GB2050908A - Method of and device for hardening machine elements having projections - Google Patents

Abstract

The element is treated by applying to the projection 1 a plastic bending force P1 and simultaneously a distributed load P2 that establishes plastic strain of the material shaft projections or gear teeth may be treated by tools 2, travelling wedges or rollers. A suitable roller 20 is shaped as shown or may be of composite form (Figure 16). <IMAGE>

Description

SPECIFICATION Method of and device for hardening machine elements having projections This invention relates generally to the hardening techniques of machine elements by modifying their stressed state and the physical characteristics of metal due to subjecting it to plastic strain, and has particular reference to a method of and device for hardening machine elements having projections.

The invention can find most utility when applied for hardening machine elements having projections and subject to alternating working load, such as gear teeth or turbine blades.

Said objects are accomplished in a method of hardening machine elements having projections, in particular those subject to reversible working load, residing in that the superficial layer of the projection is subjected to plastic bending strain applied thereto in the zone of dangerous section of said projection on the side of a bending force application, followed by treating said layer, wherein according to the invention said treatment of the superficial layer consists in applying a distributed load is imposed upon said layer to establish plastic strain of the material within the zone of dangerous section of the projection simultaneously with its being subjected to plastic bending strain.

Hardening by the proposed method makes it possible to increase the plasticity of the material by changing the state of stress on the surface of the component within the zone under treatment; as said hardening is carried out by volumetric plastic strain applied to the tensioned surface of the component, this provides for favourable anisotropy of the plastic properties of the component under treatment, adds to the durability of components operating under load of any reversibility, or those passing through any cycle of heat or thermochemical treatment. The above effect is attained due to a simultaneous increasing of the plasticity and hardness of the material of the superficial layer within the zone of dangerous section of the component, and in the area of elastoplastic bending.

This fact in combination with treating said layer by a distributed load establishing a hydrostatic pressure throughout the entire region of high tensionand-bending stresses, makes it possible to apply high bending forces and hence to carry out to a full extent a volumetric bending strain hardening and at the same time render it practicable in the case of hardening machine components subject to reversi bleworking load.

Extended range of machine components hardenable by the proposed method alongside with simplified hardening techniques and improved hardening stability owes its origin to the fact that no concurrent mechanical effect and heat treatment is produced on the same surface of the component profile. In addition, amenable to hardening according to the proposed method are such components as gears having relatively low tooth depth, featured by high requirements upon the durability and strength characteristics of the areas outside the zone of dangerous section, or those made of poorly hardenable materials exhibiting high stress concentration.

Further on, the method simplifies much the construction of the hardening devices and the hardening techniques, does not involve high skill on the part of the sttending personnel and require less amount thereof, reduces power consumption rates and requirements imposed upon safety engineering.

Realization of the method is effected with due account of the specific features of volumetric hardening encountered in treating various machine components.

It is expedient that, apart from the principal load, an additional load be applied, distributed over the end faces of the projection along the zone of dangerous section thereof.

Such an engineering solution provides for a hydrostatic pressure in the case of a transverse bending in the zone of hardening the material treated to a high degree of hardness and enables the plasticity of the material to be increased, thus rendering less possible the danger of its brittle failure in the course of treatment. In the case of a sufficiently high plasticity of the material in its initial state this feature makes it possible to increase durability and strength characteristics of the material, thus giving a possibility of increasing technological loads applied and residual stresses. As a result, the material is brought into a triaxial state of stress within the zones of the end faces being hardened, while its deformation along the geometric concentrator of the component is limited.

Thus, the method is instrumental in increasing plastic being strain of the material and the amount of residual stresses in the zone being hardened, reducing the sensitivity to changes of the hardening parameters and adding to the bearing ability of the components under treatment.

It is also expedient that the adjacent projections of the component under treatment which form a common gash, be subjected to volumetric plastic bending straining by concurrently applying loads in mutually opposite directions from the zone of their common gash.

Such a feature makes it possible to provide a state of stress of the component and residual effects symmetrical as to the nature of distribution with respect to the axis of the gash between the projections being hardened, which precludes any change in the direction of plastic straining and lowering the yield point of the material at the projection base (the so-called Bauschinger effect). In addition, the principal technological loads have unlike signs and thus compensate for each other. The resultant radial loads are also easy to compensate, for, e.g., when concurrently hardening diametrically opposite gashes.

High technological forces resulting from the bending of the projection being treated, practicable due to the absence of any heat treatment of the component and a corresponding lowering of the strength characteristics of the material thereof occurring in the course of treatment, are still more increasing from the distributed load applied within the zone of dangerous section of the projection, the effect of which owes its origin to technological shearing force, especialiy in the area below the dangerous section, thus causing high tension stresses in the zone of the pressure angles about JIx/2.

The above specific feature of the stressed state of the component under treatment enables one to efficiently harden also the zones located appreciably lower than the dangerous section of the projection, as well as to avoid stepped peening of the material at the gash bottom in the case of reversal of the strain sign (thus eliminating the effect of anisotropy of the material featured by the Bauschinger effect and the corresponding worsening of the strength properties of the component at the gash bottom).

Apart from eliminating the Bauschinger effect, the aforesaid flowsheet of the technological loading of the component under treatment, involving an additional shearing load and application of forces from a common gash, displaces the zone of maximum tension stresses towards the projection base, thus achieving an efficient hardening of the gash bottom which extends the range of machine elements that can be hardened by the proposed method, e.g., including those having a narrow rim, those featuring shrunk-fitted rim, or those of small diameter.

It is likewise expedient that the loaded portion of the surface of the component under treatment be subjected to a concurrent loading applied lengthwise the side projection surface.

Such a feature makes it possible to harden machine elements having intricately shaped profile of the projections (with the profile angle increasing towards the top), orthose having small profile angles. In this case tangential loads do not increase the radial component of a total load, while the tension stresses of the projections on the side of their common gash are increased and the compression stresses from the opposite side of the profile thereof are reduced, the distribution nature of residual stresses is improved and said stresses become higher in magnitude. Apart from that, even in the case of a widely differing profile angles of various portions of the surface under treatment, the absence of radial components of the tangential loads facilitates the regulation of the hardening parameters.

It is also expedient that the working surfaces of the projections be subjected to the effect of an additional load simultaneously with the application of the principal bending force on the same side of the profile and that said additional load be distributed over the projection in such a manner as to cause, along with the bending force applied thereto, stresses beyond the plastic limit of the material, said treatment being carried out in a lubricant medium.

It is due to the adopted procedure of load application in the zones outside the geometric concentrator, i.e., where the gradient of the bending stresses is much lower than in the concentrator, that such a solution makes it possible not only to increase hydrostatic pressure and plasticity of the material but also to markedly increase the amount of residual compression stresses, the depth of their seating and the hardness of the superficial layer, thus attaining the effectofvolumetric plastic strain and averting the danger of crack formation.At the same time favourable conditions are created, due to the effect of thermodynamic factors (temperature elevation at high pressure) in conjunction with plastic strain, for adsorption of active substances which conduces to still higher wear resistance and antijamming properties, improving running-in conditions and other adaptation properties, as well as for attaining higher quality of surface finish and endurance of hardening tools.

Such a treatment enables the machine component to be hardened outside the zone of the geometric concentrator and at the same time makes it possible to increase the magnitude of the bending force involved in the hardening process and the degree of hardness of the component within the zone of the geometric concentrator.

This, in turn, leads to a higher hardening effect of the component under treatment.

It is expedient that the base of the component adjacent to the zone of dangerous section of the projections, be subjected to the effect of compression load in the plane parallel to the dangerous section simultaneously with plastic strain applied to the projections.

Such a solution contributes to lower maximum tension stresses at the projection root and thereby is effective in increasing the technological load distributed over the active profile of the projection and, as a result, in attaining higher hardening effect and bearing ability of the component as a whole.

It is expedient that at the moment of straining the projections of a narrow-rim component the latter be compressed by applying a load distributed over the datum or locating surface until said rim acquires a required shape and is brought into a plastic-strained state so as to simulate the effect of the operating fit thereon.

Such a solution makes possible a preliminary simulation (in the case of volumetric bending strain applied to the projections) of the stress field characteristic of a heavy-drive fit. Superimposition of the two states of stress (resulting from bending and compression) occurring in subsequent forcing into a carrier component contributes to the reproduction of a symmetrical residual stress diagram characteristic of the hardened projections and showing compression stresses seated on both sides of the dangerous section ofthe projection. In addition, compressing the projection root at the moment of its bending adds to the normal component of the bending force involved in the hardening process, which results in a larger depth and higher degree of mechanical skin hardening of the active projection areas.

It is also expedient that while treating the projection of a machine element, additional shearing loads be applied to said projection in the hardening zone in the direction opposite to the shear produced by the load exerting the surface plastic strain thereon.

Such a solution enables hardening machine elements having long-sized projections featuring a long arm of bending force application, with the stresses state of the component remaining unaffected as all the advantageous features of volumetric plastic bending strain are fully realized due to compensat ing load application.

It is expedient that the base of the component adjacent to the zone of critical section be subjected to twisting simultaneously with straining the projections thereof.

Such a solution is instrumental in strain hardening by establishing a residual stress field of a preset depth and direction in the bulk of the component, adds to the load bearing ability thereof when operating under diverse loads which, in turn, contributes to higher durability of the component under treatment, e.g., when hardening such machine components as gears, or some revolving parts, such as shafts, or turbine blades.

Twisting strain applied to the component establishes plastic anisotropy of the material of the projection thereof, which agrees well with the potentialities of a directional bending strain.

It is expedient that the projection of a machine element be strained with a load uniformly distributed over the surface thereof through the effect of a compressed medium upon the surfaces of the adjacent projections which define the gas therebetween, and upon the faces thereof.

Such a solution provides for strictly identical loading conditions of all the projections of the component, thus conducing to high stability of the hardening conditions, minimizing losses of technological load applied, reduces the wear, whereby the quality of the product is enhanced and the service durability of the equipment used is increased.

The specific object of the present invention is accomplished also in a device for carrying into effect the method of hardening machine elements having projections, said device being in effect a roller with a formed working surface having a cross-sectional shape of a projection or tooth whose face is defined by the transition curves of two adjacent projections or teeth of the gear being treated, while the flank is described by the curves corresponding to the face profile of the projections or teeth of the gear being treated, wherein according to the invention the flank of the projection or tooth has a cross-sectional shape of a wedge whose angle of taper is equal to the angle bounded by the tangent lines to the modified profile of two adjacent projections or teeth of the gear being treated.

Such a constructional arrangement allows the projections of a machine component to be subjected to volumetric plastic bending strain with a simultaneous plastic straining of the projection surfaces within the zone of dangerous section thereof which contributes to higher strength characteristics of the material under treatment.

High specific pressure values developed at the points of contact of the roller with the tips of the projections or teeth being hardened results in modifying the face profile thereof.

It is expedient that the roller be provided with a support to which inside plates, side plates and a locking plate be held, said inside plates being made as spring elements spaced apart from each other and from the support with a certain clearance, whereas the side plates and the locking plate are in contact with the inside plates and are so shaped as to suit the surface of the adjacent projections of the component being hardened, such as a gear.

Such a constructional arrangement allows of performing the entire scope of technological operations involved in volumetric plastic bending strain and at the same time affords a possibility of additionally increasing the hardening effect due to utilization of the adaptability of both the construction of the device itself and of the material being hardened. Application of inside plates featuring mechanical characteristics similar to those of spring elements, enables one to apply technological loads involved in the strain hardening process within any predetermined accuracy limits and to make use of the damping properties of the device which allow for also the characteristics of the component being hardened, such asyieldability, profile machining accuracy, surface hardness.Moreover, the proposed construction of the hardening device enables the latter to finely respond to any change in the aforementioned parameters by virtue of the adaptability of the device itself.

It is expedient that with a view to hardening machine elements having projections, featuring different yieldability and adaptation properties, the side plates of the device be made as, say, disk springs.

Such a constructional arrangement extends the scope of applications of the device owing to changed power characteristics of the elements thereof and by virtue of introducing non-linear rigidity characteristics.

It is likewise expedient that the support be provided with ports for lubricant to feed to the places where the inside plates are fitted.

Such a constructional arrangement allows of feeding various lubricants to the plates where the plates contact each other, which materially changes the coefficient of friction and thereby the adaptability of the device itself, as well as enables said adaptabilityto be regulated within a broad range depending upon the requirements imposed the hardening conditions. The result is a higher stability of the strain hardening process.

Given below are some specific exemplary embodiments of the hardening conditions and parameters of some techniques involved in the proposed method of hardening machine components having projections.

Example 1 The example considers an embodiment of the proposed method when applied to a machine element having a single projection (Figure 1).

The component to be hardened is in fact that of the speed reducer of a mixed-feed pelleter plant, viz., a shaft having a projection 1 with a height H = 100 mm and a thickness S = 22 mm with a geometric concentrator shaped as a circular arc with a radius of 40 mm, made from Cr-Ni alloyed steel of the following chemical percentage composition: C = 0.45; Si = 0.18; Mn = 0.60; Ni = 1.15; P S 0.035; S S 0.035, featuring a yield point at 58 kgf/mm2.The abovesaid shaft is subjected to volumetric plastic straining by a force P1 = 70 kgf/mm applied to the surface "ab" of the projection profile to establish stresses above the yield point of the material within the zone of dangerous section "ac", and concurrently to the effect of a distributed force applied within the zone of dangerous section "ac" by virtue of a force P2 = 80 kgf/mm imposed by a press tool 2, which establishes normal loads up to 30 kgf/mm2, so as to cause a triaxial state of stress on the component surface, the effect of hydrostatic pressure, increased plasticity of the component within the zone of pressure exerted by the press tool and decreased plasticity on the opposite side of the projection.

The result is the onset of a specific anisotropy of the plastic properties of the component due to volumetric plastic straining which is instrumental in obtaining a triplex diagram of residual stresses ' as well as a great deal of reversed residual stresses within the peripheral dangerous section zones.

Upon relieving the force P, and discontinuing the action of the press tool 2 the projection 1 of the component is subjected to voiumetric plastic straining by a force P; = 80 kgf/mm applied on the side "cd" of the profile to set up a hyper-elastic stress (beyond the yield point of the material), and simultaneously to the effect of a distributed load applied within the zone of dangerous section "ac" by virtue of a pressure produced by the press tool under a force P2 = 80 kgf/mm.As a result, volumetric plastic strain is exerted only on the side "cd", thus rendering the previously obtained triplex diagram of residual stresses vO stronger, said diagram demonstrating the presence of considerable compression stresses within the zone of peripheral areas of the critical section.

The method is carried into effect by resorting to versatile equipment and machinery, such as hydraulic or mechanical presses and punches.

The treatment according to the herein-proposed method results in a more than 1.5-time increase in the load bearing ability of the shaft as for bending.

Example 2 The example considers an embodiment ofthe proposed method when applied to a thin machine component having end faces (Figure 2).

The component to be hardened is in fact the speed reducer axle of a mixed-feed pelleter plant, made from steel with a yield point at 58 kgf/mm2; the abovesaid axle is subjected to the effect of a bending force P1 =80 kgf/mm which causes plastic strain of the material within the zone of the geometric concentrator (a circular arc of 20-mm radius). Simultaneously, the tension-stressed side of the projection 1 having a height H = 158 mm, a thickness S = 34 mm and a length L = 100 mm which is being plastically strained, is acted upon by a press tool 2 under a force P2 = 300 kgf/mm, while end faces of said projection 1 is acted upon by press tools 3 under a force P3 = 120 kgf/mm2, thus establishing a stress within the zones of plastic straining of the material.

To carry said method into effect a variety of devices and machines are used, such as burnishing machines with rollers having a diameter nearly equal to half the width oftheworkpiece being treated and with rotary stops arranged coaxially with said roller.

Thus, no biaxial state of stress occurs on the end faces of the above-mentioned machine elements when the latter are being hardened (i.e., the surface thereof free from external loads features both normal stress aN and tangential stress aT equal to zero) which otherwise would result in brittle failure of dead-hardened components, or in formation of bulged material on the end faces of low-hardness components and hence in reduced residual stresses and weakening of the component in such zone.

As a result of treatment by the proposed method the durability of the thus-hardened gear speed reducer axle gets 2.2 times as high.

Example 3 Now let us consider an application of the proposed method to a machine component featuring alternative projections and gashes (Figure 3).

A driven gear 4 of the diesel locomotive traction gearing having the following parameters: module m = 10 mm; number of teeth Z = 75; rim (face) width b = 140 mm; basic rack correction factor X = 0.437; basic rack with a profile angle a = 20 ; coefficient of tooth rounding-off radius of tool basic rack, 0.4; tooth addendum coefficient, 1.25, made of steel with a yield point at 58 kgf/mm2, its teeth being subjected to high-frequency sector hardening with an interruption ofthe hardened layer.

Adjacent projections (teeth) 5 and 6 of the gear4 are subjected to a concurrent action of the following forces applied from the zone of a common gash thereof: bending force P1 = 300 kgf/mm, and a pressure exerted by the press tool 2 under radial force P2 causing the effect of distributed forces within the zone of dangerous section (located at the initial point of the active profile), and within the zone of maximum tension stresses (located at tooth bottom), equal respectively to 30 kgf/mm2 and 75 kgf/m m2.

Next similartreatment is given to the adjacent projections (teeth) 5 and 7 that define an adjacent gash, by the press tool 2, the forces P1, P2 applied from the common gash zone corresponding to the values mentioned above.

As a result of treatment by the proposed method the load bearing capacity of adjacent projections (teeth) is increased by more than 50 per cent which is not inferior to the results obtained for singleprojection machine elements.

Example 4 The embodiment of the proposed method refers to intricately shaped machine components (Figure 4).

The component being hardened is the spur gear 4 of the diesel locomotive traction gearing made of steel having a yield point at 58 kgf/mm2; the gear features its basic rack with a profile angle a = 20O; module m = 10 mm; numberofteeth Z = 75; basic rack correction factor X = 0.437; coefficient of tooth rounding-off radius 9f tool basic rack, 0.4; tooth addendum coefficient, 1.25.

Load applicator 8 shaped as a wedge featuring a profile angle' of the active portions equal to 100, is pulled along the adjacent teeth of a common gash which are lubricated with liquid hypoid oil, in such a manner that the side surfaces of said load applicator be in contact with the gear at the tops of the adjacent teeth within the transition zones thereof, and at the gash bottom, so as to establish a normal force P4 = 600 kgf/mm distributed across the rim width, a distributed normal load of a 60 kgf/mm2 intensity and tangential forces applied to the contacting surfaces of the gear teeth, equal to 460 kgf/mm and 100 kgf/mm, respectively.

Inasmuch as no tangential forces are applied in a radial direction, the compression force P5 which attenuates the effect of the bending force P1, does not rise, whereby the state of stress of the gear teeth is improved during teeth hardening.

Estimations make it evident that, as a result of treatment by the proposed method, residual compression stresses and the region of their seating are much increased, the degree of their growth depending mostly upon the profile angle in the zone of the geometric stress concentrator and deformability of the material. Thus, for instance, in the case of gear teeth with modified flank profile, wherein the above angle is still more reduced the qualitative characteristics of three-dimensional strain hardening are basically altered due to application of a tangential force directed lengthwise the tooth.

Example 5 This example deals with an embodiment of the proposed method in the case of a distributed load (Figure 5) The gear 4 is held in position, whereupon it is acted upon by a bending force P1 applied on the side "ab" of the profile of the tooth 5, said force exerting a normal stress GN on the surface of the tooth 5 and plastic strain on the transition section "ac" within the zone of the geometric stress concentrator. At the same time the active surface of the tooth 5 is additionally acted upon by a load q distributed over the active portion of the tooth profile in such a way that, acting in combination with the aforesaid bending force it establishes hyperelastic stresses in the gear teeth. Prior to such a treatment the active areas of the gear teeth are coated with a layer of molybdenum disulphide.

As a result of treatment by the proposed method a considerable increase in the contact strength and total load bearing capacity of the gears is achieved.

The resultant technico-economical effect in this case consists in a several-time gain in the durability of gears, or in a 10 to 20 per cent lower overall size thereof.

Example 6 Now let us consider an exemplary embodiment of the proposed method as illustrated in Figure 6. The machine component under treatment is a gear rack featuring a module m = 10 mm, made of steel with a yield point at 58 kgf/mm2 and having the projection 1. The abovesaid gear rack is subjected to compression by press tools 3 which exert a force of 1000 kgf/mm upon the side walls (H = 25 mm) applied in the direction facing the arrows shown in Figure 6; at the same time the press tool 2 is acted upon by a force P4 which causes a bending force P1 = 400 kgf/mm applied to the projection 1, and loads of a 30 kgf/mm2 intensity distributed over the active portions "cd" and "ef" of the profiles of the projection 1.

As the projections 1 rest upon a compressed base maximum tension stresses occurring in the zone of the stress concentrator "de" are reduced by approximately 20 kgf/mm2, and the bending force P, is thus increased. This leads also to higher bending stresses in the area of the active profiles, and the effect of hardening the rack tooth profiles is enhanced.

As a result of treatment by the proposed method a technological effect is attained, residing in that the durability of the components is three times as high.

Example 7 Now let us consider a" exemplary embodiment of the proposed method when applied to thin-rim machine components (Figures 7, 8, 9). Used as an object of treatment is an epicyclic ring gear 9 of the final drive reducer of a grain harvester, having module m = 4 mm; number of teeth Z = 69; face width b = 40 mm; rim thickness, 14.6 mm; cylinder fitting diameter, 315+ 305mm, made of normalized steel featuring Brinell hardness number HB = 210 and the following chemical percentage composition: C = 0.18; Mn = 0.85; Cr = 1.1; Ti = 0.1.

The teeth of the gear 9 are subjected to plastic strain by virtue of the load applicators 8 (Figure 8) whose profile ("abc") is illustrated in Figure 9. The amount of deflection of the line of the profile modification ("bc") at the tip of the tooth 5 is 0.2 mm.

According to the proposed method the epicyclic ring gear 9 is exposed to a compression force equal to 80 tf (correspnding to a load of about 4.1 kgf/mm2) distributed over the locating surface thereof. This is instrumental in attaining a true shape of the locating cylinder within the margin of tolerance of dia.

31 5++oo:olcooo. The induced shrinkage of the latter under the effect of said force simulates a stress-deformed state of the gear rim corresponding to a heavy drive fit of the gear 9 in the housing of the reduction unit.

The load applicators 8 placed in three equidistantly spaced gashes of the gear 9 with an interference of ca. 0.07 mm, are traversed along the gashes to cause plastic bending strain of the teeth 5 by virtue of a resultant force equal to 10 tf, accompanied by a simultaneous application of a load q = 30 to 35 kgf/m m2 distributed over the areas within the critical section zone (transition curves "ab"), are over the side faces of the teeth 5. Thus, the teeth 5 are plastic strained along the entire length until the position corresponding to the modified profile "bc".

The above process is applied repeatedly to all the remaining gashes of the gear, while returning the teeth 5 to the initial position. Once all the teeth have passed the treatment the load applicators are brought out of the gashes and the force distributed over the locating surface is relieved.

As a result of treatment of thin-rim components, such as gear toothings, the rigidity of the component is increased at the moment of hardening and the state of stress-deformation is obtained which corres ponds to the actual operating conditions. Thus, there are reproduced exactly the predetermined geometric and strength characteristics of a hardened gear toothing after its having been forced into the carrier part. The load bearing capacity of the epicyclic ring gear of the final drive reducer of a grain harvester is increased by more than 1.8 times, while kinematic error is minimized.

Example 8 Let us consider an exemplary embodiment of the proposed method as shown in Figure 10. The machine component to be hardened is the speed reducer axle of a mixed-feed pelleter plant, made of steel and having long-sized projection 1 (H = 158 mm) 34 mm thick. The abovesaid component is loaded by a bending force P1 = 300 kgf/mm applied at the tip of the projection 1, and at the same time is acted upon by a load q = 30 kgf/mm2 distributed within the zone of the geometric stress concentrator "cd" and applied on the tensioned side of the component, while applied to the opposite side thereof is a force of 660 kgf/mm, said force being imposed upon an area above the zone of the geometric stress concentrator "ef" to compensate for an additional shearing stress in the critical section "ab" resulting from the distributed load q.

Thus, the state of stress of the component is not distorted by an additional shearing stress, and the advantageous features of the bending strain hardening are realized.

The technico-economical effect resulting from application of the proposed method resides in an increased hardening effect and eventualiy in the durability of machine components featuring long arms of bending force application increased by about 1.3 times.

Example 9 Let us consider an exemplary embodiment of the proposed method when applied in the case of a concurrent bending and twisting strain (Figure 11).

Subjected to the treatment by the proposed method is the driven gear 4 of the diesel locomotive traction gearing, made of normalized and thermally refined steel forging, having the following strength characteristics: Brinell hardness number HB = 255 to 311, ultimate strength OB = 105 kgf/mm2; and geometric characteristics: number of teeth Z = 71: module m = 10 mm; tooth face width b = 140 mm.

Treating with a three-dimensional bending strain and a concurrent effect of a force distributed over the zone of teeth transition zone is carried out by a roller-type tool 120 mm in diameter by applying a technological force of 20x103 kgf and a simultaneous straining by twisting the geartoothing by two opposite moments (M) developed bya power hydraulic actuator, equal to 220 kgf.

As a result of treatment a technical effect is obtained from realization of the proposed method, residing in that the load bearing capacity of the treated machine components are increased 1.2 to 1.3 times as compared to methods involving the bending strain alone, and the durability thereof is 6 to 10 times as high; in addition, the range of application of the method is extended to various types of machine components.

Example 10 Let us consider an exemplary embodiment of the proposed method in the case of strain hardening of, say, a gear (Figures 12, 13).

The gear 4 is fixed stationary and the space of one of the gashes between the teeth 5 and 6 is hermetically sealed so that the surfaces "abc" and "cde" of the teeth 5 and 6 (Figure 12) facing inward the gash, and the faces "fce" (Figure 13) thereof close to the zone of stress concentration (zone of transition curve) remain vacant. Next fed to the thusestablished closed space is a fluid, such as liquid compressed to a hydrostatic pressure whose value depends upon the strength and geometric parameters of the component being hardened; said compressed liquid acts upon the free surfaces of the component, thus loading them with a distributed force.In addition, concurrently with the surface loading, plastic bending strain of the teeth 5 and 6 occurs owing to the bending component of the resultant force, on each of the teeth when acted upon unidirectionally by a uniformly distributed hydrostatic pressure.

The liquid may contain adsorption-active substances, such as molybdenum disulphide.

For instance, subjected to straining hardening was double-tooth specimens measuring 64x47x28 mm cut off from the spur gear of the Diesel locomotive traction gearing, having a module m = 11 mm, number of teeth Z = 68 and made of steel heat treated to a Brinell hardness number of from 311 to 255.

The specimens were milled on the fitting areas thereof, while their faces were additionally ground to size 28-0.05.

Strain hardening was performed on a plant based upon a 50-tf capacity press by loading the specimens with a normal force of a compressed fluid uniformly distributed over the teeth surfaces facing inward the gash and the teeth faces close to the stress concentration zone (zone of transition curves). The amount of hydrostatic pressure of a hydraulic bed employed as a compressed fluid was equal to 3.3 kbar which resulted in residual tooth displacement equal to 0.45 mm at the tip thereof, as well as in bulged-in material for a depth of up to 0.35 mm within the zone of the transition curves of said teeth.

As a result of treatment by the proposed method a technico-economical effect is attained, consisting in increased strength characteristics of the component under treatment, including contact and bending strength and score-resistance, a total increase of load bearing capacity by 35-40 per cent, simplified hardening techniques and extended range of machine components suitable for strain hardening.

Besides, a more accurate proportioning of technological loads contributing to high-stability hardening, is also made possible.

Furthermore, the use of a liquid possessing adsorption activity enables protective or antifriction superficial layers to be established in the components being treated, thereby adding to the perform ance quality thereof.

The above-discussed examples evidence that strain hardening of machine components having projections by the proposed method makes it possible to gain a number of advantages over the now extensively applicable principal types of surface hardening by virtue of heat treatment or surface plastic straining, or a variety of combination thereof.

The proposed method is not subject to disadvantages inherent in many heat-treatment methods, such as toxicity, high labour consumption rate, and bulkiness.

In order that the essence of the present invention may be readily understood given below are some specific practical embodiments of a method of hardening machine elements having projections and subject in particular to reversible working load, as carried into effect by a device, by way of illustration with reference to the accompanying drawings, wherein: Figures 1 to 13 illustrate diverse techniques of hardening machine elements having projecions, according to the invention; Figure 14 illustrates a schematic diagram of a plant making use of the device for carrying into effect the method of hardening machine elements having projections; Figure 15 illustrates a cross-sectional view of the device being described while in working position; Figure 16 illustrates a sectional view of one of the practicable embodiments of the device while in working position; and Figure 17 is a view of the device of Figure 16 while inoperative.

Figure 14 illustrates schematically an embodiment of the plant that makes use of the proposed device for hardening gear teeth.

A cast bed 10 accomodates a vertical reciprocating motion cylinder 11, the top portion of said cylinder carrying an arbor 12 on which a gear 14 being treated is set (said gear being indicated in Figure 14 with a dotted line. The gear 14 is fixed in position with respect to the hydraulic cylinder 11 by a hold-down strip 13 and a nut 14. A rod 14 of the hydraulic cylinder 11 is held to the bottom of the bed 10 and is made as two concentric tubes 16 and 17 one of which communicates with the top, and the other, with the bottom chamber of the hydraulic cylinder 11. Such an arrangement enables the hydraulic cylinder 11, the arbor 12 and the gear 4 under treatment to perform reciprocating motion and concurrently rotate about the rod 15 in the direction facing the arrow M indicated in the drawing.

Located on brackets 18 in the top portion of the bed 10 on both sides of the gear 4 are hydraulic cylinders actuating the hold-down motion of straining rollers, which are loosely set on transverse pivots inside cylindrical cartridges 21. Each of the cylindrical cartridges 21 is mounted in ball-bearing splines 22 and is linked to a rod 23 of the hold-down hydraulic cylinder 19 through a pillow bearing 24 so as to be free to turn or perform translatory motion.

The device illustrated in Figure 15 is essentially the roller 20 (shown in the direction of the arrow A in Figure 14), having a cross-sectional shape of a projection whose root is shaped as a wedge 25 conjugated with a top 26. Flanks "cd" and "c'd"' of the wedge 25 are defined by the modification lines of the tops of the two adjacent teeth 5 and 6 of a modified profile defined by parameters h, A a, and 2 a M which are respectively the modification length of the profile of the projection top and the angle of the wedge tapering equal to the angle bounded by the tangent lines to the modified profile of the tops of the teeth 5 and 6.Active portions "ab" and "a'b"' of the top 26 are described by the transition curves of the profiles of the teeth 5 and 6 and are conjugated with the portions "dc" and "d'c"' of the wedge 25 through curves "bc" and "b'c"' enveloping the profile of said teeth.

Another embodiment of the device for hardening machine components having projections (Figures 16, 17) is in fact a construction incorporating a set of plates, comprising power-exerting inside plates 27 made as compression spring elements and mounted with specified clearances "K" with respect to a common support 28 and to each other, outside straining side plates 29 and a locking plate 30 shaped so as to suit the profile of the surface of the teeth 5 and 6 of the gear 4 under treatment, and resting upon the inside plates 27.

To hold the set of the plates to the common support 28 use may be made of any known-type retainers that shall not restrict said plates from axial movement when in free state.

In the course of strain hardening the amount of the clearance "K" may vary within a range of O S K S Kmax, where Kmax is the clearance in a free state, while 0 may occur only with spring element in an extreme position, when maximum compressed and traversing under the effect of maximum internal loads.

Knowing the power characteristics of the spring element, one can find the amount of the clearance "K" by calculation made, say, according to standard techniques adopted for springs.

Whenever necessary, in the case of rollers having non-linear straining characteristics, use may be made of an embodiment of the straining plates as disk spring elements.

Holes 31 for lubricant to feed are provided at the places of installation of the inside plates 27 on the common support 28.

The plant (Figure 14) operates as follows. The gear 4 under treatment is held on the arbor 12 by means of the hold-down strip 13 and the nut 14.

The roller 20 (Figures 15,16) is placed into a gash between the two adjacent teeth 5 and 6 of the gear 4 and is acted upon by a predetermined force which causes bending and compression plastic strain.

When subjected to strain hardening the gear4 performs reciprocating motion along with the hydraulic cylinder 11. At the same time the hold-down hydraulic cylinders 19 impart some force to the straining rollers depending upon the straining conditions of the teeth 5 and 6. The rollers 20 travel along the gashes of the gear 4, thus straining the teeth 5 and 6 defining said gash, to a required degree of hardening. At the end of each double stroke whose length exceeds the width of toothing, the gear 4 is turned, say, through an angular pitch, whereupon a next pair of teeth is subjected to straining, and so on.

Once all the teeth of the gear 4 have passed the strain hardening treatment the drive of the operative units of the device is disconnected, and the treated gear is removed.

The practical effect gained from the application of the proposed method and the devices carrying it into effect, is made up by the following characteristics: - higher service durability; - higher load bearing capacity and hence higher power and load carrying capacity of machines; - lower metal consumption rate and overall size of machines with remaining equal strength; -reduced annual costs of repairs.

The method well agrees with various technological flow-sheets involved in treatment machine elements and enables standard equipmentto be widely used, whereas simplicity of realization of the method provides a possibility of a complete automation and monitoring of the production process.

Claims (16)

1. A method of hardening machine elements having projections, in particular those subject to reversible working load, residing in that a plastic bending strain is exerted on the superficial layer of the projection within the zone of the dangerous section thereof on the side of a bending force application, followed by an appropriate treatment of said layer of imposing a distributed load thereupon to establish plastic strain of the material within the zone of the dangerous section of the projection, simultaneously with its being subjected to plastic bending strain.

2. A method as claimed in Claim 1, wherein an additional load is imposed, apart from the principal one, upon the projection, said load being distributed over the end faces of said projection along the zone of the dangerous section thereof.

3. A method as claimed in Claim 1, wherein the adjacent projections of a machine element which define a common gash, are subjected to a volumetric plastic strain by concurrently applying loads from the zone of the common gash thereof, said loads being applied in the mutually opposite directions.

4. A method as claimed in Claim 1, wherein an additional load is imposed upon the loaded portion of the area of the machine element being hardened, said additional load being applied lengthwise the side surface of the projection.

5. A method as claimed in Claim 1, wherein the working surfaces of the projections are subjected to the effect of an additional load applied concurrently with the principal bending load on the same side of the profile and so distributed as to exert, in combination with the bending load, a strain thereon lying beyond the yield point of the material involved, the treatment being carried out in a lubricant medium.

6. A method as claimed in Claim 1, wherein the base of the machine element adjacent to the zone of the dangerous section of the projection, is subjected to a compression load applied in the plane parallel to said dangerous section, concurrently with exerting plastic strain on the projections.

7. A method as claimed in Claims 1 and 5, wherein at the moment of straining the projections, a narrow-rim component is compressed by applying a load distributed over the datum or locating surface thereof until said rim acquires a required shape and is brought into a plastic-strained state so as to simulate the effect of the operating fit thereon.

8. A method as claimed in Claim 1, wherein during the process of hardening the projection of a machine element, shearing loads are applied to said projection in the direction opposite to the shear produced by a stress establishing the superficial plastic strain.

9. A method as claimed in Claim 1, wherein the base of the machine element adjacent to the zone of dangerous section, is subjected to twisting concur rentlywith straining the projections of said element.

10. A method as claimed in Claims 1,2 and 6, wherein the above-said straining is carried out by applying a load uniformly distributed over the surface of the projections through the effect of a compressed medium upon the surfaces of the adjacent projections which define the gash therebetween, and upon the faces thereof.

11. A device for hardening machine elements having projections, such as gear teeth, carrying into effect the method as claimed in Claim 1, said device being in effect a roller with a shaped working surface having a cross-sectional shape of a projection or tooth whose face is formed by the transition curves of two adjacent projections or teeth of the gear being treated, and the flank is described by the curves corresponding to the tooth face profile of the gear being treated; said flank of the projection or tooth having a cross-sectional shape of a wedge whose angle of taper is equal to the angle made up by the tangent lines to the modified profile of two adjacent projections or teeth of the gear being treated.

12. A device as claimed in Claim 11, wherein the roller has a support to which inside plates, side plates and a locking plate are held, said inside plates being made as spring elements spaced apart with a clearance from each other and from the support, whereas the side plates and the locking plate are in contact with the inside plates and are so shaped as to suit the surface of the projections or teeth of the gear being treated.

13. A device as claimed in Claim 12, wherein the side plates are shaped as disk springs.

14. A device as claimed in Claim 12, wherein the support has ports for lubricant to feed to the fitting places of the inside plates.

15. A method as claimed in any of the preceding Claims 1 to 10 substantially as herinbefore described.

16. A device as claimed in any of the preceding Clams 11 to 14 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.