US 2809407 A
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Oct. 15, 1957 R. F. THOMSON ETAL 2,809,407
METHOD 0F MAKING A COMPOSITE METAL ARTICLE Filed Feb. 11, 1955 ATTORNEY United States Patent @fhce 2,809,407 Patented Oct. 15, 1957 METHOD OF P/IAKKNG A COMPOSITE METAL ARTICLE Robert F. Thomson, Grosse Pointe Woods, and Fred 5. Webbere, Pontiac, Mich, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application February 11, 1955, Serial No. 437,534
14 Claims. (Ci. 22-203) This invention relates. to a method of making a composite metal article and is more particularly concerned with a method of making a composite valve lifter body and similar articles.
Among the objects of the invention are the following: to provide an economical method of forming composite articles, such as valve lifter bodies and similar articles, to provide an improved method of forming composite valve lifter bodies and related articlm whereby a wide variety of foot materials may be employed without regard to the machinability characteristics thereof, to provide an improved method of forming composite valve lifter bodies and similar articles which lends itself to high production operation under conditions resulting in excellent metallurgical control and maximum uniformity of the product, and to provide an improved method of making composite valve lifter bodies and like articles wherein the main body portion may be made from relatively inexpensive metal tubing and the foot portion of cast metal metallurgically bonded thereto. Other objects and advantages of the invention will become more apparent from the following description of preferred embodiments of the invention.
In accordance with the invention there is provided an improved method of making composite articles such as valve lifter bodies and the like by metallurgically bonding a metered amount of metal forming one portion of the body to the remainder thereof. In making valve lifter bodies it is highly advantageous, if not essential, that the foot portion that engages the cam or other operating member be formed of a hard, wear resistant material. By means of the present invention the foot member, if desired, can be made of a material that is hard and relatively unmachinable. The remainder of the valve lifter or like body may be made of inexpensive metal tubing.
Reference is herewith made to the accompanying drawings in which:
Figure l is a cross-sectional View of a tubular valve lifter body portion and a replaceable cap for closing the lower end thereof.
Figure 2 is a cross-sectional view of the cap in place on the lower end of the tubular body and with a metered or measured amount of metal shot in the lower end of the tubular body above the cap.
Figure 3 is a cross-sectional view after the shot illustrated in Figure 2 has been melted and metallurgically bonded to the lower end of the tubular member but with the cap still in place.
Figure 4 is a cross-sectional view similar to that of Figure 3 but showing the cap stripped from the lower end of the tubular body and after machining and grinding operations.
Figure 5 is a view in cross-section illustrating somewhat diagrammatically another method of forming a valve lifter or like article by metallurgically bonding a metered amount of metal to a tubular member.
Figure 6 is a view in cross-section illustrating somewhat diagrammatically still another method of forming a valve lifter or like article by metallurgically bonding a metered amount of fused metal to one end of a tubular body member.
Referring especially to Figures 1 to 4, inclusive, iii indicates a tubular body member of circular shape having an upper bore of small diameter 5, an intermediate bore of larger diameter 6, and a lower bore of still larger diameter 7'. The junction between the upper and intermediate bores forms a shoulder 11. An outwardly tapered portion 9 joins the lower and intermediate bores. The bore 7 is a of such size that the lower end portion of the tubular body has a relatively thin wall 8. In the modification of the invention illustrated in Figures 1 to 4, inclusive, the lower wall portion 8 is completely removed by machining and grinding operations after the foot portion has been metallurgically bonded to the tubular member. However, it is not necessary in all applications of the invention to remove the lower wall portion 8. A cap 12 of a size sulficient to form a light press lit with the outer wall of the lower end of the tubular member is provided for closing the end of the tubular body during processing. The tubular body and cap are preferably formed of steel, a suitable and illustrative steel for the tubular body being SAE 1020 steel, while a satisfactory and illustrative material for the cap is a low carbon sheet steel.
The cap may be formed by a simple press operation.
The cap and the inner surface of the tubular body above shoulder 11 preferably are coated with a suitable stopoff as by brushing, dipping, spraying, etc., in order to prevent adherence of metal during melting. Typical stopofi materials (1} an alumina base refractory and (2) aluminum paint consisting of powdered aluminum in a suitable organic vehicle. Figure 2 shows the cap 12 in place over the lower end of the tubular body and with a measured or metered amount of metal shot such as cast iron or the like within the end of the closed tubular body. Figure 3 shows the tubular body after the metal shot has been fused and metallurgically bonded to the lower end portion of the tubular body and with the cap still in place. In this figure it: represents the solidified cast iron foot and 19 represents a zone in which carbon from the molten cast iron has diffused into the adjacent portion of the tubular body. Figure 4 shows the valve lifter body of Figure 3 with the cap stripped off of the lower end and after machining and grinding operations. The machining and grinding operations include removing the thin wall 8 at the lower end of the tubular body, forming the bore 17 and removing metal from the outer wall to form the oil feed groove 15.
Where a stop-off has been employed the caps may be reused in forming subsequent valve lifter bodies. if desired the stop-off may be omitted and in this case a metallurgical or fused bond also is formed between the cap and fused metal shot. In this case the outer band portion of the cap is sheared off. This procedure eliminates the necessity of coating the cap with a stop-off but requires an expendable cap and machining of the foot portion of the cap. It is possible also to use a coated cap pressed only part way onto the end of the tubular body. The melted shot then fills out the full inside diameter of the cap so that very little metal need be removed from the outside diameter of the tubular body. This procedure is of particular advantage where carburization is to be accomplished during fusion or immediately thereafter since it eliminates the need for intermediate machining or for an excessively thick carburized case.
Any suitable material may be employed for the shot that will fuse at a temperature less than that of the main body portion. It is preferred to employ shot materials parts and fusing the cast iron shot. 7 loaded in fixtures and the fixtures moved through the 3 that will form a wear resistant foot on the valve lifter body. From the standpoint of cost and commercial availability it is preferred to employ a cast iron shot that will form a hard and wear resistant foot. -A' presently preferred cast iron shot composition is as follows:
This composition fuses readily at 2200 F. and is one that produces a microstructure that has good Wear resistance. Higher carbon and silicon improve the fusibility but'tend to cause excessive graphitization. .This tendency may be overcome by addition of increased amounts of carbide stabilizers.
. A presently preferred practice is to employ a shot such that all of it passes a mesh'screen and such that about 60% passes a 30 mesh screen. Larger shot may be used but 10 mesh and smaller are preferred to facilitate metering of the small quantities thatare employed.
The shot is preferably cleaned before use in any suitable manner as by chemical or mechanical means.
One typical and illustrative chemical method of cleaning the shot is to first acid clean for five minutes in HQ solution, water rinse, neutralize one minute in 5% NaOI-I solution, then water rinse and drain, and then alcohol rinse to minimize subsequent rusting.
The tubular bodies with the caps and shot are then heated to melt the shot and form a metallurgical bond between the cast metal and tubular body. Any suitable non-oxidizing atmosphere is employed during the melting operation. Very satisfactory results have been obtained with any one of the following atmospheres with the dew point below F.:
1 20.7% 00, 0.8% can, 38.7% Hz and 39.8% N2, and (2) l.52.0% CO, 0.05% C92, 0% CH4, 12-25% H2 7 and 9 7.25% N2 The heating temperature in any case .is dependent on the materials employed. ciently high to melt or fuse the metal shot and not sufficiently high to melt the tubular body portion. Where the tubular body is of low carbon steel and the shot'is a cast iron shot of the illustrative example hereinbefore described, a heating cycle of 2200" F. for one hour'has proven satisfactory. Higher temperatures and shorter times may be used but because of high maintenance cost of furnaces employing higher temperatures, the lower operating temperature is preferred. The time of heating preferably only is such as to equalize the temperature of the work. the carbon from the molten cast iron' shot diffuses into the wall of the tubular steel body to an excessive extent,
' thereby lowering the melting point and eventually resulting in fusion of the wall. 7
Any suitable furnace may be employed for heating the The parts may be furnace. A simple fixture consisting of welded tube sections has proven satisfactory. 'This type fixture per- 7 mits the bottom of the parts to be in direct contact with the hearth of the furnace for maximum heat'transfer.
Since the metallurgical structure of the cast' iron foot is dependent on the cooling rate through solidification, it is important to control the cooling when cast iron is employed as the foot. material. 7 To obtain the desired carbide distribution with the presently preferred cast iron If too long a heating time is employed It must be, of course, sufficomposition given above, the foot portion is cooled as by a water cooled chill plate at the unloading end of the furnace over which the parts are moved. Modifications of the cast iron may be used which will require less rapid cooling. The composite body also may be heat treated, if desired, to modify the properties thereof. Materials also may be employed for the foot portion which are extremely hard regardless of the cooling rate during solidification.
A modification of the invention isillustrated diagrammatically in Figure 5. In the method illustrated in Figure 5 a tubular body 20 rests on carbon block 22.
Within the tubular body is a carbon block 18 of lesser length than the tubular body so that a pocket 24 is provided which will hold a metered or measured amount of molten metal. This pocket is filled with a metered amount of metal from a crucible 26 containing a supply of molten metal 28. A suitable flux may be applied to the exposed inner wall of the tube which forms the pocket so as to provide a clean surface to which the cast metal is metallurgically bonded upon solidification.
When the'tubular body is steel and the molten metal is cast iron it is preferred to heat the tube and assembled parts to a temperature on the order of 1500 F. prior to applying the metered amount of molten metal.
Another modification of the method of this invention is illustrated diagrammatically in Figure 6. ure, 3% represents a crucible containing a supply of molten metal 36. A tubular body has a porous sand core therein which is of lesser length than the tubular body 3% to form a pocket 32 for holding a measured or metered amount of metal. The outside of the tubular body adjacent the lower end has a refractory coating 34 thereon to prevent adherence of molten metal. The tubular body is dipped into the molten metal in the crucible and a vacuum applied by means of flexible conduit 42. it will be understood that the conduit is in air-tight engagement with the outside of the tubular body 'When the vacuum is applied the air is exhausted through the porous core 4% causing a metered amount of molten metal to be drawn upward until the space or pocket 32 Within the lower end of the tubular body is completely filled. 7 metal in the end thereof are then. raised and the body held in a vertical position until the molten metal has solidified. It is also contemplated that the porous core may be ornitted and the vacuum controlled to obtain the desired amountof molten metal in the end of the tubular body. 7
The tubular body member may be formedof seamless tubing or rolled welding tubing. The metal tubing can be readily cut and machined into sections of the desired length and form. Automatic machines can readily carry out these operations.
It will be apparent that this invention provides an economical method of making valve lifter and like bodies comprises metallurgically bonding a metered amount of molten metal to the inner wall of a metallic tubular body member adjacent only one end thereof thereby forming a tubular article havinga closed end.
' 2. The method of making a composite article which comprises providing a generally tubular .metallic body member, applying within the tubular body at only one 7 end thereof a metered amount, of molten metal: and
metallurgically bonding said metered metal to the inner wall of said tubular body member at said oneend.
3. The method of making a composite valve lifter which comprises providing a tubular steel body, apply- The tubular body and molten ing within the tubular body at only one end thereof a metered amount of molten cast iron and metallurgically bonding said metered cast iron to the inner wall of said tubular body at said one end only.
4. The method of making a composite valve lifter which comprises providing a tubular body member, applying a metered amount of metal shot within the tubular body adjacent only one end thereof, heating the tubular body and metal shot to fuse the shot and metallurgically bonding the fused metal to the inner wall of said tubular body at said one end.
5. The method of making a composite valve lifte which comprises providing a tubular steel body, applying a metered amount of cast iron shot within the tubular body adjacent only one end thereof, heating the tubular body and cast iron shot to fuse the shot and metallurgically bonding the cast iron to the inner wall of said tubular body at said one end.
6. The method of making a composite valve lifter which comprises providing a tubular steel body member, applying a cap member to said tubular body to close one end thereof, applying a metered amount of cast iron shot within said tubular body adjacent only the closed end thereof, heating the tubular body, cap, and shot to fuse the shot, then cooling the assembly and solidifying the fused cast iron and thereafter removing the cap.
7. The method of making a composite valve lifter which comprises forming a tubular body member, applying a plug member within said tubular member spaced from one end to form a pocket between the plug and said one end, filling said pocket with a metered amount of molten metal and thereafter solidifying said molten metal in said pocket.
8. A method as in claim 7 in which the plug is porous and the molten metal is drawn into said pocket by means of a vacuum applied through said porous plug.
9. A method as in claim 7 in which molten metal is poured into said pocket.
10. A method as in claim 7 in which the tubular body is steel and the metered metal is cast iron.
11. A method as in claim 10 in which the cast iron is composed substantially as follows:
12. A method as in claim 5 in which the cast iron is composed substantially as follows:
13. A method of making a composite valve lifter which comprises providing a tubular steel body, applying a cap member to said tubular body to close one end thereof, applying a metered amount of cast iron shot within said tubular body adjacent only the closed end thereof, heating the tubular body, cap and shot in a non-oxidizing atmosphere to fuse the shot, then cooling the assembly and solidifying the fused cast iron and thereafter removing the cap.
14. A method of making a composite valve lifter which comprises providing a tubular steel body, applying a cap member to said tubular body to close one end thereof, said cap member having a stop-01f applied thereto, applying a metered amount of cast iron shot within said tubular body adjacent only said closed end thereof, heating the tubular body, cap and shot in a non-oxidizing atmosphere to fuse the shot, then cooling the assembly and solidifying the fused cast iron and thereafter removing the cap.
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