US2277484A - Turbine blade construction - Google Patents

Description

Malrch 24, 1942. w, B, FLANDER 2,277,484

' TURBINE BLADE CONSTRUCTION Filed April 15, 1939 INVENTOR wnnnsu B. Finunsns ATTORNEY Patented Mar. 24, 1 942 Warren B. Flanders, Philadelphia, l.a., assignor to Westinghouse Electric & ManufacturingComvpany, East Pittsburgh, Pa a corporation of Pennsylvania Application April 15, 1939, Serial No. 267,964

3 Claim.

This invention relates to turbine blading and has for an object the provision of blades of materially increased root strength.

Another object of the invention is the provision of a plurality of spaced blades integral with a single root, providing increased resisting moments in the root and reduced stresses due to bending.

A further object of the invention is the provision of a side-entry root having a plurality of circumferentially-spaced blades integral therewith and whose metal structures are continuous with that of the root.

By providing a duplex blade unit, that is, a pair of blades with a single root, the stressresisting moments of that root are increased over those for a single-blade-per-root construction, regardless of the nature of the stress.

The stress due to bending decreases inversely as the square of the root dimension in the direction of the force, and inversely as the root dimension transversely of the direction of the force. Thus, under tangential loading for blades other than of the side-entry type, the stress is decreased 50%. With side-entry type, the stress is decreased more than 50% since the tangential dimension is more than double, due to the number of zones of serrations being reduced from four to two for the two blades.

As an example, consider two-side-entry blades, each with the same tangential loading and each with a root of two inches dimension between the zones of serrations and each serration zone measuring one-quarter inch. The two roots would have a total section modulus (moment of inertia divided by the distance of outer fiber from the neutral axis) of the order of 2 4-2 or 8. With the two blades-on a single root, the latter would have a moment in the order of (2+ A;,+ +2) or 20.25, the two one-quarter inch dimensions representing two zones of serrations omitted with the single root construction. Thus, it is seen that the duplex construction provides a moment which permits a blading stress less than half of that for the one-blade-per-root arrangement for the same number of blades.

Under axial loading, the section modulus for the duplex blade will exceed that for the singleblade-per-root arrangement by an amount proportional to the increased root width resulting from omission of two zones of serrations.

Corresponding improved results are attained under conditions of radial or centrifugal load ing, as the relative area is increased due to the omission of two zones of serrations.

Therefore, another object of the invention is the provision of a blade unit having increased resistance to stress under any and all conditions of loading.

These and other objects are efiected by my invention as will be apparent from the following description and claims taken in connection with the accompanying drawing, forming a part of this application, in which:

Fig. l is a side elevational view of a portion of a row of turbine blading embodying the invention;

Fig. 2 is a view taken along the line Ill-II of Fig. 1, looking in the direction of the arrows;

Fig. 3 is a side elevational view of a blade unit constructed in accordance with the invention.

Figs. 4 and 5 are elevation and plan views, respectively, of a modified shroud attachment; and,

Figs. 6 and '7 are similar views of yet another form of shroud attachment, Fig. 6 being taken along the line VI-VI of Fig. 7.

In the drawing, there is shown a turbine rotor or blade-mounting member l0 provided with a plurality of transversely-extending slots II in its periphery. These slots are formed with projections l2 and recesses I3 providing serrated sides for the slots for inter-engagement with the root portions of the duplex blade units I5.

Each blade unit i5 is comprised by a pair of blade portions I6 integral with a root portion I1, the latter being formed with projections l8 and recesses 19 providing serrations for inter-engagement with the corresponding serrations on the side walls of the slots II.

The blade units may be formed in any desired manner, as by machining them from a single block of material or by forming each blade integral with one-half of the root and then welding together the root portion to form a unitary structure. Preferably, the unit should be constructed in such a manner that the blade portions have their metal structures continuous with that of the root.

In the arrangements shown, the blade units are assembled by insertion side-ways into the slots H. Caulking pieces 20 may be provided between the bottoms of the roots I! and the bottoms of the slots II. The outer ends of the blades may be formed with integral tenons 22 adapted to project through openings 23 in shroud as in Figs, 4 and 5 and the shroud pieces 26 welded thereto by weld material 21 in the holes 28.

Another way of attaching the shroud is shown in Figs. 6 and '7 where weld material 29 is applied to the shroud 30 around the ends of the blades.

While the invention has been shown as applied to duplex blade units, it will be obvious to those skilled in the art that it is not so limited, but

is susceptible of various changes and modifica- 10 tions including three or more blades per root, and roots of various types, such as single or double-T, side-entry, straddle-T, pin, inverted, etc., without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

1. A turbine blade unit comprising a plurality of spaced blades integral with a side-entry root, said root having serrated front and back faces 5 which converge radially inward in relation to the unit and which are adapted to engage and fit rotor-blade-slot serrated faces.

2. A turbine blade unit comprising a side-entry root having serrated front and back faces adapted to engage and fit rotor-blade-slot serrated faces, and a plurality of circumferentially-spaced blades integral with the root.

I 3. A turbine blade unit comprising a side-entry root having serrated front and back faces adapt- 15 ed to engage and fit rotor-blade-slot serrated faces, a plurality of circumferentially-spaced blades integral with the root and shroud means at the-outer ends of the blades.

WARREN B. FLANDERS.

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