GB2050223A - Method of and apparatus for cutting - Google Patents

Abstract

In the cutting of a ferrous metallic or other material with a thermic lance using oxygen as a fuel, the slag produced is removed from the material being cut with a blast of air as the cutting operation proceeds. The air blast is preferably supplied through an annular outlet, from annular passage 18, which surrounds an outlet for the combustion products of the oxygen. <IMAGE>

Description

SPECIFICATION Method of and apparatus for cutting The present invention relates to a method of cutting and to apparatus for use in said method.

Thermic lances are used in cutting operations on combustible or non-combustible materials, especially in the steel industry, eg. for cutting scrap, scarfing of other ferrous material, or for cutting refractory materials or non-ferrous metals. The lance is provided with an internal stream of oxy'gen and consists basically of a tubular structure of ferrous metal which alone, or together with additional ferrous metal contained within the tubular structure, is burned with the oxygen to produce a stream of hot combustion products for effecting the cutting operation. This stream usually contains droplets of molten metal still undergoing combustion.A molten slag is produced from the combustion of the ferrous metal of the lance, and commonly also from the combustion and/or heating of the material being cut and, to keep the cutting position clear, a large excess of oxygen over that required for combustion is used to blow away the slag.

In accordance with the present invention, there is provided a method of cutting a material with a thermic lance directed at the material, in which method the slag produced is removed from the material being cut with a blast of air as the cutting operation proceeds. By using air to remove the slag in this way, the required flow of oxygen is reduced with consequent economy of operation.

The blast of air may be provided in any convenient manner but is preferably directed from an air passageway provided as part of the lance, and the invention accordingly further provides apparatus for this purpose which comprises a thermic lance, an air passageway provided as part of the lance, an oxygen supply and a compressed air supply for the lance, and valve means for regulating the flows of oxygen and air separately. Such apparatus is more convenient than apparatus in which the blast is provided by equipment separate from the lance and requiring separate manipulation by the operator.

The air passageway preferably surrounds the tubular structure for directing the blast of air so that-it surrounds the stream of hot combustion products. With this arrangement, the air passageway is burned during operation together with the tubular structure but in such a manner that a length of the air passageway is left projecting beyond the combustion-products exit of the tubular structure. This projecting length and the blast of air passing therethrough in enveloping contact with the stream of combustion products act to diminish the spreading of the stream as it travels through the atmosphere towards the workpiece.

Additionally, although the oxygen component of the air blast may be wholly or partly consumed in combustion of the tubular structure and/or the air passageway the nitrogen component greatly increases the volume of gas issuing from the apparatus, not only because of the rate at which it is supplied to the apparatus with the air, but also because it is expanded by the heat generated by the combustion. For a given rate of burning of the tubular structure the apparatus of the invention gives a more localised heating at the workpiece and improved removal of the slag for a given flow of oxygen.

The following description of a preferred form of apparatus according to the invention in which reference is made to the accompanying drawing is given in order to illustrate the invention. in the drawing: Figure 1 shows part of an apparatus according to the invention in cross-section, and Figure 2 is a diagrammatic representation of the apparatus of Fig. 1 being used in a cutting operation.

The apparatus of Fig. 1 has an oxygen supply and an air compressor diagrammatically shown at 1 and 2 respectively with control valves 3 8 4 in their supply lines 5 and 6.

Air enters the lance-part 7 of the apparatus-scale shown at S in Fig. 1-via an externally threaded tee-piece 8. An outer (air) tube 9 passes through a cap 10 threadably engaged over one outlet of the tee-piece 8 and abuts by its end 11 one end of a piece of cylindrical tubing 12 (shown in perspective at A) which is formed with four air entry ports 13 and has an outer radius less than the inner radius of the tee-piece to leave an annular space 14. The other end 15 of piece 12 abuts a length of packing material 11 3 to compress the packing material against a bottom diminishing socket 16 (also engaged with tee-piece 8) and against an inner oxygen tube 1 7.

Further packing material is provided at 213 as shown.

Oxygen from line 5 passes through tube 17. Air from line 6 passes around annular space 14 and through ports 13 to enter the annular space 18 between tubes 9 and 17.

In use, oxygen tube 17 may be packed with steel rods or other ferrous metal fuel, in a known manner for combustion in the oxygen.

The apparatus is readily dismantled for the replacement of tubes 9 and 17 as required.

Fig. 2 shows the cutting of an iron plate 20 by the stream of hot combustion products 19 (including particulate iron oxides, carbon dioxide and excess oxygen) produced in tube 17. Part 20a of plate 20 has already been cut and a hole travelling in direction 21 is being formed by melting and combustion in stream 19. The slag 23 is being cleared away by the surrounding air stream 22.

The following Examples were performed using the apparatus just described. In these Examples, the pressures quoted are guage pressures. The flame lengths quoted are visible luminous flame lengths and although these measurements may lack precision, they will be understood by those skilled in the art to be valid for comparative purposes.

Example 1 A comparative test was set up by assembling two lances, one conventional with oxygen only and one as shown in Fig. 1 with oxygen and air. The object of the test was to compare the burning rate of the two lances, and the visible flame length at constant oxygen pressure.

The oxygen pressure was set at 2.7 bars giving a flow of 150 litres/minute and the air flow was 250 litres per min.

Initial length of oxygen only lance = 1716 mm.

Final length of oxygen only lance = 1530 mm.

Duration of test = 30 seconds.

Burning rate was 372 mm/min.

Flame length was 910 mm.

Initial length of oxygen/air lance = 1314 mm.

Final length of oxygen/air lance = 1105 mm.

Duration of test = 30 seconds.

Burning rate was 419 mm/min.

Flame length was 3660 mm.

Example 2.

Example 1 was repeated using 1.25 bars oxygen pressure giving a flow of 100 litres/minute and 200 litres per min. of air.

Initial length of oxygen only lance = 1346 mm.

Final length = 1146 mm.

Duration of test = 30 seconds.

Burning rate was 400 mm/min.

Flame length was 900 mm.

Initial length of oxygen/air lance = 895 mm.

Final length = 667 mm.

Duration of test = 30 seconds.

Burning rate was 457 mm/min.

Flame length was 3660 mm.

Therefore the burning rate of the oxygen/air lance was slightly faster but the flame length was about four times as long.

Example 3 A test was done using apparatus as shown in Fig. 1 to show oxygen saving. The oxygen pressure was set at 5.3 bars psi and the flow to the centre of the lance was found to be 270 litres/min. and the outside of the lance was 250 litres per min. Air was substituted for oxygen to the outside tube at the rate of 20 libres/min. The cutting speed was 200 mm. per minute on a 38 mm. steel slab in both cases.

Therefore in the one case 520 litres/min. of oxygen was used and in the second case only 270 litres/min. of oxygen and 20 litres/min. of air was used to give the same burning rate.

It will be understood that the foregoing description of a specific construction and the foregoing Examples are given for purposes of illustration only.

Claims (10)

1. A method of cutting a material with a thermic lance directed at the material, said lance using oxygen as a fuel, in which method slag produced in the cutting operation is removed from the material being cut with a blast of air as the cutting operation proceeds.

2. A method according to Claim 1 in which the blast of air is directed from an air passageway provided as part of the lance.

3. A method according to claim 2 in which the air passageway has an annular outlet which surrounds an outlet for the combustion products of the oxygen.

4. A method according to any one of claims 1 to 3 in which the lance has an oxygen passageway containing a fuel for combustion with the oxygen therein.

5. A method according to claim 4 in which the fuel is a ferrous metallic material.

6. A method according to either of claims 4 or 5 in which the fuel is in the form of steel rods.

7. A method according to any one of Claims 1 to 6 in which the said material is metal or a non-metallic refractory material.

8. Apparatus for use in the method of Claim 2 which comprises a thermic lance, an air passageway provided as part of the lance, an oxygen supply and a compressed air supply for the lance, and valve means for regulating the flows of oxygen and air separately.

9. Apparatus for use in the method of Claim 2, substantially as hereinbefore described and illustrated by reference to the accompanying drawing.

10. A method of cutting a material with a thermic lance, substantially as hereinbefore described and illustrated by the foregoing Examples.