1. Suitability for the rigid PVC (RPVC) manufacturing process
Advantages and Suitability: Rigid PVC formulations typically contain large amounts of fillers (such as calcium carbonate) and processing aids. A well-maintained used high-speed mixer, particularly one with a deep barrel and paddles designed in a propeller or turbine style, can generate sufficient frictional heat. If the motor power of the used equipment is sufficiently high (e.g., high power per unit volume), it can effectively accommodate the "hot mixing" process required for rigid formulations, rapidly raising the material temperature to approximately 110°C–120°C before proceeding to cold mixing.
Potential Issues: Attention must be paid to the wear condition of the inner wall of the mixing vessel. Since the fillers in rigid formulations are abrasive, severe wear on the inner wall of the used equipment-resulting in increased surface roughness-will not only affect the thoroughness of discharge but may also lead to localized overheating or uneven color mixing. Additionally, wear on the shaft seal can cause powder leakage, which significantly impacts product quality in rigid PVC production.
2. Suitability for the production process of soft PVC (SPVC)
Advantages and Suitability: When producing soft PVC, the mixing temperature is typically maintained slightly lower than for rigid PVC (generally around 100°C–110°C), with the primary focus being to ensure that the liquid plasticizer is fully absorbed into the PVC resin pellets. Used mixers equipped with variable speed control are particularly well-suited for this process. During the plasticizer addition stage, low-speed mixing is typically required to prevent clumping, and the speed is increased to high after the plasticizer has been absorbed to facilitate dispersion. If the blades of the used equipment are designed to provide effective material turnover (i.e., high material circulation efficiency), this can significantly accelerate plasticizer absorption and prevent the formation of "wet slurry"-like material.
Potential Issues: If the used equipment was previously used for hard PVC production over an extended period, there may be hardened residue buildup inside the vessel. When switching to soft PVC production, this residue may flake off and mix into the finished product, causing specks or impurities. Therefore, thorough cleaning prior to the production changeover is crucial. Additionally, soft PVC production sometimes generates fumes due to plasticizer evaporation; it is necessary to check whether the exhaust vents of the used equipment are unobstructed and whether the seals are oil-resistant.
3. Suitability for PVC cable compounds and high-filler formulations
Advantages and Suitability: This type of process requires an extremely high degree of final homogeneity in the mixture. In a well-designed used high-speed mixer, the clearance between the blades and the bottom of the vessel is typically maintained at around 3–5 mm. If this clearance is properly maintained, it creates a "rolling" effect that ensures liquid plasticizers and powdered stabilizers thoroughly coat the resin. Furthermore, if the used equipment is a "hot/cold mixing unit" (i.e., equipped with a cold mixer), it is highly adaptable to cable compound processing, as the material after hot mixing requires rapid cooling to prevent plasticizer separation and caking; the cold mixer plays a critical stabilizing role.
Potential Issues: High-filler formulations (such as those containing large amounts of flame retardants or fillers) place high demands on the mixer's torque. The aged motors and belt drive systems of used equipment may slip or overload under high loads, so attention must be paid to the maintenance status of the drive system.
4. Compatibility with PVC masterbatches or modified compounds
Advantages and Suitability: This process typically requires extremely high shear forces to disperse pigment agglomerates or modifiers. If a used mixer is capable of high-speed operation (e.g., linear speeds of 25 m/s or higher) and has sharp-edged blades (not excessively worn), it will be well-suited for this process with its high dispersion requirements.
Potential Issues: The addition of modifiers (such as CPE or ACR) can sometimes make the material viscous. If the discharge valve on the used equipment is not large enough or the discharge angle is not sufficiently smooth, this may lead to discharge difficulties and prolong the production cycle.
5. Considerations for Key Components: Heating and Cooling Methods
Friction Heating vs. Electric Heating: In modern processes, rigid PVC production largely relies on friction heating to raise the material's temperature. If secondhand equipment is equipped with excessively high electric heating power, it may actually cause the material to decompose due to localized overheating. Conversely, if the equipment's insulation is severely damaged, it may be impossible to reach the required process temperature through friction heating alone during production in cold weather.
Cooling System: For processes requiring precise temperature control (such as transparent PVC products), if the jacket or cooling channels of used equipment are severely scaled or clogged, cooling efficiency will be significantly reduced, leading to uncontrolled temperatures. It is essential to verify the effectiveness of the cooling system before purchasing.