Which oil do I choose for the overhead conveyor chain through the drying oven?

For the moderate-temperature stretch, LHMT 68 is sufficient — a mineral chain oil with ISO VG 68 viscosity, a flashpoint above 200 °C, and a silicone-free formulation. For the oven section, LHHT 250 is the choice: synthetic, ester-based, usable up to 250 °C, and virtually residue-free, so no lacquer build-up forms in the links.