The Role of Feed Screws in The Plastics Melt Stream Process

Feed screws, also known as extruder screws, play a crucial role in the melt stream process of the plastics industry. The melt stream process transforms raw plastic materials into a continuous, homogenized, and viscous molten mass, which can be further shaped and processed into various products like films, sheets, pipes, profiles, and more. The feed screw is an essential component of the extruder machine, the primary equipment used in the melt stream process.

The role of the feed screw in the melt stream process is explained in detail by understanding its different sections and their functions:

1. Solid conveying (feed) zone: The feed screw consists of a helical channel or flights with a rotating shaft that runs along its length. The screw begins with a hopper where raw plastic material, usually pellets or granules, is loaded. The rotation of the screw transports the raw material forward, creating a solid conveying zone. The screw geometry in this zone efficiently moves the plastic material toward the subsequent zones.
2. Compression (transition) zone: The depth of the screw channel decreases gradually in this zone, causing the plastic material to compress. This compression generates heat through friction, which melts the plastic along with external heating elements. At the same time, the screw design ensures proper mixing and homogenization of the plastic materials.
3. Melting (metering) zone: This zone is characterized by a constant channel depth, where the plastic material becomes fully molten. The screw's geometry creates a uniform and consistent melt flow while providing sufficient back pressure to ensure the homogenization of the molten plastic. Additional mixing elements may be incorporated into the screw design to enhance mixing and homogenization further.
4. Discharge (melt) zone: In this final zone, the screw conveys the molten plastic towards the extruder die, designed to shape the material into the desired product form. A screen pack and breaker plate are typically placed before the die to filter out contaminants and ensure a uniform melt flow.

Feed screws play a vital role in the overall efficiency and quality of the melt stream process. The design of the screw and its various geometries can significantly affect the processing conditions, output rate, and final product quality. Different types of feed screws are available, tailored to the specific requirements of the plastic materials and end products, such as single-screw, twin-screw, and multi-screw extruders. These screws may also be classified based on their compression ratio, screw profile, and mixing elements.

For more information about feed screws, contact AP Corp.

https://a-pcorp.com

(508) 351-6200

Combat the Hazards of Plastics Screw and Barrel Wear

This post is abstracted from an excellent article from Plastics Technology Online
written by Jim Callari. Read the full text here.

Industrial-grade screw and barrel wear cuts throughput speeds, producing scrap before shutting down. For the first time, technology is making progress in unraveling the mystery of screw and barrel wear. 

There has been a lot of injection molding machine innovation in the past year. And now, Glycon Corp. has the technology to test wear within the plasticating device. Glycon is in the first phase of rolling this technology out in the industry. It will concentrate on extrusion and blow molding. 

With this capability, they have developed the technology to calculate the rate of wear and predict future wear. This data determines the most cost-effective time to replace these components.

Glycon has been working on measuring wear since 1986 gained their first patent as Great Lakes Feedscrews. The company expanded the invention to include measuring barrel wear and was awarded additional patents in 2006, 2007, 2008, and 2019. 

Wear and tear challenges are well documented over the years, and plastic processors know the symptoms. Many machine operators compensate by making changes to the screw speed or temperature settings. The problem is, both of these changes would ultimately result in lower efficiency and higher scrap rates. 

The new system called EMT (short for Electronic Measurement and Tracking), includes Glycon's flite-scan eddy-current sensors mounted in one or more positions within a SmartBarrel. These barrels also have SmartPorts, another innovative technology offered by Glycon. 

Measurements will be conducted routinely at the processor's plant by field technicians using a Flite-Scan sensor. Several eddy-current sensors were tried over the years. Multiple sensor manufacturers were collaborated with, but all ran into failure at high temperatures in the plasticating units. 

Micro-Epsilon, a leading manufacturer of sensors that measure displacement, distance, position, vibration, dimension and thickness, was the eventual choice because their sensors proved much more robust and provided reliable readings up to 600 F. 

The EMT system is not only to analyze the data to determine the optimum time to replace or repair worn screws or barrels to optimize productivity but also to relate the wear to:

• Materials of screw/barrel construction.
• Screw/barrel alignment. 
• Polymers being processed.
• Impact of abrasive fillers.
• Performance related to wear, including production rates, cycle times, energy consumption, melting rates, head pressures and melt temperatures.

The Glycon EMT system's advantages are that it provides precise measurement of the wear on the OD of the feedscrew and the barrel's ID and its simplicity and cost-effectiveness. It allows maintenance personnel to plan to measure intervals and to schedule changeouts at convenient times based upon wear-rate data rather than 'running to failure' and having to run inefficiently or not at all.

For more information about the new Glycon technology in New England and Upstate New York, contact AP Corp. Call them at (508) 351-6200 or visit their website at https://a-pcorp.com.

Plastics Industry Feed Screw Classification White Paper

The feed screw is used in plastics extrusion to force melting plastic resin through a die into a mold to form a desired shape. As screw designs have evolved through the years, there are several generic categories.

Glycon Corporation, the industry leader manufacturer of high performance and innovative feed screws, has put together this white paper describing the classifications of feed screws used in the plastics industry.

DOWNLOAD THE FEED SCREW CLASSIFICATION WHITE PAPER FROM THE AP CORP WEB SITE HERE

AP Corp.
https://a-pcorp.com
(508) 351-6200

Why Plastics Industry Feed Screws are Designed the Way They Are

Download the white paper here.

The selection of the proper screw for a given injection molding or extrusion application can be critical to its success.

Screw geometry — length-to-diameter ratio, profile, channel depth, compression ratio, helix angle and a host of special design features — has everything to do with how well the screw performs in a given application.

There are documented applications where customers have improved production rates or reduced cycle times by 30 or 40% simply by switching to an improved screw design. Similarly, reject rates have been lowered from more than 4-6% to less than 1% by incorporating a custom designed mixing screw.

And experience shows that the amount of color concentrate required to achieve optimum color mix can be typically reduced from 4% (of the total blend) to 2%, just by using an optimized screw design. When considering resin and concentrate costs, payback for an optimized screw and non-return valve design can be almost immediate.

This white paper, published by Glycon Corporation, provides an in-depth look into plastics industry feed screw design.

DOWNLOAD THE WHITE PAPER FROM THIS AP CORP WEB PAGE

What are Plastics Industry Feed Screws and How Are They Made?

Feed screw maintenance.

Plastics industry feed screws, or feed screw augers, are mechanisms that use rotating helical screw blades to move plastics pellets through the barrel of molding and extrusion equipment. The feed screw transports the plastic as it changes phase from solid to viscous liquid through friction, shear, and conductive heat transfer. 

A typical feed screw has three zones. Plastic pellets enters the screw feed section where the pellets are compacted and conveyed. Next is the transition (or compression) section, where the plastic is compressed, conveyed, and melted.  Finally, the liquid plastic moves to the metering section where it is precisely controlled at optimum temperature and viscosity.

For more information about feed screws, or any part of the injection molding process, contact:

AP Corp.

https://a-pcorp.com

508-351-6200

Diagram of injection molding process.