David Demchenko

An automatic technological line to produce a three-layer composite material based on a steel base and multigraphene tapes as fillers in spiral-wound gaskets was developed. It has been experimentally shown that multigraphene materials have a pronounced anisotropy of gas permeability due to a layered-porous microstructure. The longitudinal gas permeability of multigraphene materials obtained from intercalated graphite compounds is 20.3·10⁻³ mg/(m·s) for stage II and 22.9·10⁻³ mg/(m·s) for stage IV, while the transverse permeability is significantly lower and amounts to 0.75·10⁻³ mg/(m·s) for stage II and 0.85·10⁻³ mg/(m·s) for stage IV, respectively. The in-plane gas permeability of the composite based on stage II multigraphene is reduced to 5.8·10⁻³ mg/(m·s) due to the barrier effect of the metal tape. The recoverability of the composite increases to 19% with compressibility of 34%. To achieve the tightness class L0.0000001, it is proposed to manufacture spiral-wound gaskets from a three-layer composite based on stage II multigraphene with a fluoropolymer sealing coating. This made it possible to significantly reduce fugitive emissions through the composite gaskets.

This study investigates the influence of the thermal expansion parameters during the production of a multigraphene-based composite gasket on its performance properties. Under laboratory conditions (near-laminar flow), compared with 700 °C, expansion at 1000 °C increased recovery from 7.5 to 9.2% and tensile strength from 3.8 to 5.6 MPa. For continuous industrial-scale production, MGS was pneumatically transported to increase process productivity. At the expansion temperature of 1000 °C, the material obtained under these conditions exhibited lower mechanical performance than that produced in the laboratory-scale process. The transport parameters themselves also had a measurable effect on the resulting properties. At pressures of 0.2 and 0.6 MPa, recovery increased from 8.6 to 9.1%, while tensile strength increased from 3.4 to 3.7 MPa. The highest recovery (10.0%) was obtained at a feed pipe insertion depth of 100 mm within the investigated range of 50–200 mm. Increasing the feed pipe diameter from 8 to 16 mm also improved the mechanical performance, with recovery increasing from 9.0 to 10.4% and tensile strength from 3.7 to 5.4 MPa. The experimental results, supported by thermal and gas-dynamic simulations, show that processing conditions alter the length, tortuosity, and fragmentation of multigraphene structures before compaction, which in turn affects the mechanical performance of the final material. These results establish a link between thermal and gas-dynamic processing conditions and the mechanical properties of CMGMs, providing a basis for optimizing their continuous production for sealing applications.

A measurement setup was developed for leakage determination in flanged joints with diameters up to 654 mm at temperatures ranging from −196 °C to +500 °C and pressures up to 200 bar. The operating principle is based on the differential pressure method, enabling the utilization of both helium and gaseous hydrocarbons as working media. The setup was validated through specific leak rate measurements on standard DN40/PN40 multigraphene gaskets in accordance with EN 13555, showing close agreement with data obtained from the reference Amtec TEMES fl.ai1 test rig. An intrinsically safe architecture combined with strain-gauge monitoring of tightening loads enabled the transition from bench-scale characterization to in situ testing of large-scale gaskets.

This study investigates the tribological properties of graphite foils (GF) with densities of 1.0, 1.3, and 1.6 g/cm³, produced from purified natural graphite of different particle sizes (40–80 μm, 160–200 μm, >500 μm). Surface roughness was measured after cold rolling and friction testing at static (0.001 mm/s) and dynamic conditions (0.1 Hz and 1 Hz). Results showed that static friction tests yielded similar roughness values (S_a ≈ 0.5–0.7 μm, S_q ≈ 0.5–1.0 μm) across all densities and particle sizes. Dynamic friction tests revealed increased roughness (S_a from 0.7 to 3.5 μm, S_q from 1.0 to 6.0–7.0 μm). Friction coefficients (µ) decreased with higher sliding speeds, ranging from 0.22 to 0.13. GF with 40–80 μm particles had the lowest friction coefficient (µ = 0.13–0.15), while 160–200 μm particles had the highest (µ = 0.15–0.22). Density changes had minimal impact on friction for the 40–80 μm fraction but reduced friction for the 160–200 μm fraction. Young’s modulus increased with density and decreased with particle size, showing values from 127–274 MPa for 40–80 μm, 104–212 MPa for 160–200 μm, and 82–184 MPa for >500 μm. The stress–strain state in the graphite foil samples was simulated under normal and tangential loads. This makes it possible to investigate the effect of the anisotropy of the material on the stress concentration inside the sample, as well as to estimate the elasticity modulus under normal compression. Structural analyses indicated greater plastic deformation in GF with 40–80 μm particles, reducing coherent-scattering region size from 28 nm to 24 nm. GF samples from 160–200 μm and >500 μm fractions showed similar changes, expanding with density increase from 18 nm to 22 nm. Misorientation angles of GF nanocrystallites decreased from 30° to 27° along the rolling direction (RD). The coherent scattering regions of GF with 40–80 μm particles increased, but no significant changes in the coherent scattering regions were observed for the 160–200 μm and >500 μm fractions during dynamic friction tests. Microstrains and residual macrostresses in GF increased with density for all fractions, expanding under higher friction-induced loads. Higher values of both stresses indicate a higher level of accumulated deformation, which appears to be an additional factor affecting the samples during friction testing. This is reflected in the correlation of the results with the roughness and friction coefficient data of the tested samples.