Balancing method

Abstract

A method of balancing a set of retaining and locking plates used to retain a row of gas turbine engine aerofoil blades in attachment to a rotor disc, includes: (i) providing a weighing plate having a circular track; (ii) providing a non-rotating, static balancing apparatus capable of detecting unbalance in the weighing plate; (iii) positioning the weighing plate on the static balancing apparatus, and positioning the set of retaining and locking plates on the track in an arrangement corresponding to a possible arrangement for the set of plates in use in the engine; and (iv) repositioning the retaining and locking plates on the track to arrive at a balanced arrangement for the set of plates.

What is claimed is: 
     
         1 . A method of balancing a set of retaining and locking plates used to retain a row of gas turbine engine aerofoil blades in attachment to a rotor disc, the aerofoil blades having root fixings which are slidable into corresponding slots formed in the disc, the retaining plates being positioned in a circumferential row at a rim of the disc to prevent the root fixings sliding out of the slots, and the locking plates being introduced into the circumferential row between pairs of retaining plates to lock the retaining plates in position, the method including:
 providing a weighing plate having a circular track corresponding to the position of the circumferential row at the rim of the disc;   providing a non-rotating, static balancing apparatus capable of detecting unbalance in the weighing plate;   positioning the weighing plate on the static balancing apparatus, and positioning the set of retaining and locking plates on the track in an arrangement corresponding to a possible arrangement for the set of plates in the circumferential row at the rim of the disc; and   repositioning the retaining and locking plates on the track to arrive at a balanced arrangement for the set of plates which reduces unbalance produced by the set of plates to below a predetermined threshold.   
     
     
         2 . The method of  claim 1 , wherein the retaining plates have a different mass per unit arc than the locking plates. 
     
     
         3 . The method of  claim 1 , wherein the retaining plates have a different circumferential extent than the locking plates. 
     
     
         4 . The method of  claim 1 , wherein the circular track is defined at one edge by a circular abutment shoulder against which the retaining and locking plates can be located. 
     
     
         5 . The method of  claim 1 , further including:
 measuring cold build expansion gaps formed between the retaining plates when positioned on the track.   
     
     
         6 . A method of building a section of a gas turbine engine including:
 performing the method of any one of the previous claims;   providing a row of gas turbine engine aerofoil blades which are attached to a rotor disc by sliding root fixings of the aerofoil blades into corresponding slots formed in the disc; and   positioning the set of retaining and locking plates in a circumferential row at a rim of the disc to prevent the root fixings sliding out of the slots, the set of plates having the balanced arrangement in the circumferential row.