對鑄件缺陷位置和尺寸的無損檢測方法的評價[中文3726字] 【中英文WORD】,中文3726字,中英文WORD,對鑄件缺陷位置和尺寸的無損檢測方法的評價[中文3726字],【中英文WORD】,鑄件,缺陷,位置,尺寸,無損,檢測,方法,評價,中文,3726,中英文,WORD 附錄1 外文文獻原文及譯文 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. 譯文： 對鑄件缺陷位置和尺寸的無損檢測方法的評價 對鑄件裂紋探測時，選擇無損檢測方法必須注意以下幾點：a)評定缺陷類型；b)確定評定和探測缺陷的方法；c)鑄件自身相關(guān)的變化。 這些項目中的變量a)將會影響鑄件中的位置和它有關(guān)部分表面的方位；b)可使用相當(dāng)多的無損檢測的方法檢測，但在本文中只重點介紹6種廣泛應(yīng)用的方法——視覺檢測（VT）、滲透檢測（PT）、磁粉檢測（MT）、渦流檢測（ET）、射線檢測（RT）和超聲檢測（UT）；c)鑄件組成因素包括表面環(huán)境條件、幾何形狀、檢測通道等。 a)鑄件缺陷 鑄件缺陷的位置在選擇無損檢測方法時有重大影響，因此將這些位置分為三類以幫助選擇檢測方法： 1、表面開口缺陷：圈，縫，爆裂紋，砂眼，裂縫，夾渣 2、近表面缺陷：縫，披縫，夾渣，晶粒結(jié)構(gòu) 3、內(nèi)部缺陷：披縫，爆裂紋，紋理，晶粒結(jié)構(gòu)，夾渣，縮孔 下面是幾種缺陷的簡單介紹以幫助理解： 圈：折疊金屬，扁平的表面但沒有融入它 縫：線性缺陷、吹孔或鋼錠氧化斑點，這是熱加工時被加長所致 爆裂紋：斷裂故障導(dǎo)致的塑性變形，加工工藝過程中的溫度過低或過度作用的金屬 披縫：長條狀缺陷，由于金屬夾雜物沒被擠出而成細(xì)長的缺陷 紋理：平面平行排列的表面缺陷，最早起源于原錠從推出了管道 裂縫：實驗失敗，由于局部應(yīng)力造成的非均勻加熱或冷卻和拒絕使用變形 夾渣：雜質(zhì),如礦渣、氧化物和硫化物，通常來自原熔融階段鋼坯用于鍛造成形 晶粒結(jié)構(gòu)：根據(jù)工作中的程度(變形和再結(jié)晶)可以是小至0.5毫米或大如10毫米 縮孔：由于在凝固收縮時形成的空洞的中心或坯錠 砂眼：一塊外來物質(zhì)或被按卷成表面的物質(zhì) b)無損檢測方法 VT—目視檢測是無損檢測中最原始的方法，但現(xiàn)在也有它的應(yīng)用價值，且應(yīng)用廣泛。目視檢測原理是基于觀察的，經(jīng)常是由一個人來觀察，但現(xiàn)在已經(jīng)升級為數(shù)字或錄像機觀察，它們是用已知圖案去識別出一個表面區(qū)域的不相似地方。靈敏度取決于方法，但一個典型的有樣品視覺幫助的好的觀察者可以識別0.5mm的不同，用這些助視器包括放大鏡（*10），顯微鏡（*100）、光纖孔徑鏡和遠(yuǎn)攝鏡在中空的或復(fù)雜區(qū)域幫助去觀察工件內(nèi)部的細(xì)節(jié)。這種方法只用于表面開口檢測，花費在4美元到4000美元。 PT—滲透檢測是表面被覆蓋著亮麗的彩色油物（典型的為紅色或熒光），這種油液能滲透進任何表面開口，在清除掉工件表面多余的油液后，用白色粉末作為吸附劑，能夠吸走任何表面上的粘滯油。這就產(chǎn)生一種表面缺陷的顯像，這個過程和目視檢測一樣要求有敏銳的視力。但在檢測過程中顯示圖像被加強了，從“滲透”中已經(jīng)傳播出了缺陷視覺圖像，成本范圍從兩個罐的4美元到一個工藝生產(chǎn)線的8000美元。目視檢測（VT）和滲透檢測（PT）都是表面檢測系統(tǒng)，只應(yīng)用于那些表面開口的缺陷，表面的清潔度是非常重要的，尤其對滲透檢測（PT）來說。 MT—磁粉檢測，鐵磁性材料具有較大的磁通量密度，分布在內(nèi)部較多，外部只有端面處的少量。這種材料內(nèi)的任何缺陷都會影響原本材料的磁場，而且在缺陷處形成一個漏磁的小洞，吸附施加在工件表面的磁粉，磁粉會集中在缺陷處，產(chǎn)生缺陷顯像。和滲透檢測一樣，當(dāng)在適當(dāng)?shù)谋尘跋掠^察時，可以用有色磁粉加強顯示結(jié)果。然而和滲透檢測不一樣的是，這些漏洞可以通過小顆粒的顏料或金屬材料，這樣檢測的不限制于表面開口缺陷。這樣的方法可以檢查表面開口和近表面缺陷。但這些僅僅適用于鐵磁性材料，如鐵、柔性的工具鋼、鎳、鈷和馬氏體不銹鋼。它不能用于檢測順磁性材料或無磁性材料,如銅、鋁、奧氏體不銹鋼。小型電磁裝備花費只有200美元,但大型臺式機費用高達(dá)10000美元及電的成本是大部分的。 ET—渦流檢測，直流電在螺線圈流動，通過螺線圈形成一個穩(wěn)定持久的磁場區(qū)，而且存在一個特定的流動阻力。如果電流是交流的會有更深的效果——引入感應(yīng)電抗,增加了接觸電阻,成為總阻抗。此阻抗也會引起滯后電流、電壓、稱為相移。這種相移和阻抗是線圈的特性。 如果將螺線圈靠近一個導(dǎo)體表面，這個形成的磁場會在導(dǎo)體中再產(chǎn)生一個電流（即渦流），與產(chǎn)生磁場的電流方向相反。這種相反改變線圈阻抗，合適的工具也能探測到這些變化（相變角或阻抗）。對一個給定的自由缺陷表面，一個特殊的改變或許，它可以被“歸零”。當(dāng)線圈通過缺陷時，感應(yīng)中將會發(fā)生改變，這也可以用適當(dāng)?shù)墓ぞ哂涗浵聛?。然而在?dǎo)體材料內(nèi)的變化也能實現(xiàn)感應(yīng)，同樣能改變浸透力。因此，材料內(nèi)部結(jié)構(gòu)不均衡的熱處理、隔離和不同成分也會影響感應(yīng)和產(chǎn)生一種指示。另一種臨界的因素是線圈和被測表面之間的距離。這種“發(fā)射”能被用作一種積極方法去識別導(dǎo)體材料上的涂層（包層）或涂料厚處。但是同樣的，線圈中的微小變化/樣品缺陷導(dǎo)致不相應(yīng)的信號。這種方法能檢測表面和近表面缺陷，當(dāng)然僅限于導(dǎo)體材料和要求線圈于檢測表面接近。這就意味著對任何組件（除了天然的電鍍金屬板），設(shè)計特殊的探測器通常是用來探測特定輪廓組件。一個小的渦流機器可以花費只有2000美元,但是大部分自動機器可以費用高達(dá)20000美元。 RT—短波長的電磁射線能穿透很多材料，這取決于次啊聊的密度和厚度。然后在感光膠片或熒光檢查屏上產(chǎn)生一個潛影曝光，呈現(xiàn)出一個肉眼可見的工件內(nèi)部構(gòu)成的圖像。由于材料內(nèi)部結(jié)構(gòu)的不同，諸如氣孔、崩裂、爆裂，吸收射線能量不同，在感光膠片或探測器中產(chǎn)生不同密度的詳細(xì)準(zhǔn)確的圖像，這樣經(jīng)過訓(xùn)練的人就可以解讀出缺陷的信息。射線的來源是X射線管或γ射線管（銥或鈷），圖像可在感光膠片或熒光屏上顯示。缺陷的方向也是一個至關(guān)重要的因素。在射線檢測中，由于這個區(qū)別很小只能用探測器檢測。因此，一個晶粒結(jié)構(gòu)類的相對于膠片平行的缺陷，不太可能被檢測出來。但另一方面，相對于膠片垂直的裂縫會被很容易的檢測出來。因此,通常情況下, 為了檢測大多數(shù)缺陷，一個單一部件就必須從多個方向射線透照,。最后, 在任何使用射線的的環(huán)境中都是高度危險的輻射區(qū)，因此使用時必須適當(dāng)防護暴露的區(qū)域。相對于防護， X射線或γ射線的使用中的要求、監(jiān)控、報警、聯(lián)鎖和膠片本身劑量的系統(tǒng)也要加到花費中。這樣一個基本的X射線發(fā)射和附屬設(shè)備成本將耗資10000美元，另外需要再加上膠片的成本每年花費3000美元。 UT—在不同聲阻抗材料的接口之間,聲波會有一定比例的反射，余下的則透射。因此在氣孔或裂縫鑄件都能夠反映出一個大差異的聲波寬度,因為他們的聲阻抗和含金屬結(jié)構(gòu)不同。因為超聲波在特定的材料中的傳播速度是已知的（可預(yù)測的），那么聲脈沖到反射面的距離就是時間的正比例函數(shù)。缺陷的位置就能據(jù)此估計。反射回的信號幅度與反射物的大小有關(guān)，因此可以根據(jù)聲波穿透的厚度和寬度得出一個反射物的近似尺寸。這些資料在陰極射線管中可以表述成A型，在打印機或做永久記錄的帶出圖中可以表述稱B型或C型。在適當(dāng)?shù)募?xì)粒度的材料中，浸透深度可調(diào) (通過校準(zhǔn)和探頭的選擇) 范圍從10毫米到3米。然而在鑄造、鍛造或大粒材料中可能是探測不到的衰減的信號。一個典型的便攜式探傷儀將耗資約5000美元,一個完全自動化的“C型”油浸系統(tǒng)成本為20000美元。 c)與鑄件有關(guān)的變量 1、表面情況 對目視檢測和滲透檢測來講，表面度比6.3微米還好的會產(chǎn)生最好的結(jié)果。對磁粉檢測來說，存在類似情況，粗糙的表面會產(chǎn)生一個混亂的背景。因為“發(fā)射”的效果可能是不被接受的，所以渦流檢測也偏好需要光滑的表面。而對射線檢測來說，表面粗糙度超過材料的厚度1%的可能導(dǎo)致重大的靈敏度變化。不過對于超聲檢測,一個適當(dāng)粘性“耦合劑”可以協(xié)助聲音的穿透率,但入口表面上的“噪音”時基和衰減會減小靈敏度。 2、幾何 對任何檢測方法，平坦的表面是最簡單的檢查。然而,滲透檢測作為一種液體滲透的過程是受幾何影響最小的。磁粉檢測需要磁通線相對缺陷90°。因此,表面彎曲和空心部分會提供特別的問題。目視檢測要求特殊的接入設(shè)備，渦流檢測需要為曲面或不規(guī)則表面特別設(shè)計探針。因為射線檢測決定于吸收差異，厚度的變化會導(dǎo)致由于曲率大的變化產(chǎn)生的一系列攝影密度和感光膠片對比度的損失。在超聲檢測中當(dāng)探測器整個與檢測表面直接接觸時，探測器中有較好的透光率。任何曲率會導(dǎo)致探測器的“搖擺”和一系列“耦合”的損失，降低了信號振幅。 3、復(fù)雜性 　鑄造棒、鋼坯、桿、板提供簡單的形狀進行檢驗,但飛機起落架完全是一種不同的方式。滲透檢測當(dāng)使用水洗滌系統(tǒng)時是最容易受復(fù)雜的形狀影響的。目視檢測則需要更長的檢驗周期和儀器幫助,比如,鏡子,光學(xué)孔徑儀。對磁粉檢測而言，形狀越復(fù)雜,越難達(dá)到一個完整工序和個體流量/電流的不同部分。渦流檢測再次要求特殊形狀進行了探測，射線檢測需要較大數(shù)量的感光膠片的曝光和角度的照射。超聲檢測需要仔細(xì)計劃以確保完全覆蓋，如果聲音進入受限則不太可能檢測。 4、厚度 目視檢測、渦流檢測、滲透檢測和磁粉檢測都是表面檢測的方法所以不受材料厚度的影響。射線檢測在檢測鋼板時存在一個近似極限——300毫米厚的鋼板，靈敏度為2%(典型值)，這種靈敏度是指在飛機的輻射中只會記錄最大的部分為6毫米的缺陷。超聲檢測是能夠檢查晶粒結(jié)構(gòu)很好的超過2米的材料，但是低于10毫米左右比較無效的。 5、缺陷的方向 目視檢測和滲透檢測不受缺陷方向的影響。磁粉檢測最大靈敏度應(yīng)該是在磁場與缺陷方向成直角處。渦流檢測要求缺陷和線圈繞組成直角的方向，射線檢測是當(dāng)缺陷方向平行于輻射光束時有其最大靈敏度。超聲檢測是當(dāng)反射面和聲音束成直角時有最大的反應(yīng)。