A vulcanization forming processing method for a car suspension bushing

Abstract

The application discloses a kind of automobile suspension bushing vulcanization forming processing methods, belong to automobile parts processing technical field, to solve the uneven vulcanization degree of traditional constant temperature constant pressure vulcanization process, internal porosity defect is more, rubber and metal adhesive strength is low, finished product is prone to shrinkage deformation, the problem of low comprehensive qualified rate.The method sequentially includes six steps of metal framework pretreatment, mixing rubber blank preparation, in-mold preassembly, segmented gradient vulcanization, gradient cooling demolding and finished product post-processing, after vulcanization is completed by air cooling, water cooling two-stage gradient cooling demolding, supporting sand blasting roughening glueing framework pretreatment and frozen trimming post-processing process.The application can effectively improve rubber vulcanization uniformity and interface adhesive strength, reduce internal porosity and forming internal stress, finished product size precision and appearance quality are excellent, comprehensive qualified rate is significantly improved, process adaptability is strong, suitable for large-scale industrial production of automobile suspension bushing.

Description

Technical Field

[0001] This invention relates to the field of automotive parts technology, specifically to a vulcanization molding process for automotive suspension bushings. Background Technology

[0002] Automotive suspension bushings are core damping components connecting the suspension control arms to the vehicle frame. They are typically made of a metal inner tube, a metal outer skeleton, and an intermediate rubber body, all vulcanized and bonded together. Their performance directly determines the vehicle's ride comfort, handling stability, and NVH (noise, vibration, and harshness) performance. Vulcanization molding is the core process in suspension bushing production, directly affecting the bond strength between the rubber and the metal skeleton, the rubber's mechanical properties, and the dimensional accuracy of the finished product.

[0003] Existing suspension bushing vulcanization processes mostly employ a one-time temperature and pressure constant-temperature molding method, which has the following significant drawbacks: First, the rubber compound rapidly cross-links under high temperature and pressure, making it difficult for the trapped gas to escape fully, easily forming internal defects such as pores and looseness, resulting in large fluctuations and poor consistency in the bushing's static stiffness; Second, the one-time rapid temperature rise easily causes uneven vulcanization between the rubber surface and interior, with the surface over-vulcanized and aging while the interior is under-vulcanized and insufficiently cross-linked, significantly reducing the rubber's mechanical properties and aging resistance; Third, after vulcanization, direct high-temperature demolding causes the bushing to generate significant internal stress due to the sudden temperature drop, easily leading to problems such as coaxiality deviation, rubber shrinkage and deformation, and even debonding of the rubber from the metal skeleton, resulting in a low finished product qualification rate; Fourth, traditional mechanical trimming processes have poor precision and easily scratch the rubber surface, affecting the product's appearance and assembly compatibility. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a vulcanization molding method for automotive suspension bushings. By employing segmented gradient vulcanization, gradient cooling demolding, and supporting pre-treatment of the skeleton and post-treatment of the finished product, this method solves the problems of uneven vulcanization, numerous internal pores, low bonding strength, easy deformation of finished products, and low pass rate in traditional processes.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: To achieve the above objectives, this invention adopts the following technical solution: A method for vulcanizing and molding automotive suspension bushings, comprising the following steps: Step 1: Metal skeleton pretreatment. The inner metal tube and outer skeleton of the bushing are cleaned and roughened in turn. Then, rubber adhesive is evenly applied to the bonding surface of the skeleton and dried for later use. Step 2: Preparation of rubber compound blanks. Weigh the rubber matrix and compounding agents according to the ratio, mix them in an internal mixer, and then sheet them out in an open mill to obtain the rubber compound. After the rubber compound is left to mature, it is extruded into ring-shaped rubber sleeve blanks through an extruder. Step 3: In-mold pre-assembly. The annular rubber sleeve blank is fitted onto the outer wall of the metal inner tube and placed together into the lower mold cavity of the vulcanizing mold. Before mold closing, the outer skeleton is positioned and installed so that the annular rubber sleeve blank is confined within the forming gap between the metal inner tube and the outer skeleton. Step 4: Segmented gradient vulcanization. After the mold is closed, a heating medium is introduced into the flow channel of the vulcanization mold. The vulcanization molding is carried out by segmented heating and pressurization process. First, the pre-vulcanization is completed by holding the temperature and pressure at the first vulcanization temperature and the first vulcanization pressure. Then, the temperature and pressure are increased to the second vulcanization temperature and the second vulcanization pressure. The positive vulcanization is completed by holding the temperature and pressure. Step 5: Gradient cooling and demolding. After vulcanization is completed, stop the heating medium and gradually cool the vulcanization mold. Once the mold temperature drops to the preset demolding temperature, open the mold and remove the vulcanized bushing. Step Six: Finished Product Post-processing. The initial bushing is subjected to flash removal, surface finishing, and dimensional inspection to obtain the finished automotive suspension bushing.

[0006] Furthermore, the roughening treatment in step one is carried out by sandblasting, with 80-120 mesh brown corundum as the sandblasting abrasive and a sandblasting pressure of 0.4-0.6 MPa; the adhesive is a phenolic resin type rubber-metal adhesive with a coating thickness of 15-30 μm, a drying temperature of 80-100℃, and a drying time of 10-20 min.

[0007] Further, in step two, the rubber matrix comprises 60-70 parts by weight of natural rubber and 30-40 parts by weight of styrene-butadiene rubber; the compounding agents include carbon black, zinc oxide, stearic acid, accelerator, vulcanizing agent and antioxidant; the mixing temperature is 110-130℃, the mixing time is 8-12 min; the curing time of the compound is 12-24 h, and the extrusion temperature is 60-80℃.

[0008] Furthermore, in step three, the lower mold cavity of the vulcanizing mold is provided with a positioning mandrel that is adapted to the inner hole of the metal inner tube, and the outer skeleton is coaxially limited by the positioning steps on the inner wall of the cavity; before the mold is closed, the annular rubber sleeve blank is preheated at a temperature of 50-60℃ for 3-5 minutes.

[0009] Furthermore, in step four, the heating medium is heat transfer oil; the first vulcanization temperature is 120-130℃, the first vulcanization pressure is 8-12MPa, and the pre-vulcanization time is 5-8min; the second vulcanization temperature is 150-165℃, the second vulcanization pressure is 15-20MPa, and the positive vulcanization time is 12-18min.

[0010] Furthermore, during the pre-vulcanization stage, 2-3 mold venting operations are performed, each venting lasting 3-5 seconds, with an interval of 1-2 minutes between adjacent venting operations.

[0011] Furthermore, the gradient cooling in step five is divided into two stages. In the first stage, air cooling is used to reduce the mold temperature to 100-110℃, and in the second stage, water cooling circulation is used to reduce the mold temperature to 60-70℃, the demolding temperature. The initial bushing product taken out of the mold is left to cool at room temperature for no less than 30 minutes before entering the post-processing process.

[0012] Furthermore, in step six, the flash removal adopts a frozen trimming process with a freezing temperature of -60 to -40°C and a trimming time of 2-4 minutes; the surface finishing adopts water polishing; and the dimensional inspection adopts go and no-go gauges to perform full-dimensional verification of the inner hole, outer diameter and height.

[0013] Furthermore, after step six is ​​completed, a finished product performance sampling inspection step is also included. The sampling inspection items include static stiffness test, rubber-metal skeleton bonding strength test and hot air aging test. Only finished products that pass the sampling inspection can be put into storage.

[0014] The advantages of this invention compared to the prior art are: Improve vulcanization uniformity and internal quality. A segmented gradient vulcanization process is adopted. Low-temperature and low-pressure pre-vulcanization allows the rubber compound to initially cross-link and set, and then the temperature and pressure are increased to complete the positive vulcanization, avoiding the problems of surface over-vulcanization and internal under-vulcanization, and ensuring uniform cross-linking of the rubber. The pre-vulcanization stage is combined with multiple venting to fully remove the gas in the mold cavity and inside the rubber compound, which greatly reduces porosity and looseness defects and improves static stiffness stability.

[0015] Ensuring dimensional accuracy and bonding reliability. A two-stage gradient cooling demolding process is employed, gradually reducing temperature to prevent thermal stress and shrinkage deformation of the bushing due to sudden temperature drops, thus improving coaxiality and dimensional accuracy. At the same time, it reduces internal stress at the rubber-metal bonding interface, lowering the risk of debonding. Combined with roughening of the skeleton by sandblasting and a special adhesive, the interfacial bonding force is further enhanced.

[0016] Improve appearance quality and finished product pass rate. Post-processing adopts a freeze trimming process, which utilizes the low-temperature embrittlement characteristics of rubber to remove flash, resulting in neat trimming without scratching the rubber surface; combined with water polishing to improve the appearance smoothness, combined with full-size inspection and performance sampling, defective products can be effectively eliminated, resulting in a high overall pass rate of finished products.

[0017] It has strong process adaptability and is easy to scale up production. The process parameters are highly controllable and can be flexibly adjusted according to different specifications and rubber compound formulations. It is compatible with existing mainstream vulcanization equipment, without the need for large-scale production line modifications, making it easy to achieve industrialized mass production. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0019] Example 1 This embodiment provides a vulcanization molding method for automotive suspension bushings, specifically for processing control arm bushings of a certain vehicle model. The specific steps are as follows: Metal skeleton pretreatment: Select steel inner tubes and outer skeletons of matching specifications. First, use 5% sodium hydroxide alkaline solution for ultrasonic cleaning for 10 minutes to remove surface oil and rust impurities. After rinsing with clean water, place them in an 80℃ oven to dry. Then, perform sandblasting roughening treatment. Use 80-mesh brown corundum as abrasive and control the sandblasting pressure at 0.4MPa. Spray evenly onto the skeleton bonding surface to form a uniform and rough anchoring structure. After sandblasting, clean the surface dust with compressed air. Apply phenolic resin-based rubber-metal adhesive evenly to the bonding surface with a coating thickness of 15μm. After coating, place it in an 80℃ oven to dry for 20 minutes and then remove it for use.

[0020] Preparation of the compounded rubber preform: Weigh the raw materials according to the following parts by weight: 60 parts natural rubber, 40 parts styrene-butadiene rubber, 45 parts carbon black N330, 5 parts zinc oxide, 2 parts stearic acid, 1.2 parts accelerator CZ, 2 parts sulfur, and 1.5 parts antioxidant 4010NA. First, put the natural rubber and styrene-butadiene rubber into a mixer and plasticize for 2 minutes. Then, add carbon black, zinc oxide, stearic acid, and antioxidant and mix. The mixing temperature is controlled at 110℃, and the total mixing time is 12 minutes. After mixing, discharge the rubber and transfer it to an open mill. Add the accelerator and sulfur, and pass through a thin mill three times before sheeting to obtain the compounded rubber. Place the compounded rubber in a room temperature, dark environment for 12 hours to cure. Then, extrude it into ring-shaped rubber sleeve preforms using a rubber extruder. The temperature of each section of the extruder is controlled at 60℃.

[0021] In-mold pre-assembly: The annular rubber sleeve blank is preheated in a 50℃ oven for 5 minutes to soften the rubber and improve its adhesion. After removal, the rubber sleeve blank is evenly fitted onto the outer wall of the metal inner tube, and then placed into the lower mold cavity of the vulcanizing mold. Radial positioning is achieved by the positioning mandrel at the center of the cavity passing through the inner hole of the metal inner tube. Then, the outer skeleton is fitted onto the outside of the rubber sleeve blank. The coaxial positioning of the outer skeleton is achieved by the annular positioning step on the inner wall of the cavity, so that the annular rubber sleeve blank is precisely limited within the annular forming gap between the metal inner tube and the outer skeleton, completing the pre-assembly before mold closing.

[0022] Segmented gradient vulcanization: After mold closing, heat transfer oil is introduced into the vulcanizing mold flow channel for heating, and a segmented heating and pressurization process is adopted: Pre-vulcanization stage: the temperature is raised to 120℃, the pressure of the flat vulcanizing machine is controlled at 8MPa, and the temperature and pressure are maintained for 5min; during the pre-vulcanization process, two venting operations are performed, each venting time is 3s, and the interval between the two venting operations is 1min, to fully remove the gas inside the mold cavity and the rubber material; positive vulcanization stage: after venting is completed, the mold is closed, the temperature is raised to 150℃, the vulcanization pressure is increased to 15MPa, and the temperature and pressure are maintained for 18min to complete the vulcanization cross-linking molding.

[0023] Gradient cooling demolding: After vulcanization, stop the flow of high-temperature heat transfer oil and start the mold air cooling system for the first stage of cooling. After 8 minutes of ventilation cooling, the mold temperature is reduced to 100℃. Then switch to the water cooling circulation cooling system for the second stage of cooling. After 10 minutes of cooling, the mold temperature is reduced to the demolding temperature of 60℃. Open the mold and take out the vulcanized bushing. Place it stably in a room temperature ventilated environment and let it stand for 30 minutes to eliminate residual internal stress before proceeding to the post-processing process.

[0024] Post-processing of finished products: The initial bushing is sent to a cryogenic trimming machine, and liquid nitrogen is injected to control the temperature inside the chamber at -60℃. The cryogenic trimming time is 4 minutes. Taking advantage of the embrittlement of rubber flash at low temperatures, the flash is removed by shot impact. After trimming, the rubber surface of the bushing is lightly polished using a water grinding and polishing process to remove residual burrs and defects. Finally, a high-precision go / no-go gauge is used to perform full-dimensional verification of the inner hole, outer diameter and height, and products with out-of-tolerance dimensions are rejected to obtain the finished bushing.

[0025] Sampling inspection of finished product performance: Samples are randomly selected from the same batch of finished products at a ratio of 3‰ for performance testing: the deviation of static stiffness test value is controlled within ±5%, the bonding strength between rubber and metal skeleton is ≥6MPa, and the tensile strength retention rate is ≥85% after hot air aging at 100℃×72h. Finished products that pass the sampling inspection are put into storage.

[0026] Example 2 This embodiment provides a vulcanization molding method for automotive suspension bushings, specifically for processing lower control arm bushings of a certain vehicle model. The steps are basically the same as in Embodiment 1, except that the process parameters are as follows: Metal skeleton pretreatment: blasting abrasive is 100 mesh brown corundum, blasting pressure is 0.5MPa; adhesive coating thickness is 20μm, drying temperature is 90℃, drying time is 15min.

[0027] Preparation of compounded rubber preform: 65 parts natural rubber, 35 parts styrene-butadiene rubber; mixing temperature 120℃, mixing time 10min; compounded rubber compound left to mature for 18h; extrusion temperature 70℃.

[0028] In-mold pre-assembly: The annular rubber sleeve blank is preheated at 55℃ for 4 minutes.

[0029] Segmented gradient vulcanization: First vulcanization temperature 125℃, first vulcanization pressure 10MPa, pre-vulcanization time 6min; during the pre-vulcanization stage, two venting processes are performed, each lasting 4s with an interval of 1.5min; second vulcanization temperature 158℃, second vulcanization pressure 18MPa, and pre-vulcanization time 15min.

[0030] Gradient cooling demolding: The first stage is air cooling to 105℃, and the second stage is water cooling to 65℃ for demolding; the initial bushing is left to cool at room temperature for 40 minutes.

[0031] Post-processing of finished product: freezing trimming temperature -50℃, trimming time 3min.

[0032] The finished bushing prepared in this embodiment was tested and found to have the following characteristics: static stiffness deviation ≤ ±4%, bonding strength ≥ 7 MPa, tensile strength retention rate after hot air aging ≥ 88%, and product size qualification rate of 99.2%. Its overall performance is better than that of Example 1.

[0033] Example 3 This embodiment provides a vulcanization molding method for automotive suspension bushings, specifically for processing trailing arm bushings of a certain vehicle model. The steps are basically the same as in Embodiment 1, except that the process parameters are as follows: Metal skeleton pretreatment: blasting abrasive is 120 mesh brown corundum, blasting pressure is 0.6MPa; adhesive coating thickness is 30μm, drying temperature is 100℃, drying time is 10min.

[0034] Preparation of compounded rubber preform: 70 parts natural rubber, 30 parts styrene-butadiene rubber; mixing temperature 130℃, mixing time 8min; compounded rubber compound left to mature for 24h; extrusion temperature 80℃.

[0035] In-mold pre-assembly: The annular rubber sleeve blank is preheated to 60℃ for 3 minutes.

[0036] Segmented gradient vulcanization: First vulcanization temperature 130℃, first vulcanization pressure 12MPa, pre-vulcanization time 8min; three venting processes are carried out during the pre-vulcanization stage, each lasting 5s with a 2min interval between adjacent processes; second vulcanization temperature 165℃, second vulcanization pressure 20MPa, and vulcanization time 12min.

[0037] Gradient cooling demolding: The first stage is air cooling to 110℃, and the second stage is water cooling to 70℃ for demolding; the initial bushing is left to cool at room temperature for 50 minutes.

[0038] Post-processing of finished product: freezing trimming temperature -40℃, trimming time 2min.

[0039] The finished bushing produced in this embodiment has the following characteristics: static stiffness deviation ≤ ±3.5%, bonding strength ≥ 7.5 MPa, tensile strength retention rate after hot air aging ≥ 90%, and internal porosity defect rate less than 0.5%. It has the best overall performance and is suitable for the production of suspension bushings under high load conditions.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for vulcanizing and molding automotive suspension bushings, characterized in that... Includes the following steps: Step 1: Metal skeleton pretreatment. The inner metal tube and outer skeleton of the bushing are cleaned and roughened in turn. Then, rubber adhesive is evenly applied to the bonding surface of the skeleton and dried for later use. Step 2: Preparation of rubber compound blanks. Weigh the rubber matrix and compounding agents according to the ratio, mix them in an internal mixer, and then sheet them out in an open mill to obtain the rubber compound. After the rubber compound is left to mature, it is extruded into ring-shaped rubber sleeve blanks through an extruder. Step 3: In-mold pre-assembly. The annular rubber sleeve blank is fitted onto the outer wall of the metal inner tube and placed together into the lower mold cavity of the vulcanizing mold. Before mold closing, the outer skeleton is positioned and installed so that the annular rubber sleeve blank is confined within the forming gap between the metal inner tube and the outer skeleton. Step 4: Segmented gradient vulcanization. After the mold is closed, a heating medium is introduced into the flow channel of the vulcanization mold. The vulcanization molding is carried out by segmented heating and pressurization process. First, the pre-vulcanization is completed by holding the temperature and pressure at the first vulcanization temperature and the first vulcanization pressure. Then, the temperature and pressure are increased to the second vulcanization temperature and the second vulcanization pressure. The positive vulcanization is completed by holding the temperature and pressure. Step 5: Gradient cooling and demolding. After vulcanization is completed, stop the heating medium and gradually cool the vulcanization mold. Once the mold temperature drops to the preset demolding temperature, open the mold and remove the vulcanized bushing. Step Six: Finished Product Post-processing. The initial bushing is subjected to flash removal, surface finishing, and dimensional inspection to obtain the finished automotive suspension bushing.

2. The method for vulcanizing and molding automotive suspension bushings according to claim 1, characterized in that: The roughening treatment in step one is carried out by sandblasting, with 80-120 mesh brown corundum as the sandblasting material and a sandblasting pressure of 0.4-0.6 MPa; the adhesive is a phenolic resin type rubber-metal adhesive with a coating thickness of 15-30 μm, a drying temperature of 80-100℃, and a drying time of 10-20 min.

3. The method for vulcanizing and molding automotive suspension bushings according to claim 1, characterized in that: In step two, the rubber matrix comprises 60-70 parts by weight of natural rubber and 30-40 parts by weight of styrene-butadiene rubber; the compounding agents include carbon black, zinc oxide, stearic acid, accelerator, vulcanizing agent and antioxidant; the mixing temperature is 110-130℃ and the mixing time is 8-12 min; the compound is left to mature for 12-24 h and the extrusion temperature is 60-80℃.

4. The method for vulcanizing and molding automotive suspension bushings according to claim 1, characterized in that: In step three, the lower mold cavity of the vulcanizing mold is equipped with a positioning mandrel that matches the inner hole of the metal inner tube, and the outer skeleton is coaxially limited by the positioning steps on the inner wall of the cavity; before closing the mold, the annular rubber sleeve blank is preheated at a temperature of 50-60℃ for 3-5 minutes.

5. The method for vulcanizing and molding automotive suspension bushings according to claim 1, characterized in that: In step four, the heating medium is heat transfer oil; the first vulcanization temperature is 120-130℃, the first vulcanization pressure is 8-12MPa, and the pre-vulcanization time is 5-8min; the second vulcanization temperature is 150-165℃, the second vulcanization pressure is 15-20MPa, and the positive vulcanization time is 12-18min.

6. The method for vulcanizing and molding automotive suspension bushings according to claim 5, characterized in that: During the pre-vulcanization stage, the mold is vented 2-3 times, with each venting lasting 3-5 seconds and the interval between two adjacent venting operations being 1-2 minutes.

7. The method for vulcanizing and molding automotive suspension bushings according to claim 1, characterized in that: The gradient cooling in step five is divided into two stages. In the first stage, air cooling is used to reduce the mold temperature to 100-110℃. In the second stage, water cooling circulation is used to reduce the mold temperature to 60-70℃, the demolding temperature. The initial bushing product taken out of the mold is left to cool at room temperature for no less than 30 minutes before entering the post-processing process.

8. The method for vulcanizing and molding automotive suspension bushings according to claim 1, characterized in that: In step six, the flash removal adopts a frozen trimming process with a freezing temperature of -60 to -40℃ and a trimming time of 2-4 minutes; the surface finishing adopts water polishing; and the dimensional inspection adopts go and no-go gauges to perform full-dimensional verification of the inner hole, outer diameter and height.

9. The method for vulcanizing and molding automotive suspension bushings according to claim 1, characterized in that: After step six is ​​completed, a finished product performance sampling inspection step is also included. The sampling inspection items include static stiffness test, rubber-metal skeleton bonding strength test and hot air aging test. Only finished products that pass the sampling inspection can be put into storage.