US3286704A

US3286704A - Engine valve

Info

Publication number: US3286704A
Application number: US434159A
Authority: US
Inventors: Louis J Danis
Original assignee: Eaton Yale and Towne Inc
Current assignee: Eaton Corp
Priority date: 1964-01-10
Filing date: 1965-01-13
Publication date: 1966-11-22
Anticipated expiration: 1983-11-22

Description

Nov. 226, 1966 J. DANls 3,286,704

ENGINE vALvE original Filed Jan. 1o, 1964 INVENTOIL- United States Patent O 3,286,704 ENGINE VALVE Louis J. Danis, Battle Creek, Mich., assignor to Eaton Yale & Towne Inc., a corporation of Ohio Original application Jan. 10, 1964, Ser. No. 337,064. Divided and this application Jan. 13, 1965, Ser. No.

2 Claims. (Cl. 123-188) This application is a division of copending application, Serial No. 337,064, filed January 10, 1964, by Louis I. Danis for Engine Valve and Method of Making Same.

The present invention relates to .an improved method of making an engine valve and more particularly to an improved process for forming poppet-type valves of the type used in internal combustion engines employing ia ductile low-carbon steel which facilitates the formation by cold forging and/ or extrusion relatively intricate valve configurations followed by a subsequent preliminary machining and case hardening treatment and thereafter a final machining operation resulting in a valve having excellent performance characteristics and which is substantially simpler and more economical to manufacture.

Poppet-type valves for use in internal combustion engines, .and particularly intake poppet valves of the type employed in automobile engines have heretofore been made employing medium and high-carbon alloy steels by either cold or hot forging techniques. While this manufacturing technique has been satisfactory for most purposes, a continuing problem .associated with these processes has been the difculty and lack of versatility in forming intricate valve shapes under cold-forming conditions. In addition, medium and high carbon alloy steels of the types conventionally employed necessitate more complex tooling and produce .a greater tool or die wear rate resulting in increased tooling costs and in frequent down time for tool replacement. A further problem associated with the processes heretofore -known has been the limitation imposed by medium `and high-carbon alloy steels on the rate of production of valves due to the difficulty of forming and machining the material. In .addition to the problems associated with the manufacture of such valves by the processes heretofore known, the valves themselves have been found to be of less than optimum fatigue life and Wear resistance particularly in view of the increased design performance of modern internal `combustion engines.

It is accordingly .a principal object of the present invention to provide an improved method of making poppet-type engine valves and to an improved valve made by the process which overcomes the problems and dis- Iadvantages associated with technique heretofore employed.

Another object of the present invention is to provide an improved process for the manufacture of poppet-type engine valves employing a low-carbon steel which provides for substantially increased versatility and flexibility in obtaining intricate configurations and forms at room temperature while additionally providing for substantially increased production rates.

Still another object of the present invention is to provide an improved process for forming poppet-type engine valves employing a low-carbon steel which enables the use of simpler tooling and further reduces Wear on the tools providing greater die life with corresponding reductions in production down time and improved manufacturing efficiency.

A further object of the present invention is to provide an improved process and an improved poppet-type er1- gine valve manufactured thereby which is more economical .and simpler to manufacture, and which possess superior fatigue life and improved wear resistance over 3,286,704 Patented Nov. 22, 1966 ICC similar type valves made of medium and high-carbon alloy steels.

The foregoing and other objects and advantages of the present invention are .achieved by a process employing a low-carbon steel which can be r-apidly cold forged into any one of a variety of suitable shapes followed thereafter by a preliminary machining Iand a case-hardening operation after which the case-hardened rough machined valve is subjected to a final finishing operation providing the requisite dimensional vaccuracy of the valve. It is .also contemplated within the scope of the present invention that the original bar stock employed for cold forging may be annealed to increase its ductility and may also be annealed subsequent t-o the cold forging operation if desired to remove any undesirable residual stresses therein. It is further contemplated that the case-hardened valve blank can be drawn after the case-hardening operation land can be further subjected to a flame-hardening operation of the valve stem tip to provide a hard tip surface resistant to Wear by an operating push rod, cam follower, or rocker arm disposed in contact therewith.

Other objects, features and advantages of the present invention will become apparent from the subsequent description, taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic flow diagram illustrating the necessary operating steps as Well -as optional steps which .are employed in accordance with the practice of the improved process comprising the present invention;

FIGURE 2 in a side elevational View of a bar stock blank employed in subsequent cold-forming operations to form a finished valve;

FIGURE 3 is a side elevational view of the blank after .an initial cold-extrusion operation; yand FIGURE 4 is ya side elevational view of the resultant cold-forged valve blank prior to machining and case hardening.

The steel raw material used for forming the valve body may comprise any cold formable grade of low-carbon or low-alloy steel which is susceptible to case hardening such .as by lcarbonitriding or carburizing including steel having a carbon content ranging from 0.03% to about 0.6%. Carbon contents in a range of from about 0.08% to about 0.25% are prepared for maximum workability of the material as may be required in the most complex forming operations. In addition to the carbon constituents in the steel, the steel may further contain in addition to conventional quantities of impurities, up

to about 5% of intentional alloying elements employed in standard S.A.E. steel grades including alloying constituents such as nickel, manganese, chromium, molybdenum, boron, silicon, vanadium, ete.

The specific composition of the steel or low-alloy steel' -v can be varied Within the aforementioned definition to provide a resultant steel having .a degree of ductility sufficient to enable cold-formation of the steel blanks into Ia valve of the desired configuration. Accordingly, where relatively complex configurations of the valves are required necessitating a correspondingly greater degree ofi deformation of the blanks, the composition of the steel is controlled so as to provide the requisite ductility. Similarly, where a valve configuration necessitates less drasa slightly lower degree of ductility while nevertheless providing for satisfactory deformation of the blank toA the final configuration.

A steel which has been found eminently as satisfactory in accordance with the practice of the present inventionv comprises a fully annealed S.A.E. 1018 steel which has a suiiicient degree of ductility to enable cold deformation of the blank into poppet-type valve configurations of the most complex configuration presently employed in cornmercial automobile engines. The composition of an S.A.E. 1018 steel typically includes 0.l5-0.20% carbon, G60-0.90% manganese, 0.04% maximum phosphorus, 0.05% maximum sulfur, and the balance iron. Typical properties of a fully annealed S.A.E. 1018 steel are as follows:

Physical properties Yield strength, p.s.i. 30,000 Tensile strength, p.s.i 55,000 Elongation (percent to inches) 45 Reduction of area, percent 70 Brinell hardness 100 In order to employ a steel blank having the requisite degree of ductility, it is frequently desirable to subject the raw bar-stock material from which sheared blanks are cut to a complete, or partial spheroidization, or a simple subcritical annealing treatment prior to the cold-forming operation consistent with the composition of the steel, the degree of work hardness to which it has been subjected in the rolling mill, and the degree of deformation to which it is to be subjected consistent with the configuration of the valve to be manufactured. Maximum ductility of a steel blank requires complete spheroidization. A partial spheroidization or a simple subcritical annealing treatment is frequently satisfactory while in many instances no annealing treatment at all can be employed to provide a steel blank of the requisite ductility.

With reference to FIGURE l, a schematic flow sheet of the several process steps are diagrammatically indicated wherein the bar stock as received can be sheared to the appropriate length forming blanks that can be directly cold forged or alternatively the bar stock either prior to or after shearing can be subjected to an intervening annealing treatment as indicated by the dotted lines. In either event the steel blanks having a requisite degree of ductility is subjected to a cold forming operation which may comprise a single or multiple extrusion and/or cold forging operation to produce a valve blank of a configuration corresponding closely to that of the final machined valve. A typical sheared cylindrical blank indicated in FIG. 2 may for example be subjected to a cold extrusion operation wherein the stem portion of the valve is formed providing an extruded blank indicated at 12 in FIG. 3. The extruded blank 12 may thereafter be subjected to a second cold-forging operation such as a coinupsetting operation forming a valve blank indicated at 14 in FIG. 4 of a configuration corresponding substantially to that of the finished valve. The extrusion and cold forg- -ing of the steel blank 10 can be facilitated by subjecting the steel blank to a preliminary phosphating treatment forming a porous phosphate coating on the surfaces thereof which is thereafter coated or impregnated with a suitable drawing lubricant to increase the ease by which the blank is extruded and cold forged to the final shape. The use of such a phosphate coated surface is not critical to the practice of the present invention but constitutes a preferred practice particularly when the blank is to be subjected to a relatively drastic deformation.

The cold deformation of the blank either in a single or in a multiple forming operation can be achieved by any one of a variety of extrusion and/ or cold upset forging operations of the types well known in the art. By virtue of the relatively high degree of ductility of the blank, the forming operation can be achieved at rates substantially greater than those heretofore possible employing medium and high carbon alloy steels which additionally require in many instances a heating of the blank to an elevated temperature to facilitate physical deformation thereof. In accordance with the practice of the present invention the deformation of the steel blank is achieved in the cold or at a temperature below the recrystallization temperature in press equipment of the same type conventionally employed for hot forging operations.

The resultant valve blank 14 as illustrated in FIG. 4 may thereafter be directly subjected to a straightening and machining operation to provide a valve slightly oversized from its finished dimensions or alternatively can be subjected to an intervening optional annealing treatment as indicated by the dotted lines in FIG. 1. The annealing treatment is desirable for the purposes of relieving some of the residual stresses inherent in the valve blank as a result of the cold-forming operation. While very high levels of residual stresses are permissible in the forged valve 4blank it is important that such stresses are symmetrically distributed so as to avoid warpage and dimensional distortion of the valve blank during subsequent case-hardening operations. Under situations where the Valve blank has substantially symmetrical residual stresses therein and intervening annealing treatment between the cold forging and machining operation is not required. Since distortion of the valve blank during the case-hardening operation necessitates an increased degree of final machining of the case-hardened valve, it is desirable in many instances to subject the cold-forged valve blank to an annealing operation. The annealing treatment is performed for the purpose of assuring dimensional stability and freedom from warpage of the machined valve when subjected to the heat in the case-hardening such as carburizing or carbonitriding, for example.

The valve blank whether or not subjected to an intervening annealing treatment is thereafter subjected to a straightening operation so as to position the valve head `substantially perpendicular to the axis of the stem followed lby a machining operation in which the stern, tip, head, and face of the valve lare machined to within `several thousands above the iina-l finish dimension of the valve. At the completion of the straightening and machining operation the valve is thereafter subjected to a case-hardening treatment to provide ia hard surface layer on the surfaces thereof to increase its wear resistance. The depth of the hardened case can be varied consistent with the intended end use of the valve and the amount of metal that must be removed during the fina-l machining operation to provide `a valve of the desired iinish dimensions. Conventionally for intake valves employed in automobile internal combustion engines, a case-hardening depth in the finished valve of about 0.010 inch provides for satisfactory operation whereas a medium depth 1case hardening of about 0.030 inch .is preferred. Case hardening of the valve to a depth greater than about 0.30 inch does not detrimentally effect the performance and operating life of the valve and generally is not necessary due to the added cost of providing such an increase depth. The presence of a controlled case-hardened surface of a depth of :at Ileast 0.010 inch around the ductile core comprising a low :carbon or low alloy steel of the type hereinbefore Iset forth provides for valve performance characteristics superior to those heretofore obtained from valves of medium rand high carbon alloy steels.

The type of case hardening and the degree of case hardening achieved will also vary consistent with the intended end use of the valves. In many cases it is necessary that only the valve tip indicated at 16 in FIG. 4 be fully hardened to a martensitic structure while unhardened pearlitic structures may be suitable to provide suitable stem and -seat abrasion resistance in conventional automobile internal combustion engine use. For most engine applications, 1a valve made in laccordance with the present process having a Rockwell hardness on the C-scale (Rc) on the valve tip of about 50 or more and on the other surfaces of the valve of about 20 Rc or more lprovides for satisfactory operation yand high resistanc'e to wear. Since `a full martensitic struct-ure has a hardness in the range of about 50 to about 60 Rc units, a hardness in the va-lve tip of at least `about 50 Rc can lbe achieved either during the primary case hardening aesavoa operation or during la secondary localized case hardening of the tip itself such as for example by subjecting it to 1a flame-hardening treatment step as schematically illustrated in FIG. 1. Intake valves made from a type 1018 steel in accordance with the present invention having `a case depthu ranging from about 0.015 to 0.020 inch of a hardness of about Rc 30 on the face and stem thereof `and a hardness of about Rc 60 on the valve tip achieved by :a subsequent llame-hardening treatment have been found to provide excellent operating characteristics.

The case hardening of the valve surfaces may be achieved by any one of the conventional case hardening techniques including carbonitriding, carburizing, cyaniding, nitriting, induction hardening, flame hardening, and the like. In either event, the resultant valve is case hardened under conditions sufficient to provide a case hardened depth of at least about 0.010 inch of a 4hardness of at least Iabout Rc on the general surfaces of the valve and a hardness of at least about Rc 50 on the valve tip.

In carburizing, carbon is introduced into the surface portion of the machined valve blank by holding the valve -above the temperature at which austenite begins to form while in contact with a suit-able carbonacious material which may either be in a solid, liquid or gaseous form. Alternatively, the machined valve blank can be subjected to a cyaniding treatment whereby carbon and nitrogen rare introduced into the peripheral portions of the valve by maintaining it above the temperature at which austenite begins to form in contact with a molten cyanide of suitable composition. In carbonitriding, both carbon and nitrogen Iare introduced into the peripheral portions of the machined valve blank by heating it above the temperature at which austenite forms in an atmosphere that contains suitable gases such as hydrocarbon gases, carbon monoxide, and ammonia. In both llame hardening and induction hardening, the material is hardened by heating it above a preselected temperature and thereafter quenching it, form-ing a molecular structure of substantially increased hardness. In either event, the particular conditions and the duration of the case hardening operation are controlled so as to produce a hardened valve surface of a hardness and of a depth as heretofore set forth.

The heated valve blank removed from the case hardening operati-on is thereafter cooled in a manner so as to minimize warpage of the case-hardened blank. The specific cooling process employed such as air cooling, or quenching in a liquid such as oil, for example followed thereafter by air cooling will vary depending on the intensity and nonuniformity of the streses in the valve body which establish its tendency to warp during the cooling step.

At the completion of the case-hardening treatment, the case-h-ardened valve blank may be rsubjected to a drawing or tempering operation if desired to further modify the hardness characteristics of the case to within the limits hereinbefore set forth. The case-hardened valve blank, whether or not subjected to =an intervening drawing operation, may also be subjected to a localized hardening treatment ysuch as a llame hardening of the tip if the typ'e :and Iposition of the principal case-hardening treatment produced a tip hardness below labout Rc 50. Under such conditions a localized heat treatment of the valve tip and also of the face of the valve as indicated at 18 in FIGURE 4 if desired, may be accomplished so as to provide the requisite hardness characteristics consistent with its intended end use. The resultant valve is thereafter subjected to a final machining operation in which the ste-m, tip, head, and valve fa-ce are ground or otherwise machined to the final dimensional configuration and degree of surface finish.

In order to further illustrate the process comprising the present invention the following example is provided. It will be understood that the specific steps and the conditions =as set forth in the example are provided for illustrative purposes and are not intended to be limiting of the invention as set forth in the subjoined claims.

EXAMPLE A raw cylindrical bar stock having a nominal diameter of Vs inch consisting of S.A.E. 1018 mercant quality steel 'was sheared into blanks as illustrated in FIGURE 2. These banks were thereafter subjected to a spheroidizing annealing treatment at 1400 F. for a period of one hour and `at 1250 F. for a period of 16 hours after which the blanks were furnace cooled to 1000 F. and thereafter air cooled. The annealed blanks were thereafter descaled and provided with a phosphate coating on the surfaces thereof which was impregnated with a lubricant and subjected to a two-blow cold forging operation. A resultant valve blank of the general configuration shown in FIGURE 4 was produced where thereafter was roll straightened to orient the head substantially perpendicular to the stern.

The valve blanks thereafter were subjected to a preliminary machining operation wherein the stems were ground to about 0.006 to about 0.007 inch over nish diameter and the heads and seats were turned to about 0.008 to about 0.009 -inch over finish dimensions. The length of the valve blanks were ground .0.002 inch over the nish dimension. The machined valve blanks were thereafter racked and subjected to carbonitriding at a temperature of 1580 F. for one hour and forty-live minutes having an ammonia .atmosphere of from 5 to 6% and a dew point of 30 F. The carbonitrided valve blanks were thereafter further cooled to 800 F. and oil quenched to room temperature. The resultant carbonitr-ided valve banks had a case hardness of about 25 Rc and were thereafter subjected =to a second machining operation wherein the stem was semi-iinish ground and the tip was Iflame hardened with acetylene to a hardness in the range of about 55 to 60 Rc. At the completion of the llame hardening treatment, the stem end, the seat and the stem of the valve were finish ground to the final finish dimensions.

Valves made in accordance with the process as described in the specification and as illustrated in the example have been found to provide very satisfactory operating conditions in conventional commercial automobile internal combustion engines and have been found moreover to provide for a substantial improvement in the simplicity and in the economy of valve manufacture over techniques heretofore known in the art.

While it will be apparent that the preferred embodiments herein illustrated are Well calculated to fulfill the objects `above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. A poppet-type engine valve comprising a head portion integrally affixed to an elongated stem portion terminating in an integral tip, the core of said valve body consisting of a metal selected from the group consisting of carbon steel and low-alloy steel containing from about 0.03% to about 0.60% carbon -and up to about 5% of intentional alloying constituents, said core having a case hardener surface therearound extending inwardly to a depth of at least .about 0.010 inch and having a surface hardness of at least about 20 Rc on the stem and the face of said valve head and a hardness of .at least about 50 Rc on said tip of said stem.

2. A poppet-type engine valve comprising a head portion integrally affixed to an elongated stem portion terminating in an integral tip, the core of said valve body consisting of a Itype 1018 steel, said core having a case hardened surface therearound extending inwardly to a depth of at least about 0.010 inch and having a surface hardness of at least about 20 Rc on the stem and the 7 face of said valve head and a hardness of at least about 2,436,928 50 Rc on said Itip of said stern. 2,745,777 2,865,359 References Cited by the Examiner 3,028,479 UNITED STATES PATENTS 5 3,124,869 1,393,726 10/1921 Pfanstiehl 123-188 1,788,281 1/1931 De Vries 123-188 1,850,953 3/1932 Armstrong 123-188 Kempe 123-188 Clarke 123-188 Newton et a1. 123-188 Tauschek 12'3-188 Behnke et al. 29-156.7

MARK NEWMAN, Primary Examiner. AL LAWRENCE SMITH, Examiner.

Claims

1. A POPPET-TYPE ENGINE VALVE COMPRISING A HEAD PORTION INTEGRALLY AFFIXED TO AN ELONGATED STEM PORTION TERMINATING IN AN INTEGRAL TIP, THE CORE OF SAID VALVE BODY CONSISTING OF A METAL SELECTED FROM THE GROUP CONSISTING OF CARBON STEEL AND LOW-ALLOY STEEL CONTAINING FROM ABOUT 0.03% TO ABOUT 0.60% CARBON AND UP TO ABOUT 5% OF INTENTIONAL ALLOYING CONSTITUENTS, SAID CORE HAVING A CASE HARDENER SURFACE THEREAROUND EXTENDING INWARDLY TO A DEPTH OF AT LEAST ABOUT 0.010 INCH AND HAVING A SURFACE HARDNESS OF AT LEAST ABOUT 20 RC ON THE STEM AND THE FACE OF SAID VALVE HEAD AND A HARDNESS OF AT LEAST ABOUT 50 RC ON SAID TIP OF SAID STEM.