Some aspects regarding compaction of plastic bottles in stationary vertical presses

The paper presents some aspects regarding the compaction of PET bottles in a stationary vertical press, the collection and recording of data continuously from the pressing equipment being an older concern of the authors. In this regard, the vertical press was supplemented with a system for measuring displacements and compaction forces, as well as a system for acquiring and recording experimental data. Thus, the forces necessary for the separate compaction, in batches of the PET bottles, by categories (2 litres) are presented, the compaction being done in successive stages until the maximum compaction force is reached and the volume specified by the manufacturer. 2-litre bottles were used, the compaction being done in 3 loading batches, with the same type of bottles, each batch having two or three successive compactions. In the case of 2 l bottles, for a total stroke of the press plate, it was found that there is an empty stroke portion and a load stroke portion, for each compaction stage. The latter is all the bigger the fuller the pressing chamber. If at small quantities of material the displacement of the plate and the recording forces are small (about 139 daN for 77 previously undeformed PET bottles), for larger fills the registered forces increase (they can reach 500-600 daN for 129 bottles, respectively 600-700 daN for 155 bottles in the pressing chamber). Corresponding to these forces, the energy consumed at deformation increases from about 130 J (in the first stage) to 1400-1700 J (in the second stage of compaction). For three phases of filling with material and seven stages of compression-recompression (2 + 2 + 3), the average value of specific compression energy for the whole process was around 0.82 kJkg -1 of compressed material.