The production of single-screw plastificating extruders In america, extruder development was - but still is - largely seen as a machines with smooth barrels. Further advancement has tended to concentrate even more on the screws than anything else, with so-referred to as 'barrier screws' - screws where the solid materials is kept individual from the melt in the melting section - at the guts of attention. Although the earliest barrier screw was invented in Europe in 1959 by Maillefer actually, the majority of the further development work and the request of this basic principle took place in america. The 1st USA patent had not been applied for until 1961 by Geyer from Uniroyal. Even today, smooth-bore extruders with barrier screws are superior to grooved barrel extruders for most applications, given the conveying stableness is adequate. This applies specifically to applications in which fluctuating proportions of recycled or regrind materials have a disruptive impact on the standard conveying characteristics of the solid materials. In such cases, extrusion is likely to be more stable with a smooth-bore extruder. In Europe, the advancement of extruders with heat-separated grooved bushes in the feed section started out at the end of the fifties and beginning of the sixties. Grooves in the barrels to increase barrel friction and help conveying of the sturdy material have been tried out a long time before then. They were, however, not enough to process the newer high-molecular plastic sheet manufacturers excess fat HDPEs in powder and grit form. This specifically European phenomenon on the raw materials side has result from the systematic research and expansion of the grooved bush principle. Extruders with grooved bushes had been initially operated with the conventionally flighted threesection screws popular in Europe. To have better control of the melt temperatures, vented screws were produced later, and, to boost the melt homogeneity, were subsequently built with shearing/blending sections . One problem nevertheless remained: very high pressures by the end of the feed section and, as a total result, considerable wear and tear on the screw and barrel.