Study On Manufacturing Process Of DLC Coating On Precision Rubber Mold

To investigate the application prospect of DLC coating on precision rubber mold and to solve tough problems,such as easy viscosing,difficult demolding and so on,three types of DLC coatings were prepared on the 35 steel substrate(common tire mold material)and their surface properties were studied extensively.The primary contents of paper are as follows.(1)Preparing substrates and coatings.Specimens of steel(S35C)were made in strict accordance with the machining process of tire mold and DLC coatings were prepared on the surface of substrates.The hydrogenated DLC coating(a-C:H)was made by PECVD,and hydrogen free DLC coating(a-C)was deposited by AIP,and F-DLC coating was made by technology of combining magnetron sputtering with PECVD.(2)The characterizations of three classes of DLC coatings,such as the surface structure and compositions,were analyzed and compared.The characteristic Raman peaks of the coatings were analyzed by Raman spectrometer.The surface morphology,section morphology and roughness of coatings were detected by SEM and AFM.The surface element composition of the coatings was analyzed by XRF spectroscopy and EDS energy spectrum.To optimize service performances of coatings,the surface structure and compositions of coatings should be carefully analyzed.The results show that the three classes of DLC coatings are really DLC;also,they have smooth surface morphology.(3)The hydrophobic properties of three classes of DLC coatings were measured and compared.The water contact angles,alcohol contact angles,as well as,the surface energy of the specimens were measured by contact angle meter.Also,the influence of elements and roughness of surface on the hydrophobicity of coatings were descripted detailed in paper.The results show that the hydrophobicity of coatings is positively related to the value of surface roughness,and the hydrophobicity of F-DLC coating is stronger than that of DLC coating with H,which is higher than that of the DLC coating without H under the same roughness condition,and the water contact angle of F-DLC coating was 99.45o.(4)The mechanical properties of three classes of DLC coatings were examined and analyzed.The hardness and the bonding strength of coatings were studied by nano-indentation and material surface performance tester.The influence of surface roughness on bonding strength was investigated.The results show that the H(hardness)and E(elastic modulus)of a-C could reach 33.45 GPa and 349.47 GPa,better than a-C:H and F-DLC.However,the bonding strength of a-C:H was up to 15.90 N,better than F-DLC and a-C,and bonding strength enlarged slowly with the decrease of roughness.(5)The friction and wear properties of three classes of DLC coatings were tested and analyzed.The end-face friction and wear testing machine was employed to measure the friction coefficient of the coatings,and surface morphology was detected by SEM.The influence of the surface roughness on the friction coefficient was emphatically studied.The results show that the coefficient of friction of F-DLC coating was reduced to 0.2281,smaller than that of a-C:H and a-C,also,the coefficient of friction reduced clearly by decreasing surface roughness.Through the research on the prepared and surface performances of a-C:H,a-C and F-DLC coatings,also,compared with the characterization of traditional tire mold with Teflon,it can be concluded that DLC coating has great application prospect with excellent meeting the requirements of the use of precision rubber mold and F-DLC coating can be applied to the inner surface of the tire mold by completely replace of the traditional Teflon coating.