Principles to follow when using a masterbatch extruder

There are single-screw extruders and twin-screw extruders for masterbatch extrusion, and today we will talk about the principles that should be followed when using twin-screw extruders for masterbatch extrusion.

Here is the list of contents

Principle of construction

Temperature principle

Speed reduction principle

Principle of structure

The basic mechanism of the extrusion process is simply a screw that rotates inside the barrel and pushes the plastic forward. The structure of the screw is a ramp or slope wrapped around a central layer, which is designed to increase pressure in order to overcome higher resistance. In the case of an extruder, there are three types of resistance to overcome: friction, both between the solid particles (feed) and the barrel wall and between them in the first few turns of the screw (feed zone); adhesion of the melt to the barrel wall; and internal flow resistance as the melt is pushed forward.

Temperature Principle

Extrudable plastics are thermoplastics, which melt when heated and solidify again when cooled. Therefore, heat is required during the extrusion process to ensure that the plastic can reach its melting temperature. So, where does the heat to melt the plastic come from? First, the pound preheats and barrel/die heaters may play a role and are very important at startup. In addition, motor feed energy, the frictional heat generated in the barrel as the motor overcomes the resistance of the viscous melt and turns the screw, is the most important source of heat for all plastics except for small systems, low-speed screws, high melt temperature plastics, and extrusion coating applications.

Speed Reduction Principle

In most extruders, screw speed is changed by adjusting the motor speed. The drive motor typically spins at a full speed of about 1750 rpm, which is too fast for the extruder screw. If it rotates at such a fast speed, too much frictional heat is generated and a uniform, the well-mixed melt cannot be prepared because the residence time of the plastic is too short. A typical reduction ratio should be between 10:1 and 20:1 with gear or pulley set for the first stage, but gear and screw positioned in the center of the last large gear for the second stage. For some slow running machines (e.g. twin screws for UPVC), there may be three reduction stages and the maximum speed may be as low as 30 rpm or less (ratios up to 60:1). On the other hand, some very long twin screws for blending can run at 600 rpm or faster, thus requiring very low reduction rates and deeper cooling.

Nanjing Haisi Extrusion Equipment Co., Ltd. is a high-tech enterprise consisting of a team with many years of experience in R&D, design, manufacturing technology, sales, and service in the extruder industry. We now mainly focus on developing high activity single screw, twin screw, and compound extruders, along with complete factory manufacturing and related technologies. According to the material system and process flow, we realize the optimization of mixing equipment structure design, combining electromechanical and technical systems into one, fully reflecting our years of experience and comprehensive technology. Our production range includes single-screw extruders, co-rotating twin-screw compound extruders, auxiliary equipment, etc. If you are interested in our products, welcome to contact us!