Parallel screw barrel

Types of Parallel Screw Barrels

A parallel screw barrel is an essential part of the injection molding machine, which helps to convey, heat, and mix materials. The parts of the screw barrel are as follows:

• Screw

  The plasticizing screw is the heart of the parallel screw barrel. It conveys raw plastic from the feed section to the melt section and then to the injection section. The feed section is where the plastic comes in, and it can be in the form of pellets or granules. In the deep grooves of the screw, the plastic is conveyed forward. In some screws, there are heaters and coolers to help with temperature control. The sub-section of the feed section is known as the transition zone, where the plastic changes into a molten state and is then ready to be injected into the mold cavity. Once it reaches the melting zone, the melt of the plastic undergoes mixing and homogenization due to the geometric features of the screw. Finally, in the last section, the plastic is pushed down with high force into the injection nozzle to fill the mold cavity.

• Barrel

  The screw fits into the barrel, which provides support and a pathway for the plastic to move. The barrel is usually made of high-strength alloy steel to withstand the abrasion and wear of plastic. Inside the barrel, there may also be grooves like the ones on the screw to provide additional mixing of the material.

• Heating& Cooling

  Sometimes, to heat the plasticized material, heaters are installed around the barrel. In some cases, to prevent overheating, cooling systems are also installed, which can include water channels or cooling jackets around the barrel.

• End Cap and Flanges

  Finally, the end cap and flanges are where the parallel screw barrels attach to other components of the injection molding machine, providing secure connections and seals.

Specification and maintenance of the parallel screw barrel

There are two types of barrels that make up the parallel twin screw extruder: feeding and conveying barrels. Each has unique specifications.

• Feeding barrel

  The feeding barrel is shorter due to the earlier melting stage of the material. It is generally around 30-40% of the entire screw barrel. Key specifications include a flight pitch of 1.3-2 times the flight depth. The flight width can vary based on the material and ranges up to 70mm. The temperature of the feeding barrel is around room temperature to 80℃. The size can alter depending on the type of material to be processed.

• Conveying barrel

  The conveying barrel is much longer and makes up 60-70% of the parallel screw barrel. Temperature is also much higher to ensure complete melting of the material. The depth and pitch of the flights is a little more than in the feeding barrel. Flights are also narrower and can be as little as 20 mm based on the specifications of the scree barrel. In the conveying barrel the temperature rises to about 200 to 300 ° C. There are also designs where heating bands are used to melt the materials.

Maintenance tips for screw barrel:

• Clean: Regularly clean the screw and barrel to remove any material buildup or residue that could affect performance. Use specialized cleaning agents or solvents to ensure a thorough cleanup. Apart from this the extruder's feeding should also be cleaned to ensure no foreign material gets into the production line,.
• Lubrication: Apply high-temperature lubricants to the moving parts of the screw and barrel to reduce friction and wear. This will help extend the lifespan of the components and maintain their efficiency.
• Regular inspection: Check the parallel screw barrels for any signs of damage or wear, such as cracks, blisters, or deformities. Promptly repair or replace any damaged parts to prevent further damage and ensure safe operation.
• Temperature control: Maintain proper temperature control during the extrusion process to prevent overheating or over-shearing of the screw and barrel. Use temperature controllers and monitoring systems to ensure optimal temperature settings.
• Proper feeding: Ensure proper feeding of materials into the parallel twin screw extruder to avoid material bridging or backflow, which can cause excessive screw and barrel wear. Utilize feeding devices that provide uniform and continuous material feeding.
• Operator training: Provide proper training to operators on the maintenance and handling of parallel screws and barrels. It's important to ensure they understand the importance of maintenance and follow the recommended procedures to avoid mishandling and ensure equipment longevity.

Applications of parallel screw barrels

Parallel screw barrels are versatile tools that play a critical role in a wide range of industries, including food processing, chemical manufacturing, plastic processing, and rubber processing.

• In the food industry, parallel twin-screw extruders are widely used to efficiently handle and process various food materials, such as cereals, starch, protein, and additives. The extrusion-cooking process improves the digestibility of carbohydrates and the nutritional quality of the product. It also changes the structure of food to achieve puffing and other desirable qualities. Moreover, the twin-screw extruder is an effective tool for compound treatments of food materials, such as dehydration, sterilization, enzyme inactivation, and flavor improvement. Additionally, it is suitable for the processing of textured vegetable protein (TVP), aquatic feed, pet feed, and screw oil extraction.
• In the chemical industry, twin-screw extruders are widely used in polymer blending and modification. They are employed to add fillers, enhance blends, and achieve various chemical reactions, such as graft copolymerization. The chemical reaction carried out by twin-screw extruders can be used for material compounding, degradation, stabilizing treatment, and other chemical processing.
• In the plastic processing industry, twin-screw extruders are extensively used in the melt conveying and feeding of plastic materials. They are suitable for processing materials such as PVC, PS, ABS, PP, polyethylene, and engineering plastics. Parallel twin-screw extruders are also used for the blending and modification of plastic materials. They can achieve mixing, polymer reactions, filling, and other functions, thereby improving the properties and performance of plastic materials.
• In the rubber processing industry, parallel twin-screw extruders are used to uniformly mix rubber compounds and additives. They can achieve optimal dispersion and consistency of materials. Rubber parallel twin-screw extruders are also employed for the modification of rubber materials to improve their performance and adaptability in different applications.

How to choose parallel screw barrels

• Material selection

  The material of the parallel screw barrel has a significant effect on its performance and durability. Some common materials are usually used for parallel screw barrels.

  The alloy steel can ensure the screw barrel's strength, stiffness, and resistance to deformation. In addition, alloy steel offers better durability and stability under high temperature and pressure, which is suitable for high-performance and demanding applications.

• Compatibility with equipment

  It is essential to ensure that the parallel screw barrel is compatible with the existing equipment. Consider factors like size, connection form, and working parameters. The screw barrel will fit and work properly with the present device if its size and connection form match those of the equipment.

• Application requirements

  Various materials and products use parallel screw barrels, which have their distinct features and demands. Consider the particular demands of the application, such as the type and quality of the materials, processing temperature, pressure, and other factors. Select a parallel screw barrel that meets the application requirements to ensure optimal processing performance and quality.

• Cost-performance ratio

  Cost-performance ratio is an important consideration in making a decision. Comparing the performance, quality, and features of different parallel screw barrels, the one that balances cost and performance is selected to meet the budget constraints and requirements of the application.

Parallel screw barrel Q&A

Q1: How to install screw barrels into injection molding machines?

A1: Injection molding screws and barrels usually have two standard fittings. Therefore, matching the parts together will not be complicated. However, users should check the alignment of the heating bands and the barrel before lowering the screw into position. The bands should not come into contact with the barrel's insulating layer. Adjustments may be necessary if the heating bands are misaligned.

Q2: What are the trends in the screw barrel market?

A2: The market will probably grow because new innovations in material processing continue to emerge. Demand for material recycling is rising and increasing the need for parallel twin screws. Also, the adoption of 3D printing technology in manufacturing industries is boosting the market growth.

Q3: What are the properties of a good screw barrel for recycling plastics?

A3: A high-quality parallel screw barrel for recycling plastics should have good wear resistance, corrosion resistance, high temperature resistance, and high mechanical strength.

Q4: What are the common problems of a screw barrel?

A4: The screw and barrel may wear out over time, causing slippage. Damage to the drive mechanism, such as a stripped belt or a snapped pull cable, may cause the feed door not to open. Therefore, inspecting the feed port and exit section for clogs is crucial.

Q5: How much is the wear-resistant screw barrel for injection molding?

Agents can spend about 10 pieces to buy a wear-resistant screw barrel. The price will increase if they buy more pieces due to bulk savings. A wear-resistant screw barrel is parallel and designed for injection molding machines.