Study On Inner-Pressure Expansion Of Biaxially Oriented Self-Reinforced Plastic Pipes

Mechanical properties of a polymer may be considerably enhanced by deforming the polymer in the elastomeric state and thereby achieving orientation of the molecular chains. Plastic Pipes had considerably enhanced hoop strength, impact strength and resistance to fatigue from cyclic pressure by biaxially orientation.In this paper, the principle of inner-pressing expansion of PVC-U pipes with cloth tube filled with compressed air was studied, a hop-pocket expansion technique was introduced and a new industrial processing equipment of biaxially drawing plastic pipes (including reheat equipment, control unit, expansion equipment, draught equipment and so on) was designed. The main controlling technological parameters were studied. The continuously expansion process was achieved by inner-pressing expansion method. The process of the preparation consisted of :1. By the comparison of these orientation techniques of plastic pipe inside and outside, the author did biaxially oriented experiments to research the feasibility of the technique. The biaxially oriented self-reinforcement mechanism of polymer material was studied. A new producing method of biaxially oriented self-reinforcement plastic pipes was designed from the hop-pocket technique of the pyrocondensation tubes production.2. The processes of reheating, expansion and cooling were studied by theoretical models. According to elastic theory, the hoop stress and radial stress in pipe wall are near-linearly nearly distributed, and the hoop stress is nearly constant when the expansion pressure is small. The heating efficiency is got by heat transfer calculation in different oil bath temperature and heating time. It would guide experiment and production of PVC-0 pipe that compute the stress distribution in expansion process and thermal distribution in heating process.3. The biaxially drawing experiment contained ballscrew and glide tracks which could drive the mould reciprocating and realize the continuous manufacture. The technique have many advantages, such as low friction, high draw ratio, simple structure and easy to start.4. The experiments of both batch inner-pressing expansion and continuously expansion of PVC-U pipes with cloth tube filled with compressed air were done to get series of expanded pipes. The performance testing shows that the expanded pipes have uniform appearance with larger diameter and considerably higher tensile strength and elastic modulus with a little bit lower rupture elongation ratio.5. In order to determine the orientation ratio of a material, the paper studied a new method by using ultrasound method.