Patent Publication Number: US-3874814-A

Title: Closure key apparatus

Description:
Carroll et al.  
 Apr. 1, 1975 CLOSURE KEY APPARATUS Inventors: Alexander A. Carroll, Greensburg; Donald P. Ravicchio, Appolo. both of Pa.  
 Assignee: Carrier Corporation, Syracuse, NY.  
 Filed: Apr. 5, 1974 Appl. No.: 458,148  
 U.S. Cl. 415/219 C, 292/256.6, 415/199 C Int. Cl. F04d 29/40 Field of Search 415/108, 199 R, 199 A.  
 References Cited UNITED STATES PATENTS 9/1942 Fisher 292/256.6 9/1954 Alt et a1... 292/256.6 6/1955 Kopp 292/256.6 4/1969 Savory 292/256.6  
 FOREIGN PATENTS OR APPLICATIONS 10/1948 France 415/199 R Primary E.\&#39;amilzerHenry F. Raduazo Attorney, Agent, or Firm-4. Raymond Curtin; Thomas .1. Wall [57] ABSTRACT A simple key assembly for supporting an end wall structure within a rotary machine such as a turbine or a compressor. A shear key is interposed between the casing of the machine and an end wall closure carried internal the casing. A portion of the shear key is seated within an internal groove formed within the casing and a second portion thereof seated within a recessed shoulder formed in the end wall. A support key is mounted beneath the shear key within the end wall recess which serves to translate radial forces from the wall to the shear key. A pair of raised moment control pads are mounted on the casing contacting surfaces of the shear key, the pads being strategically located in relation to the center of gravity of the shear key to offset the load induced bending moments exerted thereon by the end wall and the support key.  
 5 Claims, 3 Drawing Figures CLOSURE KEY APPARATUS BACKGROUND OF THE INVENTION This invention relates to a closure key device for sup porting the end wall of a pressure vessel relatively immobile when placed under load.  
  In many pressure vessel applications, and in particular those involving rotating machinery such as a compressor or a turbine, it is essential to maintain the end wall or walls of the machine in a relatively stationary position under varying load conditions. In a rotary machine, it is conventional to support the moving machine components, typically involving the shaft and shaft supported parts, within the end wall structure. On the other hand, the coacting or cooperating stationary components of the machine are usually rigidly affixed to the casing. As can be seen, any axial shifting of the end wall structure beyond allowable limits will result in a misalignment of the coacting stationary and moving components which can give rise to serious rubbing problems and even eventual machine failure.  
 It has been found that most end wall closure devices fail because the key assembly, which serves to hold the end wall within the machine structure, is caused to bend or deflect when placed under load. Most closure keys known and used in the art, although relatively massive and complex, fail to take into consideration the effects of bending and are thus subject to failure.  
 SUMMARY OF THE INVENTION It is therefore an object of the present invention to improve keys for supporting an end wall closure within the casing of a pressure vessel.  
  It is a further object of the present invention to provide a simple end wall closure key assembly capable of minimizing the effect of load induced bending moments thereby preventing the closure wall from shifting axially under load.  
  It is yet another object of the present invention to extend the operating life of the rotary machine by reducing end wall failures.  
  These and other objects of the present invention are obtained by a relatively simple key structure including a shear key and a support key. In assembly, a portion ofthe shear key is seated within a groove formed in the interior surface of the pressure vessel casing while a second portion is seated within a recessed shoulder formed in the end wall closure structure. The support key is positioned beneath the shear key within the recessed shoulder and serves to support the shear key in assembly. A pair of raised moment control pads are provided upon the casing contacting surfaces ofthe shear key which are strategically located to substantially offset the load induced bending moments acting upon the shear key to prevent the closure wall from shifting in an axial direction.  
 BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as of the other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:  
  FIG. 1 is a partial sectional view of a rotary machine incorporating a key assembly embodying the teachings of the present invention;  
  FIG. 2 is a reduced sectional view taken along lines 22 in FIG. 1 further illustrating the structural arrangement of the key assembly embodying the teachings of the present invention; and  
  FIG. 3 is an enlarged exploded view showing the shear key and the support key making up the closure key assembly further illustrating the load forces acting thereon.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT The end wall retaining member of the present invention will herein be described with reference to a fluid compressor generally referenced 10 in FIG. 1. However, it should be clear to one skilled in the art that the apparatus of the present invention has wide suitable application in retaining and supporting any end wall structure within a pressure vessel, such as a compressor, pump or the like, and this disclosure is not intended to limit the present invention.  
  The rotary machine illustrated in FIG. 1 is what is generally referred to as a barrel type compressor. The machine is fabricated of a relatively heavy cylindrical outer casing 11 having an axially aligned cylindrical hole 12 bored therein. A second cylindrical casing 13 is mounted within the bore of the main outer casing and has secured thereto the stationary components of the machine. These include a series of diaphragms, some of which are indicated at 14, 15 and 16 in FIG. 1. The particular compressor illustrated is of the multi-stage, twosection type, having an impeller 17 located in the first stage of the first section and a second impeller 19 lo-, cated in the first stage of the second section. As shown in FIG. 1, the two impellers are mounted so as to face in opposite directions whereby the stages in the first section and the stages in the second section are aligned in a back-to-back relationship. By so opposing the stages of each section in the manner illustrated, the thrust forces exerted upon the rotor shaft 20 are minimized.  
  The last stage of the first section is arranged to discharge, via a diffuser passage and transfer crossover device (not shown), into the inlet area of the second stage between the diaphragms 14 and 15. For a more detailed description of this crossover arrangement, reference is had to US. Pat. No. l,9l0,8l l. The machine impellers are secured to the shaft 20 and the shaft, in turn, is journaled for rotation within the end walls of the machine. As viewed in FIG. 1, the left-hand end of the shaft is supported within a bearing structure 22 mounted in a horizontal wall which is an integral part of the main machine casing 11. The opposite end of the shaft is supported within a bearing structure 22 mounted within an independent end wall closure 26.  
  In this particular structure, the inner casing 13 terminates some distance inwardly from the open end of the outer casing 11. An internal annular groove 28, having a radially extending outer wall 30, a radially extending inner wall 31 and an axially extending bottom wall 32, is machined in the reinforced section 34 of the outer casing in close proximity to the open end thereof. A key assembly, generally referenced 35, is interposed between the end wall closure structure 26 and the machine casing 11 as illustrated in FIG. 1. The key assembly is made up of a first segmented shear key 39 and a support key 40.  
  As best illustrated in FIG. I, an annular shaped recessed shoulder 27 is formed in the end wall closure 26 having a radially extending rear wall 36 which penetrates the outer periphery thereof and an axially extending bottom wall 37 which is perpendicular to the rear wall and penetrates the front face of the closure. In assembly, the rear wall 36 of the recess shoulder is positioned between the vertical planes described by the two radially extended walls 30 and 31 of groove 28 in casing 11. The shear key is mounted within the groove and, as will be explained in greater detail below, is seated against the end wall 30 and bottom surface 32 of the casing groove. The body of the shear key extends downwardly into the casing opening so that the inner face of the key is in physical contact with at least a portion of the rear wall of the recessed shoulder. Sufficient contact area is provided between the rear wall of the shoulder and the inner face of the shear key to withstand the stresses developed, within allowable limits, when a machine is operating under designed load conditions.  
  A support key 40 is interposed between the bottom surface of the shear key and the axially extended bottom wall of the recessed shoulder. The support key is an annular ring having a rectangular cross-sectional ge ometry which complements the bottom portion of the shoulder.  
  In practice, the shear key is made of four distinct segments 50, 51, 52 and 53, to facilitate its insertion into the groove. The end face of each segment is arranged so that three axially aligned joints 56, 57 and 58 and one radially aligned joint 59 are established in assembly. Each segment face making up a joint is accurately machined whereby the segments coact to form a single unitized structure when they are seated within the casing groove. Upon insertion of the shear key segments into the groove, the support key or ring is passed into the end wall recess and the end wall moved laterally toward the casing opening so as to load the shear key in contact against both the rear wall of the closure and the casing groove. When so positioned, the support key is locked in place by means of cap screws 49 to prevent further movement or misalignment of the assembly.  
  The support ring further serves to translate radially acting forces from the closure wall to the shear key. Preferably, the axial width of the support key is such that the resultant radial forces acting upon the shear key are to the left of the center of gravity 65 (FIG. 3) of the shear key as viewed in FIG. 1. Similarly, the contact area between the rear wall of the recessed shoulder and the shear key is such that the resultant axial forces acting upon the key are below the center of gravity of the key. These forces are depicted as F,  
 and F on the free body diagram shown in FIG. 3. Be-  
 cause the contact area between the shear key and the end wall closure and the support key are known, the forces F, and F and thus the bending moments pro&#39; duced thereby are determinable for any given load condition of the machine.  
  As illustrated in FIG. 3, the upper surface and outer face of the shear key are both provided with raised moment control pads 67 and 68, respectively. The pads are arranged to seat against the bottom surface and outer face of the casing groove and are strategically positioned to produce moments in the key which are substantially equal, but opposite to, those moments pro duced by forces F and F As a result, the bending moments acting about the center of gravity of the shear key are substantially negated thus loading the key in compression against the casing of the machine.  
 The contact surfaces of each pad are such that resultant forces F and F are established which act at some known distance from the center of gravity of the shear key. In practice, the moment pad 67 is located so that the moment (F X d is equal to the moment (F, X 41,). Similarly, moment pad 68 is strategically located so that moment (F X d is equal to the moment (F, X d  
  By negating the bending moments in the manner herein described, the deflection of the retaining key is considerably reduced and its load carrying capacity i greatly increased. The compressive forces are resolved into a radially acting force F which is exerted against the bottom wall of the internal groove 28,and an axially acting force F which is translated to the outside radial wall 30 of the groove.  
 While this invention has been described with reference to the structure herein disclosed, it is not confined, to the details set forth and this application is intended wall and an axially extended bottom surface therebetween,  
 a shear key seated within the groove and extending f inwardly in a radial direction whereby a portion of the key extends into the opening within the casing, a recessed shoulder formed in the outer periphery of the end wall having a radially extending back wall positioned between the inner and outer end walls of said groove in the casing with the back wall of the shoulder being in contactwith the inner face portion of the shear key extending into the casing, opening, and an axially extending wall perpendicu&#39; lar to said back wall that penetrates the outer face of said end closure,  
 a support key seated against the radially and axially extending walls of the. recessed shoulder formed in the end wall with the outer surface of the support key being in contact with the bottom surface of the shear key to support the shear key within said groove, and  
 a pair of raised moment control pads mounted upon the shear key, one of said pads being in contact with the bottom surface of said groove in the casing and the other of said pads being in contact with the outer radially extending end wall of the casing, said I pads being strategically located in regard to the center of gravity of the shear key to substantially offset the bending moments exerted thereon by the support key and the back wall of the recessed shoulder formed in the end closure. 2. The apparatus of claim 1 wherein the shear key is segmented to facilitate its insertion into the casing groove.  
 3. The apparatus of claim 2 wherein the support key is an annular ring which is affixed to the end wall closure. I  
 ment control pads are of a predetermined area whereby the casing induced moments produced in the shear key are substantially opposite and equal to those induced by the end wall closure.