The following is included in this e-tech newsletter:
Don’t Forget the Anti-Seize!
It is important to use anti-seize on your screw shafts to allow you to remove and replace screw elements. There are several different types of anti-seize….. for something like a bolt thread probably any type will work. But there is one application within the extruder where the choice of anti-seize is critical: the spline shafts.
Screw elements fit onto the spline shafts with very small gap tolerances, plus low viscosity polymers tend to creep down between adjacent elements and get into this gap. With time and heat, this polymer forms a high strength adhesive, just like an epoxy. If screws are left together without being taken apart periodically, the elements get stuck, which makes the choice of anti-seize and period screw removal as a preventative maintenance measure so important. After extended periods at high temperature, degradation can turn anti-seize into a fine powder and it becomes non-functioning. To avoid this, Leistritz has found that Fuchs Gleitmo 820 performs well in this application.
Fuchs Gleitmo 820 is a white grease containing high solids with very slippery qualities that is rated for 1,150°C, and when used on shafts it doesn’t degrade into a powder. After months (or more) it’s typically still a slippery, useful greasy substance that helps your elements from getting “stuck”. Also don’t forget to remove, clean and stone the ends of the elements every six months or so.
For more information on the recommended anti-seize....
Technical Paper: Twin Screw Extrusion Developments to Process Bioplastics
Twin screw extrusion is a preferred manufacturing methodology to compound bioplastics with fillers, additives and fibers. Materials include PLA, PHA, PGLA and TPS which are converted into a variety of products, such as film/sheet for packaging, fibers and foamed parts. PLA, which is heat and shear sensitive, as well as torque intensive, is the most prevalent biopolymer processed today.
Twin screw extruders (TSE’s) utilize modular barrels and screws. Segmented screws are assembled on splined shafts. TSE motors transmit power into the gearbox/shafts and rotating screws impart shear and energy into the materials being processed. Free volume is an important design parameter for any TSE, and is directly related to the OD/ID ratio, which is defined by dividing the outer diameter (OD) by the inner diameter (ID) of each screw. With a smaller screw shaft, increased free volume is possible, but attainable torque is sacrificed.
Torque is also an important design factor, and typically limited by the cross-sectional area of the screw shaft, the shaft design, metallurgy and manufacturing technique. Deeper screw flights result in more free volume, but with less torque, since a smaller diameter screw shaft is mandated. Based on the use of a symmetrical, hammered splined shaft, a 1.55 OD/ID ratio has been deemed to result in the best balance of torque and volume.
Symmetrical splined shafts, formerly the industry standard, induce both tangential and radial force vectors into the power transmission train. The resultant force is not optimized, as the radial force is not applied in a beneficial direction. The use of an asymmetrical splined shaft design is now common that isolates the tangential force vector and results in higher torque transmission with a smaller diameter shaft. Hence, a 1.66/1 OD/ID ratio with deeper flight depths, higher free volume and increased torque is now perceived as optimum by many. The deeper flights result in a lower average shear rate with increased torque, a combination particularly beneficial for PLA processing.
The use of PLA and other bioplastics continues to increase for a wide variety of products and applications. Interest has never been more intense, as evidenced by the plethora of bioplastics industry events offered today. As research, understanding and commercialization occurs, it seems inevitable that bioplastics will be embraced as an alternative to petroleum based plastics. TSE advancements have and are being developed to improve the process-ability of heat and shear sensitive bioplastics. In many cases, the TSE system only needs to be “tweaked” for success.
To download a complete copy of this paper that includes PLA processing case studies ….
Featured HSEI TSE: ZSE-110 MAXX twin screw extruder
The ZSE-110 MAXX is a rugged, heavy duty 24 hr/day production extruder….it produces 5000 or even 10,000+ lbs/hr, and is often integrated into pelletization, sheet and fiber systems.
Some basic specifications are as follows:
To download a ZSE-110 MAXX specification sheet….
Leistritz sponsors Compounding Laboratory @ UMASS-Lowell
The Plastics Engineering Dept. at UMass Lowell has recently completed the renovation of the Leistritz Twin Screw Compounding Laboratory in their Ball Hall headquarters. UMass Lowell officially unveiled this facility during an open house which coincided with the SPI’s 2013 Annual Meeting and Fall Conference on September 19, 2013. The compounding laboratory now provides undergraduate and graduate students an opportunity for hands-on experience in developing novel thermoplastic formulations and processes.
2014 Industry events where Leistritz will participate
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