Future in Marine Fire-Fighting: High Pressure Water Mist Extinguisher with Abrasive Water Jet Cutting

This paper is dealing with the problem of extinguishing fire on ships and off-shore equipment characterized by high degree of danger caused by presence of explosive or life threatening substances. Special device Cold Cut System Cobra combining cutting possibility and production of water mist is presented. Its advantages and application possibilities are discussed. This fire extinguisher has been widely used for more than one decade but based on a literature search we suppose that its potential is not fully exploited in marine applications. In cooperation with fire-fighting rescue station in Silesian Ostrava laboratory measurement of reaction forces of Cobra slurry jet was realized at the Technical University of Ostrava. It was discovered that measured force was about 120 – 150 N therefore it represented approximately one third of the theoretical maximum value. The measured force appeared to change not only with the type of material but also with the thickness of the layer being cut, but the change was not significant from the point of view of handling the lance during intervention. Our research may deepen firefighter’s knowledge of the tool they are working with and therefore improve safety of their work

Temperature measurement during abrasive water jet machining (AWJM)

This study was undertaken to look for confirmation that heat transfer induced by abrasive water jet machining (AWJM) affects the microstructure of the material cut. The structure of S235JR carbon steel used in the experiments was reported to change locally in the jet impact zone due to the high concentration of energy generated during cutting with the abrasive water jet. It is assumed that some of the energy is transferred into the material in the form of heat. This is particularly true for materials of considerable thickness with a high thermal conductivity coefficient when cutting is performed at low speeds or with high abrasive consumption. The literature on the subject suggests that in AWJM there is little or no thermal energy effect on the microstructure of the material cut. The research described here involved the measurement of the cutting temperature with thermocouples placed at four different distances from the edge. The distances were measured using computed tomography inspection. The thermocouples used in the tests were capable of detecting temperatures of up to 100 degrees C. Locally, temperatures at the edge may reach much higher values. The results of the X-ray diffraction qualitative phase analysis reveal that locally the temperatures may be much higher than the eutectoid temperature. Phase changes occurred along the edge since austenite was observed. This suggests that the temperature in the jet impact zone was much higher than the eutectoid temperature. Optical microscopy was also employed to study the material microstructure. Finally, the material nanohardness was determined.Web of Science1520art. no. 708

Abrasive waterjet (AWJ) forces - Potential indicators of machining quality

The necessity of monitoring the abrasive waterjet (AWJ) processes increases with the spreading of this tool into the machining processes. The forces produced on the workpiece during the abrasive waterjet machining can yield some valuable information. Therefore, a special waterjet-force measuring device designed and produced in the past has been used for the presented research. It was tested during the AWJ cutting processes, because they are the most common and the best described up-to-date AWJ applications. Deep studies of both the cutting process and the respective force signals led to the decision that the most appropriate indication factor is the tangential-to-normal force ratio (TNR). Three theorems concerning the TNR were formulated and investigated. The first theorem states that the TNR strongly depends on the actual-to-limit traverse speed ratio. The second theorem claims that the TNR relates to the cutting-to-deformation wear ratio inside the kerf. The third theorem states that the TNR value changes when the cutting head and the respective jet axis are tilted so that a part of the jet velocity vector projects into the traverse speed direction. It is assumed that the cutting-to-deformation wear ratio increases in a certain range of tilting angles of the cutting head. This theorem is supported by measured data and can be utilized in practice for the development of a new method for the monitoring of the abrasive waterjet cutting operations. Comparing the tilted and the non-tilted jet, we detected the increase of the TNR average value from 1.28 +/- 0.16 (determined for the declination angle 20 degrees and the respective tilting angle 10 degrees) up to 2.02 +/- 0.25 (for the declination angle 30 degrees and the respective tilting angle of 15 degrees). This finding supports the previously predicted and published assumptions that the tilting of the cutting head enables an increase of the cutting wear mode inside the forming kerf, making the process more efficient.Web of Science1412art. no. 330

Analyses of vibration signals generated in W. Nr. 1.0038 steel during abrasive water jet cutting aimed to process control

The presented research was aimed at finding a suitable tool and procedure for monitoring undercuts or other problems such as cutting without abrasive or inappropriate parameters of the jet during the abrasive water jet (AWJ) cutting of hard-machined materials. Plates of structural steel RSt 37-2 of different thickness were cut through by AWJ with such traverse speeds that cuts of various qualities were obtained. Vibrations of the workpiece were monitored by three accelerometers mounted on the workpiece by a special block that was designed for this purpose. After detecting and recording vibration signals through the National Instruments (NI) program Signal Express, we processed this data by means of the LabVIEW Sound and Vibration Toolkit. Statistical evaluation of data was performed, and RMS was identified as the parameter most suitable for online vibration monitoring. We focus on the analysis of the relationship between the RMS and traverse speed.Web of Science151art. no. 34

Influence of local temperature changes on the material microstructure in abrasive water jet machining (AWJM)

This article considers effects of local heat transfer taking place insteel cutting by abrasive water jet machining (AWJM). The influence of temperature changes during AWJM has not been investigated thoroughly. Most studies on AWJM suggest that thermal energy has little or no effect on the material cut. This study focused on the analysis of the material microstructure and indentation microhardness in the jet impact zone and the adjacent area. The structure features revealed through optical metallography and scanning microscopy suggest local temperature changes caused by the impact of the abrasive water jet against the workpiece surface. From the microscopic examinationand hardness tests, it is clear that, during the process, large amounts of energy were transferred locally. The mechanical stress produced by the water jet led to plastic deformation at and near the surface. This was accompanied by the generation and transfer of large amounts of heat resulting in a local rise in temperature to 450 degrees C or higher.Web of Science1418art. no. 539

Influence of steel structure on machinability by abrasive water jet

Although the abrasive waterjet (AWJ) has been widely used for steel cutting for decades and there are hundreds of research papers or even books dealing with this technology, relatively little is known about the relation between the steel microstructure and the AWJ cutting efficiency. The steel microstructure can be significantly affected by heat treatment. Three different steel grades, carbon steel C45, micro-alloyed steel 37MnSi5 and low-alloy steel 30CrV9, were subjected to four different types of heat treatment: normalization annealing, soft annealing, quenching and quenching followed by tempering. Then, they were cut by an abrasive water jet, while identical cutting parameters were applied. The relations between the mechanical characteristics of heat-treated steels and the surface roughness parameters Ra, Rz and RSm were studied. A comparison of changes in the surface roughness parameters and Young modulus variation led to the conclusion that the modulus was not significantly responsible for the surface roughness. The changes of RSm did not prove any correlation to either the mechanical characteristics or the visible microstructure dimensions. The homogeneity of the steel microstructure appeared to be the most important factor for the cutting quality; the higher the difference in the hardness of the structural components in the inhomogeneous microstructure was, the higher were the roughness values. A more complex measurement and critical evaluation of the declination angle measurement compared to the surface roughness measurement are planned in future research.Web of Science1319art. no. 442

High-energy liquid jet technology - risk assessment in practice

V článku uvedeno Irena M. Hlaváčová.Objectives The contribution deals with a risk assessment in practical applications of the high-energy liquid jet technology from the point of view of the risk identification, estimation and evaluation. Materials and Methods Differences between three different types of workplaces are highlighted and analysed — the indoor, the outdoor and the research ones. Theoretical analyses are supported by particular application of the method for the risk assessment in the Laboratory of Liquid Jets at the VŠB — Technical University of Ostrava. This laboratory is primarily oriented to research. Nevertheless, the conclusions can be used also for predominantly commercial workplaces. Results Some new considerations and evaluations concerning health and safety are presented. Conclusions Failure Mode and Effect Analysis (FMEA) procedures were applied and their limitations in risk assessment of water jet-based technologies are explained.Web of Science25437436