NL2031502B1 - Method for composite surface strengthening treatment of gears - Google Patents

Abstract

Disclosed is a method for composite surface strengthening of gears, which belongs to the technical field of strengthening the surface of gears. The method comprises the following steps: (1) machining a surface structure on the surface of gears, wherein the surface structure is a concave - convex texture with a peak - valley height difference of 8 - 35 microns, and performing heating treatment; (2) shot peening treatment: extruding the concave - convex texture to generate shear deformation, so that the height difference between the peaks and valleys of the concave - convex texture is 2 - 6 microns; (3) pre - treat the gear obtained in step (2); (4) the pre - treated gear is phosphatized with manganese phosphating solution, and manganese phosphate conversion coating is obtained on the surface of the gear, thus obtaining the gear with composite strengthening on the surface, significantly improving the contact fatigue strength and bending fatigue strength of the gear, giving full play to the performance of the gear, prolonging its service life, reducing the strengthening treatment time of the gear, improving the strengthening treatment efficiency of the gear, reducing the cost, and being suitable for industrial production.

Description

Method for composite surface strengthening treatment of gears

TECHNICAL FIELD The invention relates to the technical field of gear surface strengthening treatment, in particular to a method for composite surface strengthening treatment of gear.

BACKGROUND Gears are wheel - shaped mechanical parts that rely on the meshing of teeth to transmit torque. By driving with other toothed mechanical parts (such as another gear, rack and worm), the gear can realize the functions of changing speed and torque, changing movement direction and changing movement form. Its failure mode is mainly tooth surface wear failure, and the main forms of wear failure are tooth surface matrix wear and tooth thickness reduction, which eventually leads to transmission failure and gear service life suspension. Shot peening technology is a cold working technology of metal surface, which is usually adopted by gear manufacturers as a technological means to increase the fatigue strength of gears. At present, the surface strengthening method of axle spiral bevel gear is mainly conventional shot peening, mainly centrifugal shot peening. Conventional shot peening is a full - tooth - surface shot peening. On the one hand, there is a waste of manpower and material resources; on the other hand, because of the large spray surface, it is easy to cause uneven stress distribution and problems of overshot and undershot. Moreover, the stress magnitude of each gear tooth surface is different. Using conventional shot peening makes the actual stress situation of each gear tooth surface not corresponding, that is, the gear surface performance can't be consistent, which easily leads to the problem of crack initiation, which will further affect the improvement of fatigue resistance and wear resistance of the gear tooth surface. Secondly, the conventional shot peening method has limited improvement on mechanical properties such as residual compressive stress, hardness, bending fatigue strength and contact fatigue strength of gears. In order to reduce the roughness of gear tooth surface and improve the precision of tooth surface and tooth profile, the existing processing technology is to grind the gear after shot peening, but grinding the gear will remove the residual compressive stress layer formed by shot peening. In order to meet the requirements of tooth profile precision, the wear amount can only be increased in the production process, and the effect of shot peening is sacrificed. To sum up, the strengthening effect that the existing shot peening technology can achieve is limited, and the potential of gears cannot be fully exerted.

SUMMARY The purpose of the invention is to provide a method for gear composite surface strengthening treatment method, which combines shot peening technology and manganese phosphate conversion coating technology to carry out surface treatment on gears, significantly improves the contact fatigue strength and bending fatigue strength of gears, gives full play to the performance of gears to a greater extent, improves the service life of gears, reduces the strengthening treatment time of gears, improves the strengthening treatment efficiency of gears, reduces the cost, is suitable for industrial production and has a good application prospect.

To achieve the above objective, the present invention provides the following scheme: the invention provides a method for gear composite surface strengthening treatment method, which comprises the following steps: (1) machining a surface structure on the gear surface, wherein the surface structure is a concave - convex texture with a peak - valley height difference of 8 - 35 microns, and heating to change the plastic structure of the gear tooth surface; (2) shot peening treatment, namely extruding the concave - convex texture to generate shear deformation, so that the peak - valley height difference of the concave - convex texture is 2 - 6 microns; (3) pre - treat the gear obtained in step (2); (4) phosphating the pre - treated gear with manganese phosphating solution to obtain manganese phosphate conversion coating on the surface of the gear, thus obtaining the gear with composite strengthened surface.

Further, the heating temperature in step (1) is 110 - 130°C.

Furthermore, in step (2), the shot peening intensity is controlled to be 0.2 - 0.5 A, the coverage rate is 180% - 200%, and the shot peening time is 70 - 80 s. If the shot peening time is too long, the gear surface roughness will be increased, the shot waste will be caused, and the production cost will be increased. If the shot peening time is insufficient, the shot peening coverage will be insufficient and the strengthening effect will be weakened.

Further, in step (2), the concave - convex texture is extruded by the shot sprayed by the shot peening machine.

Further, the diameter of the shot is 0.8 - 1.3 mm, and the hardness HRC is 45 - 55.

Further, the pre - treatment in step (3) is to treat the gear surface with weakly alkaline degreaser at 70 - 80°C for 2 - 3 min.

Furthermore, the manganese phosphating solution in step (4) has an acid ratio of 5.8 - 6.0, contains Fe?*, Mn?*, Ni?*, PO4?: and NO; ", and the Fe?" content is < 2g/l.

Further, the phosphating treatment time in step (4) is 10 - 15 min and the temperature is 80 - 90°C.

By adopting manganese phosphate conversion coating treatment process, superfine manganese phosphate conversion coating is produced on the surface of composite shot peening gear. The phosphating grain size of the coating is 0.2 - 0.5 um, and a soft layer of 5 -8 pm is produced on the tooth surface, which can fill up the "surface pits" of the tooth surface caused by shot peening, effectively reduce the friction coefficient of the friction pair surface and improve the contact stress of the meshing tooth surface, and effectively inhibit the deterioration of tooth surface fatigue pitting and peeling caused by composite shot peening. Manganese phosphate conversion coating has good running - in performance at the initial stage of running - in, which can effectively reduce the surface roughness of tooth surface and improve the meshing quality.

The invention discloses the following technical effects: according to the invention, the surface structure is processed before the shot peening treatment, and only one shot peening treatment is needed; meanwhile, after the shot peening treatment is adopted, a larger and deeper residual compressive stress layer and residual compressive stress with pre-set directionality can be generated on the gear surface, so that the residual compressive stress value on the outermost surface can be increased, thereby enhancing the shot peening effect, making the gear surface layer more prone to severe plastic deformation and grain refinement, and being convenient for obtaining manganese phosphate conversion coating.

According to the invention, by optimizing the process conditions, the surface of the gear can obtain higher surface residual compressive stress after composite shot peening, thus effectively improving the bending fatigue strength of the gear; at the same time, the surface roughness of the gear is adjusted, which overcomes the problems that the rough surface caused by shot peening makes the coating uniformity and bonding strength difficult to meet the requirements, and the shot peening strengthening is difficult to match with the coating thickness, uniformity and grain size, etc., so that it is perfectly combined with manganese phosphate conversion coating technology, and the hardness of the gear after composite strengthening treatment is 780 - 900 hV, and the maximum residual compressive stress is 1300 - 1500 MPa. The residual stress of the layer is 1200 - 1300 MPa, which greatly improves the wear resistance and strength. At the same time, an ultrafine manganese phosphate conversion coating with a grain size of 0.2 - 0.5 um is formed on the surface of the composite shot peening gear, which effectively reduces the friction coefficient of the friction pair surface and improves the contact stress of the meshing tooth surface, thus achieving the purpose of significantly improving the contact fatigue strength and bending fatigue strength of the gear at the same time.

DESCRIPTION OF THE INVENTION Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of some aspects, characteristics and embodiments of the present invention.

It should be understood that the terms used in this invention are only for describing specific embodiments, and are not used to limit the invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Any stated value or intermediate value within the stated range, as well as any other stated value or each smaller range between intermediate values within the stated range, are also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by the ordinary technicians in the field of this invention. Although the present invention only describes the preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and/or materials related to the documents. In case of conflict with any incorporated documents, the contents of this specification shall prevail.

Without departing from the scope or spirit of the present invention, it is obvious to those skilled in the art that many modifications and changes can be made to the specific embodiments of the present invention. Other embodiments obtained from the description of the present invention will be obvious to the skilled person. The description and example of that present invention are exemplary only.

The words "including", "comprising", "having" and "containing" used in this paper are all open terms, that is, they mean including but not limited to.

The invention has no special requirement on the kind of weakly alkaline degreasing agent, so it can achieve degreasing effect.

the acid ratio in this invention refers to the ratio of total acidity (TA) to free acidity (FA) of phosphating solution, and the acid ratio AR = TA/FA; total acidity (TA), also known as total acidity, refers to the total concentration of composite acid and free acid in phosphating bath solution. FA: refers to the concentration of free H* (hydrogen) in phosphating bath.

Example 1 (1) degreasing, derusting, cleaning and drying the gear surface, machining a surface structure on the gear surface, wherein the surface structure is a concave - convex texture with 20pm peak - valley height difference, and heating at 110°C to change the plastic structure of the gear tooth surface; (2) shot peening treatment: the gear tooth surface is strengthened by the shot from the shot peening machine, and the concave - convex texture is extruded to generate shear deformation, with the shot peening intensity controlled at 0.3A, the coverage rate of 180% and the shot peening time of 70 s, so that the peak - valley height difference of the concave - convex texture is 4 um, the shot is a rigid shot with a diameter of 0.8mm and the hardness HRC is 45;

(3) pre - treat on the gear obtained in step (2): treating the surface of the gear with weakly alkaline degreaser at 70°C for 3 minutes; {4) the pre - treated gear is phosphatized with manganese phosphating solution, the acid ratio of manganese phosphating solution is 5.8, which contains Fe?*, Mn?*, Niè*, PO:3: and 5 NO:; and the Fe?* content is <2g/l. The gear surface is treated at 80°C for 15 min to obtain manganese phosphate conversion coating, and the gear surface with composite strengthening is obtained.

Superfine manganese phosphate conversion coating is formed on the surface of the composite shot peening gear in this example. The phosphating grain size of the coating is about

0.3 um, and a soft layer of 5 - 6 um is formed on the tooth surface. The maximum residual compressive stress (MPa), surface layer residual stress (MPa), surface hardness (HV) and surface friction coefficient are shown in Table 1.

Example 2 (1) degreasing, derusting, cleaning and drying the gear surface, machining a surface structure on the gear surface, wherein the surface structure is a concave - convex texture with 30pm peak - valley height difference, and heating at 120°C to change the plastic structure of the gear tooth surface; (2) shot peening treatment: the gear tooth surface is strengthened by the shot from the shot peening machine, and the concave - convex texture is extruded to generate shear deformation, with the shot peening intensity controlled at 0.2A, the coverage rate of 180% and the shot peening time of 70 s, so that the peak - valley height difference of the concave - convex texture is 6 um, the shot is a rigid shot with a diameter of 1.0 Mm and the hardness HRC is 50; (3) pre - treat on the gear obtained in step (2): treating the surface of the gear with weakly alkaline degreaser at 75°C for 3 minutes; (4) the pre - treated gear is phosphatized with manganese phosphating solution, the acid ratio of manganese phosphating solution is 5.8, which contains Fe?*, Mn?*, Niè*, PO43- and NOs", and the Fe?* content is < 2g/l. The gear surface is treated at 85°C for 12min to obtain manganese phosphate conversion coating, and the gear surface with composite strengthening is obtained.

Superfine manganese phosphate conversion coating is formed on the surface of the composite shot peening gear in this example. The phosphating grain size of the coating is about

0.4 ym, and a soft layer of 7 - 8 um is formed on the tooth surface. See Table 1 for the maximum residual compressive stress (MPa), surface layer residual stress (MPa), surface hardness (HV) and surface friction coefficient.

Example 3 (1) degreasing, derusting, cleaning and drying the gear surface, machining a surface structure on the gear surface, wherein the surface structure is a concave - convex texture with 35 um peak - valley height difference, and heating at 120°C to change the plastic structure of the gear tooth surface; (2) shot peening treatment: the gear tooth surface is strengthened by the shot from the shot peening machine, and the concave - convex texture is squeezed to generate shear deformation, with the shot peening intensity controlled at 0.5 A, the coverage rate of 200% and the shot peening time of 80 s, so that the peak - valley height difference of the concave - convex texture is 4m, the shot is a rigid shot with a diameter of 1.0 Mm and the hardness HRC is 55; (3) pre-treating the gear obtained in step (2): treating the surface of the gear with weakly alkaline degreaser at 75°C for 2 min; (4) the pre - treated gear is phosphatized with manganese phosphating solution, the acid ratio of manganese phosphating solution is 6.0, which contains Fe?*, Mn?*, Ni?*, PO4*" and NO: ~, and the Fe?" content is < 2g/l. The gear surface is treated at 90°C for 10 Min to obtain manganese phosphate conversion coating, and the gear surface with composite strengthening is obtained.

Superfine manganese phosphate conversion coating is formed on the surface of the composite shot peening gear in this example. The phosphating grain size of the coating is about

0.5 um, and a soft layer of 6 - 8 um is formed on the tooth surface. See Table 1 for the maximum residual compressive stress (MPa), residual stress of the surface layer (MPa), surface hardness (HV) and surface friction coefficient.

Example 4 (1) degreasing, derusting, cleaning and drying the gear surface, machining a surface structure on the gear surface, wherein the surface structure is a concave - convex texture with a peak - valley height difference of 25 um, and heating at 130°Cto change the plastic structure of the gear tooth surface; (2) shot peening treatment: the gear tooth surface is strengthened by the shot from the shot peening machine, and the concave - convex texture is extruded to generate shear deformation, with the shot peening intensity controlled at 0.5 A, the coverage rate of 180% and the shot peening time of 70 s, so that the peak - valley height difference of the concave - convex texture is 2 um, the shot is a rigid shot with a diameter of 1.3 mm and the hardness HRC is 50; (3) pre-treating the gear obtained in step (2): treating the surface of the gear with weakly alkaline degreasing agent at 80°C for 2 min; (4) the pre - treated gear is phosphatized with manganese phosphating solution, the acid ratio of manganese phosphating solution is 5.8, which contains Fe?*, Mn?*, Niè2* PO,%~ and NOs", and the Fe?" content is < 2g/l. The gear surface is treated at 90°C for 10 Min to obtain manganese phosphate conversion coating, and the gear surface with composite strengthening is obtained.

The superfine manganese phosphate conversion coating is formed on the surface of the composite shot peening gear in this example. The phosphating grain size of the coating is about

0.4 um, and a soft layer of 7 - 8 um is formed on the tooth surface.

Example 5 (1) degreasing, derusting, cleaning and drying the gear surface, machining a surface structure on the gear surface, wherein the surface structure is a concave - convex texture with 35 um peak - valley height difference, and heating at 110°C to change the plastic structure of the gear tooth surface; (2) Shot peening treatment: the gear tooth surface is strengthened by the shot from the shot peening machine, and the concave - convex texture is squeezed to generate shear deformation, with the shot peening intensity controlled at 0.3A, the coverage rate of 200% and the shot peening time of 75S, so that the peak - valley height difference of the concave - convex texture is 4 um, the shot is a rigid shot with a diameter of 1.0 Mm and the hardness HRC is 55; (3) pre-treating the gear obtained in step (2): treating the surface of the gear with weakly alkaline degreaser at 75°C for 2 min; (4) the pre - treated gear is phosphatized with manganese phosphating solution, the acid ratio of manganese phosphating solution is 6.0, which contains Fe?*, Mn?*, Ni%*, PO4*-and NOs" ‚ and the Fe?* content is < 2g/l. The gear surface is treated at 85°C for 10 Min to obtain manganese phosphate conversion coating, and the gear surface with composite strengthening is obtained.

The superfine manganese phosphate conversion coating was formed on the surface of the composite shot peening gear in this example. The phosphating grain size of the coating was about 0.4 um, and a soft layer of about 8 um was formed on the tooth surface.

Example 6 (1) degreasing, derusting, cleaning and drying the gear surface are carried out, and the gear tooth surface is strengthened by the shot peening machine. The shot peening intensity is controlled to be 0.2A, the coverage rate is 180%, the shot peening time is 70 s, and the shot is a rigid shot with a diameter of 1.0 Mm and the hardness HRC is 50; (2) pre - treat the gear obtained in step (1): treating the surface of the gear with weakly alkaline degreaser at 75°C for 3 minutes; (3) the pre - treated gear is phosphatized with manganese phosphating solution, the acid ratio of manganese phosphating solution is 5.8, which contains Fe?*, Mn?*, Niè*, PO: and NOs and the Fe?! content < 2g/l. The gear surface is treated at 85°C for 12min to obtain manganese phosphate conversion coating, and the gear surface with composite strengthening is obtained.

The maximum residual compressive stress and residual stress of the surface layer of the gear in this embodiment are both below 500 MPa, and the surface hardness is about 750 hV, so the cycle life is short.

Example 7 (1) degreasing, derusting, cleaning and drying the gear surface, and heating at 120°C to change the plastic structure of the gear tooth surface; (2) shot peening treatment: the gear tooth surface is strengthened by the shot from the shot peening machine, and the extrusion concave - convex texture generates shear deformation, with shot peening strength controlled at 0.2A, coverage rate of 180%, shot peening time of 70 s, the shot being a rigid shot with a diameter of 1.0 Mm and hardness HRC of 50; (3) pre - treat the gear obtained in step (2): treating the surface of the gear with weakly alkaline degreaser at 75°C for 3 minutes; (4) the pre - treated gear is phosphatized with manganese phosphating solution, the acid ratio of manganese phosphating solution is 5.8, which contains Fe?*, Mn?*, Ni®* PO4*- and NO: , and the Fe?’ content is < 2g/l. The gear surface is treated at 85°C for 12min to obtain manganese phosphate conversion coating, and the gear surface with composite strengthening is obtained.

The maximum residual compressive stress and residual stress of the surface layer of the gear in this embodiment are both below 800 MPa, and the surface hardness is about 750 hV, so the cycle life is short.

The properties of gears prepared in Examples 1 - 3 are shown in Table 1.

Table 1 Maximum Layer residual Surface Surface Number of residual stress (MPa) hardness (HV) friction cycles compressive coefficient (times) [emmy | ww | ww ws ww |v The above - mentioned embodiments only describe the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, all kinds of modifications and improvements made by ordinary technicians in the field to the technical scheme of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims (8)

CONCLUSIONS A method for a composite surface reinforcement treatment of gears, the method comprising the steps of: (1) machining a surface structure on the surface of a gear, the surface structure being a concave - convex texture having a peak - valley height difference of 8 - 35 µm, and performing a heating treatment; (2) shot blasting treatment: extruding the concave-convex texture to produce a shear deformation, so that the peak-valley height of the concave-convex texture is 2-6 µm; (3) pre-treating the sprocket obtained in step (2); (4) phosphating the pre-treated gear with a manganese phosphating solution to obtain a manganese-phosphate conversion coating on the surface of the gear, thereby obtaining a gear with a composite-reinforced surface. The method for strengthening treatment of composite gear surfaces according to claim 1, characterized in that the heating temperature in step (1) is 110 - 130°C. The method for a composite surface reinforcement treatment of gears according to claim 1, characterized in that the hammer impact strength in the step (2) is controlled to 0.2 - 0.5 A, with the degree of coverage being 180% - 200%. The method for composite surface reinforcement treatment of gears according to claim 1, characterized in that in step (2), the concave-convex texture is extruded through the ball from the shot-blasting device. The method for composite surface reinforcement treatment of gears according to claim 1, characterized in that the diameter of the balls is 0.8-1.3mm and the hardness is HRC 45-55. The method for a composite surface reinforcement treatment of gears according to claim 1, characterized in that the pre-treatment in step (3) comprises treating the surface of the gear at 70-80°C for 2-3 minutes with a weak alkaline degreasing agent includes. The method for gear composite surface reinforcement treatment according to claim 1, characterized in that the acid ratio of manganese phosphating solution in step (4) is 5.8 - 6.0, and Fe 2 *, Mn 2 *, Nie *, PO 4 * and NO*, where the Fe?* content is < 2 g/l. The method for a composite surface reinforcement treatment of gears according to claim 1, characterized in that the phosphating treatment time in step (4) is 10-15 minutes and the temperature is 80-90°C.