On the occasion of Chinaplas, Plastics Insights spoke with Dr. Hans Wobbe, Christen Merkle and Gero Willmeroth about their many years of experience in China.

16:9

Spritzgießen

Kunststoffverarbeitung: Verfahren

Schröder, Susanne

Spritzgießmaschinen, allgemein

Kunststoffverarbeitung: Maschinen und Komponenten

Spritzgießmaschinen

Werkzeug- und Formenbau

Dienstleistungen

Werkzeug-, Formen- und Modellbau

Verbände, Institutionen, Messen

Messe Chinaplas

kunststoffe-international.com

Länderspecial China

“The Chinese Are Simply More Confident than Us”

On 1 September 2024, Tobias Baur will take over the leadership of the Sales and After Sales management division at Arburg.

Anlagen Additive Fertigung / 3D-Druck, Kunststoff

Anlagen für die Additive Fertigung

Change in the Arburg Management Team

A Arburg delegation handed over the 555th machine to Hongfa President Manjin Guo on 23 June 2024.

Proud of a long-standing, close partnership: Hongfa President Manjin Guo (right) accepts a printed circuit board equipped with Hongfa relays from an Allrounder from Arburg Managing Director Technology & Engineering, Guido Frohnhaus.

Spritzgießwerkzeuge

Werkzeuge für die Kunststoffverarbeitung

555th Allrounder for Hongfa

Husky Technologies announced that longtime company CEO John Galt will transition to the role of chairman and Husky COO Bradley Selleck will become CEO, effective 1 October 2024.

Husky Technologies Announces Leadership Transition

Mold-Masters, a developer and supplier of hot runners, controllers, auxiliary injection, and co-injection systems, has optimized the design of its PET-Series hot runner system to reduce its stack height to 260 mm on systems with 72 cavities or less using standard components.

Mold-Masters PET-Series is a hot runner system optimized for high-performance production of 2-stage PET preforms. 

Normalien und Heißkanaltechnik

Komponenten für die Kunststoffverarbeitung

Heißkanalsysteme

Länderspecial USA

Heißkanaltechnik

Messtechnik

Messung von Umgebung (Klima)

Reduced Stack Height of the PET-Series Hot Runner System

The Engel Group has acquired a stake in Electronica Plastic Machines, an Indian manufacturer of hydraulic injection molding machines. The strategic partnership will enable closer cooperation in the Indian market.

Engel Strengthens Market Position in India

CNCE Lux, the parent company of the KraussMaffei Group, is to be transferred to CNCE Group Co., Limited, which is a company of Sinochem and will hold 90,76 % of the shares. The KraussMaffei Group will then no longer be part of a listed company.

Aerial view of the KraussMaffei headquarters in Parsdorf near Munich.

CNCE Lux, the parent company of the KraussMaffei Group, is to be transferred to CNCE Group Co., Limited, which is a company of Sinochem and will hold 90,76 % of the shares.

Extrusion

Extrusionsanlagen

KraussMaffei Group to Receive Equity from Sinochem

Husky Technologies, a global leader in injection molding technology and solutions, acquires secondary injection unit and rotary platen technologies from MGS Healthcare Manufacturing (MGS), a global provider of healthcare manufacturing solutions.

Husky Takes over Technologies from MGS

Project and Sales Manager Burçin Bahşi from Elit Makina talks about current challenges of a toolmaker in the automotive industry.

Zero error tolerance: Injection molds for the production of car headlights are subject to strict quality controls.

Elit Makina as a toolmaker in the automotive industry with a focus on lighting. 

Länderspecial Türkei

Shown in the Best Light

Supplier parts from Germany, production in China and customers in Europe – Tuba and Mehmet Sarac from the injection molding company explain how this strategy works.

The siblings Tuba (right) and Mehmet Sarac in front of the currently most popular model, an all-electric SRC 120-AE.

The machine manufacturer Sarac is a true multi-cultural injection molding company: Supplier parts from Germany, production in China and customers in Europe. 

Multicultural Mechanical Engineering

View of the production area: The machine park comprises a total of 18 injection molding machines, seven of which are from Arburg.

Lid on: Whether for Toothpaste,  Chocolate or Adhesives

Needle, pin and rotary shut-off nozzles offer tailor-made solutions for various injection molding applications. From processing low-viscosity to highly filled plastics, they are precisely tailored to the respective requirements.

Shut-off nozzle in use: Precisely adapted to various injection molding processes.

Düsen, allgemein

Kunststoff-Aufbereitung

Schnecken und Plastifiziersysteme

Precise Material Control

RJG, Inc. introduces CoPilot Go – a new feature that enables molders to conduct tool trials and contain defects quickly without interfacing with the injection molding machine.

The new feature CoPilot Go  enables molders to conduct tool trials and contain defects quickly without interfacing with the injection molding machine.

Spritzgieß-Zubehör und Einzelteile

Improving Part Quality and Minimizing Defects

In cars, LEDs are taking over ever more applications and are increasingly used as differentiating design elements. In order to ensure a high luminous efficiency even with complex geometries and elongated structures, Engel has developed a new plasticizing process for manufacturing light guides.

The transformation of the automobile also strongly affects the vehicle interior. Light is gaining in importance as a design element

The Principle of Starve Feeding: Injection Molding Ultrahigh Purity Light Guides

Farbmessgeräte

Optische Mess- und Prüftechnik

LED / OLED-Systeme und Faseroptik

Lichttechnik

Less Granules  Stock Means More Quality

The required screw diameter can be ascertained on the basis of the shot volume. The formula for the average residence time can be used to estimate the degree of utilization and the thermal load on the material.

Various shapes of plasticizing screws. The correct design is approached in several steps

Part 1 of the Series Discusses the Basic Design of a Plasticizing Unit and the Correct Choice of Injection Unit

All about Plasticizing Screws

Part 2 of the Series Deals with Basic Methods for Evaluating a Screw Geometry

To be able to carry out the practical test in a resource-saving manner, the designers use simulation tools to assess the screw geometry. What is important here is explained using a 3-zone screw as an example.

Once the basic layout of a plasticizing unit has been determined and the appropriate injection unit has been selected, the development of the screw geometry enters its decisive phase. To be able to carry out the practical test in a resource-saving manner, the designers use simulation tools to assess the screw geometry. What is important here is explained using a 3-zone screw as an example.

The basic design of a plasticizing unit and the correct choice of the injection unit were discussed in the first part of this series. The way to determine the required screw diameter on the basis of the shot volume was also explained. By applying the formula for the mean residence time, the utilization rate and the thermal material load can be estimated; the latter needs to be kept low to achieve high end product quality. The maximum injection pressure and the available screw torque are additional key variables for successful injection molding production.

These considerations (see <a ext="tango:{45D59CEA-6DC5-4DBA-A9B4-CA287D7F7E2F}">Kunststoffe international 10/2020, pp. 27-29</a>) form the basis for the choice of the barrel-and-screw combination and also the starting point for further optimizations. In the second part of this series of articles, the basic methods for simulative assessment of the geometry of a given screw are presented – using the example of a 3-zone screw.

Before All Experiments Comes  the Simulation

The first question to be answered is what objectives should be pursued in developing a screw geometry. Often the goal can be clearly defined, such as increasing the flow rate, reducing the melt temperature, improving the quality of the blend, etc. The requirements become more complex as soon as the desired results are only indirectly linked to the screw geometry, or when they can be attributed to several causes, for example, when it is desired to reduce the formation of plaques, or when the wear behavior and conveying stability need to be improved.

Such multiple demands on screw aggregates often conflict with each other. Careful balancing of the layout is necessary to resolve such conflicts between several different objectives.

It has become common practice to optimize the geometry of a screw by way of simulation before the first tests are carried out with real experimental screws. With PSI/REX, Wittmann Battenfeld GmbH, Kottingbrunn, Austria, has a special software at its disposal for calculating the screw design. This software is ultra-modern and subject to continuous updates by targeted research carried out at Paderborn University, Germany.

While using the computer to calculate the screw geometry, the geometry can be varied extremely flexibly, and the resulting change can be immediately visualized on the screen. By running systematically through a pre-defined series of tests, it is possible to analyze the emerging trends. Finally, the results of all calculations are combined and compared. From the sum of this information, the corresponding screw geometry is developed and further optimized down to the last detail – until the desired result comes into view.

Only then are experimental screws produced in original size and used in practical tests. Depending on the complexity of the task, several different experimental screws may be used to approach the objective from various angles. If these tests prove successful, the optimization process is completed. Where there is still room for improvement, the development loop is re-run.

Model Case for the Optimization fo the Screw Geometry

Next, the parameters of a standard 3-zone geometry shall be discussed, and their influence on the manufacturing process shall be illustrated by an example. In order to give a full description of such a geometry in terms of process technology, the following parameters must be known (Fig. 1).

From the number of geometry parameters for only a relatively simple standard 3-zone screw, it is already apparent that there is basically a multitude of possible variants even for this type of screw. In the case of more complex geometries, such as those found in barrier screws, screws with shearing and mixing sections or shearing/mixing screws, the number of geometry parameters is many times higher. Starting basically from the recommendations available in the relevant professional literature [1], the optimization of the geometry for a screw with a diameter of 50 mm (DSC) is calculated below as an example.

It is assumed that the length of the feed zone is 50 % of the total length of the screw and the lengths of the compression zone and metering zone should each be 25 % of its total length. We set the feed zone depth at 0.1 D, i. e. 5 mm. The flight depth ratio between the feed zone and the metering zone should be 2. The L/D ratio is assumed to be 22.

A variety of different calculations can be performed for a screw with these pre-defined parameters. The present discussion focuses on the melt throughput, the pressure curve or pressure build-up capacity and the melting process.

Basic Assumptions and  Throughput Behavior

Further assumptions include the metering stroke of 85 mm and the cycle time of 35 s. The back pressure is set at 80 bar. To simulate moderate and realistic metering conditions for the material polystyrene (grade:PS 454N; manufacturer: Styrolution), a circumferential screw speed of 300 mm/s is assumed. The barrel temperature profile is slightly rising from the filling opening to the antechamber. All calculations are carried out for the 50 mm screw position (Figs. 2 and 3).

For the previously selected cycle parameters, the average metering performance is calculated at about 12.49 g/s for the present screw geometry. This means that the machine transports 12.49 g/s in the metering phase and thus takes about 12.7 s to plasticize 158 g of material. With a residual cooling time of more than 12.7 s, the machine can start a new metering stroke on time. But if plasticizing takes longer than the residual cooling time, the timing of metering impacts the total cycle time and thus reduces productivity.

The total output of 16,25 kg/h determines the amount of material consumption in the course of production. Since the screw does not dose during most of the cycle time, this output falls below the figure suggested by the average metering performance. The total output is the decisive parameter in dimensioning auxiliary equipment (dryers, material loaders, etc.).

Pressure Build-up Capacity and Melting Process Curves

During the metering phase, the pressure inside the screw channel increases from the feed opening to the back pressure in the antechamber. Depending on the screw geometry, there may be one or more pressure peaks in between.

Figure 2 shows the pressure curve over the screw length. In this particular case, the pressure curve begins to rise at about L/D = 2 and reaches the peak pressure of about 160 bar at about L/D = 14.25. In the last zone of the screw, the metering zone, the pressure drops continuously up to the check valve.

The melting process (MP) is visualized via two curves (Fig. 3): the solid bed width (green) is shown for the corresponding screw channel section, and the proportion of molten material (red) during the metering process. In addition, the development of these two parameters towards the end of the cycle is illustrated (in orange and beige).

From the results, it can be concluded that this melting process promises good melting of the material, since the proportion of melt has already reached 100 % at about L/D = 8 (proportion of melt MP = 1). In other words, the solid bed width has been reduced to 0.

It can be seen that even with a “simple” 3-zone screw, the designer has a large number of geometric parameters at his disposal to achieve the development goal. With the simulation software, the actual experimental effort can be reduced significantly. However, the results of the simulation cannot replace the practical experiments, since not all boundary conditions can be considered or are known. In a closed environment they show trends and possible need for action.

[1] Johannaber, F.; und Michaeli, W.: Handbuch Spritzgießen. Carl Hanser Verlag, München 2014

[2] Gornik, C.: Neue Erkenntnisse zur Plastifiziereinheit von Spritzgußmaschinen basierend auf experimentellen Untersuchungen, Dissertation, Montanuniversität Leoben 2007

Wittmann Battenfeld GmbH  

https://www.wittmann-group.com

Ausgabenartikel

The screw geometry is finely optimized in several calculation steps until the desired result is achieved. Subsequently, test screws are manufactured in original size and tested in practical tests with various material types

20:7

Fig. 1. Schematic diagram of a 3-zone screw with number of screw flights i = 1

Fig. 2. Pressure curve along the screw at 50 mm stroke position

Fig. 3. Melting process curves for the screw at stroke position 50 mm towards the end of the cycle

Name - Hauptartikel

<b> Filipp Pühringer</b> heads the Process Engineering Development Department at Wittmann Battenfeld GmbH in Kottingbrunn, Austria.

Part 1 of the series was devoted to the basic design of a plasticizing unit and the correct choice of injection unit and was published in Kunststoffe international (<a ext="tango:{45D59CEA-6DC5-4DBA-A9B4-CA287D7F7E2F}">issue 10/2020, p. 27–29</a>). In the 3rd part of this series of articles, the calculation results will be analyzed, and first steps towards optimization of the geometry will be outlined. It will appear in one of the next issues.