Tunnel boring machine

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http://en.wikipedia.org/wiki/Tunnel_boring_machine 

Friction-stir welding

Friction-stir welding (FSW) is a solid-state joining process (meaning the metal is not melted during the process) and is used for applications where the original metal characteristics must remain unchanged as far as possible. This process is primarily used on aluminium, and most often on large pieces which cannot be easily heat treated post weld to recover temper characteristics 

Principle of operation

Schematic diagram of the FSW process: (A) Two discrete metal workpieces butted together, along with the tool (with a probe).

(B) The progress of the tool through the joint, also showing the weld zone and the region affected by the tool shoulder.

A constantly rotated cylindrical-shouldered tool with a profiled nib is traversely fed at a constant rate into a butt joint between two clamped pieces of butted material. The nib is slightly shorter than the weld depth required, with the tool shoulder riding atop the work surface.

Frictional heat is generated between the wear-resistant welding components and the work pieces. This heat, along with that generated by the mechanical mixing process and the adiabatic heat within the material, cause the stirred materials to soften without melting. As the pin is moved forward a special profile on its leading face forces plasticised material to the rear where clamping force assists in a forged consolidation the weld.

This process of the tool traversing along the weld line in a plasticised tubular shaft of metal results in severe solid statedeformation involving dynamic recrystallization of the base material.

Advantages and limitations

The solid-state nature of FSW immediately leads to several advantages over fusion welding methods since any problems associated with cooling from the liquid phase are immediately avoided. Issues such as porosity, solute redistribution, solidification cracking and liquation cracking are not an issue during FSW. In general, FSW has been found to produce a low concentration of defects and is very tolerant to variations in parameters and materials.

Nevertheless, FSW is associated with a number of unique defects. Insufficient weld temperatures, due to low rotational speeds or high traverse speeds, for example, mean that the weld material is unable to accommodate the extensive deformation during welding. This may result in long, tunnel-like defects running along the weld which may occur on the surface or subsurface. Low temperatures may also limit the forging action of the tool and so reduce the continuity of the bond between the material from each side of the weld. The light contact between the material has given rise to the name "kissing-bond". This defect is particularly worrying since it is very difficult to detect using nondestructive methods such as X-ray orultrasonic testing. If the pin is not long enough or the tool rises out of the plate then the interface at the bottom of the weld may not be disrupted and forged by the tool, resulting in a lack-of-penetration defect. This is essentially a notch in the material which can be a potent source of fatigue cracks.

A number of potential advantages of FSW over conventional fusion-welding processes have been identified:^[5]

• Good mechanical properties in the as welded condition
• Improved safety due to the absence of toxic fumes or the spatter of molten material.
• No consumables — A threaded pin made of conventional tool steel, e.g., hardened H13, can weld over 1 km of aluminium, and no filler or gas shield is required for aluminium.
• Easily automated on simple milling machines — lower setup costs and less training.
• Can operate in all positions (horizontal, vertical, etc.), as there is no weld pool.
• Generally good weld appearance and minimal thickness under/over-matching, thus reducing the need for expensive machining after welding.
• Low environmental impact.

However, some disadvantages of the process have been identified:

• Exit hole left when tool is withdrawn.
• Large down forces required with heavy-duty clamping necessary to hold the plates together.
• Less flexible than manual and arc processes (difficulties with thickness variations and non-linear welds).
• Often slower traverse rate than some fusion welding techniques, although this may be offset if fewer welding passes are required.

mechanical battery

Most batteries that we use on a daily basis are chemical batteries. They contain chemicals that react in some way to create a flow of electrons.
Lead-acid batteries, alkaline batteries, Nickel-metal hydride batteries and lithium-ion batteries are all chemical batteries. Chemical batteries are especially handy because they can be small -small enough to fit inside a hearing aid if need be.
But there is an entirely different type of battery that is available if you don't need it to fit inside your ear canal or your pocket. These are called mechanical batteries, because they rely on mechanical energy rather than chemical energy.
A flywheel battery is one form of mechanical battery. It uses the kinetic energy stored in a flywheel to create a flow of electrons. To "charge the battery", electricity drives an electric motor that spins up a flywheel. In the simplest possible flywheel battery, the flywheel could be a heavy steel wheel mounted on an axle that might spin at a maximum of 5,000 RPM. To use the battery, a generator converts the kinetic energy stored in the spinning flywheel back into electricity. It is easy to imagine that a big steel wheel weighing 1,000 pounds could store a lot of energy, and you would be right.
Modern technology has made flywheel batteries more sophisticated than you might imagine. The problem with steel is that it can only spin so fast before it flies apart, and if it does fly apart it can be dangerous. Many of the newer flywheels are therefore made out of carbon fiber. The strength of carbon means that these flywheels can spin much more rapidly. Modern flywheels also spin in a vacuum and use magnetic bearings so there is zero friction. A flywheel about the size of a trash can can store enough power to run a typical American household for a day.
A flywheel battery has a number of advantages compared to a chemical battery. The first advantage is the ability to absorb and store quick bursts of energy much more efficiently than a chemical battery can. The second advantage is high efficiency -very little energy is lost when charging the battery (spinning up the flywheel) or discharging the battery. The third is long life -chemical batteries tend to wear out after some number of charge/discharge cycles (500 to 1,000 cycles is typical). Flywheel systems do not. That also leads to lower maintenance costs and better reliability compared to battery systems.
The main disadvantage of flywheel batteries is their minimum size. It is unlikely that a flywheel battery would ever be found in a cell phone, for example. On the other hand, a flywheel battery would be ideally suited for things like whole-house batteries or other batteries where size is not a big issue.
You might wonder why you would need a whole-house battery. One obvious application is as an emergency power supply in case of a power failure. Or, if you are powering your house off of solar panels, a whole-house battery would let you store electricity for use at night. A whole-house battery could also allow time shifting. You could buy power from the power company at night when it is much less expensive, and then use the power during the day for air conditioning. Over time, a flywheel battery used in this way would pay for itself.
There are other types of mechanical batteries available as well. At some wind farms there have been experiments with storing compressed air in huge underground salt caverns. Salt caverns are handy because they are pressure-tight and self-sealing. When the wind is blowing, electricity drives air compressors that fill the caverns with pressurized air. When the wind stops, the pressurized air drives turbines that spin generators.
Another large-scale mechanical battery can be found near select power plants. Two lakes are arranged one above the other on a hillside. At night when the power plant has excess capacity, it pumps water to the upper lake. During the day, the water falls from the upper lake to the lower lake and drives generators like those found in a hydroelectric dam.
If flywheel batteries become cheap enough and reliable enough, it is easy to imagine finding them in homes and in electric cars. They would take the place of chemical batteries in a way that is lighter and less expensive.

magnetic refrigeration

  ABSTRACT

                                     In this paper a new type of refrigeration technology, Magnetic Refrigeration has been discussed. The objective of this paper is to explain the principle, construction, working and the operating cycles of Magnetic Refrigerator. The development of this system leads to improve the COP and to reduce Ozone layer Depletion and Global Warming.

                                    The main principle behind this refrigeration system is Magneto Caloric Effect (MCE). According to this effect whenever some magnetic materials like Gadolinium are subjected to a magnetic field the temperature of that material increases. Whenever the magnetic field is removed the temperature of that material diminishes down again. This is because of the randomization and alignment of atoms in the magnetic material.

                                 The magnetic refrigerator uses the above effect in the following way. Gadolinium is arranged to pass through a magnetic field. As it passes through the field, the gadolinium heats up as it exhibits magneto caloric effect. If it is taken out of the field then it comes down to original temperature. But we will circulate the water to draw the heat out of the metal when it is in the magnetic field. As the material leaves the magnetic field, the material cools to a temperature much below the original temperature as a result of the magneto caloric effect. Then this cold Gadolinium is used to remove the heat from the refrigerator’s coils.

                                  The permanent magnets and the gadolinium don’t require any energy inputs to make them work, so the only energy it takes is the electricity for the motors to spin the wheel and drive the water pumps. Hence the power required to operate this refrigerator is also very less. Magnetic refrigerators have two main advantages over today's commercial devices: they do not use hazardous or environmentally damaging chemicals, such as chlorofluorocarbons, and they are up to 60% efficient. In contrast, the best gas-compression refrigerators achieve a maximum efficiency of about 40%.

ROBOTICS IN MANUFACTURING

The term robotics was coined in the 1940s by science fiction writer Isaac Asimov.

  Robotics is used to collectively define a field in engineering that covers the mimicking of various human characteristics. It is an automatic industrial machine replacing the human in hazardous work. Robotics includes the knowledge of Mechanical, Electronics, Electrical & Computer Science Engineering. It can work hazardous/dangerous environment. Robotic Structure, Power source, Actuation, Sensing, Manipulation, Locomotion and the explanation about all these.

WIND TURBINE GEAR BOX TECHNOLOGY

The reliability problems associated with transmission or gear box equipped wind turbines and the existing solutions of using direct drive gear less turbines and torque-splitting, are reviewed as alternative solutions we propose the Geared Turbofan Engine (GTF) technology, from the automobile industry, and discus their promise in addressing the Gear Box problems currently encountered by existing wind turbine technology. In this it includes the Introduction, Experience with Turbine Transmission, Gearless or Direct Drive Wind Turbines, Gear Box Design Options, Annular Generator, Torque Splitting and Distributed Gearing, History of Direct Drive Approach, Gear Turbofan Technology and Development, Conclusion, References.