US3851512A

US3851512A - Method of and device for gear teeth hardening

Info

Publication number: US3851512A
Application number: US00339349A
Authority: US
Inventors: G Zhuravlev; E Roslivker; E Chilevich; V Gurevich
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-03-08
Filing date: 1973-03-08
Publication date: 1974-12-03
Anticipated expiration: 1991-12-03

Abstract

The method provides for gear teeth plastic strain by curving them in the direction of application of the principal working load. The device for carrying the method into effect comprises a bed which carries a ring-shaped mechanism for setting up plastic strain of the teeth of the gear wheel being treated, and a clamping fixture for fitting the gear wheel into the ring and for turning the gear wheel with respect to the latter. The ring inner surface is provided with tooth-like projections adapted to interact with the gear teeth when the gear wheel rotates in the ring so as to curve the teeth.

Description

[ Dec. 3, 1974 METHOD OF AND DEVICE FOR GEAR 2,206,831 7/1940 Bcrthelsen......................... 2,860,077 11/1958 Adairet 211...... 3,466,909 9/1969 TEETH HARDENING [76] Inventors: German Alexandrovich Zhuravlev,

ulitsa Verkhne-Nolnaya, l0, kv.9; Efim Grigorievich Roslivker,

Primary Examiner-Lowell A. Larson Attorney, Agent, or Firm-Holman & Stern prospekt Budennovsky, 72, kv.5 l; Eduard Mikhailovich Chilevich,

pereulok Solyanoi Spusk, 6, kv.37; Vladimir Samuilovich Gurevich,

ABSTRACT prospekt Oktyabrya, 18, kv.20, all of Rostov-na-Donu, U.S.S.R.

Mar. 8, 1973 The method provides for gear teeth plastic strain by 22 Fl curving them in the direction of application of the I 1 1e principal working load. The device for carrying the method into effect comprises a bed which carries a ring-shaped mechanism for setting up plastic strain of [21] Appl. No.: 339,349

the teeth of the gear wheel being treated, and a clamping fixture for fitting the gear wheel into the ring and for turning the gear wheel with respect to the latter. The ring inner surface is provided with tooth'like projections adapted to interact with the gear teeth when the gear wheel rotates in the ring so as to curve the teeth.

1,444,259 Lothrop.............................. 148/131 9 Claims, 5 Drawing Figures PATENTEL DEC 3 I974 SHEEI 1 0F 4 PATENTLL EB 1974 SHEUEUF 4 F/EIZ MENIL ESE 31974 SHEET 30F 4 v METHOD OF AND DEVICE FOR GEAR TEETH HARDENING BACKGROUND OF THE INVENTION This invention relates generally to the sphere of hardening technique of machine parts by way of modifying the physical properties of metal due to plastic strain, and more specifically, it relates to a method of and a device for gear teeth hardening.

The invention can find most utility when employed for hardening the teeth of gear wheels upon which unidirectional load is normally imposed.

In the present-day practice, there are widespread applications for methods of improving the strength and hardness of machine parts and elements, by using plastic strain of the metal of a part set up during the process of hardening.

As a rule, plastic strain of metal in such cases is not aimed at shaping of the parts but is confined only to modifying the physical properties of metal. Referred to physical properties of metal that experience alternations in the course of such a treatment, should be the limit of elasticity, ultimate strength, hardness, macrostructure and internal stresses.

As it is known commonly, plastic strain of metal that is capable of being hardened, results in an increased limit of elasticity, ultimate strength and hardness of the material as compared to the initial values of such.

Moreover, if any cross section of the part should be in non-uniformly stressed state in the course of plastic or elasto-plastic strain, this results in residual stresses that will appear in the cross section upon relieving the applied load due to different degrees of strain on various cross-section areas.

Pertaining to the most widespread metal hardening technique that uses the physical phenomena, is the plastic strain of the surface of a part referred to as surface peening. In particular, it is widely known to use some gear teeth hardening methods by virtue of plastic strain of the surface of teeth metal. Such a plastic strain is attained due to shot-peening of the surface to be hardened or bumishing with rolls with the result that the strength characteristics of the teeth surface layer are improved and that some residual stressesare left in the layer arranged so as to favorably increase the loadbearing ability of the teeth as a whole.

In one of the prior-art methods, such a hardening is attained due to surface cold peening of gear teeth by virtue of plastic strain of metal along the entire tooth profile which occurs during the bumishing thereof with toothed rolls.

In such case, the plastic strain of metal is due to a preliminary radial displacement of the toothed rolls which are set with a definite interference corresponding to the required degree of hardening. While meshing the gear teeth being hardened, the bumishing roll teeth plastically strain the metal of the latter, thus effecting metal surface cold peening which improves its strength characteristics.

Gear teeth hardening by virtue of plastic strain is carried out, for instance, by the device according to USSR Inventors certificate US. Pat. No. 158,911, Class 18c, 1/80 (Int. C1. (21), comprising a drive and a bed carrying a mechanism to set up plastic strain, and an arrangement for fixing the gear wheel being hardened.

The mechanism for setting up plastic strain is made as a number of bumishing toothed rolls located in a common housing, mounted on eccentric pivots and imparted vertical motion along with the housing and radial motion due to the turning of the eccentric pivots.

Gear teeth hardening occurs due to an interference established between these and the teeth of the burnishing rolls.

In this known method, the effect of the teeth metal hardening is more superficial in nature is spread but to a limited depth, e.g., maximum 3 mm for the teeth of gears having a module of 10-1 1 mm. This results in the fact that the depth of residual compressive stresses is not in excess of 0.7 mm for the given particular case, on account of which the stresses exercise but insignificant influence upon the distribution of stresses in gear teeth under working load.

The bumishing rolls of the plastic strain setting-up mechanism of the known device, are capable of straining only a thin superficial layer of the teeth material which eventuates in that an improvement in the material strength characteristics and residual compressive stresses in the hardened layer result but also results in an inconsiderable increase of the teeth bending strength as a whole.

An attempt to increase the hardened layer at the expense of a higher interference between depth of the gear teeth being hardened and the teeth of the burnishing rolls failed to yield the desired effect since it only resulted in metal flaking due to its surface overhardenmg.

It should be pointed out that the depth of penetration and character of distribution of residual compressive stresses exert a decided influence upon the bending strength of gear teeth under treatment.

However, the now existing hardening methods fail to set up such a distribution of stresses at which stresses in the teeth material under working load would be distributed adequately over the entire critical cross section.

Th distribution nature of residual stresses with the use of the known hardening methods leads to the fact that maximum stresses from the effect or working load in the tooth critical cross-section occur in the subsurface layer, while the core material participates but inconsiderably, in taking-up the working load, thus practically escaping from the working process.

SUMMARY OF THE INVENTION It is therefore an essential object of the present invention to provide a method of and a device for gear teeth hardening that will enable a volumetric cold peening of teeth material in the critical tooth cross-section to increase hardening depth, as well as the value and depth of penetration of residual compressive stresses so that all this will result in a considerable increase in the bending strength of gear teeth.

This and other objects are attained in a method of gear teeth hardening by virtue of plastic strain, wherein, according to the invention the plastic strain is set up by curving the gear teeth in the direction of application of the principle working load.

Due to the fact that the teeth of the gear being treated are subjected to curving which causes crippling stresses in the tooth material having the same sign as the working load stresses, high residual stresses are developed penetrating for a considerable depth in the teeth critical cross-section, the stresses exercising a substantial influence upon redistribution of stresses under working load, thus ensuring in the gear teeth working process a more favorable energetic state of the teeth material over the entire critical cross-section, the core inclusive.

Furthermore, plastic bending strain makes it possible to effect cold peening of the teeth material on the majorportion of the critical cross-section which is unattainable by any of the known hardening methods.

It is expedient that prior to curving the teeth their contact surfaces be subjected to such a heat treatment after which the total surface hardness of every tooth within the zone of adjacency of the hardened layer and the cold-peened layer would vary adequately along the tooth height.

Such an embodiment makes it possible to ensure high contact strength of gear teeth and at the same time obviate any additional concentration of stresses which result due to the absence of hardness difference within or between adjacent zones of the hardened and the coldpeened layers.

It is likewise reasonable that the teeth surface be subjected, either simultaneously with curving (bending) or thereupon, to heating followed by cooling in the loaded state.

Such an embodiment makes it possible to attain the following:

a. in case of heat treatment carried out simultaneously with curving, to ensure high contact strentth of gear teeth made of carbon or case-hardenable steels;

b. to harden by the present method, the gear teeth made of carbon or case-hardenable steels that have passed deep hardening to high degree of hardness or a complete thermochemical treatment due to a degraded elasticity limit of the material within the teeth fillets occurring in the course of heating during heat treatment procedure;

c. in case of heat treatment occurring after teeth curving (to suit the technological requirements of a particular production practice), to ensure high contact strength and increase bending strength due to thermomechanical treatment of-the teeth fillet zone of those gears whose material is not subject to heat treatment after tooth milling process.

A device for carrying into effect the method of gear teeth hardening by virtue of plastic strain effected by curving or bending the teeth in the direction of application ofthe principle or primary working load, which device comprises a bed which carries a mechanism to set up plastic strain, a clamping fixture for the gear wheel being treated is secured, and a drive to impart relative motion to the mechanism and the gear wheel.

According to the invention, the mechanism for setting up plastic strain comprises a ring having on its inner surface at least one tooth-like projection which is adapted to successively interact with the teeth of the gear wheel along the entire length thereof in the course of the relative movements of the ring and the gear wheel set concentrically therewith on the fixture, thus curving said teeth.

Such a constructional feature makes it possible to apply to the teeth of the gear wheel under treatment a bending moment (hereinafter referred to as technological load) that sets up in the gear teeth material stresses beyond the yield point thereof and having the same sign (direction) as the working load.

It is expedient that each tooth-like projection be made as an individual straining element which is located in respective longitudinal slot provided in the ring inner surface and be free to effect movement square with the gear teeth surface being treated.

Such a constructional feature makes it possible to degrade the accuracy requirements of the mechanism for setting up or imposing plastic strain and to compensate for geometrical errors of the gear wheel under treatment due to set-up motion of the straining elements.

In case of treating gear wheels having longitudinally curvilinear teeth, the straining elements may be builtup in length, i.e., composed of at least two separate portions establishing a curvilinear surface.

Such a constructional feature makes it possible to uniformly spread technological load lengthwise the tooth which is hardly attainable with the use of a solid straining element.

In order to also impart to the mechanism for setting up plastic strain the functions of an inductor capable of heating the gear wheel being treated, the ring of the mechanism has an open-end radial groove. wherein a gasket is placed, while split ring ends are interconnected through current-leading bus-bars to a H.F. (high-frequency) current source; the ring inner surface is shaped to cooperate with the shape of the gear teeth being treated.

Such a constructional feature makes it possible, alongside with teeth curving or thereupon, to subject the teeth surface to heating followed by cooling when the teeth are in the strained state.

The current-carrying bus-bars can be made integral with the ring and be used for hanging or supporting the latter; it is also expedient to provide movable clamps located in a groove on the bed of the device and which clamps are adapted to fix the ring on the bed at the moment of application of the load setting up plastic strain.

To promote a better understanding of the essence of the present invention, specific embodiments of a method of gear teeth hardening carrying into effect by a device represented in the accompanying drawings are described in detail below, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective, fragmentarily cutaway view of an embodiment of the device for gear teeth hardening using the novel method;

FIG. 2 is an enlarged sectional view taken along the line IIII in FIG. 1;

FIG. 3 is a developed view of the slot in the mechanism for setting up or imposing plastic strain, in case of treating curvilinear tooth gears;

FIG. 4 illustrates the diagrams of normal stresses effective at a tooth root and resulting from:

A the effect of bending (technological) load;

B the effect of residual stresses;

C the effect of permissible working load for a tooth hardened by the proposed method;

C the effect of permissible load for a nonhardened tooth;

D the effect of resulting stresses; and

FIG. 5 shows another embodiment of the device for gear teeth hardening according to the novel method with the use of heat treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to FIG. 1, the device according to the invention comprises a bed 1 which carries a mechanism 2 for setting up plastic strain; a clamping fixture 3 to secure a gear wheel 4 under treatment; and a hydraulic drive 5 for turning the gear wheel 4 with respect to the mechanism 2.

The bed 1 is essentially a metal plate strong enough to sustain technological load.

The mechanism 2 for setting up plastic strain is made as a cylindrical ring 6 which is fixed in vertical position on the bed 1 by means of a stand 7.

The ring 6 has on its inner surface a number of toothlike projections made as individual detachable straining elements 8 fitted in respective longitudinal slots 9 (FIG. 2) which are equi-distantly spaced along the periphery of the ring 6.

The slots 9 are rectangular in cross section, while their spacing is multiple of the pitch of teeth 10 of the gear wheel 4 being treated.

A rear wall 11 of each slot 9 is somewhat inclined, whereas each straining element 8 is respectively wedgeshaped in longitudinal section for its setup motion square with the surface of the teeth 10 of the gear wheel 4 being treated.

A surface 12 of the straining element 8 that is adapted to interact with the tooth 10 of the gear wheel 4, is convex-shaped to ensure a linear contact with the surface of the tooth 10 being hardened.

In case the teeth 10 being hardened are of the straight involute type the surface 12 is cylindrical in shape.

In cases where the teeth 10 of the gear wheel 4 being treated are curvilinear in longitudinal direction, it is oftentime difficult to make the solid straining elemnt 8 which can ensure a linear contact ensuring a uniform load distribution over the entire length of the tooth 10.

In such cases each straining element may be made built-up in length and composed of several individual parts 13 (FIG. 3), whose working surfaces 14 form a curvilinear surface adapted to be in contact with the tooth surface being hardened.

The clamping fixture 3 (FIG. 1) to secure the gear wheel 4 being treated comprises two stands 15 connected fixedly on the bed 1 at both butt ends of the ring 6 of the mechanism 1 and carrying a horizontal splined shaft 16 mounted in the stands on radial bearings 17 concentrically with the ring 6. The shaft 16 is to mount the gear wheel 4 being treated.

The extensions of the shaft 16 protrude from the stands 15 carry single-arm levers l8 interconnected by a bar (shaft) 19 which by means of a pitman 20 is, in turn, articulated to a rod 21 of a cylinder 22 of a hydraulic drive 5 which is adapted to impart rotation to the shaft 16 along with the gear wheel 4 set thereon, with respect to the ring 6. Fluid lines are piping 23 communicate the cylinder 22 with the oil pumping stations (not shown) operating the hydraulic drive 5.

The proposed device may also be implemented according to an alternative embodiment, wherein the gear wheel 4 being treated is stationary, while the relative motion is performed by virtue of the mechanism for setting up or effecting the plastic strain.

The afore-described device operates as follows.

The gear wheel 4 being treated is mounted on the splined shaft 16 having extensions in the bearings 17 fitted in corresponding holes in the stands 15 so that the gear wheel 4 is located inside the ring 6 0f the mechanism 2 for imposing strain.

Thereupon, the straining elements 8 are installed into the slots 9 of the ring 6 at one of the butt ends thereof and are imparted setup movements perpendicular to the surfaces being hardened of the respective teeth 10 of the gear wheel 4 so as to uniformly distribute technological (bending) load between all the simultaneously hardened teeth 10.

Next, the hydraulic drive 5 is put into operation with f the result that the connecting rod 21 of the hydraulic cylinder 22, while acting through the pitman 20, moves the shaft or bar 19 which turns the levers 18 at the angle a in the direction of the arrow E (FIG. 1); (the direction should coincide with the direction of application of the principal working load imposed on the gear wheel 4) and along with the levers also the shaft 16 with the gear wheel 4 mounted thereon rotates with respect to the ring 6.

In the course of the rotation, the straining elements 8 of the ring 6 interact with the teeth 10 of the gear wheel 4, thus setting up or imposing plastic strain of the teeth 10 by curving these in the direction of application of the principle (primary) working load, with the result that the material of the teeth 10 is given bulk peening within the zone of critical cross section.

The angle a at which the gear wheel 4 turns with respect to the ring 6 is estimated or determined proceeding from the geometrical parameters of the gear wheel 4 being treated and the characteristics of the material of its teeth 10. Thus, for a spurgear with a module of 10 mm and numbering of 17 teeth made of steel alloyed with up to 1 percent of chromium and 0.4 percent of carbon and hardened to 38 l-IRC, the angle is equal to 025.

Once the splined shaft 16 has turned at the angle a, the device is automatically disengaged, the straining elements 8 participating in the hardening process are brought out of contact with the thus-treated teeth 10 of the gear wheel 4; then another group of the straining elements 8 is given setup motion, and the whole cycle is repeated.

The number of the teeth 10 that are subject to treatment at one time is determined proceeding from constructional reasons, depending upon the strength of the components of the proposed device.

As a result of treatment of gear wheels by the proposed method the material of their teeth is subjected to bulk peening for a depth h (as shown in the diagram A in FIG. 4) of the cross section. Besides, residual stresses arise in the thus-hardened tooth (see the diagram B in Residual stresses resulting from machining are distributed over the tooth cross section in such a manner as to exercise a considerable favorable influence upon the redistribution of stresses from the effect of the working load (see the diagram D in FIG. 4), which results in an increase of the permissible fatigue stress with respect to bending from to [ti- (see the diagrams C and C in FIG. 4).

Tabulated below are the characteristics of gear ent of total hardness within the zone of tooth fillet equals I HRC/mm.

Such a treatment prevents the appearance of additional stress concentrations which are liable to occur in wheels treated by the known method versus those after the zone of emergency of the end of a layer that has treatment by the proposed method for increasing teeth e Induction hardened, due to an abrupt hardness bending strength (see Table 1). difference; I

The table contains data on gear wheels having a mod- The device shown ll] 5 is adapted fOf l'8lilZZ1tlOl'l ule of 10 mm made of case-hardenable steel alloyed 0f the P P method in eases Where either Prior to with up to 1 percent of the chromium and 0.2 percent 10 vtooth eurvmg e thereupon. the teeth 6 1S f of carbon, that have been hardened by the proposed Jeeted t0 heatmg followed y eoohhg the Strthhed method, whereas data on the known method refer to Stategear wheels made of steel containing up to 1 percent of The tievlce llke fi ISt descrlbed above and liiUS- Chromium and 4 percent f carbon and hardened up trated in FIG. 1, comprises a bed 24 which carries :1 to HB 300 mechanism 25 for setting up plastic strain, a clamping An increase in load-bearing ability is expressed in the fixture for seeuhhg the gear Wheel 4 being treated ratio and a drive (not shown) for the gear wheel 4 to turn with respect to the mechanism 25.

The mechanism 25 is made as an inductor which is lnar] yl[ mu.r]H

. a H W essentially a cylindrical ring 27 whose inner surface is made to suit the shape of the teeth 10 of the gear wheel which equals to approximately 2.6-2.8. 4 being treated.

Departure e the true e e l shepe of the The rings 27 has an open-end radial slot, wherein an teeth profile ansmg f p astle e eempen' insulating gasket 28 is placed, whereas the split ends of sated ether by a prehmmary alterenon of the teeth the ring 27 are made integral with current-carrying bus- Shape or by the Subsequent machmmg of the Surface bars 29 separated by the gasket 28 and communicating thereof the ring with the source of HF current through termiln some cases a satisfactory degree of accuracy may nals L and beattaiiied due to an appropriate selection of the hard- The ring 27 is Suspended through the bus bars emhg Parameters 30 Mounted in a groove 30 on the bed 24 are movable 1h eases WheTe subleeted t0 hardening by the P clamps 31 adapted to grip the ring 27 and thus fix it on Posed methed are teeth through whese Contact the bed 24 at the moment of application of technologifaces are passed HF induction hardening currents, the cal load. latter is Preferable t Occur P130r to teeth eurvmg; 1h Mounted on the inner surface of the ring 27 in ret eesethe e of the hardhess 9 the Surface spective longitudinal slots are straining elements 32 being hatdehed Wlthlh the Q t edlaeehey to the which are similar to the straining element 8 described layer helhg eold'peehed Wlthlh the Zone of h with reference to the device illustrated in FIG. 1. tooth fillet) must be so preset that the total hardness in passageways 33 are provided in the bulk f the ring the zone after tooth curving will vary uniformly for the 27 f cooling ]iquid tooth height- The clamping fixture 26 for securing the gear wheel The P t law of Variant?" of e hardness of a layer 4 being treated in the inductor ring 27 comprises stands hardened wlt 'lF Current, 1 5eX8f1S ed y known meth- 34 mounted on the bed and carrying a splined shaft 35 ods by appropriately selecting theinductor shape and hi h i d d f Setting h gear h l 4 b i the frequency of t e supply Current treated coaxially with the ring 27.

For gear teeth having a module of 10 mm Whose The extensions of the shaft 35 carry levers 36 interterial has an lmtlal hardn of 38 and the connected through a bar 37 which in turn is associated contact surfaces that have been induction hardened, i h h d i h feature a Rockwell hardness of HRC=4 850, the g The above-described device operates as follows.

Table l Nos. Description of parameter Designa- Unit of Parameter value tion measurenon-harcase-hardenhardened harment dened ed or hardenby known dcned teeth ed over entimethod by (marre tooth proposked H) space ed methat! (marked y) 1. Depth of hardened layer h mm 2.0 2.29 8.3 2. Depth of penetration of residual compressive stresses 8 mm 2.7 0.65 3.4 3. Maximum value of residual compressive stresses 0' kgf/cm 2400 9600 5600 4. Permissible fatigue stress of material at point of zero residual stresses (1,] kgf/cm 2600 2600 3600 3600 5. Permissible fatigue stress against surface fatigue fracture [i7,.,,,] kgf/cm 2600 3500 4900 7700 6. Degree of increase in breaking [cr,,,,, /[a,,,,,,],, l 1.35 1.90 2.80

strength Similarly to the afore-described process true for the device in FIG. 1, the gear wheel 4 being treated is set on the shaft 35 so as to accommodate it in the ring 27, and the straining elements 32 are appropriately set up, whereupon by turning the levers 36 the teeth 10 of the gear wheel 4 are withdrawn from the straining elements 32 for fear of a short circuit.

Then the HF hardening arrangement is put into operation, and a high-rate surface heating of the teeth 10 of the gear wheel 4 occurs. Upon heating the surface of the teeth 10 to a temperature exceeding the hardening one by 150250C, the HF hardening arrangement is turned out (for fear of breakdown and partial melting of the teeth) and the ring 27 is gripped by means of the clamps 31 movable from the hydraulic drive along the groove 30 of the bed 24 in the direction of the arrow P. The same hydraulic drive then causes the levers 36 to move in the direction of the arrow Q, thus effecting a turn of the gear wheel 4 with respect to the ring 27.

case of elastoplastic strain of the teeth due to their curving without induced heating.

In case of using heat treatment of gear teeth with the employment of the device shown in FIG. 5, upon sub- 5 jecting the teeth to elastoplastic bending (in keeping In the course of turning the straining elements 32 interact with the teeth 10 of the gear wheel 4, thus imparting plastic strain to the teeth 10 by curving these in the direction of application of the principal working load.

During the curving process, the surface of the teeth 10 of the gear wheel 4 being treated are spray-cooled with the aid of a sprinkler nozzle (not shown) located at butt ends of the ring 27.

As one of the cycles of hardening a group of teeth by the method according to the invention is finished, a next group of the teeth 10 of the gear wheel 4 must proceed to be hardened.

Upon completing the treatment, the hardened gear wheels may be subjected to low-temperature temper.

The angle of relative turn of the gear wheel 4 in the course of treatment, for instance, for gears having a module of 10 mm and the number of teeth 17 being equals 10-20".

In cases where the proposed method is used for treating the gear teeth made of carbon steels, or of casehardenable steels that have passed chemical treatment without hardening, the whole tooth space of the gear teeth being hardened is subjected to surface heating.

Thus, there results high hardness of teeth contact surfaces that ensures high contact strength thereof and, at the same time, an additional increase in the bending stength at the expense of thermomechanical treatment of the material superficial layers within the zone of the tooth fillet. The frequency of HF current for such a treatment is 250 kHz, the heating time being 1-2 sec.

In those cases where subjected to hardening are gear teeth that have preliminarily passed heat treatment to high degree of hardness, or a complete thermochemical treatment, the surface heating is applied only to the zone of the teeth fillets, which is attained due to an appropriate selection of the inductor supply current frequency. Current frequency in such cases falls within the range of 2.5-8 kHz and heating time equals 23 sec.

As a result of heating the elasticity limit of the material is more than twice as low in the layers subject to maximum strain load, which makes it possible to obtain plastic deformation of cold material of the teeth core and establish residual stresses of the same nature as in with the requirements of every particular production technology), the proposed method proceeds with the heating of the surface of the whole tooth space which ensures high contact strength of the teeth being treated due to their thermal hardening, as well as an increased bending strength at the expense of elastoplastic deformation of the tooth core and thermomechanical treatment of the superficial layer within the zone of the tooth fillet.

The specific power consumption required for the realization of the proposed method, equals O.9-l .5 kW/cm What we claim is:

l. A method of gear teeth hardening by bulk peening comprising in combination the steps of:

A. providing a toothed gear element having a principal working surface which normally receives the principal working load when the gear is operative; and a B. applying a uniform technological load across and along selected areas of the principal working surface of the teeth of the gear element and strengthening the teeth along their length by bending the teeth and bulk peening of the principal working surface within a zone of critical cross section in the direction of application of principal working load.

2. A method as claimed in claim 1, including the step of heating contact surfaces of the gear teeth prior to applying said technological load so that the total surface hardness of every tooth within a zone of adjacency of a hardened layer and a cold-peened layer varies uniformly along the tooth height.

3. A method as claimed in claim 1 comprising the successive steps of: heating the surface of the gear teeth; applying the technological load and subsequently cooling while the teeth are in a strained state.

4. The method as claimed in claim] comprising the successive steps of: applying the technical logical load to the teeth; heating the teeth surface and subsequent cooling while the teeth are in a strained state.

5. A device for carrying into effect a method of gear teeth hardening, comprising: a bed; a mechanism capable of establishing plastic strain and mounted on said bed, said mechanism being made as a ring which accommodates a gear wheel under treatment, said gear wheel being set concentrically with said ring; means for clamping the gear wheel being treated inside said ring; drive means for imparting relative motion of said mechanism and said gear wheel under treatment; said ring of said mechanism having at least one tooth-like projection disposed on its inner surface, which is adapted in the course of relative movements of said ring and the gear wheel being treated, to successively interact with the teeth of said gear wheel along the length of the teeth, thus curving the latter.

6. A device as claimed in claim 5, wherein each said tooth-like projection is made as an individual straining element disposed in a respective longitudinal slot in the inner surface of said ring and is capable of performing set-up motion square with the gear teeth surface being hardened.

an inductor; the inner surface of said ring being shaped to suit the shape of the teeth of said gear wheel being treated.

9. A device as claimed in claim 8, wherein said current-carrying bus-bars are made integral with said ring and serve for hanging the latter, while said bed of the device carries movable clamps mounted in a groove and adapted to fix said ring at the moment of application of the load setting up plastic strain.

Claims

1. A method of gear teeth hardening by bulk peening comprising in combination the steps of: A. providing a toothed gear element having a principal working surface which normally receives the principal working load when the gear is operative; and B. applying a uniform technological load across and along selected areas of the principal working surface of the teeth of the gear element and strengthening the teeth along their length by bending the teeth and bulk peening of the principal working surface within a zone of critical cross section in the direction of application of principal working load.

4. The method as claimed in claim 1 comprising the successive steps of: applying the technical logical load to the teeth; heating the teeth surface and subsequent cooling while the teeth are in a strained state.

7. A device as claimed in claim 6, wherein said straining element is built-up in length for treating said gear wheel having longitudinally curvilinear teeth, the length being composed of at least two individual portions that establish a curvilinear surface.

8. A device as claimed in claim 5, wherein said ring has a split end and is profided with a radial groove with an insulating gasket placed therein, while the split ends of said ring are inter-connected through current-carrying bus-bars with a H.F. current-source, all this being provided for said ring to perform the function of an inductor; the inner surface of said ring being shaped to suit the shape of the teeth of said gear wheel being treated.