The surface treatment technology of rolling bearing refers to changing the surface composition, structure and performance of the parts to be treated by certain means, so as to improve the service life of the parts or their working performance. The surface treatment technologies of rolling bearings mainly include: surface coating, surface heat treatment, surface chemical heat treatment, surface mechanical strengthening, etc.
Surface coating technologies include: physical vapor deposition (PVD), chemical vapor deposition (CVD), radio frequency sputtering (RF), ion spraying (PSC), chemical plating, etc. The wear resistance and contact fatigue resistance of bearing parts can be improved and the surface friction coefficient can be reduced by surface coating. The surface coating technology of bearing steel is described below.
1. Diamond-like coating
The diamond-like carbon (DLC) coating is composed of carbon with graphite structure and diamond structure. It not only has the lubricating and low friction properties of graphite, but also has the hardness of diamond (above 1200HV). It has been applied in many industrial technologies, such as automotive fuel injection systems, valve systems, gears and rolling bearings. These coatings usually show better wear resistance under sliding conditions, However, the performance is poor under the high load rolling and mixed contact conditions of bearings, mainly because the cracks are generated and propagated in the columnar structure of the coating when the coating is applied under the high load rolling conditions, resulting in the coating peeling. In order to avoid this fracture mode of wear, this columnar structure must be eliminated. The optimization of process parameters and coating design can eliminate the submicron columnar structure of the coating, greatly improve the durability of the coating under high load rolling and mixed contact conditions, and metal doping of the coating, such as adding W, Ti, Cr, etc., can also improve the strength and wear resistance of the coating by forming fine carbides in the coating. DLC coating represents a development direction of bearing hard coating, which will be more and more applied to various bearing products in terms of reducing friction and wear, reducing surface damage and improving contact fatigue life. In recent years, coating modification design and practical application have become a hot research field of surface coating.
ECKELS. M, KOTZALAS. M. N, DOLL. G. L studied the performance of roller bearing coated with nano composite diamond-like carbon. By unbalanced magnetron sputtering, 1 μ M-thick W-aC: H coating is deposited on the roller surface. W-aC: The thickness between H coating and steel substrate is less than 1 μ M Cr transition layer to increase the adhesion between the coating and the substrate, W-aC: H coating is a kind of coating with a thickness of 3~5 μ The layer structure composed of alternating distribution of tungsten rich and carbon rich in m, and the amorphous hydrocarbon matrix in each layer contains β- W2C precipitates, the content is about 17%~20%. The indentation hardness of W-aC: H coating is 12, and the elastic modulus is 130 GPa. The test shows that the W-aC: H coating has high wear resistance and hardness, and the bearing coated with W-aC: H can greatly increase the fatigue life when working under low λ value, because the rolling contact area of the raceway is ground into a mirror by the coated roller, and the indentation formed on the raceway by the contaminated particles in the lubricant can be smoothed. In addition, W-aC: H coating can prevent scratch and short-term lubrication failure, as well as wear failure of pseudo indentation.
MUTYALA. K.C, SINGH. H, EVANS. R.D, etc. studied the effect of DLC coating on the performance of ball bearings under normal, oil depleted and debris damage conditions. There are three DLC coatings applied: WC/a-C: H, TiC/a-C and Ti/a-C: H. In normal lubrication operation, TiC/a-C coated steel balls have greater torque drop, followed by TiC/a-C: H, WC/a-C: H coated steel balls; In the test, compared with TiC/a-C: H, TiC/a-C and uncoated steel balls, WC/a-C: H coated steel balls can repair raceway damage and improve the operating efficiency after bearing debris damage. WC/a-C: H, TiC/a-C: H and TiC/a-C coating improved the anti-wear ability of the bearing by 3.5, 1.7 and 1.3, respectively, which exceeded the factor of assembling uncoated steel ball bearing under the condition of depleted oil. WC/a-C: H coated steel ball has the best protection effect under the conditions of debris damage and oil starvation, which is attributed to its favorable membrane conversion capacity.
SKF Company has been researching and applying DLC coating on the surface of bearing rings and rolling elements with PVD in recent years. The surface hardness of the DLC coating is 40%~80% higher than that of hardened bearing steel, the friction coefficient is similar to PTFE or MoS2, it has self-lubricating characteristics, good bonding with the matrix, no peeling, and the bearing life and wear resistance are greatly improved. It can still work normally when oil is cut off, The bearing coated with DLC is called "NoWear bearing". This technology has already been applied to compressor bearings, paper machine bearings, and hydraulic motor bearings. It is also planned to use the low friction performance of DLC coating to apply it to some energy-saving and consumption reducing occasions, such as new energy vehicles. TIMKEN uses W-aC: H to coat the rollers to avoid the adhesive wear (coating) caused by the sliding between rolling contact surfaces of roller bearings.
In recent years, DLC coatings have also been studied in China. In addition to DLC, Xi'an University of Technology and others have developed Cr doped Graphite like Carbon (GLC) coatings (Fig.). The adhesion between the coating and the substrate is improved by using Cr transition layers, and the coating strength is improved by using C/Cr multi-layer composite film forming technology. In addition to low friction and wear, it has no catalyst effect, lower brittleness, and better bonding strength. It has been successfully applied to cutting tools, greatly improving tool life. Preliminary application tests have also been carried out on the bearings. The bearing tests with steel ball coated with GLC show that the bearing vibration and temperature rise are significantly reduced at high speeds, and DLC can be used as a solid lubricating material to enable the bearings to operate for a certain period of time after a short oil cut, which is particularly important for aeroengine bearings.
Cr doped GLC coating
2. Solid lubricating coating
Is solid lubricating coating mainly applied? Soft materials or laminated structural materials with good lubrication performance are generally used in vacuum and other occasions where oil and grease lubrication is not easy to be used.
Soft metal coatings include Au, Ag, Pb, etc., which are generally formed by ion plating or sputtering. They are used for rolling bearings used in high vacuum or to improve the lubrication between the cage and the rolling element, such as silver plating on the cage of aeroengine bearings.
Typical laminated structural materials, such as MoS2 and graphite, are generally sputtered or sintered with organic or inorganic adhesives to form films. MoS2 is generally used for high vacuum and graphite is generally used for high temperature.
The polymer material, represented by PTFE, has a unique band structure, which shows low friction, easy to form a transfer lubricating film on the mating surface, and is resistant to chemicals, and is not easy to be affected by environmental media. It is generally sintered into a film with adhesives, and is used for bearings in clean or corrosion resistant environments.
When the nano diamond is on the rolling contact surface, it can reduce friction just like the rolling element in the bearing. The nano diamond coating can also be used as a lubricating coating. The CNx whose hardness may exceed that of the diamond can also be used as a solid lubricating material.
3. Other coatings
Yamada and others introduced insulated bearings for railway traction motors. One is to spray aluminum oxide coating on outer diameter surface and end face of outer ring and seal the hole with resin; One is to spray glass fiber reinforced PPS resin, and add non-conductive high thermal conductivity filler to improve thermal conductivity. Both coatings have high insulation performance, can avoid electric corrosion, and the temperature rise is the same as that of the uncoated bearing, which can effectively extend the life of the bearing.
Р.И.ДИ introduces the use of polymer materials to improve the service life of machine tool spindle bearings. Friction, corrosion and wear will occur on the mating surfaces of bearings, bearing seats and shafts, which will increase the fit clearance and increase the maximum contact stress in bearings. After the polymer coating is applied to the outer ring, the mating surface between the outer ring and the shaft is guaranteed to be in elastic contact. When the coating is loaded, elastic deformation occurs, which increases the effective bearing area in the bearing, reduces the maximum contact stress, and thus improves the service life of the bearing. When the outer ring is loaded cyclically and locally, the outer ring is coated with 6 Φ Sealant (0.125 mm thick) and ВК The bearing life of polymer (0.09 mm thick) is more than 3-4 times of the calculated life. In order to improve the load distribution coefficient in the bearing, the coating thickness should be as thick as possible, and materials with low elastic modulus should be selected.
SKF has studied the effect of blackening on bearing performance. Laboratory research, bearing test and field experience show that blackening provides a certain degree of anti friction chemical corrosion protection, can reduce hydrogen penetration, and can also enhance the ability to resist moisture corrosion damage (such as static corrosion). In addition, the blackened bearing steel surface improves the safety factor when the failure forms of the bearing such as adhesive wear, coating damage or surface fatigue occur under boundary or mixed lubrication conditions. In addition to using blackened bearings for new equipment, SKF also uses them as replacements for conventional bearings in routine maintenance of wind power plants. In order to achieve the best performance of the bearing, SKF recommends that the inner ring, outer ring and rolling element be blackened.
Low temperature ion sulfurizing is a surface modification technology developed in the late 1980s. Its basic principle is similar to that of ion nitriding. Under a certain vacuum degree, the sulfur gas is ionized by high-voltage direct current, and the generated sulfur ions bombard the workpiece surface, and react with iron on the workpiece surface to generate FeS based 10 μ M thick sulfide layer. Sulfide is a good solid lubricant, which can effectively reduce the friction coefficient of steel contact surface, and its friction coefficient will further decrease with the increase of load. Therefore, it can greatly improve the wear resistance of bearing under heavy load, and increase the service life of bearing by about 3 times.
The effect of low temperature phosphating is similar to that of sulfurizing. 0.05~0.25 can be obtained on the surface of the workpiece by immersing the workpiece in 40 ℃ TAP solution (tridecanoic acid phosphate) for 4 hours μ M thick Fe2O3 and Fe4 (P2O7) 3 surface layer, reducing friction coefficient and improving wear resistance. The phosphatized M50 steel bearing does not jam under the condition of short-term oil cut-off, which improves the reliability of the bearing.
By plating nickel on the rolling surface to inhibit hydrogen penetration, Kono Zhonglang greatly reduced the hydrogen content in the steel and prevented the exfoliation of abnormal white tissue.
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Features:
magnetic, electric, and mechanic ABS
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flange only
Steel Material: GCr15/52100/100Cr6
Steel Type: Forged
Ball Grade: G10
Grease: Shell
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2023-01-03