How to tighten the large bolts of the paddle runner?
1. Use the bridge machine-pulley-tensile gauge-wrench system to tighten the bolts. The reading of the tension gauge multiplied by the wrench force arm m is the bolt tightening torque. The operation steps are:
a. Tighten some bolts symmetrically and evenly, reaching 30 to 50% of the total tightening torque M [Formula (4)]. Measure the flange surface clearance should be 0 (use a 0.02mm plug ruler inspection), called preload.
b. Tighten the remaining bolts symmetrically twice, the first time reaching 50~80% of the tightening torque M, and the second time reaching the tightening torque M.
c. Tighten the top symmetrically Tighten the bolts to a tightening torque of M.
2 Use a hydraulic tensioner to tighten the bolts, and measure the bolt elongation to control the bolt pretightening force. The operation steps are:
a. Tighten some bolts symmetrically and evenly, and the bolt elongation value (the remaining elongation value after removing the oil pressure) reaches 30 of the design elongation value [calculated by formula (1)] ~50, the measured flange surface clearance should be 0 (check with a 0.02mm feeler gauge), which is called preload.
Formula (1):
ΔL=`(σ_0L)/E`
`Δ_L`; Bolt elongation value, mm;
`σ_0`; Bolt pretightening stress, MPa;
L; Calculated length of bolt, mm;
b. Tighten the remaining bolts symmetrically to achieve the bolt elongation value (The remaining elongation value after removing the oil pressure) reaches the design elongation value [calculated by formula (1)].
c. Loosen the bolts pretightened in the first step.
d. Tighten the loosened pre-tightened bolts so that the bolt elongation reaches the design value [Formula (1)].
3 Use a tubular heater to heat and tighten For bolts, the rotation angle method is used to control the nut rotation angle after heating, and the pre-tightening force is controlled by measuring the cold bolt elongation value.
Hot tightening operation steps:
a. Take the nuts of 1 to 2 bolts, do a test on the relationship between heating time, bolt elongation value ΔL and nut rotation angle Ф, and find out Get the coefficient μ value.
b. Insert all the bolts and tighten them with a sledgehammer and wrench to eliminate the flange surface gap (check with a 0.02mm feeler gauge).
c. Divide the bolts into two groups evenly distributed.
d. Heat and tighten the first set of bolts so that the nut rotation angle is 1/3 to 1/2 of the value Ф calculated in equation (2). After cooling, measure the net elongation of the bolts.
Formula (2):
Φ=`(ΔL)/P`×360°μ
Where: Φ; nut rotation angle, (°) ;
P; Thread torque, m;
μ; Coefficient, determined by experiment;
ΔL; Calculated elongation of bolt, m;
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e. Heat and tighten the second set of bolts so that the nut rotation angle is 1/3 to 1/2 of the value Ф calculated in equation (5). After cooling, measure the net elongation of the bolts.
f. Use a 0.02mm feeler gauge to measure the flange surface clearance. It should not be inserted.
g. Heat and loosen the first set of bolts. After cooling, reheat and tighten. The nut rotation angle is Ф [calculated value from formula (2)]. After cooling again, measure the net elongation of the bolts as Design elongation value [Formula (1)].
h. Heat and loosen the second set of bolts. After cooling, heat and tighten again. The nut rotation angle is Ф [calculated value from Formula (2)]. Then After cooling, measure the net elongation value of the bolt, which should be the design elongation value [Formula (1)].
i. If the net elongation value of the cold bolt does not match the design value of Equation (1), Heat to loosen. After cooling, reheat and tighten, and the nut rotation angle will be the corrected Ф′. According to the actual net elongation value of the bolt and the actual rotation angle of the nut measured in the two steps of g and h, substitute it into equation (2) to obtain the corrected μ′ value.
Then substitute the μ′ value into equation (2) to obtain the nut rotation angle Ф′ at the design elongation value. After the bolt is cold, measure the net elongation of the bolt. Repeat this step until the net elongation value of the bolt meets the design value.
5 The process flow of assembly and testing of the paddle turbine runner is: the runner body is in place (upright or inverted, depending on the runner structure) → the blade transmission mechanism is installed → the runner is turned over and upright → Blade installation → relay installation → oil pressure test → runner hoisting → machine pit installation.
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