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Steel MakingOptical System And Electrical Circuit Of The Leeds & Northrup Optical PyrometerFor extremely high temperature, the optical pyrometer is lar... Correction For Cold-junction Errors The voltage generated by a thermo-couple of an electric pyrom... Correction By Zero Adjustment Many pyrometers are supplied with a zero adjuster, by means ... Lathe And Planer Tools TO FORGE.--Gently warm the steel to remove any chill is parti... Composition Of Transmission-gear Steel If the nickel content of this steel is eliminated, and the pe... Silicon Silicon prevents, to a large extent, defects such as gas bubb... Steel Worked In Austenitic State As a general rule steel should be worked when it is in the a... Steel Before The 1850's In spite of a rapid increase in the use of machines and the ... Heat Treatment Of Gear Blanks This section is based on a paper read before the American Gea... Compensating Leads By the use of compensating leads, formed of the same materia... Chrome-nickel Steel Forging heat of chrome-nickel steel depends very largely on ... Heat Treatment Of Milling Cutters Drills Reamers Etc THE FIRE.--Gas and electric furnaces designed for high heats ... Heavy Forging Practice In heavy forging practice where the metal is being worked at... Placing Of Pyrometers When installing a pyrometer, care should be taken that it re... Carbon In Tool Steel Carbon tool steel, or tool steel as it is commonly called, us... Care In Annealing Not only will benefits in machining be found by careful anne... Introduction Of Carbon The matter to which these notes are primarily directed is the... The Quenching Tank The quenching tank is an important feature of apparatus in c... Testing And Inspection Of Heat Treatment The hard parts of the gear must be so hard that a new mill f... Corrosion This steel like any other steel when distorted by cold worki... |
Calibration Of Pyrometer With Common SaltCategory: PYROMETRY AND PYROMETERS An easy and convenient method for standardization and one which does not necessitate the use of an expensive laboratory equipment is that based upon determining the melting point of common table salt (sodium chloride). While theoretically salt that is chemically pure should be used (and this is neither expensive nor difficult to procure), commercial accuracy may be obtained by using common table salt such as is sold by every grocer. The salt is melted in a clean crucible of fireclay, iron or nickel, either in a furnace or over a forge-fire, and then further heated until a temperature of about 1,600 to 1,650 deg.F. is attained. It is essential that this crucible be clean because a slight admixture of a foreign substance might noticeably change the melting point. The thermo-couple to be calibrated is then removed from its protecting tube and its hot end is immersed in the salt bath. When this end has reached the temperature of the bath, the crucible is removed from the source of heat and allowed to cool, and cooling readings are then taken every 10 sec. on the milli-voltmeter or pyrometer. A curve is then plotted by using time and temperature as cooerdinates, and the temperature of the freezing point of salt, as indicated by this particular thermocouple, is noted, i.e., at the point where the temperature of the bath remains temporarily constant while the salt is freezing. The length of time during which the temperature is stationary depends on the size of the bath and the rate of cooling, and is not a factor in the calibration. The melting point of salt is 1,472 deg.F., and the needed correction for the instrument under observation can be readily applied. It should not be understood from the above, however, that the salt-bath calibration cannot be made without plotting a curve; in actual practice at least a hundred tests are made without plotting any curve to one in which it is done. The observer, if awake, may reasonably be expected to have sufficient appreciation of the lapse of time definitely to observe the temperature at which the falling pointer of the instrument halts. The gradual dropping of the pointer before freezing, unless there is a large mass of salt, takes place rapidly enough for one to be sure that the temperature is constantly falling, and the long period of rest during freezing is quite definite. The procedure of detecting the solidification point of the salt by the hesitation of the pointer without plotting any curve is suggested because of its simplicity. Next: Complete Calibration Of Pyrometers Previous: The Pyrometer And Its Use
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