Ball screw drives replace hydraulics in powder press

The company has introduced the new 'Direct Drive Technology' - comprising servo-electric motor driven ball screws - to its CA SP Electric and CA HM Electric series. These have replaced some formerly hydraulically driven machines, though hydraulics are retained for machines that need to deliver higher pressing forces.

Osterwalder says the pressing process can now be performed extremely accurately, with positioning tolerances down to just one micron. Moreover, the entire pressing process is controlled to improve the homogeneity of the pressed material.

In particular, precise synchronisation of movement is necessary, as interruptions or irregularities in the procedure could compromise the pressed part, which may crack during subsequent sintering or suffer dimensional errors arising from changes during contraction.

The linear movements of the new electric presses are provided by NSK’s heavy-duty HTF (high torque force) series ball screws, which provide high traverse rates combined with high precision. At the same time they can transfer extremely high axial forces, their patented geometry enabling the distribution of these forces equally over all of the balls in operation. A ball separation arrangement prevents premature wear and guarantees high reliability.

Beyond the high precision and controllability afforded by these drives, is the energy saving of around 80 percent that can be achieved. A powder press with a hydraulic drive and pressing force of 160kN has an energy consumption of up to 15kW; a servo-electric system requires only 2.5 to 3.5kW.

The electric machines are cleaner in operation and more compact, while servicing is simplified, thanks to the lack of control valves and other high-maintenance hydraulic components. They are also quieter – 58-60dB(A) as opposed to 75dB(A) for hydraulic systems.

Osterwalder began its process of ‘electrification’ with a 160kN press. Now, with more than 100 systems in operation, this has risen to 320kN. The company manufactures presses with a pressing force of up to 10,000kN and while hydraulics dominate at this end of the scale and Osterwalder confines servo-electric driven machines to the smaller power range, NSK says forces of between 4,000 and 5,000kN can still be sensibly transmitted with its HTF series.

The trend whereby servo drives with ball screws are replacing hydraulic drives can also be seen in other fields of application, such as plastic injection moulding machines and machine tools, where HTF series ball screws deliver better controllability coupled with significant energy savings.