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Axial Flow Compressor-Physical Concepts-Project Report, Study Guides, Projects, Research of Physics Fundamentals

This project is related to Physics and cover its multiple concepts. It was submitted to Sir Ahmad Yasir at Bengal Engineering and Science University. It includes: Axial, Flow, Compressor, Design, Calculations, Manufacturing, Centrifugal, Refrigerant, Cycle

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Download Axial Flow Compressor-Physical Concepts-Project Report and more Study Guides, Projects, Research Physics Fundamentals in PDF only on Docsity! 1 1. Introduction 1.1 Motivation The use of gas turbine in the petrochemical, power generation and offshore industry has mushroomed in past few years. The growth of the gas turbine in recent years has been brought about most significantly by metallurgical advances to employ high temperatures in the combustor and turbine components, and the cumulative background of aerodynamic and thermodynamic knowledge, and the utilization of computer technology in the design and simulation of turbine blade and combustor. Therefore this is very interesting field and motivated one. A lot of research is going on to improve the efficiency of the gas turbine and its operating temperature. 1.2 Objective The project objectives were as 1 Design calculation of axial flow compressor 2 components drawing 3 Manufacturing of axial flow compressor After going through initial design calculation of axial flow compressor, the manufacturing drawing of lab scale axial flow compressor is to be drawn along with assembly drawing of axial flow compressor.. In this thesis the design methodology of axial flow compressor was discussed first and then attention was focused on manufacturing of lab scale axial flow compressor. 1.3 Scope of project The significance of turbojet engine due to their use in military aircrafts makes this project tremendously important, since compressor is one of the fundamental components of engine and the performance of engine is directly dependent on the performance of compressor. docsity.com 2 1.4 Compressor Compressors are machines that compress air or gas. Compression is achieved through the reduction of the volume that the gas (or air) occupies. As a side effect of the minimization of volume, the temperature of air or gas increase. Compressors are used in refrigeration and air conditioner equipment to move heat from one place to another in refrigerant cycles [1]. Compressor could be of axial flow, centrifugal, or a combination of both types in order to produce highly efficient compressed air which can be used for useful power output. Kinetic energy is imparted to compressor in impeller part of compressor and then this kinetic energy is converted to pressure energy by passing air through diverging section called diffuser. 1.5 Design Calculation Figure 1-1 Types of compressor Types of compressor are shown in fig 1-1.positive displacement compressors confine successive volume of gas in an enclosed space where pressure increases as the volume of enclosed space decreases. They can be thought as constant volume-variable pressure machine. That is, they move a certain volume of gas with each stroke, and the pressure is that of the system into which they discharge. With dynamic compressors, the mechanical section of rotating impellers imparts pressure and velocities to the gas. They are constant pressure-variable volume machines [1]. docsity.com 5 industrial gas turbine. Improvement in power output and efficiency rests primarily on increases in turbine inlet temperature. The union of ceramics and super alloys will provide the material strength and temperature resistance necessary to facilitate increased turbine firing temperature. However, increasing firing temperature will also increase emissions. To insure continued acceptance of the gas turbine, emissions must be eliminated or significantly reduced. To reduce emissions, catalytic combustors are being developed. The catalytic combustors will reduce NOx formation within the combustion chamber. They will also reduce combustion temperatures and extend combustor and turbine parts life. While increased power (in excess of 200+ megawatts) will be provided without increasing the size of the gas turbine unit, the balance of plant equipment (such as; pre- and inter-coolers, regenerators, combined cycles, gasifiers, etc.) will increase the overhaul size of the facility. Designers and engineers must address the total plant not just the gas turbine. The size of the various process components must be optimized to match each component‟s cycle with the gas turbine cycle, as a function of ambient conditions and load requirements. Computer (microcomputer or programmable logic controller) control systems must be designed to interface and control these various processes during steady-state and transient operation [4]. Researchers will intensify their efforts to supply hydrogen, processed from non-fossil resources, for use in petroleum based equipment. The objective is to produce recoverable, cost effective, and environmentally benign energy. Ultimately the gas turbine will be required to burn hydrogen, even with a plentiful supply of fossil fuel. The use of hydrogen eliminates the fuel bound nitrogen that is found in fossil fuels. With combustion systems currently capable of reducing the dry NOx level to 25 ppmv; and catalytic combustion systems demonstrating their ability to reduce emissions to “single digits”; the use of hydrogen fuel promises to reduce the emission levels to less than 1 ppmv. The gas turbine will need to achieve this low level in order to compete with the fuel cell. Today the largest fuel cell manufactured is rated at only 200 kilowatts. This technology is available, it will be developed, and it will compete with the gas turbine [4]. Hospitals, office complexes, and shopping malls will become the prime sales targets for 1 to 5 megawatt power plants. Operating these small plants, on site, may docsity.com 6 prove to be more economical than purchasing power through the electric grid from a remote power plant. This is especially true with the current restructuring of the electric utility industry. To reduce the expense of units fewer than 5 megawatts, the next breakthrough must be in the production of axial blade and disc assemblies as a single component [4]. The greatest single obstacle to reducing gas turbine costs is the manufacturing process - machining and assembly. A typical gas turbine has over 4000 parts. About one third of these parts are made from exotic materials that incur high development cost. Each of the 4000 parts must be handled several times from initial machining to final installation. Maintaining this machine is every bit as complicated, requiring the same technical skills, as building a new unit [4]. Producing the blade and disc assembly as a single part will reduce the quantity of parts handled and relax the requirement for tight dimensional tolerances between parts. In the very small gas turbines, manufacturers are returning to the centrifugal wheel in both the compressor and the turbine. The advantage is that this design can be produced as a single part. These units operate on gaseous or liquid fuel and generate from 20 to 50 kilowatts. These units may also find an application in home power use. Furthermore, manufacturers have access to advanced design tools such as computational fluid dynamics (CFD) to optimize compressor and turbine aerodynamic designs. The gas turbine still has not found its place in land transportation use (automobiles and trucks). This application has been stifled in the past due to high production and maintenance cost. However, a hybrid electric car application may utilize the gas turbine generator as a range extender. In this capacity it will provide a constant power source to continuously charge the on-board battery pack. The gas turbine (turbofan, turbojet, and turboprop) will continue to be the major player in aircraft applications for the next 50 to 100 years. In the next 10 years, alone, over 76,000 gas turbines, turbojet and turbofans will be built. Also, the gas turbine will be used to a greater extent in marine applications, primarily in military applications but also in fast-ferries [4]. docsity.com 7 2. Axial Flow Compressor Axial flow compressors are dynamic type of compressors in which air flow is parallel to the axis of rotation. Cut way sketch of axial flow compressor is shown is figure 2-1. The axial flow compressor can achieve higher pressures at a higher level of efficiency. There are two important characteristics of the axial flow compressor high pressure ratios at good efficiency and thrust per unit frontal area [5]. Compressor usually works in two steps 1 Increase the momentum of air by doing work on it(using rotor blades) 2 Decelerate the air to increase static pressure(using stator blades) Figure 2-1 Axial flow compressor 2.1 Basic Operation Axial flow compressors are rotating, airfoil based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have a significant radial component on exit. Axial flow compressors produce a continuous flow of compressed gas, and have the benefits of high efficiencies and large mass flow capacity, particularly in relation to their cross-section. They do, however, require several rows of airfoils to achieve large docsity.com 10 Compressor cascade is shown in figure 2-4.The stagger angle  is the angle between the chord line and the axial direction and represents the angle at which the blade is set in the cascade. / 1 and /  are the camber angles of the entry and exit tangents the camber line makes with the axial direction. The blade camber angle is / / 1    . The chord c is the length of the perpendicular of the blade profile onto the chord line. It is approximately equal to the linear distance between the leading edge and the trailing edge. The pitch s is the distance in the direction of rotation between corresponding points on adjacent blades. The incidence angle i is the difference between the air inlet angle and the blade inlet angle. That is i= / 1 - /  .The air deflection angle 1     is the difference between the entry and exit air angles. For any particular test, the blade camber angle  its chord c and the pitch (or space) s will be fixed and the blade inlet and outlet angles / 1 and /  are determined by stagger angle  which is calculated from appendix A-1. [5]. Figure: 2-4 Compressor cascade and blade notation docsity.com 11 3. Designing of Axial Flow Compressor 3.1 Symbols There are three state points within a compressor that are important when analyzing the flow. They are located at the inlet guide vanes, the rotor entrance, and at the stator exit. Rotor blade is located between 1 and 3 as shown in figure 3-1 Figure 3-1 Compressor blading arrays Following is the nomenclature and symbols of different variables used which will be used to explain the basic theory. C1 Absolute velocity of fluid at inlet to stator C2 Absolute velocity of fluid at exit from stator C3 Absolute velocity of fluid at exit from rotor Ca Axial velocity of fluid U Blade speed v2 Relative velocity of fluid at rotor inlet v3 Relative velocity of fluid at rotor exit α1 Angle of C1 with axial direction α2 Angle of C2 with axial direction β2 Angle of v2 with axial direction (blade inlet angle) β3 Angle of v3 with axial direction (blade exit angle) p01/p03 Stagnation pressure ratio per stage ηs Isentropic efficiency of stage Λ Degree of reaction docsity.com 12 Cp specific heat at constant pressure ΔTs stagnation temperature difference The subscript 1 and s with T and p will represent static and stagnation temperatures and pressures respectively for any state of fluid through the compressor [5]. 3.2 Temperature Drop Coefficient (Ψ) Temperature drop coefficient (also called loading coefficient) „ expresses the work capacity of a stage, and is the ratio of stage work output to half of the blade speed. (3-1) Where stage work output= p sC T By substituting the value of stage work output in equation (3-1) the resulting equation for stage work output is given by equation (3-2) 21 2 p sC T U    (3-2) The following equation is obtained for temperature drop coefficient in terms of blade angles. Stage work output W in terms of gas angles associated with the rotor blades will be 2 3(tan tan )aW UC    (3-3) Then from equation (3-3) the following equation (3-4) is obtained for temperature drop coefficient 2 32 2 2 (tan tan ) p os a C T C U U        (3-4) 3.3 Degree of Reaction (Λ) Degree of reaction or simply reaction expresses the fraction of the stage expansion which occurs in the rotor and is defined as the ratio of static enthalpy drop in rotor to the static enthalpy drop in the whole stage. It is given by 2 3 1 3 T T T T     (3-5) And T1, T2 and T3 are the static temperatures at the three sections of the compressor. docsity.com 15 1 1 1 01 01 T P P T         Substituting the values of static temperature, stagnation temperature and pressure in equation (4-2) 1.4 1.4 1 1 299 1.01 300 P        =0.998Bar Now density at inlet can be calculated by using equation (4-3) 1 1 1 P RT   Substituting the values of static pressure and temperature at inlet and value of R in equation (4-3) 1 .998 287 299    =1.163 3/Kg m The volumetric flow rate is the product of mass flow rate and density so volumetric flow rate is calculated by using the equation (4-4) ̇= ̇ Substituting the values of mass flow rate and density at inlet in equation (4-4) =1 1.163 = 31.163 /Kg m 4.1.2 Calculation of Tip Velocity Tip velocity is calculated by using the equation (5-5) t tU r  Where w is called angular velocity and r t is root radius. N is the rotational speed. 60 t tU r    (4-6) Area at inlet can be calculated by using equation (4-7) . 1 1 1 0.0258 1.163 45a m A C      (4-3) (4-2) (4-4) (4-5) (4-6) docsity.com 16 After calculating tip radius tip velocity can be calculated by using the equation (4- 5).but first of all tip radius can be calculated by using the equation (4-8) 21 t r A r r   Substituting the values of area at inlet and root radius in equation (4-8) tip radius is given as 2.0258 .06tr    =0.1m Now tip velocity can be calculated by using the formula 60 t tU r    Substituting the values of rotational speed which is fixed N=6000 r.p.m and tip radius in equation (4-9) .1 60 tU    =62.832 m/sec Axial velocity is constant along the annulus. Tip velocity can be obtained by using equation (4-10) 2 2 t t aV U C  Substituting the value of tip velocity and axial velocity which is fixed in equation (4- 9). 2 2 262.8 45tV   77.26 / sectV m 4.1.3 Calculation of Mach Number at Inlet Now at this stage it is approximate to check Mach number relative to rotor tip at inlet to compressor Speed of sound= 1a RT  Substituting the values of static temperature and R in equation (4-11) gives the value of speed of sound. (4-8) (4-9) (4-10) (4-11) docsity.com 17 Speed of sound= 1.4 287 299a    =346.6 m/sec Mach number is calculated by the ratio of tip velocity and speed of sound. Mach number = 1 tVM a  Substituting the values of tip velocity and speed of sound in equation (4-12) gives value of Mach number at inlet 1 77.26 346.6 M  =0.223 4.1.4 Calculation of Temperature, Pressure and Density at Exit It is instructive to estimate the annulus dimension at exit from the compressor. The compressor delivery pressure is 2.02.To estimate the compressor delivery temperature it is assumed that polytropic efficiency is 0.90.Thus 1 02 02 01 01 n nP T T P         as 1 1 1 p n n       Substituting the values of polytrophic efficiency in equation (4-14) 1 1 1.4 1 0.9 1.4 n n     =0.3175 Substituting the values of stagnation temperature at inlet, stagnation pressure at inlet and outlet in equation (4-13) gives value of stagnation temperature at outlet.   0.3175 02 300 2T  =373.85K Now static pressure, temperature and density at exit can be calculated by following relationships (4-15) (4-12) (4-13) (4-14) docsity.com 20 4.1.6 Blade Angles Now blade angles can be calculated from the velocity triangle shown in the figure (4- 1).blade inlet angle can be calculated by using relationship (4-20) 1tan a U C   Substituting the values of blade speed and axial velocity in equation (4-21) 1 62.8 tan 45   1 1 62.8 tan 45   0 1 54.38  Velocity of air at inlet can be calculated by using equation (4-22) 1 1cos aCV   Substituting the values of axial velocity and blade angle at inlet in equation (4-22) 1 45 cos54.38 V  1 77.26V  In order to estimate maximum possible deflection we will apply the haller criterion 2 0.72 1 V V  .On the basis of allowable value of 1 77.26V  2 77.26V   2 55.63V  Now we can calculate balde angle at outlet by using the relationship (4-23) 2 2 cos a C V   Substituting the values in equation (4-23) 2 45 cos 55.63   (4-20) (4-22) (4-23) docsity.com 21 1 2 45 55.63 Cos  0 2 36  Now from the velocity triangle we can calculate whirl velocity which is given by relationships (4-24) and (4-25) 2 2tan y x w C   2 2tany xw C   Substituting the values of blade angle at exit and axial velocity in equation (4-24) gives the value of whirl velocity 2 tan36yw   2 32.69yw  m/sec Now 2yC can be calculated by using the equation (4-25) 2 2y y C U w  Substituting the values of blade velocity and whirl velocity in equation (4-25) 2 62.8 32.69yC   2 30.1 / secyC m Now by having blade outlet angle the air angle at outlet can be calculated by using the velocity triangle. 2 2tan y x C C   Substituting the values in equation (4-26) 1 2 30.1 tan 45   0 2 33.778  4.1.7 Stage Loading Factor Stage loading factor is given by the relationship (4-27) 1 2tan tan )      Substituting the values of blade angle at inlet at exit in equation (4-27) tan54.38 tan36)   (4-24) (4-25) (4-26) (4-27) docsity.com 22    4.1.8 Axial Force Axial force can be calculated by considering pressure difference and area.so axial force can be calculated by using the equation (4-28) 02 01( ) 2a mF P P r h      Substituting the values of stagnation pressure at inlet and exit, mean radius and height of blade in equation (4-28) (2.02 1.01) 2aF       2030aF N 4.1.9 Degree of Reaction Degree of reaction or simply reaction expresses the fraction of the stage expansion which occurs in rotor. So degree of reaction can be calculated by using the relationship (4-29) 1(tan tan 2 R        Substituting the values of flow coefficient, blade angles at inlet and exit in equation (4-29) 0 00.72 (tan54.38 tan36 2 R    0.76R  4.1.10 Number of Blades Number of blades can be calculated by using the relationship (4-30).For the calculation of number of blades the pitch is selected as half. 4 2 6 18 2 rrN S       4.1.11 Slope of Blade Slope of blade can be calculated from the ratio of difference between height of blade at inlet and outlet and root radius. So from equation (4-31) (4-28) (4-29) (4-30) docsity.com 25 that base of blade is constructed with the help of pro-e and then assembly drawing is been drawn. Table 5-2 Blade profile data parameter notation value pitch s 4 Blade inlet angle / 1 54.38 Bal outlet angle / 2 14 Pitch to chord ratio s/c 1.2 Pitch to chord ratio s/c 1.2 Height of blade h 4 Number of blades n 18 5.1 Length of Compressor for the calculation of width of stator and rotor we selected stagger angle from appendix figure A-1 The stagger angle is chosen to be 44 0 So width is given by using equation (5-3) cosw C  Substituting the value of stagger angle in equation (5-3) 3.33cos44 2.38w cm  Rotor and stator width is given by Rotor width= 2.4w cm Space between stator and rotor is given by following equation (5-4) Space= 0.5 1.2s w cm  (5-4) Inlet space of compressor is given by equation (5-5) Inlet space 1.2 0.6 2 2 s cm   Stator width 2.38s cm  outer space of compressor is given by equation (5-6) Outer space 1.2 0.6 2 2 s cm   Total length of compressor=2.4+1.2+0.6+2.38+0.6=7.2cm (5-3) (5-5) (5-6) docsity.com 26 5.2 Angle of Casing Angle of casing is being calculated by using equation (5-7) 1tan  (difference in blade height at inlet and outlet/length of compressor) (5-7) Substituting the values in equation (5-7) 1 4 2.67tan ( ) 7.2     010.5  5.3 Design of Retaining Strip Strip width for first stage rotor =0.6cm Pitch for rotor blades = 2 cm Let us assume strip as cantilever beam by taking half potion between two bolts, further calculations are given below Length of assumed beam 1.2 2 2 pitch s cm   (5-8) Axial force for rotor blades 2040 1020 2 2 aF N   M=forcedistance 1020 0.012 12.24Nm   My I   (5-9) 3 2 62 12 t M M t b t b        2 6 Mt b    250y Mpa  =yield stress of steel (from appendix A-2) F.O.S=Factor of safety=3 Substituting the values of yield stress and F.O.S in equation (5-12) 250 83.33 . . 3 y Mpa F O S      Substituting the values in equation (5-11) gives value of thickness of strip. 2 6 6 12.24 0.006 83.33 10 t     (5-10) (5-11) (5-12) docsity.com 27 0.012 12 t m t mm   5.4 Bolt Designing Consider the total length of bolt 2 4 1.867 1 2.54 1.129 Lt D Lt Lt         Diameter of bolt Now the diameter of bolt is given by equation (5-13) 1 1.129 4 4 0.4395 2 2 tL D        From appendix A-3 Size designation=1/2 Threads per inch=N=13 Tensile stress area= 20.1419tA in So length of the bolt is given by equation 1 1 2 1.25 2 4 Lt        Outer portion = 1.867 1.25 0.5149 1.308 2.54 cm     From appendix A-4 for medium carbon SAE grade number=5 Minimum proof strength =85 Kpsi p t p F A  Substituting the values in equation (5-16) 12.06 0.8 9.65 p i p i F F F F     We know that from equation 5-17 (5-13) (5-14) (5-16) (5-15) docsity.com 30 iii. The type of service under given conditions such as temperature, humidity, dustiness, acidity, etc. iv. The anticipated life of the bearing. v. Magnitude and direction of loads. vi. The proportion of thrust to radial load. 5.7.2 Deep Groove Ball Bearing Figure 5-1 Bearing number system First we calculate basic load rating from the following formula (5-24) [6] 1 60 3 61 10 H rpm C P         (5-24) P is the power of motor required to derive the shaft.N is the rotational speed in r.p.m which is 6000. Putting the values of load, hours and rpm in Equation (5.24) For 20000h, C= 0.35KN And from [Appendix Table A-5] We select 6005ZZC3 having bore diameter 25 mm with high clearance (C3) because speed is high. And its dynamic load rating is very much greater than the calculated value of load rating. 5.8 Flange Coupling A flange coupling usually applies to a coupling having two separate cast iron flanges. Each flange is mounted on the shaft end and keyed to it. The faces are turned up at right angle to the axis of the shaft. One of the flanges has a projected portion and the docsity.com 31 other flange has a corresponding recess. This helps to bring the shafts into line and to maintain alignment. The two flanges are coupled together by means of bolts and nuts . The flange coupling is adapted to heavy loads and hence it is used on large shafting. The flange couplings are of the following types: - [6]. o Unprotected type flange coupling. o Protected type flange coupling. o Marine type flange coupling For designing of flange coupling Let d = Diameter of shaft or inner diameter of hub, D = Outer diameter of hub, d1 = Nominal or outside diameter of bolt, D1 = Diameter of bolt circle, n = Number of bolts, Figure 5-2: Flange Coupling tf = Thickness of flange, The flange coupling is designed as discussed below Shear stress for shaft, bolt and key material = 46 MPa Shear stress for cast iron = 8 MPa [12] 5.8.1 Design for Hub The hub is designed by considering it as a hollow shaft, transmitting the same torque (T) as that of a solid shaft. 4 4 16 D d T c D            (5-25) Substituting the values in equation (5-25) we get T=9156 N-mm docsity.com 32 And maximum torque would be after multiplying by service factor Power (hp) 1.5,1.4,1.3 6000 r.p.m SF:1.33 1.5,1.4,1.3 1800 r.p.m SF:1.25 1.5,1.4,1.3 1200 r.p.m SF:1.15 Table 5-3 Service factor max T service factor T  (5-26) Taking service factor 1.33 for motor of power 1.5hp and 6000 r.p.m from table (5-3) then Tmax=12360.6Nmm Putting the values in equation 5.25 d=22mm but I will take d=25mm So outer diameter of hub D=2d=50mm Length of hub=L=1.5d=37.5mm Let‟s check induced shear stress in hub 4 4 16 D d T c D            (5-28) Putting the values in Equation 5.27 0.40c MPa  That is less than the permissible shear stress 8MPa in cast iron. 5.8.2 Designing of Key Crushing stress in key is calculated by using equation (5-28) 4 4 16 T c D d D            (5-28) Substituting the values in equation (5-28) 0.40ck k MPa   Diameter of shaft=d=25mm For Square key Width of key=thickness of key=10mm [Appendix Table A-7] docsity.com 35 Figure 6-3 shows the retaining strip for axial flow compressor. As mentioned earlier, it is used to stop axial movement of the rotor blades inside the rotor disks. It has 18 holes of 4mm diameter for the bolts for its fixing with the rotor disk. Two retaining strips are used for the prevention of axial moment of blades from both sides of the rotor disk of single stage axial flow compressor. Figure 6-3 Retaining strip Figure 6-4 shows inlet duct of axial flow compressor. Inlet air passes through this side of compressor. Figure 6-4 Inlet duct Figure 6-5 shows casing of lab scale axial flow compressor with stator blades inside. Stator blades are stationary blades that actually act as nozzle. Figure 6-5 Casing of axial flow compressor docsity.com 36 6.2 Two Dimensional Drawings Figure 6-6 shows two dimensional drawing of rotor disk with grooves. The rotor blades are inserted into grooves. Figure 6-6 Disk of rotor blades with grooves. Figure 6-7 shows two dimensional drawing of inlet duct of axial flow compressor. It is used as passage for flow of air into the rotor disk. Figure 6-7 Shaft with rotor disk Figure 6-8 shows two dimensional drawing of retaining strip. The basic function of retaining strip is to block the axial moment of rotor blades. docsity.com 37 RO.1 0.002 ——— Figure 6-8 Retaining strip docsity.com 40 8. Casting Casting is the process whereby molten material is poured into a mould of the required shape and then allowed to solidify. Moulding is a similar process used to form plastic materials. The mould should be shaped so that molten material flows to all parts of the mould. A sand casting or a sand molded casting is a cast part produced by forming a mold from a sand mixture and pouring molten liquid metal into the cavity in the mold. The top and bottom halves of a sand casting mould showing the cavity prepared by patterns. Cores to accommodate holes can be seen in the bottom half of the mould, which is called the drag. The top half of the mould is called the cope. The mold is then cooled until the metal has solidified. In the last stage the casting is separated from the mold. 8.1 Sand Casting Mold The oldest types of molds for aluminum casting are the molds that have been use since the time of the Egyptians. These types of molds are made when a cavity is created in sand that is held in a box or "flask". Usually the original "pattern" is made out of wood, metal or other solid material. There is also a core in the sand cavity that forms the center of the casting. Of the different aluminum casting molds, this is one that is used especially for engine blocks, engine manifolds, and other large and heavy castings. Sand casting mold has been shown in figure 8-1. Figure 8-1 Sand Casting docsity.com 41 There are two main types of sand used for molding. "Green sand" is a mixture of silica sand, clay, moisture and other additives. The "air set" method uses dry sand bonded to materials other than clay, using a fast curing adhesive. The latter may also be referred to as No bake mold casting. When these are used, they are collectively called "air set" sand castings to distinguish these from "green sand" castings. Two types of molding sand are natural bonded (bank sand) and synthetic (lake sand), which is generally preferred due to its more consistent composition. With both methods, the sand mixture is packed around a master "pattern" forming a mold cavity. If necessary, a temporary plug is placed to form a channel for pouring the fluid to be cast. Air-set molds often form a two-part mold having a top and bottom, termed Cope and drag. The sand mixture is tamped down as it is added, and the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold. Then the pattern is removed with the channel plug, leaving the mold cavity. The casting liquid (typically molten metal) is then poured into the mold cavity. After the metal has solidified and cooled, the casting is separated from the sand mold. There is typically no mold release agent, and the mold is generally destroyed in the removal process. The accuracy of the casting is limited by the type of sand and the molding process. Sand castings made from coarse green sand impart a rough texture on the surface of the casting, and this makes them easy to identify. Air-set molds can produce castings with much smoother surfaces. Surfaces can also be ground and polished, for example when making a large bell. After molding, the casting is covered in a residue of oxides, silicates and other compounds. This residue can be removed by various means, such as grinding, or shot blasting. During casting, some of the components of the sand mixture are lost in the thermal casting process. Green sand can be reused after adjusting its composition to replenish the lost moisture and additives. The pattern itself can be reused indefinitely to produce new sand molds. The sand molding process has been used for many centuries to produce castings manually. Since 1950, partially-automated casting processes have been developed for production lines . docsity.com 42 8.2 Casting of Rotor Blades According to dimensions, when pattern was made, then next step is to cast. The method which was choosing for casting that was sand casting. Material for the sand casting is aluminum ASTM 443.0.In pattern material was over allowanced. Because in casting there is some contraction in material so that is the logic of allowance. After sand casting of the blades of single stage gas turbine, Blade has been shown in Figure 8-2 Figure 8-2 Rotor Blade after Casting To make the blade with required dimension, it was filed with round file. First rough file was used, then for finishing fine file was used. Blade after filing has been shown in Figure 8-3 Figure 8-3 Blade after Finishing Cast and finished blade is shown in figure 8-4 Figure 8-4 Blade before and after finishing docsity.com 45 Finishing of casing was done with the help of lathe machine. Figure 8-9 finishing of casing of axial flow compressor 8.5 Assembling of Parts After finishing of casing of axial flow compressor the assembling of parts was done. This is shown in figure.8-10.this figure shows axial flow compressor without the base. Figure 8-10 assembling of compressor components Now base is paced at the bottom of axial flow compressor and resulting assembly with base and inlet duct is shown in figure 8-11 Figure 8-11 compressor with base docsity.com 46 9. Testing of axial flow compressor After manufacturing the components of compressor the assembling of compressor is done and in the last testing of axial flow compressor is done. Requirements for testing of compressor are. electric motor of 1.5 hp, pulleys to mount on compressor rotor shaft and motor-belt to transmit power from motor to compressor rotor, proper casing to exit the air, manometer to check the pressure at the exit of the compressor to ensure its proper functioning(compression),tachometer to measure the r.p.m of compressor. First we have to mount pulley on shaft of compressor and to the motor. Then these two pulleys are then engaged with the help of v-belt. Manometer is attached to the casing and at the exit of the compressor. Then turn on the motor which in turn derive the compressor through belt and pulley arrangement. As the rotor rotates the air at atmospheric pressure enters the inlet duct of compressor and after passing through rotor assembly of compressor enters into the stator assembly and then passes through casing on which manometer is attached for pressure measurement. With the help of this manometer the compression ratio of compressor is calculated and compared with analytical results. docsity.com 47 10. Summary and Conclusion For manufacturing of axial flow compressor, designing was done. In the design calculations, the design has been done for an inlet temperature of 300, rotational speed of 6000 rpm, and inlet pressure of 1 bars.. The inlet and outlet blade angles are calculated to be β1 = 54.38 ° and β2 =36 ° respectively. The rotor blade height comes out to be 4cm and a constant root radius of 6cm for a single stage axial flow compressor is obtained. The gross power has been calculated for single stage gas turbine that is 250kw .The values of aspect ratio and pitch to chord ratio are selected by assuming with keeping in mind the low value of number of blades, because the number of blades truly depend upon aspect ratio and pitch to chord ratio. Our value of optimum pitch to chord ratio is less than the selected value of pitch to chord ratio. . Axial, tangential and radial loads on blades and shaft have been calculated and forces on each blade have been calculated. For preventing the radial moment of blade there are grooves in rotor disk like T shape. And to lock the axial motion of blades in rotor, retaining strips are used on both sides with the help of screws of 4mm with helical spring washers. The diameter of shaft is calculated 25mm. After designing the shaft system of rotor, patterns of blades and rotor disk with shaft have been made, and then sand casting have been done by using aluminum alloy ASTM 443.0 having yield strength of 55MPa. After casting the shaft system of rotor and casing finally finishing have been done by using lathe machine and finishing of blades have been done by using file. Grooves in rotor disk have been made by using milling machines with two cutters. Then these are assembled and retained by two strips with 4mm diameter screws. For bearing seats on both sides shaft have diameter with press fit to bearings. Total shaft length is 58.2cm. docsity.com 50 Table A- 3 SAE Specification for Steel Bolts Table A- 4 SAE Specification for Steel Bolts SAE Grade No. Range inclusive, in Proof strength, kpsi Tensile strength, kpsi Yield strength, kpsi Material 1 1 1 1 4 2  33 60 36 Low or medium carbon 2 1 3 4 4  3 1 1 8 2  55 33 74 60 57 36 Low or medium carbon 4 1 1 1 4 2  65 115 100 Medium carbon, cold drawn docsity.com 51 5 1 1 4 1 1 1 1 8 2   85 74 120 105 92 81 Medium carbon,Q&T 5.2 1 1 4  85 120 92 Low- carbon martensite, Q&T 7 1 1 1 4 2  105 133 115 Medium carbon alloy, Q&T Table A- 5 NTN Catalogue for deep groove ball bearings docsity.com 52 Table A- 6 Constants of Dynamics Load Ratings ] Table A- 7 Proportions of standard parallel tapered and gib head keys docsity.com
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