【正文】 on the energy required to separate its atoms.（金屬的熔點決定于分離金屬原子所需的能量。） The temperature range within which a ponent or structure is designed to function is an important consideration in the selection of materials.（一個部件和結(jié)構(gòu)設(shè)計功能時，其里面的溫度在此案料選擇中需要重要考慮。） Because the recrystallization temperature of a metal is related to its melting point, operations such as annealing and heat treating and hot working require a knowledge of the melting points of the materials involved.（因為金屬的再結(jié)晶溫度與熔點相關(guān)，比如在退火，熱處理和熱加工操作中需要知道所涉及材料的熔點。） Alloying element have a relatively minor effect on the specific heat of metals.（合金元素在金屬比熱容中有一個相對較小的影響。） Temperature rise in a workpiece, if excessive, can decrease product quality by adversely affecting its surface roughness and dimensional accuracy, can cause excessive tool wear, and can result in undesirable metallurgical changes in the material.（工件溫度的上升，假如溫度過高，將會以平面粗糙度 和尺寸精度的不利影響來影響產(chǎn)品質(zhì)量，而且會導(dǎo)致材料中不需要的相變。） Metals generally have high thermal conductivity, while ceramics and plastics have poor conductivity.（金屬通常有高的熱傳導(dǎo)，然而陶瓷和塑料有差的熱傳導(dǎo)。） The main difficulty experienced in machining titanium, for example, is caused by its very low thermal conductivity. （在金屬鈦中主要的問題是由于它的差的熱傳導(dǎo)。） Expansion（熱膨脹） The thermal expansion of materials can have several significant effects, particularly the relative expansion or contraction of different materials in assemblies such as moving parts in machinery that require certain clearances for proper functioning.（材料的熱捧場有一些有益的影響，尤其是在裝配中不同材料的熱脹冷縮比如機械中得活動件需要特定的空隙來完成特定的功能。） For example, a part, such as a flange, is to be installed over a shaft.（比如，一個零件如法蘭，要安裝穿過一根軸。） When allowed to cool, the part shrinks and the assembly effectively bees an integral ponent.（當冷卻時，零件收縮而且這個實際裝配體變成了一個整體部件。） The word corrosion itself usually refers to the deterioration of metals and ceramics, while similar phenomena in plastics generally are called degradation. （腐蝕這個詞本身指的是金屬和陶瓷的退化，然而在塑料中類似的現(xiàn)象叫做降解。） Corrosion resistance is an important aspect of material selection for applications in the chemical, food, and petroleum industries, as well as in manufacturing operations. （耐腐蝕性在化學，食物和石油工業(yè)材料選擇中是一個重要方面，生產(chǎn)制造中也一樣。） Resistance to corrosion depends on the position of the material and on the particular environment. （耐腐蝕性取決于材料組成和所處的特殊的環(huán)境。） Nonferrous metals, stainless steels, and nonmetallic materials generally have high corrosion resistance, Steels and cast irons usually have poor resistance and must be protected by various coatings and surface treatments..（有色 金屬和非金屬材料通常有高的耐腐蝕性，鋼和鑄鐵常有較差的耐腐蝕性而且必須通過各種膜和表面處理來防止腐蝕。） Aluminum develops a thin (a few atomic layers), strong, and adherent hardoxide film (Al2O3) that better protects the surface from further environmental corrosion.（鋁形成一層?。◣讉€原子層）而強的緊貼的 Al2O3 膜，它能更好地防止平面被進一步地腐蝕。） A similar phenomenon occurs in stainless steels, which (because of the chromium present in the alloy) develop a protective film on their surfaces. （不銹鋼應(yīng)用了類似的現(xiàn)象，在它表面形成了一層保護膜（由于合金中鉻的出現(xiàn)）。） 12 Spindle Bearings (陳鵬文，有錯包含 ) A machine tool spindle must provide rotational speed, transfer torque and power to the cutting tool, and have reasonable load carrying capacity and life. （機床主軸必須提供轉(zhuǎn)速、傳遞力矩和公路到切削工具上，而且具有一個合理的負載承受能力和壽命。） Highspeed spindle bearing available today include roller, taper roller, and angular contact ball bearings.（當今可以用的高速主軸軸承包括滾珠軸承、錐型滾柱軸承和徑向止推滾珠軸承。） Angular contact bearings are the type most monly used in very highspeed spindle design. （徑向止推軸承在超高速主軸設(shè)計中是用得最普遍的。） Angular contact ball bearings have a number of precision balls fitted into a precision steel race, and provide both axial and radial load carrying capacity when properly preloaded.（徑向止推軸承有許多安裝在精確鋼槽里的精確滾珠，在正確安裝下提供軸向和徑向的負載承受能力。） However, tapered roller bearings do not allow the high speeds required by many spindles.（然而，錐型滾柱軸承不能保證 許多主軸需要的高的速度。） Light preloaded bearings allow maximum speed and less stiffness. These bearings are often used for very highspeed applications, where cutting loads are light.（輕載型軸承能保證最大速度和較小的剛度。） Heavy preloading allows less speed, but higher stiffness.（重載型軸承可以保證較低速度，較高剛度。） In this way, the bearings share the loads, and increase overall spindle stiffness.（用這種方法，軸承分擔負載，而且提高了整個主軸的剛度。） The ceramic balls, when used in an angularcontact ball bearing, offer distinct advantages over typical bearingsteel balls（應(yīng)用于徑向止推滾珠軸承中的陶瓷滾珠提供了較鋼珠軸承中鋼珠明顯的優(yōu)點。） This is significant because as a ball bearing is operating, particularly at high rotational speeds, shape of the ball. （這是有意義的，因為一個轉(zhuǎn)動的滾珠軸承尤其是在高速旋轉(zhuǎn)中，滾珠的形狀會發(fā)生變化。） Ceramic balls, with less mass, will not be affected as much at the same speed. （陶瓷滾珠具有較小的質(zhì)量，在相同速度下陶瓷滾珠受到影響不如鋼珠大。） Due to the nearly perfect roundness of the ceramic balls, hybrid ceramic bearings operate at much lower temperatures than steel ball bearings, which results in longer life for the bearing lubricant. （由于幾近完美圓度的陶瓷滾珠，混合的陶瓷軸承工作在較鋼珠軸承低得溫度，這些導(dǎo)致在軸承潤滑中有較長的壽命。） Bearing lubricant is necessary for angular contact ball bearing to operate properly.（軸承潤滑在徑向止推軸承正確工作中是必要的。） In addition, it protects surfaces from corrosion, and protects the contact area from particle contamination.（另外，它還防止平面腐蝕，保護接觸平面受磨粒影響。） It is injected into the space between the balls and the races, and is permanent. （它被注射到滾珠和滾槽之間的縫隙中，是永久的。） Generally, highspeed spindles utilizing grease lubrication do not allow replacement of the grease between bearing replacements. （通常情況下，高速主軸應(yīng)用油脂潤滑不能保證潤滑油脂在軸承替換件中的替換。） Often at high rotational speeds, lubrication with grease is not sufficient. （通常在高轉(zhuǎn)速中，油脂潤滑是不夠的。） Maintenance of the lubrication system is vital, and must be closely monitored to ensure that proper bearing conditions are maintained. （潤滑維護系統(tǒng)式非常重要的，而且必須嚴密檢測來保證維護中正確的軸承維護條件。 How much life can be expected?（預(yù)測壽命是多長呢？） All bearings will have a useful life, defined as operation time until the bearing specifications are lost, or a plete