Bolt thermal tightening rotation arc length and rotation angle
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For a M52×3 bolt, after applying the specified cold tightening torque, it is necessary to apply additional heat tightening to achieve a tightening force of 0.35 mm. What is the value of the heat tightening angle in radians? Given that the outer diameter of its cover nut is 75 mm, what should be the length of the heating arc? Correct answer: △a = [σ – (0.03 – 0.06)] * 360 / t (degrees) = (0.35/3) * 360° = 42°. The arc length is: △K = πD△a / 360 (millimeters) = (42°/360°) * 75 * 3.1416 = 27.5 mm
Heat set? To what temperature should it be heated? How to heat it?
Heating temperature = expansion coefficient corresponding to the bolt elongation, minus the ambient temperature
Length of the arc for thermal tightening of turbine bolts – Calculation of the heating arc length for bolts: (1) Elongation of the bolt: △L = εL. Here, △L represents the elongation of the bolt, and ε is a coefficient that can range from 0.0015 to 0.0018; the upper limit of this value is used for large-diameter studs in high-pressure turbines, while the lower limit is applicable to bolts or studs with smaller diameters in high-pressure or atmospheric-pressure components. L—the effective length of the bolt or stud; for double-headed bolts with cap heads, it is the free length of the bolt above the joint surface. (2) Rotation angle: a = (degrees); t – pitch of the thread (millimeters). (3) Arc length of the nut’s rotation (millimeters); D – outer diameter of the nut (millimeters). To accurately calculate the arc length of the nut’s rotation, it is necessary to take into account the effect of changes in coating thickness on the screw tension. This thickness is the difference between the thickness of the coating layer after the flange surfaces are clamped using conventional methods and the remaining thickness of the coating layer after heat compression (0.03–0.06 mm). Let σ be the thickness of the coating layer before thermal tightening. Due to changes in the coating layer thickness, the additional rotation angle of the nut is: △a = [σ – (0.03–0.06)] * 360/t (degrees). The additional rotational arc length is: △K = πD△a/360 (millimeters). The total rotational arc length of the nut is: K_total = K + △K (millimeters)