Hydraulic drives generally use gerotor pump technology to provide a compact high-power/high- torque motor that has made this style of dresser drive the mainstay of form-roll dressing applications for conventional wheels for the last 30 years. Hydraulic spindles suffer from serious thermal problems as they get hot after only a few minutes, although this can be mitigated by pumping coolant through the housing and/or flooding the exterior of the housing with coolant. Nevertheless, they are not recommended for running continuously for more than 15 min. The other problem with hydraulic motors is that they are generally designed to run counterdirectionally only with a
flow control on the input side of the motor. They can be designed to run unidirectionally using a flow control on the exhaust side of the motor, but this also requires a complete reconfiguration of the spindles design including seals, etc. Since unidirectional dressing is generally limited to newer grinders using advanced abrasives where end users are moving away from hydraulics, hydraulic — powered dressers are almost exclusively used on older grinders for dressing standard alox wheels.
Hydraulic spindles require of the order of 36 bar (approximately 500 psi) and between 19 and 38 l/min (5 to 10 gpm) flow, which should ideally be from a separate closed-loop system filtered to 10 pm. The pressure line from the pump to the spindle should be as short as possible and a minimum of 10 mm (approximately 3/8 in.) diameter. Also the exhaust hose from the motor should never be smaller than the inlet. Speed adjustment is made by use of the flow control. The hydraulics can also provide pressure and lubrication to sleeve bearings used in many of these older spindle designs and as a means of actuating retractable centers for quick roll changes.
With the trend to eliminate hydraulics on grinders, dresser spindle technology has moved away from hydraulic drives and toward electric drives.