UNDERWATER WELDING !! HOW IT IS DONE ?? EXPLAINED !!

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.

DIFFERENCE BETWEEN ORTHOGONAL AND OBLIQUE CUTTING EXPLAINED !!

Metal cutting is “the process of removing unwanted material in the form of chips, from a block of metal, using cutting tool”.

Methods of Metal Cutting:

There are two basic methods of metal cutting based on cutting edge and direction of relative motion between tool and work:

(i) Orthogonal cutting process

(ii) Oblique cutting process 

(i) Orthogonal Cutting Process:

In orthogonal cutting process, the cutting edge is perpendicular (90 degree) to the direction of feed. The chip flows in a direction normal to cutting edge of the tool. A perfectly sharp tool will cut the metal on rack surface.

(ii) Oblique Cutting Process:

In oblique cutting process, the cutting edge is inclined at an acute angle (less than 90 degree) to the direction of feed. The chip flows sideway in a long curl. The chip flows in a direction at an angle with normal to the cutting edge of the tool.

Difference between the two is discussed in detail in the table below:

WHY V-SHAPED ENGINES ARE USED ?

A V engine, or Vee engine is a common configuration for an internal combustion engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft.The primary reason to use a V-engine is largely packaging. They're shorter and more compact than an inline engine.

The first thing to consider is an engine as a purely rotational system. Imagine a one cylinder engine; the rotating crankshaft is massively out of balance. Even if the actual crankshaft was perfectly balanced, the motion of the piston and the forces it applies will never cancel out. This is why most one cylinder engines run a balance shaft; a weighted shaft geared into the crankshaft to mitigate the out-of-balance effects. A balance shaft can be run on other out of balance engines as well.

A V-engine, on the other hand, can be made to be inherently balanced. This means that no matter what speed the engine's running at, the forces from the rotating assembly will always cancel out. Most notably, a 90 degree V4 or V8 engine can be easily balanced and many race motorcycle engines use this configuration (Honda and Ducati in MotoGP). V6s and V12s run balanced at 60 degree bank angle.

Apart from this other advantages of V configuration are as follows:

1. Dimensions are compact - which are appreciated either in construction of road cars or race cars
2. The compact dimensions mean that more cylinders can be packed in, as comparable to an inline/straight engine of similar dimensions.
3. Can accommodate higher displacement cylinders, and therefore that extra power
4. Its a strong engine - which makes it ideal for racing applications
5. Can accommodate higher compression
6. High levels of refinement.

An interesting note: because a V12 is essentially two inline 6 engines stuck together they're naturally balanced regardless of bank angle. This is why V12 Jaguars have a reputation for smoothness. V6s, being two 3 cylinders stuck together, are inherently out of balance.

Talking about the limitations of V configuration engines,there are few yet they play and important role.These are mentioned below:

1. Contains more moving parts, resulting in higher cost/complexity
2. Weight. The same technicality above makes a V-engine heavy.