New screw design

Fogarty, L, Fogarty, D., and Rios, A., Turbo-Screws , New Screw Design for Foam Extrusion, SPEANTEC Tech. Papers, 47, 167 (2001)... 

In the hardwood hydrolysis experiment with the screw reactor, NREL researchers found that overmixing and an uneven flow pattern existed in the reactor. These factors have a negative effect on biomass hydrolysis. To enhance the screw conveyor reactor s performance, it was necessary to redesign the reactor to achieve adequate mixing and an even flow pattern. In the present work, CFD was utilized to analyze the flow behavior in the screw conveyor reactor, and a new screw design was proposed based on CFD analysis. 

The use of compacted talc will allow compounders to improve output rates. Enhanced compacting methods will allow the talc to be dispersed more completely in the polymer, with an improvement in impact properties. Not only will compounders be able to increase output rates through the use of compacted talc products, but these compacted talc products may be modified to improve color and dispersion. Compounders should be able to disperse talc in higher melt flow resins with new screw designs that increase work shear. Work is being done on injection molding machines that will provide adequate dispersion, which might eliminate the need for predispersed talc in composites. 

Based on these considerations, a new screw design was recently developed to reduce power consumption in materials like LLDPE the screw is often referred to as the LL-screw [4, 5]. 

The bulk density of the feedstock at ambient temperature and pressure should be measured prior to the design of a new screw, especially if it contains in-plant recycle resin. The measurement method is extremely simple and requires only a calibrated cell and a scale. A calibrated measuring cell with a volume of 500 cm can easily be constructed by welding a thin-walled metal pipe to a flat sheet of metal, as shown in Fig. 4.2. The bulk density is measured by filling the cell with feedstock, leveling the top with a steel ruler, and then weighing the cell contents. A more formal measurement technique was developed by ASTM as standard method D1895. 

As mentioned in the introduction to this chapter this is a necessary condition when approximating the cylindrical screw in the Cartesian coordinate system. The screw rotation theory, New Theory line, predicts that the rate should constantly increase as the channel gets deeper. When a fixed positive pressure occurs for the screw rotation model, the New Theory with Pressure line, the predictions fits the data very well for all H/Ws. Thus for modern screw designs with deeper channels, reduced energy dissipation, and lower discharge temperatures, the screw rotation model would be expected to provide a good first estimation of the performance of the extruder regardless of the channel depth for Newtonian polymers. 

A new screw was designed with a higher compression rate and compression ratio. The new screw was installed and the defects were totally eliminated. This case study shows a poorly developed experiment that incorrectly validated a poor... 

For this type of problem, the specific rate of operation is designed to increase with the optimized screw. When the specific rate increases, the torque required to turn the screw at the same rate will increase. If the new screw is huilt and torque is not available to turn it, then the design process will fail and the rate increase will not he achieved. The designer must perform an overall energy balance to make sure that torque is available for example, see Section 9.2. 

Christiano, J. P. and Thompson, M. R., A New Barrier Screw Design Utilizing Solid Bed Deformation with Forced Melt Removal, SPE ANTEC Tech. Papers, 46, 78 (2000)... 

Kruder, G.A. and Nichols, R.]., New Applications of Wave Screw Designs for Ultra High Output Extrusion, SPE ANTEC Tech. Papers, 31, 137 (1973)... 

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