A method for calculating the carburizing depth of rolling mill bearing parts

Abstract

A method for calculating the carburizing depth of a rolling mill bearing part is provided. The method is to calculate the maximum orthogonal shear stress depth generated inside the bearing surface side of the bearing part according to the maximum rolling force actually borne by the rolling mill bearing when working; in addition, according to the damage form and proportion of carburized layers of different depths of the rolling mill bearing part, the carburized layer is divided from the outside to the inside into a life-increasing layer (surface layer), a reliable layer (sub-surface layer), and a strengthening layer (core layer); the depth of the life-increasing layer (surface layer) and the reliable layer (sub-surface layer) and the final required carbon content are used as the design basis of the carburizing heat treatment process to ensure that the rolling mill bearing part after the carburizing heat treatment has sufficient carburizing depth and corresponding carbon content, so that the rolling mill bearing part can fully meet the working condition requirements of actual application and ensure its reliability and service life.

Description

Technical Field

[0001] The invention relates to the technical field of carburizing heat treatment of rolling mill bearing parts, and in particular to a method for calculating the carburizing depth of rolling mill bearing parts. Background Art

[0002] The carburizing depth of existing general bearing parts is designed in accordance with the "Technical Conditions for Carburizing Heat Treatment of Rolling Bearing Parts" (JBT888-2011). The depth of the carburizing layer is actually determined by the effective wall thickness of the bearing parts (bearing inner ring, bearing outer ring) or the effective diameter (bearing roller), and must meet the general working conditions P / Cr < 30% requirement (where P is the actual equivalent load and CR is the design rated dynamic load). With the continuous development of the national economy, the production efficiency of metal rolling has been greatly improved, and the working conditions of high-end plate and strip rolling mill bearings have reached P / Cr ≥ 40%. Therefore, according to the existing The calculation of the carburized layer depth of rolling mill bearing parts based on the "Technical Conditions for Carburizing Heat Treatment of Rolling Bearing Parts" is far from meeting the market's requirements for high-reliability and long-life rolling mill bearings, and has become a bottleneck restricting the further development of the domestic rolling mill bearing industry towards high-end development. At present, the rolling mill bearings used in the production of domestic high-end rolled products are mainly internationally renowned brands, such as Sweden's SKF, Germany's FAG, the United States' TMKEN, Japan's NSK, etc. The import volume is huge, and the price is 4-5 times that of the same type of domestic rolling mill bearings. Therefore, it is imperative for domestic rolling mill bearing manufacturers to develop domestic products to replace imports.

[0003] Although the existing "Technical Conditions for Carburizing Heat Treatment of Rolling Bearing Parts" can no longer meet the design requirements for the carburizing depth of rolling mill bearing parts, there is currently no theoretical guidance and calculation formula for calculating the carburizing depth of rolling mill bearing parts in China. Therefore, how to reasonably and accurately calculate the carburizing depth of rolling mill bearing parts has become a technical problem in the rolling mill bearing industry. Summary of the invention

[0004] In order to overcome the shortcomings in the background technology, the present invention discloses a method for calculating the carburizing depth of rolling mill bearing parts; the calculation of the depth of the carburizing layer of the rolling mill bearing parts is determined by calculating the maximum orthogonal shear stress depth generated inside the bearing surface side of the rolling mill bearing parts based on the maximum rolling force actually borne by the rolling mill bearing when working; in addition, according to the damage form and proportion of the carburizing layers of different depths of the rolling mill bearing parts, the carburizing layer is divided from the outside to the inside into a life-increasing layer (surface layer), a reliable layer (sub-surface layer), and a strengthening layer (core layer); the depth of the life-increasing layer (surface layer) and the reliable layer (sub-surface layer) and the final required carbon content are used as the design basis of the carburizing heat treatment process to ensure that the rolling mill bearing parts after the carburizing heat treatment have sufficient carburizing depth and corresponding carbon content, so that the rolling mill bearing parts can fully meet the working conditions of actual applications and ensure their reliability and service life.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme: a method for calculating the carburizing depth of a rolling mill bearing part, wherein the carburizing layer depth of the rolling mill bearing part is determined according to the maximum orthogonal shear stress depth generated inside the bearing surface side of the bearing part by the maximum rolling force actually borne by the rolling mill bearing when the rolling mill bearing is working; the maximum orthogonal shear stress depth calculation formula is:

[0006] Z0=F / (1.27δLi 7 / 9 ),

[0007] Among them, Z0 is the maximum orthogonal shear stress depth; F is the maximum rolling force actually carried by the rolling mill bearing; δ is the average yield strength of the material in the strain area of ​​the bearing parts; L is the effective length of the rolling element of the rolling mill bearing; i is the number of rolling element rows;

[0008] The calculation formula for the carburized layer depth of rolling mill bearing parts is:

[0009] H=KZ0,

[0010] Where H is the depth of carburized layer of rolling mill bearing parts, K is the safety factor, and K is usually calculated as 1.1;

[0011] Supplementary explanation: The derivation process of the calculation formula for the carburizing depth of rolling mill bearing parts is briefly described as follows:

[0012] F=δs …………⑴

[0013] s=a(i) 7 / 9 L; …………⑵

[0014] From Z0=0.786a, then a=1.27Z0 …………⑶

[0015] Substituting (2) into (1) we get: F = δa (i) 7 / 9 L…………⑷

[0016] Substituting (3) into (4) we get: F = 1.27Z0*δ (i) 7 / 9 L…………⑸

[0017] Calculate Z0 from (5): Z0=F / (1.27δ (i) 7 / 9 L) …………⑹

[0018] Set the bearing safety factor to K.

[0019] Then H = KZ0 = KF / (1.27δLi 7 / 9 );

[0020] Among them: F is the maximum rolling force actually borne by the rolling mill bearing (N); δ is the average yield strength of the material in the strain area of ​​the bearing parts (δ=2390Pa / mm²); s is the area of ​​the maximum contact ellipse of the contact deformation between the bearing parts in mm²; a is the width of the maximum contact ellipse (mm); i is the number of rolling element rows; L is the effective length of the rolling element of the rolling mill bearing (mm); Z0 is the maximum orthogonal shear stress depth; H is the depth of the carburized layer.

[0021] Furthermore, the carburizing depth of the rolling mill bearing parts is divided into the surface layer, the sub-surface layer, and the core layer from the surface layer inward; the thickness of the surface layer, the sub-surface layer, and the core layer are determined in turn according to empirical data: the thickness of the surface layer is 0.15H, the thickness of the sub-surface layer is 0.45H, and the thickness of the core layer is 0.4H;

[0022] The surface layer, sub-surface layer and core layer of rolling mill bearing parts are divided according to the carburizing depth, which is obtained based on the statistics and cause analysis results of the failure forms of rolling mill bearings reported by previous customers; the statistics and cause analysis results of the failure forms of rolling mill bearings reported by previous customers are as follows: surface (depth 0-0.5mm) friction spalling failure accounts for about 30%, sub-surface (depth 0.5-3mm) impact microcrack source spalling failure accounts for about 50%, and core layer (depth above 2.5mm) overload transgranular fracture failure accounts for about 20%; among them, 30% of the surface (depth 0-0.5mm) friction spalling failure is the normal form of failure of rolling mill bearing parts, while the sub-surface (depth 0.5-3mm) impact microcrack source spalling failure and core layer (depth above 2.5mm) overload transgranular fracture failure, which account for 70% of the total failure forms, are the failure forms of rolling mill bearing parts. Abnormal form, the reason is that the existing rolling mill bearing parts are not carburized deeply enough, so that the core layer stiffness is not enough to provide sufficient support for the sub-surface layer, resulting in excessive alternating stress in the sub-surface layer during operation. When the sub-surface layer produces impact microcracks due to excessive alternating stress, it will lead to the aggravation of surface friction spalling failure and core layer overload transgranular fracture failure. Therefore, in order to thoroughly solve the abnormal failure problem of rolling mill bearings in normal use, the carburizing depth H of the rolling mill bearing must be greater than the maximum depth of the core layer overload transgranular fracture failure to ensure that when the rolling mill bearing parts are loaded, the stiffness of the core layer can provide sufficient support for the sub-surface layer, thereby improving or eliminating the abnormal failure forms of sub-surface layer (depth 0.5-3mm) impact microcrack source spalling and core layer (depth above 2.5mm) overload transgranular fracture, which account for 70% of the total failure forms;

[0023] The depth of the life-prolonging layer (surface layer) and the reliable layer (sub-surface layer) and the final required carbon content serve as the design basis of the carburizing heat treatment process to ensure that the rolling mill bearing parts after carburizing heat treatment have sufficient carburizing depth and corresponding carbon content, thereby ensuring that the rolling mill bearing parts can fully meet the working conditions of actual applications and achieve the purpose of improving the reliability and service life of the rolling mill bearing parts.

[0024] Due to the adoption of the technical scheme as described above, the present invention has the following beneficial effects: the calculation of the carburized layer depth of the rolling mill bearing parts is determined by calculating the maximum orthogonal shear stress depth generated inside the bearing surface side of the bearing parts according to the maximum rolling force actually borne by the rolling mill bearing when working; in addition, according to the damage form and proportion of the carburized layer of the rolling mill bearing parts with different depths, the carburized layer is divided from the outside to the inside into a life-increasing layer (surface layer), a reliable layer (sub-surface layer), and a strengthening layer (core layer). According to the depth of the life-increasing layer (surface layer) and the reliable layer (sub-surface layer) and the final required carbon content, the design basis of the carburizing heat treatment process is used to ensure that the rolling mill bearing parts after carburizing heat treatment have sufficient carburizing depth and corresponding carbon content, so that the rolling mill bearing parts can fully meet the working conditions of actual applications and ensure their reliability and service life. The carburized depth of the rolling mill bearing calculated by the present invention and the rolling mill bearing parts after heat treatment have been tested in actual use and fully meet the working conditions of high-end plate and strip rolling mill bearings. The service life and reliability have exceeded those of internationally renowned brands, making the quality of domestic rolling mill bearings reach the international advanced level. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the maximum rolling force actually borne by the bearing parts of the rolling mill;

[0026] Figure 2 It is a schematic diagram of the maximum orthogonal shear stress depth generated inside the bearing surface side of the rolling mill bearing parts and the corresponding carburizing depth;

[0027] Figure 3 The present invention is a tracking statistical table of the actual use status of the rolling mill bearing after the method for calculating the carburizing depth of the rolling mill bearing parts of the present invention is implemented.

[0028] In the figure: 1. Roller neck; 2. Bearing inner ring; 3. Bearing roller; 4. Bearing outer ring; 5. Bearing housing; 6. Deformation area of ​​rolling mill bearing parts when they actually bear the maximum rolling force; 7. Distribution range curve of maximum orthogonal shear stress generated inside the bearing surface side of the bearing parts when the rolling mill bearing parts actually bear the maximum rolling force. DETAILED DESCRIPTION

[0029] The present invention can be explained in detail by the following examples, and the purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention.

[0030] A method for calculating the carburizing depth of a rolling mill bearing part. The carburizing layer depth of the rolling mill bearing part is determined according to the maximum orthogonal shear stress depth generated inside the bearing surface side of the bearing part by the maximum rolling force actually borne by the rolling mill bearing when the rolling mill bearing is working. The maximum orthogonal shear stress depth calculation formula is:

[0031] Z0=F / (1.27δLi 7 / 9 ),

[0032] Among them, Z0 is the maximum orthogonal shear stress depth; F is the maximum rolling force actually carried by the rolling mill bearing; δ is the average yield strength of the material in the strain area of ​​the bearing parts; L is the effective length of the rolling element of the rolling mill bearing; i is the number of rolling element rows;

[0033] The calculation formula for the carburized layer depth of rolling mill bearing parts is:

[0034] H=KZ0,

[0035] Where H is the depth of the carburized layer of the rolling mill bearing parts, K is the safety factor, and K is usually calculated to be 1.1.

[0036] Taking the 3300mm hot rolling slab mill bearing as an example, the maximum rolling force during its working process is 25000KN. It adopts the design of Japanese NSK 950R3723A (Φ950xΦ1360x1000mm) four-row cylindrical roller mill bearing, the roller design effective length is 175mm, and the hollow roller effective wall thickness is 38mm; the maximum rolling force is borne by two sets of mill bearings, each set of mill bearings bears 12500KN, and one roller in the main bearing area bears 50% of its rolling force, which is 6250000N;

[0037] According to the existing "Technical Conditions for Carburizing Heat Treatment of Rolling Bearing Parts" (JBT888-2011), the standard carburizing hardening layer depth should be no less than 2.5. If the rolling mill bearing takes a safety factor of 1.2, the final calculated carburizing hardening layer depth of the hollow roller is 3.0mm, which meets the requirements of the existing "Technical Conditions for Carburizing Heat Treatment of Rolling Bearing Parts" (JBT888-2011); however, in actual use, it cannot meet the actual working conditions. The initial failure rate within 3 to 6 months is about 24%, and the longest service life is only 24 months.

[0038] According to the method for calculating the carburizing depth of rolling mill bearing parts of the present invention, the actual known conditions F = 6250000N, L = 175mm, δ = 2390Pa / mm², i = 4 are substituted into the formula Z0 = F / (1.27δLi 7 / 9 ), calculated Z0 = 4.1mm; Substitute the calculated Z0 into the formula H = KZ0, K is 1.1, and the carburized layer depth of the rolling mill bearing parts is 4.51mm; According to the carburized layer depth of the rolling mill bearing parts, it is calculated that: the surface layer thickness is 0.68mm, the sub-surface layer thickness is 2.03mm, and the core layer thickness is 1.8mm; The surface layer, sub-surface layer, and core layer thicknesses finally calculated are used as the design basis of the carburizing heat treatment process, and the carburizing heat treatment process design is carried out for the hollow rollers of the 950R3723A rolling mill bearings;

[0039] For the actual use of the product after carburizing heat treatment according to the depth of carburizing hardened layer, please refer to the appendix of the instruction manual. Figure 3 The actual use status tracking statistics of rolling mill bearings: In actual use, there was no initial failure problem within 3 to 6 months, and the shortest service life reached 33 months, which has exceeded the shortest level of 32 months for similar foreign products.

[0040] Parts of the present invention not described in detail are prior art.

Claims

1. A method for calculating the carburizing depth of a rolling mill bearing part, characterized in that: The depth of the carburized layer of the rolling mill bearing parts is determined according to the depth of the maximum orthogonal shear stress generated inside the bearing surface side of the bearing parts by the maximum rolling force actually borne by the rolling mill bearings when they are working; the maximum orthogonal shear stress depth calculation formula is: Z0=F / (1.27δLi 7 / 9 ), Among them, Z0 is the maximum orthogonal shear stress depth; F is the maximum rolling force actually carried by the rolling mill bearing; δ is the average yield strength of the material in the strain area of ​​the bearing parts; L is the effective length of the rolling element of the rolling mill bearing; i is the number of rolling element rows; The calculation formula for the carburized layer depth of rolling mill bearing parts is: H=KZ0, Where H is the depth of carburized layer of rolling mill bearing parts, and K is the safety factor.

2. The method for calculating the carburizing depth of rolling mill bearing parts according to claim 1 is characterized in that: The carburizing depth of rolling mill bearing parts is divided into surface layer, sub-surface layer and core layer from the surface layer to the inside; The thicknesses of the surface layer, sub-surface layer and core layer are as follows: the surface layer thickness is 0.15H, the sub-surface layer thickness is 0.45H, and the core layer thickness is 0.4H.

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