Shielded Metal Arc Welding Process | Shielded Metal Arc Welding Applications | Shielded Metal Arc Welding Coating

Shielded Metal Arc Welding: (SMAW)

It is also known as Manual metal arc welding; stick welding or electric arc welding. It is a fusion welding process. Welding is performed with the heat of an electric arc that is maintained between the ends of a coated metal electrode and the work piece.

The electric energy from the arc thus formed produces temperatures of 10000 degree Fahrenheit or higher. A pool of molten metal consisting of base metal and filler metal is formed near the tip of the electrode.

Both ferrous and non-ferrous metals and alloys can be welded by arc welding processes with proper electrodes. The arc and the weld metal pool are protected by the arc flame and slag produced and controlled by the electrode coating. The arc and the weld metal pool are protected by the arc flame and slag produced and controlled by the electrode coating.

Arc time = (time arc is on)/ (Hours Worked)

01-shielded metal arc welding-smaw-arc welding process-stick welding

Arc welding equipment:

1. Arc welding equipment (AC or DC)

2. Welding cables

3. Electrode holder

4. Ground clamp

5. Welding electrodes

6. Welding helmet and hand shield

7. Protective clothing including hand gloves

8. Chipping hammer, wire brush etc

01-SMAW-Shielded metal arc weding process - stick arc welding

Electrode Coatings:

Electrode coatings are generally electrical insulators and hence permit welding in narrow grooves and limited spaces without short circuiting. Electrode coatings provide an excellent means of introducing alloying elements in the weld metal.

Functions of the electrode coating:

Depending upon its composition the coating performs some or all of the following functions:

1. The coating is consumed at a slower rate than the electrode core wire forming a sheath of the un-burnt coating material over the arc. The length of this sheath depends upon the refractoriness of the coating material and its thickness. The existence of this sheath over the arc helps in directing the arc over the weld area making it more stable, reducing thermal losses, raising the temperature at the tip of the electrode and increasing the metal deposition rate.

01-electrode coating for shielded metal arc welding - functions of electrode coating

2. The gas producing materials in the coating give out lot of gases due to dissociation and combustion. The gases so produced form a protective gaseous shield around the arc. This helps is shielding the arc and the welded metal from atmospheric oxygen, hydrogen and nitrogen. In addition to the shielding provided by the coating gases, shielding is also provided by the vapours of metallic oxides and silicates formed by the heat of the arc. The less volatile mineral ingredients in the coating help in the removal of oxides by forming a slag. The slag floats over the molten weld metal protecting it from atmospheric gases during welding and cooling. The removal of oxides by the slag improves the fluidity of the weld metal which in turn results in a sound, inclusion free joint.

3. The coating helps improve arc stability and makes possible a weld free from overlap, spattering and gas bubbles. Arc stability results from the sheath formation mentioned above and the addition of coating constituents like titanium dioxide, calcium carbonate and potassium silicates.

 

Advantages of Carbon electrodes:

1. Less expensive

2. Carry less current

3. Short life

4. Simple arc control

5. Soft material

6. Higher electrical resistance

Advantages of Graphite electrodes:

1. Comparatively costlier

2. Carry larger current

3. Long life

4. Arc control is comparatively difficult

5. Material is hard and brittle

6. Lesser electrical resistance

01-graphite welding electrodes

· The process is mostly manual and makes use of either a DC or an AC source.

· Current usually ranges from 50A to 300A

· Power requirements less than 10 KW

· Work piece thickness 3 to 19mm

01-shielded metal arc welding- shielded metal arc welding basics

Advantages of the SMAW process:

· The shielded metal arc welding process is simple, versatile and requires a smaller variety of electrodes.

. The equipment cost is low and it can be easily maintained. Welds by this process can be made in any position.

Limitation of the SMAW process:

· The process is slow

· Lot of electrode material is wasted in the form of unused ends, slag, arc gases

· If the slag is not removed properly, it remains in the bead leading to poor quality-welds.

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1. Why are Head Gaskets blown?

Normally head gasket blows, when the engine overheats and they can also blow from incorrect installation or poor design. Head gaskets expand and contract according to engine temperature, these cycles may happen after a long period of time, causes the gasket to fail. If you’re replacing the gasket, check the engine block, and head for warping. Follow proper cleaning and torque specifications during assembly.


2. What is the difference between a Fence and a Wall?

A fence is either more temporary or constructed from materials, other than concrete, stone or brick.


3. What is the Difference between a Humidifier and Vaporizer?

The basic difference between humidifiers and vaporizers is that humidifiers disperse cool mist into the air, and vaporizers heat the water to disperse hot steam. Humidifiers are normally used in cooler climates, when due to the usage of heater, the air in the house becomes too dry for comfort and also, it becomes very difficult to breathe. Humidifiers release cool moisture droplets into the air.

Vaporizers also help in moistening the dry air in the house, but vaporizers release hot vapour into the air. There is a heating element in the vaporizers, which help in releasing steam. Vaporizers heat the water and then release vapours.

The basic difference between them is that one emits cold vapours, while the other one emits hot vapours.


4. What is the Difference between a Generator and Inverter?

An inverter is only effective if there is already a source of electrical energy. It cannot generate its own. It can simply convert electrical energy that is already there. On the other hand, a traditional generator cannot make AC current into DC current.


5. What is the Difference between Quantitative and Qualitative Research?

Quantitative research involves gathering data that is absolute, such as numerical data, so that it can be examined in as unbiased a manner as possible.

Qualitative research may yield stories, or pictures, or descriptions of feelings and emotions. The interpretations given by research subjects are given weight in qualitative research, so there is no seeking to limit their bias. At the same time, researchers tend to become more emotionally attached to qualitative research, and so their own bias may also play heavily into the results.


6. Difference between Absorption and Adsorption

• In absorption, one substance (matter or energy) is taken into another substance. But in adsorption only the surface level interactions are taking place.


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7. Difference between Liquid and Aqueous

• Liquid is a state of matter, while aqueous is a special type of liquid formed by dissolving a compound in water

• All aqueous solutions are liquids, but not all liquids are aqueous solutions


8. Difference between Gas and Vapour

· Vapour can turn back and forth into liquid and solid states but a gas cannot

· Gases cannot be see while vapours are visible

· Vapours settle down on ground while gases do not


9. Difference between Boiling Point and Melting Point

– The melting point is a defined for solids when it transfers from solid state to liquid state.

– The boiling point is defined for liquids for a state change from liquid to gas.

– Boiling point is highly dependent on the external pressure whereas the melting point is independent of the external pressure.


10. Why is sound faster in warm air?

The speed of sound in air cair = 331.3 + (0.66 x T) m/s, where T is the temperature in °C.

The speed of sound is proportional to gas temperature and inversely proportional to its molar mass.

Sound is transferred by collisions of molecules. Therefore sound waves will travel faster on warm air because collisions of molecules of air in warm air is greater.