Vulcanization is still the most important operation in producing a usable rubble article.

Vulcanization

Vulcanization is still the most important operation in producing a usable rubble article. Various compounding ingredient merely modify properties, and the use of accelerators, of course, makes volume production possible. It is interesting to note that, even though vulcanization has been known and used for over 150 years, there has been little change in the basic process. Sulfur is still the most important curing ingredient, and steam is still the most important source of controlled temperature.
After rubber compounds have been properly mixed and shaped into blanks or fabricated into a composite item, they must be vulcanized by one of many processes. During vulcanization, the following changes occur:
1. The long chain of the rubber molecules become crosslinked by reactions with the vulcanizing agent to form three-dimensional structures.
2. The rubber loses its tackiness and becomes insoluble in solvents and is more resistant to deterioration normally caused by heat, light and aging.
3. The mechanical properties of compound have been increased.
Finished articles can be cured by different techniques. The four most common methods of hot vulcanization are briefly outlined as follows:
1. In moulds under hydraulic pressure between steam or electrically heated platens in a ‘daylight’ press.
2. In moulds under hydraulic pressure entirely surrounded by steam in an autoclave press.
3. Wrapped in cloth, or embedded in an inert powder such as talc, in live steam under pressure; the so-called ‘open steam’ cure.
4. Directly in hot air, at atmospheric or raised pressure, the ‘dry-heat’ method of vulcanization.
Air has relatively low thermal capacity capacity as compared with steam. Its thermal conductivity also much lower. Heat is therefore not transferred quickly by hot air to the rubber articles to be vulcanized. A given compound normally takes about twice as long to cure in hot air as in saturaled steam. On the other than mould curing. Because of the slowness of vulcanization accelerators in compounds that are vulcanized in hot air should be active at a relatively low temperature in order that the surface of the articles acquires some stability through an early onset of vulca nization.
New Words and Expressions

1.usable 可用的，可使用的
2.merely 仅仅，只不过
3.volume 卷，体积，大量，音量
4. basic 基本的
5.steam 汽，蒸汽
6.source 源，来源
7.fabricate 建造，制造，捏造
8.composite 合成的，集成的，综合的
9.item 条款，项目
composite item 组合件
10.occur 发生，存在，出现，想到
11.insoluble 不可溶解的，不能解决的
soluble 可溶解的，可解决的
12.cause 引起，使发生
原因，理由，事业
13.technique 技术，技巧，手法
（=technic）
14.brief 简短的，简洁的
摘要，大纲，扼要的
15.hydraulic 水力的，液力的，水压的，液压的
hydraulic pressure 液压
16.platen 加热板
17.daylight press 平板硫化机
18.autoclave press （立式）硫化罐
19.embed(或imbed) 埋放
20.live 活的，燃烧的，活跃的
live steam 直接蒸气
21.open steam cure 直接蒸气硫化
22.dry-heat 热空气
23.relatively 有联系的，有关系的，相对的
relative 亲戚，关系词
24.thermal capacity 热容量
25.as compared with 与……相比
26.conductivity 传导率，传导能，传导系数
thermal conductivity 导热性，导热系数
27.saturated 使湿透，使饱和
saturated steam 饱和蒸汽
28.call for 要求，需要
29.acquire 获得，带来，得到
30.stability 坚固，稳定
31.oneset 进攻，发作