US2402204A - Apparatus for assembling centrifugal impellers - Google Patents

Description

7 June 1946- A. J. PHELAN ET AL 2,402,204-

APPARATUS FOR ASSEMBLiNG CENTRIFUGAL IMPELLERS Filed Nov. 19, 1941 2 Sheets-Shet 1 jig. 1

IN V EN TORS ARTHUR J. PHELAN. Y VLADIMIR H. MVLECKA.

A T TORNE YS.

June 18, 1946. A. J. PHELAN ET AL 2,402,294

APPARATUS FOR ASSEMBLING CENTRIFUGAL IMPELLERS Filed Nov. 19, 1941 2 Sheets-Shea t 2 Ez'g. 5. 77

66 a: a; 65" las IN VEN TORS ARTHUR J. PHELAN. Y VLADIMIR H. PAVLECKA.

ATTOPNEYS.

method, within the scope of the appended clain a.

Patented June 1 8, 1946 APPARATUS FOR AsssMsLmG CENTRIFUGAL IMPELLERS Arthur J. Phelan and Vladimir H. Pavlecka, Pacific Palisades, Call! asslgnors to Northrop Aircraft, Inc, Hawthorne, Calm, a corporatlon of California Application November 19, 1941, Serial No. 4193252 4 Claims. (Cl. 113-59) bustion turbine shown, described and claimed in.

the following prior filed applications:

Serial Name Title No Filed Povlecko Gas $lll'blH6. 483,338 July 21,1941 Pavlecko and Northrop- (lompressorflm 413,731 Oct. 6.1941 Do Airplane power 418,475 Nov. 10.1941

plfill Among the objects of our invention are: To provide a light, strong and integral centrtiusol impeller; to provide a means and method oi es= sembling a centrifugal impeller; to provide a means and method of forming a oentr ugal lrnpeller by copper brazing in a hydrogen atmosphere; to provide a complement of fixtures whereby a centrifugal impeller may be assembled by copper brazing, without the use of belts or similar materials; to provide a anal method of assembling a rotor disc, centrifugal vanes and a cover into a unitary iinneller sttuc ture by brazing; to provide a centrifugal impeller having clean, smooth and fully con tours and air passages, and to provide a simple, efficient and light-weight centrifugal adapted for high speed operation.

0m invention possesses'numerous other jects and features of advantage, some of will It, together with the foregoing, will be teeth in notes the following description of specific embodying and utilizing our novel therefore to be understood that our met applicable to other apparatus, and we no not limit ourselves, in any way, to the an, ratus of the present application, as we may adopt various other apparatus embodiments, utilising in the prior applications cited above, gas combustion turbine is disclosed wherein two centrifugal impellers are utilized in series to Zero vide the supply of compressed sit for the combustion. Inasmuch as the preferable use to": such a turbine is for the propulsion of sli crait, it is essential that the impellers in the compressor be of highest strength, of light-weight, be por fectly balanced, and have clean air passages to obtain maximum efllciencyo Broadly as to method our invention comprises the assembly of centrifugal vanes on a rotor disc with the application of a cover to the vanes, the disc, vanes and cover being brazed into a single unit by the use of copper in a hydrogen furnace, this brazing being accomplished under pressure. Preferably, the copper is interposed between mating surfaces in the form of a thin strip of exact size and position, so that after the brazing has taken place only an insignificant copper fillet is present at the junction of the mating surfaces. For certain work this fillet may remain. For other work it can be removed for exceptionally clean air channels.

The more detailed assembly steps comprise turning of a mating surface on a rotor ine'nber, together with the assembly the clad in turning fixture, followed by the turning of mating surfaces on the blades. The blades placed in position on the, rotor disc tidh a thin copper strip therebetween, tools-crazed or taclnweldeci in posi 'lon. The opposite n a edges of the vanes are the totaled to enact s by grinding, to avoid disttsense of vanes clue to shock -loading thereof by intern st which would be encountered in e? A cover plate is then czuiulai'ly tL nod to mat:- with the exposed vane and con are applied to these cover plate is placed nosi s that there will be a con vane edges and he me or rotoz disc, as the case The entire assembly droe'en furnace and a colts thereto. The assembly is takes locs. The pressure the copper from between i and disc, to torn: an one: ture. -I'he insignificant t main in since for most omen pellet", or may be removed by ins oneration for most etfici air giassages oi. the iinis lifter the vans; are the rotor disc, the cute? suriaces may then be machine finished. produces an impeller wherein all surfaces, terior and interior are machined, and where the various elements of the impellers are craze into a single nronerly dimensioned operating unit without the use oi bolts or similar tie mem' rs.

Broadly as to apparatus, our invention cor prises a. rotor disc having a vane surface mechined thereon. Edges of a plurality of centrifusal vanes fit this surlace, and the vanes are held 1, .2 or posse of the in place by tack-brazing or by tack-welding, with a thin strip of copper between the vane edges and the mating surface on the disc. The opposite vane edges fit a machined cover surface, and copper strips are applied to the vane surfaces by tack-brazing or tack-welding. The cover is then placed to the vanes, and the entire assembly is placed in a holding fixture positioned within a hydrogen furnace until melting of the copper strips occurs.

While the assembly is in the hydrogen furnace, means are provided to apply pressure to the fixture so that as the copper melts, clearance are taken up and the members forced into an exact fit. Upon cooling, the rotor disc, the vanes and the cover are firmly brazed into a single operating unit, and, if desired, the small fillets formed at the edgesknay be removed to provide clean air channels.

Thus, we have provided an impeller wherein the interior is completely machined.

In the drawings, which show one preferred embodiment of our invention:

Fig. 1 is a'vlew, partly in section and partly in elevation, of a rotor disc together with two impeller vanes drawn adjacent the positions they are to occupy when Welded to the disc.

Fig. 2 me view, partly in section and partly in elevation, showing how the impeller vanes are held in position on the rotor for tack-brazing or welding.

Fig. 3 is a view, partly in section and partly in elevation, taken as indicated by the line 8-3 in i Fig. 2.

Fig. 4 is a view, partly in section and partly in elevation, taken as indicated by the line 5-45 in Fig. 3.

Fig. 5 is a view, partly in elevation and partly in section, showing the assembled impeller in po- 'sition in a hydrogen furnace ready for the brazing operation.

Fig. 6 is a view, partly in elevation and partly in section, of the finished impeller.

Fig. 7 is a view, partly in section and partly in elevation, of a portion of the impeller showing the copper strips in place.

Fig. 8 is a fragmentary view, partly in elevation and partly in section, showing a means of interlocking the blades with the impeller discs.

Fig. 9 is a sectional view taken as indicated by the line 9-9 in Fig. 8.

Referring directly to the drawings for a more detailed description of our invention, beginning with Fig; 1 to show the sequence of operation: A rotor disc I is provided, having a central flange 2 and hollow hubs 3 and 5 on opposite sides thereof. The hollow hub 5 is larger than hollow hub 3 and is positioned on the side of the rotor disc, to which impeller vanes 6 are to be attached. The end of hub 5 is also provided with an inner shoulder I which is later to be threaded. Vanes tare curved as is well known in the centrifugal compressor art, and comprise a curved basal portion I0 and an outwardly extending portion I I. Each blade also has a rotor edge 2, a cover edge I3, an angular entrance edge 94, and an exit edge I5. Disc i is also provided on its outer face with a positioning ridge I6. I

As a plurality of blades 6 are to be brazed to rotor disc I in equally spaced positions around the rotor disc, the first step toward that end is to mount the rotor disc in a lathe and by simple annular machining to produce vane face 26 to which the vanes 6 are to be brazed. The reof the contours of the vane edges 52 with the rotor disc contour 20 may be obtained.

' The next stage in the assembly is the position- I ing on the machined surface 28 of the rotor disc i, of a plurality of sheet copper strips 2i, these strips being cut to be thewidth and length of vane edges I2, which are to be brazed to surface 2!! of rotor I. These copper strips ZI are preferably about .010 thick and are tack-brazed to the surface 28 of disc 8 in the proper circumferential positions, one strip for each blade to be mounted on surface 28. Opposite edges I3 of vanes 6 are not at this time machined to final finish, but are provided with excess metal so that the final finish may take place after the vanes have been fastened on the rotor disc.

Passing now to Figs. 2, 3, and 4 for a description of how the vanes 5 are primarily held in ,place on the rotor disc, we have provided a base fixture 22 mounted on a foundation 23, on which rotor disc 8 may be placed with vane surface 20 of this disc'facing upwardly. Positioning ridgev It is used to prevent lateral motion of the disc on the fixture.

The full complement of vanes 6 is then mounted in a vane fixture 25. Vane fixture 25 is provided on the under surface thereof with an inner spacing ring 26, and an outer spacing ring 21,

these rings being provided with vane slots 28. 1

base pads 32 of sheet-lead are applied between fixture 25 and angular vane edges It to force the vanes inwardly. j

Fixture 25 with its vanes is inverted over disc I, the fixture being provided with a drop rim 33 extending over the exterior edge of the rotor I. Vane tip apertures 34 are provided adjacent end edge I5 of each vane. Fixture 25 is continued upwardly around hub 5 on the outside thereof, and vane base apertures 35 are provided on each side of entrance edges id of each vane. Threads 38 are provided on shoulder l of rotor hub 5 and an upward extension member 40 is 'screwed'into these threads. Fixture 25 terminates upwardly in a cylindrical portion M, sliding freely on ex-' tension Aid. Extension dd is provided with end threads 32 and a nut Q3 is utilized to force fixture 25 against upper edges I3 and Id of vanes 6 and thereby force each vane B into intimate contact with the copper strips 2I positioned between each vane and the surface 2% of rotor disc I.

After this locking together of the parts in their proper position is accomplished, the vanes 6 are,

tack-brazed, preferably in three places, to rotor I. This is accomplished by inserting the brazing torch for example, through openings 36 and brazing each vane to the rotor I at an entrance edge spot 65. The brazing torch is then inserted further into this opening 36, and the vane is brazed to rotor I at a curvature spot 58. The brazing quired number of vanes 6 are then mounted in "is torch is also inserted through end openings 34 and the vane brazed to the rotor I at a vane end spot 41.

Thus each vane at this time is securely held in position on the rotor I although not in final posi tion, due to the thickness of the copper strips 2i.

Fixture 25 and extension 48 may then be removed from the rotor disc I and the rotor disc i removed from foundation member 22, carrying with it now a full complement of impeller vanes 8.

The partially assembled impeller is then ready to. have the finishing operation performed on edges it of the vanes to which edges an impeller cover is to be brazed. This machining operation is performed preferably by grinding in order to minimize disturbance ,of the vanes on the rotor disc, due to shock-loading which would be encountered by the intermittent cutting oil a lathe tool, in case annular turning of the vane edges were to be attempted. 'fiy grinding however, this shock-loading may be entirely eliminated, and edges is of the vanes may be readily finished to size and contour without disturbing the tackhrazlng or the vanes to the rotor.

After surfaces l3 of the vanes have been machined to their finished dimensions while mounted on rotor I, the rotor and its tack-brazed vanes is provided with copper strips 49 required for the blazing of the edges H to a cover 50.

These latter copper strips however, are not applied to cover 5B but are applied directly to edges 13 of the vanes, and are tack-brazed in proper position thereon.

Cover 50 has a vane mating surface 5| whichhas been machined by annular turning to mate properly with the final finished dimensions and contour of edges 43 of the vanes, and this cover is then positioned on the vanes 8, resting on the copper strips 49 that have been applied to edges 18 of the vanes. The assembled, but not yet brazed, impeller is then ready to go into a hydrogen furnace for the final brazing operation. This hydrogen furnace will next be described, and is showninFig. 5.

A heavy base member 80 is provided supporting an overhead member 8! by upright bars 82. Mounted on base 50 is a metal pressure plate 84, preferably circular in plan form, carrying a layer of heat insulating material 65 on which is mounted an impeller support member 68 havin I an upper surface thereon roughly shaped to receive and properly support the outer surface of rotor disc I. It will be noted that shoulder i8 may again be utilized to properly position the impeller on the impeller support 88. Pressure plate 64 and insulation 85 form part of the lower wall of the oven, the remainder of the bottom of the oven, the side walls thereof, and most of the top being of conventional structure of circular plan form and comprising fire-brick 88, held together by properly fire-resistant mortar 69, and enclosed by a thin metal cover 70.

The top of the oven is provided with a central opening It through'which a pressure cylinder 12 is freely movable, this pressure cylinder, however, being of heat insulating material and sufiiciently strong to transmit to the interior of the oven, hydraulic pressure through an exterior metal pressure fitting is from a hydraulic cylinder 74 by means of a piston rod 15 operated in converttional manner by a piston 16 within the cylinder 14, as is well known in the art. The cylinder is supplied with oil or the like from inlet 11.

The interior of the oven is provided with electrical heating elements 18 of the proper capacity in hr-irm the interior" of the oven up to proper .it can at all times be told that the oven is receiving its full complement of hydrogen gas.

The oven may be opened in any convenient manner, such as by end doors 80 set in one end of the oven. The impeller rotor disc is placed on the support member 88, with the cover in place on the vanes. We prefer to insert asbestos pads Bl between support 66 and the outer, now lower, face of rotor disc l. Similar asbestos pads 82 are placed between the outer, and in this position, upper surface of cover 50 and a clamping dome 83, which extends upwardly around hub 5 of the impeller rotor disc to terminate in an upper surface 88 immediately below pressure cylinder 752. We also prefer to provide asbestos pads 3'! between the dome 3'4 and the angular entrance edges M of each vane so that the vanes will be moved. inwardly by vertical pressure.

Thus the assembled but not yet brazed impeller is clamped between the basal support memher it and the dome 84, with asbestos pads between the clamping members and the impeller structure. These asbestos pads are utilized to prevent any possibility of any brazing occurring between'the metal clamping members and the exterior surfaces of the assembled impeller. Further, we prefer to form support member 88 and dome 84 of high nickel-chromium heat resisting alloy ribbed and finned to provide maximum strength with the least weight in order to conserve heat.

The entire assembly of clamping members and impeller is then properly centered in the oven beneath the hydraulic press arrangement, and the top surface 86 of the dome is connected with pressure cylinder 72 of the hydraulic press by means of an asbestos cushion 90 and shims 8!, so that there will be no slack in the hydrauli drive.

The oven doors 8!! are then closed,,the hydrogen atmosphere fully established, and the current to the heating element '55 is switched on.

Pressure is continuously applied to the elements of the rotor by the use of suitable liquid injection into cylinder M. As the temperature gradually rises and as this temperatru'e approaches 2100 F., the copper strips 2| and 69 melt and brazing is accomplished with the parts moved by the application of the hydraulic pressure into pressfit engagement, both radially and axially. The material selected for the impeller element is preferably of steel such as SAE 4340 and therefore is not substantially affected by the heating to 2100" F.

As the copper melts, a perfect braze is accomplished and the tacking spots which have previously been made, merely melt into the final brazing. The copper which is between the vane edges and the impeller rotor and cover, is squeezed out as it melts to form a very slight fillet on each side of these edges, and the vanes come to rest, under pressure, with exact mating relationship of the machined edges of the rotor and cover to which they are opposed. Thus the impeller after the final brazing has been accomplished is of exact dimensions. is brazed into a complete asoaaoe unified structure, which can operate as a unit without the useof any bolts, rivets or equivalent tie members. The interior surfaces are entirely machined and the fillet caused by the copper in the strips being forced outwardly, may easily be removed by running a small gouge or similar tool along the junction of the vanes and the rotor and cover, this tool being readily inserted from the periphery fr the straight runs of the edges, and.

from the basal openings for the curved portions of the edges. After the impeller is removed from the oven, as shown in Fig. 6, it can then be mounted in the lathe so that the exterior of the surfaces of the rotor and the cover may be machined into the desired final dimensions, including the removal of ridge it. 7

Thus we have provided a centrifugal impeller having clean machined surfaces throughout, both inside and outside the impeller. The impeller is formed solely by brazing without the use oi additional tie members. The impeller in this manms may be made very light in weight, exceedingly accurate as to dimensions, the air channels are clean, and the impeller may be perfectly bal-' I anced. The copper brazing provides" adequate strength in use, particularly as temperatures even approaching the brazing temperatures, are never encountered in the normal use of the impeller. However it is to be noted that the melting temperature of copper is high, and for that reason impellers made as described herein can be used inthe high pressure end of a compressor, as has been'described in the applications cited above, even though the exit air temperatures should rise, due to the air compression, to the neighborhood of 500-600 F.

It can be seen from, the above description of our method of copper brazing "that the application' of external pressure, particularly an external pressure which is continued as the copper melts, provides a complete, strong connection with exact mating of opposed surfaces. Hitherto, it has been thought feasible to copper-weld only parts held in a press-fit engagement prior to the application of the copper thereto. Nowhere, so

. far as we are aware, has copper brazing been practiced by the application of continuous external pressure to parts spaced by thin copper sheet. Hitherto, clamped pants have been copper brazed, but this method has not been found to be completely satisfactory, in that the preload due to clamping almost invariably diminishes with temperature, due to heat sagging of the clamp. The pressure between parts then diminishes, and the danger of misalinement' arises. Gravitational clamping, using merely the weight ,of the parts, again has not proved to be satisfactory, because misalinement may still arise and also because the pressure thus produced is not sumcient for successful brazing. However, by our method, Where hydraulic pressure is utilized, continuously operating. before, during, and after,

the melting of the copper strips, so that the parts are forced into exact mating engagement as the copper strips melt, with all the parts held completely in alinement, it can be seen that even though the parts before the brazing occurs are spaced, the forces acting on the parts a? such as to copper-weldthe parts with a press-fit engagement, with copper uniformly bonding the parts throughout the engaged surfaces.

In case rotational stresses are so great as to call for more than dependence on the copper alone for the joint between the vanes, disc 8, and cover 59, shear ribs Hill may be provided for ribs its fitting slots ml cut in the vane edges, as shown in Figs. 8 and 9. After brazing has occurred, the shear and other stresses are taken by the ribs as well as by the copper, and the vanes cannot straighten out even when rotated at high speeds. V

We claim: 1. Apparatus for brazing a centrifugal impelle assembly involving an impeller disc, a vane cover, vanes positioned between said disc and cover, copper strips between mating edges of said vanes and adjacent surfaces of said disc and cover, said apparatus comprising a hydrogen furnace wherein said disc, cover and vanes are positioned, means for heating said furnace, and positioning means for supporting said disc on the bottom of said furnace, and said second means comprises a dome positioned over said cover and extending upwardly to terminate adjacent the top of said furnace, a movable heat insulating section'of the top of said furnace engaging the termination of said dome, and means for applying pressure to said section, said disc positioning means and said dome being of metaLwith non-metallic pads positioned between said positioning means and disc and between said dome and cover to prevent brazing therebetween, said dome having a surface exerting pressure on exposed portions of said vanes through additional non-metallic pads, said vares being curved with respect/t0 said disc and requiring an inwardly radial movement to mate ments for receiving said assembly with the axisof said assembly vertical, a dome positioned to apply pressure to said cover, a movable insulating portion positioned to apply pressure to said dome, and a hydraulic cylinder having a piston connected to said movable insulating portion by a piston rod and pressure block.

3. Apparatus in accordance with claim 2 wherein said disc is supported on a block and wherein an asbestos pad separates said block from said lisc, and wherein an asbestos pad separates said cover from said dome, such apparatus including means for creating an atmosphere of a reducing gas around said assembly during heating.

4. Apparatus in accordance with claim 2 wherein said disc is supported on a block and wherein an asbestos pad separates said block from said disc, wherein an asbestos pad separates said cover from said dome, and wherein said vanes are provided with curved basal portions and angular edges, said dome transmitting pressure to

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