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20. February 2005

Three new multi-density metering technologies

Linden Industries, Cuyahoga Falls, Ohio, USA, introduced three new technologies for processors who wish to produce varying densities of foam from a single mixing head or machine. Advanced high-pressure polyurethane metering equipment provides the capability of modifying polyol and isocyanate ratios on-the-fly. Multiple density foams allow processors the flexibility to produce different products with different densities on a production line in addition to single products such as seats that require a soft centre and firm sides. Hydraulic driven 2-position orifices for multi-density metering technology This technology was developed for processors who need to automatically modify the throughput/ratios in the mixing head but do not have the budget for computer controlled servo orifices. Linden has developed a hydraulically operated mechanism attached to the mixing head that can switch the mixing head between two different through­puts/ratios. The high and low throughput positions are programmed into the shot profile data on the machine and can be selected as required. Hydraulic two-position orifices can be easily and inexpensively added to existing machines that have variable frequency drives. The modification involves reprogramming the machine to use alternate settings. Multiple density mixing problems With multiple density foams from the same mix head, the variation in polyol to isocyanate ratios can be as much as 4-to-1. Mixing difficulties can be experienced particularly when variations in the material viscosities exist. By using an L-style mixing head, the position of the mixing head’s clean-out piston can be adjusted to impede the flow of material and create additional turbulence and mixing. The clean-out piston position will typically be set to optimise the mix for the higher throughput pour. This may not always provide the optimal mix for low throughput ratios and cause mixing challenges. If the backpressure from the impedement rises too much, it may cause crossover between the material orifices. Hydraulic operated 2-position clean-out piston Linden has developed a two-position clean-out piston, operated by the existing mix head hydraulics. The mix head can be tuned for optimal mixing of both the high and low throughput situation with stops to lock in the alternate settings. As with the orifices, the two positions are programmed into the machine’s shot profile data and utilized when required. The capability for a two-position clean-out piston can be easily and cost-effectively added to existing machines that have variable frequency drives. Infinite ratio variations with servo controlled clean-out piston If the processor requires more than two combinations of ratios/throughputs, such as production lines manufacturing a wide range of products in varying densities, servo controlled systems involving closed-loop pressure feedback are typically used. Linden introduced servo controlled orifices in 2000, which allow infinite through-put/ratio variations as fast as 0.5 seconds while maintaining pour pressures at ± 3.45 bar (50 psi). To optimise the mixing with servo orifices, Linden developed the technology to program and servo control the position of the clean-out piston based upon closed-loop pressure feedback. Moulders can now run a variety of formulations and output ranges on the same production line with a single metering machine and optimised mixing.

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