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Articles by Mark Spalding
The goal of all troubleshooting operations is to restore the extrusion process to its original performance as quickly as possible. Troubleshooting can range from solving a very simple problem, such as replacing a malfunctioning barrel heater, to a very difficult flow problem that is complicated to diagnose.
What You Should Know About Transfer Lines
Transfer lines are pipes that connect the extruder to downstream equipment such as gear pumps, screen changers and dies, and are essential to every extrusion line. This article provides guidance on the design of transfer lines. Transfer lines must be designed to minimize pressure consumption while mitigating resin degradation. For example, a small-diameter transfer line will minimize resin degradation at the wall but can have a very high pressure consumption.
Consider the Incumbent Resin Effect When Purging Your Blown Film Dies
Most polyethylene (PE) blown film lines are used to produce many different types of products, meaning they’re not dedicated to a single product running a single resin. When changing the line over, the extruder, transfer line and spiral mandrel die must be essentially free of the incumbent resin to produce the product. Otherwise, some small fragments of the incumbent resin — poorly mixed into the new resin — may discharge from the die and get labeled as gels.
The Cargo You Can’t See Leaving the Gulf: Biofouling, the Shadow Fleet, and a Submerged Supply-Chain Risk at the Strait of Hormuz
The Ocean Foundation watches the Strait of Hormuz the way the energy desks do — but our attention is below the waterline. As the world’s community foundation for the ocean, we see the current crisis in the Strait through two lenses that the freight and commodity markets tend to miss: the transfer of invasive species and the climate and pollution costs of a global fleet now operating under abnormal conditions. Both are converging into a supply chain risk that will not remain submerged.
Spotting and Solving Resin Degradation in Molded Gray Parts
Resin degradation can decrease the yield of injection molded parts. Moreover, degradation can be difficult to identify, especially for items tinted gray using a color masterbatch. This article provides methods for identifying resin degradation in dark and gray parts. For example, an injection molder was producing a light gray-colored part using a high-impact polystyrene (HIPS) resin and a gray-pigmented masterbatch. Many of the parts produced were rejected because of dark streaks, as shown by Fig. 1.
How To Produce Highly Filled Compounds on Co-Rotating Twin-Screw Extruders
Highly filled compounds such as polyolefins filled with calcium carbonate or talc can have mineral filler contents of 70-80% by weight and even higher, especially for calcium carbonate compounds. These compounds are often used as masterbatches for other processes. Because these mineral fillers are usually fed via two to three side feeders, a considerable amount of air is introduced into the twin-screw extruder.
Understanding Pump Ratio for Two-Stage, Vented Single-Screw Extruders
Two-stage, vented single-screw extruders are common for many applications and resins. Venting is common with many styrenic resins and most applications involving postconsumer recycled (PCR) resins. A properly designed extruder and screw will be able to remove upwards of 90% of the volatiles through the vent, operate stably without flow surging at the die, and not have material flowing out through the vent opening.
Mitigate Resin Degradation With Nitrogen Sparging in the Hopper
Resin degradation can reduce the value of a product and decrease the yield and operational time of a line, especially for polyethylene (PE) films. Most of the degradation occurs in the final processing operations using single-screw extruders, which shows up as gels in the film product. (See typical gels in PE films in Figure 1.) Figure 1: Crosslinked gels in low-density polyethylene (LDPE) films.
Pressure Measurement Basics for Single-Screw Extruders
Measuring pressure at key locations in an extrusion line is very important to the analysis and safety of the process. A pressure transducer (sensor) at the discharge is by far the most critical location for measuring the pressure. If the discharge pressure becomes too high, safety issues can be a concern since the screen changers, gear pumps and dies must operate at pressures less than the maximum design pressure.
Installing, Removing and Cleaning Single-Screw Extrusion Screws
Good preventative maintenance on single-screw extruders requires the periodic removal of the screw and the measurement of the outside diameter and overall inspection of the screw. Typically, the screw should be removed and inspected at least once a year or when the processing performance changes. This article provides a guideline for the safe removal and installation of screws. New and rebuilt screws are inspected by the fabricator prior to shipment to the end user.
A horizon scan of biological conservation issues for 2026
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ReviewOnline nowOpen access 1Conservation Science Group, Department of Zoology, Cambridge University, The David Attenborough Building, Cambridge, CB2 3QZ, UK 2BirdLife International, David Attenborough Building, Cambridge, CB2 3QZ 3National Trust, Heelis, Swindon, SN2 2NA, UK 4The Wildlife Trusts, The Kiln, Newark, NG24 1WT, UK 5Natural England, Eastbrook, Cambridge, CB2 8DR, UK 6Environment Agency, Horizon House, Bristol, BS1 5AH, UK 7Darwin-Hamied Centre, Christ’s College, Cambridge, CB2...
By William J. Sutherland, Stewart Clarke, Nigel Doar, Helen Doran, Daniel J. Field, Erica Fleishman, Kevin J. Gaston, James E. Herbert-Read, Alice Hughes, Hermanni Kaartokallio, Luke Maggs, James E. Palardy, James W. Pearce-Higgins, Lloyd S. Peck, Nathalie Pettorelli, Irene R. Schloss, Mark Spalding, Anastasiya Timoshyna, Nicolas Tubbs, Thiago Kanashiro Uehara, James Watson, Jonathan Wentworth, Jeremy Wilson Verified, Ann Thornton, Imogen C. Douglas
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Cell Press
Verified
Understanding Screw Temperature in Single-Screw Extruders
The surface temperature of the root of the screw is an important factor for solids conveying, melting and the conveying of molten resin in a single-screw extruder. Only the solids conveying section of the feed zone, however, is typically temperature controlled. Moreover, measuring the surface temperature is extremely difficult due to sensor placement and transferring electrical signals through a rotating shaft. In almost all processes, the temperature of the screw is unknown.
Designing a Twin-Screw Compounding Process: Home in on Screw Design, Barrel Setup, Degassing Ports
Twin-screw compounding processes must operate at high rates and with acceptable and low wear rates to be profitable. Many compounders, however, operate their corotating twin-screw extruders with suboptimal designs and conditions. These issues often involve the screw design as well as the barrel setup and its degassing ports. Such mistakes can lead to numerous problems that affect product quality, reduce rates, and increase wear on the barrel, screw elements and gear box.
Remembering Bruce Maddock: A Pioneer in Single-Screw Extrusion Technology
Bruce H. Maddock was a pioneer in early technology development for single-screw extruders and wire insulation materials. His career started at Bakelite after graduating from the University of Michigan in 1934 in Engineering Physics. At Bakelite he developed electrical insulation materials for wires and started his processing journey in extrusion. Bakelite was acquired by the Union Carbide Corp. (UCC) in 1939.
Back to Basics: Tandem Foam Sheet Extrusion
Tandem foam sheet extrusion is a complex process that requires optimization to produce quality sheets at high rates. Foam sheets are commonly produced using high molecular weight polystyrene (PS) or polyolefin (PO) resins on tandem foam sheet extrusion lines. The sheet is used for many applications, among them food trays, clamshell takeout containers and egg cartons. The most common application is thermoforming the sheet into trays and containers.
Add Screw Cooling for More Process Control, Output in PC Extrusion
Operating extrusion lines at higher rates is a proven method to decrease costs and increase the profitability of a process. In the April 2025 issue, my article demonstrated the cost reduction and profitability for polyethylene (PE). Here, I’ll look at the impact that adding screw cooling can have on a polycarbonate (PC) extrusion process. Single-screw extruders can be rate limited by lack of motor torque, screw speed, high discharge temperatures and flow surging.
Let's Take a Deeper Dive on Compression Ratio for Single-Screw Extruders
As discussed in the May 2025 issue of this magazine, two very important screw design parameters are the metering channel depth and the compression ratio. In that article, we showed data for melting capacities, specific rates, pressure profiles and discharge temperatures for the extrusion of linear low-density polyethylene (LLDPE) resin pellets as a function of the compression ratio. The optimal compression ratio was shown to be 2.8, consistent with commercial operations.
How Compression Ratio Impacts Extruder Performance
Single-screw extrusion at high rates and high qualities, and discharging at the proper temperature and pressure depends on numerous process features, including operational set points and the screw design. Two very important screw design parameters are the metering channel depth and the compression ratio. If the compression ratio is too low, low rates and low specific rates can occur. If the ratio is too high, melting rate limitations and high screw wear can occur.
Use a Process Assessment to Determine the Benefits of Screw-Design Modification
Many extrusion processors wait too long to change out worn screws. And while delaying the purchase of a new screw, they are operating with a disadvantaged process and decreasing the profitability of the line. A new screw will restore the economic advantages of the line, such as higher rates, improved mixing and lower discharge temperatures.
How To Identify Resin Degradation in Single-Screw Extruders
Resin degradation products often cause defects in finished goods such as polyethylene (PE) film, sheet and injection molded parts. Most often the degradation is caused by segments of the process that are stagnant to flow, allowing the resin to be at high processing temperatures for extended periods of time. Once formed, small process instabilities will cause the degradation products to separate from the screw and contaminate the product.
Cómo se funde el polímero en extrusoras de un solo husillo
El proceso de fusión (o desvitrificación) puede limitar la velocidad para algunas extrusoras de un solo tornillo. Para estas situaciones, el tren de accionamiento de la extrusora, la temperatura de extrusión y el equipo aguas abajo no limitan la velocidad. A medida que se incrementan la velocidad y la tasa del tornillo se producirá una tasa máxima, en la que el extruido esté completamente fundido y libre de fragmentos de polímero sólido.
Optimizing Melt-Fed Single-Screw Extruders on Compounding Lines
Some compounding lines feature a twin-screw extruder or continuous mixer for the compounding operation followed by a melt-fed, single-screw extruder for material pressurization for pelletization. A typical configuration is provided by the schematic in Figure 1. Schematic of a compounding line using a continuous mixer for compounding and a melt-fed, single-screw extruder for pressurization for the pelletizer.
A proposed model for filler incorporation in polymer fluids in a twin‐screw extruder
The advice contained herein is based upon tests and information believed to be reliable, but users should not rely upon it absolutely for specific applications since performance properties will vary with processing conditions. It is given and accepted at user's risk and confirmation of its validity and suitability in particular cases should be obtained independently.
The Overlooked Carbon Storage Potential of Tidal Marshes
It’s all about the mud. Following our release of a “best ever” map of tidal marshes (call them saltmarshes if you prefer, it’s approximately the same), in a new paper in the journal Nature Communications we’ve now calculated how much carbon is packed away in their soils. Tidal marshes are globally distributed, but for those of us working in the academic and financial hotspots of North America, Europe and East Asia these are our ecosystems.
What You Need to Know About Melt-Temperature Measurement in Single-Screw Extruders
Figure 1: Schematic of a variable-depth thermocouple positioned in a flange of a transfer line. Source: Mark Spalding To be profitable, a single-screw extruder must operate at the maximum rate while discharging at a specified pressure and temperature. Measuring the rate and discharge pressure from an operating extruder is easy and straightforward. Measuring the discharge temperature, however, is not so simple, especially using thermocouples positioned in the transfer line just upstream of the die.
Soil carbon in the world’s tidal marshes - Nature Communications
Abstract Tidal marshes are threatened coastal ecosystems known for their capacity to store large amounts of carbon in their water-logged soils. Accurate quantification and mapping of global tidal marshes soil organic carbon (SOC) stocks is of considerable value to conservation efforts.
What's Restricting My Output Rate?
A well-designed screw using a barrier flighted melting section can provide higher rates — up to 20% — and lower discharge temperatures compared to a conventional flighted melting section. When combined with a downstream Maddock mixer, the quality and rate of the extrudate can be optimized for the application, maximizing productivity.
How to Decrease the Extrudate Temperature in Single-Screw Extruders
Many plasticating, smooth-bore, single-screw extrusion processes benefit from decreasing the extrudate or discharge temperature. These processes include foam sheet, pipe and profile extrusion, and blown film. For example, foam sheet will typically have a higher quality when the extrudate temperature is decreased. This is because the foam will be less likely to collapse at the lower discharge temperature, maintaining a low foam density and high surface aesthetics.
In Single Screw Extruders, Mixing Starts in the Melting Process
The melting process for plasticating, single-screw extruders is also an excellent mixing process. A low level of mixing can occur during pellet blending before being placed in the hopper. But the first major mixing process occurs during melting. Figure 1 – ABS resin in the transition section after a Maddock solidification experiment. The feedstock mixture was 200 parts white ABS and one part black ABS in pellet form. Source: M. Spalding This mixing is obvious by studying the photograph in Figure 1.
Troubleshooting Flow Surging in Single-Screw Extruders
Flow surging is defined as the oscillatory change in the rate of the extruder while maintaining constant set point conditions. Moreover, process parameters such as motor current, barrel temperatures and screw channel pressures can also oscillate. Flow surging can originate from many different sources, including improper solids conveying, melting instabilities and improper control algorithms.
Understanding the Incumbent Resin Effect
New and innovative products are constantly produced on pilot and manufacturing lines using a variety of processes, including PE blown and cast films using single-screw extruders. Many times, these films will be sent to end users for evaluation. Acceptable quality and properties of the films are key to the success of the new product. Most of the time, the new film produced has acceptable quality (very low gels) and great physical properties.
The distribution of global tidal marshes from Earth observation data
1 INTRODUCTION Tidal marsh ecosystems are vegetated coastal wetlands located in areas of regular to occasional tidal inundation, formed by a broad variety of herbaceous and woody vascular plants (Adam, 2002). Whilst dominated by saline and brackish marshes, they include areas of freshwater tidal marsh (Barendregt, 2018; Mitsch & Gosselink, 2015). They occur along many of the world's sheltered, sediment-dominated coastlines, particularly in temperate and arctic regions (Tiner & Milton, 2018).
Choosing the Right Gearbox and Motor for Your Single-Screw Extruder
Gearbox and motor selection are important keys to the successful and economically optimized single-screw extrusion process. That is, the motor and gearbox should be selected such that the extruder operates at near 70% motor current load and about 70% of the maximum normal screw speed. This will allow a rate increase in the future and the extrusion of resins that are more viscous while minimizing the capital costs for the motor and gearbox.
Soil carbon in the world's tidal marshes
Abstract Tidal marshes are threatened coastal ecosystems known for their capacity to store large amounts of carbon in their water-logged soils. Accurate quantification and mapping of global tidal marshes soil organic carbon (SOC) stocks is of considerable value to conservation efforts.
What You Need to Know About the Design and Operation of Maddock Mixers
Maddock mixers are popular and effective mixers for single-screw extruders (and injection molding plasticators) because of their low cost to build and their ability to provide a uniform level of dispersive mixing. If the mixer is designed properly, all entering solid polymer fragments and certain types of polyethylene (PE) gels can be trapped and dispersed into the matrix resin.
Optimizing Barrel Temperatures for Single-Screw Extruders
Fellow, Dow Barrel temperature settings are important to the optimal operation of smooth-bore, single-screw extruders. Barrel temperatures are key to the control of solids conveying, melting and the adjustment of the discharge temperature. If properly set along with an optimized screw design, the extruder will be operating at peak performance, providing maximum profitability.
How Polymer Melts in Single-Screw Extruders
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.
The First World of Map of Tidal Marshes
Not far from some of the most crowded corners of England you can still find wilderness. You can stand in an ecosystem untouched by humans, where a carpet of green – decorated with bright sprays of pink thrift and purple sea lavender – is broken by myriad pools and twisting channels. The occasional wild piping of oystercatchers fills the air, or the haunting echoes of curlews.
The distribution of global tidal marshes from earth observation data
Thank you for your interest in spreading the word about bioRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. Message Subject (Your Name) has forwarded a page to you from bioRxiv Message Body (Your Name) thought you would like to see this page from the bioRxiv website.
Generating Finance for Blue Economy Transition
Task Force 6: Accelerating SDGs: Exploring New Pathways to the 2030 Agenda 1. Challenge ‘Blue Economy’ Defined Blue Economy implies the sustainable use of ocean resources for economic growth as well as improved livelihoods and jobs, while preserving the health of the marine ecosystem. Blue Economy activities recognise the ocean as a critical space for sustainable development, balancing conservation with resource use and promoting regeneration.
Troubleshooting Screw and Barrel Wear in Extrusion
Keeping single-screw extruders running at peak performance is a constant challenge for processors, especially for older machines. Typically, as an extruder runs in production, the screw and barrel will show signs of wear. The main signs include a reduction in specific rate and higher discharge temperatures. Specific rate is simply the rate (lb/hr or kg/hr) divided by the screw speed. For small reductions in specific rate, the processor can just increase the screw speed to maintain output rate.
The Value of Words + Pictures
For years the idea that nature and tourism are linked has been kept largely—and unhelpfully— confined to a series of studies on wildlife watching or scuba diving and filed under the heading: “nature-based tourism.” But that doesn’t come close to telling the whole story of how closely tourism is actually tied to nature, especially in places like the Eastern Caribbean, where tourism is the most important industry, largest employer and greatest foreign-exchange earner in the region.
How Screw Design Can Boost Output of Single-Screw Extruders
A capacity increase for an extrusion line can occur by an increase in run time or by a rate increase. For lines that are sold out, increasing the line rate can be very lucrative and can delay the installation of costly new equipment. Recent examples of rate improvement by optimizing the screw for PE resins are provided in the accompanying table. For the applications cited, new screws were designed with deeper, optimized channels.
Troubleshooting Vent Flow Problems in Single-Screw Extruders
Two-stage extruders with a vent port downstream from the first stage are common in many types of plasticating extrusion processes where volatiles or entrained air need to be removed. These extruders are used for the processing of styrenics, polycarbonate, pelletization of post-consumer recycle (PCR), and repelletization of foam in-plant recycle, to name a few. To be economically viable, the extruder must be stable, operate at high rates, and remove volatile materials from the resin.
How Screw Design Can Mitigate Gels in PE Films
By Mark A. Spalding, Dow Inc. The term “gel” is commonly used to refer to any small defect that distorts a film product, reducing the quality of the film. There are many types of gels.
Is a Gear Pump Right for Your Single-Screw Operation
Fellow, Dow A gear pump positioned between an extruder and downstream equipment can improve the performance of a line. The advantages include the mitigation of pressure surges and as a result flow surges from the extruder; plus a decrease in the discharge temperature by generating part of the pressure required for the die by the pump, which reducesing resin consumption and enables rate increases.
The New Blue Economy: Taking Care of the Ocean to Sustain Us
The New Blue Economy: Taking Care of the Ocean to Sustain Us Mark J. Spalding 2020-01-28 04:23:06 Published by Technology Systems Corporation. View All Articles. This page can be found at http://digital.ecomagazine.com/article/The+New+Blue+Economy%3A+Taking+Care+of+the+Ocean+to+Sustain+Us/3590812/648052/article.html.
The Overlooked Tourism Value of Mangroves
Our small boat slipped silently through a low tunnel of arching branches that closed off the sky. The late afternoon light was already muted and the air around seemed to glow with the emerald of leaves and the bronzed gold of the trees. A large iguana lay on branch nearby, further off a fat snake coiled like a carving around the high branches. My fellow travellers felt safe enough to be fascinated.
Commentary: The ocean is changing - it’s getting more acidic
WASHINGTON: Ocean acidification, a change in the ocean’s chemistry, is increasingly posing a threat to ocean health. While this change may be invisible, its effects are not. It is creating conditions that threaten a range of marine species and ecosystems, and thus the economies of coastal communities. All life on earth would eventually be affected as an increasingly warm and acidic ocean produces less oxygen.
From Constellation to Coral Reefs
The value of coral reefs to humanity may well be the key to saving them. More sectors—tourism, insurance, engineering, tech—are getting involved, and our scientific understanding of complex coral functions and their interconnectedness with people is evolving rapidly. In the Caribbean, the fishing and tourism industries are major driving forces behind local economies, establishing coral reefs as crucial drivers of growth.
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