Bearing Radial Clearance
Calculate the radial clearance of a journal bearing, c = (D_bore − D_shaft) ÷ 2, subtracting the shaft diameter from the bearing bore diameter and dividing by two. The result is the radial space between shaft and bearing, where the lubricant oil film forms. Clearance is a critical design parameter: too small hampers film formation and heat dissipation (seizure risk); too large reduces load capacity and increases vibration and noise. A rule of thumb uses a radial clearance of about one thousandth of the diameter. Enter the bore and shaft diameters.
Resultado
—
Folga radial de mancal
Num mancal de deslizamento, o eixo tem diâmetro ligeiramente menor que o furo do mancal — e esse pequeno espaço é onde o filme de óleo se forma e faz toda a mágica da lubrificação hidrodinâmica. A folga radial é metade da diferença dos diâmetros: c = (D_furo − D_eixo) ÷ 2 (a folga diametral, mais fácil de medir, é a diferença inteira dos diâmetros; a radial é a metade). Apesar de minúscula — tipicamente da ordem de um milésimo do diâmetro (um eixo de 50 mm pede folga radial de ~0,025 a 0,05 mm) —, essa folga é um dos parâmetros mais sensíveis do projeto. Folga pequena demais dificulta a formação do filme, restringe a vazão de óleo (que também serve para remover calor) e, com a dilatação térmica do eixo em operação, pode levar ao agarramento (o eixo 'cola' no mancal). Folga grande demais reduz a capacidade de carga (o filme fica menos rígido), aumenta a vibração, o ruído e o consumo de óleo, e pode gerar instabilidade dinâmica (oil whirl). A folga ideal equilibra esses efeitos e é especificada via ajustes normalizados (sistema ISO de tolerâncias furo-eixo, ex.: H7/g6). Ela entra diretamente na razão r/c do número de Sommerfeld. Informe os diâmetros do furo e do eixo.
Related Tools
Eccentricity Ratio
Calculate the eccentricity ratio of a hydrodynamic bearing, ε = e ÷ c, dividing the eccentricity e (shaft centre offset from bearing centre) by the radial clearance c. The result (between 0 and 1) describes the shaft position within the bearing under load: ε = 0 means a centred shaft (no load); ε near 1 means the shaft nearly touches the bearing (heavily loaded, minimum film at the limit). Eccentricity grows with load and decreases with viscosity and speed. The minimum film thickness is h_min = c·(1 − ε). Enter the eccentricity and the radial clearance.
Bearing Power Loss
Calculate the power dissipated by friction in a bearing, P = T × ω, multiplying the friction torque T by the angular velocity ω (rad/s). The result, in watts, is the mechanical energy converted to heat per unit time by friction — a loss that reduces efficiency and heats the lubricant and components. This heat must be dissipated (by convection or oil circulation) to keep a safe operating temperature, since overheating degrades the lubricant and can cause seizure. Estimating the dissipated power is essential to size the cooling and the oil flow. Enter the friction torque and the angular velocity.
Bearing PV Factor
Calculate the PV factor of a bearing or self-lubricating bushing, PV = P × V, multiplying the specific pressure P (load over projected area) by the sliding velocity V at the surface. The result, in MPa·m/s, is the limiting criterion for selecting materials for non-force-lubricated bearings (sintered bronze bushings, polymers like PTFE and nylon): each material has a maximum allowable PV value, above which the friction heat cannot be dissipated and the bearing fails by melting or accelerated wear. PV is kept below the material limit with a safety margin. Enter the specific pressure and the velocity.
Equivalent Dynamic Load (Bearing)
Calculate a bearing's equivalent dynamic load under combined loading, P = X·F_r + Y·F_a, from the radial load F_r (N), the axial load F_a (N) and the factors X and Y (dimensionless, tabulated by the maker per bearing type and the F_a/F_r ratio). Most bearings actually carry RADIAL (perpendicular to shaft) and AXIAL (along shaft) loads at once, but catalog life and capacity formulas are defined for an equivalent pure radial load. The equivalent dynamic load is that fictitious radial load that would give the SAME bearing life as the real load combination. The X and Y factors depend on the bearing type (deep-groove ball, angular contact, self-aligning, tapered roller) and the axial-to-radial ratio — for mainly radial loads, X≈1 and Y≈0 (axial negligible); when axial grows past a limit (the e factor), Y starts to contribute. Computing P correctly is the first step in any bearing design, since P enters the life formula L10 = (C/P)^p and the capacity check. Wrong factors (or ignoring axial load) give an incorrect life estimate. Enter the radial load, axial load and the X and Y factors.
Sommerfeld Number
Calculate the Sommerfeld number of a journal bearing, S = (r ÷ c)²·(μ·N ÷ P), from the radius-to-clearance ratio (r/c), the lubricant dynamic viscosity μ, the rotational speed N (rev/s) and the specific pressure P (load over projected area). The dimensionless result is the characteristic parameter defining a hydrodynamic bearing's behaviour: it sets the minimum oil film thickness, shaft position, friction and lubricant flow. Low values mean a heavily loaded bearing (contact risk); high values, excessive clearance. It is the basis of bearing design via Raimondi-Boyd charts. Enter the r/c ratio, the viscosity, the speed and the pressure.
Hersey Number
Calculate the Hersey number of a bearing, H = μ·N ÷ P, from the dynamic viscosity μ, the rotational speed N and the specific pressure P. The dimensionless result is the horizontal-axis variable of the Stribeck curve, which maps the lubrication regimes: very low values indicate boundary lubrication (metal-to-metal contact, high friction and wear); intermediate values, mixed lubrication; and high values, full hydrodynamic lubrication (complete film, minimum friction). Tracking the Hersey number helps keep the bearing in the hydrodynamic regime, away from contact. Enter the viscosity, the speed and the pressure.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.