CA1206075A - Inductor and method for annealing work hardened portions of structural beams - Google Patents

Abstract

INDUCTOR AND METHOD FOR ANNEALING WORK
HARDENED PORTIONS OF STRUCTURAL BEAMS
Abstract of the Disclosure A method and inductor are provided for annealing the corners of an elongate hollow structural beam in which the corners become work hardened when the beam is produced by cold working initially flat metal plate to the hollow beam configuration. The corners of the beam are inductively heated progressively along the length of the beam in a manner which concentrates heat in the corners and controls the spreading of heat into the sides of the beam from the corners so that the work hardened areas are annealed to provide for the corners and walls to be more uniform in hardness and strength in connec-tion with use of the beam as a structural member. The inductor for so controlling the heating encircles the beam and has arcuate portions each magnetically coupled with a corner of the beam and progressively diverging with respect to the walls of the beam adjacent thereto, and portions between the arcuate portions which overlie the side walls of the beam and are offset radially outwardly with respect to the arcuate portions.

Description

a~;i INDUCTOR AND METHOD FOR ANNEALING WORK
HARDENED PORTIONS OF STRUCTURAL BEAMS
Background of the Invention This invention relates ~o the art of induction heat-ing and, more particularly, to a method and inductor for in-ductively heating and annealing work hardened portions of a structural beam.
It is well known that structural beam members are often produced by csld forming initially fla~ metal plate to a desired configuration in which the beam has at least two planar walls with a rela~ively sharp corner therebe~ween. One such con-figuration is a hollow beam which is square in cross-section, and the present invention is described in detail herein in connection with such a beam configuration. However, i~ will be appreciated that the invention is applicable to other beam configurations .
In cold orming a hollow beam from initially f~at sheet metal, the sheet is bent to provide the beam with opposed pairs of plan r wall portlons having rela~ively sharp corners between adj acent ones o the wall portions. The longitudinally ex-tending outer side edges of the sheet generally abut centrally of one of the side portions and are welded together to complete the beam. The cold working process resul~s in work hardening of ~he me~al in the corner areas of the beam, where~y the corner areas are much harder than the wall portions o the beam.
Therefore, when the beam i5 loaded, such as in compression for example, the load is primarily borne by the corners of the beam as opposed to being uniformly distributed through the corners and wall portions of the beam. Accordingly, it be-comes desirable to reduce the hardiless in the corner portions withou~ cha~ging the hardness in the wall portions ~nd so that the corner portions and wall portions are of substantially the same hardne~s.
Summary of ~he Invention In accordance with the present invention, annealing of th~ work hardened corner between adjacent wall portions of a cold formed beam of steel plate material is achieved by progressively inductlvely heating thP corner along the length ~2~

thereof with an inductor and in a manner whereby heat is concen~rated in the corner and the spreading of heat into the wall portions adjacent thereto is controlled to op~imize achieving a uniform hardness in the corner and walls of the beam, The desired induction heating is achieved with an inductor having a first inductor portion magnetically coupled with the beam corner and progressively diverting with respect to the wall portions adjacent the corner, and second inductor portions extending from the opposite ends of the first portion in radially outwardly offset relationship with respec~ to the corresponding end, The magnetic coupling of the first inductor portion with the eorner provides for heating the hardest por-tion of the work hardened corner to a desired temperature for annealing, and the diverging of the first inductor portion relative to the wall portions and the radially outward offset relationship of the second inductor porti.ons relative to the first portion provides for progress:ively reducing the ~empera-ture and controlling the spread of heat from the corner into the wall portions, Thus, work hardened areas adjacent the corner but of progressiv~ly decreas:ing hardness relative thereto are heated to reduce the hardness thereof, while areas of ~he wall portions which are not work hardendd by ~he forming operation are not heated so as ~o af~ect the original hardness thereof, In performing the annealing process in conn2ction with a hollow beam, an encircling inductor having such first and seeond portions associated wi~h the corners and walls is supported coaxially with the beam,the inductor is energized across a suitable source of power, and the beam and inductor are axially displaced relative to one another to achieve scanning of the beam along the length ther~of and at a scanning rata which provides the desired induction heating of the corner portîons of the beam. Pre~erably, a cooling arrangement is provided behind the inductor with respect to the direction o rPlative ~isplacement between the inductor and beam, the spacing there-3S between being sufficient: to prevent quench hardening of the ~(16075 beam material.
It is accordingly an outstanding object of the present invention to provide a method of annealing work hardened corners of elongate cold formed metal beams.
~nother object is the provision of a method of induc-tively heating a work hardened corner between planar wall portions of an elongate cold formed metal beam in a manner which enables reducing the hardness of the metal in the corner portion without changing the hardness of the metal in ~he wall portions of the beam, Yet another object is the provision of a method of annealing a work hardened corner along the length of a cold formed metal beam by scanning the corner along the length of the beam with an inductor and in a manner which provides con-centrated induction heating of the material in the corner and control of heating of wall portions of the beam adjacent the corner so as to reduce the hardness of the material in the corner without changing the hardness o the material in the wall portions, A further obJect is the provision of an inductor for inductively heating and annealing a work harden~d corner be-tween planar wall portions of an elongate cold fo~med metal pla~e structural beam.
Still a fur~her object is the provision of an inductor of the foregoing character operable to reduce the hardness of the beam material in the corner thereof without changing ~he hardness of the wall portions of the beam.
Still a further object is the provision of an encircling inductor operable to simultaneously inductively hea~ and anneal the corners of a hollow cold formed metal plate beam without changlng the hardness oE the material of the beam in the wall port$ons between adjacent corners.
Brief Description of the Drawings The foregoing objects, ancl others, will in part be 3S o~vious and ln part pointed out more fully hereinafter in . .

~L2~ 5 conjunction with a written description of a preferred embodi-ment of the invention illustrated in the accompanying drawings in which:
FIGURE 1 is an end elevation view showing an inductor constructed in accordance with tle presen~ invention in associ-ation with a cold formed tubular beam having work hardened corners to be annealed;
FIGURE 2 is a side elevation view of the inductor and beam in FIGU~E l; and, FIGUP~E 3 is a cross-sectional view through the induc~or ,. and beam taken along line 3-3 in FIGURE 1.

Descript~on of a Preferred Embodiment Referring now in greater detail to the dra~ing w~erein the showings are for the purpose of i.llustra~ing a preferred embodiment of the invention only and not for the purpose of llmiting the invention, FI~URES 1 and 2 illus~rate encircling inductor 10 surrounding a hollow strtlctural beam 12 which is square in cross-section and comprisecl of planar walls 14 having ~elatively sharp eorners 16 between adjacent ones o~ the walls.
In the embodiment illustrated~ beam 12 is formed by cold work-ing a mild carbon steel plate to the configuration shown and .~ jolning the initial longitudinally outer side edges of the plate such as by a weldment 18 ex~ending longi~udinally along the length of the beam. With further regard to the em~odiment illus-,l trat~d, th~ plate material has a thickness of about 0.375 inch and ~he beam has a cross-sectional dimension of six inches transverse to axis A o the beam and measured between the outer surfaces of opposed ones of the walls 14. The beam can of course be of any desired axial length and, for example, may be ten feet long. The cold forming operation by whlch the beam is produced results ln work hardening of the steel material in the T~

are.as of corners 16 along the length of the beam, whereby the corners are harder than the walls therebetwe.en.
Inductor 10, when properly associated with beam 12 during an annealing,operation is coaxial with axis A and is comprised of a plurality of arcuate first inductor portions 20 each extend-ing clrcumferen~ially of axis A across a corresponding one of the beam corners 16. Each of ~he inductor portions 20 ls of uniEorm radius between its circumferentially opposite ends 20a with respect to axis A and is circumferentially symmetrical with respect to line R through axis A and bisecting the correspond-ing beam corner 16. Thus, i~ will be appreciated that each of the inductor portions 20 progressively diverges with respect to walls 14 on the circumferentially opposite sides of line R
of the corresponding corner. Inductor 10 further includes a plurality o second inductor portions 22 each extending circum-ferentially between an adjacent pair of the first inductor por-tions 20, and each of the inductor portions 22 is clrcumferentially symmetrica~ with respect to a line S through a~is A perpendicular to and bisecting the corresponding wall 14 of beam 12. The inductor has opposite ends 24 and 26 adapted to be connected across a suitable source of power 28, and it will be appreci-ated that the second inductor portion 22 to which ends 24 and 26 are connected is circumfe~entially divided to provlde separate portions 22a and 22b defining entrance and exit ends for the inductor with respect to the flow of current therethrough.
Inductor 10, including end portions 24 and 26, is constructed of tubular conductive material, such as copper, whereby it will be appreciated that ends 24 and 2S are also ; adapted to be connected to a suitable source of coolan~ for circulation thereof through the induc~or. Preferably, inductor portions 20 and 22 are rectangular in cross-section and have the same cross~sectional dimensions. Furthermore, Lnductor portions 20 and 22 are c:oplanar and, in use of the inductor, the plane thereof -ls perpendi~ular to axls A, The rectangular conflguratlon of the inductor portions provides for each to have axially extendinc radially spaced apart inner and outer walls and axially spaced apart radially extending end walls therebetween. As will be appreciated from FIGURE 3, this provides for each of the inductor portions 20 to have inner and outer walls 30 and 32, respectively, and axially spaced apart end walls 34 and 36 and, as will be appreciated from FIGURE 1, provides for each of ~he inductor portions 22 to have inner and outer walls 38 and 40, respectively, and axially spaced apart e.nd walls 42 and 44. In the embodiment illustrated, end walls 34, 36~ 42 and 44 have a radial dimen-sion of 0.500 inch and walls 30, 32, 38 and 40 have an axial dimension of 0.750 inch.
As mentioned hereinabove, each of the arcuate inductor portions 20 is of uniform radius of curvature between the circum-ferentially opposite ends 20a thereof, and in connection with a beam 12 having the dimensions referred to hereinabove, the radius of curvature of inner side wall 30 of each inductor portion 20 is 4.50 inches as measured along the corresponding line R from axis A~ This provides for each inductor portion 20 to extend circumferentially across a corresponding beam corner 16 in magnetically coupled relationship therewlth when the inductor is energized. Each of l:he inductor por~ion~ 22 extends circumfer~ntially between ends 20a of ~he adjacent pair of inductor portions 20 and is radia:Lly outwardly offset with respect to the radius of curvature of portions 20. In the embodi-ment illustrated, each of the inductor portions 22 includes an intermediate leg ~6 perpendicular to the corresponding line S, and legs 48 at the circumferentiaLly opposite ends of leg 46 and extending at an angle therefrom to end 20a of the adjacent inductor portion 20, In connection wi~h a beam 12 havlng the dimension~ referred to hereinabove, the radial offset as measured along the corresponding line S provides :Eor inner wall 38 of intermediate LeO 46 of each inductor por-tion 22 to be spaced about 0.50 lnch radially outwardly from an imaginary ,; 35 line C representing a continuati.on of the line oE curvature ,:

~ .. ... , . ~ . .

o inner walls 30 of the adjacent inductor portions 20. Further, the arcuate extent of inductor portions 20 between opposite ends 20a ~hereof provides for ends 20a of circumferentially adjacent inductor portions 20 to be linearally spaced apart a distance L
between the radially inner edges of ends 20a, and which dimension in connection with the embodiment disclosed is about 2.50 inches.
Further in connection with the disclosed embodiment, inner wall 38 of intermediate leg 46 of each inductor portion 22 has a length in the direction of dimension L cf about one inch.
In connection with the annealin~ of the work hardened corners 16 of 'beam 12 to achieve a uniform hardness of the corner6 and walls 14 therebetween, it is impor~ant to control the heat so as to achieve annealing of the work hardened por-tions wh-ile avoiding overheating of the wall portions which are not work hardened. In this respect, as will be seen from FIGURE l, the work hardening in the corners resulting from ~he cold forming thereof provides for the material directly in the corner and in the area designated by numeral 16a to be the hardest, and for such hardness to progressively decrea~e from the corner laterally into the adjacent areas in the sides of the be~m as designated by numerals 16b. The original hardness of the sheet metal in the areas la~erally inwardly of areas 16b i~ unchanged by the forming. Therefore, to achieve uniform hardness throughou~ the cross-section of the beam, it is '25 desirable to op~imi~e concen~ration of heat in the corner areas 16a, and to control the temperature and spread of heat so as to heat the beam material laterally adjacent the corners in areas 16b to achieve annealing thereof, while minimi~ing heating o the sides laterally inwardly u-f areas 16b wherein ~he beam ma~erlal is not work hardened.
Controlled heating in the foregoing manner is achieve with inductor 10 as a result oE the divergence of inductor por-tions 20 relatlve to walls 14 and the radia'lly outward offset relationship between inductor por~ions 22 and inductor portions 20. In this re~pect, it will be appreciated ~'hat the magnetic r ~

7~ii coupling of inductor portions 20 with corners 16 provide for the highest temperature of heating to be in areas 16a, that the divergence of inductor portions 20 relative to wall 14 pro-~ides or progressively reducing the temperature from portions 16a through portions 16b and into ~he areas of walls 14 there-beyond, and that the radial outwa~d o~fset o in~uo~or portions 22 minimizes heating in the central areas of walls 14. In order to optimize achieving uniform hardness throughout the cross-section of the beam, flux concentrators 50 are provided on inductor portions 20 along a portion of the length thereof and in circumferentially sym~etrlcal relationship with respect to the eorresponding line R, Flux concentrators 50 can be csnstructed from lamlnations of a suitable magnetic sheet mater-al, ox can be formed rom a material such as Ferrocon which, as well known in the art, compris~ partlcles of ~agnetic material in a plastic binder. As is further well known in the art of course, flux concentrators 50 serve to concentrate magnetic flux in a par.ticular area in a workpiece and, accordingly, in connection with the annealing of bPam corners in accordance with the present invention concentrate the magne~ic flux in the corner portions o~ the beam. In connection with the inductor and beam as described here-inabove, each flux concentrator 50 has a circumferential length of about three inches.
With respect to annealing the corners of a bPam con-toured and dimensioned as described herein, using inductor 10, the beam and inductor are coaxially aligned and suitably supported to enable relative axial displacement therebetween during which the inductor is energized or the corners o the beam to be inductive~y heated c.luring such relativ2 displace-ment. Satisfactory annealing to obtain a desired uniormity oE hardness ~n the corners and wall portions of the beam is achieved by incluctive:Ly heating the beam corners -to a tem~era-ture between 1250DF to 1350F. With the inductor herein illus-trated and described, such heating and ~hus the desired anneal-ing oE the beam corners is achieved by energiz.ing the inductor 7~;

. g across a power source at a level of betwePn about 85 Kw to 100 Kw and relatively axially displacing the beam and in-ductor at a 6peed o about 0.5 inch per second. It will be appreciated, of course, that the latter scanning rate ~an be increased while maintaining heating of the cornPrs to the desired temperature by employing a plurality of inductors coaxially aligned and axially spaced apart with respect to one another. Such a multiple inductor arrangement can also be used to achieve the desired heating of the corner~ on a be2m having a wall thickness greater than that of the beam de~cri.bed herein. In connection with a continuous produc~lon operation, for annealing beam corners, it may be desirable to cool the heated beam such as through the use of a quPnching ring to facilitate handling the beam following almealing there-of. Such an annealing ring, while not shown in the drawing, would be positioned behind the induc~or with respect to the clire~ion of progressive heating of the beam and would be positioned sufficiently behind the inductor to prevent quench hardening of the beam corners. In connection with the scanning ra~e mentioned hereinabove, for example, the quench ring loca~
tlon would provide for about a orty second ~lelay between a given area being heated and ~he subslequent quenching of the given area. At the same time, it will be apprecia~ed that ~he inductively heated beams can be allowed to cool to room temperQ-ture following ~he annealing process without such intentional cooling thereofO
While considerable emphasis has been placed herein on the cross-sectional configuration of the inductor tubing, it wilL be appreciated that other cross-sectional configurations call be employed, the rectangular tubing being preEerred rom the standpoint of economy of construction of the induetor.
Further, while the arcuate contour of inductor portions ?0 and the linear contour of the legs o~ inductor portlons 22 is preerred, it will be appreciated ~hat other contours can be e~ployed for the inductor por-tions. It i5 only essential ~za~c~

in accordance with the present invention ~o achieve ~he desired hPating of the beam corners and controlled heating la~erally therefrom into the adjacent wall portions that inductor portions 20 extend acros~ the corresponding beam corner so that the cen-ter of the inductor portion is close to the outer surface of the corner and the inductor portion extends in circ~lmferentially opposite directions from the corresponding line R in progress-ively increasing spaced relationshlp with respect to the outer surfa e of the beam corner and the adjacent wall por~ions of the beam, and that inductor portions 2~ are offset radially outwardly : with respect to the ends of adjacent ones of the inductor por-: tions 20, Furthermore, while specifie dimensions ha~e been ; : set forth with respect to the embodiment herein deseribed, ~ it will be appreciated that such dimensions will vary in accordance with varia~ions in the dimensions of the b am.
~-,i`` Accordingly, it is to be distinctly unders~ood that the ~ore-; ~ going descriptive matter is to be interpreted merely as illus-~, trative of the present invention and. not as a limitation.
;,: .:, ~ ~' 1. . . ',: , I ..

Claims (20)

Having thus described the invention, it is claimed:

1. A method of inductively heat treating an elongate structural beam of metal plate material cold formed to provide angularly related adjacent wall portions and a work hardened corner therebetween, said method comprising inductively heating said work hardened corner progressively along the length of said beam to a given temperature for annealing said work hardened corner, and controlling said inductive heating for the temperature of heating in the direction from said corner into each of said adjacent wall portions to be progressively reduced below said given temperature, whereby said corners and wall portions have substantially the same hardness following said heat treatment.

2. The method according to claim 1, and progressively cooling said beam following said heating.

3. The method according to claim 1, wherein said metal plate material is mild steel and said given temperature is be-tween about 1250°F and 1350°F.

4. The method according to claim 1, and inductively heat-ing said corner with inductor means including means to concen-trate magnetic flux in said corner.

5. The method according to claim 1, wherein said metal plate material is mild steel and has a thickness of about 0.375 inch, and inductively heating said corner with inductor means energized at a power level of between about 85 Kw to 100 Kw.

6. The method according to claim 1, wherein said metal plate material is mild steel, inductively heating said corner with inductor means including means to concentrate magnetic flux in said corner, and inductively heating said corner for said given temperature to be between about 1250°F and 1350°F.

7. The method according to claim 6, and progressively cooling said beam following said heating.

8. The method according to claim 1, wherein said beam is hollow and has opposed pairs of parallel wall portions and work hardened corners between adjacent wall portions, and simul-taneously progressively inductively heating each of said corners along the length of said beam to said given temperature.

9. The method according to claim 8, wherein said metal plate material is a mild steel, and said given temperature is be-tween about 1250°F and 1350°F.

10. A method of inductively heat treating a hollow structural beam of metal plate material cold formed to provide opposed pairs of planar wall portions and work hardened corners between adjacent ones of said wall portions comprising, providing an encircling inductor extending about said beam transverse to the axis of said beam and having first inductor portions each magnetically coupled with a corresponding one of said corners and second inductor portions between adjacent ones of said first inductor portions and offset radially outwardly there-from with respect to said beam axis, energizing said inductor, and relatively axially displacing said beam and inductor to anneal said work hardened corners.

11. The method according to claim 10, and progressively cooling said corners behind said inductor with respect to the direction of said relative axial displacement.

12. The method according to claim 10, and providing each of said first portions of said inductor with means to concentrate magnetic flux in the corresponding corner of said beam.

13. The method according to claim 12, wherein said metal plate material is mild steel, and heating said corners to a temperature of between about 1250°F and 1350°F.

14. The method according to claim 13, wherein said metal plate material has a thickness of about 0.375 inch, and energizing said inductor at a power level of between about 85 Kw to 100 Kw.

15. The method according to claim 14, and progressively cooling said corners behind said inductor with respect to the direction of said relative axial displacement.

16. An encircling inductor for inductively heating and annealing work hardened corners of an elongate hollow structural beam cold formed to provide opposed pairs of planar walls with said work hardened corners between adjacent ones of said walls, said inductor having an axis and circumferentially spaced apart first inductor portions each corresponding to a different one of said corners of said beam, each said first portion being radially spaced from said axis a given distance, second inductor portions extending circumferentially between and interconnecting adjacent ones of said first portions, each said second portion overlying a portion of the planar wall of said beam between the corners corresponding to said adjacent ones of said first portions, and each said second portion being offset radially outwardly with respect to said adjacent ones of said first portions.

17. The inductor according to claim 16, wherein said first and second inductor portions are coplanar.

18. The inductor according to claim 16, and flux concentrating means on each of said first portions of said inductor.

19. The inductor according to claim 16, wherein said beam has an axis and said work hardened corners are in dia-metrically opposed pairs with respect to said beam axis, said first inductor portions being in diametrically opposed pairs each symmetrical with respect to a line through said beam axis and bisecting the corresponding opposed corners, and said second inductor portions being in diametrically opposed pairs each symmetrical with respect to a line through said beam axis and perpendicular to the corresponding opposed beam walls.

20. The inductor according to claim 19, wherein said first inductor portions are arcuate and of uniform radius with respect to said inductor axis.