Planetary Screw Assemblies

Rexroth opens up new fields of applications with planetary screw assemblies with new sizes. The drive elements with screw diameters up to 75mm and leads up to 20mm achieve static load capacities up to 1,496 kN while featuring a compact design. They are ideal for use in medium sized and heavy-duty machinery such as presses, plastic injection molding machines and machine tools.

All electric presses and injection molding machines are reaching increasingly higher performance classes. This places more exacting demands on mechanical axis systems, which have to transmit exponentially higher forces. Rexroth now meets these requirements with planetary screw assemblies that feature diameters of 60 and 75mm as well as leads of 10 and 20mm each. Moreover, screw diameters of 20, 30, 39 and 48mm with leads of 5 and 10mm are available. The new sizes cover dynamic load capacities up to 544 kN and static load capacities up to 1,496 kN within a minimum of installation space. The drive units represent robust drive solutions for use in high force applications, such as process or plastic injection molding machines. The design principle of planetary screw assemblies allows a high load capacity in relation to the installation dimensions. The planets rotate with a defined contact profile in a nut around a screw in parallel to the axis. This ensures very smooth running and reduces noise emission. Numerous contact faces result in high axial stiffness and load capacities, thus allowing for a long service life. These screw assemblies feature a high positioning accuracy and repeatability, also with minimal travel movements. Planetary screw assemblies can reach travel speeds of up to 1.5 m/s (90 m/min), thereby meeting increased dynamic requirements for shorter machine cycles. When combined with a servomotor and drive controller, the user gets a mechatronic unit from a single source, which moves large forces within a minimum of installation space.

Compact cylindrical single nuts, flange single nuts and split flange single nuts for all tolerance classes offer the designer a high degree of freedom. For applications with more demanding precision requirements, all nut types are available preloaded. This allows backlash-free operation in tolerance classes T7 and T5.

Rexroth's innovative sealing technology in planetary screw assemblies results in long lubrication intervals. This reduces maintenance costs and spares the environment due to a lower consumption of lubricants. In manufacturing the screws, Rexroth benefits from its experience in the efficient roll-forming process. This technology, which has proven successful in large series production, achieves the same accuracy levels as the more expensive grinding process. Rexroth supplies the planetary screw assemblies ready-to-install with machined ends.