Abstract
Cementitious composites reinforced with silica, silicon carbide or carbon microfibres are designed, manufactured, characterised and tested as porous restrictor for aerostatic bearings. Carbon microfibres are residues obtained from the cutting process of carbon fibre-reinforced polymers. Porosity, permeability, flexural strength and stiffness are quite relevant in the design of aerostatic porous bearings. A 3141 full factorial design is carried out to identify the effects of particle inclusion and water-to-cement ratio(w/c) factors on the physical and mechanical properties of cementitious composites. Higher density material is achieved by adding silicon carbide. Higher porosity is obtained at 0.28 w/c level when silica and silicon carbide are used. Carbon microfibres are not effective under bending loads. Higher compressive strength is reached especially when silica particles are combined with 0.33 or 0.35 w/c. According to the permeability coefficient values the cementitious composites consisted of CMF (0.28 w/c), silica (0.30 w/c) or silicon carbide (0.30 w/c) inclusions are promising as porous restrictor; however, carbon microfibre porous bearings achieved the lowest air gap variation under the tested working conditions.
Highlights
Rolling-element bearings are commonly used due to their low cost and high rigidity, but they have limits of application when high speeds, low friction, repetitive movements, high temperatures or even special applications are required.[1]
The aerostatic bearings use a thin layer of pressurised air to provide relative movement between surfaces with friction close to zero, avoiding problems related to friction, wear and lubrication
The patterns for all cementitious composites show the presence of hydrated cement products, such as:
Summary
Rolling-element bearings are commonly used due to their low cost and high rigidity, but they have limits of application when high speeds, low friction, repetitive movements, high temperatures or even special applications are required.[1]. The aerostatic bearings use a thin layer of pressurised air to provide relative movement between surfaces with friction close to zero, avoiding problems related to friction, wear and lubrication. Aerostatic bearings have been a key component in the highprecision system, and the accuracy of movement and positioning of the nanometre scale has been achieved due to near-zero friction and low heat generation of gas lubrication.[3]. Pressurised air feeds an aperture between two bearing surfaces through a restrictor, being released in the surrounding environment from the outlet edges of the bearing gap to form a thin film acting as a lubricant. Motion surfaces do not come into contact, avoiding many conventional bearing problems, such as wear and friction, and offering distinct merits for precise positioning.[4] The aerostatic bearings can be classified as ‘orifice’ or ‘porous’ media types. The porous restrictor provides a more homogeneous air pressure distribution, attributed to a large
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