Self-lubricating composite material and application thereof, composite friction-reducing layer and preparation method thereof

Abstract

The application provides a kind of self-lubricating composite material and its application, composite friction-reducing layer and its preparation method, and relates to the technical field of friction pair friction-reducing.The self-lubricating composite material provided by the application includes polyamide-imide 85-95%, graphite 4-14.9% and silicon dioxide powder 0.1-1% by mass percentage.The polyamide-imide (PAI) has good mechanical properties, wear resistance and scratch resistance;the graphite is a solid lubricant and has good lubricating property;SiO2 is a reinforcing agent and can form a friction surface sub-surface enrichment in the friction process, which has a reinforcing effect on the friction surface.The self-lubricating composite material of the application can greatly reduce the friction coefficient of cylinder and plunger body when used in the friction-reducing layer of friction pair, reduce friction heat, and PAI and steel will not cold weld, which fundamentally improves the reliability and stability of plunger pump.

Description

Technical Field

[0001] This invention relates to the field of friction pair friction reduction technology, and in particular to a self-lubricating composite material and its application, a composite friction-reducing layer and its preparation method. Background Technology

[0002] The high-pressure plunger pump is the heart of the engine; the reciprocating motion of the plunger pair, like the contraction of the heart, provides the engine with blood and energy. The plunger pump has three main friction pairs: the plunger pair, the slipper pair, and the distributor plate friction pair. The tribological properties of these friction pairs directly affect the performance of the plunger pump.

[0003] Traditionally, a tin bronze anti-friction layer is diffused and welded onto the surfaces of the three friction pairs to avoid direct steel / steel friction. However, the friction between tin bronze and steel has the following drawbacks: First, the wear form between tin bronze and steel is abrasive wear. During the friction process, a large amount of wear debris is generated. This wear debris is repeatedly squeezed between the steel and tin bronze to form hard particles, causing more severe wear on the tin bronze and leading to failures such as plunger jamming. Second, the friction coefficient between tin bronze and steel is 0.4 to 0.6. The high friction coefficient leads to a large amount of frictional heat and frictional work. On the one hand, it prevents the plunger pump speed from increasing, and on the other hand, it easily causes the tin bronze to jam due to thermal expansion. Third, during the friction process, the tin bronze anti-friction layer is prone to cold welding with the plunger body. There are three basic conditions for cold welding: (1) fresh surface, during the friction process, the surface oxide layer falls off and a fresh surface is exposed; (2) a certain temperature, frictional heat can lead to local temperature rise; (3) pressure, the plunger movement generates pressure. When these conditions are met, Cu in tin bronze and Fe in steel will form CuFe intermetallic compounds, resulting in cold welding, which affects the reliability and stability of the plunger pump. Summary of the Invention

[0004] The purpose of this invention is to provide a self-lubricating composite material and its application, a composite friction-reducing layer and its preparation method. Using the self-lubricating composite material provided by this invention as a friction-reducing layer for plunger pairs can improve the reliability and stability of plunger pump operation.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The present invention provides a self-lubricating composite material comprising, by weight percentage, 85-95% polyamide-imide, 4-14.9% graphite, and 0.1-1% silica powder.

[0007] Preferably, the graphite has a particle size of 2–75 μm; the silica powder has a particle size of 20–100 nm; and the polyamide-imide has a particle size ≤75 μm.

[0008] This invention provides the application of the self-lubricating composite material described above in the friction-reducing layer of a friction pair.

[0009] The present invention provides a composite friction-reducing layer comprising a copper bonding layer, a tin bronze three-dimensional network layer, and a self-lubricating coating sequentially stacked and attached to the surface of a plunger cylinder; the self-lubricating coating and the tin bronze three-dimensional network layer are interlocked; the self-lubricating coating is formed from the self-lubricating composite material described above.

[0010] Preferably, the thickness of the copper bonding layer is 10–15 μm; the thickness of the tin bronze three-dimensional network layer is 0.1–0.3 mm; and the thickness of the self-lubricating coating is 0.1–0.3 mm.

[0011] This invention provides a method for preparing the composite friction-reducing layer described above, comprising the following steps:

[0012] Copper is plated on the inner surface of the plunger cylinder body to form a copper bonding layer, thus obtaining the first plunger cylinder body;

[0013] The first plunger cylinder is filled with tin bronze powder and sintered to form a tin bronze three-dimensional network structure. The tin bronze three-dimensional network structure is then processed to the target thickness to form a tin bronze three-dimensional network layer, resulting in the second plunger cylinder.

[0014] A polytetrafluoroethylene (PTFE) core rod is placed at the center of the second plunger cylinder, with an annular space left between the PTFE core rod and the tin bronze three-dimensional network layer. The self-lubricating composite material is filled into the annular space, and axial pressure is applied to both the PTFE core rod and the self-lubricating composite material simultaneously. A second sintering is then performed. During the second sintering process, the self-lubricating composite material enters the gaps in the tin bronze three-dimensional network layer and forms an interlocking structure with the tin bronze three-dimensional network layer. The PTFE core rod is then removed to form a self-lubricating coating, thus obtaining the composite friction-reducing layer.

[0015] Preferably, the tin bronze powder is spherical with a particle size of 60–200 μm.

[0016] Preferably, the temperature of the first sintering is 760-800℃, and the holding time is 1-3h.

[0017] Preferably, the axial pressure is 30 to 70 MPa.

[0018] Preferably, the second sintering temperature is 360-380°C and the holding time is 1-3 hours.

[0019] This invention provides a self-lubricating composite material, comprising, by weight percentage, 85-95% polyamide-imide, 4-14.9% graphite, and 0.1-1% silica powder. Polyamide-imide (PAI) possesses excellent mechanical properties, wear resistance, and scratch resistance; graphite, as a solid lubricant, exhibits good lubrication properties; and SiO2, as a reinforcing agent, forms a subsurface enrichment on the friction surface during friction, thus enhancing the friction surface. Using this self-lubricating composite material as a friction-reducing layer in friction pairs can significantly reduce the friction coefficient between the cylinder block and the plunger body, reducing frictional heat. Furthermore, PAI does not undergo cold welding with steel, fundamentally improving the reliability and stability of the plunger pump.

[0020] This invention provides a composite friction-reducing layer, comprising a copper bonding layer, a tin bronze three-dimensional network layer, and a self-lubricating coating sequentially stacked and adhered to the surface of a plunger cylinder. The self-lubricating coating is interlocked with the tin bronze three-dimensional network layer. The self-lubricating coating is formed from the self-lubricating composite material described above. In this invention, the copper bonding layer enhances the bonding strength between the cylinder and the tin bronze three-dimensional network layer; the tin bronze layer has a three-dimensional network structure and interlocks with the self-lubricating coating, improving the bonding strength of the self-lubricating coating. The composite friction-reducing layer of this invention has high bonding strength with the plunger cylinder, and can withstand both the reciprocating friction of the plunger and the high-pressure scouring of the oil during plunger compression. Moreover, during operation, the self-lubricating coating is in contact with the plunger body, exhibiting good lubrication performance.

[0021] This invention provides a method for preparing the composite friction-reducing layer described above. Since the PAI composite powder (i.e., self-lubricating composite material) must be in a high-temperature molten and pressurized state to enter the three-dimensional network structure of tin bronze and form an interlocking relationship, and the composite powder cannot be directly pressurized by a hydraulic press on the annular inner wall of the plunger, the molding of the composite powder is the difficulty and key point of this invention. The coefficient of thermal expansion of polytetrafluoroethylene (PTFE) is approximately 10 times that of steel, resulting in a large expansion volume at 360°C. This invention utilizes a limiting sintering method to restrict the axial expansion of PTFE, transforming the axial pressure into radial compression of the PAI composite powder by PTFE, thereby achieving physical interlocking between PEEK and tin bronze. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the composite friction-reducing layer of the present invention. Detailed Implementation

[0023] The present invention provides a self-lubricating composite material comprising, by weight percentage, 85-95% polyamide-imide, 4-14.9% graphite, and 0.1-1% silica powder.

[0024] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0025] The self-lubricating composite material provided by the present invention comprises 85-95% polyamide-imide, preferably 88-93%, and more preferably 90-91% by mass percentage. In the present invention, the particle size of the polyamide-imide is preferably ≤75 μm. In the present invention, polyamide-imide (PAI) exhibits good mechanical properties, wear resistance, and scratch resistance.

[0026] The self-lubricating composite material provided by the present invention comprises 4-14.9% graphite, preferably 5-13%, and more preferably 8-10% by mass percentage. In the present invention, the particle size of the graphite is preferably 2-75 μm, more preferably 10-70 μm, and even more preferably 20-50 μm. In the present invention, the graphite is a solid lubricant with good lubrication properties.

[0027] The self-lubricating composite material provided by this invention comprises 0.1-1% silica powder, preferably 0.2-0.8%, and more preferably 0.4-0.6% by mass percentage. In this invention, the particle size of the silica powder is preferably 20-100 nm, more preferably 40-80 nm, and even more preferably 50-70 nm. In this invention, SiO2 is a reinforcing agent, which forms a subsurface enrichment on the friction surface during friction, thus enhancing the friction surface.

[0028] Using the self-lubricating composite material of the present invention as the friction-reducing layer of the friction pair can significantly reduce the friction coefficient between the cylinder and the plunger body, reduce frictional heat, and at the same time, PAI and steel will not undergo cold welding, fundamentally improving the reliability and stability of the plunger pump.

[0029] The present invention does not have any special requirements for the preparation method of the obtained self-lubricating composite material; the components can be directly mixed evenly.

[0030] This invention provides a composite friction-reducing layer, such as Figure 1 As shown ( Figure 1 The copper bonding layer (not shown) includes a copper bonding layer, a tin bronze three-dimensional network layer, and a self-lubricating coating that are sequentially stacked and attached to the surface of the plunger cylinder; the self-lubricating coating is interlocked with the tin bronze three-dimensional network layer; the self-lubricating coating is formed by the self-lubricating composite material described in the above scheme.

[0031] The composite friction-reducing layer provided by this invention includes a copper bonding layer attached to the surface of the plunger cylinder. In this invention, the thickness of the copper bonding layer is preferably 10–15 μm. In this invention, the copper bonding layer can improve the bonding strength between the plunger cylinder and the tin bronze three-dimensional network layer.

[0032] The composite friction-reducing layer provided by this invention includes a tin bronze three-dimensional network layer attached to the surface of the copper bonding layer. In this invention, the thickness of the tin bronze three-dimensional network layer is preferably 0.1–0.3 mm, more preferably 0.15–0.25 mm. In this invention, the tin bronze three-dimensional network layer is tightly bonded to the outer cylinder body through sintering, and the self-lubricating composite material filling can be embedded into the network structure under pressure. This structure improves the bonding strength between the self-lubricating coating and the cylinder body.

[0033] The composite friction-reducing layer provided by the present invention includes a self-lubricating coating attached to the surface of the tin bronze three-dimensional network layer; the self-lubricating coating and the tin bronze three-dimensional network layer are interlocked. In the present invention, the thickness of the self-lubricating coating is preferably 0.1 to 0.3 mm, more preferably 0.15 to 0.25 mm.

[0034] In this invention, the tin bronze layer has a three-dimensional network structure and is interlocked with the self-lubricating coating, which improves the bonding strength of the self-lubricating coating. The composite friction-reducing layer of this invention has a high bonding strength with the plunger cylinder. During the plunger compression process, it can withstand the reciprocating friction of the plunger and the high-pressure scouring of the oil. Moreover, during operation, the self-lubricating coating is in contact with the plunger body and has good lubrication performance.

[0035] This invention provides a method for preparing the composite friction-reducing layer described above, comprising the following steps:

[0036] Copper is plated on the inner surface of the plunger cylinder body to form a copper bonding layer, thus obtaining the first plunger cylinder body;

[0037] The first plunger cylinder is filled with tin bronze powder and sintered to form a tin bronze three-dimensional network structure. The tin bronze three-dimensional network structure is then processed to the target thickness to form a tin bronze three-dimensional network layer, resulting in the second plunger cylinder.

[0038] A polytetrafluoroethylene (PTFE) core rod is placed at the center of the second plunger cylinder, with an annular space left between the PTFE core rod and the tin bronze three-dimensional network layer. The self-lubricating composite material is filled into the annular space, and axial pressure is applied to both the PTFE core rod and the self-lubricating composite material simultaneously. A second sintering is then performed. During the second sintering process, the self-lubricating composite material enters the gaps in the tin bronze three-dimensional network layer and forms an interlocking structure with the tin bronze three-dimensional network layer. The PTFE core rod is then removed to form a self-lubricating coating, thus obtaining the composite friction-reducing layer.

[0039] The present invention involves plating copper on the inner surface of a plunger cylinder body to form a copper bonding layer, thereby obtaining a first plunger cylinder body.

[0040] This invention does not impose any special requirements on the plunger cylinder body; any plunger cylinder body from a plunger pump well-known in the art can be used. In the embodiments of this invention, the plunger cylinder body is made of 40CrNiMoA, a material commonly used in the industry.

[0041] This invention does not have special requirements for the copper plating; any copper plating method well known in the art can be used, such as chemical plating. In this invention, the thickness of the copper bonding layer is preferably 10–15 μm.

[0042] After obtaining the first plunger cylinder body, the present invention fills the first plunger cylinder body with tin bronze powder and performs the first sintering to form a tin bronze three-dimensional network structure.

[0043] In this invention, the tin bronze powder is preferably spherical, with a particle size preferably of 60–200 μm, more preferably 75–150 μm, and even more preferably 100–150 μm. The material of the tin bronze powder is preferably CuSn10. Before the first sintering, the tin bronze powder is preferably densely packed using a vibratory feeder, and then pressed. There are no special requirements for the pressing; the tin bronze powder only needs to fill the first plunger cylinder and have a smooth surface. The vibration frequency of the vibratory feeder is preferably 1000 times / minute.

[0044] In this invention, the temperature of the first sintering is preferably 760–800°C, more preferably 770–790°C, and even more preferably 775–785°C; the holding time is preferably 1–3 hours, more preferably 2 hours; the first sintering is preferably carried out under a protective atmosphere; the protective atmosphere is preferably a hydrogen or argon atmosphere. In embodiments of this invention, the first sintering is preferably carried out in a protective atmosphere sintering furnace.

[0045] This invention enables the tin bronze powder to form a strong connection through the first sintering, creating a three-dimensional network structure with a certain strength, which is then firmly connected to the cylinder body.

[0046] After forming the tin bronze three-dimensional network structure, the present invention processes the tin bronze three-dimensional network structure to the target thickness to form a tin bronze three-dimensional network layer, thereby obtaining the second plunger cylinder body.

[0047] The present invention does not impose any special requirements on the processing method; any processing method well known in the art can be used. In the present invention, the thickness of the tin bronze three-dimensional network layer is preferably 0.1–0.3 mm, more preferably 0.2 mm.

[0048] After obtaining the second plunger cylinder body, the present invention places a polytetrafluoroethylene (PTFE) core rod at the center of the second plunger cylinder body, leaving an annular space between the PTFE core rod and the tin bronze three-dimensional network layer, filling the annular space with a self-lubricating composite material, and simultaneously applying axial pressure to the PTFE core rod and the self-lubricating composite material.

[0049] In this invention, the polytetrafluoroethylene (PTFE) core rod is preferably cylindrical; the diameter of the PTFE core rod is preferably 3-5 mm smaller than the inner diameter of the second plunger cylinder. In this invention, the top end of the PTFE core rod is preferably flush with the top end of the second plunger cylinder.

[0050] In this invention, the axial pressure is preferably 30-70 MPa, more preferably 40-65 MPa, and even more preferably 50-60 MPa.

[0051] After applying axial pressure, the present invention performs a second sintering under the applied axial pressure. During the second sintering process, the self-lubricating composite material enters the gaps of the tin bronze three-dimensional network layer and forms an interlocking with the tin bronze three-dimensional network layer. The polytetrafluoroethylene core rod is removed to form a self-lubricating coating, thus obtaining the composite friction-reducing layer.

[0052] In this invention, the temperature of the second sintering is preferably 360-380°C, more preferably 365-375°C, and even more preferably 370°C; the holding time is preferably 1-3 hours, more preferably 2 hours; the second sintering is preferably carried out in an argon atmosphere; in this invention, the second sintering is preferably carried out in a hot press.

[0053] The coefficient of thermal expansion of polytetrafluoroethylene (PTFE) is about 10 times that of steel, and it produces a large expansion volume at 360°C. This invention utilizes a limiting sintering method to restrict the axial expansion of PTFE, thereby converting the axial pressure into radial compression of PAI composite powder by PTFE, thus achieving physical intercalation between PEEK and tin bronze.

[0054] The present invention does not have special requirements for the method of removing the polytetrafluoroethylene core rod; it is sufficient to remove the polytetrafluoroethylene.

[0055] After removing the polytetrafluoroethylene core rod, the present invention preferably further includes machining the inner hole to the final size to form a self-lubricating coating of the target thickness.

[0056] The following detailed description, in conjunction with embodiments, illustrates the friction-reducing materials and their applications provided by this invention, as well as the methods for improving the friction-reducing performance of plunger pairs. However, these descriptions should not be construed as limiting the scope of protection of this invention.

[0057] Example 1

[0058] (1) Copper is plated on the cylinder body surface to form a copper bonding layer with a thickness of 10-15 μm, thus obtaining the first plunger cylinder body;

[0059] (2) Fill the first plunger cylinder with spherical tin bronze powder CuSn10 with a particle size of 100-150μm, use a vibrating plate to make the spherical tin bronze powder form a dense packing structure, the vibration frequency is 1000 times / minute, and then press it.

[0060] (3) Sintering in a protective atmosphere sintering furnace at a sintering temperature of 760℃ for 2 hours, with hydrogen as the protective atmosphere, to form a three-dimensional network structure of tin bronze.

[0061] (4) Machining the tin bronze three-dimensional network structure to a thickness of 0.2 mm to obtain the second plunger cylinder body;

[0062] (5) PAI, graphite and SiO2 powder are mixed in proportions of 85% PAI, 14.9% graphite and 0.1% SiO2 powder. The particle size of PAI is 30-75 μm, the particle size of graphite is 2-20 μm and the particle size of SiO2 powder is 75-100 nm to obtain a self-lubricating composite material.

[0063] (6) Install the PTFE core rod at the center position of the second plunger rod body;

[0064] (7) Fill the gap between the mandrel and the cylinder with the self-lubricating composite material in (5), and apply an axial pressure of 30 MPa to the PTFE mandrel and the self-lubricating composite material at the same time;

[0065] (8) Sintering is carried out on a hot press using the limiting sintering method, with nitrogen as the protective atmosphere, sintering temperature of 360℃ and holding time of 2h.

[0066] (9) Machining the inner hole to the final size to obtain a plunger cylinder with a PAI friction-reducing layer.

[0067] Example 2

[0068] (1) Copper is plated on the cylinder body surface to form a copper bonding layer with a thickness of 10-15 μm, thus obtaining the first plunger cylinder body;

[0069] (2) Fill the first plunger cylinder with spherical tin bronze powder CuSn10 with a particle size of 100-150μm. Use a vibrating plate to make the spherical tin bronze powder form a dense packing structure with a vibration frequency of 1000 times / minute. Then use a hydraulic press to press it at 5MPa to compact it.

[0070] (3) Sintering in an atmosphere-protected sintering furnace at a sintering temperature of 800℃ for 2 hours, with hydrogen as the protective atmosphere, to form a three-dimensional network structure of tin bronze.

[0071] (4) Machining the tin bronze three-dimensional network structure to a thickness of 0.2 mm to obtain the second plunger cylinder body;

[0072] (5) PAI, graphite and SiO2 powder are mixed in proportions of 90% PEEK, 9% graphite and 1% SiO2 powder. The particle size of PAI is 30-70 μm, the particle size of graphite is 30-50 μm and the particle size of SiO2 powder is 20-50 nm to obtain a self-lubricating composite material.

[0073] (6) Install the PTFE core rod at the center position of the second plunger rod body;

[0074] (7) The self-lubricating composite material in (5) is filled in the gap between the core rod and the cylinder, while applying an axial pressure of 60 MPa to the PTFE core rod and the self-lubricating composite material.

[0075] (8) The sintering is carried out on a hot press using the limiting sintering method, with nitrogen as the protective atmosphere, sintering temperature of 380℃ and holding time of 2h.

[0076] (9) Machining the inner hole to the final size to obtain a plunger cylinder with a PAI friction-reducing layer.

[0077] Example 3

[0078] (1) Copper is plated on the cylinder body surface to form a copper bonding layer with a thickness of 10-15 μm, thus obtaining the first plunger cylinder body;

[0079] (2) Fill the first plunger cylinder with spherical tin bronze powder CuSn10 with a particle size of 100-150μm. Use a vibrating plate to make the spherical tin bronze powder form a dense packing structure with a vibration frequency of 1000 times / minute. Then use a hydraulic press to press it at 10MPa to compact it.

[0080] (3) Sintering in an atmosphere-protected sintering furnace at a sintering temperature of 800℃ for 2 hours, with hydrogen as the protective atmosphere, to form a three-dimensional network structure of tin bronze.

[0081] (4) Machining the tin bronze three-dimensional network structure to a thickness of 0.2 mm to obtain the second plunger cylinder body;

[0082] (5) PAI, graphite and SiO2 powder are mixed in proportions of 95% PAI, 4% graphite and 1% SiO2 powder. The particle size of PAI is 30-70 μm, the particle size of graphite is 30-50 μm and the particle size of SiO2 powder is 20-50 nm to obtain a self-lubricating composite material.

[0083] (6) Install the PTFE core rod at the center position of the second plunger rod body;

[0084] (7) The self-lubricating composite material in (5) is filled in the gap between the core rod and the cylinder, while applying an axial pressure of 60 MPa to the PTFE core rod and the self-lubricating composite material.

[0085] (8) The sintering is carried out on a hot press using the limiting sintering method, with nitrogen as the protective atmosphere, sintering temperature of 380℃ and holding time of 2h.

[0086] (9) Machining the inner hole to the final size to obtain a plunger cylinder with a PAI friction-reducing layer.

[0087] Comparative Example 1

[0088] PAI self-lubricating material

[0089] (1) Weigh 90g of polyamide-imide powder (≤75μm) and 8g of graphite powder (≤20μm);

[0090] (2) Mix using a jaw mixer for 3 minutes;

[0091] (3) The mixture is loaded into the mold and cold-pressed on a hydraulic press at a pressure of 50MPa. The cold-pressed blank is then demolded.

[0092] (4) Free sintering in a PTFE sintering furnace at a sintering temperature of 375℃ for 3 hours.

[0093] Comparative Example 2

[0094] Tin bronze dynamic sealing material

[0095] (1) Weigh out 180g of tin bronze QSn663 powder (≤78μm), 8g of graphite powder (≤10μm), and 12g of lead oxide powder (≤78μm);

[0096] (2) The material was mixed using a planetary ball mill with a grinding ball to raw material volume ratio of approximately 1:1, a rotation speed of 150 rpm, and a mixing time of 5 hours.

[0097] (3) The mixture is loaded into the mold and cold-pressed on a hydraulic press at a pressure of 500MPa. The cold-pressed blank is then demolded.

[0098] (4) Sinter the cold-pressed blank in an atmosphere-protected sintering furnace at a sintering temperature of 800℃ and hold for 1 hour.

[0099] The compressive strength was measured according to GB / T 1041-2008, the coefficient of friction was measured on a TMT-800 high-temperature friction tester, and the wear track width was measured under a projector.

[0100] Table 1. Performance of the anti-friction layers in the examples and comparative examples.

[0101] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Compressive strength (MPa) 286 335 440 280 320 Coefficient of friction (600℃) 0.15 0.19 0.16 0.24 0.28 Grinding mark width (mm) 2.2 2.8 2.4 4 5.8

[0102] As shown in Table 1, Examples 1-3, using a PAI friction-reducing layer and a tin bronze nested structure, significantly reduced the friction coefficient between the cylinder block and the plunger body, decreased frictional heat, and improved the reliability and stability of the plunger pump. Example 3 exhibited the best overall performance. Comparative Example 1, using a PAI composite material without the support of a tin bronze nested network, showed a significant reduction in wear resistance. Comparative Example 2, using a tin bronze composite material, exhibited poorer friction coefficient and wear resistance compared to the composite friction-reducing layer of this invention.

[0103] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite friction reducing layer, characterized in that, The composite friction-reducing layer comprises a copper bonding layer, a tin bronze three-dimensional network layer and a self-lubricating coating which are sequentially attached to the surface of the plunger cylinder body; the self-lubricating coating and the tin bronze three-dimensional network layer are embedded with each other; the self-lubricating coating is formed of a self-lubricating composite material; the self-lubricating composite material is composed of polyamide-imide 85-95%, graphite 4-14.9% and silicon dioxide powder 0.1-1% by mass percentage; The preparation method of the composite friction-reducing layer comprises the following steps: Copper is plated on the inner surface of the plunger cylinder body to form a copper bonding layer, thereby obtaining a first plunger cylinder body; Tin bronze powder is filled into the first plunger cylinder body, and first sintering is performed to form a tin bronze three-dimensional network structure; the tin bronze three-dimensional network structure is processed to a target thickness to form a tin bronze three-dimensional network layer, thereby obtaining a second plunger cylinder body; A polytetrafluoroethylene core rod is placed in the center of the second plunger cylinder body, leaving an annular space between the polytetrafluoroethylene core rod and the tin bronze three-dimensional network layer; a self-lubricating composite material is filled into the annular space; axial pressure is applied to the polytetrafluoroethylene core rod and the self-lubricating composite material simultaneously; second sintering is performed; in the second sintering process, the self-lubricating composite material enters the gaps of the tin bronze three-dimensional network layer and is embedded with the tin bronze three-dimensional network layer; the polytetrafluoroethylene core rod is removed, thereby forming a self-lubricating coating, and the composite friction-reducing layer is obtained.

2. The composite friction reducing layer of claim 1, wherein The thickness of the copper bonding layer is 10-15 μm; the thickness of the tin bronze three-dimensional network layer is 0.1-0.3 mm; and the thickness of the self-lubricating coating is 0.1-0.3 mm.

3. The composite friction reducing layer of claim 1, wherein The particle size of the graphite is 2-75 μm; the particle size of the silicon dioxide powder is 20-100 nm; and the particle size of the polyamide-imide is ≤75 μm.

4. A method of producing the composite friction-reducing layer according to any one of claims 1 to 3, characterized in that, The preparation method of the composite friction-reducing layer comprises the following steps: Copper is plated on the inner surface of the plunger cylinder body to form a copper bonding layer, thereby obtaining a first plunger cylinder body; Tin bronze powder is filled into the first plunger cylinder body, and first sintering is performed to form a tin bronze three-dimensional network structure; the tin bronze three-dimensional network structure is processed to a target thickness to form a tin bronze three-dimensional network layer, thereby obtaining a second plunger cylinder body; A polytetrafluoroethylene core rod is placed in the center of the second plunger cylinder body, leaving an annular space between the polytetrafluoroethylene core rod and the tin bronze three-dimensional network layer; a self-lubricating composite material is filled into the annular space; axial pressure is applied to the polytetrafluoroethylene core rod and the self-lubricating composite material simultaneously; second sintering is performed; in the second sintering process, the self-lubricating composite material enters the gaps of the tin bronze three-dimensional network layer and is embedded with the tin bronze three-dimensional network layer; the polytetrafluoroethylene core rod is removed, thereby forming a self-lubricating coating, and the composite friction-reducing layer is obtained.

5. The preparation method according to claim 4, characterized in that, The tin bronze powder is spherical and has a particle size of 60-200 μm.

6. The production method according to claim 4 or 5, characterized by, The temperature of the first sintering is 760-800 ℃, and the holding time is 1-3 h.

7. The preparation method according to claim 4, characterized in that, The axial pressure is 30-70 MPa.

8. The production method according to claim 4 or 7, characterized by, The temperature of the second sintering is 360-380 ℃, and the holding time is 1-3 h.

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