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Engineer's Toolbox:
Lightweight Harmonic Drive gear sets use DuPont Vespel bearing cages

DuPont Vespel TP bearing cages (top) retain and guide the ball bearings in Harmonic Drive gear units (bottom). [Image courtesy: Courtesy Harmonic Drive AG]

 

 

 

 

Harmonic Drive AG of Limburg, Germany, has developed an inventive type of component gear set that is considerably lighter and more compact than conventional gears, yet can deliver higher torque and achieve a reduction ratio range from 30:1 to 320:1 in just a single stage without backlash. The gear set is used in industrial service robots, medical technology, aerospace, and semi-conductor manufacturing.

The company specified DuPont Vespel TP thermoplastic bearing cages to play a key role in achieving low weight and compactness in its Harmonic Drive CPL component sets. These wear-resistant Vespel TP parts offer a low coefficient of friction against steel with good mechanical strength and toughness. They help ensure the lightweight, compact component sets operate reliably even at very high or low temperatures.

Performance beyond standard engineering plastics
Working closely with DuPont Performance Polymers (DuPont), Harmonic Drive AG developed the Vespel TP bearing cages specifically for applications requiring superior resistance to aggressive, high-performance lubricants at high temperatures, or the ability to operate in a vacuum -- performance beyond that of cages made from standard engineering plastics. The Vespel TP bearing cages resist additive-enhanced greases and oils used to provide lifetime lubrication (approx. 30,000 hr), at ambient temperatures between -40 degrees C and 120 degrees C.

"Depending on the application, the forces transmitted from the ball bearings can induce high flexural stress into the cage clips, particularly during start up, a change in speed, or a reverse in rotational direction," says Matthias Mendel, design and development manager at Harmonic Drive. "In light of the minimized wall thickness, extreme load cases can lead to premature cage clip wear or breakage in cages made from standard engineering polymers. In comparison, Vespel TP bearing cages have proved to be durable and reliable under such conditions, even in extreme operating environments."

The company has extended the use of these components, in diameters from 15 mm to 130 mm, to other gear products, including its latest high-performance CobaltLine range.

Low-friction, low-wear Vespel TP parts
Vespel TP parts combine low friction and low wear performance in lubricated and non-lubricated applications with the ease of processing into forms and shapes of standard thermoplastics, providing broad design freedom and suitability for mass production. They offer an impressive combination of mechanical strength, chemical resistance to common fuels and lubricants, as well as a high continuous operating temperature with minimal out-gassing in vacuum environments. Other typical applications include journal bearings and sliding components, guide bushings, and thrust washers.

Harmonic Drive gear units are comprised of DuPont Vespel TP thermoplastic bearing cages, a Wave Generator (a thin-raced ball bearing fitted into an elliptical plug serving as a high-efficiency torque converter), the Flexspline (a flexible steel cylinder with external teeth and a flanged mounting ring), and the Circular Spline (a solid steel ring with internal teeth). [Image courtesy: Harmonic Drive AG]

 

 

 

 

The Vespel TP parts used in Harmonic Drive gear units withstand high mechanical loads due to the material's high flexural strength (215 MPa @ 23 degrees C), high dimensional stability, and exceptional creep resistance, and they allow service at continuous operating temperatures up to 244 degrees C (HDT).

DuPont offers a variety of high-performance polymer-based (predominantly polyimide) Vespel parts and shapes in thermoplastic TP and thermoset S product families, among others, with numerous grades in each product family that offer an optimum material solution for the specific demanding application.

Learn all about DuPont Vespel (including product data sheets, technical literature, and some great design guides) by clicking here.

Source: DuPont

Published October 2012

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