US2124459A - Method of heat treating metals - Google Patents

Description

July 19, 1938. Q O, BURGESSA )2,124,459

METHOD A0F HEAT TREATING METALS Filed May 4, 1953 2 Sheets-Sheet vl INVENTOR l H5/g55 0 5W/9655s ATTORN EY July 19, (1.o. BURGESS 2,124,459

METHOD OF HEAT TREATING METALS .l Filed May 4, 1933 2 Sheets-Sheet 2 Jil INVEN TOR @www O, 50296555 M@ LW ATTORN@ the case satisfactory Patented July 19, 193s PATENT OFFICE Marnon or HEAT Tammo METALS.

Charles O. Burgess, New York,

N. Y., assignor, by

mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application May 4, 1933, Serial No. 669,292 15 Claims. (Cl. 148-21) This invention relates to methods of heat treating metals. More particularly this invention relates to an improved method of forming a case hardened surface on steel and alloy crank-shafts 'and on other cylindrical, conical or similar objects, such as shafting and trunnions.

Numerous methods have been devised for producing hardened surfaces on various steel and alloy objects such as shafting, valves, wheels, rails, gear teeth and other metal parts subject to severe wear. The early method of rotating the object and heating at one point on the surface while simultaneously quenching at a point on the heated area has not been found to be entirely on account of the annealing effect which occurs Where the heating fiame completes the end of one revolution of the object and overlaps onto the area that has been quenched and previously hardened. Even with careful manipulation of the heating flame a joint or line of softer material appears where the annealing takes place and a narrow axial annealed zone is the result.

Some oi the disadvantages of these prior methods have been overcome by the process disclosed in Patent No. 1,759,603 in which valves are case hardened while rapidly rotating in the chuck of a drill press, the heat being supplied by an oxy-acetylene blowpipe or an electric arc and quenching being accomplished by lowering the valve into a bath. Patent No. 1,536,416 also discloses a method of heat treating an object by directing a flame against the periphery during rotation and by cooling in the open air. However or layer bf hardened surface metal resulting from these methods and other methods previously known has not been entirely uniform.

An object of this invention is therefore to provide a method for producing a uniform, case hardened surface on cylindrical, conical or other similar metallic bodies. Another object of this invention is to provide a method for producing a uniformly hard surface cn the trunnions of crankshafts. These objects and others together. with the novel features of this'invention will 'be apparent from the following description and the accompanying drawings, of which Fig. 1 is a view of a crankshaft as set up in a lathe in position for, heat treatment;

Fig. 2 is a view of one form of apparatus adapted to carry out the method of this invention;

Figs. 3, 4, 5, and 6 are end vi shown in Fig. 2;

Fig. 7 is a view of another form of blowpipe ws of the blowpipe apparatus also adapted to carry out the method of this invention;

Figs. 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17 are end views of the blowpipe apparatus shown in Fig. 7; and

Fig. 18 is a side View of the blowpipe apparatus shown in one operating position relative to a cylindrical object.

In accordance with this invention an object to be heat treated, such as a crankshaft C may be set up in a lathe A or in similar apparatus adapted to rotate the object. A blowpipe B is employed to raise the temperature of the object C to the critical range for hardening while being held in any suitable manner at a short distance from the sur- 15 face to be heat treated.

During the preliminary heating of the object C to the critical range of temperature prepara-tory to sudden quenching, the speed of rotation of the object C may be regulated so as to obtain uniform heating of the entire surface exposed to the vblowpipe flame or ames. With the majority of carbon steels and alloy steels it has been found that a speed of 120 R. P. M. is a satisfactory rate of revolution during both heating and quenching, but other speeds may be employed. When the speed of rotation is sufficiently great there will be no signicant temperature diderence between Aany two circumi'erentially separated points on the surface of the object. Heat is applied long enough to obtain the required surface temperature and depth of hardening. The surface hardness and depth of hardness may be varied at will by regulating the quantity and rate of heat application, as by using different sizes of ames or a multiplicity of ames. When the proper surface temperature or hardening temperature has been reached, the blowpipes or sources of heat are removed and immediately a duid quenching medium is applied to the surface of the rotating object, thus obtaining uniform quenching conditions around the periphery of the object.

The preferred method of quenching is by means of a jet of water having an appreciable velocity head for breaking through any protecting steam envelope which may form around the object during the quenching action. An effective and thorough cooling of the object may be thus obtained so that the hardened area is substantially of the same measured renitence at all points around the periphery. When water or other suitable quenching medium is directed under pressure against the object to be hardened, the quench occurs immediately and nearly simulta- 55 face.

Ineously over the entire areaunder treatment as the object is maintained in rotative movement.

The depth of the hardened surface, or the socalled case, may be varied by changing the length of the interval of subjecting the object to heat after the critical temperature of the metal has been reached. On longer application of heat to the surface the temperature is -raised beyond the critical point to a considerable depth beneath the surface of the object, and when the object is quenched, the sudden chilling causes hardening to the desired depth.

As disclosed and claimed in my copending divisional application, Serial No. 104,660, filed October 8, 1936, a blowpipe has beenv devised which is especially adaptable to the case hardening o'f cylindrical or conical objects, such as shafting or the journals 4and bearing surfaces of crankshafts. Such a blowpipe may comprise a head 20, as shown in Fig. 2, for receiving mixed combustible gases and for delivering these gases to a plurality of tips or nozzles 2| supported in the head. The nozzles 2| are readily removable from the head and, as shown in Figs. 4, 5, and 6,

plugs 22 may be substituted for certain of the nozzles, depending on the shape of the object to be heat treated. v

Where the object to be hardened has free ends, as a short shafting, or roller bearing, all of the nozzles 2| are preferably left in the head 20 with the exception of those in the four corners, which are removed and replaced by plugs 22. as shown in Fig. 3. A full sheet of name will thus be produced which has slightly less intensity at the ends than at the center in order to offset the effect of conductance at the center area of the bearing, where heat is dispersed into the body of the bearin-g more rapidly than at the ends. In the case of small objects, such as short roller bearings, ladditional nozzles areblocked oi, as shown in Fig. 4, so that more heat is directed against the central area than at the ends. When the temperature-'is raised substantially equally at'all points of the object .being heat treated, the hardened area produced by quenching will be uniformly renitent.

The trunnions of crankshafts are bordered at.

each end by cheeks, and for that reasonare best heat treated by applying more heat nearthe ends than at the center. The nozzles of the blowpipe 20 are blocked olf, as in Fig. 5, leaving a row of tips at each end and a single row laterally across the face of the blowpipe. The additional heat supplied at the ends of the trunnion is absorbed by the cheeks of the crankshafts so that the surface of the trunnion is brought to the critical range of temperature at all points f the sur; In hardening the ends of bodies having surfaces of rotation, such as shafting, an arrangement of tips, as shown in Fig. 6, may be made whereby nozzles are plugged oi at the end of the blowpipe which is adapted to direct flames to the free end of the shafting'.

As further disclosed and claimedin my cc-l pending divisional application, a blowpipe may be employed which comprises a multi-unit head, as shown in Fig. 7. Any convenient number of gas distributing heads 30, preferably three, may beassembled in close relation with one another, being adjustably supported bya. block 3|. Each head has oneor more outlets into which are screwed or otherwise secured a-corresponding number of blowpipe nozzles 32.' Gas conducting and water cooling conduits 31 and 38 respectively are connected with each of the headsv 3|) and are shieldedy by larger conduits 33 which lead through a slot 34 in the block 3|. In order to allow the heads 30 to be positioned in various arrangements for heating objects of different shape, the conduits 33 are movable sideways along the slot 34 and vertically through the slot. Nuts 35 and 36 threadedly engage the conduits 33'and lock the conduits against the block 3|.

when the desired arrangement of the heating heads 3has been` obtained.

Any one, two or all three of the heads 30 may be used in heating objects to Ue case hardened. An arrangement of the heads with two withdrawn and the gas supply to these heads shut off as shown in Fig. 8, is suitable `for heating objects of short altitude or of -small diameter. Objects having greater diameters may be heated by two or three of the heads, as shown in Figs. 9 and 10, and objects of greater length may'be best heated by two or three of the heads arranged end to end, as in Figs. 11 and l2. When only one end of the object tobe heat treated is free and the other end is attached, the heads may be arranged, as in Fig. 13, 14, or 15, with one or two of the heads at right angles to the object.` If the object is free at the ends and attached'at the middle, the center head only'may be positioned at a right angle to the work, as shown in Fig. 16, and if both the ends are attached, then the heads at each end may be arranged at right angles to the work, as shown in Fig. 17.

The heads 360i the adjustable apparatus may be arranged in any convenient manner with respect to the axis of the object to be heated. However for treating cylindrical objects, as shown in Fig. 18, the heads 30 are preferably aligned parallel with the axis of the object and the center head is retracted for a short distance so that heat of equal intensity is produced on the surface of the object by the jets from all three of the heads. 'I'he center head may be adjusted to conform with larger or smaller radii of differently sized objects, and the distance between the nozzles of the heads and the surface of the object may be maintained so as to eifectively utilize the heat produced.

It will be appreciated that the multi-unit blowpipe is adaptable to -heat objects of many dif,

ferent sizes and lengths by changing the arrangement of the nozzle-bearing heads.. Such changes arc readily effected by loosening the nuts 35 and 36 and by moving the conduits 33' to changed positions with respect to the block 3|.

Although more than one embodiment of this invention has been described and illustrated, it should be understood that other changes may be made without departing from the scope of this 2. A method of heat treating a roller bearing.

which comprises `rotating the bearing; applying a varying source o f high temperature heat to the surface of the bearing, said high temperature heat being of greater intensity at the middle portion of the bearing where heat is conducted away most rapidly; raising the temperature of the surface of the bearing uniformly to the critical range; and quenching the heated surface while still rotating by directing a jet of cooling medium against said bearing.

3. A method of heat treating the end portion of an object having a surface of rotation which comprises rotating the object about the axis of said surface; applyingfa varying source of high temperature heat to the surface of the object at said end portion, said high temperature heat being of less intensity toward the free end and of greater intensity toward the attached end of the portion under treatment; raising the temperature of the surface of the object at the end portion uniformly to the critical range; and quenching the heated surface while still rotating by directing a.y jet of cooling medium thereon.

4. A method of heat treating a metallic body of which the cross-section is circular but the outline is irregular which comprises rotating said body about its axis at a relatively high speed, uniformly heating the surface of said body to the required temperature and depth by applying thereto during rotation a heat source of which the shape and-intensity are such as to fit and compensate for differences in heat conductivity of various portions of said body due to the irregular' outline thereof, and thereafter quenching said body.

5. 'I'he method of heat treating a metallic body of a circular diametrically varying cross-section which comprises the steps of rotating said body about its axis, heating simultaneously each longitudinal portion of the surface of said body by applying thereto a heat source varying in intensity in accordance with the heat conducting properties of each of said portions so as to heat the entire surface of said body uniformly to the desired temperature, and thereafter quenching such heated surfaces during continued rotation of said body.

6. The method of heat treating the end portion of a circular body which comprises the steps of rotating said body about its axis, heating simultaneously each longitudinaly portion of the surface of said end portion by applying thereto a heat source varying in intensity in accordance 'with the heat conducting"`properties of each of said portions so as to heat the entire surface to be treated uniformly to the desired temperature, and thereafter quenching such heated portions during continued rotation of said body.

7. A method of hardening a surface of a metallic body, which comprises applying high temperature heat to said surface While rotating said body at a relatively high speed to rapidly move said surface relatively to the high temperature heating means; discontinuing the application of such heat when said surface has been heated to a predetermined high temperature; and thereupon, and while said body continues to rotate, directing ajet of cooling uid against such heated surface to quench the same.

8. A method of hardening a surface of a metallic body, which comprises applying high temperature heat to said surface while rotating said body at a relatively high speed to rapidly move said surface relatively to the high temperature heating means; discontinuing the application of such heat when said surface has been heated to a predetermined high temperature; and thereinto said cheeks will be compensated for upon, and while said body continues to rotate,

quenching such heated surface by directing against the same a cooling water jet of sufficient velocity to break through any steam envelope which may form on said surface during such quenching.

9. .A method of substantially uniformly hardening a surface of a metallic body having portions differing in their capacity to hold heat, such method comprising applying high temperature heat to said surface while rotating said body at a relatively high speed to rapidly move said surface relatively to the high temperature heating means; so adjusting the amount of heat applied by such heating means relatively to the differing heat-holding'capacity of said body that said surface is substantially uniformly heated to a predetermined high temperature; discontinuing the application of such heat when said surface has been heated to such predetermined temperature; and thereupon, and While said body continues to rotate, directing a jet of coolingr fluid against such heatedsurface to quench the same.

10. A method of substantially uniformly hardening a surface of a metallic body having portions differing in their capacity to hold heat, such method comprising applying high temperature heat from a localized source to said surface While rotating said body at a relatively high speed to rapidly move said surface relatively to such source of high temperature heat; so adjusting said source that the amount of heat applied thereby relatively to the differing heat-holding capacity of said body will be such that saidsurface will be substantially uniformly heated to a predetermined high temperature; discontinuing the application of such heat when said surface has been heated to such predetermined temperature; and thereupon, and while continuing such rotation of said body, quenching such heated surface by directing against the same a cooling Water jet of sufcient velocity to break through any quenchretarding steam envelope that may form on said surface during such quenching.

. ll. A method of hardening a surface of av metallic body having a portion adjacent a boundary of said surface which Will tend to cause heat to be removed at a faster rate by conduction from such boundary 'than from the central part of said surface, such method comprising applying a high temperature heating medium directly to said surface and in such a manner as to concentrate heat at such'boundary so that the entire surface to be hardened will be heated uniformly to a temperature at or above the critical range and ow of heat by conduction to the portion adjacent the boundary will be compensated for; discontinuing the application of said heating medium; and subsequently cooling said surface so as to harden the same.

12. A method of heat treating a trunnion between cheeks of a crankshaft, said cheeks tending to remove heat by conduction at a faster rate vfrom the ends of the surface of said trunnion than the rate at which heat is conducted from the remainder of the surface of said trunnion, such temperature heat tosaid trunnion, said high tema greater amount of heat to one portion of the surface of saidtrunnion than to another; so adjusting the amount of heat applied by said source so as to apply a greater amount of heat adjacent said cheeks in order that the conduction of heat and the perature source of heat being adapted to supply cheek to cheek, said trunnion having an interior composed of tough unhardened metal having the same chemical composition as said hardened surface portion.

14. A method of substantially uniformly hardening a surface of a metallic body having portions differing in their heat-holding capacity and a portion adjacent a boundary of said surface which will tend to cause heat to be removed at a faster rate by conduction from such boundary than from the central part of said surface, such method comprising applying a high temperature heating medium directly to said surface so as .to concentrate heat-at such boundary and in such a manner relatively to the differing heat-holding capacities of said portions so as to heat said surface uniformly to a predetermined high temperature; moving said surface and said high temperature heating medium relatively with respect to each other at a relatively rapid rate and in such a manner that said 'surface is traversed by said heatin medium a plurality of times; discontinuing the application of said heating medium; and subsequently cooling said surface so as to harden the same. l5. A method of substantially uniformly hardening asurface of a metallic body having portions differing in their heat-holding capacity in one direction of said surface, such portions including a portion adjacent a boundary of said surface which willtend to cause heat to be removed at ajfaster rate by conduction from such boundary than from the central part of said surface, such method comprising applying a high temperature heating medium directly to said surface in such a manner as to concentrate heat at said boundary and also in such a manner relatively to the differing heat-holdingcapacities ofsaid I portions so as to compensate for the differences in heat conduction; effecting a relative movement between said heating medium and saidsurface in a direction substantially transversely to said first-mentioned direction and in such a manner thatl said surface is traversed by said heating medium a plurality of times; discontinuing the application of said heating medium; and subsequently cooling said surface so as to harden the same. l.

CHARLES O.

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