GB/T 16823.3-2010Fasteners -- Torque/clamp force testing (English PDF)

5.1 General

The tightening torque acts smoothly on the bolt-nut connection pair or the screw-nut connection pair to generate the clamping force, measure and/or determine one One or more fastening characteristics. These characteristics include friction coefficient, total friction coefficient, thread friction coefficient, bearing surface friction coefficient, yield clamping Force, yielding tightening torque, corner and ultimate clamping force. In the range of elastic deformation, the torque and the clamping force are theoretically linear.

Note. Only the coefficient of friction of the thread can be measured for the stud.

There are two different purposes of the experiment.

a) Under standard conditions, the fastener's fastening characteristics test (see Chapter 8), ie using the test pads specified in 7.2.2 and 7.2.3 or Test washers (HH or HL type), and test and test bolts specified in 7.3 and 7.4.

b) In special cases, the tightening characteristics test of fasteners is given in Chapter 9.

The relationship between the fastening characteristics to be measured and the parameters/projects is shown in Table 2.

The torque-clamping force relationship of the bolted joints in different surface states and lubrication states is described by different methods, see 5.2~5.4.

Table 2

Measurable

Fastening characteristics Measured parameters/items Clamping force F Tightening torque T Thread torque Tth Bearing surface friction Torque Tb Corner theta Article number Torque factor - - - - - 10.1 Total friction coefficient - - - - - 10.2 Thread friction coefficient - - - - - 10.3 Friction coefficient of bearing surface - - - - - 10.4 Yield clamping force - - - - - 10.5 Yield tightening torque - - - - - 10.6 Ultimate clamping force - - - - - 10.7 Ultimate tightening torque - - - - - 10.8

5.2 Determination of friction coefficient

Under the most common friction conditions, if the shape and size of the fastener are not considered, it can be used to determine various friction coefficients (see 10.2~).

10.4). The coefficient of friction is a dimensionless data calculated from measurable physical properties, depending on the type of surface to be joined and What shape. The required measurement method is quite expensive because there must be a sensor that measures the clamping force and at least two different torques.

The sensor and all relevant geometric dimensions (d2, P, Db) need to be measured. To determine the coefficient of friction, under the same friction conditions, for all Fasteners within the specification range can be calculated using torque-clamping force.

5.3 Determination of torque coefficient K (K-index)

The method of measuring the torque factor K is relatively simple and can be calculated from the formula K=T/(Fd) (see 10.1). under these circumstances, Only relevant to d. This means that the K-index is limited by only one size. To determine K, the clamping force F and the tightening torque T need to be measured.

On fasteners of the same frictional condition, the same dimension d and the same geometrical area, the K-index can be used for the calculation of the torque-clamping force.

5.4 Determination of ratio T/F

The simplest and most advanced method is to measure the relationship between pure theoretical torque and clamping force. The ratio of T/F is only used for very special Connection research. At this time, it is not necessary to know the size and shape of the fastener.

6.1 Testing machine

The test machine shall be capable of applying tightening torque either automatically or by manually rotating a nut or bolt (nail) head and is capable of measuring the conditions listed in Table 2.

For the installation of the project, the relative error of the measurement shall be within 2% unless otherwise specified. The angle measurement allows an error of 2° or 2% of the measured value (taken the larger of the two). When arbitrating, it should be tightened with a controllable maneuvering tool that can rotate at a constant speed. The test results are recorded by electronic instruments.

The stiffness of the test machine, including the load cell and the stiffness of the fixture, is important and cannot be changed throughout the test.

6.2 Test fixture

The test fixture shall be capable of withstanding the combined load of the tightening axial force and the frictional torque of the bearing surface, and shall not cause permanent deformation and displacement. Figure 1 gives the basic requirements of the test fixture.

When testing the studs, the installation of the clamp and test piece is similar to that shown in Figure 1a). However, it can only be tested and screwed into the nut end. Before the test, the stud is screwed into the base.

The body end should not rotate.

a) nut test piece b) bolt test piece 1---test gasket, test gasket or special gasket;

2---nut test piece;

3---test bolt (or test screw);

4---test device (clamping element);

5---bolt (or screw) test piece;

6---Test nut.

a The test gasket or test washer and bolt head or nut should be fixed in a suitable manner to prevent rotation and should be handled.

b Lt is at least 1d when the yield clamping force or ultimate clamping force is reached.

Cd4 meets the requirements of the GB/T 5277 precision assembly series.

Figure 1 Fixture and test piece setup

7.1 General

The test part should match the part test piece.

Under standard conditions, the test parts (test washers, test gaskets, test snails) shall be tested for bolts, screws or nuts.

Mother, test bolt, test screw), see Figure 1. Test parts shall be in accordance with 7.2 to 7.4.

All grease, oil and other contaminants on the test piece should be removed before testing. Ultrasound should be used as well as health and safety requirements the solution removes oil. In case of dispute, the method of removing oil is determined by agreement between the parties.

7.2 Test gasket or test gasket

7.2.1 Type

Test gaskets or test gaskets are available in high hardness (hardened, HH type) or low hardness (HL type). Unless the buyer has it at the time of ordering He requested that suppliers should select test gaskets or test gaskets and their surface conditions empirically.

7.2.2 HH type test gasket or test gasket

Hardness. 50HRC~60HRC.

Surface roughness. Ra 0.5 ± 0.3.

Through hole. hole diameter (dh) according to GB/T 5277 medium assembly series, no chamfering, no counterbore.

Thickness. The minimum thickness h of the test gasket or test gasket shall comply with the provisions of GB/T 96.1.

The difference in thickness (deltah) of the same part is shown in Table 3. For the definition of the difference in thickness of the same part, see GB/T 3103.3.

Flatness. According to the A grade of GB/T 3103.3.

Surface state. a) The surface is not coated, no oil;

b) Press A1J (GB/T 5267.1 electro-galvanized, 1µm, bright-colorless) and remove grease.

Parts should be free of burrs.

The basic dimensions of the test gasket or test gasket are shown in Figure 2.

7.2.3 Type HL test gasket or test gasket

Hardness..200HV~300HV.

Surface roughness. when the thickness is less than or equal to 3mm, the roughness is Ra1.6µm; when the thickness is greater than 3mm~6mm, it is Ra3.2µm (According to GB/T 96.1).

Through hole. hole diameter (dh) according to GB/T 5277 medium assembly series, no chamfering, no counterbore.

Thickness. The minimum thickness h of the test gasket or test gasket shall comply with the provisions of GB/T 96.1.

The difference in thickness (deltah) of the same part is shown in Table 3. For the definition of the difference in thickness of the same part, see GB/T 3103.3.

Table 3 is in millimeters

d 3~5 6~10 12~20 22~33 36 deltah 0.05 0.1 0.15 0.2 0.3 Flatness. According to the A grade of GB/T 3103.3.

Surface condition. a) the surface is unplated and degreased;

b) Press A1J (GB/T 5267.1 electro-galvanized, 1µm, bright-colorless) and remove grease.

Parts should be free of burrs.

The basic dimensions of the test gasket or test gasket are shown in Figure 2.

Figure 2 Test gasket or test gasket (HH type and HL type)

The shape of the test gasket or test gasket is not specified, but the diameter Dp should be larger than the bolt test piece (or the nut test piece, or the pad of the screw test piece) the outer diameter D0 of the gasket of the bearing surface or the bearing surface of the screw and washer assembly.

7.3 Test nuts for testing bolts, screws or studs

When testing bolts, screws and studs with a performance level equal to or lower than 10.9, the test nuts used shall comply with GB/T 6170 or Class 10 specified in GB/T 6171; when testing bolts, screws and studs of class 12.9, the test nuts used shall comply with GB/T 6175 or Level 12 as specified in GB/T 6176.

Surface condition. a) the surface is unplated and degreased;

b) Press A1J (GB/T 5267.1 electro-galvanized, 1µm, bright-colorless) and remove grease.

When detecting the screwing of the short screw or stud into the nut end, the test nut can be replaced by a spacer with an internal threaded hole; the screwing length of the thread not less than 0.8d.

7.4 Test bolt or test screw for testing nut

When testing the nut, the test bolt or test screw used shall comply with GB/T 5782, GB/T 5783, GB/T 70.1, GB/T 5785, GB/T 16674.1 or GB/T 16674.2, the performance level is equivalent to the nut test piece, but should not be lower than 8.8. Thread should be rolled Forming.

Surface condition. a) the surface is unplated and degreased;

b) Press A1J (GB/T 5267.1 electro-galvanized, 1µm, bright-colorless) and remove grease.

When the nut test piece is fitted with the test gasket or the test washer, the test bolt or test screw should extend 2 to 7 times the length of the pitch (by the snail the type of the test piece is determined). When tightening the nut test piece, there should be at least two complete threads in the sandwich. The end of the test bolt should be flat and inverted angle. The threaded portion should have no burrs or dirt that affect the tightening torque.

10.1 Determination of Torque Coefficient K

Use the following formula to determine the torque factor based on the relationship between tightening torque and clamping force.

K=TFd

Unless otherwise specified, the clamping force shall be 75% (0.75 Fp) of the guaranteed load of the test part or part test piece, and the comparison between the two Small value.

10.2 Determination of total friction coefficient µtot

For the tightening torque T, the following formula is based on the Kelermann and Klein formulas.

P 1,154×pi×µth×d2

Pi-1,154×µth×

Do dhé

The total friction coefficient µtot is calculated and determined by the approximate formula according to the ratio of the tightening torque to the clamping force.

Totot=

2pi

0,577d2 0,5Db

In the formula.

Db=Do dh2

Note. The error caused by the approximation formula is about 1%~2%, which can be ignored.

If the measured value of Db is used, it shall be agreed by both parties to the contract.

The total friction coefficient is only used to compare the bolted joints under different friction conditions. The formula for calculating the total friction coefficient is to assume the thread friction system.

The number is equal to the friction coefficient of the bearing surface.

Unless otherwise specified, the clamping force shall be 75% (0.75 Fp) of the guaranteed load of the test part or part test piece, and the comparison between the two Small value.

10.3 Determination of thread friction coefficient µth

The coefficient of friction of the thread should be calculated and determined according to the relationship between the thread torque and the clamping force by the following approximate formula.

Thth=

Tth

2pi

0,577d2

Unless otherwise specified, the clamping force shall be 75% (0.75 Fp) of the guaranteed load of the test part or part test piece, and the comparison between the two Small value.

Note. The thread torque can be calculated from the measured tightening torque and the frictional torque of the bearing surface.

Tth=T-Tb

10.4 Determination of friction coefficient µb of bearing surface

The friction coefficient of the bearing surface should be calculated and determined according to the relationship between the friction torque of the bearing surface and the clamping force by the following approximate formula.

0,5DbF

In the formula.

Db=Do dh2

For the annular bearing contact surface, if the measured value of Db is used, it shall be agreed by both parties to the contract.

Unless otherwise specified, the clamping force shall be 75% (0.75 Fp) of the guaranteed load of the test part or part test piece, and the comparison between the two Small value.

Note. The bearing surface friction torque can be calculated from the tightening torque and the thread torque. The formula is as follows.

Tb=T-Tth

10.5 Determination of yield clamping force Fy

The yield clamping force should be determined by the clamping force and the angle of rotation or other equivalent relationship. There are several ways to determine the yield clamping force, specifically the method is agreed by both parties to the contract.

10.6 Determination of yield tightening torque Ty

The yield tightening torque should be read when the yield clamping force is reached. There are several ways to determine the yield tightening torque, the specific method of use by contract Agreement between the two parties.

10.7 Determination of the ultimate clamping force Fu

The ultimate clamping force should be read during...