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EPP pre-expanders from Kurtz are high-quality machines, designed for the automatic pre-expansion of expandable polypropylene (EPP), which have been continuously improved and developed in many years of experience and in a lively exchange with raw material suppliers. They impress with high productivity, quality and reliability, which equips EPP users against the price increase on the EPP raw material and energy markets.
The modern control concept of the EPP pre-expanders is realized on a touch panel with integrated PLC. A precise vapor pressure control in the range of +/- 0.1 bar and an electronic weighing device allows the user to pre-expand homogeneous bulk densities in the range of 15-60 g/l with the smallest deviation of +/- 1 g/l. Kurtz thus offers the possibility to compensate for the large bulk density variations within the raw material of +/- 2-5 g/l during pre-foaming.
With the use of a Kurtz EPP pre-expander, a truck can transport up to five times the raw material weight per trip, resulting in enormous cost savings. The potential savings in raw material consumption that can thus be achieved make it possible to amortize the cost of the investment within 2 years at a throughput of approximately 100 t per month.
The EPS raw material is conveyed as granules to the preexpander, where it is heated by means of wet steam. The hot steam softens the polystyrene beads and activates the blowing agent dissolved in them. This evaporates and causes the softened beads to expand. The bulk density can be adjusted by the weight of the raw material and the foamed volume. The EPS beads pre-expanded in this way are then cooled and stabilized in a fluidized bed on an air cushion before being conveyed by blower via a rotary feeder into the silos.
Welding of the end products: During the subsequent intermediate storage, the blowing gas diffuses out of the pre-expanded polystyrene beads and air penetrates. This "packed air" is further processed in the converting process on an automatic moulding machine or in a block mould. To achieve low bulk densities, EPS can also be post-foamed in a second pass. For expandable polypropylene (EPP), EPP/HP pre-expanders are available for lightweight foaming.