Making It
Making it
TDC
Kevin Cameron
NOTHING'S NEW. I AM DIGGING INTO A big book I just received, Lyle Cummins’ new history of submarine diesel-engine development through 1945. I see that in 1912 oil jets were being used to cool pistons, just as they are today.
Even before 1912, Frederick Lanchester had proposed such oil jets. I also learn that engineers were wrestling with the problems of cylinder-head cracking caused by too many valves, too close together, years before this was enunciated as a design principle by a Professor Gibson in 1916 in Britain. And during the 1990s, some of Ferrari’s enthusiastic work with five valves per cylinder was considerably deflated when some of their five-valve prototypes failed to re-start after fuel stops. The valve seats had warped and the valves no longer sealed well enough to provide sufficient compression to start.
Ideas most often come into being as a result of need, not as a result of abstract curiosity. So it makes sense that engineers, told by harried management that their submarine engines must hit numbers for power and weight never before achieved, would make mistakes as they reached for solutions. Aha, valves have to be farther apart than X in this material! As they strove to make crankcases of the light weight necessary for submarine duty, they leaped from iron (easy to cast into intricate shapes, but easy to crack as well) to cast steel-in sections as thin as 5mm (0.20-inch). Steel castings didn’t always succeed, so some crankcases were cast in bronze. Why? Same reason cannon were cast in bronze rather than iron around 1800. Foundrymen understood bronze then better than they did iron (and gun crews strongly preferred to serve guns that didn’t explode and kill them all when fired).
The market pushed for solutions. Railways made heavy industry possible in the first place because labor, iron and coal are seldom all found in the same place. Rail brought everything together economically. But to haul ever-greater loads at higher speeds, more power was needed. That meant longer fire grates and longer locomotive frames to support them and the larger boilers they served. In a great many trials and errors, the technology of steel casting was worked out-because the railroads needed those bigger engines and they couldn’t be built of iron.
A French motorcycle dealer, Marcel Guiguet, worked through the 1920s to be able to cast much of his MGC motorcy-
cle’s structure and its fuel tank as a single aluminum casting. He succeeded only partly; porosity had to be sealed, and most of these complex castings were unsound. As Glen Curtiss’ associate Charlie Kirkham had already tried and failed to make crankcase and cylinder blocks of V-12 aircraft engines as single castings, this isn’t surprising. Guiguet had tried to make things easier for himself by using a highly fluid, easy-pouring aluminumsilicon alloy. Today sportbike chassis are routinely cast in four large pieces and then welded together to result in durable structures. Guiguet and Kirkham would be proud.
New casting methods employ sealed, heated molds that are evacuated to prevent the formation of slushy aluminum oxide. These methods have been developed step by difficult step because a need existed. Before these methods, 500cc GP bikes had chassis welded from pressed and machined elements, costing many thousands. Today all motorcyclists can enjoy their advantages at much lower cost.
Heat causes chemical changes in foods, enabling us to chew them more easily. We don’t chew pistons or valves, but heat acting over time changes them, too. Gilera in the 1950s employed a piston alloy containing magnesium-and had periodic piston break-ups in GP roadracing that may have caused that company to buck the trend toward shorter strokes and larger
bores. If pistons are fragile, make them smaller, just as Lanchester had suggested before 1910. Unfortunately, the magnesium alloy lost its properties with exposure to the heat of service.
So did some exhaust-valve materials. One path to high hardness in metals is to create in the material a tremendous number of tiny precipitated particles. These act as keys to prevent the gliding of layers of metal atoms across each other. In the heat of operation, these tiny particles acted just as do the tiny ice crystals in ice cream kept in a too-warm freezer. Bigger crystals grow at the expense of smaller, giving “old” ice cream its unpleasantly gritty texture. In the hard-working valve, the precipitated particles on which hardness and strength depended behaved like the ice crystals in ice cream, becoming larger and few; er. Denied their strength-boosting effect, the metal yielded and r/ the valves broke. Each time failures like these get in the way of what humans want to do, analysis is focused on them. Fracture surfaces are examined under magnification. Grain structure is compared with that of new parts. Specialists are set to work on the problem, directed research is initiated. When a workable, affordable answer is found, it goes into the great book of what we know about the real world. Each step can be quite expensive-but then so are the effects of broken connecting-rod cap bolts. In general, knowledge is cheaper than failure.
Military aviation decided titanium was required-strong as steel but only 60 percent of its weight. Large-scale production began in the U.S. about 1953. The Soviets, seeing the same benefits, decided to tackle the formidable problems of making entire submarine hulls out of the novel, bright metal. Thanks to all this cost-no-object effort, we can now have motorbike exhaust systems made of titanium, weighing a papery 7 pounds. Just as the aluminum in our chassis and crankcases may have existed previously as B52 fuselages or Budweiser cans, so the titanium fasteners and pipes we currently admire may in another life have “run silent, run deep” as part of a Cold War sub. Now we have our choice among many attractive titanium alloys-one for fasteners, some for engine valves, another for its ability to be formed into tubing and bent into exhaust pipes.
