What's the process and methods of pvc extruder?

Plastic extrusion is a process in which plastic materials are transformed from solid to liquid and remade into finished products. First, the plastic particles are gravity fed from the hopper into the sheathed screw. When the screw rotates around its axis, it conveys, melts and pressurizes the plastic. From there, the molten material is forced through a mold, which shapes it into a specific cross section to produce parts with a potentially wide range of lengths. During the twin screw extrusion machine process, the plastic changes from a solid to a liquid and then back again without sacrificing its unique properties. Therefore, waste parts can be ground and re-extruded with minimal degradation, making extrusion a popular method to reduce or recycle plastic waste. In this article we mainly discuss about the detail process and methods of pvc extruder.

 

The following knowledge points are listed below:

l  Raw thermoplastic resins for pvc extruder

l  Single screw extrusion machinery process of pvc extruder

l  Extrusion mold of pvc extruder

l  Cooling and sizing of pvc extruder

 

Raw thermoplastic resins for pvc extruder

Many plastic resin manufacturers sell raw materials and recyclable products made from extruded waste, which are remelted and returned to pellets. These companies often purchase excess inventory, obsolete parts, or unused resin from the production process for regranulation. This type of recycling can be a cost-effective and valuable method to eliminate industrial plastic waste.

Instead of recycling, virgin thermoplastic resin can be purchased and laboratory purity certified, and standard technical grades can also be used for general purposes. In addition, biodegradable plastics are becoming more common, especially in the production of blow-molded bottles.

Resin manufacturers may add colorants, enhancers, or flocking agents to the material for transportation. Later, when the manufacturing company receives the plastic raw material, it can be poured into a hopper and extruded without further pretreatment for pvc extrusion machine.

Single screw extrusion machinery of pvc extruder

There are many hardware considerations that affect the quality of pvc extrusion. For example, screw geometry, screw speed, and barrel heater temperature must be calibrated to suit the specific type of plastic being manufactured. Incompatible settings may hinder production and even damage equipment.

As the main component of the pvc extruder, the screw can accomplish multiple tasks, including moving, melting, and pumping the plastic before it passes through the mold. A gearbox driven by a variable speed motor usually turns a screw, which is sealed in a tightly fitting cylinder. The mechanism is divided into three parts, dedicated to performing a series of specific tasks.

The feeding part is located at the rear of the screw unit and contains a hopper that feeds resin pellets into the machine. When the screw rotates, it uses threads or "flyers" to pull the plastic forward. The barrel heater helps the plastic form a sticky surface to improve the friction between the plastic and the barrel wall. Without this friction, it is difficult for plastics to achieve lateral movement.

When the plastic moves forward, it enters the transition zone, the melting zone. At this stage, the diameter of the root of the screw is increased, while the size of the blade is reduced to melt the plastic by compressing and shearing the wall of the plastic barrel for pvc two stage extruder.

The design of the barrier screw specifically considers the transition section. These screws fly with special barriers to improve mixing and melting by dividing molten plastic and solid plastic into different channels. The diameter of the obstacle flight is smaller than that of the conventional flight, providing a passage for molten plastic while blocking solid particles until they liquefy. As the plastic continues to flow along the transition section, the width of the melt channel increases and the solid portion decreases until there are no plastic particles.

After the plastic is melted and compressed, it is introduced into the metering section. Here, the plastic is pumped under pressure, while the screw root diameter and flight size remain unchanged. Some extrusion screws use special mixing heads to homogenize the plastic before entering the next section

Extrusion mold of pvc extruder

The product is finally designed in the mold. The plastic enters the front flange of the mold from the metering part, which is bolted to the end of the pvc extruder barrel. It flows around a metal separation tool or "mandrel" suspended in the center of the channel. At the rear of the mandrel, there is a pin and a boss to adjust the size of the product. Both the pin and the welding ring are detachable, which makes it relatively simple to reconfigure the mold or replace worn parts.

Compressed air is introduced into a support of the mandrel and discharged from the mold pin. This airflow prevents the product from collapsing when it leaves the mold. Then, the parts undergo post-processing.

Cooling and Sizing of pvc extruder

When the product leaves the mold, it enters the vacuum chamber, where it is pulled through the dimensional ring. The combination of vacuum stretching and air pressure forces the plastic to conform to the shape of the ring. If the size ring is worn, it will leave longitudinal scratches on the product. The vacuum chamber is filled with water, which cools the plastic into a hard solid. The cooled product is pulled by a belt slide, cut into a certain length or wound on a reel.

That’s all about the process of pvc pellet making extruder.