Advantages of Twin Screw Extruders For XPS and PE Foam Extrusion


There is a a wide variety of extruders , produced today in the world; in general, they can be classified into two main families , that is: single screw and twin screw machines.


While single screw extruders  need no other specifications, twin screws  can further be classified into different categories:


- Corotating or counter- rotating

- Intermeshing or non intermeshing

- Straight or conical  (tapered) screws


The screws themselves  can have single or multiple principle, compact  (meaning that they are built in a single piece) or modular ( when different screw sections are mounted on a grooved rod) construction; they can, or cannot , be provided with inside oil-cooling circulation, etc.


The corotating twin screw extruders - manufactured today by SARAsrl - develop very little heat through mechanical work,  far below the amount needed for the material to reach the temperature required for gas mixing ; additional heat is applied in order to reach it. After the mixing , no more heat is applied, and due to the low shear developed, the temperature of the melt will decrease ; because of the relatively slow movement down the barrel, with a reasonable little cooling, temperature will easily reach the one required for the extrusion.


The very special principle of operation that characterizes  SARAsrl corotating intermeshing twin-screws extruders can be summarized as follows:


- The screws can be starve-fed by an independent mechanism so that screws speed setting does not affect output.


- Positive forwarding action eliminates problems like the bridging or slipping of solid material in the feed section, allowing  the feed of pellets, beads or powder.


- Shear rate is very low, and additional external heat, much easier to control, is added; the shear stress distribution can be adjusted by changing screw speed and/or output.


- Stock temperature can be raised to the desired level without exceeding it, and low temperature extrusion is easily obtainable.


- Positive conveying of the melt eliminates surging and promotes better dimensional control of the extrudate.


- Mixing is also positive and accomplished without overheating the material.


- Better  dispersing and homogeneisation.


- Self-cleaning is fast and complete and accomplished without overheating the material.


- Lower HP required per rated output, resulting in lesser stress on the machine.


- Energy saving, as the actual energy consumption is very close to the theoretical value needed.


Therefore, SARA srl extruders are especially suitable for the extrusion of heat- sentitive polymers, for products that have to be extruded at low temperature, for the extrusion of uncompounded dry blends and for materials that present difficulty in feeding or have to be thoroughly degassed.


Finally, with the proper screw configuration, foamed products can be produced by mixing additives, melting at relatively high temperature, injecting the blowing agent, and then cooling the melt to the lower temperature required  for foaming; all these operations are performed in one extruder.


Main construction features


Drive motor

AC motor with inverter control;  V- belt drive.



High resistance steel with ground profile.


Thrust bearings

Special design for maximum pressure absorption and exceptionally long life.



Hardened steel segments, with modular assembly on tie rod; optional internal oil cooling system.



Nitrited steel construction, in single or split section. Heated by electric heater bands; optional oil cooling system.


Control board

The control board is tropicalized, i.e. it is supplied with air conditioners.


The system includes a diagnosis device showing on a display failures of the line main functions.


Safety system against cold starts as well as displays for absorbed current and screws rpm are fitted on this section too.


The extrusion process, the alarms diagnostic, the record of the process parameters, the blowing agent  and raw materials flow rates and the relevant trends are operated by "Monitoring System


Melt cooler

SARAsrl special design static melt coolers, for a perfect homogeneization and cooling of the melt before the extrusion.



Round or flat gap dies, with continuous gap adjustment, interchangeable lips.


The extruders


RS0  - Max. screws X 32 mm. - max. 80 rpm - L/D 18:1 - Output 3 - 10 Kg/h


RS10 - Max. screws X 42 mm. - max. 80 rpm - L/D 18:1 - Output 6 - 16 Kg/h


RS20 - Max. screws X 60 mm. - max. 40 rpm - L/D 18:1 - Output 10- 22 Kg/h


RS40 - Max. screws X 90 mm. - max. 30 rpm - L/D 16:1 - Output 20- 50 Kg/h


RS60 - Max. screws X 90 mm. - max. 30 rpm - L/D 22:1 - Output 20- 80 Kg/h


RS80 - Max. screws X 98 mm. - max. 30 rpm - L/D 25:1 - Output 30 - 130 Kg/h


RS120 - Max. screws X109 mm. - max. 30 rpm - L/D 22:1 - Output 90 - 180 Kg/h


RS160 - Max. screwsX132 mm. - max. 30 rpm - L/D 25:1 - Output 140 - 300 Kg/h


RS500- Max. screws X180 mm. - max. 30 rpm - L/D 22:1 - Output 400- 600 Kg/h


RS800- Max. screws X180 mm. - max. 30 rpm - L/D 26:1 - Output 600- 750 Kg/h


RS1000- Max. screws X210 mm. - max. 30 rpm - L/D 26:1 - Output 800- 950Kg/h



8 January 2018 Monday
Click for news archive
Polmak Plastik 2011 - 2021. All Right Reserved.