For rubber products, raw rubber is required to have a certain degree of plasticity. For example, the plasticity of raw rubber is required to be about 0.25 to 0.35 for the rubber of molded industrial products. The plasticity requirements for calendering, extrusion, sponge glue, mucilage and other sizing materials are about 0.4 to 0.6. If the plastic lift does not reach the required plasticity, it will bring great difficulties to the mixing, and at the same time, the quality of the product cannot be guaranteed. Therefore, the raw rubber with high Mooney viscosity must be masticated to obtain the required plasticity to ensure the smooth progress of the subsequent processes. If the plasticity is too high or too low, what adverse effects will it have on rubber processing and products? If the raw rubber is insufficiently mixed and the plasticity does not meet the requirements, the mixing will be difficult, and the phenomenon of roll off will occur; in addition, the shrinkage of the rubber compound will occur. rate increased. If the raw rubber is excessively plasticated, the hardness and tensile strength of the mixed rubber will decrease, and the resistance to aging of the medium will decrease. Therefore, it is very important to do a good job in the plasticization of raw rubber according to the requirements of different products.
Not every raw rubber needs to be masticated. This depends on the rubber mastication characteristics, Mooney viscosity, etc. Under normal circumstances, the Mooney viscosity (ML100°C 1+4) below 80 does not need to be masticated, except for special-purpose rubber compounds, and it can be kneaded several times before kneading. The raw rubber with Mooney viscosity (ML100℃1+4) above 80 needs to be masticated, but this is not entirely the case. For example, although the Mooney viscosity of fluororubber is 65-180, its molecular chain is rigid and stable in nature. After a long time of plasticizing, the viscosity of raw rubber not only decreases very little, but sometimes increases. Therefore, fluororubber can be directly mixed without mastication.
From the perspective of the domestic rubber processing industry, the main plasticizing products are unsaturated natural rubber and hard nitrile rubber. For EPDM, butyl, neoprene, cis-butadiene and acrylate adhesives, if used for molded products, they do not need to be masticated and can be directly mixed. But for calendered, extruded and sponge products, in order to ensure that the shrinkage rate of the product is small and the surface of the product is smooth, even if the raw rubber can be mixed without mastication, multi-stage mastication should be carried out to improve the plasticity of the raw rubber. Produce qualified products. In recent years, soft butadiene rubber imported from abroad, such as Japanese nitrile 240S, Russia's CKH-26, etc., has a low Mooney viscosity value. Generally, it is not necessary to carry out mastication, but to carry out kneading directly.
The following will speed up the plasticizing methods and precautions of natural rubber and nitrile rubber.
Because of its high Mooney viscosity and high mechanical strength, natural rubber is very difficult to mix if it is not masticated (here mainly refers to 1#~5# smoked sheet rubber). Therefore, natural rubber must be masticated before mixing in order to obtain suitable plasticity.
Because natural rubber is crystalline rubber, especially in winter, if the crystallization is not removed, it will bring great difficulties to cutting rubber and damage the equipment. Therefore, before cutting the glue, it is necessary to bake the glue. Baking glue is generally carried out in the glue drying room, the temperature is about 60 ℃, and the time is 48 hours.
After the raw rubber is taken out from the drying room, first remove the impurities on the surface of the raw rubber, and then use a rubber cutting machine to cut into small pieces of about 5 kg for use. It is best to separate the glue blocks with a release agent to avoid sticking to each other and keep them clean. The cut rubber block needs to be broken, and the factory is generally carried out on the rubber mixing machine. Taking a 14-inch rubber mixer as an example, first narrow the baffle (the working surface accounts for about 2/3 of the length of the roller), and adjust the roller distance (0.5mm), in order to prevent the rubber mixer from being overloaded and causing " trip” and damage the equipment. Then put the rubber blocks into the rubber mixing machine one by one by one end of the big cone, and the amount of glue is about 20 kg. When loading glue, you should face the rubber mixing machine sideways or stand on the side of the rubber mixing machine to prevent the glue from popping out and hurting people, and at the same time turn on the cooling water. The broken raw rubber should be masticated in time, and should not be parked for a long time. Because of the long time of parking, the raw rubber will re-stick into a ball. It is more troublesome to cut and break the glue again.
When plasticizing, put the raw rubber into the plasticizer, and let it fall directly into the material tray through the roll distance, without wrapping the roll. It is repeated for about 30 minutes, and the roll temperature is controlled below 50°C. If the temperature is too high, the phenomenon of false plasticity will occur (once the plasticized rubber has cooled, the phenomenon of recovery will occur). In order to avoid this phenomenon, the lower the temperature of the roller, the better, and the increase of the mechanical shear force is conducive to the degradation of rubber macromolecules, so as to obtain the plasticizing effect.
In the first ten minutes after the start of mastication, the natural rubber mastication effect is very obvious. The increase in plasticity slows down over time. If the mixing is stopped at this time, it will be quickly reflected during the mixing: the plastic compound is not easy to wrap the roll, even if the roll is wrapped, the surface is not smooth, and the powder cannot be added. At this time, the plasticized rubber should be re-thinned and plasticized. until a satisfactory result is obtained.
From the above situation, despite the continuous extension of time, the increase in the plasticity of natural rubber is not as significant as in the first ten minutes. But it does not mean that only ten minutes of plasticizing will do. On the contrary, subsequent plasticizing is necessary. Otherwise, the labor intensity will be increased and the mixing time will be prolonged during mixing, and the quality of the mixed rubber cannot be guaranteed.
The level of plasticization and the quality of it can be observed by those with operating experience through the naked eye. The plasticized raw rubber surface is smooth and translucent. At this time, the raw rubber has basically reached its plasticity. If you are inexperienced, you can also relax the roll distance (2 to 3 mm) to wrap it around the front roll. If the surface of the raw rubber is not smooth, it means that the mastication is not enough. If the surface is smooth, it means that the mastication is good. Of course, if the plasticizing is not enough, it must be re-plasticized until a satisfactory plasticizing effect is obtained.
The roll distance of plasticized raw rubber is relaxed to 2-3mm for the lower sheet. The film is 80 cm long, 40 cm wide and 0.4 cm thick. Cool naturally, and then use a barrier agent. You can also directly use the scale to weigh the required amount of the mixed rubber. The plasticized raw rubber is generally used after being parked for 8 hours.
Nitrile rubber, here mainly refers to hard nitrile rubber, the initial Mooney viscosity is 90-120, and the plasticity and process performance are extremely poor. If it is not masticated, the mixing cannot be carried out. Its raw rubber has high toughness and high heat generation in plasticizing, so plasticizing is particularly difficult. Compared with natural rubber, the plasticizing temperature of nitrile rubber is lower than that of natural rubber (about 40°C), and the loading capacity is about 15 kg less (70% of natural rubber). As the acrylonitrile content of nitrile rubber increases, the mixing becomes easier. Under normal circumstances, nitrile-26, nitrile-40, these nitrile rubber compounds used for molded products, can be plasticized for a period of about 40 minutes. The nitrile rubber with special requirements needs to undergo multi-stage mastication in order to obtain satisfactory plasticity. For nitrile-18, after a period of mastication, the plasticity is only about 0.18, which is too low for rubber products, and multi-stage mastication must be carried out. After 35 minutes of plasticizing, the nitrile rubber-18 has a plasticity of about 0.23, which basically meets the processing requirements.
The methods of plasticizing nitrile rubber and plasticizing natural rubber are basically the same. The low-temperature thin-pass method and the segmented plasticizing method are usually used. The surface of the plasticized raw rubber is smooth and shiny, and there are no large or small holes on the surface after wrapping.
In the process of plasticizing, there are many factors that affect the plasticizing effect of raw rubber. But for the specific operators, it is nothing more than the influence of the temperature, roll distance, time, rubber loading capacity and operation proficiency of the rubber mixing machine.
Practice has proved that the lower the roll temperature, the better the plasticizing effect. However, in actual operation, the cooling of the roller is limited by various objective reasons, and it is impossible to fully achieve the desired effect. Therefore, the segmented plasticizing method is often used to make up for its deficiencies. The cold air circulation climbing frame device can also be used to speed up the cooling of the film and improve the plasticizing effect.
The smaller the roll distance, the better the plasticizing effect. The raw rubber is passed through the rollers with a small roll distance. On the one hand, the shearing force of raw rubber is large, which makes the rubber macromolecules degrade rapidly; on the other hand, the thinner the film, the faster the heat dissipation. This is of great benefit to the plasticizing effect. We have done a comparative test. Compared with the roll distance of 0.5mm and the roll distance of 1mm, the larger the roll distance, the longer the plasticizing time, about 10 minutes. And the plasticizing quality without small roll distance is good.
Similarly, the amount of glue loaded also directly affects the plasticizing effect of raw rubber. It can be imagined that the raw rubber with a large amount of glue will pass through the gap for a long time. In the same plasticizing time, the plasticizing effect with a small amount of glue is better than that with a large amount of glue. Some operators are greedy for speed during plasticizing, and the amount of glue loaded is much higher than the specified requirements, which is very wrong. If the amount of glue loaded is too much, firstly the equipment cannot bear it. Under overload operation, it is very easy to "trip" and also increase the risk of damage to the equipment; not good too. Therefore, the amount of glue loaded depends on the equipment and type of glue, and the amount of glue loaded cannot be arbitrarily increased. Generally, the loading amount of synthetic rubber is about 20% less than that of natural rubber.
Some synthetic rubbers are unstable in quality during synthesis, and the quality of each piece of rubber varies greatly. A person with operating experience can see at a glance which piece of rubber takes a relatively short time for plasticization, and which piece of rubber takes longer to plasticize. Experienced operators often pay less attention to the concept of time when plasticating, and rely on the effect of plasticating. For raw rubber with poor quality, the plasticizing time is often longer than the specified time. We have a less mature experience. Taking nitrile-26 as an example, if the raw rubber block is black, then the rubber is easy to be masticated. If the raw rubber is whitish, it is not easy to masticate. As for whether the content of acrylonitrile in the above two blocks is different? Or other problems during synthesis, we have not done any tests in this regard, so we cannot jump to conclusions. During mastication, the whitish raw rubber only feels that the "moisture" is large, and it is difficult for the raw rubber to pass through the roll gap, which increases the mixing time. If the same mixing time is used, the quality of the rubber compound is definitely not good. The domestic EPDM rubber also has the above problems. The black raw rubber is easy to wrap the roll during mixing, and the white raw rubber is more difficult to wrap the roll. For some raw rubber, it takes about 20 minutes to wrap the roll, and the mixing time is prolonged invisibly.
Disclaimer: The picture materials and articles on this platform come from the Internet, so the copyright belongs to the original author. If there is any infringement on your copyright and interests, please contact us, we will apologize and delete it quickly. Article source: Rubber Technology Network
Latest news
- The Combination and Foaming Process of
- Famous tire enterprise with multiple d
- Ministry of Commerce Initiate a final
- The Effect of Carbon Black on the Cutt
- Stop work orders encounter rising pric
- Lanzhou Petrochemical's carboxylated n
Contact us
- ADD: Room 4210, CEC Business Hall, No. 121-4, Nanjing South Street, Heping District, Shenyang
- TEL: 13644907299
- FAX: 024-25361668
- E-mail: boss@long-green.cn
> Company new