What distributors and tier-one buyers should verify before placing a planetary gear order — from material certification to contact pattern.
2026-09-18 · Conocimiento
Planetary sets carry the highest load density in a heavy-truck transmission. Three or four planet gears share the torque that would otherwise pass through a single mesh, so a small dimensional error in one planet is multiplied into an uneven load split across the whole carrier. That is why buying planetary gears is mostly a question of consistency, not of catalogue specifications.
Start with the material trail. 20CrMnTi remains the workhorse for carburised planet gears in China, with 20CrMo and 42CrMo for larger sections or higher core hardness. Ask for the steel certificate with heat number, the forging lot, and the carburising record — a supplier who cannot link these three is guessing about its own process.
Then check the geometry that actually governs life: tooth profile and lead modification, bore-to-face runout, and the case depth at the root rather than at the pitch point. Case depth measured only at the flank is the most common hidden deviation in incoming inspection.
Finally, ask how the supplier controls distortion during quenching. Press quenching and properly designed fixtures hold bore roundness within a few microns; free quenching followed by straightening introduces residual stress that shows up as noise at 80,000 km rather than at the test bench.
