1. Why should rubber be masticated?
The purpose of rubber mastication is to make the rubber cut short macromolecular chains under the action of mechanical, thermal and chemical, so that the rubber temporarily loses its elasticity and increases the plasticity to meet the process requirements in the manufacturing process. For example, the compounding agent can be easily mixed in, easy to be calendered and pressed out, the molding pattern is clear, the shape is stable, the flowability of the molding and the injection molding compound is increased, the rubber compound is easy to penetrate into the fiber, and the dissolution and adhesion of the rubber compound can be improved. . Of course, some low viscosity, constant viscosity rubbers are sometimes not necessarily plasticized, domestic standard granules, standard Malaysian rubber (SMR).
2. What factors affect the rubber mastication in the mixer
The plastic mixer plastic mixer is a high temperature plasticizing, the temperature is at least 120 ° C, generally between 155 ° C -165 ° C. The raw rubber is subjected to high temperature and strong mechanical action in the cavity of the internal mixer, which produces intense oxidation and can obtain ideal plasticity in a short period of time. Therefore, the main factors affecting the mixing machine for raw rubber molding are:
(1) Equipment technical performance, such as speed, etc.
(2) Process conditions such as time, temperature, wind pressure and capacity.
3. Why are the rubberizing properties of various rubbers different?
Rubber mastication is closely related to its chemical composition, molecular structure, molecular weight and molecular weight distribution. Due to the different characteristics of structure and properties of natural rubber and synthetic rubber, it is generally easier to plasticize natural rubber, and it is difficult to synthesize plastic. In the case of synthetic rubber, isoamyl rubber, neoprene is close to natural rubber, styrene-butadiene rubber, butyl rubber, and nitrile rubber is the most difficult.
4. Why use raw rubber plasticity as the main quality standard for plasticating rubber
The plasticity of raw rubber is related to the difficulty of the whole manufacturing process of the product, which directly affects the physical and mechanical properties of the vulcanized rubber and the important properties of the product. If the plasticity of the raw rubber is too high, the physical and mechanical properties of the vulcanized rubber will be lowered. However, the plasticity of raw rubber is too low, which will cause difficulty in the processing of the next process, making the rubber compound difficult to mix evenly, calendering, and the surface of the semi-finished product is not smooth when pressed out, the shrinkage rate is large, and it is difficult to grasp the size of the semi-finished product. It is difficult to rub into the fabric, causing the phenomenon that the rubber curtain cloth is peeled off, and the adhesion between the cloth layers is greatly reduced. Uneven plasticity will result in inconsistent process performance and physical and mechanical properties of the rubber compound, and even affect the inconsistent performance of the product. Therefore, correctly understanding the plasticity of raw rubber is a problem that cannot be ignored.
5. What is the purpose of mixing?
The mixing is to mix the raw rubber and various compounding agents through the rubber equipment according to the proportion of the compounding agent specified by the rubber compound formula, and uniformly disperse the various compounding agents in the raw rubber. The purpose of the compounding of the rubber compound is to obtain uniform physical and mechanical performance indexes and meet the specifications of the rubber compound in the formula to facilitate the operation of the lower process and ensure the quality of the finished product.
6. Why do the ingredients get together?
The reasons for the agglomeration of the compounding agent are: insufficient plasticizing of the raw rubber, excessively large roll gap, excessively high roll temperature, excessive packing capacity, coarse particle or agglomerate in the powder compounding agent, and gelation. The improvement method is to take specific conditions: full mastication, appropriate adjustment of small roller pitch, reduction of roller temperature, attention to feeding method; powder drying and screening; cutting should be appropriate during mixing.
7. Why does the excessive amount of carbon black in the rubber compound cause a “dilution effect”?
The so-called "dilution effect" is due to the excessive use of carbon black in the rubber compound formulation, and the relative decrease in the amount of rubber, resulting in close contact between the carbon black particles, which cannot be well dispersed in the rubber compound. It is the "dilution effect". In this way, because there are many large particles of carbon black particles, the rubber molecules cannot penetrate into the carbon black particles, and the interaction between the rubber and the carbon black is reduced, and the strength is lowered without the expected reinforcing effect.
8. What is the effect of the structure of carbon black on the properties of the compound?
Carbon black is produced by thermal decomposition of hydrocarbon compounds. When the raw material is natural gas (the components of which are mainly aliphatic hydrocarbons), a six-membered ring of carbon is formed; when the raw material is a heavy oil (higher aromatic content), further dehydrogenation is carried out because of the six-membered ring containing carbon. Condensation forms a polycyclic aromatic compound, thereby forming a hexagonal network structure of carbon atoms, and such a layer of 3 to 5 overlaps becomes a crystal. The spherical particles of carbon black are amorphous crystals composed of several groups of such crystals which are not oriented in a certain standard. There are unsaturated free bonds around the crystals. This bond causes the carbon black particles to agglomerate each other and form a number of branched small chains. This is called carbon black structure.
The structure of carbon black varies according to the method of preparation. Generally, the structure of carbon black is higher than that of channel black, and the structure of acetylene black is the highest. In addition, the structure of carbon black is also affected by raw materials, and the aromatic content of raw materials is high. The structure of carbon black is high and the yield is high; on the contrary, the structure is low and the yield is low. The smaller the diameter of the carbon black particles, the higher the structure. In the same particle size range, the higher the structure, the easier the extrusion, and the surface of the extruded product is smooth and the shrinkage is small. The structure of carbon black can be measured by the size of the oil absorption. In the case of the same particle size, a large oil absorption value indicates a high structure, and a reverse structure indicates a low structure. High-structured carbon black is difficult to disperse in synthetic rubber, but soft synthetic rubber requires a higher modulus of carbon black to enhance its strength, and fine-particle high-structure carbon black can improve the wear resistance of the tread rubber. The low-structure carbon black has the advantages of high tensile strength, high elongation, low tensile strength, low hardness, soft rubber and low heat generation, but the wear resistance is inferior to that of the same-sized high-structure carbon black.
9. Why does carbon black affect the scorch performance of rubber compounds?
The structure of carbon black has an effect on the scorch time of the rubber: the structural high scorch time is short; the smaller the particle size of the carbon black, the shorter the scorch time. The surface properties of carbon black particles are affected by coke burning: mainly refers to the oxygen content on the surface of carbon black, high oxygen content, low pH value, and acidity, such as black groove and long scorch time. The amount of carbon black used in the focus burn time: the amount of energy can significantly shorten the scorch time is because the increase in carbon black to form a combination of rubber has a tendency to promote scorch. The effect of carbon black on the Mooney scorch time of the rubber in different vulcanization systems is different.
10. What is a piece of mixing, what is a two-stage mixing
One section of mixing is to add plastic compounding rubber and various compounding agents (for some non-dispersible or less-purpose compounding agents, which can be pre-formed into the masterbatch), one by one according to the requirements of the process regulations, that is, the masterbatch is mixed in the internal mixer. Refining, then adding sulfur or other vulcanizing agents to the tablet press and some super accelerators that are not suitable for inclusion in the internal mixer. In short, a piece of mixing is a mixture that is not parked in the middle and completed once.
The second-stage mixing means that the various compounding agents other than the vulcanizing agent and the super-accelerator are uniformly mixed with the raw rubber to form a masterbatch, and the lower piece is cooled, parked for a certain period of time, and then carried out on an internal mixer or an open mill. Add processing to add vulcanizing agent.
11. Why should the film be cooled before it can be stored?
The temperature of the film cut by the tablet press is very high. If it is not cooled immediately, it is easy to produce early vulcanization, and it will stick to the glue, which will cause trouble to the process. Our factory is down by the tablet press, and is immersed in the film cooling device to isolate, dry and slice. The general cooling requirement is to cool the film temperature to below 45 °C. The compounding time should not be too long, otherwise it will cause the rubber to bloom.
12. Why do you want to control the sulfur temperature below 100 °C?
This is because when the mixing compound is added with sulfur and a promoter, if the temperature exceeds 100 ° C, it is easy to cause early vulcanization (ie scorch) of the rubber compound. In addition, at high temperatures, sulfur dissolves in the rubber, and after cooling, sulfur condenses on the surface of the rubber, causing blooming, and causes uneven dispersion of sulfur.
13. Why do you want to park the film for a certain period of time?
The purpose of the mixed film after cooling is fourfold: (1) to restore the rubber to fatigue, to mechanical stress during relaxation and mixing; (2) to reduce the shrinkage of the rubber; (3) to make the compounding agent Continue to spread during the parking process to promote uniform dispersion; (4) Further bond rubber between the rubber and the carbon black to enhance the reinforcing effect.
14. Why do you strictly follow the staged dosing and pressurization time?
Dosing sequence and pressurization time are important factors affecting the quality of mixing. Sub-dosing can improve the mixing efficiency and increase its uniformity. Moreover, the order of addition of some medicines has special provisions. For example, liquid softeners should not be added at the same time as carbon black to avoid agglomeration. Therefore, segmental dosing must be strictly performed. If the pressurizing time is too short, the rubber and the drug will not be fully rubbed and kneaded, resulting in uneven mixing; if the pressurizing time is too long, the temperature of the mixing chamber will be too high, affecting the quality, and reducing the efficiency. Therefore, the pressurization time must be strictly performed.
15. What effect does the loading capacity have on the quality of mixing and plasticizing rubber?
The loading capacity refers to the actual mixing capacity of the internal mixer, which often accounts for only 50-60% of the total capacity of the mixing chamber of the mixer. If the capacity is too large, the mixing does not have sufficient voids, and sufficient agitation cannot be performed, resulting in uneven mixing; if the temperature is raised, the rubber is likely to be self-sulphur; and the motor is overloaded. The capacity is too small, there is not enough friction resistance between the rotors, and there is idling, which also causes uneven mixing, which affects the quality of the rubber mixture and reduces the utilization rate of the equipment.
16. When the rubber compound is mixed, why should the liquid softener be added last?
When the rubber compound is mixed, if the liquid softener is added first, the raw rubber will be excessively expanded to affect the mechanical friction between the glue molecules and the filler, reduce the compounding speed of the rubber compound, and also cause uneven dispersion of the powder. Even the group. Therefore, liquid softeners are generally added at the time of mixing.
17. Why does the compounding compound take a long time to "self-sulfur"?
The main reasons for the occurrence of “self-sulfur” during the mixing of rubber compound are: (1) the vulcanizing agent used, too much accelerator; (2) the large filling capacity, the temperature of the rubber mixing machine is too high, and the film cooling is insufficient; Or prematurely add sulfur, the uneven dispersion of the drug causes local concentration of accelerator and sulfur; (4) Improper parking, that is, the temperature of the parking place is too high, and the air is not circulating.
18. Why does the mixer mix have a certain wind pressure?
In the mixing process, in addition to the raw rubber and the medicine, there are still a considerable part of the voids in the mixing chamber of the mixer. If the pressure is insufficient, the raw rubber and the medicine will not get enough friction and kneading, resulting in no mixing. After the pressure is increased, the rubber compound will be subjected to strong friction and kneading up and down, so that the raw rubber and the compounding agent are quickly mixed evenly. In theory, the greater the pressure, the better, but due to the limitations of equipment and other aspects, the pressure can not be unlimited. In general, the wind pressure is about 6Kg/cm2.
19. Why do the two rolls of the open mixer have a certain speed ratio?
The purpose of the open mixer design speed ratio is to enhance the shearing action, mechanical friction and molecular chain breakage of the rubber compound, and promote the dispersion of the compounding agent. In addition, the forward rolling speed is slow, which is also conducive to operation and is conducive to safe production.
20. Why does the mixer cause pinching?
There are three reasons for the pinch of the mixer: (1) The equipment itself has problems, such as: air leakage from the top, (2) insufficient wind pressure, (3) improper operation, such as not paying attention when adding softener It often causes the top plug and the wall of the mixer to stick to the rubber compound. If it is not cleaned in time, it will be clipped over time.
twenty one. Why does the compound film break down?
When mixing, it is often dissipated due to carelessness. There are many reasons for this. The main reasons are: (1) the order of dosing in violation of the technical regulations or the over-dosing; (2) the temperature of the mixing room is too low during mixing; (3) It is possible to use too much filler in the formulation. The compound is crushed due to poor mixing. After the dispersing, the rubber compound should be added with the rubber compound or the masterbatch. After being pressed and discharged, it is treated as technically.
twenty two. Why do you want to specify the dosing order?
The purpose of the dosing sequence is to improve the mixing efficiency and ensure the quality of the compound. Generally speaking, the order of dosing is: (1) softening with plasticizing rubber, and mixing with compounding agent. (2) Adding small drugs: zinc oxide, stearic acid, accelerators, anti-aging agents, etc. These are important ingredients of the rubber compound, which are first added so that they can be uniformly dispersed in the rubber compound. (3) Carbon black or other fillers such as clay, calcium carbonate, and the like. (4) Liquid softener, the swelling of the rubber makes the carbon black and the glue easy to mix. If you do not follow this dosing sequence (except for special requirements), it will seriously affect the quality of the compound.
twenty three. Why are there several kinds of raw rubber used in the same formula?
With the development of rubber industry raw materials, the variety of synthetic rubber is increasing. In order to improve the rubber compound and improve the physical and mechanical properties of the vulcanized rubber, improve the processing performance of the rubber compound and reduce the cost of rubber products, there are several kinds in the same formula. Raw rubber is used together.
twenty four. Why does the compound produce plasticity that is too high or too low?
The main reason for this is that the plasticity of the plastic compound is not appropriate; the mixing time is too long or too short; the mixing temperature is improper; the rubber is not blended well; the plasticizer is added or added less; the carbon black is less added Or the use of the wrong type of the product will be produced. The improvement method is to properly grasp the plasticity of the plastic compound, control the mixing time and temperature, and mix the rubber evenly with the glue, and the compounding agent should be accurately weighed and strengthened.
25. Why does the compounding compound produce too much weight?
The cause is the inaccurate weighing, mismatching and mismatching of the compounding agent. Carbon black, zinc oxide, calcium carbonate more than the specified amount of raw rubber, oil plasticizer, etc. less than the specified amount, there will be a situation in which the proportion of rubber exceeds the specified. On the contrary, the result is reversed. In addition, when the rubber compound is mixed, the powder flies too much or sticks to the wall of the container (such as a small pill box), and the feeding fails to be cleaned, which can cause the specific gravity of the rubber to be too large or too small. The improvement method is to check the matching. Whether there is any error in weighing, strengthen the operation, prevent the powder from flying and pay attention to the uniform mixing of the rubber.
26. Why is the hardness of the compound compound too high, too low?
The main reason for the hardness of the rubber compound is that the weighing of the compounding agent is not accurate. For example, the weighing of the vulcanizing agent, the reinforcing agent and the accelerator is higher than the formula dosage, resulting in the hardness of the vulcanized rubber being extremely high; on the contrary, the rubber and the plasticizer are weighed more. The amount of the formula or the reinforcing agent, vulcanizing agent and accelerator are less than the amount specified in the formula, which will inevitably result in the hardness of the vulcanizate being low. The improvement measures are the same as the factors that overcome the plasticity fluctuation. In addition, after adding sulfur, if the smelting is uneven, it will also cause hardness fluctuations (partially too large or too small).
27. Why does the rubber compound produce a slow starting point?
The main reason for the slow start of vulcanization of the rubber is that the accelerator is weighed less than the specified amount, or the mixture is added with zinc oxide or stearic acid. Secondly, the carbon black variety is wrong, and sometimes the retardation rate of the rubber compound is delayed. . The improvement measures are to strengthen the three inspections and to accurately weigh the medicines.
28. Why does the rubber produce less sulfur?
The sulfur produced by the rubber compound is mainly caused by the leakage or less distribution of the accelerator, the vulcanizing agent and the zinc oxide. However, if the mixing operation is improper, the powder flying too much may cause the rubber to be less sulfur. The improvement measures are: in addition to accurate weighing, strengthening the three inspections, not missing or mismatching the medicine, it should also strengthen the mixing process, and prevent the powder from flying a lot.
29. Why are the physical and mechanical properties of the compounded compound inconsistent?
The weighing of the compounding agent is not accurate, mainly the fluxing and mismatching of the reinforcing agent, vulcanizing agent and accelerator, which will seriously affect the physical and mechanical properties of the compounded rubber after vulcanization. Secondly, if the mixing time is too long, the order of dosing is unreasonable, and the mixing is uneven, it can also cause the physical and mechanical properties of the rubber to be unqualified after vulcanization. Take measures to strengthen the fine work and implement the three-inspection system to prevent mismatching and dispensing of medicines. However, for poor quality compounds, they must be supplemented or used in qualified compounds.
30. Why does the rubber produce scorch?
There are several reasons for the scorch of the rubber: the formulation is not reasonable, such as vulcanizing agent,