US2971504A - Fused product - Google Patents

Description

Feb.

Ill

14, 1961 E. A. THOMPSON FUSED PRODUCT Original Filed Dec. 50, 1957 II 4/4 J .J

7 0 PNE Y United States Patent FUSED PRODUCT Earl A. Thompson, Ferndale, Mich.

Original application Dec. 30, 1957, Ser. No. 706,116,

now Patent No. 2,935,596, dated May 3, 1960. Divided and this application July 13, 1959, Ser. No 826,755

7 Claims. (Cl. 12S-90) This invention relates to an improved fused product. The invention is more particularly concerned with fused cast iron and steel -tappets for automotive engines in which a cast iron base is directly joined to a tubular steel sleeve or body in a single short application of heat and pressure. i

This application is a division of co-pending application Serial No. 706,116, led December 30, 1957, now Patent 2,935,596 of May 3, 1960, which is, in turn, a continuation-in-part of abandoned application Serial No. 637,589, filed January 3l, 1957, and which in turn is a continuation-in-part of abandoned application Serial No. 407,005, filed January 29,1954.

It has been recognized that the wearing properties of cast iron are well suited for service as a `follower member in direct contact with an automotive camshaft and that the body portion of a tappet-is most desirably formed of steel. Such two-piece tappets have heretofore been difficult to manufacture because of the problems of forming a reliable joint between the cast iron and the steel which will stand the impact forces involved and which can be produced in quantity at reasonable cost. Various proposals have been made for joining the cast iron and steel directly by an electric heating process Without, however, achieving a commercially satisfactory machine or method for producing a thoroughly reliable junction economically. One difficulty involved resides in the diiference in melting points between cast iron and steel. When a heating current high enough to melt the iron is applied, the steel does not melt but the molten ironwill ow as a liquid which instantaneously leaves the zone of juncture, preventingadherence of the two pieces.

It is an object of the present invention to provide an improved product of cast `iron directly joined to steel by` both fusion of the cast iron and mechanical upsetting of the steel wherein the line of demarcation between the two metals in the finished joint is a moreV intimate bond than has heretofore been possible to obtain and which, when the edge of the joint is machined, is invisible i to the unaided eye.

. parts of a two-piece tappet inposition in a fusing machine and ready for fusing.

Fig. 2 is a view corresponding to Fig. 1 showing the l rice Figs. l through 4 the work engaging parts of a fusing machine which is fully disclosed in the parent application above identified. A work piece abutment 172 forms a stationary support against which the worl: may be pressed by a downwardly moving upper electrode 276 under the control of suitable motivating means. Mounted for horizontal relative movement are a pair of clamping electrodes 148 which are of semicircular form to provide for tightly clamping a tubular steel Work piece 414 between the opposed cavities of the electrodes 148. At their top portions, the electrodes 148 each carry an insulated die 156 of stainless steel or other high melting point material. Mounted on top of the tube 414, and temporarily centered by the retractible plunger 206, is a cast iron button 446 having a shoulder :resting on the tube and a smaller annularV extension telescoping into the tube with a fairly large radial clearance.

Operation of the machine by motivating electrode 276 applies a high pressing force, pushing the button into the end of the tube. The application of the heating current between electrodes 276 and 148 along with the pressure causes theupper end of the steel tube to soften, but not melt, and results in a swaging, or upsetting, of the tube wall, both inwardly and outwardly in a radial direction. Thus, the steel is swaged into mechanical contact with the side wall of the telescoping portion of the button and is also swaged outwardly into contact with the insulated die 156. A At the same time the cast iron is heated above `its melting point locally adjacent the contacting faces of the two parts. The molten cast iron tends to ow away from the joint face" at first, but is prevented from ilowing inwardly by the mechanical seal established by the inwardly upset end of the tube. Thus, the molten cast. iron may only ow outwardly into contact with the die 1.56. Here it is blocked against downward iiow by the outward upset of the steel tube and can only How upwardly. That flow is stopped almost as soon as it starts by the chilling effect of the die 156 leaving a random edge formation as shown at 415- It will be understood that the characteristics of the joint obtained may be varied depending upon anumber of factors. Thus, for example, if the buttons are preheated to 400 F. or 500 F., the iron melts suiciently soon during the swaging that the iron ows out to contact the die and solidify in the manner described. On the other hand, if the buttons are utilized at room temperature, or with considerably less pre-heating, the swaging of the steel may continue before the iron melts so as to extrude a portion of the steel'upwardly past the boundary of the cast iron and into the clearance space between the button and the die before the cast iron can reach that space. In either event, a fusion of the iron to the red-hot, but unmolten, steel is obtained at thev junction of the two pieces. This is supplemented by a mechanical bond through swaging or upsetting along the lower telescoping protuberance of the cast iron button.

The intensity of the heating current and the time of application are subject to some variation depending upon the size of the parts to be joined and the composition of their` metals. In a typical automotive tappet of 'Ma diameter tubular stock with about 1,46 wall thickness, a heating time of about 30 cycles of 60 cycle current is suitable. The power usage may be of the order of magnitude of 7S kva.

If desired, the heating current may be applied in stages, first at a low value for pre-heating the pieces. During the pre-heating step the upper end of the tube 414 and the adjacent4 facial region of the button, which is in contact with the tube, may be brought to a temperature which is just below the melting temperature of cast iron, that is, around 2000* F. When the tube 414 is a steel 3 tube, the top end will be brought, during the pre-heating step, to a forging temperature of about l800 F. The current will take the shortest path between the electrodes 148 and electrode 276, and therefore, only the upper end of the tube 4M, above electrodes 148, as well as the button 446 will be heated any substantial amount. After the pre-heating stage, the final fusing current of high value may be applied to raise the temperature of the cast iron button above its melting point locally adjacent the interfacial areas between the tube and button as previously described. With the use of a pre-heating stage, the steel tube may be brought to a higher forging temperature and thus a more extensive upset, or forging thereof. may be obtained.

While the parts are described as being directly joined, the use of that and like expressions is intended to include joining parts which may have thin coatings on them of a different metal or other material and which may be-` come embedded or alloyed in the metal forming the zone of juncture.

It will thus be seen that the present invention provides an improved method performed through the use of a chilling die adjacent the faces of nieces to be ioined and produces an improved joint in the final product which has a high mechanical strength and which is of a hornogeneous nature in that there is no extraneous material separating the two metals. Due to the migration of carbon from the cast iron to the steelthe joint has a zone of signicant width across which the carbon conten-t varies from a high value in the cast iron to a low value in the steel. The joint is formed'with such an intimate bond between the two metals that there is no line visible. except under a microscope, when the edge of the joint has been machined smooth. and the fused piece looks. when finished, as though made from a single bodv of metal.

The use of an end piece having an annular portion projecting into the tube but with a central recess similar to that illustrated provides afoot piece well adapted to serve as a cam follower. Bv this construction the end piece is especially suited to casting with a maximum hardness at the center of the end area since there is equal opportunity for heat to escape to the surface from all portions of the piece and thus rapid and uniform cooling of the end area is assured. Likewise, the provision of the central recess formed bv the annular extension facilitates the central seating of a spring or push rod which mav abut the same when in use. While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

l. As a new article of manufacture a blank for a valve tappet body comprising a base piece of cast iron fusion lbonded directly -to a tubular steel body wherein the surtelescoped in and fusion bonded directly to a tubular steel body wherein the surface of junction has one end portion in which solid state cast iron and solid state steel are in tight mechanical abutment, wherein the cast iron, along at least the mid portion of the surface, is in a fused bond with the steel, and wherein the surface of junction terminates at the opposite end in a zone of die-formed and chilled cast iron material displaced beyond the original confines of the two pieces.

3. As a new article of manufacture a Valve tappet comprising a base piece of cast iron fusion bonded directly to a tubular steel body wherein the surface of junction has one end portion in which solid state cast iron and solid state steel are in tight mechanical abutment, wherein the cast iron, along at least the mid portion of the surface, is in a fused bond with the steel, and wherein the surface of junction terminates at the opposite end in a zone of die-formed and extrudedsteel material ,displaced beyond the original contines of the two pieces.

4. A valve tappet comprising a tubular steel body, a cast ferrous base end piece, said end piece having a head portion of substantially the same diameter as the tubular body and a part of smaller diameter extending within the tubular body with the head portion overlying the end of lthe tubular body, the external surfaces of said part of the end piece and internal surfaces of the body on the one hand, and end surfaces of the tubular body and the overlying surfaces of lthe head of the end piece Von the other hand, being in interfacial relationship and welded together. l

5. A valve tappet comprising a tubular metal body, a metal end piece, said metal body being made of a metal having a melting` temperature higher than the melting temperature of the end piece, said end piece having a head portion of substantially the same diameter as the tubular body and a part of smaller diameter extending Wi-thin the Vtubular body with the head portion overlying the end of the tubular body, said tubular body and said end piece having interlapping surfaces and being fusion bonded at said interlapping surfaces.

6. A valve tappet comprising a body portion of tubular steel and an end portion of cast iron joined by fusion and hot swaging, the joint between the two extending lengthwise a substantial distance with the steel lying in a telescoped relation with the cast iron, the joint having a first terminal zone where the cast iron and 'steel are fused together and a second terminal zone where the steel is upset into lintimate contact with the unfused cast iron.

7. A valve tappet comprising a tubular metalvbody, a metal end piece, said metal body beingmade of a metal having a melting temperature higher than the melting temperature of the end piece, said end piece having a headfportion of substantially-the VSame diameter as the tubular body and an annular extension of smaller diameter extending within the tubular body with the head portion overlyingthe end of the tubular body, said ar1- nular extension providing a central recess, said tubular body and said end piece having interlappingsurfaces and being fusion bonded at said interlapping surfaces.

References Cited inthe le of this patent UNITED STATES PATENTS i 2,887,098 Thompson May 19, 1959

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