江西制造职业技术学院 江西制造职业技术学院 English for Mechanical Engineering Reading Comprehension 机械专业英语阅读

Unit One : The Foundation of Metalworking

Passage Two Dimension and Tolerance

Learning Objectives To understand the whole passage. To master how to read the dimension of part in English correctly. ★ ★ ★ To know different kinds of fit.

Training Target In this part, you should try your best to form good reading habit. In order to avoid your ill habits such as regression, you should read with the card showed to you in the preface of this book.

Teaching Procedures Step D: Assignment Step C: Structural Analyzing Step B: Passage Understanding Step A: Lead in

Lead-in: Do you know? Do you know how to read a dimension in English ?

Lead-in: Do you know? mm: millimeter cm: centimeter dm: decimeter nm: nanometer

Lead-in ： Do you know? How to read the dimension in English: ＋ plus, add, and; － minus × multiple ÷ divide 63.5± 0.08mm: sixty three point five plus minus zero point zero eight millimeter.

29.98± 0.03mm: twenty nine point nine eight plus minus zero point zero three. Lead-in ： Do you know? 30± 0.15mm: Thirty plus minus zero point one five.

New words and expressions Tolerance. n. 公差，容忍， vt. 给 …… 规定公差 e.g. zero tolerance 零允差 basic tolerance 基本公差 tolerance deviation 容许偏差 tolerance limit 公差极限 tolerance frequency 容限频率 salt tolerance 耐盐度

1.What is close tolerance? 3. What is nominal size? Passage understanding 2.What is allowance? Find out the answers after fast reading.

Passage understanding The definition of close tolerance: Close tolerance: Dimensions given close tolerances mean that part must fit properly with some other part. 紧公差的尺寸表示该零件要与其他零件恰 当的配合。

Passage understanding The definition of allowance: Allowance: It is the minimum clearance space intended between mating parts and represents the condition of tightest permissible fit. 容差是在两个配合零件间可允许的最小间 隙，表示配合可允许的最紧状态 。

Passage understanding The definition of nominal size ： Nominal size: In dimensioning a drawing, the numbers placed in the dimension lines represent dimensions that are only approximate and do not represent any degree of accuracy unless so stated by the designer.

Difficult Point In dimensioning a drawing, the numbers placed in the dimension lines represent dimensions that are only approximate and do not represent any degree of accuracy unless so stated by the designer. 状语 : in dimension a drawing 主语： the numbers; 定语 : placed in the dimension lines 谓语： represent; 宾语： dimensions 定语从句： that are only…

Difficult Point However, it is almost impossible to produce any component to the exact dimension through any of the known manufacturing processes. 然而，用已知的任何一种制造方法都不可能将零件 加工出完全精确的尺寸。 基本句型： It is impossible to do sth 介词 : through= by 方式状语 : any of the known manufacturing processes.

Difficult Point In mass production, where mating parts must be interchangeable, unilateral tolerances are customary. 状语 : in mass production 主语： unilateral; 系表结构 : are customary 非限制性定语从句： where mating parts must be interchangeable 在大规模生产中，要求互相配合的零件是可互换的， 因此单向公差更适合。

Structural Analyzing Para 1. What is dimension and tolerance. Para 2. Three different kinds of fit. Para 3. The definition of close tolerance. Para 4. What is allowance. Para 5. Two main types of tolerance. The main idea of each paragraph.

exercises Translate the following words into English. 公称尺寸 单向公差 容差 过盈配合 极限尺 寸标注 间隙配合 偏差 过渡配合 尺寸 双向公差 Nominal size Unilateral tolerance allowance Interference fit Limit dimensioning Clearance fit deviation Transition fit dimension Bilateral tolerance

exercises Write true or false beside the following statements about the text. 1. The normal size is the designation used for the purpose of general identification. 2. Each dimension is allowed a certain degree of variation within tolerance. 3. Manufacturing costs decrease as tolerance become smaller. 4. A tolerance is the total permissible variation in the size of a part. ( T ) ( F ) ( T )

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