Rapid chain stretch and black carbon on bakery and dryer oven chains are usually caused by the oil and how it is applied, not by the chain. How to check, clean and select.
In a bakery, noodle-drying or steaming line, the oven conveyor chain is usually the hardest lubrication point in the plant. It runs non-stop at 180–280 °C, picks up steam, flour dust and sugar, and in many layouts travels directly over open product. When that chain starts stretching, seizing up or shedding black crust onto the guides, maintenance tends to blame the chain itself or the oven temperature. In most of the oven chains Hop Tien has surveyed in Vietnam, neither was the cause. The chain was sound and the oven was within spec; the problem was the oil in use and the way it was being applied.
A conventional lubricating oil begins to evaporate and oxidize rapidly from roughly 150 °C. At oven temperature the light fractions are gone within a few hours; that is the smoke and the smell. What remains oxidizes to a gummy resin and then bakes into hard black carbon. This carbon forms exactly where the oil is needed most, in the clearance between pin and bushing, and it blocks fresh oil from getting in. The operator sees a dry chain and oils it again; the new oil burns onto the old crust, and the cycle repeats. The stretch you measure is not the outer plates wearing. It is the pins and bushings inside wearing because they are running dry on carbon. That is also why a new chain fitted without any change to lubrication practice is back in the same state within a few months.
Where the chain runs above open product there is a second consequence. Oil vapor and flakes of burnt deposit can land on the product, and if the oil is not registered for incidental food contact that is a nonconformity in a food-safety audit.
Oil only protects the chain once it is inside the pin-bushing clearance, and it can only get there while the chain is still fairly cool and has time to wick in. The right place to apply it is therefore the return strand, after the chain has left the hot zone and is at its coolest, aimed at the inner edge of the link plates so the oil penetrates to the pins rather than sitting on the rollers. Small, frequent doses beat one heavy dose: an automatic drip lubricator or a timed brush applicator keeps the oil film on the chain steady, never so much that the surplus burns into carbon and never so little that the joints run dry. Hand-spraying an aerosol onto a hot chain at the start of the shift is the worst option. Most of the oil flashes off the surface immediately, and what is left cokes before it ever reaches the pin clearance.
No new oil, however good, will soak through a crust of carbonized old oil. Before converting to a different oil the chain has to be cleaned: dissolve the deposits with a suitable chain cleaning oil following the manufacturer's directions, wipe down guides and sprockets, and only then start applying the new oil. For the first few days after changeover, loosened old carbon will keep flaking off and the oil on the chain may look darker than expected. That is the chain cleaning itself, not the new oil burning, but the guides will need wiping more often during this period.
High-temperature chain oils differ in their upper temperature limit, volatility, how much residue they leave and whether they carry food-contact registration, and the right ISO VG viscosity grade depends on chain speed and the application method. A correct selection rests on three numbers from the checks above: the measured chain temperature, the chain speed, and whether the chain is over product. Hop Tien engineers start from those three numbers with the plant, propose the oil type, viscosity grade, application method and cleaning procedure, and then track chain elongation through the first two months to confirm the result.
This article is general guidance; the specific conditions of each machine must be assessed by an engineer.
