Precision Rack and Pinion Drives for Textile Machinery

Client Background#

The customer is a textile machinery enterprise. Its high-speed textile machines are driven through precision rack-and-pinion drives. Because the travel of the machine is longer than a single rack, the racks have to be joined end to end, and the accuracy of the drive depends on how well each joint is made rather than on a single rack alone.

Requirement & Challenge#

• Module M4, accuracy grade GB 6
• Cumulative error for multi-rack joining of 0.05 mm/m or less
• High-frequency induction hardening of the tooth surface, HRC 45~50

The cumulative figure is the difficult one. It does not describe a single rack but the result over the whole joined length, so pitch consistency along each rack and positioning accuracy at each joint both count towards the same number. The hardened tooth surface has to hold up under the continuous run of a high-speed machine.

Solution & Process#

1. Gear milling + gear grinding - The racks are milled and then precision ground, and grinding keeps the tooth pitch consistent along the full length of the rack, so that no single rack contributes a large share of the cumulative error.
2. Joint positioning - A dedicated fixture is used at the joints to hold jointing accuracy, so the racks can be joined end to end on site and the joined length still meets the cumulative tolerance.
3. Full dimensional inspection - Each gear rack is delivered with its own inspection report, which allows the joined length to be checked joint by joint against the requirement.

Result & Feedback#

• Cumulative joining error came out at 0.03 mm/m or less
• Mass delivery of 500 gear racks, with no complaints

For the same class of high-speed textile equipment, thin precision shafts are also supplied, held to 0.005 mm accuracy with a surface roughness of Ra ≤ 0.4 μm.