GB2078586A

GB2078586A - A Head for a Plasma Arc Cutter

Info

Publication number: GB2078586A
Application number: GB8021766A
Authority: GB
Original assignee: NPK za Kontrolno Zavarachni Raboti
Current assignee: NPK za Kontrolno Zavarachni Raboti
Priority date: 1980-07-02
Filing date: 1980-07-02
Publication date: 1982-01-13
Also published as: DE3024339A1; GB2078586B

Abstract

The head comprises: an outer body (20); a cathode holder (21) provided with a replaceable cathode head (22) housed in the body (20); a substantially frusto-conical nozzle (3) located at a forward end of the body (20); and a lid (13) arranged over the nozzle (3) and attached to the forward end of the body (20) in such a way as to form a substantially frusto-conical recess (15) between the nozzle (3) and the lid (13). The recess (15) is in communication with a substantially concentric opening (18) at a forward end of the head. First and second channels (7) are formed in the body (20), a substantially cylindrical surface (4) is formed at the outer surface of the wide end of the nozzle (3), and a substantially cylindrical, rotatable member (5) is fitted on the said substantially cylindrical surface (4). The member (5) has an outer surface (6) which substantially coincides with the inner surfaces of the said first and second channels (7). <IMAGE>

Description

SPECIFICATION A Head for a Plasmotron This invention relates to a head for a plasmotron (plasma arc cutter). Such a plasmotron could be for processing metals in an air medium or underwater and could, for example, be used in ship-building and marine construction.

A plasmotron (plasma arc cutter) is known for processing metals in an air medium or underwater, which consists of a hermetic metallic body in which is placed a cathode holder which has a replaceable cathode head mounted on its front end, while at the back are an orifice for water and the power supply cable. Inside the cathode holder, a pipe which forms a concentric recess around it is fixed. Along the outer surface of the cathode holder a cylindrical insulator with a cross-connecting opening is placed. In the metallic body two opposite to each other sector channels are machined. The cross-connecting opening, in the cylindrical insulator, is connected, at one end, to the concentric recess of the cathode holder and, at the other end, to one of the two sector channels.At the front inside' end of the hermetic metallic body is placed a replaceable conical nozzle, above which are situated the openings of the sector channels. Laterally in the nozzle are drilled small-diameter channels, which are tangentially connected to the main cylindrical channel of the nozzle. The plasmotron is closed with a front closing hood, which is screwed on the outer surface of the metallic body. Between the nozzle and the internal surface of the front-end conical closing hood is formed a closed (when the plasmotron is with a closed cooling system), or open (when the plasmotron is with an open cooling system) in front conical recess, which at its rearward end is connected with the sector channels in the body. Laterally in the hermetic body an opening with a thread is made, which is used for screwing on a device for manually starting the plasmotron.

A disadvantage of this plasmotron is that, when cutting in an air medium, and in particular when cutting an opening in sheet metal with maximum thickness for cutting, a strong reversed thermal flow is obtained. This flow strongly impacts on the nozzle of the plasmotron, the front-end of the closing hood and the metallic body and produces fast wear-off. Aside from that, this thermal flow effect creates favorable conditions for emergence of dual arcs, which lead to internal and outer ruptures in the plasmotron.

Another disadvantage is that, when plasma cutting under water, increasing the depth increases the hydrostatic pressure. In order to maintain the quality of the processed material it is necessary to change continuously the gas dynamic and energy parameters of the working mode.

According to the invention there is provided a head for a plasmotron (plasma arc cutter) comprising: an outer body; a cathode holder provided with a replaceable cathode head housed in the body; a substantially frusto-conicai nozzle located at a forward end of the body; a lid arranged over the nozzle and attached to the forward end of the body in such a way as to form a substantially frusto-conical recess between the nozzle and the lid, which recess is in communication with a substantially concentric opening at a forward end of the head; first and second channels formed in the body; a substantially cylindrical surface formed at the outer surface of the wide end of the nozzle; and a substantially cylindrical, rotatable member fitted on the said substantially cylindrical surface and having an outer surface which substantially coincides with the inner surfaces of the said first and second channels.

The invention will now be described, by way of example, with reference to the single figure of the accompanying drawing, which shows a partial vertical section of a plasmotron (plasma arc cutter) provided with a head according to the invention.

Referring to the figure, the piasmotron comprises an outer, hermetic (hermetically sealed) body 20 in which are installed a device 1 for manually starting the plasmotron and a cathode holder 21 provided with a replaceable cathode head 22. The hermetic body 20 is located on a cylindrical insulator (not shown), in which the cathode holder is built-in and at the back end of which an orifice is provided for a power cable (not shown). The outer surface of the hermetic body 20 is covered with a fixed insulating medium. Afrusto-conical nozzle 3 is fitted in an inside, metallic end of the hermetic body 20, which nozzle 3 is covered by a closing lid 13. The closing lid 13 is screwed on the metallic end of the hermetic body 20 in such a way as to form a conical recess 1 5 between the conical nozzle 3 and the closing lid 13.The front end of this conical recess 1 5 forms a concentric opening 18. In the hermetic body 20 are machined sector channels 7. Also, along the wide end of the outer conical surface 2 of the nozzle 3 there is machined a cylindrical surface 4 on which surface 4 is fitted a cylindrical rotatable member or whirling device 5. The outer diameter 6 of the whirling device 5 coincides with the inside line (inner edge) of the sector channels 7. On a front surface 8 of the whirling device 5, channels (or passageways) 9 are machined tangentially to the inside diameter. These tangential channels 9 are in communication, via their outer ends, with a cylindrical recess 10 formed by inner horizontal (11) and vertical (12) surfaces of the closing lid 13, a metallic front surface 14 of the hermetic body 20 and the upper outer surface 6 of the cylindrical whirling device 5.The other end of the tangential channels 9 is in communication with the conical recess 1 5. The tangential channels 9 are side closed by the internal vertical surface 12 of the closing lid 13, the inside conical surface 16 of the closing lid 13 having an angle 17 with the horizontal, identical to that of the outer conical surface 2 of the nozzle 3. The front, concentric opening 18, between the nozzle 3 and the closing lid 13, has an inside diameter equal to the diameter of the small base 19 of the frustoconical nozzle 3.

The operation of the plasmotron is as follows: Water enters along the sector channels 7 to the cylindrical recess 10 and on through the tangential channels 9 of the cylindrical whirling device 5 from which it is directed tangentially towards the conical recess 1 5 and the outer conical surface 2 of the frusto-conical nozzle 3.

This tangential directing forces the water in the conical recess 1 5 to undergo rotating and forward motion in a direction identical with that of the plasma gas, or reversed, depending on the direction of the tangential channels 9 of the cylindrical whirling device 5. The moving water increases its speed of rotation and forward motion when approaching the front, concentric opening 1 8 because the cross-section of the conical recess 1 5 is continuously reduced.

When the resultant water stream emerges from the front, concentric opening 18, it has the shape of a hollow truncated cone, which cone has as an upper base having the diameter of the concentric opening 18, the whole cone being twisted around its axis. By changing the pressure of the water fed along the sector channels 7, it is possible to change the shape of this cone. By increasing the pressure the cone increases its lower base by slightly lifting itself upwards, while creating a barrier in front of the whole body of the plasmotron. When working under water, the shape of the water stream is changed according to the working depth and the pressure of the water fed along the sector'channels 7.

The plasmotron described can be used not only for cutting metal but also for drilling metal because the occurrence of the reversed thermic flow effect is avoided. For this reason also, the body of the plasmotron can be made from a plastics material, thus giving a reduction in weight.

In the figure, the head of the plasmotron is shown being used against a surface 23 of a workpiece (only part of which is shown). The arrows 24 indicate the rotational motion of the water emerging from the head of thw plasmotron.

Claims

1. A head for a plsmotron (plasma arc cutter) comprising: an outer body; a cathode holder provided with a replaceable cathode head housed in the body; a substantially frusto-conical nozzle located at a forward end of the body; a lid arranged over the nozzle and attached to the forward end of the body in such a way as to form a substantially frusto-conical recess between the nozzle and the lid, which recess is in communication with a substantially concentric opening at a forward end of the head; first and second channels formed in the body; a substantially cylindrical surface formed at the outer surface of the wide end of the nozzle; and a substantially cylindrical, rotatable member fitted on the said substantially cylindrical surface and having an outer surface which substantially coincides with the inner surfaces of the said first and second channels.

2. A head according to claim 1, wherein the; body is hermetic (hermetically sealed).

3. A head according to claim 1 or 2, further comprising a device for manually starting a plasma arc cutter in use.

4. A head according to any preceding claim, wherein the lid is screwed on to the body.

5. A head according to any preceding claim, wherein the first and second channels are machined in the body.

6. A head according to any preceding claim, wherein the said substantially cylindrical surface is machined on the nozzle.

7. A head according to any preceding claim, wherein at a forward surface of the rotatable member, and tangential to its inside diameter, are machined passageways, one end of the passageways being in communication with the other end of a substantially cylindrical recess formed by internal horizontal and vertical surfaces of the lid, a forward surface of the body and outer surface of the rotatable member, the other end of the passageways being in communication with the substantially frusto-conical recess.

8. A head according to any preceding claim, wherein the forward sides of the passageway are defined by an inner vertical surface of the lid.

9. A head according to any preceding claim, wherein the inner surface defining the substantially frusto-conical recess makes an angle with the axis of the head which angle is substantially equal to that made with the said axis by the outer surface of the nozzle.

10. A head according to any preceding claim, wherein the said substantially concentric opening has a diameter substantially equal to the diameter of the smaller, forward end of the frusto-conical nozzle.

1 A head for a plasmotron (plasma arc cutter) substantially as herein described with reference to the accompanying drawing.

12. A plasmotron (plasma arc cutter) provided with a head according to any preceding claim.

1 3. A plasmotron for processing metals in an air medium and under water, which consists of an outer hermetic body into which are fitted a device for manual start and cathode holder with replaceable cathode head, where to the front metallic end of the hermetic body a conical nozzle is fitted, which is covered from above by a closing lid, screwed on the upper metallic part of the hermetic body in such a way as to form a conical crevice between the conical nozzle and the closing lid, which crevice in front is shaped as a concentric opening and in the hermetic body are machined sector channels, which characterized by that, along with the side end of the outer conical surface of the conical nozzle a cylindrical surface is machined, on which is fitted a cylindric whirling device with outer diameter, coinciding with the inside line of the sector channels.

14. A plasmotron according to claim 13, which is characterized by that the front side plane of the cylindrical whirling device are machined tangential to its inside diameter channels, connected with the upper end to the cylindrical crevice, formed by the internal horizontal and vertical surface of the closing lid, the front metallic surface of the hermetic body and the upper inside surface of the cylindrical whirling device, while the other end of the tangential channel is connected to the conical crevice, formed by the conical surface of the closing lid and the outer surface of the conical nozzle.

15. A plasmotron according to claim 13 or 14, characterized by that the tangential channels are closed from the sides by the inside vertical surface of the closing lid, where its inside conical surface has an angle equal to that of the outer cone of the conicalnnozzle, while the front concentric opening between the conical nozzle and the closing lid is with an inside diameter equal to the diameter of the smaller base of the conical nozzle.