Gasket Compression Calculations for Pressure Transducer Port Glands
Optimizing transducer port sealing demands balancing 15 to 25 percent gasket squeeze against volumetric fill below 85 percent to prevent mechanical die offset.
Motosh Equation
Torque Distribution
Mathematical models for bolted joints establish the relationship between applied assembly torque and the resulting axial clamping force. The Motosh equation divides the input torque into thread friction, underhead friction, and thread pitch torque. This calculation accounts for the geometry of the thread and the friction coefficients of the sliding surfaces.
Precise determination of the clamping force prevents joint separation under cyclic loading.
Thread Friction
Frictional components are calculated separately to identify where energy is lost during the tightening process. In the Motosh equation, the thread friction torque is calculated using the effective diameter of the thread and the helix angle. The underhead friction torque depends on the contact radius of the bolt head.
These friction coefficients are measured during torque tension testing.
Metrological Application
Calibration of industrial torque wrenching systems is verified by comparing the measured torque against the actual bolt tension using a load cell. Using the Motosh equation requires precise knowledge of the surface finishes and the lubricant used. Small errors in the estimated friction factors lead to severe deviations in the tension.
The test certificate must document the lubricant type and the thread class of the fasteners. Electronic tension sensors are used to measure the bolt stretch and confirm the accuracy of the calculation.
Dynamic Behavior
Dynamic wear and thermal expansion alter the friction factors during service, causing a drift in the clamping force. Surface degradation increases the resistance in the threads, reducing the clamping force achieved for a given torque.