Development of powder coating for suspension spring of automobile shock absorber

Abstract: The appearance and performance of powder coatings for springs (including impact resistance, flexibility, adhesion, crush resistance, neutral salt spray resistance, oil resistance, solvent resistance, Water resistance, anti-clumping) impact, and finally prepared a powder coating to meet the requirements of automotive shock absorber suspension spring coating, the coating has excellent mechanical properties and high corrosion resistance, and in health and environmental protection, energy saving and storage stability has an advantage.
0 Introduction
With the improvement of china's living standards, the quality of automotive products is also more and more demanding, the quality of auto parts is also higher and higher. Among them, the automotive shock absorber (car shock absorber schematic shown in Figure 1) uses different specifications of springs, in order to ensure its mechanical properties, the coating needs to be

. At present, most coatings use solvent-based coatings, and a small number use water-based coatings and powder coatings. However, solvent-based coatings in the use of solvents will be volatile, not only will cause environmental pollution, but also to the health of coating operators caused certain harm. In addition, due to the particularity of water-based coating structure, in anti-corrosion and water resistance performance is not as good as solvent-based coatings. The powder coating process is solvent-free, does not cause harm to the environment and human body, while the use of the process can be recycled. In addition, powder coating can be achieved through a process of coating thickness, in mechanical properties and corrosion resistance can also meet the requirements, so powder coating is the most ideal coating coating for automotive parts.
This study, by comparing different reaction systems and screening of resins and promoters, determined a suitable formula, developed a shock absorber suspension spring powder coating, its mechanical properties and corrosion resistance to meet the shock absorber suspension spring coating application requirements.
1 Experimental part
1.1 Raw materials
-based polyester resins (A, B, C, D, E): commercially available; BPA epoxy resins (a, b, c): commercially available; phenolic curing agents (1, 2): commercially available; powder coating general additives (leveling agents, sabbaths, wax powders, promoters, brighteners): industrial grade, imported.
1.2 Experimental Instrument
-30 Twin Screw Extruder: SLJ-30, Donghui; DFY-5 million-energy Chinese medicine shredder: Wenling Linda Machinery; ACM-02 grinding powder Systems: Yantai Dongyuan Chemical Equipment Co., Ltd.; SURE COAT small electrostitectrical spray equipment, Nordstration spray gun, GPH-30 high temperature oven: Espeke Environmental Instruments (Shanghai) Co., Ltd.; DSC differential scanning volume heat meter: Shanghai and Yan Instrument Technology Co., Ltd.
1.3 Powder coating and coating preparation
according to the preset formula called to take each raw material, with a 10-power Chinese medicine shredder premixed after the use of twin screw extruder in the set temperature range melt extruded, extruded film material after cooling crushing, oversieve, electrostitive spraying, thermoset into a film, and finally test the coating performance.
1.4 Performance test
the impact of the coating film by GB/T1732-1993, the weight of 1 kg from 50cm height fell, the coating film is not damaged, as passed; /T1731-1993 measured film flexibility, GB/T9286-1998 film adhesion, GMW14700-B film resistance to gravel impact, GB/T9274-1988 to determine oil resistance, alkaline and acid resistance.
2 Results and discussion of the impact of
2.1 film-forming system on mechanical performance and corrosion resistance
This experiment compares the mechanical and corrosion resistance of the two reaction systems, and the results are shown in Table 1.
From Table 1, it can be seen that the corrosion resistance of both systems meets the requirements required for spring powder spraying, but the mechanical performance of pure epoxy system relative to epoxy/polyester hybrid system is poor, so this study mainly selects polyester/epoxy mixed resin substrate as a film-forming system for optimization research.
2.2 Hybrid resin screening
The film-forming system of the hybrid powder coating developed in this study consists of polyester resin and epoxy resin, and the polyester/epoxy mass composition ratio is set to 50/50, 60/40 and 70/30. In order to obtain a resin system that meets the requirements of spring powder spraying, different polyester resins and epoxy resins were selected for resin in this study, and the performance results of powder coatings prepared with 3 mixed resins and related additives were found in Table 2.
it can be seen that powder coatings with polyester/epoxy mass composition ratios of 50/50 and 60/40 look good but less tough than 70/30, polyester/epoxy mass composition ratio of 70/30 powder coatings ensure a good coating appearance, while other properties such as impact resistance and corrosion resistance meet the requirements of spring powder spraying. Therefore, the study selected a polyester/epoxy mass composition ratio of 70/30 mixed resin.
different polyester and epoxy preparation coatings for polyester/epoxy blends. From the above study, the composition ratio of polyester/epoxy is 70/30, and epoxy a and polyester resin C are mixed resins, which can obtain good mechanical properties.
According to the requirements of shock absorber suspension spring in curing mode, appearance, mechanical performance and corrosion resistance, different manufacturers at home and abroad are selected to produce epoxy resin and polyester resin for further comparative testing, the results can be seen in Table 3 and Table 4. Figure 2 shows the mechanical properties and adhesion of powder coatings prepared with different epoxy resins.
from the test results of Tables 3 and 4, it can be seen that epoxy equivalent of epoxy resin is 700 to 750g/eq, softening point interval is 90 to 98 degrees C, and the average molecular weight distribution range is narrow, while polyester resin viscosity range is 550 0 to 6500MPa.s, Tg in 58 to 60 degrees C, the resulting products in the appearance, materialization performance (impact resistance, flexibility, adhesion, salt spray corrosion resistance) excellent, at the same time has a better resistance to clumps, which is conducive to production and transportation. Through the above series of detailed comparative test research, the selection of epoxy resin c and polyester resin C to produce spring powder, not only to meet the spring powder in the appearance of leveling and other performance requirements, but also to improve the product in the storage and transportation process of anti-clump performance.
2.3 Promoter type and dosage of the impact on spring powder performance
In order to adapt to the current shock absorber suspension spring production process, need to be baked at low temperature, in addition to the use of low temperature resin, need to add a certain amount of promoter, so that curing can be fully complete, to ensure mechanical properties and corrosion resistance can meet the requirements of coating spraying.
with 70/30 type (polyester resin C/ epoxy resin c) hybrid system as the main body, according to the filler content (35%) design formula, different types of promoters and different dosages of research, the results can be seen in Table 5 and Table 6.
As can be seen from Table 5, methane, amines and other promoters will affect leveling, and the impact strength is poor, corrosion resistance is poor, while end-steroidal polyester compounds such as latent promoter curing can be gentle, in the basic without reducing the leveling performance of the premise of increasing the density.
can be seen from Table 6, the amount of latent promoter can also affect the appearance and performance of the coating. When the amount of latent agent is too small, the degree of coating curing is not enough, and the impact resistance is poor. The amount of latent agent is too much, it will affect the appearance of the coating at the same time the powder's anti-grouping difference, so the latent dose of 3 to 1% is more appropriate.
2.4 Technical requirements and current product level
through the resin system, resin types and promoter research, has developed a car shock absorber suspension spring coating requirements of powder coating requirements, product level and automotive shock absorber spring coating technical requirements see Table 7.
3 Conclusion
This study, based on the spraying requirements of automotive shock absorber suspension spring coating, studied resin system, resin type and promoter, developed a powder coating suitable for automotive shock absorber suspension spring and determined a better formula: using epoxy/polyester hybrid system with a mass ratio of 30/70; Epoxy resins with an equivalent of 700 to 750g/eq, epoxy resins with softening point ranges from 90 to 98c and viscosity ranges from 5,500 to 6500MPa.s and Tg at 58 to 60c;
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