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.
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Fator PV de mancal
Nem todo mancal tem óleo bombeado sob pressão: muitos usam buchas autolubrificantes — de bronze sinterizado impregnado de óleo, de polímeros como PTFE (teflon), nylon ou acetal, ou de materiais compostos — que funcionam com lubrificação limítrofe ou a seco. Para esses, o critério-chave de seleção não é a pressão nem a velocidade isoladamente, mas o produto das duas: o fator PV = P × V, onde P é a pressão específica (carga dividida pela área projetada do mancal, em MPa) e V é a velocidade de deslizamento da superfície (m/s). O resultado, em MPa·m/s, é proporcional à taxa de geração de calor por atrito por unidade de área — e é justamente o calor o grande inimigo: como não há óleo circulando para removê-lo, o calor se acumula, eleva a temperatura da bucha e, se ultrapassar o limite do material, causa amolecimento, fusão (nos polímeros), expansão e travamento, ou desgaste acelerado. Por isso cada material tem um PV máximo admissível tabelado pelo fabricante (o PTFE puro tem PV baixo; compostos de PTFE com cargas, bem mais alto; bronze sinterizado, ainda mais). O projeto consiste em garantir que o PV de operação fique abaixo do limite do material com margem de segurança — e atenção aos limites separados de P (que causa deformação/extrusão) e de V (que causa fusão superficial), pois o mesmo PV pode ser atingido com combinações perigosas. Informe a pressão específica e a velocidade.
Related Tools
Bearing Speed Factor
Calculate a bearing's speed factor, A = n·d_m, from the rotation n (rpm) and the bearing mean diameter d_m (mm, = (D + d)/2, the average of outer and inner diameters). The n·d_m factor (often in mm·rpm, or m/min times the perimeter) is the key indicator of a bearing's SPEED DUTY, and governs several application limits. It sets the operating LIMIT SPEED: each bearing (and each lubrication type) has a maximum n·d_m above which friction heating, centrifugal force on the rolling elements and dynamic effects make operation unfeasible — grease lubrication tolerates lower values, oil higher, and special systems (oil jet, mist) the highest (high-speed bearings, like turbine and machine-tool spindle bearings, reach n·d_m in the millions). The speed factor also influences the bearing type choice (balls take more speed than rollers), the lubricant and the internal clearance (fast bearings may need larger clearance to accommodate thermal expansion). Comparing the application's n·d_m with the bearing limit is an essential check in medium- and high-speed rotating machines. Enter the rotation and the mean diameter.
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.
Reliability-Adjusted Life (Bearing)
Calculate a bearing's adjusted life for a reliability other than 90%, L_na = a_1·L10, from the reliability factor a_1 (dimensionless) and the nominal life L10 (in millions of revolutions). The standard L10 life corresponds to 90% reliability (10% failures). But many CRITICAL applications — where a bearing failure is unacceptable (turbines, aerospace, medical equipment, continuous-process machines) — require HIGHER reliabilities (95%, 99%, 99.9%). Since demanding higher reliability means accepting FEWER failures, the corresponding life is SHORTER: a_1 is below 1 for reliabilities above 90%. Typical values: a_1 = 1.0 for 90% (L10), 0.64 for 95% (L5), 0.21 for 99% (L1), 0.093 for 99.9% (L0.1). For example, to ensure 99% of bearings survive (instead of 90%), the design life drops to about 21% of L10. This is one of the 'modified life' corrections in the standards (ISO 281), which also include factors for material and lubricant quality and contamination (the more sophisticated a_ISO factor). Adjusting life for required reliability is essential in critical designs: simply using L10 (90%) would be too risky for a turbine, and too conservative for a household fan. Enter the reliability factor and the L10 life.
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.