What Happened to Babbitt Bearings? The Soft Metal That Kept Heavy Machines Running – Transcript

00:00June 1912 on the Susuana River in Pennsylvania, engineers lower a new bearing beneath 220 tons of spinning machinery. Its working face is lined with a metal soft enough to carve with a pocketk knife. When they later measure the wear, they calculate it will last more than,300 years. For a century, that soft gray metal sat beneath almost everything that turned. factory shafts,

00:24locomotive axles, ship engines, the crankshaft of the Ford Model T. Every mechanic knew how to melt it, pour it, and scrape it to a perfect fit. Then the ladles went cold. The pouring shops closed, and most mechanics working today have never held a bar of it. The easy answer is that ball bearings and stronger steel made it obsolete. That is only half true.

00:48Because Babbot never really left, it retreated to places almost no one ever sees. So what pushed it out of sight? And why can engineers still not let it go? Every episode, we tell the story of one machine, mechanism, or maker that once ran the world and then quietly slipped out of sight. Subscribe if that kind of history matters to you. From a Boston foundry to the power plants of today. This is how the wrong metal

01:15became the right answer. To understand why anyone would line a machine with soft metal, start with what machines were like before it. In the 1830s, a spinning shaft rested in a box. The shaft was iron. The box was usually brass or cast iron.

01:32Between them went whatever grease was at hand, often animal fat. For slow machinery, a water wheel or a grain mill. That was enough. But the 1830s were not slow. Steam engines were turning faster every year. Railroads were spreading across Britain and the United States, and every car rode on axles that spun for hours under tons of load. Hard metal ran against hard metal.

01:56When the grease thinned or ran dry, the surfaces heated, tore at each other, and seized. An overheated axle box could stop a train. A scored shaft could put an engine out of work for days. Builders knew a softer lining might help. Tin and lead had both been tried in the previous century without success. One problem was obvious. Under real weight, soft metal does not stay put. It spreads outward

02:22like clay under a thumb and the bearing is gone. The man who solved that problem was not an engineer. He was a goldsmith. Isaac Babbot was born in 1799 in Taton, Massachusetts and trained in the metal trades as a young man. His interest was alloys and in particular a bright tinbased metal called Britannia, a close cousin of pewtor. Bratannia table wear was being imported from England in

02:48quantity. In 1824, Babbot worked out how to make it himself, the first produced in the United States, and went into business selling it. The business did not pay. Babbot withdrew and in 1834 he moved to Boston for a very different job. superintendent at the South Boston Iron Company, known locally as Alger's Foundaries. The goldsmith who had cast table wear was now casting cannon. He is

03:14credited with producing the first brass cannon made in the country. It was there by his own later account around 1836 while casting cannon for the government that the idea came to him. He knew heavy machinery. He knew what ruined its bearings. And from his years with Britannia, he knew a tin alloy that poured easily and ran smooth against iron. What he needed was a way to keep it from spreading. His answer was a

03:41matter of shape. Take the ordinary cast box that holds the shaft. Form raised rims or ledges around its inner edges. Coat the inside with a thin layer of tin so that [clears throat] molten metal will grip it. Then pour the soft alloy in and let it freeze in place. The hard box carries the load. The ledges lock the lining in so that it has nowhere to go. And the only surface the shaft ever

04:06touches is the soft one. On the 17th of July 1839, the United States Patent Office granted him patent number 1,252 for a mode of making boxes for axles and gudgeons. A gudgeon is simply an old word for the end of a shaft. The patent named railroad cars and locomotive engines directly. And here is the strange part. Almost in passing, Babbot mentioned a recipe he had found to work

04:33well. About 50 parts tin, five of antimony, and one of copper. Then he added that he did not intend to confine himself to that mixture. He never claimed the alloy. The patent protected the box, the ledges, and the method of pouring. The metal itself, the thing that would carry his name around the world, was left unprotected.

04:54The following year, he had to narrow his claim even further, conceding in writing that part of it probably covered something he had not been the first to invent. So, the most famous bearing metal in history was, legally speaking, an afterthought. It did not matter. The line boxes worked and people who ran machinery noticed quickly. In 1841, a Massachusetts mechanics association awarded Babbot its gold medal. The next

05:22year, the idea reached Washington. The Navy was building steam warships, and its yards had been testing what the official papers called Babbot's anti-attrition metal. The engine under construction for a new steamer, the Princeton, was being fitted with it. In 1842, the Secretary of the Navy agreed to buy the right to use the patented box and the metal throughout the fleet. The price was $20,000. Patents followed in

05:48Britain and in Russia. In America, the patent was extended and it ran until 1860. In time, his surname became a common noun. Mechanics did not ask for tin alloy. They asked for Babbot. Yet, almost nobody using it could explain why it worked. Every instinct in the machine shop said a bearing should be harder than the load it carries. This one was softer than the shaft, softer than the box around it, soft enough to be shaped

06:15with hand tools, and it outlasted them all. The reason was hiding inside the metal itself. Start with what goes wrong when two hard metals rub. No machine surface is truly smooth. Under a strong enough lens, polished steel looks like a mountain range. When a shaft turns inside a hard box, those tiny peaks meet. Under heavy load, the pressure at each peak is enormous. The peaks heat, weld together for an instant, and tear

06:41apart. Each tear leaves a rougher surface than before. Machinists call it gling. Left alone, it ends with the shaft locked solid in its box. Babbot metal refuses to play that game. And the reason lies in its structure. Cut a piece open, polish it, and look closely.

07:01It is not one uniform metal. It is two things at once. Most of it is a soft background rich in tin. Scattered through that background are small hard crystals formed where the tin has combined with the copper and the antimony. Think of a road surface.

07:18Asphalt is soft tar holding hard stones. The tar alone would rut under the first truck. The stones alone would scatter. Together they carry traffic for years. Babbot works the same way at a scale too small to see. In the classic explanation, the soft background wears down very slightly. The hard crystals stand a little proud and oil settles in the shallow spaces between them. That

07:44structure gives the metal three habits that hard bearings do not have. The first is that it gives way. No shaft is perfectly straight and no housing is perfectly aligned. A hard bearing meets a slightly crooked shaft at one edge and that edge takes all the punishment.

08:01Babbot yields. Over the first hours of running, it settles into the exact shape of the shaft it carries. The second is that it swallows dirt. A grain of grit caught between hard surfaces will plow a groove around the shaft. In Babot, the same grain is simply pressed down into the lining like a pebble stepped into mud and buried where it can do no harm.

08:23The third is that it does not cling to steel. Where a brass or iron box might seize, Babbot smears and lets go. Put those together and you arrive at the real idea. The lining is meant to lose.

08:36If something must be damaged, let it be the cheap soft part that can be melted out and poured again, and never the expensive shaft. And pouring it again was remarkably easy because Babbot melts below 500° F, far cooler than brass or iron. The mechanic set the shaft in its housing, roughly where it would run. He blackened the shaft with soot so that nothing would stick to it. He packed the open ends with clay to make a dam. Then

09:03he heated a ladle of babbot and poured it into the gap where it froze around the shaft in seconds. That gave him a rough bearing. The fit came next. He wiped the shaft with a thin blue dye, set it back in place, and turned it by hand. When he lifted it out, the dye had rubbed off wherever the lining stood too high. He shaved those spots with a hand scraper a few thousand of an inch at a

09:27time, and tried again. blue turn, lift, scrape. An hour or more for a single bearing until the color spread evenly across the whole surface. Then came oil, a slow first run, and the bearing was ready for years of work. The men who did this knew it worked. What they did not know was that the soft metal they had fitted so carefully was not really carrying the load at all. The answer arrived in 1883 in England, and it

09:54arrived by accident. That year, the Institution of Mechanical Engineers hired an engineer named Boscham Tower to settle a practical question. What was the best way to oil the axle bearings of railway cars? Tower built a test rig, a steel shaft turned beneath a railway type bearing with its lower side running in a bath of oil and a heavy load pressing the two together. At one point, he drilled a small hole down through the top of the bearing, intending to fit an

10:21oiler. When the machine started, oil began rising out of that hole and spilling over the cap. It made a mess, so Tower pushed in a cork. The cork came out. He drove in a wooden plug. With the shaft turning, the plug crept slowly upward and was forced out as well.

10:38Something inside the bearing was pushing back. Tower screwed a pressure gauge into the hole and started the machine again. The needle climbed past 200 lb per square in. That was far more than the load alone could explain. If the metal surfaces were simply resting on each other, there was only one reading of the result. The shaft was not touching the bearing. It was floating.

11:00Here is what was happening. A shaft is always made slightly smaller than the hole it runs in. At rest, it sits at the bottom, metal on metal. But as it begins to turn, oil clings to its surface and is dragged around with it. That oil is pulled into the narrowing gap beneath the shaft. a gap shaped like a thin wedge. More oil is forced in than can easily escape. Pressure builds and at a certain speed that pressure is enough to

11:26lift the shaft clear. Drivers know a version of this. On a wet road at speed, a tire can ride up on a wedge of water and lose contact with the pavement. On the highway, that is a danger. Inside a bearing, it is the entire point. Once the shaft is riding on oil, there is no rubbing metal at all. The film may be thinner than a human hair, yet it carries the full weight, and the only friction left is oil sliding over oil. 3