Bronze

Bronze is a metal produce by alloying copper and tin in various amounts according to the need of work. Modern bronze alloy has a configuration of 88% copper and 12% tin. Commercial bronze 90% copper and 10% zinc and architectural bronze 57% copper, 3% lead, 40% zinc are more properly regarded as brass alloys because they contain zinc as the main alloying ingredient. They are commonly used in architectural applications.

face made of bronze metal

Bismuth bronze is a bronze alloy with a composition of 52% copper, 30% nickel, 12% zinc, 5% lead, and 1% bismuth. It is able to hold a good polish and so is sometimes used in light reflectors and mirrors.

Plastic bronze is bronze containing a significant quantity of lead which makes for improved plasticity. Other bronze alloys include aluminium bronze, phosphor bronze, manganese bronze, bell metal, arsenical bronze, speculum metal and cymbal alloys.

bronze bearings

Properties

• they have less melting point than steels,
• they are softer and weaker than steel,
• they resists sea water corrosion better than steel,
• they resists metal fatigue better than steel,
• bronze struck against a hard surface will not generate sparks, as steels do,
• good conductor of heat and electrcity than steel,
• bronze also has very low metal-on-metal friction,
• they are non magnetic, but if contain iron or nickel they shows the magnetic behavior.

Uses

• it is used in boats and ship fittings,
• as ship propellers and submerged bearings,
• bronze parts are tough and are used for bearings, clips, electrical connectors and springs.
• used in  automobile transmission pilot bearings,
• phosphor bronze is particularly suited to precision-grade bearings and springs. It is also used in guitar and piano strings.
• bronze struck against a hard surface will not generate sparks, so it along with beryllium copper is used to make hammers, mallets, wrenches and other durable tools to be used in explosive atmospheres or in the presence of flammable vapors.
• bronze is the preferred metal for top-quality bells,
• bronze has been used in the manufacture of various types of medals,
• used for making coins.

Stainless Steel

Stainless steel also known as inox steel, is a metal alloy formed by alloying chromium with steel, It generally contains 10.5% chromium content by mass. Stainless steel does not readily corrode, rust or stain with water, because the chromium makes an oxide film on the surface of the steel.

stainless steel rods

There are other elements used to make stainless steel as well, including nickel, nitrogen and molybdenum. Bringing these elements together forms different crystal structures that enable a variety of properties in machining, welding and forming.

stainless steel pipes

High oxidation-resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% by weight chromium, and up to 26% is used for harsh environments. The chromium forms a passivation layer of chromium(III) oxide (Cr₂O₃) when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous. The layer is impervious to water and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium. Corrosion-resistance can be adversely affected if the component is used in a non-oxygenated environment.

Types of stainless steel 

There are four major types of stainless steel:

•  Austenitic stainless steel: Austenitic  stainless steels have an austenitic crystalline structure, which is a face-centered cubic crystal structure. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy.

• Ferritic stainless steel: Ferritic stainless steels generally have better engineering properties than austenitic grades, but have reduced corrosion resistance, because of the lower chromium and nickel content. Most compositions include molybdenum; some, aluminium or titanium.

• Martensitic stainless steel: Martensitic stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly machinable, and can be hardened by heat treatment. Martensitic stainless steel contains chromium (12%–14%), molybdenum (0.2%–1%), nickel (less than 2%), and carbon (about 0.1%–1%) giving it more hardness but making the material a bit more brittle. It is quenched and magnetic.

• Duplex stainless steel: It have a mixed microstructure of austenite and ferrite. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19%–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels.

 Applications:

• cookware, 

• cutlery, 

• household hardware,

•  surgical instruments,

•  industrial equipment e.g, in sugar refineries,

•  as an automotive and aerospace structural alloy,

•  construction material in large buildings,

•  Storage tanks and tankers used to transport orange juice and other food are often made of stainless steel, because of its corrosion resistance.

Brass forging

Brass forging is a process in which a forging press places places extreme pressure on a single piece of brass that has been heated to about 815 degrees C. The softened metal is then forced, beaten, and shaped to produce a part made from a single piece of brass and free of imperfections.

The brass forging process actually makes the metal around 15% stronger than mold cast parts as the process does not change the structure of the metal. Extruded brass stock is made into a shape already close to the final part that it will be forged into when the brass is heated.

forged brass products

The various types of brass forging include closed die forging, open die forging, cold forging, and seamless rolled ring forging:

• Closed die forging, also known as impression-die forging, utilizes two or more dies made in the shape of the part desired. The brass is heated until it becomes malleable, or reaches a plastic state, and is then compressed by the die machine. This forging process creates brass parts that have enhanced density, aligned grain flow, and high strength. Closed die brass forging produces extremely strong and durable products. 

• In open die forging the heated, malleable brass is not confined in a die or mold. Instead, it is accomplished with the use of two flat die surfaces with no type of impression. This type of brass forging is typically used to create and shape very large single pieces of brass up to 36,000 kg or more.

• Cold brass forging only requires that the brass be heated to a few hundred degrees. Cold forging is typically used to create things like coins, automotive steering parts, anti-lock braking systems, and other smaller parts. This process produces parts that require high strength and close tolerances. 

• Rolled ring forging uses round, open ring-shaped parts that were shaped using the open die forging process. This type of forging is accomplished through the forced pressure of two axial rolls, a driver roll and an idler roll. The ring of brass is rotated by the idler roll while applying pressure to the inside of the ring. The driver roll applies pressure to the outside edge of the ring. As the process progresses, the ring becomes flatter until the desired ring diameter is achieved.

Advantages

• Forging brass parts reduces metal scrap and is faster than machining the parts. 

• The forging process also produces a pore-free surface which makes for a more attractive brass part. 

• It produces strong and durable products.

Electromagnet

An electromagnet is a magnet in which the magnetic field is produced due to the flow of electric current. The magnetic field disappears when the current is turned off.

electromagnet

An electric current flowing in a wire creates a magnetic field around the wire. To concentrate the magnetic field, in an electromagnet the wire is wound into a coil with many turns of wire lying side by side. The magnetic field of all the turns of wire passes through the center of the coil, creating a strong magnetic field there. A coil forming the shape of a straight tube or helix is called a solenoid. Much stronger magnetic fields can be produced if a ferromagnetic material, such as soft iron, is placed inside the coil. The ferromagnetic core increases the magnetic field to thousands of times the strength of the field of the coil alone, due to the high magnetic permeability ( μ ) of the ferromagnetic material. This is called as ferromagnetic-core or iron-core electromagnet. The direction of the magnetic field through a coil of wire can be found from a form of the right-hand rule. If the fingers of the right hand are curled around the coil in the direction of current flow through the windings, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the north pole.

 

The main advantage of an electromagnet over a  permanent magnet is that the magnetic field can be rapidly varied over a wide range by controlling the amount of electric current. But, a continuous supply of electrical energy is required to maintain the field.

Side effects in electromagnets

• Ohmic heating: The power consumed in a DC electromagnets is due to the resistance of winding, and is dissipated as heat. This heating is called ohmic heating and in large electromagnets require cooling water circulating through pipes in the windings to carry off the waste heat. Since power dissipation, P = I²R, increases with the square of the current but only increases approximately linearly with the number of windings, so the power lost in the windings can be minimized by reducing I and increasing the number of turns N . For example halving I and doubling N, halves the power loss. This is the one reason most electromagnets have windings with many turns of wire.

•  Lorentz forces: In powerful electromagnets, the magnetic field exerts a force on each turn of the windings, due to the Lorentz force (qv *B) acting on the moving charges within the wire. The Lorentz force is perpendicular to both the axis of the wire and the magnetic field. It has two effects on an electromagnet's windings:

• The field lines within the axis of the coil exert a radial force on each turn of the windings, tending to push them outward in all directions. This causes a tensile stress in the wire.
• The leakage field lines between each turn of the coil exert a repulsive force between adjacent turns, tending to push them apart.

• Core losses: In alternating current (AC) electromagnets, used in transformers, inductors, AC motors and generators, the magnetic field is constantly changing. This causes energy losses in their magnetic cores that are dissipated as heat in the core. The losses occurs due two processes:  

• Eddy currents:  From Faraday's law of induction, the changing magnetic field induces circulating electric currents inside nearby conductors, called eddy currents. The energy in these currents is dissipated as heat in the electrical resistance of the conductor, so they are a cause of energy loss. Eddy currents are closed loops of current that flow in planes perpendicular to the magnetic field. The energy dissipated is proportional to the area enclosed by the loop. To prevent them, the cores of AC electromagnets are made of stacks of thin steel sheets, or lamination, oriented parallel to the magnetic field, with an insulating coating on the surface.
• Hysteresis losses: Reversing the direction of magnetization of magnetic domains in the core material each cycle causes energy loss, because of the coercivity of the material. These loses are called as Hysterisis. To minimize this loss, magnetic cores used in transformers and other AC electromagnets are made up of "soft" or "low coercivity" material, such as silicon steel or soft ferrite.

 Uses of electromagnets

Electromagnets are widely used in electric and electromechanical devices, including:

• Motors and generators,
• Transformers,
• Electric bells and buzzers,
• Loudspeakers and earphones,
• Actuators,
• Magnetic recording and data storage equipment: tape recorders, VCRs, hard disks,
• Scientific instruments such as MRI machines and mass spectrometers,
• Particle accelerators,
• Magnetic locks,
• Magnetic separation equipment, used for separating magnetic from nonmagnetic material,
• Industrial lifting magnets,
• Electromagnetic suspension used for MAGLEV trains.

 

Permanent magnets

A magnet is a material that produces a magnetic field. This magnetic field is invisible but is responsible for the property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.

Permanent magnets are made out of substances like magnetite (Fe₃O₄), the most magnetic naturally occurring mineral, or neodymium, a powerfully magnetic synthetic substance. The Earth itself is a huge permanent magnet, though its magnetic field is quite weak relative to its size. Humans have used the magnetic field of the Earth for navigation since the compass was invented in ancient China.

Every permanent magnet generates a magnetic field, which circulates around the magnet in a distinct pattern. The size of the magnetic field is related to the size of the magnet and its strength. The easiest way to view a magnetic field generated by a permanent magnet is to scatter iron filings around a bar of  magnet, which quickly orient themselves along the field lines. 

Every permanent magnet has two poles, named north and south, Similar poles repel while opposite poles attract. It takes a lot of effort to hold repelling poles of a magnet together, while it takes a lot of effort to remove attracting poles.

Even the most powerful permanent magnet is not as strong as the stronger electromagnets, so their applications are limited, but they still have many uses. The most significant use is as refrigerator magnets, but magnets can be found everywhere, including your hard disk, ATM and credit cards, speakers and microphones, electric motors, and toys. Electric motors work through an interaction between an electromagnet and a permanent magnet.

Hydraulics

When we talk about hydraulics then a question arise in our mind that how could it works, and the answer is by using a pressurized liquid.

Hydraulic technology provides a more environmental friendly way to power everything from automobiles to heavy machinery through the use of liquid. The basic idea behind any hydraulic system is very simple: Force that is applied at one point is transmitted to another point using an incompressible fluid. 

Hydraulic systems are based on Pascal's Law,that pressure at any one point in a confined liquid is
the same in every direction and applies equal force on equal areas. So when we apply less force on smaller area then the liquid applies a greater force on larger area That's why hydraulic system is very popular in engineering field.

Pascal's law and Hydraulics

 

A hydraulic system contains a master cylinder connected with the lever and with delivery tank. The delivery tank stores the hydraulic liquid. The master cylinder is connected with secondary cylinders with hydraulic lines or pipes, These secondary cylinders are those points where the output is needed. So when we push the lever the piston pushes the incompressible hydraulic liquid and due to smaller area of pipes and in-compressibility the pressure of liquid increases and it reaches to the secondary cylinders and pushes them to get desired output. A drain line is also provided in every cylinder to drain the used liquid back to the delivery tank. The delivery tank or reservoir collects the used or fresh liquid and sends it to the master cylinder after passing through a filter and the whole process repeats itself.

 

An example of braking system powered by hydraulics

Some places where hydraulics are frequently used are:

•  Steering wheel,

• Brakes, 

•  Lifts,

•  Cranes, 

• Aircraft, etc

Some hydraulic fluids are:

•   Arnica, 

•  Tellus, 

• Durad, 

• Fyrquel, 

• Houghto-Safe, 

• Hydraunycoil, 

• Lubritherm Enviro-Safe,

•  Pydraul,

•  Quintolubric,

•  Reofos, 

• Reolube,

• Valvoline Ultramax,

• Skydrol. etc

Advantages:

• It uses incompressible liquid which results in a greater, more efficient & consistent work or power output. And minimal energy loss is experienced and work applied is directly transferred to the actuating surfaces.

• Hydraulic fluid operates very well in a very hot working environment, it is able to sustain its airworthiness viscosity, density & fluid temperature even if it subjected under extreme heat.

•  Hydraulic systems can perform on very heavy loads.

• They have a very high accuracy.

Disadvantages:

• Leakage is its major disadvantage.

• Maintenance  is very difficult.

• Hydraulic fluid is highly corrosive to most of the aircraft materials.

• If disposed improperly, a hydraulic fluid is an environmental risk.

• Mishandling and constant exposure to hydraulic fluid and its gas fumes without proper equipment and precautions is a health risk.

Gears

A gear is a rotating machine part having cut teeth or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. An advantage of gears is that the teeth of a gear prevent slipping.

gears

Types of gears:

• External gear: An external gear is one with the teeth formed on the outer surface of a cylinder.

external gears

• Internal gear: An internal gear is one with the teeth formed on the inner surface of a cylinder or cone.

internal gears

• Spur gear: Spur gears are the simplest type of gear. They consist of a cylinder with the teeth projecting radially, the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel shafts.

spur gears

• Helical gear: The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Since the gear is curved, this angling causes the tooth shape to be a segment of a helix. Helical gears can be meshed in parallel or crossed orientations. The angled teeth engage more gradually than do spur gear teeth, causing them to run more smoothly and quietly.

helical gears

• Bevel gear:  A bevel gear is shaped like a right circular cone with most of its tip cut off. When two bevel gears mesh, their imaginary vertices must occupy the same point. Their shaft axes also intersect at this point, forming an arbitrary non-straight angle between the shafts. The angle between the shafts can be anything except zero or 180 degrees.

bevel gears

• Hypoid:  Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect. The pitch surfaces appear conical but, to compensate for the offset shaft, are in fact hyperboloids of revolution. Hypoid gears are almost always designed to operate with shafts at 90 degrees.

hypoid gears

• Crown:  Crown gears are a particular form of bevel gear whose teeth project at right angles to the plane of the wheel; in their orientation the teeth resemble the points of a crown. A crown gear can only mesh accurately with another bevel gear, although crown gears are seen meshing with spur gears. A crown gear is also sometimes meshed with an escapement such as found in mechanical clocks.

crown gears

• Worm gear: Worm gears resemble screws. A worm gear is usually meshed with a spur gear or a helical gear, which is called the gear, or worm wheel. Worm-and-gear sets are a simple and compact way to achieve a high torque, low speed gear ratio.

worm gears

• Rack and Pinion:  A rack is a toothed bar or rod that can be thought of as a sector gear with an infinitely large radius of curvature. Torque can be converted into linear force by meshing a rack with a pinion: the pinion turns; the rack moves in a straight line. Such a mechanism is used in automobiles to convert the rotation of the steering wheel into the left-to-right motion of the tie rod.

rack and pinion gears