GB2278647A

GB2278647A - Method of fixing flow-straightening blades in a turboshaft engine

Info

Publication number: GB2278647A
Application number: GB9410036A
Authority: GB
Inventors: Jean-Louis Charbonnel; Jacky Serge Naudet; Gerard Gabriel Miraucourt
Original assignee: Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA; SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1990-12-27
Filing date: 1994-05-19
Publication date: 1994-12-07
Anticipated expiration: 2011-12-03
Also published as: GB9410036D0; GB2278647B

Abstract

A stemmed blade 1 for flow-straightener blading of a turboshaft engine comprises at least one shank 3 at the head of the blade forming a stem for use in fixing the blade 1. The shank 3 has a notched portion 5 situated adjacent the head of the blade and an end portion 6 separated from the notched portion 5 by a zone 7 of lower tensile strength. The fixing of the blade 1 to the engine casing 8 is carried out by fitting the blade in position with the shank 3 projecting radially outwards through a hole 11 in the casing and then crimping a bush 14 on to the notched portion of the shank using a suitable crimping tool 15, 16 which exerts a compressive force on the bush 14 while exerting a traction on the end 6 of the shank until the zone 7 of lower tensile strength breaks. <IMAGE>

Description

METHOD OF FIXING FLOW-STRAIGHTENING BLADES IN A TURBOSHAFT ENGINE The present invention relates to the fixing of blades in turboshaft engines and, more precisely, to the fixing of blades to form flow-straightening blading of a turboshaft engine, each blade comprising at least one shank at its head forming a stem intended for the fixing of the blade.

In general, the blades of a flow straightener are fixed at their head to the outer casing of the turboshaft engine, and their inner ends are interconnected by internal annular members defining the inner profile of the active fluid flow path and ensuring a seal with the rotor of the engine.

It is known practice to connect several blades rigidly together on a common sector forming part of the annular member, the blades having threaded radial shanks integral with the heads of the blades and designed to pass through corresponding holes provided in the outer casing of the engine. These shafts serve to fix the blades through cooperation with nuts. The disadvantage of this method of fixing is that it involves high production costs and, in the event of the deterioration of a blade, necessitates dismantling a whole sector of blades.

Also known are rotor blades which comprise studs at their heads intended for the fixing of an outer ring. In this regard US Patent 2 197 335 shows segments capping the blades and fixed to them by bushes and crushing of the studs. The application of this technique to the fixing of the blades of a flow straightener stage to the outer casing of the turboshaft engine would necessitate special tooling for crushing the studs.

In our application No. 9125636 (Serial No. 2253444) a flow straightener blade for a turboshaft engine is described and claimed which can be individually fixed to the casing by a quick-fix fastening and which brings about a reduction in weight of the turbo shaft engine, the blade comprising at least one shank at its head extending from a platform of the blade and forming a stem for the fixing of the blade, the shank having a notched portion adjacent the platform and an end portion separated from the notched portion by a zone having a lower tensile strength than the notched portion and the end portion.

The present invention is concerned with the fixing of blades of this general type, and provides a method of fixing a flow-straightener blade to the outer casing of a turboshaft engine, said blade comprising a shank at its head forming a stem for the fixing of the blade to the casing, and the shank having a notched portion adjacent the head of the blade and an end portion separated from the notched portion by a zone of lower tensile strength, the method comprising fitting the shank of the blade through a hole in the casing so that the shank projects radially outwards through the hole, placing a deformable bush over the notched portion of the shank projecting outwards through the hole, and using a crimping tool to force the bush against the casing and crimp it onto the notched portion of the shank while exerting traction on the end of the shank until the shank breaks in the area of the zone of lower tensile strength.

The present invention also provides a method of fixing an assembly of flow straightener blades to an outer casing of a turboshaft engine, each blade comprising at least one shank at its head forming a stem for the fixing of the blade to the casing, the shank having a notched portion adjacent the head of the blade and an end portion separated from the notched portion by a zone of lower tensile strength, w" -rein the shank of each blade is fitted through a corresponding hole in the wall of the casing so that the shank extends radially outwards from the casing, and each blade is then fixed to the casing by placing a plastically deformable bush around the notched portion of the shank of the blade from outside the casing and then forcing the bush against the outer wall of the casing and crushing it around the notched portion by means of a crimping tool designed to exert a compressive force on the bush while exerting traction on the end portion of the shank until the said shank breaks at the zone of lower tensile strength.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows the head of a flow-straightener blade which can be fixed by a method in accordance with the invention; and, Figure 2 is a diagrammatic part-sectional view showing the method of fixing the blade to the outer casing of a turboshaft engine.

The blade 1 shown in the drawing is of the type with a stem at its head. It comprises a platform 2 to which is firmly attached a shank 3 which extends outwards along the longitudinal axis of the body 4 of the blade. The shank 3 has a notched portion 5 adjacent the platform 2, and a free end portion 6 separated from the notched portion 5 by a zone 7 of lower strength. Preferably, the shank 3 is made of the same material as the platform 2, and between the notched portion 5 and the end portion 6 it has an annular groove 7a forming the zone of lower strength 7. The end portion 6 has a diameter close to that of the average diameter of the notched portion 5.

The outer casing 8 to which the blade 1 is fixed has on its inner face 9 a recess 10 which receives the platform 2 of the blade 1. A hole 11 is provided in the wall of the casing 5 at or near the centre of the recess 10, this hole 11 being positioned and of a size such that the shank passes through it and the edges 12 of the platform 2 abut against the side walls 13 of the recess 10.

The length of the notched portion 5 is such that it extends at least partly outside the casing 8 when the platform 2 is received in the recess 10.

The fixing of the blade 1 is achieved with the aid of a bush 14 which is plastically deformable under compression. The bush 14 has an inner bore of a diameter at least equal to the maximum diameter of the shank 3.

The blade 1 is fitted to the outer casing 8 in the following manner. The shank 3 is passed through the hole 11 so as to locate the platform 2 in the recess 10, and the bush 14 is placed in position around the notched portion 5 from the outside of the casing 8. An appropriate crimping tool is then used, the tool having, on the one hand, jaws 15 capahle of gripping the end portion 6 of the shack 3 and exerting a traction T on the shank, and, on the other hand, an annular part 16 capable of pressing on an end face of the bush 14 and compressing the bush. The bush 14, being plastically deformable, is flattened against the outer face 17 of the casing 8 and crushed around the notched portion 5. When the traction force exerted on the shank 3 by the crimping tool becomes greater than the maximum resistance of the shank 3, the latter breaks at the position of the zone of least strength 7.

The foot of the blade is preferably embedded in an inner annular member. The blade is firmly attached to the annular member by a plastic product cast into the recess which receives the foot of the blade, but any other solution for connecting the foot of the blade to the annular member may be used.

To remove a blade, it is sufficient to cut away the plastic material joining the foot to the annular member and then to either drill or grind away the bush 14 at the head. The blade 1 is then lowered into the annular member so as to free the platform 2 from its recess 10, whereupon the blade 1 can be tilted and extracted from the annular member.

It should be noted that to allow the tilting of the blade 1 during refitting, the slot in the annular member which receives the blade 1 must be sufficiently large.

Claims

1. A method of fixing a flow-straightener blade to the outer casing of a turboshaft engine, said blade comprising a shank at its head forming a stem for the fixing of the blade to the casing, and the shank having a notched portion adjacent the head of the blade and an end portion separated from the notched portion by a zone of lower tensile strength, the method comprising fitting the shank of the blade through a hole in the casing so that the shank projects radially outwards through the hole, placing a deformable bush over the notched portion of the shank projecting outwards through the hole, and using a crimping tool to force the bush against the casing and crimp it onto the notched portion of the shank while exerting traction on the end of the shank until the shank breaks in the area of the zone of lower tensile strength.

2. A method of fixing an assembly of flow straightener blades to an outer casing of a turboshaft engine, each blade comprising at least one shank at its head forming a stem for the fixing of the blade to the casing, the shank having a notched portion adjacent the head of the blade and an end portion separated from the notched portion by a zone of lower tensile strength, wherein the shank of each blade is fitted through a corresponding hole in the wall of the casing so that the shank extends radially outwards from the casing, and each blade is then fixed to the casing by placing a plastically deformable bush around the notched portion of the shank of the blade from outside the casing, and then forcing the bush against the outer wall of the casing and crushing it around the notched portion by means of a crimping tool designed to exert a compressive force on the bush while exerting traction on the end portion of the shank until the said shank breaks at the zone of lower tensile strength.

3. A method acording to claim I, substantially as described with reference to the accompanying drawings.