US2831788A

US2831788A - Method of differentially heat treating a cutter bar

Info

Publication number: US2831788A
Authority: US
Publication date: 1958-04-22
Anticipated expiration: 1975-04-22

Description

April 22, 1953 A. E. BRIDGE ETAL 2,831,788

METHOD OF DIFFERENTIALLY HEAT TREATING A CUTTER BAR Original Filed Feb. 23, 1950 2 Sheets-Sheet 1 M N 0 0 1 M65 EDB mmv ms T MW B D A A W B Tm ATTORNEYS April 22, 1953 A. E. BRIDGE ETAL 2,831,788

METHOD OF DIFFERENTIALLY HEAT TREATING A CUTTER BAR Original Filed Feb. 25, 1950 2 Sheets-Sheet 2 Q em 3 R 3 @m e w 0 w M. mw w M/ W 05 M 1.] m. m R S w m m L 56 m Mm mm 5 A @mvw H mm kt mt v@ mm Om Om Q United States Patent METHOD OF DIFFERENTIALLY HEAT TREATING A CUTTER BAR Adam E. Bridge, Franklin, and Albert G. Gibson, Middletown, Ohio, assignors to The Black-Clawson Company, Hamilton, Ohio, a corporation of Ohio Original application February 23, 1950, Serial No. 145,838, now Patent No. 2,686,460, dated August 17, 1954. Divided and this application April 29, 1954, Serial No. 426,532

13 Claims. (Cl. 148-105) This invention relates to cutter bars or knives for refining apparatus of the type utilized for the treatment of cellulose fibers and the like in the preparation of paper making stock.

The invention has particular application to cutter bars for refiners such as Jordans and beaters wherein a plurality of bars are carried by a plug or other rotating member in such manner that they are arranged generally axially of the axis of the plug with their outer edges exposed for working on the fibers in the stock, the invention being applicable to both the bars carried by the rotating member and also to the cooperating stationary bars such as in the shell of a Jordan. These outer edges of the bars accordingly constitute their working edges which are subjected to a major portion of the wear in operation, and it is desirable that they possess adequate hardness to Withstand continued use over long periods and that the degree of hardness along these working edges be properly correlated with the degree of toughness required in the remainder of the bar, including the portion secured to the plug or other rotating member.

For example, in a common construction of bars for the plug of a Jordan, the cutter bars are retained on the plug by means of a series of rings interfitting with hook portions of the bars which are formed along their inner edges and are subjected to substantial stresses, including centrifugal force, during operation. These working stresses are accordingly of importance in determining the degree of hardness which can be imparted to the bar as a whole without having the hook portions become so brittle as to be in danger of breaking in use. If the bar is of optimum hardness for the working edge, it would be too brittle along the hook portions of the bar. On the other hand, if the bar is of optimum toughness for the hook portions, the working edge would not be hard enough and would tend to erode too rapidly and to burr, forming sharp edges which would cause cutting of the fibers instead of the desired rubbing action, and if it is attempted to overcome these disadvantages and to obtain different degrees of hardness and toughness along the edges of the bar by means of a surface or edge coating or by welding or otherwise securing a harder working edge portion to a backing of tougher metal, the cost of production tends to become too high to compensate for such improved results as may be obtained.

The usual result for bars which are uniformly heat treated in a furnace is accordingly a compromise, with a resultant shorter useful life than if the bar were differentially hardened to give the desired hardness or toughness at each point. A further factor atfecting the useful life of such uniformity heat treated bars is that with the hook portions formed therein by punching before the heat treatment, scratch lines are formed transversely of the bar which constitute stress points at which cracks tend to develop during the subsequent heat treatment, thus materially weakening the bar and increasing the possibility of breakage of these hook portions. Similar disadvantages exist in the case of such bars which do not have hook or lug portions in that the back edge portion of the bar must be tough enough to prevent premature failure.

It is accordingly one of the principal objects of the present invention to provide a cutter bar of the above character which is integrally formed, as distinguished from a welded or other composite structure, and which possesses properties of differential hardness and toughness across the width thereof such that a minor portion of the bar extending lengthwise of and including its working edge is hardened to a predetermined high degree of hardness while the remainder of the bar including its opposite edge portion is substantially less hard and forms a tough supporting portion for the hardened working edge.

Bars having these desired characteristics are produced in accordance with the invention by a controlled method of heat treatment in which the heat is applied successively to different localized portions of the bar to obtain the desired properties of differential hardness and toughness. Thus in the first heating step, the heat is applied only to the minor portion of the bar along its working edge where maximum hardness is desired in the finished bar, this step being readily carried out by passing the bar through a high frequency induction field of high intensity which is limited in its effective cross-sectional dimensions to receive only the desired limited portion of the bar therethrough. This portion of the bar is thus heated very rapidly to a predetermined high temperature, and it is then immediately quenched with a suitable fluid such as oil in order to limit the cross-sectional area of the bar in which the hardening takes place.

Following quenching, heat is again applied to the bar but only to the direction thereof along its back edge which was not directly heated during the first heating step, and this second heating step may similarly be carried out by means of a high frequency induction field, with the intensity of this field and hence the heating eifect being lower than that of the first step to limit the temperature reached in the bar during this second heating step to a lower range such that the temper is drawn from the back edge portion of the bar. This second heating step is readily carried out before the bar has cooled completely from the first heating step, and in fact while another portion of the same bar is undergoing the first heating step, and it has been found desirable to cool the bar slowly in air at room temperature after drawing rather than to quench it. During this slow cooling, heat will flow by conduction to the working edge portion of the bar to a sufficient extent to effect reduction in the hardness therein as compared with the hardness imparted thereto during the first heating step, and thus in the finished bar the portion of the bar where wear takes place in use is hardened as desired, while the balance of the bar is substantially less hard. It is also found that with the drawing heat thus applied to the back portion of the bar followed by slow cooling, such warping as may tend to take place along the bar as a result of the first heating step is substantially compensated for without requiring additional corrective treatment.

This method not only is capable of continuously producing cutter bars having the properties of diiferential hardness and toughness referred to, but it also offers the advantage of ready control of the degree of hardness and toughness in the several portions of the bars by suitable adjustment of the draw temperature. This is particularly advantageous in view of the fact that different degrees of hardness are desired in cutter bars for Jordans and other refiners depending upon the particular stock to be worked on and the particular type of paper for which the stock is intended. With the method of the present invention, adjustment of the intensity of one or both O of the induction fields employed in the heating steps, and of the temperature and pressure of the quenching fluid, will control the hardness properties of the finished bars, and after the proper set of conditions is determined, each of a plurality of successive bars treated under these conditions will be found to possess uniformly the desired properties of differential hardness and toughness.

It is accordingly another object of the invention to provide a simple, economical and practical method of heat treating cutter bars of the above character under controlled conditions such that the degree of hardness of the finished bar is readily predetermined and controlled and a desired high degree of hardness is obtained along the working edge of the bar while the portion of the bar along its back edge in which the retaining hook portions are formed is of a substantially lower degree of hardness and substantially greater degree of toughness for withstanding the centrifugal force and other stresses on the bar incident to use thereof.

It is also an object of the invention to provide simple apparatus for continually heat treating successive cutter bars of the above character by induction heating under controlled conditions such that the working edge portion of each bar is hardened to a predetermined extent While the opposite edge portion of the bar is caused to become substantially less hard and substantially tougher than the working edge, and wherein provision is made for ready adjustment and control of the heating conditions in accordance with the particular degree of hardness or toughness desired in different portions of each bar.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings- Fig. l is a view in side elevation of a Jordan bar constructed in accordance with the invention;

Fig. 2 is a diagrammatic perspective view illustrating successive steps of the heat treating method for producing the bar of Fig. 1;

Fig. 3 is a side elevation of the Jordan plug;

Fig. 4 is an enlarged detail view in section showing one of the bars mounted in the Jordan plug;

Fig. 5 is a fragmentary side elevation of the mounting or back edge portion of the bar of Fig. 4 and including one of the hook portions therein;

Fig. 6 is a graph aligned with Figs. 4 and 5 to show respectively the typical hardness of the bar from edge to edge before heat treatment, after hardening but before drawing, and in the finished bar after both hardening and drawing;

Fig. 7 is a diagrammatic plan view of apparatus in accordance with the invention for carrying out the heat treating method;

Fig. 8 is a fragmentary side elevation of the apparatus of Fig. 7;

Fig. 9 is an enlarged detail view in section on the line 9-9 of Fig. 8; and

Fig. 10 is an enlarged detail view in section on the line 10-10 of Fig. 8.

Referring to the drawings, which illustrate a preferred embodiment of the invention, Fig. 1 shows a Jordan bar on which the working edge is identified as 20, and which has hook portions 22 formed along its edge 23 opposite working edge for engaging the usual retaining rings of the Jordan plug, the complete plug being shown at 25 in Fig. 3. A lug 26 is formed at one end of the bar to receive the usual keeper ring 27 at the smaller end of the plug, and bar 15 also has a head 28 which runs along each side thereof approximately midway between the working edge 20 and back edge 23. The bar 15 as shown is one of many designs of cutter bars, both rotating and stationary, adaptable and responsive to differential heat treatment in accordance with the invention to give it properties of differential hardness and toughness such that a minor portion thereof running along the working edge .20 is hardened to a 4 comparatively high degree in order to give the desired resistance to abrasion in this portion of the bar, while the portion of the bar extending along its back edge 23 and including the hooks 22 is substantially less hard and substantially tougher than the working edge to support the bar on the plug during operation of the Jordan.

A controlled method of heat treatment for imparting these properties to successive cutter bars is illustrated diagrammatically in Fig. 2, which shows a plurality of bars 30 arranged in end-to-end relation for travel in the direction indicated by the arrow 31 through a pair of high frequency

induction heating fixtures

33 and 34. As shown, the fixture 33 includes a portion of generally saddle shape arranged to straddle the limited portion of the bar which is intended to form the working edge in the finished bar, shown as its upper edge, and fixture 33 is proportioned to receive only about one-quarter of the width of the bar. This fixture includes an induction coil which is supplied with current at a predetermined high wattage to create the desired high intensity field across the portion of the fixture through which the upper edge of each bar 30 passes.

The drawing fixture 34 is of channel shape and of such proportions as to receive approximately the entire lower portion of each bar 30 which was excluded from the hardening coil fixture 33, i. e., the lower approximately three-quarters of the bar, and fixture 34 is shown as spaced from fixture 3-3 but suificiently close thereto to receive the leading end of each bar before its trailing end has left fixture 33. This fixture 34 also includes a high frequency induction coil, and in carrying out the above method, it is supplied with current at a predetermined wattage lower than the hardening coil of the fixture 33 to effect heating of the portion of the bar passing therethrough to a predetermined lower temperature than is reached in the portion of the bar heated by the fix ture 33.

A fixture indicated generally at 35 is provided for applying quenching fiuid to the edge portion of the bar heated in the fixture 33, this quenching fixture 35 being preferably arranged as shown to discharge a stream of oil against each side of the heated edge portion of the bar. It has been found desirable to apply the quenching oil at substantial pressure and constant temperature in order to produce rapid cooling of the heated working edge portion of the bar before the corresponding point on the opposite edge of the bar reaches the drawing fixture 34, and the quenching fixture 35 is accordingly positioned closely adjacent the hardening fixture 33, this immediate and rapid quenching being also desirable in minimizing distortion of the bar as a result of the edge hardening step. The application of the drawing heat at the fixture 34 only along the back edge portion of the bar is also of material importance in controlling and preventing distortion of the bar and thus substantially eliminating the necessity for further corrective treatment.

Further control over the temperatures reached in the bar and thus increased accuracy of control over the hardness properties in the finished bars is obtained by regulating the temperatures of the fixtures 3-3 and 34 themselves, as by circulating a cooling fluid through the fixtures as indicated at 36 and 37. This may be readily and satisfactorily done by connecting the two fixtures with the same source of quenching fluid used to supply the quenching fixture 35. Also, in order to rcducc burr ing of the quenching oil as the bars pass through the drawing fixture 34, an air blast 38 may be locutol as shown between

fixtures

34 and 35 to strip excess oil from each bar before it reaches fixture 34.

The power input to each of the

coil fixtures

33 and 34. and hence the temperature reached in the her during the heating and drawing steps, is readily predetermined and controlled in accordance with the initial composition of the bar and the desired final properties of differential hardness and toughness, and these properties are further afiected by the rate of travel of the bars through the fixtures and also by the temperature and pressure of the quenching fluid. For example, Figs. 4 to 6 illustrate these properties of a section of a bar 15 treated as described in connection wtih Fig. 2 and having substantially the following initial percentage composition:

Carbon 0.60 to 0.70 Manganese 0.70 to 0.80 Phosphorus s 0.04 max. Sulphur 0.04 max. Silicon 0.20 to 0.30 Nickel 0.40 to 0.50 Chromium 0.30 to 0.40 Molybdenum 0.20

Iron Balance Fig. 6 illustrates the changes in the hardness properties of a typical bar 15 of this composition resulting from treatment by the method as illustrated in Fig. 2 under the following conditions:

Bar width inches 2% Bar thickness do A Rate of bar travel -inches per minute 24 Power input to hardening fixture "kw" 23 Distance between hardening and quenching fixtures inches 1 Distance between hardening and drawing fixtures inches 12 Quenching fiuid temperature F 98 Quenching fluid pressure pounds per sq. inch" 10 Power input to drawing fixture kw 17 Under these conditions, with the dimensions of the hardening fixture 33 such as to give an effective length of approximately 4 inches for the field therein, the upper edge portion of the bar reaches a temperature of the order of 1575 F. With the quenching fluid applied to the bar substantially immediately at the temperature and pressure indicated, the temperature of the upper portion of the bar will drop to a range of the order of 400 to 500 F. before the bar reaches the drawing fixture 34, and with the dimensions of this fixture 34 such as to give an effective length of approximately 9 inches for the field therein, the drawing temperature in the lower portion of the bar will reach approximately 1200" F. Also, although the heat is applied in this fixture only to the previous unheated portion of the bar, there will be a flow of heat by conduction to the upper edge 20 of the bar to raise its temperature materially, to a range of the order of 1000 F., and similarly during the subsequent air cooling period, the temperature throughout the entire bar will be substantially equalized by conduction.

In Fig. 4, the bar 15 is shown fragmentarily as mounted in the Jordan plug 25 with its hard working edge 20 outermost, and the graphs in Fig. 6 are aligned with Figs. 4 and to illustrate the changes in the hardness of the bar from edge to edge resulting from heat treatment under the above operating conditions. The continuous line 40 represents the initial hardness of the bar before treatment as measured on the Rockwell C scale, and it will be noted that this hardness is uniform across the entire width of the bar at a value of approximately 28 Rockwell C. The long and short dash curve 42 shows the hardness of the bar following hardening in the fixture 33 and quenching but before drawing. As shown, the hardness of the bar along and adjacent its working edge 20 is increased to between 60 and 62 Rockwell C, but the hardened area covers only a little over a quarter of the width or the bar, with the hardness dropping sharply to a range not materially different from that of the untreated bar over the remaining portion of its width.

-The curve 44 comprising short dashes shows the hard ness of the bar following completion of the drawing step in the fixture 34 and subsequent air cooling at room temperature. It will be noted that the hardness at the working edge 20 has been reduced to approximately 39 Rockwell C, and this hardness is relatively uniform near the edge 20 and over approximately one-quarter of the width of the bar. at which point it drops sharply to about 27 Rockwell C. The hardness remains in this range across the adjacent intermediate portion of the bar, which is approximately equal in extent to the hard portion, and then it again drops comparatively rapidly at about the middle of the bar to a range between approximately 20 and 22 Rockwell C across the remaining approximately 50% of the width of the bar.

In other words, following completion of the heat treatment under the above conditions, the bar comprises a minor portion, amounting to about one-quarter of its width, extending along and including the working edge which has a hardness substantially greater than the initial hardness of the untreated bar. At the same time, approximately one-half the width of the bar, including its back edge 23 and the hook portion 22, has a hardness which not only is substantially lower than that along the working edge but is materially lower than the initial hard ness of the untreated bar. The intermediate portion of the bar which connects the hard and soft portions is of an intermediate range of hardness not materially different from that of the untreated bar.

These properties of differential hardness and toughness can be obtained with a high degree of uniformity in a plurality of successive bars of the same composition which are heat treated as described under the same conditions. A full set of bars of substantially identical hardness properties for the plug or shell of a refiner or beater can thus be produced by this method, as contrasted with sets of bars heat treated as a batch according to the usual practice, since when a set of bars is batch treated in a furnace, it is commonly found that all bars in the set are not heated to the same extent and that the quenching conditions are not uniform for all bars in the set. These non-uniform results are avoided in the method of the present invention, which provides for treatment of each successive bar of a set under identical conditions.

Different degrees of hardness in the bars can also be obtained by adjustment of the operating conditions in accordance with the desired results in the finished bar. Thus in the above example, the hardness of the bar along its working edge can be changed as desired by appropriate adjustment of the power input to the drawing coil 34. For example, if the power input is reduced from 17 kw. to 15 kw., the hardness along the working edge of the bar will measure in the neighborhood of 42 Rockwell C, and if the power input is increased to 19 kw., the hardness of the working edge 20 will be reduced to the neighborhood of 33 Rockwell C. Also, the rate of travel of the bars through the heating fixtures is of importance in determining the temperatures to which the several portions of the bars are heated. For example, in order to obtain the same properties as shown in Fig. 6 in bars of or /3 inch in thickness, the rate of travel should be reduced to from 20 to 22 feet per minute if the other operating conditions remain the same, and similarly for a bar of i inch thickness, the rate of travel should be increased to from 28 to 30 feet per minute.

It will thus be apparent that the properties desired in each portion of the bar can be effectively determined in advance and produced in successive bars as desired. As a result, it is possible and practical in accordance with the invention to obtain bars for the plug or shell of a Jordan or other refiner which are harder along their working edges than the bars previously obtainable by methods of heat treatment in which the hardness along the working edge required compromise with the degree of toughness necessary along the supporting edge of the bars. Also, since as noted the method of the operation makes possible the reduction of the degree of hardness along the back edge of the bar as compared with the initial hardness of the untreated bar, when mounting hooks or lugs such as the hooks 22 are desired, they can be formed therein by punching after heat treatment, thus eliminating the development of cracks at the hook portions such as tend to be caused when the hooks are punched prior to heat treatment of the bars.

Figs. 7 to illustrate more or less diagrammatically a machine for continuously performing the heat treating method described in connection with Fig. 2. The main body of the machine is shown as an elongated channel arranged on one edge and having a plate 51 secured within its open side and a front cover 52, and the base of the machine is indicated generally at 53. The induction coil fixture 33 is shown as supported on a housing 55 containing its associated electrical equipment. and the drawing coil fixture 34 is similarly supported by a housing 56 for its associated electrical apparatus.

The quenching fixture 35 is shown as supported by a bracket 61 adjacent the hardening coil, and this fixture is shown as a quench ring adapted to receive the upper portion of the bar 30 as shown fragmentarily in Fig. 10. The quenching oil is supplied to the ring 60 by a pair of pipes 62 which are connected by a hose 63 and valve 64 with a main oil supply pipe 65 running along the front of the machine. This pipe is in turn supplied with oil under pressure by means of the pump 66 and reservoir 67, and the oil is maintained at constant temperature by circulation through a cooling chamber 68 supplied with a suitable cooling medium such as water as indicated at 69.

The channel 50 supports a series of driven conveyor units 70 for continuously conveying the bars 30 through the coils 55 and S7 and the quenching ring 60. Referring to Fig. 9, each of these conveyor units includes a quill 71 supported by the channel 50 and plate 51 and having a spindle 72 rotatably mounted therein by means of bearings 73 and 74. At its inner end, each spindle carries a friction wheel 75 counterbored on one side to receive a smaller friction wheel 76 having a serrated or otherwise roughened periphery. A wheel 77 is positioned between the friction wheel 76 and a shoulder 78 on the spindle, and a coil spring 80 is held in engagement with the outer face of friction wheel 75 by a nut 81 threaded on the end of the spindle. These parts are proportioned to form a groove between the wheels 75 and 77 for receiving the lower edge portion of the bar 30. with the spring 80 serving to maintain axial pressure on the bar between wheels 75 and 77.

The outer or forward end of each spindle 72 carries a sprocket wheel 83, and a chain 84 engages each sprocket 83 and the two

end sprockets

85 and 86. The end sprocket 85 is shown as on the same shaft with a sprocket 87 driven through chain 88 and sprocket 89 by a motor 90 provided with a variable transmission such as a Reeves drive 91 for adjusting the speed of sprocket 89. The end sprocket 86 has a tensioned mounting comprismg a fork 92 extending through the end plate 93 and carrying a spring 94 held under compression against plate 93 by nut 95. A guard 96 extends along the channel 50 above the sprockets 83 to insure proper driving cngagement of the chain 84 with each sprocket.

With this arrangement, the spindles 71 are all positively driven and thus cause rotation of the wheels 75. 76 and 77 to convey the successive bars 30 lengthwise of the machine and through the hardening and drawing coils and the quenching fixture. Since the bars are heated to high temperatures as described, it is desirable to prevent undue heating of the parts of this conveyor mechanism which come into contact with them, and accordingly provision is made for cooling the conveyor. As shown in Fig. 9, each of the spindles 71 is provided with a central bore 99 which extends from its outer end to approximately the mid-plane of the small friction wheel 76, and a tube 100 of smaller outer diameter than bore 99 is inserted therein to a position near the inner end thereof. The other end of each of these tubes is connected with the oil supply pipe 65 through a pet cock 101, and thus oil from the same source as the quenching oil for fixture 34 is supplied under pressure to the inner end of each bore 99, whence it flows to the outer end and discharges as indicated by the arrows 102 into a trough 103 connected with reservoir 67, from which it is withdrawn by pump 66 at 104 and returned to the system through the cooling chamber 68.

Pressure rolls are provided above certain of the conveyor rollers for maintaining the bars 30 in proper vertical alignment as they travel through the machine and also for assuring frictional contact between the lower edges of the bars and the friction wheels 76. Referring to Fig. 10, each pressure roll is grooved to receive the upper edge of the bars 30 and is rotatably mounted on one end of a crank arm 111 having its opposite end journaled in a bearing block 112 mounted on channel 50. A coil spring 115 is mounted between a lug 116 on the block 112 and a lug 117 on the crank 111 in position to bias the arm in clockwise direction as viewed in Fig. 8, and a bolt 118 carried by arm 111 serves as an adjustable stop limiting downward movement of the pressure rolls.

In operation as the successive bars travel through the machine, they pass under the rolls 110 and cause the latter to rise against the springs 115, the springs thus serving to exert downward pressure on the bars to maintain them in driven contact with the friction wheels 76. Furthermore, with the rolls 110 grooved as shown, the bars are held in proper lateral and vertical relation with the

coil fixtures

33 and 34 to assure that only the desired portion of each bar passes through these fixtures as described. It should in this connection be noted that each of the rolls 110 in Fig. 8 is provided with the biased crank mounting described, the showing of this mechanism being eliminated for most of rolls 110 in Figs. 7 and 8 for simplicity of illustration.

This machine is accordingly well suited for performing the heat treating method described in connection with Fig, 2, and it has been successfully operated to produce Jordan bars having the properties of differential hardness illustrated by Fig. 6. The machine is readily adjustable as desired in accordance with the temperatures at the heating fixtures, the temperature and pressure of the quenching oil and the rate of travel of the bars required to produce a predetermined condition of differential hardness in the finished bars, and thus it provides for accurate repetition of the same conditions for each of a plurality of successive bars to assure uniform properties in all the bars of a set.

This application is a division of our application Serial No. 145,838, filed February 23, 1950, now Patent No. 2,686,460, issued August 17, 1954.

While the article and method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise article, method and form of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

l. The method of differentially hardening an integrally formed and initially homogeneous elongated cutter bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of applying heat to said bar throughout the thickness thereof along a limited portion of the width of said bar adjacent said working edge to heat said working edge portion to a predetermined relatively high temperature range. quenching said bar to cause hardening of said working edge portion, thereafter applying heat to said bar through another limited portion of the width thereof including said supporting edge, and controlling said last named heating step to limit the maximum temperature in said bar during said step to a temperature range substantially lower than said high temperature range to draw the temper along said supporting edge portion and to provide said increased toughness therein.

2. The method of differentially hardening an integrally formed and initially homogeneous elongated cutter bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the Working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of applying heat to said bar throughout the thickness thereof along a limited portion of the width of said bar adjacent said working edge to heat said working edge portion to a predetermined relatively high temperature range, quenching said bar to cause hardening of said working edge portion, thereafter applying heat to said bar through another limited portion of the width thereof including said supporting edge while excluding said working edge portion from the direct application of heat, controlling said last named heating step to limit the maximum temperature in said bar during said step to a temperature range substantially lower than said high temperature range to draw the temper along said supporting edge portion and to provide said increased toughness therein, and air cooling said bar to effect reheating of said working edge portion thereof by conduction from said supporting edge portion and resulting reduction in the degree of hardness of said working portion from the degree of hardness imparted thereto by said first named heating step and quenching step.

3. The method of differentially hardening an integrally formed and initially homogeneous elongated cutter bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of applying heat to said bar throughout the thickness thereof along a limited portion of the width of said bar adjacent said working edge to heat said working edge portion to a predetermined relatively high temperature range, quenching said bar to cause hardening of said working edge portion, thereafter applying heat to said bar through another limited portion of the width thereof including said supporting edge, and controlling said last named heating step to limit the maximum temperature in said bar during said step to a temperature range substantially lower than said high temperature range to draw the temper along said supporting edge portion and to provide said increased toughness therein, and thereafter machining said supporting edge portion to provide attaching means for said bar.

4. The method of differentially hardening an integrally formed and initially homogeneous elongated cutter bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of applying heat to said bar throughout the thickness thereof along a limited portion of the width of said bar adjacent said working edge to heat said working edge portion to a predetermined relatively high temperature range, substantially immediately quenching said bar to cause hardening of said working edge portion without materially affecting the hardness of the remainder of said bar, then applying heat to said bar through another limited portion of the width thereof including said supporting edge while excluding said working edge portion from the direct application of heat but before cooling of said working edge portion to room temperature, controlling said last named heating step to limit the maximum temperature in said bar during said step to a temperature range substantially lower than said high temperature range to draw the temper along said supporting edge portion and to provide said increased toughness therein, and air cooling said bar to effect reheating of said working edge portion thereof by conduction from said supporting edge portion and resulting reduction in the degree of hardness of said working portion from the degree of hardness imparted thereto by said first named heating step and quenching step.

5. The method of differentially hardening an integrally formed and initially homogeneous elongated cutter bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of passing a limited portion of the width of said bar adjacent said working edge through a first high frequency induction field of predetermined high intensity to heat said working edge portion to a predetermined relatively high temperature range, quenching said bar to cause hardening of said working edge portion, thereafter passing another limited portion of the width of said bar including said supporting edge through a second high frequency induction field of predetermined lower intensity to heat said supporting edge portion to a temperature range lower than said high temperature range and thus to draw the temper therefrom and provide said increased toughness therein, and air cooling said bar to effect re heating of said working edge portion thereof by conduction from said supporting edge portion and resulting reduction in the degree of hardness of said working portion from the degree of hardness imparted thereto by said first named heating step and quenching step.

6. The method of dilferentially hardening an integrally formed and initially homogeneous elongated cutter bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of continuously advancing successive said bars lengthwise thereof through first and second heating stations, applying heat at said first heating station to a limited portion of the width of each successive said bar adjacent the working edge thereof to heat said working edge to a predetermined relatively high temperature range, quenching each said successive bar intermediate said heating stations to cause hardening thereof along said working edge, applying heat at said second heating station to a limited leading portion of each said successive bar along said supporting edge thereof simultaneously with the application of heat at said first heating station to a trailing portion of said bar adjacent said working edge thereof, and controlling the heat applied to said bars at said second heating station to a substantially lower temperature range than said high temperature range to draw the temper along said supporting edge portion and to provide said increased toughness therein.

7. Apparatus for heat treating a plurality of successive integrally formed and initially homogeneous elongated cutter bars of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge of said bars and increased toughness along the opposite or supporting edge, comprising a frame, means on said frame for continuously conveying successive said bars lengthwise thereof along said frame, heating means forming a first heat ing station for applying heat to said bars, means supporting said heating means on said frame in position to apply heat only to a limited portion of the width of each successive said bar adjacent the working edge thereof, means for controlling the heat applied to each said bar at said first heating station to heat said working edge to a predetermined relatively high temperature range, means on said frame adjacent said first heating station for quenching each said bar to cause hardening thereof of said bar along said working edge, additional heating means forming a second heating station, means supporting said additional heating means on said frame in pqsi:

tion to apply heat to each successive said bar only in a limited portion thereof adjacent the supporting edge thereof following passage of said bar beyond said quenching means, and means for controlling the heat applied to said bar at said second heating station to limit the maximum temperature in said bar at said second heating station to a temperature range substantially lower than said high temperature range to draw the temper along said supporting edge and to provide said increased toughness therein.

8. Apparatus for heat treating a plurality of successive integrally formed and initially homogeneous clongated cutter bars of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge of said bars and increased toughness along the opposite or supporting edge, comprising a frame, means on said frame for continuously conveying successive said bars lengthwise thereof along said frame, heating means on said frame for applying heat to each said bar throughout the thickness thereof along a limited portion of the width of said bar adjacent said working edge to heat said working edge portion to a predetermined relatively high temperature range, means adjacent said heating means for quenching each said bar to cause hardening of said working edge portion, and additional heating means on said frame spaced from said quenching means for applying heat only through another limited portion of the width of each said bar adjacent said supporting edge thereof following quenching of said bar to heat the portion of said bar adjacent said supporting edge to a predetermined temperature range substantially lower than said high temperature range and thus to draw the temper along said supporting edge portion and to provide said increased toughness therein.

9. Apparatus for heat treating a plurality of successive integrally formed and initially homogeneous elongated cutter bars of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge of said bars and increased toughness along the opposite or supporting edge. comprising a frame, means on said frame for continuously conveying successive said bars lengthwise thereof along said frame, means including a first fixture for creating a first high frequency induction field of predetermined high intensity, means supporting said fixture on said frame in position to receive through said field a limited portion of the width of each successive said bar adjacent the working edge thereof to heat said Working edge portion to a predetermined relatively high temperaturc range. means on said frame adjacent said first fixture for quenching each said bar to cause hardening of said working edge portion, means including a second fixture for creating a second high frequency induction field of predetermined lower intensity than said first field, and means supporting said second fixture on said frame in spaced relation with said first fixture and said quenching means in position to receive through said second field another limited portion of the width of each said bar including the supporting edge thereof to heat said supporting edge portion to a temperature range substantially lower than said high temperature range and thus to draw the temper along said supporting edge and to provide said increased toughness therein.

l0. Apparatus for heat treating a plurality of successive integrally formed and initially homogeneous elongated cutter bars of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge of said bars and increased toughness along the opposite or supporting edge. comprising a frame, means on said frame for continuously conveying successive said bars lengthwise thereof along said frame, heating means on said frame for applying heat to each said bar throughout the thickness thereof along a limited portion of the width of said bar adjacent said working edge to heat said working edge portion to a predetermined relatively high temperature range, a supply source of quenching fiuid on said frame, means adjacent said heating means for directing quenching fluid from said supply source upon each said bar to cause hardening of said working edge portion thereof, additional heating means on said frame spaced from said quenching means for applying heat along another limited portion of the width of each said bar including said supporting edge thereof following quenching of said bar to heat the portion of said bar adjacent said supporting edge to a predetermined temperature range substantially lower than said high temperature range and thus to draw the temper along said supporting edge portion and to provide said increased toughness therein, and means for circulating quenching fluid from said supply source in heat exchanging rclation with said conveying means to prevent overheating thereof.

ll. Apparatus for heat treating a plurality of successive integrally formed and initially homogeneous elongated cutter bars of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge of said bars and increased toughness along the opposite or supporting edge, comprising a frame, a plurality of conveyor units arranged in spaced relation on said frame and each including rotatable means for supporting one edge of one of said bars, means for maintaining said bars in frictional contact with said rotatable means, means for driving said rotatable means to cause lengthwise travel of said successive bars along said frame, means including a first fixture on said frame for applying a first high frequency induction field of predetermined high intensity to a limited portion of the width of each said bar adjacent the working edge thereof to heat said working edge portion to a predetermined relatively high temperature range, means on said frame adjacent said first fixture for quenching each said bar to cause hardening of said working edge portion, means including a second fixture on said frame in spaced relation with said quenching means for applying a second high frequency induction field of predetermined lower intensity than said first field to another limited portion of the width of each said bar including said supporting edge thereof to heat said portion to a temperature range substantially lower than said high temperature range and thus to draw the temper along said supporting edge and to provide said increased toughness therein, and means for adjusting the speed of said driving means in accordance with the intensities of said fields to control said temperature range.

12. The method of differentially hardening an integrally formed and initially homogeneous elongated cuttcr bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of applying heat at a first heating station to said bar through working zone thereof adjacent said working edge and of substantial cross-section less than one-half the width of said bar while limiting said application of heat to a relatively small portion of the length of said bar, controlling said heating step to heat said zone to a predetermined relatively high temperature range, continuously moving said bar with respect to said heating station to cause said application of heat progressively to said zone along the entire length of said bar, continuously quenching said heated zone of said bar at a quenching station closely adjacent said heating station to cause hardening of said zone, thereafter applying heat at a second heating station to said bar along another zone thereof including said supporting edge and extending across less than the full width of said her to exclude said working zone thereof while limiting said application of heat at said second heating station to a relatively small portion of the length of said bar, controlling said last named heating step to limit the maximum temperature in said bar during said step to a range substantially lower than said high temperature range to draw the temper along said supporting edge portion and to provide said increased toughness therein, and continuously moving said bar with respect to said second heating station to cause said application of heat progressively to said bar along the entire length thereof.

13. The method of differentially hardening an integrally formed and initially homogeneous elongated cutter bar of the character described having a width greatly in excess of the thickness thereof to provide increased hardness along the working edge thereof and increased toughness along the opposite or supporting edge which comprises the steps of applying heat at a first heating station to said bar through a limited working zone thereof adjacent said working edge and of substantial cross-section less than one-half the width of siad bar while limiting said application of heat to a relatively small portion of the length of said bar, controlling said heating step to heat said zone to a predetermined relatively high temperature range, continuously moving said bar with respect to said heating station to cause said application of heat progressively to said zone along the entire length of said bar, continuously quenching said heated zone of said bar at a quenching station closely adjacent said heating station to cause hardening of said working zone, thereafter applying 'heat at a second heatlog station to said bar through another limited zone thereof including said supporting edge and extending across less than the full width of said bar to exclude said working zone thereof while limiting said application of heat at said second heating station to a relatively small portion of the length of said bar, controlling said last named heating step to limit the maximum temperature in said bar during said step to a range substantially lower than said high temperature range to draw the temper along said supporting edge portion to provide said increased toughness therein, continuously moving said bar with respect to said second heating station to cause said appiication of heat progressively to said bar along the entire length thereof, and air cooling said bar to effect reheating of said working zone thereof and resulting reduction in the degree of hardness of said working zone from the degree of hardness imparted thereto by said first heating step and said quenching step.

References Cited in the file of this patent UNITED STATES PATENTS 2,358,834 Sonics Sept. 26, 1944 2,371,459 Mittelmann Mar. 13, 1945 2,424,794 Brown July 29, 1947 2,598,694 Herbenar June 3, 1952 2,604,419 Herbenar July 22, 1952 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent No. 2,831,788 Adam E. Bridge et a1. April 22, 1958 It is hereby certified that error appears in the printed specification of ;he above numbered patent requiring correction and that the said Letters Patent :hould read as corrected below.

line 34, for "to the direction" read to the portion read Bar thiclmess Bar thickness do k line 1'7, for "siad" read said Column 2, :olumn 5, line 23, for Lnch column 13,

Signed and sealed this 24th day of June l958.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Cunnissioner of Patents Attesting Officer

Claims

1. THE METHOD OF DIFFERENTIALLY HARDENING AN INTEGRALLY FORMED AND INITIALLY HOMOGENEOUS ELONGATED CUTTER BAR OF THE CHARACTER DESCRIBED HAVING A WIDTH GREATLY IN EXCESS OF THE THICKNESS THEREOF TO PROVIDE INCREASED HARDNESS ALONG THE WORKING EDGE THEREOF AND INCREASED TOUGHNESS ALONG THE OPPOSITE OR SUPPORTING EDGE WHICH COMPRISES THE STEPS OF APPLYING HEAT TO SAID BAR THROUGHOUT THE THICKNESS THEREOF ALONG A LIMITED PORTION OF THE WIDTH OF SAID BAR ADJACENT SAID WORKING EDGE TO HEAT SAID WORKING EDGE PORTION TO A PREDETERMINED RELATIVELY HIGH TEMPERATURE RANGE, QUENCHING SAID BAR TO CAUSE HARDENING OF SAID WORKING EDGE PORTION, THEREAFTER APPLYING HEAT TO