Anti-wear precise chain roller with smooth surface and preparation method thereof

Abstract

The invention belongs to the technical field of chains, and particularly relates to a precise chain roller with a smooth surface and abrasion resistance and a preparation method thereof. The invention provides a steel roller which is provided with a DLC final working surface on an excircle mirror surface, an excircle has no texture, and only an inner hole is provided with a micron-sized spiral microgroove. The process is implemented according to the sequence of carburizing / quenching / tempering-shot blasting-fine grinding-superfinishing-vacuum PVD, a diamond-like carbon composite coating is formed on an outer circle, and oil storage and capillary pumping are carried out through control of an outer edge fillet, residual compressive stress and DLC adhesive force and an inner hole microgroove, so that work division of antifriction bearing and oil supply functions is realized. A chain provided with the anti-abrasion precision roller with the smooth surface gives consideration to low friction, low noise and stripping resistance under the boundary lubrication and impact-rolling composite working conditions.

Description

Technical Field

[0001] This invention belongs to the field of chain technology, specifically relating to a smooth, wear-resistant precision chain roller and its preparation method. Background Technology

[0002] Roller chains operate under complex environments such as high loads, boundary lubrication, and dust. Repeated impacts and rolling contacts occur between the outer circumference of the rollers and the sprocket teeth. During startup and low-speed phases, micro-scratches and galling are highly likely to occur because the oil film has not yet been established. Simultaneously, the roller and bushing assembly experiences abrasive wear and increased noise under radial loads and micro-slippage. To improve lifespan, the industry has long adopted a "heat treatment plus surface engineering" approach: introducing residual compressive stress through carburizing or through-hardening and shot peening, and applying a hard coating to the contact surfaces to reduce friction and wear. Represented by Chinese patent CN112236251A, a general technical solution for applying hard material coatings to chain drive components is disclosed. It points out that PVD produces a thinner coating on the inside of holes or narrow inner surfaces, while CVD can achieve relatively uniform coating on loosely packed small parts. These conclusions indirectly confirm the differences in processing-coating accessibility and process constraints of different surfaces (outer working surface and inner hole) of chain components.

[0003] On the other hand, CN1450285A directly addresses the contact area of ​​the chain by proposing the formation of a hard coating on at least the inner surface of the sleeve. Examples of coating materials include TiN, CrN, DLC, Ni-P, etc. It further mentions that a hard metal layer can be applied to the surface of the connecting pin to improve oxidation resistance and suppress abnormal elongation. However, its technical focus is on the general idea of ​​"applying a coating to the contact surface" and does not limit the parameters between the target roughness of the outer circle of the roller, the outer edge transition fillet, the residual compressive stress and the coating adhesion. It also does not propose any technical inspiration to transfer the lubrication retention structure from the outer working surface of the roller to the inner hole of the roller.

[0004] In summary, firstly, using hard coatings (including DLC) on chain components and improving the substrate strength and toughness through heat treatment or shot peening is a mature approach. Secondly, while there has been discussion regarding coating accessibility and differences between inner and outer surfaces, the focus has been primarily on the deposition process, without structurally translating this understanding into a functional division design at the chain roller level. From an engineering perspective, while introducing oil reservoirs or textures directly onto the outer working surface of the traditional approach may benefit initial lubrication, it can lead to fluctuations in meshing stiffness, contact stress concentration, and the risk of localized peeling, potentially resulting in increased high-frequency noise. Conversely, pursuing excessively thick coatings can shorten the DLC lifespan due to repeated impacts and edge tensile stress. Furthermore, from a manufacturing feasibility perspective, physical vapor deposition (PVD) has limitations in 10... -4The process, carried out at -10 Pa and several hundred degrees Celsius, limits the coating efficiency and thickness of the pore inner wall. While chemical vapor deposition (CVD) can improve the coverage inside the pore, its typical process temperature is high and it imposes constraints on material-dimensional stability and batch economics. Therefore, simply relying on depositing a thick film inside the pore to solve the problem of internal pore lubrication and durability is not the optimal engineering approach. Summary of the Invention

[0005] To overcome the above-mentioned technical problems, the present invention achieves low friction, low noise and long service life of roller chains under boundary lubrication and impact-rolling conditions by concentrating the friction reduction load on the outer circular mirror surface DLC (outer circular texture) and dividing the function of pumping and transferring oil to the inner micron-level spiral groove.

[0006] To achieve the above-mentioned technical objectives, the present invention provides the following technical solution.

[0007] A smooth, wear-resistant precision chain roller includes a steel base and a surface layer located on the outer circumferential surface of the base. The outer circular surface layer is a diamond-like carbon (DLC) composite coating. The composite coating includes a metal transition layer and a DLC top layer from the inside to the outside. The metal transition layer is composed of Cr and / or CrN and has a thickness of 0.2-0.5 μm. The DLC top layer has a thickness of 0.6-1.2 μm. The composite coating constitutes the final friction surface of the outer circle. The outer circular surface is free of any oil-retaining texture (including grooves, pits, mesh patterns, or laser micro-textures). The arithmetic mean roughness Ra on the outer circular surface after coating is completed is ≤0.05μm, and the radius of the outer edge transition fillet is 0.10-0.30mm. The inner surface of the roller is provided with a continuous spiral microgroove structure. The groove depth of the spiral microgroove is 2-5μm, the pitch is 0.5-1.0 mm, and the helix angle is 15-35°. It is used to retain and pump the lubricant. The spiral microgroove is on the micrometer scale and does not extend to the outer surface. The combination of the outer DLC coating and the spiral microgroove in the inner hole is used to reduce friction and noise and suppress coating peeling under meshing and boundary lubrication conditions.

[0008] Preferably, the DLC is hydrogenated amorphous carbon (aC:H) and / or tetrahedral amorphous carbon (ta-C).

[0009] Preferably, the residual compressive stress on the outer circular surface is ≤-600 MPa, the critical adhesion force Lc2 of the DLC coating is ≥30 N, and Ra is ≤0.05 μm measured on the outer circular surface after coating film formation.

[0010] Preferably, the cylindricity of the outer circular surface is ≤0.005 mm, and the coaxiality between the outer circle and the inner hole is ≤0.01 mm.

[0011] Preferably, the spiral microgroove has a top radius of 5-20 μm, a dome or isosceles trapezoidal shape, and a microgroove coverage of 15-35% of the inner hole surface area. Furthermore, the surface roughness Ra of the inner hole after microgroove processing is 0.2-0.4 μm.

[0012] Preferably, the matrix is ​​20CrMnTi treated with carburizing or carbonitriding and quenching and tempering, with a surface hardness of 60-64 HRC; or it is GCr15 treated with through quenching and tempering, with a surface hardness of 60-64 HRC.

[0013] Preferably, the metal transition layer is a gradient transition layer, which gradually changes from Cr to CrN along the thickness direction to improve adhesion to the DLC top layer and suppress edge peeling.

[0014] The present invention also discloses a method for manufacturing the above-mentioned precision chain roller, comprising the following steps: a) Carburizing or through-hardening and tempering are performed on steel roller blanks to form a hardened layer; b) Shot peening is applied to the outer circumference of the steel rollers to introduce a compressive stress layer; c) Grind and hone the outer diameter and inner hole of the steel roller, and round the outer edge to R0.10-0.30 mm; d) Only the inner hole is machined to form a spiral microgroove, with a groove depth of 2-5 μm, a pitch of 0.5-1.0 mm, and a helix angle of 15-35°; e) Perform ultra-precision machining on the outer diameter of the steel roller to achieve a surface roughness of Ra≤0.05μm; f) Sequentially deposit a Cr and / or CrN metal transition layer (0.2-0.5 μm) and a DLC top layer (0.6-1.2 μm) on the outer surface of the steel roller. g) Final inspection: Confirm that the outer surface of the steel roller simultaneously meets the requirements of Ra≤0.05 μm, residual compressive stress≤-600 MPa and DLC scratch critical adhesion force Lc2≥30 N; if not, iteratively correct the requirements by adjusting the shot peening intensity and the amount of ultra-finishing until they are met.

[0015] Preferably, step f) involves sequentially depositing a Cr and / or CrN transition layer and a DLC top layer using vacuum PVD, with ion beam cleaning performed before deposition, and the substrate temperature being 120-180 °C and the substrate negative bias being 50-200 V during the deposition process.

[0016] The present invention also discloses a chain comprising a plurality of rollers, at least a portion of which are the aforementioned precision chain rollers, to reduce meshing noise and improve wear life under rated load and standard lubrication conditions.

[0017] The steel substrate of this invention uses mirror-finished DLC as the final working surface on its outer circle. It constructs a low-shear, low-adhesion interface by virtue of its low surface energy and high hardness. The absence of texture on the outer circle avoids local stress concentration and contact stiffness fluctuations. The outer edge fillet and the residual compressive stress on the outer circle together inhibit crack initiation and edge spalling. The inner hole is arranged with micron-level spiral microgrooves to form a capillary-spiral coupled passive pumping and oil storage channel, maintaining film supply in the boundary and mixed lubrication zone, thereby realizing the solution of "the outer circle bears the friction reduction load and the inner hole is responsible for oil holding and supply". At the same time, it ensures the structural stability and long-term adhesion of the coating under impact-rolling composite load.

[0018] The beneficial technical effects of this invention are as follows: The design of this invention can quickly establish a stable lubricating film during the start-up and low-speed phases, reducing the risk of adhesion and scratches, and suppressing high-frequency noise caused by meshing stiffness fluctuations. During long-term cycling, the outer cylindrical mirror-like DLC maintains uniform contact and low friction, and the residual compressive stress and rounded corner geometry work together to delay edge micro-cracks and spalling. The inner spiral microgroove continuously supplies oil and enhances adaptability to harsh working conditions. Overall, this results in reduced wear, lower noise, improved dimensional stability and lifespan. At the same time, in terms of manufacturing, it can be implemented by simply optimizing the sequence and process of existing heat treatment, shot peening, ultra-finishing and PVD processes, ensuring consistency and manufacturability. Attached Figure Description

[0019] Figure 1 This is an electron microscope image of the internal spiral microgroove of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0021] The precision chain roller of the present invention adopts an outer circular mirror DLC as the final friction surface, combined with a continuous spiral microgroove arranged in an inner hole, to form the following functional division.

[0022] Outer circumference: The final friction surface is a composite coating consisting of a metal transition layer and the top layer of DLC. The outer circumference has no oil-retaining texture, and the outer edge uses a small rounded corner transition. Inner hole: Micron-level continuous spiral microgrooves are incorporated. Under rolling-impact combined loads and boundary lubrication, a stable oil film supply channel is established in the contact area between the inner hole and the outer circumference through capillary and micro-flow pumping effects. This avoids edge stress concentration and early peeling of the DLC caused by textured surfaces on the outer circumference. This design reduces friction and noise in the finished product and inhibits coating peeling.

[0023] I. Materials and Dimensions The steel matrix can be selected from 20CrMnTi (carburized) or GCr15 (through-quenching and tempering). The typical geometry of the rollers is determined according to the target chain specifications. It is preferred that the outer circle cylindricity be ≤0.005 mm and the outer circle-inner hole coaxiality be ≤0.01 mm to ensure meshing consistency and low noise.

[0024] II. Manufacturing Process Flow Taking 20CrMnTi as an example, the process includes the following steps (also applicable to GCr15 with corresponding adjustments to heat treatment parameters): S1. Blank and Pre-machining: Turning / stamping—cold extrusion—re-turning, leaving a finishing allowance of 0.05-0.10 mm. S2. Heat Treatment: Carburizing or carbonitriding (carburizing temperature 900-940°C, carbon potential 0.9-1.2%) → oil quenching → low-temperature tempering, surface hardness 60-64 HRC, effective hardened layer depth 0.6-1.2 mm, core hardness ≥35 HRC. S3. Shot Peening: S170-S230, Almen strength 0.20-0.35 mmA, coverage ≥200%, placed before fine grinding to construct a compressive stress layer on the outer surface. S4. Precision Forming: Fine grinding and honing of the outer diameter, chamfering the outer edge to R0.10-0.30 mm; fine honing of the inner hole to control Ra to 0.2-0.4 μm. S5 Internal Hole Microgrooving: Continuous spiral microgrooves are formed only in the internal holes; the preferred machining methods are micro-drill diamond single-point turning or ultra-short pulse laser engraving; groove depth 2-5μm, pitch 0.5-1.0 mm, helix angle 15-35°, and groove top radius 5-20μm. S6 External Diameter Ultra-finishing: Ultra-finishing and mirror polishing are performed on the external diameter, controlling Ra≤0.05μm. S7 Coating Deposition (PVD): Vacuum PVD is used to sequentially deposit a Cr / CrN metal transition layer (0.2-0.5μm) and a DLC top layer (0.6-1.2μm), with ion beam cleaning for 30-180 s before deposition; substrate temperature 120-180 °C, substrate negative bias 50-200V. S8 Final Inspection and Grouping: Ra, XRD residual stress, scratch adhesion (Lc2), cylindricity, and coaxiality are tested on the external diameter; qualified parts are then warehoused and assembled.

[0025] Note: Ni–P–SiC composite plating can also be used as an alternative top layer, but DLC system is preferred.

[0026] III. Key Process Parameters Outer circle: Ra≤0.05μm; outer edge R=0.10-0.30 mm; residual compressive stress≤-600 MPa (compressive stress is negative); DLC Lc2≥30 N.

[0027] Inner hole spiral microgroove: depth 2-5μm, pitch 0.5-1.0 mm, helix angle 15-35°, groove top radius 5-20μm; inner hole Ra=0.2-0.4μm.

[0028] IV. Experimental Methods and Evaluation Indicators Roughness Ra: ISO 4287, white light interferometer, measuring point 6, take the mean ±SD (final surface of outer circle); Cylindricity and coaxiality: CMM coordinate measuring machine; Residual stress: XRD, taking the values ​​in the principal stress directions; Adhesion: ISO 26443 scratch test, record Lc2.

[0029] Friction and wear: Test bench 1: Pin-disc method (ASTM G99); load 20 N, lubricant ISOVG32, 25 °C; record starting friction μ0, steady state μS, and volumetric wear V.

[0030] Test bench two: Chain-sprocket meshing test bench, with pitch and number of teeth according to the corresponding specifications, axial tension of 1000 N, chain speed of 5 m / s; quantitative lubrication dripping oil of 0.20 mL / min; recording meshing noise dB(A), temperature rise, and elongation. Noise level is measured according to IEC 61672-1 Class 1 sound level meter, placed 100 mm away from the chain in the normal direction.

[0031] durable: Impact-rolling composite durability: Cycle load 0.8-1.2×F rated, 20-25 °C, RH≤60%; record the number of cycles Npeel until the first edge peeling occurs (SEM / metallographic criterion).

[0032] Corrosion-lubrication retention: Retest μ and V after 24-72 h according to ISO 9227 NSS.

[0033] V. Examples and Comparative Examples Example 1 (E1: 20CrMnTi material of the present invention) Material heat treatment: 20CrMnTi carburizing at 930 °C for 4.5 h with a carbon potential of 1.0%, oil quenching at 70 °C, and tempering at 170 °C for 1.5 h; surface hardness 62 HRC, hardened layer 0.9 mm; Shot peening S230, 0.30mmA, coverage ≥200%; Outer diameter precision grinding: Ra=0.035μm; outer edge R=0.2 mm; Inner hole microgrooves: single-point diamond machining, depth 3μm, pitch 0.7 mm, helix angle 25°, groove top radius 10μm; inner hole Ra=0.3μm; PVD: Cr / CrN 0.35μm, DLC 0.9μm; ion cleaning 90s; substrate 150 °C, negative bias 120 V.

[0034] Final inspection: XRD residual stress on the outer circle -720 MPa; Lc2=36 N; cylindricity 0.003 mm, coaxiality 0.007 mm.

[0035] Example 2 (E2: GCr15 material of the present invention) Material heat treatment: GCr15 oil quenched at 850 °C, tempered at 165 °C for 2 hours; hardness 63 HRC; The rest is the same as E1, but the DLC thickness is 0.8μm; final inspection: residual stress -680 MPa; Lc2=34 N.

[0036] Comparative Example 1 (C1: 20CrMnTi material, with shallow texture and DLC on the outer circle; no groove in the inner hole) Same as E1, but with shallow dimples (diameter 60-80μm, depth 3-5μm, surface density 8-10%) laser-etched on the outer circle; no microgrooves are machined on the inner hole.

[0037] Comparative Example 2 (C2: 20CrMnTi material, inner annular groove (non-spiral), DLC; outer circle without texture) Same as E1, but the inner hole is changed to 3 annular grooves (3μm deep, 0.15 mm wide, 0.7 mm apart), without continuous spiral; outer circular mirror surface DLC.

[0038] Comparative Example 3 (C3: 20CrMnTi material, outer circular mirror DLC; no groove in the inner hole) Same as E1, but without the internal hole machining groove; the external cylindrical mirror finish DLC is retained.

[0039] The number of samples in each group is n=6, and the mean ± standard deviation is taken.

[0040] VI. Results and Discussion Table 1. Surface and adhesion, geometric properties (mean ± SD) As shown in Table 1, the Ra, residual stress, and Lc2 of the five groups of outer circles all meet the standards, and the differences in surface and geometric quality do not constitute the main influencing factors.

[0041] The test results of friction, wear and meshing noise of the sample are shown in Table 2.

[0042] Table 2 Friction, Wear and Noise (Boundary Lubrication: VG32 0.2 mL / min; Chain Speed ​​5 m / s; T=25 °C) As shown in Table 2, compared to C3, E1 exhibits a decrease of approximately 17% in starting friction μ0, a decrease of approximately 46% in wear volume V, and a decrease of approximately 2.1 dB(A) in noise. Compared to C1 and C2, E1 is significantly superior in both noise and wear. The various indicators of E2 are slightly higher than those of E1, but are still better than those of C1, C2, and C3.

[0043] The durability test results of the samples are shown in Table 3.

[0044] Table 3 DLC edge peel life (roll-impact composite, 20-25 °C) As can be seen from Table 3, the edge peeling lifetime of Examples E1 and E2 is significantly higher than that of Comparative Examples C1, C2 and C3.

[0045] In summary, under rolling-impact conditions, the edges or notches of the DLC are the source of peeling. Although the textured outer circle can retain oil, the local tensile stress generated at the textured edge will significantly reduce Npeel (as shown in Comparative Example C1). This invention chooses to leave the outer circle untextured and use rounded corners to blunt the edges, combined with a shot-peeled compressive stress layer and high-adhesion DLC, thus inherently eliminating common peeling trigger points. The continuous spiral microgroove in the inner hole creates a pumping effect: compared to the annular groove (Comparative Example C2), the continuous spiral provides an axially connected capillary and shear coupling flow path in reciprocating and / or oscillating contact, maintaining an oil film in the contact area even with extremely low dripping (boundary lubrication). Starting friction and steady-state friction are reduced simultaneously, and noise is reduced by decreasing interference and vibration amplitude. The microgroove depth of 2-5 μm, the pitch of 0.5-1.0 mm, and the helix angle of 15-35° together ensure that "effective oil return and supply can be formed without causing a significant decrease in hole wall strength and assembly accuracy"; the outer circle Ra≤0.05μm, the residual compressive stress≤-600 MPa, and Lc2≥30 N together ensure the adhesion and crack resistance of DLC on the mirror substrate.

[0046] It should be understood that: materials can be replaced with equivalent steels such as 20CrMnTi, 20CrMo, SCM420, and GCr15; the DLC type can be selected between aC:H and ta-C; process parameters such as Cr / CrN transition layer, bias voltage, matrix temperature, ion cleaning time, shot peening Almen intensity, and ultra-finishing peak removal amount can be adjusted equivalently within the stated range according to product specifications and equipment capabilities; if corrosion resistance is emphasized in the working conditions, a thin Ni-P layer can be placed in front of the DLC as a barrier, but macroscopic textures must not be formed on the outer circle; the groove depth, pitch, helix angle, and coverage of the internal microgroove can be replaced equivalently according to the lubricant viscosity and target linear speed; the processing method of the internal microgroove can be replaced by diamond micro-blade, ultra-short pulse laser, chemical anisotropic etching (with mask), etc., as long as continuous spiral and micron-level window are met; detection methods, benchmarks, and criteria can also be replaced by industry-recognized equivalent methods. Without departing from the spirit and essence of this invention, any equivalent substitution, optimization, or arbitrary combination of the technical features (including cross-combination of features from different embodiments) shall fall within the protection scope of this invention.

Claims

1. A smooth, wear-resistant precision chain roller, comprising a steel substrate and a surface layer located on the outer circumferential surface of the substrate, characterized in that, The outer circular surface layer is a diamond-like carbon (DLC) composite coating. The composite coating includes a metal transition layer and a DLC top layer from the inside to the outside. The metal transition layer is composed of Cr and / or CrN and has a thickness of 0.2-0.5 μm. The DLC top layer has a thickness of 0.6-1.2 μm. The composite coating constitutes the final friction surface of the outer circle. The outer circular surface has no oil-retaining texture. The arithmetic mean roughness Ra on the outer circular surface after coating is completed is ≤0.05μm, and the outer edge transition fillet radius R is 0.10-0.30 mm. The inner surface of the roller is provided with a continuous spiral microgroove structure. The groove depth of the spiral microgroove is 2-5μm, the pitch is 0.5-1.0 mm, and the helix angle is 15-35°. The spiral microgroove is on the micrometer scale and does not extend to the outer circular surface.

2. The precision chain roller according to claim 1, characterized in that, The DLC is hydrogenated amorphous carbon (aC:H) and / or tetrahedral amorphous carbon (ta-C).

3. The precision chain roller according to claim 1, characterized in that, The residual compressive stress on the outer circular surface is ≤-600 MPa, the critical adhesion force Lc2 of the DLC coating is ≥30 N, and Ra≤0.05μm is measured on the outer circular surface after the coating is formed.

4. The precision chain roller according to claim 3, characterized in that, The cylindricity of the outer circular surface is ≤0.005mm, and the coaxiality between the outer circle and the inner hole is ≤0.01mm.

5. The precision chain roller according to claim 1, characterized in that, The spiral microgroove has a top radius of 5-20 μm, a dome or isosceles trapezoid shape, a microgroove coverage of 15-35% of the inner hole surface area, and an inner hole surface roughness Ra of 0.2-0.4 μm after microgroove processing.

6. The precision chain roller according to claim 1, characterized in that, The matrix is ​​20CrMnTi, which has been carburized or carbonitrided and quenched and tempered, with a surface hardness of 60-64 HRC; or it is GCr15, which has been quenched and tempered through, with a surface hardness of 60-64 HRC.

7. The precision chain roller according to claim 1, characterized in that, The metal transition layer is a gradient transition layer, which gradually changes from Cr to CrN along the thickness direction to improve adhesion to the DLC top layer and suppress edge peeling.

8. A method for manufacturing the precision chain roller according to any one of claims 1-7, characterized in that, Includes the following steps: a) Carburizing / through-hardening and tempering are performed on the steel roller blank to form a hardened layer; b) Shot peening is applied to the outer circumference of the steel rollers to introduce a compressive stress layer; c) Grind and hone the outer diameter and inner hole of the steel roller, and round the outer edge to a radius R of 0.10-0.30 mm; d) Helical microgrooves are machined only in the inner bore of steel rollers, with a groove depth of 2-5 μm, a pitch of 0.5-1.0 mm, and a helix angle of 15-35°; e) Perform ultra-precision machining on the outer diameter of the steel roller to achieve a surface roughness of Ra≤0.05 μm; f) A Cr and / or CrN metal transition layer (0.2-0.5 μm) and a DLC top layer (0.6-1.2 μm) are sequentially deposited on the outer surface of a steel roller using a vacuum PVD process. g) Final inspection: Confirm that the outer surface of the steel roller simultaneously meets the requirements of Ra≤0.05μm, residual compressive stress≤-600 MPa and DLC scratch critical adhesion Lc2≥30 N; if not, adjust the shot peening intensity and superfinishing amount until they are met.

9. The method according to claim 8, characterized in that, In step d), Cr and / or CrN transition layers and DLC top layer are deposited sequentially by vacuum PVD. Ion beam cleaning is performed before deposition. During the deposition process, the substrate temperature is 120-180 °C and the substrate negative bias voltage is 50-200 V.

10. A chain comprising a plurality of rollers, characterized in that, At least a portion of the rollers are precision chain rollers as described in any one of claims 1-7, to reduce meshing noise and improve wear life under rated load and standard lubrication conditions.

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