Plasticization (1)

Plasticization (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 Plasticization
This 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 140F
The 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 Expressions
1. 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
37. compact 紧密的,简洁的,合同,协定,契约
38. gradually 逐渐地
39. period 时期.期间
40. strip 胶条,剥除
41. take up 吸取,接纳,开始
42. Fahrenheit 华氏温度表