Wear-resistant lightweight driver push rod guide sleeve and manufacturing method thereof

Abstract

The application relates to the field of injection molding technology, in particular to a wear-resistant lightweight driver push rod guide sleeve and a manufacturing method thereof, which comprises POM, LDPE, a crystallization regulation component for regulating and controlling the uniformity of POM resin crystallization and a lubricating component for reducing frictional resistance, the crystallization regulation component comprises an organic nucleating agent and organic montmorillonite, and the lubricating component comprises dimethyl silicone oil, so as to maintain the dimensional stability of the guide sleeve in a long-term use thermal environment.

Description

Technical Field

[0001] This application relates to the field of injection molding technology, and in particular to a wear-resistant and lightweight actuator push rod guide sleeve and a method for manufacturing the same. Background Technology

[0002] The actuator push rod guide sleeve, which enables the actuator push rod to move in a directional manner, needs to possess good wear resistance to ensure that the push rod's movement direction is not easily deviated. Furthermore, traditional guide sleeves made of metal materials, such as bearing steel or copper alloys, while possessing good wear resistance, are too dense and heavy, failing to meet the lightweight requirements of mobile devices such as robots. Engineering plastic guide sleeves, with their advantages of low density, self-lubrication, corrosion resistance, and ease of processing, are gradually becoming an ideal alternative to metal guide sleeves. Among them, polyoxymethylene (POM) is widely used due to its excellent overall performance.

[0003] For example, the publication CN101724222B describes a high wear-resistant self-lubricating polyoxymethylene composite and its preparation method. Through the synergistic effect of low-density polyethylene, nano-silica, and silicone oil, it achieves high wear-resistant self-lubricating properties while maintaining or even improving the mechanical and heat resistance properties of the material.

[0004] However, the above technology uses a POM (polyoxymethylene) / LDPE (low-density polyethylene) composite system. The two polymers have significantly different crystallization characteristics; that is, POM and LDPE have different crystallization temperatures, leading to different crystallization rates. During the injection molding and cooling process, POM first crystallizes rapidly at high temperatures, forming a rigid matrix framework. LDPE, on the other hand, crystallizes slowly at lower temperatures. Its crystallization process is restricted by the already crystallized POM matrix, causing inconsistent shrinkage at the interface between the two polymers, thus creating residual internal stress.

[0005] This residual internal stress does not show obvious effects in the early stages of product molding. However, during long-term service of the guide sleeve, the temperature is high, and the internal stress will be gradually released with the thermal movement of the molecular chains, causing irreversible dimensional creep in the guide sleeve. Dimensional expansion will lead to an increase in the fit clearance between the guide sleeve and the push rod, which in turn will cause a decrease in motion accuracy, an increase in vibration and noise, and in severe cases, even jamming, leading to the failure of the entire actuator. Summary of the Invention

[0006] To maintain the dimensional stability of the guide sleeve under long-term thermal conditions, this application provides a wear-resistant and lightweight actuator push rod guide sleeve and its manufacturing method.

[0007] Firstly, the wear-resistant and lightweight actuator push rod guide sleeve provided in this application adopts the following technical solution.

[0008] A wear-resistant and lightweight actuator push rod guide sleeve includes POM, LDPE, a crystallization regulating component for regulating the crystallization uniformity of POM resin, and a lubricating component for reducing frictional resistance. The crystallization regulating component includes an organic nucleating agent and an organomontmorillonite, and the lubricating component includes dimethyl silicone oil.

[0009] By adopting the above technical solutions, the organic nucleating agent can promote the formation of a more uniform crystalline structure in POM and reduce the shrinkage difference caused by local uneven crystallization; the organic montmorillonite can play a role in layer restriction and dimensional stabilization in the POM matrix, reducing the shrinkage inconsistency in the thickness direction of the guide sleeve and at the interface between the two phases; the dimethyl silicone oil can reduce the frictional resistance of the guide sleeve; thus, while meeting the requirements of wear resistance and lightweight, the guide sleeve can reduce the risk of internal hole size drift, roundness reduction and guiding accuracy reduction under long-term thermal environment.

[0010] Optional, by weight, it includes: 90-98 parts of POM, 1-5 parts of LDPE, 0.05-0.5 parts of organic nucleating agent, 0.03-0.5 parts of organomontmorillonite, 0.3-1.5 parts of dimethyl silicone oil, 0.1-1 parts of antioxidant, and 0.05-0.8 parts of formaldehyde absorbent.

[0011] By adopting the above technical solutions, the amount of POM is controlled at 90-98 parts, which can ensure that POM forms a continuous matrix in the guide sleeve material, so that the guide sleeve has sufficient structural strength and wear resistance. The amount of LDPE is controlled at 1-5 parts, which can improve the lightweight and lubrication performance, while avoiding the decrease in rigidity of the guide sleeve or the increase in the difference in phase shrinkage caused by excessive LDPE content.

[0012] When organic nucleating agents and organomontmorillonite are used in combination within the above-mentioned range, they can improve the crystallization uniformity of POM and inhibit dimensional drift after molding; dimethyl silicone oil within the above-mentioned range can reduce frictional resistance and is less likely to affect the mechanical properties of the material due to excessive addition; antioxidants can reduce the risk of thermo-oxidative degradation during melt blending and injection molding; formaldehyde absorbents can absorb trace amounts of formaldehyde generated during POM processing, improving the material processing stability and the long-term reliability of the product.

[0013] Optional, by weight, it includes: 95 parts POM, 1.5-3 parts LDPE, 0.1-0.3 parts organic nucleating agent, 0.05-0.2 parts organomontmorillonite, 0.5-1 parts dimethyl silicone oil, 0.1-0.4 parts antioxidant, and 0.1-0.5 parts formaldehyde absorbent.

[0014] By adopting the above technical solutions, within the preferred ratio range, POM can form a stable continuous phase, LDPE can form an appropriate amount of dispersed phase, organic nucleating agents and organomontmorillonite can synergistically improve crystallization uniformity and size stability, and dimethyl silicone oil can provide a good low-friction effect.

[0015] This formulation achieves a good balance between wear resistance, lightweight, frictional resistance, and long-term dimensional stability, making it particularly suitable for precision plastic parts such as actuator push rod guide sleeves that require long-term reciprocating guiding fit.

[0016] Secondly, the manufacturing method of a wear-resistant and lightweight actuator push rod guide sleeve provided in this application adopts the following technical solution.

[0017] A method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve, specifically comprising the following steps:

[0018] S1. POM, LDPE, organic nucleating agent, organomontmorillonite, dimethyl silicone oil, antioxidant and formaldehyde absorbent are dried and mixed to obtain the mixture to be extruded;

[0019] S2. The mixture to be extruded is melt-blended, extruded, cooled and pelletized to obtain modified polyoxymethylene composite particles;

[0020] S3. Injection molding using modified polyoxymethylene composite particles;

[0021] S4. Perform high-temperature, pressure-controlled crystallization;

[0022] S5. Perform controlled cooling;

[0023] S6. Remove the guide sleeve blank and perform sizing and cooling;

[0024] S7. Perform thermal stabilization treatment on the guide sleeve blank to obtain the driver push rod guide sleeve.

[0025] By adopting the above technical solution, the moisture content of the raw materials is first reduced by drying and mixing and the initial dispersion uniformity of each component is improved. Then, LDPE, organic nucleating agent, organomontmorillonite, dimethyl silicone oil, antioxidant and formaldehyde absorbent are uniformly distributed in the POM matrix by melt blending to obtain modified polyoxymethylene composite particles suitable for injection molding.

[0026] After injection molding, high-temperature and pressure-holding crystallization is used to form a relatively uniform crystalline matrix of POM under pressure. Subsequently, controlled cooling is used to allow the LDPE dispersed phase to gradually crystallize and shrink in the POM matrix, thereby mitigating the inconsistency in interfacial shrinkage between POM and LDPE caused by differences in crystallization temperature range and shrinkage characteristics. Then, sizing cooling is used to limit the free deformation of the guide sleeve's inner hole. Finally, thermal stabilization treatment is used to release some of the residual internal stress from molding in advance, so that the guide sleeve has better inner hole dimensional stability and guiding accuracy retention under long-term thermal conditions.

[0027] Optionally, in S3, the mold cavity temperature before injection molding is 105-115℃, and the mold core temperature is 110-120℃.

[0028] By adopting the above technical solution, both the mold cavity and the core are kept in a high temperature range, which can prevent the melt from cooling and freezing too quickly on the surface and inner hole side of the guide sleeve after entering the mold, allowing the POM matrix to have sufficient crystallization time. The core temperature is higher than the cavity temperature, which helps to delay the rapid cooling of the material near the push rod guide hole, reduce the risk of large residual stress and uneven shrinkage on the inner hole side of the guide sleeve, thereby improving the roundness and dimensional stability of the inner hole of the guide sleeve.

[0029] Optionally, the holding pressure in S4 is 45-65 MPa, and the holding time is 12-25 s.

[0030] By adopting the above technical solution, the volume shrinkage of the guide bushing blank during the initial cooling stage can be compensated, so that the melt maintains a relatively stable pressure state in the mold cavity and promotes the formation of a more uniform crystal structure of the POM matrix. If the holding pressure is too low or the holding time is too short, it is easy to cause shrinkage cavities, unstable inner hole dimensions or uneven local shrinkage in the guide bushing blank. If the holding pressure is too high or the holding time is too long, it may increase internal stress or reduce production efficiency.

[0031] Optionally, in step S5, the mold cavity temperature is first reduced to 85-95℃, the mold core temperature is reduced to 90-100℃, the mold cavity temperature is then reduced to 60-75℃, and the mold core temperature is reduced to 65-80℃.

[0032] By adopting the above technical solution, the controlled cooling process is carried out in two stages, which can avoid excessive temperature difference between the inner and outer layers of the guide sleeve caused by a sudden drop in mold temperature. In the first stage, the cavity and core are cooled to the intermediate temperature range, allowing the POM matrix to continue to crystallize and solidify under relatively gentle cooling conditions; in the second stage, the temperature is further reduced to a lower temperature range, allowing the LDPE dispersed phase to gradually complete crystallization and shrinkage. The core temperature is always higher than or not lower than the cavity temperature, which helps to reduce rapid shrinkage and local deformation near the ejector guide hole, and reduce ellipticization of the guide sleeve inner hole, dimensional drift, and abnormal changes in the fit clearance.

[0033] Optionally, the temperature of the heat stabilization treatment in S7 is 80-90℃, and the holding time is 1-3h; after the heat stabilization treatment is completed, the guide sleeve blank is cooled to below 40℃ with the furnace.

[0034] By adopting the above technical solution, the heat stabilization treatment temperature of 80-90℃ is close to the higher operating temperature that the guide sleeve may experience. This allows the guide sleeve blank to release some residual internal stress in a controlled environment in advance, reducing the possibility of dimensional creep or internal hole drift during subsequent service. Holding at this temperature for 1-3 hours ensures that the internal temperature of the guide sleeve blank is fully balanced and the stabilization treatment is completed. Cooling in the furnace to below 40℃ avoids the introduction of new thermal stress due to rapid cooling after the heat stabilization treatment.

[0035] Optionally, in S1, POM is dried at 75-85℃ for 3-4 hours, and LDPE is dried at 60-70℃ for 1-2 hours.

[0036] By adopting the above technical solutions, the moisture content of POM can be effectively reduced, thereby minimizing the risk of hydrolysis or degradation during melt blending and injection molding. Drying LDPE at 60-70℃ for 1-2 hours removes surface moisture while preventing particle adhesion or performance fluctuations caused by excessively high drying temperatures. By separately controlling the drying conditions of POM and LDPE, the stability of subsequent melt blending and the molding quality of the finished product can be improved.

[0037] Optionally, in S2, the temperature of the melt blending is controlled sequentially from the feed end to the die head within the range of 145-180℃, the screw speed is 250-350rpm, and the vacuum degree of the vacuum exhaust section is -0.06MPa to -0.09MPa.

[0038] By adopting the above technical solutions, the melt blending temperature is controlled within the range of 145-180℃, which enables POM and LDPE to reach a suitable melt plasticization state, while reducing the risk of POM overheating and degradation. The screw speed is controlled at 250-350 rpm, which ensures that each component is fully sheared and dispersed, so that LDPE, dimethyl silicone oil, organic nucleating agent and organomontmorillonite are evenly distributed in the POM matrix. The vacuum exhaust section is maintained at -0.06MPa to -0.09MPa, which can remove moisture, volatiles and trace gases generated during processing from the melt, thereby reducing porosity, silver streaks and internal defects in the guide sleeve products.

[0039] In summary, this application includes at least the following beneficial effects:

[0040] By combining POM and LDPE, the guide sleeve maintains good wear resistance and guiding support capabilities while having a lower weight compared to metal guide sleeves, making it suitable for drive structures such as robots and linear actuators that require lightweight design.

[0041] By using organic nucleating agents and organic montmorillonite as crystallization regulating components, the crystallization uniformity of the POM matrix can be improved, and the shrinkage inconsistency between the two phases of POM and LDPE and in the thickness direction of the guide sleeve can be reduced, thereby improving the dimensional stability of the guide sleeve during long-term use.

[0042] Using dimethyl silicone oil as a lubricant can reduce the frictional resistance and wear between the push rod and the guide sleeve, making the push rod reciprocating movement smoother.

[0043] By combining high-temperature pressure crystallization and controlled cooling, the crystallization and shrinkage processes of the POM matrix and LDPE dispersed phase are made more gradual, reducing residual internal stress caused by excessively rapid cooling or asynchronous crystallization.

[0044] By sizing cooling and thermal stabilization treatment, the guide bushing blank is further stabilized in size after forming, reducing the risk of internal hole size drift, roundness reduction and guiding accuracy reduction under long-term thermal environment. Attached Figure Description

[0045] Figure 1 This is a flowchart of a method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve according to this application. Detailed Implementation

[0046] The present application will be further described in detail below with reference to the accompanying drawings.

[0047] This application discloses a wear-resistant and lightweight actuator push rod guide sleeve, comprising, by weight: 90-98 parts of POM, 1-5 parts of LDPE, 0.05-0.5 parts of organic nucleating agent, 0.03-0.5 parts of organomontmorillonite, 0.3-1.5 parts of dimethyl silicone oil, 0.1-1 parts of antioxidant, and 0.05-0.8 parts of formaldehyde absorbent.

[0048] The organic nucleating agent can be sorbitol-based, amide-based, or other organic nucleating agents suitable for the POM system. The antioxidant can be hindered phenolic antioxidants, phosphite antioxidants, or a combination of both. The formaldehyde absorbent can be melamine, dicyandiamide, or other additives capable of absorbing formaldehyde.

[0049] This application also discloses a method for manufacturing a wear-resistant and lightweight actuator pushrod guide sleeve, referring to... Figure 1 Specifically, it includes the following steps.

[0050] S1. POM, LDPE, organic nucleating agent, organomontmorillonite, dimethyl silicone oil, antioxidant and formaldehyde absorbent are dried and mixed to obtain the mixture to be extruded.

[0051] Weigh out the following components according to the predetermined weight: POM, LDPE, organic nucleating agent, organomontmorillonite, dimethyl silicone oil, antioxidant, and formaldehyde absorbent. Dry the POM at 75-85℃ for 3-4 hours. The moisture content of the dried POM should not exceed 0.03%. Dry the LDPE at 60-70℃ for 1-2 hours.

[0052] The organic nucleating agent and organo-montmorillonite are added to a high-speed mixer and premixed for 2-5 minutes to obtain a crystallization-regulating premix. In one embodiment, the mass ratio of the organic nucleating agent to organo-montmorillonite is 2:1, the high-speed mixer speed is 600-1000 rpm, and the premixing time is 3 minutes. Premixing allows the organic nucleating agent and organo-montmorillonite to form a more uniform crystallization-regulating component before entering the main mixing process, thereby improving the dispersion uniformity of both in the POM matrix.

[0053] Subsequently, the dried POM, dried LDPE, crystallization regulator premix, antioxidant, and formaldehyde absorbent are added to a high-speed mixer and mixed at 1000-1400 rpm for 4-6 minutes. During the mixing process, the material temperature inside the mixer is controlled at 40-50℃ to avoid material agglomeration or additive aggregation due to excessive local temperature rise.

[0054] When the main mixing has been in progress for 2-4 minutes, dimethyl silicone oil is sprayed into the high-speed mixer through a liquid metering pump, so that the dimethyl silicone oil is evenly attached to the surface of the particles of POM, LDPE, organic nucleating agent, organic montmorillonite, antioxidant and formaldehyde absorbent. Then, mixing continues for 1-3 minutes to obtain the mixture to be extruded.

[0055] S2. The mixture to be extruded is melt-blended, extruded, cooled and pelletized to obtain modified polyoxymethylene composite particles.

[0056] The extrusion mixture obtained in step S1 is added to a twin-screw extruder for melt blending. The melt blending temperature is controlled sequentially from the feed end to the die, within the range of 145-180℃. Specifically, the twin-screw extruder can be configured as follows: Zone 1 145-155℃, Zone 2 160-170℃, Zone 3 168-175℃, Zones 4 to 8 172-180℃, and the die 168-175℃. This temperature range allows POM and LDPE to reach a suitable melt plasticization state while preventing POM from undergoing significant thermal degradation due to prolonged exposure to excessively high temperatures.

[0057] The screw speed of the twin-screw extruder is 250-350 rpm. The vacuum exhaust section has a vacuum level of -0.06 MPa to -0.09 MPa to remove moisture, volatiles, and trace gases generated during processing from the melt, thereby reducing porosity, silver streaks, and internal defects in subsequent guide sleeve products.

[0058] The mixture to be extruded is melt-blended by a twin-screw extruder and then extruded through a die to form a strip. The strip enters a water-cooling tank for cooling, with the water temperature controlled at 20-30℃. After cooling, the strip is dried by a drying device to remove surface moisture and then pelletized by a pelletizer to obtain modified polyoxymethylene composite granules. The particle size of the modified polyoxymethylene composite granules can be controlled within 2.5-3.5mm.

[0059] After pelleting, the modified polyoxymethylene composite particles can be dried again at 75-85℃ for 1.5-2.5 hours, and then sealed and stored for later use to reduce the amount of moisture reabsorbed by the particles during cooling, pelleting and storage.

[0060] S3. Injection molding using modified polyoxymethylene composite particles.

[0061] The modified polyoxymethylene composite granules obtained in step S2 are added to the hopper of the injection molding machine. The injection molding machine hopper can be equipped with a drying air system, and the drying air temperature is controlled at 75-85℃ to prevent the granules from reabsorbing moisture during the injection molding process.

[0062] The barrel temperature of the injection molding machine can be set sequentially from the rear section to the nozzle: rear section 165-175℃, middle section 175-185℃, front section 180-190℃, and nozzle 175-185℃. This temperature setting can ensure that the modified polyoxymethylene composite particles are fully plasticized, while reducing the risk of POM overheating and degradation.

[0063] Injection molds include a mold cavity and a mold core. The mold cavity forms the outer peripheral structure of the guide bushing, and the mold core forms the inner hole of the guide bushing for the directional movement of the ejector pin. The mold cavity and mold core are each connected to an independent mold temperature control circuit to allow for differentiated temperature control of the outer side and the inner side of the guide bushing.

[0064] Before injection molding, the mold cavity temperature is controlled at 105-115℃, and the mold core temperature is controlled at 110-120℃. The core temperature is higher than the cavity temperature, which can delay the rapid cooling of the material near the ejector guide hole and reduce the problem of large residual stress or uneven shrinkage caused by excessively rapid freezing on the inner side of the guide sleeve.

[0065] During injection, the injection pressure can be controlled at 80-110MPa, and the injection speed can be controlled at 30-70mm / s. The melt enters the mold cavity through the gate and forms a guide bushing blank between the mold cavity and the mold core.

[0066] S4. Perform high-temperature and pressure-controlled crystallization.

[0067] After injection molding, high-temperature holding and pressure crystallization is performed with the mold closed. The holding pressure is 45-65 MPa, and the holding time is 12-25 seconds. During the high-temperature holding and pressure crystallization process, the mold cavity temperature is maintained at 105-115℃, and the mold core temperature is maintained at 110-120℃. Under these temperature and pressure conditions, the POM matrix can gradually form a relatively uniform crystalline structure under pressure, compensating for the volume shrinkage of the guide bushing blank during the initial cooling stage.

[0068] S5. Perform controlled cooling.

[0069] After high-temperature pressure crystallization is completed, the mold remains closed, and controlled cooling is achieved through independent mold temperature control loops for the mold cavity and mold core.

[0070] Controlled cooling includes a first cooling phase and a second cooling phase.

[0071] In the first cooling stage, the mold cavity temperature is reduced to 85-95℃, and the mold core temperature is reduced to 90-100℃. This stage is used to allow the POM matrix to continue to crystallize and solidify under relatively gentle cooling conditions, avoiding excessive temperature difference between the inner and outer layers of the guide sleeve caused by a sudden drop in mold temperature.

[0072] In the second cooling stage, the temperature of the mold cavity is further reduced to 60-75℃, and the temperature of the mold core is further reduced to 65-80℃. This stage is used to allow the LDPE dispersed phase to gradually complete crystallization and shrinkage in the POM matrix, thereby mitigating the inconsistency in interfacial shrinkage caused by the difference in crystallization temperature range and shrinkage characteristics between POM and LDPE.

[0073] During controlled cooling, the mold core temperature remains consistently higher than or equal to the mold cavity temperature. This setting reduces rapid material shrinkage near the ejector guide hole, minimizing ellipticization of the guide sleeve inner hole, dimensional drift, and abnormal changes in fit clearance.

[0074] S6. Remove the guide sleeve blank and perform sizing and cooling.

[0075] Once the guide bushing blank has sufficient demolding strength, open the mold and remove the guide bushing blank. During demolding, avoid excessive ejection speed to prevent deformation of the guide bushing blank. The ejection speed can be controlled between 50-120 mm / s.

[0076] After the guide sleeve blank is removed, it is immediately placed on the sizing mandrel for sizing and cooling. The outer diameter of the sizing mandrel corresponds to the target inner diameter of the guide sleeve bore. For example, when the target inner diameter of the guide sleeve bore is 10 mm, the outer diameter of the sizing mandrel can be controlled to be 9.98-10.00 mm. The surface roughness Ra of the sizing mandrel should not exceed 0.4 μm to avoid scratching the inner diameter of the guide sleeve.

[0077] After the guide bushing blank is fitted onto the sizing mandrel, it is cooled at room temperature for 10-20 minutes. The sizing mandrel supports and constrains the inner hole of the guide bushing blank, which reduces the risk of ellipticization or dimensional drift of the inner hole due to free shrinkage after demolding.

[0078] S7. Perform thermal stabilization treatment on the guide sleeve blank to obtain the driver push rod guide sleeve.

[0079] The guide sleeve blank, fitted onto the sizing mandrel, is placed in a hot air circulating oven for heat stabilization treatment. The heat stabilization treatment temperature is 80-90℃, and the holding time is 1-3 hours. The heat stabilization treatment temperature is close to the highest operating temperature the guide sleeve may experience, which allows the guide sleeve blank to release some of the residual internal stress from molding under controlled conditions in advance, reducing the possibility of dimensional creep, inner hole drift, or roundness loss during subsequent long-term service.

[0080] After the heat stabilization treatment, the guide sleeve blank is cooled in the furnace to below 40°C. Furnace cooling avoids the reintroduction of thermal stress due to rapid cooling. Once the guide sleeve blank has cooled to below 40°C, it is removed from the sizing mandrel to obtain the driver push rod guide sleeve.

[0081] In scenarios requiring higher guiding accuracy, the push rod guide hole can be precision reamed, honed, or polished after thermal stabilization treatment to achieve the required inner diameter, roundness, and surface roughness.

[0082] The following examples and comparative examples further illustrate this point.

[0083] Example 1:

[0084] A wear-resistant and lightweight actuator push rod guide sleeve comprises, by weight: 90 parts of POM, 1 part of LDPE, 0.05 parts of organic nucleating agent, 0.03 parts of organomontmorillonite, 0.3 parts of dimethyl silicone oil, 0.1 parts of antioxidant, and 0.05 parts of formaldehyde absorbent.

[0085] A method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve includes the following steps.

[0086] S1. POM, LDPE, organic nucleating agent, organomontmorillonite, dimethyl silicone oil, antioxidant and formaldehyde absorbent are dried and mixed to obtain the mixture to be extruded.

[0087] POM was dried at 75℃ for 3 hours. The moisture content of the dried POM was no higher than 0.03%. LDPE was dried at 60℃ for 1 hour.

[0088] S2. The mixture to be extruded is melt-blended, extruded, cooled and pelletized to obtain modified polyoxymethylene composite particles.

[0089] The twin-screw extruder can be set to: Zone 1 145℃, Zone 2 160℃, Zone 3 168℃, Zones 4 to 8 172℃, and Die 168℃.

[0090] The twin-screw extruder has a screw speed of 250 rpm. The vacuum level in the vacuum exhaust section is -0.06 MPa.

[0091] After pelleting, the modified polyoxymethylene composite granules can be dried again at 75℃ for 1.5h, and then sealed and stored for later use.

[0092] S3. Injection molding using modified polyoxymethylene composite particles.

[0093] The barrel temperature of the injection molding machine can be set sequentially from the rear section to the nozzle as follows: rear section 165℃, middle section 175℃, front section 180℃, nozzle 175℃.

[0094] Before injection molding, the temperature of the mold cavity is controlled at 105℃ and the temperature of the mold core is controlled at 110℃.

[0095] During injection, the injection pressure can be controlled at 80MPa and the injection speed can be controlled at 30mm / s.

[0096] S4. Perform high-temperature and pressure-controlled crystallization.

[0097] The holding pressure is 45 MPa, and the holding time is 12 s. During the high-temperature holding and crystallization process, the mold cavity temperature is maintained at 105℃, and the mold core temperature is maintained at 110℃.

[0098] S5. Perform controlled cooling.

[0099] In the first cooling stage, the temperature of the mold cavity is reduced to 85°C and the temperature of the mold core is reduced to 90°C.

[0100] In the second cooling stage, the temperature of the mold cavity is further reduced to 60°C, and the temperature of the mold core is further reduced to 65°C.

[0101] S6. Remove the guide sleeve blank and perform sizing and cooling.

[0102] After the guide sleeve blank is fitted onto the sizing mandrel, it is cooled at room temperature for 10 minutes.

[0103] S7. Perform thermal stabilization treatment on the guide sleeve blank to obtain the driver push rod guide sleeve.

[0104] The guide sleeve blank, fitted onto the sizing mandrel, is placed in a hot air circulating oven for heat stabilization treatment. The heat stabilization treatment temperature is 80℃, and the holding time is 1 hour.

[0105] Example 2:

[0106] The difference from Example 1 is that:

[0107] A wear-resistant and lightweight actuator push rod guide sleeve comprises, by weight: 95 parts POM, 1.5 parts LDPE, 0.1 parts organic nucleating agent, 0.05 parts organic montmorillonite, 0.5 parts dimethyl silicone oil, 0.1 parts antioxidant, and 0.1 parts formaldehyde absorbent.

[0108] Example 3:

[0109] The difference from Example 1 is that:

[0110] A wear-resistant and lightweight actuator push rod guide sleeve comprises, by weight: 95 parts POM, 3 parts LDPE, 0.3 parts organic nucleating agent, 0.2 parts organic montmorillonite, 1 part dimethyl silicone oil, 0.4 parts antioxidant, and 0.5 parts formaldehyde absorbent.

[0111] Example 4:

[0112] The difference from Example 1 is that:

[0113] A wear-resistant and lightweight actuator push rod guide sleeve comprises, by weight: 98 parts POM, 5 parts LDPE, 0.5 parts organic nucleating agent, 0.5 parts organic montmorillonite, 1.5 parts dimethyl silicone oil, 1 part antioxidant, and 0.8 parts formaldehyde absorbent.

[0114] Example 5:

[0115] The difference from Example 1 is that:

[0116] A method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve includes the following steps.

[0117] S1. POM, LDPE, organic nucleating agent, organomontmorillonite, dimethyl silicone oil, antioxidant and formaldehyde absorbent are dried and mixed to obtain the mixture to be extruded.

[0118] POM was dried at 85℃ for 4 hours. The moisture content of the dried POM was no higher than 0.03%. LDPE was dried at 70℃ for 2 hours.

[0119] S2. The mixture to be extruded is melt-blended, extruded, cooled and pelletized to obtain modified polyoxymethylene composite particles.

[0120] The twin-screw extruder can be set to: Zone 1 155℃, Zone 2 170℃, Zone 3 175℃, Zones 4 to 8 180℃, and Die 175℃.

[0121] The twin-screw extruder has a screw speed of 350 rpm. The vacuum level in the vacuum exhaust section is -0.09 MPa.

[0122] After pelleting, the modified polyoxymethylene composite granules can be dried again at 85℃ for 2.5 hours, and then sealed and stored for later use.

[0123] S3. Injection molding using modified polyoxymethylene composite particles.

[0124] The barrel temperature of the injection molding machine can be set sequentially from the rear section to the nozzle as follows: rear section 175℃, middle section 185℃, front section 190℃, nozzle 185℃.

[0125] Before injection molding, the temperature of the mold cavity is controlled at 115℃ and the temperature of the mold core is controlled at 120℃.

[0126] During injection, the injection pressure can be controlled at 110 MPa and the injection speed can be controlled at 70 mm / s.

[0127] S4. Perform high-temperature and pressure-controlled crystallization.

[0128] The holding pressure is 65 MPa, and the holding time is 25 s. During the high-temperature holding and crystallization process, the mold cavity temperature is maintained at 115℃, and the mold core temperature is maintained at 120℃.

[0129] S5. Perform controlled cooling.

[0130] In the first cooling stage, the temperature of the mold cavity is reduced to 95°C and the temperature of the mold core is reduced to 100°C.

[0131] In the second cooling stage, the temperature of the mold cavity is further reduced to 75°C, and the temperature of the mold core is further reduced to 80°C.

[0132] S6. Remove the guide sleeve blank and perform sizing and cooling.

[0133] After the guide sleeve blank is fitted onto the sizing mandrel, it is cooled at room temperature for 20 minutes.

[0134] S7. Perform thermal stabilization treatment on the guide sleeve blank to obtain the driver push rod guide sleeve.

[0135] The guide sleeve blank, fitted onto the sizing mandrel, is placed in a hot air circulating oven for heat stabilization treatment. The heat stabilization treatment temperature is 90℃, and the holding time is 3 hours.

[0136] Comparative Example 1:

[0137] The difference from Example 1 is that:

[0138] A method for removing dimethyl silicone oil from the guide sleeve of a wear-resistant and lightweight actuator push rod.

[0139] Comparative Example 2:

[0140] The difference from Example 1 is that:

[0141] Organic nucleating agents are removed from the guide sleeve of a wear-resistant and lightweight actuator push rod.

[0142] Comparative Example 3:

[0143] The difference from Example 1 is that:

[0144] A method for removing organic montmorillonite from the guide sleeve of a wear-resistant and lightweight actuator push rod.

[0145] Comparative Example 4:

[0146] The difference from Example 1 is that:

[0147] A method for removing organic montmorillonite and organic nucleating agent from the guide sleeve of a wear-resistant and lightweight actuator push rod.

[0148] Comparative Example 5:

[0149] The difference from Example 1 is that:

[0150] In S3, the temperature of both the mold cavity and the mold core are controlled at 70℃ before injection molding.

[0151] Comparative Example 6:

[0152] The difference from Example 1 is that:

[0153] In S4, high-temperature holding and crystallization are not performed; instead, the pressure is held for 8 seconds according to the conventional injection molding process.

[0154] Comparative Example 7:

[0155] The difference from Example 1 is that:

[0156] S5 does not employ staged controlled cooling; instead, it cools the mold under conventional cooling water conditions until it can be demolded.

[0157] Comparative Example 8:

[0158] The difference from Example 1 is that:

[0159] In S7, no thermal stabilization treatment is performed. After sizing and cooling, the guide sleeve blank is directly removed from the sizing mandrel to obtain the driver push rod guide sleeve.

[0160] Based on the above embodiments and comparative examples, the corresponding indicators were tested.

[0161] The change in the inner diameter of the guide sleeve after heat aging was investigated. Five guide sleeves were randomly selected from each group, and their inner diameter before heat aging was measured using a pneumatic gauge, an inside micrometer, or a coordinate measuring machine. Three measurement sections were selected along the axial direction for each guide sleeve: the front end, the middle, and the rear end. Measurements were taken at four angles (0°, 90°, 180°, and 270°) for each section, and the average value was taken as the initial inner diameter D0. The guide sleeves were then aged in a hot air circulating oven at 80±2℃ for 1000 hours. After aging, the guide sleeves were removed and equilibrated at 23±2℃ for 24 hours, and the inner diameter D1 was measured again using the same location and method. The rate of change of inner diameter δ was measured. D = (D1 - D0) / D0 × 100%. The larger the inner diameter change rate, the weaker the heat aging resistance of the guide sleeve.

[0162] The reciprocating resistance of the push rod was tested by inserting the guide sleeve into a uniformly sized actuator housing or simulated mounting base, and then inserting a steel push rod of the same diameter. An electric linear drive test bench was used to drive the push rod in reciprocating motion at a stroke of 30 mm and a speed of 50 mm / s, for 1000 cycles. The average motion resistance during the stable operation phase of the push rod was recorded using a force sensor. Lower motion resistance indicates lower frictional resistance of the guide sleeve and smoother push rod operation.

[0163] For operating noise, during the resistance test of the push rod's reciprocating motion, the sound level meter was positioned 300mm from the guide sleeve installation location, and the background noise of the test environment was no higher than 35dB(A). The push rod reciprocated at a speed of 50mm / s, and the equivalent continuous sound level during the stable operation phase was recorded. The lower the noise, the less friction, gap impact, and vibration there is between the push rod and the guide sleeve.

[0164] The specific results are shown in Table 1.

[0165] Table 1:

[0166]

[0167] As can be seen from Examples 1 to 5, within the formulation and manufacturing process defined in this application, the inner diameter change rate after thermal aging is controlled between 0.10% and 0.18%, the reciprocating resistance of the push rod is controlled between 6.4 and 9.2 N, and the operating noise is controlled between 39 and 45 dB(A). This indicates that the composite system formed by POM, LDPE, organic nucleating agent, organomontmorillonite, and dimethyl silicone oil, combined with high-temperature pressure crystallization, controlled cooling, sizing cooling, and thermal stabilization treatment, enables the guide sleeve to maintain good dimensional stability under long-term thermal conditions and keeps the push rod running with low resistance and low noise.

[0168] After thermal aging, the inner diameter change rate of Example 3 was 0.10%, the reciprocating resistance of the push rod was 6.8 N, and the operating noise was 40 dB(A), indicating superior overall performance. This is because the LDPE, dimethyl silicone oil, organic nucleating agent, and organomontmorillonite in Example 3 were all within a suitable and preferred range, which could reduce frictional resistance and improve dimensional stability through crystallization-controlled composition. Example 4 had the lowest operating resistance and noise, at 6.4 N and 39 dB(A), respectively, indicating that higher contents of dimethyl silicone oil and LDPE are beneficial for reducing frictional resistance. However, its inner diameter change rate after thermal aging was 0.14%, slightly higher than that of Example 3, indicating that when the lubricating and lightweight components are too high, dimensional stability may not continue to improve synchronously.

[0169] Comparative Example 1, which removed dimethyl silicone oil, showed an inner diameter change rate of 0.19% after thermal aging, close to 0.18% in Example 1. However, the reciprocating resistance of the push rod increased from 9.2 N in Example 1 to 14.5 N, and the operating noise increased from 45 dB(A) to 54 dB(A). This indicates that dimethyl silicone oil is not the most significant factor affecting long-term dimensional stability, but it has a significant effect on reducing the frictional resistance between the guide sleeve and the push rod, reducing operating noise, and improving the smoothness of push rod operation.

[0170] Comparative Example 2, which removed the organic nucleating agent, showed an inner diameter change rate of 0.36% after thermal aging, significantly higher than the 0.18% in Example 1. Comparative Example 3, which removed the organo-montmorillonite, showed an inner diameter change rate of 0.33% after thermal aging. This indicates that both the organic nucleating agent and organo-montmorillonite play important roles in the long-term thermal dimensional stability of the guide sleeve. Specifically, the organic nucleating agent mainly promotes the formation of a more uniform crystalline structure in POM, while the organo-montmorillonite mainly reduces the inconsistency in shrinkage along the thickness direction of the guide sleeve and at the interface between the two phases through its lamellar confinement effect.

[0171] Comparative Example 4, which removed both the organic nucleating agent and organomontmorillonite, showed an increase in inner diameter change rate to 0.52% after thermal aging, an increase in push rod reciprocating resistance to 12.0 N, and an increase in operating noise to 50 dB(A). This result was significantly worse than Comparative Examples 2 or 3, which removed either the organic nucleating agent or organomontmorillonite alone. This indicates a synergistic effect between the organic nucleating agent and organomontmorillonite; both act as crystallization regulating components, more effectively reducing the size drift of the POM / LDPE system under thermal conditions.

[0172] Comparative Example 5, where both the mold cavity and core were controlled at 70℃, showed the highest inner diameter change rate after heat aging at 0.55%, the highest among all groups. Operating resistance and noise also increased to 12.6N and 51dB(A), respectively. This indicates that conventionally low mold temperatures cause the melt to cool and freeze quickly after entering the mold, making it difficult to adequately mitigate the crystallization and shrinkage processes of the POM matrix and LDPE dispersed phase. This can easily lead to dimensional drift in the guide sleeve's inner hole and unstable fit. Therefore, controlling the pre-injection cavity temperature to 105-115℃ and the core temperature to 110-120℃, as described in the document, is of practical significance.

[0173] Comparative Example 6, without high-temperature holding-pressure crystallization, only underwent conventional injection molding with a holding pressure of 8 seconds. Its inner diameter change rate after heat aging was 0.48%, its operating resistance was 12.2 N, and its operating noise was 50 dB(A). Compared to Example 1, these results demonstrate that high-temperature holding-pressure crystallization can compensate for the volume shrinkage of the guide sleeve blank during the initial cooling stage and promote the formation of a more uniform crystalline structure in the POM matrix under pressure, thereby improving the dimensional stability of the guide sleeve after subsequent heat aging.

[0174] Comparative Example 7, without staged controlled cooling, exhibited an inner diameter change rate of 0.43% after thermal aging, an operating resistance of 11.5 N, and an operating noise level of 49 dB(A). This indicates that without controlled cooling, the crystallization and shrinkage processes of the POM matrix and LDPE dispersed phase lack buffering, making it easier for inconsistent shrinkage to occur at the inner and outer layers of the guide sleeve and at the interface between the two phases. This, in turn, leads to inner hole size drift, increased operating resistance, and increased noise.

[0175] Comparative Example 8, without heat stabilization treatment, exhibited an inner diameter change rate of 0.39% after heat aging, an operating resistance of 11.0 N, and an operating noise level of 48 dB(A). This indicates that if the guide sleeve blank is directly removed and used after sizing and cooling, the residual internal stress from molding is not released in advance, making it more susceptible to dimensional creep and inner hole drift under subsequent 80℃ thermal conditions. This demonstrates that heat stabilization treatment at 80-90℃ for 1-3 hours significantly improves the long-term dimensional stability of the guide sleeve.

[0176] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A wear-resistant and lightweight actuator push rod guide sleeve, characterized in that: It includes POM, LDPE, a crystallization regulating component for controlling the crystallization uniformity of POM resin, and a lubricating component for reducing frictional resistance. The crystallization regulating component includes an organic nucleating agent and an organomontmorillonite, and the lubricating component includes dimethyl silicone oil.

2. The wear-resistant and lightweight actuator push rod guide sleeve according to claim 1, characterized in that: By weight, it includes: 90-98 parts POM, 1-5 parts LDPE, 0.05-0.5 parts organic nucleating agent, 0.03-0.5 parts organomontmorillonite, 0.3-1.5 parts dimethyl silicone oil, 0.1-1 parts antioxidant, and 0.05-0.8 parts formaldehyde absorbent.

3. The wear-resistant and lightweight actuator push rod guide sleeve according to claim 2, characterized in that: By weight, it includes: 95 parts POM, 1.5-3 parts LDPE, 0.1-0.3 parts organic nucleating agent, 0.05-0.2 parts organomontmorillonite, 0.5-1 parts dimethyl silicone oil, 0.1-0.4 parts antioxidant, and 0.1-0.5 parts formaldehyde absorbent.

4. A method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve, comprising manufacturing a wear-resistant and lightweight actuator push rod guide sleeve as described in any one of claims 1-3, characterized in that: Specifically, the steps include the following: S1. POM, LDPE, organic nucleating agent, organomontmorillonite, dimethyl silicone oil, antioxidant and formaldehyde absorbent are dried and mixed to obtain the mixture to be extruded; S2. The mixture to be extruded is melt-blended, extruded, cooled and pelletized to obtain modified polyoxymethylene composite particles; S3. Injection molding using modified polyoxymethylene composite particles; S4. Perform high-temperature, pressure-controlled crystallization; S5. Perform controlled cooling; S6. Remove the guide sleeve blank and perform sizing and cooling; S7. Perform thermal stabilization treatment on the guide sleeve blank to obtain the driver push rod guide sleeve.

5. The method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve according to claim 4, characterized in that: The temperature of the mold cavity before injection molding in S3 is 105-115℃, and the temperature of the mold core is 110-120℃.

6. The method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve according to claim 4, characterized in that: The holding pressure in S4 is 45-65 MPa, and the holding time is 12-25 s.

7. The method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve according to claim 4, characterized in that: In step S5, the mold cavity temperature is first reduced to 85-95℃, the mold core temperature is reduced to 90-100℃, the mold cavity temperature is then reduced to 60-75℃, and the mold core temperature is reduced to 65-80℃.

8. The method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve according to claim 4, characterized in that: The temperature for heat stabilization treatment in S7 is 80-90℃, and the holding time is 1-3h. After the heat stabilization treatment is completed, the guide sleeve blank is cooled to below 40℃ with the furnace.

9. The method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve according to claim 4, characterized in that: In S1, POM is dried at 75-85℃ for 3-4 hours, and LDPE is dried at 60-70℃ for 1-2 hours.

10. A method for manufacturing a wear-resistant and lightweight actuator push rod guide sleeve according to claim 4, characterized in that: In the S2 process, the temperature of the melt blending is controlled sequentially from the feed end to the die head within the range of 145-180℃, the screw speed is 250-350rpm, and the vacuum degree of the vacuum exhaust section is -0.06MPa to -0.09MPa.

Images