LY/T 3219-2020Self-tapping screws for timber structures (English PDF)

6.1 Raw materials

The raw materials of self-tapping screws should be cold heading, carburized steel or stainless steel. The raw materials of carbon steel should meet the requirements of GB/T 28906, the raw materials of stainless steel should meet the requirements of GB/T 4232, or use other materials equivalent to or better than the above standards.

6.2 Dimensions and allowable deviation

6.2.1 Dimensions

6.2.1.1 The nominal diameter d should not be less than 2.4 mm and should not be greater than 24 mm.

6.2.1.2 The thread bottom diameter d1 should not be less than 0.6 times the nominal diameter, and should not be greater than 0.9 times the nominal diameter.

6.2.1.3 The thread length lg should not be less than 4 times the nominal diameter.

6.2.2 Allowable dimensional deviation

6.2.2.1 The deviation of the nominal length l is ±2.5%.

6.2.2.2 The deviation of the nominal diameter d is ±2.5%.

6.2.2.3 The deviation of other dimensions is ±5%.

6.3 Surface quality

6.3.1 Appearance

The appearance should be smooth, without obvious scars or burrs, and without corrosion.

6.3.2 Surface treatment

6.3.2.1 The surface of self-tapping screws can be electroplated, or mechanically galvanized or painted on the surface of paint. If other surface treatments are required, Negotiation between the supply and demand parties.

6.3.2.2 When electroplating is used, the surface of the electroplated layer should be uniform and shiny, and the adhesion should be firm, and there should be no blistering, peeling, black spots or missing plating.

And other defects, and should meet the requirements of GB/T 5267.1.

6.3.2.3 When mechanical galvanizing is used, the surface of the coating should be free of plating, black spots, and peeling, uniform and smooth, and firmly attached;

Should meet the requirements of JB/T 8928.For the mechanically galvanized surface, as long as the thickness of the zinc layer is not less than the specified value, the surface to be plated is allowed There are areas of dark or light gray color unevenness.

6.3.2.4 When using paint for surface coating, the coating layer should cover evenly and firmly, and there should be no missing or falling off; the coating should pass the corresponding Anti-corrosion environment test.

6.4 Mechanical properties

6.4.1 The core hardness of the heat-treated self-tapping screw is not less than 270HV, and the surface hardness is not less than 450HV.

6.4.2 The bending angle should satisfy (45/d0.7 10)° without breaking, and the unit of nominal diameter d is mm.

6.4.3 The average value of flexural yield strength shall meet the requirements of Table 1.

6.4.4 The minimum tensile strength of heat-treated self-tapping screws is 600 MPa.

6.4.5 The pull-through strength and pull-out strength of the nail cap and the density (or range) of the wood material used in the corresponding test shall be publicized.

7.1 Testing of raw materials, surface treatment and net content

Raw material, surface treatment and net content inspection shall be carried out in accordance with GB 27704.

7.2 Dimensions and dimensional deviations

The size and size deviation detection shall be carried out in accordance with JB/T 9151.3.

7.3 Mechanical properties

7.3.1 Bending angle performance test

The bending angle performance test shall be carried out according to 5.2.3 of GB/T 14210-93.

7.3.2 Breaking torque

The breaking torque test shall be carried out in accordance with 6.2.2 of GB/T 3098.5-2016.

7.3.3 Pull-out strength

7.3.3.1 The depth lp of self-tapping screws into wood elements is between 8 d and 20 d; but for self-tapping screws with a nominal diameter d less than or equal to 2 mm Tapping the screw, lp is at least 12 d. The schematic diagram of the test is shown in Figure 3.

7.3.3.2 When testing the pull-out strength on the front and side surfaces of the timber diameter section and the chord section and the structural wood composite material, the width and thickness of the wood member the degree is at least (lp 5d) and the length is at least 30 d.

7.3.3.3 When testing the pull-out strength on the end face of the wood member, the width of the wood member shall be at least 15 d, the thickness shall be at least 10 d, and the length shall be at least (2lp 5d).

Figure 3 Schematic diagram of pull-out strength test

7.3.3.4 Within (90 ± 30) s, load and pull out a self-tapping screw at a uniform speed, and record the maximum load Fmax. Press formula (1) to confirm pull out Intensity wf, the calculation result retains 3 significant digits.

7.3.4 Flexural yield strength

7.3.4.1 Test device

It is carried out on a universal testing machine with an accuracy of 5 N. The structure of the test device is shown in Figure 4.The requirements are as follows.

a) Indenter. Steel cylindrical indenter with a diameter of 10 mm, connected to the pressure sensor of the testing machine;

b) Support. steel cylindrical support, the diameter of the support is 10 mm, according to the different diameter of the test self-tapping screw, the two can be adjusted Distance between supports;

c) Adjustment and recording. The testing machine can set the test speed, record the test load and record the displacement of the indenter.

7.3.4.2 Test procedure

7.3.4.2.1 The distance between the supports for the bending yield strength test of self-tapping screws is 11.5 times the thread bottom diameter d1, rounded to 1mm, and the smallest distance between supports the distance should be 25 mm.

7.3.4.2.2 The self-tapping screw is placed on the support, and the loading indenter should be in the middle of the two supporting points. If the nail rod is in the same shape, self-tapping the two ends of the screw should be equidistant from the support; if the shape of the nail shank is inconsistent, the junction of the smooth part and the non-smooth part of the nail shank should be as far as possible Near the middle of the two support points. The maximum loading speed is 6.5 mm/min, load and record sufficient load and deflection, and plot load-deflection curve line.

7.3.4.2.3 Draw a straight line segment of the load-deflection curve obtained from the control test, and move 5% of the base diameter d1 to the right along the abscissa, and then draw another A straight line parallel to it, and the load value at the intersection of the straight line and the load-deflection curve is taken as the yield load of the nail. If the line is not If the load-deflection curve intersects, the maximum load is taken as the yield load of the nail. The load-deflection curve of the self-tapping screw bending test is shown in Figure 5.

7.3.4.2.4 Calculate the bending yield strength of self-tapping screws according to formula (2), and the accuracy is 1 MPa.

7.3.5.2 The axial direction of the self-tapping screw shall be perpendicular to the surface of the wood member, and the position shall be at the center of the wood member. The test diagram is shown in Figure 6(b).

7.3.5.3 Test loading and calculation

The test piece shall be tested as shown in Figure 6(b) and loaded at a uniform speed to the self-tapping screw cap to pull through the wooden member. Ensure that the penetration force is loaded along it is carried out axially with self-tapping screws. Reach the maximum load Fmax within (300±120) s and record it. Calculate from formula (3) for the pull-through strength of the tapping screw cap, the calculation result retains 3 significant figures.