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Original Date: 10/18/1999
Revision Date: 01/18/2007
Information : Butler Newall High Speed Blade Tip Grinder
When the F404 engine program began in 1984, the common practice for replacing damaged blades consisted of using a modified engine lathe to manually grind the blades. These high-pressure, compressor rotor blades were set at their innermost position and ground at a speed of 35 rpm. In addition, the method for measuring a blade’s radius was equally crude and unreliable. At Orenda Turbines, a lathe setup with probes inserted into a calibrated master block was used to measure the blade tips. Although better than most methods at the time, this approach was still unable to produce consistently sized rotors as specified by program requirements. In 1987, the Canadian Forces asked Orenda Turbines to investigate ways of improving the accuracy of rotor tip radius measurements and of producing a rounder and more consistently sized rotor.
As a result of its investigation, Orenda Turbines purchased a Butler Newall High Speed Tip Grinder in 1989 at a cost of $2.25 million (Canadian). Significant features of this machine include providing hardcopy readouts of all blade sizes; highlighting out-of-tolerance blade readings; achieving a repeatability accuracy of 0.0005 of an inch; and grinding rotor blades at a speed of 3,000 rpm. This latter feature allows blades to be extended to their fullest length, thereby simulating the operational mode of the rotors and resulting in a consistently round finished rotor. Setup of the rotor is accomplished off the machine by using modular fixtures. This design offers quick changeout from one rotor to the next. Blade tip measurements are performed by a built-in laser measuring system. The information is then relayed to the controller which provides a visual readout for the operator as well as a printed hardcopy report. The machine can also handle rotors up to 36 inches in diameter and up to 59 inches in length.
Although there are 52 of these machines currently in service throughout the world, Orenda Turbines has the only one being used in Canada. Additionally, the accuracy of the Butler Newall High Speed Tip Grinders has resulted in General Electric using it to check and verify its Master F404 HPC Rotor.
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