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How Polymer Melts in Single-Screw Extruders | Plastics Technology

A 360-degree look at resin conveying systems: types, operation, economics, design, installation, components and controls.

This Knowledge Center provides an overview of resin moisture and the drying process, including information on the best drying practices for your manufacturing facility. Mini Thermoforming Machine

How Polymer Melts in Single-Screw Extruders | Plastics Technology

Everything you need to know about plastics compounding technology—from feeding solutions to application profiles and expert advice.

Combat the skilled labor shortage using this comprehensive resource to train your own plastics processing experts.

Deep dive into the basics of blending versus dosing, controls, maintenance, process integration and more.

This Knowledge Center provides an overview of the considerations needed to understand the purchase, operation, and maintenance of a process cooling system.

Learn about sustainable scrap reprocessing—this resource offers a deep dive into everything from granulator types and options, to service tips, videos and technical articles.

Flat-to-downward trajectory for at least this month.

A mixed bag, though prices likely to be down if not flat for all this month.

Trajectory is generally flat-to-down for all commodity resins.

Flat-to-down trajectory underway for fourth quarter for commodity resins.  

Generally, a bottoming-out appears to be the projected pricing trajectory.

PS prices to see significant drop, with some potential for a modest downward path for others. 

Resin drying is a crucial, but often-misunderstood area. This collection includes details on why and what you need to dry, how to specify a dryer, and best practices.

Take a deep dive into all of the various aspects of part quoting to ensure you’ve got all the bases—as in costs—covered before preparing your customer’s quote for services.

In this collection of articles, two of the industry’s foremost authorities on screw design — Jim Frankand and Mark Spalding — offer their sage advice on screw design...what works, what doesn’t, and what to look for when things start going wrong.

In this collection, which is part one of a series representing some of John’s finest work, we present you with five articles that we think you will refer to time and again as you look to solve problems, cut cycle times and improve the quality of the parts you mold.

Gifted with extraordinary technical know how and an authoritative yet plain English writing style, in this collection of articles Fattori offers his insights on a variety of molding-related topics that are bound to make your days on the production floor go a little bit better.

In this three-part collection, veteran molder and moldmaker Jim Fattori brings to bear his 40+ years of on-the-job experience and provides molders his “from the trenches” perspective on on the why, where and how of venting injection molds. Take the trial-and-error out of the molding venting process.

Mike Sepe has authored more than 25 ANTEC papers and more than 250 articles illustrating the importance of this interdisciplanary approach. In this collection, we present some of his best work during the years he has been contributing for Plastics Technology Magazine.

In this collection of content, we provide expert advice on welding from some of the leading authorities in the field, with tips on such matters as controls, as well as insights on how to solve common problems in welding.

Mold maintenance is critical, and with this collection of content we’ve bundled some of the very best advice we’ve published on repairing, maintaining, evaluating and even hanging molds on injection molding machines.

Thousands of people visit our Supplier Guide every day to source equipment and materials. Get in front of them with a free company profile.

The global plastics industry has been navigating through what is arguably the most volatile period in decades. Unprecedented amounts of new production capacity are scheduled to start in North America, Europe, and China in the near term and compete for demand during a period of economic challenges. How will trade flows shift? Will this lead to regional cost disparities and rationalization? Energy transition and sustainability targets continue transforming the plastics market and increasing the competitive landscape. As the market evolves, what impact will new technology, policy, regulation, the growing role of chemicals versus fuel and other factors have on industry restructuring and business models? At GPS 2024, leading global experts will come together to discuss pivotal impacts and initiatives shaping the plastics industry. Join us and participants from across the globe to gain the latest insight and deep analysis as you connect with your peers and industry professionals. This year’s conference will explore the theme Disruptive Global Dynamics Reshaping Plastics and include a full day workshop focused on the Global Plastics Business and Plastics Transition to Circularity, 1.5 days of expert content and numerous networking functions.

Every three years, leaders from almost every major industry gather at NPE to advance their businesses through innovations in plastics. The largest plastics trade show in the Americas, NPE offers six technology zones, keynote speakers, workshops and opportunities to build partnerships. 

The 3D Printing Workshop @ NPE2024 – The Plastics Show, is an immersive, half-day workshop focused on the emerging possibilities for part production via 3D printing and additive manufacturing. Presented by Additive Manufacturing Media, Plastics Technology and MoldMaking Technology, the 3D Printing Workshop will build upon a successful model first introduced at IMTS 2014. Attendees will benefit from a program focused on practical applications of 3D technologies related to plastics processing. This event will conclude with a 3D Printing Industry Reception sponsored by Additive Manufacturing Media.

The Society Plastics Engineers (SPE) Extrusion Division and the SPE Eastern New England Section will co-host the Screw Design Conference-Topcon on June 19-20, 2024 @ UMass Lowell in Lowell, MA.  This highly technical program will focus upon screw design principles for single and twin screw extruders with wide ranging topics relating to screw designs for feeding, melting, mixing, venting and pumping plastics products and parts.   Areas of focus will include screw designs for melt temperature and gel management, gel minimization, bioplastics, recycled materials and foaming.   In addition to the technical sessions, a tour of the UMass Lowel Plastics Processing Laboratories will be integrated into Day 2 of the event.    This program is not just for screw designers, but to help anyone responsible for any type of extrusion operation to evaluate existing extrusion equipment; and also to prepare for future projects. Price to attend:  Less than $1000!  Registrations will be accepted in early 2024. Call for papers – To be considered to give a presentation, please submit a talk title and abstract on or before December 15 to:   Technical Chair: Eldridge M. Mount III, e-mail emmount@msn.com Corporate sponsorships - A limited # of corporate sponsorships (15) are available on a 1st come basis.  Included is a 6’ tabletop display (must fit on table), denotation in all promotional activities, and 1 no charge registration.  To become a sponsor contact: Charlie Martin, Leistritz Extrusion, e-mail cmartin@leistritz-extrusion.com, cell 973-650 3137 General information:   A reception on Day 1 and a tabletop display area will allow the attendees to meet and discuss state-of-the-art screw technologies with industry experts.  The SPE Extrusion Division will issue a “Screw Design Certificate” to all participants who have attended the program.  Students are encouraged to attend and will receive a discounted rate.   For additional information contact:  Program Chair:  Karen Xiao, Macro Engineering, KXiao@macroeng.com

Debuting in 2010, the Parts Cleaning Conference is the leading and most trusted manufacturing and industrial parts cleaning forum focused solely on delivering quality technical information in the specialized field of machined parts cleansing. Providing guidance and training to understand the recognized sets of standards for industrial cleaning, every year the Conference showcases industry experts who present educational sessions on the latest and most pressing topics affecting manufacturing facilities today.  Discover all that the 2022 Parts Cleaning Conference has to offer!

Presented by Additive Manufacturing Media, Plastics Technology and MoldMaking Technology, the 3D Printing Workshop at IMTS 2024 is a chance for job shops to learn the emerging possibilities for part production via 3D printing and additive manufacturing. First introduced at IMTS 2014, this workshop has helped hundreds of manufacturing professionals expand their additive capabilities.  

In today's manufacturing environment, robust processes that meet strict industry and regulatory standards are essential. With the advent of servo-driven ultrasonic welding technology, enhancing product quality and maintaining consistency has become remarkably effortless. Discover the fundamentals of ultrasonic welding, delve into vital components within these systems, explore how servo-driven ultrasonic welding enhances weld quality via advanced control features and gain insights into optimizing your assemblies for welding in these high-performing machines. Join Dukane to unlock the potential of ultrasonic welding in modern manufacturing for plastic devices and components. Agenda: Fundamentals of ultrasonic welding Key components in an ultrasonic welding system Using servo-driven ultrasonic systems to control your welding process Designing your parts and components for servo-controlled ultrasonic welding

This webinar will help you make informed decisions to confirm the equipment access stairs in your facility are OSHA compliant and meet the highest standards of safety and ergonomics. Agenda:  Identifying opportunities to increase safety in the work place Utilizing space saving stairways Ensuring code compliance for equipment access

4.0, EUROMAP, OPC, OLE, QC, DSN, SQL, VNC, MES, ERP, FTP, CMS, SPI — are you confused by all buzzwords being tossed around in the plastics industry? Not convinced the data collection is necessary? Or are you unsure of how it could be implemented and improve your molding processes? Wittmann has been on the cutting edge of the data collection push for nearly 20 years. In this webinar, take a step back from the idea of the manufacturing facility of the future and discuss what you can do today to improve your process. Using readily-available technology, Wittmann can help reduce downtime, limit scrap and wasted material, and predict required maintenance. Let the experts at Wittmann help you understand: what data can be collected, what that data can be used for, what systems are used, and how to implement them. Agenda: Demystifying the terminology Tracking the material flow and lot information through the material handling system The data available from various auxiliary equipment, such as: dryers, blenders, mold temperature controls and robots Automating the process through changes in the data collected at the machines during production Adding visualization to increase productivity

Learn how targeted, modular, dosing and blending solutions — covering powders, granules, regrinds and liquids — provide plastics processors of all kinds with best-in-class accurate dosing while delivering significant raw material savings and ensuring highest quality.  Agenda:  Introduction to Movacolor Blending in plastics applications Movacolor feeding and dosing technology Hybrid blending to combine high material throughput and dosing accuracy

This presentation will explore the in-situ polyurethane (PU) overmolding of injection-molded and composite parts, allowing for direct out-of-mold class "A" surfaces. KraussMaffei will review the process and equipment required. It will also discuss tooling types currently available for PU systems for this process. KraussMaffei will compare the pros and cons of this technology over currently-available coating and painting systems. Agenda: Introduction and evolution of the ColorForm technology Overview of the ColorForm process Equipment required Tooling and PU systems Benefits of the system compared to typical spray-applied coatings Pros and cons of the technology

Consistent quality is paramount within the production of pipe and tubing applications. Additionally, significant material savings can be obtained by tightly controlling product dimensions with the correct process equipment. In this webinar, Conair will cover gravimetric control of an extruder and production line speed to ensure optimal quality and cost savings are achieved in your product run. A detailed discussion of the upstream material handling system includes: blending resins upstream of the feed throat, detection of the extruder rate at the throat, control of the extruder rpm and control of the product itself in feet per min — all accomplished with a simple recipe configuration which includes product weight per length desired and production line speed.

Medical-component specialist LightningCath has carved a niche meeting the needs of small to medium-sized entrepreneurs with complex catheter designs … quickly.

Fast Track service from BPM can repair every brand of rotor in two weeks or fewer.  

Adds 52,000 square feet to Lebanon plant.

Nextpoint announced a $2 million investment, part of a $7.7 million raise for PlantSwitch, which uses agricultural waste to manufacture plastic.

Life cycle analysis of production at four plants in Mexico and Germany was conducted by C7-consult.

Tahara’s new eight-head, double-sided coex machine has many new mechanical and electronic features.

Topping five other entries in voting by fellow molders, the Ultradent team talks about their Hot Shots sweep.

Serendipitous Learning Opportunities at PTXPO Underscore the Value of Being Present.

Introduced by Zeiger and Spark Industries at the PTXPO, the nozzle is designed for maximum heat transfer and uniformity with a continuous taper for self cleaning.

Ultradent's entry of its Umbrella cheek retractor took home the awards for Technical Sophistication and Achievement in Economics and Efficiency at PTXPO. 

technotrans says climate protection, energy efficiency and customization will be key discussion topics at PTXPO as it displays its protemp flow 6 ultrasonic eco and the teco cs 90t 9.1 TCUs.

Shibaura discusses the upcoming Plastics Technology Expo (PTXPO) March 28-30

Ahead of the first NPE since 2018, PLASTICS announced that its triennial show will stay in Orlando and early May for ’27, ’30 and ’33.

New features of NPE2024 aim to “bring the whole plastics ecosystem together to innovate, collaborate and share findings.”  

Hundreds of tons of demonstration products will be created at NPE2024 next spring. Commercial Plastics Recycling strives to recycle all of it.

After what will be a 6-year hiatus caused by the COVID-19 pandemic, registration is open for the triennial show, which will take place May 6-10, 2023, in Orlando, Florida.

The Plastics Industry Association has hired from within, elevating Matt Seaholm to CEO and Glenn Anderson to COO.

Long-time leaders hailing from the U.S., Japan, Germany and Austria and across the entire supply chain, from machinery and materials to training and moldmaking, will be inducted.

Mixed in among thought leaders from leading suppliers to injection molders and mold makers at the 2023 Molding and MoldMaking conferences will be molders and toolmakers themselves. 

After successfully introducing a combined conference for moldmakers and injection molders in 2022, Plastics Technology and MoldMaking Technology are once again joining forces for a tooling/molding two-for-one.

Multiple speakers at Molding 2023 will address the ways simulation can impact material substitution decisions, process profitability and simplification of mold design.

When, how, what and why to automate — leading robotics suppliers and forward-thinking moldmakers will share their insights on automating manufacturing at collocated event.

As self-imposed and government-issued sustainability mandates approach, injection molders reimagine their operations.

August 29-30 in Minneapolis all things injection molding and moldmaking will be happening at the Hyatt Regency — check out who’s speaking on what topics today.

Get your clicking finger in shape and sign up for all that we have in store for you in 2023.  

Molding 2023 to take place Aug. 29-30 in Minnesota; Extrusion 2023 slated for Oct. 10-12 in Indiana.

Key technologies — such as multicolor molding, film molding and PUR overmolding for both exterior and interior applications — are at the forefront of this transformation. Join this webinar to explore the vast potential of eMobility in molding large components — including those with fiber reinforcements — thereby driving the need for large injection molding cells with a clamping force of up to 11,000 tons. You will also gain insight into Engel's innovative two-stage process, a solution for future recycling processes. This webinar will provide an in-depth overview of challenging applications, production concepts and best practices, including:       BMW iX front panel production cell Smart rear panels concept based on IMD and 2C molding Sustainability concepts based on two-stage process Large tonnage equipment for battery moldings

In today's manufacturing environment, robust processes that meet strict industry and regulatory standards are essential. With the advent of servo-driven ultrasonic welding technology, enhancing product quality and maintaining consistency has become remarkably effortless. Discover the fundamentals of ultrasonic welding, delve into vital components within these systems, explore how servo-driven ultrasonic welding enhances weld quality via advanced control features and gain insights into optimizing your assemblies for welding in these high-performing machines. Join Dukane to unlock the potential of ultrasonic welding in modern manufacturing for plastic devices and components. Agenda: Fundamentals of ultrasonic welding Key components in an ultrasonic welding system Using servo-driven ultrasonic systems to control your welding process Designing your parts and components for servo-controlled ultrasonic welding

This webinar will help you make informed decisions to confirm the equipment access stairs in your facility are OSHA compliant and meet the highest standards of safety and ergonomics. Agenda:  Identifying opportunities to increase safety in the work place Utilizing space saving stairways Ensuring code compliance for equipment access

4.0, EUROMAP, OPC, OLE, QC, DSN, SQL, VNC, MES, ERP, FTP, CMS, SPI — are you confused by all buzzwords being tossed around in the plastics industry? Not convinced the data collection is necessary? Or are you unsure of how it could be implemented and improve your molding processes? Wittmann has been on the cutting edge of the data collection push for nearly 20 years. In this webinar, take a step back from the idea of the manufacturing facility of the future and discuss what you can do today to improve your process. Using readily-available technology, Wittmann can help reduce downtime, limit scrap and wasted material, and predict required maintenance. Let the experts at Wittmann help you understand: what data can be collected, what that data can be used for, what systems are used, and how to implement them. Agenda: Demystifying the terminology Tracking the material flow and lot information through the material handling system The data available from various auxiliary equipment, such as: dryers, blenders, mold temperature controls and robots Automating the process through changes in the data collected at the machines during production Adding visualization to increase productivity

Learn how targeted, modular, dosing and blending solutions — covering powders, granules, regrinds and liquids — provide plastics processors of all kinds with best-in-class accurate dosing while delivering significant raw material savings and ensuring highest quality.  Agenda:  Introduction to Movacolor Blending in plastics applications Movacolor feeding and dosing technology Hybrid blending to combine high material throughput and dosing accuracy

This presentation will explore the in-situ polyurethane (PU) overmolding of injection-molded and composite parts, allowing for direct out-of-mold class "A" surfaces. KraussMaffei will review the process and equipment required. It will also discuss tooling types currently available for PU systems for this process. KraussMaffei will compare the pros and cons of this technology over currently-available coating and painting systems. Agenda: Introduction and evolution of the ColorForm technology Overview of the ColorForm process Equipment required Tooling and PU systems Benefits of the system compared to typical spray-applied coatings Pros and cons of the technology

Fast facts SPE International Polyolefins Conference 2024: The Preeminent Polymer Conference in the World dedicated to Polyolefins since 1975 The conference will in-person and virtual The powerful software platform for the conference will allow access to all papers on-demand, even several months after the conference, access to the program, access to virtual exhibitor/sponsor booths, and easy communication with speakers and other participants In-person participants can download a mobile or web app for the conference to access all the features of the software platform for the conference We anticipate over 900 people from around the globe to participate in-person or virtually The improved layout of the exhibit floor offers easy access and flow for the 60+ companies that we anticipate to exhibit Over 20 sponsors expected 150+ Technical papers, Sunday afternoon Tutorial Student Poster Competition 2 Networking Socials Meeting rooms available for rent to meet with customers and suppliers Exhibits from Monday through Wednesday until noon The Conference is organized by the SPE South Texas Section, the SPE Polymer Modifiers and Additives Division, the Thermoplastic Materials and Foams Division, the Engineering Properties and Structures Division, the Building and Infrastructure Division, and the Flexible Packaging Division.

The global plastics industry has been navigating through what is arguably the most volatile period in decades. Unprecedented amounts of new production capacity are scheduled to start in North America, Europe, and China in the near term and compete for demand during a period of economic challenges. How will trade flows shift? Will this lead to regional cost disparities and rationalization? Energy transition and sustainability targets continue transforming the plastics market and increasing the competitive landscape. As the market evolves, what impact will new technology, policy, regulation, the growing role of chemicals versus fuel and other factors have on industry restructuring and business models? At GPS 2024, leading global experts will come together to discuss pivotal impacts and initiatives shaping the plastics industry. Join us and participants from across the globe to gain the latest insight and deep analysis as you connect with your peers and industry professionals. This year’s conference will explore the theme Disruptive Global Dynamics Reshaping Plastics and include a full day workshop focused on the Global Plastics Business and Plastics Transition to Circularity, 1.5 days of expert content and numerous networking functions.

Every three years, leaders from almost every major industry gather at NPE to advance their businesses through innovations in plastics. The largest plastics trade show in the Americas, NPE offers six technology zones, keynote speakers, workshops and opportunities to build partnerships. 

The 3D Printing Workshop @ NPE2024 – The Plastics Show, is an immersive, half-day workshop focused on the emerging possibilities for part production via 3D printing and additive manufacturing. Presented by Additive Manufacturing Media, Plastics Technology and MoldMaking Technology, the 3D Printing Workshop will build upon a successful model first introduced at IMTS 2014. Attendees will benefit from a program focused on practical applications of 3D technologies related to plastics processing. This event will conclude with a 3D Printing Industry Reception sponsored by Additive Manufacturing Media.

The Society Plastics Engineers (SPE) Extrusion Division and the SPE Eastern New England Section will co-host the Screw Design Conference-Topcon on June 19-20, 2024 @ UMass Lowell in Lowell, MA.  This highly technical program will focus upon screw design principles for single and twin screw extruders with wide ranging topics relating to screw designs for feeding, melting, mixing, venting and pumping plastics products and parts.   Areas of focus will include screw designs for melt temperature and gel management, gel minimization, bioplastics, recycled materials and foaming.   In addition to the technical sessions, a tour of the UMass Lowel Plastics Processing Laboratories will be integrated into Day 2 of the event.    This program is not just for screw designers, but to help anyone responsible for any type of extrusion operation to evaluate existing extrusion equipment; and also to prepare for future projects. Price to attend:  Less than $1000!  Registrations will be accepted in early 2024. Call for papers – To be considered to give a presentation, please submit a talk title and abstract on or before December 15 to:   Technical Chair: Eldridge M. Mount III, e-mail emmount@msn.com Corporate sponsorships - A limited # of corporate sponsorships (15) are available on a 1st come basis.  Included is a 6’ tabletop display (must fit on table), denotation in all promotional activities, and 1 no charge registration.  To become a sponsor contact: Charlie Martin, Leistritz Extrusion, e-mail cmartin@leistritz-extrusion.com, cell 973-650 3137 General information:   A reception on Day 1 and a tabletop display area will allow the attendees to meet and discuss state-of-the-art screw technologies with industry experts.  The SPE Extrusion Division will issue a “Screw Design Certificate” to all participants who have attended the program.  Students are encouraged to attend and will receive a discounted rate.   For additional information contact:  Program Chair:  Karen Xiao, Macro Engineering, KXiao@macroeng.com

Debuting in 2010, the Parts Cleaning Conference is the leading and most trusted manufacturing and industrial parts cleaning forum focused solely on delivering quality technical information in the specialized field of machined parts cleansing. Providing guidance and training to understand the recognized sets of standards for industrial cleaning, every year the Conference showcases industry experts who present educational sessions on the latest and most pressing topics affecting manufacturing facilities today.  Discover all that the 2022 Parts Cleaning Conference has to offer!

Understanding how polymer melts in a single-screw extruder could help you optimize your screw design to eliminate defect-causing solid polymer fragments.  

The melting (or devitrification) process can be a rate-limiting process for some single-screw extruders. For these situations, the extruder drive train, extrudate temperature and downstream equipment are not rate limiting. As the screw speed and rate are increased, a maximum rate will occur where the extrudate is completely molten and free of solid polymer fragments. At slightly higher screw speeds, solid polymer fragments start to appear in the extrudate, causing defects in the product.

If fresh resin and masterbatch resins or color concentrates are fed to the extruder, the defects will be solid polymer fragments from one of the resins. But since the fresh resin is added at the highest level, statistically the defects are likely to be from the fresh resin. If the drive train is not limiting, this defect can be eliminated via screw design.

Solid polymer fragments are likely to be discharged from the extruder at high screw speeds because of the processes governing solid conveying, melting, and the metering sections. For example, if the screw speed is doubled the pumping capacity of solids conveying and the metering sections will also double. The melting flux, however, will only increase by a factor of about 1.4 times. The melting flux has units of kg/(hr m2) where the unit area term is the area of the barrel wall where melting is occurring.

The melting capacity is defined as a melting flux times the barrel area available for melting.

The melting capacity is defined as a melting flux times the barrel area available for melting. As the screw speed is increased and because the melting flux does not increase at the same rate as solids conveying and metering, additional area at the barrel wall is needed for melting. Thus, the solid bed is forced downstream such that more area at the barrel wall will be used to melt the additional resin.

Because of limited barrel surface area, eventually some solids will not be melted and will instead discharge with the extrudate. A photograph of a black- tinted HDPE thin-wall pipe cross section is shown in Fig. 1. Here the large white areas do not contain pigment because they were discharged from the extruder as a solid fragment. The fragments exited the extruder because the rate was higher than the melting capacity of the machine. Short term, the only solution to mitigate these fragments is to decrease the extrusion rate.

FIG 1 Solid-black fragments in thin-wall HDPE pipe. The feedstock was a natural-colored resin with a black masterbatch.

The melting process can be studied using a Maddock solidification experiment. For this experiment, a small amount of color masterbatch is added to fresh resin at a ratio of about 200 parts fresh resin to one-part masterbatch. The mix is added to the hopper.

When the discharge becomes fully tinted by the colorant, the rotation of the screw is stopped, and the barrel zones are placed on full cooling. The die and transfer line are removed, and the pellets in the hopper are removed using a vacuum cleaner. After the resin is solidified in the extruder, the screw is pushed out, as shown by Fig. 2 for an ABS terpolymer. Next, the solidified resin is removed from the screw and sectioned, as shown in Fig 3 and 4.

FIG 2 Screw with solidified ABS resin from a Maddock-solidification experiment. 

A cross section early in the melting process is shown in Fig. 3. The white regions were compacted pellet solids at the moment that screw rotation was stopped. The black regions were molten resin. A thin melt film exists between the solid bed and the barrel wall. The rotation of the screw causes viscous dissipation of energy to occur in this film. Some of the energy conducts into the solid bed and melts additional resin.

The newly molten resin is carried away in the melt film and conveyed to the melt pool by the motion of the screw. About 80% of the melting occurs at the barrel side, and the remainder occurs at the other edges of the solid bed. This is why the melting process requires area at the barrel wall and why the melting process is presented as a melting flux with units of kg/(hr m2).

FIG 3 Cross section in the early portion of the screw’s melting section. White areas were solids at the time screw rotation was stopped. Black areas were molten resin.

The melting profile for a 21-diam long extruder is provided in Fig 4. Notice the solid bed becomes smaller, and the size of the melt pool becomes larger as melting progresses downstream. Eventually melting is completed. If the screw speed is increased, the solid bed will move downstream and into the metering channel as more surface area at the barrel wall is required for melting.

At diameter 18, the cross section shows that solids are not present, but at diameter 19 some solids are visible. This indicates that solid bed breakup has occurred. Solid bed breakup decreases the melting capacity of the extruder, and it is more likely to occur at higher screw speeds. Moreover, it typically leads to solid polymer fragments in the extrudate.

Solid bed breakup decreases the melting capacity of the extruder, and it is more likely to occur at higher screw speeds. 

If the screw speed is high enough, then solid polymer fragments can be discharged with the extrudate. As an example, the same extruder was operated with the same blend of natural resin (with a small level of TiO2) and black colored masterbatch as a function of screw speed. The extrudate was passed through a 0.5-in. diam die to make logs. The cross sections of the logs are shown in Fig 5.

At screw speeds less than about 70 rpm, the extrudate is fairly well mixed and free of solid polymer fragments. At higher screw speeds, solid polymer fragments are apparent in the logs. Moreover, the level of solids increases with increasing screw speed. As before, the best short-term solution to the problem is to decrease the rate until the polymer fragments are not observed.

All screws will discharge solid polymer fragments if the screw speed is high enough. Some design styles, however, can operate at higher rates without discharging solids. These design types include screws with a combination of a barrier melting section followed by a Maddock mixer and several patented high-performance screws. These designs all work by forcing all of the molten resin through segments of the screw that have tight dispersive mixing clearances.

FIG 4 Melting profile for a 21-diam long extruder running a mixture of ABS and a small amount of black masterbatch.

For example, a Maddock mixer on a 3.5-in. diam screw would have a mixing flight undercut that is about 0.025 to 0.050 inch. As the material flows across the undercut, solid polymer fragments are trapped, melted, and dispersed into the molten resin, ng the extruder to operate at higher screw speeds and rates. Eventually, a screw speed will be reached where solid fragments are discharged from these screws too.

The melting process is the first opportunity for mixing, as shown in Fig. 3. For this experiment, the resin was 200 parts natural resin and only one part of a black masterbatch.

Here, primary mixing occurs during the melting process in the melt film. That is, as melting is taking place the newly molten resin is accelerated and stretched before ending up in the melt pool. This is evident by the relative uniformity of the black color in the melt pool. A downstream Maddock mixer or some other dispersive mixer would provide a secondary level of mixing and likely result in a homogenous extrudate.

For most processes, solid polymer fragments in the extrudate can be eliminated via screw design. Maddock mixers are excellent at trapping, melting, and dispersing solid polymer fragments. Moreover, a smaller undercut on the mixing flight provides an improvement in eliminating solids. For a 3.5-inch diam screw, the mixing flight undercut can be as small as 0.015 in, providing a gap between the mixing land and the barrel wall of 0.019 in (0.004 in flight clearance). This small gap will mitigate even small solid fragments.

FIG 5 Cross-sectional views of extrudate samples at a letdown ratio of 100 to 1 of a natural ABS (with a small level of TiO2) resin with a black color concentrate. The large round white regions for the cross sections at screw speeds of 90 rpm and higher are solid polymer fragments discharged with the extrudate.

About the Author: Mark A. Spalding is a Fellow in Packaging & Specialty Plastics and Hydrocarbons R&D at Dow, Inc. in Midland, Mich. During his 37 years at Dow, he has focused on development, design, and troubleshooting of polymer processes, especially in single-screw extrusion. He co-authored Analyzing and Troubleshooting Single-Screw Extruders with Gregory Campbell. Contact: (989) 636-9849; maspalding@dow.com; dow.com.

Just like selecting the extruder size and drive combination, the L/D should be carefully evaluated.

When it comes to vacuum conveying systems for plastics processing, custom powder handling solutions are not always required. Pre-engineered, turnkey solutions can be a perfect option for powders and bulk solids in a wide range of industries.

All extrusion processes depend to some degree on the melt strength of the polymer, and this property is generally a no-show on data sheets.

By referring to the power-law coefficient, the effect of barrel override in the metering section of many screws can be explained and anticipated.

Extrusion processors often ask screw designers to estimate the output and melt temperature of a new design in the works. Projected output of a new screw can usually be estimated fairly accurately. Melt-temperature estimate, however, is another story

You can better visualize the melting process by “flipping” the observation point so that the barrel appears to be turning clockwise around a stationary screw.

Just drop it in and mix it up? Sorry, there’s a lot more to it than that. Here is some of what you need to consider.  

How Polymer Melts in Single-Screw Extruders | Plastics Technology

Diy Plastic Extruder Plastics Technology covers technical and business Information for Plastics Processors in Injection Molding, Extrusion, Blow Molding, Plastic Additives, Compounding, Plastic Materials, and Resin Pricing. Learn More