individual project dissertation

DESIGN AND MANUFACTURE GAS TURBINE BLADE ARUNTHIHAN RAMAJEYAN

FACULTY OF SCIENCE, ENGINEERING AND COMPUTING

School of Aerospace and Aircraft Engineering

BSc (Hons) DEGREE

IN BSc Aerospace Engineering

Name: Arunthihan Ramajeyan

ID Number: K1359820

Project Title: DESIGN AND MANUFACTURE GAS TURBINE BLADE

Date: April 2016

Supervisor: Dr Hossein Mirzaii

WARRANTY STATEMENT

This is a student project. Therefore, neither the student nor Kingston University makes any

warranty, express or implied, as to the accuracy of the data or conclusion of the work

performed in the project and will not be held responsible for any consequences arising out of

any inaccuracies or omissions therein.

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DECLARATION

I, the undersigned Arunthihan Ramajeyan student of BSc Honours degree in Aerospace Engineering

hereby declare that the project work presented in this report is my own work and has been carried

out under the supervision of Dr Hossein Mirzaii of Kingston University London.

This work has not been previously submitted to any other university for any examination.

Word count: 6853

Name: Arunthihan Ramajeyan

Student ID: K1359820

Date: 25/04/2016

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ACKNOWLEDGEMENTS

First and foremost, I would like to express my sincere gratitude to my module supervisor, Dr Hossein

Mirzaii, who has been guiding me throughout this project. His advice and guidance made me give my

best to complete this project. He shared his expertise with me, which gave me a better

understanding of the concept and also his friendliness made me enjoy this project. It is the main

reason which led me to finish this project successfully to the best of my ability.

I would also like to thank the lab technicians, Mr. Martin Theobald, Mr Dean Wells and Mr. Dave

Haskell for guiding and helping me complete my 3D printed components and for helping me

throughout the investment casting process. I would like to express my sincere gratitude to my family

and my colleague Mr. Nirojan Paranjothy who did the same project with me.

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ABSTRACT

There are so many methods of casting alloys, turbine blades are manufactured by investment casting

method or normally as lost-wax method. The investment casting method was developed over 5500

years ago and can trace its roots back to both ancient Egypt and China. This is the key method which

is used presently in Aviation industry for manufacturing the gas turbine blades. Investment casting

method is mainly used because it has wide range of advantages. It forms the component with

undercuts, can produce a very smooth surface which is formed without a parting line in the

component and accuracy. This dissertation looks detailed into the theoretical and practical side of

designing method used with the aid of Solid Works and investment casting method.

AIMS AND OBJECTIVES

The endmost aim of this project is to Design and Manufacture Gas turbine blade

Research methods of casting

Create the design of Gas turbine blade

Manufacturing the turbine blade using investment casting method

Research materials and their effectiveness on turbine blades

METHODOLOGY

The methods that I’m going to use to achieve my aims and objectives are as follows:

Create a design of turbine blade as a tree design using Solid Works

Create the 3D printed object using 3D printer.

Create the final metal blade using investment casting method

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Contents

DECLARATION........................................................................................................................................2

ACKNOWLEDGEMENTS..........................................................................................................................3

ABSTRACT..............................................................................................................................................4

AIMS AND OBJECTIVES......................................................................................................................4

METHODOLOGY.................................................................................................................................4

1 INTRODUCTION..................................................................................................................................7

2 Gas Turbine engine.............................................................................................................................8

2.1 Types of jet engines...................................................................................................................10

2.1.1 Turbojet..............................................................................................................................10

2.1.2 Turboprops.........................................................................................................................11

2.1.3 Turbofans............................................................................................................................11

2.1.4 Turboshafts.........................................................................................................................12

2.1.5 Ramjets...............................................................................................................................13

2.2 Gas turbine design.................................................................................................................13

2.2.1 Fans.....................................................................................................................................14

2.2.2 Compressor.........................................................................................................................14

2.2.3 Combustion chamber..........................................................................................................15

2.2.4 Turbine...............................................................................................................................15

2.3 Gas Turbine blade......................................................................................................................17

2.4 Turbine Blade failure.................................................................................................................19

2.4.1 High cycle fatigue................................................................................................................19

2.4.2 Environmental attack..........................................................................................................20

2.4.3 Creep damage.....................................................................................................................20

2.4.4 Erosion/Wear......................................................................................................................20

2.5 Materials used...........................................................................................................................21

2.6 Cooling system...........................................................................................................................22

3. Methods of Casting......................................................................................................................23

3.1.1 Sand casting............................................................................................................................23

3.1.2 Die casting..............................................................................................................................24

3.1.3 Shell Mould Casting................................................................................................................25

3.1.4 Lost foam casting....................................................................................................................25

3.1.5 Investment Casting.................................................................................................................26

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3.1.6 Cooling systems......................................................................................................................28

3.2 Designing Process..........................................................................................................................28

3.3 SolidWorks Design...............................................................................................................30

4. Manufacturing Process................................................................................................................32

4.2 Investment Casting Process...........................................................................................................33

4.2.1 Silicon Mould making..............................................................................................................33

4.2.2 Making the Wax model...........................................................................................................35

4.2.3 Ceramic Coating......................................................................................................................37

5 CONCLUSION....................................................................................................................................38

6 References........................................................................................................................................40

Figure 1 Newton's third law...................................................................................................................9

Figure 2(Durham, 2012).......................................................................................................................10

Figure 3Turbojet engine......................................................................................................................11

Figure 4Turboprop...............................................................................................................................12

Figure 5Turbofans................................................................................................................................13

Figure 6Turboshaft..............................................................................................................................13

Figure 7Ramjets...................................................................................................................................14

Figure 8Design.....................................................................................................................................14

Figure 9Compressor............................................................................................................................15

Figure 10Combustion chamber...........................................................................................................16

Figure 11Turbine.................................................................................................................................17

Figure 12Impulse Turbines..................................................................................................................17

Figure 13Impulse and Reaction turbines.............................................................................................18

Figure 14Gas turbine blades................................................................................................................19

Figure 15HCF blade..............................................................................................................................20

Figure 16Creep damage curve.............................................................................................................21

Figure 17Sand casting..........................................................................................................................25

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Figure 18Die Casting............................................................................................................................25

Figure 19Shell mould casting...............................................................................................................26

Figure 20Lost Foam Casting.................................................................................................................26

Figure 21Investment casting method..................................................................................................28

Figure 22Turbine blade design............................................................................................................30

Figure 23Turbine blade aero foil design..............................................................................................30

Figure 24Turbine blade side view........................................................................................................30

Figure 25Aerofoil view with the dimensions in mm............................................................................31

Figure 26Aerofoil blade twist angle 9˚.................................................................................................31

Figure 27Blade heights 1.76 in............................................................................................................31

Figure 28Blade view............................................................................................................................31

Figure 29Blade root.............................................................................................................................32

Figure 30blade root side view.............................................................................................................32

Figure 31Final blade views...................................................................................................................32

Figure 32Final blades with the tree.....................................................................................................32

Figure 33UP BOX.................................................................................................................................33

Figure 34Removing off the Turbine blade...........................................................................................34

Figure 35Turbine blades with the sheet..............................................................................................34

Figure 36Mould box.............................................................................................................................34

Figure 37Silicon mould Cut into half....................................................................................................35

Figure 38Breaking off the Mould box..................................................................................................35

Figure 39Silicon settling.......................................................................................................................35

Figure 40Pouring Silicon into the mould box.......................................................................................35

Figure 41Mixing silicon with curing agent...........................................................................................35

Figure 42Assembly...............................................................................................................................37

Figure 43Wax blades and tree.............................................................................................................37

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Figure 44Wax blades...........................................................................................................................37

Figure 45Wax Tree model....................................................................................................................37

Figure 46Wax poured..........................................................................................................................37

Figure 47ceramic coating left to dry....................................................................................................38

Figure 48Ceramic first coating.............................................................................................................38

Table 1Failure Severity........................................................................................................................20

Table 2(Tantalum - element information, properties and uses, no date)............................................22

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1 INTRODUCTION

Any aircraft which moves through air is moved by the force called thrust. “For every action, there is

an equal and opposite reaction” according to Isaac Newton’s third law of motion. When any two

objects get interface with each other, whether it gets directly interacted or at a distance, they exert

forces each other equally.

Any device which converts heat energy of fuel into mechanical energy is known as engine or heat

engine. Engine is widely used in automobile industries or an engine can be even called as the heart

of automobile. To make an aircraft move forward, there need to be a pushing force or thrust which

is created by making the air accelerate between the front and the back of the engine. Any device

which converts heat energy of fuel into mechanical energy is known as engine or heat engine. Engine

is widely used in automobile industries or an engine can be even called as the heart of automobile.

To make an aircraft move forward, there need to be a pushing force or thrust which is created by

making the air accelerate between the front and the back of the engine. It converts the energy from

burning fuel by three elements which it has in it. They are compressor, combustor and turbine. A gas

turbine can create thrust by accelerating air or make electricity, turn pumps and ship propellers by

driving generators. (reserved, 2016)

The turbine blade is a very complex shape which consists of a root at the bottom of the blade. It has

an aerofoil shape which extracts the thermal energy from the hot exhaust gases. The root of the

blade is attached to a disc. There will be hundreds of blades attached in a single disc, which is called

a stage. There are several stages in each section of the engine. (IMPRESS education: Circular motion,

no date)

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2 Gas Turbine engine

As I indicated above in my introduction, “For every action, there is an equal and opposite reaction”.

To explain it with an example, as you sit in a chair, your body acts with one force on the chair, and

the chair reacts with another force on your body. It is that “when you sit in a chair, the force of

gravity is balanced by the force of the chair pushing up” (Newton’s Third law of motion: Examples of

the relationship between two forces - video & lesson transcript, 2003).

Basically Gas turbine engines are used for two purposes, first for power production and secondly for

generating thrust for aircraft. They are very simple; they have three simple parts which are

Compressor, combustion area and turbine. Compressor compresses the incoming air to high

pressure. Combustion area is where the fuel and produces high-pressure, high-velocity gas. Turbine

extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber.

To elaborate it briefly, a gas turbine engine moving forward uses a simple principle. Just like the

reaction force produced by a balloon, the reaction force produced by the high speed jet at the tail of

the jet engine makes it move forward. The higher the speed of the jet the greater the thrust force.

The thrust force makes an aircraft move forward. Such high speed is achieved by a combination of

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Figure 1 Newton's third law


techniques. If you can heat the incoming air to a high temperature, it will expand tremendously and

will create the high-velocity jet. For this process, a combustion chamber is used. The fuel is burnt in

the combustion chamber. Effective combustion requires air to be moderately high temperature and

pressure. To bring the air to this condition, a set of compressor stages are used. The rotating blades

of the compressor add energy to the fluid and its temperature and pressure rise to a level suitable to

sustain combustion. The compressor receives the energy for the rotation from a turbine which is

placed right after the combustion chamber. The compressor and turbine are attached to the same

shaft. The high energy fluid that leaves the chamber makes the turbine blades turn.

The turbine blades have a special air foil shape which creates lift force and make them turn. As the

turbine absorbs energy from the fluid its pressure drops. Through these steps a really hot high

speed air emitted through the exit of the engine.(Learn Engineering, 2015)

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Figure 2(Durham, 2012)


2.1 Types of jet engines

2.1.1 Turbojet

The term ‘turbojet’ is commonly used for a number of engines such as turbojet, turboprop, turbofan

and turboshaft, because all of them use a common principle. In simple terms, as engine ejects burnt

mixture backwards a forward force is created on the engine of the aircraft. In this case, greater the

backward force the greater the forward force. (Turbojet engines, 2011)

The basic idea of turbojet engine is simple. First Air is taken into the front of the engine and

compressed to 3 to 12 times of its original pressure in compressor. Then fuel is added to the air in

the combustion chamber and burned in a combustion chamber to raise the temperature of the fluid

mixture to about 1,100˚F to 1,300˚F. The hot air is passed through a turbine, which drives the

compressor. If the turbine and compressor are efficient enough, the pressure at the turbine will be

nearly twice the atmospheric pressure. This pressure which is excess is sent then to the nozzle to

produce a high-velocity gas which produces thrust. Increase in thrust can be obtained by usinga

afterburner. Afterburner is a second chamber which is positioned after the nozzle. This increase in

temperature is will increase about 40 percent in thrust at take-off.

The turbojet is also known as a reaction engine. In a reaction engine, The turbojet sucks air in and

squeezes or compresses it. Then the gases flow through the turbine and make it spin. These gases

bounce back and shoot out of the rear of the exhaust, which pushes the plane forward. (Engines, no

date)

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Figure 3Turbojet engine


2.1.2 Turboprops

Turboprop engines are used in some transport aircraft and small airliners. A turboprop engine has a

propeller attached in it. The hot gases turn the turbine at the back, and this turns a shaft that rotates

the propeller. The turboprop consists of a compressor, combustion chamber, and the turbine like a

turboprop to run the turbine, So that the turbine creates power to drive the compressor. The

turboprop propulsion efficiency is higher than compared with a turbojet engine for speeds below

500 mph. Recent turboprop engines have lots of blades with fewer diameters to give a more

efficient operation at higher flight speeds. In a turboprop engine the blades are scimitar-shaped with

swept-back leading edge in the blade tips. (Engines, no date)

2.1.3 Turbofans

A turbofan consists of a large fan at the front side of the engine which is used to suck in air. Normally

the air flows around the outside of the engine which will make it give it more thrust at low speeds

and for making it quitter. In a turbofan only some air goes into the combustion chamber, the

remainder passes through a fan, low-pressure compressor, and is ejected directly mixed with the

gas-generator exhaust to produce a hot jet whereas all the air entering the intake passes through

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Figure 4Turboprop


the gas generator, which is made up with the compressor, combustion chamber and turbine. It

achieves this by increasing the total air-mass flow and reducing the velocity within the total energy

supply as the same. (Engines, no date)

2.1.4 Turboshafts

This engine is much like a turboprop system. It provides power for a helicopter without driving a

propeller in it. This turboprop engine is designed so that helicopter rotor speed is free of the rotating

speed of the generator and is not dependent with it. Even when the generator is varied to modulate

the amount of power reduced, the turboprop permits the rotor speed to be kept in the same level.

(Engines, no date)

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Figure 5Turbofans

Figure 6Turboshaft


2.1.5 Ramjets

The ramjet is the simplest jet engine which has no movable part in it. Air entering it is compressed by

the movement of the vehicle. It has a long duct into which fuel is fed at a controlled rate. The fuel is

ignited by the incoming heated compressed air. A Ramjet will only start work above a speed of 485

km/h. The Ramjet is more fuel efficient than turbojets and turbofans above Mach 3 making them

better for use on missiles. (Darling, no date)

2.2 Gas turbine design

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Figure 7Ramjets

Figure 8Design


2.2.1 Fans

The fan in the front of the engine and it is a gas turbine which draws air into the engine; it

compresses the bypass stream to produce 80 percent of the engine’s thrust, and feeds air to the gas

turbine core. (reserved, 2016a)

2.2.2 Compressor

The compressor is driven by the turbine. It rotates at high speed, adding energy to the airflow and

compressing into a smaller space. So compressing the air increases the pressure inside the engine.

The purpose of a compressor is to increase the pressure of the air inside the gas turbine engine.

Then it sends the compressed air into the combustion chamber. (reserved, 2016a)

The compressor is assumed to contain fourteen stages of rotor blades and stator vanes. In an axial

flow compressor, each stage normally boosts the pressure from the previous stage. A single stage of

compression consists of a set of rotor blades attached on a disk, followed by stator vanes attached to

a stationary ring.

In general, the compressor rotor blades convert mechanical energy into gaseous energy.

2.2.3 Combustion chamber

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Figure 9Compressor


The combustion chamber is the area inside the engine where the fuel or air mixture is compressed

and ignited. It is normally formed on one side by the shape cast into the cylinder head, in the other

side by the top of the piston. The chamber is at its smallest dimension when the piston is at top-

dead-centre. And at this time the fuel/air will be in a condition where it is ready to be ignited.

2.2.4 Turbine

There are four stages in a turbine. The turbine converts the gaseous energy of the burned fuel/air

mixture out of the combustor into mechanical energy to drive the compressor, through a reduction

gear, the propeller. It converts gaseous energy into mechanical energy by expanding the hot, high-

pressure gases to a lower temperature and pressure. Each stage consists of stationary vanes which

are followed by rotating blades. The vanes and blades are air foils that provide for a smooth of the

gases. As the airstream enters the turbine from the combustion section, it is accelerated by the

stator vanes in the first stage. Then the stator vanes form the convergent ducts that convert the

gaseous heat and pressure energy into higher velocity gas flow.

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Figure 10Combustion chamber


As the high velocity gas flows across the turbine blades, the gaseous energy is converted to

mechanical energy.AT this stage velocity, temperature and pressure of the gas are compromised to

rotate the turbine to generate power from the engine. (FUNDAMENTALS OF GAS TURBINE ENGINES,

2010)

There are two basic types of steam turbines, impulse turbines and reaction turbines, in which he

blades are designed to control the speed, pressure and direction of the steam as it passes through

the turbine.

2.2.4.1 Impulse Turbines

The steam jets are kept at the turbine’s bucket shaped rotor blades directly where the pressure

exerted by the jets causes the rotor to rotate and the velocity of the

stream to reduce as it imparts its kinetic energy to the blades. But the

blades change the direction of flow of the steam however its

pressure remains the same as it passes through the rotor blades as

the gap between the blades are constant. Therefore Impulse turbines

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Figure 11Turbine

Figure 12Impulse Turbines


are known as constant pressure turbines. So the next series of fixed blades reverses the direction of

the steam before it passes to the second row of moving blades.

2.2.4.2 Reaction Turbines

The rotor blades of the reaction turbine are more like aerofoils; they are arranged where the cross

section in-between the chambers formed are fixed blades which reduces the inlet side of the blades.

The chambers between blades form nozzles so that as the steam progresses through the chambers,

its velocity increases and the pressure decreases. Also the pressure decreases in both the fixed and

moving blades. So as the steam enters in a jet in between the rotor blades, the steam creates a

reactive force on the blades which in turn creates the turning moment on the turbine rotor just like

in a steam engine. (Shukla, 2013)

2.3 Gas Turbine blade

Turbine blade is the rotating component within the turbine which gives challenges to the design and

manufacturing communities. It is an individual component which makes the turbine section of a gas

turbine engine. Blades are responsible for extracting energy from the high temperature, high

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Figure 13Impulse and Reaction turbines


pressure gas produced by the combustor. They are exposed to more tough environments in a gas

turbine.

Therefore turbine blades are carefully designed to resist all these tough conditions and make up with

the suitable material which can resist all these conditions. There are some more methods done to

withstand all these problems such as cooling system, boundary layer, thermal bearing coatings and

internal air channels. The Gas turbine blade is designed in an aerofoil design and reformed in such a

way where it provides equal space between adjacent blades. The area of the cross-section of each

blade is fixed by the allowed stress in the material used and by the size of the holes which is required

for blade cooling purpose. The trailing edge of the blade is designed thin in considering preventing it

from blade cracking which may occur due to the change in temperature while the engine works.

One of the most important things considered in gas turbine blade is attaching the blade to the

turbine disc because the stress in the disc around the fixing and in the blade root has a key

behaviour on the limiting rim speed.

This design of fixing the blade to the disc which is used in most of the gas turbine engines presently

is known as ‘fir-tree’ fixing, whereas in past the blade is fixed by the de Laval bulb rooting fixing. This

‘fit-free’ ensures that the loading on the blade is shared by all the serrations. The blade is free in the

serrations when the turbine is still and is rigid in the root by centrifugal loading when the turbine is

rotating. A shroud is fitted at the tip of the blade and a small

segment is made up at the tip of the blades which forms a

tangential ring around the blade which is formed to reduce the loss

of efficiency through gas leakage across the blade tips.(166837

EB161 rolls royce the jet engine fifth edition gazoturbinnyy

dviga, no date)

2.4 Turbine Blade failure

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Figure 14Gas turbine blades


Failure means that a thing does not meet its desirable objective; in this case a turbine blade failure

means that it’s no longer suitable for use but can be used till the limited amount of time given for it

to be used.

2.4.1 High cycle fatigue

High cycle fatigue is the main problem of a turbine blade it is generally caused aerodynamic

excitations and by self-excited vibration and flutter which is because of the repeated cycling of the

load on a structural member. HCF damage occurs when the stress levels are above the fatigue

strength. It occurs after a number of load cycles that results in cracking. The crack will then gradually

increase through the material with each stress cycle.

2.4.2 Environmental attack

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Table 1Failure Severity

Figure 15HCF blade


The environment should be considered in turbine blade failure as they are exposed to be damaged

from oxidation, corrosion and sulphidation. It does not lead the blade to a enormous failure but it

has a role in it which can slowly damage the blade with time.

2.4.3 Creep damage

This damage occurs when the blade is operated overtime under high stresses and temperature. As a

rough rule, a 15° increase in blade metal temperature cuts creep life by 50 percent. This shows the

importance of effective cooling. ([CSL STYLE ERROR: reference with no printed form.])

2.4.4 Erosion/Wear

This cause catastrophic blade failure rarely, but it contributes to some other blade failures which can

cause a blade replacement. In addition to the primary damage caused by erosion, a reduction in the

surge margin can occur if the tips of the blades get severely eroded.

2.5 Materials used

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Figure 16Creep damage curve


Modern gas turbines have the most advanced technology in all aspects, Turbine blades are exposed

to the extreme operating condition. It is exposed to around 1400°C – 1500°C, high pressure, high

rotational speed, vibration, small circulation area and so on.

So to overcome it, Gas turbine blades are made using advanced materials and super alloys that

contains up to ten significant elements, it consists of rectangular locks of stone stacked in a regular

array with narrow series of cement to stick them together. Presently tantalum is used replacing

intermetallic form of titanium which has been used in the past. (NEW TECHNOLOGY USED IN

GAS TURBINE BLADE MATERIALS, no date)

Tantalum is an incredibly useful metal with unique properties that make it the choice for a range of

places to be used where strength, durability, corrosion, resistance, ductility and a high melting point

are critical. (Tantalum (Ta), 2015).

Table 2(Tantalum - element information, properties and uses, no date)

Since the 950’s, 250°C of allowable metal temperatures has been yielded from wrought to

conventionally cast to directionally solidified to single crystal turbine blades. In the other side,

cooling developments have nearly doubled the temperature which enters the turbine.

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If metallurgical development can be exploited by reducing the cooling air quantity this is a

potentially important performance enhancer.

2.6 Cooling system

Turbine blades presently focus to on blade cooling system which is important to reduce the blade

metal temperature to acceptable levels for the materials increasing thermal capability of the engine.

Turbine blade cooling is classified into two sections such as internal cooling system and external

cooling system.

Internal blade cooling: It is where the heat is removed by a variation of convection and

impingement cooling configurations, where high velocity air flows and hits the inner surface of the

turbine blades.

External blade cooling: It is where cold air is injected through the cooling holes of the external

surface of the turbine blade surface to create a thin film cooling layer.

However in both cases they are implemented to keep the entire blade cool enough to ensure that

the high temperature does not damage the blades. There are more sub-parts inside Internal cooling

system and External cooling system which is not necessary to explain in the report as it is not done in

throughout project. This is a general brief of how cooling systems work and the purpose of it. (2016,

2014)

3. Methods of Casting

Casting is a manufacturing which is mostly used to make more complex methods. It is a process in

which normally liquid material is poured into a mould, which has a hollow cavity of the desired

shape in which we expect our solid finished material should be. Then the solidified part is ejected or

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broken out of the mould to complete the casting process. In my project, I have used investment

casting method to manufacture the gas turbine blade. So in this report as it takes more time, I have

explained the types of casting as an overview summarising and concentrated more on Investment

casting method. Basic types of casting: Sand casting, Die casting, Shell mould casting, lost-foam

casting, and investment casting.

3.1.1 Sand casting

It is a metal casting process characterised by using sand as the mould material. In addition to the

sand, clay is mixed with the sand. The mixture is moistened with water, sometimes with some other

substances to develop strength and plasticity of the clay to make the combination suitable for

moulding. The word ‘sand casting’ is referred to an object produced by the sand casting process.

Over 70% of all metal castings are produced by a sand casting process. This casting method is

relatively cheap and obstinate even for steel foundry use.

Basic Process:

Place a pattern in sand to create a mould.

Incorporate the pattern and sand in a gating system.

Remove the pattern

Fill the mould cavity with molten metal

Allow the metal to cool

Break away the sand mould and remove the casting.

25 K1359820Figure 17Sand casting


3.1.2 Die casting

It is a meal casting process which forces molten metal under high pressure into a mould cavity. The

mould cavity is made using two hardened steel dies which works more similar like an injection

mould during the process.

3.1.3 Shell Mould Casting

It is a metal casting process in manufacturing industry in which the mould is a thin hardened shell of

sand and thermosetting resin binder, with some other material.

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Figure 18Die Casting

Figure 19Shell mould casting


3.1.4 Lost foam casting

It is a type of evaporative-pattern casting which is similar to investment casting except in this foam is

used for the pattern instead of wax.

3.1.5 Investment Casting

Investment casting which is also known as lost was investment casting, is a precision casting process

used to create more complex metal parts from almost any alloys. The use of this casting method

accelerated in 1940s as a result of demand for specialised tools. Following World War II, the

technique expanded into many industrial and commercial applications.

The term “investment” refers to ceramic materials that are used to build a hollow shell into which

molten metal is poured in to make castings. (Investment casting FAQs, no date)

Requirements for investment casting:

Metal die

Wax

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Figure 20Lost Foam Casting


Ceramic slurry

Furnace

Molten metal

Advantages:

Reliability – It provides reliable process controls and

repeatability that are maintained from casting to casting.

Tolerances – It holds tolerances of ±.005˚

Amortization Lowers tooling cost – It is lower than other

casting tooling costs.

Better for the Environment – It is produced from 9 wax

patterns which in most cases can be reclaimed and used

again.

Intricate Design – Can easily incorporate features such as

logos, product ID’s/numbers, and letters into their

component. (Advantages of investment casting vs. Sand

casting, die casting, no date)

Process:

Pattern creation – The wax patterns are typically injected moulded into a metal die and are

formed as one piece.

Mould creation – This “pattern tree” is dipped into slurry of fine ceramic particles, coated

with more coarse particles, and dried to form a ceramic shell around the patterns.

Pouring – The mould is pre-heated in a furnace to approximately 1000˚C and the molten

metal is poured from a ladle into the gating system of the mould, filling the mould cavity.

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Cooling – After the mould is filled, the molten metal is allowed to cool and solidify in to the

shape of the final casting.

Casting removal – After the molten metal has cooled, the mould is broken and the casting is

removed.

Finishing – Heat treatment or grinding or sand blasting the part at the gates to harden the

final part. (CustomPartNet, 2009)

3.1.6 Cooling systems

Turbine blades lifetime is reduced as it is exposed to very hot temperatures. Therefore, turbine

cooling is necessary to increase the blades working time. Due to the contribution and the

development of turbine cooling systems the turbine has been lasted long. Turbine blade cooling is

classified into two sections; they are internal cooling system and external cooling system.

Internal cooling system: It is where the heat is removed by a variation of convection and

impingement cooling configurations, where velocity air flows and hits the inner surface of the

turbine blades.

External Cooling system: It is where the cold air is injected through the film cooling holes which are

on the external blade surface to create a thin film cooling layer.

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Figure 21Investment casting method


Internal cooling system and external cooling system are implemented to the turbine blade to keep

the entire blade cool and ensure that temperature gradients within the blade are kept to an

acceptable level. (2016, 2014)

3.2 Designing Process

The turbine blade is an aero foil shape and when designing a turbine blade, each stage of the blade

has different dimensions. First I couldn’t find a realistic design of a turbine blade, as this is a design

and manufacturing project, struggled in finding the realistic dimension. Discussed with the lab

technicians and finally found the actual blade which is used in the University lab. Got the dimensions

of the blade used more accurately with a digital Vernier calliper. Below are the Design of the Turbine

blade used.

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Figure 22Turbine blade aero foil design Figure 23Turbine blade design

Figure 24Turbine blade side view


3.3 SolidWorks Design

The SolidWorks software is a 3D mechanical design, which allows to design any three Dimensional

objects. Below is the blade and root design which was designed using the SolidWorks software.

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Figure 26Aerofoil blade twist angle 9˚Figure 25Aerofoil view with the dimensions in mm

Figure 27Blade viewFigure 28Blade heights 1.76 in

Figure 30Blade root Figure 29blade root side view

Figure 31Final blade views Figure 32Final blades with the tree


4. Manufacturing Process

4.1 Start of manufacturing process – 3D printing

My final design of the turbine blade is confirmed by my supervisor and was ready to the 3D printing

process. The 3D printer does the 3D printing procedure automatically when we import the CAD

design to it. The university provided me the 3D printer, in which the masterpiece 3D printed model is

printed out as an ABS plastic turbine blade. The 3D printer which printed my blade is known as UP

BOX. UP BOX specifications:

Material used – ABS plastic

Resolution – 100 microns

Dimension of the UP BOX:

Width – 255 mm

Height – 205 mm

Depth – 205 mm

To print it out the first step I did was, saved the file in STL format and sent it to the lab technician

Mr. Dave Haskell. Then Opened the CatalystEX software and modified the dimensions in the

software to keep it within the machine requirements. Selected print properties and adjusted

resolution and orientation as the lab technician instructed me to do. The machine calculated

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Figure 33UP BOX


how much material will be used and the estimated duration of the printing. The duration of my

blade to be printed took 10 hours. Set the machine to print, the machine printed my blade all

night and I took it out the following day in the morning. The 3D printed turbine blade was fixed

to the ABS plastic sheet inside the UP BOX, removed the blade sheet and unwanted materials

using pliers, shears and a scraper off the blade.

4.2

Investment Casting Process

4.2.1 Silicon Mould making

The first step to start off made a mould box with the suitable dimensions of the turbine blade to

attach it fixed inside the blade with the aid of wires. The box must wider on either side by the same

length of the blade and the height of the blade should be three times the height of the blade.

Length 136mm

Width 103mm

Height 100mm

Table 37 Dimensions

After making the mould box, the blade must be kept inside the blade stable so that it stays still when

pouring the silicon inside the box. To do this, Drilled some holes in the

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Figure 34Turbine blades with the sheet Figure 35Removing off the

Turbine blade

Figure 36Mould box


blade and in the root of the blade. Kept the blade using copper wires inside the blade and held a

thick metal at the bottom of the root so that wax will be poured in it and the copper wires are used

so that after the silicon mould is complete, the copper can be removed and the copper holes will be

used as air pockets to suck out air when pouring the wax.

The turbine blade is taped making a parting line before it was kept inside the mould box so that

when cutting the silicon mould, the parting line will make it easy to cut the silicon blade.

Calculated the volume of the silicon to be poured in to the mould box

Length × Width × Height

136 mm × 103 mm × 100 mm

Volume =1400800 mm3

Volume =1400.8 cubic centimetres

With the help of the lab technician, mixed curing agent with the Silicon. Amount of curing agent

mixed was 10% of the silicon which is 140.08 cubic centimetres and mixed it with the hardener to

allow it to settle. After mixing them, kept it in the vacuum chamber to remove any air inside with

setting up it to -1 bar pressure. After it, poured the silicon into the box and kept it in the vacuum

chamber again so that it removes any more air trapped in it. The mould box with the silicon is kept

inside the vacuum chamber overnight to settle and taken out the following day morning.

Next day morning removed the mould box off after the silicon mixture settled overnight. Cut the

silicon mould into half, and it is very important to cut the silicon mould and with the splitting line

where the tape was put. So that the mould can be easily opened and closed for wax pouring.

34 K1359820Figure 37Mixing silicon with curing agent

Figure 38Pouring Silicon into the mould box

Figure 39Silicon settling

Figure 40Breaking off the Mould box

Figure 41Silicon mould Cut into half


4.2.2 Making the Wax model

After cutting, took out the ABS plastic 3D printed blade and tree design out, sprayed mould release

in both the silicon mould where the wax blade the tree design silicon mould sticks. Sprayed mould

release in both the silicon mould where the wax blade sticks in and stapled both together tightly so

that the wax blade is stable inside the wax mould and taped it tightly. Put the top of the moulds with

tape so that the excess molten wax does not overflow.

In the afternoon, after keeping the mould in the oven for couple of hours with the temperature of

30˚C to be warm and recycled wax which was kept in a separate oven at 100˚C to be melt. Poured

wax in the moulds with the help of lab technician in the hole of where a thick metal was placed as in

the mould making process above. Used gravity method to pour the wax into the mould as the lab

technician told me in past years it is the way they were being doing in this method. Kept the mould

so that the wax to be cooled and settled for three hours in the mould properly.

Safety precautions:

Lab coat

Safety boots

Pair of gloves

Safety goggles

After three hours, Separated the mould off and took the wax blade and tree design out. The wax tree

design was a success in the first pouring as the wax blade has some air bubbles in it. It is because the

air rises did not release the air out properly. Following day morning, made the moulds ready for the

second pouring as in the first process mentioned above but with making the air rising holes more

clear so that the blade does not get any air bubbles in it.

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Poured wax in the moulds. Saw the air rises filled with the wax properly in the second pouring. After

keeping the blade to cool for another couple of hours, separated the moulds off and took out the

wax models. This time, blade was not up to the desired level. Discussed with the lab technician

about the problem and came to a conclusion of pre-heating the silicon mould at 35˚C warm so that

the wax can flow through all the complex parts. After keeping it to cool for another couple of hours,

separated the wax model off the mould. It still didn’t come to the desired level. Then realised the

blades has some complex parts in which wax can’t flow through the gravity method of pouring. Did

seven pouring of wax and four of the blades were good enough to progress with the next process as

time was a problem in this process. It needs quite more patience in this process to get the desired

level of outcome. Started assembling process, attached the wax turbine blades to the tree design

using hot gun. Used hot glue gun to attach two turbine blades in a tree.

4.2.3 Ceramic Coating

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Figure 45Wax poured

Figure 42Wax Tree model

Figure 43Wax blades Figure 44Wax blades and tree

Figure 46Assembly


This process consists of three steps which is coating, stuccoing and hardening. It is a

repeated process in which the wax model is dipped in the ceramic. The first step of ceramic

coating is to get the amount of ceramic which is going to be used in the tree design. Used

340 ml of ceramic material with 470 ml of binder and stirred together.

The initial idea is to coat the turbine blades for about three to four layers with the time

interval of forty to forty five minutes with the ceramic mixture.

Future works to be done:

Complete the wax coating

Burnout/ De-Wax

Pour molten metal and Break the Ceramic Coating

5 CONCLUSION

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Figure 49Ceramic first coating Figure 48ceramic coating left to dry

Figure 47 Ceramic coated blade


The gas turbine blade is a unique component with an aero foil design which undergoes more tough

environments such as high temperatures and pressures, whereas exposed to approximately 1500

degree C. The turbine blade experiences major failures like creep and fatigue failures which is due to

high dynamic stresses caused by vibration and resonance within the operating range. These failures

lead to the end of the life of blade as well. To overcome this, Engineers work hard to prevent these

failure problems by implementing cooling systems and manufacturing the blades in metallic alloys,

such as nickel based alloys, which has high melting point, toughness and light weight.

The turbine blade is manufactured using investment casting method, which is a process that needs

more patience. This process is a very lengthy process, being a future engineer this process gave a lot

of experience in patience and at the same time learned how to manage time with work. This process

also gave quite much experience in working as an engineer with a technician in the lab.

In this the author of this report likes to share the success and problems faced in this project. To start

off with, Designing the blade was the second step to this project in which background research

played a major role for the author as this is the first individual project experienced. For designing the

turbine blade, dimensions were needed. It was one of the biggest challenges faced as all the turbine

blade manufacturing companies did not help to give the dimensions. Mailed and tried to contact

more than ten manufacturing companies, still not even a single company replied nor gave their

blade dimensions. As the project had a limited amount of time to manufacture the turbine blade,

started designing the blade with an appropriate design chose and with some assumptions.

At the middle of the designing process, Mr Dave Haskell, lab technician found a turbine blade and

gave as this project was already been discussed with him. Then took the dimensions of the turbine

blade and designed the blade with all accurate dimensions and got approved by the Supervisor for

the design created using SolidWorks.

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Once the design is done, took the blade design to the lab technician as it was already been discussed

with them for making this project. Unfortunately, due to repair in 3D printer it took quite a couple of

weeks to get through 3D printing process. As the 3D printing machine started working, started the

manufacturing process. The lab technicians were busy because most of the students used lab for

their final projects and the technicians gave time for this project as 3 days in a week which was not

enough to finish this project as some of the wax models were failure. Lab technician, Mr Dave

Haskell also told that this manufacturing process takes only two to three weeks to be finished but

then when met him two months ago but in the end they were all busy. The factor which affected this

project also includes not planning properly as the supervisor advised. This project could not be

finished on time includes the reason that it was not easy as it was thought to be.

Future works to be done:

It is the simplest part to be done comparing this whole project which can be done in the following

week. As mentioned above with some lab issues the process took some more time than the

expected date of deliverable. Two steps away from finishing this project, they are finishing the shell

forming with ceramic and metal model making.

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Documents

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