Mixing is one of the most important and complex steps in rubber processing. It is also one of the processes most prone to quality fluctuations. The quality of the rubber compound directly affects the quality of the product. Therefore, it is very important to do a good job of rubber mixing.
As a rubber mixer, how to do a good job of rubber mixing? I think in addition to strictly mastering the necessary knowledge of each rubber type, such as the mixing characteristics and dosing sequence, it is necessary to work hard, think hard, and mix rubber with heart. Only in this way is a more qualified rubber smelter.
To ensure the quality of the mixed rubber during the mixing process, the following points should be done:
1. All kinds of ingredients with small dosage but great effect should be fully mixed and evenly mixed, otherwise it will cause scorch of the rubber or undercooked vulcanization.
2. Mixing should be carried out in strict accordance with the mixing process regulations and the feeding sequence.
3. The mixing time should be strictly controlled, and the time should not be too long or too short. Only in this way can the plasticity of the mixed rubber be guaranteed.
4. Do not throw away the large amount of carbon black and fillers, but use them up. And clean the tray.
Of course, there are many factors that affect the quality of compound rubber. However, the specific manifestations are uneven dispersion of the compounding agent, frost spray, scorch, etc., which can be observed visually.
Uneven dispersion of compounding agent In addition to the particles of compounding agent on the surface of the rubber compound, cut the film with a knife, and there will be compounding agent particles of different sizes on the cross-section of the rubber compound. The compound is mixed evenly, and the section is smooth. If the uneven dispersion of the compounding agent cannot be solved after repeated refining, the roller rubber will be scrapped. Therefore, the rubber mixer must strictly abide by the process regulations during the operation, and from time to time, take the film from both ends and the middle of the roller to observe whether the compounding agent is evenly dispersed.
Frosting, if it is not a problem of formula design, then it is caused by the improper order of dosing during the mixing process, or the uneven mixing and the agglomeration of the compounding agent. Therefore, it is necessary to strictly control the mixing process to avoid the occurrence of such phenomena.
Scorch is one of the most important problems in the mixing process. After the rubber material is scorched, the surface or the internal part has elastic cooked rubber particles. If the scorch is slight, it can be solved by the thin pass method. If the scorch is serious, the rubber material will be scrapped. From the perspective of process factors, the scorch of the rubber compound is mainly affected by the temperature. If the temperature of the rubber compound is too high, the raw rubber, vulcanizing agent and accelerator will react during the mixing process, that is, scorch. Under normal circumstances, if the amount of rubber during mixing is too large and the temperature of the roller is too high, the temperature of the rubber will increase, resulting in scorch. Of course, if the feeding sequence is improper, the simultaneous addition of vulcanizing agent and accelerator will also easily cause scorch.
The fluctuation of hardness is also an important factor affecting the quality of rubber compound. Compounds of the same hardness are often mixed with different hardnesses, and some are even far apart. This is mainly due to the uneven mixing of the rubber compound and the poor dispersion of the compounding agent. At the same time, adding less or more carbon black will also cause fluctuations in the hardness of the rubber compound. On the other hand, the inaccurate weighing of the compounding agent will also cause fluctuations in the hardness of the rubber compound. Such as the addition of vulcanizing agent and accelerator carbon black, the hardness of the rubber compound will increase. The softener and raw rubber are weighed more, and the carbon black is less, and the hardness of the rubber compound becomes smaller. If the mixing time is too long, the hardness of the rubber compound will decrease. If the mixing time is too short, the compound will harden. Therefore, the mixing time should not be too long or too short. If the mixing is too long, in addition to the decrease in hardness of the rubber, the tensile strength of the rubber will decrease, the elongation at break will increase, and the aging resistance will decrease. At the same time, it also increases the labor intensity of operators and consumes energy.
Therefore, the mixing only needs to be able to fully disperse various compounding agents in the rubber compound, and to ensure the required physical and mechanical properties and the requirements of calendering, extrusion and other process operations.
As a qualified rubber mixer, not only has a strong sense of responsibility, but also must be familiar with various raw rubbers and raw materials. That is, not only to understand their functions and properties, but also to be able to accurately name their names without labels, especially for compounds with similar appearance. For example, magnesium oxide, nitric oxide and calcium hydroxide, high wear-resistant carbon black, fast-extrusion carbon black and semi-reinforced carbon black, as well as domestic nitrile-18, nitrile-26, nitrile-40 and so on.
Post time: Apr-18-2022
