对铸件缺陷位置和尺寸的无损检测方法的评价[中文3726字] 【中英文WORD】

对铸件缺陷位置和尺寸的无损检测方法的评价[中文3726字] 【中英文WORD】,中文3726字,中英文WORD,对铸件缺陷位置和尺寸的无损检测方法的评价[中文3726字],【中英文WORD】,铸件,缺陷,位置,尺寸,无损,检测,方法,评价,中文,3726,中英文,WORD 附录1 外文文献原文及译文 原文： An evaluation of NDT methods for the location and sizing of forging discontinuities In selecting an NDT method for flaw detection in forgings a number of variables must be considered: a) the type of discontinuity to be assessed; b) the method to be used for detection and evaluation, and c) the variables associated with the forging itself The variables in item a) will govern the location within the forging and its orientation with respect to a particular surface Item b) could include a considerable array of NDT methods, but for the purpose of this paper only the six most widely used are considered一visual testing (VT), penetrant inspection(PI), magnetic particle inspection(MI), eddy current testing (ET), radiographic inspection (RT) and ultrasonic inspection (UI). In the last item c) the component race include such things as condition, geometry access for inspection. a) Forging discontinuities The location of the discontinuity will have a significant influence on the selection of the NDT method to be used and they are therefore grouped into three categories, to aid this selection: 1. open to the surface: laps, seam, burst, slugs, cracks and inclusions 2. slightly subsurface: seam, stringers, inclusions and grain structure variations 3. internal: stringers, burst, lamination, grain structure, inclusions and piping A brief review of these terms may be helpful: Lap: folded metal, flattened into the surface but not fusing with it Seam: linear flaws due to oxidized blow holes or ingot splashes, which are elongated by hot working Burst: ruptures caused by failure of plastic deformation by processing at too low a temperature or excessive working of metal Stringers: a bar stock defect, due to non metallic inclusions being squeezed out into long and thin strings Lamination: planar defect aligned parallel to surface, originating in the original ingot from rolled out piping Cracks: transgranular failure, due to localized stresses resulting from non-uniform heating or cooling and non-plastic deformation Inclusions: impurities, such as slag, oxide and sulphides, often from the original molten stage in forming the billet used for forging Grain structure: depending upon the extent of working, (deformation and recrystllisation) can be as small as 0.5mm or as large as 10mm Piping: a cavity at the centre of the ingot or billet, caused by shrinkage during solidification Slug: a piece of foreign matter that has been pressed or rolled into the surface of the material b) The NDT Method VT—visual testing is the oldest of the NDT methods but still valid and widely used today The system is based upon observation, usually by a human observer, but now increasingly by digital/video cameras which use pattern recognition to locate dissimilar areas in a surface. The sensitivity will depend upon the method but typically a good observer with simple visual aids can resolve 0.5mm differences aids will include magnifying glasses (up to x10), microscopes(up to x100) and fibred-optic bores copes and endoscopes for viewing internal details in hollow or complex sections. The system is used for surface inspection only with costs in the range $4 to $4000. PT一the surface is covered with brightly covered oil (typically red or fluorescent), which will penetrate any surface openings. After removal of excess, an absorbent, white powder is applied, which draws any trapped oil to the surface. This creates an indication of the presence of the surface opening. This process, like visual inspection, also requires visual acuity, but the indications are ‘enhanced’ by the process, since ‘bleed-out’ spreads the visual image. Costs can range from as little as $4 for a couple of cans, to $8000 for a process ‘line’. Both VT and PT are surface inspection systems only arid will therefore detect only those discontinuities that have a definite surface opening Surface cleanliness is very important, particularly with PT. MT一ferromagnetic materials carrying a large flux density; retain the presence internally, with little external evidence other than at the poles. Any discontinuity in the material will disturb this uniform flux and create a small ‘leakage’ at the site of the discontinuity. This leakage can be detected by the fact that finely divided; ferromagnetic particles collect at the-site, creating an indication. As with PT, the particles can be colored, to increase contrast, which when viewed under suitable lighting, create a clear visual image of the discontinuity. However, unlike PT the leakage can pass through thin layers of paint or plating materials, so that the discontinuity does not have to be open to the surface. The system can therefore detect surface AND slight subsurface discontinuities. However this is only possible in ferromagnetic materials, such as iron, mild and tool steel, nickel, cobalt and martenstic stainless. It will not operate on Paramagnetic or Diamagnetic materials, such as copper, aluminum and austenitic stainless steel. A small electromagnet can cost as little as $200, but a large `bench type' machine can cost up to $10 000 and the cost of electricity can be substantial. ET一Direct current flowing in a coil, sets up a longitudinal magnetic, field through the coil, and exhibits a particular resistance to flow. If the current is alternating, then a further effect一inductive reactance, adds to this resistance, the total being impedance. This impedance also causes a lag between the current and the voltage, called a phase shift. This shift and impedance are characteristics of the coil. If the coil is now placed close to a conducting surface, the reversing magnetic field induces a reversing current in the conducting (eddy current) which opposes the inducing field. This opposition alters the impedance of the coil and a suitable instrument can detect these changes (both phase angle and/or impedance).For a given ,discontinuity-free surface , a specific alteration will be present which can be zeroed .If the coil now passes over a discontinuity, a change in induction will occur which will be registered by the instrument. However, a change in the conductivity of the material will also effect the induction, as will changes in permeability. Thus, non-uniform heat treatment, segregation and in homogeneities in material composition and structure will also effect the induction and create an ‘indication’. Another critical factor is the distance between the coil and the test surface. This ‘lift off’ can be used in a positive way to determine coating or paint thickness’, on conducting materials. But equally, differences in the coil/specimen gap can result in non-relevant signals. The system can therefore detect surface AND slight subsurface discontinuities. However this is only possible in conducting materials and the proximity of the test coil to the test surface is critical. This means that for any component (other than flat plate), special probes are usually designed to follow specific component contours. A small eddy current machine can cost as little as $2000, but a large automated machine can cost up to $20 000 RT一Short wavelength, electromagnetic radiation will pass through many materials, depending upon density and thickness, and then create a range of exposures on either film or a fluoroscopic screen, to present a visual image of the internal composition of the item. Differences in absorption within the material due to such things as gas holes, cracks and bursts will create photographic density differences on the film or detector, which can be interpreted by trained personnel. The source of radiation can be an X-ray tube or a gamma source (such as Iridium or Cobalt) and the images can be generated on either film or as real-time images on fluoroscopic screens. Defect orientation is a vital factor in radiography since it is thickness differences, which the process detects. Hence, a lamination type defect, parallel to the film would be almost impossible to detect. On the other hand, a crack perpendicular to the film would almost certainly be detected. It is therefore often the case that a single component would have to be radio graphed from more than one direction, in order to detect most defects. Finally, the radiation used is highly hazardous and therefore any environment in which it is used, must suitably shielded, to prevent exposure of the operator. As well as shielding the use of X or gamma rays will also require, monitors, alarms, interlocks and personal dosimetry systems, which along with the film itself, adds to the cost. A basic X-ray set up would cost around $10000 and with ancillary equipment and film could cost $3000 per year to run. UT—At an interface between materials of differing acoustic impedance, a sound wave will have a proportion reflected and the remainder transmitted. Thus a gas hole or crack in a forging will reflect a sound beam because of their large difference in acoustic impedance with the metal structure containing them. Since ultrasound travels in a given material at a known (predictable) velocity, then the distance to a reflector will be a direct function of this time of flight of the pulse of sound. Its location can therefore be estimated .Since the amplitude of the returning signal is also related to the size of the reflector, then an approximation can be made of the extent of the reflector, in terms of length through-wall thickness and width. The data can be presented as an ‘A’ scan, on a cathode ray tube (requiring skilled interpretation) or as a ‘B’ or ‘C’ scan, where the data are plotted on printers or strip charts as a permanent record. Depths of penetration can be adjusted (by calibration and probe selection) from 10mm to 3 meters in suitable, fine-grained material. However cast, or large grained forged material, could be attenuate signals to the extent that they are untestable. A typical portable flaw detector and probes would cost around $5000, a fully automated ‘C’ scan immersion system could cost $2000. c) The variables associated with the forging 1.Surface condition For VT and PT surfaces better than 6.3um Ra would yield the best results. For MT a similar situation exists, where a confusing background could result from rough surfaces. ET also requires a smooth a surface for preference, since ‘lift-off’ effects could be unacceptable. For RT a surface roughness exceeding 1% of material thickness could result in a significant loon of sensitivity. However for UT, a suitably viscous ‘couplant’ could assist in sound transmittance, but entry surface ‘noise’ on the timebase and attenuation would reduce sensitivity. 2.Geometry Flat surfaces are the simplest to inspect, by any method. However, PT is least influenced by geometry, being a liquid process. MT requires that the flux be at 90 to the discontinuity and thus, curved surfaces and hollow sections offer particular problems. VT may require special access equipment and ET will need specially designed probes for curved or irregular surfaces. Since RT relies on absorption differences, variations in thickness due to curvature will result in large variations in photographic density and a consequent loss of film contrast. In UT the probe has best transmittance when it is whole face is in direct contact with the surface. Any curvature will result in “rocking” of the probe and a consequent loss of “coupling” and reduced signal amplitude. 3.Complexity Forged bar, billet, rod and plate offer simple shapes for inspection, but aircraft landing gear is an entirely different manner. PT is the least influenced by complex shapes when using the water washable system VT will require longer inspection periods and aids such as mirrors and bores copes. For MT, the more complex the shape, the more difficult it is to arrive at an all over procedure and individual flux/current tor the various sections ET will again require specially shaped probes and RT a larger number of film exposure and angled shots UT will need careful planning to ensure complete coverage and may not be possible if access is limited. 4.Thickness VT, ET, PT and MT are all unaffected by thickness since they are surface methods. RT has an approximate thickness limit of 300mm in steel and at 2% sensitivity (a typical value), will only record discontinuities of 6mm maximum section, in the plane of the radiation. UT is capable of inspecting beyond 2 meters in fine-grained material but is less effective below 10mm or so. 5.Discontinuity Orientation VT and PT are unaffected by orientation. In MT, for maximum sensitivity the flux should be at right angles to the discontinuity. ET requires that the discontinuity be at right angles to the coil windings and RT has its maximum sensitivity when the discontinuity lies parallel to the radiation beam. UT has the maximum response when the reflector is at right angles to the sound beam. 译文： 对铸件缺陷位置和尺寸的无损检测方法的评价 对铸件裂纹探测时，选择无损检测方法必须注意以下几点：a)评定缺陷类型；b)确定评定和探测缺陷的方法；c)铸件自身相关的变化。 这些项目中的变量a)将会影响铸件中的位置和它有关部分表面的方位；b)可使用相当多的无损检测的方法检测，但在本文中只重点介绍6种广泛应用的方法——视觉检测（VT）、渗透检测（PT）、磁粉检测（MT）、涡流检测（ET）、射线检测（RT）和超声检测（UT）；c)铸件组成因素包括表面环境条件、几何形状、检测通道等。 a)铸件缺陷 铸件缺陷的位置在选择无损检测方法时有重大影响，因此将这些位置分为三类以帮助选择检测方法： 1、表面开口缺陷：圈，缝，爆裂纹，砂眼，裂缝，夹渣 2、近表面缺陷：缝，披缝，夹渣，晶粒结构 3、内部缺陷：披缝，爆裂纹，纹理，晶粒结构，夹渣，缩孔 下面是几种缺陷的简单介绍以帮助理解： 圈：折叠金属，扁平的表面但没有融入它 缝：线性缺陷、吹孔或钢锭氧化斑点，这是热加工时被加长所致 爆裂纹：断裂故障导致的塑性变形，加工工艺过程中的温度过低或过度作用的金属 披缝：长条状缺陷，由于金属夹杂物没被挤出而成细长的缺陷 纹理：平面平行排列的表面缺陷，最早起源于原锭从推出了管道 裂缝：实验失败，由于局部应力造成的非均匀加热或冷却和拒绝使用变形 夹渣：杂质,如矿渣、氧化物和硫化物，通常来自原熔融阶段钢坯用于锻造成形 晶粒结构：根据工作中的程度(变形和再结晶)可以是小至0.5毫米或大如10毫米 缩孔：由于在凝固收缩时形成的空洞的中心或坯锭 砂眼：一块外来物质或被按卷成表面的物质 b)无损检测方法 VT—目视检测是无损检测中最原始的方法，但现在也有它的应用价值，且应用广泛。目视检测原理是基于观察的，经常是由一个人来观察，但现在已经升级为数字或录像机观察，它们是用已知图案去识别出一个表面区域的不相似地方。灵敏度取决于方法，但一个典型的有样品视觉帮助的好的观察者可以识别0.5mm的不同，用这些助视器包括放大镜（*10），显微镜（*100）、光纤孔径镜和远摄镜在中空的或复杂区域帮助去观察工件内部的细节。这种方法只用于表面开口检测，花费在4美元到4000美元。 PT—渗透检测是表面被覆盖着亮丽的彩色油物（典型的为红色或荧光），这种油液能渗透进任何表面开口，在清除掉工件表面多余的油液后，用白色粉末作为吸附剂，能够吸走任何表面上的粘滞油。这就产生一种表面缺陷的显像，这个过程和目视检测一样要求有敏锐的视力。但在检测过程中显示图像被加强了，从“渗透”中已经传播出了缺陷视觉图像，成本范围从两个罐的4美元到一个工艺生产线的8000美元。目视检测（VT）和渗透检测（PT）都是表面检测系统，只应用于那些表面开口的缺陷，表面的清洁度是非常重要的，尤其对渗透检测（PT）来说。 MT—磁粉检测，铁磁性材料具有较大的磁通量密度，分布在内部较多，外部只有端面处的少量。这种材料内的任何缺陷都会影响原本材料的磁场，而且在缺陷处形成一个漏磁的小洞，吸附施加在工件表面的磁粉，磁粉会集中在缺陷处，产生缺陷显像。和渗透检测一样，当在适当的背景下观察时，可以用有色磁粉加强显示结果。然而和渗透检测不一样的是，这些漏洞可以通过小颗粒的颜料或金属材料，这样检测的不限制于表面开口缺陷。这样的方法可以检查表面开口和近表面缺陷。但这些仅仅适用于铁磁性材料，如铁、柔性的工具钢、镍、钴和马氏体不锈钢。它不能用于检测顺磁性材料或无磁性材料,如铜、铝、奥氏体不锈钢。小型电磁装备花费只有200美元,但大型台式机费用高达10000美元及电的成本是大部分的。 ET—涡流检测，直流电在螺线圈流动，通过螺线圈形成一个稳定持久的磁场区，而且存在一个特定的流动阻力。如果电流是交流的会有更深的效果——引入感应电抗,增加了接触电阻,成为总阻抗。此阻抗也会引起滞后电流、电压、称为相移。这种相移和阻抗是线圈的特性。 如果将螺线圈靠近一个导体表面，这个形成的磁场会在导体中再产生一个电流（即涡流），与产生磁场的电流方向相反。这种相反改变线圈阻抗，合适的工具也能探测到这些变化（相变角或阻抗）。对一个给定的自由缺陷表面，一个特殊的改变或许，它可以被“归零”。当线圈通过缺陷时，感应中将会发生改变，这也可以用适当的工具记录下来。然而在导体材料内的变化也能实现感应，同样能改变浸透力。因此，材料内部结构不均衡的热处理、隔离和不同成分也会影响感应和产生一种指示。另一种临界的因素是线圈和被测表面之间的距离。这种“发射”能被用作一种积极方法去识别导体材料上的涂层（包层）或涂料厚处。但是同样的，线圈中的微小变化/样品缺陷导致不相应的信号。这种方法能检测表面和近表面缺陷，当然仅限于导体材料和要求线圈于检测表面接近。这就意味着对任何组件（除了天然的电镀金属板），设计特殊的探测器通常是用来探测特定轮廓组件。一个小的涡流机器可以花费只有2000美元,但是大部分自动机器可以费用高达20000美元。 RT—短波长的电磁射线能穿透很多材料，这取决于次啊聊的密度和厚度。然后在感光胶片或荧光检查屏上产生一个潜影曝光，呈现出一个肉眼可见的工件内部构成的图像。由于材料内部结构的不同，诸如气孔、崩裂、爆裂，吸收射线能量不同，在感光胶片或探测器中产生不同密度的详细准确的图像，这样经过训练的人就可以解读出缺陷的信息。射线的来源是X射线管或γ射线管（铱或钴），图像可在感光胶片或荧光屏上显示。缺陷的方向也是一个至关重要的因素。在射线检测中，由于这个区别很小只能用探测器检测。因此，一个晶粒结构类的相对于胶片平行的缺陷，不太可能被检测出来。但另一方面，相对于胶片垂直的裂缝会被很容易的检测出来。因此,通常情况下, 为了检测大多数缺陷，一个单一部件就必须从多个方向射线透照,。最后, 在任何使用射线的的环境中都是高度危险的辐射区，因此使用时必须适当防护暴露的区域。相对于防护， X射线或γ射线的使用中的要求、监控、报警、联锁和胶片本身剂量的系统也要加到花费中。这样一个基本的X射线发射和附属设备成本将耗资10000美元，另外需要再加上胶片的成本每年花费3000美元。 UT—在不同声阻抗材料的接口之间,声波会有一定比例的反射，余下的则透射。因此在气孔或裂缝铸件都能够反映出一个大差异的声波宽度,因为他们的声阻抗和含金属结构不同。因为超声波在特定的材料中的传播速度是已知的（可预测的），那么声脉冲到反射面的距离就是时间的正比例函数。缺陷的位置就能据此估计。反射回的信号幅度与反射物的大小有关，因此可以根据声波穿透的厚度和宽度得出一个反射物的近似尺寸。这些资料在阴极射线管中可以表述成A型，在打印机或做永久记录的带出图中可以表述称B型或C型。在适当的细粒度的材料中，浸透深度可调 (通过校准和探头的选择) 范围从10毫米到3米。然而在铸造、锻造或大粒材料中可能是探测不到的衰减的信号。一个典型的便携式探伤仪将耗资约5000美元,一个完全自动化的“C型”油浸系统成本为20000美元。 c)与铸件有关的变量 1、表面情况 对目视检测和渗透检测来讲，表面度比6.3微米还好的会产生最好的结果。对磁粉检测来说，存在类似情况，粗糙的表面会产生一个混乱的背景。因为“发射”的效果可能是不被接受的，所以涡流检测也偏好需要光滑的表面。而对射线检测来说，表面粗糙度超过材料的厚度1%的可能导致重大的灵敏度变化。不过对于超声检测,一个适当粘性“耦合剂”可以协助声音的穿透率,但入口表面上的“噪音”时基和衰减会减小灵敏度。 2、几何 对任何检测方法，平坦的表面是最简单的检查。然而,渗透检测作为一种液体渗透的过程是受几何影响最小的。磁粉检测需要磁通线相对缺陷90°。因此,表面弯曲和空心部分会提供特别的问题。目视检测要求特殊的接入设备，涡流检测需要为曲面或不规则表面特别设计探针。因为射线检测决定于吸收差异，厚度的变化会导致由于曲率大的变化产生的一系列摄影密度和感光胶片对比度的损失。在超声检测中当探测器整个与检测表面直接接触时，探测器中有较好的透光率。任何曲率会导致探测器的“摇摆”和一系列“耦合”的损失，降低了信号振幅。 3、复杂性 　铸造棒、钢坯、杆、板提供简单的形状进行检验,但飞机起落架完全是一种不同的方式。渗透检测当使用水洗涤系统时是最容易受复杂的形状影响的。目视检测则需要更长的检验周期和仪器帮助,比如,镜子,光学孔径仪。对磁粉检测而言，形状越复杂,越难达到一个完整工序和个体流量/电流的不同部分。涡流检测再次要求特殊形状进行了探测，射线检测需要较大数量的感光胶片的曝光和角度的照射。超声检测需要仔细计划以确保完全覆盖，如果声音进入受限则不太可能检测。 4、厚度 目视检测、涡流检测、渗透检测和磁粉检测都是表面检测的方法所以不受材料厚度的影响。射线检测在检测钢板时存在一个近似极限——300毫米厚的钢板，灵敏度为2%(典型值)，这种灵敏度是指在飞机的辐射中只会记录最大的部分为6毫米的缺陷。超声检测是能够检查晶粒结构很好的超过2米的材料，但是低于10毫米左右比较无效的。 5、缺陷的方向 目视检测和渗透检测不受缺陷方向的影响。磁粉检测最大灵敏度应该是在磁场与缺陷方向成直角处。涡流检测要求缺陷和线圈绕组成直角的方向，射线检测是当缺陷方向平行于辐射光束时有其最大灵敏度。超声检测是当反射面和声音束成直角时有最大的反应。