Overtightened and undertightened bolt joints
| Authors: Syromyatnikov V.S., Garcia Martinez Juan Marcos, Samora Quintana Laura Angelica, Ortega Rosales Miguel Gersaun | Published: 01.08.2014 |
| Published in issue: #8(653)/2014 | |
| Category: Calculation and Design of Machinery | |
| Keywords: bolt joint, correct tightening, tightening error, probability, safety factor, overtightening, undertightening |
Errors appearing when screwing bolts are random in nature and depend on the torque accuracy. The torque deviation from the design value can lead to both overtightening and undertightening. Undertightening causes more than 90 percent of damages, such as misalignment of parts, disconnection of joints, leaks in hydraulic systems, etc. Tension in an overtightened bolt can cause its break. To reduce the tension, a safety factor is assigned on the basis of general recommendations. Since the torque accuracy is not taken into account in this case, the safety factor is overvalued, which increases the size and weight of the joint. It is shown that overtightening and undertightening are caused mainly by inaccurate assembling and have equal probabilities. To determine the optimal size of a joint, a method for calculating the design tightening torque and safety factors depending on the torque accuracy has been developed. This approach makes it possible to reduce the probability of both overtightening and undertightening and decrease the size, weight, and cost of the part without deteriorating the joint efficiency.
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