|Vol.7 No.4 August/September1999 ISSN:0971-4413|
Investment Castings for an Auxiliary Power Unit
The main engine of the LCA uses a jet fuel starter (JFS) for starting the engine. JFS is essentially a small gas turbine engine consisting of two sets of rotors and stators. One set, the gas generator turbine, drives the compressor while the other, free power turbine, provides power output in the form of shaft power. The rotor and the stator castings have been developed by DRDO using the vacuum investment casting technique.
Investment casting is a precision casting process, also known as the Lost-Wax process, wherein disposable patterns are injection-moulded in wax. The patterns are assembled on to a central sprue which is dipped into a slurry of refractory material suspended in a liquid binder. Fine grained refractory particles are stuccoed to the assembly followed by drying. This process of dripping, stuccoing and drying is repeated until 6 to 7 coats are formed. Molten nickel-base superalloy is poured into the moulds under vacuum. The casting has met the user specification in terms of mechanical properties, microstructure, non-destructive tests, actual ground tests in engine assembled condition including over-speed tests.
More than sixty castings have been supplied to the user HAL/ADB, Bangalore. Performance trials in static engine tests have been found satisfactory and further evaluation is in progress.
Synthetic lubricating oils and lubricants are the key requirements for aero engines, helicopters, launchers of missiles, radio altimeters, mechanical time fuse, aircraft controls, etc. DRDO has developed synthetic diester-base oils by using various raw materials available indigenously. The lubricants conform to all required specifications. The indigenous technological development of synthetic lubricants is a potential import substitute.
Isothermal Forging & Hot Die Forging Technology
Conventional closed die forging uses dies that at ambient temperature or 100-200oC above the ambient temperature leads to substantial die chilling effects. In order to utilise the heat content of the work piece, forging is carried out at the highest possible speed. Since the available deformation is limited, several forging steps are required needing a number of die sets. In several aerospace forging alloys, such as titanium alloys, there is also a significant strain rate sensitivity of the flow stress. The lower strain rate possible in isothermal or hot die forging enables forging at much lower stress. The hot dies ensure that there are no chilled surface layers and hence forging is possible closer to the net shape. Moreover, smaller draft angles and close to near net or net shape can be obtained thus savings in material as well as machining costs.
DRDO has designed, fabricated and commissioned a special press for this purpose. The technology has been developed on a laboratory scale with Ti-6Al-4V alloy. It is now being scaled up for the discs required for Adour and Kaveri engine with another titanium alloy. Gamma titanium aluminides have recently been successfully forged in this press.
Impregnated Active Carbon for Defence Use
Detoxification of air, contaminated with various pollutants, is an important aspect as it is a primary need of all living beings. In Defence environment, basically two types of pollutants/toxicants needs to be removed from the air to make it fit for human consumption, i.e., chemical warfare (CW) agents and obnoxious gases released by human being/equipment. DRDO has developed three types of impregnated active carbon for removal of CW agents, obnoxious gases, and carbon monoxide respectively.
The technique involves coconut shell-based activated carbon of high surface area (more than 1200 sq m/g) impregnated with suitable metal salts and stabilisers. Such impregnated active carbon still possesses high surface area, around 1000 sq m/g, and facilitates both physical adsorption and chemisorption. These impregnated carbons are being used in various types of air filters designed for use in respirators, infantry combat vehicles, ships, shelters, and submarines. The technology for development of impregnated active carbon for removal of CW agents has been transferred to two production agencies.
Electrodialysis DesalinationAn indigenous rugged desalination plant has been designed and developed based on the principle of electrodialysis using ion-exchange membranes. The plant is easy to operate and maintain, can be static as well as mobile by mounting on a 3-ton vehicle, and operated on a 440 V AC, KVA/ generator.
Electrodialysis desalination plant effectively removes all dissolved salts including health affecting ions, e.g., fluoride, nitrate, sulphate, etc. up to 70 per cent from an input salinity up to 5000 ppm to less than 1500 ppm and can give 30 cubic meter potable water per day.
Electrodialysis reverse polarity system has also been developed for use in domestic electrodialyser. The unit can be operated by domestic power as well as non-conventional energy sources like solar photo voltaic cells (30 V, 2 Amp), and can be designed to a capacity from 5 to 15 l/hr.
Field Kit for Water Testing
Field kit for water testing helps in assessing the physico-chemical and bacteriological quality of water in the field. The tests are qualitative to assess the potability of water. The chemical assessment based on determination of eight parameters, viz., TDS, chloride, fluoride, nitrate, iron, hardness, nitrite and free chlorine is completed in 30 min whereas bacteriological examination is carried out in 4-10 hrs by determining presence of E.Coli by a new culture medium developed by the laboratory.
Materials/ Products& Processes/ Technology