PU nylon coated glovesWhat are the preparation processes for raw rubber plasticizing? The open mill is mainly used for rubber plasticizing, mixing, hot refining, sheeting and rubber supply. It can also be used for crushing, kneading and refining in the production of recycled rubber. In addition, it is also widely used in plastic processing and coating pigment industrial production.
The open mill is classified according to the rubber processing technology in the finger cot, mainly including plastic (} Kun) mill (raw rubber plasticizing, rubber mixing), hot mill (rubber preheating), tablet press (tablet pressing, rubber supply), rubber crusher (crushing natural rubber), rubber washing machine (removing impurities in raw rubber, waste rubber or rubber tape)quality), refining machine (removing hard impurities in reclaimed rubber), reclaimed rubber kneading machine (kneading reclaimed rubber), fine rubber crushing machine (crushing waste rubber and making reclaimed rubber), raw rubber sheeting machine (making smoked sheets and crepe sheets of natural rubber), experimental rubber mixing machine (small amount of rubber material experiment).
Open mixing mills are classified according to their structural form and transmission form. Currently, there are three types: standard type, integral type, and dual-motor transmission type.
The specifications of the open mill are indicated by the Chinese phonetic symbol in front of the value of the roller diameter to indicate the model and purpose of the machine. For example, XK-400, X means rubber, K means non-open mill, and 400 means the diameter of the working part of the roller is 400ram. For example, X(S)K-400, means plastics. This type of open mill is suitable for both rubber and plastics. For some special purpose rubber mixing mills, sometimes a symbol is added after the code, such as XKP for non-breaking rubber mixing mill and XKA for hot mixing mill.
There are many types of mixing mills, but their basic structures are similar. It is mainly composed of rollers, roller bearings, frames and beams, machine bases, spacing and safety devices, temperature control devices, lubrication devices, transmission devices, emergency brake devices and brakes.
Commonly used closed rubber mixers (I~2T for short) have two types: tangential rotor type and intermeshing rotor type. The main structural difference between the internal mixer with tangential rotor and the internal mixer with intermeshing rotor is the rotor. The cross section of the tangential rotor is elliptical, and the spiral ridges are of two or four ridges. The two rotors have a speed difference (speed ratio), and the spiral ridges do not mesh with each other. The cross section of the intermeshing rotor is circular, the two rotors have the same speed, and the spiral ridges mesh with each other.
According to the rotor speed of the internal mixer, it can be divided into: slow internal mixer (rotor speed below 20r/min), medium speed internal mixer (rotor speed around 30r/min) and fast internal mixer (rotor speed above 40r·/min).
According to the different cross-sectional shapes of the internal mixer rotor, it can be divided into three types: elliptical rotor internal mixer, cylindrical rotor internal mixer, and triangular rotor internal mixer.
According to whether the internal mixer rotor speed can be changed, it can be divided into single-speed internal mixer, double-speed internal mixer (the rotor has two speeds); four-speed; variable-speed internal mixer, etc.
The specifications of the internal mixer are generally expressed by the total volume of the mixing chamber and the speed of the long rotor (active rotor). At the same time, a symbol is placed in front of the total capacity to indicate what type of machine it is. For example, XM-80×40, where X represents rubber, M represents internal mixer, 8
represents the total volume of the mixing chamber is 80L, and 40 represents the speed of the long rotor is 40r·／min. For example, XM-270/20×40, it means a rubber mixer with a total mixing chamber capacity of 270L and a dual speed (20r/min, 40r/min). If the symbol in front is X(S)M, S means plastic, which means this mixer is suitable for both rubber and plastic.
Internal mixers are generally composed of a mixing chamber rotor, a feeding and pressing device, a discharging device, a transmission device, a heating and cooling system, and air pressure, hydraulic, and electronic control systems.
(1) The raw rubber in the finger cot is mostly in large blocks (such as the natural rubber bag mass is generally 50-100kg). The viscosity is very high at room temperature. Especially in winter, the raw rubber is often hardened or crystallized, making it difficult to cut and further process. Therefore, the rubber must be baked before plasticizing to heat and soften the rubber or remove the crystallization to make it easier to process. The baking equipment can be divided into baking room, oven, infrared, high-frequency current, etc. The drying room is suitable for large-scale production; the oven is suitable for small-scale production and scientific research departments and laboratory tests; infrared and high-frequency current are suitable for advanced industrial production. The temperature and time of baking the rubber should be appropriate. The baking temperature of natural rubber is 50-60°C, and the baking time is generally 24-48 hours in spring, summer and autumn, and 36-72 hours in winter; the baking temperature of chloroprene rubber in finger cots is 50-60°C, and the time is 150-180 minutes, or the baking temperature is 24-40°C, and the time is 4-6 hours; the baking temperature should not be too high, otherwise it will cause rubber aging and affect the physical and mechanical properties.
(2) Rubber cutting The natural rubber cutting block is generally 10~20kg, the chloroprene rubber block is generally not more than 10kg, and the other synthetic rubber blocks are generally 10~15kg. The rubber block is preferably in a triangular diamond shape so that it can smoothly enter the roller gap when the rubber is cut. Rubber cutting generally adopts two types: single-blade hydraulic vertical rubber cutting machine and multi-blade horizontal rubber cutting machine. The former is suitable for small and medium-sized industrial production and synthetic rubber cutting, and the latter is suitable for large-scale industrial production.
(3) Rubber breaking Rubber blocks such as natural rubber and chloroprene rubber need to be broken by a rubber breaker before plasticizing to improve plasticizing efficiency. Other synthetic rubber blocks are generally not broken and can be directly plasticized (or mixed) without rubber breaking. In addition, the use of a large-capacity internal mixer does not require rubber breaking. The rubber breaking roller distance is generally 2 to 3 mm, and the roller temperature is controlled below 45°C.
① Open mill plastication Open mill plastication is the earliest plastication method used. The two rollers of the open mill rotate relative to each other at different speeds. The rubber is brought into the roller gap by the rollers under the action of friction. Under the action of the roller shear force, the rubber molecular chain is stretched and broken, and the rubber plasticity in the finger sleeve increases. The open mill plastication method has high labor intensity, low production efficiency, and poor operating conditions, but the plasticized rubber has uniform plasticity, low thermoplasticity, wide adaptability, relatively flexible, and low investment. Therefore, it is suitable for occasions with more changes in rubber types and less rubber consumption.
There are usually several methods for plasticating on a mixing mill, such as thin-pass plasticating, roll-wrapped plasticating, and plasticating with the addition of chemical peptizers. The thin-pass plasticating method is to pass the raw rubber through the roller gap at a roller gap of 0.5 to 1 mm, without wrapping the roller, and thin-pass it onto a plate. Repeat the thin-pass method for a specified number of times or time until the required plasticity is obtained. The roll-wrapped plasticating method is to wrap the raw rubber with a larger roller gap (5 to 10 mm) F and then continuously pass the roller for plasticating until the specified time. It is divided into one-stage plasticating and segmented plasticating. One-stage plasticating, The plasticizing time is long and the efficiency is low. It is not suitable for plasticizing raw rubber with high plasticity requirements. The plasticizing is carried out in sections, and the roller is plasticized for 10 to 15 minutes. After the sheet is removed, cooled and parked for 4 to 8 hours, the next plasticizing is carried out until the required plasticity is reached. The chemical plasticizer plasticizing method is a method of adding chemical plasticizers to the above-mentioned thin-pass plasticizing method and the one-time plasticizing method. It can improve the plasticizing efficiency, shorten the plasticizing time, and reduce the elastic recovery and shrinkage of the plasticized rubber.
② Internal mixer plasticizing After the material is added to the internal mixing chamber from the feeding hopper, the feeding door is closed, and the upper bolt of the pressing device drops to pressurize the material. Under the action of the pressure and friction of the upper push bolt, the material is brought into the gap between two rotors with spiral edges, speed ratio and relative rotation, so that the material is subjected to the strong kneading action of constantly changing and repeated shearing, tearing, stirring and friction in the kneading system composed of rotor and rotor, rotor and mixing chamber wall, upper push bolt and lower push bolt, so as to achieve the purpose of plastication. The plastication of the internal mixer not only has large production capacity and high plastication efficiency, but also has high degree of automation, low power consumption, and improved labor intensity and sanitary conditions. However, when the internal mixer is plasticating, the physical and mechanical properties of the vulcanized rubber will be reduced due to the high temperature and oxidative cracking of the rubber material. In addition, the equipment cost is high, the floor space is large, the cleaning and maintenance are difficult, and the adaptability is narrow. Therefore, it is generally suitable for industrial production with few rubber types and high rubber consumption.
The methods of plasticating in internal mixers usually include one-stage plasticizing, segmented plasticizing and plasticizing with chemical plasticizers. One-stage plasticizing is to put the raw rubber into the internal mixer at one time and continuously plasticize it under certain temperature and pressure conditions to the required plasticity requirements. Segmented plasticizing is usually carried out in two stages. First, the raw rubber is placed in the internal mixer for plasticizing for a certain period of time (the plasticizing time of a 20r/min internal mixer is 10 to 15 minutes), then the rubber is discharged, pounded, pressed, unrolled, cooled, and parked for 4 to 8 hours before the second stage of plasticizing (time is 10 to 15 minutes) is carried out to meet the plasticity requirements. The plasticity of the second-stage plasticized rubber can reach 0.35 to 0. 50 (Weishi). The addition of chemical peptizers is the same as the one-stage plasticizing. The amount of chemical peptizers added is generally 0.3% to 0.5% of the raw rubber, and it is added in the form of masterbatch to improve the dispersion effect. After using chemical peptizers, the plasticizing temperature can be reduced.
③ Screw plasticizer plasticizing Screw machine plasticizing is a continuous plasticizing method that uses the mechanical action between the screw and the bushing with serrated threads to crush, rub and stir the raw rubber and obtain the plasticizing effect at high temperature. The equipment used is mainly a single-screw one-stage plasticizer and a twin-screw two-stage plasticizer. Screw machine plasticizing has the advantages of continuity, high degree of automation, large production capacity, low power consumption, small footprint, and low labor intensity. It is most suitable for large-scale industrial production with few raw rubber varieties and high rubber consumption.
