Domestic Substitution of Elevator Worm Gear Pairs

Customer Background#

An elevator manufacturing enterprise had been using imported worm gear pairs in its elevator drive units. The imported pairs were costly and came with a long procurement lead time, so the company looked for a domestic substitution route that would meet the same performance requirements against the same drawings.

Requirement & Challenge#

• Center distance 160 mm, module M6, number of worm starts 2
• Self-locking performance, safety factor ≥1.5
• Service life ≥20000 hours

Self-locking is a safety-related characteristic of a worm drive. It depends on the lead angle of the worm, on the friction pairing between the steel worm and the bronze wheel, and on the accuracy of the worm thread. The service life target depends on the hardness of the worm, on the load capacity of the bronze wheel and on the running-in condition of the pair. Delivering a domestic replacement part meant that all three items had to be controlled during production, not only specified on the drawing. Because the center distance and the module are fixed by the customer’s drawing, the substitution work had to stay within the existing mounting interface instead of asking the customer to change the host machine.

Solution & Process#

1. Material optimization: the worm is made of 40Cr carburized and hardened, and the worm wheel is cast in ZCuSn10P1 by centrifugal casting.
2. Process upgrade: the worm is ground to DIN 5 grade, and the worm wheel is machined with a dedicated hob, so that the worm thread and the wheel teeth are produced as one matching set of parameters.
3. Pair running-in: every worm gear pair undergoes paired running-in inspection before delivery, which verifies the contact condition of the pair rather than checking the two parts separately.

Result & Feedback#

• The pairs fully replace the imported ones, and performance meets standards.
• They have been supplied in batches for 3 years, with a cumulative total of 5000+ pairs.

The specification is delivered against rolling orders, and the same production and running-in flow has been kept for it throughout the three years of batch supply.