US2503914A - Elastic fluid turbine casing - Google Patents

Description

April 1950 F. c. LINN ELASTIC FLUID TURBINE CASING Filed July 22, 1946 .I ll I.

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Patented Apr. 11, 195

ELASTIC FLUID TURBINE CASING Frank C. Linn, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 22, 1946, Serial No. 685,503

3 Claims.

My invention relates to elastic fluid turbomachines, such as steam turbines, having large and heavy casings divided into halves substantially along a diametral plane, particularly to the arrangement of the casing at the high pressure end of such a machine.

While applicable to any such machine in which the inlet temperature of the motive fluid is subject to material changes within short periods of time, it has been found particularly useful in the high pressure end of the low pressure cylinder of marine propulsion turbines having more than one turbine in series flow relation. In such turbines, it is frequently required, when maneuvering, that the load on the turbine be almost instantly changed from no-load to full load ahead or full load reverse, and vice versa. Such operation produces an appreciable and varying temperature difierential between the steam inlet chest of the turbine casing and the comparatively cooler portions of the casing including the horizontal flanges and the shaft seal structures which are radially spaced inwardly from the inlet chest. It has been discovered that such fluctuating temperature gradients cause certain temporary warpage of the casing halves, with the result that the joint between the sections distorts sufliciently to permit a small amount of leakage between the flanges. The steam is at or near its dew point and therefore may erode the surfaces of the easing joint. This resulting erosion increases with time unless corrective measures are taken. Because of the difliculty and cost of disassembling the turbine in a marine powerplant for repair of the horizontal joint flanges, and the resulting loss of utilization of the ship, it is imperative that such partial top view taken on the plane 33 of Fig. 2,

showing the arrangement of the horizontal flanges which secure together the two halves of the turtegral with the two halves of the casing is a steam leakage and erosion :be eliminated or reduced to a minimum.

The object of my invention is to provide an improved casing arrangement for the high pressure end of a large heavy turbine casing of the type described which eliminates the above-mentioned leakage difllculties, which may be encountered with pre-existing designs.

Other objects and advantages will be apparent from the following description taken in connection with the accompanying drawings, in which Fig. 1 is a vertical section through the axis of a turbine with a casing incorporating my invention; Fig. 2 is a partial end view of the turbine casing taken on the irregular plane 22; and Fig. 3 is a inlet chest I. As shown in the drawing the steam chest is provided in both halves of the casing, extending completely around the casing adjacent to the first stage bucket-wheel 8. It will of course be obvious to those skilled in the art that my invention is equally applicable to turbines having partial arc admission in the first stage, in which event the steam inlet chest I may be provided in only one section of the turbine casing. Supported in the turbine casing in cooperating relation with the inlet chest I is a ring 9 defining a plurality of circumferentially spaced nozzles l0 adapted to supply motive fluid to the buckets of the first stage wheel 8.

The shaft I is supported in a suitable bearing indicated generally at H, the structural details of which are not essential to an understanding of the present invention. Surrounding shaft i is a packing assembly l2 including a number of axially spaced packings consisting of segments l3 of soft metal or carbon arranged to be biased into sealing engagement with the shaft by suitable springs I4 which engage the respective segments [3. Packings of this general type are well known in the art and further mechanical details are also believed unnecessary to an understanding of the present-invention.

As will be understood by those familiar with steam turbines for marine propulsion, the casing halves of such machines are massive units formed with heavy sections to withstand the forces involved without detrimental distortion under the severe conditions encountered in marine service. For instance, the inlet end of the casing, as represented in Fig. 1, may be of the order of 5 feet in outside diameter; while the exhaust end (not shown) may be of the order I! feet in outside diameter. One half of such a casing may weigh between 5,000 and 10,000 pounds.

The casings represented in the drawings may be fabricated by welding from rolled or forged steel sections. It will of course be understood that my invention is also applicable to cast casings.

It will be observed in Fig. 1 that the steam chest 1 is radially spaced from the shaft packing assembly II. For low load operation of the low pressure element of a marine turbine of the type described, the temperature of the metal walls of chest 1 may be of the order of 300 F., while the shaft and packing may be at about 240 F. Normally in starting, the turbine will be operated at low load until all parts of the turbine reach their respective steady state temperatures. However, at certain times, as when leaving the dock,

it is necessary to instantaneously increase the turbine load to its full rated value or nearly so. As a result, the temperature of the inlet chest I may quickly rise to the neighborhood of 400 F.,

while the portions of the casing radially inward from the steam chest may remain at about 250 F. If the turbine continues to operate at full load or thereabouts, a new steady state temperature level will be reached at the end of about one hour's time, when the parts in the neighborhood of the shaft seal and bearing assemblies may be in the neighborhood of 335 F. This differential (as compared with the 400 inlet chest temperature) may be sufficient to produce opening of the horizontal flange to allow continuous steam leakage which will result in progressively increasing erosion. The above-described transient temperature differential occurring when the load is suddenly changed from minimum to maximum of course produces a similar efiect to a greater degree.

I have found that the leakage difficulties heretofore experienced with the massive casings ordinarily used can be completely eliminated by the interposition of a flexible casing section between the comparatively hot inlet chest 1 and the cooler shaft region with its seal and bearing assemblies H, II. In Fig. 1 this flexible section is indicated at I 5. It comprises a ring member of thin fiat cross-section which is dished inwardly in an axial direction and extends from the inner casing ring member l6 radially outward to the ring 11, the latter being welded to the inlet chest I in a manner which may be seen in Fig. 3.

In 'Fig. 2 can be seen a plan view of the flexible ring and its relation to the inner and outer rings l6, l1 and flange to which it is welded. Also shown are two of the bolts which secure the casing halves together. It will be understood that a row of studs I8 are secured in the flange 2| of the lower casing half, nuts 19 serving to force the flange 20 of the upper easing into tight sealing engagement with the flange 21 of the lower casing. The plane mating surfaces of these flanges are carefully finished so as to provide a steam tight seal when the flanges are clamped together by the threaded fastenings I 8, l9. To provide a sufficiently tight fit, the studs 18 may first be heated with a blow-torch and then the nuts I! assembled and tightened down firmly. The ensuing shrinkage of studs I8 as they cool will produce very considerable forces to hold the casing halves together.

As may be seen in Fig. 3, by arranging the curved ring I i so that it bows inwardly (that is,

is concave as viewed from the outside of the cas ing), additional room is provided on the flange 20 for locating an additional stud Ma. The line of action of the force provided by this stud lid is substantially in the plane of the rings l5, l1 and therefore provides particularly effective sealing engagement between flanges 20, 2| immediately adjacent the shaft seal assembly II. This is an important advantage of my arrangement, for leakage through the casing joint at thi point has been particularly troublesome.

With my invention it has been found that the massive casings for turbines of the type described can be readily manufactured so as to be completely leakproof at the casing joint over long periods of exacting service in marine powerplant installations.

While my invention has been described as applied to a steam turbine for marine propulsion powerplants, it may also flnd utility in analogous casings of other turbo-machines, such as multistage axial fiow compressors, etc.

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

1. An elastic fluid turbo-machine subject to rapid and material changes in temperature of the operating medium comprising a casing having a radially extending end wall portion thereof divided into at least two sections along an axial plane with joint flanges around the periphery of the respective sections, fastening means clamping the joint flanges together, and rotor shaft sealing means supported by said end wall portion, the high temperature end of the casing forming a high temperature fluid chamber radially spaced from the shaft seal means, said casing end wall having a radially inner portion connected to the shaft seal means and an outer circumferential portion connected to the radially inner wall portion of the high temperature fluid chamber and including a thin-walled portion having a cross section forming a simple arcuate curve bowed inwardly relative to the casing so as to have appreciable flexibility in a radial direction, whereby differential thermal expansion of the high temperature chamber relative to the shaft seal means may take place without distortion of the casing section at the dividing plane therebetween, the inwardly curved flexible section providing maximum available space for the fastening means on the joint flanges, a part of said flange clamping means being located immediately adjacent the shaft seal means with the line of action thereof lying substantially in the plane of the casing end wall portions to which the flexible section is connected.

2. An elastic fluid turbo-machine subject to rapid and material changes in temperature of the operating medium comprising a casing having a radially extending end wall portion divided into at least two sections along an axial plane with joint flanges around the periphery of the respective sections, fastening means clamping the joint flanges together, rotor shaft sealing means supported by the casing end wall portions, the end of the casing adjacent said radially extending wall portion forming a high temperature fluid chamber radially spaced from the shaft seal means, said casing end wall having a radially inner portion connected to the shaft seal means and an outer circumferential portion connected to the radially inner wall of the high temperature fluid chamber and including a thin-walled portion of curved cross-section having appreciable flexibility in a radial direction, whereby 8,508,014 7 5 I 6 limited differential thermal expansion or the fluid chamber walls relative to the shaft seal means REFERENCES CITED may occur without distortion of the casing The following references are of record in the tions at the axial dividing plane therebetween me of this patent:

3. An elastic fluid turbo-machine casing ar- 5 UNITED STATES PATENTS,

rangement in accordance with claim 2 in which the curved flexible section is bowed inwardly so i 5 ggg: P

as to appear concave from the exterior or the 167o'452 Kaehler f y- 1928 3851118, whereby maximum o ting space is made 6 Lysholm M 1 37 available n the flanges immediatel adjacent thg o v shaft seal means. A

FRANK C. LINN.

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