Steer pushes 40-mm twin-screw extruder to record throughput

(Bangalore, India) used a co-rotating intermeshing Omega H-40 twin screw to melt a compound of 40% talc-filled polypropylene (PP) at what it calls a world record throughput of 900 kg/hr. Steer says the accomplishment (see video here), is the culmination of work undertaken at the company’s Indian application development center and was made possible in part by its next-generation Extruder Processing Zone (EPZ) CPU.

In a release, Babu Padmanabhan, Steer’s founder and managing director, said the system allows processors to manipulate and maintain shear rates, shear-rate uniformity, and residence time. The company says its shovel intake elements boost intake capacity to improve feed-limited applications that use low bulk density and slippery ingredients, and the fractional lobed geometry of the screw allows greater throughput. In this instance, a 40-mm twin extruder ran ultrafine talc. Steer says the Omega line is suitable for a variety of compounding applications, including coloring and alloying to incorporating organic and inorganic fillers and reinforcing materials.

MPW fielded the opinion of two extrusion consultants regarding Steer’s claims. Allan Griff, an extrusion consulting engineer provider of Griff Extrusion Seminars who’s based from El Cerrito, CA, was struck by the relatively small size of the extruder used: 40 mm. “They have to run it at very high screw speed, which is a feed challenge for both talc and PP,” Griff said. For the technology to have a broader impact in the market, Griff said Steer will either have to show a significantly lower investment for the system, including projected maintenance, compared to a larger extruder capable of running 900 kg/hr, or, the Omega would need to show a significantly lower operating cost in terms of $/kg processed. In addition to that, the system would need to confirm there are no issues with material feed and high melt temperatures.

Chris Rauwendaal, president of Rauwendaal Extrusion Engineering Inc., visited with Steer at NPE2009, where the company had video of the technology. Rauwendaal said high-speed extrusion for single-screw extruders is being commercialized, with 75-mm lines able to achieve throughputs of 2000 kg/hr. Given that, Rauwendaal said you could expect a 40-mm single screw to have a throughput of 300 kg, so a twin-screw, which Steer used, could reach 500 kg/hr at a screw speed of 1500 rpm with an unfilled PP. To get to 900 kg/hr, Rauwendaal says Steer could have altered the channel depth of the screw, making that level of throughput, at 1500 rpm, feasible. “I think that the numbers that Steer has listed in the press release and video are possible,” Rauwendaal said. “Steer has been quite active in pushing the limits in twin-screw extrusion and has developed a good reputation.”                         —[email protected]