GB2330102A - Air-arc gouging - Google Patents

Abstract

A process of arc gouging is based on continuously feeding a consumable electrode of a specially formulated wire or strip. The process allows constant conditions to be maintained throughout the gouging process removing the need to continually reposition the electrode and holding the air blast at a fixed distance ensuring consistent dross removal. The air blast is channeled through a contact tip that is designed in such a way as to allow free rotation to set the air blast in the appropriate place.

Description

AIR-ARC GOUGING PROCESS Introduction This application for patent relates to the field of arc gouging. This is a method of removing metal or metallic alloys by generating an electric arc between the workpiece (the metal from which the material is to be removed) and an electrode. The material melted by the arc is removed from the workpiece by means of a stream of air or other gas impinging on the molten pool; however, instead of using a carbon arc or similar, a continuously fed consumable electrode is used, thereby maintaining constant gouging parameters and not introducing undesirable carbon into the gouged area.

In all relevant cases of arc gouging the electrode is burnt away during the process and hence is a process consumable.

Prior Art The main industrial application in which this patent can usefully replace an existing process is Air Carbon Arc Gouging. This is a method of cutting or removing metal by melting it with an electric arc struck between the workpiece and a carbon/graphite electrode. Most of the material so melted is then blown away by compressed air. This air jet is external to the consumable electrode and emanates from the end of the electrode clamp. The jet impinges on the molten metal immediately behind the arc.

The main limitations of Air Carbon Arc Gouging are as follows: 1.The electrode length and hence the resistance heating within the body is continually changing. As the process proceeds the carbon/graphite is used up and the length between the contact point and the workpiece is reduced. Consequently total resistance, which decreases linearly with electrode length, (equivalent to I2R, where I is the current flowing in the electrode and R is the electrical resistance of the electrode) alters the gouging parameters. The resulting gouged groove may thus change in width and depth as the process proceeds.

2. As the carbon/graphite electrode is consumed the distance between the compressed air jet and the molten metal is also continually changing thereby altering the amount of molten metal that is blown away.

3. The process must be repeatedly stopped to reset the carbon/graphite electrode at the correct length, mating the process time consuming.

4. Some carbon is absorbed/adsorbed by the molten metal and the base metal. This residual material is most undesirable in many cases where cleanliness and low carbon conditions are essential. This can be exacerbated by a number of manual handling or torch setting faults and can result in fissuring and other undesirable changes in the properties of the material subject to gouging.

5. When operating in manual mode the stub ends of the graphite electrodes are frequently discarded, resulting in material loss reaching 20%.

The invented process, herein described, overcomes the above problems as will be described further in the text. statement of Invention This application for a patent describes an invention covering the process of arc gouging and is based on continuously feeding a consumable electrode of specially formulated wire or tape and establishing and arc between the consumable electrode and the metal to be gouged. The arc is designed to melt metal by using the energy dissipated in the are as a heat source and blowing away the molten metal with a gas that can be air or any other suitable gas. The process can be used on any metal and is primarily useful on ferrous metals, non-ferrous alloys and generally any conductive material on which an arc can be established The process shall work in such a way that the stick out, i.e. the length of wire or strip protruding from the contact tip, is held constant. This then allows an are to be established that has a constant energy, as the length of wire or strip that is subjected to resistance heating is maintained at or close to a set value The invented process allows constant conditions to be maintained throughout the gouging process removing the need to continually stop the process to reposition the electrode and giving constant control of the arc conditions by maintaining the electrode extension. This has the additional advantage of holding the air blast at a fixed distance ensuring consistent dross removal.

The directed air blast or jet is achieved by designing a contact tip and accessories that can be attached to a hand held or machine held gun, whose function is to guide the consumable electrode, establish an electrical contact between the conductor and the consumable electrode and as a channel for the air blast that may flow through channels associated with the contact tip. The contact tip may be manufactured from a single or multiple pieces in such a way as to channel the air blast internally to exit at a point close to the exit point of the wire. The gun should allow free rotation of the contact tip. either in its own right or as part of a sub-assembly, enabling the air blast to be maintained at the correct point around the arc to ensure the molten metal is ejected in the desired direction.

The invented process utilises a continuously fed wire or strip that is speeifically formulated to suit the metal that is being gouged. This overcomes the problems of carbon contamination and also the only wastage is that at the end of a reel.

The process can be used in an automatic mode when performed by suitable equipment and as a semi-automatic process, if a welder or operator manipulates a specially designed torch by hand A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates a typical set up for a hand held semi-automatic torch; and Figure 2 illustrates a typical set up for an automatic process.

Figure I shows the electrode 6 being fed through the central core of the complete torch assembly.

The front end of the torch is illustrated at point 1, into this slots a collar 2 made from an insulating material. An inner sleeve 3 is also attached to the end of the torch I. The contact tip 4 is then screwed into the collar and, as the collar and contact tip assembly is only pressed into the end of the torch, this assembly is rotated to best align the air blast holes. A shroud 5 is then is then placed over the entire assembly firmly holding the collar in place.

This construction then forces the air blast 7 to take the following route; From the end of the torch 1 the air blast is turned inwards by the collar 2 and the contact tip 4, it then proceeds down slots machined in the inner sleeve 3 to the inside of the contact tip whereupon it exits through the holes along one side of the electrode exit point.

Figure 2 shows the electrode 6 being fed through the central core of the complete torch assembly.

The inner sleeve 3 and the outer sleeve 4 are fixed together, for example by brazing, and these are attached to the end of the torch 1 by means of a lock nut 2. The contact tip 5 is screwed into inner sleeve 3 forming a seal against the outer sleeve 4.

The air blast 7 enters through the torch land down the centre of the inner sleeve, out through the holes to the slots, down to the area behind the contact tip and out through the holes at the side of the electrode exit hole.

Claims (6)

CLAIMS AIR ARC GOUGING PROCESS

1. An automatic machine controlled process of gouging that is able to maintain constant operating parameters by using a continuous or intermittent arc, established between a continuously fed wire or strip consumable electrode and a conductive base metal, to partially melt the base metal and concurrently use a directed jet of gas for removal of the liquid metal.

2. A hand held semi-automatic device performing the same process as described in 1.

3. Any process using air under pressure and otherwise as described in claims 1 and 2.

4. Any process using a consumable electrode continuously fed of a cross section specially designed to produce grooves of a defined shape and otherwise as described in 1,2 and 3.

5. Any automatic gouging process that uses an electronic or similar device to maintain constant the extension of the wire past the contact tip and otherwise as described in the above claims.

6. Any automatic or semi-automatic process that allows the rotation of the gas jet around the arc with or without any of the above claims.