Manufacturing custom-contoured wheelchair seating: A state-of-the-art review

Background:Custom-contoured wheelchair seating lowers risk of pressure injury and postural deterioration while custom-contoured wheelchair seating lowers risk of pressure injury and postural deterioration while increasing the stability and functional activity of the wheelchair occupant. Producing custom-contoured seating systems has historically been a labour-intensive process custom-contoured seating systems is historically labour-intensive.Objectives:Evaluate the strengths and limitations of current manufacturing processes for custom-contoured wheelchair seating to suggest potential future manufacturing processes.Study Design:Literature review of the state of the art.Methods:Research conducted through a literature review focused on the performance of different types of custom-contoured wheelchair seating products and processes over the last 40 years. Recent literature in orthotics and prosthetics was also consulted to assess future trends in seating.Results:There are five main manufacturing processes currently used to produce custom-contoured wheelchair seating systems. No single process is yet suitable for all wheelchair users, but many manufacturers are transitioning to computer numerical controlled (CNC) milling to reduce manual labour. Adjustable micro-modular seating and moulded seat insert manufacturing are also prevalent and offer alternative seating to soft foam carving.Conclusion:There is a need in the custom wheelchair seating sector for processes that are fast, cost-effective, produce little to no material waste, and that can effectively maintain a comfortable seating micro-climate. Additive manufacturing may meet these criteria, but further evaluation is required.Clinical relevanceThis review suggests that the custom-contoured wheelchair seating manufacturers are moving away from labour-intensive processes towards digital techniques, like CNC foam milling. Additive manufacturing is a potential new process that may reduce overall costs, the lead time in preparing seats and has the potential to better manage the seating micro-climate.

High temperature corrosion behaviour of aluminised FC 25 cast iron using pack cementation

Purpose This study aims to apply the pack cementation to develop the Fe-Al layers on the surface of FC 25 cast iron in order to increase the high-temperature corrosion resistance of the alloy. Design/methodology/approach Pack cementation was applied on the surface of FC 25 cast iron at 1,050°C. The bare and aluminised alloys were subjected to the oxidation test in 20 per cent O2-N2 at 850 °C. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD) were used for characterisation. Findings The layers of pack cementation consisted of Fe2Al5, FeAl2 and FeAl, and solid solution alloyed with Al. The oxidation kinetics of the bare cast iron was parabolic. Mass gain of the aluminised cast iron was significantly decreased compared with that of the bare cast iron. This was because of the protective alumina formation on the aluminised alloy surface. Al in the Fe–Al layer also tended to be homogenised during oxidation. Originality/value Even though the aluminising of alloys was extensively studied, the application of that process to the FC 25 cast iron grade was originally developed in this work. The significantly reduced mass gain of the aluminised FC 25 cast iron makes the studied alloy be promising for the use as a valve seat insert in an agricultural single-cylinder four-stroke engine, which might be run by using a relatively cheaper fuel, i.e. LPG, but as a consequence requires the higher oxidation resistance of the engine parts.

Design and operation of a new multifunctional wear apparatus for engine valve train components

The increasingly strict emission regulations in combustion engines are raising high requirements for the engine valve train system. In this paper, a novel multifunctional wear apparatus is designed to study the performance of engine valve train components. The apparatus employs a mechanical loading system, which consists of a special eccentric wheel and disc springs that apply the combustion loads, and the contact configurations and loading conditions of valve train components are simulated. It has three test functions for different components through specifically designed fixtures. The first function aims to evaluate the interaction between the valve seating face and the seat insert at high temperatures and loads. The second function is used to study the friction and wear properties of the valve stem and the valve guide. The third function is designed to evaluate the performance of the valve seals. At last, a verification test was carried out by the proposed experimental method. A pair of new exhaust valve and seat insert is tested for the performance evaluation of the first function. The wear mechanisms acting on the pairs interface are shown to be a combination of oxidative wear, adhesive wear, as well as fatigue flaking.

Research on Wear Surface Morphology of PCBN Tools in High-Speed Machining Valve Seat Insert

A series of experiments was conducted in high speed dry turning of valve seat insert with PCBN cutters. The main tool wear surface morphology was observed by utilizing scanning electron microscopy and digital microscope. The experimental results indicate that the tool wear surface morphology is rake face wear, flank wear, chipping, flaking and breakage.

Fully Nitrided Valves for Medium and Heavy Duty Engines

For certain applications in the world of internal combustion engines (ICE), it has been found that nitrided valves have a better performance against wear than those which are seat hard faced and chrome plated. This alternative has not been significantly explored in the Medium Duty (MD) and Heavy Duty (HD) markets. Fully nitrided MD/HD valves, mostly hard faceless, would be less expensive than chromed ones. They may become a cost effective product with better tribological performance, higher fatigue strength and improved resistance to thermal shock. In addition to this, a proper selection of the counterpart materials, those of the valve seat insert (VSI) and the valve guide (VG) will have a synergetic effect on the valve set performance, also leading to its cost improvement. Not less important is the replacement of the well-known salt bath nitriding by the gas nitriding technique, an environmentally friendly process that maintains valve performance with the advantage of employing a lower nitriding temperature providing a higher tip end and seat hardness combined with a lower distortion level in the final product. The aim of this work is to present the development and introduction of fully nitrided valves as a reliable solution for nowadays MD/HD applications. It is based on a deep process and product validation including the development of the gas nitriding process, wear, fatigue and engine tests.