Mounting disc

Abstract

Mounting discs ( 20, 30, 40, 50 ) are used in gas turbine engines to present turbine or compressor blades. These discs ( 20, 30, 40, 50 ) incorporate a bore or cob end 31, 41, 51 which in turn previously had a flat end face surface. Such flat end face surfaces are weight efficient but can lead to reduced component life and a limitation with regard to rotational speed due to Von-Mises stresses. By providing a deviation ( 39, 49, 59, 69 ) in the end face from a flat aspect, a reduction in axial stress is achieved with a marginal increase in hoop stress but with a net result that there is a reduction in the general operational Von-Mises stresses and therefore improvement in disc life or potential rotation speed capacity or both.

1 . A disc for mounting rotating components, the disc characterised in that the bore end has an end face with deviation from a flat perpendicular aspect relative to radial plane. 
   
   
       2 . A disc as claimed in  claim 1  wherein the deviation is a convex curve. 
   
   
       3 . A disc as claimed in  claim 2  wherein the convex curve has a consistent convex radius. 
   
   
       4 . A disc as claimed in  claim 2  wherein the convex radius has a maximum radius equivalent to half of the axial width of the disc across the radial plane. 
   
   
       5 . A disc as claimed in  claim 2  wherein the convex curve is a smooth curve. 
   
   
       6 . A disc as claimed in  claim 2  wherein the convex curve is conic. 
   
   
       7 . A disc as claimed in  claim 2  wherein the convex curve is semi circular. 
   
   
       8 . A disc as claimed in  claim 1  wherein the deviation comprises a trapezoidal shape for the bore end. 
   
   
       9 . A disc as claimed in  claim 8  wherein the trapezoidal shape has a side projection relative to the radial plane having an angle in the range 5-45°. 
   
   
       10 . A disc as claimed in  claim 1  wherein the deviation is triangular. 
   
   
       11 . A disc as claimed in  claim 10  wherein an apex for the triangular deviation is rounded. 
   
   
       12 . A disc as claimed in  claim 1  wherein the cob end has a stepped portion to achieve a desired weight distribution in the disc. 
   
   
       13 . A disc as claimed in  claim 1  wherein a ratio of the depth of the deviation divided by width of the mounting disc across from the flat perpendicular to the radial plane is in the range 0.03 to 0.5. 
   
   
       14 . A disc as claimed in  claim 1  wherein the shape and extent of deviation provided is subject to material and rotational speed determined to substantially provide zero compression axial stress differential across the mounting end. 
   
   
       15 . A disc as claimed in  claim 1  wherein the deviation is outward.