Large Gearboxes for Papermaking Machinery

Customer Background#

A papermaking machinery company whose paper machine drive system requires large gear sets, with individual pieces weighing over 500kg. Because of the size and the weight of the parts, the set cannot be produced in a normal gear workshop: the hobbing, the hardening and the matching of every piece have to be planned around the capacity of large gear machines.

Technical Requirements#

• Module M12~M20, outer diameter up to Φ1200mm
• Accuracy GB grade 7, tooth surface hardening hardness HRC 50~55
• Single-piece weight 500~1200kg

The module range spans M12 to M20, so one drive system may contain gears of several sizes, from medium module to heavy module, and the machine platform has to cover the whole range without moving the work to a second supplier. At piece weights of 500~1200kg the difficulty is not only cutting the teeth: the dimensions have to stay stable through hardening, and the two parts of a pair have to be matched so that they can be assembled on site without trimming or rework.

Solution#

1. Large gear hobbing: the gears are machined on large gear hobbing machines, with module up to M20, covering the M12~M20 range on one machining platform.
2. Tooth surface hardening: tooth surfaces are hardened by medium-frequency induction hardening, giving uniform hardness over the tooth width and avoiding the distortion that a heavier hardening cycle would bring to a large thin-walled rim.
3. Matched machining: gear pairs are match-machined, so that the two parts of a pair are produced against each other and the meshing accuracy is set in the workshop instead of at the assembly site.

Results#

• Batch delivery of 50 sets, with good dimensional consistency across the batch
• Smooth assembly, no fitting or rework required
• The customer continues to place repeat orders

Repeat orders for the same gear sets indicate that the parts assembled and ran as expected on the customer’s paper machines, and that batch-to-batch consistency has been maintained over successive deliveries.