US2499191A

US2499191A - Vertical loop furnace

Info

Publication number: US2499191A
Application number: US50538A
Authority: US
Inventors: Norman B Jones; James L Mcfarland
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1948-09-22
Filing date: 1948-09-22
Publication date: 1950-02-28
Anticipated expiration: 1967-02-28

Description

Feb. 28, 1950 N. B. JONES, ETAL 2,499,191

VERTICAL LOOP FURNACE Filed Sept. 22, 1948 Inventors: N Norman 8. Jones,

James L rvicFarlanci Their At c onneg.

Patented Feb. 28, 1950 VERTICAL LOOP. FURNACE NT OFFICE Norman-. B; Jones, Ballston Lake, and JamesL. McFarland,1 Schenectady, N. Y., assignors to I New York GeneralElectric Company, a corporation of Application September 22, 1948, Ser-ialNo, 50,538

our invention relates to annealing. furnaces cf. the type adapted fcrthecontinuous heat treating of vthin v strip material, such as steel strip, particularly. where they surface of the strip to be annealed is, bright or: highly. polished and must not beoxidizedor scratchedin the process. It is the obj ectof our invention to provide an improved fiirnaceof'thistype which is suitable forheating strip totemper-aturesas high as 2300-F;-, or more; Our furnace is the vertical loop type, utilizing what might be called a vertical cat'enary loop; That is the loop is in the shape of a catenary with the open end' turned upward and the vertical length of thecatenary is greater than its width horizontally. Previous vertical loop furnaces such as that disclosed in United States Patent No; 2,009,856, granted'to'-Albert Ni Otis and James L. McFarland onJ u1y30, 1935, have utilizedstraight loops, that is, loops approximately semi-circular inform, with the strip entering and leavingthe loop-vertically. One advantage of the vertical loop construction is that thetensionon the strip is lowest at the pointof highest temperature which is ator near the bottom of theloop. Our vertical cat'enary loop furnace retains this ad vantage and at thesame time, because of the greater stabilityof a catenary loop' plus the stepped type construction employing aplurality of heating chambers, and other features of our furnace described later inmore detail, it is unnecessary to use supports or seals: of; any kind touching thestrip whileitis in the heating-sew tion of the furnace;

' Other furnacesemploying a catenary loop are known, for example, that disclosed by United States Patent'No. 2,060,634"; granted toAlbert N; Otis on November 10, 1936, but they use a flat catenary, that is, a catenary with a horizontal dimension much greaterthan the, verticalv dimension, representing in effect merely a sag in the strip-as it passes through thefurnace. In contrast itis an object of our invention: to employ a'vertical catenaryloop with thevertical' dim'en sio'n greater than the horizontal in orderto minimize the stress on the strip at the center-portion of the catenary at the bottom of the loop where the temperature is the highest.

Gun-invention will bebetter understood from the following description taken in connection with the accompanying-drawing, and'itsscope will be pointedout in the appended claims. In the drawing, Fig. l is aside view, partly in section, ofoneembodiment of our invention and Fig. 2 is a sectional view along the line 22 of Fig. 1.

In Fig; 1 of the drawing, the strip which is to receive the heat treatment is represented at I. This strip may be withdrawn from a coil (not shown) and fed to the furnace by means of the Pinch rolls 2 and is finally withdrawn from the furnace by the pinch rolls 3, the two sets of rolls being driven by, suitably synchronized driving means, whereby the strip is driven at the same speed by each set. The strip first passes over an idler roller 4 as it entersthe heating section of the furnace, which idler roll supports oneend of the vertical catenary loop.

As the strip l passes through the furnace, it passes first through a catenary shaped heating sectionwhich is, composed of, '7 interconnected chambers in the particular construction illustrated. The heating sectioniis composed of en trance chamber 5, heating chambers 6, I, 8 ands, chamber I0, and exit chamber I I. Eachiof the chambers has an outer metal casing l2, a layer of heat'insulating material l3, and an, interior lining M of suitable heat refractory material, Adjacent theside walls of chambers 6, T and. 9 are'provided electric heating elements I 5 to maintain each chamber at the desired temperature.

The lowest heating chamber 8 which surrounds the bottom portion of the catenary loop has electric heating elements IS on the side andbottom walls. Chamber 8 is the chamber having the highesttemperature which, for example; may be approximately 2300'F.

- Theouter walls ofchambers 6-, l and Bare supported in elevated position by structural steel framework I6. The inner walls of these three chambers-are supported by refractory arches H which alsoform apart ofthe interior-refractory lining ofthe next: lower chamber in each case; Entrance chamber 5 is supported principally by heating chamber-6; Exit chamber is supported principally by chamber lilwhich in turn is sup ported principally by heating chamber 9. Heating. chamber 8 is supported on I-beams l8. There- 'are'verticai. members, i 8' on both sides; of the'heating'sc'ction tot-provide additional: upport for-all"chambers;

The useof a plurality of chambers following the contour of the strip being heated, as illustrated by Fig. 1 gives a number of advantages over a furnace having a single heating chamber. It allows the walls to be broken up into relatively small sections. This decreases the unit stress on the brick or other heat refractory material H, a factor which is highly important at temperatures of 2300" F., since it is well-known that the crushing strength of refractory materials in common use today is greatly reduced at such a high temperature. The use of a plurality of chambers also requires a minimum of wall area for a given strip length, thus permitting maximum economy in the use of refractory and other material. A further advantage is that the heating elements follow closely the contour of the strip which gives improved efliciency and more accurate temperature control. Also, with this construction the strip is not touched by supports or seals of any kind while it is in the heating section of the furnace; hence, it cannot be scratched from this cause. By the time the strip reaches exit roller 2| its temperature is reduced sufliciently that it will not be scratched by the roller.

On the exit side of the heating section of the furnace, chamber H is provided with adjustable radiation bafiies ii! to aid in confining the heat to the heating chambers. It is also provided with a blower 20 of the type disclosed in United States Patent No. 2,195,310, granted to Allen G. Hotchkiss on March 26, 1940, to prevent or at least partially counteract the flow of the protective atmosphere, or other gases if no protective atmosphere is used, out of the heating chambers and into the subsequent cooling section of the furnace. It is customary to equip high temperature electric furnaces of this type with means for providing an artificial non-oxidizing protective atmosphere utilizing such gases as hydrogen, a mixture of hydrogen and oxygen, or atmosphere converter gas which is made by burning suitable natural or manufactured gas with a controlled deficiency of air. Such furnaces are occasionally operated without an artificial protective atmosphere, however, for some kinds of material. Our invention is suitable for application to furnaces with or without artificial protective atmosphere. I

Asthe strip leaves the chamber H it passes over a roll 2|, which supports the other end of the vertical catenary loop in the heating section, thence over a second roll 22 and into cooling section23. The cooling section is composed of two vertical chambers, as shown in Fig. 1. Thestrip passes downward in the left chamber,'beneath rolls 24 and 25at the bottom of the cooling section, upward in the right chamber, over roll 26 and out of the furnace through pinch rolls 3'. While the embodiment of our invention illustrated in the attached drawing employs only one cooling section, two or more cooling sections may be used, if necessary, to provide the strip with th desired characteristics. The cooling section is provided with both electric heating elements 2T'and pipes 28 extending across the'chambers at spaced points. Cooling fluid, such as air or water, is circulated through pipes 28 and by correlating the cooling action of these pipes and the heat supplied to the chambers by heaters 21 the cooling of strip I may be accurately controlled.

In the operation of this furnace, a suitable control means (not shown) is utilized to maintain the'proper tension on'th'e strip in order to main tain the vertical catenary loop.r One'suitable control means is disclosed by the above-mentioned United States Patent No. 2,060,634, granted to Albert N. Otis. In the system of this patent, means are provided for adjusting the speed of the outgoing pinch rolls 3 with relation to the speed of the incoming pinch rolls 2 in order to maintain the loop in the heating section of the furnace at the desired height. While pinch rolls 2 and 3 operate at approximately the same speed, it may be necessary to vary the speed of rolls 3 slightly with respect to rolls 2 because of slight variations in construction of the twomotors which drive the rolls and of the rolls themselves, differences in temperature of the strip engaged by the two sets of rolls, and particularly, the

- elongation of the strip due to its higher temperature at the point of leaving the furnace than at the entrance point. In certain cases it may be found desirable to drive one or more of rolls 4, 2| and 22; these rolls along with

rolls

24, 25 and 26 are shown as idler rolls on the attached drawing. I

Fig. 2 of the accompanying drawing is a sectional view along the line 2-2 of Fig. 1, showing details of the construction of heating chamber 8. Refractory arch H, which supports the inner walls of heating chambers 1 and 9, can be clearly seen in this View. Fig. 2 also illustrates additional details of the construction of blower 20.

While wehave chosen the particular embodi ment described above as illustrative of our invention, it will be apparent that various other modifications may be made without departing from the spirit andscope of our invention, which modifications we intend to cover by the appended claim.

What we claim as new and desire to secure by Letters Patent of the United States is: i

A vertically disposed furnace for heating mov ing strip material while-it is suspended in the form of 'a catenary loop comprising, a plurality of interconnected heating chambers disposedalongthe contour of said catenary loop, the enclosures of said heating chambers being in close proximity to but not in contact with said strip material, said heating chambers being arranged so that said strip material passes'consecutively through said heating chambers, each heating chamber enclosure comprising an outer metal casing, a layer of heat insulating material within said metal casing and an interior lining of heat refractory material within said layer of insulating material, an internal arch of refractory material in each heating chamber except the topmost chamber on each'leg of the catenary for supporting in part the heating chamber immediately above each such chamber, heating means in said heating chambers, an entrance chamber mounted on one of said topmost heating chambers and supported principally thereby and interconnected in strip conducting relation therewith, an exit chamber mounted on the other of said topmost heating chambers and supported principally thereby and interconnected in strip conducting relation therewith, an entrance roll in said entrance chamber for supporting one end of said catenary loop, an'd-an exit roll in said exit chamber for supporting the other end of said catenary loop.

" (References on following page) REFERENCES CITED UNITED STATES PATENTS Number Name Date Goodson May 9, 1905 Eustis Feb. 12, 1924 Scarles Nov. 18, 1924 Little Apr. 13, 1926 Von Maltitz et a1. June 24, 1930 Shover et a1 June 23, 1931 Reading Feb. 20, 1934 Russ Apr. 24, 1934 Number Number Name Date Otis et a1 July 30, 1935 Otis Nov. 10, 1936 Otis et a1 Mar. 31, 1942 Edge Apr. 14, 1942 Cooper et a1 Mar. 28, 1944 Schefe Sept. 7, 1948 Martin May 3, 1949 FOREIGN PATENTS Country Date Great Britain Sept. 21, 1926 Great Britain Oct. 9, 1930