Method of case-hardening an arcuate member

BACKGROUND OF THE INVENTION

Heretofore, an arcuate member, such as a large pitch gear, having a first tooth and a second tooth provided with opposed flanks and a root section which defined a valley 35 was hardened by heating the entire gear in a conventional furnace followed by quenching in a suitable quench. The member is then softened by tempering to achieve necessary toughness, which results in a surface much less wearresistant than if the member had been case-hardened. ⁴⁰Large pitch gears are in the range of .500-.625 diametral pitch where diametral pitch is number of teeth pitch diameter 45

Such large pitch gears are not commonly case-hardened because of the deep cases required and because modern applications require that the case follow the complete contour of the valley formed by two teeth. Contour hard- ₅₀ening is needed to impart compressive prestress at the valley radii increasing the fatigue strength at this critical area. The conventional method to contour case-harden by induction would require a much greater power source than is normally employed and would likely burn the sur- 55 face in achieving the deep cases required. Another known induction technique, the tooth enveloping coil, cannot harden the root of the valley and cannot control the contour of the case.

OBJECTS OF THE INVENTION ⁶⁰

It is the general object of the present invention to avoid and overcome the foregoing and other difficulties of and objections to prior art practices by the provision of an improved method of case-hardening an arcuate 65 member, such as a large pitch gear, having a first tooth and a second tooth provided with opposed flanks and a root section which define a valley, which method:

(1) requires a minimal power requirement to case-harden γθ the arcuate member;

(2) provides uniform control of the depth of and the location of the hardened case on the flanks and root section of the arcuate member;

(3) is adapted to case-harden arcuate members of any diameter;

(4) provides a tough ductile core in the arcuate member, which core is not affected by the case-hardening process and is not undesirably hardened or embrittled;

(5) case-hardens the arcuate member economically without burning or melting the flanks and root section of such arcuate member; and (6) imparts a compressive prestress at the radii of the root section, thereby increasing the fatigue strength of the arcuate member.

BRIEF SUMMARY OF THE INVENTION

The aforesaid objects of this invention and other objects which will become apparent as the description proceeds are achieved by providing an improved method of surface or case-hardening including the steps of:

(1) supporting the arcuate member;

(2) preheating a moving heated area on the flanks and the root section;

(3) heating the moving heated area above the hardening temperature of the arcuate member without burning the arcuate member; and (4) quenching the moving heated area to case-harden such moving heated area to a predetermined uniform depth.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagrammatic side elevational view of the apparatus for surface hardening the arcuate member, such as the large pitch gear, and including the supporting means, the case-hardening means and the drive means;

FIG. 1A is a fragmentary side elevational view taken along the line IA—IA of FIG. 1 in the direction of the arrows and showing the details of the drive means;

FIG. 2 is a perspective view of two adjacent teeth on the arcuate member or gear and showing the preheating means, the heating means and the quenching means about to enter the valley defined by the opposed flanks and root section of the two adjacent teeth preparatory for the casehardening of such flanks and root section;

FIG. 3 is a fragmentary side elevational view of two adjacent teeth on the gear and showing the tapered spacing of, for example, the preheating means from the opposed flanks of such teeth and the spacing of the preheating means from the adjacent root section and the uniform case-hardening thereof;

FIG. 3A is a schematic fragmentary vertical sectional view taken along the line ΠΙΑ—ΠΙΑ of FIG. 3 and showing the moving preheated area, the moving heated area and the hardened case; and

FIG. 4 is a fragmentary view similar to FIG. 1 wherein the supporting means is reciprocable on the frame of the surface-hardening apparatus by the drive means.

Although the principles of this invention are broadly applicable to the case-hardening of arcuate members, this invention is particularly adapted for use in conjunction with the controlled, low-power induction heating of arcuate members, such as large pitch gears, to case-harden them and hence it has been so illustrated and will be so described.

DETAILED DESCRIPTION

With specific reference to the form of this invention illustrated in the drawings, and referring particularly to

FIG. 1, a surface-hardening apparatus is indicated generally by the reference numeral 10.

This surface-hardening apparatus 10 is employed to case-harden an arcuate member, such as a large pitch

3,592,702 gear 12 (FIG. 1), having a first tooth 14α and a second tooth 146, each provided with opposed flanks 16α and 166 respectively and a root section 18 which define a valley 20. As shown in FIG. 3 the root section 18 extends along the bottom of the valley 20 from A to A, and has a root radius R. This gear 12 has a core 22 and is provided with a central mounting hole 24.

SUPPORTING MEANS 26

The apparatus 10 has a supporting means 26 (FIG. 1) for supporting the gear 12. In order to mount and support the gear 12, the supporting apparatus 26 has plates 28 mounted in the mounting hole 14 and on a shaft 30, which shaft 30 is supported on rolls 32 journaled in a stationary portion of the frame 34 of the apparatus 10.

CASE-HARDENING MEANS 36 IN GENERAL

Referring to the left-hand portion of FIG. 1, case- hardening means 36 are mounted in registry with the valley 20 for case-hardening the flanks 16α and 166 and the root section 18 of the valley 20. The structure utilized to mount the case-hardening means comprises bus bars 38α and 386 (with only bus bar 386 being shown in FIG. 1) to which fluid-cooled half blocks 40α and 406 (FIGS. 1, 2) of the case-hardening means 36 are secured by bolts 42. The bus bars 38α and 386 are in turn connected to an electric power source, suitably a transformer 44 (FIG. 1). In order to permit relative movement between the transformer 44 and the case-hardening means 36 and the gear 12 and the frame 34 the transformer 44 is mounted on a table 46 (FIGS. 1, 1A, 2), which table 46 has slides 47α, 476 reciprocable respectively in guides 48α and 486 mounted on side rails 50α, 506 (FIG. 1) respectively of the frame 34. For the purpose of maintaining the casehardening means 36 in registry with the valley 20, a guide roll 52 (FIG. 1) projects from a bracket 54 upstanding from the table 46 and engages a valley 20α between two other teeth 14c, 14d of the gear 12 (in this case substantially diametrically offset from the teeth 14α, 146 which define the valley 20).

DRIVE MEANS 54

Drive means 54 (FIGS. 1, 1A) are connected to one of the supporting means 26 and the case-hardening means 36 (in this case the case-hardening means 36) to cause relative movement between the valley 20 and the casehardening means 36 so that the case-hardening means 36 passes through the valley 20 (FIG. 2). The drive means 54 has a pair of screws 56 journaled in end bearings 58 (FIG. 1A) and one of the screws 56 (in this case the right-hand screw 56) is driven by a reversible D-C motor 59 (FIG. 1A) mounted on such right-hand screw 56 and supported by the adjacent end bearing 58 (FIG. 1A). The left-hand screw 56 is connected to the right-hand screw 56 and driven thereby by sprockets 59α, 596 (FIG. 1) and a chain 59c (FIGS. 1, 1 A). In turn a pair of depending brackets 60 depend from the table 46 and terminate in collars 62, which collars 62 have journaled therein a screw collar 64 which rides on the adjacent screw 56. Referring to the lower right-hand portion of FIG. 1, the motor 59 is connected to a suitable D-C supply indicated by the legend “D-C SUPPLY” by three leads 66α, 666 and 66c (FIG. 1). For the purpose of reversing the motor 59, a reversing switch 68 alternately connects the leads 66α and 666 to one side of such D-C supply. The means utilized to control the speed of the motor 59 is a control member, such as the variable resistor 67.

SPECIFIC DETAILS OF THE CASE-HARDENING MEANS 36

The case-hardening means 36 has a preheating means 70 generally contoured (FIG. 2) to the valley 20 to preheat a moving area Amp (FIG. 3A) on the flanks 16α, 166 and the root section 18. In addition, heating means 72 (FIG. 2) also generally contoured to the valley 20, is disposed adjacent the preheating means 70 to raise the temperature of the moving preheated area Amp above the hardening temperature forming the deeply heated area Amh (FIG. 3A). In addition, quenching means 74 are connected by pipe 90, 90α to a fluid source (indicated by the legend “FROM FLUID SOURCE,” FIG. 2) and are disposed adjacent the heating means 72 for quenching and case-hardening the moving heated area Amh. The preheated area Amp preceding the hardening heat enables deeper penetration of the heated area Amh without burning or melting of the surface.

As shown in FIG. 2, the two hollow half blocks 40α, 406 are each provided with elongated mounting slots 76 to facilitate the mounting of such half blocks 40α, 406 by means of the bolts 42 on the bus bars 38α, 386 respectively. In order to electrically insulate the two half blocks 40α, 406 from each other and to integrate the blocks 40α, 406, an insulating spacer 78 formed of a dielectric material, such as Bakelite or the like, is disposed therebetween and the half blocks 40α, 406 are mounted on an insulating block 80, suitably Bakelite or the like, by bolts 42 (not shown in the right-hand portion of FIG. 2) extending through the insulating block 80 and threadable into the half blocks 40α, 406. A side mounting plate 82 is mounted on the half block 406 and is insulated and spaced from such half block 406 and the bolts 42 by an insulating spacer 78, insulating washers 84 and an insulating sleeve (not shown) disposed about the bolts 42. Bakelite is the trade name of a dielectric material manufactured by Union Carbide Corporation, New York, N.Y.

For the purpose of carrying cooling water to the preheating means 70 and heating means 72, conduits 86α, 866 (FIG. 2) extend from a suitable fluid source indicated by the legend “FROM FLUID SOURCE” into the half blocks 40α, 406 respectively and adjacent conduits 88α, 886 depend from the respective half blocks 40α and 406 downwardly therefrom. The left-hand conduit 88α extends to the preheating means 70, suitably an induction preheating coil 70α formed of, for example, copper tubing, which induction preheating coil 70α is connected by a bridge conduit 88c to the heating means 72, suitably an induction heating coil 72α, in series with the preheating induction coil 70α. The other end of the induction heating coil 72α is connected to the other conduit 886.

In order to minimize the width of the moving heated area Amh (FIG. 3A) and concentrate the heating effect of coil 72α on the flanks 16α, 166, and the root section 18, intensifying means, such as the intensifiers 88 (FIG. 2), are mounted on portions of the heating induction coil 72α which move adjacent such flanks 16α, 166 and the root section 18. In order to obtain balanced preheating of the difficult to heat root section 18, similar intensifiers 88 are mounted on the bottom portion of the preheating induction coil 70α adjacent the root section 18. These intensifiers 88 are formed of ferromagnetic plastic, for example, powdered iron, dispersed in a plastic binder as disclosed in U.S. Pat. 2,777,041, issued Jan. 8, 1957 to H. C. Dustman, or of the type known as Ferrotron and manufactured by the Polymer Corporation, Reading, Pa.

The quenching means 74 is suitably a quenching head 74α formed of hollow copper tubing, for example, which tubing has a generally diamond-shaped horizontal cross section and is provided with a plurality of quenching holes 746 on the rearward face 74c (as viewed in FIG. 2) of the quenching head 74α to prevent adverse premature cooling of the already-heated portion Amh of the valley 20. The quenching head 74α is joined to a fluid supply conduit 90 at 92, which supply conduit 90 is affixed to the side mounting plate 82 and continues via pipe 90α to the fluid source indicated in the upper right-hand portion of FIG. 2 by the legend “FROM FLUID SOURCE.” The fluid employed in the preheating induction coil 70α, and the heating induction coil 72α is water. The fluid employed in the quenching head 74α may, for example, be water, oil, or a mixture of water and Aqua Quench, a water-soluble resinous material used as a water additive for water3,592,702 quenching systems to provide a quenching rate between that of water and the fastest quenching oil. Aqua Quench is manufactured by the E. F. Houghton and Company, Philadelphia, Pa.

For the purpose of cooling the intensifiers 88 on the heating induction coil 72« and on the preheating induction cojl 70«, spray heads 94 (FIG. 2) are directed at such intensifiers 88 and are connected by lines 96«, 96/?. The lines 96«, 96b have their upper portions affixed to a manifold block 98 on the side mounting plate 82. The manifold block 98 is connected by the supply line 100 to the fluid source indicated in FIG. 2 by the legend “FROM FLUID SOURCE.” The supply fluid material in this case is water. The intensifiers 88 are cooled below a temperature in the range of about 450-500° F., their break-down temperature by a fine atomized mist from the spray heads 94. The fluid from the quenching head 74a and the spray heads 94 are collected in a tray 102 (FIGS. 1, 4) mounted on the transformer 44.

EXAMPLES

If the gear 12 is composed of a type 1050 steel having about 0.50% by weight carbon and 0.91% manganese, the preheating coil 70« must raise the temperature of the moving preheated area Amp (FIG. 3A) above the temperature of about 500 to 600° F. and the heating coil 72α must raise such moving heated area Amh above a hardening temperature of about 1650° F. to austenitize the gear 12 without burning or melting such gear 12. Prompt cooling by the quenching head 74α below about 200° F. will provide a proper martensitic content with a Rockwell hardness of about 60.

When a gear 12 is formed, for example, of a modified type 4150 alloy steel having by weight a carbon steel content of about 0.55%, a manganese content of about 0.60%, a chromium content of about 1.03%, a molybdenum content of about 0.19% and a nickel content of about 0.36%, the preheating coil 70α and the heating coil 72α raise the moving heated areas Amp and Amh (FIG. 3A) above the temperature of about 450-500° F. and about 1550° F. respectively and upon self-quenching through the mass of the gear 12 below 450° F., a Rockwell hardness of about 55 is produced.

Gears 12 having a diametral pitch in the range of about .500-.625 were case-hardened to uniform case depths Wd (FIG. 3) of about Va to % inch using 100 kw., 10,000 cycle power with the spacing di of the coils 70«, 72α from the root section (FIG. 3) equal to about Vz the spacing d₂ of such coils 70«, 72α from the top of the flanks 16«, 166. Along the flanks 16«, 16/> the spacing increased upwardly gradually from to d₂. Closer proximity is employed at the root to balance the heating of the more difficult to heat root with the more easily heated flanks. The coils 70α, 72b and quenching head move through the valley 20 having a width Wi (FIG. 3A) of about three inches at a speed of about six inches per minute.

ALTERNATIVE EMBODIMENTS

It will be understood by those skilled in the art that alternatively, as shown in FIG. 4, the supporting means 26⁴ has a carriage 104 having slides 47α, 47 b which are reciprocable in guides 48«, 48Z> provided in the frame 34 and the drive means 54⁴ is connected to the carriage 104.

METHOD

It will be understood from the above description of the improved apparatus 10, 10⁴ shown in FIGS. 1, 4, that an improved method is also provided for surface-hardening an arcuate member, such as a large pitch gear 12, having a first tooth 14α and a second tooth 146 provided with opposed flanks 16α, 166 respectively and a root section 18 which define a valley 20. This method includes the steps of supporting the arcuate member or gear 12, preheating a moving preheated area Amp (FIG. 3A) on the flanks 16«, 16b and the root section 18, heating the moving heated area Amh above the hardening temperature of the arcuate member or gear 12 without burning or melting such gear 12, and quenching the moving heated area Amh to case-harden such moving heated area Amh.

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION

It will be recognized by those skilled in the art that the objects of this invention have been achieved by providing an improved method of case-hardening the arcuate member or gear 12, which method requires minimal power to case-harden the arcuate member 12, provides uniform control of the depth W_d (FIG. 3) and the location of the hardened case HC (FIG. 3) on the gear 12, is adapted to case-harden gears 12 of any diameter, provides a tough ductile core 22 (FIG. 3) in the gear 12, which core 22 is unaffected by the case-hardening process and is not undesirably hardened or embrittled, which satisfactorily and economically case-hardens the gear 12 without burning or melting it, and imparts a compressive prestress at the radii R (FIG. 3) of the root section 18, thereby measurably increasing the fatigue strength of the gear teeth 14α, etc.

While in accordance with the patent statutes preferred and alternative embodiments of this invention have been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.