US 3328867 A
Description (OCR text may contain errors)
P. GUENGANT TURBINE BLADI'NG `luly 4, 1967 2 Sheets-Sheet l Filed June 25, 1963 INVENTOR Pau L G'Ulengom nl;
, WM/JWM ATTORNEYS July 4, 1967 P. GUENGANT 3,328,867
TURBINE BLADING Filed June 25, 1963 2 sheds-sheet -/J5 9 ZQ jo.
I NVENTOR E PCM/L Guengcm BY WJWWM ATTORNEYS United States Patent O 3,328,867 TURBINE BLADING Paul Guengant, Drancy, France, assignor to Aktiengesellschaft Brown, Boveri & Cie., Baden, Switzerland, a
joint-stock company Filed .lune 25, 1963, Ser. No. 290,430 Claims priority, application gil-ance, July 11, 1962,
Research into improving eiciency and safety in large steam or gas turbines leads to all or some of the blades being made with a head, the heads of the blades in a given row being adjacent, and thus forming a substantially continuous strip covering the blades at the end opposite to their fixing feet. This arrangement gives a reduction in leakage losses, an increase in the characteristic vibration frequency of the blades, and may damp accidental vibration.
-In order to make such a covering strip without the aid of any direct or indirect physical connection, it has been proposed to shape the heads of the blades, seen in plan View, in the form of a parallelogram whereof the sides intended to be in Contact with one another are suitably inclined with respect to a direction parallel to the axis of the turbine, and to twist the body of each blade about its longitudinal axis by a suitable amount, and in such a direction, that upon assembly the heads of a given row are pressed against one another under the effect of this twisting torque alone.
The present invention relates to a process for placing these blades in position with an initial twist, hereinafter called the ultimate twist, which process is particularly advantageous in the case in which all the blades are similar and are itted by being slid by the foot into circumerential grooves in the periphery of the rotor element of the turbine.
This process resides, when a row of n blades is being fitted, in imparting to the body of each of the first (n-l) blades a twist of a greater value that the said ultimate twist and lower than the elastic limit of the blade, so as temporarily to reduce the total bulk of their heads in the peripheral direction, such reduction being sufiicient to allow for insertion of the head of the last blade in the sp-ace remaining for it, at least obliquely with respect to its ultimate position, after which this last blade is placed in this ultimate position and the adjacent blades are then brought into contact with it, via suitable spacing wedges in the case of the feet and directly in the case of the heads, the twist being reduced to its ultimate value, and so forth for the other blades in the row.
The embodiment of steam-turbine blading according to the invention is described hereinafter, the blades being fitted in a circular groove in the periphery of the turbine rotor not illustrated.
FIGURE l shows a group of blades.
FIGURE 2 shows one of them seen in profile.
FIGURE 3 is a sectioned view of FIGURE l in the plane III, III.
FIGURE 4 is a plan view of FIGURE 1 in the direction of the arrow F.
FIGURES 5 and l0 are explanatory diagrams.
FIGURE 6 shows the insertion of the foot of the last blade.
FIGURES 7 to 9 show a device for imparting a twist in plan and section respectively, in the planes VIII, VIII and IX, IX.
FIGURE l shows three adjacent blades in elevation, outside their fixing groove. In this Figure, 1 designates the foot of a blade, 2 are notches enabling the fixing to be carried out by sliding into the said groove, 3 is the body or active part of the blade, 4 is the head of the 3,328,867 Patented July 4, 1967 ICC blade which is integral with the part 3. The profile of the blade may be seen in FIGURE 3.A
The face 5 of the foot of the blade at the base of the body 3, and likewise the external face 6 of the head, are projected to form elongated parallelograms which may be seen in FIGURES 3 and 4 respectively. Their respective sides 5a, 6a are oblique with respect to a direction parallel to the axis of the turbine, and are at a definite angle to this direction.
The feet of adjacent blades are separated by spacing wedges 7 which include fixing notches '7a aligned with the notches 2 in the blade feet 1. These wedges are, in known manner, cut into two equal parts, as illustrated, in a plane perpendicular to the axis of the turbine.
In order to place the blades in position on the turbine, the foot of each one is introduced into the groove G on the turbine rotor with the narrow sides of the parallelogram configured blade foot generally parallel to the sides of the groove, the width of the rotor groove being greater than the distance between the longer sides 5a of the foot as is evident from FIG. 6 so as to permit insertion of the blade foot in the groove. The blade foot is then turned until the shorter sides 5b come to bear against the corresponding edges of the groove. In order to leave enough room between the first blade and the penultimate one to introduce the last one, the feet of the first (n-1) blades are introduced without the wedges 7. The corners of the foot of this last blade, may, if required or desired, be slightly cut oli, as shown at 8 in FIG. 6 so as to enable this last blade to be inserted in the rotor groove in a somewhat oblique manner so as not to require the creation of as much space between the blades on either side thereof. Furthermore, according to the invention, and in order to obtain suiiicient space for the head of this last blade to pass, a twisting torque is applied to the heads of the first (n-l) blades, so that the rotation thus imparted to them causes the space which they occupy to be temporarily reduced, consideredin the peripheral direction.
FIGURE 5 shows the result of the operation diagrammatically. Rotating the head of a blade, having the shape of a parallelogram with the angle /8 through an angle a and circumferentially displacing the adjacent blade in order to bring the adjacent faces of their heads into contact reduces the length occupied in the peripheral direction by the edge 6b from tto sin a te (a+) The value of u is so determined that the total gain over the heads of the (n-l) blades corresponds to the desired space for the head of the last blade, that is to say is greater than the major diagonal of the parallelogram. This angle is also such that the twist on the body of the blade is lower than the elastic limit of the latter.
FIGURES 7 to 9 show a device for applying the aforementioned twisting torque to the heads of the blades. It is a stirrup in the form of a sector 9 carrying screws 10. In combination with this stirrup, the invention provides for temporarily giving each blade a head 4a radially larger than the ultimate head 4, for making therein a groove 12 equal in length to the sides 6b and centered on the transverse plane passing through the center of gravity of the body 3 of the blade, and for inserting a wedge 11 with an easy tit in this groove.
The stirrup is intended to cover a few blades, five for example, and its internal outline matches the external outline of the heads 4a, with a certain amount of clearance in order to allow the latter to rotate. The screws 10 exert their pressure `on the wedges 11 in parallel fashion to the axis of the turbine. They are so accommodated in the stirrup as to come to bear in groups of 3 two at the ends yand on each side of each wedge 11 (FIGURE 7).
Apertures 13 enable the edges 6a of the heads to be seen. The twist on the first blade having been checked by suitable measurement, these apertures enable the other heads to be subsequently aligned with the first.
The following procedure may be used in order to t a row of n blades:
The first (u-l) blades having been placed in the groove, three stirrups such as 9 are placed in position side-by-side on the wedges 11. FIGURE 10 shows these three stirrups diagrammatically at 14, and 16, and a few blades at 17. The desired twist is successively applied to each blade by means of the screws 10, and then a sliding motion is i-mparted to the blades by a mallet so as to make all the heads contiguous again. Then the screws in the stirrup 15 are slackened, and it is transferred to 18, whereupon the stirrup 16 is transferred to 19 in the same manner, and so forth.
When the last blade has been placed in position, adjacent blades are brought closer to one another until their heads make contact, the wedges 7 being inserted between their feet. And so forth for the rest of the row. The thickness of these wedges has been so calculated that the blades retain the said desired ultimate twist. The stirrups 9 may, if desired, be used to impart this ultimate twist to the blades. Since there is bound to be insufficient space remaining to introduce the last two wedges 7, the latter are made in three pieces by a current method.
When all the blades have been fitted, the wedges 11 are removed, and all the heads 4a are machined on a lathe in order to reduce them to the dimensions of the ultimate heads 4.
In the process for placing a row of n blades in position in a circumferential groove in the drum of a steam or gas turbine, these blades having a head in the shape of a parallelogram and bearing against one another under the action of a twist imparted to each blade as it is being fitted, the improvement which resides in the steps of initially imparting to the body of each of the rst (n-1) blades in succession a twist of a greater value than its ultimate twist and lower than the elastic limit of the blade, subsequently forcing the sides of the twisted heads of adjacent blades together so as temporarily to reduce the total bulk of all their heads in the peripheral direction, such reduction being suicient to allow for insertion of the head of the nth blade in the space remaining for it, at least obliquely with respect to its ultimate position, placing the nth blade in the resultant space, and bringing the adjacent blades into contact with said nth blade via insertion of suitable spacing wedges in the case of the feet and directly, in the case of the heads, by reducing the twist to said ultimate value.
468,547 10/1950 Canada. 377,593 7/1932 Great Britain.
JOHN F. CAMPBELL, Primary Examiner.
P. M. COHEN, I. D. HOBART, Assistant Examiners.