How to use a torque wrench correctly to check and tighten building fasteners?
The correct use of torque wrenches to check and tighten building fasteners is the key to ensuring that the clamping force of fasteners meets the standard and ensuring the stability of scaffolding. The following steps and specifications should be followed:
1、 Preparation before use
Tool selection
Choose a pre installed torque wrench that has been calibrated and qualified, with a range that covers the required 40-65N · m range for fasteners (recommended range 50-200N · m, accuracy within ± 4%), to avoid using pointer or digital wrenches that may cause inaccurate torque due to operational errors.
Inspection of fasteners and bolts
Confirm that the fastening bolts and nuts have no loose threads or rust, and the threads are intact; Clean up the debris (such as cement and rust) inside the fastener clip to ensure a tight fit between the steel pipe and the fastener, and avoid affecting torque transmission due to gaps.
Pre set torque value
According to the specifications, adjust the preset torque of the wrench to 40-65N · m (with a priority calibration of 50N · m, taking into account clamping force and bolt life), lock the preset value, and lightly test the wrench to ensure that a "click" prompt sound can be emitted when triggered.
2、 Tightening operation steps
Initial pre tightening
First, manually tighten the fastening bolts to a snug fit (with no gap between the nut and the fastening cover plate), ensuring that the bolts pass vertically through the fastening holes to avoid tilting and uneven force distribution.
Torque wrench operation
Grasp the middle of the wrench handle, align the socket with the nut, and slowly apply force until the wrench makes a "click" sound. Stop applying force at this point (to avoid excessive tightening that may cause the bolt to stretch and deform).
Single fasteners need to be tightened to the preset torque at once, while double fasteners (main and auxiliary fasteners) need to first tighten the main fastener to 65N · m, and then tighten the auxiliary fastener to 40N · m (to prevent force imbalance between the main and auxiliary fasteners).
Symmetrical twisting
For multi bolt connection parts such as right angle fasteners (such as special nodes), they need to be tightened 2-3 times in diagonal order, with an interval of 10 seconds between each time, to avoid deformation of the fasteners caused by one-sided force.
3、 Inspection and Calibration
Check after tightening
Torque check: For the already tightened fasteners, lightly rotate the nut 1/4 turn in reverse and then tighten it again with a wrench. If the "click" sound is triggered again and the torque is within the range of 40-65N · m, it is considered qualified.
Appearance inspection: After tightening, the fastener cover plate should be tightly attached to the steel pipe without obvious gaps; The outer thread of the bolt should retain 2-3 teeth. If it is too short, it may cause the nut to fall off, and if it is too long, it will affect the torque stability.
Regular review
Within 24 hours after the first tightening, tighten again (due to the stress release of the steel pipe and fasteners, the torque may decrease); During the use of scaffolding, 10% of the fasteners are randomly inspected every week, with a focus on load concentration areas (such as the bottom of the uprights and the joints of the crossbars), to ensure that the torque is always within the standard range.
4、 Precautions
Do not use a hammer to forcefully tighten the handle of the wrench to avoid damage to the internal gears or bolt breakage of the wrench.
After use, the wrench should be adjusted to the minimum torque value for storage to avoid long-term force failure of the spring; Calibrate the torque accuracy once a month to ensure that the error does not exceed ± 5%.
When the bolt is corroded and difficult to tighten, it needs to be replaced and operated again. It is forbidden to use lubricating grease to assist in tightening (it will reduce thread friction and cause excessive torque).
Through the above steps, it can be ensured that the clamping force of the building fasteners reaches 2.5-3.5kN, meeting the requirements of anti slip bearing capacity and effectively preventing scaffold safety hazards caused by loose bolts.
