Umbra Cuscinetti s use of ceramic balls spaced by smaller idler steel balls creates a cage effect in its ballscrews to optimize rigidity and eliminate wear issues.
Ballscrews in injection-molding applications operate in a high-pressure, unforgiving, and often neglectful environment. However, one ballscrew manufacturer is tackling longevity and repeatability issues in poorly lubricated molding applications. It's employing a special ballscrew that uses Cerbec silicon-nitride balls from Saint-Gobain Advanced Ceramics.
Umbra Cuscinetti, part of Italian conglomerate the Umbra Group, uses large ceramic balls spaced by small idler steel balls that create a cage effect. This design optimizes rigidity so that wear is no longer an issue.
"Components with ceramic balls are very forgiving," says Luciano Pizzoni, stress analyst and R&D chief engineer at Umbra. "Using both ceramic and steel balls, which resist adhesion, provides high-load capacity, reliability, and an increase in cycles."
Because of unidirectional rotation at the point of contact, pure rolling replaces the friction of a traditional steel configuration. Also, the absence of metallic debris on the track, due to less wear and the low affinity between steel and ceramic (reduction in micro adhesions), makes for a clean contact area and improved Hertzian pressure distribution.
Umbra reports that ballscrews with Cerbec components handle loads up to 1,800 kNm and deliver axial speeds between 5,905 and 6,299 ipm with 3-G acceleration. Although ballscrew speed is generally not an important factor in injection molding, reliability and long life are.
In addition to high-load situations, Umbra says its special ballscrews excel when little lubrication is present. Because of the ceramic/steel ball mix, molders can switch from oil to grease lubrication, which is more environmentally friendly and lengthens time between relubrications.
Saint-Gobain Advanced Ceramics
East Granby, Conn.