Engineering approach

sometimes calculations are really complex and to be unable to settle or sometimes only complex because of this reasons engineers developed a idea which named as engineering approach.According to engineering approach for example if you calculate heat transfer of patato you have to neglect somethings or you have to accept patato is a water because waters heat transfer rate can be easily calculated than patato and calculated values approximately patatos heat transfer rate if we want to shorten time of calculation or avoid calculation errors we have to use engineering approach but we have to use factor of safety for accidental stuations.

Quenching media during the heat treatment

quenching media is very important to hardening because it is a very effective of hardness of the material
quenching medias:

Water:
water is fairly good quenching medium.it is cheap,readily available, easily stored nontoxic nonflammable smokeless and easy to filer and pump but with water quench the formation of bubbles may cause soft spots in the metal.Agitation is recommended with use of water quench.Still other problems with waterquench inclued its oxidizing nature,its corrosivity and the tendency to excessive distortion and cracking although this bad properties for plain carbon steels.

Brine (salt water) : Brine is a more severe quench medium than water.Unfortunately it tends to accelerate corrosion problems unless completely removed.Sodium or potasium hydroxide can be used when very severe quenching is desiredand one wishes to obtain good hardness in low carbon steels

Oil: When slower cooling rate is desired oil quenches can be employed.The slower cooling throug the ms to mf temperature range leads to a milder temperature gradient and a reduced likelyhood of cracking.Problems associated with quenchants include water contamination,smoke and fire hazards.in addition quench oils tend to be somewhat expensive.

Air: Low alloy steels in light sections and high alloy steels may be succesfully hardened by means of compressed air or still air.The advantages of using air are that distortion is negligible and that the steel can easily be straigtened during cooling precess.One drawback here is that the surface may be oxidized the cooling.

There is Something About Engineering

it is well known job, engineering but nobody knows what the engineering means,engineering is art which is collect and mixture art and science in addition engineers have to be economic when they create some work
engineers have to select material which is strong and cheap for instance steel steel is very cheap and strong then other materials in this days a lot of subdivision of industy choose steel for structure
but on the other hand carbon fiber is new and more strong and more light than steel and they can use it on f 1 cars but it is more expensive then steel
finally we can say engineering is art of economy in the industry.

What is mechanical engineering ?

Mechanical engineering is concerned with the design, construction, and operation of power plants, engines, and machines. It deals mostly with things that move. One common way of dividing mechanical engineering is into heat utilization and machine design. The generation, distribution, and use of heat is applied in boilers, heat engines, air conditioning, and refrigeration. Machine design is concerned with hardware, including that making use of heat processes.

Factor Of Safety

factor of safety is very importan thing for engineers and all engineers use this factor for their projects.But what is factor of safety ?
engineers use very useful calculation for their projects but everytime they have to neglect somethings for example transverse shear for strength of materials or air resistance for some aerodynamics calculation and sometimes they use some materials but the material!s properties can be changeble because of this reasons mechanical engineers use factor of safety. but how ve can calculate factor of safety it is so easy first of all the calculations done and then make a decision for factor of safety value for example 1.8 is food value for strength of materials applications if we made calculation and we have found for example 100 mpa then we will divide it with 1.8 and we can find new value
new value=calculated value/f.s

Heat Treatment

Heat treatment is the controlled heating and cooling of metals for the purpose of altering their properties because both mechanical and physical properties can be alterede by heat treatment and it is one of the most important and widely used manifacturing processes.the designer who select material and the engineer who determines its processing must be aware of the possible changes in properties.

some heat treatments for steel are;

spheroidizing annel
recyrstallization annealing
stress relief annealing
full annealing
normalizing

and if you want to see annealing temperatures on carbon-temperature diagram ;

Quenching

the rapid cooling necessary to harden a steel is known as quenchingand the liquid in to which the steel is immersed to promote this rapid cooling is called the quenching bath. heat tratment process consists of heating the steel to a temperature just above its critical point holding the metal at this temperature for suffcient time then quenching it by using a suitable quenching bath.
some quenching methods are;
direct quenching to martensite:
the first quenching method was direct quenching.according to this method the steel is cooled or quenched directly from hardening temperature to the room temperature the cooling medium is usually water sometimes oil and sometimes air.this method has some big disadvantages a most important disadvantage is distortions because of temperature differance in center of material with surface of the material.
martempering:
in this treatment the cooling takes place in two stages fist tool quenched in a molten salt bath,kept at a temperature somewhat above that at which the austenitic structure of the steel starts to transform to martenzite.the steel is held there until temperature equalization is complate than it is allowed to cool freely in air.the advantage of this method is less residual stresses and distortions than direct quenching but it has a big disadvantage this method can not be usable for all kind of materials.after the this process you have to do tempering
austempering:
it is an isothermal heat treatment which produces a bainite structure in some plain carbon steels.it is an alternative procedure to quenching and tempering for increasing the thoughness and ductility of some steels it likes martempering but it has some differences; first material quenched in salt bath to the temperature which is kept above the matersite formation.keeping time has to sufficient for austenine to completely transformed to bainite.the materials which cabaple being martempered also be austempered.because of long time for complate transformation the high alloy steels are not capable for being austempered.austempering usually improves ductilitiy and impact resistance of certain steels over those values obtained by direct quenching and tempering.it also causes decreased distortion of the quenched material.