US 2660779 A
Description (OCR text may contain errors)
Dec. 1, 1953 J. ATKINSON 2,660,779
METHOD OF FORMING BLADE ROOTS Filed Jan. 13, 1949 2 Sheets-Sheet l FIG! FIG.2
a H gave/1101' mt fzr ncys Dec. 1, 1953 J. ATKINSON METHOD OF FORMING BLADE ROOTS 2 Sheets- Sheet 2 Filed Jan. 15, 1949 I I 1 zgenfor A flor'neyJ Patented Dec. 1, 1953 UNITED STATES PATENT OFFICE it 2,660,779 I M OD F 0 v Gl LADE RO JosephAtkinson, London, England Application January 13,1949, Serial No. 70,723
Claims priority, application Great Britain January 15, 1948 This invention relates to an improved method for forming the root or anchor portion of the blades used in bladed fluid-flow machines such as turbines and compressors, and relates particularly to blades of the type'which areformed with a profiled root adapted to be secured in a socket (hereinafter referred to as blades of the type described).
, The invention is mainly of interest in connection with the production of blades which are subjected in use to high temperatures and stresses, and which therefore require to be made of specially developed steels or alloys, such as nickel-chrome alloys, which may be diilicult and expensive to machine. E'xamplesof such blades are the turbine rotor blades of gas turbine ,machines, and in a lesser degree the compressor rotor blades (in cases where bladed compressors of the axial flow type are used).
One known method of securing the blades to the turbine rotor disc of a gas turbine is to provide the periphery of the rotor disc with serrated slots extending in a generally radial direction, complementary serrations being formed on the blade roots so that they can be pressed into the slots and secured, for instance by peeping. Where the serrated blade root, and the corresponding slot, are tapered, such a method of blade mounting is generally known in the art (from the profile of the blade root) as the firtree mounting, and it will be hereinafter designated by this term. At present fir-tree mountings are in wide use.
Fir-tree roots have hitherto been usually made by a machining operation, such as broaching, and one object of the present invention is to provide an alternative method of making such roots which eliminates or reduces machining operations, thus cheapening production, and which, at least in the case of some materials, also has a beneficial effect on the material treated.
Broadly the invention provides, for blades of the type described, the method of forming the root contour wholly or partly by means of pressure-working. I
By pressure-working is meant a rolling, swaging, stamping, coining or similar operation.
The pressure working may most advantageously comprise a rolling operation, which will usually be cold, but may be hot if the nature of the material which is being worked requires it. The rolls may be of any suitable material, such as hardened steel or tungsten carbide.
Cold pressure working provides an improved surface finish for most of the metallic materials I 3 claims. .(01. se -156.8)
' likely tobe useful for the turbine blades of;gas
turbine machines, and may have abeneficial eiiect in other respects; for example, alloys of the 18 chromium 8 nickel type can'have their creep limit raised by cold work (see Zschokke,
BrownBoveri Review 1946, v. 33, pp. 227-233). Other highly alloyed steels are also improved in the same respect by cold work (see Cornelius, Metallwirtschaft, 1939, v. .18 pp. 399-403, and pp. 419-421). The degree of such improvement does however, depend on .the proximityoi the operating temperature of the blade root to the re-crystallisation temperature. With the general run of turbine rotor disc rim temperatures the diil'erence between the operating temperature and the re-crystallisation temperature is such that substantial improvement results.
Some alloys, intended to operate at lower temperatures, such as aluminum alloys, bronzesand stainless steels, for compressor blades, lose a portion of their highly creep-resisting properties when cold worked. With such alloys, or where the operating temperature is near to re-crystallisation temperature, it is preferable to subject at least the root of the blade (after pressure workmachine in which the work is held stationary and the rolls are moved linearly over the .work. Fig. .1 is a front elevation of the movable ram carrying the rolls, Fig. 2 is a transverse section through the ram, showing the stationary table in which the blades are fixed, and Fig. 3is a side elevation of the ram. 7
Fig. 4 is a side e1evati0n, and Fig. 5 is a fragmentary plan, of an alternative rolling machine in which the blades are fed linearly through the rolls.
Figs. 6 and '7 are detail views ofmo'dified types of roll.
Referring to Figs. 1-3, the machine there shown comprises in essentials a vertically movable ram I, in which three slides 2 are mounted for horizontal sliding movement. Each slide is resiliently biassed to a central position by a spring-pressed ball or plunger device 3, and the slide can move against such spring pressure in