| Filament Wound Composite Road Tanker |
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PR Basak, Sangeeta Baksi & S Biswas
In India, the road tankers are typically used for transportation of acids, alkalis, milk, petroleum products, edible oils, drinking water etc. Traditionally metallic tankers of cylindrical or ellipsoidal cross section are being used for carrying such liquids. For corrosive liquids like acids or alkalis, the mild steel containers require protective rubber lining on the inner wall. The initial rubber lining lasts only for four years and the tanker life can further be increased by two more years by relining them. This causes operational outage for steel tankers and adds to their maintenance cost. For tankers used for transporting water, rusting on the inner wall results into contamination of water. Composite or glass fibre reinforced plastic (GFRP) road tankers are most ideal for transportation of corrosive liquids due to their lightweight and corrosion resistance. While such containers had been in use extensively in advanced countries, their application did not pick up in India mainly due to the lack of good design, technological capability and manufacturing facility in the country. On assessing the merits and market potential of such composite road tankers over the conventional ones, a project for design & development of composite road tankers using filament winding technique was initiated by the Advanced Composites Programme of Technology Information, Forecasting & Assessment Council (TIFAC) with an industry partner, Modern Engineering & Plastics Pvt. Ltd., Mettur (Tamil Nadu) and technology support from NGN Composites, Chennai. The technology consultant carried out the mechanical & structural design of the composite tankers keeping in view the safety, functionality and durability requirements along with the design of the collapsible mandrels. Further, NGN Composites assisted in filament winding of the tankers and designed the tanker mounting mechanism on the vehicle chassis. India’s first prototype filament wound composite road tanker with typical cross section for horizontal mounting on truck was successfully developed under the aforesaid project. The prototype composite tanker has a capacity of 15.12 KL (length: 5.70 m, width: 2.10 m & height: 1.60 m) and weight of 1.16 MT. 12 mm thick filament wound composite layer was provided on 2.50 mm thick resin rich chemically passive liner to give a total thickness of 14.50 mm for the tanker. A net weight saving of about 1.00 MT could be achieved in case of composite tanker as compared to steel one of identical capacity. An increased tanker length up to 6.55 m could be accommodated on the same vehicle chassis; this would enhance its carrying capacity to about 17.00 KL of water to garner the advantage of weight savings by using composites. The added capacity would directly benefit the transporters with better operational economics. Filament wound composite tankers would be structurally superior with consistent product quality and reproducibility compared to the ones fabricated by hand lay up technique. The winding process also helps make the main shell and end domes in one integrated operation. The winding angle and thickness of filament wound layers are based on application & load requirement. The innermost layer of the wall could be made chemically resistant by using either thermoplastic or thermoset liners. The thermoplastic liner could be of PVC, PP, PVDF or PTFE depending upon the chemicals to be handled. The thermoset barrier may consist of a gel coat with surface veil mat and 2 - 4 layers of CSM with antistatic additives added to the resin. The resin system of isophthalic, bisphenol, vinylester or epoxy could be used depending on the chemicals handled and the structural performance required. While vinylester would be suitable for the tanker designed for the transportation of caustic soda, isophthalic resin could be used for tanker carrying water. Two anti-sloshing perforated baffles, placed at 850 mm apart from the centre, were provided inside the tanker shell with a passage cutout to reduce pressure in the longitudinal direction that occurs during sudden acceleration and deceleration of the truck. The tanker is also equipped with suitable nozzles for inlet, out let & over flow of liquids. Two manholes of 500 mm dia. openings were provided at the top. The tanker could be mounted horizontally on the truck supported on six nos. saddles, which are at a distance of 1.00 m from each other. The saddles were fastened to the tanker wall in a manner such that they can withstand the peel failure that may occur due to sudden acceleration. A comprehensive Code of Practice for design, manufacturing, prototype testing & evaluation of composite road tankers has been formulated after receiving inputs from various user agencies & others in order to arrive at the appropriate quality norms. Safety factor has been appropriately considered as per various provisions of BS-4994 for composite vessel design since no separate standards are available for road tankers. A 4-axes CNC filament winding system developed indigenously by M/s. CNC Technics, Hyderabad was used for helical winding on cylindrical portion and polar winding for the end domes. CADFil software was used for controlling the winding process. Technological challenges had been the polar winding of the end domes with typical elliptical cross section. After several rounds of winding trials, the process was perfected on establishing the compatibility between the software and the winding machine. The length of carriage traverse for the filament-winding machine has been suitably chosen so as to facilitate manufacturing of bigger size railway tankers in future. The general specifications of the 4-axes horizontal bed filament-winding system used in the project are as follows:
Even with the marginally higher initial cost, the composite road tanker works out to be an economically attractive proposition based on its superior life cycle of 15 years with zero maintenance compared to only six years for the rubber lined steel tanker. Additional carrying capacity for the composite tanker makes it further cost effective. The winding machine could be used for developing tankers for other applications such as for transportation of, edible oil, chemicals etc. The collaborative efforts by TIFAC and M/s. Modern Engineering Plastics have lead to the development of a new composite application in India by an automated filament winding process. The step is expected to go a long way to cater to the demands and aspirations of a rapidly industrializing country. Contributors for the article : PR Basak, Sangeeta Baksi & Soumitra Biswas NG Nair R Raman |
