What Does a Plastic Extruder Barrel Do?
Date:2022-6-29 Author:hcscrew
01 What is an Extruder Barrel?
The barrel part of an extruder is rarely mentioned in the content that describes the screw. However, the extruder barrel, along with the screw, is one of the core components of an extrusion system. The barrel operates under high temperatures, high pressures, and abrasive conditions, and sometimes even corrosive environments. It contains pressurized and heated material, with internal pressures reaching up to 55 MPa and working temperatures typically between 180-250°C. Inside the barrel, plastic is plasticized and pressed. Thus, the barrel is equipped with a heating system and cooling system to transfer heat to and from the material.
02 Heating and Cooling Systems for the Barrel
Several methods are used to heat the barrel, including resistance heating, electric induction heating, cast aluminium heater heating, and far-infrared heating. The cooling system prevents the plastic from overheating or cools it quickly when the barrel is shut down to avoid resin degradation or decomposition. Water cooling and air cooling are both employed for barrel cooling. Additionally, the barrel has a machine head and a filling port. The roughness of the barrel’s inner surface and the presence of grooves significantly affect the extrusion process.
03 Structure of the Barrel
There are two types of barrels: integral and assembled.
Integral Barrel: Machined from a single blank, this design offers superior manufacturing and assembly precision, facilitating the setup and disassembly of heating and cooling systems. It features axially distributed heating systems and is frequently used in production. However, it requires high machining standards. High-productivity screw barrels with L/D ratios of 33 to 40 can reach lengths exceeding 5 meters.
Assembled Barrel: Constructed from several barrel sections, this design allows for adjusting barrel length according to the use and product type, enhancing versatility. Assembled barrels require higher accuracy as they are connected primarily by flange bolts, which may reduce heating uniformity, increase heat loss, and alter the heating and cooling system. Choosing a reputable manufacturer for assembled barrels is crucial to ensure precision and stability.
04 Barrel Materials and Wear Resistance
To meet the requirements and reduce costs, barrels are usually made from carbon steel or cast steel with an alloy steel bushing inside to enhance wear resistance. Xaloy alloy, developed in recent years, is an abrasion and corrosion-resistant material cast inside the barrel, offering up to ten times higher wear resistance than nitrided steel. Custom SKD steel bushings can also be inserted into the barrel wall to increase friction resistance.
05 Parameters of the Barrel
To improve the carrying capacity of solid materials, longitudinal grooves are opened in the inner wall of the barrel’s charging section, near the hopper. This section is conical, with the groove length typically being about (35)D. The taper size is adjusted based on material particle size and screw diameter, reducing as the screw diameter increases.
The shape and location of the feed opening on the barrel significantly impact feeding efficiency. The barrel feed opening should ensure smooth and efficient material entry, preventing bridging. Common shapes include round, square, and rectangular, with rectangular openings being most prevalent.
06. Barrel Mounting Accessories
A porous plate and a strainer are located between the barrel’s front end and its head. The porous plate features holes with diameters of 3 to 6 mm, covering 30 to 79% of its surface area, transforming rotary material flow into linear flow and ensuring uniform plasticization. It also prevents impurities and unplasticized materials from passing through. The porous plate supports the filter if the barrel has one, but it increases extrusion viscosity, making it unsuitable for materials with poor thermal stability like hard PVC.
Summary
Extruder barrels play a critical role in the extrusion process. This article provides valuable information to help you optimize your barrel construction. For more details on extruder barrels and customization services, contact HUACHEN Screw, a professional screw barrel manufacturer.
About HUACHEN Screw
Since 1993, HUACHEN Screw has been a leading screw barrel manufacturer in Zhoushan Jintang. We specialize in designing and processing twin screw barrels and high-speed extruder screw barrels, offering a wide range of services, including design, modification, and customization. We have successfully exported and supplied screw barrels to customers worldwide.
For more information on optimizing your extruder single screw barrel design, contact HUACHEN Screw.
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