US2753858A - Valve seat insert ring - Google Patents

Description

July 10, 1956 R. N. HONEYMAN ET AL 2,753,858

VALVE SEAT INSERT RING Filed May 27, 1952 h P 5 2'12: .2 7 5 Eoaser JY HavEwm/v I'own e0 6". Pate 3636 M M, 9 W by H/Zys.

VALVE SEAT INSERT RING Robert N. Honeyman, Lyndhurst, and Edward G. Pekarek, Willoughby, Ohio, assignors to Thompson Products, Inc, Cleveland, Ohio, a corporation of Ohio Application May 27, 1952, Serial No. 290,222

3 Claims. (Cl. 123-188) The present invention relates to a powdered metal valve seat insert for internal combustion engines, the insert having a body portion with desired expansion characteristics and a seating face portion with desired wear and corrosion resistant properties. The invention is also directed to a method of preparing such a powdered metal valve seat insert by means of which an intimate bonding is achieved between the powdered metal making up the facing portion and the powdered metal comprising the body portion of the valve seat insert.

In the process of the present invention, the body or base of the powdered metal insert is provided by placing finely divided iron particles, or other ferrous compositions containing predominating amounts of iron in a suitable die, and then positioning thereover powdered refractory metal particles having good oxidation resistance and hot strength properties. The composite powdered metal charge is then molded under suitable pressure conditions to provide a self-sustaining green compact. The green compact is then sintered to secure a good bonding of the ferrous material with the facing material, coined, and infiltrated with a metal having good heat conducting properties. The infiltrant metal forms a network within the pores of both the facing and the ferrous body portions and improves the bond between the powdered metals of these portions.

in order to further improve the physical characteristics of the infiltrated ferrous base material, the infiltrated valve seat insert is then solution heat treated and precipitation hardened. In this way, the body or base of the insert can be formed of a metal or mixture of metals which have thermal expansion characteristics similar to those of the metal of the particular engine into which the ring is to be seated. In a preferred embodiment of the present invention, small amounts of aluminum, up to 5% by weight, are included in the ferrous compact making up the body portion of the valve seat insert, as we have found that the addition of the metallic aluminum to the ferrous base reduces shrinkage of the iron base material so that it will match the shrinkage of the facing material during sintering. The expansion characteristics of the body or base portion can thus be controlled to compensate for any difference in shrinkage of the materials of the body and of the facing portions that might otherwise occur during sintering. The addition of aluminum has the further advantage that aluminum acts as a deoxidizer in the iron and reduces any oxidized particles in the region of the interface between the dissimilar powdered metals to produce a uniformly good bond.

The facing portion of the valve seat insert is formulated from highly refractory materials, alloys, or mixtures of metals capable of effectively resisting the severely corrosive conditions occasioned by the presence of lead compounds in the combustion zones that result from the burning of fuel containing tetraethyl lead. The refractory metal may contain high proportions of chromium and need not be weldable, since the mechanical pressing, sinter "nited States Patent' ice ing, and the infiltrant network develop the required bond with the body metal.

Heretofore, valve facing materials were selected with a view to their Welding characteristics so that they could be effectively puddled onto the base metal. The available base metals were likewise limited to those metals which were compatible with the puddled-on facing material and which could be suitably fabricated. The present inven tion now makes possible the selection of metals for the base which are best suited for a particular engine block or head and metals for the facing which are best suited for resisting wear and corrosion. Both the base and the facing are porous and are united by a metal'of good thermal conductivity. The facing is capable of dissipating substantially more heat than would be the case if the facing surface were deposited on the body in the form of a puddled-on deposit.

In a preferred form of the invention, the body metal consists of finely divided iron particles obtained by reducing mill scale and containing carbon in amounts from 0.01 to 1.7% by Weight. The addition of small amounts of aluminum, up to 5% by weight of the mixture, is also highly desirable in order to reduce shrinkage of the iron base material. The ferrous powder has an average particle size of from minus to about 325 mesh. Ungraded fines, finer than 325 mesh, may be present in amounts up to 20%.

The material for the facing may be selected from a large variety of metals and alloys which possess oxidation resistance characteristics, but is not necessarily limited to those metals or alloys which have good welding characteristics. Typical among the alloys which can be used for the process of the present invention is the alloy identified commercially as AMS-5373A containing from 63% to 68% cobalt, 27% to 30% chromium, and 2% to 6% tungsten. Other suitable alloys include nickel base alloys, particularly those alloys containing from 15% to 25% chromium, 50% to 80% nickel, balance iron with about 0.1% carbon. A mechanical mixture containing 50% powdered iron and 50% powdered chromium by weight is also suitable. An alloy having exceptional oxidation corrosion resistance, and suitable for the purposes of the present invention, is one containing 50% to 65% by weight nickel, 20% to 35% by weight chromium, 6% to 9.5% tungsten or molybdenum, or mixtures of the two; 1.0% to 2.5% carbon, 0.05% to 0.5% silicon, 0.01% to 0.10% zirconium, and the balance iron.

In a preferred form of the invention, the refractory alloy powder is prepared by an atomizing process in which a molten aloy is atomized with water jets, thereby producing finely divided, generally rounded, as well as spherical particles. This powder has about the same particle size as the iron powder but the particles are more nearly spherical in shape. When compacting particles of this type, the rounded shapes provide only limited areas of contact with the adjoining particles, so that the re fractory metal particles upon compacting are quite porous, having a density only of about 60% of theoretical before coining, and about 80% after coining. The shaped particles are desirable in facilitating infiltration because they provide a network of cavities between the particles which are easily filled by the infiltrant metal. If desired, the metal for the facing can be mixed in a ball mill with about 5% by weight of the infiltrant metal, such as copper. The infiltrant metal thereby coats the particles and this coating further facilitates infiltration. In addition to the atomizing process, other processes for obtaining prealloyed powder can be employed for the purposes of this invention. Instead of using a prealloyed powder, a premixture of the proper composition of ingredients within the ranges given above may be used. An object of the present invention is to provide an improved method for manufacturing valve seat inserts for internal combustion engines by means of which two dissimilar powders are united together into a single well bonded compact, and the compact is then infiltrated with a lower melting metal having good heat conducting properties.

Another object of the present invention is to provide a method for mechanically bonding together two powder compositions of different chemical composition into an integral self-sustaining shape prior to sintering of the compact and infiltration of the compact with a molten infiltrant metal.

Another object of the present invention is to provide an improved valve seat insert for internal combustion engines containing a body portion consisting essentially of a ferrous compact clad with a facing material integrally united therewith, the facing material consisting of a compacted mass of refractory metal or refractory alloy particles.

Another object of the present invention is to provide an improved valve seat insert for an internal combustion engine in which the ferrous body portion of the composite valve seat insert contains added amounts of aluminum to reduce shrinkage of the iron base material, and further for improving the bonding characteristics of the two dissimilar powdered metal compositions making up the composite valve seat insert.

Other objects and features of the invention will be apparent to those skilled in the art from the following description of the annexed sheet of drawings, which, by way of preferred examples only, illustrates the method and articles of the present invention.

On the drawings:

Figure l is a cross-sectional view, with parts in elevation, illustrating the manner in which the ferrous particles making up the body of the valve seat insert are introduced into the compacting die assembly;

Figure 2 is a view similar to Figure l and illustrates the position of the lower punch element of the die assembly after it has been lowered to allow the ferrous material to settle and leave a predetermined void at the top of the die cavity;

Figure 3 is a view similar to Figures 1 and 2 and illustrates the two powder compositions within the compacting die cavity, and also illustrates the'position of the upper punch member which cooperates with the lower punch member to compact the powder compositions into an integral structure;

Figure 4 is a cross-sectional view of the completed valve seat insert;

Figure 5 is a plan view of the insert; and

Figure 6 is a cross-sectional view, with parts in elevation, of a modified form of the valve seat insert produced according to the present invention.

As shown on the drawings:

The compacting assembly illustrated in Figures 1 and 3, inclusive, comprises a compacting die 10 having a cylindrical cavity, cylindrical core rod 11 disposed therein and an annular lower punch member 12 slidably receivable within the annular space between the wall of the die cavity and the core rod 11 and closely fitting relationship therewith. A supply of finely divided iron particles 13, which may contain added amounts of carbon and aluminum as previously explained is distributed in the cavity of the die 10 over the upper surface of the lower punch member 12. The excess iron powder is struck off from the surface of the die 10, so that the surface of theiron particles 13 is substantially flush with the upper surface of the die 10. A molding lubricant such as zinc stearate, in amounts of about 1% by weight is mixed into the iron powder to facilitate compression.

After the ferrous particles have been distributed in the cavity, the lower punch member 12 is lowered as indicated in Figure 2 to leave the void 15 in the die cavity above the ferrous particles 13, as shown in Figure 2.

Refractory metal particles, identified by numeral 16 in Figure 3 are distributed into the void 15 above the ferrous particles 13.

An annular upper punch member 13 having an axial bore 17 of sufficient diameter to engage the outer periphery of the core rod 11 is then lowered into the die cavity to compress the ferrous particles 13 as well as the refractory particles 16 into a single, self-sustaining compact. Depending upon the ultimate density to be achieved in the compact, compacting pressures of from 30 to 80 tons per square inch may be employed. 7 In most instances, sufficient pressure will be employed to produce a compact in which the ferrous particles have about 70% of the theoretical density of iron, while the refractory particles, because of their spherical shape, have a density of only about 60% of theoretical density. In general, the porosity of the ferrous compact will be in the range from 15% to 40%, with 30% being preferred.

After molding, the green compact is sintered at tem peratures from about 1900" F. to about 2500 F. in a non-oxidizing atmosphere such as hydrogen. After sintering, the compact is cold coined to desired dimensions at pressure of about 30 to 80 tons per square inch, and at this stage, the ferrous body ring has a density of about 75% to 90% of theoretical.

The cold pressing of the two powder compositions together in the molding cavity, as well as the addition of aluminum, produces a good mechanical bond between the dissimilar metal compositions making up the bimetallic valve seat insert. The heat and corrosion resistant facing material is securely bonded to the ferrous base by an intermingling of powder particles during die filling and pressing, as well as by the sintering operation.

The sintered composite metal insert is then infiltrated .with a low melting metal having good heat conductivity,

- such as manganese, nickel, chromium, silicon, and

titanium in amounts from about 0.1% to about 2% may be added. While copper and copper alloys are the preferred infiltrant materials, other alloys such as nickel alloys, cobalt alloys, chromium alloys, and other good heat conducting metals such as silver and silver alloys can also be employed as infiltrants.

The single compact may be infiltrated by providing a ring of copper or copper alloy, and disposing it above a preformed compact. This assembly is then introduced into an infiltrating furnace maintained at temperatures above the melting point of the infiltrant. When a copper alloy is the infiltrant material, temperatures of about 2000 F. to 2300 F. are used.

Since the forrous body ring will ordinarily have a porosity of about 30%, while the refractory metal facing will have a slightly higher porosity, and since the infiltrant metal substantially fills the pores of the rings, the resulting infiltrated compact will contain at least about 30% copper. The proportion of copper, however, can be varied over a wide range, and may extend from about 5% to about 35%. In order to improve the strength and wear properties of the infiltrated compact, the assembly is solution heat treated to diffuse the cuprous metal into the ferrous matrix of the ferrous ring. In addition, the refractory metal or alloy and the ferrous matrices of the composite ring are diffused into the cuprous infiltrant phase{ The solution heat treatment is carried out at temperatures within the range from about 1000 F., to 2000 F., and preferably at 1600 F. for a relatively short period of time such as one-half hour. After solution heat treatment, the infiltrated insert is oil quenched and reheated to effect precipitation hardening. The heat treatment precipitates both iron and some refractory metal alloy constituents from the copper phase, and copper from the iron and refractory alloy phase. Temperatures for precipitation hardening are in the range from about 900 F. to 1200 F., the periods of time of treatment depending upon the temperatures employed. At a temperature of 925 F., a suflicient amount of precipitation hardening can be effected by a treatment time of one hour, followed by air cooling.

The finished valve seat insert is illustrated in Figures 4 and 5, and includes a ferrous matrix 20 and a refractory metal matrix 21 joined together at this interface 22 by means of mechanical bonding as well as by interdiffusion of the materials during sintering and an infiltrant network which extends through the pores of the compacts and is alloyed with the metals of both matrices.

An alternative embodiment of the present invention is illustrated in Figure 6 of the drawings. In this form of the invention, ferrous metal particles are distributed in the molding die and then shaped with a strike-off tool prior to filling of the die cavity with the refractory metal particles to provide a generally arcuate surface 24. Subsequently, refractory metal particles are introduced into the mold cavity over the arcuate surface 24, and the surface of the refractory metal particles is made flush with the top of the die. By compacting, sintering and infiltration of the two powder compositions, the ferrous metal 25 and the refractory metal 26 are joined together along the contoured parting line 24. This structure reduces the amount of refractory metal composition used as well as providing for better intermingling of the ferrous particles and the refractory metal particles during compression of the powdered compositions.

From the foregoing description, it will be understood that this invention provides a powdered metal composite valve seat insert with a facing composed of a metal or alloy which is best suited for valve facing purposes, and a body ring composed of a metal which is best suited for its compatability with the engine body or block in which it is to be mounted. The two powdered metal compositions are united in the form of an integral compact and further united through the medium of a common infiltrant metal network which has good heat transfer properties, so that the facing is in good heat transfer relation with the engine body.

It will be understood that various modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

We claim as our invention:

1. A valve seat insert for an internal combustion engine comprising an annular body portion including a powdered iron compact, a facing consisting of a powdered refractory metal compact, said facing having substantially the same inner and outer diameter as said annular body portion, said facing being in face to face contact with said annular body portion with the interface between said facing and said body portion containing intermingled particles of refractory metal and iron, and a network of an infiltrant metal extending into said facing and said iron compact strengthening the bond holding the same together into an integral structure.

2. A valve seat insert for an internal combustion engine comprising an annular body portion including a powdered iron compact, containing carbon in amounts up to 1.7% by weight and aluminum up to 5% by weight, a facing consisting of a powdered refractory metal, said facing having substantially the same inner and outer diameters as said annular body portion, said facing being in face to face contact with said annular body portion with the interface between said facing and said body portion containing intermingled particles of refractory metal and iron, and a cuprous network extending through said facing and said iron compact.

3. A valve seat insert for an internal combustion engine comprising an annular powdered iron compact having an axial bore and a flared upper surface, an annular facing consisting of a refractory powdered metal compact having a complementarily flared surface in face to face contact with said flared surface of said powdered iron compact, the interface between said facing and said body portion containing intermingled particles of refractory metal and iron, and a cuprous network extending through said facing and said iron ring.

References Cited in the file of this patent UNITED STATES PATENTS 1,959,068 Stoll May 15, 1934 2,004,259 Weiger June 11, 1935 2,035,165 Jardine Mar. 24, 1936 2,048,222 Rehmann July 21, 1936 2,100,620 Wirrer et al Nov. 30, 1937 2,136,690 Jardine Nov. 15, 1938 2,154,288 Scholz Apr. 11, 1939 2,401,483 Hensel et al. June 4, 1946 2,456,779 Goetzel Dec. 21, 1948 2,549,939 Shaw et al. Apr. 24, 1951 FOREIGN PATENTS 432,974 Great Britain Aug. 7, 1935 565,520 Great Britain Nov. 14, 1944 OTHER REFERENCES Materials and Methods, April 1946, Cemented Steels, by Peters; pp. 987-988.

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