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遼寧科技大學(xué)本科生畢業(yè)設(shè)計 第14頁
Process for Straightening Tube and Method for Producing Tube Therewith
TECHNICAL FIELD
The present invention relates to a tube straightening process and a tube production method, in which tube bending in an axial direction and distortion of cross section (hereinafter referred to as ovality) are suppressed. More particularly ,the present invention relates to a tube straightening process in which generation of the ovality associated with bending correction is suppressed while tube bending correction accuracy is ensured, whereby a ratio (so-called S/N ratio) of signal to base noise in flaw detection can be enhanced in an eddy current test from inside of a tube by inserting an inner probe and a tube production method in which the tube straightening process is used.
RACKGROTLND ART
A U-shaped heat transfer tube utilized in a heat exchanger, such as a steam generator and a feed water heater ,which is used in a thermal or nuclear power plant is produced by bending a small-diameter and long-length heat transfer tube with an outside diameter of 30 mm or less into a U-shape .In the U-shape heat transfer tube, an inspection is performed to detect flaws by the eddy current test from the tube inside as a pre-service inspection after the U-shaped heat transfer tube is assembled in the heat exchanger or as an in-service inspection or a periodic inspection after the U-shaped heat transfer tube is in-service for a certain period. The eddy current test from the tube inside applies strict test criteria because of the need to ensure safety of nuclear power plant facilities.
The eddy current test applying the test criteria similar to that of the pre-service inspection or periodic inspection is also required for an inspection before shipment after the heat transfer tube is produced. As a result of the eddy current test, the heat transfer tube which fails the test criteria becomes nonconforming material. Even within the test criteria, it is necessary that the result of the eddy current test be recorded in each tube while correlated with relevant positions in an axial direction of the heat transfer tube.
Usually the heat transfer tube is produced through cold working such as cold drawing and cold rolling and a heat treatment using a mother tube produced by hot extrusion. The bends in an axial direction and ovality of the tube, generated after the cold working and heat treatment, are corrected during a subsequent finishing process using a roll straightening machine. Not only many heat transfer tubes having small
diameters are used in the heat exchanger, but also an installation space of the heat transfer tube becomes narrowed with miniaturizing heat exchanger. When the bend is generated in the heat transfer tube, a trouble such as interference with other parts is generated in assembling the heat transfer tube into the heat exchanger. Accordingly, it is necessary to ensure bend correction accuracy in the roll straightening machine. Usually a cross roll type straightening machine, in which plural drum type rolls are combined, is adopted in a configuration of the roll straightening machine used in the straightening. There are many configurations in the cross type roll straightening machine according to a combination of the number of rolls, a layout (vertical and horizontal directions),and roll arrangement (opposing type and zigzag type).
The FIG. 1 is a view showing an example of the roll layout of the cross roll type straightening machine. Plural pairs of straightening rolls Ra and Rb (collectively referred to as R) are provided in the roll straightening machine. The pairs of straightening rolls Ra and Rb each are vertically disposed as opposed to each other in such a state that directions of rotating axes cross in a plan view (actually, cross-wise pass each other in a spaced-apart relation in a front view). In the roll layout of FIG. 1, three pairs of straightening rolls Ral and Rbl, Rat and Rb2, and Ra3 and Rb3 are disposed on an inlet side, the center, and an outlet side respectively, the rolls of each pair being opposed to each other, and auxiliary roll Rc is provided at an exit of the outlet-side straightening rolls. Usually the roll straightening machine having such roll layout of FIG. 1 is called (2-2-2-1) type straightening machine of a straightening roll pair Ral and Rbl. A height position in a vertical direction of a first pair of straightening rolls Ral and Rbl and a height position of a second pair of straightening rolls Rat and Rb2, adjacent to the first pair, can be also adjusted separately .In the bend correction, across angle 0oftherotating axis of each straightening roll R to a tube to be corrected 1, that is, a roll angle is adjusted such that contact faces of the tube to be corrected 1 fit in contours of the straightening roll ,the opposing rolls clearance between the straightening rolls Ral and Rbl is set slightly smaller than an outside diameter of the tube to be corrected 1 to impart a crush, and an offset is imparted to straighten the bend and correct ovality by adjusting the crush amount of the second pair of straightening rolls Rat and Rb2, adjacent to the first pair.
Since high rigidity and wear-resistant properties are required for straightening rolls, the straightening roll is made of tool steel or ceramic, and the surface of the straightening roll is formed by a curved line constituting a drum shape in consideration of a contact surface with a tube to be corrected so as to enable the tube having the outside diameter within a predetermined range to be straightened. After the heat treatment, the heat transfer tube whose bends and ovality are corrected by the roll straightening machine is subjected to aprocess such as cutting, and the inspection before shipment is performed to the heat transfer tube by the eddy current test from the tube inside.
FIG. 2 is an example of a chart showing result of the eddy current test from inside of the heat transfer tube. As shown in FIG. 2, Signal S from Standard Flaw defined in the test criteria and signal N having a predetermined period P are shown in the chart. The signal N is called base noise, and is caused by a minute dimensional fluctuation generated in an axial direction of the heat transfer tube. It is necessary that the magnitude of the signal N be decreased as much as possible in order not to mistake the signal N for a signal caused by the detected flaw and in order to swiftly judgment whether the signal indicates the flaw to thereby improve the inspection efficiency. Hereinafter, a ratio of Signal S from Standard Flaw to Noise N is referred to as "S/N ratio" .For example, in the case where automatic judging is made based on the signals shown in the chart during the eddy current test from tube inside, the large noise, that is, the small S/N ratio hides a signal from a small defect behind the base noise, which makes distinction between the small defect signal and the base noise harder .As described above, the base noise is caused by the minute dimensional fluctuation generated in an axial direction of the heat transfer tube. Therefore, in order to reduce the base noise, it is necessary to suppress the dimensional fluctuation such as bends and ovality in an axial direction of the heat transfer tube, that is, to enhance the dimensional accuracy along an axial direction of the heat transfer tube.
Usually, in straightening the tube by the roll straightening machine, as shown in FIGS. 3 to 5, it is necessary that the roll angle, crush amount, and offset amount which are the setting conditions be determined to suppress the dimensional fluctuation such as the bends and the ovality in an axial direction of the heat transfer tube.FIG. 3 is a view explaining a relationship between the roll angle of the roll straightening setting conditions and a corresponding travel distance of the tube to be corrected .Assuming that mm) is an outside diameter of the tube to be corrected 1 and θ (0) is an angle (hereinafter referred to as "roll angle") formed by an axial center of the tube to becorrected 1 and the rotating axis of the straightening roll R, a travel distance (hereinafter referred to as "feed pitch") M(mm) of the tube to be corrected 1 per one rotation of the straightening roll R is defined by the following equation (2): 。FIG. 4 is a view explaining the crush amount of the roll straightening setting conditions. As shown in FIG. 4, the tube to be corrected 1b, to which the crush is applied by the roll straightening, is rolled, while being pressed, and deformed into an elliptic shape. A crush amountｃ(mm) is indicated by a difference between an outside diameter d of a pre-deformation tube to be corrected la and an opposing rolls clearance s of the straightening rolls Ra and Rb, and corresponds to a rolling reduction of the outside diameter of the tube to be corrected 1. The bend correction is performed to the tube to be corrected 1 by repeatedly rolling while pressing the tube to be corrected 1 across the total length. The crush amount (mm) is set by raising/lowering the straightening roll Ra.FIG. 5 is a view explaining the offset amount of the roll straightening setting conditions. An offset amount 8(mm) is indicated by a deflection in crush/roll height between the central pair of straightening rolls Rat and Rb2, and the bend correction is performed by imparting a bending stress to the tube to be corrected 1. The crush height is set by raising the straightening roll Rb2, thereby adjusting the offset amount 8 (mm).As described above, in performing the straightening by the roll straightening machine, it is necessary that a certain level of load such as the crush and the offset be applied onto the tube in order to straighten the bends. However, sometimes dimensional fluctuation such as the ovality associated with the load becomes significant.
Specifically, in the conventional process for straightening the heat transfer tube such as the steam genera for and the feed water heater, the tube having the excellent pre-straightening dimensional accuracy, for example, the heat transfer tube to which drawing is performed with a high-pressure drawing machine, sometimes increases in ovality after straightening to deteriorate the S/N ratio compared with the cross-sectional shape of the pre-straightening tube due to the straightening performed by the roll straightening machine. On the other hand, when the bend correction is insufficiently performed in straightening the heat transfer tube, the interference with other component is frequently generated in assembling the heat transfer tube into the heat exchanger, which makes the assembly work difficult. Accordingly, in straightening the heat transfer tube, it is necessary
that the dimensional fluctuation associated with the bend correction be suppressed while the tube bend correction accuracy is ensured. Therefore , there have been conventionally proposed various straightening techniques.
In a straightening process disclosed in Japanese Patent Application Publication No. 61-286025, in order to perform the straightening without deteriorating roundness of the inner surface of the tube used in a hydraulic cylinder tube and the like, the offset is imparted to the tube using a cross opposing type roll straightening machine, and the straightening is performed while a predetermined load which does not substantially impart the crush is applied to the tube.
In a straightening process disclosed in Japanese Patent Application Publication No. 2004-330297, in order to suppress roundness deviation in turning inner and outer surfaces of a cut ring used in a bearing race or the like, a residual stress generated in the tube after the straightening is lowered by a multi-roll straightening machine in which the offset amount is set at 12 mm or more and the crush amount is set at 0.6 mm or less, thereby obtaining a seamless steel tube having little dimensional fluctuation during the turning and excellent roundness.
In a process disclosed in Japanese Patent Application Publication No. 60-184424, the roll offset amount and the crush amount are determined from a relationship between an index indicating a plastic region of the tube and a presumptive offset and crush amounts, picked in advance, and the roll position is set to perform the tube straightening, thereby improving the tube bend and/or roundness.
However, in the straightening processes proposed in Japanese Patent Application Publication Nos. 61-286025,2004-330297, and 60-184424, it is not intended that the ovality or bends in an axial direction of the tube be corrected in order to enhance the S/N ratio in the eddy current test from the tube inside.
DISCLOSURE OF THE INVENTION
As described above, in order to enhance the S/N ratio, it is necessary to suppress the minute dimensional fluctuation generated in an axial direction of the tube. As the dimensional fluctuation in the tube is increased, the base noise is increased during the eddy current test, and the distinction between signals and base noises is hardly made in detecting the extremely small defect in the tube inner surface .In view of the problem relating to the straightening of the tube which is the target of the eddy current test with inner coil method, an object of the present invention is to provide a tube straightening process in which, by properly managing the straightening operation as a finishing process after the tube cold working, the generation of the dimensional fluctuation such as the ovality associated with the bend correction is suppressed while the tube bend correction accuracy is ensured, whereby the S/N ratio can be enhanced in the eddy current test from the tube inside, and a tube production method in which the tube straightening process is used .After various studies on the relationship between the roll straightening conditions and the S/N ratio in the eddy current test from the tube inside were made to solve the problem, the inventors focused attention on the fact that the constant period P (hereinafter referred to as "noise pitch") of the base noise N emerging in the eddy current test substantially matches with the tube feed pitch M of the straightening roll R shown in FIG. 3.
On the basis of the fact, the inventors investigated an influence of the post-roll straightening tube on the S/N ratio and possibly remaining bends using the heat transfer tube ,when the crush amount(and the roll angle 0 of the roll straightening conditions were changed while the offset amount 6 was kept constant (10 mm). The seven-roll (2-2-2-1) type straightening machine shown in FIG. 1 was used as the roll straightening machine, and a roll covered with a urethane resin having the spring type hardness Hs of 95 was used as the outlet-side three pairs of straightening rolls. A Ni-base alloy of ASME SB-163 UNS NO 6690 was used as a testing material, and a tube with the finished dimension comprising anoutside diameter of 19.14 mm, a wall thickness of 1.125 mm and a length of 10000 mm obtained through the cold drawing by the high-pressure drawing machine was used. Table 1shows the setting conditions of the roll straightening machine and results
The remaining bends shown in Table 1 is obtained by inspecting, in particular, the bends near a tube end portion (hereinafter also referred to as "nose bend") as the post-straightening tube bends. The nose bend is a bend after the bends generated in the cold working such as the cold drawing and the cold rolling and the subsequent heat treatment is straightened by the roll straightening machine. In the remaining bends of Table 1, "o" indicates good bend correction in which a bend amount over a distance from a tube end to the position of 1000 mm away from the end becomes 1 mm or less, and "x" indicates insufficient bend correction in which the bend amount exceeds 1mm .In the S/N ratio, the eddy current test was performed from the tube inside under conditions of frequency of 550 kHz and differential bobbin coil type, a drilling through-hole of 0.66 mm was used as Standard Flaw, and a minimum value in overall S/N ratios that are derived by segmenting the total length of the tube into each segment of one feet and assessing a S/N ratio in each segment was set as the S/N ratio of the tube. In the case where the crush amount E and the roll angle 0 were changed while the offset amount 8 was kept constant, although the good correction was performed with little remaining bends for all the conditions, the S/N ratio could not reach 30 or more, which was the target value .Then, the tube was straightened by changing the offset amount while the crush amount and the roll angle were kept constant, and it was found that setting the offset amount within a proper range can eliminate the nose bend to ensure the bend correction accuracy after the tube straightening and enhance the S/N ratio to 30 or more, which is the target value in the eddy current test from the tube inside.
The present invention is completed based on the above-described findings, and the gist thereof includes (1) a tube straightening process and (2) a tube production method therewith。
FIG.1
FIG.2
FIG.3
FIG.4
FIG.5
鋼管矯直工藝以及生產(chǎn)鋼管的方法
技術(shù)領(lǐng)域
本發(fā)明涉及到鋼管矯直進程和管生產(chǎn)的方法，其中包括管在軸向的彎曲和橫截面（下文中將它定義為橢圓度）的曲解，尤其，本發(fā)明與管矯直過程有關(guān)，其中與彎曲修正量有關(guān)的橢圓度的產(chǎn)生被阻止當(dāng)管彎曲糾正精度被確定的時候。憑借一個信號比率（所為的S/N比率）對于裂縫檢測中的基干擾能夠在管內(nèi)部的渦流探傷測試（通過嵌入一個內(nèi)探測器）中被加強。鋼管矯直的生產(chǎn)方法在管被矯直的過程中使用。
背景技術(shù)
一個Ｕ型的熱傳導(dǎo)管在熱交換的過程中被使用，例如鍋爐和供熱水器，它被使用在熱或核電廠的生產(chǎn)中，通過彎曲一個小直徑的并且長距離的帶著一個３００ｍｍ或者更少外徑熱交換管到Ｕ型。在Ｕ型的熱交換鋼管中，一個檢查被執(zhí)行，去發(fā)現(xiàn)一個瑕疵通過對管的內(nèi)部進行渦流探測，作為一個預(yù)先檢測在這個Ｕ型傳熱管在熱交換器中被裝配或者作為一個在職檢測或者一個周期性的檢測在這個Ｕ型傳熱輥工作了一段時間。從鋼管內(nèi)部進行的渦流測試施行嚴(yán)格的測試標(biāo)準(zhǔn)，因為必須確保核電廠設(shè)施的安全。
渦流測試使用的這個測試標(biāo)準(zhǔn)類似于預(yù)先檢測的那個標(biāo)準(zhǔn)或者周期檢測，同樣要求在熱傳導(dǎo)管生產(chǎn)以后裝運之前進行一次檢測。渦流測試的結(jié)果是沒有達到測試標(biāo)準(zhǔn)的熱傳導(dǎo)輥變成了不合格的材料。即使達到了測試的標(biāo)準(zhǔn)，這也是很有必要的對于渦流測試的結(jié)果被記錄在每個管子上當(dāng)符合相關(guān)位置在熱傳遞輥軸線方向上。
通常情況下熱傳遞輥通過冷加工的方式被生產(chǎn)，如冷拔、冷軋和熱處理（通過熱擠壓的方法使用一個母管進行生產(chǎn)）。在軸方向上的彎曲和管子（生產(chǎn)在冷拔和熱處理之后）的橢圓度通過使用一個軋輥矯直機被修正。不僅許多有小直徑的傳熱管被使用在熱交換器上。而且熱傳導(dǎo)輥的安裝空間變的狹窄由于使用熱交換器。當(dāng)在熱傳導(dǎo)輥中彎曲產(chǎn)生的時候，一個麻煩例如其它部分的干擾會產(chǎn)生在裝配這個熱交換輥到熱交換器上的過程中，因此，這是很有必要的對于在輥式矯直機中確定彎曲修正精度。通常一個跨輥式矯直機，與復(fù)數(shù)滾筒式卷相結(jié)合，是通過在配置滾動矯直機矯直中使用的。有許多配置中的交叉型輥矯直機根據(jù)組合的數(shù)目卷布局（垂直和水平方向）,并滾動安排（反對型和鋸齒型）。
圖片一是一個例子關(guān)于交叉輥式矯直機的布局。多元對矯直輥RA和Rb（統(tǒng)稱為R ）是提供給輥矯直機的。這對矯直輥Ra和Rb每個都是垂直處置的，而不是彼此方向旋轉(zhuǎn)軸交叉在這個國家的計劃期內(nèi)（實際上，跨輥通過彼此的間隔，除了與在前面觀看外）。在輥布局圖1中， 3對矯直輥Ra1、Ra2和Ra3，且Ra3被分別設(shè)置在內(nèi)測，中心和外側(cè)，每對輥體彼此相反布置，輔助輥Rc被提供給矯直輥的外側(cè)。通常輥矯直機輥具有這種布局圖。 1被稱為（ 2-2-2-1 ）型矯直機。反對輥間隙和交叉角可以在矯直輥Ra1和Ra2中分別進行調(diào)整。第一對矯直輥Ra1和Ra2在垂直方向的高度位置和第二對矯直輥Rb1和Rb2在垂直方向的高度位置相臨近，彼此也能夠被調(diào)整。在彎曲校正中，每個矯直輥R的旋轉(zhuǎn)軸的跨越角用管予以糾正1，即滾轉(zhuǎn)角調(diào)整這種聯(lián)系面臨的管子的接觸面以糾正1適合的輪廓矯直輥，相反矯直輥Ra1和Rb1之間的輥間隙設(shè)置和被糾正1的管子外部直徑相比微小，并且傳授給拉直彎曲和糾正調(diào)整壓榨量的補償是通過第二對矯直輥Ra1和Rb2對第一對相比完成的。
科學(xué)的高剛性和耐磨損性能對于矯直輥來說是必須的，矯直輥是由工具鋼或陶瓷制成的，并且矯直輥的接觸面應(yīng)該是被修正的，為了使鋼管的外直徑保持在一個預(yù)定的范圍內(nèi)被矯直。在熱處理之后，傳熱輥的彎曲和橢圓度在輥式矯直機的矯直過程中被修正，例如剪切和在裝運前通過在鋼管內(nèi)部渦流探傷測試之后視察
圖二是一個通過表格顯示在鋼管內(nèi)表面渦流探傷測后結(jié)果的一個例子。就像在圖二中顯示的那樣。信號S源于在測試標(biāo)準(zhǔn)中的缺陷界定標(biāo)準(zhǔn)，在圖表中顯示信號N有一個預(yù)先確定的期限P。信號N被稱作基干擾。它是由熱傳到管在軸線方向上的微小空間波動產(chǎn)生的。這是很有必要的對于發(fā)現(xiàn)的缺點所引起的信號N，并且可以迅速判斷是否信號表明該漏洞，從而提高檢測效率。在下文中，來自于缺陷標(biāo)準(zhǔn)中的信號s與基干擾N的比率被定義為“S/N”。例如，在這種情況下自動判斷功能是基于鋼管內(nèi)部渦流測試圖表中的信號。干擾越大，也就是說小S/N比隱藏的信號是一個小缺陷背后的基干擾，這使得區(qū)分小缺陷信號和基干擾更難。因此，一個觀察員仔細的觀察在渦流測試中自動生成的結(jié)果。當(dāng)一個可疑信號測試生成再次以較低的速度來區(qū)分小缺陷和基干擾，從而降低了檢測效率。如上所述，基干擾是由熱傳到管在軸線方向上的微笑空間波動產(chǎn)生的。。因此，為了降低基干擾，有必要制止三維波動，如彎曲和橢圓度在沿著熱傳導(dǎo)管軸方向上。這就是說要提高沿?zé)醾鲗?dǎo)管軸線方向上的尺寸精度。
通常情況下，在用輥式矯直機矯直鋼管的過程中，像圖3到圖5中所顯示的那樣。矯直輥的放置角度、壓下量和補償量等設(shè)置參數(shù)都是為了去減少空間波動例如在熱傳導(dǎo)管軸線方向上的彎曲和橢圓度。圖三是一種觀點用來解釋輥式矯直機輥角的設(shè)定條件和與被矯正的鋼管相應(yīng)偏移距離之間的關(guān)系。如果該矯直管的外徑d被修正1，并且θ代表一個角度（下文中被定義為輥角），它的形成是通過輥的中心軸的，被修正1，矯直輥R的旋轉(zhuǎn)軸，沿管的一個移動距離（下文中被定義為同步孔距）M被修正為1，矯直輥R每轉(zhuǎn)動一圈被定義為下面的等式（2）M=π·d·tanθ。圖四是一種觀點用來解釋輥矯直機在設(shè)定條件下的壓下量，就像圖四中所指的那樣，鋼管被修正為1b，當(dāng)被壓下的時候，形成橢圓形。一個壓下量被表示成被修正為1a的反變形管和一個反向的輥Ra和Rb之間的縫隙s，其相當(dāng)于軋制被修正為1的管的外徑被減少的量。彎曲修正量表示通過反復(fù)軋制管在貫穿整個管的全長范圍內(nèi)被修正為1。壓下量被設(shè)定通過抬高或降低矯直輥Ra。圖五是一種觀點用來解釋矯直機在設(shè)定條件下的補償量，補償量δ被定義為在中間一對輥Ra2和Rb2之間的一個偏離量。 彎曲矯正被定義為給管施加一個彎曲應(yīng)力使其達到1.壓下高度通過抬高矯直輥Rb2設(shè)定，從而抵消補償量δ。如上所述，為了把這個彎度矯直，這是很有必要的把負荷的某一物理量，例如壓下量和和補償量應(yīng)用在鋼管上。然而，有時空間波動例如與負載有關(guān)的橢圓度也變得很重要。
具體而言，在傳統(tǒng)的矯直熱傳導(dǎo)管工藝過程中，例如鍋爐和熱水器，鋼管具有良好的預(yù)矯直精度，例如：熱傳導(dǎo)管被用一個高壓牽拉機進行牽拉。有時在矯直后增加橢圓度，為了破壞S/N的比率與通過矯直機矯直的預(yù)矯直管的橫截面相比。另一方面，當(dāng)彎曲矯正在矯直熱傳導(dǎo)管過程中不能達到要求時，其他部分的干擾經(jīng)常會導(dǎo)致把這些熱傳導(dǎo)管裝配到熱交換器上。這會使