November 29, 2021
Rubber mixer mixing process
1.confidentialinternalclosedis abbreviated as internal mixer, which is mainly used for the plasticization and mixing of rubber.
An internal mixer is a machine that is equipped with a pair of rotors with a specific shape and relatively rotating, which can intermittently plasticize and mix polymer materials in a closed state with adjustable temperature and pressure. It is mainly composed of a mixing chamber and a rotor. Rotor sealing device, feeding and pressing device, unloading device, transmission device and machine base and other parts.
The internal mixer is a kind of high-strength intermittent mixing equipment developed on the basis of the open mixer. Since the emergence of the real Banbury type internal mixer in 1916, the power of the internal mixer has gradually been recognized by people. It has shown a series of characteristics superior to the open mixer in the rubber mixing process. Such as: large mixing capacity, short time, high production efficiency; better overcome dust flying, reduce loss of compounding agents, improve product quality and working environment; safe and convenient operation, reduce labor intensity; beneficial to realize mechanical and automated operations, etc. . Therefore, the appearance of the internal mixer is an important achievement of rubber machinery, and it is still a typical important equipment in plasticizing and mixing, and it is still being developed and improved.
Basic knowledge of internalBasic structure mixerInternal mixer generally consists of a mixing chamber, two relatively rotating rotors, upper top bolt, lower top bolt, temperature measurement system, heating and cooling system, exhaust system, safety device, and discharge device And recording device. The surface of the rotor has spiral ribs. The number of ribs is two-sided, four-sided, six-sided, etc. The cross-sectional geometry of the rotor is triangular, cylindrical or elliptical, and there are two types: tangential and meshing. . The temperature measurement system is composed of thermocouples, which is mainly used to measure the temperature changes in the mixing chamber during the mixing process; the heating and cooling system is mainly used to control the temperature of the rotor and the surface of the cavity wall in the mixing chamber.
Working principle When the internal mixer is working, the two rotors rotate relative to each other, and the material from the feeding port is clamped and brought into the roll gap. It is squeezed and sheared by the rotor. After passing through the roll gap, it hits the sharp edge of the bottom pin and is divided into two parts. , Respectively along the gap between the front and rear chamber walls and the rotor and then back to the top of the roll gap. During the flow around the rotor, the material is subjected to shearing and friction everywhere, causing the temperature of the rubber to rise sharply and the viscosity to decrease, increasing the wettability of the rubber on the surface of the compounding agent, and making the rubber and the surface of the compounding agent fully contact. The compound agglomerates along with the rubber material pass through the gap between the rotor and the rotor, the gap between the rotor and the upper and lower top bolts, and the inner wall of the mixing chamber, and are sheared and broken, surrounded by stretched and deformed rubber, and stabilized in a broken state. At the same time, the ribs on the rotor make the rubber material move along the axial direction of the rotor, and play a role of stirring and mixing, so that the compounding agent is evenly mixed in the rubber material. The compounding agent is repeatedly sheared and broken in this way, and the compound is repeatedly deformed and restored. The continuous stirring of the rotor ribs makes the compounding compound uniformly dispersed in the compound and reaches a certain degree of dispersion. Because the shearing effect of the rubber material during mixing with the internal mixer is much greater than that of the open mixer, and the mixing temperature is high, the mixing efficiency of the internal mixer is much higher than that of the open mixer.
Main parameters:Rotor speed and speed ratio; rotor edge ratio and internal wall gap of the mixing chamber; production capacity and filling factor; unit pressure of the top bolt on the rubber; power.
2. Mixing process of internal mixer Mixing is the process of mixing raw rubber or plasticized raw rubber and compounding agents into a rubber compound with a rubber mixing machine. It is the most important production process for rubber processing. Essentially, it is a process in which the compounding agent is uniformly dispersed in the raw rubber. The granular compounding agent is in the dispersed phase and the raw rubber is in the continuous phase. Open mixer, internal mixer and screw continuous mixer can be used for mixing. The rubber mixing process is essentially a process in which the compounding agent is uniformly dispersed in the raw rubber. The granular compounding agent is in the dispersed phase and the raw rubber is in the continuous phase. During the mixing process, the rubber molecular structure, molecular weight size and distribution, and the aggregation state of the compounding agent all change. Through mixing, the rubber and compounding agent play a physical and chemical role, forming a new structure. Rubber compound is a dispersion system with complex structural characteristics. Due to the high viscosity of the raw rubber, in order to make the compounding agent penetrate into the raw rubber and be uniformly mixed and dispersed therein, the strong mechanical shearing action of the rubber mixer must be used. The operation of mixing with an internal mixer is safe, and the labor intensity is low, and it is the most common application at present. Mixing requires the compounding agent to be uniformly dispersed in the raw rubber to form a colloidal dispersion so that the vulcanized rubber has the best performance. At the same time, there are also certain requirements for the plasticity of the compounded rubber, so that it can meet the requirements of the subsequent process. There are one-stage and two-stage mixing methods. The former is to gradually add compounding agents to the rubber. The latter is to add softeners and powdered fillers for the first stage of rough mixing. After the rubber is cooled and placed for a certain period of time, sulfur and accelerators are added for the second stage of mixing. The rubber processing technology in which rubber (raw rubber) and various compounding agents (see rubber compounding) are uniformly mixed in a rubber mixing machine. In order to be able to add the powdery compounding agent to the rubber, the raw rubber must be masticated to improve its plasticity and fluidity. The mixing process is the most basic process of rubber processing. The quality of the mixed rubber compound after adding the compounding agent has a decisive influence on the process performance of the semi-finished product and the quality of the finished product.
Preparatory work before the dry running test of the internal mixer 1: The dry running test of the internal mixer must be carried out after the foundation is completely dry. 2: Check whether there is any foreign matter in each part of the internal mixer, and whether the connecting parts and fasteners are loose. 3: Check whether the lubrication pipelines and hydraulic pipelines of the internal mixer are connected correctly, whether the lubrication and hydraulic oil used are appropriate, whether the oil level is proper, and whether the lubrication parts are in place. 4: The ancillary equipment of the internal mixer needs to undergo a separate inspection test before dry operation to verify whether its performance meets the specified requirements. 5: Check whether the coordination between the electrical equipment of the internal mixer and the hydraulic system and air control system is correct. 6: Before connecting the internal mixer to the coupling, run the main motor idling for 20 minutes. After there is no abnormality, install the coupling and install the protective cover. 7: At the high-speed shaft end of the main reducer of the internal mixer or at the coupling, manually turn the transmission system to make the rotor rotate for two weeks, and confirm that there is no abnormal phenomenon.
Operation method of internal mixer1. According to the capacity of the internal mixing chamber and the appropriate filling factor (0.6～0.7), calculate the primary mixing volume and the actual formula; 2. According to the actual formula, accurately weigh the various raw materials in the formula Dosage, put the raw rubber, small materials (ZnO, SA, accelerator, antioxidant, solid softener, etc.), reinforcing agent or filler, liquid softener, sulfur separately, and arrange them in order on the shelf; 3 , Turn on the power switch and heating switch of the internal mixer, preheat the internal mixer, and check whether the wind pressure, water pressure, and voltage meet the process requirements, and check whether the temperature measurement system, timing device, power system indication and record are normal; 4. After the internal mixer is preheated, it is stable for a period of time to prepare for mixing; 5. Lift the top plug, put the cut raw rubber into the internal mixer from the feeding port, drop the top plug, and mix the rubber for 1 min; 6 , Lift the top plug, add small ingredients, drop the top plug and mix for 1.5min; 7. Lift the top plug, add carbon black or filler, drop the top plug and mix for 3 minutes; 8. Lift the top plug, add liquid to soften Drop the top plug and mix for 1.5min; 9. Discharge the rubber, measure the temperature of the rubber with a thermocouple thermometer, record the initial temperature of the mixing chamber, the temperature of the mixing chamber at the end of the mixing, and the discharge temperature, the maximum power, and the rotor 10. Adjust the roller pitch of the open mill to 3.8mm, turn on the power switch, make the open mill run, open the circulating water valve, and then throw the rubber discharged from the internal mixer to the top roll of the open mill. When the temperature of the rubber material drops below 110°C, add sulfur, and the left and right cutters twice. When all the sulfur is eaten in, the surface of the rubber material is relatively smooth, and the rubber material is cut. 11. Adjust the roller distance of the open mill to 0.5mm, put in the rubber thin pass, tap the triangle bag, and pass the thin pass 5 times, adjust the roller distance to about 2.4mm, put in the rubber bag roller, and wait until the surface is smooth and free of bubbles. Weigh the total mass of the rubber, place it on a flat, clean metal surface and cool it to room temperature, put a label on it and indicate the rubber formula number and mixing date, and park it for later use.
The mixing process test report for each batch of the internal mixer should record: the temperature at the start of mixing, mixing time, rotor speed, top bolt pressure, rubber discharge temperature, power consumption, the difference between the quality of the mixed rubber and the total quality of the raw materials And the type of internal mixer.
Note: When starting the mixing experiment, you can first mix a compound with the same formula as the test compound to adjust the working state of the internal mixer, and then formally mix; for the same batch of mixed rubber, the control conditions of the internal mixer The mixing time should remain the same.
Precautions for daily operation of internal mixer1. During the first week of production, the fastening bolts of each part of the mixer must be tightened at any time, and then tightened once a month in the future. 2. In the case of low temperature, in order to prevent the pipeline from freezing, it is necessary to drain the cooling water from the cooling pipeline of the machine, and spray the cooling water pipeline clean with compressed air. 3. Shut down according to the requirements of the last batch of materials during the load trial run. After the main motor stops, turn off the lubricating motor and hydraulic motor, cut off the power supply, and then turn off the air source and cooling water source. 4. When the weight of the machine is in the upper position, the discharge door is in the closed position and the rotor is rotating, the charging door can be opened to feed the mixing chamber. 5. When the internal mixer is temporarily stopped for some reason during the mixing process, after troubleshooting, the main motor can be started after the rubber material in the internal mixing chamber is discharged. 6. The feeding volume of the mixing chamber shall not exceed the design capacity, the current at full load operation generally does not exceed the rated current, the instantaneous overload current is generally 1.2 to 1.5 times the rated current, and the overload time is not more than 10s. 7. For large-scale internal mixers, the mass of the rubber block should not exceed 20kg when feeding, and the temperature of the raw rubber block should be above 30°C during plasticizing.
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