Patent Application
20050111973
The present invention relates to loading pins for reaction nozzles and, more particularly, to improved loading pin configurations for securing the reaction nozzles against the retaining surfaces of the carrier with sufficient force to maintain the design amount of twisting in the airfoil section.
A conventional turbine structure includes a rotor having a plurality of rotating blades (buckets) mounted thereto. The blades are mounted in rows to extend radially outward from an outer surface of the rotor. Typically, the blades in a given row are identical to each other but the rotating blades of one row will differ in length and/or shape from those of the other rows spaced therefrom. Each rotating blade has a foil portion that extends radially outwardly from the rotor and a base portion for mounting the blade to the rotor. To that end, the base portion includes a root received in a correspondingly shaped groove.
A stationary casing is coaxially supported around the rotor and has a plurality of stationary blades (nozzles) arranged in rows to alternate with the rows of rotating blades. All stationary blades include a foil portion extending from the inner surface of the stationary casing and a base portion including a root for being received in a corresponding groove of the stationary casing.
The root of the stationary blade and/or the groove of the stationary housing will be provided with a notch or recess to define a space between the root of the stationary blade and the groove. It is conventional to provide a caulking material or loading pin in the space defined by the notch and/or recess to interconnect the casing and root. Conventionally, the loading pin is formed from brass and is made by machining a surface onto a piece of round stock along its axis so that the pin has a constant cross-section that is generally “D” shaped along its entire length. Thus, conventional loading pins are straight with a machined surface parallel to the longitudinal axis of the pin.
Integral cover reaction nozzles have been designed to maintain an assembled pre-twist that we have recognized cannot be achieved with the previous, conventional nozzle radial loading pin designs. Thus, the invention provides a wedge-like nozzle radial loading pin, preferably formed from steel, that contacts the bottom of a reaction nozzle along a graduated, that is inclined or stepped, surface. This contact will secure the reaction nozzle radially inward against the retaining surface of the carrier dovetail with sufficient force to maintain the designed airfoil pre-twist. Two embodiments of the improved radial loading pin of the invention are described and illustrated by way of example herein below.
In a first embodiment, the graduated surface is defined as a continuous taper made by machining a substantially continuously inclined surface into a piece of round stock, along its axis, such that the cross-section through any point of the pin is shaped by the letter “D”. The machined surface is made at an angle to the axis of the pin to create a substantially continuously tapered face that mates with a generally correspondingly tapered surface on the bottom of the reaction nozzle.
In an alternative embodiment, rather than a substantially continuous inclined surface, the loading pin comprises one or more discrete steps. More specifically, in an exemplary alternate embodiment, each end of the pin is machined generally parallel to the pin center line but at a different height from the pin centerline, creating two distinct surfaces and a length of machined surface at a slight angle is provided to interconnect the two flat machined surfaces.
Thus, the invention may be embodied in a method of installing stationary blades of a turbine comprising: arranging a plurality of stationary blades in a plurality of rows with each stationary blade of a row having a root and an airfoil portion, the stationary blades of a row being mounted by the roots in an annular groove provided in a turbine casing, each annular mounting groove having two opposite sidewalls and a bottom wall at least one of the root of the stationary blades and a wall of said mounting groove defining a recess; inserting a loading pin in the recess, between each said root and the groove, thereby keying the stationary blade root to the casing, said loading pin comprising a part-circumferential wall portion, generally corresponding in cross-sectional shape to cross-sectional shape of said recess, and a graduated wall portion, so that said pin is generally wedge-shaped.
The invention may also be embodied in a turbine structure comprising: a rotor having a plurality of rotating blades or buckets mounted thereto, the blades being mounted in rows to extend radially outward from an outer surface of the rotor; a stationary casing is coaxially supported around the rotor and having a plurality of stationary blades or nozzles arranged in rows to alternate with the rows of rotating blades, at least some of said stationary blades including a foil portion extending from an inner surface of the stationary casing and a base portion including a root for being received in a corresponding groove of the stationary casing; at least one of the root of the stationary blade and the groove of the stationary housing including a recess defining a space between the root of the stationary blade and the groove; a loading pin disposed in the space defined by the recess to interconnect the casing and root, said loading pin comprising a part-circumferential wall portion, generally corresponding in cross-sectional shape to cross-sectional shape of said recess, and a graduated wall portion, so that said pin is generally wedge-shaped.
These and other features and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
Elastically pre-stressed blades installed under controlled conditions display excellent damping characteristic and are in the position of absorbing dynamic stresses under all operating conditions without endangering their long-term reliable life span. For blades with a sufficient amount of pre-stress, there is no frictional wear and no blade loosening. Therefore, it is important to maintain the prescribed pre-stress.
Thus, a design objective is that all installed blades are twisted inside the corresponding groove by a specific twist. The configuration of the nozzle airfoil and the dimensions of the root are selected so that the blade can assume the position inside the groove which is defined by the design criteria.
A loading pin provided in accordance with the present invention provides a wedge contact for radially loading the nozzle to secure the nozzle radially inward against the retaining surface of the carrier dovetail with sufficient force to maintain the designed airfoil pre-twist.
In a first embodiment, illustrated in
A groove 130 is optionally defined longitudinally of the loading pin defining a part circular recess extending from the proximal to the distal ends of the pin. The groove allows the pin material to swage or upset from its original surfaces, thereby increasing the contact area between the pin and the nozzle. The groove also allows, e.g., insertion of a pin removal tool (not shown) so that the pin may be engaged and displaced proximally even if fully inserted below a respective nozzle 120. Although a part circular groove 130 is illustrated it is to be understood that the cross-sectional shape of this groove is non-critical and a V-shaped, rectangular or other groove configuration could be provided without departing from this invention.
As will be appreciated, the insertion of the tapered loading pin 116 illustrated in
An alternate embodiment of the invention is illustrated in
A groove 230 is optionally defined longitudinally of the loading pin defining a part circular recess extending from the proximal end 228 to the distal end 226 of the pin 216. As in the first described embodiment, the groove 230 is provided to allow the pin material to swage or upset from its original surfaces, thereby increasing the contact area between the pin and the nozzle. The groove also allows, e.g., insertion of a pin removal tool (not shown) so that the pin may be engaged and displaced proximally even if fully inserted below a respective nozzle 212. As mentioned above, although a part circular groove 230 is illustrated for pin retrieval it is to be understood that the cross-sectional shape of this groove is non-critical and a V-shaped, rectangular or other groove configuration could be provided without departing from this invention.
As will be appreciated, the insertion of the tapered loading pin 216 illustrated in
As noted above, it is to be understood that while a continuously inclined surface and a single stepped surface are illustrated as embodiments of the invention, the inclined surface need not be continuously inclined but can be provided as a series of discrete steps. Furthermore, the discrete flats 226, 228 of the steps may themselves be provided as surfaces that are generally parallel to the longitudinal axis of the pin as illustrated in
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
