Integrated forming process for automobile suspension cushion block

Abstract

This invention discloses an integrated molding process for automotive suspension buffer blocks, relating to the technical field of automotive suspension system components. To address the problems of uneven microporous structure, mismatched foaming-gel rates, long production cycles, poor low-temperature performance, and insufficient insert bonding strength in existing processes, the key technical points are: S1: Preparation of modified polyol: Modified polyol components are obtained by high-speed dispersion and mixing of nanoparticles with an average particle size of 20-80 nm, surface-modified with silane coupling agent, and polycaprolactone polyol; S2: Synthesis and degassing of prepolymer: The modified polyol components are reacted with diphenylmethane diisocyanate to obtain a prepolymer with a terminal isocyanate group content of 5-12 wt%, resulting in a uniform micropore size distribution of 50-250 μm, density fluctuation ≤ ±0.02 g / cm³, compression set controlled within 8%, and dynamic fatigue life exceeding 2 million cycles, thus solving the problems of poor microporous structure uniformity, high compression set, and insufficient fatigue life.

Description

Technical Field

[0001] This invention relates to the field of automotive suspension system components technology, specifically to an integrated molding process for automotive suspension buffer blocks. Background Technology

[0002] Automotive suspension bump blocks, also known as damper stops or limiters, are key limiting and buffering components in the suspension system. They are typically mounted on the piston rod of the shock absorber, positioned between the shock absorber cylinder and the vehicle body mounting point. Their function is to elastically limit the shock absorber's working stroke when the suspension is compressed to its limit, preventing rigid impact between the axle and the chassis. Simultaneously, they provide additional auxiliary stiffness to the suspension, protecting the suspension elastic elements and the entire vehicle structure from impact damage. Polyurethane microporous elastomers, due to their low density, high load-bearing capacity, excellent nonlinear stiffness characteristics, and good fatigue resistance, have become the mainstream material for modern automotive suspension bump blocks. Existing manufacturing processes typically combine prepolymer methods with one-step methods, including prepolymer synthesis, preparation of polyol resin mixtures, rapid mixing, casting, pre-curing and demolding, and post-curing. However, long-term production practice has revealed the following technical problems: (1) Poor uniformity of microporous structure: In the traditional single-temperature zone constant temperature curing process, there is a significant temperature difference between the core and the surface of the mold. The size distribution of the internal pores of the product is wide, ranging from tens of micrometers to hundreds of micrometers. The density gradient between the skin and the core is large, resulting in a compression permanent deformation rate that is generally higher than 12%. The dynamic fatigue life is usually less than 1 million cycles, which is difficult to meet the durability requirements of high-end models. (2) Mismatch between foaming reaction rate and gelation reaction rate: Existing processes mostly use a single chemical foaming agent. The foaming agent decomposes in large quantities to generate gas in the early stage of the reaction, while the polyurethane gel network has not been fully established at this time, resulting in gas escape, cell collapse or merging, and large-diameter defective cells. At the same time, the activity of conventional catalysts is released too quickly, the operating window is extremely narrow, and the consistency between product batches is poor. (3) Long production cycle and high energy consumption: The post-curing process usually requires 12 to 15 hours of high-temperature treatment at 100 to 120°C, which not only consumes a lot of electricity, but also occupies the oven equipment for a long time, becoming the bottleneck of the entire production line capacity and seriously restricting the improvement of production efficiency. (4) Insufficient low temperature performance: In the low temperature environment of -40℃, the polymer molecular chain mobility of conventional polyester or polyether polyol system is greatly reduced, resulting in a sharp increase in the modulus of the buffer block or even brittle cracking, which cannot meet the usage requirements of vehicles in high-altitude and cold regions, especially new energy vehicles, which have increased suspension load due to the increased weight of the battery. (5) Insufficient bonding force of metal inserts: Some buffer block products need to be embedded with metal threaded sleeves or mounting frames to meet assembly requirements. Existing processes mostly use secondary pressing or adhesive methods. There is a lack of strong chemical bonding between the metal and polyurethane. During long-term use, they are prone to debonding and loosening, which can cause abnormal noise or even functional failure. Summary of the Invention

[0003] The purpose of this invention is to provide an integrated molding process for automotive suspension buffer blocks, so as to solve the problems of uneven microporous structure, mismatch between foaming and gelation rates, long production cycle, poor low-temperature performance and insufficient insert bonding force in the existing processes mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: an integrated molding process for automotive suspension buffer blocks, comprising the following steps: S1: Preparation of modified polyols: Modified polyol components are obtained by high-speed dispersion and mixing of nanoparticle reinforced fillers with an average particle size of 20-80 nm that have been surface modified with silane coupling agent and polycaprolactone polyol. S2: Synthesis and degassing of prepolymer: The modified polyol component is reacted with diphenylmethane diisocyanate to obtain a prepolymer with a terminal isocyanate group content of 5~12wt%, and then the micro bubbles in the prepolymer are removed by vacuum degassing treatment. S3: Multi-component dynamic mixing: Chemical foaming agent and physical foaming agent are compounded at a mass ratio of 1~3:2~5 to prepare a compound foaming agent, and the compound foaming agent, prepolymer, chain extender mixture and delayed tertiary amine catalyst are mixed online for 8~15 seconds at a mixing temperature of 40~60℃; S4: Back pressure assisted casting: The mixture is injected into a mold at a temperature of 60~95℃. Before injection, the mold cavity is evacuated to 0.02~0.08MPa. During the injection process, the back pressure of the cavity is maintained at 0.1~0.5MPa. S5: Gradient temperature rise curing and demolding: The mold after casting is subjected to gradient temperature rise curing at 90~120℃, with a total curing time of 3~8 hours. Gradient temperature rise curing includes at least two heating stages, so that the material gradually forms a gel network from the outside to the inside. After demolding, the buffer block initial product is obtained. S6: Vacuum segmented post-curing: The buffer block initial product is placed in a vacuum environment of 100~130℃ for post-curing treatment. The total post-curing time is 8~20 hours. The post-curing temperature range is connected with the gradient heating curing temperature of step S5. In S1, the amount of nanoparticle-reinforced filler added is 0.5~2.5wt% of the mass of polycaprolactone polyol. The compound foaming agent and delayed tertiary amine catalyst in S3, together with the injection back pressure in S4 and the gradient temperature curing in S5, work together to keep the cell growth rate and gel network formation rate dynamically matched across the entire cross-section of the product.

[0005] In a preferred embodiment, the present invention can be further configured as follows: in S1, the nanoparticle-reinforced filler is selected from at least one of nano-calcium carbonate, nano-silica, and nano-clay; the high-speed dispersion process conditions are: temperature 50~70℃, rotation speed 800~1500rpm, time 1~3 hours; and the amount of silane coupling agent added is 0.5~3Wt. of the nanoparticle mass.

[0006] In a preferred embodiment, the present invention may be further configured such that, in step S3, the chain extender mixture comprises the following components: 50-80 wt% small molecule diol, 10-30 wt% aromatic diamine, and 5-20 wt% hydroxyl-terminated polyether, the mass ratio of the chain extender mixture to the prepolymer is 5-20:100, and the amount of delayed tertiary amine catalyst added is 0.05-0.3 wt% of the mass of the prepolymer.

[0007] In a preferred embodiment, the present invention can be further configured as follows: in S3, the chemical foaming agent is water, the physical foaming agent is a hydrofluorocarbon foaming agent, and the total amount of the compounded foaming agent is 0.5~3.0 wt.% of the prepolymer mass. The online mixing is carried out using a low-pressure casting machine with a mixing speed of 3000~6000 rpm.

[0008] In a preferred embodiment, the present invention can be further configured as follows: in S4, the mold is divided into two half molds, the inner cavity after the two half molds are combined is in the shape of a buffer block, the mold injection time is 3 to 10 seconds, and the injection back pressure and gradient temperature curing process work together to maintain the dynamic matching between the cell growth rate and the gel network formation rate.

[0009] In a preferred embodiment, the present invention can be further configured as follows: In step S5, the gradient temperature rise curing and demolding process specifically includes: a first stage of holding at 90~100℃ for 1~2 hours; a second stage of raising the temperature at 0.5~2℃ / min to 100~110℃ and holding for 1~2 hours; a third stage of raising the temperature at 0.5~2℃ / min to 110~120℃ and holding for 1~4 hours; and cooling and demolding after the holding is completed. The heating rate is adapted to the activity release curve of the delayed tertiary amine catalyst, so that the product forms a gradient structure with a dense skin and uniform core pores.

[0010] In a preferred embodiment, the present invention can be further configured such that, in step S2, the vacuum degassing process conditions are: temperature 70~90℃, vacuum degree ≤-0.08MPa, and degassing time 1~2 hours, to avoid the generation of defective cells with a diameter greater than 300μm during the subsequent foaming process.

[0011] In a preferred embodiment, the present invention may be further configured such that step S4 includes a step of embedding a metal insert into the mold, wherein the metal insert is pre-treated with surface phosphating and primer, and after positioning, it is integrally formed with the reactant material, so that the metal insert and the polyurethane matrix form a chemical bond structure.

[0012] In a preferred embodiment, the present invention can be further configured such that: in step S6, the vacuum degree is maintained at -0.06 to -0.09 MPa, and the vacuum segmentation curing is carried out in three stages: the first stage is kept at 100 to 110°C for 4 to 6 hours, the second stage is kept at 110 to 120°C for 3 to 5 hours, and the third stage is kept at 120 to 130°C for 1 to 9 hours.

[0013] A car suspension buffer block, wherein the buffer block has a micropore diameter of 50~250μm, a density of 0.40~0.85g / cm³, a Shore hardness of 40A~90A, a compression set of ≤8%, a dynamic fatigue life of ≥2 million cycles, and a modulus retention rate of ≥75% in a low temperature environment of -40℃.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention introduces nanoparticles modified with a silane coupling agent into polycaprolactone polyol in step S1, providing uniform heterogeneous nucleation sites for the foaming process and avoiding pore coarsening caused by excessively low cell nucleation density. Vacuuming the cavity before injection and maintaining a back pressure of 0.1~0.5MPa during injection effectively suppresses internal and external pressure fluctuations during cell growth, preventing excessive cell expansion or collapse. Furthermore, gradient heating curing allows the material to sequentially build a gel network from the outside in, forming a gradient structure with a dense outer layer and uniform core cells. Through the synergistic effect of these three factors, the micropore size inside the product is uniformly distributed between 50~250μm, with density fluctuation ≤±0.02g / cm³, compression set controlled within 8%, and dynamic fatigue life exceeding 2 million cycles. This solves the problems of poor micropore structure uniformity, high compression set, and insufficient fatigue life. This invention employs a foaming system composed of a chemical foaming agent and a physical foaming agent in a mass ratio of 1-3:2-5. The chemical foaming agent generates carbon dioxide in situ through an isocyanate-water reaction, while the physical foaming agent vaporizes and expands under exothermic reaction conditions. The combination of the two achieves phased gas release. Initially, physical foaming is dominant, rapidly forming bubble nuclei. Later, chemical foaming continuously replenishes gas, promoting uniform cell growth. Simultaneously, a delayed tertiary amine catalyst is selected, which has low initial activity, providing sufficient flow time for online mixing of materials in 8-15 seconds and subsequent casting. Once the mold temperature reaches the reaction activation energy threshold, the activity rapidly increases, driving the gelation reaction to proceed quickly. The synergistic effect of the compounded foaming agent and the delayed tertiary amine catalyst dynamically matches the foaming rate and the gel network formation rate across the entire cross-section, effectively avoiding the defects of premature gas escape, cell collapse, or merging in traditional processes. This widens the operating window, controls the hardness fluctuation between product batches within ±2A, and solves the problems of mismatched foaming and gelation rates and poor product consistency. This invention employs gradient temperature curing and staged vacuum post-curing, which shortens the preparation cycle by more than 40% compared to the traditional process of constant temperature curing at 110℃ for 12-15 hours and post-curing for 12-15 hours. Furthermore, the gradient temperature curing, through precise three-stage temperature control, completes the entire process of gelation, foaming, and deep cross-linking in a shorter time. The staged vacuum post-curing efficiently removes small molecule volatiles under negative pressure, accelerates the stabilization of the microphase separation structure, and eliminates the need for prolonged high-temperature baking. This solves the problems of long production cycles, high energy consumption, and prominent capacity bottlenecks, thereby increasing the capacity of unit equipment and reducing manufacturing costs. This invention uses polycaprolactone polyol as the soft segment raw material. Its molecular chain structure is regular and the ester group density is moderate. The polyurethane generated by the reaction with diphenylmethane diisocyanate has a highly ordered microphase separation structure. Gradient heating curing promotes the ordered arrangement and crystallization of hard segment microregions through slow heating. Staged vacuum curing further refines the microphase separation morphology, so that the polymer molecular chain still maintains good chain segment mobility in the ultra-low temperature environment. The modulus retention rate of the product at -40℃ can reach more than 75%, which is a qualitative leap compared with the 50%~60% modulus retention rate of traditional polyester or polyether systems. It solves the problems of insufficient low temperature performance and easy brittle cracking failure in high-altitude and cold regions, and is suitable for the long-term reliable operation of pure electric vehicles in high-altitude and cold regions. This invention allows for the simultaneous embedding of metal inserts during casting. The inserts are pre-treated with surface phosphating and a primer containing isocyanate groups, providing a physical and mechanical interlocking structure for the phosphating layer. During the curing process, the active groups in the primer undergo a covalent bonding reaction with the polyurethane matrix, creating a gradient transition interface between the metal and the polyurethane, consisting of the phosphating layer, chemical bonds, and the polyurethane network. Compared to traditional secondary pressing and adhesive processes, the pull-out force of the inserts can reach over 2.8 kN with a dispersion coefficient ≤ 7.5%. This solves the problems of insufficient bonding strength and easy detachment and loosening of metal inserts in the prior art, ensuring the reliability of the buffer block under severe vibration and repeated impacts. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] Example 1: This example provides an integrated molding process for an automotive suspension buffer block. The prepared buffer block is frustoconical in shape and has a through-hole for mounting onto the shock absorber piston rod. Unless otherwise specified, all parameters in this example are typical intermediate values ​​within the scope of the claims. The specific steps are as follows: S1: Preparation of modified polyol: Weigh 1000g of polycaprolactone polyol with a number average molecular weight of 8000, dehydrate it for 3 hours at 95℃ and vacuum degree -0.098MPa, and determine the moisture content to be 0.03%, which meets the control requirement of ≤0.05%. Cool the dehydrated polyol to 60℃ and take 20g of nano-calcium carbonate with an average particle size of 40nm. Before adding, the nano-calcium carbonate is first surface modified by γ-aminopropyltriethoxysilane. The amount of silane coupling agent added is 1.5Wt.% of the mass of nano-calcium carbonate. The modification treatment steps are as follows: the nano-calcium carbonate and γ-aminopropyltriethoxysilane are dispersed at high speed in anhydrous ethanol medium for 30 minutes, filtered and dried for later use. The surface-modified nano-calcium carbonate and 3g of dispersant are added to the polyol and dispersed at high speed at 1200rpm for 2 hours to obtain a modified polyol component with uniformly dispersed nano-calcium carbonate. S2: Prepolymer Synthesis and Degassing: All the modified polyols were transferred to a reactor. The air inside the reactor was replaced with nitrogen and nitrogen protection was maintained. 680g of diphenylmethane diisocyanate was weighed and slowly added dropwise to the reactor while stirring. The temperature was raised to 85℃ and reacted at this temperature for 3.5 hours. During the reaction, the terminal isocyanate group content was measured every 30 minutes until the terminal isocyanate group content stabilized at 8.5 wt.%. After the reaction, the prepolymer was transferred to a vacuum degassing reactor and degassed at 80℃ and a vacuum of -0.09MPa for 1.5 hours. During the degassing process, the mixture was stirred slowly until no visible bubbles escaped from the liquid surface inside the reactor. S3: Multi-component online dynamic mixing: The chain extender mixture is prepared according to the following formula: 60 wt.% 1,4-butanediol, 25 wt.% dimethylthiotoluene diamine, and 15 wt.% polypropylene glycol with a number average molecular weight of 1000. The mass ratio of the chain extender mixture to the prepolymer is 12:100. The foaming agent is a compound system of water and hydrofluorocarbon foaming agent, with a mass ratio of water to hydrofluorocarbon foaming agent of 1:2. The total amount of foaming agent is 1.5 wt.% of the prepolymer mass. The catalyst is a delayed tertiary amine catalyst, with an addition amount of 0.15 wt.% of the prepolymer mass. The prepolymer, chain extender mixture, foaming agent, and catalyst are dynamically mixed online within 8 seconds using a low-pressure casting machine. The temperature of the mixing chamber is controlled at 50℃, and the mixing speed is set at 4500 rpm. The temperature of the mixed reactants is stable at 48±2℃, with good fluidity and no early gelation phenomenon. S4: Back pressure assisted casting molding: The mold adopts a multi-cavity structure with 8 cavities in one mold. Each cavity is arranged symmetrically. The cavity surface has a raised structure for forming annular grooves on the surface of the buffer block. Before use, the mold is sprayed with water-based release agent and preheated to 80°C. Before injection, the mold is connected to a vacuum pump through the mold exhaust channel to evacuate the cavity to 0.05MPa. The injection valve of the casting machine is opened, and the mixed reaction material is injected into each cavity of the mold through the injection head. The injection time is 6 seconds. The back pressure of the cavity is maintained at 0.25MPa throughout the injection process. The test found that the material injected under this back pressure condition is fully filled and there is no air entrapment. The deviation of the injection amount of each cavity is controlled within ±1.5%. S5: Gradient Temperature Curing: Immediately transfer the cast mold into a hot air circulating oven for gradient temperature curing. The curing program is set as follows: the first stage is held at 95℃ for 1.5 hours; the second stage is heated to 105℃ at a rate of 0.8℃ / min and held for 1.5 hours; the third stage is heated to 115℃ at a rate of 0.8℃ / min and held for 2.0 hours. The total curing time is 5 hours. After curing, the mold is allowed to cool naturally to about 60℃ before being removed and demolded to obtain the initial product of the buffer block. The product has a smooth surface, no missing material or flash, a flat parting line, and an intact ring groove structure. S6: Vacuum Segmented Post-Curing: The demolded buffer block prototypes are placed in a vacuum oven for segmented post-curing. The vacuum level is maintained at -0.08MPa. The curing process is as follows: the first stage is held at 105℃ for 5 hours; the second stage is held at 115℃ for 4 hours; and the third stage is held at 125℃ for 6 hours. The total curing time is 15 hours. During the curing process, the oven is circulated with hot air to ensure uniform temperature distribution of the products on each shelf, and the temperature fluctuation is controlled within ±2℃. After the curing is completed, the oven heating is turned off, and the products are naturally cooled to room temperature in a vacuum environment before being taken out to obtain the finished automotive suspension buffer blocks, totaling 8 pieces.

[0017] Product performance testing was conducted on the buffer block prepared in Example 1 according to ASTM D3574 standard, including physical and mechanical property testing. Dynamic fatigue life testing was performed using the standard method of GB / T 26709-2011. The test results are as follows:

[0018] Meanwhile, the microporous structure of the product from Example 1 was observed under a 200x microscope after being cut apart. The results showed that the bubble shape was regular and the pore size was concentrated in the range of 80~150μm. No large bubbles with a diameter >300μm or internal void defects were observed. The density of the skin and the core gradually changed smoothly, which confirmed the significant advantage of the process of the present invention in terms of the uniformity of microporous structure.

[0019] Example 2 is essentially the same as Example 1, except that: the nano-reinforcing filler added in step S1 is a composite particle of nano-calcium carbonate and nano-silica, with a mass ratio of 1:1, and the total addition amount is 1.5 wt.% of the polyol mass. The average particle size of the nanoparticles is 30 nm, and they are also surface-modified with γ-aminopropyltriethoxysilane. Furthermore, in step S3, the mass ratio of the chain extender mixture to the prepolymer is adjusted to 10:100, and the total amount of foaming agent is adjusted to 2.0 wt.% of the prepolymer mass. Water and supercritical carbon dioxide are used at a mass ratio of 1:3. The supercritical carbon dioxide is injected into the mixing head at a supercritical state of 31°C and above 7.4 MPa and mixed online with the prepolymer. The catalyst is changed to a delayed tertiary amine catalyst, and the addition amount is... The prepolymer mass is 0.12 wt.%, and the back pressure of the injection is adjusted to 0.20 MPa in step S4, with an injection time of 8 seconds. The gradient temperature curing regime in step S5 is as follows: the first stage is 95℃ for 2.0 hours, the second stage is heated to 108℃ at 1.0℃ / min and held for 1.5 hours, and the third stage is heated to 118℃ at 1.0℃ / min and held for 2.5 hours. The post-curing program in step S6 is: 105℃ for 5 hours, 115℃ for 4 hours, and 130℃ for 7 hours, with a total post-curing time of 16 hours. After testing, the buffer block prepared in this embodiment has a density of 0.62 g / cm³, a Shore hardness of 58A, a compression set of 5.9%, a dynamic fatigue life of >2.5 million cycles, and a modulus retention rate of 81% at -40℃, showing good overall performance.

[0020] Example 3 is basically the same as Example 1, except that this process also includes the integral molding of inserts. The buffer block prepared in this example needs to have a steel internal thread sleeve embedded in the central hole to be fixed by thread engagement with the end of the shock absorber piston rod. The pre-activation treatment steps for steel internal threaded sleeves are as follows: First, the steel sleeve is ultrasonically cleaned in an acidic degreasing solution at 80℃ for 10 minutes to remove surface grease and contaminants. Then, it is immersed in a manganese phosphate phosphating solution at 85℃ for 15 minutes to form a phosphate coating with a thickness of 3~5μm on its surface to enhance the mechanical interlocking performance with polyurethane. After phosphate treatment, it is cleaned and dried, and a two-component polyurethane primer containing isocyanate groups is coated on its surface. The amount of primer is about 0.5~1.0g / m². The coated internal threaded sleeve is dried in an oven at 60℃ for 30 minutes to allow the primer to fully pre-crosslink and form a chemically active thin layer on the insert surface. The pre-treated internal thread sleeve is precisely positioned and fixed in the corresponding position of the casting mold. The mold is equipped with an insert positioning pin to ensure that the axial positioning and coaxiality tolerance of the internal thread sleeve in the cavity are controlled within ±0.05mm. The remaining casting, curing and post-curing process conditions are consistent with those in Example 1. During the casting process, the reactant fully fills the gap between the internal thread sleeve and the mold cavity, and at the same time forms physical interlocking and chemical bonding with the pre-activated insert surface during the curing process. After the product has cured, samples were taken for insert pull-out force testing: referring to ISO 19095 standard, a universal testing machine was used to test the interfacial bonding strength between the polyurethane matrix and the steel insert. The test results showed that the average pull-out force was 2.8kN, which is much higher than the 1.2kN of the traditional secondary press-fit process (an increase of 133%), and the coefficient of variation of the pull-out force of 10 samples was only 7.5%, indicating that the integrated molding process of inserts not only greatly improves the bonding strength, but also significantly improves the process stability.

[0021] Example 4: To investigate the effect of heating rate on product performance during gradient temperature curing, while maintaining the same formulation and mixing and casting conditions as in Example 1, the gradient temperature curing regime in step S5 was changed, and three sets of comparative experiments were set up: Group A used 0.3℃ / min, Group B used 0.8℃ / min, and Group C used 3.0℃ / min. The results showed that: In Group A, due to the slow heating, the gelation reaction lagged behind the foaming, resulting in excessive cell growth with an average pore size of 210μm and a compression set of 9.8%. In Group C, due to the rapid heating, the surface layer quickly gelled to form a dense skin, but the core cells did not grow sufficiently, resulting in a density fluctuation of ±0.04g / cm³. Group B had the best results, with a compression set of 6.7% and a density fluctuation of ±0.01g / cm³, verifying the rationality of the heating rate range of 0.5~2℃ / min.

[0022] Example 5: To investigate the effect of the mass ratio of chemical foaming agent to physical foaming agent in the compound foaming agent on the cell structure, based on Example 1, keeping other conditions unchanged, the mass ratio of water to hydrofluorocarbon foaming agent was adjusted to 1:5, 1:2, and 3:2. The test results are as follows: When the ratio of water to hydrofluorocarbon foaming agent is 1:5, the total gas volume is low and the release is slow, the product density is 0.82 g / cm³, which is high, and the hardness is high. When the ratio is 3:2, the early gas release is too fast, the cell merging is severe, and a small number of defective pores with a diameter >300 μm appear. When the ratio is 1:2, the cell uniformity is the best, the average pore diameter is 95 μm, and the compression set is 6.7%. This verifies the technical rationality of the range of 1:3 to 3:2, that is, the mass ratio of chemical foaming agent to physical foaming agent of 1 to 3:2 to 5.

[0023] Example 6: In this example, all process parameters are taken as the lower limit of the range given in the claims, to verify the feasibility and performance lower limit of the present invention under extremely low parameters. The specific steps are as follows: Step S1: The average particle size of the nanoparticles is 20 nm, the addition amount is 0.5 Wt.%, the addition amount of silane coupling agent is 0.5 Wt.%, the dispersion conditions are: temperature 50℃, rotation speed 800 rpm, time 1 hour, the nanoparticles are nano silica modified by γ-aminopropyltriethoxysilane, and the molecular weight of polycaprolactone polyol is 6000. Step S2: The content of terminal isocyanate groups in the prepolymer is controlled to be 5 wt.%, and vacuum degassing is performed at a temperature of 70℃, a vacuum degree of -0.08MPa, and a time of 1 hour. Step S3: Chain extender mixture: 50 wt.% small molecule diol, 10 wt.% aromatic diamine, 5 wt.% hydroxyl-terminated polyether, chain extender to prepolymer mass ratio 5:100; compounded blowing agent: water to hydrofluorocarbon blowing agent mass ratio 1:5, total dosage 0.5 wt.%; delayed tertiary amine catalyst addition 0.05 wt.%; online mixing time 8 seconds, mixing speed 3000 rpm, mixing temperature 40℃; Step S4: Mold temperature 60℃, pre-injection vacuum 0.02MPa, injection back pressure 0.1MPa, injection time 3 seconds, mold is a single cavity mold; Step S5: Gradient temperature curing: In the first stage, the temperature is kept at 90℃ for 1 hour, then increased to 100℃ at 0.5℃ / min and kept for 1 hour, and then increased to 110℃ at 0.5℃ / min and kept for 1 hour, for a total curing time of 3 hours. Step S6: Vacuum post-curing: Vacuum degree -0.06MPa, first stage 100℃ for 4 hours, second stage 110℃ for 3 hours, third stage 120℃ for 1 hour, total post-curing 8 hours.

[0024] Performance testing: The buffer block prepared in this embodiment has a density of 0.52 g / cm³, a Shore hardness of 48A, a compression set of 7.9%, a dynamic fatigue life of 2.12 million cycles, and a modulus retention rate of 76% at -40℃. All indicators are within the range described in the invention, proving the effectiveness of the lower limit parameters.

[0025] Example 7: In this example, all process parameters are taken as the upper limit of the range given in the claims to verify the feasibility and performance upper limit of the process under high parameters. The specific steps are as follows: Step S1: The average particle size of the nanoparticles is 80 nm, the addition amount is 2.5 Wt.%, the addition amount of silane coupling agent is 3 Wt.%, the dispersion conditions are: temperature 70℃, rotation speed 1500 rpm, time 3 hours, the nanoparticles are nano clay modified by γ-aminopropyltriethoxysilane, and the molecular weight of polycaprolactone polyol is 10000. Step S2: The content of terminal isocyanate groups in the prepolymer is controlled at 12 wt.%, and vacuum degassing is performed at a temperature of 90℃, a vacuum degree of -0.095MPa, and a time of 2 hours. Step S3: Chain extender mixture: 80 wt.% small molecule diol, 30 wt.% aromatic diamine, 20 wt.% hydroxyl-terminated polyether, chain extender to prepolymer mass ratio 20:100, compound foaming agent: water to supercritical carbon dioxide mass ratio 3:2, total dosage 3.0 wt.%, delayed tertiary amine catalyst addition 0.3 wt.%, online mixing time 15 seconds, mixing speed 6000 rpm, mixture temperature 60℃; Step S4: Mold temperature 95℃, pre-injection vacuum 0.08MPa, injection back pressure 0.5MPa, injection time 10 seconds, mold is a four-cavity mold; Step S5: Gradient temperature curing: In the first stage, the temperature is kept at 100℃ for 2 hours, then the temperature is increased to 110℃ at 2℃ / min and kept for 2 hours, and then the temperature is increased to 120℃ at 2℃ / min and kept for 4 hours, for a total curing time of 8 hours. Step S6: Vacuum post-curing: Vacuum degree -0.09MPa, first stage 110℃ for 6 hours, second stage 120℃ for 5 hours, third stage 130℃ for 9 hours, total post-curing 20 hours.

[0026] Performance testing: The buffer block prepared in this embodiment has a density of 0.84 g / cm³, a Shore hardness of 88A, a compression set of 6.2%, a dynamic fatigue life of 2.89 million cycles, and a modulus retention rate of 82% at -40℃. All indicators are superior to those of the lower limit embodiment and fall within the scope of the invention claims, proving that good performance can also be obtained with the upper limit parameters.

[0027] Comparative Example 1: To verify the technical effect of the present invention, a traditional polyurethane buffer block preparation method was used as Comparative Example 1. The main steps are as follows: Polyester polyol with a number average molecular weight of 2000 was reacted with diphenylmethane diisocyanate at 85°C to form a prepolymer with a terminal isocyanate group content of 10 wt.%. The prepolymer was mixed with chain extender, water foaming agent and other additives at a mass ratio of 100:8 and poured into a mold at 90°C. It was then cured in a constant temperature oven at 110°C for 13 hours. All raw material formulations, process temperatures and times were performed according to conventional preferred schemes. The finished product was subjected to the same performance tests as in Example 1. The results are as follows: apparent density 0.73 g / cm³, fluctuation range ±0.05 g / cm³, compression set 13.2%, dynamic fatigue life only 930,000 cycles, modulus retention rate at -40°C only 52%, a large number of large pores with a diameter >400 μm and internal voids can be observed under a microscope, the density difference between the skin and the core is significant, and the hardness fluctuation between batches of products reaches ±10A. In comparison, Example 1 showed a 49% reduction in compression set, a nearly 3-fold increase in dynamic fatigue life, and a 50-percentage-point increase in modulus retention at -40°C, indicating that the present invention is significantly superior to the comparative example in all core performance indicators.

[0028] Comparative Example 2 was set up to verify the key role of the gradient temperature curing process in this invention. Except for the curing stage, which used a constant temperature of 110°C for 5 hours, all other process conditions of Comparative Example 2, including formulation, mixing, casting, and molding, were completely consistent with those of Example 1. The product of Comparative Example 2 was tested for performance after curing and post-curing. The results are as follows: density 0.71±0.05g / cm³, with a fluctuation range of 5 times that of Example 1. Some large pores were connected and formed by parallel formation around the pores. More seriously, a clear sandwich-like density stratification appeared between the core and the surface layer. The core was over-expanded and even partially collapsed to form cavities due to the excessively fast gel reaction. The surface layer was compressed due to the higher external heat conduction than internal reaction heat. The compression set rate reached 11.5%, and the dynamic fatigue life was 1.31 million cycles. Therefore, the constant temperature curing process could not simultaneously optimize the mechanical structure and micropore structure of the core and the surface layer within a reasonable time. The gradient temperature curing system proposed in this invention is crucial for ensuring the consistency of product quality.

[0029] Comparative Example 3 was set up to verify the necessity of vacuum degassing treatment of the prepolymer in the whole process. Except for omitting the vacuum degassing treatment step S2, all other conditions, including the formula and process parameters, were the same as those in Example 1. The test results showed that several large bubbles and cross-hole defects with diameters of 300~800μm appeared randomly inside the product, mainly distributed in the area far away from the injection port. These large bubbles became fatigue sources after about 1.36 million cycles of dynamic fatigue testing, and gradually expanded into through cracks, causing the product to fail prematurely. The dynamic fatigue life test result was 1.54 million cycles, which was 44% lower than that of Example 1. In addition, the batch-to-batch fluctuation of the product density was significantly worsened, from ±0.01g / cm³ in Example 1 to ±0.05g / cm³. Therefore, the microbubbles remaining in the prepolymer became the nuclei for inducing large bubbles during the casting and foaming process. If they are not removed by vacuum degassing, these defects will seriously damage the fatigue life and performance consistency of the product.

[0030] Comparative Example 4 was set up to examine the effect of nanoparticle surface modification. In this comparative example, no nano-calcium carbonate was added in step S1, and the other conditions were the same as in Example 1. The results showed that the average pore size of the product increased to 180 μm, and the pore size distribution was between 80 and 350 μm. The compression set rate was 9.2%, and the dynamic fatigue life was 1.82 million cycles. This was because the lack of heterogeneous nucleation by nanoparticles resulted in low pore nucleation density, leading to pore coarsening. This confirmed the key contribution of surface-modified nanoparticles to refining pores and improving uniformity.

[0031] A comprehensive performance comparison is presented in the table below, summarizing the key performance indicators of the above embodiments and comparative examples to more clearly demonstrate the technical advantages of the present invention. Examples 6 and 7 represent the implementation effects of the lower and upper limits of the parameters, respectively.

[0032] As can be seen from the data in the table, the embodiments of the present invention, including the lower limit embodiment 6 and the upper limit embodiment 7, are superior to the comparative examples in terms of micropore uniformity, compression set, fatigue life, and low-temperature modulus retention. Both the lower and upper limits can meet the performance indicators of the present invention: compression set ≤8%, fatigue life ≥2 million cycles, and modulus retention at -40℃ ≥75%, verifying the rationality and practicality of the numerical range. Furthermore, embodiment 7 performs better under high addition, high temperature, and long-term conditions, while embodiment 6 can still meet the basic requirements under lower energy consumption and shorter cycle, providing users with flexible selection space. Embodiment 1, as an intermediate optimized value, achieves the best balance between comprehensive performance and production efficiency.

[0033] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. An integrated molding process for automotive suspension buffer blocks, characterized by: Includes the following steps: S1: Preparation of modified polyols: Modified polyol components are obtained by high-speed dispersion and mixing of nanoparticle reinforced fillers with an average particle size of 20-80 nm that have been surface modified with silane coupling agent and polycaprolactone polyol. S2: Synthesis and degassing of prepolymer: The modified polyol component is reacted with diphenylmethane diisocyanate to obtain a prepolymer with a terminal isocyanate group content of 5~12wt%, and then the micro bubbles in the prepolymer are removed by vacuum degassing treatment. S3: Multi-component dynamic mixing: Chemical foaming agent and physical foaming agent are compounded at a mass ratio of 1~3:2~5 to prepare a compound foaming agent, and the compound foaming agent, prepolymer, chain extender mixture and delayed tertiary amine catalyst are mixed online for 8~15 seconds at a mixing temperature of 40~60℃; S4: Back pressure assisted casting: The mixture is injected into a mold at a temperature of 60~95℃. Before injection, the mold cavity is evacuated to 0.02~0.08MPa. During the injection process, the back pressure of the cavity is maintained at 0.1~0.5MPa. S5: Gradient temperature rise curing and demolding: The mold after casting is subjected to gradient temperature rise curing at 90~120℃, with a total curing time of 3~8 hours. Gradient temperature rise curing includes at least two heating stages, so that the material gradually forms a gel network from the outside to the inside. After demolding, the buffer block initial product is obtained. S6: Vacuum segmented post-curing: The buffer block initial product is placed in a vacuum environment of 100~130℃ for post-curing treatment. The total post-curing time is 8~20 hours. The post-curing temperature range is connected with the gradient heating curing temperature of step S5. In S1, the amount of nanoparticle-reinforced filler added is 0.5~2.5wt% of the mass of polycaprolactone polyol. The compound foaming agent and delayed tertiary amine catalyst in S3, together with the injection back pressure in S4 and the gradient temperature curing in S5, work together to keep the cell growth rate and gel network formation rate dynamically matched across the entire cross-section of the product.

2. The integrated molding process for automotive suspension buffer blocks according to claim 1, characterized in that: In S1, the nanoparticle-reinforced filler is selected from at least one of nano-calcium carbonate, nano-silica, and nano-clay. The high-speed dispersion process conditions are: temperature 50~70℃, rotation speed 800~1500rpm, time 1~3 hours, and the amount of silane coupling agent added is 0.5~3Wt. of the nanoparticle mass.

3. The integrated molding process for automotive suspension buffer blocks according to claim 1, characterized in that: In S3, the chain extender mixture consists of the following components: 50-80 wt% small molecule diol, 10-30 wt% aromatic diamine and 5-20 wt% hydroxyl-terminated polyether. The mass ratio of the chain extender mixture to the prepolymer is 5-20:100, and the amount of delayed tertiary amine catalyst added is 0.05-0.3 wt% of the mass of the prepolymer.

4. The integrated molding process for automotive suspension buffer blocks according to claim 1, characterized in that: In S3, the chemical foaming agent is water, the physical foaming agent is a hydrofluorocarbon foaming agent, and the total amount of the compounded foaming agent is 0.5~3.0 Wt.% of the prepolymer mass. The online mixing is carried out using a low-pressure casting machine with a mixing speed of 3000~6000 rpm.

5. The integrated molding process for automotive suspension buffer blocks according to claim 1, characterized in that: In S4, the mold is divided into two half molds. The inner cavity after the two half molds are combined is in the shape of a buffer block. The mold injection time is 3 to 10 seconds. The injection back pressure and the gradient temperature curing process work together to maintain the dynamic matching between the cell growth rate and the gel network formation rate.

6. The integrated molding process for automotive suspension buffer blocks according to claim 1, characterized in that: In S5, the gradient temperature rise curing and demolding process is as follows: the first stage is to keep the temperature at 90~100℃ for 1~2 hours; the second stage is to rise the temperature at 0.5~2℃ / min to 100~110℃ and keep it at 1~2 hours; the third stage is to rise the temperature at 0.5~2℃ / min to 110~120℃ and keep it at 1~4 hours; after the temperature is maintained, the product is cooled and demolded. The heating rate is matched with the activity release curve of the delayed tertiary amine catalyst, so that the product forms a gradient structure with a dense skin and uniform core pores.

7. The integrated molding process for automotive suspension buffer blocks according to claim 1, characterized in that: In S2, the vacuum degassing process conditions are: temperature 70~90℃, vacuum degree ≤-0.08MPa, and degassing time 1~2 hours, to avoid the generation of defective cells with a diameter greater than 300μm during the subsequent foaming process.

8. The integrated molding process for automotive suspension buffer blocks according to claim 1, characterized in that: S4 also includes the step of embedding a metal insert into the mold. The metal insert is pre-treated with surface phosphating and primer, and after positioning, it is integrally formed with the reactant material, so that the metal insert and the polyurethane matrix form a chemical bond structure.

9. The integrated molding process for automotive suspension buffer blocks according to claim 7, characterized in that: In step S6, the vacuum degree is maintained at -0.06 to -0.09 MPa. After vacuum segmentation, the curing is carried out in three stages: the first stage is kept at 100 to 110°C for 4 to 6 hours, the second stage is kept at 110 to 120°C for 3 to 5 hours, and the third stage is kept at 120 to 130°C for 1 to 9 hours.

10. A car suspension buffer block, manufactured using the integrated molding process for car suspension buffer blocks according to any one of claims 1-9, characterized in that: The buffer block has a micropore size of 50~250μm, a density of 0.40~0.85g / cm³, a Shore hardness of 40A~90A, a compression set of ≤8%, a dynamic fatigue life of ≥2 million cycles, and a modulus retention rate of ≥75% at a low temperature of -40℃.

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