US2275265A

US2275265A - Furnace control system

Info

Publication number: US2275265A
Application number: US313367A
Authority: US
Inventors: Harold G Mead
Original assignee: Leeds and Northrup Co
Current assignee: Leeds and Northrup Co
Priority date: 1940-01-11
Filing date: 1940-01-11
Publication date: 1942-03-03
Anticipated expiration: 1959-03-03

Description

March 3, 1942. H. G. MEAD FURNACE CONTROL SYSTEM Filed Jan. 11, 1940 2 Sheets-Sheet l March 3, 1942. H. G. MEAD I FURNACE CONTROL SYSTEM Filed Jan. 11., 1940 2 Sheets-Sheet 2 Patented Mar. 3, 1942 UITE STATES rric FURNACE CONTROL SYSTEM Application January 11, 1940, Serial No. 313,367

8 Claims.

My invention relates to control of rate of input of heat to a continuous furnace to ensure that the temperature of the billets, slabs, or the like, at discharge from the furnace is of desired or predetermined magnitude different from that of the furnace.

In accordance with my invention, the temperature of the billets is measured as they in succession approach the discharge end of the furnace by a radiation pyrometer having a sighting tube extending through wall structure of the furnace with its open end adjacent the path of the billets and provided with, or constructed to serve as, a shield limiting the radiation measured substantially entirely to that from the billets themselves to the exclusion of radiation from sources at the same or other temperatures, such as wall structure and the like within the furnace; preferably a fluid medium, such as air or other suitable gas, is forced through the tube to protect the pyrometer from overheating and, which is more important, to keep the path of radiation to the pyrometer from the billet surface under observation free of smoke, fumes, flames or other medium.

Further, in accordance with my invention, the heat input to the furnace, or to one or more zones thereof, is automatically controlled by the radiation pyrometer to control, preferably maintain equal and uniform, the temperatures of the successively discharged billets.

My invention further resides in the features of construction, combination and arrangement hereinafter described and claimed.

For an understanding of my invention, reference is made to the accompanying drawings in which:

Fig. 1 is an elevational view, with parts in section, of the discharge end of a furnace and associated control apparatus;

Figs. 2, 2A, 3 and 3A, in perspective and on enlarged scale, illustrate modifications of shield structure shown in Fig. 1;

Fig. 2B is a detail view, on enlarged scale, of one of the link elements of Fig. 2A;

Figs. 4, 5, 6A, 6B and 6C are explanatory figures referred to in discussion of the control system of Fig. 1;

Fig. 'lis an elevational view, in section, of a furnace having several heating zones.

Referring to Fig. 1, there is shown the dis charge end of furnace F exemplary of the type used for heating billets, slabs, or the like to temperature suitable for rolling, drawing, or equivalent operation. In the particular furnace shown, the billets B are pushed along the inclined floor i of the furnace in the direction of the arrow and each in turn slides down the steeper incline 2 for discharge from the furnace through and beyond its door 3; any other suitable arrangement for feeding the billets through the furnace may, of course, be utilized.

The heat input to the furnace is supplied by a plurality of burners 4 directed into the heating chamber or zone 5, generally through the side and end walls, and is controlled by valves 6 in the fuel lines 1 supplying gas, oil or other fuel to the burners.

In the operation of furnaces of this type, the billets do not, except occasionally by chance, remain in the furnace long enough to effect equality of their temperature with the furnace temperature; it has heretofore been the practice in the operation of such furnaces to control the heat input to maintain the furnace temperature constant at predetermined magnitude suitably higher than the desired rolling temperature of the billets; otherwise stated, it was sought to maintain a constant temperature head or constant temperature differential. To that end, the furnace temperature was measured by thermocouples within protecting tubes inserted through the furnace walls. However, because of such factors as variations in the rate of billet feed through the furnace, in the number of billets within the furnace at different times in a run, in the room or ambient temperature, in the absorption of heat by the furnace walls and in the effect of flame and smoke upon the response of the thermocouple, the temperature of the discharged billets was not uniform throughout a run but varied to substantial extent with consequent adverse effect upon the rolling operations. With this prior method of control, it was not unusual for the temperatures of different billets to vary as much as 300 F.

With the control system of Fig. 1, the heat input to the furnace is not controlled in accord with the temperature of the furnace, but in accord with the temperature of billets within the final zone of the furnace; thetheat input to the furnace is varied in proper sense and extent to obtain the uniformity of the billet temperature regardless of whether the consequent changes in heat input increase or decrease the furnace temperature.

As the billets move through the final zone of furnace F, they in turn pass, during continuous, open and unrestricted exposure to the furnace atmosphere or gases, adjacent the open or apertured end of the tube 8 extending through a wall, specifically the roof 9, of the heating chamber 5. At or upon the other end of tube 8 is mounted a radiation pyrometer unit or head l0, preferably of the multi-couple type disclosed in Letters Patent 2,232,594, granted February 18, 1941, to Dike upon his application Serial No.

' 215,499, filed June 23, 1938, for producing an electromotive force representative of the quantity of radiation entering the lower open end of tube 8. To exclude from the measurements the eifect of radiation from the furnace walls or from the flames, the lower end of tube 8 is provided with a shield ll, attached to or integral therewith, and extending outwardly to suitable extent from the periphery of tube 8. The tube and shield are of non-metallic refractory material, such as Carborundum, or of metal or metal alloy such as nickel-chromium alloy suited to afford reasonably long life at the temperatures involved which may be, for rolling steel billets, generally of the order of 1500 F. to 2200 F. The tube 8 may conveniently be of circular crosssection and, for example, of about 3 or 4 inches in diameter; its length is determined by the size of the furnace and the location of the pyrometer head.

In those installations in which there is danger of the billets piling up or for some other reason striking the lower end of tube 8 or shield ll,

there may be utilized the modified arrangement shown in Fig. 2 in which the tube 8 terminates well above the path of the billets, the plate H and the closely spaced chains A depending therefrom serving as a shield to prevent radiation from the walls of the furnace and from the flame from being reflected by the upper face of the billets into the sighting tube. The chains 1 IA yield in event they are struck by a billet pi ed up upon another or otherwise out of position, but upon passage of the billet the chains return to their normal positions and so preserve the integrity of the shield.

In the similar arrangement shown in Fig. 2A, the flexible shield structure A comprises plate links I 9, Fig. 2B, suitably joined to form a curtain for interception of radiation to the upper face of a billet under observation from the fumace' walls or the flame.

Other suitable and preferred forms of shield are shown in Figs. 3 and 3A; in both figures, the shield is a funnel or cone-shaped member suitably fastened at its smaller end to the lower end of tube 8; in Fig. 3 shield B is attached by bolts to a flange 8A extending outwardly from the lower end of tube 8; in Fig. 3A, the lower end of tube 8 is provided with bayonet slots 16 for receiving pins I! extending radially from sleeve l8 at the upper end of conical shield NC.

The path of radiation from the billet surface under observation to the pyrometer head I is maintained free of smoke and flame, or other media which would otherwise cause the output voltage of the radiation pyrometer unpredictably to vary to magnitudes lower or higher than the voltage corresponding with the billet temperature, by forcing air, orother suitable fluid medium, downwardly through tube 8. In the particular arrangement shown,-a small blower I! having its discharge duct l3 connected to tube 8 outside of the furnace and adjacent the pyrometer head continuously forces air through tube 8. The stream of air in addition to maintaining the sighting tube 8, substantially free of smoke and flame, also serves to cool it and so prolongs its effective life.

The absorption of radiation by the introduced air is a constant compensated for by the calibration of the pyrometer.

The thermocouple device within pyrometer l0 may connect to any suitable voltage-responsive device or arrangement, for example, a voltmeter provided with a scale calibrated in units of temperature, or a measuring network such as a potentiometer having a rebalancing slidewire associated with a temperature scale. With such information available to him, an operator may manually adjust the fuel valves 6, or equivalent means for varying the heat input, to maintain the observed temperature of the billets about to be discharged from the furnace at the desired magnitude. Preferably, however, control of the valves 6 or equivalent is effected automatically as by controller I! which, for example, may be of any of the types disclosed and claimed in U. S. Letters Patent 2,155,346 to Davis, 2,154,065 to Davis et al. and 2,113,069 and 2,096,064 to Ross et al. With each valve 6 may be associated a reversible motor I3 connected by conductors M to a control switch within controller l2 which, in response to departure of the temperature of the observed billets from their desired temperature, varies the heat input to the furnace and particularly to the final zone thereof, in proper sense to restore the billet temperature to the desired magnitude; the instrument 12 preferably is also, as shown in aforesaid patents, a recorder on whose chart or record sheet l5 there is traced the temperature of the billets.

The total-radiation pyrometer l 0 or equivalent automatic observer may be replaced by an optical, or partial-radiation, pyrometer and a human operator who sights through tube 8 upon the billets B as they pass beneath the open end of tube 8 to determine their temperature. In such modification, the blower I2 is retained to maintain tube 8 free of smoke, flame or other media which would, by absorption or enhancement of radiation, introduce errors into the observations; shield ll, HA, 3 or C is also retained to preclude introduction into tube 8 of radiation from sources, such as the furnace walls or flame, other than the billet or billets under observation.

My method of control of the heat input compensates for or takes into account all of aforesaid variable factors, including rate of feed of the billets, the number of billets in the furnace, ambient temperature, absorption and radiation of heat from and by the furnace walls and so, notwithstanding variations in any or all of said factors, insures uniformity of final temperature of the billets as discharged for rolling, forging or other similar operation. By way of example,

'a furnace controlled in accordance with my method discharged billets whose temperature varied throughout a run only about 5 F. from the desired temperature, whereas, with the same furnace controlled in accordance with aforesaid previous practice, the billet temperature often varied, throughout a run, as much as 300 F.; i. e., from about 1500 F. to about 1800 F.

This difference between the two methods'of control of heat input to a continuous furnace is evident from comparison of Figs. 4 and 5; referring to Fig. 4, the curve FT illustrates the substantial constancy of the furnace temperature when the heat input thereto is controlled by a thermocouple disposed within a protecting tube which projects into the heating chamber and curve WT illustrates the undesirable resulting wide variations in final or discharge temperature of the billets. In contrast therewith, the curve WT of Fig. illustrates the uniformity of the final billet temperature when the heat input is controlled by the arrangement shown in Fig. 1; the curve FT of Fig. 5 illustrates the changes in furnace temperature, or the changes in 'temperature head required to obtain aforesaid uniformity of the billet temperature.

The sensitivity of the pyrometer of Fig. 1 to changes in temperature is so high that there is indicated or recorded the variations in temperature along the individual billets; consequently, when the record of the billet temperature appears, as in Fig. 6A, with a series of teeth inclined to the right, toward higher temperature,

it indicates the preliminary zone 5A of the furnace F (Fig. 7) is cooler than the final zone 5, whereas, when the preliminary zone 5A is hotter than the final zone, the record appears as in Fig. 6B with the saw teeth inclined to the left indicating that each billet has decreased in temperature as it moved in the final zone below tube 8. When the burner 4A of the preliminary zone 5A are adjusted for proper or optimum heat input to that zone, the'record of the final billet temperature, as appears in Fig. 6C, is a smooth curve devoid of abrupt breaks or saw teeth.

The burners in the preliminary zone or subdivisions thereof may be controlled manually or automatically in response to the sense of change in temperature of the billets as they pass along the final zone.

The temperature of the billets at any one or more stages of or points in their progress through the furnace may be measured by any of the radiation-pyrometer arrangements herein described, and, if desired, the heat input to any one or more zones of the furnace may be controlled in accordance with such measurement, as broad- 1y exemplified by control of heat input in response to temperature at the discharge end or final zone, Fig. 1.

The unit, comprising sighting tube 8 with a radiation pyrometer or other radiation-responsive device at one end thereof, and with a radiation shield extending outwardly therefrom at or adjacent the other end, is not limited to use in a continuous furnace; it is utilizable to advantage as well in other types of furnaces, such for example as hardening or annealing furnaces, in which it is desired to measure the temperature of the Work with avoidance of errors due to reflection from the work surface of radiation from other sources, such as the wall structure of the furnace or flame, or due to absorption of radiation from the work surface by smoke or fumes in the furnace.

For brevity in the appended claims, it shall be understood the term billet" is generic,-and comprehends billets, slabs, or other masses or pieces of steel or other metal, or non-metallic objects, generally of like forms or dimensions.

The term sighting" as herein employed is not limited to observation by the human eye, but is used, as common in pyrometry, also to comprehend observation or sighting by any radiationresponsive element, such as a radiation pyrometer photo-electric cell or equivalent device,

" preferably one which produces an electrical efifect of magnitude representative of the temperature of the billet under observation.

What I claim is: 1. A system for measuring the temperature of billets within a continuous furnace comprising 76 a radiation pyrometer provided with a sighting tube extending lthrough wall structue of the furnace and having an open end disposed adjacent the path of said billets to view a surface of each of the successive billets during continuous and unrestricted exposure of said surface to the furnace atmosphere, and structure adjacent said open end of the sighting tube and extending laterally therefrom to prevent radiation from the interior of the furnace from being reflected into said tube by the surface of a billet under observation by the pyrometer and without interruption of exposure of that surface to the furnace atmosphere.

2. An arrangement for measuring the temperature of work within a furnace comprising a radiation pyrometer provided with an openended sighting tube having its open end adiacent the work to view a surface thereof during continuous, open and unrestricted exposure of said surface to the furnace atmosphere, and means for preventing effect upon the measurements by fiame, smoke or reflections within the furnace comprising means for forcing a fiuid medium through said tube, and a radiation shield extending laterally from said open end of the tube and at suitable distance from said surface of the work for unrestricted access to said surface of said furnace atmosphere.

3. An arrangement for measuring the temperature of work within a furnace comprising a radiation pyrometer provided with an openended sighting tube having its open end adjacent a surface of the work during continuous, open and unrestricted exposure of said surface to the furnace atmosphere and having said end flared to prevent radiation from other sources thereof within the furnace from directly reaching the pyrometer or indirectly by reflection from said exposed surface of the work.

4. An arrangement for measuring the temperature of work within a furnace comprising a radiation pyrometer provided with an openended sighting tube having its open end adjacent the work to view a surface thereof exposed to the furnace atmosphere, and structure adjacent said open end of said tube and extending laterally therefrom to prevent transmission through said tube to the pyrometer of radiation from a source other than said surface of the work itself without restriction of exposure of said surface to the furnace atmosphere.

5. A system for measuring the temperature of billets within a continuous furnace comprising a radiation pyrometer provided with a sighting tube extending through wall structure of the furnace and having an open end adjacent the path of said billets to view a surface of each of the successive billets during continuous and unrestricted exposure of said surface to the furnace atmosphere, and a plate supported adjacent said open end of said tube and extending laterally therefrom to prevent radiation from flame and from wall structure of the furnace from striking the billet surface under observation by the pyrometer without interruption of aforesaid continuous and unrestricted exposure of that observed surface to the furnace atmosphere.

6. A system for measuring the temperature of billets within a continuous furnace comprising a radiation pyrometer provided with a sighting tube extending through wall structure of the furnace and having an open end adjacent the path of said billets, and a plurality of yielding members closely spaced about said open end of said tube to define a shield preventing impingement upon that portion of the billet surface under observation by the pyrometer of measurement affecting radiation from a source other than said surface portion itself.

7. A system for procuring equality of the temperatures of billets discharged from a continuous furnace comprising a radiation pyrometer, for

measuring the temperature of successive billets as they approach the discharge end of the furnace, a sighting tube for said pyrometer extending through wall structure of the furnace and having an open end adjacent the path of the billets to view a surface of each of the successive billets during continuous and unrestricted exposure of said surface to the furnace atmosphere, structure disposed adjacent and extending outwardly from said open end of the sighting tube to prevent reflection of radiation from the interior of the furnace into said tube by the exposed surface of the billet under observation by the pyrometer without interruption of exposure of that surface to the furnace atmosphere, and

means for varying the heat input to the furnace in accordance with the measured temperature of the billets.

8. A system for procuring equality of the temperatures of billets discharged from a continuous furnace comprising a radiation pyrometer, for measuring the temperature of successive billets as they approach the discharge end of the furnace, and a "sighting tube extending through wall structure of the furnace and having an open end adjacent the path of the billets to view a surface of each of the successive billets during continuous and unrestricted exposure of said surface to the furnace atmosphere, means for preventing effect upon the measurements by flame, smoke and reflections within the furnace comprising means for forcing gas through said tube and shield structure projecting laterally of its said open end to prevent reflection into the tube from the billet surface under observation of radiation from flame and wall structure of the furnace and spaced at suitable distance from said surface to permit unrestricted flow of said gas and continuous, open and unrestricted exposure of said surface to the furnace atmosphere. and means for varying the heat input to the furnace in accordance with the measured temperature of the billets.

HAROLD G. ME