganese. At the end of the pour, all of the iron has poured out of the furnace, in a semi-plastic rather than molten, and so well below the carbon-saturation level of true cast iron). At this point, the flux begins to flow instead, and the Igbo ironmakers took it off for their next melt. 

The Igbo that our former civil servant interviewed found flux to be a fruitful subject for cosmogenic speculation. When they travelled to find a new source of charcoal (iron ore being pretty much everywhere, but charcoal rather precious) they took their flux with them. So where did the flux come from, anyway? Without flux, there would be no ironmaking Igbo, and without ironmaking Igbo, no flux! The Igbo were eternal, uncreate, the ground possibility of iron-using human life. And I have not even brought up Spiegeleisen yet!

From here, our author followed the iron to its next step. In the famous story of Abraham Darby, the metal is blasted so hot that it finally flows, ultimately being cast into shapes, or else "pigs," or ingots, of cast iron suitable for other work. As cast iron, it is a cheap and nasty metal, useful, paradoxically, more for its hard-won plasticity than its mechanical properties. The story of how cast iron was turned into the basis of an industry is an interesting one that I have touched on before. 

For jet engines, which I have not completely forgotten, the point here is that a pig of cast iron is not going to be used to make a frying pan. It is going to be used to make steel, which means getting some of the carbon that has just gone into solution in the metal back out of it. The Igbo, for whom cast iron is of little use, manage their furnaces such that the iron that comes out never achieves the maximum 4.2% carbon content, but they still are faced with a product that is not very useful. This is where the blacksmith comes in, beating and pounding and working the iron in a hot furnace until constant exposure to the flames has burnt off all of the carbon, leaving a piece of low-carbon "wrought" iron. In later versions of the technology, this was automated with water-driven trip hammers. Or, of course, a skilled worker can stop in the middle of the process, leaving what is very unlikely to be a homogeneous piece of steel, but will be "steel" for the purposes to which these methods are adequate, to get a little circular. 

Meanwhile, in the final stage of the Huntsman crucible process, a precisely measured amount of carbon is put back in the wrought iron to make steel. If this stage seems a little. . . counterproductive to you, you begin to understand how Bessemer came up with the idea of putting pigs of cast iron into a crucible, heating it up, and blasting air through it. Much to his delight, and very colourfully, eventually the very hot air ignited the phosphorus in the iron to add even more heat to the process, very quickly turning the pigs of iron into molten steel of very indifferent quality. Subsequent to that, Gilchrist and Thomas found a way of doing the same to low-phosphorus ores. 

The point of this excursion through potted-intellectual-history-of-anthropology is to take this story back to the Weald. In the earliest days of ironmaking, symbolised here by the Weald even though I have dragged the narrative through the Igbo country, the quality of the ore is out of our hands. Our curiosity about the mysteries of the process have focussed on flux, while the links I have given above emphasise fuel. (It is all about smelting iron ore with coked coal. That's the point where modernity arrives.) But mystery there is. One iron ore does not act like another. What we want to add to the furnace, and even how we choose to make the furnace, will differ from ore to ore. (Neither does one coal act like another, although the differences here are of less moment.) In the burning heat of the furnace, no-one is in charge of what the carbon monoxide reacts with, or, indeed, whether it reacts at all. Hopefully, the flux carries all of the phosphates, silicates and manganides out, but there will be bubbles of CO2 (I think) entrained in the semi-molten or molten mass. The old time, "refining" blacksmith will pound it out, but in a Bessemer-style rapid pour, the bubbles remain, unless you add a "killing" agent, such as aluminum. 

I have brought this conversation up to the outbreak of World War II before, in connection with the crisis over graphitisation in alloy steels. Today, I am talking in a vaguer way about inclusions because they are a larger and vaguer problem. The overly-killed alloy steels behind the graphitisation crisis are not at issue. What is at issue here is plain old "Bessemer steel." That is, the low grade stuff produced in very fast pours by blowing hot air through hotter pig iron until the faerie fires dance on it as the impurities are burnt off. 

When the bucket tips and the product pours out, there will be inclusions. We do not have the luxury of the Igbo village steelmaker. We will not be able to separate flux from metal. What we will do instead is take the "head" of the pour, defined as that portion at the beginning of the pour that contains all the impurities, remove it, and throw it right back into the furnace as scrap metal for another go around. 

It is an interesting fact about the heroic days of state steel production statistics that the more carelessly you make your steel, the bigger will be the head, and therefore the amount of metal that will be put right back into the furnaces to inflate your production numbers. It is another interesting fact about the heroic days of steel production that the more demand for your product, the more you will be tempted to underestimate the necessary length of the head. It is a third, and final interesting fact about the heroic days of steel production that the more that you expand your production into new and underutilised sources of ore, the less you will be able to estimate in advance the extent of the head. 

The risk here is that you will end up supplying low grade steel to manufacturers (for example, the Richmond Shipyards of Oakland, California) that contains excessive quantities of inclusions. But beyond that, there is the problem of producing good steel, suitable for demanding work, while at the same time increasing the scope of steel production overall. 

I began this discussing a question: why did the combustion gas turbine come when it did? I moved to iron, emphasising the mystery of the chemistry that makes particular kinds of iron-carbon alloys resistant to temperatures, and also to what an engineer would have called mechanical strains, and, again, to "creep," which I have not even tried to discuss here. And while we can talk about the chemistry from the point of view of laboratory analysis, I have moved on and tried to give a picture of just how far the properties of steel as they come to a would-be engine maker are out of the hands of the chemist and in the hands of a community of knowledge that knows how to work with specific combinations of ore and fuel to produce particular properties, and which cannot just simply transfer that know-how to new sources and new properties. Jakob Whitfield may not update his blog very often, but I point him out here as a researcher who is actually working on a particular point of contact between steelmaking and the jet turbine, the Armstrong-Siddeley-Metrovick nexus that gave rise to the first British axial (one compressor blade turbine after another) jet turbine. Meanwhile, the much better known story of the Power Jets centrifugal engine (a single stage of longer blades) features an exotic nickel-based alloy turbine blade that's not really relevant to the story that I am trying to tell here. 

The takeaway here, in one sense, is a plumy, Connections-style one at one level. You can't have jet turbine engines without massive progress in ferrous metallurgy from the point it was at when Bessemer was trying to round up investors. I am just reaching for something more profound. I have said before that ironmaking is so amazingly complicated that it is hard to believe that we actually managed to do it. 

Did quasi-divine nekkid ladies cavorting on Phrygian Ida give us the secret, or has it always been there in the form of the eternal recurrence of the Igbo people? Probably not. But the anthropological effort to figure out how these "primitive peoples" could do something so modern as make iron has a point. Even in 1943 we moderns were not nearly as good at making iron as we thought we were. That is why it was so hard to suss up the bad iron and catch it before it sank ships and ruined power plants. When it came time to expand iron production, the state turned to a community and an embedded and complex communal knowledge, not to top-down processes of scientific direction that were in any case not up to the challenge.

 Inevitably, I have pointed to two American mistakes. You can either find nothing mysterious about it at all, in that American steel production expanded further and brought more new sources of iron into production. Or you can say that that's because I am still arguing with Corelli Barnett in my head. 

Or you can say something more wonderful, because, if properly interpreted, it can offer us hope in these modern times: that making mistakes is part of learning, and that what was special in the America of 1943 was not a few hiccups in the war production process but the incredible opportunity that was given everyone to learn. In this case (he says, in a feeble attempt to bring the post around to its ostensible subject) to make combustion-turbine grade steel into jet turbines. 


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