Reverse engineering and refurbishing of an Mi-24 helicopter main gear box

The Mi-24 helicopter is one of the most famous heavy lift helicopters designed with a net weight of 8.4 tonnes, while its gross weight is 12.5 tonnes. This helicopter is powered by two TV3-117 turbo-engines, coupled to a VR-24 main rotor transmission gearbox, which reduces the engine speed from 15000 Revolutions Per Minute (RPM) to the main rotor speed of 240 RPM. This research aims to show the functionality of the Mi-24 helicopter main gear box, to find the opportunities to extend the running hours (before maintenance) and to refurbish the gear box locally in South Africa. The research follows the principles of Reverse Engineering (RE) and Refurbishing. The principles involve the extraction of information from an existing product in order to establish its function and to re-create specifications which can be used to make, maintain or refurbish a similar or superior item. This dissertation has exposed some of the theory of the design of the Mi-24 main gearbox components and their functionality; including similar selected helicopters’ main drive mechanisms. The probable defects that are common to helicopter transmissions, the specifications and the Computer Aided Design (CAD) drawings are also presented. The research concludes that, with the cooperation of the local aerospace industry (including the army), the academic institutions and government; it is possible to get the necessary certification, licensing, training, specialised equipment and to establish a Maintenance Organisation, to refurbish the Mi-24 helicopter gearbox locally in South Africa

Reverse engineering and refurbishing of an Mi-24 helicopter main gear box

The Mi-24 helicopter is one of the most famous heavy lift helicopters designed with a net weight of 8.4 tonnes, while its gross weight is 12.5 tonnes. This helicopter is powered by two TV3-117 turbo-engines, coupled to a VR-24 main rotor transmission gearbox, which reduces the engine speed from 15000 Revolutions Per Minute (RPM) to the main rotor speed of 240 RPM. This research aims to show the functionality of the Mi-24 helicopter main gear box, to find the opportunities to extend the running hours (before maintenance) and to refurbish the gear box locally in South Africa. The research follows the principles of Reverse Engineering (RE) and Refurbishing. The principles involve the extraction of information from an existing product in order to establish its function and to re-create specifications which can be used to make, maintain or refurbish a similar or superior item. This dissertation has exposed some of the theory of the design of the Mi-24 main gearbox components and their functionality; including similar selected helicopters’ main drive mechanisms. The probable defects that are common to helicopter transmissions, the specifications and the Computer Aided Design (CAD) drawings are also presented. The research concludes that, with the cooperation of the local aerospace industry (including the army), the academic institutions and government; it is possible to get the necessary certification, licensing, training, specialised equipment and to establish a Maintenance Organisation, to refurbish the Mi-24 helicopter gearbox locally in South Africa

Analytical and experimental investigation of rubbing interaction in labyrinth seals for a liquid hydrogen fuel pump

Cracking of the titanium knife edges on the labyrinth seals of the liquid hydrogen fuel pump in the Space Shuttle main engine is considered. Finite element analysis of the thermal response of the knife edge in sliding contact with the wear ring surface shows that interfacial temperatures can be quite high and they are significantly influenced by the thermal conductivity of the surfaces in rubbing contact. Thermal shock experiments on a test specimen similar to the knife edge geometry demonstrate that cracking of the titanium alloy is possible in a situation involving repeated thermal cycles over a wide temperature range, as might be realized during a rub in the liquid hydrogen fuel pump. High-speed rub interaction tests were conducted using a representative knife edge and seal geometry over a broad range of interaction rates and alternate materials were experimentally evaluated. Plasma-sprayed aluminum-graphite was found to be significantly better than presently used aluminum alloy seals from the standpoint of rub performance. Ion nitriding the titanium alloy knife-edges also improved rub performance compared to the untreated baseline

Influences of surface quality on the rolling contact fatique behaviour of ceramics

A novel eccentric lapping machine was designed by the author and manufactured in-house, to serve as a test bench to investigate the finishing process parameters in relation to surface quality, as well as the feasibility of accelerating the finishing process of HIPed silicon nitride balls. The kinematics of the eccentric lapping were analysed and discussed. Taguchi Methods were used to optimise the finishing parameters to achieve maximum material removal rate in lapping and to achieve minimum surface roughness value Ra in polishing. Two kinds of HIPed silicon nitride ball blanks were finished by this machine. A finishing rate of 68 µm/hour was achieved which is 15 times higher than the conventional concentric lapping (normally 3'-4µm/hour). The surface roughness and roundness of the polished ball were above grade 5, close to grade 3 precision bearing ball specification. The upper limits of lapping load and lapping speed were determined by aggressive lapping tests. The effects of various finishing parameters on the surface quality generated were studied by detailed surface analysis, including X-ray diffraction residual stress measurement. As a result, the relationship between the finishing process and surface quality has been established. Accelerated rolling contact fatigue tests were performed both under a standard 4-ball and a modified 5-ball rolling configuration, with a ceramic ball as the upper ball and steel balls as lower balls. The tests were conducted at high speed and lubricated conditions under different loads and were run for up to 135-200 million stress cycles. Tests were conducted on commercially finished balls with different surface roughness and with different surface integrity (heterogeneous porosity, star defect, grinding defect and C-cracks). Tests were also conducted on self-finished balls with different finishing parameters and with different surface roughness. After tests, the rolling tracks and failure areas were examined by detailed surface analysis. The residual stresses on the rolling tracks were measured. Finite Element Approaches were also employed to describe the contact stress status. Failure modes in relation to surface quality were discussed. The research has provided an understanding of the finishing process, surface quality and rolling contact fatigue behaviour of HIPed silicon nitride balls

Finishing of Glass Balls by Chemical Mechanical Polishing (CMP) Using Cerium Oxide - Expanding the Process Capabilities of Magnetic Float Polishing (MFP) Technology

Finishing of brittle materials requires the use of "gentle" conditions that result in minimal or no surface and subsurface damage. Conventional polishing processes make use of diamond and other hard abrasive materials, which leads to scratching and brittle fracture on the surface. While some scratches can be extremely fine, others can produce micro-cracks that could further lead to catastrophic failure of the brittle work material. This is so especially in the case of the glass finishing process where the parameters used (abrasive, polishing load, etc.) should be gentle enough to avoid brittle fracture of the surface. Magnetic Float Polishing (MFP) technology is most suitable for finishing hard and brittle materials, like ceramics and glasses. It is a "gentle" finishing process that offers flexibility and a wide range of process capabilities. This investigation stresses an extension of this technology to finish glass spheres. Due to its excellent optical properties, finished sections of glass balls are widely used in optical and medical instruments, lenses, laser and fiber optics. Glass can achieve an excellent surface finish and is also chemically resistant to a variety of materials. The finished surface of glass can provide a good seal and, hence, glass balls find wide applications in valves, pumps, flow meters, liquid dispensers, and also in special ball bearings. It is through technological advancements in chemical mechanical polishing (CMP) that the achievable level of surface finish and other parameters, such as form and sphericity, can be improved significantly. in this investigation, a methodology for finishing glass balls, MFP, with a high level of surface finish is developed. The Taguchi technique is used to determine the optimum polishing conditions for best finish and to analyze the influence of individual parameters and their levels on the polishing process. Three distinct stages in the polishing process are identified as: the first stage with emphasis on material removal rate but low surface and subsurface damage, the second semi-finishing stage with reasonable material removal rates with control over size and sphericity with again minimal or no surface damage, and the third stage of final finishing involving CMP using softer (relative to hardness of glass) cerium oxide abrasive. The use of polishing pad (lap) is introduced into the MFP system that will improve the surface finish of the glass bal'ls significantly. Surface finish - average roughness, Ra, of 10 nm (= 100 Au as measured by Talysurf characterization length of 1.5 mm) or 4.3 nm Ra (= 43 AD as measured by AFM) can be obtained using a chemically resistant synthetic polishing pad with proper combination of other process parameters derived from the Taguchi experimental design

Finishing of Advanced Ceramic Balls for Bearing Applications by Magnetic Float Polishing (Mfp) Involving Fine Polishing Followed by Chemo-mechanical Polishing (Cmp)

Mechanical Engineerin

PROTOTYPE TILTING PAD THRUST BEARING WITH NOVEL CERAMIC MATERIAL FOR HARSH SERVICE

LectureProduct-lubricated pumping applications require extremely robust bearings, especially in the case of sand-loaded lubrication fluids. For high power/high speed pump applications, tilting pad bearings are the preferred bearing solution, due to their superior rotordynamic characteristics. For product-lubricated applications, materials with good corrosion and abrasion resistance characteristics have to be used. The lubricant for the bearing in these applications is often a water based fluid (e.g. sea water) with low viscosity and with particle contamination (e.g. sand). Existing tilting pad product lubricated bearings (PLB) solutions have the issue that catastrophic failures tend to occur under severe conditions or that they are limited in available size (e.g. polycrystalline diamond (PCD) bearings). A tilting pad thrust bearing and a thrust collar made of a novel ceramic material with improved tribological properties was designed, manufactured and tested for use in such applications. This new ceramic bearing offers several advantages over existing PLB materials. • Lower coefficient of friction and reduced start-up torque • Excellent dry-running capabilities • Increased reliability and robustness • Increased wear and abrasion resistance • No size limitation due to manufacturing constraints such as for PCD bearings The novel ceramic material is a Diamond-SiC composite, and the material has been tested extensively as per its tribological and wear/erosion characteristics before its use and application in a prototype thrust bearing and thrust collar

Experimental Investigation of Unbonded Magnetic Abrasive Polishing (UMAP) of Silicon Nitride Balls

New technique known as "Unbonded-Magnetic-Abrasive-Polishing"(UMAP) was designed and built in-house, to polish silicon-nitride balls in an economical-way. UMAP is based on the combination of underling principles of magnetic float polishing, magnetic abrasive finishing and lapping. Balls to be finished were loaded between a polishing-plate and a beveled-spindle by spring action. This was placed in a chamber mounted horizontally on a lathe, containing unbonded magnetic abrasive and non-magnetic viscous fluid. Magnetic field gradient generated around the balls concentrates abrasive particles in the polishing region. Polishing action occurs due to relative-movement of balls and abrasives between the polishing-plate and the spindle, rotating in opposite directions. A bevel of less-than 25 degree with the groove was essential for improving the sphericity and surface-finish. MRR upto 1.2 micrometer/min/ball with average sphericity of 0.77 micrometer and finish of 11.6nm were obtained. The best ball measurements achieved were 0.5 micrometer sphericity and 10.4nm finish.Mechanical & Aerospace Engineerin

Tribological Behavior of Functional Surface: Models and Methods

Material loss due to wear and corrosion and high resistance to motion generate high costs. Therefore, minimizing friction and wear is a problem of great importance. This book is focused on the tribological behavior of functional surfaces. It contains information regarding the improvement of tribological properties of sliding elements via changes in surface topography. Tribological impacts of surface texturing depending on the creation of dimples on co-acting surfaces are also discussed. The effects of various coatings on the minimization of friction and wear and corrosion resistance are also studied. Friction can be also reduced by introducing a new oil