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![[image of flower]](../../ima/flowXS_07.gif)
Steam Power |
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Chronology
The invention of steam engines and turbines can be considered at the top of machines that improved labor productivity and living standards. When steam expands, it exerts a force on piston or blades that turn shafts to produce mechanical or electrical power. The steam is produced in a boiler from water. The boiler fuel was wood, then coal, and later, petroleum and gas. The steam engine uses the steam to push one or more pistons in cylinders to produce mechanical or electrical work. The steam engine is no longer used, having been replaced by the steam turbine, in which the steam is forced against blades that are connected to a shaft and either mechanical gears and pulleys, or, more commonly today, an electric generator. For many years, steam engines ran mill and shop machinery, tractors, steamboats, steamshovels, and even cars (the Stanley Steamer). There are very kinds of steam engines: Double-acting receive steam alternately on both sides of the piston, exhausting on the opposite sides through valves. Compound team engines exhaust the steam to lower pressure engines, etc. In this way, double, triple and even quadruple engines obtain maximum use of the energy contained in the steam. In 50 CE, the Greek engineer at Alexandria, Egypt, Hero, showed how a container of water with attached tubes pointing in opposite directions turned when the water was boiled. Asimov 69 Thus, the ability of steam to produce forces was known to the ancients, although they made no practice use of this principle. Later inventors will use this concept to make practical labor-saving machines. In 1665 Edward Somerset, Second Marquis of Worcester, builds a working steam fountain. In 1679 the French physicist Denis Papin (1647-1712?) invents a pressure cooker based on the principle of expanding steam. This simple, practical invention used to cook food quickly. It also had a pop-off safety valve. In 1690, Papin, invented a machine that used steam to move a piston inside a cylinder. The water within the cylinder was heated externally and as it vaporized it moved the piston upwards. As it cooled, the steam condensed and the piston moved downward under air pressure and gravity. Because the cylinder had to fulfill three functions: boiler, power-cylinder, and steam condenser, it was impractical. However, this was the first idea to use steam to do move a piston to do work. In 1707, Papin powered a boat using a form of steam engine invented by Savery (see below), but his achievement ended when angry boatmen, afraid the engine would put them out of work, destroyed his work. Carroll 11 Since antiquity, water was removed from mines by carrying it in buckets or pumping it with hand pumps. Both methods required considerable human and animal muscle power. A commercially successful water pump driven by a crude steam engine operating without a piston was invented by an English military engineer, Thomas Savery (1650?-1715), in 1698. A boiler and steam cylinder were located at the miner's level container with hot steam and then cooled it so that the steam condensed into water occupying less space, thus creating a vacuum in the vessel. A tube between the mine water and the vessel allowed the water to be sucked up to a maximum height of 33 feet at low pressure (where the water pressure from below equals air pressure from above) and then trapped by a one-way check valve and then emptied into a pipe leading away from the mine. Steam was then readmitted from the boiler into the chamber and exerts prssure behind the trapped water to force it upward past a second check valve into a discharge pipe. The condensing water and steam valves were hand operated. The vessel was cooled and the process repeated to suck up another batch of water. Savery called his machine the Miner's Friend. It could lift water up to 150 feet at higher steam pressures. This steam engine was highly inefficient because of its alternately heating and cooling the pumping cylinder, thus requiring much wood or coal fuel to create steam from water. Also, steam under high pressure in cylinders and boilers built with primitive iron metallurgy and vessel fabrication techniques could rupture, which made it a dangerous machine. Nevertheless, this crude steam engine was well-received by mine operators for several years and gave others the basic concept upon which to build better steam engines. It was less dangerous when employed to lift water from country home wells. Cummins 3-5 In 1712, ironmonder from Devon, England, Thomas Newcomen (1663-1729), and his helper, John Calley, invented a reliable and safe steam engine using a piston-in-cylinder method. Newcomen had little or no scientific learning and used the ideas of Papin and Savery and worked in partnership with Savery, who had a general patent on the steam engine. His engine used low-pressure steam (less than 5 lbs. per sq. inch) and no vacuum, which made it less dangerous. Also, the parts did not have to fit snugly, which made it cheaper than the Savery engine. It was still very inefficient, but better than its predecessor Savery engine, and popular with mine operators. Steam was used to raise a vertical piston attached to a rocking beam attached to a mine shaft pumping rod and piston rod with chains. At the hight of the stroke, the steam was condensed by spraying cold water in the cylinder. This created a vacuum which caused atmospheric pressure to push the piston down on the working stroke. The most significant advances over the previous engines were (1) not cooling the boiler with each stroke (Papin) and (2) letting the atmosphere pump the water rather than making high pressure steam blow it out (Savery). Traveling over ends formed as arcs of circles, the chains provided vertical, linear motion to the piston and pumping rods. The weight of the chains kept them taut. Two other important improvements were automatic valves controlled from the rocking beam and a "snifting valve" to blow out air trapped in the cylinder, a problem with the Savery engine. It prevented air from building up in the cylinder to improve the steam's effectiveness. At that time, no boring mills existed to accurately bore such large cylinders diameters, so Newcomen added a leather sealing flap to the top of the piston and kept the top of the piston flooded with water to seal the clearance between the piston and cylinder. Newcomen's engine was first used for a mine at Dudley Castle near Coventry. The Newcomen engine could make about an average of about 16 strokes per minute with 10 gallons of water raised over 150 feet on each stroke, or about 6 hp. The engines used cylinders ranging from 10 to 72 inches. Thermal efficiency was less than ½%. Because the Newcomen engine was unprotected by a patent, anyone could Cummins 6-7 In 1753, the first Newcomen steam engine was brought from England to Belleville, NJ, by John Schuyler to pump water from his copper mine. It was assembled by Joshua Hornblower. Carruth 35 It required continued maintenance and eventually was abandoned without much success, so steam engines were not generally adopted in the colonies. In 1764, James Watt (1736-1819), a Scottish mechanic, engineer and scientist, improved Newcomen's steam engine by using a separate condenser. By condensing the steam in a chamber separated from the piston cylinder, the latter did not have to be reheated on each cycle. The cylinder could now be kept at a uniform high temperature, which doubled the thermal efficiency of the Newcomen engine. Watt received a patent in 1769 on his condenser; it was renewed by Parliament in 1775 for 1800 so that Watt could benefit financially from his invention With the patent extension, Watt entered into partnership with Matthew Boulton (1728-1809), a successful manufacturer at Soho near Birmingham. Between 1775 aqnd 1800, almost 500 engines were put into operation by the company. Later, Watt invented the first double-acting steam engine. It had steam alternately enter both sides of the hot chamber so that it did work in both directions. Because the piston would now exert an upward force, the its chain link was replaced by arod with a parallel motion linkage to keep it vertical while the rocking-beam traveled in an arch. In 1781, Watt converted the reciprocal motion of the Newcomen engine to rotary motion by using an epicycle, or "sun and planet" gear mechanism, which converted reciprocating to rotary motion. This invention enabled the engine to drive machinery through a system of pulleys and belts. Watt first intended to use the simpler rod and crankshaft mechanism suggested by his assitant, William Murdock (1754-1839), but it was stolen and patented by an ex-employee. Although the crank mechanism was not an original idea, Watt decided not to fight it in court. When the crank patent expired in 1794, Boulton & Watt began to use it in place of the sun and planet mechanism. Murdock, who worked for the company since 1773, invented and patented the slide-valve and was the first to use an eccentric drive from a crankshaft. He also pioneered usisng coal gas for lighting. All of Watt's engines were low pressure (4 to 5 psi). The thermal efficiency of the Watt engines were about 4% by 1800, a decided improvement over the Newcomen engine. Later improvements would raise steam engin efficiency to 7%. Cummins 9-10 The Watt engine required more precise machining than the Newcomen engine. Fortunately, he enlisted the talent of John Wilkinson (1728-1808), an ironmaster from Stafforshire. Wilkinson had patented in 1774 a new cannon boring mill that could be adapted to large cylinder diameters. His firs job for Watt was to machine 30 and 50-inch cylinders. Watt also defined the output of his engines to prove how strong they were compared to horses. He decided on the horsepower (hp) units equal to 33,000 pounds lifted 1 foot in 1 minute. This was conservative by 50% so he would not be criticised for exaggerating the power of his engines. Another Watt improvement was his use of pressure gages to give maximum and minimum cylinder pressure as an indicator of engine performance. John Southern, a Watt assistant, invented in 1796 an instrument to chart cylinder pressure throughout the entire expansion-exhaust cycle. He called it an "indicator diagram". Watt also adapted from water wheels the flyball governor for speed control. The steam engine and its applications to mines and factories reigned for 100 years and was one of the most important of inventions to raise productivity and living standards across the industrial countries. Cummins 10-11 In 1836, the U.S. Mint produced its first coins in a press operated by a steam engine. The press was designed by Franklin Beale. Carruth 199 This was another use of the steam engine that replaced labor with machinery to improve productivity of a government operation and lower costs, in this case, to taxpayers. |
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