Experimental temperature measurement of oxy-acetylene cutting process.

Taraba, Bohumil ; Maronek, Milan ; Babalova, Eva 等

1. INTRODUCTION

Oxygen cutting is cutting technology with a wide range of applications. It is applied in different sectors of production, e. g. repairs, demolition of steel constructions, preparation of parent material for welding etc. Maximum thickness of materials being cut can reach several hundreds of millimeter. This is not possible by plasma and laser beam cutting methods, (Cary et al., 2005, *** 2010). The principle of oxygen cutting is based on combustion of steel in oxygen. At first, material is heated to the temperature of ignition (for low carbon steel approximately 1350[degrees]C). Then, the flow of oxygen is applied and the highly exothermic combustion process creates a liquid slug being blown out by the oxygen flow (Vasilko et al., 2003). As a result, the kerf in cutting material is formed.

2. OBJECTIVES

The aim of the work was to measure temperatures during oxy-acetylene cutting of low carbon steel plate of 25 mm in thickness. The obtained temperature relationship will be used for numerical simulation of the heat load prediction by ANSYS software.

3. EXPERIMENTAL PROCEDURE

Oxygen cutting experiments were carried out using steel plate S355J0 (DIN 1.0570). Steel S355J0 is structural steel for welding constructions with guaranteed weldability. The size of the samples was 300x120x25 mm.

3.1 The samples

There were prepared two groups of samples. The first one was made for searching of vertical temperature distribution (A series). The second one was dedicated for transverse temperature measurements (B series). The number of thermocouples was chosen with regard to measurement setup properties. Each sample had attached four thermocouples by a micro-weld.

Geometry of A series of sample was designed for location of all thermocouples at 5, 10, 15, 20 mm from the surface top of the material. The vertical thermocouples distribution is shown in Fig. 1.

[FIGURE 1 OMITTED]

Samples of B series were prepared for transverse temperature measurements. The thermocouples were located TC1: 14.25, TC2: 6.25, TC3: 4.25 and TC4: 2.75 mm from the central plane of the cut respectively. All thermocouples were located 5 mm from the top surface of the material. The transverse placement of the thermocouples is shown in Fig. 2.

[FIGURE 2 OMITTED]

3.2 Temperature sensors

A thermoelectric temperature measurement was chosen for temperature detection in several locations of sample during cutting process. Chromel-alumel "K" type thermocouples were used which are applicable within the temperature range up to 1250[degrees]C. It was necessary to place the thermocouples at the exact location and the exact depth. In order to provide this, there was necessary to drill holes in the samples and to microweld the thermocouples. The drill diameter was 2.5 mm.

3.3 Recording of measured temperatures

The measuring system consisted of a cutting machine RS 13, sample, connecting cables, module NI USB9211 and personal computer. There was used an electronic recording method for temperature measurement. The system of thermocouples was connected through input module NI USB9211 to the portable personal computer (***, 2009).

Temperatures were recorded 3 times per second. The obtained temperatures were transferred to the Origin 11 software and the temperature vs. time relationships were created.

3.4 The cutting device and cutting parameters

The horizontal oxygen cutting machine RS 13 was used. A several testing cuts with different cutting parameters were carried out before temperature measurement in order to determine the optimal cutting parameters. During this process the visual inspection of cutting edges was accomplished. The optimal cutting parameters were as follows: the pressure of preheat flame was 110 kPa, the pressure of cutting oxygen was 0.35 MPa. Cutting speed was 4.17 mm.[s.sup.-1] (250 mm.[min.sup.-1]) and nozzle to material distance was 8 mm. There was necessary to keep the same cutting parameters for all samples. The measured results were recorded by computer. The cutting device and measuring setup are shown in Fig. 3.

[FIGURE 3 OMITTED]

4. OBTAINED RESULTS

Temperature distributions in the test samples as dependence on the material thickness (A series, Fig. 4) and plane cut distance (B series, Fig. 5) were obtained.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

5. CONCLUSION

There were obtained eight temperature courses from eight points of cut sample. The measured data will be used in the next step of cutting process analysis--numerical simulation. Temperature of all thermocouples converged in the long run to the same temperature. This confirms, that all temperature measurements were correct. Analysis of temperature fall-off of TC1 and TC2 (Fig. 4) lead to assumption that these thermocouples were affected probably by the cutting nozzle heat source--temperature fall-off of TC1 and TC2 is slower and does not correspond to the TC3 and TC4 fall-off. There is also acceptable temperature course of B sample for numerical analysis (Fig. 5) Temperature gradient represented temperature difference of 457[degrees]C at perpendicular distance 12 mm from cut plane. The numerical simulation will use inverse heat transfer problem. The inverse-numerical-correlation (INC) method will be taken into account (Alifanov, 1994). The objective of numerical simulation will be solution of transient thermal fields, thermal fluxes fields and values of volumetric rate of thermal energy generation from steel combustion during cutting. The simulation model will include nonlinear thermophysical material properties and boundary conditions. The speciality of solving procedure will be change of steel to air elements of cut volume.

6. ACKNOWLEDGEMENT

This paper was realised with the support of grants: APVV 0057-07 and VEGA 1/0721/08.

7. REFERENCES

Alifanov M., A. (1994). Inverse heat transfer problems. Springer-Verlag, New York London Tokyo, 1994. ISBN 3540-53679-5

Cary, Howard B., Helzer & Scott, C. (2005). Modern Welding Technology, Upper Saddle River: Pearson Prentice Hall, 2005, ISBN 0-13-113029-3

Vasilko, K. & Kmec, J. (2003). Delenie materialu, Material cutting, Presov. 2003. ISBN 80-7099-903-9.

*** (2009) Input module NI USB9211, http://sine.ni.com/nips/cds/view/p/lang/en/nid/13880 Accessed on 2009-12-19

*** (2010) Oxygen cutting. http://www.matnet.sav.sk/index.php?ID=373 Accessed on 2010-03-01

Tab. 1. The maximum temperatures for A sample

 Distance from the Maximum
Thermocouple top of surface temperature

TC1 20 mm 399 [degrees]C
TC2 15 mm 492 [degrees]C
TC3 10 mm 528 [degrees]C
TC4 5 mm 600 [degrees]C

Tab. 2. The maximum temperatures for B sample

 Distance from the Maximum
Thermocouple center cutting plane temperature

TC1 14.25 mm 262 [degrees]C
TC2 6.25 mm 480 [degrees]C
TC3 5.25 mm 556 [degrees]C
TC4 4.25 mm 719 [degrees]C