What are the rubber processing and common problems?

Plasticizing process

Raw rubber plasticizing is the process of transforming raw rubber from a strong elastic state to a soft, easy-to-process plastic state through mechanical stress, heat, oxygen, or the addition of certain chemical reagents. The purpose of plasticizing raw rubber is to reduce its elasticity, increase plasticity and obtain proper fluidity to meet the requirements of various processing processes such as mixing, sub-derivation, pressing out, molding, vulcanization, pulp manufacturing, and sponge rubber manufacturing. Mastering the proper plasticizing plasticity is essential to the processing of rubber products and the quality of finished products. The premise of meeting the processing process requirements should be as low as possible plasticity. With the emergence of constant-viscosity rubber and low-viscosity rubber, some rubbers have been blended directly without plasticizing. In the rubber industry, the most commonly used plasticizing methods are the mechanical plasticizing method and the chemical plasticizing method. The main equipment used in the mechanical refining method is the open-type rubber refiner, closed-type rubber refiner, and screw refiner. The chemical refining method is a method of adding chemicals to the mechanical refining process to improve the refining effect. The temperature of the open refiner is generally below 80℃, which is a low-temperature mechanical mixing method. The discharge temperature of the compacting machine and screw kneader is above 120℃, or even up to 160-180℃, which belongs to high-temperature mechanical kneading. The raw rubber needs to be baked, cut, selected, and broken before it can be plasticized.

Plasticizing characteristics of several types of rubber.

When natural rubber is plasticized by an open refiner, the roller temperature is 30-40℃, and the time is about 15-20min; when the temperature reaches above 120℃ by a closed refiner, the time is about 3-5min.
Butadiene rubber's Menni viscosity is mostly between 35-60, therefore, butadiene rubber can also be used without plastic refining, but after plastic refining can improve the dispersion of the matching machine cis-butadiene rubber has a cold flow, the lack of plastic refining effect. The Menny viscosity of cis-butadiene rubber is low and can be used without plasticizing.
Neoprene rubber to get plasticity, plastic refining can be thin pass 3-5 times before, thin pass temperature at 30-40 ℃.
Ethylene propylene rubber molecular main chain is a saturated structure, plastic refining is difficult to cause molecular cleavage, so choose a variety of low viscosity without plastic refining.
Nitrile rubber plasticity is small, toughness, and plastic refining heat generation. Use a low temperature of 40 ℃ or less, small roll spacing, low capacity, and segmentation plastic refining, so that you can receive better results.

Mixing process

Mixing refers to the process of uniformly mixing various compounding agents into raw rubber on the rubber-making machine. The quality of mixing has a decisive influence on the further processing of the rubber and the quality of the finished product. Even if the formula is very good, if the mixing is not good, the dispersal of the compound will be uneven, the plasticity of the rubber is too high or too low, easy to scorch, spray frost, etc., so that the process of calendering, pressing out, coating and vulcanization cannot be carried out normally, and it will also lead to a decline in the performance of the product. The mixing method is usually divided into two kinds mixing and refining machine mixing. Both methods are intermittent mixing, which is currently the most widespread method. The mixing process of the open refiner is divided into three stages, i.e. rolls (the softening stage of adding raw rubber), eating powder (the mixing stage of adding powder), and refining (the stage of eating powder to make both raw rubber and compounding agent reach uniform dispersion). The mixing conditions of the kneading machine are different according to the type of rubber, application, and performance requirements. In the mixing, we should pay attention to the amount of rubber added, the order of adding, the roller distance, the temperature of the roller, the mixing time, the speed of the roller and the speed ratio, and other factors. Neither under-mixing nor over-mixing is possible. Mixing machine mixing is divided into three stages, namely wetting, dispersing, and nirvana, mixing machine mixing stone under high temperature and pressure. The operation method is generally divided into a mixing method and two mixing methods. The one-stage mixing method refers to the method of completing the mixing once by the compacting machine and then pressing the sheet to obtain the compounded rubber. He is suitable for all natural rubber or rubber mixed with synthetic rubber-not more than 50% of the rubber, in a mixing operation, often used in batches of step-by-step feeding method, in order to make the rubber does not rise sharply, the general use of slow-speed refining machine can also be used to double-speed refining machine, adding sulfur temperature must be lower than 100 ℃. The feeding sequence is raw rubber - small material - reinforcing agent - filling agent - oil softener - discharge - cooling - add sulfur and super accelerator. The two-stage mixing method refers to the method of kneading and pressing the rubber twice through the kneading machine to make the compound. This method is suitable for compounds with more than 50% synthetic rubber content and avoids the disadvantages of long mixing times and high temperatures of the compound in the one-stage kneading process. The first stage of compounding is the same as the one-stage compounding method, except that no vulcanization or active accelerator is added, and after the first stage of compounding, the sheet is cooled and left for a certain period of time before the second stage of compounding. After uniform mixing, the material is discharged to the press and the vulcanizing agent is added, and then the film is turned over. The mixing time is shorter, the mixing temperature is lower, the compounding agent is more evenly dispersed, and the quality of rubber is high.

Calendering process

Calendering is the process of making a film or semi-finished tape with skeleton material from blended rubber on the calendar, which includes pressing, laminating, pressing, and textile hanging operations. The main equipment of calendering process is a calendar, which generally consists of working rollers, a frame, a machine base, a transmission device, speed and distance adjusting devices, a roller heating and cooling device, a lubrication system, and an emergency stop device. There are many types of calendars, with two, three, or four working rollers, two rollers in the form of vertical and horizontal; three rollers in the form of upright, Γ and triangular; four rollers in the form of Γ, L, Z and S and so on. According to the process used, there are mainly sheet calendars (for calendering film or textile paste, most of the three rollers or four rollers, each roll has a different degree of plasticity), rubbing calendars (for textile rubbing, three rollers, each roll has a certain speed ratio, the middle roller speed is large. With the speed ratio rubbed into the textile), universal calendar (also known as universal calender, both pressing and rubbing function, three or four rollers, adjustable speed ratio), pressing calendar, laminating calender and wire calendar. The calendering process generally includes the following processes: preheating and glue supply of blended rubber; textile guiding and drying (and sometimes there is dipping) rubber in the four-roller or three-roller calender pressing sheet or hanging glue on the textile according to the machine calendering semi-finished products of cooling, rolling, cutting off, placing, etc. Before calendering, the rubber and textile need to be pre-processed. Before the rubber enters the calendar, it needs to be turned on the hot refining machine, this process is hot refining or preheating, its purpose is to improve the mixing uniformity of the rubber, further increase plasticity, improve the temperature and increase plasticity. In order to improve the adhesive properties of rubber and textile, and to ensure the quality of calendering, the fabric needs to be dried and the moisture content controlled at 1-2%, low moisture content, the fabric becomes hard and easily damaged in calendering, high moisture content, poor adhesion. The calendering performance of several common rubbers Natural rubber has a large thermoplastic shape and small shrinkage is easy to calendering, easy to adhere to the hot rollers, and should control the temperature difference between the rollers so that the film is smoothly transferred; SBR has small thermoplasticity and large shrinkage, so the rubber used for calendering should be fully plasticized. As the heat sensitivity of styrene butadiene rubber to calendering is very significant, the calendering temperature should be lower than natural rubber, the temperature difference between the rolls is high to low; neoprene in 75-95 ℃ easy to stick to the rolls, difficult to calendering, should use a low-temperature method or high-temperature method, calendering to quickly cool, mixed with paraffin wax, stearic acid can reduce the phenomenon of sticky rolls; ethylene propylene rubber calendering performance is good, can be in a wide range of temperature continuous operation, the temperature is too low when the contraction of the rubber material NBR has small thermoplasticity and large shrinkage. Adding filler or softening agent to the rubber can reduce the shrinkage, and when the weight of the filler accounts for more than 50% of the weight of raw rubber, the film can be obtained with a smooth surface.

Pressing out process

The pressing-out process is through the action of the barrel wall of the press machine and screw parts so that the rubber material achieves the purpose of extrusion and preliminary modeling, press out process also becomes the extrusion process. The main equipment of the press-out process is the press-out machine. Several types of rubber press-out characteristics: natural rubber press-out speed, semi-finished products shrinkage rate is small. The body temperature of 50-60 ℃, the head 70-80 ℃, and the mouth 80-90 ℃; butadiene rubber press out at slow speed, compression deformation, and rough surface, the body temperature of 50-70 ℃, the head temperature of 70-80 ℃, the mouth temperature of 100-105 ℃; neoprene press out before the full heat refining, the body temperature of 50 ℃, the head ℃, the mouth 70 ℃; ethylene propylene rubber press out fast, shrinkage rate Small, the body temperature 60-70 ℃, the head temperature 80-130 ℃, the mouth 90-140 ℃. Nitrile rubber press-out performance is poor, press-out should be fully hot refining. The body temperature is 50-60℃, and the head temperature is 70-80℃.

Injection process

The rubber injection molding process is a production method of injecting rubber directly from the barrel into the molded vulcanization. It includes several processes such as feeding, plasticizing, injecting, holding pressure, vulcanizing, and discharging from the mold. The most important feature of injection vulcanization is the uniform temperature of the inner and outer layers, fast vulcanization, and the possibility of processing most molded products. The equipment for rubber injection molding is a rubber injection molding vulcanizing machine.
Die-casting process
The die-casting method is also known as the transfer-mold method or the transfer-mold method. In this method, the rubber is loaded in the plug barrel of the die-casting machine, and under pressure, the rubber is cast into the mold cavity and vulcanized. Similar to the injection molding method. Such as the skeleton oil seal with this method to produce less overflow edge, and good product quality.

Vulcanization process

Earlier, the main use of natural rubber is only to do erasers; later used to manufacture small rubber hoses. In 1823, the British chemist McIntosh invented the rubber dissolved in coal tar and then coated in cloth to make waterproof cloth, which can be used to make raincoats and rain boots. However, these raincoats and boots melted in the summer, and "people were trying to figure out what to do. American inventor Charles Goodyear, who was also experimenting with rubber modification, put natural rubber and sulfur yellow together and heated them, hoping to obtain a substance that would remain dry and elastic at all temperatures throughout the year. He did not succeed until February 1839. One day he poured the rubber, sulfur, and turpentine together into a pot (the sulfur was only used for dyeing) and accidentally spilled the mixture on the hot stove. To his surprise, the mixture did not melt when it fell into the fire but remained as it was and was scorched, while the mixture that remained in the furnace and was not completely scorched was elastic. He peeled the spatter off the furnace and realized that he had prepared the elastic rubber he wanted. After continuous improvement, he finally invented rubber vulcanization technology in 1844. In the production of rubber products, vulcanization is the last process. Vulcanization is the process of cross-linking rubber macromolecules from a linear structure to a reticular structure under certain conditions. Vulcanization methods are cold vulcanization, room temperature vulcanization, and hot vulcanization. Most rubber products are vulcanized by hot vulcanization. The equipment for hot vulcanization includes vulcanizing tank, a flat vulcanizing machine, etc.

Other production processes

Other production processes for rubber products include impregnation, scraping, spraying, and Plano-plasticization.
1. Why rubber is plasticized
The purpose of rubber refining is to make rubber cut short macromolecular chains under the action of mechanical, thermal, and chemical processes, so that rubber temporarily loses its elasticity and increases plasticity to meet the process requirements in the manufacturing process. Such as: to make the compound easy to mix, easy to calendar and press out, mold pattern clear, and stable shape, and increase the fluidity of pressing, injection, and pressure rubber, so that the rubber is easy to penetrate into the fiber, and can improve the solubility and adhesion of the rubber. Of course some low viscosity, constant viscosity rubber is sometimes not necessarily plasticized, domestic standard granular rubber, standard Malaysian rubber (SMR).
2. what factors affect the rubber in the refiner plasticizing
Plasticizing raw rubber in the refiner is high-temperature refining, the minimum temperature is above 120℃, usually between 155℃ and 165℃. The raw rubber is subjected to high temperature and strong mechanical action in the cavity of the refiner, resulting in intense oxidation, and the ideal plasticity can be obtained in a short time. Therefore, the main factors affecting the plasticization of raw rubber in the refiner are.
(1) technical performance of the equipment, such as speed, etc.
(2) process conditions, such as time, temperature, air pressure, and capacity, etc. 3.
Why the plasticizing properties of various rubbers are different
The plasticity of rubber is closely related to its chemical composition, molecular structure, molecular weight, and molecular weight distribution. Natural rubber and synthetic rubber are generally easier to refine due to different structural and performance characteristics, while synthetic rubber is more difficult to refine. In terms of synthetic rubber isoamyl rubber, neoprene is close to natural rubber, butyl rubber, butyl rubber is the next most difficult, butyronitrile rubber.
4. why raw rubber plasticity is the main quality standard of plasticized rubber
The plasticity of raw rubber is related to the difficulty of the whole manufacturing process, which directly affects the physical and mechanical properties of the vulcanized rubber and the important properties of the products. If the plasticity of raw rubber is too high, the physical and mechanical properties of vulcanized rubber will be reduced. The plasticity of raw rubber is too low, it will cause difficulty in processing, so the rubber is not easy to mix evenly, calendering, and pressing out the surface of semi-finished products is not smooth, the shrinkage rate is large, not easy to grasp the size of semi-finished products, the rubber is also difficult to rub into the fabric when calendering, resulting in the phenomenon of hanging rubber curtain cloth falling skin, etc., greatly reducing the adhesion between the layers of cloth. Uneven plasticity will cause inconsistency in the process performance and physical and mechanical properties of the rubber, and even affect the use of products with inconsistent performance. Therefore, the correct grasp of the plasticity of raw rubber is a problem that cannot be ignored.
5. What is the purpose of compounding?
Mixing is mixing raw rubber and various compounding agents through rubber equipment according to the ratio of compounding agents specified in the rubber formula, and to make various compounding agents evenly dispersed in the raw rubber. The purpose of mixing rubber is to obtain uniform physical and mechanical properties and conform to the performance index of rubber as specified in the formula, so as to facilitate the next process and ensure the quality of finished products.
6. Why does the compound agglomerate?
The reasons for the agglomeration of compounds are insufficient plasticizing of raw rubber, too large roll distance, too high roll temperature, too large capacity of loaded rubber, coarse particles or agglomerates in powder compound, gel, etc. The way to improve the situation is to take the following measures: full plasticizing, adjusting the roll distance appropriately, lowering the roll temperature, paying attention to the method of adding material; drying and screening of powder; appropriate cutting when mixing.
7. Why does the excessive amount of carbon black in the rubber produce a "dilution effect"?
The so-called "dilution effect" is due to the excessive amount of carbon black in the rubber formula, the rubber in the number of relative reduction, resulting in close contact between the carbon black particles, and can not be well dispersed in the rubber, which is the "dilution effect". This is the "dilution effect". Because of the existence of many large carbon black particles, rubber molecules can not penetrate into the carbon black particles, the interaction between rubber and carbon black is reduced, and the strength decreases and does not achieve the expected reinforcement effect.
8. What is the effect of the structure of carbon black on the performance of the rubber?
Carbon black is produced by the thermal decomposition of hydrocarbon compounds. When the raw material is natural gas (whose components are mainly aliphatic hydrocarbons), a six-membered ring of carbon is formed; when the raw material is heavy oil (with a high content of aromatic hydrocarbons), as it already contains a six-membered ring of carbon, it is further dehydrogenated and condensed to form a polycyclic aromatic compound, thus generating a hexagonal mesh of carbon atoms, which becomes a crystal with 3-5 overlapping layers. The spherical particles of carbon black are amorphous crystals composed of several groups of such crystals without a certain standard orientation. The crystals are surrounded by unsaturated free bonds, which cause the carbon black particles to coalesce with each other and form small chains of branches of varying size, which is called the structure of carbon black.
In addition, the structure of carbon black is also influenced by the raw material, the aromatic hydrocarbon content of the raw material is high, the structure of carbon black is high, and the yield is also high; on the contrary, the structure is low, the yield is also low. The smaller the diameter of carbon black particles, the higher the structure. In the same particle size range, the higher the structure, the easier it is to press out, and the pressed surface is smooth and shrinkage is small. The structure of carbon black can be measured by the size of the oil absorption value, in the case of the same particle size, the larger the oil absorption value, the higher the structure, and vice versa, the lower the structure. High-structure carbon black is difficult to disperse in synthetic rubber, but soft synthetic rubber needs high modulus carbon black to improve its strength, and fine particles high structure carbon black can improve the wear resistance of tread rubber. The advantages of low-structure carbon black are high tearing strength, high elongation, low set tensile strength, low hardness, soft rubber, and low heat generation, but the wear resistance is worse than the same particle size of high-structure carbon black.
9. Why carbon black affects the coking performance of rubber
The structure of carbon black affects the scorching time of the rubber: a high structure has a short scorching time; the smaller the particle size of carbon black, the shorter the scorching time. Carbon black particle surface properties on the impact of coking: mainly refers to the carbon black surface oxygen content, high oxygen content, low PH value, acidic, such as slot black, cooking time is longer. The amount of carbon black on the impact of scorching time: the amount of carbon black can significantly shorten the scorching time because the carbon black increases the generation of combined rubber more tendency to promote scorching. Carbon black in different vulcanization systems on the impact of rubber Menny scorching time varies.
10. what is one-stage kneading and what is two-stage kneading
One-stage kneading is adding a plasticizer and various compounding agents (for some compounding agents which are not easy to disperse or the amount is small, the master rubber can be made in advance) one by one according to the process procedure, that is, do the master rubber mixing in the compacting machine, and then add sulfur or other vulcanizing agents and some super accelerators which are not suitable to be added in the compacting machine on the press. In short, one-stage kneading is the kneading done at once without stopping in the middle.
The second stage of mixing is to mix all kinds of compounding agents other than vulcanizing agent and super accelerator with raw rubber, make the master rubber, cool down the film, stop for a certain period of time, and then add vulcanizing agent in the refiner or open refiner for supplementary processing.
11. Why film should be cooled before storage
The temperature of the film cut from the press is very high, if it is not cooled immediately, it will easily produce early vulcanization and sticky glue, which will cause problems for the next process. The film is cooled by a film cooling device, dipped in isolating agent, blown dry, and sliced for this purpose. The general cooling requirement is to cool the film temperature to below 45℃, and the rubber should not be parked for too long, otherwise, it will cause the rubber to spray frost.
12. Why do we need to control the temperature of adding sulfur below 100℃?
This is because when adding sulfur and accelerator to the compound if the temperature exceeds 100℃, it is easy to cause early vulcanization of the rubber (i.e. scorching). In addition, the sulfur dissolved in the rubber at high temperature, and after cooling sulfur condensation on the surface of the rubber, resulting in spray frost, and will cause uneven sulfur dispersion.
13. Why the mixing film should be stored for a certain period of time before use
The purpose of storing the compounding film after cooling is four: (1) to restore the fatigue of the rubber and loosen the mechanical stress during mixing; (2) to reduce the shrinkage of the rubber; (3) to make the compounding agent continue to diffuse in the process of storing and promote uniform dispersion; (4) to make the rubber and carbon black further generate bonding rubber to improve the reinforcement effect.
14. Why do we need to strictly implement segmental dosing and pressurization time?
Dosing sequence and pressurization time are important factors affecting the quality of compounding. Segmental dosing can improve the mixing efficiency, and increase its uniformity, and the dosing order of certain chemicals and their special provisions, such as liquid softeners shall not be added at the same time with carbon black, in order to avoid agglomeration. Therefore, it is necessary to strictly implement the segmentation of drugs. Too short pressure time rubber and drug can not be fully rubbed kneading, and cause uneven mixing; such as pressure time being too long and making the mixing room temperature too high, affecting the quality, but also reducing efficiency. Therefore, the pressurization time must be strictly enforced.
15. What is the influence of the filling capacity on the quality of mixing and plasticizing rubber?
The loading capacity refers to the actual mixing capacity of the kneader, which often accounts for only 50-60% of the total capacity of the kneading chamber. If the capacity is too large, there will be no sufficient space for mixing, which will not allow sufficient mixing and cause uneven mixing; the temperature will rise, which will easily cause the rubber to sulphurize; it will also cause the motor to be overloaded. If the capacity is too small, there will be no sufficient friction resistance between rotors and idling, which will also cause uneven mixing and affect the quality of the compounded rubber, and also reduce the utilization rate of the equipment.
16. rubber mixing, liquid softeners why the last to add rubber in the mixing, if the first to add liquid softeners, it will make the raw rubber over-expansion and affect the mechanical friction between the rubber molecules and filler, reducing the speed of rubber mixing, but also cause uneven powder dispersion, and even agglomeration. So the mixing liquid softener is generally the last to be added.
17. why compounding rubber placed for a long time will be "self-sulfur"
The main reasons for "self-sulfur" during the placement of the compounding rubber are: (1) the use of vulcanizing agent, too much accelerator; (2) the large capacity of the loading rubber, the refining machine temperature is too high, the film cooling is not enough; (3) or prematurely add sulfur, the uneven dispersion of the material caused by the accelerator and sulfur local concentration; (4) improper parking, that is, the parking place temperature is too high, the air is not circulating.
18. why the mixing machine mixing rubber have a certain wind pressure
When mixing, the mixing machine mixing room in addition to raw rubber and medicine, there is a considerable part of gap exists, if the pressure is not enough, raw rubber and medicine will not get enough friction kneading, resulting in uneven mixing; and increase the pressure, the rubber will be subject to strong friction kneading up and down so that the raw rubber and with the agent quickly mixed evenly. Theoretically, the greater the pressure the better, but due to equipment and other restrictions, in practice, the pressure can not be unlimited large, in general, the wind pressure to about 6Kg/cm2 is good.
19. why open type refining machine two rollers to have a certain speed ratio
The purpose of the speed ratio of the open-type refiner is to strengthen the shearing effect, produce mechanical friction and molecular chain breakage on the rubber, and promote the dispersion of the compound. In addition, the slow speed of the front roll is also conducive to operation and safe production.
20. why is the thallium clamping phenomenon in the refiner
The reasons for the thallium in the mixing machine, generally speaking, there are three aspects: (1) the equipment itself is faulty, such as the upper top tether leakage, (2) insufficient wind pressure, (3) improper operation, such as adding softener without attention, often make the upper top tether and the cavity wall of the mixing machine sticky rubber, such as not timely cleaning, over time will affect.
21. Mixing film why will be pressed apart
Mixing due to carelessness, often pressed loose, caused by a number of reasons, mainly: (1) violation of the process regulations specified in the order of dosing or dosing too quickly; (2) mixing when the mixing room temperature is too low; (3) the formulation of the filler with too much, etc., are possible. Due to poor mixing, the rubber will be pressed apart. The rubber should be added with the same rubber number plasticizing rubber or master rubber after pressing and discharging, and then make technical treatment.
22. Why do we need to specify the dosing sequence?
The purpose of the dosing sequence is to improve the efficiency of the compounding process and to ensure the quality of the compounding material. Generally speaking, the dosing sequence is as follows: (1) add plastic refining rubber softening, easy to mix with the compounding agent. (2) Add small drugs: zinc oxide, stearic acid, accelerator, antioxidant, etc., these are important ingredients of rubber, first add to facilitate their uniform dispersion in the rubber. (3) carbon black or other fillers such as clay, calcium carbonate, etc. (4) liquid softening agent, rubber expansion to make carbon black and rubber easy to mix. If not in this order of dosing (except for special requirements of the formula), it will seriously affect the quality of the compounding rubber.
23. why there are several kinds of raw rubber in the same formula and use
With the development of the rubber industry raw materials, synthetic rubber varieties are increasing, in order to improve the rubber and improve the physical and mechanical properties of vulcanized rubber, improve the processing performance of rubber, and reduce the cost of rubber products, there are often several raw rubbers in the same formula.
24. why the plasticity of the rubber is too high or too low
The main reason for this situation is that the plasticity of plasticizing rubber is not appropriate; the mixing time is too long or too short; the mixing temperature is not appropriate, and the rubber is not mixed well; the plasticizer is added more or less; the carbon black is added less or more or the variety is used wrong, etc. can be produced. The improvement methods are to master the plasticity of plasticizing rubber, control the mixing time and temperature, and use rubber to mix evenly, and the compounding agent should be weighed accurately and checked.
25. Why the specific gravity of compounding rubber is too big and too small
The reasons for this are inaccurate weighing of compounding agents, omission, and mismatching. Carbon black, zinc oxide, and calcium carbonate more than the specified amount and raw rubber, oil plasticizer, etc. less than the specified amount, there will be a specific gravity of rubber more than the specified situation. Conversely, the result is also the opposite. In addition, when mixing the rubber, the powder flies too much or sticks to the wall of the container (such as on the small medicine box), adding material can not pour clean and can cause the specific gravity of the rubber to be too large or too small, the improvement method is to check with the weighing there is no error, strengthen the operation, to prevent the powder flies and pay attention to the rubber mixing evenly.
26. Mixing rubber hardness why will produce too high, or too low The main reason for the hardness of the rubber material is inaccurate weighing with the agent, such as vulcanizing agent, reinforcing agent, or accelerator weighing higher than the formula dosage, resulting in in high hardness of vulcanized rubber; on the contrary, such as rubber, plasticizer weighing more than the formula dosage or reinforcing agent, vulcanizing agent, accelerator weighing less than the formula dosage, is bound to cause the hardness of vulcanized rubber material is low. . The improvement measures and overcome the plasticity fluctuation factors are the same. In addition, after adding sulfur, such as pounding unevenly, will also cause hardness fluctuations (too big or too small).
27. Why does the rubber have a slow starting point of vulcanization?
The main reason for the slow starting point of vulcanization of rubber is that the weight of the accelerator is less than the specified amount, or the mixing is missing to add zinc oxide or stearic acid; secondly, the wrong variety of carbon black can sometimes cause a delay in the vulcanization speed of rubber. The improvement measures are to strengthen the three checks and weigh the material accurately, etc.
28. Why does the rubber material produce under sulfur
The lack of sulfur in the rubber is mainly due to the omission of an accelerator, vulcanizing agent, and zinc oxide, but the improper mixing operation and too much powder flying can also lead to the lack of sulfur in the rubber. Improvement measures are: in addition to accurate weighing, strengthen the three checks, not to miss or mismatch materials, but also should strengthen the mixing process operation, and prevent a large number of powder flyaway dispersion.
29. Why are the physical and mechanical properties of compounding rubber inconsistent
Inaccurate weighing of compounding agents, mainly reinforcing agents, vulcanizing agents, and accelerator omission and mismatch, will seriously affect the physical and mechanical properties of the compounded rubber after vulcanization. Secondly, such as mixing time is too long, unreasonable dosing order, and uneven mixing can also cause the physical and mechanical properties of the rubber to after vulcanization failed. Measures to strengthen the first fine work, the implementation of the three inspection systems, to prevent mismatching and omission of drugs. But for the poor quality of the rubber material, it must be supplemented processing or mixed with qualified rubber material.

30. Why does the rubber scorch?
There are several reasons for the scorching of glue material: unreasonable formula design, for example, too much vulcanizing agent and accelerator; too much loading capacity, improper operation of glue refining, such as the high temperature of the glue refining machine, not sufficiently cooling after the film, too early addition of sulfur or uneven dispersion, resulting in a high concentration of vulcanizing agent and accelerator; storage without thin heat dissipation and roll, too big roll or too long storage time, etc., will all cause the scorching of glue material. The rubber scorching can be caused.
31. how to prevent scorching of rubber
To prevent scorching is mainly to take measures for the reasons of scorching.
(1) To prevent scorching, such as strictly controlling the mixing temperature, especially the sulfur addition temperature, improving the cooling condition, adding materials in order according to the process regulations, and strengthening the rubber management, etc.
(2) Adjust the vulcanization system in the formula and add an anti-coking agent appropriately. 32.
32. why add 1-1.5 % stearic acid or oil when dealing with heavily scorched rubber
For general lightly scorched rubber, thin pass (roll distance 1-1.5mm, roll temperature below 45℃) on the open refiner 4-6 times, stop for 24 hours, and mix into the good material. The amount of blending is controlled at less than 20%. However, for the heavy scorched rubber, there are more vulcanization bonds in the rubber, and the addition of 1-1.5% of stearine will make the rubber swell and speed up the destruction of the cross-linked structure, even if this rubber is treated well, the proportion of blending in good rubber should not be higher than 10%. Of course, for some scorching degree of serious rubber, in addition to stearic acid, add 2-3% oil softeners to help expansion, after treatment can only be downgraded to use. As for the more serious scorched rubber, it can't be treated directly, but can only be used as raw material for recycled rubber.
33. why the rubber should be stored on the iron plate
Plastic and compounding rubber are very soft, if put on the ground, gravel, dirt, wood chips, and other debris are easy to stick in the rubber, and not easy to be found, mixed in will seriously reduce the quality of products, especially for some thin products is fatal, if the metal debris mixed in, it will cause machine and equipment accidents. So the rubber must be stored on the special iron plate, according to the designated place.
34. Why the plasticity of the compounding rubber sometimes varies a lot
The plasticity of the compounding rubber changes, affecting many factors, mainly: (1) plastic rubber sampling is not uniform; (2) mixing plastic rubber with improper pressure; (3) the number of incorrect softeners; (4) changes in raw materials, especially raw rubber and carbon black changes, the main measure to solve the above problems is to strictly implement the process procedures, always pay attention to the technical notice of raw material changes.
35. After the discharge of the compounding rubber from the refiner, why should the thin pass reverse refining
The temperature of the rubber discharged from the compacting machine is generally above 125℃, while the temperature of adding sulfur should be below 100℃. In order to bring down the temperature of the rubber quickly, it is necessary to repeatedly reverse refining of the rubber, and then add sulfur and an accelerator.
36. What should be noted during the processing of rubber with insoluble sulfur?
Insoluble sulfur is unstable, and it can be converted to general soluble sulfur. The conversion is slow at room temperature but accelerates with the increase of temperature to 110 ℃ or more, and then it can be converted into ordinary sulfur within 10-20 minutes. Therefore, this sulfur should be stored at the lowest possible temperature. Care should also be taken to keep the temperature low (below 100°C) during the batching process to prevent its conversion to common sulfur. Insoluble sulfur is often difficult to disperse evenly due to its insolubility in rubber, and due attention should also be paid to the process. Insoluble sulfur is only used to replace the general soluble sulfur and does not change the vulcanization process and the performance of the vulcanized rubber. Therefore, its use does not make sense if the process is too hot, or if it is stored at higher temperatures for a long time.
37. Why sodium oleate used in the film cooling unit should be circulated
Sodium oleate, the isolating agent used in the film cooling unit's cold water tank, will not achieve the purpose of cooling the film due to continuous operation, and the film coming down from the press will constantly leave the heat in the sodium oleate, which will cause its temperature to rise rapidly. In order to reduce its temperature, it is necessary to carry out circulation cooling, which is the only way to make the cooling effect and isolation effect of the film cooling device more effective.
38. Why mechanical hobbing is better than electric hobbing for film cooling devices
The film cooling device has been tried to use an electric hob, which has a complicated structure, difficult maintenance, easy early vulcanization of rubber at the knife mouth, and unsafe, and then changed to use mechanical hob, which is easy to maintain and repair, and ensures product quality and safe production.