Technical Information

B-3 Technology of Maximizing Capacity with Extra-Deep Channel

B-3 Technology of Maximizing Capacity with  Extra-Deep Channel

The co-rotating twin screw extruder is used in extensive fields due to its outstanding separating & kneading function and adaptability. Toshiba Machine has improved its productivity and quality dramatically with high-speed rotation and use of deep channel screw, by fully utilizing designing, manufacturing and forming technologies cultivated through years of experience and achievements. Especially, we have reduced and homogenized the thermal history and local heat generation which deteriorate the extrusion quality, and contribute largely to sheet and film direct forming fields saving energy and the number of processes without compounding.

[Platform]
B. Processing and Molding Machine Engineering Abilities.
[Applications]
Twin-screw compounding and extruding machine.

[Technical points]

  • Channel depth ratio of screw (engagement depth): 1.8 compared with the previous value of 1.5 to 1.6.
  • Decrease of screw crest width by 40% and increase of feed volume by 40%.
  • Realization of high quality is achieved by reduction of power consumption (energy-saving of more than 30%) and resin temperature decrease (5°C lower than the previous machine),
  • Development of a hybrid twin-screw extruder (CS type), fully utilizing the advantages of the previous machine and extra-deep channel profile machine.

1. Introduction

At present, each company is under severe excessive competition in the global market, and is tackling contribution to the society and strengthening market competitiveness. Even the plastic industry is making every effort to realize energy conservation by highly efficient production, reduction in environmental impacts such as volatile organic compound reducing measures and development of new polymer, differentiation of high-performance resin due to conjugation and low price. On the other hand, users' needs for plastic products are being diversified and a condition contrary to the highly efficient production as stated above is prevailing. To make these needs compatible, each extruder manufacture has supplied various process-saving and conjugation technologies under joint development with users. Especially, co-rotating twin-screw extruder (hereinafter called the twin-screw extruder) is applied in the extensive fields as the key component for process and energy-saving due to its outstanding separation / mixing function and adaptability. Expansion of applicable fields is in progress now. In this report, we explain the running characteristics and application expansion of the twin-screw extruder equipped with the latest extra-deep channel profile, which we started development a few years ago and has promoted marketing since then.

2. Extra-deep channel profile machine TEM-DS series

2.1 Mechanical features

The basic performance of the twin-screw extruder can be evaluated with the basic specification values of "permissible transmission torque of screw", "permissible screw rotation speed" and "channel depth ratio of screw = ratio of screw outer diameter to root diameter, index of engagement depth." The best feature of this machine is that channel depth ratio of the screw is 1.8. This value is determined so that minimum required screw crest width that gives effective shearing action can be assured with maximized feed volume. Compared with our previous machine TEM-SS series (channel depth ratio 1.5 ~ 1.6), screw crest width reduces 40% and feed volume increases 40%. Increase in feed volume dramatically enhances productivity of low bulk density material at the same time that the residence time can be increased during an operation in which extruder output is kept constant.
Also, decrease in screw crest width will reduce the shearing action. Reduction of excessive heat generation can achieve less burn or carbide generation and contaminants to quality stability of products during a long running operation.

2.2 Various running characteristics and mild compounding ability

Fig. 1 Distribution of section temperature of previous machine and extra-deep channel profile machine

Fig. 1 Distribution of section temperature of previous machine and extra-deep channel profile machine

The extra-deep channel profile machine is superior in conveying performance due to its large empty volume, the best feature of the machine, and allows to increase the processed volume of fine powder with low bulk density or crushed large grain material with low bulk density as used for the recycling application. (When this happens, however, full consideration should be given in terms of process, such as optimization of a screw structure.) Meanwhile, decrease in screw crest width realizes redacting energy consumption due to reduction in excessive local shearing action, and together with the energy-saving effect, leads high quality of products due to drop in resin temperature.
Fig. 1 shows the results of CAE analysis of our previous machine and extra-deep channel profile machine. In the extra-deep channel profile machine, partial temperature rise in the vicinity of screw crest is observed rarely, and resin temperature fluctuation is low level. When compared with the previous machine under the same running conditions, resin temperature of the extra-deep channel profile machine is 5°C lower than that of the previous machine. In the past, one case showed pressure fluctuation reduced by 50% when extruder output was changed by stepping action. Thus, the extra-deep channel profile machine allows mild compounding and is capable of coping with change in runningconditions with more flexibility, compared with the previous machine.
Especially, when the filler compounding with the low thermal stability resin, extruder output by the extra-deep channel profile machine was increased by 1.5 times under the condition of lower temperature of the permissible resin temperature, due to optimization of the screw structure and running conditions. Additionally, it is confirmed that the extra-deep channel profile machine having large empty volume has longer residence time, compared with our previous machine. Thus, together with the excellent homogeneous compounding characteristic, the extra-deep channel profile machine is expected to be applied for the devolatilization extrusion processing and reactive processing requiring the long residence time and favorable mixing performance in the coming years.

2.3 Expanding applications of deeper-channel screw

Fig. 2 Comparison of electric power consumption between twin-screw extruder with extra-deep channel profile and single-screw extruder

Fig. 2 Comparison of electric power consumption between twin-screw extruder with extra-deep channel profile and single-screw extruder

Introduction of the twin-screw extruder with extra-deep channel profile, which can reduce the resin temperature according to users' requirements for high quality and high performance of products, has increased year by year. Where this machine is actually used as a sub-extruder on the multi-layer film forming line, energy saving by more than 30% can be achieved together with low resin temperature, compared with the previous equipment. (See Fig. 2)

Fig. 3 New twin-screw extruder TEM-CS type

Fig. 3 New twin-screw extruder TEM-CS type

Recently, the twin-screw extruder with extra-deep channel profile is widely used for extrusion forming of functional sheets and films for the optical and energy-related area. For the compounding applications, the twin-screw extruder with extra-deep channel profile is also used to develop a new hybrid twin-screw extruder, together with the previous profile, fully utilizing the advantages of both machines (channel depth ratio 1.55 by the previous machine and channel depth ratio 1.8 by the letter machine).

Fig. 4 Comparison of running characteristics Between TEM machines

Fig. 4 Comparison of running characteristics Between TEM machines

The new twin-screw extruder (CS type) as shown in Fig. 3 combines the extra-deep channel screw profile with large feed volume on the material feed section and the previous screw profile with high shearing action on the compounding zone to realize both favorable dispersion and low resin temperature. Thus, the new machine has brought out the synergistic effects of the both machines advantages and succeeded in maximizing the processing capability without deteriorating the dispersion performance. (See Fig. 4)

3. Conclusion

As the twin-screw extruder has excellent mechanical characteristics better than the other extruders, its applications are expected to expand increasingly in the future. The twin-screw extruder with extra-deep channel profile we have introduced this time can be defined in a sense as the new generation twin-screw extruder. Expansion of applications of the twin-screw extruder with extra-deep channel profile just started, and we will proceed the development with our customers, based on their incessant support and valuable advices.