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What is Extrusion...[continued]

Single-screw extruders

In a single-screw extruder, the screw has a deep-channeled feed section that transports solids from the feed throat and compresses them, a transition or compression section where the channels become shallower and the polymer is melted, and a shallow-channeled metering section where the melt is conveyed to the Extrusion Diagramadapter and die. Different polymers process best with different compression ratios (the ratio of the feed zone depth to the metering zone depth). Some resins melt better in a screw that has barrier flights in the transition section to separate the melt pool from the remaining solids bed. Some screw designs incorporate mixing devices such as pins or barriers to flow. Static mixers, which interrupt the melt flow, create distributive mixing and are used to make melt temperature more uniform. Single-screw extruders are used in simple compounding operations, such as mixing color and additives into a polymer, although Kneaders and twin-screw extruders are more often used for compounding extrusion that requires highly dispersive mixing. Relatively new mixing screws for single-screw extruders improve both distributive and dispersive mixing for more demanding compounding operations. Extrusion Diagram

Single-screw extruders are widely used for extruding film, sheet, and other applications that use pre-compounded pellets.

The Buss Kneader is a special type of single screw extruder with a screw that both rotates and oscillates axially. The Kneader has a full spiral screw in the feeding and devolatilizing zones. In the mixing and kneading zone, the spiral is interrupted with kneading flights that intermesh with kneading teeth or pins fixed inside the barrel. The Kneader is widely used for compounding PVC pellets, because it operates at low shear and low temperature. It is also used for direct extrusion of PVC calendered film.

Twin-screw extruders

Corotating and counterrotating fullySeveral different types of twin-screw extruders (TSE) are used for different applications. Parallel twin-screw extruders have two screws that rotate in the same direction (corotating) or opposite direction (counterrotating), with non-intermeshing or fully intermeshing flights. Parallel twin screws are modular, and the screw design can be changed by rearranging feeding, venting, mixing, and pumping elements along the screw shaft. Corotating TSE are commonly used for compounding, while counterrotating TSE are often used for direct extrusion.

Types of parallel twin screw extruders.

Conical, counter-rotating twin screws are tapered and made in one piece. Conical TSE are used primarily for processing PVC into pipes and profiles. The lower shear of conical TSE is an advantage for shear-sensitive materials like PVC. CPM conical counterrotating twin screw extruder screw shafts

While single-screw extruders are typically flood fed, with the feed filling the screw channel, twin-screw extruders are typically starve fed, with only a partially filled screw channel. Because the screw channel is not completely filled, downstream feedports or vents can be easily added. Adding shear- or heat- sensitive ingredients downstream, after the polymer is melted, helps keep them from degrading. Fibers can be added downstream to reduce screw wear and to preserve their aspect ratio. Vents are used to remove volatiles, such as water entrained in the mixture, from the melt. Compared to single-screw extruders, TSE are better at feeding and conveying, especially of powdered material or large amounts of fillers, and typically create more dispersive mixing.

 

 

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Davis-Standard provides this Community!

 

Making sure that you get the most production and efficiency out of your existing extrusion equipment is important to us.
Davis-Standard, LLC manufactures compounding systems for applications in the polymer compounding, polyurethanes, textiles and nonwovens markets
We manufacture both single screw and coextrusion systems for the rubber industry. Systems are available with a range of elastomer extruders including multipurpose, hot and cold feed, silicone, vacuum vented, pin barrel, smooth barrel and custom designs, as well as gear extruders.
Our extensive experience in monofilament, multifilament, melt blown, spun bonded, and other fiber processes have made us a leading extruder source among OEMs in the fiber industry.
Our foam systems are used in R&D and production applications by leading companies in the packaging, automotive, industrial, and graphic arts industries. We supply single screw systems, single screw tandem lines, twin screw tandem lines, and in-line foam extrusion coating systems.
We manufacture a complete line of laboratory and pilot equipment for cast film, blown film, tubing, sheet, coating, fiber, compounding, elastomer, and fine wire applications.
Our pipe, profile and tubing extruders and systems are engineered to help you manufacture tight tolerance products with minimal downtime.
We offer a full line of control systems to accommodate a range of budgets and process parameters. From discrete control to complete supervisory control, we have some of the industry’s most efficient control solutions.
We supply a complete line of reclaim extruders and systems for post industrial and post consumer processing.
Our sheet systems are globally recognized for reliability, accuracy, high outputs, and processing efficiency. We manufacture equipment for foam, flexible and rigid sheet extrusion, and single and multi-layer coextrusion applications up to nine layers.
The combined technologies of Davis-Standard and Merritt Davis Electric have created a powerful force in the wire and cable marketplace.
  • Facilities
    Davis-Standard has three manufacturing facilities in the United States as well as one at each of its subsidiaries in Germany and the United Kingdom. Sales or representative offices are located in France, Russia, the Philippines and China. Research and development centers are located in Pawcatuck, Connecticut; Bridgewater, New Jersey; and Fulton, New York.

  • Markets
    Davis-Standard, LLC serves customers in the agriculture, flexible packaging and web converting, automotive, building, medical, communications, consumer and industrial product industries.

  • History
    Davis-Standard was founded in 1848. The company entered into extruder manufacturing in 1948, and by 1955 was designing and manufacturing extruders for the wire and cable, plastic and rubber industries.

  • Since then, the company has grown to include the Betol, Black Clawson Converting Machinery, Brookes, Clipper Machines, Egan, ER-WE-PA, Harrel, Killion, KU-KA-MA, Merritt Extruder, NRM Extrusion, Repiquet and Sterling product lines.


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Our barrel production facility in the UK is equipped with state-of-the-art equipment to manufacture bimetallic barrels

 

 

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