US2341860A - Method of making chambered metallic articles - Google Patents

Description

Feb. 15, E E L is. METHOD OF MAKING CHAMBERED METALLIC ARTICLES Filed Feb. 9. -1942 INVENTOR fbwme 5 ELL/5 BY 1r i fcustomary and usually METHOD OF METALIJC ARTICLES Edward Ernest Ellis, Detroit, li iicln,

assignor to The S. K. Wellman Company, Cleveland, Ohio, a corporation of Ohio Application February-9, 1942, Serial No. 429,996

1 Claim. 75-22) This invention relates to a method for making metal articles having internal cavities and/or external contours of intricate configuration.

Various articles such as valve bodies, engine pistons, and like hollow articles have been made in the past by casting molten metal about suitably shaped cores by the processes generally known as permanent mold casting or die casting. Some articles of the type described are of such configuration, however,.that the core which is used cannot be removed readily from the castin except by breaking it apart. Sand and plaster cores predominate for such articles, soft or green" cores being used generally. Casting processes, however, sometimes ,i'ail to meet the requirements of a production plan which involves a high rate of production at low cost. This difficulty, so far as hollow articles are concerned, has heretofore been avoided to some extent by parting the articl in such a. manner that it may be built up from a number of difierent pieces corresponding to different ticle.

parts of the finished ar- Under such a plan the various pieces are formed separately from each other by casting in sand, by die-casting, by permanent-mold castingvor otherwise, and are subsequently machined, where necessary, and assembled together by bolting, riveting or otherwise so as to form a composite article having the desired configuration. It will be appreciated, however, that a built-up or composite article made in this latter 'manner necessarily includes a number of joints which ordinarily would not be liquid or gas tight. Where such fluid tight Joints are required, it is necessary to finish the matching surfaces of the separate pieces by a lapping 'process or by other similar fine finishing process. Such finishing operations are apt to be ex ensive and, even when employed, may not produce a joint which can be relied upon to re-. main gas or l quid tight over prolonged'periods of use in service.

so as to form a composite briquette having substantially the configuration desired in the finished article. .The composite briquette is then sintered with or without the application of pressure and at a temperature which is sufiiciently high to bond the individual briquettes together into an integrated whole. By giving adequate consideration to the briquetting pressures, the

sintering temperature, and sintering' pressure (when used) the joints between the various briquettes can be almost wholly efl'aced, and the porosity of the article may be made so low that the finished article compares favorably with cast metals so far as liquid or gas tightness at low pressures is concerned.

The objects and features of merit of 'the invention may be explained more fully through reference to the accompanying drawing:

' Fig, 1 is a longitudinal sectional view of a valve structure, the body of which may be made in accordance with the invention, the section being taken on the line i-l of Fig. 2.

Fig. 2 is a transverse sectional view oi the mechanism taken on the line 2-2 of Fig. 1.

Fig. 3 is an-inner side view of one-half of the valve bodS as made in accordance with the invention.

Fig. 4 is a sectional view taken on the line 4- 4 I of Fig.3.

- The present invention is directed to a process for making built-up or composite articles of the type described which are free from such joints and which therefore avoidthe unreliability and expense mentioned above. According to the invention, an article such as alow pressure valve body having a rather intricate series of cavities within it is formed by powder metallurgical processes. In practicing the invention. a number of different work pieces, each of which corresponds to a different part of the desired article. are formed by briquetting metal powders. These individual briquettes are then assembled together Fig. 5 is an inner side view of the other half of the valve body. v

Fig. 6 is a sectional view taken on the line 6-6 of Fig. 5.

Fig. 7 illustrates one mode of briquetting a half of the valve body by using a male die on the compression ram. v

Fig. 8 illustrates diagrammatically one manner in which pressure may be applied to the composite briquette during sintering.

. The valve structure shown in Fig. 1 consists of a valve body I having a central bore 2 extending longitudinally therethrough; a series of concentric grooves 3, 3 is provided in spaced relation along the bore, and each communicates through an outlet tube A to the machine or device which is to be controlled by the valve assembly. An inlet tube 5 conducts fluid into the central bore, and a piston 6 is arranged to slide longitudinally in the bore thereby to control the passage of fluid to the various outlet tubes.

In accordance with the present invention, the

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to the desired density. The powder layer within the mold is compressed under suitable pressure to form a brlquette which may be handled when it is subsequently removed from the mold and which will sinter to the required low porosity. The pressure needed for [this purpose will, of course. depend upon the kind and nature of the powder which is being formed, and upon its composition. Where the powder is reduced-oxide iron powder. a pressure of about 68 tons per square inch is suitable.

The bore holes and-grooves which are required in the briquette may be provided in several ways. For example, the pllmger 8 which is used to eflect compression of the powder layer. may carry a suitable male die 8 capable of forming the halfbores and half-grooves in the powder as the latter is being briquetted. This method is illustratedin Fig. 7. .Alternatively, the face of the plunger 8 may be flat so that it forms a smooth faced briquette having neither the bore nor the grooves in it. In the latter case, the brlquette is removed from the mold and the grooves and bores are then machined into it: It will be understood that the briquette is strong enoughbefore sintering to be handled and to be subjected to machining operations, but that it yet lacks the strengthand toughness of a metallic body; Consequently, it may be machined quite easily, behaving much ister with the bores and grooves of the other half. 4 The assembly is then introduced into a furnace. .Preferably the furnace should be capable of subjecting the assembly to moderate pressure while heating it, and preferably it should be constructed to provide a neutral or non-oxidizing atmospherearound the assembly during heating.

' Such a fumace is indicated diagrammatically in I Fig. 8. For a more detailed description of its structure, reference should be made to United States Patent No. 2,258,431. issued to S. K. Wellman. The furnace consists of a base l having a central loading stage II on which the brlquettes are placed. A plate I! of graphite may be disposed between the stage and the briquette, as

illustrated. A sheet metal s ell I! of cup-shaped construction is placed with its open side down so as to surround the briquette and the loadin stage, and so that its bottom edges extend into a loose layer ll of suitable granular sealing material, such as sand. Heat is applied by means of a bell-shaped cover l5 having-electric resistors l8 suitably carried on its inner sidewalls. The

bell-shaped cover rests on top of shell I! so that its weight may be carried by the brlquette. The bottom flange I! on the cover extends into the layer ll of sealing material. If the weight 18 form the briquettes.

80 sintering step.

pressure to the briquette, addiflonal pressure may be appliedto the top wall of the cover, as indi-.

cated. .A graphite plate ll may separate the shell I! from the top of the briquette, and a suit- I able bearing plate I! may be disposed between the shell and the-top wall of cover I. Provision is made for introducing a neutral or non-oxidizing gas into the chamber formed by shell ll around the briquette. .This may be done conveniently I. by means of inlet tube 2| and outlet tube 2!.

The pressure which is applied to the composite assembly of briquettes during slntering should be suillcient to press the two halves firmly together,

'- but of course, should not .be so excessive as to de- A pressure of between about 5 and 50 pounds per square inch of the surfaces to be united is usually suilicient, but the pressure which is used depends largely on the kind of powdered metal which is used and its so composition. As will be explained below, the

28 which is needed varies also. Where the. bri-' quettes are formed of ironpowder which has been brlquetted at pressures ranging from about 44 to 66 tons per square inch, a pressure of about pounds per square inch is suillcient during the During sintering, the temperature should not exceed the melting point of the predominant- 35 the briquettes to melt.- Where the briquettes are formed of a mixture of metal powders, or of alloy powders mixed or not with single metal powders,- the sintering temperature may be sumciently high to melt one or more of the minor 4o.components of the mixture iwlthout melting the major components. Wherelthe briquettes are composed of iron, for example, a temperature of 1800 F. is adequate if the briquettes are heated to this temperature for a period of about 5 minutes or more.

tering operation is efiective' in uniting the two halves firmly together. Under proper conditions, such as those indicated heretofore for iron powders, the joint may be so completely efiaced that microscopic inspection of the assembly after sintering will fail to show that a' joint originally existed between the two briquettes. Alter the as-.

sembly has-been, sintered under such conditions, y it exhibits most of the properties of dense metal and may be drilled and tapped, if necessary, and

o may have the inlet tube 5 and the outlet tubes 4,

l secured to it by soldering or brazing or otherwise. Due in part to shrinkage which is sometimes apt to occur during sintering, the sintered assembly may need to be subjected toa finishing o operation. In valve body I, this finishing operation. would usually consist merely in reaming bore 2 so as to fit piston 8. It will "be understood that the dimensions of the briquette maybe adjusted so as to compensate at least in part for any 7 shrinkage which 'may occur during si tering.

-I have found that when the val body is composed of iron, and has been briquetted and sintered in' a reducing or non-oxidizing atmosphere under the conditions indicated above, thev of the cover is not enough to apply the'desired "density is around of that oicast iron. I

assnsco have also found that, as would be expected from such a density, the valve body has adequate gas and liquid tightness when tested under such moderate pressures as 50 pounds per square inch.

Without wishing to be limited by the theory .here expressed, I wish to indicate the factors which, in my opinion, are responsible at least. in part for the low porosity of the assemblies made .by my process, and for the eiiacement of the this mobility has been attained, the cold-worked particles of metal undergo grain growth by accretion; that is, the more severely strained particles undergo an atomic rearrangement or recrystallization in which-the fundamental crystal structure of the metal is restored, but in undergoing this rearrangement, adjacent particles may also be absorbed into the new structure. The result is that certain fragments of the cold-worked metal increase in size by gradually consuming other adjacent fragments. It is my opinion that such action, which occurs when the cold-pressed briquettes are sintered, unites the particles of powder much more closely than is the case when unstrained powders are sintered together. This closer uniting of the particles is believed to account in part for the reduced porosity. I believe also that the occurrence of recrystallization and grain growth aids materially in eflacing the joints between the various briquettes since when conditions are such that grain growth is sufficiently pronounced during thesintring operation, the growth will take place across the-various joints or the composite assembly. Such growth accordingly integrates the particles of different briquettes into new grains which are as much a part of onebriquette as of another. The result is that the particles of metal lying in the interface between two briquettes recrystallize and grow into solid grains of metal which Join the two briquettes into one, thereby eflacing the Joint.

From the foregoing disclosure oi the invention. it will be recognized that the invention is characterized by the joining together or cold pressed, unsintered briquettes by a sintering process carried out at temperatures which utilize the tendency of the cold worked particles of metal in the As is well-known, cold briquettes to undergo recrystallization and grain, growth. It is characterized further by the use of briquettes which are made by process steps which produce cold worked and strained particles within and particularly at the surfaces oi. the briquettes. It is also characterized by the concept of using such cold pressed and strained briquettes to form an uniointed hollow body by uniting to gather a plurality of separately formed briquettes. When these characterizing principles are employed, a process is provided which ofiers numerous advantages over prior art processes. For example, all the well-known advantages of the powder metallurgy art over the casting art are embodied. These include a low unit cost of manufacture, a high. production rate, accuracy of details, and the opportunity which is aflorded to employ the aggregative characteristics and properties of sintered conglomerate compositions as distinguished from homogeneous compositions.

Furthermore, the process makes it possible to proclaimed is:

The method 01 making a chambered metallic fitting having one or more cavities therein which are substantially symmetrical about a plane extending through the body, said method comprising thesteps of briquetting reduced-oxide iron powder under a pressure between about 44 and 66 tons per square inch to form a pair of briquettes which correspond to the two parts of the said chambered metallic fitting as parted along said.

plane; assembling said briquettes together with their marginal boundaries and cavities in register with each other; applying pressure of upwards of 35 pounds per square inch to said assembled briquettes on lines perpendicular to the parting plane between them and meanwhile heating said assembled briquettes to a sintering temperature of about 1800 F. to substantially eflace visible joints between the said halves.

EDWARD ERNEST EL'LJS.

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