US1697470A

US1697470A - Method of casting gears or the like of manganese steel with soft-iron centers

Info

Publication number: US1697470A
Application number: US140089A
Authority: US
Inventors: Walter H Nourse
Original assignee: Electric Steel Foundry Co
Current assignee: Electric Steel Foundry Co
Priority date: 1926-10-07
Filing date: 1926-10-07
Publication date: 1929-01-01
Anticipated expiration: 1946-01-01

Description

1,697,470 E O LIKE OF MANGANESE ERS 2 Sheets-Sheet 1 gnventov W. H. NOURS TING GEARS OR THE EEL WITH SOFT IRON CENT Filed (kit. 7, 1926 METHOD OF CAS ST Jan. 1, 1929.

Jan. 1, 1929. 1,697,470

W. H. NOURSE METHOD OF CASTING GEARS OR THE LIKE 0F MANGANESE STEEL WITH SOFTIRON CENTERS Filed Oct. 1926 2 Sheets-Sheet 2 Patented 1, 1929.

UNITED, STATES.

1,697,470 P TENT OFFICE.

WALTER n.- NOIURSE, or ronrLANnonEGoN, Ass xenon 'ro ELECTRIC swam. FOUNDRY,

F PORTLAND, OREGON, A CORPORATION OF OREGON.

METHOD or casrmo (mans on THE LIKE-0,25 meanest STEEL WITH SOFT-IRON CENTERS. 1 1

Application filed October 7, 192's. Serial No. 140,089.

My invention relates to casting gears, pinions, and other machine elements cast of hard metal, such as manganese steel, and Whose bore must be fitted for firmly mounting on a shaft. Since manganese steel is not readily machined by any other processthan grind ing, the casting is provided with a center of machinable metal, such as soft iron.

This construction is particularly required,

10 for example, in gears and pinions intended for repairs of geared locomotives; for, with themajority of repairs on these locomotives, it is necessary to bore each gear or pinion to suit the diameter of the line shaft.

the locomotive is in service,.the diameters of the line shafts are unknown at the shop where the replacement gear or pinion is supplied; and therefore, it is the custom to order the pinion or gear'rough-bored, ready to finish-bore to suit the diameters of the line shaft at the time the locomotive is-laid up for repairs. In the method of casting heretofore generally followed, the soft iron center was in the form of a continuous ring or bushing, constituting a hub or boss-like section. The difliculty with such method wasthe solid center tended to set up excessive strains in the hub section duringthe casting operation, which resulted in cracking the hub, and rendering the center loose in the casting. I

Such cracking of the hub or boss-section is due to unequal expansion and shrinkage, during the casting operation, between the soft iron center and the mass of manganese steel cast about it.

According to m observation, manganese steel has a define elastic limit which may not be exceeded with impunity. And experiments with manganese steel have established the fact that this metal has a co-efficent expansion of approximately .00001 inches per inch per de ree Fahrenheit, while soft iron,-acc0rding to ents Mechanical Engineers Hand Book, has a co-efiicient of expansion of approximatel .0000065 inches per inch per degree Fahren eit.

Furthermore, the soft iron center has to have sufficient thickness to permit machining as required to render the bore of proper size. The soft iron center heats up relatively slowly during the casting operation, and after the manganese steel is cast, the center When continues" to expand while the manganese steelis cooling.

.At thls instance, the manganese steel is ex-.

tremely tender, and the unequal expansion of'the two metals'tends to burst the tender casting, thus causing the gear, or other machine element to be unfit for further service. The strains imposed by unequal shrinkage of the two metals under the said old method of casting is apt to be particularly severe, because after the gear or pinion is permitted to cool, it is again heated to about -1800 Fahrenheit, and then plunged in cold water,

to effect the so-called heat treatment for ren- 'ganese-steel-will flow into, and form in said spaces between the segments. The spacing must be 'such as to give the said integral 'tongues of manganese steel sufiicient mass in cross-sectional area to compensate for the difl erence in shrinkage in the cooling of said two metals; in that way avoiding the setting up of the excessive strains which would tend. to crack'the hub section of the gear or pinion.

Furthermore, the arrangement of the parts must be such that the segments will be firmly held in the cast body of the manganese steel against moving longitudinally in the bore, or into the bore of the gear. This is con-. veniently accomplished b firmly wedging the segments between sai integral tongues.

The manner of carryingmy invention into practise is illustrated in my accompanying drawings with respect to the casting of a pinion. p

In the drawings:

Fig. 1 shows a front elevation of a pinion embodying my invention, and mounted on its shaft which is shown in section, the central portion of the pinion is also shown in section, in order to disclose the'arrangemen't of the soft metal segments, their spacing apart, and the integral tongues of the cast manganese steel formed between them; and

cooling of said two metals.

Fig. 2 shows a section taken on the line 22 of Fig. 1 lookingdown on the lower half of the pinion, as indicated by the arrows.

Fig. 3 shows the particular form of central core employed by me in making my casting;

and

Fig. 4 shows the machinable segments secured to such central core with the latter inserted, and the core box readyfor making the casting.

My invention as above mentioned is to be applied to gears, pinions, and other machine elements cast of hard metal,.such as manganes'e steel, and provided with a machinable softer metal center. v

- My center'insert consists of a circular segments as a, b, and arranged about the center of the pinion, or gear, to be cast, and supported'jin place, during the casting operation, by a proper core prepared for that purpose. The lateral sides of the segments must be spaced a substantial distance-apart, as illustrated by Fig. 1. v 7

These cuts a is formed with a key-bass d. The ody e of the pinion or gear is then.

cast about said segments, thus causing integral tongues of the castmanganese steel to how in between the sides of the spacedsegments as indicated at f. The sides of the faces g of thesegmentsexposed to the core of the pinion will project beyond .the correspending faces of the tongues f a sufiicient distance to provide metal for machining the center as may be required.

In order to provide for looking or wedging of segments firmly between their integral tongues, the sides of the segments are preferably formed to lines radial with the centerof the pinion orvgear; thus forming these segments into key-like or wedge-like sections, larger at their. outer periphery than at their inner periphery, and thereby securely holding the segments from moving into the bore of the pinion.

I preferably make the center of my gear or pinion of three parts or segments,-a, b, c-

so as to get athree-point bearing effect. But each of these parts may be composed of two or more units, as -may e required where the diameter of the pinion or gear is considerable.

In either case, the three segments of the centers should be disposed approximately on plurality of 1 centers of 120 as above stated; thus with the spacings of the segments about to degrees apart- -for pinions having a bore of three to four inches diameter. Any lesser spacing is apt to cause the severe strains in cooling, which is the purpose of my invention to avoid.

My experience has dempnstrated that .a relatively greater'shrinkage takes place in the cross-section of the tongues f on the casting entering between the segments (1,6, and 0 than in the body of the metal cast about the segments, similarly to. the shrinkage of the teeth or cogs in the casting oiman'ganese'steel gears and pinions, the teeth of which have to be cast of such thickness as to compensate for their relatively greater shrinkage in crosssection than the shrinkage in the body of the gear or pinion.

That is to say there is a definite relation between .the cross-sectional areas of the 'seg-- ments and that of the casting, otherwise the chilling effect of the segments upon the hot metal cast about it will tend to set up undue stresses and strains during the casting oper-.

ation, tending tocrack the hub section of'the casting.

In making my casting, I first make a cylindrical core 13 formed with peripheral recesses as 7', shown by Fig. 3, and insert the same in the center of the core box k. On such-centrah core in its said recesses are secured the segments (1, b, and a, by means of a wireql, and

the central core with the segments secured in place is then inserted in the core bore whereupon the latter is ready for the casting. The peripheral projections m of the core extending between the said segments serve to produce the tongue f between the segments and hold back the flow of the hard metal to a circle ofgreatcr diameter than that of the circle touched'by said segments, thus causing the latter to projectbeyond the hard metal body into the center of the casting, and thereby providing ample machinable 'metalin the eye of the pinion, or similar-machine'elemcnt.

I-claim:

The method of casting a pinion and similar machine element of; hard metal with a machinable center, which consists in mounting a plurality of soft metal segments in spaced relation on a core, and then casting the harder metal about said'eore, whereby tongues of the hard metal will flow into and form between the said segments and lock the same in place, the fiow of said tongues being confined to a circle of greater diameter than that of the circle touched by the said soft metal segments, and the latter segments projecting beyond thehard metal body in the center, and the spacings between the segments being proportioned substantially as described.

WALTER H. NOURSE.