Procesamiento de los datos

This is a welding process where a molten slag of high resistivity is used to aid weld metal deposition. The process is mainly used for thick section vertical up butt welds.

First a highly resistive granulated flux is placed in the bottom of the joint on the striking plate and a set of water-cooled copper shoes are attached to each side of the joint. An arc is struck which melts the flux producing a molten slag that is kept from flowing out of the joint by the copper shoes. The arc is extinguished and the wire now feeds into the molten flux bath, which is highly resistive. The heat generated is sufficient to melt both the wire and the sidewalls of the welded joint. The wire and welding head may be traversed (oscillated) backwards and forward along the joint line to produce an even fusion rate. Many wires may be used when welding thicker sections. Welding takes place and both the weld and copper shoes rise to the top of the seam. On completion the shoes are removed and the weld is cleaned. The high heat energy of this process (typically around 50 – 60 kj/mm) results in a large and brittle grain structure. If good toughness is required in the joint then a complete normalise heat treatment must be done to the steel.

This is an expensive heat treatment but it is often the case that the high cost of heat treatment is very much offset by the speed of welding thick section vertical butt welds.

A further development of this process is Consumable Guide Electro-Slag welding (Shown Below) where the welding head remains stationary and the wire is fed down through an oscillating guide, which also becomes consumed in the weld. This increases the range of chemical compositions of weld metal available to the Welding Engineer, as the resultant weld is comprised of the wire, the base metal and the guide. The Elector-Slag principle is often applied to strip cladding processes.

1) The copper shoes are attached and the granulated flux is placed in the joint, and the arc is struck.

The flux melts and the arc is extinguished. The wire now feeds into the resistive slag

2) As the weld continues the weld metal rises and copper shoes must also rise up the joint. The wire may also be traversed. The weld metal solidifies beneath the slag

3) The finished weld Water-cooled

copper shoes

Resistive slag Completed weld Granulated flux

Oscillating consumable guide delivering the wire electrode

Striking plate

Welding Inspection of Steels WIS 5

Section 09 Introduction to Welding Processes Rev 09-09-08 Copyright 2009 TWI Middle East

9.14 WORLD CENTRE FOR

MATERIALS JOINING TECHNOLOGY

9) Brazing, Soldering and Braze/Bronze Welding

The soldering, brazing and braze welding processes are not classified as fusion processes as only partial or surface fusion takes place during the process, however there are a number of elements that require explanation as follows:

Brazing (93) In the correct use of the term Brazing 2 elements need to be satisfied:

a) The use of a filler material with a solidification temperature > 550C

b) A joint design using capillary action between 2 faces as the prime method of joining Soldering (94) Conditions of this process are generally the same as for Brazing but with the solidification of the filler alloy being < 550C. This process is most commonly used in the joining of copper electrical components and wire connections.

Braze/Bronze welding (97) This process may use similar filler alloy materials as when brazing. The fundamental difference between them is that the joint design does not rely alone on capillary action between the 2 surfaces to be joined, and a butt or fillet weld is generally produced in the joint area. An example of where this is used is in the braze of a cast iron butt joint where in order to maximise the joint surface area the preparation may appear like the following

All group 9 processes rely primarily on a surface adhesion of the filler alloy from within the grain boundaries of the base metal to produce a sound joint although a degree of finite surface alloying may also occur. The success and thus the main inspection points of this group of processes are mostly concentrated around the joint preparation and cleanliness.

9 BRAZING, SOLDERING & BRAZE WELDING 91 Brazing

912 Flame brazing 913 Furnace brazing 914 Dip brazing

93 Other brazing processes 94 Soldering

942 Flame soldering

952 Soldering with soldering iron 96 Other soldering processes 97 Braze welding

971 Gas braze welding 972 Arc braze welding

Increasing the joint surface area through preparation angles and studding.

A braze or bronze welded butt joint

THE WELDING INSTITUTE

Welding Inspection of Steels WIS 5

Section 09 Introduction to Welding Processes Rev 09-09-08 Copyright 2009 TWI Middle East

9.15 WORLD CENTRE FOR

MATERIALS JOINING TECHNOLOGY

WIS 5 Section 9 Exercises:

1) Complete the 4 basic requirements to be satisfied for fusion welding processes?

1. A

Heat source

Of a high enough intensity to melt the base metals

3.

4.

2) Complete the basic parameters to be considered in resistance spot welding?

1

. Current

2.

3.

3) List 4 other elements to be considered when using the Electro Slag process?

1.

Joint type ______

2. ___________________________________

3. ___________________________________

4. ___________________________________

5. ___________________________________

4) Describe the main differences between Soldering Brazing and Braze Welding?

WIS 5

Preparatory for CSWIP 3.0/3.1