How to calculate the bolt force
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σ= F/A≤[ σ] F is tensile force
a= π D-H / 6) ^ 2 (empirical formula), where h is the thread tooth height, for 60 ° For triangle thread, H = 0.866p, P is pitch, for trapezoidal and rectangular thread, H = 0.5p, D is minor diameter
according to the principle of work, when the screw is rotated for one circle under the action of power f, the work of F on the screw is F2 π L When the screw rotates for one circle, the weight is raised by one screw pitch (that is, the vertical distance between the two threads). The work done by the screw to the weight is GH. According to the principle of work, f = (H / 2) π L)/G Because pitch h is always greater than 2 π L is much smaller. If a small force is applied to the screw handle, the weight can be lifted
extended data:
in view of the difference between the permeability of possible defects (such as cracks, slag inclusion, mixture, etc.) of bolts and the permeability of steel, the magnetic field at the discontinuity of these materials will change after magnetization, forming a leakage magnetic field on the surface of some parts where the magnetic flux leakage occurs, thus attracting magnetic powder to form the accumulation of magnetic powder at the defect
The bolt rod ofA and B bolt is processed by lathe, with smooth surface and accurate size. Its material performance grade is 8.8, and its fabrication and installation are complex, and its price is high, so it is rarely used
The bolt ofC grade is made of raw round steel, the size is not accurate enough, and its material property grade is 4.6 or 4.8. Shear connection has large deformation, but it is easy to install and has low proction cost. It is mostly used for tensile connection or temporary fixation ring installation
The brief summary is as follows:
in the process of using bolts, the maximum safety tension of bolts is equal to the allowable stress of bolts multiplied by the minimum cross-sectional area of bolts
can be expressed as follows:
A = B / C = b/ π DXD / 4) where B is the force on the bolt, C is the cross-sectional area of the bolt and D is the minor diameter of the bolt
extended data:
bolt detection methods:
are divided into manual and machine
manual detection is the most primitive and common method of consistent detection. In order to rece the outflow of defective procts as much as possible, the general proction enterprise personnel visually inspect the packaged or delivered procts to eliminate the defective procts (including tooth injury, mixing, rust, etc.)
another way is full-automatic machine testing, mainly magnetic particle testing
magnetic particle inspection is based on the interaction of magnetic flux leakage field and magnetic powder at the defect of bolt, aiming at the difference of magnetic permeability between the possible defects (such as cracks, slag inclusion, mixture, etc.) of bolt and steel
after magnetization, the magnetic field at the discontinuity of these materials will change and form a magnetic flux leakage field on the surface of the workpiece at the part of magnetic flux leakage, which will attract the magnetic powder and form the magnetic powder accumulation magnetic mark at the defect
Under proper illumination conditions, the position and shape of the defects can be seen, and the accumulation of these magnetic particles can be observed and explained to eliminate the defective proctsBearing capacity = strength x area
The cross-sectional area of M24 bolt is 353 square mm instead of 24 diameter circle area, which is called effective area.
the tensile strength of ordinary bolt grade C (grade 4.6 and 4.8) is 170n / square mm
Then the bearing capacity is 170x353 = 60010n According to relevant standards, the performance grades of carbon steel and alloy steel bolts can be divided into more than 10 grades, such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9 and 12.9, among which grade 8.8 and above bolts are made of low carbon alloy steel or medium carbon steel and heat treated (quenched and tempered), which are generally called high strength bolts, The rest are called common bolts. There are two parts in the performance grade of bolt, which are the nominal tensile strength value and yield strength ratio of bolt material For bolts with low hardness and strength, ordinary bolt materials are proced with ordinary screw wires, and the hardness, tensile strength and torque of ordinary bolt materials are not very highhigh strength bolt generally refers to the bolt of high strength grade. Its screw material, bolt material and bolt material are relatively good, and its hardness is also relatively high. Moreover, after manufacturing, the bolt will be hardened. Make the bolt reach the grade strength requirement of high strength bolt
The results show that: (1) under different tensile stress, the thickness of oxidation layer increases with the increase of oxidation time, and the increasing rate of thickness increases with the increase of tensile stress; When the oxidation time is short, the applied tensile stress does not promote the oxidation, and the thickness of the oxide layer on the surface is smaller than that on the surface without tensile stress When the oxidation time is extended to 80 h, the thickness of oxide layer on the surface with tensile stress is larger than that without tensile stress, and increases with the increase of tensile stress; The growth of oxide film follows the exponential relation of power function, and the oxidation index is positively correlated with the applied tensile stress (2) when the applied tensile stress is less than 80MPa, dense oxide film is formed on the surface of the steel after oxidation at 650 ℃ for 400H. When the tensile stress reaches 120MPa, microcracks appear on the surfaceAccording to material and effective diameter (area)
if the material of the bolt is Q235 and the effective diameter is 10.3mm, the maximum bearing force of the bolt is 210 × three point one four × 3 / 2) ^ 2
cylindrical threaded fastener with nut. A kind of fastener composed of head and screw (cylinder with external thread), which is used to connect two parts with through hole. This kind of connection is called bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection
extended data:
according to the manufacturing accuracy, ordinary bolts can be divided into three grades: A, B and C. grade A and B are refined bolts and grade C are rough bolts. For connecting bolts used in steel structure, unless otherwise specified, they are generally common rough C-grade bolts. The processing methods of different levels are different
based on the interaction between magnetic flux leakage field and magnetic powder at the defect of bolt, aiming at the difference between magnetic permeability of possible defects (such as cracks, slag inclusion, mixture, etc.) and steel permeability, the magnetic field at the discontinuity of these materials will change after magnetization, forming a partial magnetic flux leakage field on the workpiece surface
Hello, how to calculate the torque value of nut and bolt
The calculation formula is: tightening torque = torque coefficient × Preload × Nominal diameter of threadthe key is the torque coefficient. With the same thread specification, the torque coefficient of different surface treatment is different, and some even differ by one time. Therefore, it is not appropriate to calculate the torque according to 0.12 in some manuals or standards. The torque coefficient shall be obtained by test. The torque value of bolt is shown in the figure below. Hope to be able to help you, thank you
the bolt manufacturer will give certain parameters, and the torque corresponding to the bolt axial tension can also be determined by test, which requires the use of torque meter, bolt axial force meter and other experimental equipment
for the situation you said, in actual operation, the torque wrench that has been accurately calibrated is generally used for tightening. For example, in the process of tightening bolts, if the manual torque wrench reaches the predetermined torque value, it will make a sound to remind workers to stop
for the error range you mentioned, I checked the data. When the torque wrench used for construction is calibrated, the allowable error shall not be greater than the torque value used ± 5% The error of torque wrench for correction should be controlled within ± Within 3%
isn't the actual torque tolerance controlled by tool accuracy? If you calibrate the torque wrench according to 44nm, then the final applied actual torque will be around 44nm, and the error will not exceed 44nm ± 5% Since the tolerance of the tool is allowed in the specification ± 5% range, then it is considered whether there is too loose or twisting risk in this range.
there are three kinds of bolt forces:
1. Loose connection has no preload, and the bolt is subjected to one time of the force, which is calculated according to the general cylinder strength
2. In the pre tightening process, the friction force is used to balance the tension stress proced by the pre tightening force on the bolt and the shear stress ring the tightening process. The bolt is subjected to 1.3 times of the force and is calculated as a cylinder
3. After preloading, axial load is applied, which is similar to the second one in case of static load (preload + tensile stress) × 1.3 is the force used to calculate, and the dynamic load is much more complex
hope to be useful to you!
The calculation of bolt tension is relatively simple, which is briefly summarized as follows. In the process of using bolts, the maximum safety tension of bolts is equal to the allowable stress of bolts multiplied by the minimum cross-sectional area of bolts. It can be expressed as follows: a = B / C = B/ π DXD / 4) where B is the force on the bolt, C is the cross-sectional area of the bolt and D is the minor diameter of the bolt