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, a small piece of the rubber material is torn off and put into the rollers. The purpose is to punch out the roll distance, so as to prevent the rubber mixing machine from being violently subjected to a large force and damaging the equipment after a large amount of rubber material is fed into the roller. 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 kneading, on the one hand, the powder is squeezed into the glue by the action of mechanical force. As a result, the mixing time is shortened, the labor intensity is reduced, and the quality of the rubber compound is good.
Post time: Apr-18-2022
