We have completed standardized cupping tests (compliant with ISO 20482) on NBR-coated steel and FKM-coated steel substrates, quantitatively validating the stretch formability, coating adhesion stability and structural integrity of two core rubber-steel composite materials for precision brake shim stamping production.

The cupping test is a fundamental industrial inspection method for evaluating the plastic deformation capacity and surface coating durability of thin metal sheets. By applying continuous vertical indentation via a standard ball punch, the test simulates the tensile and bending stress encountered during high-speed stamping and forming. It accurately assesses whether the rubber coating can remain fully bonded, crack-free and delamination-free under extreme deformation, which is the key indicator to guarantee consistent yield rate and dimensional stability of finished brake shim parts.

Performance Analysis of Two Coated Steel Materials

NBR Coated Steel/Nitrile-coated Steel

During cupping deformation, the NBR rubber layer maintains excellent ductility and robust interfacial adhesion with the steel substrate. The material achieves balanced formability with uniform stress distribution, showing no surface cracking, edge peeling or localized delamination after standard indentation displacement. Featuring reliable mechanical matching and cost-efficiency, NBR coated steel delivers stable forming performance for conventional passenger vehicle brake shims, fully adapting to routine stamping processes and general road operating conditions.

FKM Coated Steel/Viton Coating Metal Material

FKM-coated steel exhibits superior deformation resistance and coating integrity under equivalent cupping test conditions. The high-performance fluororubber layer retains tight bonding strength with the steel base even under larger plastic strain, with zero coating failure and structural fracture. Beyond qualified stamping formability, FKM composite material retains stable physical properties against high temperature, engine oil, brake fluid and chemical corrosion. It is engineered for heavy-duty vehicles, high-load braking systems and harsh industrial operating scenarios where extreme durability is required.

Test Conclusion & Production Value

Both NBR and FKM coated steel substrates pass the full ISO-standard cupping assessment with qualified IE values. The verified formability ensures reliable mass stamping feasibility, eliminates coating failure risks during post-processing, and guarantees long-term vibration damping performance and service life of finished brake shims. The standardized test data further validates the quality consistency and application reliability of our rubber-steel composite materials, supporting customized material solutions for diverse automotive braking system requirements.

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