WO1989008528A1

WO1989008528A1 - Arc cutting method and apparatus

Info

Publication number: WO1989008528A1
Application number: PCT/FI1989/000042
Authority: WO
Inventors: Ensi Kyösti Juhani NIINIVAARA
Original assignee: Niinivaara Ensi Kyoesti Juhani
Priority date: 1988-03-11
Filing date: 1989-03-08
Publication date: 1989-09-21
Also published as: AU4189189A

Abstract

The invention relates to an arc cutting method and an apparatus for cutting electrically conductive material by means of electric arc. In the method according to the invention the arc cutting medium is heated by electric arc generated between the arc cutting electrode and an object ment to be cut. For removing the melt material, heated arc cutting medium is conveyed through the arc cutting electrode and directed to the arc area as at least one jet. The apparatus according to the invention comprises, as adapted inside its mantle-like frame (1), of an arc cutting medium chamber (2) and a rod-like arc cutting electrode (16) including an axial arc cutting medium discharge conduit (13), both for conveying arc cutting medium from the chamber (2) into the discharge conduit (13): first tube means (3, 6) for conveying arc cutting medium from the chamber (2) into heat exchanger means (7) wherein part of the heat energy generated by the electric arc transmits to the arc cutting medium; second tube means (8, 10) for conveying heated arc cutting medium from the heat exchanger means (7) into the discharge conduit (13).

Description

Arc cutting method and apparatus

The present invention relates in general for arc cutting electrically conductive materials by means of an electric arc, especially the invention concerns an arc cutting method according to the introducing part of the claim 1 and an arc cutting apparatus according to the introduc¬ ing part of the claim 2. Arc cutting is used generally for cutting metal plates and beams both for making weld¬ ing grooves.

The traditional arc cutting is based on the fact that metal, like usual iron and unalloyed steel and most of the metal alloys and cast iron are in conditions on the earth easily involved to such a condition when the metal will burn in pure oxygen. By this kind of cutting is used a gas blow pipe with two nozzles, one nozzle for heating the metal to be cut and the other for feeding oxygen for the cutting. After the preheating the pure oxygen jet is directed directly towards the heated material, whereby it will blaze up and will burn. The heat generated in the burning process will spread into the the basic material and cause hence preheating necessary for continious gas cutting. Metal oxides being prodused by the burning must have such a low melting- point that the oxygen jet blows them away and hence ^■ oxygen jet can continiously meet new metal.

Aluminium and copper has too high heat conducting capasity and stainless stell has tendency to generate slag with too high melting point for cuttingto by means of traditional method' above. For cutting this kind of materials are therefore used methods by which it is possible to reach higher remperatures. As a method of this kind can be mentioned a carbon arc cutting by a carbon rod electrode and pressurized air jet and disc arc cutting by a rotating disc like electrode. In carbon arc cutting by means of a supported carbon rod is generated between the end of the carbon rod and an objecttoch an arc which will melt material and by means of pressurized air the melted material is blown away.

In disc arc cutting a rotating disc is movede along the object, whereby betweenthe periphery of the disc and the object target is generated an arc which will melt material and the rotational movement of the disc will remove the melted material away from the object.

The most signifant limitation of the above mentioned arc methods relates to the use thereof. Namely said methods are suitable excluding said disc arc cutting with their own limitations without problems only for circumstances on earth. In under water conditions cutting with oxygen blow pipe is existing all the time a potential risk for gas explosion and for powerful pressure wave caused thereof - when the oxygen gas, which is gathered into pockets between material layers of the plate to be cut, blows up. The use of the carbon arc cutting in under¬ water circumstances is limited for the fact that the carbon rod will get damp and for electric conducting problems caused thereof. As one significant problem of the gas cutting can also be mentioned that cutting result is very often very uneven because the right amount the oxygen gas is very difficult to optimize accurately.

The main problems in relation to the disc arc cutting are security risks caused of the rotational movement of the disc both the demand to change the out running disc which especially in underwater circumstances when getting prolonged will essentially reduce the effective time for working. The main goal of the present invention is to eliminate the defects and weaknesses relating to the previously known cutting methods both to accomplish a new-like arc cutting method and apparatus which could make the arc cutting safe despitethe kind of the basic material and the surrounding circumstamces.

This goal has achieved by means of arc cutting method and apparatus mentioned in the beginning, characteriz¬ ing features thereof are presented in the accompanying claims.

Of the most significant benefits of the present invention can be mentioned, that the apparatus is suitable to be used in circumstances both on earth and underwater, that the apparatus is on its construction simple and hence reliable, and that the apparatus do not include moving parts. About the benefits can future be mentioned that the arc cutting apparatus can be hold like any arc cutting device at a constant distance from the object during the whole arc cutting process, whereby the result of the burn cut is very even.

The function of the apparatus is based on that new and genious idea, that cutting medium is circulated and heated inside the apparatus by the pressure surrounding the apparatus and by thermal energy of the arc generated between the end of the arc electrode and the object to be cut and then the heated possibly even vaporized cutting medium is sprayed through the arc cutting electrod directly to the arc area for removing the material melted by the arc.

The invention is described in the following by means of one advantageous embodiment thereof by way of an example with reference to the accompanying grawing presenting a simplified cross-section wiev the arc cutting apparatus according to the invention. As shown in the drawing the arc cutting apparatus, which is in the following referred with definition arc tool, includes a mantle- like frame part 1 bended to an angle, one part of which acts as a handle and is provided with an inner arc cutt¬ ing medium chamber 2, and a second part of which forms a tip part which is ment to be directed towards a object to be cut, and inside of which is fitted arc cutting electrode 16. As the arc cutting electrode can be used either so called unconsumable electrode or as in the drawing a consumable and by consuming cont^'iniously pro¬ truding electrod for example carbon rod.

For igniting the arc between the end of cutting electrod rod 16 and the metal to be cut the cutting rod 16 is connected to positive pole of a current source and the metal to cut to negative pole of the current source. Naturally connection of the poles of the current source can be choosen vice versa. As shown in the drawing the end of the cutting rod 16 is fitted at its free end moveably inside hollow current conducting means 14 which are fitted inside the tip part of frame 1 of the arc tool and the cutting rod is provided with an electrical¬ ly conductive current slide 15, the outer periphery of which is against the inner periphery of the hollow current conducting means 14 and slides in relation thereof. As further presented in the drawing the other end of the current conducting means 16, i.e. the end protruding from the handle of the arc tool frame 1, is connected by a locking part 18 with the current cable 17, which is connected to the above mentioned pole of the current source.

For removing material melted by the arc tool from the cutting object it is used a jet of the cutting medium, which heated, possibly even vaporized, by the thermal energy of the arc generated between the arc tool and the cutting object. As the cutting medium is then advan¬ tageously water. In order to generate said cutting mediun jet the cutting medium flows from, advantageously ring shaped, cutting medium chamber 2, which is fitted inside the handle of the frame, and in which exists pressure which is higher that the surrounding pressure, through a cutting medium down-flow conduit 3,6 fitted inside the tip part of the frame 1 into a heating or vaporizing chamber 7, which is formed mainly ring like, and which fitted around the cutting rod 1 and inside the tip part of arc tool frame 1 to be directed towards the object to be cut, and which is hence in a thermal transfer connection with the arc either directly or via a end wall of the frame part 1. For maximizing the heat transfer area the walls of the heating or vaporizing chamber 7 can be corrugated or provided with ribs, whereby in the chamber 7 the inner energy of the cutting medium increases as the result of transmitting heat current origin from the arc. The cutting medium having an increased energy potential flows then through a cutting medium up-flow conduit 8,10, which is fitted in¬ side the tip part of the frame 1, into a cutting medium receiving space above the cutting rod 16, said space being most advantageously an expanding cutting medium space 11 and defined on one hand by the inner surface of the hollow space of the current conducting means 14 both on the other hand by the upper head surface of the current slide 15. For removing the melted metal cutting medium flows From the the expanding space through a flow regulation valve 12 and a discharge conduit 13, which exists in the cutting rod 16 and extends in axial direction centrally therethrough, further into the arc area.

As further can be seen fron the drawing the cutting medium down-flow conduit 3, 6 is provided with two valves, one of them being a pressure regulation valve 4 o and the second a one direction valve 5. With the pressure rugulation valve 4 is controlled on one hand the the cutting medium flow amount into the heating or vaporizing chamber 7 and on the other hand is regulated as well as hold constant the pressure of the cutting medium flow into the chamber 7. With the one direction valve 5 is prevented back flow of the cutting medium, which isw pressurized in the heating or vaporizing chamber to a pressure higher than the entry pressure. The presure regulating valve 4 is a manually operated and the driving means therof are placed onto the outer periphery of the frame part 1 to an easily reachable place.

The cutting medium up-flow conduit 8,10 connects the heating or vaporizing chamber 7 with the expanding space 11 and is provided, for example by a manually setable, pressure egualizing valve 9 for accomplishing a continious and a desired cutting medium flow with optimumically setable constant pressure from the chamber 7 into expansion space 11, despite the surrounding circumstances and the material to be cut, the driving means for the pressure equalizing valve 9 are placed onto the outer periphery of the arc tool frame 1 to an easily reachable place.

Besides the fact that the the cutting medium with in¬ creased energy potential is intended to accomplish a jet which removes the melted material from the arc area it is also intended to move the arc cutting rod most advan¬ tageously with a speed corresponding the out running speed thereof. This is accomplished in the arc tool according to the invention so that the flow regulation valve 12 is manually setable, whereby it is possible to maintain inside the expansion chamber a constant pressure, which is higher that the surrounding (i.e. the use on earth and the underwater use) pressure, and which loads on the head surface of current slide 15, which de¬ fines to the expansion chamber, a constant force which tends to push the current slide 15 and cutting rod 16 connected thereto outwards.

There is a reason to mention that when it is used so call ed unconsumable cutting rod the protruding of the cutting rod is naturally not desired. Hence the protruding can be prevented without constructive modifications and without using any further locking means so that the regulation valve 12 is opened so much that the energy corresponding the increased energy potential is converted totally a kinetic energy of the arc cutting jet, whereby naturally the efficiency of the jet will increase.

In order to create flow from the chamber 2 into the heating chamber 7 and therefrom further through the expansion chamber 11 into the discharge conduit 13 in¬ side the chamber 2 is kept a continious pressure, which is higher than the surrounding pressure. In circum¬ stances on earth it is enough even a very little over pressure, advantageous is, however, to use overpressure of 10 kPa. Maintaining of the over pressure can be accomplished simply so that the chamber is connected by means of inflow pipe 22 and inflow valve 21 with the arc cutting medium source under over pressure (not shown in the drawing), which can for example be composed of a central arc cutting medium chamber connected by a flow pipe with the valve 21.

Thinking now the underwater use of the arc tool for maintaining constant over pressure one end wall of the arc cutting medium chamber 2 is composed advantageously of a body part 19 moving like a piston. The head surface of the body part is faced towards the rear end of the handle part of the frame 1 and is in connection with the surrounding through openings, for instance borings, at- the end wall of the handle part. Hence when the surrounding pressure increases the pressure.- in- he chamber 2 the part 19 tends to be pushed inwards due to the hydraulic pressure caused by the surroundings, whereby correspondingly the pressure in the chamber in¬ creases.

For the safety of the arc tool in which is used remark¬ ably high current it is advantageous that the arc tool frame 1 as well as the chamber 2, arc cutting flow pipes 3,6,8,10 both and heating and expansion chambers 7,11 are electrically insulated from the electrically concuc- tive parts of the arc tool, which are current concucting means 14, current slide 15 and rod 16. This can be accomplished for example so that the parts ment to be electrically unconductive are made of electrically un- conductive materials or their surfaces opposite or against the electrically conductive parts are provided with an insulating layer.

The invention is described above only by means its one advantageous embodiment. This is naturally not ment to limit the invention to consern this kind of an indivi¬ dual embodiment. So the invention can be varied and mo¬ dified remarkably within the scope of the accompanying claims.

Claims

1. Arc cutting method, characterized in that arc cutting mediu is heated by means of an electric arc generated between an arc cutting electrode and an object to be cut for melting the obje and that for removing the melted material heated arc cutting medium is conveyed through the arc cutting electrode and direc ed to the arc area as atleast one jet .

2. Arc cutting apparatus by which an arc cutting medium flow i directed to arc area for removing material melted by the electric arc, and which apparatus comprise: a frame (1) includ ing a first part forming a handle of the arc cutting apparatus for taking up the arc cutting apparatus and a second part form ing a tip part which is ment to be directed towards an object be cut and wherein is adapted a rod-like arc cutting electrode (16) which is connected to a current conducting means (14) whi are adapted inside the frame (1); and a current cable (17) connected advantageously detachably by the current conducting means with one pole of a current source, characteriz^l in that the arc cutting apparatus include inside the frame (1) an arc cutting medium chamber (2), in which exists a pressure higher that a surrounging pressure, that the rod-like arc cutting electrode (16) comprises an axial arc cutting medium discharge conduit (13) , and that for conveying arc cutting medium from the chamber (2) to the discharge conduit (13) the arc cutting apparatus comprise as adapted inside the frame (1): first conduit means (3,6) for conveying arc cutting medium from the chamber (2) into the heat exchanger means (7), wherein a part the heat energy generated by the electric arc transmits to arc cutting medium, whereby inner energy of the arc cutting medium increases; and second conduit means (8,10) for conveying arc cutting medium with increased energy potential from the heat e changer means (7) into the discharge conduit (13), advantageou ly through a receiving chamber (11) of the arc cutting medium having an increased energy potential, said chamber being in connection with the discharge conduit (13) through a flow regulation valve (11).

3. Arc cutting apparatus according to the claim 2, characteri in that the heat exchanger means include advantageously a rin like heating and/or vaporizing chamber (7) surrounding the ar cutting electrode (16) said chamber being adapted inside the frame (1) at that end of the tip part, which is ment to be directed towards an object to be cut, so that its one end wa is either directly or through a wall of the frame (1) in a h transfer contact with the arc area, and that the chamber (7) in flow connection

- with the arc cutting medium chamber (2) through a down-flo conduit (3,6) comprising a pressure regulation valve (4) and one direction valve (5) and

- with the receiving chamber (11) for arc cutting medium thr an up-flow conduit (8,10) comprising a pressure regulation v (9), said receiving chamber being advantageously a volume-va able expansion chamber for arc cutting medium.

4. Arc cutting apparatus according to the claim 3, character in that the rod-like arc cutting electrode (16) is fastened current slide (15) which moves slideably inside a hollow inn space of the current conducting means (14) in relation to th current conducting means (14), and that the expansion chambe (11) is defined on one hand by.the inner surface of the holl space of the current conducting means (14) and on the other by a continiously moving upper, i.e. in relation to an end s face of the hollow space of the current conducting means (14 opposite, head surface of the current slide (15).

5. Arc cutting apparatus according to the claim 4, character in that the arc cutting electrode (16) is moved out from the of the frame (1) by the current slide (15) by means of the a cutting medium which flows into the expansion chamber and wh therein swells expanding, and that protruding speed of the a cutting electrode (16) is adjusted essentially constant by regulating amount of the arc cutting medium flowing into the discharge conduit by means of a flow regulation valve (12), which is adapted at the end of the arc cutting electrode, and which connects the expansion chamber (11) with discharge cond (13).

6. Arc cutting apparatus according to any of the preceeding claims 1...5, which apparatus is ment mainly for underwater c ditions and/or for conditions under pressure which is essenti¬ ally higher that the atmospheric pressure, characterized in t one of the end walls defining the inner space of the chamber ( is composed of a moving piston-like body part (19), which is i connection with the surrounding pressure through an opening (2 at an end wall of the handle of the frame (1) .