Flux-Cored Wire – The Future of Welding

By Prof. R. Sreedaran

Abstract

This article brings the specific and special merits of flux-cored wire in the method of production and application in Industries. It also helps to appreciate how it is going to be the best method of making electrode in terms of quality & cost-effectiveness for all future welding applications. The simple and elegant design of the manufacturing system helps to make any type of electrode to a desired specification to the customer’s needs at short notice.

FCAW Welding

Flux-cored wire is basically a tubular electrode. The conventional electrode has the core the wire and the flux is coated outside. In tubular electrode, flux becomes the core and tube becomes the holding system. Instead of the coating factor we have a FILLING FACTOR which guides the flux to metal ratio. The above concept makes the making of electrode easier and simulation techniques can be very easily adopted to make various types of electrodes to specific customer needs and specifications.

The method of production is made simpler, easier to operate and get the desired quality of welding consumables. This is possible due to the best and relevant technology in flux preparation, flux filling, tube forming and wire drawing methods and with special protective coatings. The digital technology and computers, software have brought the above major changes. The changes in the machine designs have helped in making high quality welding consumables.

Manufacturing process

One of the earliest methods was filling the tube of standard diameter, wall thickness, length and weight with flux. The principle of vibrating method was used in this method. The vibro fill method consists of vibrating table of specified dimensions and either a mechanical or electrical vibrator attached to it. The vibration is designed that it ensures unidirectional flow material from bottom to top layer of the drawn tube mounted on the vibrating table in the form of filled bobbin. This operation takes a few hours as the case may be. Normally the design is made to take care of two bobbins. Each bobbin weighs around 500 kgs. The predetermined and calculated amount of flux is filled. The specified quality control system is followed to ensure the desired values will be attained.

Flux preparation is though similar to the conventional method; care should be taken to ensure that grain size and flux density are consistent and maintained uniformly. Throughout the entire process of filling this should be maintained. The purpose of this to ensure that there is no segregation of the particle or of the different materials which is part of the flux. Special additives and binding materials are used for this purpose. The next step is to draw the tubes to the intermediate size for heat treatment. This is done by special type tube drawing machine and drawn to desired size for annealing /heat treatment process.

The drawn wire in the form of coils are annealed either in inert gas atmosphere or vacuum annealing furnace to get the desired results. The above wire coils are drawn by wiredrawing machines to the desired final size with copper coating or special coating as the case may be.

The latest trend

The above method is slowly changed to a simple method of straight line drawing and also avoided heat treatment by selecting suitable composition of tube of soft material to facilitate the drawing without heat treatment. The earlier method of flux-cored wire production is not popular due to many operational difficulties and involved a discontinuous process.

The most popular and proven system consists of the following operational methods.

1. A batch house of computer controlled system to produce flux of desired specifications.
2. Inline strip dispenser with tube forming/folding system after filling the desired flux.
3. Flux dispenser with monitoring systems to ensure the correct amount of filling of the flux. The above unit is the part of the system.

4. Tube closing unit and size reduction unit to give a closed tube filled with flux of desired specifications.
5. Optional welding and annealing unit for facilitating easier wire drawing.

   

6. Special type coil carrier/take-up unit for taking up the above product.
7. Straight line, torsion-free wire drawing with take up bobbin. In specific cases a coating line is also included.

8. Special type layer winding machine to fill the flux-cored wire to the desired weight both in spools and reel less system.

Material selection and quality procedures

The tube for the material depends on the end product what is desired. The tube can be conventional mild steel, carbon alloy steel, stainless steel or special alloy material. In the case of strips, strip of mild steel, alloy material can be used. In both the cases the above tube, strip forms the equivalent of the core wire in electrode. But in some cases the alloying elements in the flux also changes the final weld metal composition. Two kind of fluxes are normally used which are in the granulated form or powder form as per the desired process and also by the research experience of the flux-cored wire producers.

Generally the method of flux preparation is similar to the one that is used for stick electrodes in the earlier designs. In the later designs additions of alloying materials are done at the time of dosing by special methods to ensure the allot materials are not separated and are of the expected value by adding at the time of filling in the case of strip to flux-cored wire unit. The feeders are normally belt feeders either of single belt design or dual belt design. The dosing, monitoring systems are of computer controlled design that ensures consist ent quality of flux is fed to the strip before tube formation.

Process methods and controls for quality production

The system operates on proven techniques and quality methods well established in the welding industry. The quality of the above processed wire is consistent and meets all industrial standards’.

The future is based on automation & computer application with more precise results and quality welding. Flux-cored wire will become the most economical and trusted welding consumable.

The author acknowledges and thanks all the sources of information and details given by various companies & the same will be useful for the academic reference as well as industrial applications.