Direct current, Mechanical Engineering

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. 

Posted Date: 9/14/2012 8:26:00 AM | Location : United States







Related Discussions:- Direct current, Assignment Help, Ask Question on Direct current, Get Answer, Expert's Help, Direct current Discussions

Write discussion on Direct current
Your posts are moderated
Related Questions
Difference between SI and CI engines SI engine stands for spark ignition engine while CI engine stands for compression ignition engine. SI engine works on the principle of w

Traveling at a speed of 16.0 m/s, the driver of an automobile suddenly locks the wheels by slamming on the brakes. The coefficient of kinetic friction between the tires and the roa

We have a reciprocating compressor operating at 800 rpm. Suction pressure and discharge pressure are held constant by other systems that have nothing to do with the compressor. W

A triangle PQR with vertices P(2,1), Q(4,4) , R(1,3) is to be translated by 2 units in x - direction and 4 units in y direction. Using the homogenous coordinate system, calculate t

Evaluate mechanical work in different steady flow process: Work done by steady flow process   and work done in non flow process,   1. Constant Volume Process; W 1-2 = V

What is ignition angle offset

Q. Measurement of river water levels? In designing bridges and other engineering structures on rivers, maximum discharge and highest flood level form essential data for design

A cantilever truss is loaded and supported as shown in the figure given below. Find the out value of P , which would produce an axial force of magnitude 3KN in member AC .

Determine the Properties of foundation Soil profile together with natural type and properties of each strata will have a bearing on the choice of foundation. The fact that loa

Expected quarterly sales in Year 1 (vehicles) The work content of a single unit of each product in each process has been estimated at: Using MS-Excel, calculate the workloads