Application of the latest materials and surface te

Application of new materials and surface technology in rolling elements

with the development of mechanical industry technology, higher requirements are put forward for bearings. The ways to improve bearing performance are:

① adopt advanced design technology

② adopt advanced manufacturing technology

③ adopt new materials

④ adopt advanced management concepts and methods

this paper discusses the application of new materials and surface engineering technology in rolling element manufacturing

common (traditional) rolling element materials

1, high carbon chromium bearing steel

high carbon chromium bearing steel includes GCr15, gcr9, gcr6, GCr15SiMn, etc., which are used to manufacture bearing rolling elements under normal working conditions. At present, the consumption accounts for more than 85% of the production of rolling elements

2. Carburized bearing steels

carburized bearing steels include 08, 10, 25, 15mn, G20 CrMo, G20 CrNiMo, G20 crni2mo, G20 cr2ni4, g10crni3mo, G20 cr2mn2mo, etc., which are used to manufacture impact bearing rolling elements. Generally, carbon steel balls are used to manufacture bearings with low prices, and alloy carburized bearing steel is used to manufacture bearings for automobiles and rolling mills

3. Stainless bearing steel

stainless bearing steel includes 9Cr18, 9Cr18Mo, 0Cr18Ni9, 1Cr18Ni9, 1Cr18Ni9Ti, 1Cr17Ni2, 1Cr13, 2Cr13, 3Cr13, 4Cr13, etc., which are used to manufacture bearing rolling elements in corrosive media

special rolling element materials include

1, high temperature bearing steel

high temperature bearing steel includes Cr4Mo4V (M50), W9Cr4V2Mo, cr15mo4v, W18Cr4V, W6Mo5Cr4V2, etc., which are used to manufacture high temperature bearing rolling elements and high temperature high-speed bearings such as gas turbines and aeroengines

2. Medium carbon bearing steel

medium carbon bearing steel includes gcr10, 40cra, 65Mn, 50crnia, 55SiMoV, etc., which are used to manufacture rolling elements subject to impact load, such as 55SiMoV, which is used to manufacture rolling elements of turbodrill bearings

3. Non magnetic bearing materials

non magnetic bearing materials include G52, G60, 25cr18ni10w, ocr40ni55a13, qbe2.0, NICU 5。

① G52 is used to manufacture non-magnetic high temperature and high pressure water bearing rolling elements

② G60 is used to manufacture bearing rolling elements in non-magnetic high temperature, high vacuum and oxidizing media

③ 25cr18ni10w is used to manufacture non-magnetic bearing rolling elements

④ ocr40ni55a13 is used to manufacture non-magnetic bearing rolling elements

⑤ qbe2.0 is used for non-magnetic low temperature corrosion-resistant bearing rolling element

⑥NiCu.. 5. It is used to manufacture non-magnetic corrosion-resistant steel balls

new rolling element materials

1, engineering ceramic materials

engineering ceramic materials include silicon nitride ceramics, zirconia ceramics, boron nitride ceramics

① silicon nitride ceramics (Si3N4): manufacturing high-speed or high-temperature, corrosion-resistant precision ceramic bearing balls or rollers

② zirconia ceramics (ZrO2): manufacturing high temperature, corrosion-resistant medium and low speed ceramic bearing balls or rollers

③ boron nitride ceramics (BN): manufacturing high-temperature, corrosion-resistant, self-lubricating all ceramic bearings. Table I comparison of properties of engineering ceramic materials and bearing steel (GCr15)

Project silicon nitride Si3N4 zirconia ZrO2 boron nitride BN bearing steel GCr15 density (g/cm3) 3.25.8~6.051.8~2.197.85 hardness (HV) 1700 (9) 1300 (7) Mohs 2700 bending strength (MPA) ~ fracture toughness (MPA · m1/2) 6~87~1425 modulus of elasticity (GPA) 320150 ~ coefficient of thermal expansion (/k) 3.28.7~11.42~7.511.8 resistivity (Ω· mm2/m) 1017~ 1~1 service temperature (℃) good and bad dimensional stability, good and bad corrosion resistance

2. Silicon nitride ceramic material

its characteristics are:

① polycrystalline material, crystal structure belongs to hexagonal system

② the appearance of silicon nitride ceramics is gray white, blue gray and gray black

③ theoretical density: 3.19 ± 0.1g/cm3, low density

④ high hardness, good wear resistance, low friction coefficient (self grinding 0.02~0.07), good self lubrication

⑤ high temperature resistance and good thermal shock resistance

⑥ it has high fracture toughness and good impact resistance

⑦ it has good corrosion resistance, can resist the corrosion of all acids (except hydrofluoric acid), can resist the corrosion of weak bases, and is unstable to most strong bases and molten salts

⑧ similar contact fatigue life and fatigue spalling form to bearing steel

⑨ silicon nitride powder performance:

particle size 0.5~0.8 μ m. Low impurity content and oxygen content <2wt%, α Phase content> 90wt%

⑩ manufacturing method of silicon nitride powder:

A. silicon powder direct nitridation method 3si+2n2 → Si3N4

the method commonly used in China requires ball milling to obtain fine powder, which is easy to introduce impurities

b, sicl4+6nh3 → Si (NH) 2+4nh4cl

3si (NH) 2 → si3n4+n2+3h2

the silicon imine decomposition method has high purity, fine and uniform fineness, and high manufacturing cost

c, carbothermal reduction nitridation method 3sio2+2n2+6c → si3n4+6co

d, chemical vapor deposition method 3sicl4+4nh3 → si3n4+12hcl

need to be stimulated and induced. The powder has high purity, fine and uniform fineness, and the manufacturing cost is very high

(11) manufacturing method of dense silicon nitride ceramics:

a, hot pressed silicon nitride (HP SN)

method: the silicon nitride mixed powder is heated and axially pressurized in the graphite mold at the same time, the sintering temperature is 1650~1850 ℃, the pressure is 15~30mpa, and the holding time is 1~4h. Features: dense, basically reaching the theoretical density (99~100%), the product shape is simple, it is difficult to mass produce, it can produce roller blanks, and the finished product is expensive

b, normal pressure sintering silicon nitride (s SN)

method: silicon nitride mixed powder is formed by molding or cold isostatic pressing, and sintered in N2 atmosphere in a sintering furnace at 1700~1800 ℃, for a few hours, and the pressure is 0.1MPa (1atm)

features: low cost, easy to mass produce, relative density 95~99%, more pores, not suitable for manufacturing bearing balls

c, atmosphere pressure sintering silicon nitride (GSP SN)

method: silicon nitride mixed powder is formed by cold isostatic pressing, and sintered in high-pressure N2 atmosphere with atmosphere pressure sintering furnace. The sintering temperature is 1800 ℃, the time is several hours, and the pressure is 5~10mpa

features: good performance, dense (relative density 97~99%), easy to mass produce, widely used in China, can manufacture bearing balls, and the cost is high

d, hot isostatic pressing sintered silicon nitride (hip SN)

method: silicon nitride mixed powder is formed by molding or cold isostatic pressing, s or GPS sintering, hot isostatic pressing furnace, ar2 or N2 gas as pressure transmission medium, and silicon nitride is densified under high temperature (1700~1999 ℃) and high pressure (150~200mpa), so that the previously sintered RBSN, SSN, srbsn further eliminate pores. Low additive content

features: excellent performance, basically completely compact (99~100%), mass production, high-performance ceramic bearing balls, widely used abroad, high cost

(12) summary

ceramic bearing roller: HP Sn hip Sn

ceramic bearing ball: GPS Sn hip Sn

general purpose ceramic ball: s Sn SRB Sn

3. Zirconia ceramic material

its characteristics are:

① crystal structure: partially stable zirconia (PSZ), cubic phase (cub) structure + monoclinic phase (mono) structure

② high toughness (the highest among all ceramic materials), bending strength up to 1300mpa, but fracture toughness is sensitive to temperature, which should be paid attention to when applying at high temperature

③ the commonly used zirconia ceramic is mg PSZ

④ high hardness, wear resistance, not easy to scratch the dual parts

⑤ corrosion resistant, stable to most acids and bases

⑥ the contact fatigue life is quite different from that of bearings, so it is not suitable for manufacturing high-speed and heavy-duty ceramic bearings

⑦ ceramic bearings for light load, medium and low speed corrosion occasions can be manufactured

⑧ manufacturing method of zirconia powder:

zircon (ZrSiO4) sand reacts with coke and chlorine at 800~1200 ℃ to produce gas-phase ZrCl4 and SiCl4

4. Polyoxymethylene engineering plastics

polyoxymethylene is a kind of thermoplastic engineering plastics with high melting point and high crystallinity, which is divided into homopolymer and copolymer formaldehyde. It is one of the engineering plastics closest to metal in mechanical properties (properties are shown in the table below)

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project homoformaldehyde copolyformaldehyde

density (g/cm3) 1.42 1.41

variable strength (MPA) 9098

compressive strength (MPA) 127 110

impact strength (j/m) Notch 7665

no notch 1310 1140

Rockwell hardness M94 M80

friction coefficient 0.35 0.35

service temperature -40~100

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performance characteristics:

① specific strength and specific rigidity close to metal

② high elastic modulus

③ high rigidity and hardness

④ good impact strength, creep resistance and fatigue resistance

application:

① manufacturing light load low-speed corrosion-resistant bearing rolling elements

② manufacture light load low-speed self-lubricating bearing rolling elements

5, other materials

① cermet materials: cemented carbide, etc. Today's focus:

② aluminum alloy material

③ copper alloy material

④ titanium alloy material

choose rolling element material reasonably according to different service conditions

surface engineering technology

1. Overview

the failure of mechanical products is often caused by the failure of individual parts, and the failure of parts is often caused by local surface failure. Corrosion starts from the surface of parts, friction and wear occur on the surface of parts, and fatigue cracks extend from the surface to the inside. The application of surface engineering technology can prolong the failure period of the vulnerable surface of those vulnerable parts, and improve the overall performance of the product

bearings are typical surface working parts. If there is slight wear, fatigue, corrosion and other failures on the bearing surface, the whole set of bearings can be invalidated. The state of the bearing working surface can be improved through surface engineering technology to improve the service life of bearings

① surface engineering technology is a systematic engineering that changes the morphology, chemical composition, microstructure and stress of solid metal surface or non-metal surface through surface coating, surface modification or multiple surface technology composite treatment after surface pretreatment, so as to obtain the required surface properties

② surface engineering technology is a new discipline formed and rapidly developed in recent ten years for electromechanical products to meet the needs of high temperature, high pressure, high speed, heavy load, corrosive media and harsh working conditions. It has the remarkable characteristics of multidisciplinary intersection and integration when some electronic tensile machines are loaded to its scope, which can effectively promote the improvement of product quality and environmental protection. Surface engineering technology has achieved outstanding results in solving the problems of wear resistance, corrosion prevention and providing functional coatings

③ main functions of surface engineering technology:

A, improve surface wear resistance or corrosion resistance, fatigue resistance, oxidation resistance and radiation resistance

b, improve the heat transfer or heat insulation of the surface

c, improve the conductivity or insulation of the surface

d, improve the magnetic conductivity or electromagnetic shielding of the surface

e, improve the brightening, reflective or absorbing properties of the surface

f, improve the adhesion or non adhesion of the surface

g, improve the oil absorption or dry friction of the surface

h, improve the friction coefficient of the surface (increase or decrease)

i. improve the decorative or antique antiquity of the surface

④ surface engineering technology is a system engineering technology, including

A. basic theory of surface engineering:

surface failure analysis theory; Surface friction and wear theory; Theory of surface corrosion and protection; Surface interface bonding and composite theory

b, surface engineering technology and composite surface engineering technology:

composite surface technology; Chemical conversion membrane technology; Surface coating (thick film) technology; Surface film technology; Surface chemical bonding technology;