Different Types of Extrusion Screw

Different Types of Extrusion Screw

The process of extrusion involves varying amounts of heat, pressure, and chemical energy. Different types of screw can be used to process different materials. Some types are dispersive, while others are shear. While both can be effective, they can cause more energy consumption and increase the melt temperature. Distributive mixers can help homogenize temperature, colors, and additive distribution.

Barrier screw

A barrier screw is a mechanical device that mixes raw materials thoroughly before extrusion. These screws are made using high-quality raw materials sourced from trusted vendors in the market. They are widely recognized for their precision and dimensional accuracy. The following are the characteristics of these screws. They have the potential to meet the needs of various industries.

Among the advantages of barrier screws is the ability to precisely pinpoint the melting point of the plastic. This is not possible with a conventional screw. In conventional screw designs, melting takes place in the compression section where the channel depth is gradually reduced. This forces the unmelted polymer to the outside of the screw. The resulting high shear forces cause the polymer to melt.

Distributive mix/melt type screw

The screw is the key element of a screw extruder that mixes the feed material. Mixing is defined as the process of reducing the non-uniformity of composition through physical motion of the ingredients. There are two types of mixing in a screw extruder: dispersive mixing and distribution mixing. Distributive mixing results in more random distribution of particles, whereas dispersive mixing reduces the size of cohesive particles.

The mixing action in a screw extruder varies depending on the materials involved. In processes using one screw, mixing is important for homogenizing regrind with virgin resin and incorporating color concentrates. The mixing process is a vital part of a process, and many presentations have been given on its importance. Unfortunately, many processors confuse poor mixing with poor melting. In fact, mixing and melting are not the same thing. This is why mixing and melting issues often require different solutions in the same screw design.

Dispersive mixer after barrier section

A Dispersive mixer after the barrier section of an extrusion screw improves the solid conveying rate of the product. Its high surface area makes it suitable for high-speed processes. Furthermore, this process can increase the solid conveying rate and increase the output of the product.

The mixing section includes a central shaft 34 and several screw flights 30. The flights convey material forward and mix it. The screw diameter (D) is determined by the distance between the flights 30. The screw flight 30 has a front pushing face 36 and a rear face 38. The cross-section profile of the flight 30 is indicated by reference character 40.

The Distributive mixer is available in a variety of configurations. The type chosen depends on the composition and properties of the melt. The L/D of the extrusion screw also determines the choice of the mixer.

Torx drive pan head

Torx Drive pan head screws feature a chamfered or curved head, a recessed torx drive, and a locking nut. The screws are often used in a variety of applications, such as automotive, consumer electronics, and construction. They're easily installed using a six-lobed torx wrench, and they provide excellent torque transfer and lower wear on tools. They also don't damage surface coatings.

Another advantage of the Torx drive is that it can handle higher torques than a conventional hex socket head. Furthermore, the vertical sidewalls maximize tool engagement while minimizing the risk of cam-out forces. The Torx drive design also enables drivers to use smaller head sizes for the same torque, which is advantageous in applications with limited space.

High shear mixing element

Extrusion screw mixing elements can be designed for good dispersive mixing. For example, in film extrusion, the screw must have a mixing section to homogenize the melt before the process begins. The screw's rheological properties must also be taken into account during design.

In an extrusion screw, the mixing element consists of a plane in which material flows around the screw. This zone is called the intermesh region, where surface velocities are largely the same. The material in the intermesh region flows from one screw to the next, while in flighted regions the flow tends to follow a figure-eight pattern. The mixing element of a screw can be either a single screw or two twin screws that are joined together by an intermesh structure.

The screw rotation also helps to improve dispersive mixing. The rotation of the screw enables material to pass through the high-stress areas, which is necessary for dispersion.