Simultaneous extrusion of polyvinyl chloride profiles with a PS foam core is challenging due to the different processing conditions and has not been performed before. A trial plant for researching this process has now been set up at the SKZ.

Method for the Simultaneous Extrusion of Window Profiles with a Foam Core

Extrusion

Kunststoffverarbeitung: Verfahren

Schaumstoffe und Vorprodukte

Kunststoff Werkstoffe

PVC-Profile

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

Schaumstoffe

Polystyrol

Thermoplaste

Polyvinylchlorid

Dichtungsschäumen

Schäumen / Reaktive Verarbeitung

Rohr- und Profilextrusion

Foamed and Still Extruded  in One Step

Manufacturers of standard extruders sometimes incorporate oversized drives into their machine designs in order to be able to cover a wide range of requirements. In times of high energy prices, however, this is no longer economical. An extruder should be equipped with a drive package that is matched to the gearbox and the processing unit. But what are the requirements governing the design of the drive system?

Process-Oriented Design of the Main Drive for the Extruder

Elektrische Antriebe

Antriebe

Flachfolien- und Plattenextrusion

Extruder

Kunststoffverarbeitung: Maschinen und Komponenten

Extrusionsanlagen

Ingenieurwissenschaften

Elektrotechnik

Energieeffizienz

Energy-Efficient Use of Drives

Global PVC demand has increased further. This is also forecast for the coming years. Besides product innovations, growth is mainly driven by infrastructure expansion. As a resource-efficient, durable and recyclable material, PVC could, in addition, benefit from growing environmental awareness.

Continuing on a Growth Trajectory

Weichmacher

Additive

PVC-Additive

Andere Werkstoffe

Werkstoffe für additive Verfahren

Granulat, PVC- (Compound)

PVC-Pulvermischungen

PVC-weich (Compounds)

Standardkunststoffe

PVC-Pasten

Schlagfestmacher für PVC

Verstärkungsstoffe

Polyvinyl Chloride (PVC)

New polymer composites for the production of multi-layer small tubes are being developed to give products specific functions. With suitable co-extrusion dies and a thermal barrier option, even complex layer composites with melt temperature differences of more than 50 °C can be processed reliably and in high quality.

Combining Polymers with Very Different Processing Temperatures

Temperiergeräte

Gießanlagen

Temperiertechnik

Baugewerbe (Hoch- und Tiefbau)

Medizintechnik (KU)

Kunststoffverarbeitung

Bautechnik, Sanitär

Extrusionswerkzeuge

Werkzeuge für die Kunststoffverarbeitung

Extruder-Folgeeinrichtungen

Extrusions-Zubehör

Automotive

Fahrzeugbau

Co-Extrusion with Thermal Control

In the area of pipe and profile extrusion, the focus remains on increasing efficiency. In addition to energy-saving systems, the focus on efficiency increasingly includes flexibilization of plants and processes, as well as reproducibility of quality in production.

Optimization of Components and Expansion of Plant Control Systems Offer Potential  for Improvement

Kreislaufwirtschaft

Efficiency Remains the Order of the Day

Production of PVC pipe in Bitterfeld, Germany, in 1935 ushered in the use of plastics for pipe production. This required exact knowledge of material properties, life expectancy and permissible loads. This was recognized from the very beginning and pursued systematically. 

Qualitätsnachweise

Looking Back: Materials for Pipes – Meeting Changing Requirements 

After a few selective modifications, the production of PVC-based WPC dryblends in a heating-cooling mixer and the subsequent processing to form profiles can be copied from PVC processing. Attention has to be paid, however, to the influences of formulation, process technology and process parameters during the production of the mixture. 

Verbundwerkstoffe / Werkstoffverbunde

Wood Plastic Composites (WPC): From the Formulation to the Finished Product 

The Italian company Bausano offers a new service for the operational leasing of extrusion lines. This provides customers with an alternative financing option for increasing their production capacities.

Extrusionsanlagen für KU-Verarbeitung

Kunststoffverarbeitungsmaschinen

Bausano Offers Rental Model for Extrusion Lines

The pipe manufacturer used a new generation conEX extruder to replace an older model in an existing extrusion line and was then immediately able to meet all requirements in terms of quality standards and output.

Fränkische Rohrwerke Invests in conEX NG Extruders

Continuous fiber-reinforced thermoplastic composites have also become established with thin-walled housings for consumer electronics and information technology. Not only do they offer high stiffness and help to reduce weight, but also enable the integration of classy appearance and functions. What is more, if the housings are produced using the hybrid molding process, costs, processing steps, and cycle times can be reduced.

Composites Reduce Weight and Simplify Production of Electronics Housings

Composite-Halbzeuge

Glasfasern / -matten

Kohlenstofffasern / -matten

Kunststoff

Bauwesen

Baustoffe

Faserverbundwerkstoffe

Kunststofffasern

Organobleche (gewebeverstärkte Thermoplast-Halbzeuge)

Lightweight to Fit in a Pocket

Recently, the first plant in the Middle East for producing composite pipes with diameters up to 1,200 mm was commissioned. Not only is the production line the first of its kind in the Middle East, but it is also noteworthy for the entire plastic pipe manufacturing business because of its specific properties and a throughput of up to 2,000 kg/h. 

High-Strength Pipes for Extreme Demands Coextruded from PE-RC Materials 

Polyethylen

Kunststoff-Rohre

Bedded on Rocks 

In industrial production monitoring, fast, reliable results are required to evaluate product quality. Suitable test methods must be available for this purpose. The time-consuming method previously used to determine the degree of crosslinking of PE-X pipes can now be replaced by rapid rheological measurements.  

Rapid, Reliable Determination of the Degree of Crosslinking of Polyethylene  

Werkstoffprüfung, mechanisch

Quality Monitoring of PE-X  Semi-Finished Products 

Today, online measuring devices with controlling function are standard in extrusion lines. The used measuring devices include, amongst others, gauge heads, which measure the inner and outer diameter of the hose and tube during the extrusion process. Described are two product series based on laser technology for continuous online quality control. Operators can choose between classic and high-end orientated technologies. 

Online Diameter Control during Hose and Tube Extrusion 

Messtechnik

Measuring the Diameter  

With a paternoster system KraussMaffei Berstorff offers a cost-effective alternative to conventional cooling systems, providing an up to tenfold increase in the cooling time of PE insulation foam tubes. The space-saving paternoster system is now available for ISO-Tube Schaumex and Schaumtandex lines.  

Paternoster System Increases the Cooling Time for PE Insulation Foam Tubes  at Minor Space Requirements  

More Time for Big Foam Tubes  

Plant technology continues to develop in ways that are as broadly varied as the products it extrudes. Besides increasing mass throughput, the main objective is to master diversification as it applies to flexibility, efficiency and quality. 

Market-Oriented Processes Drive Efficiency Increases in Pipe and Profile Extrusion 

Further Improvements in  Mass Throughput and Flexibility  

Extrusion of Rigid PVC without Dry Blend Production

Before the direct extrusion of profiles made of polyvinyl chloride was developed, it was previously necessary to produce a dry blend. This process is expensive and energy-intensive and, in contrast to direct extrusion, discontinuous. The direct extrusion of PVC using planetary roller extruders promises an improvement. In addition to soft PVC, rigid PVC can also be processed in this way with a few adjustments.

Polyvinyl chloride (PVC) is one of the most used plastics. PVC is mainly used in the construction sector for the manufacture of pipes and fittings, rigid profiles or window profiles, rigid foils and plates, cables, floor coverings etc. <a href="http://[1]">[1]</a>. However, the manufacturing process of PVC differs significantly from that of other thermoplastics. Before the actual processing, a dry blend must be produced in a discontinuous batch mixing process. Only then the PVC can be processed on an extruder into semi-finished products such as films, sheets, profiles or pipes. Dry blend production is generally carried out in heating/cooling mixers (HCM). By rotation of the mixing tool, the powdery components of the PVC formulation are mixed and heated, and additives can diffuse into the PVC grain.

This dry blend manufacturing process is energy-intensive and expensive. Another disadvantage of classic PVC processing is the combination of a discontinuous process, the dry blend production, and a continuous process, the extrusion. For this reason, there is great potential for savings by simplifying the overall process. The research institute SKZ – Das Kunststoff-Zentrum and the planetary roller extruder manufacturer Entex Rust & Mitschke GmbH have therefore researched the potential for processing rigid PVC without prior dryblend production and developed a direct extrusion process in a joint project.

Potential Savings due to Planetary Roller Extruders

Planetary roller extruders (PRE) offer themselves as a machine type for exploiting this savings potential. PRE have long been used in PVC processing. At the beginning of the 1950s, the permanently increasing requirements in this area led to the development of this plant system that can process the PVC dry blend gently. The main idea in the development of this machine was to transfer the concept of the known discontinuously working mixing and rolling mills to a continuous machine. In the PRE, several planetary spindles rotate around the temperature-controlled central spindle in a cylinder that is also temperature-controlled (Fig. 1). In modern machines, several of such modules are connected in series. In addition, peripheral devices such as twin-screw side feeders, liquid injections and degassing systems can be integrated (Fig. 2).

The modularity in combination with the large inner surface for temperature control of the material and the good mixing effect of the rotating planetary spindles make it possible to eliminate the dry blend production before the PVC extrusion when using a PRE [2, 3].

In a previous project, Entex has already examined the suitability of the PRE for the direct processing of soft PVC. A two-module system was used for this set-up and tested (Fig. 3). In the first module, the surface of the PVC grain is broken up by overrunning at moderate heat and thus the diffusion of the additives is made possible. Thereby, stabilizers and additives are mechanically pressed into the grain. This shortens the diffusion paths. The result is a quick effectiveness of the stabilizers. In addition, the initial degradation of PVC material is prevented by a precise temperature control.

Melting or gelling and homogenizing takes place in both modules. However, the first section of the extruder is crucial for this. The mechanical and thermal energy input must be carefully selected to prevent damage to the PVC, which is still inadequately stabilized. This requires the selection of a suitable planetary spindle configuration.

The type and number of planetary spindles affect both the mechanical energy input as well as dispersive and distributive mixing effects. The temperature profile also plays an important role, because between sufficient diffusion speed and thermal damage there is a fine line. Other important influencing factors are the speed and the diameter of the dispersion ring. In the second module it is also possible to degas the melt. The technology has already been successfully established for the granulation of soft PVC (PVC-P, plasticized) and calender feeding.

Challenges in Setting up the Direct Extrusion Line

Based on the successful implementation of the direct processing of soft PVC on the PRE, in the joint project with the SKZ it was examined whether the knowledge obtained can be transferred to rigid PVC (PVC-U, unplasticized). The aim of the project was to extrude rigid PVC directly on the PRE with constant heat and without prior dryblend production. The implementation of rigid PVC is much more complex than that of soft PVC. There is no softener in the formulation of rigid PVC, which is why pure solids are transported at the beginning. In addition, the temperature must be controlled even more precisely in the process than with soft PVC. At the same time, good dispersion of all components must be ensured in order to be able to guarantee the requirements for the mechanical properties. Furthermore, the pressures when processing rigid PVC are usually significantly higher than with soft PVC.

The two-module PRE set-up served as the basis for the direct extrusion line. Since the planetary roller extruder cannot build up enough pressure for profile extrusion, a pressure build-up unit suitable for rigid PVC had to be determined and tested (Fig. 4).

PVC Granulates as Alternatives  to Dry Blends

The extent to which the PRE is suitable for the continuous processing of rigid PVC was examined at the beginning of the project. For this purpose, three PVC mixtures were prepared in different ways and tested. The first mixture was produced in accordance with the classic batch process using a HCM and was available as a dry blend. The second mixture (HCM + PRE) was also produced by means of a HCM and additionally granulated on the PRE. Regarding the third mixture (PRE), the individual components of the formulation were cold premixed (cold mixture) and processed and granulated on the PRE. A standard PVC formulation for window profiles that is customary at the SKZ was selected for the examinations. The three mixtures were then processed into profiles on a counter-rotating twin-screw extruder (DSE). Appropriate test specimens were taken from the extruded profiles and their thermal stability and mechanical properties were tested.

To check the PVC stability, inter alia the mean molar mass was determined by gel permeation chromatography. The mean molar mass of the three samples was in each case at the same level (Fig. 5). Thus, there was no degradation of the polymer chains in any of the samples.

To assess the mechanical properties, tensile tests and the determination of the Charpy impact strength were carried out. The tensile strength of the PRE sample was slightly lower compared to the other two samples (Fig. 6).

However, a significant decrease in the mechanical properties was found when determining the impact strength (Fig. 7). While the samples HCM and HCM + PRE were at the same level, the PRE sample showed a significant drop in impact strength.

This is presumably due to an insufficient dispersion of the fillers. An expansion of the PRE to three modules can counteract this. This means that PVC granulates can be produced with this process without having to mix the material into a dry blend beforehand.

Which Pressure Build-up Unit  Is Suitable?

When carrying out the strand granulation, a pressure of approx. 30 bar is necessary. This pressure could easily be built up with the PRE. Significantly higher pressures are required for the extrusion of semi-finished products. In order to use the PRE as a pure continuous processing mixer for the direct extrusion, this should be decoupled from the pressure build-up. Therefore, a pressure build-up unit is additionally required for processing in constant heat.

In principle, a gear pump, a single-screw extruder (ESE) or a short counter-rotating DSE could be used to build up pressure. After consultation with various gear pump manufacturers, these are not suitable for the direct extrusion of rigid PVC, because the risk of PVC degradation in the bearings is too high in permanent operation. Tests with a counter-rotating DSE available at the SKZ showed that a pressure-free transfer does not guarantee a sufficient feeding of the melt. A transfer via a melt pipe failed due to the pressure required to overcome the pipe. A direct flange-mounting of a counter-rotating extruder could not be realized in the project due to time and cost reasons. Even if this variant is interesting from a procedural point of view, the focus was therefore on the pressure build-up with an ESE.

The project partners opted for an ESE 120 from Entex with an L/D ratio (L = length of the flow channel, D = screw diameter) of 5.5, which is also used for pressure build-up during the extrusion of soft PVC or plastics filled with wood fibers. In contrast to conventional plastification extruders, this extruder fed with melt has a liquid temperature control, which ensures good melt temperature control.

A prototype line was set up in the technical center of Entex. In order to examine the pressure build-up, direct extrusion tests were carried out with a simple profile tool with a variable outlet geometry without calibration. Three different mixing scenarios were prepared for the direct extrusion. The first mix was the ready mix (warm mix), which was produced in the HCM. The second mixture was the mixture premixed without energy input (cold mixture). The third mixture was divided into three dosing feeders in order to reproduce the addition of individual components.

The pressure build-up capacity of the different dies was examined by means of warm mixture. The highest pressure of approx. 180 bar could be built up with an oval die, the dimensions of which were 32 mm x 4 mm. With this die, it was possible to achieve a pressure that comes very close to a profile tool. In the next step, the cold mixture was tested on the line. At the same throughput, the PVC cold mixture was after both the PRE and ESE as just homogeneous as in the reference test with the warm mixture. A pressure of approx. 180 bar could also be built up in this test. Finally, the test was carried out with single components as direct extrusion. In this test, too, a homogeneous PVC mixture could be realized with the same throughput (Fig. 8).

This made it possible to achieve a pressure of approx. 170 bar. The results show that the PRE is very well suited for PVC processing without prior dryblend production allowing to skip the HCMs and thus reducing production costs. The tests demonstrate that a suitable pressure build-up device can be used for a direct extrusion of PVC.

With this process, Entex and the SKZ have developed an option for continuous PVC granulate production without prior dryblend production. Compounds produced in the process have mechanical and thermal properties comparable to those of a discontinuously produced dry blend. Furthermore, a prototype plant for PVC direct extrusion was successfully set up and tested in the Entex technical center. The results of the conceptual work will be used in the future to implement a direct extrusion line for the production of rigid PVC profiles.

SKZ - KFE gGmbH  

https://www.skz.de

Entex Rust & Mitschke GmbH  

https://www.entex.de

Ausgabenartikel

The direct extrusion of PVC profiles on planetary roller extruders can save costs and energy and simplify the process

Fig. 1. Schematic view of a process module of the PRE: several planetary spindles rotate  around the temperature-controlled central spindle in a temperature-controlled cylinder assembly

Fig. 2. With current PRE types, several process modules are connected in series. Moreover, additional systems for process improvement can be integrated

Fig. 3. The two-module PRE has already proven itself for soft PVC. A few adjustments were necessary for processing rigid PVC

Fig. 4. Schematic view of the direct extrusion line for rigid PVC: a connected pressure build-up unit provides the pressure required for extrusion

Fig. 5. Results of the gel permeation-chromatographic test with the two-module PRE set-up: the mean molar mass of the three samples is largely identical

Fig. 6. The sample PRE has a slightly lower tensile strength  than the samples processed in the other two processes 

Fig. 7. In the tests of the Charpy impact strength, the sample processed in the PRE fell significantly below the other two. However, if three modules are used instead of two, it even achieves better values

Fig. 8. With the installed line, a direct extrusion of rigid PVC using planetary roller extruders is possible

KUint5-21_SKZ_Yatsenko - Hauptartikel

 Dipl.-Ing. Serhiy Yatsenko has been a research associate in the Compounding and Extrusion Group at the SKZ since 2011; <a href="mailto:s.yatsenko@skz.de">s.yatsenko@skz.de</a>

Dipl.-Ing. Johannes Rudloff has headed the Compounding and Extrusion Group at the SKZ since 2016.

Marc Waffenschmidt, <a href="http://M.Sc">M.Sc</a>., is Deputy Head of Process Development at Entex.

Dr. Marieluise Lang has headed the department Materials, Compounding, Extruding at SKZ since 2015.

Dr. Thomas Hochrein has been Managing Director of Education and Research at the SKZ since 2017.

Prof. Dr. Martin Bastian has been Institutional Director of the SKZ since 2006.

The joint project “Development of a pressure build-up unit for dry blend planetary roller extruders and a profile extrusion demonstrator line” by the SKZ and Entex was funded by the Federal Ministry of Economics and Technology as part of the ZIM program based on a resolution by the German Bundestag (funding code ZF4026625EB7). The authors thank you for the financial support.

<ol><li>PlasticsEurope: „Plastics – the Facts 2019“, published on the occasion of the special exhibition of K 2019, 2019</li><li>Kohlgrüber, K. et al.: „Polymer-Aufbereitung und Kunststoff-Compoundierung“, Carl Hanser Verlag München, 2019</li><li>Michaeli, W.: „Einführung in die Kunststoffverarbeitung“, 3. Auflage, Carl Hanser Verlag München Wien, 1992</li></ol>

Read the German version of the  article in our magazine Kunststoffe or at  <a href="https://www.kunststoffe.de/a/fachartikel/auf-direktem-weg-zum-pvc-profil-320882" target="_blank">www.kunststoffe.de</a>