Measuring torque coefficient test construction torque can be calculated according to formula M=K@D@P: H is the torque value on the applied nut, KNM; K is the torque coefficient, determined by the test; D is the nominal diameter of the bolt, mm; P is The axial tightening force of the bolt (axial force), KN, is given by design.
When the steel girder is attached to the steel girder, it is fixed by 50% of the total bolt number and 50% of the ordinary bolt, and then the nail and the ordinary bolt are replaced by high-strength bolts, thereby entering the high-strength bolt construction stage. When installing the steel beam, use 30% of the total number of bolts and 20% of the ordinary bolts, then replace the high-strength bolts with the nails and ordinary bolts, and enter the high-strength bolt construction stage.
High-strength bolts are applied to the high-strength bolts of the bridge using the torque method, which is divided into two parts: initial tightening and final tightening. Before applying the screw, check whether the nail and temporary bolt connection of the assembled part meet the design requirements. When installing the high-strength bolt, pay attention to the direction of penetration and facilitate the screwing and maintenance, and the overall consistency. Pad method of the washer: the washer head of the bolt head is chamfered to the bolt head, and the washer on the side of the nut is chamfered to the nut. For bolt holes that cannot be penetrated freely by bolts, it is not allowed to penetrate intensively, and the reamer is used for reaming.
High-strength bolts shall be applied to the nut in the order of outward expansion from the middle of the bolt group. The initial torque is 50% of the final tightening torque. After the initial tightening, the tapping method is used to check one by one. After the inspection, the white paint is used to mark the bolts, nuts, washers and steel members in a straight line. The torque applied during final screwing must be smooth and continuous, and the bolt washers must not be rotated with the nut. Otherwise, the high-strength bolt coupling pair should be replaced. Mark the nut with red paint after the final screwing. Each fixed torque motor is equipped with an independent stable power supply. The electric wrench should be calibrated before and after use, and the torque error is not more than 5%. High-strength bolt construction is prohibited in rainy days.
High-strength bolt application quality inspection Initial tightening inspection: For all high-strength bolts after initial screwing, tap the nut with 013kg small hammer to check for looseness or leakage. Final screw inspection: First, observe whether the exposed length of the bolt thread meets the requirements of 14 pitches; secondly, observe whether the relative position of the initial screw mark is rotated to prevent leakage; again, take 5% for final screw inspection. The inspection adopts the loose buckle and the rebate method, and the inspection is performed by using a dial type manual wrench which has been inspected and calibrated by the technical supervision department. First check the wrench sleeve and the surface of the splice plate, then loosen the bolt about 30 degrees, then screw the nut back into place, the torque value is within the tolerance. If the number of unqualified persons exceeds 20% of the total number, the sampling shall be continued. If 80% of the total accumulated is qualified, the bolts for under-tightening (drag) shall be tightened and the over-bolted bolts shall be replaced.
The measures for stabilizing the torque wrench standard value and actual output value are as follows: (1) Wrench on-site calibration. The wrench is idling for 3 minutes before calibration. The pre-class calibration value pre-consides the change of climatic conditions on the day, and takes the upper or lower limit within 5% of the allowable variation range; (2) the construction site voltage remains stable; (3) reasonable arrangement Time and steps to determine where to use each set of wrenches. Under the high temperature conditions, take care of shading and ventilation to avoid the sun exposure of the control box. The spare wrench should be prepared and replaced in time to prevent the output torque from being disturbed due to the long time of use of the electric wrench.
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