US2526194A - Method of manufacturing turbine wheels - Google Patents

Description

Oct. 17, 1950 c. H BRAUCHLE 2,526,194

METHOD OF MANUFACTURING TURBINE WHEELS Filed May 22, 1947 4 Sheets-Sheet 1 Summer 1 M l Lkzaudis liBmzwIzler Oct. 17, 1950 c. H. BRAUCHLER 2,526,194

METHOD OF MANUFACTURING TURBINE WHEELS Filed May 22, 1947 I 4 Sheets-Sheet 2 Zinnentor ChandisHBrauchler W 'qa Gttornega Oct. 17, 1950 c. H. BRAUCHLER 2,526,194

um'mon OF MANUFACTURING TURBINE mans Filed May 22, 1947 4 Sheets-Sheet 3 I l/ x "Mk 7 2? Fig.4 24

F 5 a a filzandisliBrauclzler 54mm M Oct. 17, 1950 c, H, BR E 2,526,194

METHOD OF MANUFACTURING TURBINE WHEELS Filed May 22, 1947 whens-sheet 4 Snoentor Chandis HBmlwhler Patented Oct. 17, 1950 OFFICE METHOD OF MANUFACTURING TURBINE WHEELS Chandis H. Brauchler, Canton, Ohio Application May 22, 1947, Serial No. 749,703 4 Claims. (Cl. 29156.8)

Owing to the physical properties of such heat resistant alloys, it is impossible to sufficiently draw the same in forging operations to form an integral shaft upon the wheel, and it is therefore present practice to form the shaft of a different material, such as a medium carbon alloy steel, and attach this shaft to the heat resistant alloy wheel by welding.

It is present practice in the manufacture of such turbine wheels and the like to forge the wheel to finished shape from a heat resistant alloy which may contain relatively large amounts of a combination of alloys taken from a group comprising chrome, nickel, molybdenum, titanium, columbium and cobalt and a relatively small percentage of carbon.

These heat resistant alloys can not be drawn sufficiently to permit the shaft to be forged integrally upon the wheel and they can only be hardened by cold working and a relatively high percentage of reduction in the final heating operation.

It is therefore common practice to form a separate shaft from another material, such as a medium carbon alloy steel, which may be hardened by conventional heat treatment.

Under present practice the turbine wheel is made by hot forging the heat resistant alloy at about 2000 F., to substantially finished size and shape and then cold working the wheel at a temperature of not over 1250" F. to build up hardness in the wheel as it is forged to the final finished shape.

The medium carbon alloy steel shaft, which requires heat treatment t harden, is then welded at one end to the central portion of the finished heat resistant wheel, the welding temperature exceeding 2000 F. and resulting in ruining the hardness which has been built up in the finished wheel by cold working, and in putting strains therein which can not be relieved.

Obviously, if the medium carbon alloy-steel shaft is heat treated before it is welded to the wheel the higher temperature of the welding operation will also destroy the hardness in the 2 shaft, while on the other hand if the shaft is heat treated after it is welded to the wheel, this will only tend to further destroy the hardness of the wheel.

As it is thus not possible under present practice to properly harden both the wheel and the shaft, turbine wheels made in the manner above described have not proven satisfactory and will not withstand high running temperatures for any considerable period of time and in a number of cases such turbine wheels have completely disintegrated or exploded while in operation making the use of the same in jet propelled planes highly dangerous and impractical.

This invention contemplates a method of making such turbine wheel forgings in a manner formed of another material such as medium carbon alloy steel.

A further object is to provide such a wheel and shaft structure in which the wheel and shaft are formed integrally from a plural metal cast blank or ingot comprising a heat resistant alloy head portion, from which the wheel itself is forged, and a medium carbon alloy steel shaft integrally bonded therein.

A still further object is to form such a wheel and shaft forging from a plural metal cast blank or ingot having a head portion of greater thickness and less diameter than desired in the finished wheel and having a shaft portion of substantially the diameter and length required in the finished shaft.

Another object of the invention is to provide a method by which the cast ingot above referred to is forged in closed dies to forge the wheel to almost finished size and shape, the shaft being heat treated to harden the same and the wheel being cold worked to final finished size and shape in order to harden the same.

A further object is to provide such a method of forging a turbine wheel and shaft structure, or the like, in which a grain flow is developed in the wheel to give the highest strength in the finished forged wheel.

The above objects together with others which will be apparent from the drawings and following description. or which ma be later referred to, may be attained by constructing the improved turbine wheel forging in the manner here nafter described in det il and illustrated in the accompanying drawings, in which;

Figure 1 is a sectional view through a mold in which the plural metal blank or ingot may be cast, showing a shaft positioned in the mold preparatory to the casting of the enlarged head portion of the ingot or blank;

Fig. 2 a sectional view through the upper portion of the mold showing a cast blank or ingot therein;

Fig. 3 a vertical sectional view through the hot forging dies in which the enlarged head portion of the ingot is forged to nearly finished shape, showing the dies in open position with an ingot located therein;

Fig. 4 a similar view showing the dies in closed position with the wheel itself forged to nearly finished shape and dimensions at which stage all as cast structure has been eliminated by the forging operations and a grain structure has so been developed as to give the highest strength for this section of the wheel;

Fig. 5 a vertical sectional view through the cold working dies in which the wheel itself is cold worked to final finished shape and hardened;

Fig. 6 a side elevation of the finished integral wheel and shaft forging; and,

Fig. '7 a longitudinal sectional view through the finished forging showing the grain flow in the head or wheel portion thereof.

The method to which the invention pertains is applicable to the manufacture of various forgings comprising an enlarged head or wheel portion and a reduced shaft or shank portion, but for the purpose of illustration the invention is described and shown herein as carried out in the manufacture of a particular design of turbine wheel forging used in a type of gas turbine engine now being manufactured for the United States Air Forces.

The particular design of turbine wheel referred to is illustrated in Fig. 6 and comprises generally the disc-like wheel l0 having the truncated conical portions II and I2 formed on opposite sides thereof, a small central boss [3 protruding from one side of the wheel and a shaft l4 being provided at the other side thereof.

Such turbine wheels are necessarily formed of heat resistant alloys which will withstand the high running temperatures to which they are subjected, the alloys which are suitable for this purpose containing large amounts of various metals such as chrome, nickel, molybdenum, titanium, columbium and cobalt.

Two groups of austenitic materials are suitable for this purpose, one group being composed of crucible alloys such as l9-19-DL, 16-25-6 and similar heat resistant alloys which require about a 20% reduction in the final heating operation and cold working to final finished size and shape to build up hardness in the finished forging.

The other group is composed of Inconel X, N-155 containing carbon .3, chromium- 20.0, nickel 20.0, cobalt 20.0, molybdenum 3.0, tungsten 2.0, columbium 1.0, Refract-alloy and similar high temperature alloys which require close control of grain size for maximum physical properties, this grain size control being possible only by reduction of the cross section usually not less than 20% and without reheating to 1800 F. for subsequent forgings and preferably without any reheating unless followed by further reduction of 20% or more.

These forgings are commonly made from a bar blank of the desired heat resistant alloy and since the physical properties of such alloys as above referred to prohibit the drawing of the bar blank therein.

These differences in the physical properties of the two metals of which the wheel and shaft are made under present practice produce a problem in the manufacture of such turbine wheel and shaft structures, and such turbine wheels as have been made under present practice do not give satisfactory results in that they can not withstand the high running temperatures to which they are subjected for any considerable length of time.

Under present practice the heat resistant alloy turbine wheel is hammer forged from a bar blank of the heat resistant alloy, and where alloys from the first group are used, this is accomplished by hot forging the wheel at about 2000 F. with a reduction of about 20% and then cold working it at about 1250" F. to build up hardness in the wheel as it is forged to final shape.

Where the wheel is forged from alloys of the second group, a bar blank is heated to about 1800 F. and forged to partially completed shape, with a reduction of about 20% during each heat, the final forging to finished shape being accomplished without further reheating.

The shaft is formed of a medium carbon alloy steel capable of developin a Brinell hardness after quenching from the proper temperature and tempering it at a temperature about 1250" F. the temperature of the alloy steel from which the shaft is made being preferably about 1300 F.

The separate shaft of medium carbon steel is then welded to the heat resistant alloy wheel at a temperature exceeding 2000 F. ruining the hardness of the heat resistant alloy wheel and putting strains therein which can not be relieved.

If, on the other hand, the medium carbon alloy steel shaft is heat treated before the welding operation, it is obvious that this high welding temperature will destroy the hardness in the shaft while if the shaft is heat treated after the welding operation, this heat treatment requires a temperature higher than the cold working temperature of the heat resistant alloy wheel and tends to further destroy the hardness thereof.

In carrying out the method of making the turbine wheelto which the invention pertains, the shaft indicated at I4 is formed to finished size and shape from suitable material, such as medium carbon alloy steel or the like, and a blank or ingot of the desired heat resistant alloy is cast around one end portion of the shaft, the two metals being fused together in the casting process so as to form an integral blank from which the integral wheel and shaft structure may be forged.

This operation may be performed in a mold such as shown in Figs. 1 and 2 of the drawings and indicated generally at I5 therein. This mold has a cavity l6 at its upper end of the size and shape desired in the heat resistant alloy blank or ingot to be cast, there being a depending central bore I! through the mold communicating with the bottom of the cavity l6, of suitable size and shape to receive the shaft l4 and hold it in proper position with the upper end thereof extending for some distance into the mold cavity lSg-as indicated at l8.

The heat resistant alloy ingot or head is then cast within the mold cavity l6 as indicated at I!) in Fig. 2, the molten heat resistant alloy fusing with the upper end portion l8 of the shaft ll as indicated at 20 in said figure, forming an integral blank comprising the heat resistant alloy head I9 and the medium carbon steel shaft l4. By means of the knock-out in the lower end of the mold I5, indicated generally at 2!, this blank may then be removed from the mold.

This casting of the heat resistant alloy head upon the medium carbon alloy steel shaft may be accomplished by the pluri-metal process which has recently come into use, or by any other casting method which will cause the shaft and head to be fused together in an integral structure.

The forged blank thus produced by the casting method as above described comprises the shaft [4 of medium carbon alloy-steel, or the like, of the length and diameter required in the finished structure, and the cast heat resistant alloy head is of considerably greater thickness and less diameter than required in the finished turbine wheel.

The heat resistant alloys from which the turbine wheel itself may be formed contain relatively large amounts of various combinations of chrome, nickel, molybdenum, titanium, columbium and cobalt, and a very small amount of carbon. As an example of the first group of these alloys, a type of heat resistant alloy which has been successfully used for the purpose contains 16% chrome, 25% nickel, 6% molybdenum and about .08% to .12%% carbon.

Where the head I9 is formed of one of the first group of heat resistant alloys it is then hot forged in dies at a temperature of approximately 2000 F. to reduce the thickness and increase the diameter of the head [9 to form the turbine wheel itself, the reduction being at least 20% with each heat.

In order to thus reduce the thickness and increase the diameter of the head portion IQ of the blank, the same may be hot forged in the dies 22 and 23 as shown in Figs. 3 and 4. The lower die '22 has a central bore 24 communicating with the die cavity 25, of suitable size and shape to receive the finished shaft M of the blank, the cast heat resistant alloy head l9 being received in the cavity 25 of the lower die 22 and reduced in thickness and enlarged in diameter by the hammering or pressing of the upper dies 23 toward the lower die finally shaping the head as indicated generally at 26 in Fig. 4, to conform to the cavities 25 and 21 in the lower and upper dies respectively, the head being reduced at least 20% in this operation and being of slightly less diameter and slightly greater thickness than desired in the finished wheel.

The partially completed product shown in Fig. 4 is then removed from the dies 22 and 23 and the shaft I4 is heated to 1250 F. or 1300" F. and tempered and quenched to produce the desired Brinell hardness.

the procedure will be the same as above described except that the wheel is heated to about 1800 F. by forging and at least 20% reduction is accomplished byv forging during each heat, and instead of cold working to final finished size and shape,

the wheel is forged to finished size immediately after the previous forging operation in the dies 22 and 23 without reheating.

By making the integral wheel and axle structure in the manner above described, a grain flow is developed in the wheel in the first forging operation and is further developed, compressed and refined in succeeding forging operations, this grain flow conforming to the contour of the forged wheel, as shown in Fig. 7, and giving the highest strength in the wheel.

With the method above described an integral, one-piece turbine wheel and shaft is produced,- the wheel being forged from heat resistant alloys and the shaft being formed of medium carbon alloy steel or the like, the wheel being hardened by cold working thus developing the grain flow to obtain the highest physical properties required in the wheel, and the shaft being hardened by a .draw and quench operation overcoming the difliculties and objections present in common practice where the wheel is formed of heat resist-' ant alloys which can be hardened only by cold working and the shaft is formed separately of another material such as medium carbon alloy steel which is hardened by a draw and quench operation and welded to the heat resistant allow wheel.

I claim:

1. The method of making an integral wheel and shaft forging comprising a heat resistant alloy wheeland an integral shaft of other steel, which consists in forming the shaft to the desired finished size and shape, then casting a head of heat resistant alloy around one end of the shaft and fusing the shaft and head together, then heating the head to forging temperature, hot forging the head to the finished size and shape desired in the wheel, obtaining approximately a twenty per cent reduction in each heat, hardening the shaft by a draw and quench operation, and then cold working the wheel to harden the same.

The partially completed product is then forged' 2. The method of making an integral head and shank forging comprising a head portion of heat resistant alloy and a shank portion of medium carbon alloy steel, which consists informing a medium carbon alloy steel shank to the desired finished size and shape, then casting a head of heat resistant alloy around one end of the shank and fusing the shank and head together, and then hot forging the head to reduce the thickness and increase the diameter thereof, hardening the shaft by a draw and quench operation and then cold working the wheel to harden the same.

3. The method of making an integral wheel and shaft forging comprising a heat resistant alloy wheel and an integral shaft of other steel, which consists in forming the shaft to the desired finished size and shape, then casting a head of heat resistant alloy around one end of the shaft and fusing the shaft and head together, heating the head to forging temperature, hot forging the head to substantially finished size and shape, hardening the shaft by heat treating and then cold working the wheel at a temperature below the heat treating temperature of the shaft to harden the wheel.

4. The method 01' making an integral wheel and shaft forging comprising a heat resistant alloy wheel and an integral shaft of other steel, which consists in forming the shaft to the desired finished size and shape, then casting a head of heat resistant alloy around one end of the shaft and fusing the shaft and head together, then heating the head to about 2000 F. and hot forging it to substantially the finished size and shape desired in the wheel, hardening the shaft by heat treating at 1250 to 1300" F., and then cold working the wheel at 1250 F. or less, slightly reducing the thickness and slightly increasing the diameter thereof to the desired finished size and shape to harden the wheel.

CHANDIS H. BRAUCHLER.

REFERENCES CITED The following references are of record in the tile 01 this patent:

UNITED STATES PATENTS Number Name Date 1,290,529 Ellery Jan. 7, 1919 1,498,583 Spire June 24, 1924 1,607,968 spire Nov. 23, 1926 1,794,942 Boyle Mar. 3, 1931 1,880,704 Bissell' Oct. 4, 1932 2,037,340 Rich Apr. 14, 1936 2,095,055 Campbell et a1. Oct. 5, 1937 2,134,670 Parsons Oct. 25, 1938 2,398,702 Fleischmann Apr. 16, 1946 2,432,616 Franks et a1 Dec. 16, 1947 2,447,897 Clarke Aug. 24, 1948 2,453,598

Schaei'er Nov. 9, 1948

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