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CHAPTER XX. GENERALISATION OF SHOP PROCESSES.
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Having thus far treated of such general principles and facts connected with practical mechanics as might properly precede, and be of use in, the study of actual manipulation in a workshop, we come next to casting, forging, and finishing, with other details that involve manual as well as mental skill, and to which the term "processes" will apply.

As these shop processes or operations are more or less connected, and run one into the other, it will be necessary at the beginning to give a short summary of them, stating the general object of each, that may serve to render the detailed1 remarks more intelligible2 to the reader as he comes to them in their consecutive3 order.

Designing, or generating the plans of machinery4, may be considered the leading element in engineering manufactures or machine construction, that one to which all others are subordinate, [75] both in order and importance, and is that branch to which engineering knowledge is especially directed. Designing should consist, first, in assuming certain results, and, secondly5, in conceiving of mechanical agents to produce these results. It comprehends the geometry of movements, the disposition6 and arrangement of material, the endurance of wearing surfaces, adjustments, symmetry; in short, all the conditions of machine operation and machine construction. This subject will be again treated of at more length in another section.

Draughting, or drawing, as it is more commonly called, is a means by which mental conceptions are conveyed from one person to another; it is the language of mechanics, and takes the place of words, which are insufficient7 to convey mechanical ideas in an intelligible manner.

Drawings represent and explain the machinery to which they relate as the symbols in algebra8 represent quantities, and in a degree admit of the same modifications9 and experiments to which the machinery itself could be subjected if it were already constructed. Drawings are also an important aid in developing designs or conceptions. It is impossible to conceive of, and retain in the mind, all the parts of a complicated machine, and their relation to each other, without some aid to fix the various ideas as they arise, and keep them in sight for comparison; like compiling statistics, the footings must be kept at hand for reference, and to determine the relation that one thing may bear to another.

In the workshop, the objects of drawing are to communicate plans and dimensions to the workmen, and to enable a division of the labour, so that the several parts of a machine may be operated upon by different workmen at the same time—also to enable classification and estimates of cost to be made, and records kept.

Drawings are, in fact, the base of shop system, upon which depends not only the accuracy and uniformity of what is produced, but also, in a great degree, its cost. Complete drawings of whatever is made are now considered indispensable in the best regulated establishments; yet we are not so far removed from a time when most work was made without drawings, but what we may contrast the present system with that which existed but a few years ago, when to construct [76]a new machine was a great undertaking10, involving generally many experiments and mistakes.

Pattern-making relates to the construction of duplicate models for the moulded parts of machinery, and involves a knowledge of shrinkage and cooling strains, the manner of moulding and proper position of pieces, when cast, to ensure soundness in particular parts. As a branch of machine manufacture, pattern-making requires a large amount of special knowledge, and a high degree of skill; for in no other department is there so much that must be left to the discretion11 and judgment12 of workmen.

Pattern-makers have to thoroughly13 understand drawings, in order to reproduce them on the trestle boards with allowance for shrinkage, and to determine the cores; they must also understand moulding, casting, fitting, and finishing. Pattern-making as a branch of machine manufacture, should rank next to designing and drafting.

Founding and casting relate to forming parts of machinery by pouring melted metal into moulds, the force of gravity alone being sufficient to press or shape it into even complicated forms. As a process for shaping such metal as is not injured by the high degree of heat required in melting, moulding is the cheapest and most expeditious14 of all means, even for forms of regular outline, while the importance of moulding in producing irregular forms is such that without this process the whole system of machine construction would have to be changed. Founding operations are divided into two classes, known technically15 as green sand moulding, and loam16 or dry sand moulding; the first, when patterns or duplicates are used to form the moulds, and the second, when the moulds are built by hand without the aid of complete patterns. Founding involves a knowledge of mixing and melting metals such as are used in machine construction, the preparing and setting of cores for the internal displacement17 of the metal, cooling and shrinking strains, chills, and many other things that are more or less special, and can only be learned and understood from actual observation and practice.

Forging relates to shaping metal by compression or blows when it is in a heated and softened18 condition; as a process, it is an intermediate one between casting and what may be called the cold processes. Forging also relates to welding or joining [77] pieces together by sudden heating that melts the surface only, and then by forcing the pieces together while in this softened or semi-fused state. Forging includes, in ordinary practice, the preparation of cutting tools, and tempering them to various degrees of hardness as the nature of the work for which they are intended may require; also the construction of furnaces for heating the material, and mechanical devices for handling it when hot, with the various operations for shaping, which, as in the case of casting, can only be fully19 understood by experience and observation.

Finishing and fitting relates to giving true and accurate dimensions to the parts of machinery that come in contact with each other and are joined together or move upon each other, and consists in cutting away the surplus material which has to be left in founding and forging because of the heated and expanded condition in which the material is treated in these last processes. In finishing, material is operated upon at its normal temperature, in which condition it can be handled, gauged20, or measured, and will retain its shape after it is fitted. Finishing comprehends all operations of cutting and abrading21, such as turning, boring, planing and grinding, also the handling of material; it is considered the leading department in shop manipulation, because it is the one where the work constructed is organised and brought together. The fitting shop is also that department to which drawings especially apply, and other preparatory operations are usually made subservient22 to the fitting processes.

Shop system may also be classed as a branch of engineering work; it relates to the classification of machines and their parts by symbols and numbers, to records of weight, the expense of cast, forged, and finished parts, and apportions23 the cost of finished machinery among the different departments. Shop system also includes the maintenance of standard dimensions, the classification and cost of labour, with other matters that partake both of a mechanical and a commercial nature.

In order to render what is said of shop processes more easily understood, it will be necessary to change the order in which they have been named. Designing, and many matters connected with the operation of machines, will be more easily learned and understood after having gone through with what may be called the constructive24 operations, such as involve manual skill.
 
(1.) Name the different departments of an engineering establishment.—(2.) What does the engineering establishment include?—(3.) What does the commercial department include?—(4.) The foundry department?—(5.) The forging department?—(6.) The fitting department?—(7.) What does the term shop system mean as generally employed?

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1 detailed xuNzms     
adj.详细的,详尽的,极注意细节的,完全的
参考例句:
  • He had made a detailed study of the terrain.他对地形作了缜密的研究。
  • A detailed list of our publications is available on request.我们的出版物有一份详细的目录备索。
2 intelligible rbBzT     
adj.可理解的,明白易懂的,清楚的
参考例句:
  • This report would be intelligible only to an expert in computing.只有计算机运算专家才能看懂这份报告。
  • His argument was barely intelligible.他的论点不易理解。
3 consecutive DpPz0     
adj.连续的,联贯的,始终一贯的
参考例句:
  • It has rained for four consecutive days.已连续下了四天雨。
  • The policy of our Party is consecutive.我党的政策始终如一。
4 machinery CAdxb     
n.(总称)机械,机器;机构
参考例句:
  • Has the machinery been put up ready for the broadcast?广播器材安装完毕了吗?
  • Machinery ought to be well maintained all the time.机器应该随时注意维护。
5 secondly cjazXx     
adv.第二,其次
参考例句:
  • Secondly,use your own head and present your point of view.第二,动脑筋提出自己的见解。
  • Secondly it is necessary to define the applied load.其次,需要确定所作用的载荷。
6 disposition GljzO     
n.性情,性格;意向,倾向;排列,部署
参考例句:
  • He has made a good disposition of his property.他已对财产作了妥善处理。
  • He has a cheerful disposition.他性情开朗。
7 insufficient L5vxu     
adj.(for,of)不足的,不够的
参考例句:
  • There was insufficient evidence to convict him.没有足够证据给他定罪。
  • In their day scientific knowledge was insufficient to settle the matter.在他们的时代,科学知识还不能足以解决这些问题。
8 algebra MKRyW     
n.代数学
参考例句:
  • He was not good at algebra in middle school.他中学时不擅长代数。
  • The boy can't figure out the algebra problems.这个男孩做不出这道代数题。
9 modifications aab0760046b3cea52940f1668245e65d     
n.缓和( modification的名词复数 );限制;更改;改变
参考例句:
  • The engine was pulled apart for modifications and then reassembled. 发动机被拆开改型,然后再组装起来。 来自《简明英汉词典》
  • The original plan had undergone fairly extensive modifications. 原计划已经作了相当大的修改。 来自《简明英汉词典》
10 undertaking Mfkz7S     
n.保证,许诺,事业
参考例句:
  • He gave her an undertaking that he would pay the money back with in a year.他向她做了一年内还钱的保证。
  • He is too timid to venture upon an undertaking.他太胆小,不敢从事任何事业。
11 discretion FZQzm     
n.谨慎;随意处理
参考例句:
  • You must show discretion in choosing your friend.你择友时必须慎重。
  • Please use your best discretion to handle the matter.请慎重处理此事。
12 judgment e3xxC     
n.审判;判断力,识别力,看法,意见
参考例句:
  • The chairman flatters himself on his judgment of people.主席自认为他审视人比别人高明。
  • He's a man of excellent judgment.他眼力过人。
13 thoroughly sgmz0J     
adv.完全地,彻底地,十足地
参考例句:
  • The soil must be thoroughly turned over before planting.一定要先把土地深翻一遍再下种。
  • The soldiers have been thoroughly instructed in the care of their weapons.士兵们都系统地接受过保护武器的训练。
14 expeditious Ehwze     
adj.迅速的,敏捷的
参考例句:
  • They are almost as expeditious and effectual as Aladdin's lamp.他们几乎像如意神灯那么迅速有效。
  • It is more convenien,expeditious and economical than telephone or telegram.它比电话或电报更方便、迅速和经济。
15 technically wqYwV     
adv.专门地,技术上地
参考例句:
  • Technically it is the most advanced equipment ever.从技术上说,这是最先进的设备。
  • The tomato is technically a fruit,although it is eaten as a vegetable.严格地说,西红柿是一种水果,尽管它是当作蔬菜吃的。
16 loam 5xbyX     
n.沃土
参考例句:
  • Plant the seeds in good loam.把种子种在好的壤土里。
  • One occupies relatively dry sandy loam soils.一个则占据较干旱的沙壤土。
17 displacement T98yU     
n.移置,取代,位移,排水量
参考例句:
  • They said that time is the feeling of spatial displacement.他们说时间是空间位移的感觉。
  • The displacement of all my energy into caring for the baby.我所有精力都放在了照顾宝宝上。
18 softened 19151c4e3297eb1618bed6a05d92b4fe     
(使)变软( soften的过去式和过去分词 ); 缓解打击; 缓和; 安慰
参考例句:
  • His smile softened slightly. 他的微笑稍柔和了些。
  • The ice cream softened and began to melt. 冰淇淋开始变软并开始融化。
19 fully Gfuzd     
adv.完全地,全部地,彻底地;充分地
参考例句:
  • The doctor asked me to breathe in,then to breathe out fully.医生让我先吸气,然后全部呼出。
  • They soon became fully integrated into the local community.他们很快就完全融入了当地人的圈子。
20 gauged 6f854687622bacc0cb4b24ec967e9983     
adj.校准的;标准的;量规的;量计的v.(用仪器)测量( gauge的过去式和过去分词 );估计;计量;划分
参考例句:
  • He picked up the calipers and gauged carefully. 他拿起卡钳仔细测量。 来自《现代汉英综合大词典》
  • Distance is gauged by journey time rather than miles. 距离以行程时间而非英里数来计算。 来自辞典例句
21 abrading 8e12dee288abd0a8c2c417fe66346d69     
v.刮擦( abrade的现在分词 );(在精神方面)折磨(人);消磨(意志、精神等);使精疲力尽
参考例句:
22 subservient WqByt     
adj.卑屈的,阿谀的
参考例句:
  • He was subservient and servile.他低声下气、卑躬屈膝。
  • It was horrible to have to be affable and subservient.不得不强作欢颜卖弄风骚,真是太可怕了。
23 apportions 181643bb1f47110c81fddc8412d7a4fa     
n.分摊,分配( apportion的名词复数 )
参考例句:
24 constructive AZDyr     
adj.建设的,建设性的
参考例句:
  • We welcome constructive criticism.我们乐意接受有建设性的批评。
  • He is beginning to deal with his anger in a constructive way.他开始用建设性的方法处理自己的怒气。


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