Comparison of Welding Electrodes Of Type E6013 & E7018

E7018:

It is a basic coated low hydrogen iron powder electrode suitable for welding heavy structures, high tensile strength jobs where impact strength at sub-zero temperatures are required. With an increased metal recovery due to the presence of iron powder, enhances the welder to complete the job faster. The basic coated formulation ensures a defect-free radiographic quality weld. The superb and well established flux formulation ensure excellent performance of the electrode in AC/DC(+) in all welding positions except vertical down.

Advantages:

• Uniform and soft metal transfer

• Easy to control weld pool and slag.

• Suitable in DC (+) and in AC too.

• Increased weld deposit of about 115% ensures faster welding.

• Neat weld profile in fillet joints.

• High tensile strength and excellent toughness in sub-zero temperatures.

• Suitable for highly restrained joints.

Applications:

It is suitable for all sorts of joining, repairing and fabrication of structural works medium and high tensile steels of grade 550 N/sqmm., The applications include; welding of Structures, highly restrained joints, bridges, railway coaches & wagons, plants, ships, tugs, barges, trawlers, dredgers, storage tanks, boilers, pipelines, grills etc.

Typical Chemical Composition of Weld Metal:

Current Conditions: 

Typical Mechanical Properties of Weld Metal:

Diffusible Hydrogen Content: 5 ml/100gms. of weld

Moisture content in the flux covering: 0.6%

Re baking recommendations: The electrodes should be re-baked at 350°C for one hour prior to use and maintained warm till the job is completed.

E6013:

It is a rutile based, medium coated general purpose electrode suitable for welding mild steels. The superb and controlled flux formulation ensures excellent performance of the electrode in AC/DC(±) in all welding positions. With its soft, forceful & steady arc, easy slag detachability, fine rippled & shiny bead, and characteristics like easy maneuverability in all positions make E6013 a

Welder-friendly electrode.

ADVANTAGES:

• Uniform metal transfer

• Easy to control weld pool and slag in all positions.

• Suitable for either polarity in DC and in AC with OCV as low as 45V.

• Takes care of poor fit-up joints and fills wider gaps with superior quality weld.

• It can be used as a touch electrode.

APPLICATIONS:

It is suitable for all sorts of joining, repairing and fabrication of structural works in mild steels. The applications include; welding of Structures, bridges, automobile bodies, automobile parts, machinery fabrication, steel furniture, railway coaches & wagons, ships, tugs, barges, trawlers, dredgers, storage tanks, boilers, pipelines, grills etc.

Typical Chemical Composition of Weld Metal:

CURRENT CONDITIONS:

TYPICAL MECHANICAL PROPERTIES OF THE WELD METAL:

Comparison:

For welding first of all we select a suitable electrode. While selecting an electrode we follow some rules to select a suitable electrode.

v The first rule says that the electrode must be selected according to the composition of Base metal.

v The tensile strength of base metal must be close to the tensile strength of electrode being selected.

v While selecting an electrode, the moisture content must be considered. If it has moisture then it must be baked before its use.

In our practical we were facing the sputtering during welding when we were using electrode E7018, but when we used E6013 then there was not much sputtering and we were getting a fine bead.  After the research work I found these factors that were affecting our welding.

v In E7018, it has 0.6% moisture content and we did not baked it before its use and E6013 has no moisture content, so it could be used without baking.

v The composition of our sample was not known, but we can say that there is a possibility that the composition of E7018 was not matching with our base metal.

v After using E7018 and E6013 we could say that the tensile strength of our base metal was low and we were using electrode with 70,000 Psi Tensile strength. So it could also be the reason of sputtering.

Conclusion:

                  At the end we may conclude that the sputtering was due to Moisture content, different composition of base metal and electrode and due to the much difference in tensile strength of base metal and Electrode.

Defining Welding and its Types

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing fusion, which is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal. In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material (the weld pool) that cools to form a joint that is usually stronger than the base material. Pressure may also be used in conjunction with heat, or by itself, to produce a weld.
The main Types of welding used in industry and by home engineers are commonly referred to as Mig welding, Arc welding, Gas welding and Tig welding.

GMAW or Gas Metal Arc Welding: 


More commonly called MIG welding this welding type is the most widely used and perhaps the most easily mastered type of welding for industry and home use. The GMAW process is suitable for fusing mild steel, stainless-steel as well as aluminium.

GTAW or Tungsten Inert Gas:


TIG welding is comparable to oxy acetylene gas welding and needs a lot more expertise from the operator. Employed for carrying out high-quality work when a superior standard of finish is needed without making use of excessive clean up by sanding or grinding.

Arc Welding or SMAW:

Generally known as stick or arc welding. Arc welding is the most basic of all welding types, is easy to master in a home welding situation.

Stick welding can be used for manufacturing, construction and repairs, very much well suited for heavy metal size 4 millimetres upwards. Thinner sheet metals and alloys are usually more suited to the mig welding types.

Gas or Oxy Acetylene Welding And Cutting:

Not used as widely for general welding of mild steel. Consists of mixing oxygen and acetylene gas to greate a flame capable of melting steels. Mostly used today for maintenance work and gas metal cutting. Also common for brazing softer metals such as copper and bronze. Can also be used for welding delicate aluminium parts such as refrigeration pipes, gas cutting equipment for metal construction and maintenance. The most accessible of thermal cutting gear is by qxy-acetylene gas cutting and plasma cutting machines. Other methods include the use of a thermal cutting electrode for use with the arc welder machine.

Basic Principles of Eddy Current Inspection

Eddy current inspection is one of several NDT methods that use the principal of “electromagnetism” as the basis for conducting examinations. Several other methods such as Remote Field Testing (RFT), Flux Leakage and Barkhausen Noise also use this principle.

Eddy currents are created through a process called electromagnetic induction. When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around the conductor. This magnetic field expands as the alternating current rises to maximum and collapses as the current is reduced to zero. If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor. Eddy currents are induced electrical currents that flow in a circular path. They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right.

In order to generate eddy currents for an inspection, a "probe" is used. Inside the probe is a length of electrical conductor material which is formed into a coil.

One of the major advantages of eddy current as an NDT tool is the variety of inspections and measurements that can be performed. In the proper circumstances, eddy currents can be used for:

• Crack detection
• Material thickness measurements
• Coating thickness measurements
• Conductivity measurements for:
  • Material identification
  • Heat damage detection
  • Case depth determination
  • Heat treatment monitoring

Some of the advantages of eddy current inspection include:

• Sensitive to small cracks and other defects
• Detects surface and near surface defects
• Inspection gives immediate results
• Equipment is very portable
• Method can be used for much more than flaw detection
• Minimum part preparation is required
• Test probe does not need to contact the part
• Inspects complex shapes and sizes of conductive materials

Some of the limitations of eddy current inspection include:

• Only conductive materials can be inspected
• Surface must be accessible to the probe
• Skill and training required is more extensive than other techniques
• Surface finish and and roughness may interfere
• Reference standards needed for setup
• Depth of penetration is limited
• Flaws such as delaminations that lie parallel to the probe coil winding and probe scan direction are undetectable

Defining and building concept of Metallurgy

Different process involved in metalurgical process:
The process of extracting a metal from its ore and refining it, is called metallurgical process or simply as metallurgy.
The actual process of extraction of a metal from its ore depends upon the nature of the ore and the metal. There is no universally operational method for the extraction of metals. Certain common steps however, are involved in all metallurgical processes.

Steps involved in a metallurgical process

The extraction of a metal from its ore involves the following steps:
Mining of ore
Most ores generally occur deep inside the Earth. Some may occur only a few metres under the earth's surface. 'Mining' is the process of taking out the ores from the mines. When an ore occurs near the surface of the Earth, it can be directly dug out. Such mining is termed as open-pit mining. When an ore is taken out from greater depths, then the mining is termed deep-mining.

Crushing of the ore

Extracted ore often occurs in big lumps. It is essential to break it into smaller pieces The lumps are crushed to smaller pieces by hammering in a hammer mill or by help of a jaw-crusher.
Grinding and pulverization of the crushed ore
The crushed ore is then finally pulverized to fine powder state in a stamp mill or a pulveriser.

Concentration of the ore (ore dressing)

The removal of the undesired foreign impurities i.e., gangue, from the ore is called concentration (or beneficiation) of the ore. Either of the following methods is used for concentrating the ores:

Hand picking

If the impurities present are quite distinct from the ore, and are of large size, these may be removed by hand picking. This method is slow and is generally adopted in the initial stages of concentration.

Gravity or levigation method

When the ore particles are heavier than the gangue particles, the ore is fed into a running stream of water and impurities are washed away. This separation is by way of gravity or levigation method and is commonly used for oxide ores such as hematite and native ore of Au, Ag, etc. In order to concentrate the ore in bulk, a slanting vibrating wooden table with wooden strips called riffles is introduced in the process. Such tables are termed Wilfley tables. The ore is continuously washed with a fine spray of water and the rocking motion sieves the heavier portions, while allowing the impurities to filter away.

Fig: 1.1 - Wilfley table for washing of the ore

Sometimes in the gravity method, a hydraulic classifier based on the gravity method is used. Ore is agitated by a powerful current of water pushing upwards through the bottom of a conical reservoir. The heavier ore particles settle down and are continuously removed from another opening near the bottom, while the lighter particles are washed away by water.

Fig: 1.2 - Hydraulic classifier

Magnetic separation

Magnetic separation is done especially in the case of haematite ore, whereby the powdered ore is dropped on to leather or brass conveyer belt, which moves over two rollers one of these rollers, is magnetic. When the ore passes over the magnetic roller, it sticks to the belt due to the force of attraction and falls nearer due to the force of attraction of the magnetized roller. The gangue falls over readily, further away. The ore and the magnetic impurity are collected as two separate heaps.

Fig: 10.4 - Magnetic separation

Froth flotation process

This process is used for concentrating sulphide ores, as such ores are preferentially wetted by oil while the gangue particles are wetted by water. Powdered ore is mixed with water and a little pine oil and the mixture is vigorously stirred by passing compressed air. The froth, which is produced rises to the surface and carries the ore particles along with it. The gangue is left behind.

Fig: 10.5 - The froth flotation process

Leaching process

In this method, the ore is treated chemically with a suitable reagent that preferentially dissolves the active component of the ore. The concentrated ore form is then recovered from the solution by a suitable chemical method.

A typical example of ore concentration by leaching process is the purification of bauxite using NaOH solution as a leachant. The Bauxite is digested with concentrated solution of caustic soda at 150°C in an autoclave. The Aluminium oxide dissolves in NaOH leaving behind the insoluble impurities, which are removed by filtration.

Ore concentration by leaching process 

The solution of NaAlO2 (sodium meta-alumiinate) is then treated with freshly prepared Al(OH)3 when the entire aluminium in the solution gets precipitated as Al(OH)3

hydrolysis of sodium meta-alumiinate

The precipitate of Al(OH)3 is removed, washed and dried to get Al2O3.

Leaching of silver ore

Leaching process is also employed in the recovery of some precious metals. Silver is extracted from its ores (argentite, Ag2S; horn silver, AgCl) by cyanide process. The finely powdered concentrated ore is treated with a dilute aqueous solution of NaCN (sodium cyanide) and a current of air is passed through the solution. Silver present in the ore gets dissolved due to the formation of soluble sodium argento-cyanide complex, Na[Ag(CN)2] viz.,

Leaching of silver ore 

Na2S so formed gets oxidized (by air) to Na2SO3, Na2SO4 and thus allow the reaction to go in the forward direction. The solution of Na[Ag(CN)2) is then treated with zinc scrap to recover silver.

formation of silver from sodium argentocyanide

With horn silver (AgCl), the reaction with NaCN can be written as,

reaction of horn silver with NaCN

Leaching of gold ore

Gold-containing ore gets dissolved in KCN solution in the presence of air to give a solution containing K[Au(CN)2]. Gold can then be recovered from this solution by either precipitation or electrolytic method.

Electrostatic concentration and liquation are other methods of concentrating of ores. The usage of these methods depend on the nature of the ores and the type of impurities present.

Calcination

The concentrated ore is converted into oxide by calcination i.e., heating it strongly in the absence of air or roasting (heating it strongly in presence of air). This helps in removing volatile impurities like CO2, SO2, organic matter, and moisture from the ore. For example,

It removes moisture from bauxite.

It removes CO2 from carbonate ores e.g.,