US 3198182 A
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Description (OCR text may contain errors)
Aug 3, 1965 G. H. RoBlNsoN ETAL 3,198,182
VALVE LIFTER Filed Aug 17, 1962 i, 52 i 50 V/l/l//Il/ ATTORNEY United States Patent O 3,198,182 VALVE LIFTER George H. Robinson, Rochester, and Edward R. Mantel,
Warren, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation ot Delaware Filed Aug. 17, 1962, Ser. No. 217,700 Claims. (El. 12S-$0) This is a continuation-in-part of the now abandoned United States application Serial No. 114,697, filed June 5, 1961, and assigned to the assignee of the present invention.
This invention relates to valve lifters for transmitting movement from a cam or the like to the stem of a poppet valve such as is used in internal combustion engines and more particularly to an improved valve lifter and a method for manufacturing the valve lifter.
The general design of valve lifters in common use today comprises a generally cup-shaped cylinder which is slidably reciprocable in a bore provided therefor in the engine crank case so as to Contact the engine driven cam and a separately formed member which is thrustably supported in the lifter cylinder and serves to transmit movement from the lifter to the push rod, lt is particularly important in valve lifter construction that the valve lifter working surface or foot as it is called in the art, operating against the cam, be formed of a wearresistant material since these contacting parts are subject to severe wear conditions in service. It is the object of this invention to provide an improved valve lifter and a method for its manufacture. It is a more specific object of this invention to provide a valve lifter having a more wear-resistant foot portion.
These and other objects are accomplished by preparing an intimate mixture of powdered carbon, tungsten, molybdenum, silicon and iron in certain proportions nad compressing them to form a thin briquette or wafer in a manner well known in powdered metallurgy art. The valve lifter working end is preferably provided with a peripheral retaining ridge or lip whereby a shallow cavity is formed within the ridge. The briquette is then placed within the cavity and the briquette and adjacent valve lifter surface are subjected to heat at a temperature in the vicinity of 2200 F. for a time sumcient to cause the constituents of the briquette to fuse together and effect a diiiusion bond with the steel face. On completion of the fusion cycle the interior of the steel body is cooled rapidly to promote directional solidication of the coating alloy from the valve lifter surface alloy interface outward, thus preventing formation of internal shrinkage cavities in the coating.
Other objects and advantages of the invention will be apparent from the following detailed description made in relation to the accompanying drawing, in which:
FlGURE 1 is a fragmentary elevation View of a valve tappet in its engine environment;
- FIGURE 2 is a cross-sectional View of a valve tappet body; and
FlGURES 3, 4 and 5 are fragmentary cross-sectional views illustrating sequential steps in the process of this invention.
As shown in FIGURE 1 of the drawings, a valve lifter consists of a cylindrical-shaped body closed at one end 12 and open at the opposite end 13, which is slidably re- 3,103,182 Patented Aug. 3, 1965 ice ciprocable in a bore 1d of an internal combustion engine crank case 16. Within the open end 13 there is received the lower end of a push rod 18 and a push rod seat meniber 20 seated on an annular shoulder 21 of the body 10 by which thrust is transmitted between the lifter body 10 and the push rod during engine operation. Overlying the seat member 20 and the shoulder 21 there is provided a thin metal retaining washer 23. The washer is relatively exible and of somewhat greater diameter than the opening 15 so that on being radially deflected and forced against this opening, as shown, it will contract su'lciently to enable it to enter the opening. It may readily be seen that an upward movement of the rod 18 causes the washer to lock or wedge against the opening 15 and to lock the seat 20 within the valve lifter.
This invention is concerned with a method of making a lifter body 10 and in particular a method of providing the closed end 12 with an end face 2d or foot of a wearresistant material. In general the method involves first forming a cup-like member consisting of a cylinder which is closed on one end sach as is shown in FIGURE 2 by a simple upsetting or cold extrusion operation. The dies employed in this operation also provide the closed end of the valve lifter with the' peripheral ridge 26 of about 0.015 inch in height which terminates in a relatively narrow edge 28 and has an inwardly slanting side 30. This side 30 may suitably slant at an angle of about 45. The height of the ridge 26 may suitably vary from about 0.010 inch to about 0.030 inch. As will be hereinafter explained in detail, the process of this invention involves the application of a wear-resistant alloy within the cavity defined by the ridge 26.
After the upsetting operation the surfaces of the lifter between the ridge 2o are preferably grit blasted to clean them. A powdered metal mixture is next prepared which preferably consists of, by weight, 2.6% carbon, 4% molybdenum, 4% tungsten, 2.0% silicon and the balance iron. These materials are present in the form of powders preferably having a particle size which will pass a mesh screen. The powders are thoroughly mixed and then compressed under a pressure of about 30 tons per square inch into a briquette 32, FIGURE 3, preferably having a thickness of about 0.15 inch.
Suitable valve lifter working surfaces may be made in accordance with this invention by providing a briquette in which the carbon is present between about 2.0% and 3.5 by weight, the molybdenum at least 2.0% by weight, and the tungsten at least 2.0% by weight, the sum of the `molybdenum and tungsten being not greater than about 12.0% by weight, and the silicon about 1.0% to 3.5% by weight and the balance substantially iron. Preferably the retaining lipy 26 is formed about 0.02 inch in height and the briquette is maintained within a thickness range of 0.1 inch to 0.2 inch.
After the briquette has been formed, it is preferably sintered to obtain increased strength for handling efficiency and then placed within the contines of the cavity of the retaining lip 26. The briquette is preferably suiciently smaller in diameter than the valve lifter so that it rests liatly on the lifter surface within the ridge 26 as shown in FIGURE 4. Preferably a linx such as boraX is next sprinkled over the briquette. The briquette and adjacent valve lifter surface are then subjected to heat within a temperature range of about 2200 F. to 2400" F. by means of an induction coil 22 as shown in FIGURE face and the briquette. Heatingtemperatures in excess of 2400 F. may be used. However, no advantage is obtained at higher temperatures. Higher 'heating'temperatures tend to cause excessive erosion of the retaining ridge 26 and for this reason are undesirable. The heating operation causes the powdered metal to fuse to form a coating alloy 24` In this heating operation the flux pro- Y the fused coating has a composition ofabout. 2.1% 'carv bon,1.5% Vsilicon,.4.0% tungsten, 4.0% molybdenum, and .the balance iron. It will be noted that the composition kof the fused coating involves a loss of about 0.5 by Weight each of carbon and silicon. During the fusion composition. This reduces the melting point of the iron to a temperature inthe Vicinity of 2200 F. At this temperature, the tungsten and molybdenum dissolve into the molten ferrous metal. The molten alloy flowsacross the valve lifter surface so as to form a relativelysmooth coating extending betweenfthe extremities of the ridge 26. During the heating step, the alloy, and particularly the 4carbon thereof, diffuses into the steel body to form a strong diffusion bond. It Will, of course, be understood that it is the diffusion coating ranges which are essential to the high quality performance of the valve lifter of this 1 invention.` `The briquette composition may be varied to take intor account process variables which may result in a greater orlesser loss of carbon and silicon.
On completion of the fusion cyclefthe interior of the steel body is cooled rapidly, preferably by means of a,
small water jet 34 inserted Withinthe valve lifter body as shown in FIGURE 5 to promote directional solidilication ofthe coating alloy from the alloy-steel interface outward, thus preventing formation of internal shrinkage cavities in the coating. Preferably the heating operation is conducted in a protective atmosphere of nitrogen or suitable endothermic generated gas to prevent excessive oxidation of the metals during heating. After cooling, the coating is ground to a thickness Preferably in the range of about 0.01 inch to 0.03 inch and other portions of the valve lifter are ground to size. Finally, the entire valve lifter is carburized to provide the side Walls thereof with a Wear-resistant surface. This involves heating the lifter in a suitable carburization atmosphere to a temperature in the range of about 155051?. to 1650 F. As a consequence of this heating operation a carbon case is,
ran important advantage of this inventtion.
'The method of this invention has a numbef of important advantages. In addition to its excellent Wear resistance, the use of an iron base alloy briquette or coating cycle, the carbon diffuses into the iron. particles which in their original form are of a relatively pure lovv carbon 0.010V inch to 0.020 inch in. thickness. The method of this invention may be employed to apply wear-resistant coatings of any thickness and especially thin coatings with a negligible Waste of coating materials. The presence of the retaining lip 26 is Yessential in that it serves as a dam while the coating alloy is yet molten and thereby insures that the coating layer will' be of a satisfactory thickness which will extend uniformly over the entire area of the valve lifter Working surface... Although induction heating is preferred because the heating is thereby carefully controlled, satisfactory results have been obtained by heating with an-acetylene llame.
In `the preferred embodiment of the invention as described above. the valve lifter body is formed from an extrudible low carbon steel such as,l for example, SAE 1018 steel-containing about 0.15% to 0.20% carbon, 0.6% to 0.9% manganese, a maximum of 0.04% phosphorus and a maximum of V0.05% sulfur. In some instances, it may be desired to make the valve lifter of a stainless steel to provide it With resistance to corrosion. VIt has beenfound that typical hardenable stainless ysteels such as those containing 0.95% to 1.2% carbon and 16% to 18% chromium tend to harden-during the-application of the footvcoatingasdescribed above. This results in a cracking of the coating due to volume increase or transformation stresses produced in the hardening Aoperation. Howevenstainless steel valve lifters may be provided in accordance with this invention by using a non-v hardenable stainless steel such as the SAE 430 stainless steel containing about 0.172% carbon maximum and 14% to 18% chromium. The Wear-resistant coating is applied to the foot as described above. The lifter Vis then ground tosize and carburized as in the case of the low carbon steel.
While this Vinventionhas been described with vreference toV certain preferred embdiments and Conditions, it Vwill be understood'that the invention is not limited thereby and that changes and modifications will be apparent to those Vskilled in theV art VWithoutdeparting from the spirit and principles `of the invention.
We claim: 1
1.Y A valve liftercomprising a metal tubular body closed on one end thereofto form a base,`said base having a fused coating thereon comprising by Weight 1.5% to 3.0%
carbon, at least 2% molybdenum and at least Y2% tungsten, the sum of thel molybdenum and tungsten being not greater'than 10%, silicon 0.5 to 3.0% and the balance substantially iron. f f
2. A valve lifter LcomprisingV a low vcarbon steel tubular body element closed on one Vend thereof to form a base, said base having a fused coating thereon comprising by Weight 1.5% to 3.0% carbon, at least 2% molybdenum and at least 2% tungsten, the sum of the molybdenum and tungsten being not greater than 10%,(silicon 0.5 to 3.0% and the balance'substantiallyiron 3. A valve lifter comprising a ferrous metal tubular body closed at one end thereof to form a base and a wear- -resistant ferrous alloycoating on said base comprising promotes the formation of a strong diifusionbond between the coating and theA steel body. In addition the relatively high carbon content of the alloy results in carburization of the underlying steel during the fusing vprocess and thus provides a layer 36 of harder steel for supporting` theV coating Vunder high contactloads. The carburized layer 36 in the preferred embodiment is abouty 0.015 inch. Typically, this ,carburized layer is about by Weight 1.5 %to 3.0% carbon, at least 2% molybdenum and at least 2% tungsten, the sum of the molybdenum and tungsten being not greaterthan 10%, silicon 0.5 to 3.0% and the balance substantially iron, the ferrous metal base underlying said coating having a carburized layer forming a hard support for said coating. l
4. A'valve lifter comprisinganintegrally formed ferrous metal tubular body closed at one end thereof to form a'base and having a peripheral ridge projecting from said base forming .a recess and a Wear-resistant ferrous alloy coating on said base within said recess comprising by weight 1.5% Yto 3.0% carbon,'at leastV 2% molybdenum and atleast 2% tungsten,the sum of the molybdenum and tungsten being not greater than 10%, silicon 0.5% Yto 3.0% and the balance substantially iron, the ferrous metal base underlyingY said coating having a carburized layer forming a hard support for said coating.
5. A machine element having a surface resistant to Wear under high contact stress and high sliding velocity conditions comprising a ferrous metal base having a fused coating thereon forming said surface comprising by Weight 1.5 to 3.0% carbon, at least 2% molybdenum and at least 2% tungsten, the sum of the said molybdenum and said tungsten being not greater than 10%, silicon 0.5% to 3.0% and the balance substantially iron.
References Cite by the Examiner UNITED STATES PATENTS 3/32 Wetherald 29-156.7 7/51 Gippert 75-123 2/58 Bolkcom et al. 75-123 6/58 Purchas 123-90 8/58 Cobo 123-90 5/61 Carlson 29-156.7
FOREIGN PATENTS 9/58 Great Britain.
FRED E. ENGELTHALER, Primary Examiner.
KARL J. ALBRECHT, RICHARD B. WILKINSON,