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    Home > Coatings News > Paints and Coatings Market > Development and application of waterborne coatings for high-speed EMU bogies

    Development and application of waterborne coatings for high-speed EMU bogies

    • Last Update: 2022-10-14
    • Source: Internet
    • Author: User
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    The bogie is one of the most important components of high-speed EMU trains, and protection with organic paint coating is an important way
    to improve the service reliability of the bogie.
    High-speed EMUs can run at a maximum speed of 350km/h, and the operating environment is complex and changeable, the bogie is the closest component to the track and the ground in addition to the wheels, its operating environment is more humid, and the debris and other debris brought up during the operation of the vehicle will also cause some damage
    to the surface coating of the bogie.
    For the harsh operating environment, in the design of the coating system, not only should the protection performance of salt spray resistance and high and low temperature cycle alternation requirements be taken into account, but also the mechanical properties of the coating such as stone breakage and adhesion should be taken into account coatingol.
    com
    .


    The traditional coating of bogie mostly uses solvent-based coatings, and the use of waterborne coatings instead of solvent-based coatings has become a development trend
    .
    However, waterborne coatings use water as a dispersion medium, resulting in a gap between them and solvent-based coatings in terms of construction performance, protective properties and mechanical properties, etc.
    In the construction process, thick coatings are prone to hanging, cracking and other problems, and rust and coating peeling often occur in the later protection process, which challenges the application of waterborne coatings on the bogie
    .


    In addition, in the current high-speed EMU bogie conventional construction process, generally first coated with 60 ~ 70μm primer, baked and dried, after polishing and then coated 130 ~ 170μm topcoat (also known as "heavy anti-corrosion coating" in the rail transit industry), the final dry film thickness reached after baking and drying again is about 200μm, the existing high-speed EMU bogie paint and coating construction period is long and the energy consumption of baking and drying is large
    .


    In this paper, for the construction characteristics of coatings for high-speed EMU bogie, this paper develops water-based coatings that can achieve the thickness required for bogie coating in one coating, and conducts performance tests
    such as salt spray resistance, high and low temperature cycle alternation test, and stone breakage resistance.


    1 Experimental section


    1.
    1 Raw materials

    Waterborne epoxy dispersion D.
    E.
    R.
    900: Olin;waterborne epoxy dispersion EP386w/52WA:Allnex; Waterborne epoxy dispersion EPI-REZ3540-WY-55: Hexion; Titanium dioxide Ti-PureR-900: Chemours; DispexUltraPA4560 dispersant, Wetting agent DispexUltraFA4425:Basf; Defoamer Airex902W: Tego; Leveling agent BorchiGolLA200: OMG; Rheur-C: Imported; Wood fiber ExilvaF01-V: Lehvoss; Bentonite-A: commercial; Anti-flash rust agent Raybo 60: Raybo; Waterborne polyamine adjugate resin VEH2849w-80WA: Allnex; Glass scale AIR60: Langfang Tiantuo Company; Silane coupling agent KH560: DowCorning
    .
    The above raw materials are industrial grade
    .


    1.
    2 Experimental equipment

    High-speed dispersing machine Omega60, grinding machine LabStar: NETZSCH (Shanghai) Mechanical Instrument Co.
    , Ltd.
    ; Salt Spray Box Q-Fog: Q-Lab Company; High and low temperature humidity and heat alternating test chamber YP-HW-100L: Dongguan Yipin Instrument Equipment Co.
    , Ltd.
    ; Automatic digital display pull-out adhesion tester PosiTestAT-A: DeFelsko; Viscometer KU-2: Brookfield; Hanging instrument: Standard Geda Precision Instrument (Guangzhou) Co.
    , Ltd.
    ; Electronic balance: METTLER TOLEDO; Air spray gun Jet5000: Sata
    .


    1.
    3 Preparation of waterborne coatings

    1.
    3.
    1 Preparation of the main agent


    According to the formula of Table 1, deionized water and waterborne epoxy resin are added to the stainless steel dispersion tank, and the defoamer, wetting agent and dispersant are added sequentially under stirring conditions, and the stirring is carried out for 3min; Increase the speed, add pigments and fillers in turn, disperse at high speed for 15min, and then grind to a fineness of ≤30μm; Reduce the speed, add defoamer, leveling agent, anti-flash rust agent, rheology agent, stir for 15min, and use 100 mesh filter filter.


    Table 1 The basic composition of waterborne paint for the bogie


    1.
    3.
    2 Preparation of curing agent


    In the case of stirring, the polyamine addition resin and deionized water are added to the paint mixing container in turn, mixed evenly, filtered and set aside
    .


    1.
    3.
    3 Preparation of modified glass scales


    The glass flakes are modified with the silane coupling agent KH-560 so that their surface is equipped with epoxy groups, which is more conducive to the stable presence in the main agent containing epoxy resin, the specific steps are: the glass flakes are added to the aqueous solution of the silane coupling agent KH-560 mass fraction of 5%, placed in a 50 °C constant temperature water bath for 24h, removed and washed and fully dried
    .


    1.
    3.
    4 Preparation of coatings


    The main agent and curing agent are mixed evenly by mechanical stirring, and an appropriate amount of deionized water is added to dilute until the viscosity is 30~50s (DIN6 out of the cup) and then sprayed for construction, and the surface of the steel plate after sandpaper grinding and cleaning is leveled for 15min, baked at 80 °C for 60 min, and the coating thickness is (200±20) μm
    .


    1.
    4 Performance test

    According to GB/T5210-2006 test coating pulling adhesion method; According to Q/CR546.
    6-2016 Appendix A provisions of the sand type stone strike test method to test the coating stone breaking, the impact particles are GB/T6170-2000 provisions of the 8-grade M61 hexagonal nut, the total amount is 1kg; According to GB/T1771-2007 salt spray resistance test, the test time is 1000h, using ISO4628-2 coating film foaming grade evaluation, ISO4628-3 coating film corrosion level evaluation to evaluate the coating after salt spray testing; According to QCR546.
    4-2016 cold and hot cycle alternating test, the test conditions are: (80±2) °C, relative humidity (95±5)%, keep 4h, at 1 °C / min temperature rate down to −40 °C, in (-40±2) °C to maintain 4h, at 1 °C / min temperature rate up to 80 °C, relative humidity of 95%, above 1 cycle, the test time is 60 cycles, The ISO4628-2 coating film foaming grade evaluation is used to evaluate the coating that has undergone alternating hot and cold cycles
    .


    2 Results and discussion


    2.
    1 Effect of epoxy emulsion type on the mechanical properties of the coating

    The physical and chemical parameters of the three types of epoxy resins selected in this paper are shown in
    Table 2.


    Table 2 Physical and chemical indexes of waterborne epoxy resin


    2.
    1.
    1 Adhesion


    Waterborne coatings were prepared using 3 different types of epoxy resins, and different types of epoxy resins were compounded with a mass ratio of 1:1, and another 3 waterborne coatings were prepared by cross-combination, and these 6 resins were numbered 1 (D.
    E.
    R.
    900), 2 (EP386w/52WA), 3 (EPI-REZ3540-WY-55), 4 (D.
    E.
    R.
    900 and EP386w/52WA compounding), respectively.
    5 (D.
    E.
    R.
    900 and EPI-REZ3540-WY-55 compound) and 6 (EP386w/52WA and EPI-REZ3540-WY-55 compounding).

    For parallel comparisons, the solids fractions of epoxy and curing agent resins were consistent with the lean base ratio in the 6 group formulations, and the molar ratio of the epoxy group to the reactive hydrogen in the curing agent was also consistent
    .
    The above preparation of the six kinds of waterborne paint sprayed on the sandblasted steel plate, cured into a film, test adhesion, the data as shown in Table 3, the number of models pulled apart the fracture interface as shown in
    Figure 1.


    Table 3 Adhesion strength of coatings prepared with different types of epoxy resins


    Figure 1 Adhesion strength of coatings prepared with different types of epoxy resins


    In the coating for high-speed EMU bogies, the general requirements for adhesion are ≥5MPa, as can be seen from Table 3, only the adhesion of resin numbers 3 and 6 does not meet the requirements, and the main reason for the analysis is that the epoxy equivalent of epoxy resin is large, the epoxy group is small, and the crosslinking density is low
    .


    2.
    1.
    2 Stone breakdown resistance


    The stone breakage resistance test results of the six waterborne coatings are shown in
    Table 4.


    Table 4 Effect of epoxy resin on the resistance of coating to stone breakage


    In the rail transit vehicle industry, the general requirements for the resistance to stone breakage of bogie coatings are the number of coating breakage levels ≤3, and the coating damage size level ≤M level, as can be seen from Table 4, the resistance of the three groups of coating stones to break down is not up to the requirements.
    The analysis reason is that the waterborne epoxy emulsion D.
    E.
    R.
    900 epoxy equivalent is small, the crosslinking density is high, the flexibility is insufficient, the coating shows brittleness characteristics, and the coating damage level is high when it is subjected to the rapid impact of the nut; the waterborne epoxy dispersion EPIREZ3540-WY-55 crosslinking density is low, the coating adhesion is weak, and the coating damage size level is high
    when subjected to the rapid impact of the nut.


    Based on the above research, it can be seen that although the coating prepared by D.
    E.
    R.
    900 has high adhesion strength, the brittleness is too large and the stone breakage resistance cannot be satisfied; the coating prepared by EPI-REZ3540-WY-55 has good toughness, but the crosslinking density is too low to meet the adhesion and adhesion requirements; the coating prepared by EP386w/52WA can meet the adhesion and flexibility requirements
    。 However, it was found that when D.
    E.
    R.
    900 was combined with EP386w/52WA, the prepared coating had the characteristics of both macromolecular epoxy and small molecule epoxy, and the adhesion and stone breaking resistance were the best, and it was more suitable for the preparation of water-based coatings
    for high-speed EMU bogies.


    2.
    2 Effect of silane-modified glass flakes on the protective properties of coatings

    2.
    2.
    1 Salt spray resistance


    Changing the amount of silane-modified glass flakes added to prepare water-based coatings with different Yan base ratios, the salt spray resistance (1000h) test results of the coating are shown in Table 5, and the sample status is shown in
    Figure 2.


    Table 5 Effects of different face-to-face ratios on salt spray resistance of coatings

    Fig.
    2 Effect of Yan-base ratio on salt spray resistance of coating


    From Table 5 and Figure 2, it can be seen that after the 1000h salt spray test, only the sample with a Yan base ratio of 1.
    0:1.
    0 meets the requirements
    of no foaming and no rust on the plate surface, the corrosion width at the scratch is ≤ 2mm (one-way), and the scratch test ≤ level 1.


    2.
    2.
    2 Alternating test of hot and cold cycles


    When the skin ratio is different, the alternating test of hot and cold cycles (60 cycles) is carried out according to QCR546.
    4-2016, and the test results are shown in
    Table 6.


    Table 6 Experimental results of alternating cold and hot cycles of coatings at different skin ratios


    As can be seen from the test results, When the Yan base ratio is 1.
    0:1.
    0, the salt spray resistance and the alternating test of hot and cold cycles are the best, when the Yan base ratio is lower than 1.
    0:1.
    0, the silane-modified glass scales in the coating are too few, it is difficult to play a shielding role, in the 1000h salt spray test process, the moisture will penetrate between the coating and the substrate, resulting in foaming; when the Yan base ratio is higher than 1.
    0:1.
    0, the silane-modified glass scales in the coating are too much, the resin can not effectively fill the bond between the glass scales, the shielding effect will weaken with the increase of the filler, and the amount of resin reduces the bonding strength and the moisture is easier to penetrate between the coating and the substrate , resulting in the appearance of large bubbles
    .


    2.
    3 Effect of rheology type on construction performance

    Waterborne coating rheology agents can be divided into two categories: inorganic and organic
    .
    At present, montmorillonite, sepiolite and attapulgite are the most widely used inorganic rheology agents in waterborne coatings; Organic rheological agents are mainly divided into two categories: non-associative and associative types, non-associative rheological agents include hydroxyethylcellulose (HEC), alkali swelling acrylic emulsion (ASE); Related rheological agents include hydrophobically modified hydroxyethyl cellulose (HMHEC), hydrophobically modified alkali swelling acrylic acid emulsion (HASE), hydrophobically modified polyurethane (HEUR) and so on
    .


    Hydrolysis failure due to the susceptibility of HEC type rheology agents to mold erosion in waterborne coating systems; ASE type rheology agent is more sensitive to the electrolyte in the coating, water resistance, alkali resistance is poor, so do not make a choice
    .
    In this paper, the new rheological agent wood fiber ExilvaF01-V is selected to be compared
    with the inorganic rheology agent bentonite-A and hydrophobically modified polyurethane HEUR-C.
    The structural formula of the wood fiber ExilvaF01-V is shown in
    formula (1).

    Three groups of waterborne coatings were prepared, and the rheology agents in the formula were 0.
    5% ExilvaF01-V, HEUR-C, and bentonite-A
    , respectively.
    The rheology-related test data in the diluted construction state is shown in
    Table 7.


    Table 7 Effect of rheological agent on the rheological properties of coatings in the application state

    As can be seen from Table 7, in the case of the viscosity of the outgoing cup is basically the same, the viscosity of the waterborne coatings prepared by rheostatic agent HEUR-C has the highest viscosity at medium and high shear rates, and according to the experience, there will be a problem of spraying atomization defects
    , and the waterborne coatings prepared by ExilvaF01-V and bentonite-A have relatively low viscosity at high shear rates, and have excellent spray atomization.


    The coating status of the above three waterborne coatings on the surface of the sandblasted steel plate is shown in
    Figure 3.

    Fig.
    3 Coating state of coatings prepared by different rheological agents under thick coating conditions


    As can be seen from Figure 3, the surface of the coating prepared with the rheological additive ExilvaF01-V is free of particles, pinholes, bubbles, wrinkles, and is in good condition; The surface of the coating prepared by the rheology agent HEUR-C has obvious cracking; The coating prepared by bentonite-A is used with a large area of flow on the
    surface.
    The reason for the analysis is that the specific surface area of ExilvaF01-V microfibers is large, and the surface is rich in hydroxyl groups, so that it has very good water retention, thereby prolonging the opening time of the coating surface, making the bottom and surface layer of the coating dry and synchronous, reducing the stress caused by cracking, on the other hand, ExilvaF01-V microfibers can form a network structure in the wet film state, with strong pseudoplasticity, to prevent the appearance
    of hang-up.


    By comparing the appearance state of the actual spray coating, ExilvaF01-V microfibers were selected as rheological agents, and the coating surface was in good condition under the condition of meeting the thickness of 200μm in one coating, which is suitable for the preparation of water-based coatings
    for bogie.


    2.
    4 Performance indicators and application of waterborne coatings

    The performance indicators of waterborne coatings for high-speed EMU bogie prepared in this study meet the technical requirements of the coating and supporting coating system for the protective coating of EMU bogie according to the enterprise standard Q/CR546.
    4-2016 "Coatings for EMUs and Coatings for Bogie and Coating System", and the main performance test results are shown
    in Table 8 when the total thickness of the dry film is (200±20) μm.


    Table 8 Main performance test results of waterborne coatings for bogie of high-speed EMUs

    After the construction of the test of the coating of the scratching method adhesion, gloss, color difference, appearance and other conventional performance, the indicators have reached the requirements, the coating film surface is flat, no hanging, cracking, bubbles, pinholes and other drawbacks, excellent
    construction effect.


    3 Conclusion


    Using high and low epoxy equivalent compound resin as a film-forming substance, silane-modified glass flakes as anti-corrosion fillers, microfibrous wood fibers as rheological agents, and adding other functional additives and other raw materials, the prepared water-based coatings have a salt spray resistance of more than 1000h on the steel substrate, the adhesion of the pulling method is greater than 5MPa, and the stone shattering level 2 meets the Q/CR546.
    4-2016 "Paint for EMUs and Paint and Coating System for Bogie Coatings and Coating Systems".
    It can replace the solvent-borne coatings
    that are currently commonly used.
    At the same time, in the actual application process, according to the existing construction conditions, can be normal spraying, a coating thickness of up to 200μm or more, to obtain the ideal coating effect, compared with the current rail transit industry commonly used in the primer plus topcoat twice to meet the thickness requirements of the traditional coating shorten the construction cycle, improve production efficiency, reduce drying and baking energy consumption, to meet the rail transit vehicle industry green coating requirements
    .


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