US1728895A - Method of making field rings - Google Patents

Description

' Sept. 17 11929 F. A. HAUGHTQN METHOD OF MAKING FIELD RINGS Filed Oct. 26, 1926 2 Sheets-Sheet. l

Sept. 17, 1929. F. A. HAUGHTQN 1,728,895

METHOD OF MAKING FIELD RENGS Filed Oct. 26, 1926 V 2 Sheets-Shea}; 2

Inventor i Patented Sept. 17, 1929 UNITED STATES PATENT OFFICE FRANK.A. EAUGHTON, OF SGHENEOT ADY, NEW YORK, ASSIGNOB TO Gm ELEG- TRIC COMPANY, A CORPORATION OF NEW YORK METHOD OI MAKING- I'IELD BRIG-S Application filed October 26, 1926. Serial No. 144,886.

My invention relates to the -manufacture of ring-shaped structures and particularly to field rings for direct current dynamo-electric machines. A common practice in the past has been to construct such field rings of gray iron or steel castings, the latter being preferred by reason of their more suitable magnetic properties and greater strength.

'20 uniformity in magnetic properties inasmuch as hidden defects are likely to exist which are not easily detected. For these and other reasons the use of rolled steel for the field frames of large dynamo-electric machines has been recognized as highly desirable but because of the high cost of frames so made there has been little, if any, inducement to make such a substitution. This high cost is due first, to the cost of the material employed, for example plate stock or even forgings, and

second to the ,cost of labor or special machines or both for shaping the material to the proper form. These considerations are particularly important in the case of machines of large size.

It is an object of my invention to provide improved steel rings suitable for the field frames of dynamo-electric machines which are superior to and which may be manufactured at lower costs than the rings now used together with the process of their manufacture. As a result of my invention large economies are obtained both by reason of the material employed and the simple and inexpen- 5 sive method utilized in working that material, the use of s ecial and expensive tools and highly skille labor being rendered unnecessary.

.In accordance with my invention I construct rings of a comparatively cheap form of rolled steel, namely, rerolling slabs or forging billets these being the terms generall applied in the trade to the product of the st rolling process to which the steel is sub ected in the steel mill after the casting of the ingot. The surface of these slabs, which term will be used hereafter for convenience to apply to both rerolling slabs and 1jiggingbillets, have a more or less rough and 1s ed surface but have" magnetic properties which are superior to those of steel castlugs to the extent that they can be made ma terially smaller in cross section for the same capacity machine. K In utilizing these slabs in accordance with my invention I pass them while at a forging temperature one or more times as may be found necessary throu h common bending rolls to give them the esired curvature. As a result of this rolling process a slab will be bent uniformly throughout its length with the exception of the two end portions, which as is well known to those skilled in the art, will remain more or less straight. The slab having been given the desired curvature is removed from the bending rolls and the straight or improperly bent end portions are then out off by means well known to the steel worker. The end faces of the bent sections are then machined to obtain a flat surface and suitable means are provided for securing end to end the ring segments thus formed. Suitable supporting brackets or feet also may be secured to one. or more of the ring segments.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed outin the appended claims.

Referring to the drawing, Fig. I shows-a rerolling slab as it appears when received from the rolling mill; Fig. 2 shows the same slab being bent in the bending rolls; Fig. 3 shows the bent slab after removal from the bending rolls; and Fig. 4 shows a dynamoelectric machine having a split field magnet constructed in accordance with my invention of two such bent slabs, the armature and the bearing supports therefor being omitted.

The rerolhng slab 1, shown by ltself in Fig.

1, as has already been pointed out above is the product of the first rolling process to which the ingot is subjected in the steel mill. It is more or less crooked and unshapely and dis tinctly shows the imprint 2 of the ragging rolls between which it is passed in this first rolling process. The slabs also usually have one or more blisters or other defects on their surfaces which it is the practice of the mill to cut away by hand before further rolling of the slabs. lln the present use 'of the slabs, however, such defects are not objectionable and need not be removed. Slabs are obtained in various sizes 1n accordance with the sizesof the machines to be constructed, for ex-.

ample, the slab shown in Fig. 1 is about eight and one half inches thick and about twentythree feet long, weighing approximately seven tons.

The slab is first uniformly heated in a suitable furnace to a forgin temperature whence it is removed and while ot is passed through common bending rolls. In Fig. 2 I have shown the slab 1 being passed'through the bending rolls 3 which are variously conthe slab through the bending rolls also hasthe effect of partially smoothing out the ragging and other irregularities on the surface of theislab as shown in Figs. 2, 3 and 4 and what remains is an advantage rather than an objection since it provides a better surface to which may cling the putty and paint finish of the machine. The slab is thus given the desired bend throughout the greater portion of its length but its two end portions 6 will remain substantially straight or unbent for a certain distance, as indicated on the drawing. These end portions 6 will be referred to hereafter as unbent inasmuch as they do not have the curvature of the intermediate portion of the ring. If the field ring being constructed 1s to comprise two ring segments of 180 degrees each, as illustrated by way of example in the drawing, the length of each slab must be suflicient to obtain the 180 degrees of the intermediate or uniformly bent portion plus the unbent end portions. After the bending operation is complete the slab is removed from the bending rolls and the unbent ends {5 are cut 0E squarely, the line of out 01f being indicated by the dotted lines 7 in Fig. 3. In cutting off the ends suflicient material maybe left to allow for subsequent machining if necessary to obtain flat end faces. The end masses portions which have been cut off while constituting a waste is in reality only small amount in comparison with the remaining segment and has relatively small value being more than offset by the saving in labor and material resulting from this method. In a I have shown the two ring segments secured together by bolts 9 passing through lugs 10 at the adjacent ends of the ring segments, also the lower ring segment provided with supporting brackets or feet 11. The lugs and feet may be secured to the ring segments in any suitable manner for example by welding and I have found it to be of some advantage to secure the lugs 10 to the ring segments so that the lugs and the end faces of the ring segments may be machined simultaneously whereby a larger area of contact is provided between the adjacent surfaces of the segments. After securing the segments together the ring 12 formed thereby may be machined on its inner surface to which field pole pieces, shown for example at 13 having windings 14, may be attached. The end faces of the field ring may also be machinedto which end heads may be secured for supporting the armature, brush holders, etc.

As has been pointed out above the field frames of dynamo-electric machines heretofore have commonly been made of steel castings. As is well known, castings require'patterns which in the case of large machines are in themselves costly. Variations in shrinkage and draft requirements of castings necessitate due allowance in the dimensions of the parts and in the making ofsteel castings moreover it is necessary also to provide large swells and projections for risers. In the finishing process all this excess material must be machined oif requiring much time and labor. 7

By using rerolling slabs a pattern is not reuired, he ring segments can be formed much 0 oser to size and more nearly circular, no draft allowance need be provided and there are no swells or riser projections to be machined off. Hence there is a decided economy in weight and in cost of machining off surplus metal. As rings formed of rerolling slabs do not contain blow holes, sand holes, scabs, etc. there is no loss due to such defects which are inherent with castings. Moreover such rings are not subject to commutator troubles in the completed machine which sometimes occur where cast frames are used in which hidden defects are present. The magnetic proper ties of rerolling slabs of low carbon content of say .1 to 2% carbon are very satisfactory as compared with iron or steel castings and experience has shown that frames made from such slabs may be constructed materially lighter in net'weight. In the design of machines with cast steel frames 2. flux'fdensity of 75,000 lines per square inch heretofore has been allowed but with frame constructedof lao masses 3 rerolling slabs a flux density of 90,000 lines is being regularly employed, due to their greater permeability.

Rerolling slabs having been given only the 5 first rolling and hence subject to a minimum labor costare the cheapest form of so-called semi-finished steel and can be purchased at the present time for about one quarter of the price of steel castings. This saving in initial cost of material taken together with the economies resulting from the above described method of formin a finished ring from that material has been %ound in the case of a number of machines to amount to from 30% to 40% in factory costs of the finished frames ready for the attachment of poles and other parts.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. The method of forming a ring-shaped member from steel slabs which comprises passing the slabs through bending rolls to give them the desired curvature, cuttin ofi the unbent end portions, and joining the ent portions end to end.

2. The method of forming a ring segment from a steel slab which comprises passing the slab through bending rolls to bend only a portion intermediate the ends thereof to the desired curvature and then cutting ofi the unbent end portions. 7

3. The method of forming a field ring for a dynamo-electric machine from thick steel slabs which comprises passing the slabs in a heated condition through bending rolls to form ring segments, cutting ofi the unbent end portions of each segment to form flat end faces and securing the segments together end to end.

4. The method of forming a split field ring for a dynamo-electric machine from rerolling slabs which comprises heating the slabs, passing them through bending rolls to form ring segments and to produce a more smooth surface, cutting off the unbent end portions of the segments, machining the end faces and firmly securing the segments together to form a ring.

In witness whereof, I have hereunto set my hand this 23rd day of October, 1926.

FRANK A. HAUGHTON.

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