The following is included in this e-tech newsletter:

Leistritz Twin Screw Extrusion Workshop to be held December 4-5, 2019

Dates: December 4-5, 2019
Place: Classroom sessions, Clinton, NJ. Demonstrations are at the Leistritz Process Laboratory.
Cost: $800 before Nov. 8th, $900 thereafter

Leistritz will host its' annual Twin Screw Extrusion Workshop on December 4-5, 2019 in NJ. Although focused on plastics, many representatives from Life Science have benefited by attending this program.

A partial list of topics includes:


"Hands-on" demonstrations at Leistritz NJ process laboratory will include:

Screw assembly training session at recent Twin Screw Workshop

In addition to Leistritz staff, industry and academia will contribute to the technical program. For the latest program information or to register for the Leistritz Twin Screw Workshop see HERE.

Installation of a twin screw extruder system…. it’s all about planning and preparation!

Preparation phase: Installing a twin screw extruder system is a big job. Site preparation and coordination of the many divergent tasks that are required to install and successfully commission equipment is best not left to chance. Even modest planning will yield benefits far beyond the installation and start-up phases of a new project.

ZSE-180 MAXX twin screw system with material handling, LIW feeders and underwater pelletizing system

Before starting, it is recommended that all timeline aspects be defined in a written specification. Bid documents need to be thoughtfully prepared to facilitate effective communication with vendors and contractors to obtain accurate information from both price and timeline perspective. Using local and experienced contractors that are familiar with plant personnel and local codes, where possible, generally helps the project efficiencies.

Each of these phases should be considered critical for success:

Preparation phase:

Installation phase:

Start-up phase:

For the complete article with detailed examples of items/actions for each phase CLICK HERE.

Barrel alignment procedures for twin screw extruders

The alignment of the barrel to gearbox on an extruder is important to minimize screw and barrel wear, as well as avoid fatigue cracks in the shafts. Required tools include a precision millwright's level and wrenches (to adjust the barrel support nuts).

ZSE-MAXX process section

The barrels are all rigidly aligned to each other and to the gearbox lantern by dowel pins, so there is no adjustment barrel-to-barrel. What's important is that the relationship of the barrels to the gearbox are properly adjusted at the barrel supports. Step by step procedures are as follows:

1. Remove the screw set. The alignment procedure can be done with the barrels either hot or cold.

2. Place the level on the extruder base where the gearbox sits. This is the reference level for the entire machine. Note what the level measurement indicates, which then needs to be matched at the barrel support adjustment points.

3. The level is then placed on the top of the barrels (longitudinally) at the barrels support location on the flanges or the flat surface between the flanges. Either position is OK because the barrels are machined parallel to the bore axis. The level needs to match the level of the previously measured base reference. Adjustments are made via the height adjuster nuts on the barrel supports.

4. On small extruders this may be one simple threaded adjuster. For small scale TSEs with flangeless, strain-bar assembly the strain bars must be cross-torqued to the correct figure.

5. The transverse alignment should also be checked.

6. Heat up the barrels and slide the screw set back in the machine. The screws should slide easily into the drive couplings. If force is required, determine what's wrong before operating the extruder (i.e. bent barrel dowel pins.

Managing Melt Temperature in a Twin Screw Extruder

Abstract:
The co-rotating, intermeshing twin screw extruder (TSE) is the most prevalent device for continuous mixing of polymers with additives and fillers. Exotic formulations that utilize atypical active ingredients are also processed. Materials exposed to high shear and temperatures will degrade. Most products benefit by strategically managing how shear (and energy) is imparted into the materials being processed and measured by the resulting melt temperature. Various factors are considered to manage and control the melt temperature, including operating conditions and screw design. In this paper, emphasis is focused on the melting zone in the screws.

A series of experiments were performed on a ZSE-27 MAXX (28.3 mm dia. screws and 1.66 OD/ID ratio) to compare the resulting melt temperature for different melting zone screw configurations for a 2 MFI PP. An "aggressive" melting zone with melting completed by barrel position 3 (12 L/D) was compared to an "extended" melting zone, where melting was completed by barrel position 4 (16 L/D). Only a single kneading block set was specified after melting to help isolate and compare the different melting zone configurations, and the resulting melt temperature. A low-pressure discharge die was used to minimize the effects of pressure on melt temperature. Both flush and immersion melt temperature probes were utilized in the experiments. Various rates and screw rpm tests were performed and compared.

Aggresive melting zone
Extended melting zone

Comparing the two melting zones, it was shown that the aggressive melting zone caused a significant temperature rise and lower attainable rates when compared to the extended melting zone. The higher temperatures inherent with the aggressive screw design indicated significant degradation. Significantly different melt temperature readings were also observed when comparing the flush to the immersion probes.

To see the complete study and paper CLICK HERE.

TSE formula: Temperature rise caused by pressure

Pressure generation in the extruder front-end caused results in a temperature rise. The more restrictive the front-end, the higher the pressure and melt temperature rise, which may adversely effect product quality. A temperature rise formula is as follows:

∆ T (°C) = ∆ P (bar) / 2

Units:

∆ T = Change in temperature in °C
∆ P = Change in pressure (1 bar = 14.503 PSI)

For example: If a TSE is processing 500 kgs/hr and the die pressure is 40 bar (580 PSI) then the associated melt temperature rise can be 20°C (∆ T = 40/2).

This formula is meant to be insightful, not necessarily accurate. Of course, the TSE rpm, and the geometry of the discharge screw elements are significant factors in the actual melt temperature. The moral of the story, don't underestimate the role discharge pressure might be contributing to the melt temperature.

Gear pump attached to twin screw extruder for 3D filament production
Side view gear pump (courtesy Witte Pumps)

The use of a gear pump or single screw pump can be integrated into the TSE system to keep the discharge pressure low and decrease melt temperature as compared to directly pressuring the downstream die/filtration system. Oil temperature control of the gear pump or intensive cooling of screw pump can help minimize the temperature rise associated with either device.

Test, don’t guess! Leistritz USA process laboratory expanded and improved

The Leistritz USA process laboratory includes 5 twin screw extruders and can test a 50 gram batch or run a process @ 1000 kgs/hr. A wide array of upstream and downstream equipment is available to allow testing of cutting edge technologies. A partial list of capabilities follows:

LHLG air quench pelletizer installed on ZSE-50 MAXX in Leistritz USA process laboratory

A few of the recent additions include:

Leistritz also has a collaborative agreement with the Polymer Processing Institute for Analytical Testing.
See this LINK for more details.

Leistritz Extrusion Technology brochure

A 16 page brochure is available that describes the current range of twin screw technologies and services available from Leistritz.

To download the Leistritz Technology brochure click HERE.

Visit Leistritz at these upcoming industry events:

 

We are looking forward to meeting you there!

Your Leistritz team

Leistritz Extrusion
175 Meister Ave.
Somerville, NJ, 08876, USA
ph: 908 685-2333
email: sales@leistritz-extrusion.com