This shows but two of the operations and for a single furnace. The total costs for all operations on the 30,000 lb. of gears per 24 hr. is shown in Table 29.

TABLE 29.—COMPARATIVE ANNUAL PRODUCTION COSTS FOR 30,000 POUNDS OUTPUT IN 24 HOURS

No. Equipment Installation cost - - 1 2 3 I Oil $179,000.00 II Oil and electric 213,000.00 III Natural gas 117,000.00 IV (A) Natural gas containing furnaces 120,000.00 V Natural gas and electric 181,000.00 VI City gas 122,000.00 VII City gas and electric 182,000.00 VIII Water gas 214,000.00 IX Water gas and electric 238,000.00 X Producer gas 246,000.00 XI Producer gas and electric 255,000.00 XII Coal and electric 194,000.00 XIII Electric 257,000.00

- Annual operating expenses Cost No. Total per lb. Fixed Heat Labor metal, charges cents - - - - 1 4 5 6 7 8 I $26,850.00 $156,000.00 $105,000.00 $287,850.00 $3.19 II 31,950.00 142,770.00 97,000.00 271,720.00 3.02 III 17,550.00 44,250.00 97,000.00 158,800.00 1.78 IV 18,000.00 41,000.00 94,000.00 153,000.00 1.70 V 27,150.00 73,820.00 90,000.00 190,970.00 2.13 VI 18,300.00 123,200.00 94,000.00 235,500.00 2.62 VII 27,300.00 128,820.00 90,000.00 246,020.00 2.74 VIII 18,600.00 104,000.00 94,000.00 216,600.00 2.41 IX 27,450.00 117,420.00 90,000.00 234,870.00 2.62 X 18,900.00 69,300.00 90,000.00 178,200.00 1.98 XI 27,750.00 92,520.00 90,000.00 210,270.00 2.34 XII 29,100.00 87,220.00 90,000.00 206,320.00 2.30 XIII 38,550.00 135,000.00 84,000.00 257,550.00 2.86 -

NOTE.—Producer plant fixed charges are included in the cost of gas and are charged as "heat" in column 5, so they are omitted from column 4.



CHAPTER XII

PYROMETRY AND PYROMETERS

A knowledge of the fundamental principles of pyrometry, or the measurement of temperatures, is quite necessary for one engaged in the heat treatment of steel. It is only by careful measurement and control of the heating of steel that the full benefit of a heat-treating operation is secured.

Before the advent of the thermo-couple, methods of temperature measurement were very crude. The blacksmith depended on his eyes to tell him when the proper temperature was reached, and of course the "color" appeared different on light or dark days. "Cherry" to one man was "orange" to another, and it was therefore almost impossible to formulate any treatment which could be applied by several men to secure the same results.

One of the early methods of measuring temperatures was the "iron ball" method. In this method, an iron ball, to which a wire was attached, was placed in the furnace and when it had reached the temperature of the furnace, it was quickly removed by means of the wire, and suspended in a can containing a known quantity of water; the volume of water being such that the heat would not cause it to boil. The rise in temperature of the water was measured by a thermometer, and, knowing the heat capacity of the iron ball and that of the water, the temperature of the ball, and therefore the furnace, could be calculated. Usually a set of tables was prepared to simplify the calculations. The iron ball, however, scaled, and changed in weight with repeated use, making the determinations less and less accurate. A copper ball was often used to decrease this change, but even that was subject to error. This method is still sometimes used, but for uniform results, a platinum ball, which will not scale or change in weight, is necessary, and the cost of this ball, together with the slowness of the method, have rendered the practice obsolete, especially in view of modern developments in accurate pyrometry.

PYROMETERS

Armor plate makers sometimes use the copper ball or Siemens' water pyrometer because they can place a number of the balls or weights on the plate in locations where it is difficult to use other pyrometers. One of these pyrometers is shown in section in Fig. 109.

SIEMENS' WATER PYROMETER.—It consists of a cylindrical copper vessel provided with a handle and containing a second smaller copper vessel with double walls. An air space a separates the two vessels, and a layer of felt the two walls of the inner one, in order to retard the exchange of temperature with the surroundings. The capacity of the inner vessel is a little more than one pint. A mercury thermometer b is fixed close to the wall of the inner vessel, its lower part being protected by a perforated brass tube, whilst the upper projects above the vessel and is divided as usual on the stem into degrees, Fahrenheit or Centigrade, as desired. At the side of the thermometer there is a small brass scale c, which slides up and down, and on which the high temperatures are marked in the same degrees as those in which the mercury thermometer is divided; on a level with the zero division of the brass scale a small pointer is fixed, which traverses the scale of the thermometer.



Short cylinders d, of either copper, iron or platinum, are supplied with the pyrometer, which are so adjusted that their heat capacity at ordinary temperature is equal to one-fiftieth of that of the copper vessel filled with one pint of water. As, however, the specific heat of metals increases with the temperature, allowance is made on the brass sliding scales, which are divided according to the metal used for the pyrometer cylinder d. It will therefore be understood that a different sliding scale is required for the particular kind of metal of which a cylinder is composed. In order to obtain accurate measurements, each sliding scale must be used only in conjunction with its own thermometer, and in case the latter breaks a new scale must be made and graduated for the new thermometer.

The water pyrometer is used as follows:

Exactly one pint (0.568 liter) of clean water, perfectly distilled or rain water, is poured into the copper vessel, and the pyrometer is left for a few minutes to allow the thermometer to attain the temperature of the water.

The brass scale c is then set with its pointer opposite the temperature of the water as shown by the thermometer. Meanwhile one of the metal cylinders has been exposed to the high temperature which is to be measured, and after allowing sufficient time for it to acquire that temperature, it is rapidly removed and dropped into the pyrometer vessel without splashing any of the water out.

The temperature of the water will rise until, after a little while, the mercury of the thermometer has become stationary. When this is observed the degrees of the thermometer are read off, as well as those on the brass scale c opposite the top of the mercury. The sum of these two values together gives the temperature of the flue, furnace or other heated space in which the metal cylinder had been placed. With cylinders of copper and iron, temperatures up to 1,800 deg.F. (1,000 deg.C.) can be measured, but with platinum cylinders the limit is 2,700 deg.F. (1,500 deg.C.).

For ordinary furnace work either copper or wrought-iron cylinders may be used. Iron cylinders possess a higher melting point and have less tendency to scale than those of copper, but the latter are much less affected by the corrosive action of the furnace gases; platinum is, of course, not subject to any of these disadvantages.

The weight to which the different metal cylinders are adjusted is as follows:

Copper 137.0 grams Wrought-iron 112.0 grams Platinum 402.6 grams

In course of time the cylinders lose weight by scaling; but tables are provided giving multipliers for the diminished weights, by which the reading on the brass scale should be multiplied.

THE THERMO-COUPLE

With the application of the thermo-couple, the measurement of temperatures, between, say, 700 and 2,500 deg.F., was made more simple and precise. The theory of the thermo-couple is simple; it is that if two bars, rods, or wires of different metals are joined together at their ends, when heated so that one junction is hotter than the other, an electromotive force is set up through the metals, which will increase with the increase of the difference of temperature between the two junctions. This electromotive force, or voltage, may be measured, and, from a chart previously prepared, the temperature determined. In most pyrometers, of course, the temperatures are inscribed directly on the voltmeter, but the fact remains that it is the voltage of a small electric current, and not heat, that is actually measured.

There are two common types of thermo-couples, the first making use of common, inexpensive metals, such as iron wire and nichrome wire. This is the so-called "base metal" couple. The other is composed of expensive metals such as platinum wire, and a wire of an alloy of platinum with 10 per cent of rhodium or iridium. This is called the "rare metal" couple, and because its component metals are less affected by heat, it lasts longer, and varies less than the base metal couple.

The cold junction of a thermo-couple may be connected by means of copper wires to the voltmeter, although in some installations of base metal couples, the wires forming the couple are themselves extended to the voltmeter, making copper connections unnecessary. From the foregoing, it may be seen that accurately to measure the temperature of the hot end of a thermo-couple, we must know the temperature of the cold end, as it is the difference in the temperatures that determines the voltmeter readings. This is absolutely essential for precision, and its importance cannot be over-emphasized.

When pyrometers are used in daily operation, they should be checked or calibrated two or three times a month, or even every week. Where there are many in use, it is good practice to have a master pyrometer of a rare metal couple, which is used only for checking up the others. The master pyrometer, after calibrating against the melting points of various substances, will have a calibration chart which should be used in the checking operation.

It is customary now to send a rare metal couple to the Bureau of Standards at Washington, where it is very carefully calibrated for a nominal charge, and returned with the voltmeter readings of a series of temperatures covering practically the whole range of the couple. This couple is then used only for checking those in daily use.

Pyrometer couples are more or less expensive, and should be cared far when in use. The wires of the couple should be insulated from each other by fireclay leads or tubes, and it is well to encase them in a fireclay, porcelain, or quartz tube to keep out the furnace gases, which in time destroy the hot junction. This tube of fireclay, or porcelain, etc., should be protected against breakage by an iron or nichrome tube, plugged or welded at the hot end. These simple precautions will prolong the life of a couple and maintain its precision longer.

Sometimes erroneous temperatures are recorded because the "cold end" of the couple is too near the furnace and gets hot. This always causes a temperature reading lower than the actual, and should be guarded against. It is well to keep the cold end cool with water, a wet cloth, or by placing it where coal air will circulate around it. Best of all, is to have the cold junction in a box, together with a thermometer, so that its temperature may definitely be known. If this temperature should rise 20 deg.F. on a hot day, a correction of 20 deg.F. should be added to the pyrometer reading, and so on. In the most up-to-date installations, this cold junction compensation is taken care of automatically, a fact which indicates its importance.

Optical pyrometers are often used where it is impracticable to use the thermo-couple, either because the temperature is so high that it would destroy the couple, or the heat to be measured is inaccessible to the couple of ordinary length. The temperatures of slag or metal in furnaces or running through tap-holes or troughs are often measured with optical pyrometers.

In one type of optical pyrometer, the observer focuses it on the metal or slag and moves an adjustable dial or gage so as to get an exact comparison between the color of the heat measured with the calor of a lamp or screen in the pyrometer itself. This, of course, requires practice, and judgment, and brings in the personal equation. With care, however, very reliable temperature measurements may be made. The temperatures of rails, as they leave the finishing pass of a rolling mill, are measured in this way.

Another type of optical pyrometer is focused on the body, the temperature of which is to be measured. The rays converge in the telescope on metal cells, heating them, and thereby generating a small electric current, the voltage of which is read an a calibrated voltmeter similar to that used with the thermo-couple. The best precision is obtained when an optical pyrometer is used each time under similar conditions of light and the same observer.

Where it is impracticable to use either thermo-couples or optical pyrometers, "sentinels" may be used. There are small cones or cylinders made of salts or other substances of known melting points and covering a wide range of temperatures.

If six of these "sentinels," melting respectively at 1,300 deg., 1,350 deg., 1,400 deg., 1,450 deg., 1,500 deg., and 1,550 deg.F., were placed in a row in a furnace, together with a piece of steel to be treated, and the whole heated up uniformly, the sentinels would melt one by one and the observer, by watching them through an opening in the furnace, could tell when his furnace is at say 1,500 deg. or between 1,500 deg. and 1,550 deg., and regulate the heat accordingly.

A very accurate type of pyrometer, but one not so commonly used as those previously described, is the resistance pyrometer. In this type, the temperature is determined by measuring the resistance to an electric current of a wire which is at the heat to be measured. This wire is usually of platinum, wound around a quartz tube, the whole being placed in the furnace. When the wire is at the temperature of the furnace, it is connected by wires with a Wheatstone Bridge, a delicate device for measuring electrical resistance, and an electric current is passed through the wire. This current is balanced by switching in resistances in the Wheatstone Bridge, until a delicate electrical device shows that no current is flowing. The resistance of the platinum wire at the heat to be measured is thus determined on the "Bridge," and the temperature read off on a calibration chart, which shows the resistance at various temperatures.

These are the common methods used to-day for measuring temperatures, but whatever method is used, the observer should bear in mind that the greatest precision is obtained, and hence the highest efficiency, by keeping the apparatus in good working order, making sure that conditions are the same each time, and calibrating or checking against a standard at regular intervals.

THE PYROMETER AND ITS USE

In the heat treatment of steel, it has become absolutely necessary that a measuring instrument be used which will give the operator an exact reading of heat in furnace. There are a number of instruments and devices manufactured for this purpose but any instrument that will not give a direct reading without any guess work should have no place in the heat-treating department.

A pyrometer installation is very simple and any of the leading makers will furnish diagrams for the correct wiring and give detailed information as to the proper care of, and how best to use their particular instrument. There are certain general principles, however, that must be observed by the operators and it cannot be too strongly impressed upon them that the human factor involved is always the deciding factor in the heat treatment of steel.

A pyrometer is merely an aid in the performance of doing good work, and when carefully observed will help in giving a uniformity of product and act as a check on careless operators. The operator must bear in mind that although the reading on the pyrometer scale gives a measure of the temperature where the junction of the two metals is located, it will not give the temperature at the center of work in the furnace, unless by previous tests, the heat for penetrating a certain bulk of material has been decided on, and the time necessary for such penetration is known.

Each analysis of plain carbon or alloy steel is a problem in itself. Its critical temperatures will be located at slightly different heats than for a steel which has a different proportion of alloying elements. Furthermore, it takes time for metal to acquire the heat of the furnace. Even the outer surface lags behind the temperature of the furnace somewhat, and the center of the piece of steel lags still further. It is apparent, therefore, that temperature, although important, does not tell the whole story in heat treatment. Time is also a factor.

Time at temperature is also of great importance because it takes time, after the temperature has been reached, for the various internal changes to take place. Hence the necessity for "soaking," when annealing or normalizing. Therefore, a clock is as necessary to the proper pyrometer equipment as the pyrometer itself.

For the purpose of general work where a wide range of steels or a variable treatment is called for, it becomes necessary to have the pyrometer calibrated constantly, and when no master instrument is kept for this purpose the following method can be used to give the desired results:

CALIBRATION OF PYROMETER WITH COMMON SALT

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.

COMPLETE CALIBRATION OF PYROMETERS.—For the complete calibration of a thermo-couple of unknown electromotive force, the new couple may be checked against a standard instrument, placing the two bare couples side by side in a suitable tube and taking frequent readings over the range of temperatures desired.

If only one instrument, such as a millivoltmeter, is available, and there is no standard couple at hand, the new couple may be calibrated over a wide range of temperatures by the use of the following standards:

Water, boiling point 212 deg.F. Tin, under charcoal, freezing point 450 deg.F. Lead, under charcoal, freezing point 621 deg.F. Zinc, under charcoal, freezing point 786 deg.F. Sulphur, boiling point 832 deg.F. Aluminum, under charcoal, freezing point 1,216 deg.F. Sodium chloride (salt), freezing point 1,474 deg.F. Potassium sulphate, freezing point 1,958 deg.F.

A good practice is to make one pyrometer a standard; calibrate it frequently by the melting-point-of-salt method, and each morning check up every pyrometer in the works with the standard, making the necessary corrections to be used for the day's work. By pursuing this course systematically, the improved quality of the product will much more than compensate for the extra work.

The purity of the substance affects its freezing or melting point. The melting point of common salt is given in one widely used handbook at 1,421 deg.F., although chemically pure sodium chloride melts at 1,474 deg.F. as shown above. A sufficient quantity for an extended period should be secured. Test the melting point with a pyrometer of known accuracy. Knowing this temperature it will be easy to calibrate other pyrometers.

PLACING OF PYROMETERS.—When installing a pyrometer, care should be taken that it reaches directly to the point desired to be measured, that the cold junction is kept cold, and that the wires leading to the recording instrument are kept in good shape. The length of these lead wires have an effect; the longer they are, the lower the apparent temperature.

When pyrometers placed in a number of furnaces are connected up in series, and a multiple switch is used for control, it becomes apparent that pyrometers could not be interchanged between furnaces near and far from the instrument without affecting the uniformity of product from each furnace.

Calibration can best be done without disturbing the working pyrometer, by inserting the master instrument into each furnace separately, place it alongside the hot junction of the working pyrometer, and compare the reading given on the indicator connected with the multiple switch.

Protection tubes should be replaced when cracked, as it is important that no foreign substance is allowed to freeze in the tube, so that the enclosed junction becomes a part of a solid mass joined in electrical contact with the outside protecting tube. Wires over the furnaces must be carefully inspected from time to time, as no true reading can be had on an instrument, if insulation is burned off and short circuits result.

If the standard calibrating instrument used contains a dry battery, it should be examined from time to time to be sure it is in good condition.

THE LEEDS AND NORTHRUP POTENTIOMETER SYSTEM

The potentiometer pyrometer system is both flexible and substantial in that it is not affected by the jar and vibration of the factory or the forge shop. Large or small couples, long or short leads can be used without adjustment. The recording instrument may be placed where it is most convenient, without regard to the distance from the furnace.

ITS FUNDAMENTAL PRINCIPLE.—The potentiometer is the electrical equivalent of the chemical balance, or balance arm scales. Measurements are made with balance scales by varying known weights until they equal the unknown weight. When the two are equal the scales stand at zero, that is, in the position which they occupy when there is no weight on either pan; the scales are then said to be balanced. Measurements are made with the potentiometer by varying a known electromotive force until it equals the unknown; when the two are equal the index of the potentiometer, the galvanometer needle, stands motionless as it is alternately connected and disconnected. The variable known weights are units separate from the scales, but the potentiometer provides its own variable known electromotive force.

The potentiometer provides, first, a means of securing a known variable electromotive force and, second, suitable electrical connections for bringing that electromotive force to a point where it may be balanced against the unknown electromotive force of the couple. The two are connected with opposite polarity, or so that the two e.m.f.s oppose one another. So long as one is stronger than the other a current will flow through the couple; when the two are equal no current will flow.

Figure 107 shows the wiring of the potentiometer in its simplest form. The thermo-couple is at H, with its polarity as shown by the symbols + and -. It is connected with the main circuit of the potentiometer at the fixed point D and the point G.



A current from the dry cell Ba is constantly flowing through the main, or so-called potentiometer circuit, ABCDGEF. The section DGE of this circuit is a slide wire, uniform in resistance throughout its length. The scale is fixed on this slide wire. The current from the cell Ba as it flows through DGE, undergoes a fall in potential, setting up a difference in voltage, that is, an electromotive force, between D and E. There will also be electromotive force between D and all other points on the slide wire. The polarity of this is in opposition to the polarity of the thermo-couple which connects into the potentiometer at D and at G. By moving G along the slide wire a point is found where the voltage between D and G in the slide wire is just equal to the voltage between D and G generated by the thermo-couple. A galvanometer in the thermo-couple circuit indicates when the balance point is reached, since at this point the galvanometer needle will stand motionless when its circuit is opened and closed.



The voltage in the slide wire will vary with the current flowing through it from the cell Ba and a means of standardizing this is provided. SC, Fig. 111, is a cadmium cell whose voltage is constant. It is connected at two points C and D to the potentiometer circuit whenever the potentiometer current is to be standardized. At this time the galvanometer is thrown in series with SC. The variable rheostat R is then adjusted until the current flowing is such that as it flows through the standard resistance CD, the fall in potential between C and D is just equal to the voltage of the standard cell SC. At this time the galvanometer will indicate a balance in the same way as when it was used with a thermo-couple. By this operation the current in the slide wire DGE has been standardized.



DEVELOPMENT OF THE WIRING SCHEME OF THE COLD-END COMPENSATOR.—The net voltage generated by a thermo-couple depends upon the temperature of the hot end and the temperature of the cold end. Therefore, any method adopted for reading temperature by means of thermo-couples must in some way provide a means of correcting for the temperature of the cold end. The potentiometer may have either of two very simple devices for this purpose. In one form the operator is required to set a small index to a point on a scale corresponding to the known cold junction temperature. In the other form an even more simple automatic compensator is employed. The principle of each is described in the succeeding paragraphs, in which the assumption is made that the reader already understands the potentiometer principle as described above.

As previously explained the voltage of the thermo-couple is measured by balancing it against the voltage drop DG in the potentiometer.

As shown in Fig. 111, the magnitude of the balancing voltage is controlled by the position of G. Make D movable as shown in Fig. 112 and the magnitude of the voltage DG may be varied either from the point D or the point G. This gives a means of compensating for cold end changes by setting the slider D. As the cold end temperature rises the net voltage generated by the couple decreases, assuming the hot end temperature to be constant. To balance this decreased voltage the slider D is moved along its scale to a new point nearer G. In other words, the slider D is moved along its scale until it corresponds to the known temperature of the cold end and then the potentiometer is balanced by moving the slider G. The readings of G will then be direct.



The same results will be obtained if a slide wire upon which D bears is in parallel with the slide wire of G, as shown in Fig. 113.

AUTOMATIC COMPENSATOR.—It should be noted that the effect of moving the contact D, Fig. 113, is to vary the ratio of the resistances on the two sides of the point D in the secondary slide wire. In the recording pyrometers, an automatic compensator is employed. This automatic compensator varies the ratio on the two sides of the point D in the following manner:

The point D, Fig. 114, is mechanically fixed; on one side of D is the constant resistance coil M, on the other the nickel coil N. N is placed at or near the cold end of the thermo-couple (or couples). Nickel has a high temperature coefficient and the electrical proportions of M and N are such that the resistance change of N, as it varies with the temperature of the cold end, has the same effect upon the balancing voltage between D and G that the movement of the point D, Fig. 114, has in the hand-operated compensator.

Instruments embodying these principles are shown in Figs. 115 to 117. The captions making their uses clear.



PLACING THE THERMO-COUPLES

The following illustrations from the Taylor Instrument Company show different applications of the thermo-couples to furnaces of various kinds. Figure 118 shows an oil-fired furnace with a simple vertical installation. Figure 119 shows a method of imbedding the thermo-couple in the floor of a furnace so as to require no space in the heating chamber.



Various methods of applying a pyrometer to common heat-treatment furnaces are shown in Figs. 120 to 122.



LEEDS AND NORTHRUP OPTICAL PYROMETER

The principles of this very popular method of measuring temperature are sketched in Fig. 123.



The instrument is light and portable, and can be sighted as easily as an opera glass. The telescope, which is held in the hand, weighs only 25 oz.; and the case containing the battery, rheostat and milliammeter, which is slung from the shoulder, only 10 lb.



A large surface to sight at is not required. So long as the image formed by the objective is broader than the lamp filament, the temperature can be measured accurately.



Distance does not matter, as the brightness of the image formed by the lens is practically constant, regardless of the distance of the instrument from the hot object.



The manipulation is simple and rapid, consisting merely in the turning of a knurled knob. The setting is made with great precision, due to the rapid change in light intensity with change in temperature and to the sensitiveness of the eye to differences of light intensity. In the region of temperatures used for hardening steel, for example, different observers using the instrument will agree within 3 deg.C.



Only brightness, not color, of light is matched, as light of only one color reaches the eye. Color blindness, therefore, is no hindrance to the use of this method. The use of the instrument is shown in Fig. 127.

OPTICAL SYSTEM AND ELECTRICAL CIRCUIT OF THE LEEDS & NORTHRUP OPTICAL PYROMETER.—For extremely high temperature, the optical pyrometer is largely used. This is a comparative method. By means of the rheostat the current through the lamp is adjusted until the brightness of the filament is just equal to the brightness of the image produced by the lens L, Fig. 123, whereupon the filament blends with or becomes indistinguishable in the background formed by the image of the hot object. This adjustment can be made with great accuracy and certainty, as the effect of radiation upon the eye varies some twenty times faster than does the temperature at 1,600 deg.F., and some fourteen times faster at 3,400 deg.F. When a balance has been obtained, the observer notes the reading of the milliammeter. The temperature corresponding to the current is then read from a calibration curve supplied with the instrument.



As the intensity of the light emitted at the higher temperatures becomes dazzling, it is found desirable to introduce a piece of red glass in the eye piece at R. This also eliminates any question of matching colors, or of the observer's ability to distinguish colors. It is further of value in dealing with bodies which do not radiate light of the same composition as that emitted by a black body, since nevertheless the intensity of radiation of any one color from such bodies increases progressively in a definite manner as the temperature rises. The intensity of this one color can therefore be used as a measure of temperature for the body in question. Figures 124 to 126 show the way it is read.

CORRECTION FOR COLD-JUNCTION ERRORS

The voltage generated by a thermo-couple of an electric pyrometer is dependent on the difference in temperature between its hot junction, inside the furnace, and the cold junction, or opposite end of the thermo-couple to which the copper wires are connected. If the temperature or this cold junction rises and falls, the indications of the instrument will vary, although the hot junction in the furnace may be at a constant temperature.

A cold-junction temperature of 75 deg.F., or 25 deg.C., is usually adopted in commercial pyrometers, and the pointer on the pyrometer should stand at this point on the scale when the hot junction is not heated. If the cold-junction temperature rises about 75 deg.F., where base metal thermo-couples are used, the pyrometer will read approximately 1 deg. low for every 1 deg. rise in temperature above 75 deg.F. For example, if the instrument is adjusted for a cold-junction temperature of 75 deg., and the actual cold-junction temperature is 90 deg.F., the pyrometer will read 15 deg. low. If, however, the cold-junction temperature falls below 75 deg.F., the pyrometer will read high instead of low, approximately 1 deg. for every 1 deg. drop in temperature below 75 deg.F.

With platinum thermo-couples, the error is approximately 1/2 deg. for 1 deg. change in temperature.

CORRECTION BY ZERO ADJUSTMENT.—Many pyrometers are supplied with a zero adjuster, by means of which the pointer can be set to any actual cold-junction temperature. If the cold junction of the thermo-couple is in a temperature of 100 deg.F., the pointer can be set to this point on the scale, and the readings of the instrument will be correct.

COMPENSATING LEADS.—By the use of compensating leads, formed of the same material as the thermo-couple, the cold junction can be removed from the head of the thermo-couple to a point 10, 20 or 50 ft. distant from the furnace, where the temperature is reasonably constant. Where greater accuracy is desired, a common method is to drive a 2-in. pipe, with a pointed closed end, some 10 to 20 ft. into the ground, as shown in Fig. 128. The compensating leads are joined to the copper leads, and the junction forced down to the bottom of the pipe. The cold junction is now in the ground, beneath the building, at a depth at which the temperature is very constant, about 70 deg.F., throughout the year. This method will usually control the cold-junction temperature within 5 deg.F.

Where the greatest accuracy is desired a compensating box will overcome cold-junction errors entirely. It consists of a case enclosing a lamp and thermostat, which can be adjusted to maintain any desired temperature, from 50 to 150 deg.F. The compensating leads enter the box and copper leads run from the compensating box to the instrument, so that the cold junction is within the box. Figure 129 shows a Brown compensating box.



If it is desired to maintain the cold junction at 100 deg.: the thermostat is set at this point, and the lamp, being wired to the 110- or 220-volt lighting circuit, will light and heat the box until 100 deg. is reached, when the thermostat will open the circuit and the light is extinguished. The box will now cool down to 98 deg., when the circuit is again closed, the lamp lights, the box heats up, and the operation is repeated.



BROWN AUTOMATIC SIGNALING PYROMETER

In large heat-treating plants it has been customary to maintain an operator at a central pyrometer, and by colored electric lights at the furnaces, signal whether the temperatures are correct or not. It is common practice to locate three lights above each furnace-red, white and green. The red light burns when the temperature is too low, the white light when the temperature is within certain limits—for example, 20 deg.F. of the correct temperature—and the green light when the temperature is too high.



Instruments to operate the lights automatically have been devised and one made by Brown is shown in Fig. 130. The same form of instrument is used for this purpose to automatically control furnace temperatures, and the pointer is depressed at intervals of every 10 sec. on contacts corresponding to the red, white and green lights.



AN AUTOMATIC TEMPERATURE CONTROL PYROMETER

Automatic temperature control instruments are similar to the Brown indicating high resistance pyrometer with the exception that the pointer is depressed at intervals of every 10 sec. upon contact-making devices. No current passes through the pointer which simply depresses the upper contact device tipped with platinum, which in turn comes in contact with the lower contact device, platinum-tipped, and the circuit is completed through these two contacts. The current is very small, about 1/10 amp., as it is only necessary to operate the relay which in turn operates the switch or valve. A small motor is used to depress the pointer at regular intervals. The contact-making device is adjustable throughout the scale range of the instrument, and an index pointer indicates the point on the instrument at which the temperature is being controlled. The space between the two contacts on the high and low side, separated by insulating material, is equivalent to 1 per cent of the scale range. A control of temperature is therefore possible within 1 per cent of the total scale range. Figure 131 shows this attached to a small furnace.



PYROMETERS FOR MOLTEN METAL

Pyrometers for molten metal are connected to portable thermocouples as in Fig. 132. Usually the pyrometer is portable, as shown in this case, which is a Brown. Other methods of mounting for this kind of work arc shown in Figs. 133 and 134. The bent mountings are designed for molten metal, such as brass or copper and are supplied with either clay, graphite or carborundum tubes. Fifteen feet of connecting wire is usually supplied.

The angle mountings, Fig. 134, are recommended for baths such as lead or cyanide. The horizontal arm is usually about 14 in. long, and the whole mounting is easily taken apart making replacements very easy. Details of the thermo-couple shown in Fig. 132 are given in Fig. 135. This is a straight rod with a protector for the hand of the operator. The lag in such couples is less than one minute. These are Englehard mountings.

PROTECTORS FOR THERMO-COUPLES

Thermo-couples must be protected from the danger of mechanical injury. For this purpose tubes of various refractory materials are made to act as protectors. These in turn are usually protected by outside metal tubes. Pure wrought iron is largely used for this purpose as it scales and oxidizes very slowly. These tubes are usually made from 2 to 4 in. shorter than the inner tubes. In lead baths the iron tubes often have one end welded closed and are used in connection with an angle form of mounting.



Where it is necessary for protecting tubes to project a considerable distance into the furnace a tube made of nichrome is frequently used. This is a comparatively new alloy which stands high temperatures without bending. It is more costly than iron but also much more durable.

When used in portable work and for high temperatures, pure nickel tubes are sometimes used. There is also a special metal tube made for use in cyanide. This metal withstands the intense penetrating characteristics of cyanide. It lasts from six to ten months as against a few days for the iron tube.

The inner tubes of refractory materials, also vary according to the purposes for which they are to be used. They are as follows:

MARQUARDT MASS TUBES for temperatures up to 3,000 deg.F., but they will not stand sudden changes in temperature, such as in contact with intermittent flames, without an extra outer covering of chamotte, fireclay or carborundum.



FUSED SILICA TUBES for continuous temperatures up to 1,800 deg.F. and intermittently up to 2,400 deg.F. The expansion at various temperatures is very small, which makes them of value for portable work. They also resist most acids.

CHAMOTTE TUBES are useful up to 2,800 deg.F. and are mechanically strong. They have a small expansion and resist temperature changes well, which makes them good as outside protectors for more fragile tubes. They cannot be used in molten metals, or baths of any kind nor in gases of an alkaline nature. They are used mainly to protect a Marquardt mass or silica tube.

CARBORUNDUM TUBES are also used as outside protection to other tubes. They stand sudden changes of temperature well and resist all gases except chlorine, above 1,750 deg.F. Especially useful in protecting other tubes against molten aluminum, brass, copper and similar metals.

CLAY TUBES are sometimes used in large annealing furnaces where they are cemented into place, forming a sort of well for the insertion of the thermo-couple. They are also used with portable thermo-couples for obtaining the temperatures of molten iron and steel in ladles. Used in this way they are naturally short-lived, but seem the best for this purpose.



CORUNDITE TUBES are used as an outer protection for both the Marquardt mass and the silica tubes for kilns and for glass furnaces. Graphite tubes are also used in some cases for outer protections.

CALORIZED TUBES are wrought-iron pipe treated with aluminum vapor which often doubles or even triples the life of the tube at high temperature.

These tubes come in different sizes and lengths depending on the uses for which they are intended. Heavy protecting outer tubes may be only 1 in. in inside diameter and as much as 3 in. outside diameter, while the inner tubes, such as the Marquardt mass and silica tubes are usually about 3/4 in. outside and 3/8 in. inside diameter. The length varies from 12 to 48 in. in most cases.

Special terminal heads are provided, with brass binding posts for electrical connections, and with provisions for water cooling when necessary.



APPENDIX

TABLE 32.—Temperature Conversion Tables.

TABLE 33.—Comparison Between Degrees Centigrade and Degrees Fahrenheit.

TABLE 34.—Weight of Round, Octagon and Square Carbon Tool Steel per Foot.

TABLE 35.—Weight of Round Carbon Tool Steel 12 In. in Diameter and Larger, per Foot.

TABLE 36.—Decimal Equivalents of a foot.

TEMPERATURE CONVERSION TABLES

By ALBERT SAUVEUR

-459.4 to 0 0 to 100 100 to 1000 - - C. F. C. F. C. F. C. F. C. F. - - - - -273 -459.4 -17.8 0 32 10.0 50 122.0 38 100 212 260 500 932 -268 -450 -17.2 1 33.8 10.6 51 123.8 43 110 230 266 510 950 -262 -440 -16.7 2 35.6 11.1 52 125.6 49 120 248 271 520 968 -257 -430 -16.1 3 37.4 11.7 53 127.4 54 130 266 277 530 986 -251 -420 -15.6 4 39.2 12.2 54 129.2 60 140 284 282 540 1004 -246 -410 -15.0 5 41.0 12.8 55 131.0 66 150 302 288 550 1022 -240 -400 -14.4 6 42.8 13.3 56 132.8 71 160 320 293 560 1040 -234 -390 -13.9 7 44.6 13.9 57 134.6 77 170 336 299 570 1058 -229 -380 -13.3 8 46.4 14.4 58 136.4 82 180 358 304 580 1076 -223 -370 -12.8 9 48.2 15.0 59 138.2 88 190 374 310 590 1094 -218 -360 -12.2 10 50.0 15.6 60 140.0 93 200 392 316 600 1112 -212 -350 -11.7 11 51.8 16.1 61 141.8 99 210 410 321 610 1130 -207 -340 -11.1 12 53.6 16.7 62 143.6 100 212 413 327 620 1148 -201 -330 -10.6 13 55.4 17.2 63 145.4 104 220 428 332 630 1166 -196 -320 -10.0 14 57.2 17.8 64 147.2 110 230 446 338 640 1184 -190 -310 -9.44 15 59.0 18.3 65 149.0 116 240 464 343 650 1202 -184 -300 -8.89 16 61.8 18.9 66 150.8 121 250 482 349 660 1220 -179 -290 -8.33 17 63.6 19.4 67 152.6 127 260 500 354 670 1238 -173 -280 -7.78 18 65.4 20.0 68 154.4 132 270 518 360 680 1256 -169 -273 -459.4 -7.22 19 67.2 20.6 69 156.2 138 280 536 366 690 1274 -168 -270 -454 -6.67 20 68.0 21.1 70 158.0 143 290 554 371 700 1292 -162 -260 -436 -6.11 21 69.8 21.7 71 159.8 149 300 572 377 710 1310 -157 -250 -418 -5.56 22 71.6 22.2 72 161.6 154 310 590 382 720 1328 -151 -240 -400 -5.00 23 73.4 22.8 73 163.4 160 320 608 388 730 1346 -146 -230 -382 -4.44 24 75.2 23.3 74 165.2 166 330 626 393 740 1364 -140 -220 -364 -3.89 25 77.0 23.9 75 167.0 171 340 644 399 750 1382 -134 -210 -346 -3.33 26 78.8 24.4 76 168.8 177 350 662 404 760 1400 -129 -200 -328 -2.78 27 80.6 25.0 77 170.6 182 360 680 410 770 1418 -123 -190 -310 -2.22 28 82.4 25.6 78 172.4 188 370 698 416 780 1436 -118 -180 -292 -1.67 29 84.2 26.1 79 174.2 193 380 716 421 790 1454 -112 -170 -274 -1.11 30 86.0 26.7 80 176.0 199 390 734 427 800 1472 -107 -160 -256 -0.56 31 87.8 27.2 81 177.8 204 400 752 432 810 1490 -101 -150 -238 0 32 89.6 27.8 82 179.6 210 410 770 438 820 1508 -95.6 -140 -220 0.56 33 91.4 28.3 83 181.4 216 420 788 443 830 1526 -90.0 -130 -202 1.11 34 93.2 28.9 84 183.2 221 430 806 449 840 1544 -84.4 -120 -184 1.67 35 95.0 29.4 85 185.0 227 440 824 454 850 1562 -78.9 -110 -166 2.22 36 96.8 30.0 86 186.8 232 450 842 460 860 1580 -73.3 -100 -148 2.78 37 98.6 30.6 87 188.6 238 460 860 466 870 1598 -67.8 -90 -130 3.33 38 100.4 31.1 88 190.4 243 470 878 471 880 1616 -62.2 -80 -112 3.89 39 102.2 31.7 89 192.2 249 480 896 477 890 1634 -56.7 -70 -94 4.44 40 104.0 32.2 90 194.0 254 490 914 482 900 1652 -51.1 -60 -76 5.00 41 105.8 32.8 91 195.8 488 910 1670 -45.6 -50 -58 5.56 42 107.6 33.3 92 197.6 493 920 1688 -40.0 -40 -40 6.11 43 109.4 33.9 93 199.4 499 930 1706 -34.4 -30 -22 6.67 44 111.2 34.4 94 201.2 504 940 1724 -28.9 -20 4 7.22 45 113.0 35.0 95 203.0 510 950 1742 -23.3 -10 14 7.78 46 114.8 35.6 96 204.8 516 960 1760 -17.8 0 32 8.33 47 116.6 36.1 97 206.6 521 970 1778 8.89 48 118.4 36.7 98 208.4 527 980 1796 9.44 49 120.2 37.2 99 210.2 532 990 1814 37.8 100 212.0 538 1000 1832

1000 to 2000 2000 to 3000 - C. F. C. F. C. F. C. F. - 538 1000 1832 816 1500 2732 1093 2000 3632 1371 2500 4534 543 1010 1850 821 1510 2750 1099 2010 3650 1377 2510 4552 549 1020 1868 827 1520 2768 1104 2020 3668 1382 2520 4560 554 1030 1886 832 1530 2786 1110 2030 3686 1388 2530 4588 560 1040 1904 838 1540 2804 1116 2040 3704 1393 2540 4606 566 1050 1922 843 1550 2822 1121 2050 3722 1399 2550 4622 571 1060 1940 849 1560 2840 1127 2060 3740 1404 2560 4640 577 1070 1958 854 1570 2858 1132 2070 3758 1410 2570 4658 582 1080 1976 860 1580 2876 1138 2080 3776 1416 2580 4676 588 1090 1994 866 1590 2894 1143 2090 3794 1421 2590 4694 593 1100 2012 871 1600 2912 1149 2100 3812 1427 2600 4712 599 1110 2030 877 1610 2930 1154 2110 3830 1432 2610 4730 604 1120 2048 882 1620 2948 1160 2120 3848 1438 2620 4748 610 1130 2066 888 1630 2966 1166 2130 3866 1443 2630 4766 616 1140 2084 893 1640 2984 1171 2140 3884 1449 2640 4784 621 1150 2102 899 1650 3002 1777 2150 3902 1454 2650 4802 627 1160 2120 904 1660 3020 1182 2160 3920 1460 2660 4820 632 1170 2138 910 1670 3038 1188 2170 3938 1466 2670 4838 638 1180 2156 916 1680 3056 1193 2180 3956 1471 2680 4854 643 1190 2174 921 1690 3074 1199 2190 3974 1477 2690 4876 649 1200 2192 927 1700 3092 1204 2200 3992 1482 2700 4892 654 1210 2210 932 1710 3110 1210 2210 4010 1488 2710 4910 660 1220 2228 938 1720 3128 1216 2220 4028 1493 2720 4928 666 1230 2246 943 1730 3146 1221 2230 4046 1499 2730 4946 671 1240 2264 949 1740 3164 1227 2240 4064 1504 2740 4964 677 1250 2282 954 1750 3182 1232 2250 4082 1510 2750 4982 682 1260 2300 960 1760 3200 1238 2260 4100 1516 2760 5000 688 1270 2318 966 1770 3218 1243 2270 4118 1521 2770 5018 693 1280 2336 971 1780 3236 1249 2280 4136 1527 2780 5036 699 1290 2354 977 1790 3254 1254 2290 4154 1532 2790 5054 704 1300 2372 982 1800 3272 1260 2300 4172 1538 2800 5072 710 1310 2390 988 1810 3290 1266 2310 4190 1543 2810 5090 716 1320 2408 993 1820 3308 1271 2320 4208 1549 2820 5108 721 1330 2426 999 1830 3326 1277 2330 4226 1554 2830 5126 727 1340 2444 1004 1840 3344 1282 2340 4244 1560 2840 5144 732 1350 2462 1010 1850 3362 1288 2350 4262 1566 2850 5162 738 1360 2480 1016 1860 3380 1293 2360 4280 1571 2860 5180 743 1370 2498 1021 1870 3398 1299 2370 4298 1577 2870 5198 749 1380 2516 1027 1880 3416 1304 2380 4316 1582 2880 5216 754 1390 2534 1032 1890 3434 1310 2390 4334 1588 2890 5234 760 1400 2552 1038 1900 3452 1316 2400 4352 1593 2900 5252 766 1410 2570 1043 1910 3470 1321 2410 4370 1599 2910 5270 771 1420 2588 1049 1920 3488 1327 2420 4388 1604 2920 5288 777 1430 2606 1054 1930 3506 1332 2430 4406 1610 2930 5306 782 1440 2624 1060 1940 3524 1338 2440 4424 1616 2940 5324 788 1450 2642 1066 1950 3542 1343 2450 4442 1621 2950 5342 793 1460 2660 1071 1960 3560 1349 2460 4460 1627 2960 5360 799 1470 2678 1077 1970 3578 1354 2470 4478 1632 2970 5378 804 1480 2696 1082 1980 3596 1360 2480 4496 1638 2980 5396 810 1490 2714 1088 1990 3614 1366 2490 4514 1643 2990 5414 1093 2000 3632 1649 3000 5432 -

NOTE.—The numbers in bold face type refer to the temperature either in degrees Centigrade or Fahrenheit which it is desired to convert into the other scale. If converting from Fahrenheit degrees to Centigrade degrees the equivalent temperature will be found in the left column, while if converting from degrees Centigrade to degrees Fahrenheit, the answer will be found in the column on the right. These tables are a revision of those by Sauveur & Boylston, metallurgical engineers, Cambridge, Mass. Copyright, 1920.

INTERPOLATION FACTORS

C. F. C. F. 0.56 1 1.8 3.33 6 10.8 1.11 2 3.6 3.89 7 12.6 1.67 3 5.4 4.44 8 14.4 2.22 4 7.2 5.00 9 16.2 2.78 5 9.0 5.56 10 18.0

Those using pyrometers will find this and the preceding conversion table of great convenience:

TABLE 33. COMPARISON BETWEEN DEGREES CENTIGRADE AND DEGREES FAHRENHEIT - Degrees Degrees Degrees Degrees Degrees Degrees Degrees - - - - - - - F. C. F. C. F. C. F. C. F. C. F. C. F. C. - - - - - - - - - - - - - - -40 -40.0 3 -16.1 46 7.7 89 31.6 132 55.5 175 79.4 275 135.0 -39 -39.4 4 -15.5 47 8.3 90 32.2 133 56.1 176 80.0 300 148.8 -38 -38.8 5 -15.0 48 8.8 91 32.7 134 56.6 177 80.5 325 162.7 -37 -38.3 6 -14.4 49 9.3 92 33.3 135 57.2 178 81.1 350 176.6 -36 -37.7 7 -13.8 50 10.0 93 33.9 136 57.7 179 81.6 375 190.5 -35 -37.2 8 -13.3 51 10.5 94 34.4 137 58.3 180 82.2 400 204.4 -34 -36.6 9 -12.7 52 11.1 95 35.0 138 58.8 181 82.7 425 218.3 -33 -36.1 10 -12.2 53 11.6 96 35.5 139 59.4 182 83.3 450 232.2 -32 -35.5 11 -11.6 54 12.2 97 36.1 140 60.0 183 83.8 475 246.1 -31 -35.0 12 -11.1 55 12.7 98 36.6 141 60.5 184 84.4 500 260.0 -30 -34.4 13 -10.5 56 13.3 99 37.2 142 61.1 185 85.0 525 273.8 -29 -33.9 14 -10.0 57 13.8 100 37.7 143 61.6 186 85.5 550 287.7 -28 -33.3 15 -9.3 58 14.4 101 38.3 144 62.2 187 86.1 575 301.6 -27 -32.7 16 -8.8 59 15.0 102 38.8 145 62.7 188 86.6 600 315.5 -26 -32.2 17 -8.3 60 15.5 103 39.4 146 63.3 189 87.2 625 329.4 -25 -31.6 18 -7.7 61 16.1 104 40.0 147 63.8 190 87.7 650 343.3 -24 -31.1 19 -7.2 62 16.6 105 40.5 148 64.4 191 88.3 675 357.2 -23 -30.5 20 -6.6 63 17.2 106 41.1 149 65.0 192 88.8 700 371.1 -22 -30.0 21 -6.1 64 17.7 107 41.6 150 65.5 193 89.4 725 385.0 -21 -29.4 22 -5.5 65 18.3 108 42.2 151 66.1 194 90.0 750 398.8 -20 -28.8 23 -5.0 66 18.8 109 42.7 152 66.6 195 90.5 775 412.7 -19 -28.3 24 -4.4 67 19.4 110 43.3 153 67.2 196 91.1 800 426.6 -18 -27.7 25 -3.8 68 20.0 111 43.8 154 67.7 197 91.6 825 440.5 -17 -27.2 26 -3.3 69 20.5 112 44.4 155 68.3 198 92.2 850 454.4 -16 -26.6 27 -2.7 70 21.1 113 45.0 156 68.8 199 92.7 875 468.3 -15 -26.1 28 -2.2 71 21.6 114 45.5 157 69.4 200 93.3 900 482.2 -14 -25.5 29 -1.6 72 22.2 115 46.1 158 70.0 201 93.8 925 496.1 -13 -25.0 30 -1.1 73 22.7 116 46.6 159 70.5 202 94.4 950 510.0 -12 -24.4 31 -0.5 74 23.3 117 47.2 160 71.1 203 95.0 975 523.8 -11 -23.8 32 -0.0 75 23.8 118 47.7 161 71.6 204 95.5 1,000 537.7 -10 -23.3 33 +0.5 76 24.4 119 48.3 162 72.2 205 96.1 1,100 593.3 -9 -22.7 34 1.1 77 25.0 120 48.8 163 72.7 206 96.6 1,200 648.8 -8 -22.2 35 1.6 78 25.5 121 49.4 164 73.3 207 97.2 1,300 704.4 -7 -21.6 36 2.2 79 26.1 122 50.0 165 73.8 208 97.7 1,400 760.0 -6 -21.1 37 2.7 80 26.6 123 50.5 166 74.4 209 98.3 1,500 815.5 -5 -20.5 38 3.3 81 27.2 124 51.1 167 75.0 210 98.8 1,600 871.1 -4 -20.0 39 3.8 82 27.7 125 51.6 168 75.5 211 99.4 1,700 926.6 -3 -19.4 40 4.4 83 28.3 126 52.2 169 76.1 212 100.0 1,800 982.2 -2 -18.8 41 5.0 84 28.8 127 52.7 170 76.6 213 100.5 1,900 1,037.7 -1 -18.3 42 5.5 85 29.4 128 53.3 171 77.2 214 101.1 2,000 1,093.3 0 -17.7 43 6.1 86 30.0 129 53.8 172 77.7 215 101.6 2,100 1,148.8 +1 -17.2 44 6.6 87 30.5 130 54.4 173 78.3 225 107.2 2,200 1,204.4 2 -16.6 45 7.2 88 31.1 131 55.0 174 78.8 250 121.1 2,300 1,260.0 -

9 x degrees C. Degrees Fahrenheit = ——————— + 32 5

5 x (degrees F. - 32) Degrees Centigrade = ——————————- 9

Three other useful tables are also given on the following pages.

TABLE 34. WEIGHT OF ROUND, OCTAGON AND SQUARE CARBON TOOL STEEL PER FOOT Size Size in Round Octagon Square in Round Octagon Square inches inches - 1/16 0.010 0.011 0.013 2-1/2 16.79 17.71 21.37 1/8 0.042 0.044 0.053 2-5/8 18.51 19.52 23.56 3/16 0.094 0.099 0.120 2-3/4 20.31 21.42 25.86 1/4 0.168 0.177 0.214 2-7/8 22.20 23.41 28.27 5/16 0.262 0.277 0.334 3 24.17 25.50 30.78 3/8 0.378 0.398 0.481 3-1/8 26.23 27.66 33.40 7/16 0.514 0.542 0.655 3-1/4 28.37 29.92 36.12 1/2 0.671 0.708 0.855 3-3/8 30.59 32.27 38.95 9/16 0.850 0.896 1.082 3-1/2 32.90 34.70 41.89 5/8 1.049 1.107 1.336 3-5/8 35.29 37.23 44.94 11/16 1.270 1.339 1.616 3-3/4 37.77 39.84 48.09 3/4 1.511 1.594 1.924 3-7/8 40.33 42.54 51.35 13/16 1.773 1.870 2.258 4 42.97 45.34 54.72 7/8 2.056 2.169 2.618 4-1/4 48.51 51.17 61.77 15/16 2.361 2.490 3.006 4-1/2 54.39 57.37 69.25 1 2.686 2.833 3.420 4-3/4 60.60 63.92 77.16 1-1/8 3.399 3.585 4.328 5 67.15 70.83 85.50 1-1/4 4.197 4.427 5.344 5-1/4 74.03 78.08 94.26 1-3/8 5.078 5.356 6.646 5-1/2 81.25 85.70 103.45 1-1/2 6.044 6.374 7.695 5-3/4 88.80 93.67 113.07 1-5/8 7.093 7.481 9.031 6 96.69 101.99 123.12 1-3/4 8.226 8.674 10.474 7 131.61 138.82 167.58 1-7/8 9.443 9.960 12.023 8 171.90 181.32 218.88 2 10.744 11.332 13.680 9 217.57 229.48 277.02 2-1/8 12.129 12.793 15.443 10 268.60 283.31 342.00 2-1/4 13.598 14.343 17.314 11 325.01 342.80 413.82 2-3/8 15.151 15.981 19.291 12 386.79 407.97 492.48

High-speed steel, being more dense than carbon steel, weighs from 10 to 11 per cent more than carbon steel. This should be added to figures given in the table.

TABLE 35. WEIGHT OF ROUND, CARBON TOOL STEEL 12 IN. IN DIAMETER AND LARGER, PER FOOT Diameter, Weight Diameter, Weight Diameter, Weight inches per foot inches per foot inches per foot - - - 12 386.790 15-7/8 677.527 19-3/4 1,049.010 12-1/8 395.518 16 687.600 19-7/8 1,061.705 12-1/4 404.246 16-1/8 699.017 20 1,074.400 12-3/8 412.974 16-1/4 710.435 20-1/8 1,088.502 12-1/2 421.702 16-3/8 721.852 20-1/4 1,102.605 12-5/8 430.430 16-1/2 733.270 20-3/8 1,116.707 12-3/4 439.158 16-5/8 744.687 20-1/2 1,130.810 12-7/8 447.886 16-3/4 756.105 20-5/8 1,144.912 13 456.615 16-7/8 767.522 20-3/4 1,159.015 13-1/8 465.343 17 778.940 20-7/8 1,173.118 13-1/4 474.071 17-1/8 790.358 21 1,187.220 13-3/8 482.799 17-1/4 801.777 21-1/8 1,201.322 13-1/2 491.527 17-3/8 813.195 21-1/4 1,215.425 13-5/8 500.255 17-1/2 824.614 21-3/8 1,229.527 13-3/4 508.983 17-5/8 836.030 21-1/2 1,243.630 13-7/8 517.711 17-3/4 847.447 21-5/8 1,257.732 14 526.440 17-7/8 858.863 21-3/4 1,271.835 14-1/8 536.512 18 870.280 21-7/8 1,285.937 14-1/4 546.585 18-1/8 883.105 22 1,300.040 14-3/8 556.657 18-1/4 895.920 22-1/8 1,315.485 14-1/2 566.730 18-3/8 908.740 22-1/4 1,330.930 14-5/8 576.802 18-1/2 921.560 22-3/8 1,346.375 14-3/4 586.875 18-5/8 934.380 22-1/2 1,361.820 14-7/8 596.947 18-3/4 947.200 22-5/8 1,377.265 15 607.020 18-7/8 960.020 22-3/4 1,392.710 15-1/8 617.092 19 972.840 22-7/8 1,408.155 15-1/4 627.165 19-1/8 985.035 23 1,423.600 15-3/8 637.237 19-1/4 998.230 23-1/8 1,454.490 15-1/2 647.310 19-3/8 1,010.925 23-1/4 1,485.380 15-5/8 657.382 19-1/2 1,023.620 23-3/8 1,516.270 15-3/4 667.455 19-5/8 1,036.315 24 1,547.160

To find the weight of discs made of carbon steel, in diameters up to and including 12 in., without any allowance for finishing multiply the per foot weight of round bar steel, shown herewith by the decimal equivalent of a foot given in the following table:

TABLE 36. DECIMAL EQUIVALENTS OF A FOOT - In. 0 1/8 1/4 3/8 1/2 5/8 3/4 7/8 - - - - - - - - - 0 0.000 0.010 0.021 0.031 0.042 0.052 0.063 0.073 1 0.083 0.094 0.104 0.115 0.125 0.135 0.146 0.156 2 0.167 0.177 0.188 0.198 0.208 0.219 0.229 0.240 3 0.250 0.260 0.270 0.281 0.292 0.302 0.313 0.323 4 0.333 0.344 0.354 0.364 0.375 0.385 0.396 0.406 5 0.416 0.427 0.437 0.448 0.458 0.469 0.479 0.480 6 0.500 0.510 0.520 0.531 0.542 0.552 0.563 0.573 7 0.583 0.594 0.604 0.615 0.625 0.635 0.646 0.656 8 0.666 0.677 0.687 0.698 0.708 0.719 0.729 0.740 9 0.750 0.760 0.770 0.781 0.792 0.802 0.813 0.823 10 0.833 0.844 0.854 0.865 0.875 0.885 0.896 0.906 11 0.916 0.927 0.937 0.948 0.953 0.969 0.979 0.990 -

EXAMPLE.—If the weight of a carbon steel disc 7 in. diameter, 1-5/8 in. thick is desired, turn to page 233, where the per foot weight of 7 in. round is given as 131.6 lb. Multiply this by the decimal equivalent of 1-5/8 in., or 0.135, as shown in the above table, and the product will be the net weight of the disc.

131.61 lb. = the weight of 1 ft. of 7 in. round. 0.135 = the per foot decimal equivalent of 1-5/8 in: —————— 65805 39483 13161 —————— 17.76735 lb. = weight of disc 7 in. diam. 1-5/8 in. thick without any allowance for finishing.



AUTHORITES QUOTED

A

ADDIS, W H. AMERICAN MACHINISTS' HANDBOOK AMERICAN STEEL TREARERS' SOCIETY AMERICAN GEAR MFRS. ASSO. AUTOMATIC AND ELECTRIC FURNACES LTD. ARNOLD, PROF. J. O.

B

BURLEIGH, R. W. BORDEN, B. BOKER, HERMAN & Co. BROWN INSTRUMENT Co. BROWN-LIPE-CHAPLIN Co.

C

CAMPBELL, H. H. CARHART, H. A. CLAYTON, C. Y. CURTIS AIRPLANE Co.

E

ENGLEHARD, CHARLES ENSAW, HOWARD

F

FIRTH-STERLING STEEL Co. FIRTH, THOMAS & SONS FOWLER, HENRY

G

GILBERT & BARKER

H

HAYWAHD, C. R. HOWE, DR. H. M. HOOVER STEEL BALL CO. HEATHCOTE, H. L. HARRIS, MATTHEW HUNTER, J. V.

J

JANITZKY, E. J. JOHNSTON, A. B. JUTHE, K. A.

L

LATROBE STEEL CO. LUDLUM STEEL CO. LEEDS & NORTHRUP CO. LYMAN, W. H.

M

MANSFIELD, C. A. MIDVALE STEEL Co. McKENNA, ROY C. MOULTON, SETH A.

N

NILES, BEMENT, POND

P

PARKER, S. W. POOLE, C. R.

R

RAWDON, H. S.

S

S. A. E. (SOCIETY AUTOMOTIVE ENGINEERS) SAUVEUR, ALBERT SPRINGFIELD ARMORY SELLACK, T. G. SMITH, A. J. SHIRLEY, ALFRED J.

T

TAYLOR INSTRUMENT Co. THUM, E. E. TIEMANN, H. P.

U

U. S. BALL BEARING Co. UNITED STEEL Co. UNDERWOOD, CHARLES N.

V

VAN DE VENTER, JOHN H.

W

WALP, H. O. WOOD, HAROLD F. WHEELOCK, LOVEJOY & Co.



INDEX

A

ABC of iron and steel Absorption of carbon, rate of Air hardening steels Analysis of high speed steel Allotropic modifications Alloy steel, annealing properties of Alloys and their effect in high speed steel in steel, value of upon steel Alpha iron Annealing care in furnace high-chromium steel high speed tools in bone methods proper rifle components rust-proof steel steels temperature Arrests Austentite Automotive industry, application of Liberty engine materials to temperature control Axles, heat treatment of

B

Balls, making steel Barium chloride process Baths for tempering Bessemer converter Beta iron Blending compounds Blister steel Blue brittleness Bone, annealing in Boxes for case hardening or carburizing Breaking test gears Brinell hardness Broach hardening furnace Brown automatic pyrometer Burning

C

Calorized tubes Carbon content at various temperatures content of case hardened work in cast iron, ix in tool steel introduction of penetration of steel steel forgings, Liberty engine steel tools steels, S. A. E. steels, temper colors strengthens iron tool steel, forging Carbonizing, see Carburizing Carborundum tubes Carburization, preventing Carburizing by gas boxes compounds gas consumption by local material nickel steel or case hardening pots for Carburizing, process of short method sleeves with charcoal See Case hardening Car door type of furnace Case, depth of Case hardening boxes cast iron local or surface carburizing treatments for various steels see Carburizing Cast iron, carbon in case hardening Cementite Center column furnace Centigrade table Chamotte tubes Chart of carbon penetration heat treatment shape Chrome steel Chrome-nickel steel steel, forging Chrome-vanadium steel Chromium steels, S. A. E. Chromium-cobalt steel Chromium-vanadium steel, S. A. E. Classification of steel Clay tubes Cold end compensator junction errors shortness worked steel Color in tempering Colors on carbon steels Combination tank Comparison of fuels Compensating leads Compensator for cold ends automatic Composition of steel Compound, blending separating from work Compounds for carburizing Connecting rods, Liberty motor Continuous heating furnace Converter, Bessemer Cooling curves Cooling quenching oil, roof system rate of, for gear-forgings Copper, effect of, in medium carbon steel Copper-plating to prevent carburizing Corrosion of high-chromium steel of rust-proof steel Corundite tubes Cost of operating furnaces Cracks in hardening, preventing Crankshaft, Liberty motor Critical point Crucible or tool steel Cutting off high speed steel Cyanide bath for tool steel

D

Decarbonizing of outer surface preventing Depth of case Detrimental elements in steel Dies, drop forging quenching soft spots in tempering round Drawing ends of gear teeth Drop forging dies Ductility

E

Effect of alloys of different carburizing material of size of piece of copper in medium carbon steel Elastic limit Electric process of steel making Electrode Elements, chemical Elongation Endurance limit Energizer, 81 Enlarging steel Equipment for heat treating Eutectoid

F

Fahrenheit temperature table Fatigue test Ferrite File test Flame shields Flange shields for furnaces Forging furnace high speed tools improper of steel practice, heavy rifle barrels Forgings, carbon steel Liberty engine Formed tools, high speed Fractures, examining by Furnace, continuous heating crucible data electric Heroult open hearth records Furnaces annealing broach hardening car door type center column cost of operating data on forging, heavy fuels for gas fired high speed steel lead pot manganese steel muffle oil fired operating costs screens for tool Furnaces, water cooled fronts Fuels, comparison of for furnaces

G

Gages, changes due to quenching tempering Gamma iron Gas, carburizing by consumption for carburizing fired furnace illuminating, for carburizing Gear blanks, heat treatment of forgings, rate of cooling for Liberty engine hardening machine steel, transmission teeth, drawing ends of Gears, Liberty engine Gleason tempering machine Grade of steel Grain, refining size Graphitic carbon Grinding high speed steel

H

Hair lines in forgings Hardening carbon steel for tools cracks, preventing dies gears high speed steel high speed tools of high-chromium steel of rust-proof steel room, modern Hardness tests Heating, effect of size for forging Heat, judging by color treating departments equipment forgings inspection of Liberty motor Heat treating, of axles of chisels of gears of high speed steel of steel S. A. E. Heat treatment Heroult furnace High-chromium steel annealing of corrosion of hardening of Highly stressed parts of Liberty engine High speed steel, analysis of annealing cutting off forging furnace hardening heat treatment of instructions for manufacture pack hardening structure of Hints for steel users

I

Illuminating gas for carburizing Impact test Improper forging Influence of size on heating Inspection of heat treatment Internal stresses, relieving Introduction of carbon

J

Jewelers' tools Judging heat of steel by color

L

Latent heat Lathe and planer tools tools, high speed Latrobe temper list Lead bath pot furnace Leeds & Northrup potentiometer optical pyrometer Liberty engine, highly stressed parts of Liberty engine materials, application to automotive industry motor connecting rods motor, crankshaft motor piston pin Local case hardening Luting mixture

M

Machineability of steel Machinery steel, annealing Magnet test Making steel in electric furnace Manganese steel furnace Manufacture of high speed steel Marquardt mass tubes Martensite Medium carbon steel, effect of copper on Metallography Microphotographs Microscopic examination Milling cutters, high speed Mixture for luting Modern hardening room Molten metal pyrometers Molybdenum Muffle furnace

N

Nickel Nickel-chromium steel steels, S. A. E. Nickel, influence of, on steel steel affinity for carbon steels, S. A. E. Non-homogeneous melting Non-shrinking steels Normalizing

O

Oil bath for tempering cooling on roof fired furnace hardening steel, forging steels temperature of quenching Open hearth furnace Operating costs of furnaces Outer surface decarbonizer Over-heated steel, restoring Overheating dies

P

Pack-hardening high speed steel Packing work for carburizing Paste for hardening dies Pearlite Penetration of carbon carbon, chart of in case hardening Phosphorus Pickling Liberty motor forgings Pig iron Piston pin, Liberty motor Placing pyrometers Planer tools, high speed "Points" of carbon in steel Potentiometer, Leeds & Northrup Pots for carburizing Press for testing gears Preventing carburization cracks in hardening Properties of alloy steels of alloy steels, table of steel Protective screens for furnaces Puddled iron Punches and chisels, steels for Pyrometers calibration copper ball indicating inspection iron ball molten metal optical placing recording Siemens testing water

Q

Quality and structure of high speed steel of steel Quenching, after carburizing dies in tank obsolete method oil, temperature of tank tool steel

R

Rate of absorption of carbon Recording temperatures Red shortness Refining the grain Regenerative open hearth furnace Restoring overheated steel Rifle barrels, forging components, annealing Roof system of cooling oil Rust-proof steel annealing of corrosion of hardening of

S

S. A. E. carbon steels chromium steels chromium-vanadium heat treatments nickel-chromium steels nickel steels screw stock silico-manganese steel standard steels Salt bath for tempering Scleroscope test Scratch hardness Screens for furnaces Screw stock, S. A. E. Sensible heat Sentinels, melting of Separating work from compound Shields for furnace doors Shore Scleroscope Short method of carburizing Shrinking steel Silica tubes Silico-manganese steels, S. A. E. Silicon Silversmiths' tools Size of piece, effect of Slags Sleeves, carburizing hardening and shrinking shrinking Solid solution Sorbite Specimens, test Standard S. A. E. steels Steel, balls, stock for bolts, making composition of deoxidation for chisels and punches forging of give it a chance heat treatment of high speed making Bessemer process crucible process electric furnace process open hearth tools, carbon, in users' hints Structure of high speed steel Sulphur

T

Tables, air, oil and water hardened steel alloy steels, properties of carbon content carbon steels case hardening changes due to quenching chromium steels chromium-vanadium steels colors and temperature composition of steels cost of furnaces effect of size fuels, comparison of high-chromium steel nickel-chromium steels nickel steels operating cost of furnaces production cost of furnaces S. A. E. steels screw stock silico-manganese steels stock for balls temperature conversion tempering temperatures weight of steel Tank for quenching dies Taylor instruments Temper, colors of list, Latrobe of steel Temperature recorders tables Temperatures for tempering Tempering colors on carbon steels gages high speed tools machine, Gleason round dies temperatures theory of Tempers of carbon steel Tensile test Testing heat treatment Tests of steel Test specimens Theory of tempering Thermocouple base metal cold end placing protectors rare metal Time for hardening Tool furnace, small Tool or crucible steel, annealing Tool steel, cyanide bath for quenching Tools, carbon in different carbon steel of high speed steel sulphur in tempers of various transformation points Transmission gear steel Treatments for various steels Troosite Tubes, calorized carborundum Chamotte clay Marquardt mass silica Tungsten steel

U

Ultimate strength Users of steel, hints for

V

Vanadium steel

W

Water annealing cooled furnace fronts Weight of steel bars Working instructions for high speed steel Wrought iron, ix

Y

Yield Point

THE END