As remarked in the case of other machines treated of, there is no use of describing the mechanism1 of trip-hammers; it is presumed that every engineer apprentice2 has seen trip-hammers, or can do so; and the plan here is to deal especially with what he cannot see, and would not be likely to learn by casual observation.
One of the peculiarities4 of trip-hammers as machines is the mechanical difficulties in connecting them with the driving power, especially in cases where there are a number of hammers to be driven from one shaft5.
The sudden and varied6 resistance to line shafts7 tends to loosen couplings, destroy gearing, and produce sudden strains that are unknown in other cases; and shafting8 arranged with the usual proportions for transmitting power will soon fail if applied9 to driving trip-hammers. Rigid10 connections or metal attachments11 ace12 impracticable, and a slipping belt arranged so as to have the tension varied at will is the usual and almost the only successful means of transmitting power to hammers. The motion of trip-hammers is a curious problem; a head and die weighing, together with the irons for attaching them, one hundred pounds, will, with a helve eight feet long, strike from two to three hundred blows a minute. This speed exceeds anything that could be attained13 by a direct reciprocal motion given to the hammer-head by a crank, and far exceeds any rate of speed that would be assumed from theoretical inference. The hammer-helve being of wood, is elastic14, and acts like a vibrating spring, its vibrations15 keeping in unison16 with the speed of the tripping points. The whole machine, in fact, must be constructed upon a principle of elasticity17 throughout, and in this regard stands as an exception to almost every other known machine. The framing for supporting the trunnions, which one without experience would suppose should be very rigid and solid, is found to answer best when composed of timber, and still better when this timber is laid up in a manner that allows the structure to spring and [107] yield. Starting at the dies, and following back through the details of a trip-hammer to the driving power, the apprentice may note how many parts contribute to this principle of elasticity: First—the wooden helve, both in front of and behind the trunnion; next—the trunnion bar, which is usually a flat section mounted on pivot18 points; third—the elasticity of the framing called the 'husk,' and finally the frictional belt. This will convey an idea of the elasticity required in connecting the hammer-head with the driving power, a matter to be borne in mind, as it will be again referred to.
Another peculiar3 feature in trip-hammers is the rapidity with which crystallisation takes place in the attachments for holding the die blocks to the helves, where no elastic medium can be interposed to break the concussion19 of the dies. Bolts to pass through the helve, although made from the most fibrous Swedish iron, will on some kinds of work not last for more than ten days' use, and often break in a single day. The safest mode of attaching die blocks, and the one most common, is to forge them solid, with an eye or a band to surround the end of the helve.
At the risk of laying down a proposition not warranted by science, I will mention, in connection with this matter of crystallisation, that metal when disposed in the form of a ring, for some strange reason seems to evade20 the influences which produce crystalline change. A hand-hammer, for example, may be worn away and remain fibrous; the links of chains and the tires of waggon21 wheels do not become crystallised; even the tires on locomotive wheels seem to withstand this influence, although the conditions of their use are such as to promote crystallisation.
Among exceptions to the ordinary plans of constructing trip-hammers, may be mentioned those employed in the American Armoury at Springfield, U.S., where small hammers with rigid frames and helves, the latter thirty inches long, forged from Lowmoor iron, are run at a speed of 'six hundred blows a minute.' As an example, however, they prove the necessity for elasticity, because the helves and other parts have to be often renewed, although the duty performed is very light, such as making small screws.
(1.) What limits the speed at which the reciprocating22 parts of machines may act?—(2.) What is the nature of reciprocal motion produced by cranks?—(3.) Can reciprocating movement be uniform in such [108] machines as power-hammers, saws, or pumps?—(4.) What effect as to the rate of movement is produced by the elastic connections of a trip-hammer?
点击
收听单词发音
收听单词发音 |
1
mechanism
|
|
| n.机械装置；机构，结构 | |
参考例句： |
|
|
|
|
2
apprentice
|
|
| n.学徒，徒弟 | |
参考例句： |
|
|
|
|
3
peculiar
|
|
| adj.古怪的，异常的；特殊的，特有的 | |
参考例句： |
|
|
|
|
4
peculiarities
|
|
| n. 特质, 特性, 怪癖, 古怪 | |
参考例句： |
|
|
|
|
5
shaft
|
|
| n.(工具的)柄，杆状物 | |
参考例句： |
|
|
|
|
6
varied
|
|
| adj.多样的，多变化的 | |
参考例句： |
|
|
|
|
7
shafts
|
|
| n.轴( shaft的名词复数 )；（箭、高尔夫球棒等的）杆；通风井；一阵（疼痛、害怕等） | |
参考例句： |
|
|
|
|
8
shafting
|
|
| n.轴系；制轴材料；欺骗；怠慢 | |
参考例句： |
|
|
|
|
9
applied
|
|
| adj.应用的；v.应用，适用 | |
参考例句： |
|
|
|
|
10
rigid
|
|
| adj.严格的，死板的；刚硬的，僵硬的 | |
参考例句： |
|
|
|
|
11
attachments
|
|
| n.（用电子邮件发送的）附件( attachment的名词复数 )；附着；连接；附属物 | |
参考例句： |
|
|
|
|
12
ace
|
|
| n.A牌；发球得分；佼佼者；adj.杰出的 | |
参考例句： |
|
|
|
|
13
attained
|
|
| （通常经过努力）实现( attain的过去式和过去分词 )； 达到； 获得； 达到（某年龄、水平、状况） | |
参考例句： |
|
|
|
|
14
elastic
|
|
| n.橡皮圈，松紧带；adj.有弹性的；灵活的 | |
参考例句： |
|
|
|
|
15
vibrations
|
|
| n.摆动( vibration的名词复数 )；震动；感受；（偏离平衡位置的）一次性往复振动 | |
参考例句： |
|
|
|
|
16
unison
|
|
| n.步调一致，行动一致 | |
参考例句： |
|
|
|
|
17
elasticity
|
|
| n.弹性，伸缩力 | |
参考例句： |
|
|
|
|
18
pivot
|
|
| v.在枢轴上转动；装枢轴，枢轴；adj.枢轴的 | |
参考例句： |
|
|
|
|
19
concussion
|
|
| n.脑震荡；震动 | |
参考例句： |
|
|
|
|
20
evade
|
|
| vt.逃避，回避；避开，躲避 | |
参考例句： |
|
|
|
|
21
waggon
|
|
| n.运货马车，运货车；敞篷车箱 | |
参考例句： |
|
|
|
|
22
reciprocating
|
|
| adj.往复的；来回的；交替的；摆动的v.报答，酬答( reciprocate的现在分词 )；（机器的部件）直线往复运动 | |
参考例句： |
|
|
|
| 欢迎访问英文小说网 |