US3078905A - Method and apparatus for enlarging rings - Google Patents

Description

Feb- 26,- 1963 R. R. soMERs ETAI. 3,078,905

METHOD AND APPARATUS FOR ENLARGING RINGS Feb. 26, 1963 R. R. soMERs ETAL METHOD AND APPARATUS FoR ENLARGING RINGS Filed- June 2l, 1960 2 Sheets-Sheet 2 /NVE/VTRS 05E-RTR. 50ML-@50nd JOHN E. STE/NER Wer United States Patent Oiitice 3,078,905 Patented Feb. 26, 1963 a corporation or' New Jersey Filed June 21, 1960, Ser. No. k37,719 S Claims. (Cl. 153-79) This invention relates, as indicated, to al method and apparatus for enlarging steel rings. It relates, more par-vv ticularly, to generator retaining rings and to a method and apparatus for expanding such rings to nal size by a cold-working operation.

Nonmag-netic steel retaining rings are commonly used to hold in place therotor windings of large electrical generators. They are made in various sizes, generally stated and depending on the capacity of the generator and the diameter of its rotor, of from 20' to 65 inches in diameter as measured at the mid-point of the wall thickness thereof, axial length of from 17 to 30 inches, wal-l thickness of 2 to 4 inches, and weight of from 12,000 to 4,000 pounds. Since they are subject to large centrifugal forces in operation, commercial specifications presently require steels having, for example, a minimum 0.2 percent offset yield strength of from 100,000 toV 160,000 p.s.i., and correspondingly higher minimum ten sile strengths of from 115,000 p.s.i. to 175,000 p.s.i. To

meet such specifications, generator retaining rings are` presently fabricated from austenitic stainless steels such as austenitic manganese or manganese-nickel steel characterized by carbon content within the rangev 0.40 to 0.85Y percent, manganese content within the range 8.0 to 19.0 percent, nickel content up to 7.00 percent and chromium content within the range 3.5 to 5.0 percent, having the ability, when cold worked by amounts of 20 to 40 percent in elongation (or expansion in the form of a ring), to develop 0.2 percent offset yield strength of from 100,000 to 145,000 p.s.i., with good ductiiity and toughness. Within these composition ranges it is usual to adjust carbon and manganese content lower as nickel content is raised and to adjust carbon content independently as well as making adjustments in the amount of cold work (expansion) to achieve the yield strength desired for a particular ring. Still other steels that require various combinations of cold working and aging or stress relieving to develop yield strengths in excess of 160,000 p.s.i. have been proposed for the production of generator retaining rings. While such other steels are inherently incapable of withstanding an expansion of 40%, expansions on the order of 15 to 30% can be anticipated and will be effective to develop the required physical properties.

In fabricating nonmagnetic retaining rings, steel of the desired composition is melted in an electric furnace, poured as a killed in'got, and forged at about 2200" F. in a forging press. A hole is then punched in the center of the forged ingot, which is then forged on a mandrel to enlarge the hole. The forging is reheated, as necessary, during the hot forging, punching, and mandrelforging steps. After the' mandrel-forging step, the forged piece is water-quenched, rough-machined, solution-annealed at about 2,000o F. for 2 to 4 hours, and waterquenched, in that order. The ring is then expanded to about its final dimension, the diameter of the piece being increased approximately 20 to 40% in this operation, by cold-working the steel either at room temperature or at temperatures above which martensite will not form during deformation of austenite to develop the required properties.

According t'o present commercial practices, the final cold-working expansion of the forging ring is effected by placing a plurality ofA expandingv shoes at circumferen-A tially spaced intervals about the inner surface of the ring and then forcing a large tapered drift pin centrally' through the shoes, thereby causing the shoes to expand the retaining ring. The expansion of the ring that can be` effected in this manner is limited, and liners arel subsequently inserted between the shoes and the retaining ring to enable further expansion. To effect a- 30% expansion of the retain-ing ring, three successive drift pin expansion operations of this character are usually re quired. Expansion of retaining ringsy by this practice has several disadvantages, among which are high initial cost of tooling and low production rates due to the tedious and laborious nature of the operation, 6 to 8 hours being required to expand a ring in this manner.

One of the principal objects of this invention is to provide an improved method and apparatusl for expanding non'magnetic generator retaining rings that comparedV to conventional expanding practice reduces the initial cost of toolingand increases the production rate` by decreasing the time required to expand a ring by cold Working to its final size. A further and related object. is to provide an improved method and apparatus of this character that requires only a single working tool and one press operation, insures complete lubricant retention at pre-v heat temperatures of approximately 500 F., can expand retaining rings of substantially greater length than thosev presently produced by the expansible shoe process, and requires little or no handling or special tool alignment care.

Other objects and advantages of the invention willV become apparent from the following description and the accompanying drawings.

In the drawings:

FIGURE 1 is an elevational view of the expanding mandrel of this invention showing its relation with re-v spect to the dies or platens of a forging press and a ring tov be expanded mounted in operative position thereon; l t

FIGURE 2 is a sectional view of the mandrel shown in lIGURE l;

FIGURE 3 is a fragmentary elevational' view of the upper end of the mandrel supporting post shown in FIG- URE 1s and.

FIGURES 4 through 12 respectively illustrate some what diagrammatically successive operations and steps of the apparatus and method of this invention.

The apparatus of this invention comprises, generally stated, the lower and upper dies or platens 1 and Z of a conventional forging press, a cylindrical supporting post 3 on the lower platen 1, and an expanding mandrel 4Y removably supported on the upper end of the post 3. It provides for successive expansion of cylindrical forged blanks B and further includes an auxiliary pusher ring, which may be either a ring 5 having the dimensions of an expanded ring as shown in FIGURE 12, or a successive ring B to be expanded as shown in FIGURE '7. The lower platen 1 constitutes part of a conventional slid-` ing base plate by which the assembly of the post 3, mandrel 4 and the blank B are moved to and from a position arranged vertically underneath the upper platen 2 as shown in FIGURE l. The upper platen 2y is mounted for vertical movement toward and away from the lower platen 1 and requires in a manner to be described at least two successive lowering movements to force a blank B over the mandrel 4 to effect' its ex pansion. In FIGURE l, a forged steel blank BY is shown assembled on the mandrel 4 in position to be expandedthereby. In this position, the upper end 6 of the mandrel 4 is received in the lower end 7 of the blank B which is thus supported on the mandrel 4 with its axis extendingv vertically and aligned with respect to the axis of the mandrel 4 and its supporting post 3. Upon downward movement the press platen 2 engages the upper end 8 of the blank B and forces it downwardly over the mandrel 4 to effect an initial expansion thereof.

The post 3 has a cylindrical centering pin 9 projecting axially from its upper end which is received in an opening in -the mandrel 4 for axially aligning its position with respect to the post 3. The pin 10 has a transversely extending opening 11 in which a bar (not shown) may be inserted to enable handling by a crane hoist chain. A recessed eyelet 12 is mounted in the upper end of the mandrel 4 for engagement with a crane hook to facilitate movement of the mandrel 4 to and from an assembled position on the post 3.

The mandrel 4 has a convex or bullet-shaped working surface 13 that is machined to the arc of a circle having its center at a point located on an extension of a diameter of its lower end 14. While a conical working surface could be employed, the convex shape of the working surface 13 is preferred since it effects a more uniform force distribution and enables a more constant pressure to be maintained over the working surface of the mandrel during expansions. With a convex mandrel contour as illustrated in the drawings, the taper of the mandrel working surface 13 is greatest at its upper end 6 where initial expansion takes place, and is progressively less in the lower portions adjacent its lower end 14 where strain hardening yof the ring being expanded becomes more appreciable. While the axial length of the mandrel 4 must be shorter than the final length of the ring after expansion to provide for successive expansion of forged blanks B in accordance with preferred embodiment of the invention, the mandrel 4 preferably has a length that approaches the final length of the expanded ring in order to maintain the working pressures on the mandrel surface 13 at a minimum. In addition, the inner diameters of the blank B before and after expansion determine the diameters of the upper end 6 and the lower end 14 of the mandrel 4. The diameter of the upper mandrel end 6 is less than the inside diameter of the blank B to provide for its assembly on the mandrel 4 as shown in FIG- URE l, and the diameter of the lower mandrel end 14 must be the same as the desired inside diameter of the expanded ring. The post 3 has a diameter that is sufliciently less -tban the maximum diameter of the lower mandrel end 14 to provide for free axial movement of an expanded ring relative thereto and for its removal from the apparatus in a manner to be described.

Prior to assembly of a blank B on the mandrel 4 as shown in FIGURE l, a coating of lubricant is applied to the mandrel surface 13 and the inner surface of the blank B. Since -there are a number of conventional lubricants suitable for this purpose,. it will be suliicient to indicate that a mixture of three parts beeswax and one part turpentine, or of molybdenum disulfide in a mineral oil carrier, may be used. After applying the lubricant, the assembly of post 3, mandrel 4 and ring B is moved to a position under the forging press upper platen 2 as shown in FIGURES 1 and 4 of the drawings. The forging press is then operated to lower the platen 2 and force the blank B downwardly over the mandrel 4. As downward movement of the platen 2 takes place in this manner, it engages the upper end 8 of the blank B and forces it downwardly through the intermediate position shown in FIGURE 5 to the position shown in FIGURE 6 in which further movement is prevented by engagement of the platen 2 with the upper end 6 of the mandrel 4. The downward movement of the platen 2 in this manner takes place at a suiciently low rate of speed to provide for expansion of the blank B by cold flow of the metal therein and without cracking. This initial downward movement results in an expansion of the lower end of the ring B, the upper end 8 of which is unexpanded and concentric with respect to the upper end 6 of the mandrel.

After movement to the position shown in FIGURE 6. the platen 2 is raised and a second cylindrical ring B is mounted concentrically on the upper end of the partially expanded blank B as shown in FIGURE 7. The platen 2 is then moved downwardly through the position shown in FIGURE 8 to the position shown in FIGURE 9 in which its movement is again interrupted by engagement with the upper end 6 of the mandrel 4. During this movement of the platen 2, the downward movement of the first ring B over the mandrel 4 is completed so that its upper end 8 is expanded by movement over the lower end 14 of the mandrel 4. The first ring B being fully expanded drops onto the base 15 of ythe post 3, and the second ring B is partially expanded. The assembly of the post 3 and mandrel 4 is then withdrawn from underneath the platen 2 and the mandrel 4 is removed from the post 3 to permit removal of the fully expanded ring B on the base 15, after which -the mandrel 4 with the partially expanded ring B thereon is replaced on the supporting post 3. Another ring B to be expanded is then placed concentrically on top of 'the partially expanded ring B and the assembly is returned to the position shown in FIGURE 7, and the aboved described operation is repeated as required to complete the expansion of successive rings. In operation to expand successive rings, it will be noted that only the first ring B moves through the steps shown in FIGURES 4, 5 and 6.

While the last ring B forced onto the mandrel may be stored with the mandrel for a later production run, it may be fully expanded by following the procedure illustrated diagrammatically in FIGURES l0, 1l and l2. This is accomplished by stripping the partially expanded ring B from the mandrel 4 and reversing its position on the mandrel 4 with the upper end of the mandrel 4 received in its unexpanded end as shown in FIGURE l0. The platen 2 is then moved downwardly to a position in which it engages the upper end 6 of the mandrel 4 and this moves the ring B downward to the position shown in FIGURE 11, thereby completing its expansion. A second ring 5, which may be either a previously expanded ring or a dummy ring having the dimensions of a fully expanded ring as explained above, is then inserted between the platen 2 and the mandrel 4 as shown in FIGURE l2. The platen 2 is then forced downwardly to continue the movement of the blank B over the mandrel 4 so that it will drop to a position supported on the base 15. The

assembly of post 3 and mandrel 4 is then withdrawn from underneath the platen 2 for removal of the expanded ring from the base 15 as explained above.

While one embodiment of our invention has been shown and described it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

We claim:

l. Apparatus for expanding cylindrical rings comprismg, in combination, a tapered expanding mandrel having its upper end received in the lower end of and supporting a ring to be expanded in a position with its axis extending vertically, a platen mounted above said mandrel and the upper end of said ring for relative vertical movement toward and away from said mandrel, said platen being operative during an initial downward movement thereof to engage the said upper ring end and force said ring downwardly over said mandrel to a position in which its said upper end is opposite the said upper end of said mandrel, and means comprising an auxiliary pusher ring for insertion between said platen and said ring after an upward movement of said platen following said initial downward movement to render said platen effective during a subsequent downward movement thereof for completing the downward movement of said cyJ lindrical ring over said mandrel.

2. Apparatus for expanding cylindrical rings comprising, in combination, upper and lower platens mounted for relative movement toward and away from each other, a vertical post on said lower platen, an expanding mandrel removably mounted on the upper end of said post for axial movement through a ring to be expanded, said man drel having an upper end initially received in the lower end of and supporting said ring in a position with its axis extending vertically, said upper platen being operative during an initial relative movement toward said man drel to engage the said upper ring end and force said ring downwardly over said mandrel to a position in which it-s said upper end is opposite the said upper end of said mandrel, and means comprising an auxiliary pusher ring for insertion between said upper platen and said ring after movement of said upper platen away from said mandrel following said initial movement to render said upper platen etiective during a subsequent movement toward said mandrel for completing the downward movement of said ring over said mandrel to a position with its said lower end supported on said lower platen and arranged concentrically about said supporting post, said mandrel being thereafter removable from the upper end of said post to provide for removal of said ring lby axial movement thereof relative to -said post.

3. Apparatus for expanding cylindrical rings comprising upper and lower platens mounted for movement toward and away from each other, a vertical post on said lower platen, an expanding mandrel removably supported on the upper end of said post, said mandrel and upper platen being adapted to have initial engagement with opposite ends of a ring to be expanded so that subsequent movement of said platens toward each other will force the lower end of said ring over said mandrel, and means comprising an auxiliary pusher ring for insertion between said upper platen and said ring after movement of said platens away from each other following said initial movement to render said upper platen effective during a subsequent movement toward said mandrel for completing the downward movement ot' said ring over said mandrel to a position with its said lower end supported on said lower platen and arranged concentrically about said supporting post, said mandrel being thereafter removable from the upper end of said post to provide for removal of said ring by axial movement thereof relative to said post.

4. A ring expanding apparatus as dened in claim 3 characterized by said expanding mandrel having ya. tapered external surface that increases in diameter from its upper end to a maximum at its lower end, and by said post having a diameter less than said maximum diameter to provide for free axial movement of said ring relative theret0.

5. An apparatus for successively expanding a plurality of rings comprising the apparatus defined in claim 3 characterized further by said Iauxiliary pusher ring comprising a successive cylindrical ring to be expanded, and by said successive ring having its lower end forced over said mandrel and expanded thereby during said subsequent movement of said platens toward each other to complete the movement of said first cylindric-al ring over said mandrel.

6. A method of expanding cylindrical rings which comprises placing opposite ends of a ring to be expanded between and in engagement with an expanding mandrel and a platen, moving said platen and mandrel toward each other to force one end of ysaid ring over said mandrel, withdrawing said platen relative to said mandrel and insenting an auxiliary pusher rin-g between said platen and the other end of said ring, and then moving said platen and mandrel toward each other so that said pusher ring operates to complete the movement of said cylindrical ring over said mandrel.

7. A method of expanding a cylindrical ring which comprises forcing one end of said ring over an expanding mandrel, stripping said ring from said mandrel and forcing the other end thereof over said mandrel in a reverse direction, and then placing an auxiliary pusher ring in abutting engagement with said one ring end and applying an endwise force to the other end thereof to continue the axial movement of said ring in said reverse direction over said mandrel.

8. In the process of cold working non-magnetic stainless steel generator retaining rings having a relatively short axial length compared to Ithe diameter thereof and a thick wall section to etect an increase in minimum yield strength and an increase in diameter of from 20% to 40%, the -steps which comprise placing opposite ends of a ring to be expanded between and in engagement with an expanding mandrel and a platen, moving said platen and mandrel toward each other to force one end of said rin-g over said mandrel, withdrawing said platen relative to said mandrel and inserting an auxiliary pusher ring be tween said platen and the other end of said ring, and then moving said platen and mandrel toward each other so that said pusher ring operates to complete the movement of said cylindrical ring over lsaid mandrel.

References Cited in the tile of this patent UNITED STATES PATENTS 2,493,127 Franck lan. 3, 1950 2,652,620 Sutowski Sept. 22, 1953 2,679,681 Resler June 1, 1954 2,850,796 Kaplowitz et al Sept. 9, 1958 2,961,744 Jagen Nov. 29, 1960

Claims (1)

1. APPARATUS FOR EXPANDING CYLINDRICAL RINGS COMPRISING, IN COMBINATION, A TAPERED EXPANDING MANDREL HAVING ITS UPPER END RECEIVED IN THE LOWER END OF AND SUPPORTING A RING TO BE EXPANDED IN A POSITION WITH ITS AXIS EXTENDING VERTICALLY, A PLATEN MOUNTED ABOVE SAID MANDREL AND THE UPPER END OF SAID RING FOR RELATIVE VERTICAL MOVEMENT TOWARD AND AWAY FROM SAID MANDREL, SAID PLATEN BEING OPERATIVE DURING AN INITIAL DOWNWARD MOVEMENT THEREOF TO ENGAGE THE SAID UPPER RING END AND FORCE SAID RING DOWNWARDLY OVER SAID MANDREL TO A POSITION IN WHICH ITS SAID UPPER END IS OPPOSITE THE SAID UPPER END OF SAID MANDREL, AND MEANS COMPRISING AN AUXILIARY PUSHER RING FOR INSERTION BETWEEN SAID PLATEN AND SAID RING AFTER AN UPWARD MOVEMENT OF SAID PLATEN FOLLOWING SAID INITIAL DOWNWARD MOVEMENT TO RENDER SAID PLATEN EFFECTIVE DURING A SUBSEQUENT DOWNWARD MOVEMENT THEREOF FOR COMPLETING THE DOWNWARD MOVEMENT OF SAID CYLINDRICAL RING OVER SAID MANDREL.

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