【正文】 ical gears of opposite hand, mounted side by side on the same shaft. They develop opposite thrust reactions and thus cancel out the thrust load. When two or more single helical gears are mounted on the same shaft, the hand of the 10 gears should be selected so as to produce the minimum thrust load. Crossedhelical, or spiral, gears are those in which the shaft centerlines are neither parallel nor intersecting. The teeth of crossedhelical fears have point contact with each other, which changes to line contact as the gears wear in. For this reason they will carry out very small loads and are mainly for instrumental applications, and are definitely not remended for use in the transmission of power. There is on difference between a crossed helical gear and a helical gear until they are mounted in mesh with each other. They are manufactured in the same way. A pair of meshed crossed helical gears usually have the same hand。 the two angles are equal for a 90deg. Shaft angle. When gears are to be used to transmit motion between intersecting shaft, some of 11 bevel gear is required. Although bevel gears are usually made for a shaft angle of 90 deg. They may be produced for almost any shaft angle. The teeth may be cast, milled, or generated. Only the generated teeth may be classed as accurate. In a typical bevel gear mounting, one of the gear is often mounted outboard of the bearing. This means that shaft deflection can be more pronounced and have a greater effect on the contact of teeth. Another difficulty, which occurs in predicting the stress in bevelgear teeth, is the fact the teeth are tapered. Straight bevel gears are easy to design and simple to manufacture and give very good results in service if they are mounted accurately and positively. As in the case of squr gears, however, they bee noisy at higher values of the pitchline velocity. In these cases it is often good design practice to go to the spiral bevel gear, which is the bevel counterpart of the helical gear. As in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, and hence are useful where high speed are encountered. It is frequently desirable, as in the case of automotive differential applications, to have gearing similar to bevel gears but with the shaft offset. Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution. The tooth action between such gears is a bination of rolling and sliding along a straight line and has much in mon with that of worm gears. A shaft is a rotating or stationary member, usually of circular cross section, having mounted upon it such elements as gears, pulleys, flywheels, cranks, sprockets, and other powertransmission elements. Shaft may be subjected to bending, tension, pression, or torsion loads, acting singly or in bination with one another. When they are bined, one may expect to find both static and fatigue strength to be important design considerations, since a single shaft may be subjected to static stresses, pletely reversed, and repeated stresses, all acting at the same time. The word “shaft” covers numerous variations, such as axles and spindles. An axle is a shaft, wither stationary or rotating, nor subjected to torsion load. A shirt rotating shaft is often called a spindle. When either the lateral or the torsion deflection of a shaft must be held to close limits, the shaft must be sized on the basis of deflection before analyzing the stresses. The reason for this is that, if the shaft is made stiff enough so that the deflection is not too large, it is probable that the resulting stresses will be safe. But by no means should the designer assume that they are safe。簡言之，可成功地達(dá)到顯著提高夾具生產(chǎn)效率和效益。柔性夾具是以它們對(duì)不同工件的高適應(yīng)性和以少更換低費(fèi)用為特征的。因?yàn)閵A具作用力和同步化裝置是各自獨(dú)立的，該同步裝置可以用精密的滑移裝置來替換而不影響夾具作用力。 如果任何進(jìn)行性形式 的磨損任由繼續(xù)發(fā)展，最終磨損速率明顯地增加而刀具將會(huì)有摧毀性失效破壞，即刀具將不能再用作切削，造成工件報(bào)廢，那算是好的，嚴(yán)重的可造成機(jī)床破壞。在許多情況中和對(duì)于實(shí)際的切削狀況而言，前刀面磨損比起后刀面磨損要輕，因此后刀面磨損更普遍地作為刀具失效的尺度標(biāo)志。后刀面磨損既發(fā)生在主刀刃上也發(fā)生副刀刃上。這表明如何人從切削參數(shù)來確定切削溫度那是很合適的。 實(shí)質(zhì)上由于在金屬切削中所做的全部功能都被轉(zhuǎn)化為熱，那就可以預(yù)料：被切離金屬的單位體積功率消耗曾家的這些因素就將使切削溫度升高。一般來說，在其他條件相同時(shí)，進(jìn)給量與切削速度成反比。 切削刀具必須用一種合適的材料來制造，它必須是強(qiáng)固、韌性好、堅(jiān)硬而且耐磨的。一般來說，通過利用貴重設(shè)備而又無需特種加工條件下，幾乎可以以任何種類原材料開始，借助機(jī)械加工把原材料加工成任意所 需要的結(jié)構(gòu)形狀，只要外部尺寸足夠大，那都是可能的。這樣從充分滑移到完全鎖住的任何狀態(tài)都可以獲得。這種離合器通 常使用裝在外套筒和內(nèi)軸件之間的滾子或滾珠。他們可能在圓周面上加工齒，以便他們 以圓柱周向配合來結(jié)合或者在配合元件的端面上加工齒來結(jié)合。因?yàn)閹缀涡螤畹闹匾允巧岜砻妗? 由于他們的功能相似，將離合器和制動(dòng)器一起處理。因此，如若軸要做得有足夠的剛度以致?lián)锨惶?，那么合?yīng)力符合安全要求那是完全可能的。通常有圓形橫截面。 另外一個(gè)難題，發(fā)生在難于預(yù)示錐齒輪輪齒上的應(yīng)力，實(shí)際上是由于齒輪被加工成錐狀造成的。一個(gè)裝 置中的蝸桿和蝸輪正像交錯(cuò)軸斜齒輪那樣具有相同的齒向，但是其斜齒齒角的角度是極不相同的。與其相配的齒輪叫做蝸輪，蝸輪不是真正的斜齒輪 。因此他們只能傳遞小的載荷和主要用于儀器設(shè)備中 ，而且肯定不能推薦在動(dòng)力傳動(dòng)中使用。它是齒輪逐漸進(jìn)行嚙合并平穩(wěn)的從一個(gè)齒到另一個(gè)齒傳遞運(yùn)動(dòng)，那樣就使斜齒 輪具有高速重載下平穩(wěn)傳遞運(yùn)動(dòng)的能力。傾斜角度每個(gè)齒輪都一樣，但一個(gè)必須右旋斜齒，而另一個(gè)必須是左旋斜齒。通過加工制造它們可以分為許多的型號(hào)，分別用于許多的場合。我們將研究作用力具有三維坐標(biāo)的齒輪。如果我展開這張紙，在血角刃邊上的每一個(gè)點(diǎn)就發(fā)生一漸開線曲線。雙斜齒輪（人字齒輪）是與反向的并排地裝在同一軸上的兩個(gè)斜齒輪等效。一對(duì)相嚙合的交錯(cuò)軸斜齒輪通常具有同樣的齒向，即左旋主動(dòng)齒輪跟右旋從動(dòng)齒輪相嚙合。然而蝸桿蝸輪傳動(dòng)機(jī)構(gòu)中 馬棚網(wǎng)存在齒間有較大滑移速度的缺點(diǎn)，正像交錯(cuò)軸斜齒輪那樣。雖然錐齒輪通常制造成能構(gòu)成 90度軸交角，但它們也可產(chǎn)生任何角度的軸交角。在這些情況下，螺旋錐齒輪比直齒輪能產(chǎn)生平穩(wěn)的多的嚙合作用，因此碰到高速運(yùn)轉(zhuǎn)的場合那是很有用的。因?yàn)閱胃S可以承受靜壓力，變應(yīng)力和交變應(yīng)力，所有的應(yīng)力作用都是同時(shí)發(fā)生的。這就減低了彎矩，因而減小變形和彎曲應(yīng)力。在分析這些裝置的性能時(shí)，我們應(yīng)注意到作用力，傳遞的扭矩，散失的能量和溫升。 混合式離合器包括幾個(gè)類型，例如強(qiáng)制接觸離合器、超載釋放保護(hù)離合器、超越離合器、磁液離合器等等。 有些裝置例如線性驅(qū)動(dòng)裝置或電機(jī)操作螺桿驅(qū)動(dòng)器必須運(yùn)行到一定的限度然后停頓下來。因此該離合器與具有一定數(shù)量齒的棘輪棘爪機(jī)構(gòu)等效。盡管在某些場合，工件無承受情況下，使用移動(dòng)式裝備來實(shí)現(xiàn)加工，但大多數(shù)的機(jī)械加工是通過既支承工件又支承刀具的裝備來完成。許多零件，如果用別的其他方法來生產(chǎn)屬于大批量生產(chǎn)的話，那么在機(jī)械加工中則是屬于低公差且又能滿足要求的小批量生產(chǎn)了。為了有效地加工，切削速度高低必須適應(yīng)特定的工件 —— 刀具配合。粗加工比起精加工來，吃刀深度較深。未變形切屑厚度的增加趨勢必導(dǎo)致通過工件的熱的總數(shù)上產(chǎn)生比例效應(yīng)，刀具和切屑仍保持著固定的比例，而切削溫度變化傾向于降低。該項(xiàng)技術(shù)是建立在高速鋼刀具截面金相顯微測試基礎(chǔ)上，目的是要建立顯微結(jié)構(gòu)變化與熱變化規(guī)律圖線關(guān)系式。在大多數(shù)實(shí)際切削條件下，由于主前刀面先于副前刀面磨損，磨損到達(dá)足夠大時(shí)，刀具將實(shí)效，結(jié)果是制成不合格零件。 刀具的主后刀面磨損帶的尾部是跟未加工過的工件表面相接觸，因此后刀面磨損比沿著磨損帶末端處更為明顯，那是最普通的。以下幾種現(xiàn)象之一均是刀具嚴(yán) 重失效開始的特征：最普遍的是切削力突然增加，在工件上出現(xiàn)燒損環(huán)紋和噪音嚴(yán)重增加等。因此，生產(chǎn)的最后階段，裝配因生產(chǎn)計(jì)劃、批量和產(chǎn)品設(shè)計(jì)的變更而顯得特別脆弱。最后，必須計(jì)算、調(diào)整、組裝可拆裝的或標(biāo)準(zhǔn)夾具元件的所需位置，以便使工件牢牢地被夾緊在夾具中。 9 GEAR AND SHAFT INTRODUCTION Abstract: The important position of the wheel gear and shaft can39