Rubber processing process flow and common problems

Rubber processing process flow:

Plastic refining process

Raw rubber molding is the process of transforming raw rubber from a strong elastic state to a soft and easy to process plastic state through methods such as mechanical stress, heat, oxygen, or the addition of certain chemical reagents. The purpose of raw rubber molding is to reduce its elasticity, increase its plasticity, and obtain appropriate fluidity to meet the requirements of various processing processes such as mixing, sub derivatization, extrusion, molding, vulcanization, and rubber slurry manufacturing, sponge rubber manufacturing, etc. Mastering the appropriate plasticity is crucial for the processing and quality of rubber products. On the premise of meeting the processing requirements, the plasticity should be minimized as much as possible. With the emergence of constant viscosity rubber and low viscosity rubber, some rubbers no longer need to be molded and are directly mixed. In the rubber industry, the most commonly used molding methods are mechanical molding and chemical molding. The main equipment used in the mechanical mixing method is an open type rubber mixer, a closed type rubber mixer, and a screw plastic mixer. The chemical molding method is a method of adding chemicals to improve the molding effect during the mechanical molding process. The temperature during the opening of the mixer is generally below 80 ℃, which belongs to the low-temperature mechanical mixing method. The discharge temperature of internal mixer and screw mixer is above 120 ℃, even up to 160-180 ℃, belonging to high-temperature mechanical mixing. Before mixing, raw rubber needs to undergo pre processing such as baking, cutting, selecting, and breaking before it can be molded.

The plastic properties of several adhesives:

When natural rubber is molded using an open mill, the roller temperature is 30-40 ℃ and the time is about 15-20 minutes; When the temperature reaches 120 ℃ or above, the mixing time is about 3-5 minutes using an internal mixer.

The Mooney viscosity of styrene butadiene rubber is mostly between 35 and 60, so styrene butadiene rubber does not need to be plasticized. However, after plasticization, the dispersibility of the blending machine can be improved. The butadiene rubber has cold fluidity and lacks plasticizing effect. The Mooney viscosity of cis-1,4-polybutadiene rubber is low, so it does not need to be molded.

Neoprene rubber has high plasticity and can be thinned 3-5 times before molding, with a temperature of 30-40 ℃.

The molecular main chain of ethylene propylene rubber is a saturated structure, and it is difficult to cause molecular cracking during molding. Therefore, it is necessary to choose a variety with low Mooney viscosity instead of molding.

Nitrile rubber has low plasticity, high toughness, and high heat generation during molding. When starting the smelting process, it is necessary to use low temperature below 40 ℃, small roller pitch, low capacity, and segmented molding to achieve good results.

Mixing process

Mixing refers to the process of evenly mixing various ingredients into raw rubber seeds on a rubber mixer. The quality of mixing has a decisive impact on the further processing of the rubber material and the quality of the finished product. Even if the formula of the rubber material is good, if the mixing is not good, it will lead to uneven dispersion of the mixing agent, high or low plasticity of the rubber material, easy scorching, frost spraying, etc., which will prevent the normal operation of rolling, extrusion, coating, and vulcanization processes, and also lead to a decrease in product performance. The mixing method is usually divided into two types: open mixer mixing and internal mixer mixing. Both of these methods are intermittent mixing, which is currently the most widely used method. The mixing process of the opening mill is divided into three stages, namely the roll wrapping (softening stage with the addition of raw rubber), the powder feeding (mixing stage with the addition of powder), and the turning (stage where the raw rubber and the compounding agent are evenly dispersed after the powder feeding). The mixing process of the opening mixer varies depending on the type, purpose, and performance requirements of the rubber material. During mixing, attention should be paid to various factors such as the amount of glue added, the order of feeding, roll spacing, roll temperature, mixing time, roller speed and speed ratio. Neither insufficient mixing nor excessive refining is allowed. The mixing process in the internal mixer is divided into three stages, namely wetting, dispersing, and refining, and the mixing of stones in the internal mixer is carried out under high temperature and pressure. The operating methods are generally divided into one stage mixing method and two stage mixing method. One stage mixing method refers to the method of completing mixing through an internal mixer in one go and then pressing to obtain mixed rubber. It is suitable for all natural rubber or rubber materials mixed with synthetic rubber not exceeding 50%. In a single mixing operation, the step-by-step feeding method is often used in batches. In order to prevent the rubber material from increasing sharply, a slow speed mixer or a dual speed mixer can be used, and the temperature when adding sulfur must be below 100 ℃. The feeding sequence is raw rubber - small material - reinforcing agent - filler - oil softener - discharge - cooling - adding sulfur and super accelerator. The two-stage mixing method refers to the method of mixing and pressing pieces twice through an internal mixer to produce mixed rubber. This method is suitable for rubber materials with a synthetic rubber content exceeding 50%, which can avoid the disadvantages of long mixing time and high rubber temperature during a single mixing process. The first stage of mixing is the same as the first stage mixing method, except for the absence of vulcanization and high activity promoters. After the first stage of mixing is completed, the lower plate is cooled, parked for a certain period of time, and then the second stage of mixing is carried out. Mix evenly and transfer the material to the tablet press before adding vulcanizing agent. After mixing, lower the tablet. The segmented mixing method has a shorter mixing time, lower mixing temperature, more uniform dispersion of the compounding agent, and higher quality of the rubber material.

Rolling process

Calendering is the process of making mixed rubber into film or semi-finished rubber fabric with skeleton materials on a calender. It includes operations such as lamination, lamination, molding, and fabric gluing. The main equipment of the rolling process is the rolling machine, which generally consists of a working roller, a frame, a base, a transmission device, a speed control and distance adjustment device, a roller heating and cooling device, a lubrication system, and an emergency stop device. There are many types of rolling machines, with two, three, or four different working rollers arranged in vertical and horizontal forms; The three rollers have a vertical type Γ Type and triangle; Four rollers with Γ There are various types, including L-type, Z-type, and S-type. According to the purpose of the process, there are mainly laminating and calendering machines (used for calendering film or textile adhesive pasting, most of which have three or four rollers with different plasticity), erasing and calendering machines (used for textile adhesive pasting, with three rollers, each roller has a certain speed ratio, and the middle roller speed is large. The speed ratio is used to rub into the textile fabric), universal calendering machines (also known as universal calendering machines, which have both laminating and erasing functions, and three or four rollers, with adjustable speed ratio), pressure forming and calendering machines Bonding and wire rolling machines. The rolling process generally includes the following processes: preheating and feeding of mixed rubber; The cooling, coiling, cutting, and placement of semi-finished products on a four or three roll rolling machine or by hanging glue on the textile fabric during the guiding and drying (sometimes with glue immersion) of the adhesive material. Before rolling, it is necessary to preprocess the rubber material and textile fabric. Before the rubber material enters the rolling machine, it needs to be turned over and melted on the hot mixer. This process is called hot mixing or preheating, and its purpose is to improve the mixing uniformity of the rubber material, further increase plasticity, increase temperature, and increase plasticity. In order to improve the adhesion performance of adhesive and textile fabrics and ensure the quality of rolling, it is necessary to dry the fabric with a moisture content controlled at 1-2%, low moisture content, hardening of the fabric, easy damage during rolling, high moisture content, and poor adhesion. The rolling performance of several common rubbers: natural rubber has a large thermal deformation, low shrinkage rate, easy rolling, and easy adhesion to hot rollers. The temperature difference between each roller should be controlled to facilitate smooth film transfer; Styrene butadiene rubber has low thermoplastic properties and high shrinkage rate, so the rubber used for rolling should be fully molded. Due to the significant thermal sensitivity of styrene butadiene rubber to rolling, the rolling temperature should be lower than that of natural rubber, and the temperature difference between each roller can vary from high to low; Chloroprene rubber is easy to stick to rollers at 75-95 ℃ and is difficult to roll. Low temperature or high temperature methods should be used, and rolling should be quickly cooled. Adding paraffin and stearic acid can reduce the phenomenon of roll sticking; Ethylene propylene rubber has good rolling performance and can be continuously operated over a wide temperature range. When the temperature is too low, the rubber material has a large shrinkage and is prone to producing bubbles; Nitrile rubber has low thermoplastic properties and high shrinkage. Adding fillers or softeners to the rubber material can reduce the shrinkage rate. When the weight of the filler accounts for more than 50% of the weight of the raw rubber, a smooth surface film can be obtained. Nitrile rubber has low viscosity and is prone to sticking to cold rolls.

Extrusion process

The extrusion process is to achieve the purpose of extrusion and preliminary molding of the rubber material through the action of the cylinder wall and screw components of the extruder, and the extrusion process is also known as the extrusion process. The main equipment of the extrusion process is the extruder. The extrusion characteristics of several types of rubber: natural rubber has a fast extrusion speed and a small shrinkage rate of semi-finished products. The body temperature is 50-60 ℃, the nose temperature is 70-80 ℃, and the mouth shape is 80-90 ℃; SBR has slow extrusion speed, large compression deformation, rough surface, body temperature of 50-70 ℃, nose temperature of 70-80 ℃, and mouth temperature of 100-105 ℃; Before pressing out the chloroprene rubber, there is no need to fully heat it. The body temperature is 50 ℃, the head temperature is ℃, and the mouth shape is 70 ℃; Ethylene-propylene rubber has fast extrusion speed and low shrinkage rate. The body temperature is 60-70 ℃, the head temperature is 80-130 ℃, and the mouth shape is 90-140 ℃. Nitrile rubber has poor extrusion performance and should be thoroughly hot tempered during extrusion. The body temperature is 50-60 ℃, and the nose temperature is 70-80 ℃.

Injection process

Rubber injection molding process is a production method that injects rubber directly from the machine barrel into mold vulcanization. This includes several processes such as feeding, plasticization, injection, pressure maintaining, vulcanization, and demolding. The biggest characteristic of injection vulcanization is that the temperature of the inner and outer layers of the rubber material is relatively uniform and consistent, and the vulcanization speed is fast, which can process most molded products. The equipment for rubber injection molding is a rubber injection molding vulcanization machine.

Die-casting process

Die casting method is also known as transfer mold method or transfer mold method. This method involves placing the rubber material in the stopper tube of the die-casting machine and casting it into the mold cavity for vulcanization under pressure. Similar to injection molding method. For example, using this method to produce skeleton oil seals has less overflow and good product quality.

Vulcanization process

Previously, the main use of natural rubber was only for erasing words; Later, it was used to manufacture small rubber pipes. It was not until 1823 that British chemist Mackintosh invented the method of dissolving rubber in coal tar and coating it on a cloth to make a waterproof cloth, which could be used to make raincoats and boots. However, these raincoats and boots melt down in summer, "people are all trying to figure out a way. American inventor Charlie Goodyear is also conducting experiments on rubber modification. He heats natural rubber and sulfur together, hoping to obtain a substance that remains dry and elastic at all temperatures throughout the year. It was not until February 1839 that he achieved success. One day, he mixed rubber, sulfur yellow, and turpentine into a pot (sulfur is only used for coloring), and accidentally the mixture from the pot splashed onto the hot stove. To his surprise, the mixture did not melt after falling into the fire, but remained as it was and charred. The incomplete charred mixture remaining in the furnace was elastic. He peeled off the splash from the stove 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 process of rubber products, vulcanization is the last processing step. Vulcanization is the cross-linking process of rubber macromolecules from linear structure to network structure under certain conditions. There are three vulcanization methods: cold vulcanization, room temperature vulcanization, and hot vulcanization. Most rubber products use thermal vulcanization. The equipment for hot vulcanization includes vulcanization tanks, flat vulcanization machines, etc.

Other production processes

The production processes of rubber products include impregnation method, coating and scraping method, spraying method, banana plastic method, etc.

Common problems in rubber processing:

1.Why does rubber need to be molded?

The purpose of rubber molding is to shorten the macromolecular chains of rubber under mechanical, thermal, chemical, and other actions, causing the rubber to temporarily lose its elasticity and increase its plasticity, in order to meet the process requirements in the manufacturing process. For example, making the compounding agent easy to mix, easy to roll out, clear molding patterns, stable shape, increasing the flowability of molding and injection molding rubber, making the rubber easy to penetrate fibers, and improving the solubility and adhesion of the rubber. Of course, some low viscosity and constant viscosity rubbers may not necessarily be molded, such as domestic standard particle rubber and standard Malaysian rubber (SMR).

2. What factors affect the plasticization of rubber in an internal mixer

The internal mixer for refining raw rubber belongs to high-temperature molding, with a minimum temperature of 120 ℃ or above, usually between 155 ℃ and 165 ℃. Raw rubber is subjected to high temperature and strong mechanical action in the internal mixer chamber, resulting in severe oxidation and achieving ideal plasticity in a relatively short period of time. Therefore, the main factors that affect the raw rubber molding process of the internal mixer are:

(1) Equipment technical performance, such as speed, etc,

(2) Process conditions, such as time, temperature, wind pressure, and capacity.

3.Why are the plastic properties of various rubbers different

The molding of rubber is closely related to its chemical composition, molecular structure, molecular weight, and molecular weight distribution. Due to their different structural and performance characteristics, natural rubber and synthetic rubber are generally easier to plastic than synthetic rubber. In terms of synthetic rubber, isoprene rubber and chloroprene rubber are close to natural rubber, followed by styrene butadiene rubber and butyl rubber, while nitrile rubber is the most difficult.

4.Why is the plasticity of raw rubber used as the main quality standard for plastic compound

The plasticity of raw rubber is related to the difficulty of the entire manufacturing process of the product, and directly affects the physical and mechanical properties of vulcanized rubber and the important properties of the product's usability. If the plasticity of raw rubber is too high, it will reduce the physical and mechanical properties of vulcanized rubber. However, if the plasticity of raw rubber is too low, it will cause difficulties in the next process, making it difficult for the rubber material to mix evenly. During rolling, the surface of the semi-finished product is not smooth and the shrinkage rate is high, making it difficult to grasp the size of the semi-finished product. During rolling, the rubber material is also difficult to rub into the fabric, causing peeling of the hanging rubber cord fabric and greatly reducing the adhesion between the fabric layers. Uneven plasticity can lead to inconsistent processing and physical and mechanical properties of the adhesive, and even affect inconsistent product performance. Therefore, mastering the plasticity of raw rubber correctly is an issue that cannot be ignored.

5. What is the purpose of mixing

Mixing is the process of mixing raw rubber and various additives together through rubber equipment according to the proportion of additives specified in the rubber formula, and ensuring that all additives are evenly dispersed in the raw rubber. The purpose of mixing rubber materials is to obtain uniform and consistent physical and mechanical performance indicators that meet the formula requirements, in order to facilitate process operations and ensure the quality requirements of the finished product.

6. Why does the mixture clump

The reasons for the caking of the compounding agent are: insufficient plastic mixing of raw rubber, too large roll spacing, too high roll temperature, too large glue loading capacity, coarse particles or caking substances contained in powder compounding agent, gel, etc. The improvement method is to adopt specific measures based on the specific situation: fully plasticizing, appropriately adjusting the roller spacing, reducing the roller temperature, and paying attention to the feeding method; Drying and screening of powder; Cutting should be appropriate during mixing.

7. Why does excessive use of carbon black in the rubber compound produce a "dilution effect"

The so-called "dilution effect" refers to the phenomenon where the amount of carbon black used in the rubber formulation is too high, resulting in a relative decrease in the quantity of rubber, resulting in close contact between carbon black particles and inability to disperse well in the rubber material. This is called the "dilution effect". Due to the presence of many large carbon black particle clusters, rubber molecules cannot penetrate into the carbon black particle clusters, and the interaction between rubber and carbon black is reduced, The strength decreases and the expected reinforcement effect is not achieved.

8. What is the effect of the structure of carbon black on the performance of the rubber compound

Carbon black is generated by the thermal decomposition of hydrocarbon compounds. When the raw material is natural gas (mainly composed of fatty hydrocarbons), a six membered ring of carbon is formed; When the raw material is heavy oil (with a high content of aromatic hydrocarbons), the six membered ring containing carbon is further dehydrogenated and condensed to form a polycyclic aromatic compound, resulting in the formation of a hexagonal network structure layer of carbon atoms. This layer has 3-5 overlapping layers, forming crystals. The spherical particles of carbon black are amorphous crystals composed of several sets of such crystals without certain standard orientation. There are unsaturated free bonds around the crystal, which cause carbon black particles to condense with each other, forming varying numbers of branched small chains, which is called the structure of carbon black.

The structure of carbon black varies depending on the production method. Generally, the structure of furnace method carbon black is higher than that of tank method carbon black, and the structure of acetylene carbon black is the highest. In addition, the structure of carbon black is also affected by the raw material. If 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 and the yield is also low. The smaller the diameter of carbon black particles, the higher their structure. Within the same particle size range, the higher the structure, the easier it is to press out, and the surface of the pressed product is smooth with small shrinkage. The structure of carbon black can be measured by its oil absorption value. When the particle size is the same, a high oil absorption value indicates a high structure, while a low oil absorption value indicates a low structure. High structure carbon black is difficult to disperse in synthetic rubber, but soft synthetic rubber requires high modulus carbon black to improve its strength. Fine particle high structure carbon black can improve the wear resistance of tread rubber. The advantages of low structure carbon black are high tensile strength, high elongation, low constant elongation, low hardness, soft rubber, and low heat generation. However, its wear resistance is worse than that of high structure carbon black with the same particle size.

9. Why does carbon black affect the scorching performance of rubber materials

The influence of the structure of carbon black on the scorching time of the rubber material: high structure and short scorching time; The smaller the particle size of carbon black, the shorter the coking time. The effect of surface properties of carbon black particles on scorching: mainly refers to the oxygen content on the surface of carbon black, which is high in oxygen content, low in pH value, and acidic, such as slot black, which has a longer scorching time. The effect of the amount of carbon black on the scorching time: A large amount can significantly shorten the scorching time because the increase in carbon black produces a tendency to promote scorching by forming bound rubber. The effect of carbon black on the Mooney scorch time of rubber compounds varies in different vulcanization systems.

10. What is first stage mixing and what is second stage mixing

One stage mixing is the process of adding plastic compound and various additives (for some additives that are not easily dispersed or have a small dosage, they can be pre made into a master rubber) one by one according to the process requirements, that is, mixing the master rubber in the internal mixer, and then adding sulfur or other vulcanizing agents and some super accelerators that are not suitable for adding in the internal mixer on the tablet press. In short, a mixing process is one that is completed in one go without parking in the middle.

The second stage mixing refers to the process of evenly mixing various additives, except for vulcanizing agents and super accelerators, with the raw rubber to produce the master rubber. The lower part is cooled and left for a certain period of time, and then supplementary processing is carried out on the internal mixer or open mixer to add vulcanizing agents.

11. Why do films need to be cooled before storage

The temperature of the film cut off by the pressure machine is very high. If not immediately cooled, it is easy to produce early vulcanization and adhesive, causing trouble for the next process. Our factory comes down from the tablet press, and through the film cooling device, we soak it in isolation agent, blow dry it, and slice it for this purpose. The general cooling requirement is to cool the film temperature below 45 ℃, and the storage time of the adhesive should not be too long, otherwise it may cause the adhesive to spray frost.

12. Why should the temperature of sulfur addition be controlled below 100 ℃

This is because when adding sulfur and accelerator to the mixed rubber material, if the temperature exceeds 100 ℃, it is easy to cause early vulcanization (i.e. scorching) of the rubber material. In addition, at high temperatures, sulfur dissolves in the rubber, and after cooling, sulfur condenses on the surface of the rubber material, causing frost spraying and uneven dispersion of sulfur.

13. Why do mixed films need to be parked for a certain period of time before use

The purpose of storing mixed rubber film after cooling is four:

 (1) to restore fatigue of the rubber material and relax the mechanical stress during mixing;

 (2) Reduce the shrinkage of the adhesive material; 

(3) Continue to diffuse the compounding agent during the parking process, promoting uniform dispersion;

 (4) Further generate bonding rubber between rubber and carbon black to improve reinforcement effect.

14. Why is it necessary to strictly implement segmented dosing and pressurization time

The dosing sequence and pressurization time are important factors that affect the mixing quality. Segmented dosing can improve mixing efficiency and increase its uniformity, and there are special regulations for the dosing sequence of certain chemicals, such as: liquid softeners should not be added at the same time as carbon black to avoid agglomeration. Therefore, it is necessary to strictly implement segmented dosing. Insufficient friction and kneading between rubber and medicinal materials due to short compression time, resulting in uneven mixing; If the pressurization time is too long and the mixing room temperature is too high, it will affect the quality and also reduce efficiency. Therefore, the pressurization time must be strictly enforced.

15. What is the impact of rubber loading capacity on the quality of mixed and plastic rubber

The loading capacity refers to the actual mixing capacity of the internal mixer, which often only accounts for 50-60% of the total capacity of the mixing chamber of the internal mixer. If the capacity is too large, there is no sufficient gap in the mixing and sufficient mixing cannot be carried out, resulting in uneven mixing; Elevated temperature can easily cause self vulcanization of the rubber material; It can also cause the motor to overload. If the capacity is too small, there is not enough friction resistance between the rotors, resulting in idling, which also causes uneven mixing and affects the quality of the mixed rubber, while also reducing equipment utilization.

16.Why do liquid softeners need to be added last during rubber mixing?

When mixing rubber materials, if liquid softeners are added first, it will cause excessive expansion of the raw rubber and affect the mechanical friction between the rubber molecules and fillers, reduce the mixing speed of the rubber materials, and also cause uneven dispersion and even agglomeration of the powder. So during mixing, liquid softeners are usually added last.

17. Why does the mixed rubber material "self sulfurize" after being left for a long time

The main reasons for the occurrence of "self sulfur" during the placement of mixed rubber materials are: (1) too many vulcanizing agents and accelerators are used; (2) Large glue loading capacity, high temperature of the mixing machine, insufficient film cooling; (3) Or adding sulfur too early, uneven dispersion of the drug material causes local concentration of accelerator and sulfur; (4) Improper parking, such as excessive temperature in the parking area, lack of air circulation, etc.

18. Why does the internal mixer require a certain amount of air pressure to mix rubber materials

During mixing, in addition to the presence of raw rubber and medicinal materials in the mixing chamber of the internal mixer, there is also a considerable amount of voids. If the pressure is insufficient, the raw rubber and medicinal materials will not have sufficient friction and kneading, resulting in uneven mixing; After increasing the pressure, the rubber material will be subjected to strong friction and kneading up, down, left, and right, making the raw rubber and the compounding agent quickly mix evenly. In theory, the higher the pressure, the better. However, due to limitations in equipment and other aspects, the actual pressure cannot be unlimited. Generally speaking, a wind pressure of around 6Kg/cm2 is better.

19. Why does an open rubber mixing machine require a certain speed ratio between the two rollers

The purpose of designing a speed ratio for an open rubber mixing machine is to strengthen the shear effect, generate mechanical friction and molecular chain breakage on the rubber material, and promote the dispersion of the mixture. In addition, the slow forward rolling speed is also beneficial for operation and safety production.

20. Why does the internal mixer produce thallium inclusion phenomenon

Generally speaking, there are three reasons for the inclusion of thallium in the mixer: (1) there are problems with the equipment itself, such as air leakage from the top bolt, (2) insufficient air pressure, (3) improper operation, such as not paying attention to adding softeners, often causing adhesive to stick to the top bolt and the wall of the mixer chamber. If not cleaned in a timely manner, it will affect over time.

21. Why does the mixed film compress and disperse

Due to carelessness during mixing, it is often crushed and dispersed, resulting in many reasons. The main ones are: (1) violating the dosing sequence specified in the process regulations or adding drugs too quickly; (2) The temperature in the mixing room is too low during mixing; (3) Excessive dosage of fillers in the formula is possible. Due to poor mixing, the rubber material was crushed and dispersed. The dispersed rubber material should be added with the same grade of plastic compound or master rubber, and then subjected to technical treatment after being compressed and discharged.

22. Why should the dosing sequence be specified

The purpose of the dosing sequence is to improve the efficiency of rubber mixing and ensure the quality of the mixed rubber material. Generally speaking, the order of dosing is as follows: (1) adding plastic to soften the compound, making it easy to mix with the compounding agent. (2) Add small drugs such as zinc oxide, stearic acid, accelerators, antioxidants, etc. These are important components of the rubber material. Firstly, add them to make them evenly dispersed in the rubber material. (3) Carbon black or other fillers such as clay, calcium carbonate, etc. (4) Liquid softener and rubber swelling make carbon black and rubber easy to mix. If the dosing sequence is not followed (except for formulas with special requirements), it will seriously affect the quality of the mixed rubber material.

23. Why are there several types of raw rubber used together in the same formula

With the development of raw materials in the rubber industry, the variety of synthetic rubber is increasing. In order to improve the physical and mechanical properties of rubber and vulcanized rubber, improve the processing performance of rubber, and reduce the cost of rubber products, there are currently several types of raw rubber commonly used in the same formula.

24. Why does the rubber material have high or low plasticity

The main reason for this situation is that the plasticity of the plastic compound is not appropriate; Mixing time is too long or too short; Improper mixing temperature; Not mixed well with adhesive; Excessive or insufficient addition of plasticizers; Carbon black can be produced by adding too much or using the wrong variety. The improvement method is to appropriately grasp the plasticity of the plastic compound, control the mixing time and temperature, and mix the compound evenly. The mixing agent should be accurately weighed and inspected.

25. Why does the specific gravity of mixed rubber materials become too large or too small

The reasons for this include inaccurate weighing of the compounding agent, omissions, and mismatches. If the amount of carbon black, zinc oxide, and calcium carbonate exceeds the specified amount, while the amount of raw rubber, oil plasticizers, etc. is less than the specified amount, there will be situations where the specific gravity of the rubber material exceeds the specified amount. On the contrary, the results are also opposite. In addition, when mixing rubber materials, excessive powder flying or sticking to the wall of the container (such as on a small medicine box), and failure to pour the material thoroughly can cause the specific gravity of the rubber material to be too large or too small. The improvement method is to check if there are any errors in the weighing during the mixing, strengthen the operation, and prevent powder flying and even mixing of the rubber material.

26. Why does the hardness of mixed rubber materials become too high or too low?

The main reason for the high and low hardness of the rubber material is the inaccurate weighing of the compounding agent, such as the weight of vulcanizing agent, reinforcing agent, and accelerator being higher than the dosage of the formula, resulting in the ultra-high hardness of the vulcanized rubber; On the contrary, if the weight of rubber and plasticizers exceeds the prescribed amount in the formula, or the weight of reinforcing agents, vulcanizing agents, and accelerators is less than the prescribed amount in the formula, it will inevitably lead to a low hardness of the vulcanized rubber material. The improvement measures are the same as overcoming the factors of plasticity fluctuations. In addition, after adding sulfur, uneven compaction can also cause fluctuations in hardness (locally too large or too small).

27. Why does rubber material have a slow vulcanization starting point

The main reason for the slow vulcanization starting point of the rubber material is that the weight of the accelerator is less than the specified amount, or zinc oxide or stearic acid is missing during mixing; Secondly, the wrong type of carbon black can sometimes cause a delay in the vulcanization rate of the rubber compound. The improvement measures are to strengthen the three inspections and accurately weigh the medicine materials.

28. Why does the rubber material produce sulfur deficiency

The lack of sulfur in the rubber material is mainly caused by missing or insufficient additives such as accelerators, vulcanizing agents, and zinc oxide. However, improper mixing operations and excessive powder flying can also lead to the lack of sulfur in the rubber material. The improvement measures are as follows: in addition to achieving accurate weighing, strengthening the three inspections, and avoiding missing or mismatched ingredients, the mixing process operation should also be strengthened to prevent a large amount of powder from flying and losing.

29. Why are the physical and mechanical properties of mixed rubber materials inconsistent

Inaccurate weighing of the compounding agent, mainly due to missing or mismatched reinforcing agents, vulcanizing agents, and accelerators, can seriously affect the physical and mechanical properties of the vulcanized rubber compound. Secondly, if the mixing time is too long, the dosing sequence is unreasonable, and the mixing is uneven, it can also cause unqualified physical and mechanical properties of the rubber after vulcanization. Take measures to first strengthen precision work, implement the three inspection system, and prevent mismatching and missed dispensing of pharmaceutical materials. However, for rubber materials with poor quality, supplementary processing or incorporation into qualified rubber materials must be carried out.

30. Why does the rubber material produce scorching

The reasons for the scorching of rubber materials can be summarized as follows: unreasonable formula design, such as excessive use of vulcanizing agents and accelerators; Excessive loading capacity, improper mixing operation, such as excessive temperature of the mixing machine, insufficient cooling after unloading, premature addition of sulfur or uneven dispersion, resulting in a high concentration of vulcanizing agents and accelerators; Storage without thin cooling, excessive rolling or prolonged storage time can cause burning of the rubber material.

31. How to prevent rubber material from burning

Preventing coking mainly involves taking corresponding measures to address the causes of coking.

(1) To prevent coking, such as strictly controlling the mixing temperature, especially the sulfur addition temperature, improving cooling conditions, adding materials in the order specified in the process regulations, and strengthening rubber management.

(2) Adjust the vulcanization system in the formula and add appropriate anti coking agents.

32. Why add 1-1.5% stearic acid or oil when dealing with rubber materials with high degree of scorching

For rubber materials with a relatively light degree of scorch, thin pass (roll pitch 1-1.5mm, roll temperature below 45 ℃) 4-6 times on the open mill, park for 24 hours, and mix them into the good material for use. The dosage should be controlled below 20%. However, for rubber materials with a high degree of scorching, there are more vulcanization bonds in the rubber material. Adding 1-1.5% stearic acid can make the rubber material swell and accelerate the destruction of the cross-linking structure. Even after treatment, the proportion of this type of rubber added to the good rubber material should not be higher than 10% Of course, for some severely burnt rubber materials, in addition to adding stearic acid, 2-3% oil softener should be appropriately added to aid swelling. After treatment, it can only be downgraded for use. As for the rubber material with more severe scorching, it cannot be directly treated and used, so it can only be used as a raw material for recycled rubber.

33. Why do rubber materials need to be stored on iron plates

Plastic and mixed rubber are very soft. If placed on the ground randomly, debris such as sand, soil, and wood chips can easily stick to the rubber material, making it difficult to detect. Mixing them can seriously reduce the quality of the product, especially for some thin products. If metal debris is mixed, it can cause mechanical equipment accidents. So the adhesive material must be stored on a specially made iron plate and in a designated location.

34. Why does the plasticity of mixed rubber sometimes vary greatly

There are many factors that affect the plasticity changes of mixed rubber, mainly including: (1) inconsistent sampling of plastic rubber; (2) Improper compression of plastic compound during mixing; (3) Incorrect quantity of softeners; (4) The main measure to address changes in raw materials, especially changes in raw rubber and carbon black, is to strictly follow the process procedures and pay attention to technical notifications of raw material changes at any time.

35. Why is it necessary to perform thin pass reverse mixing after the mixed rubber is discharged from the internal mixer

The temperature of the discharged rubber material from the internal mixer is generally above 125 ℃, while the temperature for adding sulfur should be below 100 ℃. In order to quickly reduce the temperature of the rubber material, it is necessary to repeatedly pour the rubber material, and then carry out the operation of adding sulfur and accelerator.

36. What should be paid attention to during the processing of using insoluble sulfur adhesive

Insoluble sulfur is unstable and can be converted into general soluble sulfur. The conversion is slower at room temperature, but accelerates with increasing temperature. When it reaches above 110 ℃, it can be converted into ordinary sulfur within 10-20 minutes. Therefore, this sulfur should be stored at the lowest possible temperature. During the ingredient processing, it is also important to maintain a low temperature (below 100 ℃) to prevent it from converting into ordinary sulfur. Insoluble sulfur is often difficult to evenly disperse due to its insolubility in rubber, and full attention should also be paid in the process. Insoluble sulfur is only used to replace general soluble sulfur, without changing the vulcanization process and the properties of the vulcanizate. Therefore, if the temperature is too high during the process, or if it is stored at a high temperature for a long time, then using it is meaningless.

37. Why does the sodium oleate used in the film cooling device need to be recycled

The isolation agent sodium oleate used in the cold water tank of the film cooling device, due to continuous operation, the film from the press continuously retains heat in the sodium oleate, which will rapidly increase its temperature and fail to achieve the purpose of cooling the film. In order to reduce its temperature, it is necessary to carry out circulating cooling, only in this way can the cooling effect and isolation effect of the film cooling device be more effectively utilized.

38. Why is a mechanical roller better than an electric roller for film cooling devices

The film cooling device was initially tested with an electric heating roller, which had a complex structure and was difficult to maintain. The rubber material at the blade was prone to early vulcanization and was unsafe. Later, a mechanical roller was used, which was easy to maintain and repair, ensuring product quality and safe production.

Equipment used in plastic processing:

Plastic falling mixer