The Development of RubberHere is a story about rubber.In the early part of the eighteen-hundreds, the Americans made use of natural for the first time. First they made overshoes to keep their feet dry. Then came a certain Mr. Mackintosh, who made coats of cloth covered with natural rubber. But these first rubber overshoes and raincoats were all soft and sticky in summer, and hard and unelastic in the winter when it was cold, the rubber we have today is not sticky but soft and elastic, though very strong-even in the warmest summer and the coldest winter. There would be no automobiles such as we have today without it. But at that time every attempt to make rubber hard and strong come to nothing. The early overshoes and raincoats were simply not good enough and their makers went out of business.Goodyear was living near some of these poor men and he got to work on this question of making rubber hard and strong. Once he started on this work, he was the sort of man who simply had to go on till he had overcome the trouble. First came the discovery that nitric acid (HNO3) made the rubber much better, and in a short time he was doing a small business in rubber shoes produced in this way.Water, a friend of his had the idea that rubber might be made hard and strong if mixed with sulphur and put in the sun. Goodyear put his idea to the test , and saw that it did have more or less the desired effect, but only on the outside of the rubber. It is common knowledge now that the way to make rubber hard and strong-to“vulcanize” it ,as we say , is by heating it with sulphur. Goodyear spent another four years, in which things went very hardly with him, before he made the discovery how to vulcanize rubber completely. When at last he did it, he had nothing left at all. Everything of the smallest value had used to get money, even his children’s school-books.Almost every discovery or invention has come a sort of story behind it though they are not all quite such unhappy stories.New Words and Expressions1.made use of 使用,利用2.overshoe 套鞋(常用复数)3.sticky 粘性的,(天气)湿热的4.elastic 弹性的,灵活的,有伸缩性的5.unelastic 没有弹性的6.not…..but…… 不是…..而是…..7.automobile rr (美语)汽车e to nothing 没有结果,失败9.simply 简单地,真正地,朴素地10.out of business 停业,歇业11.get to work on sth 开始做某事12.overcome 克服13.overcame, overcome14.nitric 含氮的15.acid (化学)酸,酸的16.nitric acid 硝酸17.sulphur, sulfur (化学)硫,硫磺18.put…..to the test 对……进行试验19.vulcanize 硫化20.at all 究意,全然,一点儿21.value 价值,评价22.school-books 教科书The Part by Rubber in Modern CivilizationRubber is indispensable to modern civilization. Its importance in every form of transport for tyres and tubes is self-evident and has been fully brought out. About 80 per sent of all rubbers is used in the motor industry, mainly for tyres. This applies to passangers, goods transport, and private cars. Without rubber, the rarious form of transportation could not run, the communication system would break down.A large proportion of the remainder goes into what are known as mechanical goods, which include such articles as belting, packing, moulded good, hose and innumberable other tyres of products. Most of these articles are absolutely vital to the operation of the industry in general. Without them industry would come to a stand still.Rubber is of the greatest possible importance in tyres on tractors for agricultural use. The change-over form steel wheels to pneumatlics has had a profound affect on agricultural development.The electrical industry is the large consumer. Rubber is of outstanding significance in the electrical industry as insulation, particularly for eables. The reasons for its preeminent position are outstanding electrical properties, the good mechanical properties, and the ease with which it can be handled.Now Words and Expressions1.to play a part in 在…方面起作用，对…起作用2.modern 现代的，近代的，新式的3.civilization 文明，文化4.indispensable 绝对必要的，不可缺少的5.transport 运输6.tyre, tire 轮胎7.tube 管子，内胎8.self-evident 自明的，不言而喻瓣9.bring out 说明，产生，显出，发表，出版10.per cent 百分数11.motor 发动机，电动机，马达12.industry 工业，产业，刻苦13.mainly 主要地，大部分14.apply 应用，申请15.passenger 乘客，旅客16.private 私人的，私有的，秘密的munication 通讯，传播，交通18.system 系统，体制，制度communication system 通讯系统，交通体系19.proportion 比例20.remainder 剩余，余数，剩下的人21.to be known as 通称的，以…著称22.mechanical 机械的，力学的，工业的23.article 物品，文章24.belt 带，胶带25.pack 包，捆，堆，垫圈26.mould 模型27.hose 软管，皮带管28.inaumberable 无数的，数不清的29.absolutely 绝对地，完全地30.vital 生命的，非常的，有生命力的31.in general 总之，通常，一般说来e to a stand 停顿33.tractor 拖拉机34.agricultural 农业的35.change-over 调换，转换36.wheel 车轮37.pneumatic 装满空气的38.profound 深远的，很深的39.affect 影响40.electrical 电的41.consumer 消费者，消费品42.outstanding 显著的，杰出的，未解决的43.significance 意义，重要性44.insulation 绝缘体45.cable 电缆46.pre-eminent 杰出的，卓越的47.property 财产，性质48.with ease with 轻易地Lesson ThreeNatural Rubber 、Synthetic Rubber and Reclaimed RubberNatural Rubber is a high molecular weight hydrocarbon which comes from the latex of many plants and is obtained by coagulation with chemicals, by drying, electrical coagulation and other processes. The most important producer is Hevea Brasiliensis. The wild rubber produced form latex contains, besides the hydrocarbon, small quantities of protein, carbohydrates, resin-like substances, mineral salts and fatty acids. These other constituents act in part as natural accelerators and anti-oxidants and give the product processing properties which do not exist in the pure hydrocarbon.［Natural rubber is cis-1, 4-polyisoprene with the empirical formular (C5H8)n］and the structural formular.CH3︳[—CH2—C＝CH—CH2—]When vulcanized, rubber becomes highly extensible, shows fast recovery, and is highly elastic.“Synthetic rubber” is the common term, in fact incorrect, for chemically different polymers with rubber-like properties. Since the term rubber applies to the original product, i.c. polyisoprene, the term synthetic rubber should strictly lerased only for synthetic “Natural Rubber”(cisl,4-polyisoprence). For polymers, with rubbery properties, which do not have an identical structure to natural rubber, the terms artificial rubber, chemical rubber or synthesized rubber have been suggested. In modern usago the term rubber no longer refers to a chemically defined product but relates so physical properties, all synthetic polymers with properties similar to those of natural rubber may therefore be classified as properties rubbers.In general, it may be stated tht synthetic rubber do not have all qualities of natural rubbers, but their special properties have made them more suitable than natural rubber for certain applications and they have achieved a phenomenal technical importance.Reclaimed rubber is obtained by treating scrap vulcanized rubber by one of several methods, so that it becomes plastic again and can be handled on a mill and incorporated in a rubber compound, together with crude rubber.Reclaimed rubber contains all the ingredients of the original compound, except for the uncombined, or free sulfur. It was first used for economical resean that is to reduce the manufacturing cost. However, it was found that has also other advantages in addition to its lower cost. It fancilitates mastication and has very beneficial effect on calendaring and extruding. The quantity used varies to a great extent and some compounds are based exclusively on reclaimed rubber. However, reclaimed rubber affects some of the mechanical properties of the vulcanize ate unfavorably. Therefore, it is not used in case where high abrasion of tear resistance or tensile strength is required.Now Words and Expressions1.natural 天然的，自然的，简单的2.synthetic 人工的，合成的3.reclaim 收回，改正4.molecular 分子的5.hydrocarbon 烃，碳氢化合物tex 胶乳7.coagulation 凝固，凝结，凝聚8.producer 生产者9.Hevea Brasiliensis 巴西三叶橡胶树10.wild 野生的11.quantity 数量，数12.protein 蛋白质13.carbohydrate 碳水化合物14.resin-like 类树脂的15.substance 物质16.mineral 矿物，矿质的17.salt 盐mineral salt 金属盐18.fatty 脂肪的fatty acid 脂肪酸19.constituent 成分，组分20.accelerator 促进剂21.oxidant 氧化剂anti-oxidant 防老剂，抗氧剂22.process 方法，过程23.exist 存在24.pure 纯的，纯净的25.cis-polyisoprene 顺式聚异戊二烯26.empirical 经验主义的，以经验为根据的27.formula 式，公式，配方28.structural 结构上的29.extensible 可伸长的30.recovery 复原，复原性31.in fact 事实上，实际上32.incorrect 不正确的33.polymer 聚合物34.original 最初的，原来的35.i.e. 那就是，即36.strict 严格的37.identical 同一的，完全相同的38.artificial 人工的，人造的39.synthesise 合成，综合age 使用，用法，惯例，习惯41.refer 读到，提到refer to 参考，查阅，指42.define 解释，给……下定义43.relate 叙述，讲，有关，涉及（to）44 classify 分类，分级，把…分类45.state 陈述46.quality 质量47.suitable 合适的48.application 使用，应用49.phenomenal 惊人的50.scrape 刮，削，擦l 开炼机52.incorporate 加入，综合的pound 化合物，胶料54.crude 天然的，未加工的55.ingredient 配料，配合剂56.uncombined 未化合，未结合57.economical 经济的，节约的58.manufacture 制造59.cost 成本，花费60.in addition 另外61.facilitate 使容易，使便利，推进62.mastication 塑炼63.beneficial 有益的，有利的64.calendar 压延机，压延65.extrude 挤出，压出66.extent 范围，广阔，程度67.to be based on 以…为根据，根据68.exclusive 孤高的，排外的，专有的，唯一69.vulanizate 硫化胶70.unfavorably 不利的，不顺利地71.case 情况，事例72.abrasion 摩擦，磨损73.tear 撕裂74.resistance 抗耐性，耐力75.tensile 拉力的，抗张力的76.strength 力，强度Lesson FourVulcanizing Agents、Accelerators and ActivatorsDuring vulcanization, the long chain of the rubber molecules become crosslinked by reactions with the vulcanizing agent to form three-dimensional structures. In pratice, sulfur is used almost exclusively for vulcanization of rubber. Other vulcanizing agents, such as sulfur chloride, selenium, tellurium, and thiuram disulfide, are used only in special cases.Accelerations can increase the speed of reaction between sulphur and rubber, or lower the vulcanization temperature. They can also decrease the physical and technical properities of the vulcanizate.Inorganic accelerators were discovered accidentally early in the history of the rubber industry when inorganic compounds were added go rubber as coloring agents and fillers. Among the basic salts and metal oxide recommended as accelerators, line, magnesium oxide, and litharge were the most common ones, litharge is still used to some extent, but its blackening effect on the vulcanizate limits its application to black compounds.Oenslager’s discovery, in 1906, of the acceleration effect of aniline marked the beginning of a long line of organic accelerators which belong to many different groups.A very small quantity, about 1 per cent, of these organic compounds has a remarkable accelerating effect. Organic accelerators were classified according to their technical effects and were placed in the following categories:ultra-acceleratorssemi-ultra-acceleratorsmedium-fast-acceleratorsslow acceleratorsActivators activate accelerators. Most accelerators are much more active in presence of activators than they are alone. The activator reacts with the accelerators. As a result, an intermediate complex is formed. The complex is more effective in activating the sulphur present in the rubber mixture.There are two large classes of activators: metal oxides and fatty acids. Representatives of both groups must be present simultaneously. The most common member of the first group is zinc oxide which is in the proportion of about 3 to 5 percent as activator in almost every rubber compound. The second group includes oleic palmatic and especially stearic acid. They are used in amounts of 0.5 to 3 percent.New Words and Expressions1.agent 剂，媒介物，代理人2.activator 活化剂3.vulcanization 硫化4.chain 链，链条5.molecule 分子6.crosslink 交联7.reaction 反应8.dimensional 维的，度的，尺寸的9.structure 结构10.chloride 氯化物11.selenium 硒12.tellurium 碲13.thiuram 秋兰姆14.disulfide 二硫化物15.special 特殊的，专门的16.increase 增加，提高17.temperature 温度18.decrease 减少，降低19.considerably 相当，大大地20.inorganic 无机的21.accidentally 意外地，无意地，偶然地22.recommend 介绍，推荐23.lime 氧化钙，生石灰24.magnesium 镁25.oxide 氧化物magnesium oxide 氧化镁26.zinc 锌27.litharge 一氧化铅28.limit 限制，限度29.aniline 苯胺anic 有机的31.remarkable 显著的，明显的32.according 依照according to 按照，依据33.technical 技术的，专门的34.category 种类，部门，范畴35.ultra 超，过渡的ultra-accelerators 超促进剂36.semi 半37.medium 中等（的），适度，普通38.activate 活化39.intermediate 中间的plex 络合物，合成物，复杂的41.effective 有效的42.representative 代表，代表的43.simultaneously 同时发生地，同时进行44.include 包括45.oleic 油酸的46.palmatic 棕榈酸47.stearic acid 硬脂酸Lesson FiveFillersMost rubber products contain fillers which belong to two groups: reinforcing and inert fillers. Generally speaking reinforcing fillers improve various physical properties of rubber compounds such as tensile strength, tear and abrasion resistance. Inert fillers impart certain processing properties, and reduce.By far the most important filler is carbon black, whose introduction revolutionized the industry. It is used all rubber articles which have to meet severe service condition except light color products.The carbon black used in rubber compounding are prepared by three different processes, each yielding a special class of carbon blacks. They are the channel process, the furnace process and thermal process.From the practical angle, carbon blacks are classified as reinforcing and semi-reinforcing. Their qualities are indicated by initials, such as EPC(easy processing channel), SRF(semi-reinforcing furnace),HMF(high medulus furnace), etc. The variety used most extensively today is HAF (high abrasion furnace).Inert fillers consists of fillers which can be incorporated in rubber compounds without substantially reducing their mechanical properties. Consequently, they make possible a lower manufacturing cost of rubber goods which need not be of very high quality. Many substances belong to the class of inert fillers such as whiting, barium sulfate, lithopone, etc.New Words and Expressions1.filler 填充剂2.Contain 包含3.reinforce 加强，补强4.inert 惰性的，无活动性的5.tear 撕裂6.impart 赋予，给予7.by far 最……，非常……8.carbon 碳9.introduction 引言，序言，介绍10.revolutionize 使发生革命11.severe 严重的，严酷的，苛刻的12.prepare 制备，准备13.channel 槽，海峡14.furnace 炉子15.thermal 热的16.angle 角17.indicate 指示18.initial 字头，开头的19.modulus 模量，定伸强度20.substantially 物质地，实质地，显著地，大体上21.consequently 因而，所以，因此22.whiting 碳酸钙，白垩23.barium 钡24.sulface 硫酸盐25.lithopnone 立德粉（硫酸钡70～72%与氧化锌28～30%的混合物Lesson SixAntioxidantsAntioxidants are used to reduce aging processes in vulcanizate. They function by slowing down the deterioration of rubber produces.Rubber antioxidants are mostly phenols and amines, and more particularly their condensation products with other compounds. Usually 1 to 2 per cent is added to a rubber formulation. The most common one is phenyl naphthylamine.Some classical mixtures of antioxidants are available and also several proprietary products the composition of which has not been disclosed. In general, it is preferable to use mixtures as they not only protect against oxygen, but have also other desirable properties. Some of them give resistance go cracking by flexing, others provide protection against heat or light, still others protect against the detrimental effects of metals, such copper, etc.The resistance to cracking on repeated flexing (called flex cracking) has been extensively studied. This phenomenon may be considered dynamic aging of rubber while oxidation at rest may be regarded as static aging. Finally, the best means found so far is adding waxy substances to rubber compounds. After vulcanization, these have a tendency to bloom on the surface of the rubber article, thus forming a protective film.New Words and Expressions1.antioxidant 防老剂2.aging 老化3.function 作用，功能4.slow 尽职，起作用，有效用5.deterioration 减慢6.phenol 破坏，败坏7.amine 胺8.condensation 凝结，浓缩9.formulation 配方10.phenyl 苯基11.naphthylamine 萘胺phenyl-naphthylamine 苯基萘胺12.classical 传统的，经典的13.available 有用的14.proprietary 所用的，专利的，独占的15.disclose 公开，宣布，透露16.preferable 较好一点的17.protect 保护protect…against(from)保护……免受……之害18.desirable 想望的，理想的19.crack 裂缝，破裂，发生裂缝，弄出裂缝20.flex 弯曲，伸缩21.detrimental 有害的22.copper 铜23.repeat 重复24.phenomenon 现象phenomena 现象（复数）25.dynamic 动态的26.oxidation 氧化27.rest 休息，静止，其余at rest 静止状态28.static 静态的29.so far 迄今，到目前为止30.waxy 蜡状的，蜡样的31.tendency 趋势32.bloom 喷霜，喷出33.film 薄膜喷霜，喷出喷霜，喷出喷霜，Lesson SevenPlasticizers or SoftenersAny material that can be added to rubber to either aid mixing, promote greater elasticity, produce tack, or extend (or replace) a portion of the rubber hydrocarbon (without a loss in physical properties), can be classified as a softener.Making rubber plastic is an expensive operation that can be facililated by the use of plasticizers or softeners. Many substances, such as vegetable and mineral oils, waxes, paraffins, pitch, tar and resins have been used for this purpose. The principle plasticizers are the fatty acid, expecially stearic acid, pine tar, and the so-called mineral rubbers, which are natural asphalts.The most important effects of plasticizers or softeners are as follows:They reduce the cost of mechanical treatment necessary for plasticizing the rubber.They facilitate the addition and uniform distribution of fillers.They allow mastication performed at lower temperature, thus avoiding scorching of the compounded rubber.They make highly filled rubber compounds sufficiently soft for moulding.They increase the adhesiveness of the compound and give tackiness when this is desirable.In the use of plasticizers of softeners, many factors should be considered so that the desired degree of plasticity and adhesiveness can be achieved, and sticking of the compound to rolls and its excess ive softening at elevated temperature can be avoided.Also, too much plasticizer has a harmful effect on the mechanical and aging properties of the finished product. Therefore, plasticization is not a simple problem. Sometime several plasticizers are combined to obtain satisfactory results.Softrners are used in relatively small quantities, 0.5 to 5.0 percent on the rubber, except in some very special cases where the mechanical properties are sacrificed in order to obtain other advantages.In addition to the before mentioned types of softeners, new varieties have been developed form petroleum. They are found, in general, in the aromatic fractions obtained from refining highgrade lubricating oil by selective solvent methods, or by vacuum distillation. These softeners may be used in larger quantities without causing excessive reducing in the mechanical properties.New Words and Expressions1.plasticizer 增塑剂2.softener 软化剂3.promote 提升，增进，晋级4.elasticity 弹性5.tack 自粘6.extend 充填，增充，延伸，扩大7.portion 部分，一份8.operation 操作，作业9.expensive 昂贵的，高价的10.paraffins 石蜡11.pitch 沥青（石油），螺距，节距12.tar 柏油13. .. r esin 树脂14.principal 主要的15.pine 原则，校长pine tar 松树16.mineral 松焦油17.asphalt 矿质橡胶18.plasticize 沥青（煤焦油）19.uniform 增塑，塑炼20.distribution 均匀的21.perform 分布，分配22.scorch 完成23.sufficiently 焦烧24.adhesiveness 足够地25.tackiness 粘合性26.factor 因素27.degree 度，程度28.stick 粘着stick to 粘着，坚持，忠于29.roll 辊筒30.excessive 过量的，过渡的31.elevate 上升elevated 高尚的，高架的，高的32.relatively 相对地33.sacrifice 牺牲，损失，亏本34.addition 附加物，增加，加法（数学）in addition 又in addition to 除……之外，加之35.mention 提到，注意before mentioned 前述的36.variety 变化，种种，多样37.petroleum 石油petro 汽油（英）gasoline, gasoline 汽油（美）38.aromatic 芳香的39.fraction 馏分，级分40.refine 提炼，炼制41.grade 级42.lubricate 使润滑lubricating oil 润滑油43.selective 选择的44.solvent 溶剂，溶解（的）45.vacuum 真空真空的46.distillation 蒸馏47.facilitate 使容易，使得到Lesson EightThe Effect of Rubber Compounding on Rubber PropertiesWe have just discussed the various compounding ingredients and have indicated their prinecipal affects, new we shall look at rubber compounding from a different angle. We shall describe how the properties of the vulcanizate can be modified and how the rubber compound can adapt to manufacturing operations by the addition of suitable ingredients.Tensile Strength This property, which is seldom encountered in the service conditions of rubber, is often used as a measure of their quality.We have noted the effect of reinforcing and inert fillers on the tensile strength. We have also mentioned that addition of reclaimed rubber, factice, crumb rubber and plasticizers would adversely affect the tensile strength, Besides these factors the tensile strength to a certain degree.Modulus A high value of the modulus indicators that the vulcanizate is hard and stiff and a low value points to a soft, flexible product. The modulus can be controlled best by proper choice of accelerator and fillers.Hardness Rubber article seldom call for a lower hardness than that of a pure gum stock. If necessary, the hardness can be reduced by addition of large quantities (up to 80 PHR) or factices or softeners but this also causesreduction in the mechanical product will be.Tear And Abrasion Resistance These two properties vary in substantially the same manner within certain limits. If the highest possible values are sought, carbon black should be used. Additional improvement in these properties can be achieved by proper choice of the accelerator MBT and its derivatives being especially recommended. Reclaimed rubber, factices, and curmb rubber cause a pronounced decrease in these properties.Aging And Fatigue Resistance For resistance to repeated deformations, overfilled, or highly pigmented compounds should be avoided; also, it is imperative to use optimum vulcanization conditions.For heat resistance, large quantities of fillers of plasticizers and sulfur should be used, The EV and SEV systems have been employed recently in many heatresistant compounds and prove successfully due to higher bond energy of mono and disulfur linkages.New Words and Expressions1.modify 改良,改性2.adapt 适应,改编3.adapt to 适应于4.factice 油膏5.crumb 颗粒,点滴,面包屑6.crumb rubber 颗料胶7.adversely 相反地8.influence 影响9.stiff 僵硬的10.gum 纯胶,树胶,涂树胶11.stock 胶料12.manner 方式,态度13.seek 寻求,企图14.derivative 衍生物15.pronounce 发音,宣告,表示16.pronounced 显著地,断然地17.fatigue 疲劳,使疲劳18.deformation 变形19.overfill 过量填充20.overfilled 过量填充的21.pigment 着色剂22.imperative 强制的,不得不的23.optimum 最佳的,最适宜的24.employ 使用,雇用25.due 应付,适当,应到的26.due to 由于,起因于27.bond 键,联络,契约28.mono- 单，一29.di- 双，二30.mono and dissulfur 单硫和双硫31.linkage 键Lesson NineRubber ProcessingThe raw material of rubber manufacture is crude or raw rubber in which various ingredients are incorporated to prepare a compound. This compound is brought into the desired frm and the finished products is obtained by vulcanization or cure.Rubber articles are manufactured by several operations, the most important ones being as follws.Physical treatment of the raw rubber makes it suitable for incorporation of compounding ingredients. This operation is called plasticization of mastication, which is carried out on a mill, in an interal mixer, or in a “plastlentor”----a highspeed screw extruding machine.Incorporation of various substances especially fillers into rubber is called mixing, which is also effected on a mill or in an interal mixer.Pretreatment of the mix to make it suitable for the preparation of the desired product may consist of calemdering, extrusion, impregnating or spreading, depending on the article to be made.Forming the product to be manufactured consists. in general, of the use of a mold with the desired shape and dimension. This step is called molding.Vulcanization or curing the molded article will give the rubber properties which will meet the specifications. This operation is carried out in an autoclave or press.New Words and Expressions1.raw 生的,未加工的,未训练的2.raw material 原料3.crude 天然的,未加工的,粗制的4.bring into 引进,实现,产生5.desire 要求,愿望6.cure 硫化7.several 几个,个别,单独8.physical 物理的,体力的,自然的,物质的9.plasticization 塑化,塑练10.carry out 进行,执行11.internal 内部的12.mixer 混合器,开练机,密练机13.internal mixer 密练机14.plasticator 螺杆塑练机15.screw 螺杆16.pre- 预先17.pretreatment 预加工,预处理18.preparation 制备,准备19.consist of 包括,由……组成20.calender 压延21.extrusion 压出22.impregnate 浸渍,浸浆23.spread 涂胶,刮胶24.mold , mould 模型25.dimension 尺寸26.specification 规格,规定27.autoclave 硫化罐28.press 平板硫化机,压力,出版社,压力机Lesson TenPlasticization (1)Raw rubber, especially natural rubber, has to be plasticized to allow incorporation of the ingredients. The main mechanism of plasticization is chain scission, molecular weight reduction and plasticity increase .It makes the material more easily processable.There are three ways to masticate rubber as follow.Mechanical PlasticizationThis can be carried out on a mixing mill or in an internal mixer, or in a special machine designed for this purpose called plasticator. This is a force chemical process. A thigh temperature (大于175F) and in the presence of air. Rubber down primarily by oxidative degradation. At room temperature the main mechanism of molecular weight reduction is mechanical chain scission.A mixing mill consists essentially of two horizontal side by side rolls which are rotating at different speeds in opposite opposite directions and can be heated or cooled. The gap between the rolls is adjustable and this gap is called the “nip “in rubber terminology. Raw rubber is placed between the rolls which usually have a diameter of 10-20 inch and are water cooled to maintain their temperature at about 140FThe two rolls which are made of special steel are mounted on a support made of last iron or molded steel. In genernal, the bearings of the rear roll are stationary and those of the front roll movable, so that the clearance between the rolls can be varied. The rolls are driven by an electric motor and gear boxes. The front roll is rotated at a speed of about 15-25 r .p .m. The speed of the rear roll is higher, the ratio being 1:1.2 to 1:1.5.Passing the raw rubber repeatedly between the two rolls of the mill will change its physical properties. The hard and compact raw rubber gradually becomes soft. It loses its elestioity and becomes plastic. After a given tim period, which varies with the condition of working from some 10 to 20 minutes, the raw rubber pieces form a soft and plastic strip which rotates together with the front roll. the raw rubber is then considered to be plasticized and is suitable for taking up fillers and other ingredients.New Words and Expressions1.mechanism 机构,机械作用,机理,作用原理2.scission 切断3.chain scission 断链(作用)4.plasticity 塑性5.processable 可加工的6.masticate 塑炼7.force-chemical process 力化学过程8.presence 存在,出度,在场9.primarily 首先,根本上10.oxidative 氧化的11.degradation 降解,裂解12.essentially 实质地,必须地,精华地13.horizontal 水平的14.gap 间隙,缝隙15.adjust 调节16.adjustable 可调节的17.nip 辊缝18.terminology 术语,专门名词19.diameter 直径20.inch 英寸21.maintain 保持,维持22.mount 安装23.support 机架,车架.支架24.cast 铸,25.cast iron 生铁26.bearing 轴承27.rear 后的28.real roll 后辊.29.stationary 固定的,30.movable 可动的31.clearance 缝隙32.gear 齿轮33.gear box 齿轮箱34.revolution 革命,公转,旋转,一转35.r . p . m.(revolution per minute) 每分种转速36.ratio 比,速比pact 紧密的,简洁的,合同,协定,契约38.gradually 逐渐地39.period 时期.期间。