A processing method of a high-wear-resistance inner hole barrel

Abstract

The application relates to the technical field of extruder barrels, and particularly discloses a machining method of a high-wear-resistance inner hole barrel, which comprises the following steps: S1, selecting a rough-machined steel blank to perform a quenching and tempering treatment; S2, placing the quenching and tempering treated barrel blank in a deep cooling box, cooling the barrel blank to-140 DEG C to-196 DEG C, keeping the temperature for 24-48 hours, and then increasing the temperature to 120 DEG C-180 DEG C to perform a tempering treatment; S3, preparing a wear-resistant layer on the inner hole surface of the deep cooling treated barrel, the wear-resistant layer is prepared by one of the following two ways: way one: adopting a supersonic speed flame spraying technology; way two: laser cladding a 1mm nickel-based alloy transition layer on the inner hole surface of the barrel, then laser cladding a 4.2-4.4mm nickel-containing tungsten carbide alloy on the nickel-based alloy transition layer, and finally eliminating stress through tempering; and S4, precisely grinding the inner hole surface of the barrel to make the surface roughness Ra reach 0.05-0.1 mu m.

Description

Technical Field

[0001] This invention relates to the field of extruder barrel technology, and more specifically to a method for processing a high wear-resistant inner bore barrel. Background Technology

[0002] As a key component of core equipment such as plasticizers and extruders, the barrel is subjected to the high-speed rotation of the screw, friction of materials, high temperature and high pressure during operation. It is prone to wear, which leads to increased clearance, decreased plasticizing capacity, increased energy consumption, and ultimately affects the life of the equipment and product quality.

[0003] Currently, the industry commonly uses nitriding and bushing treatments to improve the wear resistance of barrels. While nitriding can increase the hardness of the substrate, the nitrided layer thickness is generally only 0.5~0.6mm, resulting in limited improvement in wear resistance. Furthermore, the wear resistance degrades rapidly as the surface wears down, making it difficult to meet the demands of extreme operating conditions. Bushing treatment, which involves inserting wear-resistant alloy bushings into the barrel, offers better wear resistance, but suffers from bonding strength issues, making the bushings prone to loosening or falling off, and it also incurs high processing costs. Therefore, there is currently a lack of a comprehensive solution that can simultaneously ensure the toughness of the barrel substrate, achieve an order-of-magnitude improvement in the hardness and wear resistance of the inner bore surface, and maintain stable processing and controllable costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for processing a high wear-resistant inner bore barrel to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for processing a high wear-resistant inner bore barrel, which includes the following steps:

[0006] S1. Select the rough-machined steel blank and perform heat treatment to obtain a barrel blank with a hardness of HB260~300.

[0007] S2. Place the quenched and tempered barrel blank in a cryogenic chamber and cool the barrel blank to -140℃ to -196℃. Hold it at this temperature for 24-48 hours, and then heat it to 120℃-180℃ for tempering.

[0008] S3. Prepare a wear-resistant layer on the surface of the cryogenically treated inner bore of the barrel. The wear-resistant layer is prepared using one of the following two methods:

[0009] Method 1: Using supersonic flame spraying technology, a nano-coating with a thickness of 0.3-0.8mm is deposited on the surface of the inner hole of the barrel. The material of the nano-coating is nano WC-10Co4Cr powder or nano Al2O3-TiO2 ceramic composite powder.

[0010] Method 2: Laser clad a 1mm nickel-based alloy transition layer on the inner surface of the barrel, then laser clad a 4.2~4.4mm nickel-based tungsten carbide alloy on the nickel-based alloy transition layer, and finally relieve stress by tempering;

[0011] S4. Perform precision grinding on the inner surface of the barrel until the surface roughness Ra reaches 0.05-0.1μm.

[0012] Furthermore, in step S2, the cryogenic process adopts a gradient cryogenic process, which involves first cooling to -120℃ at a rate of 5℃ / h and holding for 12h, then cooling to -196℃ at a rate of 3℃ / h and holding for 36h, followed by heating to -80℃ at a rate of 10℃ / h and holding for 4h, and then heating to 150℃ at a rate of 15℃ / h and holding for 6h.

[0013] Furthermore, in step S3, the particle velocity during the spraying process is >700m / s and the temperature is <600℃.

[0014] Furthermore, in step S3, after laser cladding on the barrel, a graded tempering process is performed. First, the barrel is tempered at 450°C for 2 hours, then the temperature is raised to 600°C for 3 hours, and finally it is furnace cooled to 300°C and then air-cooled.

[0015] Furthermore, in step S4, for barrels with wear-resistant layers prepared using method one, the inner bore surface of the barrel is precisely ground using a resin-bonded grinding wheel, resulting in a final Ra of 0.06-0.1 μm and a wear-resistant layer thickness of ≥0.4 mm. For barrels with wear-resistant layers prepared using method two, the inner bore surface of the barrel is precisely ground using a CBN grinding wheel, resulting in a final Ra of 0.05-0.08 μm and a wear-resistant layer thickness of ≥4.0 mm.

[0016] Furthermore, the following steps are included between steps S3 and S4:

[0017] S3'. Use an IPG fiber laser to process multiple micro-pits on the surface array of the wear-resistant layer. The micro-pits are conical or bowl-shaped structures with a diameter of 50-200μm and a depth of 20-50μm, and their surface coverage is 10-30%.

[0018] Furthermore, prior to step S1, the following steps are also included:

[0019] S1'. Conduct a comprehensive inspection of the worn old barrel to assess the degree of damage and remaining strength of its base material. For the worn area of ​​the inner hole of the old barrel, use a boring process to enlarge the hole, remove the fatigue layer and damaged structure, and then process the old barrel according to steps S1-S4.

[0020] The beneficial effects of this invention are as follows: the ultra-deep cryogenic treatment of this invention improves the hardness and stability of the substrate, and the wear-resistant layers inside the barrel made by the two methods have excellent wear resistance. Both methods effectively alleviate the difference in thermal expansion coefficient between the high-hardness wear-resistant layer and the steel substrate, reduce interfacial stress concentration, improve coating bonding strength and anti-peeling ability, and can cover different chemical conditions, making it economical and widely applicable. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process flow of the processing method of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely one embodiment of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0023] To make the objectives, technical solutions and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and specific embodiments.

[0024] In the following description, references to "an embodiment," "an embodiment," "an example," "example," etc., indicate that the described embodiment or example may include a particular feature, structure, characteristic, property, element, or limitation, but not every embodiment or example necessarily includes that particular feature, structure, characteristic, property, element, or limitation. Furthermore, the repeated use of the phrase "an embodiment according to this application," while possibly referring to the same embodiment, does not necessarily refer to the same embodiment.

[0025] like Figure 1 As shown, this invention discloses a method for processing a high wear-resistant inner bore cylinder, which includes the following steps:

[0026] S1. Select the rough-machined steel blank and perform heat treatment to obtain a barrel blank with a hardness of HB260~300.

[0027] In the embodiments, blanks made of 42CrMo or 38CrMoAl alloy structural steel are preferred. For 42CrMo steel, oil quenching with a holding temperature of 860±10℃ for 1 hour and air cooling tempering with a holding temperature of 580±10℃ for 4-5 hours are used; for 38CrMoAl steel, oil quenching with a holding temperature of 940±10℃ for 1 hour and air cooling tempering with a holding temperature of 620±10℃ for 5 hours are used. Since 38CrMoAl is a special nitriding steel, its core design goal is to obtain a uniform and stable matrix structure to ensure the bonding strength and dimensional accuracy of the supersonic spray coating; while 42CrMo is a general-purpose high-strength structural steel, and its core design goal is to obtain the best match between high strength and high toughness to provide solid support for the thick laser cladding layer.

[0028] After tempering, the substrate hardness is controlled between HB260-300 to obtain a uniform tempered sorbite structure, ensuring a tensile strength ≥850MPa, a yield strength Rp0.2 ≥750MPa, and an impact energy KV2 ≥70J. This hardness range has been optimized to provide sufficient rigidity support for subsequent coatings while preventing cracking of the cladding layer or peeling of the sprayed coating due to excessive substrate hardness. If the hardness is below HB260, the substrate support is insufficient, and the coating is prone to indentation and deformation; if the hardness is above HB300, the substrate brittleness increases, making it prone to cracking during laser cladding and peeling of the sprayed coating.

[0029] S2. Place the quenched and tempered barrel blank in a cryogenic chamber, so that the barrel blank is in a liquid nitrogen environment, cool the barrel blank to -140℃ to -196℃, hold it for 24-48 hours, and then heat it to 120℃-180℃ for tempering treatment.

[0030] This process promotes the near-complete transformation of residual austenite into martensite after quenching and tempering, significantly improving the hardness and wear resistance of the matrix. During cryogenic treatment, supersaturated martensite precipitates dispersed nanoscale ε-carbides, which act as precipitation strengthening agents, while simultaneously refining the grain size and improving the impact toughness of the matrix. Furthermore, low-temperature tempering eliminates internal stresses generated during cryogenic treatment, stabilizes the martensitic structure, and prevents dimensional deformation during subsequent processing and use, thus improving the dimensional stability of the barrel.

[0031] S3. Prepare a wear-resistant layer on the surface of the cryogenically treated inner bore of the barrel. The wear-resistant layer is prepared using one of the following two methods:

[0032] Method 1: Using supersonic flame spraying technology, a nano-coating with a thickness of 0.3-0.8mm is deposited on the inner surface of the barrel. The nano-coating material is nano WC-10Co4Cr powder or nano Al2O3-TiO2 ceramic composite powder. It is suitable for medium working conditions, that is, for situations where the barrel wear allowance is small. The manufacturing cost is lower than that of laser cladding, the production efficiency is high, and it meets the needs of most general plasticizing equipment.

[0033] The specific operating steps are as follows:

[0034] (1) Clean the inner hole surface with acetone to remove oil stains, and roughen it with brown corundum blasting (pressure 0.5MPa, spray angle 45°) to make the surface roughness reach Ra3.2-6.3μm and improve the mechanical adhesion of the coating.

[0035] (2) A nano-coating is deposited using an HVOF device. The preferred coating material is nano-WC-10Co4Cr powder, which is suitable for abrasive wear conditions or nano-Al2O3-TiO2 ceramic composite powder, which is suitable for corrosive wear conditions. The prepared nano-coating has a thickness of 0.3-0.8 mm, a porosity of <1%, a bonding strength of >70 MPa, and a hardness of HV1200-1400.

[0036] Method 2: A 1mm nickel-based alloy transition layer is laser-clad onto the inner surface of the barrel, followed by a 4.2~4.4mm nickel-based tungsten carbide alloy laser-clad onto the nickel-based alloy transition layer. Finally, stress is relieved by tempering. This method is suitable for extreme working conditions, such as heavy-load barrels and high wear allowances. It achieves metallurgical bonding and thick-layer wear resistance, solving the industry problem of rapid barrel wear in high-glass fiber and continuous production scenarios.

[0037] The operating steps are as follows:

[0038] (1) Clean the inner hole surface with anhydrous ethanol, preheat the entire barrel to 150-200℃ using induction heating, and maintain the interlayer temperature at 120-150℃ to prevent the cladding layer from cracking.

[0039] (2) A semiconductor laser and an inner wall laser head are used to clad a nickel-based alloy transition layer with a thickness of 1.0 mm in a radial spiral scanning manner; the laser power is 1300-1500W, the scanning speed is 6-8mm / s, the powder feeding rate is 10-12g / min, and the overlap rate is 50%.

[0040] (3) Immediately clad a nickel-based tungsten carbide alloy layer with a thickness of 4.2-4.4 mm onto the transition layer. The alloy powder contains 30-40 wt% WC particles, and the nickel-based binder has the same composition as the transition layer. The laser power is 1600-1800 W, the scanning speed is 5-6 mm / s, the powder feeding rate is 10-12 g / min, and the overlap rate is 50%.

[0041] (3) Tempering to relieve stress. The composite wear-resistant layer prepared by this process is metallurgically bonded to the substrate with a bonding strength >700MPa and a wear-resistant layer hardness of HV1100-1300. Due to the in-situ settling effect caused by the density difference of WC particles, a gradient distribution of WC content gradually increases from the surface to the bottom layer, so as to achieve no reduction in wear resistance.

[0042] Both methods of barrel production effectively mitigate the difference in thermal expansion coefficients between the high-hardness wear-resistant layer and the steel substrate, reduce interfacial stress concentration, and improve coating bonding strength and anti-peeling ability.

[0043] S4. Precision grind the inner surface of the barrel until the surface roughness Ra reaches 0.05-0.1μm. This reduces the frictional resistance between the screw and the barrel, lowers energy consumption, and improves plasticizing efficiency. At the same time, it removes burrs and slag generated by laser micro-forming, ensures the effectiveness of the micro-pit structure, and avoids sharp edges scratching the screw.

[0044] In one embodiment, in step S2, the cryogenic process adopts a gradient cryogenic process, which involves first cooling to -120°C at a rate of 5°C / h and holding for 12 hours, then cooling to -196°C at a rate of 3°C / h and holding for 36 hours, followed by heating to -80°C at a rate of 10°C / h and holding for 4 hours, and then heating to 150°C at a rate of 15°C / h and holding for 6 hours.

[0045] Traditional cryogenic direct liquid nitrogen immersion, with a cooling rate >50℃ / h, leads to excessive temperature differences between the inside and outside of the barrel, generating enormous thermal stress and making it prone to microcracks at stress concentration points. This invention, however, employs slow cooling rates of 5℃ / h and 3℃ / h, ensuring uniform temperature changes inside and outside the barrel, reducing thermal stress, and preventing thermal shock cracks.

[0046] The intermediate stage of holding at -120℃ for 12 hours allows for the initial transformation of the matrix structure and the elimination of most of the retained austenite; then, the temperature is lowered to -196℃ and held for 36 hours to further reduce the content of retained austenite.

[0047] The slow heating and cooling process provides ample time for carbon atoms to diffuse, resulting in smaller and more uniformly distributed ε-carbides, and a more significant improvement in wear resistance.

[0048] The intermediate heating stage of holding at -80℃ for 4 hours eliminates the low-temperature internal stress generated during the deep cryogenic process; then the temperature is raised to 150℃ for tempering to further stabilize the microstructure and control the residual stress of the barrel matrix under ideal compressive stress.

[0049] In one embodiment, in step S3, the particle velocity during the spraying process is >700m / s and the particle temperature is <600℃.

[0050] Particle velocity is the most critical factor determining the bonding strength of HVOF coatings. When the particle velocity is >700 m / s, the particles undergo intense plastic deformation upon impacting the substrate surface, forming a composite interface of mechanical interlocking and metallurgical bonding, thereby enhancing the bonding strength. Furthermore, the full deformation of high-speed particles makes the coating denser, reducing porosity and effectively preventing corrosive media from penetrating into the substrate, thus improving the coating's corrosion resistance.

[0051] WC particles readily decompose at high temperatures, forming brittle W₂C and η phases, leading to a decrease in coating toughness. This invention controls the particle temperature below 600℃, reducing the WC decomposition rate and ensuring high hardness and toughness of the coating. Simultaneously, it reduces the thermal impact on the substrate, i.e., reduces the probability of substrate microstructure changes and deformation, ensuring the dimensional accuracy of the barrel.

[0052] In one embodiment, in step S3, after laser cladding on the barrel, a staged tempering process is performed. First, tempering is carried out at 450°C for 2 hours to eliminate instantaneous thermal stress and prevent cracking of the coating during heating. Then, the temperature is raised to 600°C for 3 hours, and finally, the coating is furnace cooled to 300°C and air-cooled. This eliminates residual stress and improves the fatigue resistance of the coating. Furthermore, the high-temperature tempering at 600°C promotes elemental diffusion between the transition layer and the substrate, and between the transition layer and the wear-resistant layer, thereby forming a diffusion layer and improving interfacial bonding strength. Additionally, it can induce the transformation of residual austenite generated during laser cladding, eliminating metastable phases and preventing dimensional deformation caused by microstructural changes during subsequent finishing and use. Moreover, the precipitation of dispersed carbides during tempering refines the grains, improving the impact toughness of the coating and effectively resisting the impact load of the screw.

[0053] In one embodiment, in step S4, the barrel with the wear-resistant layer made using method one is precision ground on the inner bore surface using a resin-bonded grinding wheel, resulting in a final Ra of 0.06-0.1 μm and a wear-resistant layer thickness of ≥0.4 mm. The barrel with the wear-resistant layer made using method two is precision ground on the inner bore surface using a CBN grinding wheel, resulting in a final Ra of 0.05-0.08 μm and a wear-resistant layer thickness of ≥4.0 mm.

[0054] While supersonic spraying produces high-hardness coatings, it also results in poor toughness and thinness. Using resin-bonded diamond grinding wheels, with their good elasticity and low grinding force, prevents coating peeling and cracking. Furthermore, the supersonic spraying route is suitable for medium-duty applications, controlling Ra to 0.06-0.1μm, reducing processing costs while maintaining performance. Simultaneously, maintaining a thickness ≥0.4mm ensures coating integrity and wear resistance, preventing over-grinding that could expose the substrate.

[0055] Because laser cladding coatings are characterized by high hardness and thickness, CBN (cubic boron nitride) grinding wheels are used. CBN wheels, with a hardness second only to diamond, offer excellent wear resistance and high grinding efficiency, avoiding the carbon diffusion wear seen with diamond wheels. Furthermore, laser cladding is used in extreme operating conditions requiring higher surface quality. Controlling Ra to 0.05-0.08μm further reduces the coefficient of friction. Simultaneously, maintaining a thickness ≥4.0mm ensures sufficient wear resistance reserves, resulting in a longer service life.

[0056] In one embodiment, the following steps are included between step S3 and step S4:

[0057] S3'. Use an IPG fiber laser to process multiple micro-pits on the surface of the wear-resistant layer. The micro-pits are conical or bowl-shaped structures with a diameter of 50-200μm and a depth of 20-50μm, and their surface coverage is 10-30%. If the coverage is too low, the friction reduction effect will not be obvious; if the coverage is too high, it will reduce the effective bearing area of ​​the coating and instead aggravate wear.

[0058] The micro-pit structure can store molten material during friction, utilizing the material's viscosity to create a localized microhydrodynamic pressure effect, thereby effectively reducing the friction coefficient between the screw and barrel and minimizing wear. In other words, during the operation of plasticizing equipment, the screw and barrel rely on molten plastic material for lubrication. The micro-pit structure in this invention can store molten material at the friction interface. Under the shearing action generated by the screw rotation, the material within the micro-pit is compressed, forming a localized high-pressure zone, generating a microhydrodynamic pressure effect that partially separates the two metal surfaces, thereby reducing the friction coefficient and inhibiting adhesive wear.

[0059] Furthermore, the micron-sized abrasive particles generated by the wear of the screw or barrel will be contained in the micro-pits, preventing them from embedding into the coating surface and causing three-dimensional wear, further avoiding barrel wear, and improving the overall wear resistance on the basis of the coating, thus extending the coating life.

[0060] In one embodiment, prior to step S1, the following step is also included:

[0061] S1': Conduct a comprehensive inspection of the worn old barrel to assess the degree of damage and remaining strength of its base material. For the worn inner bore area of ​​the old barrel, use a boring process to enlarge the hole, remove the fatigue layer and damaged structure, and then process the old barrel according to steps S1-S4. Alternatively, step S3' can be added between steps S3 and S4 during the repair and manufacturing of the old barrel.

[0062] The pretreatment steps for the old barrel are as follows:

[0063] (1) Remove the old barrel and then use ultrasonic testing and magnetic particle testing to detect whether there are defects such as cracks, pores, and inclusions in the matrix. Assess the remaining strength to avoid putting old barrels with safety hazards into remanufacturing and prevent breakage accidents during use.

[0064] (2) Due to the long-term use of old barrels, a fatigue layer will form on the inner surface. This layer contains a large number of microcracks and residual tensile stress, which are the main reasons for low coating bonding strength and early failure. The fatigue layer can be precisely prepared by CNC boring to expose the fresh matrix structure and provide a good bonding surface for subsequent coating preparation.

[0065] Example 1: A novel barrel processing method for preparing wear-resistant layers using supersonic flame spraying

[0066] S1. Select 38CrMoAl steel barrel blank, rough machine the outer shape and inner hole and then perform heat treatment: quench at 940℃ for 1 hour, oil cool to room temperature; temper at 620℃ for 5 hours, air cool to room temperature; test whether its matrix hardness, tensile strength and yield strength meet the standards, and whether the microstructure is uniform tempered sorbite.

[0067] S2. Place the tempered and qualified barrel into a program-controlled cryogenic chamber. First, cool it down to -120℃ at 5℃ / h and hold it for 12 hours. Then, cool it down to -196℃ at 3℃ / h and hold it for 36 hours. After that, heat it up to -80℃ at 10℃ / h and hold it for 4 hours. Then, heat it up to 150℃ at 15℃ / h and hold it for 6 hours.

[0068] S3. First, ultrasonically clean the inner hole with acetone for 15 minutes, then roughen it with brown corundum sandblasting (pressure 0.5MPa, angle 45°), achieving a surface roughness Ra4.2μm. Use a supersonic flame spraying device with technical parameters of kerosene flow rate 22L / h, oxygen flow rate 900L / h, spraying distance 380mm, powder feed rate 25g / min, particle velocity 780m / s, and temperature 550℃ to deposit a nano WC-10Co4Cr coating. After spraying, it can be annealed at low temperature to relieve stress. Check whether the total coating thickness meets the standard.

[0069] S3'. Multiple micro-pits are fabricated on the surface array of the wear-resistant layer using an IPG fiber laser. The micro-pits have a diameter of 100μm, a depth of 30μm, and a surface coverage of 20%.

[0070] S4. Use a resin-bonded diamond grinding wheel to precisely grind the inner surface of the barrel and check whether its surface roughness and coating thickness meet the standards.

[0071] Example 2: A novel barrel processing method for preparing wear-resistant layers using laser cladding.

[0072] S1. Select 42CrMo steel barrel blank, rough machine the outer shape and inner hole and then perform heat treatment: quench at 860℃ for 1 hour, oil cool to room temperature; temper at 580℃ for 4.5 hours, air cool to room temperature; test whether its matrix hardness, tensile strength and yield strength meet the standards, and whether the microstructure is uniform tempered sorbite.

[0073] S2. Place the tempered and qualified barrel into a program-controlled cryogenic chamber. First, cool it down to -120℃ at 5℃ / h and hold it for 12 hours. Then, cool it down to -196℃ at 3℃ / h and hold it for 36 hours. After that, heat it up to -80℃ at 10℃ / h and hold it for 4 hours. Then, heat it up to 150℃ at 15℃ / h and hold it for 6 hours.

[0074] S3. First, clean the inner hole with anhydrous ethanol, preheat the entire structure to 180℃ using induction heating, and maintain the interlayer temperature at 150℃ for pretreatment. Then, using a semiconductor laser and an inner wall laser head with a laser power of 1300-1500W, a scanning speed of 6-8mm / s, a powder feeding rate of 10-12g / min, and an overlap rate of 50%, clad a 1.0mm thick nickel-based alloy transition layer using a radial spiral scanning method. Then, with a power of 1700W, a scanning speed of 5.5mm / s, a powder feeding rate of 11g / min, and an overlap rate of 50%, immediately clad a 4.2-4.4mm thick nickel-based tungsten carbide alloy layer on the transition layer, with the alloy powder containing 30wt% WC particles. After cladding, the material is sent to a tempering furnace, first tempered at 450℃ for 2 hours, then heated to 600℃ for 3 hours, and finally furnace cooled to 300℃ before being air-cooled. Test whether the total thickness of the composite layer, the bonding strength, and the hardness of the wear-resistant layer meet the requirements.

[0075] S3'. Multiple micro-pits are fabricated on the surface array of the wear-resistant layer using an IPG fiber laser. The micro-pits have a diameter of 100μm, a depth of 30μm, and a surface coverage of 20%.

[0076] S4. Use CBN grinding wheels to precisely grind the inner surface of the barrel and check whether its surface roughness and coating thickness meet the standards.

[0077] Example 3: Repair of old machine barrels with wear-resistant layers prepared by laser cladding

[0078] S1'. The old barrel of a 50% glass fiber injection molding machine with a maximum inner bore wear of 0.32mm was removed. Ultrasonic testing of the old barrel showed no internal defects, and magnetic particle testing showed no surface cracks. The remaining strength was assessed to be 88% of the original design, meeting the remanufacturing requirements. Using the outer diameter of the barrel as a reference, a 1.5mm thick fatigue layer and wear layer were precisely boring away.

[0079] S1. Perform quenching and tempering treatment on the old barrel after boring: quench at 860℃ for 1 hour, oil cool to room temperature; temper at 580℃ for 4.5 hours, air cool to room temperature; test whether its matrix hardness, tensile strength, and yield strength meet the standards, and whether the microstructure is uniform tempered sorbite.

[0080] S2. Place the tempered and qualified barrel into a program-controlled cryogenic chamber. First, cool it down to -120℃ at 5℃ / h and hold it for 12 hours. Then, cool it down to -196℃ at 3℃ / h and hold it for 36 hours. After that, heat it up to -80℃ at 10℃ / h and hold it for 4 hours. Then, heat it up to 150℃ at 15℃ / h and hold it for 6 hours.

[0081] S3. First, clean the inner hole with anhydrous ethanol, preheat the entire structure to 180℃ using induction heating, and maintain the interlayer temperature at 150℃ for pretreatment. Then, using a semiconductor laser and an inner wall laser head with a laser power of 1300-1500W, a scanning speed of 6-8mm / s, a powder feeding rate of 10-12g / min, and an overlap rate of 50%, clad a 1.0mm thick nickel-based alloy transition layer using a radial spiral scanning method. Then, with a power of 1700W, a scanning speed of 5.5mm / s, a powder feeding rate of 11g / min, and an overlap rate of 50%, immediately clad a 4.2-4.4mm thick nickel-based tungsten carbide alloy layer on the transition layer, with the alloy powder containing 30wt% WC particles. After cladding, the material is sent to a tempering furnace, first tempered at 450℃ for 2 hours, then heated to 600℃ for 3 hours, and finally furnace cooled to 300℃ before being air-cooled. Test whether the total thickness of the composite layer, the bonding strength, and the hardness of the wear-resistant layer meet the requirements.

[0082] S3'. Multiple micro-pits are fabricated on the surface array of the wear-resistant layer using an IPG fiber laser. The micro-pits have a diameter of 100μm, a depth of 30μm, and a surface coverage of 20%.

[0083] S4. Use CBN grinding wheels to precisely grind the inner surface of the barrel and check whether its surface roughness and coating thickness meet the standards.

[0084] Comparative Example 1: Nitriding treatment of 38CrMoAl steel barrel

[0085] S1. Select 38CrMoAl steel barrel blank, rough machine the outer shape and inner hole and then perform heat treatment: quench at 940℃ for 1 hour, oil cool to room temperature; temper at 620℃ for 5 hours, air cool to room temperature; test whether its matrix hardness, tensile strength and yield strength meet the standards, and whether the microstructure is uniform tempered sorbite.

[0086] S2, anneal at 550℃ for 4 hours to eliminate residual stress from machining.

[0087] S3. Place it in a pit-type gas nitriding furnace, introduce ammonia gas, and adopt a two-stage nitriding process: hold at 520℃ for 15 hours and at 540℃ for 10 hours.

[0088] S4. After cooling to 200°C in the furnace, remove from the furnace and air cool.

[0089] Comparative Example 2: WR13 high-chromium wear-resistant cast iron was used as a barrel bushing with quenching treatment.

[0090] S1. Place the WR13 bushing into a box-type resistance furnace and heat it to 980℃ at 100℃ / h, then hold it for 2 hours to fully dissolve the carbides. After removing it from the furnace, immediately cool it to room temperature with oil.

[0091] S2, keep warm at 200℃ for 4 hours and then air cool.

[0092] Circular samples with a thickness of 10 mm were cut along the axial direction of the barrel for the three embodiments and two comparative examples described above. The inner diameter of the sample was Φ16 mm, which is the same as the inner diameter of the finished barrel, and the outer diameter was Φ50 mm. These samples were used for subsequent wear resistance comparison tests.

[0093] Experiment 1:

[0094] Test type: Test ring-test ring rolling friction and wear test;

[0095] Reference standard: GB / T12444-2006 "Test Methods for Wear of Metallic Materials - Sliding Wear Test of Test Rings and Blocks";

[0096] Testing equipment: M-200 wear testing machine;

[0097] Test parameters: room temperature, no lubrication, test force 40 kgf, total test revolutions 91,845 revolutions;

[0098] Sample specifications: uniformly φ16 inner hole - φ50 outer diameter - 10mm thickness circular ring.

[0099] The test results are shown in the table below:

[0100] Table 1 Results of Experiment 1

[0101]

[0102] As shown in Table 1:

[0103] 1. The hardness of Examples 1-3 is higher than that of Comparative Examples 1-2;

[0104] 2. Wear quality: This is an indicator that measures the total absolute loss of coating material, directly reflecting the wear resistance and density of the coating. The lower the wear quality, the stronger the coating's ability to resist material peeling and three-dimensional wear, and the more stable and controllable the wear process.

[0105] The wear mass of Example 1 was only 3.2026g, which is 60.6% of that of Comparative Example 1, and the relative wear resistance reached 1.65 times; it is 69.5% of that of Comparative Example 2, and the relative wear resistance reached 1.44 times.

[0106] The wear mass of Example 2 was only 3.9096g, which is 73.9% of that of Comparative Example 1, and the relative wear resistance reached 1.35 times; it is 84.8% of that of the conventional bimetallic bushing compared to Comparative Example 2, and the relative wear resistance reached 1.18 times.

[0107] The wear mass of Example 3 was only 4.0043g, which was 75.7% of that of Comparative Example 1, and the relative wear resistance reached 1.32 times; it was 86.9% of that of Comparative Example 2, and the relative wear resistance reached 1.15 times.

[0108] 3. Wear Outer Diameter: The wear outer diameter directly corresponds to the radial wear depth and is one of the most intuitive indicators of coating wear resistance. The smaller the outer diameter wear, the stronger the coating's resistance to abrasive and adhesive wear. Simultaneously, reduced outer diameter wear means less dimensional change in the barrel's inner bore during service, a longer maintenance time for the screw-barrel clearance, stable plasticizing quality, and extended equipment life.

[0109] The wear outer diameter of Example 1 was only 0.394 mm, which is 40.0% of that of Comparative Example 1, and the relative wear resistance reached 2.50 times; it is 49.3% of that of Comparative Example 2, and the relative wear resistance reached 2.03 times.

[0110] The wear outer diameter of Example 2 was only 0.480 mm, which is 48.8% of that of Comparative Example 1, and the relative wear resistance reached 2.05 times; it is 60.1% of that of Comparative Example 2, and the relative wear resistance reached 1.66 times.

[0111] The wear outer diameter of Example 3 was only 0.494 mm, which is 50.2% of that of Comparative Example 1, and the relative wear resistance reached 1.99 times; it is 61.8% of that of Comparative Example 2, and the relative wear resistance reached 1.62 times.

[0112] Therefore, the wear resistance of the barrels made by different processes in this invention is higher than that of the barrels made by conventional processes. Moreover, the wear quality and wear outer diameter of Example 3 (re-manufacturing of old barrels) are slightly lower than those of Example 2 (new barrels), which proves that the remanufacturing process of this invention can eliminate fatigue damage of old machines and restore them to the performance level of new machines, and has significant economic and environmental value.

[0113] Experiment 2:

[0114] Test type: Test ring-test ring rolling friction and wear test;

[0115] Reference standard: GB / T12444-2006 "Test Methods for Wear of Metallic Materials - Sliding Wear Test of Test Rings and Blocks";

[0116] Testing equipment: M-200 wear testing machine, equipped with a high-temperature environmental chamber to keep the sample and friction pair area at a constant temperature, a temperature controller and a continuous melt supply device;

[0117] Test parameters: Maintain temperature 260±5℃, melt wetting, that is, place PA66+30% chopped glass fiber granules (dried, moisture content <0.02%) on the sample surface, heat to the set temperature and melt to form a continuous melt film; during the test, add a small amount of granules every 10 minutes to maintain the presence of melt and ensure that the interface is always covered by melt; test force 40Kgf, total test revolutions 91845 revolutions;

[0118] Sample specifications: uniformly φ16 inner hole - φ50 outer diameter - 10mm thickness circular ring.

[0119] The test results are shown in the table below:

[0120] Table 2 Results of Experiment 2

[0121]

[0122] As shown in Table 2:

[0123] 1. Wear quality:

[0124] The wear mass of Example 1 was only 0.9478g, which was 17.9% of that of Comparative Example 1, and the relative wear resistance was 5.58 times; it was 16.9% of that of Comparative Example 2, and the relative wear resistance was 5.93 times.

[0125] The wear mass of Example 2 was only 1.1186g, which was 21.2% of that of Comparative Example 1, and the relative wear resistance was 4.73 times that of Comparative Example 2; it was 19.9% ​​of that of Comparative Example 2, and the relative wear resistance was 5.03 times that of Comparative Example 2.

[0126] The wear mass of Example 3 was only 1.1642g, which was 22.0% of that of Comparative Example 1, and the relative wear resistance reached 4.54 times; it was 20.7% of that of Comparative Example 2, and the relative wear resistance reached 4.83 times.

[0127] 2. Wear outer diameter:

[0128] The wear outer diameter of Example 1 was only 0.117 mm, which is 11.9% of that of Comparative Example 1, and the relative wear resistance reached 8.44 times; it is 11.2% of that of Comparative Example 2, and the relative wear resistance reached 8.91 times.

[0129] The wear outer diameter of Example 2 was only 0.138 mm, which was 14.0% of that of Comparative Example 1, and the relative wear resistance was 7.15 times that of Comparative Example 2; it was 13.2% of that of Comparative Example 2, and the relative wear resistance was 7.55 times that of Comparative Example 2.

[0130] The wear outer diameter of Example 3 was only 0.145 mm, which was 14.7% of that of Comparative Example 1, and the relative wear resistance was 6.81 times that of Comparative Example 2; it was 13.9% of that of Comparative Example 2, and the relative wear resistance was 7.19 times that of Comparative Example 3.

[0131] Therefore, it can be seen that the micro-pit structure can store molten material at the friction interface. Under the shearing action generated by the screw rotation, the material in the micro-pit is squeezed to form a local high-pressure zone, generating a micro-hydrodynamic pressure effect that partially separates the two metal surfaces, thereby reducing the coefficient of friction and inhibiting adhesive wear. In addition, the micro-pit can also accommodate hard particles generated by wear, preventing them from embedding into the coating surface and causing three-body wear, further extending the coating life. Its wear resistance is improved by several times compared to the comparative example.

[0132] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for processing a high wear-resistant inner bore cylinder, characterized in that: Includes the following steps: S1. Select the rough-machined steel blank and perform heat treatment to obtain a barrel blank with a hardness of HB260~300. S2. Place the quenched and tempered barrel blank in a cryogenic chamber and cool the barrel blank to -140℃ to -196℃. Hold it at this temperature for 24-48 hours, and then heat it to 120℃-180℃ for tempering. S3. Prepare a wear-resistant layer on the surface of the cryogenically treated inner bore of the barrel. The wear-resistant layer is prepared using one of the following two methods: Method 1: Using supersonic flame spraying technology, a nano-coating with a thickness of 0.3-0.8mm is deposited on the surface of the inner hole of the barrel. The material of the nano-coating is nano WC-10Co4Cr powder or nano Al2O3-TiO2 ceramic composite powder. Method 2: Laser clad a 1mm nickel-based alloy transition layer on the inner surface of the barrel, then laser clad a 4.2~4.4mm nickel-based tungsten carbide alloy on the nickel-based alloy transition layer, and finally relieve stress by tempering; S4. Perform precision grinding on the inner surface of the barrel until the surface roughness Ra reaches 0.05-0.1μm.

2. The processing method for a high wear-resistant inner bore cylinder according to claim 1, characterized in that: In step S2, the cryogenic process adopts a gradient cryogenic process, which involves first cooling to -120℃ at a rate of 5℃ / h and holding for 12h, then cooling to -196℃ at a rate of 3℃ / h and holding for 36h, followed by heating to -80℃ at a rate of 10℃ / h and holding for 4h, and then heating to 150℃ at a rate of 15℃ / h and holding for 6h.

3. The processing method for a high wear-resistant inner bore cylinder according to claim 1, characterized in that: In step S3, the particle velocity during the spraying process is >700m / s and the temperature is <600℃.

4. The processing method for a high wear-resistant inner bore cylinder according to claim 1, characterized in that: In step S3, after laser cladding on the barrel, a graded tempering process is performed. First, the barrel is tempered at 450°C for 2 hours, then the temperature is raised to 600°C for 3 hours, and finally it is furnace cooled to 300°C and then air-cooled.

5. The processing method for a high wear-resistant inner bore cylinder according to claim 1, characterized in that: In step S4, for barrels with wear-resistant layers prepared by method one, the inner surface of the barrel is precisely ground using a resin-bonded grinding wheel, resulting in a final Ra of 0.06-0.1 μm and a wear-resistant layer thickness of ≥0.4 mm. For barrels with wear-resistant layers prepared by method two, the inner surface of the barrel is precisely ground using a CBN grinding wheel, resulting in a final Ra of 0.05-0.08 μm and a wear-resistant layer thickness of ≥4.0 mm.

6. The method for processing a high wear-resistant inner bore cylinder according to claim 1, characterized in that: The following steps are also included between steps S3 and S4: S3'. Use an IPG fiber laser to process multiple micro-pits on the surface array of the wear-resistant layer. The micro-pits are conical or bowl-shaped structures with a diameter of 50-200μm and a depth of 20-50μm, and their surface coverage is 10-30%.

7. The processing method for a high wear-resistant inner bore cylinder according to claim 1, characterized in that: Before step S1, the following steps are also included: S1'. Conduct a comprehensive inspection of the worn old barrel to assess the degree of damage and remaining strength of its base material. For the worn area of ​​the inner hole of the old barrel, use a boring process to enlarge the hole, remove the fatigue layer and damaged structure, and then process the old barrel according to steps S1-S4.

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