Ball screw having solid lubricating coating

Abstract

The present application relates to the technical field of mechanical transmission elements, and provides a ball screw with a solid lubricating coating, which comprises a screw body, a gradient composite solid lubricating coating is arranged on the surface of the thread groove of the screw body; the gradient composite solid lubricating coating comprises a wear-resistant metal phase and a solid lubricant phase, and along the thickness direction of the coating, from the bottom layer close to the screw body to the surface layer away from the screw body, the content of the solid lubricant phase gradually increases, and the content of the wear-resistant metal phase gradually decreases; under the action of micro sliding friction between the ball and the thread groove, solid lubricant particles in the coating can be continuously extruded and deposited on the friction interface to form a dynamically updated solid lubricating film. The ball screw of the present application can realize dynamic self-supply of the solid lubricant under the action of micro sliding friction, thereby realizing long-term maintenance-free operation.

Description

Technical Field

[0001] This invention relates to the field of mechanical transmission components, and more specifically, to a ball screw with a solid lubricating coating, which is particularly suitable for precision transmission systems that operate stably for a long time without external lubrication. Background Technology

[0002] Ball screws are high-efficiency transmission components that convert rotary motion into linear motion, and are widely used in CNC machine tools, robots, aerospace equipment, and precision instruments. Traditional ball screws typically rely on liquid lubricants (such as lubricating oil or grease) to reduce friction, minimize wear, and extend service life. However, liquid lubricants are prone to evaporation, degradation, or leakage under special operating conditions such as high temperatures, high vacuum, clean rooms, or confined spaces, leading to lubrication failure. Furthermore, the need for regular lubrication replenishment increases maintenance costs and system complexity.

[0003] To address the aforementioned issues, existing technologies have attempted to coat the surface of ball screws with solid lubricant coatings, such as molybdenum disulfide or graphite coatings. However, traditional solid lubricant coatings often suffer from weak adhesion, inability to replenish lubricant after consumption, and easy peeling, making it difficult to meet the requirements of long-term reciprocating motion of ball screws. Therefore, there is an urgent need to develop a ball screw structure that can continuously provide stable lubrication, requires no external oil supply, and has a long service life. Summary of the Invention

[0004] The problem solved by this invention is to overcome the problems of easy depletion of the lubricating layer, increased friction coefficient and coating peeling of existing ball screws under the condition of no external lubrication. The invention provides a ball screw with a solid lubricating coating, which can achieve dynamic self-replenishment of solid lubricant under the action of micro-motion sliding friction, thereby achieving long-term maintenance-free operation.

[0005] To address the aforementioned problems, this invention provides a ball screw with a solid lubricant coating, comprising a screw body, wherein a gradient composite solid lubricant coating is disposed on the threaded groove surface of the screw body; the gradient composite solid lubricant coating comprises a wear-resistant metal phase and a solid lubricant phase, and along the coating thickness direction from the bottom layer near the screw body to the surface layer away from the screw body, the content of the solid lubricant phase gradually increases and the content of the wear-resistant metal phase gradually decreases; under the fretting sliding friction between the ball and the threaded groove, the solid lubricant particles in the coating can be continuously extruded and deposited at the friction interface, forming a dynamically renewed solid lubricant film.

[0006] Optionally, the wear-resistant metal phase is at least one of nickel-based alloy, cobalt-based alloy, or iron-based alloy; the solid lubricant phase is at least one of graphene, tungsten disulfide, molybdenum disulfide, or graphite.

[0007] Optionally, the gradient composite solid lubricant coating is prepared by laser cladding or electrical discharge deposition, and the total thickness of the coating is 10 micrometers to 200 micrometers.

[0008] Optionally, in the surface region of the coating, the volume fraction of the solid lubricant phase is 50% to 90%; and in the bottom region of the coating, the volume fraction of the solid lubricant phase is 5% to 30%.

[0009] Optionally, the content variation between the wear-resistant metal phase and the solid lubricant phase in the coating is a continuous gradient distribution, or a multi-layered gradual distribution containing at least two discrete sub-layers, wherein the content of the solid lubricant phase in each sub-layer increases layer by layer from the bottom layer to the surface layer.

[0010] Optionally, the fretting friction is generated by the reciprocating sliding between the ball and the thread groove with an amplitude of less than 100 micrometers. This fretting friction causes the coating surface to be gradually worn away and exposes new solid lubricant particles inside, thereby achieving continuous release of lubricant.

[0011] Optionally, the ball screw requires no external supply of liquid lubricant or grease during operation; its lubrication is provided solely by the lubricating film formed by solid lubricant particles released by the gradient composite solid lubricating coating under fretting friction.

[0012] Optionally, the thickness of the lubricating film formed by the coating under fretting friction is 0.1 micrometers to 5 micrometers, and the lubricating film is continuously replenished by the coating while being consumed during the rolling of the ball, so as to keep the coefficient of friction not higher than 0.10.

[0013] Optionally, in the coating, the wear-resistant metal phase forms a continuous matrix in the bottom layer, and the solid lubricant phase is dispersed in the form of particles; in the surface layer, the solid lubricant phase forms a continuous or semi-continuous network structure, and the wear-resistant metal phase exists in the form of isolated particles, thereby providing sufficient lubricant to the surface layer while ensuring the compressive strength of the surface layer.

[0014] Compared with the prior art, the ball screw with a solid lubricating coating of the present invention has the following beneficial effects: By employing a gradient composite solid lubricant coating, the bottom layer possesses a high metallic phase content, ensuring excellent adhesion and load-bearing capacity to the ball screw substrate. The surface layer, with a high solid lubricant content, provides superior lubrication performance, overcoming the problems of poor adhesion and lubricant depletion inherent in traditional solid lubricant coatings. Utilizing the inherent micro-motion sliding friction between the balls and the thread grooves, the solid lubricant particles within the coating are actively extruded, forming a dynamically renewing lubricating film. This achieves self-lubrication and self-repairing functions, eliminating the need for any external lubricant. The continuous release of solid lubricant and the dynamic balance of the lubricating film within the coating ensure that the ball screw maintains a friction coefficient no higher than 0.10 during long-term operation, significantly extending service life and reducing maintenance costs. The coating can be prepared using laser cladding or electrical discharge deposition techniques, offering controllable processes, adjustable thickness, and suitability for ball screws of various specifications. Detailed Implementation

[0015] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0016] In the description of this specification, references to terms such as "embodiment," "one embodiment," and "one implementation" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or implementation is included in at least one embodiment or illustrative implementation of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or implementation. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or implementations.

[0017] Example 1 This embodiment provides a ball screw with a solid lubricant coating. The ball screw includes a screw body, and a gradient composite solid lubricant coating is provided on the threaded groove surface of the screw body. The gradient composite solid lubricant coating comprises a wear-resistant metal phase and a solid lubricant phase, and along the coating thickness direction, from the bottom layer near the screw body to the surface layer away from the screw body, the content of the solid lubricant phase gradually increases and the content of the wear-resistant metal phase gradually decreases.

[0018] In this embodiment, the lead screw body is made of GCr15 bearing steel. After degreasing, rust removal, and sandblasting roughening treatment, a gradient composite solid lubricant coating is prepared using laser cladding technology. The wear-resistant metal phase is selected from nickel-based alloys (such as NiCrBSi), and the solid lubricant phase is selected from a mixture of molybdenum disulfide (MoS2) and graphene. The total coating thickness is 100 micrometers.

[0019] The coating employs a continuous gradient distribution: from the bottom layer to the top layer, the volume fraction of molybdenum disulfide and graphene continuously increases from 15% in the bottom layer to 70% in the top layer, while correspondingly, the volume fraction of the nickel-based alloy continuously decreases from 85% to 30%. In the bottom layer, the nickel-based alloy forms a continuous metallic matrix, and the solid lubricant particles are dispersed, ensuring excellent bonding strength and load-bearing capacity between the coating and the lead screw matrix. In this embodiment, the bonding strength is greater than 50 MPa. In the top layer, the solid lubricant phase forms a continuous or semi-continuous network structure, and the nickel-based alloy exists in the form of isolated particles, thereby providing sufficient lubricant while maintaining the compressive strength of the surface layer. In this embodiment, the compressive strength is not less than 200 MPa.

[0020] During the operation of the ball screw, fretting friction with an amplitude of less than 100 micrometers occurs between the balls and the thread grooves. This fretting friction gradually wears down the coating surface, exposing new solid lubricant particles inside. Under the action of frictional stress, these solid lubricant particles are continuously extruded and deposited at the friction interface, forming a dynamically renewed solid lubricant film. Testing showed that the thickness of this lubricant film remained stable between 0.5 and 2 micrometers, and the coefficient of friction remained below 0.08. The entire operation requires no external supply of any liquid lubricant or grease, relying entirely on the self-released solid lubricant from the coating for lubrication.

[0021] Example 2 The difference between this embodiment and Embodiment 1 is that the gradient composite solid lubricant coating is prepared using electrical discharge deposition (EDD), and the wear-resistant metal phase is a cobalt-based alloy (such as Stellite 6), while the solid lubricant phase is a mixture of tungsten disulfide and graphite. The total coating thickness is 50 micrometers. The content of the wear-resistant metal phase and the solid lubricant phase in the coating varies in multiple layers, specifically including three discrete sublayers: the bottom layer (30 micrometers thick) has a solid lubricant phase volume fraction of 10%, the middle layer (10 micrometers thick) has a solid lubricant phase volume fraction of 40%, and the top layer (10 micrometers thick) has a solid lubricant phase volume fraction of 80%. In the bottom layer, the cobalt-based alloy forms a continuous matrix, and the solid lubricant is dispersed; in the top layer, the solid lubricant forms a continuous network structure, and the cobalt-based alloy exists as isolated particles.

[0022] The ball screw in this embodiment was tested in a simulated vacuum environment. After a cumulative stroke of 1,000 kilometers, the coefficient of friction was still below 0.10, and the coating showed no peeling or significant wear, demonstrating good self-lubrication and long service life characteristics.

[0023] Example 3 The difference between this embodiment and Embodiment 1 is that the wear-resistant metallic phase is an iron-based alloy (such as FeCrMo), and the solid lubricant phase is graphene. The total coating thickness is 150 micrometers, with a continuous gradient distribution. The graphene volume fraction in the bottom layer is 5%, and the graphene volume fraction in the surface layer is 90%. The amplitude of fretting friction is controlled within 50 micrometers. The thickness of the formed dynamic lubricating film is 0.1 to 1 micrometer, and the coefficient of friction is not higher than 0.06.

[0024] In this embodiment, due to the extremely high content of solid lubricant on the surface, a low-friction lubricating film can be quickly formed during the initial operation stage, and the high metal phase content of the coating layer ensures that the lead screw does not peel off or deform under high load conditions (the test environment is that the axial load reaches 80% of the rated dynamic load).

[0025] Example 4 This embodiment focuses on describing the microstructural characteristics of the gradient composite solid lubricant coating. In the bottom layer of the coating, the wear-resistant metal phase exists as continuous columnar or equiaxed crystals, while the solid lubricant phase is uniformly dispersed in the metal matrix as nano- or submicron-sized particles, with a volume fraction of 20%. In the intermediate transition layer of the coating, the content of the solid lubricant phase gradually increases to 50%, and the metal phase gradually loses its continuity, forming a network or interdendritic distribution. In the surface layer of the coating, the volume fraction of the solid lubricant phase reaches 75%, forming a continuous lubricating matrix, in which the wear-resistant metal phase is dispersed as isolated spherical particles. This gradient structure results in a gradual change in the coating's properties in the direction perpendicular to the surface: the bottom layer has high hardness, high bonding strength, and high fracture toughness; the surface layer has extremely low shear strength and excellent lubricity; and the intermediate layer acts as a stress buffer and performance transition layer, effectively preventing interlayer delamination under alternating contact stress.

[0026] Example 5 This embodiment describes the self-lubricating dynamic balancing process of a ball screw under typical operating conditions. At the start of operation, the fretting sliding friction between the balls and the thread grooves first removes a very thin layer of the coating surface (approximately 0.01 to 0.1 micrometers thick with each slide). The exposed solid lubricant particles immediately form a transferred lubricating film in the contact area. This lubricating film is partially squeezed or peeled off during subsequent rolling, but simultaneously, new solid lubricant is continuously squeezed out and replenished from within the coating, keeping the lubricating film thickness dynamically stable within the range of 0.1 to 5 micrometers. After 100 hours of continuous operation (3000 rpm, axial load 500 N), the coefficient of friction remained consistently between 0.07 and 0.09, and no coating wear occurred, indicating that the gradient structure of the coating effectively regulates the lubricant release rate, balancing it with the consumption rate.

[0027] Comparative Example To verify the beneficial effects of the present invention, a comparative example was set up. The ball screw of the comparative example also had a solid lubricating coating applied to the thread groove surface, but the coating was a single-layer structure, consisting of a uniform mixture of molybdenum disulfide and a nickel-based alloy (volume ratio 1:1), with a total thickness of 100 micrometers. Under the same operating conditions, the initial coefficient of friction was 0.08, but after 50 hours of operation, the coefficient of friction increased to 0.18, and large-area wear and peeling occurred on the coating surface, with localized adhesive wear in the thread groove of the screw. In contrast, the ball screw of Embodiment 1 of the present invention maintained a coefficient of friction of approximately 0.08 after 500 hours of operation under the same conditions, with only slight wear on the coating surface and no peeling, demonstrating the superiority of the gradient composite structure and dynamic self-replenishing mechanism.

[0028] Brief description of preparation method The ball screw with a solid lubricating coating of the present invention can be prepared according to the following steps: Pretreatment: The surface of the threaded groove of the lead screw body is degreased, derusted, sandblasted or laser roughened to obtain a clean surface with a certain roughness (Ra 2~5μm).

[0029] Coating material preparation: Mix wear-resistant metal powder (particle size 15~45μm) and solid lubricant powder (particle size 0.5~5μm) according to the gradient design ratio to prepare composite powders for the base layer, transition layer and surface layer respectively. For continuous gradient coatings, a dual-hopper synchronous powder feeding method can be used and the powder feeding ratio can be changed in real time.

[0030] Coating preparation: Laser cladding technology (laser power 500~2000 W, scanning speed 5~20 mm / s, spot diameter 1~3 mm, overlap rate 30~50%) or electrical discharge deposition technology (voltage 30~100 V, frequency 500~2000 Hz, deposition rate 0.01~0.1 cm² / s) is used to deposit the coating sequentially from the bottom layer to the surface layer to form a gradient composite solid lubricating coating with a total thickness of 10~200 micrometers.

[0031] Post-processing: Light polishing or brushing can be performed as needed to remove loose particles from the coating surface and ensure that the surface roughness of the thread groove meets the requirements for ball screw assembly (Ra ≤ 0.4 μm).

[0032] Through the above embodiments, the present invention achieves long-term stable operation of ball screws under conditions without external lubrication, with a low and constant coefficient of friction and a significantly extended coating life, making it particularly suitable for precision transmission systems in vacuum, clean, high-temperature or maintenance-free environments.

[0033] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A ball screw with a solid lubricating coating, characterized in that, The system includes a lead screw body, on which a gradient composite solid lubricant coating is provided on the surface of the threaded groove. The gradient composite solid lubricant coating comprises a wear-resistant metal phase and a solid lubricant phase, and along the coating thickness direction, from the bottom layer near the lead screw body to the surface layer away from the lead screw body, the content of the solid lubricant phase gradually increases and the content of the wear-resistant metal phase gradually decreases. Under the action of fretting sliding friction between the ball and the threaded groove, the solid lubricant particles in the coating can be continuously squeezed out and deposited on the friction interface to form a dynamically renewed solid lubricant film.

2. The ball screw according to claim 1, characterized in that, The wear-resistant metal phase is at least one of nickel-based alloys, cobalt-based alloys, or iron-based alloys; the solid lubricant phase is at least one of graphene, tungsten disulfide, molybdenum disulfide, or graphite.

3. The ball screw according to claim 1, characterized in that, The gradient composite solid lubricating coating is prepared by laser cladding or electrical discharge deposition, and the total thickness of the coating is 10 micrometers to 200 micrometers.

4. The ball screw according to claim 1, characterized in that, In the surface region of the coating, the volume fraction of the solid lubricant phase is 50% to 90%; in the bottom region of the coating, the volume fraction of the solid lubricant phase is 5% to 30%.

5. The ball screw according to claim 1, characterized in that, The content variation between the wear-resistant metal phase and the solid lubricant phase in the coating is a continuous gradient distribution, or a multi-layered gradual distribution containing at least two discrete sub-layers, wherein the content of the solid lubricant phase in each sub-layer increases layer by layer from the bottom layer to the surface layer.

6. The ball screw according to claim 1, characterized in that, The micro-motion sliding friction is generated by the reciprocating sliding between the ball and the thread groove with an amplitude of less than 100 micrometers. This micro-motion sliding friction causes the coating surface to be gradually worn away and exposes new solid lubricant particles inside, thereby achieving continuous release of lubricant.

7. The ball screw according to claim 1, characterized in that, The ball screw requires no external supply of liquid lubricant or grease during operation; its lubrication is provided solely by the lubricating film formed by solid lubricant particles released by the gradient composite solid lubricating coating under fretting friction.

8. The ball screw according to claim 1, characterized in that, The thickness of the lubricating film formed by the coating under fretting friction is 0.1 micrometers to 5 micrometers, and the lubricating film is continuously replenished by the coating while being consumed during the rolling of the ball, so as to keep the coefficient of friction not higher than 0.

10.

9. The ball screw according to claim 1, characterized in that, In the coating, the wear-resistant metal phase forms a continuous matrix in the bottom layer, and the solid lubricant phase is dispersed in the form of particles; in the surface layer, the solid lubricant phase forms a continuous or semi-continuous network structure, and the wear-resistant metal phase exists in the form of isolated particles, thereby providing sufficient lubricant to the surface layer while ensuring the compressive strength of the surface layer.