Fluid reaction surfaces (i.e. – impellers) – Specific working member mount – Blade received by continuous circumferential channel
Reexamination Certificate
2000-02-11
2001-10-09
Ryznic, John E. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific working member mount
Blade received by continuous circumferential channel
Reexamination Certificate
active
06299411
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to fastening of turbine moving blades in a circumferential slot on the turbine rotor.
BACKGROUND OF THE INVENTION
Fastening of moving blades in turbine rotors by anchoring blade roots in a circumferential slot is known. Such fastening is used in particular in the case of smaller blades. The blade roots, in their horizontal cross section perpendicular to the blade longitudinal axis, usually have a basic rhombic shape and, in their longitudinal axis, basically have the shape of an inverted T or a hammer-head shape, which engages in serrations in the slot. In this case, the short sides, of a rhombus or axial guide surfaces, are bearing against the side walls of the slot.
During the fitting of blades in circumferential slots in the rotor, the problem of fitting the last blade of a blade row arises in each case. A known method is to ensure that there is a fitting gap, which is dimensioned in such a way that the last blade root can only just be inserted into the slot. If the blade root has a basic rhombic shape, the fitting gap needs to be at least equal to the long diagonal of the rhombus, as shown in
FIG. 1
a
and explained in more detail below. After the last blade has been inserted and rotated into the desired orientation, a residual gap remains between the first blade and the last (nth) blade. To fix the blades in the slot and to avoid displacements of the blades during operation, this residual gap is filled by means of intermediate pieces or distancing inserts which are arranged between the blade roots, as shown in
FIGS. 1
b
and
c
and explained in more detail below.
FIGS. 2
a
and
b
show individual intermediate pieces, some of which are whole intermediate pieces and others are halved intermediate pieces. In the case of the halved intermediate pieces, the sides bearing against one another in the center are straight and vertical. The intermediate pieces or distancing inserts serve not only to fix the blade roots in the slot but also to keep the blade roots at a distance from one another and to uniformly distribute the residual gap over the circumference of the slot.
The intermediate pieces in each case have the same shape as the blade roots which fix them. The blade roots of each blade row are in each case dimensioned in accordance with the size of the blades of that blade row. In this case, the blade roots of one blade row differ from those of a further blade row in their width, their length and the number of serrations and steps in the T-shape or hammer-head shape.
During the fitting of the last intermediate piece, the same problem as with the fitting of the last blade again appears. To solve this problem, the presence of a gap which is large enough for fitting a halved intermediate piece is again ensured. Finally, this smaller gap is filled by means of halved intermediate pieces, as shown in
FIG. 2
b
. (the gap which still remains at the end after insertion of these halved intermediate pieces is finally filled by a three-piece closing piece, whereupon the blades are sufficiently fixed in the circumferential slot for the operation of the turbine.)
The basic shape, or the cross section, of the whole intermediate pieces described here is rectangular, i.e. the short sides of the intermediate piece, or axial guide surfaces, lie at an angle to the side wall of the circumferential slot. The intermediate pieces therefore touch the side wall of the slot only with their corners. However, the slot and the intermediate pieces are not greatly loaded as a result, since the lateral axial force on the whole intermediate pieces is only very small.
In the fitting region, the halved intermediate pieces have a rhombic cross section, the short sides of the rhombus being at an angle to the long sides which is different from 90°. The angle is dimensioned in such a way that the short sides, or axial guide surfaces, bear flat against the side wall of the circumferential slot. Flat bearing is necessary since the lateral axial forces which act on the halved intermediate piece are much greater compared with the whole intermediate pieces. If the short sides did not bear flat against the side walls of the slot, the halved intermediate pieces would cut a notch in the side wall and damage the latter.
The difference between the axial forces on the halved intermediate pieces and the axial forces on the whole intermediate pieces is connected with the fact that there is one center of gravity in the case of the whole intermediate pieces and there are two centers of gravity, on which the centrifugal force acts, in the case of the halved intermediate pieces.
The angled configuration of the short sides of the halved intermediate pieces avoids damage to the intermediate pieces and the slot by notching. However, the production of the angled configuration is expensive.
SUMMARY OF THE INVENTION
The object of the invention, for the fastening described at the beginning of moving blades in a circumferential slot, is to provide halved intermediate pieces which can be produced more cost-effectively compared with the prior art mentioned here.
This object is achieved by moving-blade fastening, in which, when viewing the vertical cross section parallel to the long side of the basic shapes those sides of the halved intermediate pieces which face the center of the circumferential slot and the adjacent halved intermediate piece are of hook-shaped design. In this case, the hook shape of the one halved intermediate piece forms the geometric negative of the hook shape of the adjacent halved intermediate piece, so that the sides of the two halved intermediate pieces fit into one another and can be interlinked in a positive locking manner on account of their hook shape. The two intermediate pieces are thus to be regarded as geometric counterparts of one another. The basic shape or the horizontal cross section of the halved intermediate pieces interlinked according to the invention is of right-angled design.
The interlinking of adjacent, halved intermediate pieces, situated beside each other, by the hook shape according to the invention has the advantage that the two halved intermediate pieces are now connected to form a single piece having a single center of gravity. An intermediate piece is obtained which, with regard to the forces which act thereon, is equivalent to a whole intermediate piece, on which only small axial forces act. Those axial forces which act on the individual halved intermediate pieces now act on the hook-shaped inner surfaces of the intermediate pieces. The side surfaces of the intermediate pieces, which side surfaces touch the side walls of the slot, are thereby relieved. This enables the short side walls of the intermediate pieces to be produced at right angles. Since the axial forces are now smaller, notching at the slot wall does not occur. The invention thus results in the advantage that the halved intermediate pieces can also be produced at right angles and cost-effectively. The hook-shaped inner surfaces, according to the invention, of the halved intermediate pieces are produced, for example, by a laser cutting process.
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Freuschle Dieter
Hohmann Siegfried
ABB Alstom Power ( Schweiz) AG
Burns Doane Swecker & Mathis L.L.P.
Ryznic John E.
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