Direct current, Mechanical Engineering

Assignment Help:

Direct Current


Using direct current, the tungsten electrode may be connected to either the negative or the positive terminal of the supply of power. In almost all cases, electrode negative is chosen. With that polarity, electrons flow from the electrode to the work and positive ions are transferred from the work to the electrode and the connection is known as DCEN (straight polarity). When the electrode is positive, the directions of electron and positive ion flow are reversed, the connection is known as DCEP (reverse polarity). With DCEN and a t hermionic electrode such as tungsten, around 70 % of the heat is generated at t he anode and 30 % at the cathode. Since DCEN produces the greatest amount of heat at the workpiece, to  a given welding current, DCEN will provide deeper weld penetration than DCEP. DCEN is t he most common configuration used in TIG welding and is used with argon &  helium or a mixture of the two to weld most metals.


When the tungsten electrode is connected to the positive terminal (DCEP), a cathodic cleaning action is created at the workpiece surface. This action occurs with most of the metals but is most important when welding aluminium and magnesium because it removes the refractory oxide surface that inhibits wetting of the weldment by the weld  metal. Taken DCEN, in which the electrode tip is cooled by the evaporation of electrons, when the electrode is used as the positive pole, its tip is heated by the bombardment of electrons as well as by its resistance to their passage through the electrode.Therefore, to reduce resistance heating and increase thermal conduction into the electrode collet, a large diameter electrode is required for a given welding current when reverse polarity is taken. The current carrying capacity of an electrode connected to the positive terminal is approximately one tenth that of an electrode connected to the negative terminal. DCEP is generally limited to welding thin sheet metal. 


Related Discussions:- Direct current

Determine the reactions at the points of supports, Two identical rollers, e...

Two identical rollers, each of weight W= 1000N are placed by an inclined plane and a vertical wall as shown below. Determine the reactions at the points of supports A, B, and C. Su

Effect on the corrosion rate of carbon steel, Q. Effect on the corrosion ra...

Q. Effect on the corrosion rate of carbon steel? The velocity of the acid has a significant effect on the corrosion rate of carbon steel. The recommended velocity range for pi

Thermal efficiency and compression ratio, Thermal efficiency and compressio...

Thermal efficiency and compression ratio: Calculate thermal efficiency and compression ratio for automobile working on otto cycle. If energy generated per cycle is thrice whi

Explain interpoles or commutating poles, Interpoles or commutating poles ...

Interpoles or commutating poles Interpoles are ?xed to the frame in among main poles. They are used for sparkless commutation, i.e, to improve commutation.

Objectives service and maintenance procedures , Objectives After study...

Objectives After studying this unit, you should be able to explain various procedures in service and maintenance, and appreciate the importance of the inspections

Temperature measurement by using thermometers, T emperatur e Measurement ...

T emperatur e Measurement by Using Thermometers: To measure temperature at temperature scale should be devised assigning arbitrary numbers to a known specific level of hotne

Determine the diameter of wire - close coiled helical spring, Determine the...

Determine the diameter of wire - close coiled helical spring: A close coiled helical spring has to absorb 100 N-m of energy while compressed to 10 cm. The coil diameter is 10

Capp for machining process, CAPP for Machining Process This explained ...

CAPP for Machining Process This explained mainly two different approaches to Computer Aided Process Planning, i.e.  (a) Variant approach, and  (b) Generative approach.

Friction, law of static friction

law of static friction

Find out tension in the rop, Find out tension in the rop: Two blocks A...

Find out tension in the rop: Two blocks A and B are associated as shown in Figure (a). Mass of block A is 15 kg and this is resting on a surface having a coefficient of fricti

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd