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Two-speed gearbox offers efficient direct-drive option

27 February, 2015

The German drives specialist Stober has developed a two-speed gear gearbox that, it says, will improve the energy efficiency of machine tools. The PS box, which is available in two sizes (PS25 and PS30), was developed especially for use in the main spindle drives of machine tools. It offers a loss-optimised direct-drive mode (with a ratio of i=1) that delivers high speeds suitable for fine machining.

In the direct-drive mode, the planetary gear-set is fully decoupled and the motor torque is transmitted almost without loss, as if there was no gearbox in between. The friction-minimised helical planet gear set operates in reduction mode and helps to improve the energy efficiency of spindle drives, while reducing noise levels. The coupling hub has a small-diameter shaft seal ring, resulting in a relatively low level of friction.

If high motor torque is needed for machining hard materials or for extreme heavy-duty machining, the operator can switch to a gear ratio of i = 4 or 5.5.

In applications involving frequent changes between the the two speeds, for interval speed changes, and when the machine is idle due to retooling operations, splash lubrication can be provided in the sealed gear housing.

If high levels of heat are expected, a recirculating lubrication system can be added using an external tank with at least ten times the fill volume of the gearbox. If necessary, the temperature of the lubricant can be raised to an optimum level using a heat exchanger.

Stober's two-speed PS gearboxes offer a highly efficient direct-drive option for machine tool spindles

For applications where extremely high levels of heat could be developed, the splash or recirculating lubrication systems may not be sufficient. In such cases, liquid cooling can be supplied to the gearbox using an optional cooling flange. This option also reduces the heat given off to the machine spindle or machine.

The sealed gearboxes, with torque ratings from 300–1,650Nm, have hub bearings and oil seals. They can be mounted horizontally (for lathes) or vertically (for machining centres). A rigid, self-centring motor connection with a balanced EasyAdapt coupling makes it easy to attach motors. 

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