Now-a-days forged pistons are used by most of high end vehicles.The main characteristic that makes forged pistons excel in high performance applications is strength and durability. 

The high silicon content of cast pistons makes them brittle compared to forged pistons. Silicon gives the metal lubricity and is mixed in the alloy to limit heat expansion. This is primarily the reason why cast pistons require careful handling. 

Mild shock applied to it may cause the material to break. The process of forging compresses the molecules inside the alloy, which results in a denser surface area compared to a cast piston.

The Difference:

The difference between a normal or cast piston and a forged piston is the manufacturing technique. Traditional cast pistons are considered good enough by most engine manufactures when it comes to stock setups, and suffer no drawback in terms of compression and service life. The cast piston is most common on all mass-produced engines, because the casting process of making this type of piston presents a low cost opportunity to the manufacturer.

Forged pistons employ a single lump of billet alloy which is stamped by the use of a die. The shape of the die determines the size and shape of the piston.Forged pistons are also easy to manufacture as there is no need for big, heavy and expensive casting equipment as employed in the manufacture of cast pistons.

How Air Bags Work ?

Air Bags:-
An airbag is a type of vehicle safety device and is an occupant restraint system. The airbag module is designed to inflate extremely rapidly then quickly deflate during a collision or impact with a surface or a rapid sudden deceleration. 

The purpose of the airbag is to provide the occupants a soft cushioning and restraint during a crash event to prevent any impact or impact-caused injuries between the flailing occupant and the interior of the vehicle. The airbag provides an energy absorbing surface between the vehicle's occupant and a steering wheel, instrumental panel, A-B-C- structural body frame pillars, headliner and windshield/windscreen.

There are three parts to an airbag that help to accomplish this feature:
>The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.
>The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip.

>The airbag's inflation system reacts sodium azide (NaN3) with potassium nitrate (KNO3) to produce nitrogen gas. Hot blasts of the nitrogen inflate the airbag.


In fluid flows, there are two distinct fluid behaviors experimentally observed. These behaviors were first observed by Sir Osborne Reynolds.We will discuss this in detail in this article.

Laminar Flow

  1. The fluid flow in which the adjacent layers of the fluid do not mix with each other and moves parallel to each other, is called laminar flow.
  2. In the laminar flow, the fluid layer moves in straight line.
  3. The laminar flow always occurs when the fluid flow with low velocity and in small diameter pipes.
  4. The fluid flow having Reynolds number less than 2000 is called laminar flow.
  5. The fluid flow is very orderly i.e. there is no mixing of adjacent layers of the fluid and they move parallel to each other and also with the walls of the pipe.
  6. Shear stress in laminar flow depends only on the viscosity of the fluid and independent of the density.

Turbulent Flow

  1. The fluid flow in which the adjacent layers of the fluid cross each other and do not move parallel to each other, is called turbulent flow.
  2. In turbulent flow the fluid layers do not moves in straight line. They move randomly in zigzag manner.
  3. The turbulent flow occurs when the velocity of the fluid is high and it flows through larger diameter pipes.
  4. The fluid flow having Reynolds number greater than 4000 is called turbulent flow.
  5. The fluid does not flow in definite order. There is a mixing of different layers and they do not move parallel to each other but crosses each other.
  6. The shear stress in turbulent flow depends upon its density.

The difference is summarized in table below.

Hope,you got a clear picture of the difference between the two types of flow.Share this article with your friends.


Pump and compressor both are hydraulic machines used to increase the energy of fluid. Both of these devices used in industries and for domestic work. Pump is a device which is used to move the fluid (water, liquid and gases) and increase its elevation. It is mostly used to supply fluid from low elevation to high elevation. A compressor is a device which is a mechanical device just like pump but it increases the potential energy of fluid by compressing it in a closed container.

Difference between pump and compressor

The main difference between pump and compressor is that the pump is used to increase kinetic energy of fluid which further increases the elevation or pressure energy of it.  It moves the fluid from one place to another. But the compressor is mostly used to increase the potential energy (pressure energy) of fluid by pressuring it into a container. It is used to compress the fluid which increases its density and pressure. There are many other differences which are described below.

Difference between pump and compressor:


Fillet is a round corner whereas chamfer is a slant face created at the corner. 

Even though both perform same function selection of chamfer or fillet depends on how the component is manufactured.We will discuss why and when they are used while creating parts in this article.

Comparison Between Chamfer and Fillet for External Edges :

Whether we choose to select a chamfer edge, or a fillet edge, it will often depend on factors of project such as budget and time constraints. The chart below compares some of these considerations:

When to use them ?

Fillets give a part better flow and less resistance. Using a fillet also eliminates any sharp edges that can be easily damaged, or that could cause injury when the part is handled. This means there is less risk of failing an inspection for having a burr or sharp edge. Fillets also have lower stress concentration factors, meaning that they distribute stress over a broader area. This makes filleted parts more durable, and able to withstand larger loads.

Chamfers are more forgiving when designing to fit mating parts, but overall it appears that designs using fillets are preferred by senior management, industrial designers and many others.

The main points that help in deciding to choose a fillet or chamfer are the following:

1.When done manually one of the main factors that come in deciding which to apply is the machining time. A chamfer requires less machining time that a fillet radius.

2.When done on CNC both chamfer and fillet require the same time as only a tool change is required.

3.For fillets different radii of tools has to be stocked to create different radii, but a single tool can be used for creating different chamfers.

4.Higher machining time required translates into cost. Thus chamfers are less costly compared to fillets.

5.Industrial designers tend to prefer fillets compared to chamfers as these are considered to be visually pleasing.

6.One of the other reasons is that protective coating like paint are more uniformly distributed over a fillet compared to chamfer. Thickness of coating is reduced on sharp corners of chamfers so coating is lost first on these spots. Fillets have no such issues due to uniform distribution of coating.

7.Since non uniform distribution of coating can lead to accelerated rusting this may be a disadvantage.

8.Fillet gives better stress flow (less resistance) compared to chamfers. Fillets generally give a lower stress concentration factor than chamfers .

9. Chamfers are more forgiving when fitting mating parts. i.e. even if there are inaccuracies in a chamfer mating parts might fit together. But if the radius of fillet changes it will be difficult to fit the mating parts.


Propellers and impellers both provide thrust, but do it in different ways.Let us understand the difference between two with the help of examples.


If you have ever seen pictures of ships closely, you must have noticed small rotating fans on both sides of the ship. 

These are propellers that actually help in propelling the ship forward. A propeller is an open running device that has the function of providing a thrust force. There is always a propelling fan on the mouth of an aircraft also. If we go by definitions given in various dictionaries, a propeller is a device having a revolving hub with rotating blades to propel an airplane, ship etc. 

A propeller is a special type of fan with blades that convert rotational motion into a force that helps in movement forward. This is because of a pressure difference that gets created between the front and the rear surfaces of the blades. This pressure difference pushes both air and water behind the blade. This thrust or force can be easily explained with the help of Newton’s laws of motion as well as Bernoulli’s theorem. Propellers are made heavy use of both in aviation as well as in ships.


Have you ever paid attention to the working behind the water pump that is used at home that sucks water from the main pipeline passing through the main road and brings it inside your home and then lifts it to the over head tank?

The working principle behind this pump is the impeller inside a casing that creates a sucking force that draws in liquid at a great force and diverts it to your overhead tank. An impeller is always inside a casing as its purpose is to draw the liquid inside as against a propeller that provides an outward thrust and is always open. An impeller, because of its rotation and especially designed blades, increases the pressure of the fluid and thus its flow. A centrifugal pump used to draw fluid is the best example of an impeller.

In brief:

Propeller vs Impeller

• Both propeller and impeller are specially designed blades with a motor.
• While a propeller is designed to covert rotational motion into forward thrust, an impeller is designed to use rotational motion to suck fluid in.
• A propeller has an open design while an impeller is always inside a casing or housing.


Underwater Welding:-

Underwater welding is one of the most dangerous occupations in the world. Underwater, the odds are stacked against you. The pressure threatens to crush the body. Clouds of bubbles making any task difficult to perform by blocking visuals.Underwater welders are responsible for repairing pipelines, offshore oil drilling rigs, ships, dams, locks, sub-sea habitats and nuclear power facilities, to name a few.

Underwater welding is the process of welding at elevated pressures, normally underwater. Underwater welding can either take place wet in the water itself or dry inside a specially constructed positive pressure enclosure and hence a dry environment.So,it can be classified into two categories:

  1. Wet Welding
  2. Dry Welding

Wet Welding:

Wet underwater welding directly exposes the diver and electrode to the water and surrounding elements.Divers usually use around 300–400 amps of direct current to power their electrode, and they weld using varied forms of arc welding.This practice commonly uses a variation of shielded metal arc welding, employing a waterproof electrode.

Wet welding with a stick electrode is done with similar equipment to that used for dry welding, but the electrode holders are designed for water cooling and are more heavily insulated. They will overheat if used out of the water.The electric arc heats the workpiece and the welding rod, and the molten metal is transferred through the gas bubble around the arc. 

The hazards of underwater welding include the risk of electric shock to the welder. To prevent this, the welding equipment must be adaptable to a marine environment, properly insulated and the welding current must be controlled.

Dry Welding / Hyperbaric Welding:

Another method of welding underwater is hyperbaric welding or dry welding. Hyperbaric welding is the process by which a chamber is sealed around the structure that is to be welded. It is then filled with a gas (typically mixture of helium and oxygen, or argon), which then forces the water outside of the hyperbaric sphere.

In most cases, and most ideally, a dry chamber system is used. Temporary hyperbaric chambers are used to prevent water from entering the work area. The chambers house up to three welders at a time.
Underwater welding is one of the most difficult jobs on the planet and in the water. Though with advancing technologies in robotic capabilities, advancements are being made to protect underwater welders. Despite what the future may hold, today underwater welders help maintain the most integral components of many industries around the world.