EBW -2

Advantages of EBW:
1) High penetration to width can be obtained, which is difficult with other welding processes.
2) High welding speed is obtained.
3) Material of high melting temperature can be welded.
4) Superior weld quality due to welding in vacuum.
5) High precision of the welding is obtained.
6) Distortion is less due to less heat affected zone.
7) Dissimilar materials can be welded.
8) Low operating cost.
10) Reactive materials like beryllium, titanium etc. can be welded.
11) Materials of high melting point like columbium, tungsten etc. can be welded.
12) Inaccessible joints can be made.
13) Very wide range of sheet thickness can be joined (0.025 mm to 100 mm)
Disadvantages of EBW:
1) Very high equipment cost.
2) High vacuum is required.
3) High safety measures are required.
4) Large jobs are difficult to weld.
5) Skilled man power is required.
Applications of EBW
1.Electron beam welding process is mostly used in joining of refractive materials like columbium, tungsten, ceramic etc. which are used in missiles.
2. In space shuttle applications wherein reactive materials like beryllium, zirconium, titanium etc. are used.
3. In high precision welding for electronic components, nuclear fuel elements, special alloy jet engine components and pressure vessels for rocket plants.
4. Dissimilar material can be welded like invar with stainless steel.

Electron Beam Welding

Electron Beam Welding (EBW) is a fusion welding in which coalescence is produced by heating the workpiece due to impingement of the concentrated electron beam of high kinetic energy on the workpiece. As the electron beam impinges the workpiece, kinetic energy of the electron beams converts into thermal energy resulting in melting and even evaporation of the work material.

Principles:
In general, electron beam welding process is carried out in vacuum. In this process, electrons are emitted from the heated filament called electrode. These electrons are accelerated by applying high potential difference (30 kV to 175 kV) between cathode and anode. The higher the potential difference, the higher would be the acceleration of the electrons. The electrons get the speed in the range of 50,000 to 200,000 km/s. The electron beam is focused by means of electromagnetic lenses. When this high kinetic energy electron beam strikes on the workpiece, high heat is generated on the work piece resulting in melting of the work material. Molten metal fills into the gap between parts to be joined and subsequently it gets solidified and forms the weld joint.

EBW Equipment:
An EBW set up consists of the following major equipment:
a) Electron gun,
b) Power supply,
c) Vacuum Chamber, and
d) Work piece handling device.

Electron-Gun: An electron gun generates, accelerates and aligns the electron beam in required direction and spots onto the workpiece.
Emitter/Filament: It generates the electrons on direct or indirect heating.

Anode: It is a positively charged element near cathode, across which the high voltage is applied to accelerate the electrons. The potential difference for high voltage equipment ranges from 70- 150 kV and for low voltage equipment from 15-30 kV. Grid cup: Grid cup is a part of triode type electron gun. A negative voltage with respect to cathode is applied to the grid. The grid controls the beam.

Focusing unit: It has two parts: Electron focusing lens and deflection coil. Electron focusing lens focuses the beam into work area. The focusing of the electrons can be carried out by deflection of beams. The electromagnetic lens contains a coil encased in iron. As the electrons enter into the magnetic field, the electron beam path is rotated and refracted into a convergent beam. The extent of spread of the beam can be controlled by controlling the amount of DC voltage applied across the deflection plates.

Electron gun power supply: It consists of mainly the high voltage DC power supply source, emitter power supply source, electromagnetic lens and deflection coil source. In the high voltage DC power supply source the required load varies within 3-100 kW. It provides power supply for acceleration of the electrons. The potential difference for high voltage equipment ranges from 70-150 kV and for low voltage equipment 15-30 kV. The current level ranges from 50-1000 mA. In emitter power supply, AC or DC current is required to heat the filament for emission of electrons. However DC current is preferred as it affects the direction of the beam. The amount of current depends upon the diameter and type of the filament. The current and voltage varies from 25-70 A and 5-30 V respectively. The power to the electromagnetic lens and deflection coil is supplied through a solid state device.

Vacuum Chamber: In the vacuum chamber pressure is reduced by the vacuum pump. It consists of a roughing mechanical pump and a diffusion pump. The pressure ranges from 100 kPa for open atmosphere to 0.13-13 Pa for partial vacuum and 0.13-133 mPa for hard vacuum.As the extent of vacuum increases, the scattering of the electrons in the beam increases. It causes the increase in penetration.

Work Piece Handling Device: Quality and precision of the weld profile depends upon the accuracy of the movement of work piece. There is also provision for the movement of the work piece to control the welding speed. The movements of the work piece are easily adaptable to computer numerical control.

Friction Welding -2

Applications of Friction Welding

1.span over wide products for aerospace, agricultural, automotive, defense, marine and oil industries.
2.Automotive parts that are friction welded include gears, engine valves, axle tubes, driveline components, strut rods and shock absorbers
3. Hydraulic piston rods, track rollers, gears, bushings, axles and similar parts are commonly friction welded by the mmanufacturers of agricultural equipment
4. Friction welded aluminum/copper joints are in wide usage in the electrical industry.
5.Stainless steels are friction welded to carbon steels in various sizes for use in marine systems and water pumps for home and industrial use
6.Friction welded assemblies are often used to replace expensive casting and forgings
FRICTION STIR WELDING

Friction Stir Welding (FSW) is another variant process of friction welding
The basic problems with fusion welding of aluminum and its alloys are that they possess:
 Cast brittle dendritic structure,
 Micro porosity,
 Inferior mechanical and fatigue properties,
 Loss of strength in heat affected zone,
 Solidification and liquation cracking,
 Loss of alloying elements from the weld pool.

Inertia welding or (Friction Stir Welding) is a modified form of friction welding, where the moving piece is attached to a rotating flywheel. The flywheel is brought to a specified rotational speed and is then separated from the driving motor. The rotating assembly is then pressed against the stationary member and the kinetic energy of the flywheel is converted into frictional heat. The weld is formed when the flywheel stops its motion and the pieces remain pressed together. Since the conditions of the inertia welding are easily duplicated, welds of consistent quality can be produced and the process can be easily automated.

FSW Application
The industrial application of friction stir welding includes following :
 Aerospace: Wings, fuselage, cryogenic fuel tanks, aviation fuel tanks, aircraft structure, and external aircraft throw away tanks.
 Marine: Deck panes, bulkheads, floors, hull and superstructures, refrigeration plants, internal frameworks, marine and transport structures.
 Railway: High speed trains, container bodies, railway tankers, good wagon and underground rolling stocks.
 Automotive: Engine and chassis cradles, wheel rims, tailored blanks, armour plate vehicles,motorcycle and bicycle frames, buses and airfield vehicles, fuel tankers, suspension parts, crash boxes.
 Construction: Bridges, reactors for power and chemical industries, pipelines, heat exchangers, air conditioners, offshore drilling rigs etc.
 Other applications include: Electric motor housing, connectors, busbars, encapsulation of electronics and joining of aluminum to copper, food tins etc.

Friction Welding

Friction Welding (FRW) is a solid state welding process which produces welds due to the compressive force contact of workpieces which are either rotating or moving relative to one another. Heat is produced due to the friction which displaces material plastically from the faying surfaces.

In friction welding the heat required to produce the joint is generated by friction heating at the interface. The components to be joined are first prepared to have smooth, square cut surfaces. One piece is held stationary while the other is mounted in a motor driven chuck or collet and rotated against it at high speed. A low contact pressure may be applied initially to permit cleaning of the surfaces by a burnishing action. This pressure is then increased and contacting friction quickly generates enough heat to raise the abutting surfaces to the welding temperature. As soon as this temperature is reached, rotation is stopped and the pressure is maintained or increased to complete the weld. The softened material is squeezed out to form a flash. A forged structure is formed in the joint. If desired, the flash can be removed by subsequent machining action. Friction welding has been used to join steel bars upto 100 mms in diameter and tubes with outer diameter upto 100 mm.

Advantages of Friction Welding

1. No filler material, flux or shielding gases are needed.
2. It is an environment-friendly process without generation of smoke, fumes or gases.
3. No material is melted so the process is in solid state with narrow heat affected zone (HAZ).
4. Oxides can be removed after the welding process.
5. In most cases, the weld strength is stronger than the weaker of the two materials being joined. 6. The process can be easily automated for mass production.
7. The process is very efficient and comparatively very rapid welds are made.
8. Plant requirements are minimal and wide variety of metals and combinations can be welded.

Limitations of Friction Welding
1. Process is restricted to Object that can be rotated about its axis
2.one of the component must be ductile when hot, to permit deformations.
3. Preparation and alignment of the workpieces may be critical for developing uniform rubbing and heating
4. Tooling costs are high and free-machining alloys are difficult to weld

Process Parameters of AJM

The process parameters in AJM can be grouped into the following categories. The Ishikawa cause and effect diagram depicts the effect of various process parameters on the accuracy and quality of the machining operations by the abrasive jet machine.

1. The Abrasive: types, composition, strength, size, mass flow rate

2. The Gas: composition, pressure and velocity

3. The nozzle: geometry, material, stand-off distance (SOD), feed rate, inclination to work

4. The workpiece: Type of material

The selection of abrasive particles to be used in AJM depends upon the type of work material and type of machining operation which needs to be carried out. Different machining operations such as finishing, roughing require different types of abrasive for AJM operations. Commonly used abrasive for cutting include aluminum oxide and silicon carbide. In cleaning, etching and polishing operations glass beads and dolomites are recommended. The size of the abrasive particles also plays an important role in type of machining operations of AJM. Coarse grain particles are recommended for cuttingoperations while fine grains are recommended for finishing or polishing operations


The gas used in the AJM process must be non-toxic. It should be cheap and easily available. Common types of gas used in AJM applications are air, nitrogen and carbon. The recommended velocity of gas abrasive mixture ranges between 100 m/sec to 300 m/ sec depending upon the cutting or finishing operation.

The velocity of gas abrasive mixture is a function of nozzle design, nozzle pressure, and abrasive particle size. Stand-off distance (SOD) is a very important parameter. SOD is defined as the distance between the tip of nozzle and the work surface. The larger the SOD the poorer is the quality and accuracy of the cut. The effect of SOD on the accuracy of the cut is 10 – 30 micron Cutting, grooving

Abrasive Jet Machining (AJM)

In abrasive jet machining (AJM) material removal occurs on account of impact of high velocity air / gas stream of abrasive particles on the workpiece. The abrasives are propelled by a high velocity gas to erode material from the workpiece. As an outcome of impact of the abrasive particles on the workpiece, tiny brittle fractures occur at the surface of the workpiece and the carrier gas carries away the fractured fragments. AJM is also called as abrasive blasting process. It is also known by several other names such as abrasive micro-blasting, pencil blasting and micro-abrasive blasting. AJM is an effective machining method for hard and brittle materials such as glass, silicon, tungsten and ceramics. Typically the process is used for cutting intricate shapes or forms of specific edges. The process is inherently free from chatter, vibration and heat problems because the tool never touches the substrate. The schematic of AJM process set up is shown in Figure

Principle of AJM

The principle of machining / cutting by abrasive jet process is explained through the
following steps:

1. Abrasive particles of size between 10 m to 50 m (depending upon the requirement of either cutting or finishing of the work piece) are accelerated in a gas stream (commonly used gas stream is air at high atmospheric pressures).
2. The smaller abrasive particles are useful for finishing and bigger are used for cutting operations.
3. The abrasive particles are directed through the nozzle, towards the work piece surface where-ever cutting or finishing is to be done. The distance between the tip of the nozzle and the work surface is normally within 1 mm.
4. As the abrasive particles impact the surface of the work piece, it causes a small fracture at the surface of the work piece. The material erosion occurs by the chipping action.
5. The erosion of material by chipping action is convenient in those materials that are hard and brittle.
6. As the particles impact the surface of
7. The abrasive particles once used, cannot be re-used as its shape changes partially and the work piece material is also clogged with the abrasive particles during impingement and subsequent flushing by the carrier gas.

Advantages
 AJM process is a highly flexible process wherein the abrasive media is carried by
a flexible hose, which can reach out to some difficult areas and internal regions.
 AJM process creates localized forces and generates lesser heat than the conventional machining processes.
 There is no damage to the workpiece surface and also the process does not have tool-workpiece contact, hence lesser amount of heat is generated.
 The power consumption in AJM process is low. Disadvantages
 The material removal rate is low
 The process is limited to brittle and hard materials
 The wear rate of nozzle is very high
 The process results in poor machining accuracy
 The process can cause environmental pollution
Applications:
Metal working:
 De-burring of some critical zones in the machined parts.
 Drilling and cutting of the thin and hardened metal sections.
 Removing the machining marks, flaws, chrome and anodizing marks.
Glass:
 Cutting of the optical fibers without altering its wavelength.
 Cutting, drilling and frosting precision optical lenses.
 Cutting extremely thin sections of glass and intricate curved patterns.
 Cutting and etching normally inaccessible areas and internal surfaces.
 Cleaning and dressing the grinding wheels used for glass.
Grinding:
 Cleaning the residues from diamond wheels, dressing wheels of any shape and size.

Classification of Advanced Machining / Material Removal Processes:

These processes are referred to a typical group of advanced machining processes in which the excess material is removed by non-traditional source of energy arising from electrical, mechanical, thermal or chemical source. Most of these processes don’t use a sharp cutting tool, as in the conventional case. Advanced material removal processes are generally classified according to the type of energy used to remove material. The classification of these processes based on the energy is given as below The processes based on use of Electrochemical Energy are:
 Electro-Chemical Machining (ECM),
 Electro-Chemical Grinding (ECG),
The processes based on the use of Thermal Energy are:
 Electric- Discharge Machining (EDM),
 Wire-Cut Electric Discharge Machining (WEDM)
 Laser Beam Machining (LBM),
 Electron Beam Machining (EBM).
The processes based on the use of Mechanical Energy are:
 Abrasive Flow Machining (AFM)
 Abrasive Jet Machining (AJM),
 Water Jet Machining (WJM),
 Abrasive Water Jet Machining
 Ultrasonic Machining (USM),

Why are Advanced Machining / Material Removal Processes Needed?

With the advent of new materials and the requirements of complex features on them, there was a necessity to develop new processes. Some of these features are:
1. Related to material properties:
 High hardness  High strength  High brittleness 2. Related to workpiece structure:
 Complex shapes  Typical thin and delicate geometries  Parts which are difficult in fixturing 3. Related to requirements in high surface finish and tight tolerances.
4. Related to controlling of temperature rise and residual stresses.

Need For Advanced Material Removal Processes

Advanced Material Removal Processes represent one of the technologies, which emerged after the second world war to cope up with the demands of sophisticated, more durable and cost competitive products. With the advent of new materials such as metal-matrix composites, super-alloys, ceramics, aluminates and high performance polymers etc. and the stringent requirements to machine complex geometrical shapes with high precision and accuracy, a strong need existed for the development of advanced material removal processes. The processes in this category differ from conventional processes in either utilization of energy in an innovative way or, in using forms of energy that were unused for the purpose of manufacturing. The conventional machining processes normally involve the use of energy from electric motors, hydraulics, gravity, etc. and rely on the physical contact between tools and work components. On the contrary, advanced material removal processes utilize energy from sources such as electrochemical reactions, high temperature plasma, high velocity jets and loose abrasives mixed in various carriers etc. Although these processes were originally developed to handle unique problems in aerospace industry (machining of very hard and tough alloys), today wide range of industries have adopted this technology in numerous manufacturing operations.

Why dry compressed air?

The air we breathe contains contamination in the form of water vapour and airborne particles. During the compression process an air compressor concentrates these contaminants and depending on the design and age will even add to the contamination in the form of oil carry over.

Modern air compressors generally have built in after coolers that reduce the discharge temperature of the compressed air and with the help of water separators, remove the bulk of liquid water.
In some applications this may be sufficient, but the remaining dirt and moisture content suspended in aerosol form, can, if not removed, damage the compressed air system and cause product spoilage.
Air Contaminants lead to increase down time and reduced productivity. it lead to corrosion , damaged Tools , poor finish to painting Jobs etc .

Compressors & Compressed Air Systems - Post 3

Rotary compressor

Rotary compressors have rotors in place of pistons and give a continuous pulsation free discharge. They operate at high speed and generally provide higher throughput than reciprocating compressors. Their capital costs are low, they are compact in size, have low weight, and are easy to maintain. For this reason they have gained popularity with industry. They are most commonly used in sizes from about 30 to 200 hp or 22 to 150 kW.

Types of rotary compressors include:
Lobe compressor (roots blower)
Screw compressor (rotary screw of helical-lobe,where mail and female screw rotors moving in opposite directions and trap air, which iscompressed as it moves forward,)
Rotary vane / sliding- vane, liquid-ring, and scroll-type
Rotary screw compressors may be air or water-cooled. Since the cooling takes place right inside the compressor, the working parts never experience extreme operating temperatures. The rotary compressor, therefore, is a continuous duty, air cooled or water cooled compressor package.
Because of the simple design and few wearing parts, rotary screw air compressors are easy to maintain, operate and provide great installation flexibility. Rotary air compressors can be installed on any sur face that will support the static weight.

Dynamic Compressors
The centrifugal air compressor is a dynamic compressor, which depends on transfer of energy from a rotating impeller to the air. The rotor accomplishes this by changing the momentum and pressure of the air. This momentum is converted to useful pressure by slowing the air down in a stationary diffuser. The centrifugal air compressor is an oil free compressor by design. The oil lubricated running gear is separated from the air by shaft seals and atmospheric vents.

COMPRESSORS AND COMPRESSED AIR SYSTEMS - Post 2

TYPES OF COMPRESSORS
There are two basic compressor types: positive-displacement and dynamic.

In the positive-displacement type, a given quantity of air or gas is trapped in a compression chamber and the volume it occupies is mechanically reduced, causing a corresponding rise in pressure prior to discharge. At constant speed, the air flow remains essentially constant with variations in discharge pressure.

Dynamic compressors impart velocity energy to continuously flowing air or gas by means of impellers rotating at very high speeds. The velocity energy is changed into pressure energy both by the impellers and the discharge volutes or diffusers.

Positive Displacement Compressor
two types: reciprocating and rotary.

Reciprocating compressor

In industry, reciprocating compressors are the most widely used type for both air and refrigerant compression. They work on the principles of a bicycle pump and are characterized by a flow output that remains nearly constant over a range of discharge pressures. Also, the compressor capacity is directly proportional to the speed
Reciprocating compressors are available in many configurations, the four most widely used are horizontal, vertical, horizontal balance-opposed and tandem. Vertical type reciprocating compressors are used in the capacity range of 50 – 150 cfm. Horizontal balance opposed compressors are used in the capacity range of 200 – 5000 cfm in multi-stage design and up to 10,000 cfm in single stage designs
The reciprocating air compressor is considered single acting when the compressing is accomplished using only one side of the piston. A compressor using both sides of the piston is considered double acting.
A compressor is considered to be single stage when the entire compression is accomplished with a single cylinder or a group of cylinders in parallel. Many applications involve conditions beyond the practical capability of a single compression stage. Too great a compression ratio (absolute discharge pressure/absolute intake pressure) may cause excessive discharge temperature or other design problems. Two stage machines are used for high pressures and are characterized by lower discharge temperature (140 to 160oC) compared to single-stage machines (205 to 240oC).
For practical purposes most plant air reciprocating air compressors over 100 horsepower are built as multi-stage units in which two or more steps of compression are grouped in series. The air is normally cooled between the stages to reduce the temperature and volume entering the following
Reciprocating air compressors are available either as air-cooled or water-cooled in lubricated and non- lubricated configurations, may be packaged, and provide a wide range of pressure and capacity selections.

COMPRESSORS AND COMPRESSED AIR SYSTEMS - Post 1

INTRODUCTION

Industrial plants use compressed air throughout their production operations, which is produced by compressed air units ranging from 5 horsepower (hp) to over 50,000 hp. The US Department of Energy (2003) reports that 70 to 90 percent of compressed air is lost in the form of unusable heat, friction, misuse and noise . For this reason, compressors and compressed air systems are important areas to improve energy efficiency at industrial plants.
It is worth noting that the running cost of a compressed air system is far higher than the cost of a compressor itself . Energy savings from system improvements can range from 20 to 50 percent or more of electricity consumption, resulting in thousands to hundreds of thousands of dollars. A properly managed compressed air system can save energy, reduce maintenance, decrease downtime, increase production throughput, and improve product quality

Compressed air systems consist of a supply side, which includes compressors and air treatment, and a demand side, which includes distribution and storage systems and end -use equipment. A properly managed supply side will result in clean, dry, stable air being delivered at the appropriate pressure in a dependable, cost-effective manner. A properly managed demand side minimizes wasted air and uses compressed air for appropriate applications. Improving and maintaining peak compressed air system performance requires addressing both the supply and demand sides of the system and how the two interact.

Main Components of Compressed Air Systems

Consist of the Following

Intake Air Filters : Prevent dust from entering a compressor; Dust causes sticking valves, scoured cylinders, excessive wear etc.
Inter-stage Coolers : Reduce the temperature of the air before it enters the next stage to reduce the work of compression and increase efficiency. They are normally water-cooled. After-Coolers: The objective is to remove the moisture in the air by reducing the temperature in a water-cooled heat exchanger.
Air-dryers : The remaining traces of moisture after after-cooler are removed using air dryers, as air for instrument and pneumatic equipment has to be relatively free of any moisture. The moisture is removed by using adsorbents like silica gel /activated carbon, or refrigerant dryers, or heat of compression dryers
Moisture Drain Traps: Moisture drain traps are used for removal of moisture in the compressed air. These traps resemble steam traps. Various types of traps used are manual drain cocks, timer based / automatic drain valves etc.
Receivers : Air receivers are provided as stora ge and smoothening pulsating air output - reducing pressure variations from the compressor

Design Consideration for Pools

Design Consideration for Pools & Spas Swimming Pools

According to ASHRAE (1999a) the desirable temperature for swimming pools is 27c , however this will vary from the culture by so much as 5 degree Celsius. .If the geothermal water is higher in temperature then some sort of mixing or cooling by aeration or in a holding pond is required to lower the temperature . If the geothermal water is used directly in the pool , then a flow through process is neccessary to replace the used water on regular basis. In many cases the pool water must be treated with chlorine , therefore it is more economical to used a closed loop system for treatment water and have geothermal water provide heat through heat ex changer . The Water Heating System should be installed in the return line to the pool. Acceptable water circulation level vary from eight hours to six hours for a complete change of water. Heat exchanger must be designed to resist the corrosive effect of the chlorine in the pool water and scaling or corrosion from the geothermal water. This often requires in the case of plate heat exchanger using titanium plates .

Four Factors determine the sizing of the system for temperature and flow rate . These are
i) Conduction through the pool walls
2) convection through the pool surface
3 ) Radiation from the pool surface
4) Evaporation from the pool surface

Conduction is Least significant unless the pool is above ground or in contact with the cold underground water
Convection losses depends on the temperature difference between the pool water and the surrounding air and the wind speed.this substantially low for indoor pool also pool with wind speed breakers.
Radiation losses are greater at night for the outdoor pools , however their will be gain in temperature during daytime. A Floating pool Covers can reduces both radiation and evaporation losses. Evaporation loss constitute the greatest heat loss from pools -50 to 60 % in most cases. The rate of which evaporation occurs is a function of air velocity and pressure difference between the pool water and the water vapor in the air .
As the temperature of the pool water is increased or the relative humidity of the air is decreased evaporation rate increase.

The required Gethermal heating output q can be determined by the following two equations
q1 = Density of Water * Pool heat up *pool Volume * ( Desired Temp - intial Temp ) * Pool heat up time

q2 = Surface heat Transfer Coefficient * pool Surface area * ( Pool Temp - ambient temp)

then Q= q1- q2

if there is no heat up time which is typical for geothermal pools then equations (1) will be zero and only equation 2 will apply. Equation 2 will assume a wind velocity of 5 to 8 Km/h . For Sheltered Pool wind velocity factor less than 5km/h

The neccessary Heat to increase and maintain the temperature of an outdoor pool can be expressed as

H( Total) = h (Surface) + h (heat up)

h (heat up) = Volume *8.34 (lbs/gal) * ( intial Temp - Final Temp) * 1.0 / 72

72 = time required to Rise the temp of pool

h (Surface) = ks * dtw* A

where

ks = surface heat loss factor

dtw = Temp Difference between the air and surface water in the pool

A = Surface area of the pool