GB2186915A

GB2186915A - Hydraulic pump system

Info

Publication number: GB2186915A
Application number: GB08604304A
Authority: GB
Inventors: Lars Demuth; Jorgen Nyerup Nielsen
Original assignee: FLSmidth and Co AS
Current assignee: FLSmidth and Co AS
Priority date: 1986-02-21
Filing date: 1986-02-21
Publication date: 1987-08-26
Also published as: GB8604304D0

Abstract

A table (1) of a vertical roller mill is supported by a hydrostatic bearing (2) supplied with oil from a pump (4) driven by an electric motor (5). In case of failure of the motor, the pump can continue to be operated for a short time by energy from a flywheel (12) connected to the shaft of the motor (5). <IMAGE>

Description

SPECIFICATION Hydraulic pump system The invention relates to an hydraulic pump station for supplying an hydraulic system with liquid under pressure, such as an hydrostatic bearing with pressurised lubricant, and comprising at least one hydraulic pump driven by an electric motor and an energy storing accumulator.

An hydrostatic bearing is often used for supporting comparatively heavy, rotating machine parts, e.g. a grinding table of a vertical roller mill, and the hydraulic pump station supplying the hydrostatic bearing with pressurised lubricant is often equipped with an energy storing accumulator which, if the power supply to the pump station motor fails, ensures the supply of pressurised lubricant to the bearing for so long that the machine part can be stopped before the bearing is damaged.

In known hydraulic pump stations for hydraulic systems the energy storing accumulator often comprises a battery of vessels, which, by means of the pump station, are filled with hydraulic liquid, that is kept under pressure and consequently ready for use by means of a pressurized gas, e.g. nitrogen, which may be supplied to the liquid vessels from one or more vessels of pressurised gas.

To maintain the hydraulic liquid in the accumulator at a prescribed operating temperature, and thus ready for use, the liquid vessels are often encased in thermostatically controlled heating blankets.

An energy storing accumulator of the above kind, provided with the necessary control valves, pressure switches and other control equipment, in addition to the control equipment for the heating blankets, is thus a comparatively complicated system entailing the consequent possibilities of faulty functions, especially if the accumulator has been out of operation for a long time.

It is the object of the invention to overcome the above drawbacks of the known hydraulic pump stations, and according to the invention that is achieved in that the energy storing accumulator is a flywheel connected to the shaft of the drive motor.

It is known to use flywheels for other purposes, e.g. for avoiding fluctuations in the number of revolutions of a machine or motor, or for maintaining for a short period the number of revolutions of a machine, e.g. if its drive motor stops, until an emergency unit can be coupled in.

Until now flywheels have not been used in connection with hydraulic pump stations for storing sufficient energy to ensure continuous operation of the pump station, e.g. for lubrication of hydrostatic bearings, during power failures. But it has now surprisingly been found that the simple flywheel construction also fulfils the demands of ensuring the above lubrication purposes under all running conditions, including power failures.

It is an advantage of the flywheel construction over the known accumulators that the flywheel makes it possible, in a simple way, to control the rotation of the wheel to ensure that enough stored energy is available, e.g. for the lubrication of hydrostatic bearings. Further, a flywheel is cheap to manufacture and easy to maintain, which factors involve far simpler running and service conditions compared to the known accumulators.

The invention will now be explained in more detail by reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a known pump station; and, Figure 2 shows an example of a pump station according to the invention.

In the drawing a rotating machine part supported by a hydrostatic bearing is shown by way of a rotating disc 1, e.g. the grinding table of a vertical roller mill. Forthe sake of simplicity the disc 1 is shown supported by a single hydrostatic bearing biock 2, but in practice a grinding table would be supported by several bearing blocks. Hydraulic liquid is supplied to the bearing 2 via a pipe 3 from a pump 4 driven by an electric motor 5.

The known pump station shown in Figure 1 is provided with a battery of hydraulic vessels 6, connected via pipes 7 partly to a separate pump 8 driven also by the motor 5, and partly via a throttle valve 9 to the liquid supply pipe 3. At their top the liquid vessels 6 are connected via pipes 10 to a battery 11 of vessels of pressurised gas e.g.

nitrogen.

During normal operation the liquid supply to the hydrostatic bearing 2 is maintained by the pump 4 through the pipe 3, operating at normal lubricating pressure for the liquid. Simultaneously the pump 8 ensures that the battery of hydraulic vessels 6 is filled with hydraulic liquid under pressure from the nitrogen vessels 9, keeping the liquid in the vessels 6 under a higher pressure than the lubricating pressure.

The hydraulic vessels 6 are encased by thermostatically controlled heating blankets, which keep the hydraulic liquid in the battery 6 at operating temperature so that the liquid in the battery has the same viscosity as the hydraulic liquid supplied directly to the hydrostatic bearing block 2 by the pump 4.

If the power supply to the motor 5 fails, whereby both pumps 4,8 stop, and the liquid supply from pump 4 to the hydrostatic bearing 2 ceases, pressurised liquid from the battery 6 will flow via the pipes 7, the throttle valve 9 and the pipe 3 to the hydrostatic bearing 2, and thus for a certain period ensure continued liquid supply. The volume of, and the pressure in, the battery 6 is so dimensioned that sufficient liquid supply is ensured for so long that the machine part 1 can be stopped before damaging the bearing 2.

Figure 2 shows a pump station according to the invention. The hydraulic accumulator system 1 1 shown in Figure 1 with its appertaining control equipment, has been replaced by a flywheel 12 mounted on the shaft of the motor 5.

The flywheel is dimensioned to ensure through its rotational energy a continued operation of the pump 4 in case of power supply failure for the plant so that a sufficient liquid supply for the hydrostatic bearing will continue until the machine part 1 has been stopped.

EXAMPLE In a vertical roller mill having a grinding table supported by an hydrostatic bearing, the total maximum load on the bearing blocks was approx.

4MN. The pump station for the bearing originally consisted of two pump sets, each with its separate motor. The energy saving accumulator consisted of four pressure vessels with a total of 0.24 m3 of hydraulic liquid, and appertaining thermostatically controlled heating blankets, and five vessels for nitrogen. Further, the station was equipped with three pressure switches, two sequence valves, two constant flow valves and a flow-monitor.

It appeared that the entire comparatively complicated, and consequently vulnerable, accumulator system could be replaced by two flywheels, one on each pump motor, and each with a mass of 350 kg and a moment of inertia of 32 kgm2. The flywheels were capable of driving the pumps for twenty seconds with full load on the bearing and for about 2 min. with the bearing unloaded, which in both cases was sufficient time to ensure that the grinding table of the mill could be stopped before the liquid flow to the bearing became too small.

Claims

1. An hydraulic pump station for supplying an hydraulic system with pressurised hydraulic liquid, and comprising at least one hydraulic pump driven by an electric motor and then an energy storing accumulator, characterized in that the energy storing accumulator is a flywheel connected to the shaft of the drive motor.

2. An hydraulic pump station for the table of a vertical roller mill, substantially as described with reference to Figure 2 of the accompanying drawings.