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    Home > Coatings News > Paints and Coatings Market > The research and application status of graphite-based solid lubrication composite coatings

    The research and application status of graphite-based solid lubrication composite coatings

    • Last Update: 2020-11-21
    • Source: Internet
    • Author: User
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    Graphite materials have good chemical stability, high temperature resistance, corrosion resistance and self-lubrication, these properties determine its wide application in the field of solid lubrication composite materials, can play a performance maintenance, energy saving and consumption reduction, improve production efficiency. Based on the excellent electrometic properties of graphite and as the basic structural unit of carbon solid lubrication material, the development of graphite-based composite lubrication material has become a hot research topic in the field of friction. In view of the current graphite coating lubricants there are many shortcomings, such as graphite coating foundation and coating interface technology is not perfect, graphite coating solid lubrication has limitations, etc. , this paper on graphite coating lubricants and solid lubrication composite coating research and application of the status quo, dilemma and
    trends
    of comprehensive discussion;
    1, graphite-based solid lubrication composite coating type and application area
    coating type graphite solid lubrication composite material is graphite-based lubrication filler coating dry curing on the surface of the object, with solid lubrication function of composite materials, such coatings internationally commonly referred to as graphite coating lubricants, because of the construction process is widely used in various types of material surface lubrication. The composition system of the coating is about the same as that of conventional coatings, the main difference being the use of graphite with lubrication function, thus giving the coating material solid lubrication function.
    1.1 Iron-based graphite amorphomin composite coating——— laser cladding
    Zhang Xiaodong in 304L stainless steel surface using laser cladding technology to prepare a graphite-added Fe-based amorphoe composite coating, and study the addition of graphite on the composition and performance of the coating effect. The results showed that the coating without graphite was mainly composed of α-Fe, boron-containing phase (Fe23B6, CrB) and (Ni, Cr, Fe), and the amorphous phase volume fraction was 35.9%, while the coating with graphite was new to carbon-containing phase (Fe8C, CrC3), and the number of amorphous integrals in the coating increased to 41.6%. The coating binding area without graphite is dispersed with irregular particle phase, the cladding layer is rice spike-shaped, the coating binding area tissue after the addition of graphite is cytographical branch crystalline, and the laminated layer shape is a needle-like tissue with dark gray near-spherical particles. The average micro-hardness value of the sample cladding after the addition of graphite was nearly 0.5 times higher than before the addition of graphite. Pod⁃ Chernyaeva, etc., is melted by laser, and the micro-hardness of the graphite coating is 2.5 times higher than that of the substation, reaching (15±1) GPa.
    1.2 graphite/polyether ketone-based composite coating is ——— by cold pressure
    Vail and others used graphite and Teflon (PTFE) to mix and change polyether ketones (PEEK), control the quality ratio of PTFE and PEEK unchanged, and prepare PEEK-based composite coatings with different graphite mass fractions on stainless steel surfaces by cold pressure sintering, and study the effect of graphite content on coating properties and frictional properties. The results show that with the increase of graphite content, the crystallization of PEEK-based composite coating decreases gradually, the hardness of the coating increases and decreases, the coefficient of friction decreases, and the wear decreases first. With a graphite mass score of 4%, the friction coefficient is 0.0461 and the wear rate is as low as 2.06×10-6mm3/(N.m), which greatly improves the wear resistance of the coating compared to previous studies. However, the excessive amount of graphite will reduce the softness of the molecular chain, the movement of the chain segment is blocked, and the wear resistance of the coating is greatly reduced.
    1.3 Graphite/nickel-based metal brazing coating ———brazing coating
    graphite has an important role in the motor industry, adding the right amount of active metal to the nickel-based solder and preparing brazing layers on the graphite surface through innovative brazing methods to achieve a stronger connection between graphite and copper rotor in the motor exchanger, resulting in a significant reduction in the amount of wear of the graphite brush that was previously in direct contact with copper. Testing the performance of the brazing layer through tests such as DSC, XRF, SEM, EDS, XRD, ultrasonic C-scan detection, and resistance testing showed that the brazing material itself produced intermetallic compounds, and the Si and Cr elements in the brazing material produced carbide with graphite, thus forming a solid metallurgical combination between the brazing material and graphite, and the sample was brazed without affecting its conductivity as an electric brush material.
    1.4 Casting mold graphite lubrication coating——— precision casting more than
    years of production applications show that sodium-based bentonite and hydroxymethyl cellulose (CMC) as thickening agents, graphite, talcum powder, quartz powder and SPH-1 type of water-based graphite coating with low cost, easy preparation, good performance and other advantages, suitable for the production of iron core and molybric sand (core) mold. The surface roughness of the casting produced by the oil core immersion method can reach 2.5 to 6.3 m, and the surface roughness of the brush coating casting can reach 2.5 m. With the improvement of casting surface quality requirements, coupled with the particularity of the coating itself, most foundries have adopted specialized manufacturing plants to produce commercial coatings.
    1.5 diesel aluminum piston graphite spray ———swiping lubrication
    spraying graphite layer on the aluminum piston surface of diesel engine can improve the reliability of diesel engine. Because the graphite powder itself is soft and lubricating, when the diesel engine is starting or other unexpected conditions caused lubrication difficulties, the graphite layer sprayed on the piston can play a lubrication role in a short period of time, so that the piston safely through the emergency; Through more than 100 hours of on-board test to verify that 12V17 diesel aluminum piston spray graphite layer, in lubrication and reduction of the effect is better than not applying graphite layer, and graphite coating and substring metal combination is also very good.
    1.6 Artificial human repair organs self-lubricating ——— graphite repair
    Gott and others used graphite coatings for the first time in medicine, and the carbon coating developed and improved does not bond heparin, which is the best rigid material in artificial valve construction and has laid the foundation for today's carbon medical applications. The special compatible properties of carbon, non-biodegradation, bone-like mechanicality, high wear resistance and fatigue resistance make it particularly suitable for instrument repair. Coating polymers and metal surfaces of various shapes with a thin layer of carbon protection allows for a wider range of uses for these materials.
    2, technical bottleneck of graphite coating lubricants
    2.1 Graphite coating lubricants basic technology research is not perfect
    graphite coating lubricants as a special functional coatings, not enough attention, especially graphite powder The basic research work of compatibility between body and resin base material, the influence of graphite powder on paint fluidization, the processing process and coating process of graphite coating lubricant is relatively lagging behind, and the basic research of graphite coating lubricant technology needs to be perfected urgently.
    2.2 Graphite coating interface technology research is not perfect
    the interaction between graphite coating and substation interface directly affects the adhesion performance of the coating, the scientific research on graphite coating and substation interface and interface formation technology research is insufficient. Poor coating adhesion in coating application engineering is one of the main reasons for the failure of coating function.
    2.3 The study of the frictional properties of solid lubrication of graphite coating is not in-depth
    although people attach great importance to the solid lubrication properties of graphite coatings, the relationship between the structure and frictional properties of graphite coatings is not systematic, especially the study of the micro-frictional properties of coatings is relatively rough, and the study of frictional properties of solid lubrication of graphite coatings needs to be carried out urgently. By studying the frictional properties of coatings, the scientific law between graphite coating structure and solid lubrication properties can be established.
    2.4 Graphite coating lubricant product variety is not complete
    From the current graphite coating lubricant research and application status quo, graphite coating product varieties are relatively small, mainly focused on water-based graphite coating lubricants and solvent-based graphite coating lubricants. Water-based graphite coating lubricant more mature domestic products for casting mold forward graphite coating lubricant, the coating market representative for the 1980s molded SPH-1 water-based graphite coating lubricant. Solvent-based graphite coating lubricants are mainly based on traditional epoxy coatings to add graphite powder, mainly used for diesel aluminum piston surface emergency lubrication. The main research work of powder graphite coating lubricants focuses on laser cladding and cold pressure coating, and other varieties of graphite coating lubricants are rarely studied and applied.
    2.5 Graphite-coated solid lubrication has limitations
    graphite coating lubricants form coatings on the surface of the substate, on the one hand, because the interface interaction is relatively weak, resulting in weak coating adhesion;
    3, graphite-based solid lubrication composite coating functional development
    Bonavolont et al. proposed the application of transparent graphite collosite suspension to the panels of polymethyl acrylates (PMMA). The good adhesion and shear stress on the PMMA surface allow graphite nanocrystals to spread evenly and continuously, resulting in a very uniform multi-layer coating of graphene. The manufacturing process is simple and produces a thin coating. Coatings prepared by these polymers stimulate their potential application in strain sensing.
    the microstructure of the surface using differential scanning thermal methods (DSCs) and X-ray diffraction (XRD) such as Sahoo, as well as the interaction of Raman spectroscopy between graphite and PVDF. The results show that in the case of PVDF porous materials, adding a small amount of graphite powder to composite materials not only promotes the crystallization of PVDF, but also changes the surface texture and roughness, thus obtaining super-hydrophobic properties, which makes this composite material play an important role in industry.
    SSR samples were studied using abrasive wear test benches, such as Natarajan, and SS304 samples were coated at room temperature. The volume loss and wear rate of the sample were analyzed relative to the increase of graphite content in the coating. The results show that adding graphite to the coating can significantly reduce volume loss and wear rate. The composite coating has excellent wear resistance when the graphite mass score is 8%.
    Zhang and others have demonstrated that Al2O3, Al2O3-SiO2 and SiO2 sol coat natural scale graphite by making transparent Al2O3, Al2O3-SiO2, and SiO2 coatings improve the moisture and moisture of graphite, especially at high temperatures (>1100 degrees C). Adding Si to graphite slightly improves the antioxidant properties of graphite, indicating that it is possible to reduce the use of antioxidants in actual production.
    Li and other use of surfactants and acid-base catalytic flexible sol-gel legal system prepared SiO2 coated scale graphite as epoxy resin composite material conductive electric insulation filler. The volume resistivity of SiO2-coated scale graphite increased from 184 s.m. to 6391 s.m. of original graphite, and SiO2 coated graphite/epoxy composites showed high volume resistivity (3.11×109 s. m) and thermal conductivity (3.08W. M-1.k-1). Such coating studies provide a more suitable treatment for thermal conductivity and electrical insulation of high-fill epoxy-based composites.
    4, Conclusion
    Graphite and its products in the field of solid lubrication research and application, not only focus on the traditional field of systematic research and technology development, but also committed to the emerging field of scientific research and technological innovation. Graphite coating lubricant is favored by science and technology workers because of its simple preparation and convenient application, but the technical bottleneck of graphite coating lubricant must be paid attention to, and the homogeneity fossil ink polymer solid lubrication composite coating and ceramic fossil ink polymer solid lubrication pre-drive coating should be vigorously developed. With the breakthrough of basic scientific research and key technology development, graphite solid lubrication coating will usher in a new era of development.
    This article Liu He, Guo Junhong, Summer Dong, Bao Xuemei, Mu Bo, Yang Baoping, Cui Jinfeng
    Source: 2019 Paint Industry Issue 1
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