High-pressure pumps boost hole drilling efficiency

An aero engine builder has transformed the efficiency of EDM hole drilling operations in the manufacture of turbine blades by switching to a system based on Wanner Hydra-Cell pumps.

An aero engine builder has transformed the efficiency of EDM hole drilling operations in the manufacture of turbine blades by switching to a system based on Wanner Hydra-Cell pumps to deliver consistent flows of dielectric fluid at high pressure.

The new system, in which these seal-less pumps are fundamental, has simultaneously reduced production downtime, cut pump repair costs and provided a quieter working environment.

The system was designed and installed by Pumps and Equipment (Warwick).

The intricate narrow-bore cooling channels in turbine blades are produced by EDM drilling - a precise spark erosion technique used here to create holes of less than 1.4mm diameter, ranging down to 0.3mm.

An essential element of the process is the DI (deonised water) dielectric fluid which is pumped through the hollow electrode wire and flushes out debris from the hole, ensuring an uninterrupted machining cycle.

This prevents damage to the recast layer in the work piece and avoids enlarging the hole outside of tolerance.

For process conformity, flushing liquid must be delivered to the tools at constant flow and pressure.

The pumping system must also operate reliably in serving a variety of machines with flow requirements ranging from 1 to 4 litre/min.

But the single-acting diaphragm pumps installed with the original machines proved unequal to the task.

Among the problems experienced were heavy pulsation, surges in pressure and a high wear rate.

DI water is not easy to pump and destroys most pumps that incorporate a mechanical seal - consequently there were frequent breakdowns.

Air consumption was an added cost, and the pumps were noisy.

A better alternative was needed and in 2001, in collaboration with Pumps and Equipment, the company trialled a Hydra-Cell pump - chosen on the basis of its seal-less construction, low pulsation and proven compatibility with harsh, nonlubricating liquids such as DI water.

The success of this unit, running continuously 24 hours, 7 days a week for six months, led ultimately to the installation of more than 20 Hydra-Cell units with controls and interfaces designed by Pumps and Equipment.

Each Hydra-Cell G04 high-pressure pump serves three machines.

Pumps are speed controlled to give precise flows needed to maintain pressure constant within +/-1.25% of specified level.

Run-time performance reliability is linked to uptime guarantees.

Following the progressive conversion to Hydra-Cell technology, no pump failures have occurred and problems of pulsation and pressure surges have been eliminated.

In consequence, run-time guarantees have been met and there have been fewer rejects - at this stage of its manufacture, each scrapped blade represented a cost of GBP 3000 (Eur 4200).

Pump repair costs, which had totalled some GBP 240,000 (Eur 336,000) before the changeover, are now negligible.

Hydra-Cell pumps are now in use on other applications in the plant, including grinding wheel cleaning via a high-pressure stream of liquid.

Further installations on the EDM drilling operations are planned for 2006.

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