US2310841A - Device for fabricating pump impellers - Google Patents

Description

Feb. 9, 1943. w. H. CURTIS DEVICE FOR FABRICAIING PUMP IMPELLERS Filed Aug. 17, 1940 Patented Feb. 9, 1943 DEVICE FOR FABRIGATING PUMP IMPEILERS William E. Curtis, Dayton, Ohio, assignor to Curtis Pump Company, Dayton, Ohio, a corporation of Ohio Application August 17, .1940, Serial No. 353,015

1 Claim.

This invention relates to a device for fabricating pump impellers, more particularly small impellers for centrifugal and similar pumps.

It has heretofore been the practice to fabricate centrifugal pump impellers by casting them of metal in sand molds, such as are used in commercial foundries. The castings thus obtained cannot ordinarily be of such proportions as to be best suited for the duties that the impeller is intended to perform, Owing to the inherent limitations in sand mold castings. As the overall dirnensions of pump impellers becam smaller during recent years, it was found to be impossible to cast suitable metal in suificiently thin sections to permit the attainment of maximum elliciency in the operation of the impeller as an element of the completed pump. Consequently, a great deal of machine or hand labor was necessarily expended upon the casting before it could be satisfactorily employed for its intended duty.

It is also obvious that, in the production of small impellers by casting methods, the choice of material is necessarily limited to those metals or alloys that can be cast. For this reason, it often became necessary to use a metal or alloy that was not best suited to withstand the conditions to which the pump impeller would be subjected in service.

In accordance with my present invention, the vanes and impeller body are separately formed and then assembled by a brazing or similar operation. In this way, the vanes can be formed from the desired metal or alloy, as for instance a highly heat resistant steel, by a rolling or drawing operation, or by ordinary punch press procedure, while the impeller body portion may be produced either from a forging or from solid bar stock, using the same or a different metal or alloy composition. My invention thus avoids the disadvantages of casting operations heretofore used in the making of pump impellers.

It is therefore an important object of this invention to provide a device for fabricating pump impellers that 'will obviate the disadvantages heretofore attendant upon the use of casting methods, and at the same time to provide a method of fabricating pump impellers that willpermit the use of more suitable metals and alloys in the construction of the impeller.

It is a further important object of this invention to provide a device for fabricating pump impellers that lends itself to large scale production and that eliminates to a considerable extent the amount of machine and hand labor previously required in machining cast impellers to the final form and dimensions required for their efficient operation.

Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanying drawin This invention (in a preferred form) is illustrated in the drawing and hereinafter more fully described.

On the drawing:

Figure l is a top plan view of the upper cap member of a two-part jig, illustrating the manner of holding th individual impeller vanes in place on the face thereof by means of locating pins.

Figure 2 is a longitudinal sectional view taken along the line IIII of Figure 1 with the cap member in its temporary position for the mounting thereon of the vanes and the positioning over the top of the vanes of a brazing shim or the like.

Figure 3 is a longitudinal sectional view of an assembled jig with the impeller body portion, brazing shim and impeller vanes positioned in place therein.

Figure 4 is a partly diagrammatic view showing a mufile, furnace or the like, with the impeller parts assembled within the jig and positioned within the furnace for the brazing operation.

Figure 5 is a top plan view of a completely fabricated impeller with the vanes brazed in position on the impeller body.

The reference numeral I0 indicates the top part, or cap member, of a two-part jig. Said cap member ID is preferably in'the form of a cylinder having a diameter approximately equal to the outside diameter of the vanes that are to be assembled thereon. The material of which the cap I0 is formed is not important so long as it is capable of withstanding the temperatures to which it is subjected during the brazing operation without appreciable distortion, and without fusing or becomingunited to the vanes that are in contact therewith during such brazing the vanes l3 that are to be temporarily held against displacement and distortion by means of said pins ll. As shown, there are four locating pins I I for each one of the vanes I3, two of the pins being arranged to bear against one side of a vane and the other two pins to bear against the opposite side of the vane, when the vane is positioned on edge between its particular set of locating pins. The spacing and location of the pins II must be so accurately accomplished that the vanes I3 can be slipped into position without being sprung out of their original state of curvature and yet be firmly braced after insertion in place so that no distortion or displacement of the vanes will occur during the relatively high temperature brazing operation.

The vanes themselves may be conventional in their form and design, or may be of the particular design that is described and claimed in the copending application of Russell R. Curtis entitled Booster pump for aircraft fuel system, Serial No. 352,064, filed August 10, 1940. In accordance with the invention described in that application, the vanes I3 are formed of relatively thin metal as spiral segments, and are tapered along one edge, as at I4, from approximately their mid portions to their inner ends I5. Each valve I3 is thus formed with one plane edge I6 (Fig. 1) continuous throughout the'entire length of the vane, and with a shorter plane edge I'I (Fig. parallel thereto.

In assembling the vanes I3 upon the cap member III, the cap member I0 is temporarily positioned with the plane face I2 uppermost and the vanes I3 are inserted with their shorter edges I1 the bolt 3|. Various brazing materials may be employed, such as copper, copper-containing alloys or brass, and the so-called silver solders, such as alloys of silver, zinc and copper. Preferably, a silver solder is used that is relatively high in zinc and low in silver, and which melts at approximately 1250 F. Since all silver alloys, in general, require the use of a. special flux, when the brazing shim 34 is formed of.a silver alloy, a suitable flux is coated thereover. In the case of brass, a flux is also desirable, although with a pure copper shim, the flux may be omitted entirely. Suitable compositions of flux for the various brazing materials are well known to those skilled in this art.

With the cap member I0 and assembled vanes I3 in the position shown in Figures 1 and 2, and with the shim 34 in place, the base 20 is inverted and superposed above the cap member ID so as to rest upon the shim 34. The bolt 3| is then inserted in place and the nut 33 threaded home to hold the impeller body 25 and vanes I3 in their proper relationship, except for the intervention of the shim 34. After the complete assembly has been firmly closed by means of the bolt 3| and nut 33, the assembly is then inverted to its normal position (Figs. 3 .and 4) with the base memin contact with said plane surface I2, as illustrated in Figure 1. As there shown, the inner ends of the vanes I3 lie on a circle concentric with the axis A of the cap member ID, and with their outer ends I8 lying in a circle substantially coincidental with the circle of the periphery of the cap member itself. Said cap member I0 is provided with a bore I9 extending therethrough. The other part of the jig comprises a base member 20, which may also be formed of high chrome steel or other suitable metal and which is provided with a bore 2| of the sam diameter as that of the bore I9 but countersunk at both ends, as at 22 and 23. The countersunk portion 23 is of such length and diameter as to permit the insertion thereinto of the hub 24 of an impeller body part 25. The impeller body part 25 comprises a disk-shaped flange 26 having a plane face 21 and an opposite tapered face 28, centrally of which is formed the integral hub 24. When positioned on the base 20, the impeller 25 automatically seats itself, with the hub 24 extending into the countersunk bore portion 23 and with the tapered face 28 in full surface contact with a similarly tapered upper face 29 of said base 20.

The other countersunk bore portion 22 is for the reception of the head 30 of a bolt 3| which freely extends through said bores 2| and III of the base 20 and cap I0, respectively, and also through the hub 24 of the impeller 25. Said bolt 3| is provided with a threaded end 32, upon which a nut 33 is adapted to be threaded to hold the base 20, cap I0, and assembled impeller parts in their proper relation, as illustrated in Figure 3.

After the vanes I3 have been assembled upon the face I2 of the cap member I0, as previously described, and while the cap member is still in the position illustrated in Figures 1 and 2, a brazing shim 34 is laid over the then uppermost vane edges I6. The brazing shim 34 may be formed of any suitable brazing material and is preferably in the shape of a circular washer having a central opening 35 to permit the passage therethrough of her 20 at the bottom and the cap member ID thereabove. In this position, the assembly is placed within a muffle, or furnace 36, which may be suitably heated by electrical or other means (not shown). The furnace 36 is then brought to a suitable brazin temperature, which may in general be between 1000 and 2000 F., but is preferably in the neighborhood of 1200 to 1550" F. The brazing is carried out in a reducing atmosphere, preferably an atmosphere of hydrogen gas, or a mixture of hydrogen and other non-oxidizing or reducing gases, such as carbon monoxide, carbon dioxide and the like. The purpose of using a reducing atmosphere, as is well known to those skilled in the art, is to prevent oxidation of the surfaces that are to be united and also to cause the copper, brass, silver solder or other brazing material to thoroughly and completely wet the surfaces that are to be bonded together. Under such conditions, the brazing material flows by capillary action into th joints that are to be united.

As the temperature is raised in the furnace 36, the material of the brazing shim 34 fuses and flows over the contiguous surfaces of the impeller vanes I3 and of the impeller body 25. The weight of the cap member II) is such as to force the vanes I3 downwardly into close edgewise contact with the surface I2 of the impeller body 25, displacing the excess of brazing material as the same melts or fuses between such surfaces. This insures the proper bonding of the vane edge surfaces I6 with the plane surface I2 of the impeller body 25. The pins II are, of course, sufficiently short as not to interfere with the pressure exerting function of the cap member I0 during the brazing operation. Also, as previously explained, the shank of the bolt 3| extends loosely through the bore III of the cap member. In and serves merely as a guide for said cap member while the same exerts its weight due to gravity upon the assembled impeller parts.

During the brazing operation, if the vanes I3 were not laterally braced as they are by means of the locating pins II, they would undoubtedly become distorted and displaced due to expansion at the high temperatures of the brazing operation. It has been found, however, using the jig and method just described, that practically no displacement or distortion of the vanes l3 occurs during the brazing operation and that very little machining is necessary after the assembled impeller parts have been removed from the jig. The assembly may be either cooled within the furnace 36, or, preferably, is removed from the furnace and cooled in the air. Thereafter, the nut 33 is threaded off and the jig disassembled. Practically the only machining that is necessary is that requiredto remove any excess of the brazing material and to bring the overall dimensions of the now completely assembled impeller to the required proportions. It is thus possible to fabricate a centrifugal pump impeller of the desired materials without sacrifice of operating efliciency by reason of any departure from correct proportions for the respective elements. The fabricated impeller can consequently be obtained at reasonable cost by methods that may be used where high rates of production are imperative.

While the foregoing constitutes the preferred embodiment of my invention, it will be understood that the details thereof can be varied considerably. For instance, instead of using a shim or washer of brazing material, as described, it is entirely feasible to provide the surface I! of the impeller body 25 with an electrodeposit of suitable brazing material, such as copper, brass or the like, or to apply a powder, paste or paint containing the brazing material, with or without a flux, over said surface l2 or over the surfaces of the vanes i3. comparatively little brazing material by weight is required, owing to the fact that when fused in a hydrogen or other reducing atmosphere, the brazing material will flow readily and, due to the capillary nature of relatively tight joints, will preferentially seek out such joints and flow into them. Thus the brazing material automatically flows to the points where it is actually needed for effecting the bonding of the parts to be united.

The weight of the cap member I may be selected in accordance with the requirements found by actual practice to give a satisfactory bond between the vanes l3 and the surface I! of the impeller body 25. Auxiliary pressure exerting means, such as a coiled spring positioned between the nut 33 and the upper surface of the cap member I0, might be used, if desired. a

It will, of course, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claim.

I claim as my invention:

A device for insertion in a furnace to hold members to be brazed in cooperable relation to each other and to automatically move said members into intimate relation during brazing in the furnace, said device comprising a base adapted to guidingly receive and support an impeller body seated thereon, a weighted jig member disposed above said base and having spaced-apart means on its lower face adapted to guidingly receive impeller vanes disposed therebetween, shaft means on said base member and extending thereabove and guidingly entered in said jig member, said jig member and the vanes held thereby being normally spaced from said base by a normally rigid brazing shim interposed between an opposed edge of said vanes and said impeller body, means on said shaft and engaging said jig member to fixedly retain the jig member, the

vanes, the shim, the impeller body, and the base in assembled relation for initial insertion of the assembly in a furnace, and means comprising said weighted jig member-movable to move opposed edges of the vanes into intimate contact with the impeller body as the shim melts under the influence of the heat of the furnace.

WILLIAM H. CURTIS.

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