Influence of SAW parameters on flux consumption E-Book

Dr. Chandan Deep Singh

• Herausgeber: BookRix
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2018

Beschreibung

The present research has been done to investigate the influence of different input process parameters on the desired response (flux consumption) in the submerged arc welding process. Fractional factorial technique has been used to design the experiment to reduce the number of runs. The effects of welding current, arc voltage, travel speed and nozzle to plate distance have been found on the flux consumption. The Design Expert software has been used to obtain relationship between the response and parameters. The effect of all the input parameters on the output responses have been analyzed using the analysis of variance (ANOVA) and mathematical modelling.

Leseprobe

Rajdeep Singh, Dr. Chandan Deep Singh

Influence of SAW parameters on flux consumption

BookRix GmbH & Co. KG81371 Munich

Chapter 1

CHAPTER 1

Introduction

1.1 Welding Process

Welding is the most widely used fabrication technique, throughout industry, owing to its capability of providing cost-effective and high strength joints besides affording lighter weight through better utilization of materials and offering design flexibility, when used for joining of metals. Proper application of welding technology by the user makes the welds that are most suitable in virtually all kinds of service. Today’s survival of the mankind has become so much dependent on welding that without welding it would extremely become difficult to build computers, aero planes, rockets, ships, submarines, nuclear reactors, home appliances, automobiles, pressure vessels, utility stations etc. Most of the metals and alloys can be welded by one type of welding process or the other. However, some are easier to weld than others. To compare this ease in welding term ‘weldability’ is often used. The weld ability may be defined as property of a metal which indicates the ease with which it can be welded with other similar or dissimilar metals. Weld ability of a material depends upon various factors like the metallurgical changes that occur due to welding, changes in hardness in and around the weld, gas evolution and absorption, extent of oxidation, and the effect on cracking tendency of the joint. Plain low carbon steel (C-0.12%) has the best weld ability amongst metals. Generally it is seen that the materials with high castability usually have low weld ability.

1.2 Submerged Arc Welding

During 1930’s having recognized the potential advantages of mechanized welding. Several attempts were made to mechanize the arc welding process. Developing a continuous coated electrode as an extension of the manual metal arc welding, electrode was ruled out for the following reasons (a) since the coating is non conducting, arranging electrical contact with the electrode is not practicable, (b) the coating is likely to be peel off when the electrode is coiled, and the coating is also likely to be crushed when fed through the feed rolls.

In submerged arc welding also known as hidden arc welding, submerged melt welding, or sub-arc welding the arc is struck between a metal electrode and the work piece under a blanket of granular flux. The welding action takes place under the flux layer without any visible arc, spatter, smoke or flash.

The modern submerged arc welding is a welding process, in which one or more arc formed between one or more bare wired electrodes and the work piece provides the heat for coalescence. The arc is completely submerged under a blanket of granular, fusible flux, which adequately shields the arc from atmospheric contamination. The process can be fully automatic or semi automatic.

Fig1.1Submeged Arc Welding Process

In fully automatic welding, the wire is fed automatically to the welding head, the flux is fed mechanically to the joint ahead of the arc, the arc length is automatically controlled and the traverse of the arc or the work piece is also mechanized.

In the semi automatic version, the wire feed and arc control are automatic, while the welder moves the welding gun, usually equipped with flux-feeding device, along the joint at the controlled rate of travel. Flux feed may be gravity flow, throughout a nozzle concentric with the electrode from a small hopper atop the gun, or it may be through a concentric nozzle connected to air pressurized flux tank. Flux may be applied in advance of the welding operation or ahead of the arc from a hopper run along the joint.

1.2.1 Principle of operation

In the process of Submerged Arc Welding (SAW), an arc is maintained between a continuously fed bare wire electrode and the work piece underneath a blanket of fusible granular flux which shields the weld metal and the arc from the atmosphere as shown in Figure 1.2. The high deposition rates obtained in this automated process make it a very economical method of metal joining. However, during SAW as in other flux shielded processes, chemical reactions take place between the molten flux and the metal. This interaction between the slag and the metals results in compositional changes, affecting the structure and properties of the weldment.

1.2.2 Basic Equipment

The SAW equipment essentially consists of:

A wire feeder to drive the electrode to the work through the contact tube of a welding gun or welding head.

A welding power source to supply electric current to the electrode at the contact tube.

An arrangement for holding the flux and feeding it ahead of the arc.

A means of traversing the weld joint.

Fig1.2 Basic principle and equipment

1.4 Advantages of Submerged Arc Welding:

Weld metal deposited possess uniformity, good ductility, corrosion resistance and good impact strength. The advantages of the submerged arc welding are as follow:

Most widely used process for welding of heavy thick plates, boilers, pressure vessels, heat exchangers, ships etc.

Multi-wires or strip can be used for cladding.

Can be used for cladding, hard facing to increase corrosion or wear resistance.

The arc is always covered under a blanket of flux, thus there is no chance of spatter of weld.

Out of total metal deposited by welding about 10% is being contributed by SAW.

High metal deposition rate of 30 - 45 kg/hr.

No hand screen, head screen is required.

Weld metal deposited possess uniformity, good ductility, corrosion resistance and good impact strength.

Molten flux provides very suitable conditions for high current to flow. Great intensities of heat can be generated and kept concentrated to weld thicker sections with deep penetration.

Because of high heat concentration, considerably higher welding speeds can be used.

Because of high heat concentration and faster welding speeds, weld distortion is much less.

High metal deposition rates can be achieved. Single pass welds can be made in thick plates with normal equipment.

Welding is carried out without sparks, smoke, flash or spatter.

Weld metal deposited possesses uniformity, good ductility, corrosion resistance and good impact strength.

Very neat appearance and smooth weld shapes can be got.

Submerged arc process can be used for welding in exposed areas with relatively high winds.

Practically, no edge preparation is necessary for materials under 12 mm in thickness.

1.4 Limitations of Submerged Arc Welding:

Some of the limitations of the submerged arc welding are given below:

Since the operator cannot see the welding being carried out, he cannot judge accurately the process of welding. Therefore, accessories like jigs, fixtures, and pointers, light beam focusing devices or rollers guides may be used to ensure proper welding at the joints.

The flux needs pre-placing of the same on the joints which is not always possible.

The process is limited to welding in flat position and on metal more than 4.8 mm thick. In small thickness burn through is likely to occur.

Flux is subject to contamination that may cause weld porosity. Flux consumption increases with the increase in arc voltage.

Cast iron, Al alloys, Mg alloys, Pb and Zn cannot by welded by this process.

Limited to ferrous (steel or stainless steels) and some nickel based alloys.

Normally limited to long straight seams or rotated pipes or vessels.

Requires relatively troublesome flux handling systems

The process requires edge preparation and accurate fit up on the joint. Otherwise the flux may spill through the gap and arc may burn the work piece edges.

1.5 Applications of Submerged Arc Welding:

Submerged arc welding is mainly used for welding low carbon and low alloy steels, though with the development of suitable flux it can be used successfully for welding stainless steels, copper, aluminium, and titanium base alloys.