【正文】 so Mn is thought to be a better solution to the problem (54). Other examples of material studies include studying positions of austenitic stainless steels after hot rolling. These studies contained edge cracks of different size and frequency. These cracks were sensitive to the content and amount of the delta ferrite. It is believed that delta ferrite slows the migration of austenite grain boundary during solidification which leads to corrugated boundaries resistant to crack propagation, because these boundaries act as nucleation sites to increase recrystallization rates. The distribution of the material is inhomogeneous, as the highest ferrite content is located in the vicinity of the plate edge. The delta ferrite content also affects the degree of edge cracks both in number and in size (48).Contamination also es into play in the cracking. For example in electrical sheet, oxidation seems to create more cracks of greater severity (55). Oxidation is also affected by different add on materials. For example, the addition of sulfur can lead to the detrimental formation of oxides in steel billets. Often times reducing the impact of oxidation requires a certain an amount of Mn to be 。 fracture pattern that is inherent to edge cracking 1) they had previously used a fracture criterion to recreate the pattern and 2) the Gurson model was unable to create this pattern. Only when they used the Gologanu model which assumes elliptical void shapes (instead of spherical ones) were they able to recreate the cracking condition. Causes of cracking Material PropertiesAs mentioned at the beginning of this chapter, one of the required conditions for edge cracking is insufficient ductility. Therefore, studies of edge cracking in rolling often measure different material properties and microstructures and how those parameters affect ductility. Ductility is influenced by temperature, grain size, preferred orientation of the material, and position of the material (1). This is especially true with second phase inclusions which shape, size, and strength can be initiation points for edge cracking (15). Additionally in hot ductility: temperature, strain rate, position, and previous thermal and mechanical treatments are also major factors affecting ductility (48). The mechanisms of crack growth and therefore ductility in alloys differ in tensile test to that of rolling. So when looking at materials and their tensile response, some review must be done on how it varying position and microstructure actually effect specific aspects of the ductile crack process. For example, in reviewing Al Fe metal matrix posites, a material which contains randomly oriented “needles” of an intermetallic pound, the tensile test indicates that the cracking of particles controls the ductility, but for rolled samples void nucleation, growth and linkage control the ductility (52). Atomic crystalline structure can play a part of cracking likelihood. For example, in looking at a magnesium alloys which has a hexagonal close packed structure the ratio of lattice parameters (c/a) effects probability of cracking。 in the case of rolling deformation plasticity is inherent to the process (41). In addition, SIF analysis does not take into account crack creation but only deals with crack propagation. While Xie’s study could be used to describe a cold rolling situation with a light passes, which may limit the zone of plasticity, the validity of this method with hot rolling would not be appropriate (49).More relevant to the damage method used here, many authors create a fracture criterion and simply delete elements when this criterion is met. Many fracture criteria have been proposed。C below that of the first rolling pass (46).Accurately modeling rolling in the lab has created some unique testing methods。由于我的水平有限，設(shè)計中不可避免存在一些不足，在核算、設(shè)計及繪圖過程中不可避免地出現(xiàn)錯誤，請各位老師給予批評指正。在設(shè)計和核算過程中涉及、運用了許多基礎(chǔ)及專業(yè)知識，如：軋鋼機(jī)械設(shè)計、機(jī)械制造、機(jī)械原理、材料力學(xué)，理論力學(xué)、金屬工藝學(xué)等。分條圓盤式剪切機(jī)主要功能是對已經(jīng)軋制過的AZ31鎂合金板進(jìn)行分條。齒輪箱的軸承通常與齒輪使用同一潤滑系統(tǒng)，在齒輪箱體上應(yīng)有潤滑軸承的油溝。 齒輪機(jī)座的潤滑分條圓盤剪的齒輪機(jī)座連續(xù)運轉(zhuǎn)時間很長，因此機(jī)座的冷卻與潤滑是很重要的。另外，采用密封油包包覆和內(nèi)存潤滑劑的方式也可以較好地解決潤滑問題。同時分條圓盤剪的運行特點和萬向接軸所處的位置，使其潤滑較為困難，造成滑塊的磨損加快，壽命降低，嚴(yán)重影響分條圓盤剪的作業(yè)率。齒輪浸入油中的深度可視齒輪圓周速度大小決定，對圓柱齒輪一般不宜超過一個齒高，但一般不該小于10mm。當(dāng)齒輪的圓周速度時，通常是將大齒輪輪齒浸入油池中進(jìn)行浸油潤滑。因而，對齒輪傳動系統(tǒng)進(jìn)行必要的潤滑，能夠大大改善輪齒的工況，確保運轉(zhuǎn)正常及預(yù)期的壽命。特別是高速傳動，就更要做好齒輪的潤滑。潤滑脂的填充量要適中，一般為軸承內(nèi)部空間容積的。其缺點是：摩擦損失大，散熱效果差。 潤滑方式的選擇 軸承的潤滑滾動軸承潤滑的作用是降低摩擦阻力、減少磨損、防止銹蝕，同時還可以起到散熱、減小接觸應(yīng)力、吸收振動等作用。（5） 點、線接觸的摩擦表面，油膜能起到緩沖吸振的作用，能夠?qū)⑤d荷分布到較大的面積上，使最大應(yīng)力下降。（3） 液體潤滑劑能帶走摩擦所產(chǎn)生的熱量，使零件的表面工作溫度下降。在機(jī)械的摩擦副中加潤滑劑的主要作用是：（1） 減小摩擦因數(shù)，提高機(jī)械效率。由于零件磨損，機(jī)械精度下降，壽命降低，影響了正常工作而發(fā)生早期報廢。8 系統(tǒng)的潤滑 潤滑劑的作用機(jī)械零件的表面在接觸的時候產(chǎn)生相對運動，在此過程中，避免不了會產(chǎn)生摩擦。齒輪機(jī)座的軸承主要采用滾動軸承，齒輪機(jī)座箱體應(yīng)保證齒輪傳動具有良好的密封性，并具有足夠的剛性，以使軸承具有堅固的支撐，為此，應(yīng)盡可能加強箱體軸承處的強度和剛度。齒輪軸的材料為440Cr、32Cr2MnMo、35SiMn2MoV、40CrMn2MoV等。另外，在溫度發(fā)生變化時，相嚙合的齒輪軸均可自由伸縮，保證正常嚙合。由于傳遞的扭矩大，因此傳動軸的直徑很大，相比之下，齒輪的直徑很小，所以一般與傳動軸作成一體，即齒輪軸。齒輪機(jī)座通常直接安裝在基礎(chǔ)上，安裝方式有兩種，一種是將整個底座都安放在基礎(chǔ)上，另一種是由地腳安裝在基礎(chǔ)上。因為齒輪機(jī)座傳遞的扭矩較大，而中心距又受到刀盤軸中心距的限制，為了滿足強度要求，齒輪的模數(shù)較大（8~45），齒寬較寬（~），而齒數(shù)較少，通常為22~44。聯(lián)軸器的承載能力與材料屬性和熱處理有關(guān)，也與兩軸相對位移的方向和位移量大小有關(guān)，而且還與嚙合齒面間的滑動速度和潤滑狀態(tài)有關(guān)，對于標(biāo)準(zhǔn)聯(lián)軸器，可按標(biāo)準(zhǔn)規(guī)定的方法驗算： 式中 ——聯(lián)軸器的許用轉(zhuǎn)矩/； T——聯(lián)軸器長期承受的理論轉(zhuǎn)矩/； ——聯(lián)軸器工作條件系數(shù)。根據(jù)以上幾點選取聯(lián)軸器如下：在電機(jī)軸與減速機(jī)軸之間選取聯(lián)軸器型號為HL8，減速機(jī)軸和齒輪機(jī)座之間，以及傳動軸和剪切機(jī)輸入軸之間的聯(lián)軸器型號為HL10查閱文獻(xiàn)[17]。 聯(lián)軸器的選擇根據(jù)傳遞載荷的大小，刀盤軸轉(zhuǎn)速的高低，被聯(lián)接兩部件的安裝精度，參考各類聯(lián)軸器特性，選擇一種合適的聯(lián)軸器類型。剛性聯(lián)軸器對所聯(lián)兩軸間的相對位移缺乏補償能力，但有結(jié)構(gòu)簡單，制造容易，不需維護(hù)，成本低等特點，而仍有其應(yīng)用范圍；撓性聯(lián)軸器中又分為無彈性元件的撓性聯(lián)軸器和帶彈性元件的撓性聯(lián)軸器。因而，對于平鍵聯(lián)接一般只按作業(yè)面上的擠壓強度和磨損強度核算。根據(jù)刀盤軸的公稱直徑d=260mm,選擇鍵。確定安全系數(shù)后，萬向接軸的許用應(yīng)力為： 式中 ——材料的抗拉強度/Mpa； n——安全系數(shù)，最小安全系數(shù)不應(yīng)小于5。軸體中的剪力按下式計算：時： 時： 式中 ——接軸體的最小直徑。所以，B點處的合成應(yīng)力為： E及F點的合成應(yīng)力為： 軸體強度計算因為傾角的存在，接軸體在工作過程中，承受扭轉(zhuǎn)作用的同時還承受彎曲作用。 叉股斷面分析B點處的合成應(yīng)力。（3）由力距在E點或F點所產(chǎn)生的彎曲應(yīng)力為： 式中 ——斷面II對于yy軸的斷面系數(shù)。（1）在EF線上，由彎曲力矩產(chǎn)生的彎曲應(yīng)力為： 式中 ——對軸線xx的截面系數(shù)。（2）拉力: 式中 ——斷面II相對于斷面AA的傾角；——斷面II的傾角。 叉頭強度計算簡圖如果在AA斷面中心線上加上兩個大小等于P，而方向相反的力和,就可以看出將有力偶(由于P和形成)作用在叉股上，此外，還有力在叉股上引起的彎曲應(yīng)力、拉應(yīng)力和剪切應(yīng)力。力P的作用點位于距鉸中心線的地方,其中是一個叉股的寬度。 斷面II中的彎曲應(yīng)力和扭轉(zhuǎn)應(yīng)力分別為：