关键结构参数对高压除鳞喷嘴性能影响的研究

高压除鳞喷嘴广泛地应用在热轧除鳞工艺中,喷嘴结构参数的变化会对射流性能产生影响。通过数值模拟和实验测试相结合,研究了锥孔深度变化对外部射流的影响。研究表明:锥孔深度增加,射流水喷射角增加、射流速度沿轴向方向衰减变慢,射流距离增加。在相同射流距离下,锥孔深度的增加可以使打击力的大小增大、有效的射流宽度增大。     

An adaptive control strategy for the abrasive waterjet cutting process with the integration of vision-based monitoring and a neuro-genetic control strategy

This paper presents an integrated approach for the monitoring and control of abrasive waterjet (AWJ) cutting process. A machine-vision-based monitoring approach was proposed to obtain the bore diameter of the focusing nozzle from time to time. A neuro-genetic approach, proposed by Srinivasu and Ramesh Babu (Appl Soft Comput 8(1):809–819, 2008) was employed as a control strategy to modify the process parameters, such as water pressure, abrasive flow rate, and jet traverse rate, so as to maintain the desired depth of cut, with changes in the diameter of the focusing nozzle monitored with a machine vision system. By combining the monitoring and control strategies, an integrated approach for adaptive control of AWJ cutting process is realized. The effectiveness of the proposed integrated approach for adaptive control of AWJ cutting process was shown by comparing the results obtained from the experiments with the process parameters suggested by the control strategy to achieve the desired depth of cut. From the results of the study, it is seen that the proposed monitoring system is capable of monitoring the focusing nozzle diameter with a mean absolute deviation of 0.05 mm and that the neuro-genetic strategy is capable of modifying the controllable process parameters to maintain the desired depth of cut with a mean absolute deviation of 0.87 mm.     

Method of setting Nozzle intervals at the finishing scale breaker

The scale is removed from the strip by high pressure hydraulic descaling at the FSB(Finishing Scale Breaker). Recently, the spray height of nozzle has a trend to be shorter for the purpose of increasing the impact pressure by the high pressure water jet. Here, the nozzle intervals should be decided after considering the impact pressure and the temperature distribution on the strip. In other words, the minimum of impact pressure at the overlap of spray influences the surface grade of the strip due to scale and the overlap distance of the spray affects the temperature variation in the direction of the width of strip. In the present study, the impact pressure of the high pressure water jet is measured by the hydraulic descaling system and calculated with regard to the lead angle of 15° and the offset angle of 15°, and then the temperature distribution and the temperature variation are calculated at the overlap distances of 0 mm, 10 mm, 20 mm, and 30 mm, respectively. The method of setting nozzle intervals is shown by utilizing these results.     

Experimental investigation on noise of cavitation nozzle and its chaotic behaviour

The researches of cavitation noise mainly focus on the incipiency and developing of cavitation to prevent the cavititation erosion in the hydraulic machinery, while there is few report about the collapse strength of cavitation bubbles produced by water jet through the cavitation nozzle to utilize efficiently the collapse energy of cavitation bubbles. The cavitation noise signals are collected with hydrophones for the cavitation nozzle and general nozzle at the target position and the nozzle exit separately in the conditions of different standoff distance. The features of signal’s frequency spectrum and power spectrum are analyzed for various nozzles by way of classical methods. Meanwhile, based on chaotic theory, phase space reconstruction is processed and the maximum Lyapunov index is calculated separately for each cavitation signal’s time series. The results of chaotic analysis are compared with the one of conventional analysis. The analyzed data show that there are the marked differences at the spectrum between the cavitation nozzle and general nozzle at the target position while the standoff distance is 35 mm, which mainly displays at the high frequency segment (60-120 kHz). The maximum Lyapunov index calculated appear at standoff distance 35 mm, which is an optimum standoff distance for the most bubbles to collapse at the target. At the nozzle exit, the noise signal of cavitation nozzle is different from the general nozzle, which also displays at the high frequency segment. The results demonstrate that the water jet modulated by the cavitation nozzle can produce effectually cavitation, and at the target position the amplitude and energy of noise spectrum in high frequency segment for cavitation nozzle are higher than conventional nozzle and the Lyapunov index of cavitation nozzle is larger than conventional nozzle as the standoff distance is less than 55 mm. The proposed research reveals that the cavitation noise produced by collapse of cavitation bubbles attributes mainly to the high frequency segment     

硬岩掘进机高压水耦合破岩影响因素实验研究

硬岩掘进机(TBM)在硬岩甚至超硬岩段掘进时,采用高压水射流辅助破岩成为一种有效提高破岩效率的新的研究方向。由于高压水射流破岩受诸多因素影响,作用规律复杂,其破岩机理一直未能被准确揭示。主要利用正交实验方法研究水射流压力、喷嘴直径、喷嘴移动速度对破岩沟槽深度与沟槽宽度的影响,同时结合刀盘贯入度优化水射流压力、喷嘴直径、移动速度等关键参数,探索高压水射流与岩石耦合破岩规律,为进一步揭示破岩机理提供依据。     

Design and evaluation of high-pressure nozzle assembly for laser cutting of thick carbon steel

Laser cutting of carbon steel is extensively used across a range of industries, due to its advantage of high speed, low kerf and high quality. Currently, a 1-kW carbon dioxide (CO₂) laser with its subsonic nozzle assembly can be used only to cut steel plates up to around 10 mm. This paper aims to design and evaluate a high-pressure supersonic laser cutting nozzle assembly, which can enable a 1-kW CO₂ laser to cut steel of up to 50 mm thickness. Basic gas dynamic and compressible flow equations were used to design the supersonic nozzle assembly. The flow of the high-pressure gas jet inside the nozzle assembly was investigated using computational fluid dynamics (CFD), and the structural integrity of the high-pressure nozzle assembly was ensured using finite element analysis (FEA). The gas flow pattern at the exit of the nozzle assembly was computed and compared with the experimental observation made through a shadowgraph technique. Laser cutting experiments were performed with the developed supersonic nozzle assembly to demonstrate cutting of 50-mm-thick low carbon steel with 1-kW CO₂ laser.     

Predictive depth of jet penetration models for abrasive waterjet cutting of alumina ceramics

A study of the depth of jet penetration (or depth of cut) in abrasive waterjet (AWJ) cutting of alumina ceramics with controlled nozzle oscillation is presented and discussed. An experimental investigation is carried out first to study the effects of nozzle oscillation at small angles on the depth of cut under different combinations of process parameters. Based on the test conditions, it is found that nozzle oscillation at small angles can improve the depth of cut by as much as 82% if the cutting parameters are correctly selected. Depending on the other cutting parameters in this study, it is found that a high oscillation frequency (10–14 Hz) with a low oscillation angle (4–6°) can maximize the depth of cut. Using a dimensional analysis technique, predictive models for jet penetration when cutting alumina ceramics with and without nozzle oscillation are finally developed and verified. It is found that the model predictions are in good agreement with the experimental results with the average percentage errors of less than 2.5%.     

基于FLUENT的高压水射流除锈的流场仿真及射流参数优化

利用高压水射流船舶除锈取代目前的人工打砂除锈势在必行。介绍了水射流的基本结构并根据高压纯水射流除锈的工况,利用计算流体动力学（CFD）方法对高压水射流进行了模拟仿真。通过仿真介绍了流场中高压水射流的特性以及靶面的受力情况。最后,为了达到良好的除锈效果,对高压水射流的靶距和入射角度进行优化,得出在指定条件下最优靶距应为15 ~20 mm,最优入射角度（射流与靶面法线的夹角）应为30°。     

An experimentally based thermo-kinetic phase transformation model for multi-pass laser heat treatment by using high power direct diode laser

Laser-based phase transformation hardening (LPTH), based on rapid heating and cooling cycles produces hard and wear-resistant layers only at the selective region of the components. However, the bulk mass of the material’s core property is retained. The advantages of high power direct diode laser in comparison with other high power lasers (CO₂ and Nd:YAG) have put this type of laser as a main heat source for localized heat treatment. However, a tempered zone is formed in overlapping regions of a large heat-treated area during multi-pass laser heat treatment (MPLHT) that affects the uniformity of heat-treated depth of material. This study is focused on the development of a uniform hardness distribution model to minimize the tempering effect during the MPLHT process. A tool steel AISI S7 is heat treated by using different levels of laser power (1,400–1,800 W) and scanning speeds (15–25 mm/s). An experimentally based finite element (FE) thermal model is developed to predict the cross-sectional as well as surface temperature history of the MPLHT process. The temperature-dependent material properties and phase change kinetics are taken into account in the model. The laser beam is considered as a moving rectangular-shaped heat source (12 mm?×?1 mm) with a uniform distribution (top-hat) of laser power. The temperature history acquired from the FE thermal model is coupled with thermo-kinetic (TK) equations to determine the corresponding phase transformations and hardness. The tempering effect of MPLHT is studied for different sizes of overlap (1 mm–3 mm) and lengths of scan (10 mm–35 mm). The TK model results are verified with experimental ones to optimize the processing parameters. The optimized processing parameters, including laser power, scanning speed, size of overlap, and the length of scan are used to achieve a uniform hardness distribution and an even depth of heat treatment in the MPLHT area.     

Experimental and Numerical Investigation on the macroscopic characteristics of the jet discharging from gaseous direct injector

Injector design is one of the main challenges for development of direct injection and partially stratified gaseous engines. Characteristics of discharged spray from direct gaseous injector influence on combustion and emissions of these engines. In this work axial and radial (lateral) penetration of transient jet of direct gaseous injector are investigated for different nozzle diameters and different pressure ratios numerically and experimentally. High speed Schlieren imaging method is used for jet visualization and image processing technique is utilized for analyzing the images and extracting jet boundaries and its axial and radial penetrations. Finite volume based software is used for numerical calculations. Measuring of the axial and radial penetrations for different cases referred to in this paper provides more accurate formulation for the mentioned parameters for transient direct injection gaseous jet discharged from the injector. Experimental and numerical findings show that higher axial penetrations for larger diameters of nozzle and higher pressure ratios are achievable. Smaller diameter of nozzle gives higher relative lateral expansion while there is no specific distinction for different pressure ratios. Results show that the ratio of radial to axial penetration for transient jet is decreased by time and reaches to a constant value of 0.33±0.05 and the normalized jet axial penetration has a linear dependency on the square root of time for all cases with slope of 2.9±0.4.     

Numerical simulation for abrasive water jet machining based on ALE algorithm

In dealing with fluid impact and large deformation problems by traditional Lagrange grid, calculation failure often happens due to grid distortion. An abrasive water jet machining model is created to simulate the whole stage by software LS-DYNA from the jet into the nozzle to the workpiece material removal process using ALE (Arbitrary Lagrange–Euler) algorithm. The mesh for the abrasive and water is based on the ALE formulation, while the target mesh applies the Lagrange formulation. The effect of jet penetration is implemented by coupling the grids of ALE and Lagrange. The jet traverse speed is achieved by definition of the movement of ALE grid to reduce the mesh domain. The abrasive constitutive equations are also presented in this paper. The uniform mixture for abrasive and water is achieved by definition of volume percentage of the two materials in the initial ALE elements. Simulation results give the relationships between processing parameters and the cutting depth. The good agreement between simulation results and experimental data verifies the correctness of the simulation.     

收缩-扩散型喷嘴内高速泡液流稳态解的分岔

空化水射流技术的关键是空化喷嘴 ,实验证明空化喷嘴出口形状对喷嘴的空化效果影响很大。对在具有收缩 扩散形状的喷嘴内高速泡液流稳态解的分析表明 :泡液流中很小的空隙率亦强烈地影响着其流动特性。当空隙率为临界值αc=1.895 993× 10 -4时 ,泡液流稳态解出现分岔现象。收缩 扩散型出口形状更利于喷嘴产生空化     

Process and material behavior modeling for a new design of micro-additive fused deposition

The aim of this paper is to explore the limits and special requirements for additive manufacturing using polymer extrusion with a nozzle diameter much smaller than the conventional one: 0.050 mm diameter. This work is focused on the nozzle design and analyzes the effect of such a reduced diameter on the extrusion process and on the cooling of material while being deposited on the part. The approach is based on experimental and theoretical studies starting from conventional fused deposition modeling technology where the study tested swelling and cooling of filament material during deposition. Experimental work was used to assess the validity of the theoretical model and the first normal stress equation which estimated a swelling factor (diameter) of 1.249 at 0.087 g/h mass rate. The convection coefficient (h) on the plastic part was estimated as7?W/m²?K on the first deposited layer; considerably lower than some references show.     

Investigation on using high-pressure fluid jet in grinding process for less wheel loaded areas

Wheel loading entails chip accumulation in porosities between grains or welding to the top of cutting grains. It is considered one of the most prevalent problems in grinding nickel-based super alloys. Utilizing separate jet cleaning systems can significantly reduce wheel loading. In this study, a separate high-pressure coolant was supplied through a nozzle towards the wheel surface to flush out the chips. The effects of various wheel cleaning parameters on the loaded area to wheel surface ratio in relation to grinding performance were examined. It was observed that the lowest wheel loading was achieved at a nozzle standoff distance of 70 mm from the wheel’s surface. Nozzle stream direction had no significant effect. Increasing flow rate and jet speed led to a significant decrease in wheel loading and corresponding specific energy until a threshold value was reached. Furthermore, the loaded area to wheel surface ratio was reduced by 100 % and the corresponding specific energy by up to 30 % when the wheel cleaning system was employed.     

Thermodynamic Behavior Research Analysis of Twin-roll Casting Lead Alloy Strip Process

The thermodynamic behavior of twin-roll casting(TRC) lead alloy strip process directly affects the forming of the lead strip, the quality of the lead strip and the production efficiency. However, there is little research on the thermodynamics of lead alloy strip at home and abroad. The TRC lead process is studied in four parameters: the pouring temperature of molten lead,the depth of molten pool, the roll casting speed, and the rolling thickness of continuous casting. Firstly, the thermodynamic model for TRC lead process is built.Secondly, the thermodynamic behavior of the TRC process is simulated with the use of Fluent. Through the thermodynamics research and analysis, the process parameters of cast rolling lead strip can be obtained: the pouring temperature of molten lead: 360–400 °C, the depth of molten pool: 250–300 mm, the roll casting speed: 2.5–3 m/min, the rolling thickness: 8–9 mm.Based on the above process parameters, the optimal parameters(the pouring temperature of molten lead:375–390 °C, the depth of molten pool: 285–300 mm, the roll casting speed: 2.75–3 m/min, the rolling thickness:8.5–9 mm) can be gained with the use of the orthogonal experiment. Finally, the engineering test of TRC lead alloy strip is carried out and the test proves the thermodynamic model is scientific, necessary and correct. In this paper, a detailed study on the thermodynamic behavior of lead alloy strip is carried out and the process parameters of lead strip forming are obtained through the research, which provide an effective theoretical guide for TRC lead alloy strip process.     

Mechanical etching of micro pockets by powder blasting

The main objective of this research is to develop a mechanical etching technique to produce micro mould dies having micro pockets of hundreds of μm. A powder blasting technique is applied to stainless steel plates based on predefined process conditions. This paper describes the performance of a powder blasting technique and the effect of the number of nozzle scanning times and the stand-off distance of the nozzle on the depth and width of pockets. Required blasting and measurement steps are performed to extract the relationships between given process parameters and machined results. Experimental results show that increasing the number of nozzle scanning times and decreasing the stand-off distance of the nozzle increase the depth and width of machined pockets. Increase of the width of the pockets results from mask film wear. The results of this research can be a fundamental basis to produce more accurate and smaller micro pockets using the powder blasting process .     

Effect of geometrical parameters on submerged cavitation jet discharged from profiled central-body nozzle

The flow characteristics of cavitation jets are essential issues among relevant studies. The physical properties of the jet are largely determined by the geometrical parameters of the nozzle. The structure and cavitation jets characteristics of the angular-nozzle and the self-resonating cavitation nozzle have been extensively studied, but little research is conducted in the central-body cavitation nozzle mainly because of its hard processing and the cavitation jet effect not satisfactory. In this paper, a novel central-body nozzle (a non-plunger central-body nozzle with square outlet) is studied to solve above problems. Submerged jets discharged from the novel central-body nozzle are simulated, employing the full cavitation model. The impact of nozzle configuration on jet properties is analyzed. The analysis results indicate that when central-body relative diameter keeps constant, there is an optimal contraction degree of nozzle’s outlet, which can induce intense cavitation in the jet. The central-body relative diameter also affects jet profiles. In the case of large central-body relative diameter, most of the bubbles settle in the jet core. On the contrary, a smaller relative diameter makes bubbles concentrate in the interface between the jet and its surrounding fluid. Moreover, the shorter outlet part allows the cavitation zone further extend in both the axial and racial directions. The research results further consummate the study on the central-body nozzles and the correlation between cavitation jet and the structure, and elementarily reveal the mechanism of cavitation jet produced in a non-plunger novel central-body nozzle and the effect of the structure parameters on the cavitation jet, moreover, provide the theoretical basis for the optimal design of the nozzle.     

CFD modelling of flow and mixing characteristics for multiple rows jets injected radially into a non-reacting crossflow

CFD parametric study was done of flow and mixing characteristics of coolant radial jets injected outwardly from a centerline multiple rows diffuser into a heated non-reacting crossflow in a cylindrical chamber in three-dimensional model using ANSYS-FLUENT 14.5. The effects of jet-mixing ratio, nozzles diameter, diffuser diameter, number of nozzles rows number of nozzles per row on the penetration depth and mixing quality through chamber cross section were parametrically studied. The simulation results were validated with the available experimental data and good agreement was obtained. The results showed that the nozzle diameter, the diffuser diameter and the jet-mixing ratio have remarkable effects on the penetration depth and the mixing quality compared to the effects of number of nozzles per row and the number of nozzle rows. The penetration depth at downstream, the jet diffuser exit and the mixing quality at centerline of chamber exit are increased ?46% & ?49%, respectively, with increasing the jet-mixing ratio from 0.1 to 0.5. Dimensionless correlations in terms of the studied parameters for predicting the penetration depth, mixing quality and maximum temperature difference were developed and presented.     

脉冲空化多孔射流钻头的结构设计研究

在多孔射流钻头的基础上,设计了脉冲空化多孔射流钻头,分析了其工作原理:当流体冲击叶轮高速旋转时,可对侧向孔眼入口处的流场产生有规律性的扰动,形成脉冲射流;同时,高速旋转的叶轮可以降低叶轮附近流体的局部压力,可产生许多微小空泡,夹杂在射流中形成空化射流。同时形成的2种射流进而耦合成脉冲空化射流。并利用流体力学和机械设计理论对射流钻头本体、叶轮轴和叶轮的结构参数进行了研究,研究结果可为脉冲空化多孔射流钻头结构设计提供依据。     

EFFECT OF COOLANT PRESSURE,NOZZLE DIAMETER,IMPINGEMENT ANGLE AND SPOT DISTANCE IN HIGH PRESSURE COOLING WITH NEAT OIL IN TURNING Ti-6AL-4V

Though titanium alloys are being increasingly sought in a wide variety of engineering and biomedical applications, their manufacturability, especially machining and grinding imposes lot of constraints. Titanium alloys are readily machinable provided the cutting velocity is in the range of 30–60 m/min. To achieve higher productivity, if the cutting velocity is enhanced to 60–120 m/min and beyond, rapid tool wear takes place diminishing the available tool life. Tool wear in machining of titanium alloys is mainly due to high cutting zone temperature localised in the vicinity of the cutting edge and enhanced chemical reactivity of titanium with the tool material. Rapid tool wear encountered in machining of titanium alloys is a challenge that needs to be overcome. High pressure cooling in machining is a very promising technology for enhancing tool life and productivity via appropriate cooling and lubrication. The present investigation is an attempt to study the effects of jet application parameters, i.e., coolant pressure, angle of impingement of the jet, spot distance and nozzle diameter on tool wear and chip morphology and to compare the effectiveness while turning Ti-6Al-4V bars under high pressure cooling with neat oil. Results indicated that at a cutting speed of 85 m/min and feed of 0.2 mm/rev, high pressure cooling provided a tool life of 24 min vis-à-vis 12 min under cryogenic cooling.