Abrasive Jet Machining

Abrasive Jet machining is an unconventional machining process, unconventional means there is no physical contact between tools and the workpiece.

Principle

Principle behind the abrasive jet machining is very simple, a stream of jet is used for machining. Jet of air or water mixed with fine abrasive materials strikes the workpiece and in this way machining is done.

Construction

Abrasive jet machine have components as listed below:

• Gas cylinder,
• Filter,
• Pressure regulator,
• Abrasive chamber,
• Vibrator,
• Handle,
• Nozzle.

 Working

Gas cylinders contains gas which is carried out by pipes, passing away from filter, which separates the dust particles and the pressure regulator is used to maintain the required gas pressure, then the gas collects in chamber where fine abrasive particles (50micron) are present. Here gas mixes with abrasive and a vibrator is connected to the chamber for better mixing which vibrates at 50c/s. Then this mixture is carried to the nozzle which concentrates the mixture at the workpiece and erodes the material from the workpiece.

Material removal rate of abrasive jet machining is quite high as compared to conventional machining.

Hydraulic Brakes

Hydraulic brake is a braking arrangement which uses brake fluid, to transfer power from controlling mechanism to the braking mechanism.

Construction

The most common arrangement of hydraulic brakes for passenger vehicles, motorcycles, and scooters,  consists of the following:

• Brake pedal or lever,
• A push rod or actuating rod,
• A master cylinder assembly, containing a piston assembly made up of either one or two pistons, a return spring, a series of gaskets / O-rings and a fluid reservoir,
• Reinforced hydraulic lines,
• Brake caliper assembly usually consisting of one or two hollow aluminum or chrome-plated steel pistons called caliper pistons, a set of thermally conductive brake pads and a rotor also called a brake disc or drum attached to an axle.

The system is usually filled with a ethylene-glycol based brake fluid other fluids are also be used.

Working 

In hydraulic braking system there are two cylinders and a disk brake, the cylinders are connected by tubes with piston inside the cylinder. The cylinders and tubes are filled with incompressible oil. The two cylinders have the same volume, but different diameters, and thus different cross-section areas. The one with the smallest diameter is called the master cylinder. The spinning disc brake will be placed down at the piston with the larger cross-section. Suppose the diameter of the master cylinder is half the diameter of the other cylinder, then the master cylinder has a cross-section four times smaller. Now, if the piston in the master cylinder is pushed down by 80 mm, with 10 newtons (N) of force, the slave piston will then move 20 mm, with a force of 40 N.
This force can be further increased by inserting a lever connected between the master piston, a pedal, and a pivot point.
Thus a hydraulic system provides a large braking force to stop a vehicle.

Supercharger

Supercharger is an air compressor generally used in super cars to increase pressure, temperature, and density of air supplied to an internal combustion engine. The compressed air supplies a greater amount of oxygen to engine for better combustion than the natural aspiration of engine, which makes it possible for more fuel to be burned and more power is produced by the engine.

Power for the supercharger is provided mechanically by belt, chain, or gear connected to engine's crankshaft. When power is provided by turbine powered by exhaust gas then it is called turbo-supercharger.

There are mainly two types of superchargers:

Positive displacement: Positive displacement pumps delivers a fixed volume of air per revolution at all speeds.

Major types of positive displacement pumps include:

• Roots,
• Lysholm twin-screw,
• Sliding vane,
• Scroll type supercharger also called G Lader.

Dynamic compressor: Dynamic compressors works on accelerating the air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down.

Major types of dynamic compressor are:

• Centrifugal,
• Multistage axial-flow,
• Pressure wave supercharger,

Regenerative heat exchanger

A regenerative heat exchanger or a regenerator is a heat exchanger where heat from hot fluid is first passed to a storage medium and then it is passed to the cold fluid which absorbs the heat. In regenerative heat exchanger, the fluid on either side of heat exchanger can be the same fluid.

Regenerative heat exchanger was one of the most important technologies developed during industrial revolution. It is used for hot blast in blast furnace.

Also used in steel industries, glass industries, in high pressure boilers and in many chemical industries.

The first regenerator was developed by Dr. Robert Stirling in 1816 and was used as a component of his stirling engine.

Toughness

Toughness is the ability of a material to absorb energy and plastically deform without fracturing. It is also defined as the resistance to fracture of a material when stressed.

Mathematical definition

Toughness can be determined by measuring the area underneath the stress-strain curve and its energy of mechanical deformation per unit volume prior to fracture. 

Unit Of  Toughness 

Toughness is measured in units of joules per cubic metre (J/m³) in the SI system and inch-pound-force per cubic inch (in·lbf/in³) in US customary units.

Hardness

Hardness can be defined as how much the surface of any material is resistive to scratches, dents, and bends. It is a surface phenomenon, and it is not related to stresses. It only shows how much surface of any material is resistive to scratches.

There are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.

Scratch hardness: Scratch hardness is the measure of how resistant a sample is to fracture or permanent plastic deformation due to friction from a sharp object. The principle is that an object made of a harder material will scratch an object made of a softer material. The most common test is Mohs scale, which is used in mineralogy. One tool to make this measurement is the sclerometer.

Indention hardness: Indentation hardness measures the resistance of a sample to material deformation due to a constant compression load from a sharp object; they are primarily used in engineering and metallurgy fields. Common indentation hardness scales are Rockwell, Vickers, Shore, and Brinell.

Rebound hardness: Rebound hardness, also known as dynamic hardness, measures the height of the "bounce" of a diamond-tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity. The device used to take this measurement is known as a scleroscope.

stirling engine

A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work.

 Invented by Robert Stirling in 1816 in Scotland, the Stirling, engine uses simple gases and natural heat sources, such as sunlight, to regeneratively power the pistons of an engine. There are usually two pistons, at 90° to each other, that can be connected to a crankshaft to move a vehicle or a generator to make electricity. Stirling engines are used because they require no replenished source of fuel, run silently, and eject no emissions.

                          Stirling Engine

Functional description

The engine is so designed that the working gas is generally compressed in the colder portion of the engine and expanded in the hotter portion resulting in a net conversion of heat into work.
 "An internal Regenerative heat exchanger increases the Stirling engine's thermal efficiency compared to simpler hot air engines lacking this feature".

Regenerator

In a Stirling engine, the regenerator is an internal heat exchanger and temporary heat store placed between the hot and cold spaces such that the working fluid passes through it first in one direction and then the other.

 The primary effect of regeneration in a Stirling engine is to increase the thermal efficiency by 'recycling' internal heat which would otherwise pass through the engine irreversibly. As a secondary effect, increased thermal efficiency yields a higher power output from a given set of hot and cold end heat exchangers.

Annealing

Annealing, is a heat treatment that alters a material to increase its ductility and to make it more workable. It involves, heating material to above its critical temperature, maintaining a suitable temperature, and then cooling. Annealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.

Ferrous materials are cooled slowly to anneal, copper, silver and brass can be cooled slowly in air, or quickly by quenching in water.

Thermodynamics:

Annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat increases the rate of diffusion by providing the energy needed to break bonds. The movement of atoms has the effect of redistributing and destroying the dislocations in metals and in ceramics. This alteration in dislocations allows metals to deform more easily, so increases their ductility.

Stages:

The three stages of the annealing process that proceed as the temperature of the material is increased are:

•  Recovery: The first stage is recovery, and it results in softening of the metal through removal of primarily linear defects called dislocation and the internal stresses they cause. Recovery occurs at the lower temperature stage of all annealing processes and before the appearance of new strain-free grains. The grain size and shape do not change.

•  Recrystallization: The second stage is recrystallization, where new strain-free grains nucleate and grow to replace those deformed by internal stresses.

•  Grain growth:  If annealing is allowed to continue when recrystallization has completed, then grain growth the third stage occurs. In grain growth, the micro structure starts to coarsen and  cause the metal to lose a substantial part of its original strength.

Powder Metallurgy

Powder metallurgy is a process which involves converting powder into a solid object, or Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape, and then heating the compressed material in a controlled atmosphere to bond the material.

It generally consists four basic steps:

• Powder manufacture: The first step in powder metallurgy is converting raw material to a powder form. Crushing, grinding, and using chemical reactions are common ways to produce powder. Iron powders are produced by one of two processes: The sponge Iron Process or Water Atomization.

• Powder blending,

• Compacting: Powder compaction is the process of compacting metal powder in a die through the application of high pressures.The tools are held in the vertical orientation with the punch tool forming the bottom of the cavity. The powder is then compacted into a shape and then ejected from the die cavity.

•  Sintering: Solid state sintering is the process of taking metal in the form of a powder and placing it into a mold or die. Once compacted into the mold the material is placed under a high heat for a long period of time. Under heat, bonding takes place between the porous aggregate particles and once cooled the powder has bonded to form a solid piece.

"Atomization is a technique in which the material is melted into a molten liquid and forced through a small nozzle or tube at high velocity. This causes the liquid to separate into individual droplets as it exits the tube. The droplets are collected and allowed to harden, resulting in fine, grain-sized particles."

Low Carbon Steel

Low carbon steel is a type of metal that has an alloying element made up of a relatively low amount of carbon.It has a carbon content that ranges between 0.05% and 0.30% and a manganese content that falls between 0.40 and 1.5%. Low carbon steel is one of the most common types of steel used for general purposes. While the steel contains properties that work well in manufacturing a variety of goods, it is most frequently made into flat-rolled sheets or strips of steel.

As the carbon percentage rises, steel has the ability to become harder and stronger through heat treating, however it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point.

 

                Carbon Steel Bars

High Speed Steel

High Speed Steel also called HSS is commonly used for cuttin tools. It is superior than prior used carbon steels as it can withstand higher temperature without losing its hardness. It allows the HSS to cut faster than carbon steel and so the name resembles.

It is used in power-saw blades and drill bits. The main use of high-speed steels in the manufacturing of various cutting tools: drills, taps, milling cutters, tool bits, gear cutters, saw blades, etc.

High speed steels belong to the Fe–C–X  multi-component alloy system where X represents chromium, tungsten, molybdenum, vanadium, or cobalt. Generally, the X component is present in excess of 7%, along with more than 0.60% carbon.

                          HSS Tools

The major advantage of this steel was that it hardened when air cooled from a temperature at which most steels had to be quenched for hardening.

Mangalloy

Mangalloy is made by alloying steel, containing carbon 0.8% to 1.25% with 10% to 14% manganese. It is a unique non-magnetic steel with extreme anti-wear properties. The material is very resistant to abrasion and will achieve two to three times its surface hardness during conditions of impact or machining without any increase in brittleness which is usually associated with hardness. This unique property of mangalloy has many disadvantages as if we machine its surface the hardness increased that will interrupt the machining process.

Mangalloy has very good history as it was used by "SPARTANS" for the making of their swords, and this alloy gives an extra hardness to their swords.

Mangalloy was the first alloy made from carbon steel and invented by a British inventor Sir Robert Hadfield in 1882, so it is also called Hadfield steel and it was used for making helmets in world war I.

                  Helmet used in World War I

In 1860, Sir Henry Bessemer found that adding manganese and carbon to the steel after it was blown helped to remove excess sulfur and oxygen.Sulfur combines with iron to form a sulfide that has a lower melting point than steel, causing weak spots, which prevented hot rolling. Manganese is usually alloyed with most modern steels because of its powerful ability to remove sulfur, phosphorus and oxygen, which are all common impurities in steel.