US 3844011 A
A labyrinth seal, for turbine engines, disposed between the rotary blades and the shroud, composed of a powder metal honeycomb in which the cavities thereof are also filled with a powder metal material. The density of the composite and of each of its component parts may be varied to satisfy various operating requirements.
Description (OCR text may contain errors)
Mute sates atent 1 1 1 3,844,011 Eavies Oct. 29, 1974 1 POWDER METAL HONEYCOMB 2,652,520 9/1953 Studders 29/1912 ux H51 Inventor: Gail Davies, Mentor, Ohio 333152? 2/1322 355515113: .'2 9'/'1 9 i 73 Assignee; Gould Inc Chicago, "L 2,815,567 12/1957 Gould et al. 29/191 2 X 2,977,673 4/1961 Wemman 29/l91.2 X  Filed: Jan. 15, 1973 3,221,392 12/1965 Gould et al. 29/1912 X  Appl. No; 323,371 P E A B C rimary xaminer-- urtis Related Apphcahon Data Attorney, Agent, or FirmEdward E. Sachs  Continuation of Ser. No. 100,140, Dec. 21, 1970,
 ABSTRACT  US. Cl 29/1823, 29/1822, 29/1912, A labyrinth Seal, for turbine engines, disposed 75/208 R tween the rotary blades and the shroud, composed of CLf. 1322f 3/16 a powder metal honeycomb in which the Cavities 1 d 0 Search 29/1912 1823 thereof are also filled with a powder metal material.
308/239 75/208 The density of the composite and of each of its comf l 5 References Cited ponent parts may be varied to satls y various opera mg requirements.
5 Claims, 4 Drawing Figures ii POWDER METAL HONEYCOMB This is a continuation of Application Ser. No. lO,l40, filed Dec. 21, 1970, now abandoned.
This invention relates generally to a honeycomb-like structure adapted to be employed as a high temperature and low friction abradable seal, particularly for turbine engines.
Significant effort has been undertaken in the past to provide a suitable seal between the blades within a turbine rotor and the housing enclosing the blades. The nature of the gases employed to drive the turbine engines usually develop temperatures in the high, or extremely high, temperature ranges. It has been found necessary to provide a metal seal of an abradable nature to curb the leakage of gases between the rotor blade and the annular turbine housing.
Such past efforts have been concentrated mainly in the areas of honeycombs composed of rolled foil deformed into individual hexagon cells which are connected together by welding. The resulting structure is brazed to a backup shroud. In more advanced honeycombs there has lately been a tendency to fill the sheet metal honeycomb structure with a powder metal of oxidation resistant and abradable material such as a nickel-chrome alloy.
Other, and perhaps somewhat less prominently accepted, approaches include seals of felted fiber mats which are densified to to percent of theoretical density and which are either secured to a backing member or directly brazed to the annular shroud of the turbine housing.
A third type of seal which has heretofore been utilized involves abradable metal powders which are hot gas or plasma sprayed onto the shroud. Again, the materials are of the oxidation resistant type. Finally, efforts have been made to utilize a seal composed of oxidation resistant powder metal alloys with a varying density and thickness and secured on a backing member. These powder metal seals generally provide excellent abradability with, however, a relatively poor resistance to the erosive forces generated by the hot gases and the erosive particles which are present in the environment of the jet engine.
The experience with the various abradable seals of the type described above has been somewhat less than satisfactory and has led therefore to investigations for a suitable and more satisfactory substitute. For instance, it has been found that the sheet metal type honeycomb experiences leakage in the turbulent gas environment of the jet engine and is subject to flutter fatigue fairly typically at the brazed joint between the honeycomb and the attached backup strip. While such deleterious effects can be somewhat reduced by making the individual cell size smaller, this solution is unattractive due to the disproportionate increase in weight and cost of fabrication. Similar considerations are encountered when such honeycomb cells are filled with powder metals although the performance can be significantly improved.
The use of the felted matrix has been found to be troublesome in the areas of the brazed joint, i.e., between the material and the backup shroud. Aside from the problems arising with the joint, the felted fiber has found, so far, limited aplicability due to its low abradability and high wear factors.
The sprayed powder metal seals are characteristically deficient in bond strength between the particles and the substrate to which they are applied. This is due largely to the inability to apply finely divided powders in a high temperature environment without some degree of surface oxidation.
The powder metal seals with or without randomly dispersed fibers establish properties comparable to those properties established by sprayed powder metal seals. While such seals tend to have a greater structural integrity than sprayed materials the mechanical strength is still inadequate, at the density levels necessary, to provide good abradability and resistance to erosion.
A great many of the deleterious effects of the prior art construction have been essentially eliminated, or at least significantly minimized, by the concept in accordance with the invention in which a cellular surface, such as a honeycomb, is composed, itself, by densified, compacted powder metal of an oxidation resistant material. The cellular powder metal structure can be used either in the open faced honeycomb form or in a mode in which the individual cells are filled with a powder metal having the desired characteristics. The objective of the invention is to provide a material wherein all elements of brazing and welding are eliminated and wherein the structure is a unitary totally solid state bonded components of high structural integrity incorporating in solid state association the erosion resistant and abradable metal elements; such provision enabling a wide degree of adjustment of the filler and honeycomb materials not readily possible in conventional honeycomb structures, through the variation of density of the powder metal material.
characteristically, the honeycomb in accordance with the invention eliminates not only the costly welding normally employed in joining of the honeycomb elements to each other but also the subsequent need for brazing the honeycomb to a backup strip. Since the honeycomb in accordance with the invention has a solid state bond throughout it will be appreciated that the strength of the powder metal honeycomb is significantly superior, on a comparable basis to those of the prior art components.
Another significant advantage of the invention resides in the ability to provide a honeycomb structure having an extremely small cell configuration without any substantial increase in the cost of manufacture. Moreover, such small dimensional cell configurations can be accomplished with a reduction in weight over conventional small cell honeycomb.
while the invention is primarily adapted for employment as a labyrinth seal the same is not limited thereto. lt will be appreciated that because of the wide latitude of material manipulation the powder metal honeycomb lends itself for the production of clutch plates, bearing materials, disc brake pads and the like, as well as a low density structural backup for accoustical damping applications.
For a better understanding of the present invention, together with other and further objects thereof, reference is bad to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.
in the drawings:
FIG. 1 is a fragmentary, perspective and sectional view of the shrouded section of a turbine engine embodying the present invention.
FIG. 2 is an enlarged fragmentary perspective view of a powder metal honeycomb; and
FIGS. 3 and 4 are views similar to FIG. 2 showing modified versions thereof.
Referring now to the drawing there is shown in FIG. 1 a radially extending rotor blade of a turbine engine (not shown) the tip of which faces in close proximity an annular shroud 1.2 to which a seal in the form of a honeycomb-like structure 14 is secured. The honeycomb-like structure 14 provides a coherent and structurally continuous body of compacted metal powders in which by means of selectively impacted regions a net-work of cavities 16,18 is formed with the cavities being arranged and distributed uniformly in a repeating and predetennined manner substantially over the entire surface of the honeycomb. These cavities l6 and 18 may be of various geometric configurations such as diamonds, squares, circles, sinusoidal patterns, crescent or straight lines parallel to a single axis and the like.
Particular attention is invited to FIG. 1 wherein the impacted regions 16 are continuous and intersect each other at right angles as compared to the discontinuous cavities 18, shown in FIG. 3. In the preferred embodiments shown in FIGS. 2 and 3, the impacted regions provide a bottom surface, see 16 and 18, of metal powder particles densificd to a greater degree than adjacent nonimpacted or raised regions, see 20 and 22.
The honeycomb structures 14, 14a, 14b shown in FIGS. 1 to 3 can be utilized as a labyrinth seal when composed of material having suitable properties of oxidation resistance and selected abradability. The honeycomb may be used with or without a powder metal backup strip 24 composed of suitable and conventional high density material. Ordinarily, the backup strip 24 is fully dense. A bonding interlayer (not shown) interposed between the honeycomb 14 and the strip 24 is composed of a relatively fine powder metal material which may be of the same or similar to, or at least metallurgically compatible with the material used for the honeycomb-like structure, the term compatibility" being used herein to signify that the two metals will diffuse and alloy with each other.
In the preferred embodiment of this invention, the continuous and discontinuous cavities 16, 18 are filled with compacted metal powders, see 26, metallurgically compatible with the basic honeycomb-like structure 14 so that a solid state bond can be readily established between the powders in the cavities and the metal powders of the adjacent regions.
The metal powder filler material, see 26, is densified to a pre-determined level which may differ from the degree of density imparted into the honeycomb-like structure 14 and, more particularly, the raised regions 20, 22 and the impacted regions l6, 18. As a result, the total structure consisting, in this instance, of the filler material and the honeycomb, may have three different levels of density. This multi-density body can be readily achieved by a method hereinafter further described.
The honeycomb-like structure. 14, 14a and 1411, the tiller 26 and the backup layer 24 may all be composed of oxidation resistant material such as nickel, chromium, aluminum, iron, molybdenum, cobalt, tungsten or particular alloys thereof. The degree of desired abradability can be imparted to the powder metal structure by varying the density or composition.
Usually, it will be desirable to impart abradability to either the honeycomb or the tiller.
Typically, the abradable powder metal material, e.g., for the tiller, will be comprised of relatively coarse particulants and consequently less dense in the gravity sintered state providing relatively lower mechanical properties than required for the honeycomb-like structure 10, as the case may be. The honeycomb-like structure 14 (or, alternatively, the filler 26) is comprised of comparatively fine metal powder particles having the capability to sinter to relatively high densities. The density of the higher density component will range from 35 to 95 percent of theoretical density of the base material. The density of the abradable filler material 26 will generally be within the range of 20 to 60 percent of theoretical.
For most typical applications it has been found that -325 mesh powder particle size is satisfactory for the honeycomb-like structure 14, whereas the typical screen size for the comparatively coarse filler material 26 is l00 mesh. The above described invention can be fabricated by various powder metallurgy methods. The following method has been found to achieve satisfactory results.
The materials for both the honeycomb and the tiller are prepared separately. A l00 mesh alloy metal powder of weight percent nickel and 20 weight percent chrome, including possibly 1 percent aluminum and produced by water atomization, is blended with 2 percent carbon pore formers of a specific size, not to exceed l0 microns per particle, in a twin shell blender. At the proper time, prior to application to a mold, a controllable l to 2 percent alcohol is added to the mixture as a suspension vehicle. The material which forms the honeycomb-like structure 14 is prepared in the same fashion using a -325 mesh alloy of the same composition which is blended with a 1 percent carbon pore former. Again, prior to its application, a l to 2 percent addition of alcohol is added to this material to act as a suspension agent. A graphite die having a channel of width sufiicient to accommodate the desired strip plus trim and of sufiicient thickess to compensate for sinter shrinkage is prepared by pre-coating with a slurry of magnesium oxide which is subsequently dried.
The foil backup strip 24 has a thickness of l to 5 mils and is composed of the same or similar alloy which is properly cleaned to render it devoid of surface contaminants. The strip 24 is then sprayed with a suitable volatile adhesive and, while still wet, a dusting of fine 400 mesh metal powder is applied over the strip 24 to provide a high density bonding interface to the strip 24. The excess material after the adhesive has dried is dusted off. The coated foil backup 24 is then placed in the die cavity. Following this step, the powder forming the honeycomb is placed upon the backup strip 24 and together they are placed into a furnace and sintered in vacuum for 1 hour at a suitable temperature. After cooling, the strip is compressed l to 3 percent between steel plates in a hydraulic press to flatten the same to uniform dimension. Thereafter, the network of continuous or discontinuous cavities which form the honey comb is imparted into the sintered structure by means of a tool which is pressed into the structure. The tool has a configuration complementary to the pattern desired. The punch or tool is pressed over the sintered material with a load sufficient to provide penetration to the depths desired, usually 80 thousandths of an inch. For a diamond pattern, the punch is rotated in order to establish the desired configuration. The structure is then dusted to remove loose material and placed in a fixture for application of the filler 26 material. Metal powder composing the filler material is doctored into the cavities established by the tool and the excess is removed by standard blade strike-off techniques. The resulting honeycomb structure in which the cavities are filled is then re-sintered in vacuum under suitable conditions, for instance, at a maximum pressure of 1 micron and at a temperature of 2,100F for 1 hour. if desired, the filler material within the cavities is compacted before and after sintering to the desired degree.
lt will be understood by those skilled in the art that the honeycomb-like structure may be made with or without a back-up plate 24 and with (as shown in FIG. 3) impacted regions constituting the bottom of the cavities or a honeycomb-like structure in which such impacted regions have been completely removed as shown in FIG. 4. The honeycomb-like structure Me of FIG. 4 is in all other respects identical to the embodiment described with the respect to FIG. 3.
While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.
What is claimed is: 1. A grid-like structure of powder metal, comprising:
a coherent and continuous body of porous material of compacted metal powders providing a grid established by mechanical impacting of selective regions thereby forming a network of cavities arranged and distributed in a repeating and predetermined manner uniformly over substantially the entire surface of the grid with said body having a density of 35 to percent of theoretical, and sintered in situ material of compacted metal powders within and substantially filling said cavities and having a density of 20 to 60 percent of theoretical, with the area in said body of the grid below each cavity having a density substantially greater than the density of the wall areas defining said cavity.
2. A grid-like structure according to claim 1, wherein the material establishing said grid is dissimilar in composition from the material filling said cavities.
3. A grid-like structure according to claim 1, and a metal backing strip on said grid closing off one end face of said cavities.
4. A grid-like structure according to claim 3, wherein said backing strip is diffusion bonded to said grid.
5. A grid-like structure according to claim 1, wherein said body is composed of an abradable material selected from the group consisting of nickel, chromium, aluminum, iron, molybdenum, cobalt, tungsten and alloys thereof.