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 grasping the necessary knowledge of each rubber type, such as mixing characteristics and dosing sequence, it is also 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.
Frost spray, if it is not a problem of formula design, then it is caused by improper order of dosing during the mixing process, or uneven mixing and agglomeration of compounding agents. 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 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.
Mixing of rubber. Most units and factories use open rubber mixers. Its biggest feature is that it has great flexibility and mobility, and is especially suitable for the mixing of frequent rubber variants, hard rubber, sponge rubber, etc.
When mixing with an open mill, the order of dosing is particularly important. Under normal circumstances, the raw rubber is put into the roll gap along one end of the pressing wheel, and the roll distance is controlled at about 2mm (take a 14-inch rubber mixer as an example) and roll for 5 minutes. The raw glue is formed into a smooth and gapless film, which is wrapped on the front roller, and there is a certain amount of accumulated glue on the roller. The accumulated rubber accounts for about 1/4 of the total amount of raw rubber, and then anti-aging agents and accelerators are added, and the rubber is tamped several times. The purpose of this is to make the antioxidant and accelerator evenly dispersed in the glue. At the same time, the first addition of the antioxidant can prevent the thermal aging phenomenon that occurs during high temperature rubber mixing. And some accelerators have a plasticizing effect on the rubber compound. Zinc oxide is then added. When adding carbon black, a very small amount should be added at the beginning, because some raw rubbers will come off the roll as soon as carbon black is added. If there is any sign of off-roll, stop adding carbon black, and then add carbon black after the rubber is wrapped around the roller smoothly again. There are many ways to add carbon black. Mainly include: 1. Add carbon black along the working length of the roller; 2. Add carbon black to the middle of the roller; 3. Add it close to one end of the baffle. In my opinion, the latter two methods of adding carbon black are preferable, that is, only a part of the degumming is removed from the roller, and it is impossible to remove the entire roller. After the rubber compound is taken off the roll, the carbon black is easily pressed into flakes, and it is not easy to disperse after being rolled again. Especially when kneading hard rubber, the sulfur is pressed into flakes, which is particularly difficult to disperse in the rubber. Neither refinishing nor thin pass can change the yellow "pocket" spot that exists in the film. In short, when adding carbon black, add less and more frequently. Don't take the trouble to pour all the carbon black on the roller. The initial stage of adding carbon black is the fastest time to "eat". Do not add softener at this time. After adding half of the carbon black, add half of the softener, which can speed up the "feeding". The other half of the softener is added with the remaining carbon black. In the process of adding powder, the roll distance should be gradually relaxed to keep the embedded rubber within an appropriate range, so that the powder naturally enters the rubber and can be mixed with the rubber to the maximum extent. At this stage, it is strictly forbidden to cut the knife, so as not to affect the quality of the rubber compound. In the case of too much softener, carbon black and softener can also be added in paste form. Stearic acid should not be added too early, it is easy to cause roll off, it is best to add it when there is still some carbon black in the roll, and the vulcanizing agent should also be added at a later stage. Some vulcanizing agents are also added when there is still a little carbon black on the roller. Such as vulcanizing agent DCP. If all the carbon black is eaten, the DCP will be heated and melted into a liquid, which will fall into the tray. In this way, the number of vulcanizing agents in the compound will be reduced. As a result, the quality of the rubber compound is affected, and it is likely to cause undercooked vulcanization. Therefore, the vulcanizing agent should be added at the appropriate time, depending on the variety. After all kinds of compounding agents are added, it is necessary to further turn to make the rubber compound evenly mixed. Usually, there are "eight knives", "triangle bags", "rolling", "thin tongs" and other methods of turning.
"Eight knives" are cutting knives at a 45° angle along the parallel direction of the roller, four times on each side. The remaining glue is twisted 90° and added to the roller. The purpose is that the rubber material is rolled in the vertical and horizontal directions, which is conducive to uniform mixing. "Triangle bag" is a plastic bag that is made into a triangle by the power of the roller. "Rolling" is to cut the knife with one hand, roll the rubber material into a cylinder with the other hand, and then put it into the roller. The purpose of this is to make the rubber compound evenly mixed. However, "triangle bag" and "rolling" are not conducive to the heat dissipation of the rubber material, which is easy to cause scorch, and is labor-intensive, so these two methods should not be advocated. Turning time 5 to 6 minutes.
After the rubber compound is smelted, it is necessary to thin the rubber compound. Practice has proved that the compound thin pass is very effective for the dispersion of the compounding agent in the compound. The thin-pass method is to adjust the roller distance to 0.1-0.5 mm, put the rubber material into the roller, and let it fall into the feeding tray naturally. After it falls, turn the rubber material by 90° on the upper roller. This is repeated 5 to 6 times. If the temperature of the rubber material is too high, stop the thin pass, and wait for the rubber material to cool before thinning to prevent the rubber material from scorching.
After the thin pass is completed, relax the roll distance to 4-5mm. Before the rubber material is loaded into the car, first tear off a small piece of the rubber material and put it into the roller, the purpose is to punch out the roll gap, so as to avoid a large amount of rubber material entering the roller, the rubber mixer will be violently subjected to a large force and damage the equipment. After the rubber material is loaded on the car, it must pass through the roll gap once, and then wrap it on the front roll, continue to turn it for 2 to 3 minutes, and unload and cool it in time. The film is 80 cm long, 40 cm wide and 0.4 cm thick. Cooling methods include natural cooling and cold water tank cooling, depending on the conditions of each unit. At the same time, it is necessary to avoid contact between the film and soil, sand and other dirt, so as not to affect the quality of the rubber compound.
In the mixing process, the roll distance should be strictly controlled. The temperature required for the mixing of different raw rubbers and the mixing of various hardness compounds is different, so the temperature of the roller should be mastered according to the specific situation.
Some rubber mixing workers have the following two incorrect ideas: 1. They think that the longer the mixing time, the higher the quality of the rubber. This is not the case in practice, for the reasons described above. 2. It is believed that the faster the amount of glue accumulated above the roller is added, the faster the mixing speed will be. In fact, if there is no accumulated glue between the rollers or the accumulated glue is too small, the powder will easily be pressed into flakes and fall into the feeding tray. In this way, in addition to affecting the quality of the mixed rubber, the feeding tray must be cleaned again, and the The falling powder is added between the rollers, which is repeated many times, which greatly prolongs the mixing time and increases the labor intensity. Of course, if the accumulation of glue is too much, the mixing speed of the powder will be slowed down. It can be seen that too much or too little accumulation of glue is unfavorable for mixing. Therefore, there must be a certain amount of accumulated glue between the rollers during mixing. During mixing, the powder is squeezed into the glue by mechanical force on the one hand, and on the other hand, the glue is easy to form folds under the action of mechanical force, and the powder is easily drawn into the glue along with the folds. As a result, the mixing time is shortened, the labor intensity is reduced, and the quality of the rubber compound is good.
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
> Industry news