With the continuous expansion of market demand for biodegradable materials, the quality requirements of products are getting higher and higher, and the requirements for the processing technology of biodegradable materials are also getting higher and higher.
Among them, extrusion molding is the most versatile processing method in the field of biodegradable material processing with good plasticizing effect, strong adaptability, high production efficiency, and continuous production. The screw combination is the key factor that affects the twin-screw extrusion effect.
The twin-screw extruder is mainly plasticizing in the pelletizing process, and it has both mixing and dispersing functions. The screw combination is an important factor in achieving the above functions. The properties of the main and auxiliary materials, the feeding sequence and position, the position of the exhaust port, the size of the negative pressure, and the temperature setting of each section of the barrel must be taken into account.
At the same time, because the objects of mixing are very complex, there is a problem of reasonable screw combination for each specific mixing process. Obviously, this combination is also diverse. The current combination design mainly depends on the accumulation of experience.
Nevertheless, the screw combination of the twin-screw extruder still has its basic rules to follow. The following is a detailed description and practical examples of the following three aspects for the universal application of biodegradable materials:
1. The science of screw
2. The importance of temperature control
3. Key points of screw adjustment
The twin screw extruder is divided into the following system parts:
1. Feeding system: including hopper, mixing motor, and feeding motor. It can prevent material accumulation and facilitate its smooth entry into the feed inlet.
2. External heating system: heating rods and cylinders are mainly used to efficiently heat up materials and promote plasticization.
3. Cooling system: Use a heat exchange system composed of heat transfer oil or water to reduce the heat of the fuselage, so as to effectively control the temperature of the cylinder.
4. Hydraulic screen changing system: Use replaceable filter screen to intercept impurities, improve the degree of plasticization, and ensure the uniformity and stability of the quality of the output materials.
5. Vacuum system: extract the moisture and other low molecular volatiles from the material.
6. Electronic control system: responsible for monitoring and controlling the related equipment of the main and auxiliary material system.
7. Screw system: The most important part of the extruder can be divided into conveying section, melting section (exhaust port), plasticizing section (vacuum port), and discharging section.
The screw system mainly completes the plasticization and conveying process of the material, which has a great influence on the performance and quality of the finished product. The screw parameter settings of different models and equipment of different manufacturers are different, which needs to be paid attention to.
The importance of temperature control ：
Biodegradable materials can only maintain the physical properties of the materials to the greatest extent within a specific temperature range that matches them. The twin-screw extruder must work within the above-mentioned temperature range, so effective temperature control is very important for the stability of product quality.
If the temperature fluctuates excessively, or because the amount of lubricant in the formulation system is not appropriate, the temperature in a certain zone will continue to rise, which will directly affect the use effect of the twin-screw extruder and cause the physical properties of the finished product unstable.
