Research On Molding Technology Of Railway Ties Made From New Polymer Composites

In recent years, synthetic resin and plastics processing industriesare developing rapidly in China. Plastic products have covered everycorner of society. Waste plastics recycling technology is one of theimportant research contents of circular economy. Traditional woodsleepers and cement, reinforced concrete sleepers have their ownshortcomings. Timber sleepers require constant maintenance andupdation.because of their bad weathering resistance. Cement, concretesleepers are lack of flexibility, and the vehicle and the road wear. In thisarticle composite materials were made from waste plastics and wastephosphogypsum mixture replacing wood sleepers. By doing this，it cannot only alleviate the problems of environmental pollution, but also cansolve the defects of traditional railway ties. Foreign R&D prove thatpolymer composite sleepers can achieve wooden sleepers mechanicalperformance, good economy, and are the ideal substitute for the existingsleepers.The present plastic sleepers are mainly PS reinforced HDPEcomposite sleepers, phosphorus gypsum reinforced polyolefin compositesleepers, rubber plastic composite sleepers, glass fiber reinforced HDPE composite sleepers and glass fiber reinforced polyurethane compositesleepers etc…Molding or intermittent extrusion molding method iswildly used in molding waste plastic railway sleepers. But because itsprocessing is not continuous, it has a low production efficiency. There isalso a way of continuous extrusion molding mathod which hasdifficulties in molding mainly because sleepers have a large section, andthey are solid. It is difficult to cool down waste plastic railway sleepershaving great heat, which demands high cooling and molding technology.Waste polymer and waste phosphogypsum which is theby-production in the production of phosphoric acid in chemical plantwere used as materials to extrude polymer composite ties. The planetaryand single screw two-stage extruders were used to make new polymercomposite railway ties. There are mainly three parts in the research. Thefist is material composition and mechanical performance test. Thesecond is setting processing equipment. The last one is molding process,particularly the cooling process determination. The three parts mainlyinclude:1、In order to meet the performance requirements of sleeper, theeffects of composite components with different content on themechanical properties of the sleeper were analyzed;2、In order to achieve stable industrial production, parametersmatching and processing temperature of double step extrusion system were determined;3、Cooling condition of railway sleepers’ molding was explored,and the software of ANSYS was used to simulate the molding of runnerof cooling mould.The results showed that the optimal formula was: mass fraction ofwaste phosphogypsum, waste PS, waste HDPE, waste PP, plasticizer andcoupling agent is respectively48.6%,3.5%,28.8%,13.7%and5.4%;the bending modulus, the flexural strength and the compressive strengthof composites with this formula are greater than foreign productsavailable. Two step extrusion system composed of a planetary extruderand a single screw extruder comparing other systems, processing suchlarge size and solid composite material products, its plasticizingcapability is better and production efficiency is greater. Four groups oflength with respectively3m,3.5m,4m and4.5m meters of water coolingmould and air cooling can meet the demand of cooling and shapingsleeper. The research and development of this project, is an effectiveextension of waste plastics and waste phosphogypsum new applications,and has expanded new products replacing the wooden sleeper, which hassignificant and positive meaning to promote the technical progress.