Passenger coaches: Filament-wound composite undercarriage water tank

(Published on October – November 2007 – JEC Magazine #36)

RAVI SHRIVASTAVA, GENERAL MANAGER, MARKETING AND PROJECTS, KINECO

The development project was taken up in association with the Advanced Composites Programme of TIFAC (Ministry of Science & Technology, Govt. of India) and the Indian Institute of Technology in Bombay, with active participation from Indian Railway including their R&D wing Research, Designs & Standards Organization (RDSO).

Setting up the filament winding facility

As part of the development project, a state-of-the-art four-axis CNC filament winding facility (Figure 1) was created to wind components up to 4 metres in diameter and 10 metres in length. To make it more versatile, the filament winding facility was designed with one additional X-axis. While the first spindle can wind diameters up to 1.5 meters at high rotational speeds, the second spindle can wind diameters up to 4 meters at relatively slower speeds. The second spindle can hold a component and mandrel weight up to 6 tonnes. This facility is equipped with sophisticated computerized controls supported by the

CADWIND filament winding software from Material SA, Belgium. This is the first and largest locally manufactured filament winding machine in India designed and fabricated by CNC Technics, Hyderabad, in consultation with IIT-Bombay and Kineco technology experts.

Design objective and challenges

Undercarriage water tanks are mainly used for water storage in air-conditioned passenger coaches. Water is pumped from the tank into the train coach. The AC unit in such coaches is roofmounted and hence there is no space available for overhead water tanks. Each air-conditioned passenger coach is equipped with two undercarriage water tank modules, each module having two tanks with a holding capacity of 450 litres each.

The filament-wound composite undercarriage water tank module (Figure 2) was developed for Indian Railway’s airconditioned passenger coaches with the following main objectives in mind:

• The water contained in the undercarriage tanks should not be contaminated by the container material;
• The undercarriage tank should withstand the impact of normal ballast (stone) hits while running on the tracks;
• The tare weight of coaches should be reduced (for similar capacity tanks);
• The tank material should not corrode in the course of its service;
• The tank design should allow for easy cleaning and maintenance;
• The tank should have a good life span;
• Apart from fitment on new coaches, the new undercarriage water tank module design should be suitable for retrofitting on existing coaches.

It was a real challenge to design a composite pressure vessel for train undercarriage applications without compromising the tank water holding capacity, while meeting the space constraint and ballast protection requirements. Conventional undercarriage water tanks are in metal with flat ends (unlike filament-wound pressure vessels) and a number of other undercarriage components are fitted beside the tanks. Being undercarriage, the tank is considered a safety item and also has to maintain the stipulated safety dimension from rail level. During the design phase, the tank was subjected to a number of changes to reach an optimized design fulfilling all the necessary criteria. The composite water tank module developed saved 120 kg per coach.

Technical specifications, constructional details and manufacturing

The vessel was designed considering filament winding on a rotomoulded thermoplastic liner with integral dish ends which doubles up as the mandrel for winding. As it needs to offer optimum performance, the dome has to be designed with a geodesic shape providing a non-slip fibre path. This helps balance the internal pressure by stretching along the fibre direction. The shape of the dish end is nearly semi-ellipsoidal. The layered analysis of the shell was carried out using specialized software. The nozzles were designed according to relevant design standards and joined with proper reinforcement at the cut-outs.The composite undercarriage water tank was designed in compliance with BS 4994:1987 to fulfil the following technical specifications and requirements:

The undercarriage water tank module assembly consists of the following main parts:

Thermoplastic liner

A food-grade thermoplastic liner which also acts as mandrel was designed with sufficient thickness to withstand the winding tension while allowing the fixing of the central shaft. Depressions/niches were provided on the thermoplastic liner for additional padding (around the metal supports) and nozzle fitting.

Structural shell with integral dish ends

The structural composite shell was designed as a glassreinforced polyester construction (E-glass rovings and isophthalic acid-based unsaturated polyester resin system) with the necessary thickness. It was manufactured using filament winding, combining helical winding at + 15 degrees to the longitudinal axis and balance hoop winding at 90 degrees in the straight portion. Hoop winding was also used around the metal supports that hold the two tanks together and fix them to the coach underframe.

Tank fixing arrangement

The tank fixing arrangement was designed to allow both retrofitting and fitting to new coaches. The two tanks are held together and mounted to the coach underframe with a specially designed stainless steel (SS 304) fixing arrangement. The suspension arrangement and fixing brackets are analyzed for specific loads.

Protective shield

A specially designed polypropylene protective shield is fixed to the lower half of the undercarriage tank module with a certain gap, thus allowing the main shell to protect the tank from ballast hits while the train is running on the tracks.

Testing and field trials

A prototype tank was fabricated and tested for all basic material properties. All the welded metal joints were tested using the diepenetration test while the complete tank was subjected to hydro testing. On successful completion of fabrication/testing and clearance from RDSO, the prototype tank was mounted on a train for field trials. It has now completed over two and a half years of extensive field trials.

In view of the highly satisfactory and successful field trials, RDSO has already approved the new composite undercarriage water tank and Indian Railway is in the process of introducing it on a mass scale.